THE INSTITUTION OF ENGINEERS, SRI LANKA
TRANSACTIONS 2012 VOLUME I – PART B Technical Papers
“To promote the acquisition and interchange of technical knowledge, advance the science and practice of engineering in all its branches and regulate professional activities in Sri Lanka.”
THE INSTITUTION OF ENGINEERS SRI LANKA
Transactions – 2012 VOLUME I – PART B Technical Papers
This Institution does not, as a body, hold itself responsible for statements made or opinions expressed either in the Papers read or the discussions which have occurred at the Meetings.
Executive Secretary
ii
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The Institution of Engineers, Sri Lanka 120/15, Wijerama Mawatha Colombo 07 Tel : 2 698426, 2685490, 2 699210 Fax : 2 699202 E-mail :
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CONTENTS Editor’s note
vi vii
1.
Investigation of Operating Conditions for Optimum Biogas Production in Plug Flow Type Reactor by: Eng. (Ms.) Kulupanage Upuli Chathurika Perera, Eng. (Dr.) Gamini Kulathunga and Mr. Joseph Olwa
1
2.
Study the Factors Influencing Coir Pith Drying by: Eng. (Dr.) A.D.U.S. Amarasinghe, Mr. M.A. Tharanga, Mr. T.T. Alwis, Mr. H.B.B. Anuradha and Mr. D.R.D.H. Dasanayaka
9
3.
Study the Effect of Co-Digestion of Kitchen Waste with Sewage by: Eng. (Ms.)R.M.D.S. Gunarathne and Mr. D.M. Punchibanda
14
4.
Development of Catalysts for the Conversion of Syngas to Aromatics in a Single Step by: Eng. K.G.H. Kodagoda, Mr. T. Auttanat and Dr. (Mrs.) S. Jongpatiwut
20
5.
Production of Biodiesel in Pilot-Scale using Locally Available Feedstock Materials by: Eng. D.R.S. Hewa Walpita, Eng. (Dr.) (Mrs.) F.M. Ismail and Eng. (Dr.) S.H.P. Gunawardena
25
6.
The Development of a Process to Synthesize Carbon Nanotubes from Biogas by: Eng. (Ms.) Komathy Vamathevan, Eng. (Dr.) (Ms.) Manisha Y Gunasekera and Prof. Ajith de Alwis
33
7.
Design of a Solar Hybrid Dryer for Copra Drying by: Mr. H.P.K. Udana and Eng. (Dr.) A.D.U.S. Amarasinghe
38
8.
Development of a Water Processing Plant to Reduce Fluoride and Hardness in Drinking Water by: Eng. W.M. Jayawardhane and Mr. J.P. Padmasiri
46
9.
Development of a Methodology for Assessing Inherent Environmental and Safety Hazards by : Mrs. S. Warnasooriya and Eng. (Dr.) (Ms.) M.Y. Gunasekera
53
10.
Evaluation of Landscape along a Tropical Expressway based on Landscape Components: Case Study based on Southern Expressway, by: Mr. D. Gunawardhana, Dr. (Ms.) G.N. Samarasekara, Mr. K. Fukahori and Mr. H.A.C. Chaminda.
61
11.
Effectiveness of Bio-Filter for Removal of Ammonia, Hydrogen Sulphide and Phenolic Compounds Emanating from Agricultural Sources by: Eng. W.R.K. Fonseka and Eng. (Ms.) D.M.H.S. Dissanayake
70
3iv
12.
Quantitative Risk Assessment of Ancient Earth Dams in Sri Lanka: Preliminary Assessment of Nachchaduwa Dam as a Case Study by: Eng. S. Premkumar and Eng. (Dr.) L.I.N. De Silva
76
13.
Development of a Risk Assessment Framework for Safety Evaluation of Earthen Dams in Sri Lanka by: Eng. S. Premkumar and Eng. (Dr.) L.I.N. De Silva
85
14.
Comparison of Performance against Predictions in a Water Distribution Network by: Eng.(Ms.)W.K. Illangasinghe
95
15.
Ecological Design Considerations in High-Rise Buildings with Reference to CO2 Levels by: Eng. (Dr.) R.U. Halwathura, Ms. G.H.E. Silva, Mr. H.A.D. Mahanama, Mr. P.M.S. Jayamanna and Mr. A.G.T.N. Jayaweera
104
16.
Structural Effects on Existing Buildings due to Installation of Rooftop Towers by: Eng. Nadira Gunathilaka
112
17.
Mitigating the Scale of Urban Heat Island Effect in Cities with Implementation of Green Roofs by: Eng. (Ms.) S.N. Wijerathne and Eng. (Dr.) R.U. Halwatura
120
18.
Simulation of Air Movement in a Cinnamon Chips Dryer using Computational Fluid Dynamics by: Mr. B.D.G.P. Nandadeva, Eng. (Dr.) A.D.U.S. Amarasinghe and Eng. (Dr.) P.G. Rathnasiri
127
19.
Seismic Demand Prediction of Eccentrically Loaded Steel Bridge Piers subjected to Moderate Earthquakes by: Eng. (Dr.) K. A. S. Susantha and Eng. H. H. M. Gunasoma
133
20.
Characterization of Locally Available Montmorillonite Clay using FTIR Technique by: Eng. (Dr.) S.U. Adikary and Eng. D.D. Wanasinghe
140
21.
Influence of Plasticity Index on Sub-Base Material: Experimental Review by: Mr. D.G.S. Tharaka, Ms. B. Suvetha and Eng. (Dr.) W.K. Mampearachchi
146
22.
Causes and Effects of Delays in Construction of Medium Scale Drinking Water Supply Projects in Sri Lanka by: Eng. W.D.A. Perera and Eng. (Dr.) R.U. Halwatura
151
23.
Study of Northern Province Medium Voltage Network Interconnection with the Sri Lankan Power Grid by: Eng. (Ms.) A. Ananthasingam, Eng. (Ms.) R. Shailajah, Eng. (Ms.) N. Yoganathan, Eng. S. Arunprasanth, Eng. (Dr.) A. Atputharajah and Eng. (Prof.) M.A.R.M. Fernando
160
v
4
24.
Viability of Grid Connected Small Wind and Solar Photovoltaic Home Systems in Sri Lanka by: Eng. (Dr.) Mahinsasa Narayana
169
25.
Condition Assessment of Current Transformers - Chemical and Electrical analysis of transformer Oil by: Eng. M.A.A.P. Bandara, Eng. B.S.H.M.S.Y. Matharage, Eng. (Prof.) M.A.R.M. Fernando and Eng. G.A. Jayantha
176
26.
Mathematical Model for Generation Planning, Daily Dispatch Scheduling and Power System Economic Analysis Based on the Daily Load Profile by: Mr. B.W.H.A. Rupasinghe and Eng. A.S. Wickramasinghe
185
27.
Enhancement of Interference Cancellation Systems through Eigen Filter Base Subspace Separation by: Mr. B.B.K.J. Jayasekara, Mr. S.M.R.A. Jayathilaka, Dr. M.P.B. Ekanayake, Eng. (Dr.) G.M.R.I. Godaliyadda and Dr. J.V. Wijayakulasooriya
193
28.
A Fault Detection Method for a Roadway Sensor Using a Hidden Markov Model by: Eng. (Dr.) D.I.B. Randeniya
202
29.
Remote Monitoring and Analyzing of Low Voltage Distribution System by: Mr. H.M.D.N. Bandara, Mr. H.R.K. Dhananjaya, Mr. D.W.A. Jayathilake, Dr. S.G. Abeyratne and Mr. K.M.M.W.N.B. Narampanawe
211
30.
A Study of Possible Modifications in 16 QAM Modulation Scheme to Compensate the Nonlinear Phase Noise in Long-haul Optical Communication System by: Mr. S. Tharranetharan, Mr. S. Sathyaram, Mr. M. Saranraj and Dr. V.R. Herath
217
31.
Socio-Economic Impacts of Rural Electrification by: Eng. (Ms.) R.K.P.S. Gunatilake and Eng. (Dr.) R.U. Halwatura
224
32.
Dynamic Reactive Power Compensation in MV/LV Distribution System A Case Study in Kandy Area by: Mr. A. Gajananan, Mr. C. Gajanayake, Eng. (Prof.) M.A.R.M. Fernando, Eng. (Dr.) A. Atputharajah and Eng. C. A. B. Karunarathna
234
33.
Performance of Coconut Oil as Transformer Liquid Insulation During Simulated Thermal and Electrical Faults by: Eng. B.S.H.M.S.Y. Matharage, Eng. M.A.A.P. Bandara, Eng. (Prof.) M.A.R.M. Fernando, Eng. G.A. Jayantha and Eng. C.S. Kalpage
241
34.
Fast ICA Algorithm for Non-Gaussian Signal Separation by: Mr. A.M.S.D. Alahakoon, Ms. H.P.N. Madhubhashini, Mr. W.N.M. Soysa, Eng. (Dr.) G.M.R.I. Goddaliyadda, Dr. M.P.B. Ekanayake and Dr. J.V. Wijayakulasooriya
250
35.
259 Investigation of the Influence of Cement Fineness on Properties of Cement Mortar by: Eng. (Ms.) N.A.C.R. Nissanka, Eng. S.W. Nelundeniya, Eng. H.M.I.C. Ratnayake and Eng. (Prof) . S M.A. Nanayakkara
vi5
36.
Development of Fly Ash Based Geopolymer Concrete by: Mr. S.V.A. Silva, Mr. J.N.J. Kithalawa Arachchi, Mr. C.L. Wijewardena and Eng. (Prof.) S.M.A. Nanayakkara
267
37.
Regression Models for Proportioning of Self-Compacting Concrete Mixes and Estimating Their Rheological Properties in Terms of Bingham Constants by: Eng. H.M.G.U. Karunarathna, Eng. H. Abeyruwan, Eng. H.H.M. Gunasoma and Eng. S.D.J.M.T. Situge
274
38.
Service Life Evaluation of Reinforced Concrete Structures in Sri Lanka by: Eng. B.H.J. Pushpakumara, Eng. (Dr.) G.S.Y. De Silva and Eng. (Dr.) (Mrs.) G.H.M.J. Subashi De Silva
281
39.
The Effect of a Mix of Carbon Black and Silica in a Tubeless Tyre Inner Liner Compound Prepared with a Blend of Chlorobutyl Rubber and Natural Rubber by: Eng. (Dr.) S.M. Egodage, Mr. T.A.A.I. Siriwardane and Mrs. D.G. Edirisinghe
290
40.
Some Important Legal Aspects Relevant to Dispute Resolution in Construction 297 Contracts by: Eng. U.G. Mallawaarachchi
41.
Web Based Information Systems for the Construction Industry by: Eng. (Prof.) A.A.D.A.J. Perera
305
42.
Study on the Delays in Construction Projects in Water Sector in Sri Lanka by: Eng. S.B. Wijekoon and Eng. S.B. Uduweriya
313
320
Author Index
vii 6
Editor’s Note -------------------------------------------------------------------------------------------------------------------------From the day of the start of life, people have been trying to make their quality of life better. In doing so, we have been trying innovative approaches to our day to day activities. What is inside innovation is the careful investigation of the sciences and the use of technology to make those scientific processes around us to make more effective and productive outcomes. We have thus far have come a long way in making such innovations, and in the past couple of decades, the world has seen an unprecedented amount of innovations. It is not an exaggeration to say that everyday some new innovative products are available in the market place. Sri Lanka, despite the fact that it is not keeping an equal pace with the highly developed nations in the race of development, is also making contributions in innovations, and in this post civil war era, it is imperative that the nation’s innovativeness produces outputs to strengthen the development process. As engineers, we have to constantly engage in research and development activities to produce innovative applications and share the work with others by publicizing them for the benefit of the society. In this regard, this publication is a gateway for those who engage in engineering discipline to publicize their innovative work, and I am proud to have been responsible for the publication that disseminates the innovative ideas to the community. I wish to extend my appreciations to all those who have been assisting me in the publication process. First and foremost, I wish to thank the authors who submitted valuable manuscripts, and the referees who reviewed them. Without them, this task would have not been realized. I also wish to thank those who assisted me in the administrative work from the inception to the completion of the process. Feeling a sense of a great accomplishment, I believe that this work gets more and more challenging and creates even better outcomes in the years ahead.
Eng. (Prof.) K.P.P. Pathirana B.Sc. Eng.(Peradeniya), M.Eng., PhD, C.Eng., FIE(Sri Lanka), MICE (London) Editor, Technical Papers for the Transaction of The Institution of Engineers, Sri Lanka
viii vii
Annual Transactions of IESL, pp. [1-8], 2012 © The Institution of Engineers, Sri Lanka
Investigation of Operating Conditions for Optimum Biogas Production in Plug Flow Type Reactor Kulupanage Upuli Chathurika Perera, Gamini Kulathunga and Joseph Olwa Abstract: Plug flow type biogas digesters are suitable for treating green vegetations, municipal waste, and food wastes. Comprehensive understanding of controlling variables for optimum performance is important for effective operation of plug flow digesters. Objective of this study was to establish operating conditions for optimum biogas generation in a plug flow type biogas digester using food wastes as feed material. Steady state experiments were conducted in digesters fabricated from plastic barrels, for feed rates of 0.7, 1.4, 3, and 6 kg/day. Highest Average Specific Methane Production (ASMP) was 0.341 m 3/kgVSday at 1.4 kg/day. Highest Average Volatile Solids Reduction (AVSR) was 93.48% at 0.7 kg/day. Highest AVSR at lowest feed rate is due to satisfactory retention time. Lengthwise VFA variation shows distribution of acidogenisis to methanogenisis phases along the digester at intermediate feed rates. Keywords: Biogas, Plug flow digester
1.
Chanakya, et al. [2] mentioned the failures in converting other types of biomass into manure like slurries for biogas production. This reason has led them to introduce two designs for the successful use of other types of biomass for biogas production. They are plug flow digesters and solid state stratified bed digesters (Chanakya, et al., [2]).
Introduction
Biogas is generated by anaerobic digestion of organic matter. Organic matter refers to agricultural residues, manure, garbage and sewage waste. They originate from wide variety of sources spread throughout the world. Since they can be derived from relatively recent living material than fossil fuel, they are sustainable.
Plug flow type digester has been used to deal with wastes like green leaves and other floating type vegetations. Plug flow reactor is capable of transforming more organic solid waste into biogas. They are capable of converting feed stocks with total solids content of 11-14 % [3]. There is no longitudinal mixing in ideal plug flow digesters. When the new manure is added the previous feed stocks move in plugs towards the outlet. Operation of plug flow digesters has rather complex behaviour than described above. Some of feed stock will travel faster than the others, and some will settle in the digester [4].
Great potential exists in Sri Lanka for biogas generation and it is one of the sustainable solutions for the waste disposal problem in the country, for rural development in the country and in reduction of fossil fuel imports. The very first biogas digesters were continuous flow type digesters. Continuous flow biogas reactors require regular water supply and is preferred for animal and human wastes. Considering these facts a new biogas digester was developed by National Research and Development Centre (NERDC) of Sri Lanka which is called as Dry Batch Reactor (DBR). Preferred material inputs for DBR is straw and animal waste. Moisture content of the input material should be more than 85% while for the continuous type digester solid content should be 9 to 10 % [1]. Disadvantages of the DBR are difficulty in loading and unloading, large quantity of bio sludge in larger digesters, unstable gas generation rate, and long operating periods.
Eng. (Ms.) Kulupanage Upuli Chathurika Perera, Department of Agriculture Engineering and Postharvest Technology, National Engineering Research and Development Centre of Sri Lanka , Ekala, Ja Ela, Sri Lanka. Eng. (Dr.) Gamini Kulathunga, Department of Agriculture and Plantation Engineering, Faculty of Engineering Technology , The Open University of Sri Lanka, Nugegoda, Sri Lanka. Mr. Joseph Olwa, Department of Energy Technology, Royal Institute of Technology, Stockholm, Sweden.
1
No well established information is available for optimum operation of these types of biogas plants; hence the use of plug flow type has been neglected compared to other types. Therefore, establishing the parameters which affect the optimum digester is important biogas production in plug flow type biogas for optimum utilization of feed stock resources and of the biogas produced. This will guide the path to sustainable use of bio energy.
2.
Two identical digesters were fabricated in order to carry out two parallel tests with two loading rates simultaneously. One of the digesters is shown in Figure 2.
Experimental Set-Up
Plastic barrels available in the local market were used for the fabrication of the digester. Size was decided by considering space requirement to keep the unit, the structural stability and the feasibility in supporting and length to width ratio for plug flow digesters [3].
Figure 2 - Digester 1
3.
Initial Preparation
Anand et al. [5] used 50 kg/day of leaf biomass in a 5 m3 digester initially and then increased to 100 kg/day. 50 m3 digester for market garbage treatment was designed by Sustainable Energy Authority of Sri Lanka and intended to feed of 1000 kg/day but was able to treat only 500 kg/day at operating conditions. Plug flow digesters developed by the NERDC of Sri Lanka has the capacity to treat 10 kg/day in their one cubic meter total volume of the digester.
Diameter of the digester used was 0.47 m and length of the digester was 1.58 m. The digester volume was therefore 0.27 m3. The working volume used was 0.188 m3. Inlet of the digester was fabricated with a PVC pipe of diameter 11 cm. The digester had three windows to observe the inside flow of digestion medium. Three sampling ports were placed in order to facilitate sample withdrawal.
In this study, daily feed stock allowed for the total volume of digester was taken as 10 kg per day per 1 m3 total digester volume.
Gas Outlet
Since the digester volume was 0.27 m3 the daily feedstock was set at 3.0 kg per day.
Outlet Inlet 01
02 Sampling Ports
03
Other feed rates selected were 0.7 kg, 1.4 kg and 6 kg. Operating time was 20 days for each feed rate.
Gas Collecting Holder
Figure 1 - Schematic Diagram of the Digester Bacteria culture was introduced by feeding cow dung for seven days. Feeding rate of food waste was increased in steps in order to achieve the expected feeding rate and to avoid acidification. Feed stocks were ground into small sizes using a domestic grinder to reduce the particle size. Calcium carbonate was used for the pH adjustment. The day time temperature variation was between 28oC 31oC.
Gas holder was fabricated with two plastic barrels both with one end opened. One barrel was filled with water and other which has an inlet and an outlet was dipped in water. Two plastic tubes of diameter 12.74 mm were used for the inlet and the outlet. Gas produced in the digester flows to gas holder and lifts it up and produced gas can be estimated by the diameter of the barrel and the height of the holder that has lifted above the water level. Schematic diagram of the digester is shown in Figure 1.
Feed rates are numbered from E1 to E4 respectively for 0.7kg per day to 6.0 kg per day in ascending order.
2
4.
E1-0.7 kg per day (Digester 2) E2-1.4 kg per day (Digester 1) E3-3.0 kg per day (Digester 1) E4-6.0 kg per day (Digester 2)
Experiments were conducted during steady period of operation. Feed stocks were analysed for, Total Solids Content (TSC) and Volatile Solids Content (VSC). Material discharged from the outlet was in liquid form. Effluent was analysed for Chemical Oxygen Demand (COD), TSC, and VSC. Material obtained from three sample ports along the length of the digester was tested for Volatile Fatty Acid (VFA) concentration and pH. The pH and VFA measurement are numbered from 1 to 3 respectively from inlet to outlet. Average TSC and VSC for different feed rates are shown in Table 2. TSC and VSC measurements were used to calculate Organic Loading Rates (OLR) in Table 3.
Table 1 shows composition of feed stock for different feed rates. Table 2 shows the feedstock characteristics and Table 3 shows the feeding plan followed in the experiment. Table 1 - Composition of Feed Stocks Experiment Numbers
Food waste & other (g)
Vegetable residue (g)
350
450
-
-
E2
450
900
50
-
E3
450
900
50
1600
E4
900
1800
100
3200
E1
Fruit waste (g)
Water (g)
Daily production of gas quantity was measured from the height of the gas holder lifted above the water level. Gas composition was analysed daily.
Table 2 - Feedstock Characteristics Experiment Average T SC (%) Average VSC (% VS)
E3
5.
E1
E2
21.9
16.1
5.7
5.7
91.9
93.3
92.3
92.3
Analytical Procedure
Results
E4
Table 3 - Feeding Plan Experiment
Organic Loading Rate (kgVS/m3day)
Operating Time (days)
E1
0.75
20
E2
1.12
20
E3
0.83
20
E4
1.67
20
Figure 3 - Daily Average Biogas Production
3
Figure 4 – CH4 Percentage of Biogas for Three Feed Rates
Figure 5 – CO2 Percentage of Biogas for Three Feed Rates
Figure 6- pH Variation in E1
4
Figure 7- pH Variation in E2
Figure 8 - pH Variation in E4
Figure 9 - VFA Variation along the Digester Length in E1
Figure 10 - VFA Variation along the Digester Length in E4
5
Figure 11 - COD Variation of Effluent for Different Feed Rates As shown in Figure for 6 kg per day and 1.4 kg per day, higher volume of biogas has been generated.
gas for and 6 kg/day. Insufficient retention time and high VFA concentration due to high organic load reduces methane production which results in low ASMP and low methane content in biogas. Highest ASMP was observed for intermediate OLR which is a lower feed rate with high TSC. When the OLR is increased total feed rate is reduced by increasing TSC. At this condition the process is more stable and the HRT increases due to lower feeding rate.
Table 4- Process Performance
Average Volatile Solids Reduction (%)
Average Specific methane production (m3/kgVS per day)
93.48
0.320
1.4
91.37
0.341
6.0
85.92
0.219
Feed rate(kg/day)
0.7
ASMP production is in the same range as mentioned in literature for similar experiments. ASMP for similar studies are shown in Table 5. Figure 7 shows the rise of pH from inlet towards the end of the digester. Clear variation of pH cannot be identified from Figure 6 and Figure 8 which is due to internal mixing and flow instability of inside substrate. VFA concentration along the length of the digester shows a large reduction from inlet to the middle span as in Figure 10. VFA pattern in Figure 9 shows the mixing behaviour due to insufficient feed rate. Figure 10 shows large fluctuations of VFA for samples taken near the inlet and middle of the digester. Lengthwise VFA variation and pH variation show that acidogenisis phase near the inlet and mathanogenisis.
**Leakages occurred during the experiment. The highest average specific methane production (ASMP) was 0.341 m3/kgVS per day at Organic Loading Rate (OLR) of 1.12 kgVS/m3 per day which is shown in Table 4. For OLR of 1.67 kgVS/m3day ASMP is 0.219 m3/kgVS per day. Low ASMP at feed rate of 6 kg per day is due to the insufficient HRT for the larger quantity of feedstock to be digested inside the digester and due to the high VFA concentration produced at higher feed rate. OLR of 0.75 kgVS/m 3day showed the highest Average Volatile Solids Reduction (AVSR) of 93.48 %. OLR of 1.67 kgVS/m 3day showed the lowest AVSR of 85.92 %. Low methane content in biogas for 6 kg/day can be observed from Figure 4. Simultaneously Figure 5 shows high carbon dioxide content in
6
6.
Table 5 - Comparison between Similar Studies done in Plug Flow Digesters Waste type
Specific Methane Yield (m3/kgVS)
Food Waste 0.320
0.341
0.219
Conditions
Reference
0.75 kgVS/m3day Temperature :28-31 oC 1.12 kgVS/m3day
The VFA variation along the digester shows the variation of acidogenisis to methanogenisis stages along the digester length which is more prominent at intermediate feed rates. This pattern prevents the obstruction of biogas process at higher feed rates in plug flow digester.
Present Study
Temperature :28-31 oC 1.67 kgVS/m3day
Co digestion of food waste with cattle dung, sewage waste or other suitable sources help to control the high VFA concentrations.
Temperature :28-31 oC Used cooking grease with swine manure
0.310
Botero, et al[6]
Effluent can be treated in a second digester or the length of the digester has to be increased to convert COD in the effluent to biogas.
Chaudhry [7]
Studies should conduct to study the effect of TSC in the feedstock for biogas production. Studies should focus on importance of flow induced by the effect of pressure inside the plug flow digester on biogas production and its composition.
Temperature: 22-26 oC
Food waste, Anaerobic sludge,
Cooking grease 2.5 %,
0.278
Digestate, Cow dung 0.2259
0.146
Organic loading rate2.5 kgVS/m3day Temperature: 55 oC 3.3 kgVS/m3day
Effluent nutrient content should be tested to be used as an organic fertilizer.
Temperature: 55 oC 3.9 kgVS/m3day
GHG potential of methane in the biogas is 20% [9] higher than carbon dioxide. Therefore, it should be carefully trapped and used to avoid leakages.
Temperature: 55 oC Cassava peel
0.377
3.6 kgVS/m3day
Conclusion
Highest ASMP and high methane content in biogas was observed at 1.4 kg per day which has high TSC. Highest AVSR was observed at the lowest feed rate with high TSC which is 0.7 kg per day.
Cuzin, et al.[8]
References
Temperature :35-39 °C
According to Figure 10, VFA concentration exceeded the inhibitory limits mentioned in the literature. This did not cause full process destruction but resulted in low methane content in the biogas. Distribution of biogas production stages along the length of the digester reduces negative effect of high VFA concentrations at higher loading rates. Table 4 shows the highest average VS reduction for the lowest total feed rate with high TS content. Lowest AVSR was observed at highest OLR which is the highest total feed rate. Figure 11 illustrates high COD concentrations in the effluent. This is due to insufficient HRT.
7
1.
SLSI; 2006, “Code of Practice for Design and Construction of Biogas Systems, Part 1Domestic Biogas Systems”, Sri Lanka Standard1292: 2006, UDC 662.767.2, Colombo, Sri Lanka, 2006.
2.
Chanakya H.N., Modak J.M., Rajabapaiah P., “Evolving Biomass Based Biogas Plants: The ASTRA experience”, Current Science, Vol 87, pp 917-925, 2004.
3.
Natural resources conservation service, “Anaerobic Digester-Controlled Temperature”; 2004 Code 366, Natural
resources conservation service, Conservation practice standard, 2004, [Visited 15 March 2011]. 4.
Graves R.E., Richard T., Topper P.A., “The Fate of Nutrients and Pathogens during Anaerobic Digestion of Dairy Manure”, Agricultural and Biological Engineering, Cooperative Extension, College of Agricultural Sciences.
5.
Anand V., Chanakya H.N., Jagadish K.S., Rajabapaiah P., “Plug Flow Digesters for Biogas Generation from Leaf Biomass”, Biomass and Bioenergy, Vol14, pp 415-423, 1998.
6.
Botero R.B., Lansing S., Martin J.F., Silva E.D., Silva T.G., “Methane Production in Low-Cost Unheated, Plug-Flow Digesters Treating Swine Manure and used Cooking Grease”, Bioresource Technology, Vol 101, pp4362–4370, 2010.
7.
Chaudhry B.K., “Dry Continuous Anaerobic Digestion of Municipal Solid Waste in Thermophillic Conditions”, Asian Institute of Technology, Thailand, 2008.
8.
Cuzin N., Farinet J. L., M. Labat, Segretain B C., “Methanogenic Fermentation of Cassava Peel using a Pilot Plug Flow Digester”, Bio-Resource Technology, Vol 41, pp 259-264, 1992.
9.
Wightman J., “Production and Mitigation of Green House Gases in Agriculture”, Climate Change and Agriculture: Promoting Practical and Profitable Responses, Cornell University, New York, 2005.
8
Annual Transactions of IESL, pp. [9-13], 2012 © The Institution of Engineers, Sri Lanka
Study the Factors Influencing Coir Pith Drying A.D.U.S. Amarasinghe, M.A. Tharanga, T.T. Alwis, H.B.B. Anuradha and D.R.D.H. Dasanayaka Abstract: Coir pith is considered an excellent growing medium due to its water retention capacity, pH and high mineral concentration and therefore, it has a good demand in the horticulture industry. Sri Lanka currently utilizes solar and flash drying to reduce the moisture content of raw coir pith. Quality of the dried coir pith was found to be significantly affected due to the drawbacks in the current drying methods. This study was carried out to identify suitable conditions for coir pith drying, specially the drying temperature. Results indicated that coir pith sample dried at 150 C had the highest water retention capacity of 7.96 (w/w) but, it showed relatively low volume expansion ratio of 2.6 (mm/mm). Volume expansion ratio could be improved up to 3.35 by mixing equal amounts of flash dried and raw coir but, it had the lowest water retention capacity of 7.16 (w/w). Drying at 200 C gave relatively high volume expansion and water retention capacity compared to drying at other temperatures. This study further revealed that both the volume expansion and the water retention capacities of coir pith bricks had gradually reduced with time. Keywords:
1.
Coir pith, Flash drying, Coconut based products, Coir briquettes
water. Coir pith derived from different extraction processes have inheritably different water retention capacities and coir pith derived from Ceylon Drum method has the best water retention capacity [3]. Therefore, coir pith manufactured in Sri Lanka is considered to be one of the best types of coir pith which can be used as a growing medium.
Introduction
Coir is a fibrous material that constitutes the mesocarp of the coconut fruit (Cocosnucifera). In the process of extracting coir from coconut husk, short fibres and coir dust are obtained as waste products known as coir pith or coco-peat. 1.1 Research Background Because of its properties such as pH, electrical conductivity, water retention capacity, carbon – nitrogen ratio, cation exchange capacity, and the concentration of calcium, magnesium, phosphorus and potassium coir pith has been recognized as an alternative to peat which is an excellent growing medium [1]. Hence, currently coir pith has a high demand in horticulture industry and about 750 MT of coir pith has been manufactured in the year 2010 in Sri Lanka [2]. Even though coir pith industry has a huge potential to play a significant role in the export market, only a few research studies has been conducted to address the related technical issues.
In order to manufacture stiff coir pith bricks, it is desired to have a moisture content below 20% (dry basis) and traditionally solar drying is widely used to dry the raw coir pith to reduce the moisture content from around 70% down to about 20% [5]. With the growth of the industry, processing by solar drying has become inefficient. As a result, the coir pith industry has moved into finding new techniques such as flash drying which can produce large quantities within a short period of time. The new drying techniques have caused a severe drawback to the industry as both the expansion and water absorption properties of the coir bricks were considerably affected. As a result, the demand
Coir pith has a high water absorption capacity. Its mean wet bulk density is 0.79 g/cm3 whereas the mean dry bulk density is 0.06 g/cm3 [3]. Coir pith is also a highly porous material. For particle sizes in the range of 0.098 to 0.925 mm, porosity varies from 0.623 to 0.862 [4]. Hence, coir pith is dried and compressed into bricks in order to reduce transportation cost. Dried and compressed coir pith bricks expand back to original volume by absorbing
Eng. (Dr.) A.D.U.S.Amarasinghe, B.Sc. Eng. (Moratuwa), PhD (Cambridge), MIE (Sri Lanka), Head of the Dpt., Department of Chemical & Process Engineering, University of Moratuwa. M.A. Tharanga,B.Sc. Eng. (Moratuwa), Lecturer (Prob.), Department of Chemical & Process Engineering, University of Moratuwa. T.T. Alwis, Final year student, Department of Chemical & Process Engineering, University of Moratuwa. H.B.B. Anuradha, Final year student, Department of Chemical & Process Engineering, University of Moratuwa. D.R.D.H. Dasanayaka, Final year student, Department of Chemical & Process Engineering, University of Moratuwa.
1
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for these products in the foreign market has been notably affected.
reduces down to 20% in order to manufacture coir bricks. Generally coir bricks are manufactured with a compression ratio of 1:6. These bricks regain their original volume once again by absorbing water.
Since drying characteristics and corresponding quality variations of coir pith have not been established, it has become difficult for the local coir pith industry to come out with a suitable drying technique.
1.4 Chemical Characteristics Expansion properties of the coir bricks depend on their chemical properties. Table 1 illustrates the average composition of coir pith.
1.2 Objective The objective of this research is to study the expansion and the water retention properties of coir bricks with respect to drying temperature, storage time and the temperature of the water added for expansion.
Table1 - Coir Substrate; Main Physical and Chemical Characteristics [7] Parameter Total organic matter- % dry basis Organic Carbon- % dry basis Ash - % dry basis Lignin - % dry basis Cellulose - % dry basis General Porosity - % volume Air content at full water capacity - % volume Water retention capacity - % volume Specific gravity kg/m3 Cetin Exchanger capacity (CEC) meg/100g Total Nitrogen - % dry basis C/N ratio pH in water EC level (mS/cm)
1.3 Technical Background Coir husk is 5-10 cm thick fibrous covering of the coconut fruit which envelops the hard shell structure of 3.5 mm thickness [6]. The husk is full of long, coarse fibers, all running in one direction. The fibers are embedded in a matrix of material called coir dust. Since husks are porous, they absorb and retain water. Following four methods are mainly used to extract coir from the coconut husks [3], Ceylon Drum method Decorticator method Defibre method D1 method Among these coir extracting methods, Ceylon Drum method is a traditional method which is unique to Sri Lanka. Coir pith is obtained as a waste product from these coir extracting methods and in order to reduce the moisture content of coir pith, solar drying or flash drying is being used.
2.
Value 94-98 45-50 3-6 65-70 20-30 94-96 10-12 80-85 65-110 60-130 0.5-0.6 up to 220 5.0-6.8 0.25-0.50
Methodology
2.1
Effect of Drying Temperature and Storage Time Effect of drying temperature on the water retention and the volume expansion of coir pith bricks were studied. Similar bricks (60 g, cylindrical) were made using coir pith dried under different conditions. Three temperatures were used to dry the samples in an oven; 150C, 200 C and 240 C. One sample was prepared by sun drying. Another sample was prepared by mixing wet coir pith (moisture content of 56%) with completely dried (moisture content of 0%) coir pith. A final moisture content of 20% was achieved for all the samples. For each condition, 6 coir pith bricks were prepared for evaluation.
Coir pith obtained in these methods inherits slightly different chemical and physical properties. Coir dust having greater capacity for water holding and expansion can be produced by Ceylon Drum method while Coir dust with high compressibility and wet bulk density can be produced by Decorticator method. Decorticator method might provide raw coir dust for the production of best quality value-added horticultural substrates. Good quality coir dust is collected according to the parameters which should be maintained such as pH. In the manufacturing process, coir dust particles are first washed using clean water in order to remove impurities. After that they have to be dried until the moisture content
Volume expansion of examined by using a arrangement as shown arrangement, volume
10
coir pith bricks was tripod with a mesh in the Figure 1. By this expansion could be
2.2
Effect of Water Temperature on the VE and WRC Two types of coir pith bricks were used to analyse the effect of the temperature of water which was added on the expansion and water retention. Both brick samples were prepared by using the sun dried coir pith and the processing was very similar to the industrial practice. The only difference between the two samples was that one sample was newly made and the other was 3.5 months old. Four bricks were prepared from each type and the effect of temperature on the WRC and VE was examined by using water at 5 C, 30 C, 55 C and 80 C.
converted into a height expansion. When brick absorbs water, the 3 supports prevent the brick being collapsed. Weight of the apparatus and the weight of all sample bricks were measured before adding water. Initial heights of the bricks were also measured. Water was added to the bricks from top and it was stopped when water started to drain through the mesh. After allowing the excess water to be drained, final weight of the apparatus was measured. At the same time, final heights of the bricks were also measured.
3.
Results and Discussion
3.1 Effect of Storage Time Figure 2 shows that WRC decreases with time for all the samples which were dried under different conditions. This may be a result of the plant cell death which happens naturally over a period of time. Even though similar trends can be observed, the actual water retention capacities at any given time of samples prepared at different drying conditions are significantly different to each other. 8.3 WRC (w/w)
Figure 1 - Volume Expansion of Coir Pith Bricks Water retention capacity which will be referred as WRC and the volume expansion which will be referred as VE were calculated by using the following equations.
Weight of absorbed water (W 1 ) Initial weight of coir sample (W 0 )
Increased Height (H 1 ) Initial height of coir sample (h 0 )
7.7
7.3 7.1 6.9
…. (1)
6.7
���������� ) �� � �� � � � � � �� � � (� � � � VE =
7.9
7.5
�������� �������������� ) ����������� (� � � � � � WRC =
8.1
1
2
3
4
5
6
Storage Time (weeks)
…. (2)
Sun dried
150
200
240
Mix
where,
Figure 2 -Variation of WRC with Storage Time
W 1 = W f - (W e +Wo) H1 = hf - ho W o = Initial weight of coir sample W e = Weight of equipment W f = Final weight of equipment with sample ho = Initial height of coir sample hf = Final height of coir sample
Figure 3 shows the variation of VE with the storage time. A similar trend to the variation of WRC can be observed for VE also.
This study was carried out for a period of three months and the VE and water retention were measured in every other week. 3
11
at 150 C, 200 C and 240 C. Usually sun drying technique is not practiced in a controlled manner and the bacterial and fungal actions may be at a very high level compared to the controlled drying. As a result, the plant cell death may be promoted and this in turn affects the quality of coir brick.
VE (mm/mm)
4.0 3.5 3.0 2.5
Sample
Mix
2.0
240 200
1.5 1
2
3
4
5
6
150
Storage Time (weeks) Sun dried
150
200
240
Sun dried
Mix
Figure 3 - Variation of VE with Storage Time
0.0
1.0
2.0
3.0
4.0
Average VE (mm/mm)
Sample
3.2 Effect of the Drying Temperature Generally the coir pith bricks are used within a time period of 3 months and the time of use may be any time in between 1 week to 12 weeks. Therefore in order to evaluate different drying conditions, the average values of WRC and VE for the entire period had been calculated and the results are given in Figures 4 and 5.
Figure 5 - Average VE for Different Drying Conditions Results indicate that the WRC and the VE have opposite trends. This is evident with the low WRC and high VE for mix sample and the high WRC and low VE for drying at 150 C. Figure 2 suggests that WRC is strongly influenced by the plant cell death which occurs naturally over a period of time. Drying at very high temperatures such as 240 C can also give a similar effect. Mix sample contains a large portion of completely dried coir pith and hence, the plant cell death in the mix sample may be significantly higher than the other samples.
Mix 240 200 150
In the industrial practice, coir pith is dried to achieve moisture content around 15 – 20 C in order to make stiff bricks in which the bonding between particles are strong. VE is highly influenced by the level of bonding. Since the mix sample has a high proportion of dead cells which are weakly bonded, the VE of mix sample is the highest. On the other hand, the sample prepared under 150 C has the highest amount of active cells which can retain a significantly high amount of water and the particles can be strongly bonded. As a result, the VE becomes comparatively less.
Sun dried 6.5
7.0
7.5
8.0
Average WRC (w/w)
Figure 4 - Average WRC for Different Drying Conditions Figure 4 clearly indicates that the samples made under drying at 150 C had the highest average water retention capacity of 7.96 (w/w). However, the VE of samples made under drying at 150 C is comparatively less. Lowest WRC was observed for the mix sample. However, the mix sample gave the highest volume expansion. Sun drying is the conventionally practiced method in the industry. Results indicated that both WRC and VE of sun dried sample were considerably low compared to the samples obtained from drying
3.3 Effect of Water Temperature Figure 6 shows the average WRC and Figure 7 shows the average VE of the old and new coir pith bricks when water at different temperatures was added.
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12
WRC (w/w)
Horticulture is more popular in countries with cold weather conditions and hence, it is recommended to add water at temperatures above 30 C to achieve the best performance of the coir pith brick. It is interesting to note that the coir pith bricks as old as 3.5 months can be expanded to a greater extent by adding water at temperatures above 80 C.
10 9 8 7 6 5 4 3 2 1 0
References
5
30
55
1.
Abad, M., Noguera P., Puchades R., Maquieira A. and Noguera V., “Physico-Chemical and Chemical Properties of Some Coconut Dusts for use as a Peat Substitute for Containerized Ornamental Plants”, Biores. Technol., Vol. 82, pp. 241-245, 2002.
2.
Central Bank of Sri Lanka, Annual Report National Output and Expenditure, 2010, Chapter 02, pp. 33-34, 2010.
80
Water Temperature (0C) Old sample
New sample
Figure 6 - Effect of Added Water Temperature on Water Retention Capacity
VE (mm/mm)
Results suggest that both WRC and VE of old samples were highly influenced by the temperature of the added water while the new sample showed less effect. Both of these properties are dependent on the amount of active cells in the brick. The cell walls of coir pith become deactivated with the storage time and it may be difficult to reactivate them by adding water at low temperatures. However, fraction of these cells may be reactivated by adding water at high temperatures.
3. Tharanga S.A.R., Wathulanda H.K.P.B., Weerakkody W.A.P., and Gamlath S., “Variation of Chemical and Physical Properties of Raw Coir Dust with Reference to Age, Origin and Extraction Method”, Sri Lankan J. Agric. Sci., Vol. 42 , pp. 1-11, 2005. 4.
Manickama Neethi and Subramanian P., “Study of Physical Properties of Coir Pith”, International Journal of Green Energy, Vol. 3, Issue 4, pp. 397-406, 2006.
5.
http://www.ieashc.org/task29/projects/coir_pith_drying_indi a.htm , Visited, 30th April 2012.
6.
Tejano E.A., “State of the Art of Coconut Coir Dust and Husk Utilization “Philippine Journal of Coconut Studies, Volume 10 , pp. 01, December 1985.
7.
http://www.freshplaza.com/news_detail.asp? id=34321/ , Visited, 20th October 2011.
6 5 4 3 2 1 0 5
30
55
80
Water Temperature (0C) Old sample
New sample
Figure 7 - Effect of Water Temperature on Volume Expansion
4.
Conclusions
In horticulture industry, both the VE and the WRC are expected to be at a higher level in a good coir pith brick. Therefore, 200 C can be considered as the best drying temperature as it possesses relatively high VE and a good water retention capability.
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Annual Transactions of IESL, pp. [14-19], 2012 © The Institution of Engineers, Sri Lanka
Study the Effect of Co-Digestion of Kitchen Waste with Sewage R.M.D.S. Gunarathne and D.M. Punchibanda Abstract: Continuous Chinese type fixed dome anaerobic digester with 5 m 3 capacity was developed at National Engineering Research & Development Centre (NERD) for evaluation of the performance of co-digestion of kitchen waste with sewage. The digester was specially designed for storing more gas compared to conventional designs with similar size and incorporated a kitchen waste feeding unit. Digester was initially charged only with sewage. After stabilization of the process and two months monitoring period, kitchen waste feeding was started and monitored for another four months. CH4 content and calorific value of biogas after stabilization was around 75% and 28 MJ/Nm3, respectively. It was observed that co-feeding of kitchen waste enhance the biogas production but with slight reduction of methane content. It showed a linear increasing trend with the increase of kitchen waste quantity. At water boiling experiments with a gas burner having around 41% overall efficiency as calculated, daily energy output obtained were 0.8, 1.2, 1.7 and 2.1 MJ with 0, 1, 2 and 3 kg kitchen waste feedings, respectively. It will fulfil 8, 13, 18 and 22% of daily cooking energy requirements of an average family and may be further increased with high evacuation frequency. The leachate properties were in acceptable limits in both cases. Keywords:
1.
Co-digestion, Kitchen waste, Sewage
optimum capacity.
Introduction
Garbage disposal is one of the major problems faced by urban housewives in Sri Lanka. If the total waste management is concerned, local authorities face a big problem in separation of mixed waste in further processing. Further, increased prices of high grade cooking fuels such as electricity and Liquefied Petroleum Gas are not affordable especially for middle class families. Therefore, by solving these two problems together, it will make a considerable impact on family economy and the environment as well.
nutrient level and better buffering
In literature [3], when kitchen waste (rich in carbohydrates) was added as co-feedstock, a substantial increase in the gas production has been observed. On the other hand, food waste is highly biodegradable and has a much higher volatile solids destruction rate (86-90%) than sewage. As a result, even though additional material is added to the digesters, the end residual will only increase by a small amount [2]. Therefore, existing digesters designed only for sewage can be co-fed with kitchen waste without any limitation to its holding capacity.
Anaerobic digestion of sewage is not a novel concept to Sri Lanka. Sewage has a lower energy density as it is pre digested [1]. But it has several plus points such as neutral pH, higher buffering capacity, availability of naturally occurring mix of microbes, nutrients and the ability to pump etc. Kitchen waste or food waste on the other hand have higher energy density and in a study done by East Bay Municipal Utility District it was revealed that food waste has up to three times as much energy potential as sewage [2]. But the use of food waste in anaerobic digestion is limited by its acidic nature, absence of microbes in the feed, and lack of nutrients. Therefore, adding these two feed stocks together to form a substrate for anaerobic digestion results in
Co-digestion results in higher CO 2 content in biogas because undigested kitchen waste releases high quantities of CO2 [3]. Eng. R.M.D.S. Gunarathne, B.Sc. Eng. (Moratuwa), Research Engineer, Department of Renewable Energy, National Engineering Research & Development Centre of Sri Lanka. Eng. D.M. Punchibanda, B.Sc. Eng. (Peradeniya), Principal Research Engineer, Department of Renewable Energy, National Engineering Research & Development Centre of Sri Lanka.
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ENGINEER
Further, food waste has high nitrogen content due to the high protein component. As a result, during anaerobic digestion high level of ammonia is generated which is toxic to the acetoclastic methanogens which is one of the two types of methanogens. As a result, methane content is slightly reduced by the addition of food waste [4]. Co-digestion of kitchen waste with sewage is practiced in domestic level, but no detailed study has been conducted and therefore, information on the enhancement of biogas production by co-digestion is lacking. This hinders the effective use and popularization of this technology. Figure 2 - Feeding Kitchen Waste
2.
Objective 3.2 Feeding and Monitoring Main feedstock for the unit was sewage fed through the National Engineering Research & Development Centre (NERD) security staff toilet which is averagely used by 5 people per day. This can be taken as a representation of an average family.
The research work reported here was aimed at analysing the effect of co-digestion of kitchen waste with sewage in order to effectively use biogas technology for replacing significant portion of domestic cooking energy requirement.
3.
Assuming sewage generation per person per day as 0.4 kg and average number of users as 5, daily generation of human excreta can be estimated to be 2 kg per day.
Methodology
3.1 Digester Design Digester was specially designed by increasing the height of the dome by 9 inch above the ground level as shown in Figure 1. By this method 0.7 m3 of additional gas can be stored while maintaining the water level at desired depth. Another feature incorporated in this design is the kitchen waste feeding unit as shown in the Figure 2. This unit enables the user to conveniently feed kitchen waste to the digester.
Initially, the digester was only fed with sewage and it was taken five months to stabilize the process. Then, the process was monitored for another two months. Then co-feeding was started and depending on the availability of kitchen waste, measured amount of kitchen waste was daily fed to the system along with sewage for another four months. The system was monitored for biogas composition, biogas pressure, energy output and leachate properties for both cases. Gas Chromatograph was used to analyse the biogas composition and calorific values were calculated based on the calorific value of methane (35.814 MJ/Nm3) and methane content of biogas. Series of water boiling experiments were carried out by boiling one litre of water at a time in an open container (Figure 3). This was repeated until all the biogas collected is utilized.
Figure 1 – Digester with Feeding Unit
ENGINEER
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The amount of energy consumed was calculated from biogas volume consumed and from calorific value of biogas. Burner efficiency was calculated by ratio between amount of energy (sensible and latent heat) acquired by water and amount of energy consumed by burning biogas. Energy content of a 12.5 kg Liquefied Petroleum Gas cylinder is 575 MJ. Average family consumes a gas cylinder within approximately two months. Then, daily cooking energy consumption is 9.58 MJ. Based on this fact, percentage fulfilment of domestic cooking energy need by biogas was calculated for different feed conditions such as feeding sewage alone and for different ratios of sewage to kitchen waste.
Figure 3 – Water Boiling Experiment The burner used was a normal LPG burner modified for using biogas as the fuel and consists of 6 numbers of holes in the inner ring and 35 numbers of holes in the outer ring having average diameter of 2 mm. A U-tube manometer filled with water was used to measure the biogas pressure inside the digester before and after the experiments and these values were used to calculate the biogas volume consumed at atmospheric pressure.
4.
Results
4.1.
Variation of Biogas Composition
Figure 4 represents the variation of biogas composition with time from the start up.
Only sewage
Sewage & kitchen waste
Figure 4 – Variation of Biogas Composition with Time When only the sewage feeding was practiced, methane content reached around 75% and carbon dioxide content reached around 10% after stabilizing the process.
4.2 Variation of Calorific Value of Biogas The period taken for biogas to be combustible was 85 days. It can be seen from Figure 4, that there is a rapid increase of CH4 content after about 50 days.
When kitchen waste feeding was started along with sewage feeding, methane content reduced to 70% and carbon dioxide content reached around 30%.
Figure 5 shows the flame generated by biogas.
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ENGINEER
After stabilizing the process, calorific value reached 28 MJ/Nm3 and after starting adding kitchen waste, calorific value fell back to 25 MJ/Nm3, as shown in Figure 6.
Figure 5 – Biogas Flame
Only sewage
Sewage & kitchen waste
Figure 6 – Variation of Calorific Value of Biogas with Time 4.3 Burner Efficiency Figure 7 shows the variation of energy output with energy input obtained by series of water boiling experiments.
From the gradient of the graph, it can be seen that the useful energy output was around 41% of input energy.
Figure 7 – Variation of Energy Output with Energy Input ENGINEER
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4.4 Effect of Kitchen Waste Quantity Biogas generation (m3) with variation of kitchen waste quantity added is shown in Figure 8. (the sewage quantity was constant at 2 kg). Variation of energy content (kJ) against varying kitchen
waste quantities is shown in Figure 9. The benefit of co-digestion of sewage/ kitchen waste is summarized in Table 1.
Figure 8 – Variation of Biogas Volume with Varying Kitchen Waste Quantity
Figure 9 – Variation of Total Energy Output with Varying Kitchen Waste Quantity
Table 1 – Effect of Addition of Varying Quantities of Kitchen Waste with 2 kg of Sewage Sewage quantity fed (kg)
Kitchen waste quantity added (kg)
Ratio of sewage to kitchen waste
Biogas volume (m3)
Energy output (MJ)
Fulfilment of domestic cooking energy requirement (%)
A
2
0
1:0
0.07
0.8
8
B
2
1
2:1
0.12
1.2
13
C
2
2
1:1
0.17
1.7
18
D
2
3
2:3
0.22
2.1
22
5
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ENGINEER
4.5 Leachate Properties Properties of leachate generated with two cases were compared with standard tolerance limits as given in Table 2. Table 2 – Leachate Properties Parameter BOD (mg/l) COD (mg/l) TSS (mg/l) pH Faecal coliform (MPN/100 ml)
5.
Standard tolerance limit 250 400 N/A 5.5 – 9
Feed: only sewage 176 251 2 6.9
Feed: sewage + kitchen waste 75 146 20 7.25
40
Not measured
20
that limited usage of security toilet. Further, multiple gas withdrawal method could not be practiced due to time limitations within the working hours of the institute. These are some limitations of this study and can be avoided by field testing at domestic level as a future work.
Discussion
It was observed that methane content reduced and carbon dioxide content increased after kitchen waste was added. This result is totally agreed with the literature. Slight reduction in calorific value after kitchen waste addition is due to the reduction of methane content.
It is highly recommended to use co-digestion technology in domestic scale which has triple benefits; as a cooking energy source, on-site waste management option and organic fertilizer for plantations.
It was found that the efficiency of the burner used is around 41% and it is comparable with literature values around 45% [5]. Daily energy output obtained with 3 kg kitchen waste co-feeding was 2.1 MJ and it will fulfil 22% of daily cooking energy requirements of an average family.
References 1. http://www.extension.org, visited 13th July 2012.
The rate of gas evacuation from a digester affects the volume of gas produced. Gas yield is higher when multiple draws per day is practiced due to enhancement of activities of active microbes when biogas is removed from the digester [6]. When Sri Lankan cooking pattern is concerned, cooking is normally done twice a day. Therefore, the advantage of multiple draw also can be taken.
2. Environmental protection agency (US), “The Benefits of Anaerobic Digestion of Food Waste at Wastewater Treatment Facilities”. 3. Lohri C., Vogeli C., Oppliger Y., Mardini A, Giusti R., Zurbrugg A., “Evaluation of Biogas Sanitation Systems in Nepalese Prisons”, Proceedings of the IWA-DEWATS Conference on Decentralized Wastewater Treatment Solutions in Developing Countries, 2010 March 23-26, Surabaya, Indonesia.
The leachate properties were in acceptable limits in both cases and can be safely discharge to the lands used for agricultural purposes. 6.
4. http://www.wrap.org.uk visited 23rd March 2012. 5. Tribhvan University (India), “Efficiency Measurement of Biogas, Kerosine and LPG stoves”, Lalitpur, 2001.
Conclusions
6. Okoroigwe E.C. and Agbo S.N., “Gas evacuation effect on the quantity of gas production in a biogas digester”, Trends in Applied Sciences Research, Vol. 2, No. 3, pp. 246-250, 2007.
Biogas generated from sewage and kitchen waste co-digestion can be effectively used to replace significant portion of domestic cooking energy requirement. According to the research findings, this percentage is 22% and it can be enhanced further by practicing multiple gas usages per day. However, since the research was carried out in institutional level, there was no direct control of sewage feeding and sometimes it could be seen ENGINEER
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Annual Transactions of IESL, pp. [20-24], 2012 © The Institution of Engineers, Sri Lanka
Development of Catalysts for the Conversion of Syngas to Aromatics in a Single Step K.G.H. Kodagoda, T. Auttanat and S. Jongpatiwut Abstract: Aromatics are important petrochemical feedstock, which are typically produced by petroleum naphtha reforming. With the emerging concept of green economies, biological origin for aromatic production seems to have a high potential in the future. Fe and Co based catalysts are commercially proven for converting syngas, which can be produced from biomass, to linear hydrocarbons via Fischer-Tropsch synthesis. Pt/KL and HZSM5 catalysts are well known for aromatization activity. Ru is also considered as an active catalyst for Fischer-Tropsch synthesis. In addition, Ru could improve the CO tolerance of Pt catalysts. The objective of this study is to investigate the conversion of syngas to aromatics over bimetallic Pt-Ru/KL catalysts and hybrid Fe based Fischer-Tropsch catalysts (i.e. Fe/KL or FeCoK) with aromatization catalysts (Pt/KL or HZSM5) in a single step at 310 °C and 20 barg. The results show that at the tested condition, Pt-Ru/KL yielded light hydrocarbon without aromatics. For the hybrid catalysts it was observed that, Fe/KL catalyst physically mixed with Pt/KL zeolite catalyst showed a better aromatic selectivity than the coimpregnated catalyst with the same active metal contents but decreased its selectivity drastically in short time due to deactivation of Pt sites by CO. Further, combined effects of HZSM5 and FeCoK showed that increasing HZSM5 in the hybrid catalyst shows the best performance at the HZSM5 to FeCoK ratio of 2 giving 4.7% aromatic yield. Key Words:
1.
Syngas, Aromatics, Hybrid catalysts utilizing the combined effects of different FT catalysts and aromatization catalysts. The present study is concentrated on studying the combined effects of Fe and Ru based FT catalysts such as Fe/KL, Ru/KL or FeCoK catalysts and aromatization catalysts such as Pt/KL or HZSM5 on direct syngas aromatization with co-impregnated bimetallic or physically mixed hybrid catalysts.
Introduction
Aromatics, today considered as a significant and essentially an important fraction of feedstock for petrochemical industry, which usually produced only by means of fossil originated hydrocarbons. With the emerging green concepts all over the world, biological origin for aromatic production will have a high potential in the future, which provides sustainability to petrochemical industry with new regulations and escalated feedstock price. Bio-mass can be converted to syngas using gasification technology and the technology which converts syngas to linear hydrocarbons is known as Fischer-Tropsch (FT) synthesis. FT reactions can be catalysed by Fe, Co, or Ru metal catalysts. Aromatization of linear hydrocarbons can be done with selected carbon range by using metal-acid bi-functional catalysts. Also, Pt/KL zeolite is proven for aromatization due to the metallic function of Pt and pore structure of KL zeolite. Further, HZSM5 or GaZSM5 are also active for aromatization for a range of carbon numbers.
2.
Experimental Details
2.1
Catalyst Preparation
2.1.1
Incipient Wetness Impregnation (IWI)
Pt/KL, Fe/KL Ru/KL and PtFe/KL catalysts were prepared by IWI technique and KL zeolite (supplied by TOSCH CORPORATION SiO2/Al2O3 = 6.1, BET surface = 290 m 2/g) were used as support. KL zeolite was dried at 110°C overnight and calcined at 400°C for 5 hr for removal of residual organic compounds. Tetraamineplatinum (II) nitrate [Pt(NH3)4 (NO3)2 ] (supplied by SIGMA-ALDRICH with 99.995%), Iron(III) nitrate nonahydrate [Fe(N O3)3.9H2O] (supplied by SIGMA-ALDRICH Eng. K.G.H. Kodagoda, B.Sc. Chemical Engineering (UOM), Msc Petroleum(Th)], MBAin MOT (UOM) Chemical Engineer in Ceylon Petroleum Corporation. T. Auttanat, M.Sc Petroleum(Th.), B.Eng.(Th). Dr. (Mrs.) S. Jongpatiwut, B.Sc Chemical Engineering (Th), MSc Petrochemical(Th), Ph.D Petrochemical(Th), Asst. Professor in Chulalongkorn University, Thailand .
The direct conversion of syngas to aromatic hydrocarbons is a significant and extremely important effort for petrochemical industry by 1
20
determine the surface morphology and the surface composition with HITACHI/S-4800 instrument. The CP FeCoK catalyst was expected to have surface area above 5 m 2/g and the porosity in the catalyst was required to observe in SEM images and elemental composition is determined by SEM-EDX in different locations to observe the metal distribution over the catalyst.
with 99.999%) and Ruthenium(III) acethylacetonate [Ru(C5H7O2)3] (Supplied by SIGMA-ALDRICH with 97% purity) were dissolved in exact amount of deionised water (DI) which is equivalent to 0.69 cm 3/g of pore volume for KL support [1]. In the case of coimpregnated PtFe/KL catalysts, relevant amount of each precursor is dissolved together in DI water. The resulted mixture after IWI was dried at 110 °C followed by calcination at 500°C with 100 cm3/min.g of air. The prepared catalyst was then stored in a desiccator.
2.2.3 X-Ray Diffraction (XRD) The XRD analysis for Fe/KL and FeCoK catalysts before and after reaction was conducted from 2θ of 10.0° to 80.0° with 0.02° steps with BRUKER/XAS, D8 advance x-ray diffraction instrument. Catalysts were tested before and after the activity testing to observe the formation of carbide phases in the reaction and to observe the form of oxide presence before reduction.
2.1.2 Co-Precipitation (CP) FeCoK catalyst was prepared by using coprecipitation with presence of glycolic acid in order to form better surface area for the catalyst. Iron (III) nitrate nonahydrate and Cobalt (II) nitrate hexahydrate ([Co(NO3)2.6H2O] supplied by SIGMAALDRICH with 98% purity) were dissolved in DI water and the stoichiometric amount of glycolic acid ([HOCH2CO2H] supplied by SIGMA-ALDRICH with 99% purity) was added with 5% excess. The solution is evaporated at 80°C to obtain solid and then, dried at 80°C overnight. The dried catalyst was then calcined at 350°C with 2°C/min heating rate and holding for 2 hr and cooled to room temperature. Addition of K was done by impregnation of potassium nitrate ([KNO3] supplied by CARLO-ERBA with ≥ 99% purity) solution on Fe and Co oxides. The impregnated mixture was then dried at 110°C overnight followed by calcining at 350°C with 2 °C/min heating rate and holding for 2 hr and cooled to room temperature. The prepared catalyst is then stored in a desiccators [2]. 2.2
Catalyst Characterization
2.2.1
Nitrogen Adsorption/Desorption
2.2.4 Temperature Programmed Oxidation (TPO) TPO tests were carried out to determine the amount and properties of coke formed in the reaction. All spent catalysts were analysed by using the instrument, which consists of methanator to convert CO2 produced to methane and online FID to detect methane. Coke in the catalyst was burnt with 2% O2 in He. 2.3 Catalyst Activity Testing Catalyst activity testing was carried out in a stainless steel continuous down flow isothermal fixed bed reactor (0.402″ ID) with 0.5 g FT catalyst in the middle of the reactor and the amount of other catalyst in hybrid catalysts varied to have required ratio while maintaining the amount of FT catalyst amount at 0.5g. Catalysts were in-situ reduced with 100 3 cm /g.min of pure H2 at 400°C with heating rate of 4°C/min for 3 h in the case of Fe/KL catalysts and Pt/KL catalysts. A special treatment was carried out with FeCoK containing catalyst which is reduction of catalyst with 100 cm 3/g.min of H2 at 400°C with heating rate of 1 °C/min and holding for 10 hr and cooled to 100°C followed by carbiding treatment. The special carbiding treatment was conducted with a gas mixture of He:H2:CO = 75:15:10 in order to obtain good carbide mixture [2].
Brunauer-Emmett-Teller (BET) method with AUTOSORB 1MP instrument was used with micro-pore analysis to find surface area, pore volume, and pore diameter of KL zeolite support as well as 9.5Fe/KL catalyst in order to determine the possible pore blockage with Fe addition. In addition, FeCoK catalyst was tested to measure the surface area which is one key factor for the activity of bulk catalysts. Samples were outgassed at 300°C for more than 8 hr prior to the N2 adsorption/desorption at liquid N2 temperature.
Syngas containing H2/CO of 1.5 was used as feed throughout the research. CO conversion and product selectivity were calculated as percentage of CO moles converted and
2.2.2 Scanning Electron Spectroscopy with Energy Dispersive X-Ray (SEM-EDX) SEM imaging and SEM-EDX were especially conducted for FeCoK catalyst in order to 2
21
TPO analysis of spent catalysts show that coke formation is increased in 9.5Fe/KL catalyst with increasing temperature and also decreased with increased HZSM5 content in hybrid catalyst due to dilution with HZSM5 as shown in Table 1. Further, XRD analysis of catalysts before and after the reactions shows the formation of carbide phases which gives the activity to the catalyst together with α-Fe. It can be observed that the pre-calcining temperature is not giving a significant influence on the forms of oxide in catalyst.
percentage of converted atoms which goes to each product Activity testing was carried out in three key steps as testing the FT activity of Fe/KL and FeCoK catalysts, syngas aromatization with coimpregnated FePt/KL and physically mixed catalysts, and syngas aromatization with physically mixed hybrid catalysts of FeCoK and HZSM5 (with different proportions). The catalysts containing X percentage of HZSM5 is noted as XZFeCoK.
3.
3.2 Catalyst Activity Testing The aromatic production with Fe-based FT and Pt/KL catalyst shows that physical mixture of catalyst has better performance than coimpregnated catalysts. This result is due to the pore blockage in KL zeolite with 9.5% Fe addition as observed in N2 adsorption/ desorption results. The aromatic selectivity and conversion for these catalysts are in Figure 3.
Results and Discussion
3.1 Characterization of Catalysts Mainly four techniques were used to characterize the catalysts and the results of characterization are presented in following sections. BET surface area, pore volume and pore diameter tests were carried out to test the possible pore blockage of KL zeolite after impregnation of Fe. The BET results show a significant decrease implying that the pores are blocked by Fe. Further, the plot of pore volume (DFT technique) and BET surface area against pore diameter clearly shows that the microspore volume related to pore size below 0.85 nm is disappeared with Fe addition as presented in Figure 1. Further, the BET surface area of FeCoK is observed as 36.445 cm 2/g which is greater than requirement of 5 cm 2/g for sufficient FT activity [3].
RuPt/KL catalysts showed an insignificant production of aromatics showing a higher selectivity to light paraffinic hydrocarbons deviating from our objectives. In syngas aromatization with FeCoK and HZSM5 hybrid catalysts, it was observed that the syngas conversion is not significantly changed with HZSM5 content in the catalyst but best aromatic selectivity is obtained at ratio of HZSM5/FeCoK = 2 (67ZFeCoK) leading to 4.7% aromatic yield after 430 min on stream.
SEM images of FeCoK catalysts shows a significant porosity in the catalyst after calcination and this is in line with the BET surface area results. The SEM images are presented in Figure 2.
Table 1 – Carbon Content after Reaction wt. % of C in the Spent Catalyst FT synthesis with 9.5Fe/KL
Aromatization with Fe/KL and Pt/KL
240 °C
300 °C
400 °C
Physical mix
3.62
4.56
25.19
13.27
Aromatization with FeCoK and HZSM5
Coimpregnated 5.48
3
22
FeCoK
67ZFeCoK
75ZFeCoK
86.58
31.74
23.54
Figure 1 – Surface Area and Pore Volume Analysis for KL Zeolite and 9.5Fe/KL Catalyst by N2 Adsorption/Desorption (a) Cumulative Pore Volume (b) Cumulative Surface Area
Figure 2 – SEM Images of FeCoK Catalyst with Different Magnifications
Figure 3 – Syngas Aromatization with 9.5Fe0.5Pt/KL and Physically Mixed 9.5Fe/KL and 0.5Pt/KL at 400 °C, 1 atm, 6000 cm 3/g.h (a) CO Conversion (b) Aromatic Selectivity
4
23
Figure 4 – Syngas Aromatization with FeCoK and HZSM5 Catalysts at 310 °C, 20 bar, 4800 cm 3/g.h (a) CO Conversion (b) Aromatic Yield
4.
Martinez, A., and Lopez, C., The influence of ZSM-5 zeolite composition and crystal size on the in situ conversion of Fischer-Tropsch products over hybrid catalysts. Applied Catalysis A: General, 294, pp.251-259, 2005.
3.
Soled, S.L. and Fiato, R.A., Process for preparing high surface area Iron-Cobalt Fischer-Tropsch slurry catalysts. US Patent (4,518,707). May. 21, 1985, (Filed – Dec. 14, 1983, Assignee – Exxon Research and Engineering Company, Florham, N.J.).
Conclusions
Physically mixed Fe/KL and Pt/KL catalyst shows a better performance over coimpregnated due to availability of accessible Pt sites in Pt/KL zeolite but Pt in KL zeolite is inaccessible due to pore blockage by Fe. Further, in the case of hybrid catalyst of FeCoK and HZSM5 show best performance at HZSM5/FeCoK = 2 (67 wt% of HZSM5) among studied catalysts giving highest aromatic yield. This behaviour is characterized by insufficient HZSM5 in the case of lower HZSM5 content and excess cracking with higher amount of HZSM5.
.
Acknowledgement The authors take this opportunity to thank the Petroleum and Petrochemical College and the National Center of Excellence for Petroleum, Petrochemicals, and Advanced Materials, Thailand for the financial support granted for this work.
References 1.
2.
Jongpatiwut, S., Sackamduang, P., Rirksomboon, T., Osuwan, S., and Resasco, D.E., n-Octane aromatization on a Pt/KL catalyst prepared by vapor-phase impregnation. Journal of Catalysis, 218, pp.1– 11, 2003.
5
24
Annual Transactions of IESL, pp. [25-32], 2012 © The Institution of Engineers, Sri Lanka
Production of Biodiesel in Pilot-Scale using Locally Available Feedstock Materials D.R.S. Hewa Walpita, F.M. Ismail and S.H.P. Gunawardena Abstract: Biodiesel or fatty acid methyl ester is a fuel that can be produced from lipid sources. It is popular as a totally renewable, nontoxic and biodegradable alternative for fossil based diesel due to its numerous environment benefits associated with its use. Currently, biodiesel is produced mainly using edible oils and the rest is covered by non-edible oils, animal fats and waste cooking oils (WCOs). The lab-scale studies of the research identified that, locally available feedstock materials such as Coconut, Palm, Rubber Seed Oil (RSO), Jatropha, Neem, Lard and WCO can be successfully converted into biodiesel. The study used alkali-catalyzed transesterification process to produce biodiesel from oils with FFA content less than 2.0%. The oils with free fatty acid content greater than 2.0% were pretreated using acid-esterification. The produced biodiesel were compatible with ASTM D 6751 and EN 14214 standards. A 50 litre portable reactor system was designed and fabricated with multi disciplinary units based on lab-scale results for pilot-scale studies. The designed unit is capable of carrying out complete biodiesel production process from pre-treatment to drying. The potential of using the pilot-unit in biodiesel production was studied using Palm oil and WCO as feedstock materials. The studies also successfully tested the quality of the biodiesel produced in its pure form using a diesel three-wheeler. Keywords:
1.
Biodiesel, Pilot-scale, Reactor
vehicle manufactures recommend only using biodiesel blends up to 20% in their diesel vehicles.
Introduction
Various alternative fuels have been investigated to replace conventional petroleum fuels since the first oil crisis of the 1970’s. The initial interest was mainly as a supply security, but recently more attention has been focused on the use of renewable fuels in order to reduce the CO2 emissions from combustion sources [1]. Though, unmodified vegetable oils have the potential to be used as fuels for diesel engines, prolong operation of engines were impossible even with fully refined oils. However, it was found later that vegetable oils and fats after transesterification with short chain alcohols such as ethanol or methanol can be used in diesel engines without any complications [2]. Since this transesterified oil could be directly used in diesel engines it was known as “biodiesel”. In addition to vegetable oils and animal fats, waste greases both yellow and brown are also commonly used in biodiesel preparation [3]. Biodiesel can be used as conventional diesel in diesel engines because its properties are very close to petroleum-based diesel. For example, biodiesel has the proper viscosity, a high flash point, a high cetane number, and therefore, researchers have found out no engine modifications are required when using biodiesel [1,4]. However, still most of the
As a point of comparison, the calorific value of pure biodiesel (B100) is about 90% of conventional diesel, and hence, the engine performance is only reduced by 10%. Biodiesel, however, is made from renewable resources, is biodegradable and nontoxic, and has a higher flash point than normal diesel. In addition, biodiesel increases lubricity (even at blends as low as 3% or less), which prolongs engine life and reduces the frequency of engine part replacement. Another significant advantage of biodiesel is its low emission profile and its oxygen content of 10-11%. Additionally, it is also capable of reducing carbon and total particulate emissions as well as carbon monoxide (CO) and unburned hydrocarbons
Eng. D. R. S. Hewa Walpita, B.Sc. Eng. (Moratuwa), M.Sc. (Moratuwa), Eng. (Dr.) (Mrs.) F. M. Ismail, B.Sc. Eng. (Moratuwa),Grad. IChem.C (SL), Ph.D (UMIST,UK), Senior Lecturer, Dept. of Chemical & Process Engineering, University of Moratuwa Eng. (Dr.) S. H. P. Gunawardena, B.Sc. Eng. (Moratuwa), Ph.D. (Birmingham), Senior Lecturer, Dept. of Chemical & Process Engineering, University of Moratuwa.
1 25
significantly. Biodiesel is regarded as an environmentally friendly biofuel since it provides a means to recycle carbon dioxide (CO2) and hence, biodiesel does not contribute to global warming [3].
Oil or Fat Estimation of FFA
FFA < 2% Since the quality of biodiesel is a key factor when using it as an alternative to conventional diesel, several standards (i.e. ASTM D 6751 and EN 14214) have been introduced. When these standards are met, biodiesel or its blends can be used in most of the modern engines within the manufactures recommended limits without modifications while maintaining the engine’s durability and reliability.
FFA > 2% H2SO4 + Methanol
Acid Esterification FFA > 2% FFA < 2% Transesterification
KOH + Methanol
Biodiesel Purification (Layer separation, washing and drying)
Currently, biodiesel is prepared by transesterification of oils/fats using short chain alcohols in the presence of an alkaline catalyst. Industrially, NaOH and KOH are preferred with alcohols like methanol due to their wide availability and low cost [3]. If the free fatty acid (FFA) level of oil is greater than 2%, the FFA level of the oil or fat has to be reduced by esterification to avoid soap formation in transesterification. This is done by reacting FFA with KOH or NaOH in the presence of an acid catalyst. The flow diagram of the biodiesel production process is shown in Figure 1.
Biodiesel Figure 1 – Flow Diagram of the Biodiesel Production Process
2.
Design and Construction of Pilot-Scale Reactor System
2.1 Process Design The pilot-scale reactor system has been designed as a semi-automated, pilot-scale portable demonstration rig with a 50 litre reactor capacity. The designed system is capable of producing 20-35 litres of biodiesel per batch depending on the quality of feedstock. It is capable of handling all the steps of the biodiesel production from feedstock pre-treatment to biodiesel purification.
The cost of biodiesel, however, is the main hurdle in commercialization of the product. Use of low-cost raw-materials such as “waste cooking oil” (WCO) and adaption of high quality glycerol recovery systems for the byproducts are some primary options which can lower the cost of biodiesel [5]. Sri Lanka as a petroleum fuel importing country can reduce fuel importing cost if biodiesel is produced locally. When considering the feedstock materials, Sri Lanka is rich in wide range of oils and fats including edible oils, nonedible oils, animal fats and restaurant waste oils. Hence, it is important to evaluate the feasibility of using such oils and fats in biodiesel production.
The reactor system was designed with 3 multifunctional units; reactor unit, a mixing unit and a storage unit. In addition to these 3 major units, a condenser unit was attached to the reactor and an air sparger was included to the storage unit to fulfil additional process requirements. Non-compulsory units such as storage vessels which are not directly involved to the process were omitted from the design. Block diagram of the pilot-plant is given in Figure 2. 2.2 Reactor Unit The reactor unit was designed as a closed toriconical bottomed cylindrical vessel unit to avoid methanol evaporation during pretreatment and biodiesel reactions. The reactor is equipped with an electrical heating system and a condenser unit. Jet mixing was used as
26
the mixing mechanism since it facilitates to keep the reactor as a completely closed system. The system was designed as a single side-entry nozzle system with a pump and an external circulation path with a downward pointing nozzle at the releasing end. An additional nozzle was placed at the middle of the reactor to make it possible to operate the reactor with smaller batches. Two control valves were used with the nozzles to select the appropriate nozzle according to the operating liquid level.
MV – MANUAL VALVE SV – SOLENOID VALVE SV6
REACTOR UNIT
SV5
MV 3
SETTTLING UNIT MIXING UNIT
SV2 SV3
SV1 MV1
MV2
Pipe material - SS 304L Pipe size - 0.75’ scheduled 40
SV4 CENTRIFUGAL PUMP
KOH STORAGE
H2SO4 STORAGE
METHANOL STORAGE
Figure 3 – Piping Diagram of the Biodiesel Unit
Manually controlled
Full / semi automated
MIXING UNIT
Essential components
2.5 Unit Arrangement The processing units of the plant were mounted on a single structure and connected using two pipe lines with manual and automated valves as necessary to carryout the overall process. Piping diagram of the biodiesel unit is given in Figure 3. Pilot plant included a semi automated control system to control the plant operations. The final appearance of the pilot-scale biodiesel reactor system is as in Figure 3.
Neg lected components
LOW FFA FEEDSTOCK TANK
REACTOR UNIT
HIGH FFA FEEDSTOCK TANK
STORAGE UNIT
WATER TANK
CRUDE METHANOL
GLYCERINE TANK
WASHED W ATER TANK
2.6 Mechanical Design Mechanical design of the pilot plant was carried out according to British Standard PD 5500, EN 13445 and ASME Code Section VIII. For the mechanical design, the design temperature was taken as 125°C, and the pressure of the reactor vessel was taken as 29.49 kPa. SS 304L was used as the fabrication material for vessels and 0.75’ scheduled 40 pipes was used for pipe lines which are in contact with H2SO4, water and water vapour to avoid corrosion. Carbon steel was used for the plant structure where it does not have any contact with reactive materials.
PURE BIODIESEL STORAGE TANK
Figure 2 – Block Diagram of the Biodiesel Plant 2.3 Settling Unit Toriconical bottomed cylindrical vessel with 50 litre capacity is used as a settling unit to support in non-reaction operations such as settling, layer separation and washing. A removable air sparger system consisted of a mesh-like tube structure placed at the bottom of the vessel provides tiny air bubbles during the washing process. 2.4 Mixing Unit A similar shaped mixing unit with 9.9 litre capacity was designed to use as both methoxide reactor and H2SO4-methanol mixing unit based on the results obtained in lab-scale studies. A stirred tank agitation method was selected as the mixing mechanism pitched blade type turbine impeller and was powered by a AC motor.
3.
Materials and Method
3.1
Materials
Both lab-scale and pilot-scale studies were done using locally purchased/collected feedstock oils and fats. In lab-scale studies coconut oil, rubber seed oil (RSO), WCO, jatropha, neem and lard were used as feedstock materials and the pilotscale studies were done using WCO and palm oil. Laboratory grade KOH, laboratory grade H2SO4 and industrial grade methanol were used as reactants in both lab-scale and pilot-scale studies.
27
separated bottom layers were settled further for another 22 h. Then the AV of the further settled layers was measured and the FFA amounts were calculated. If this value is greater than 2%, then acid esterification step was repeated and if it is less than 2%, pretreated oil was used for biodiesel production. Alkali-catalyzed transesterification Lab-scale alkali-catalyzed transesterification reactions were carried using 100 ml of pretreated oil and coconut oil samples. The amounts of KOH require for the reactions were estimated as given in [6]. Methanol-KOH mixtures were prepared by dissolving measured amount of KOH in 20 ml methanol (20% of the oil). Then, oil samples were preheated to 55°C, and the prepared methanolKOH mixtures were introduced. Reaction was carried out for 90 min by maintaining the temperature at 55°C while mixing. After completion of the reactions, the mixtures were settled for 24 hrs and the top layers were separated. The separated top layers were then water washed using tap water for several times until clear water layers are obtained. The washed biodiesel was then heated at 110°C for sufficient time to remove moisture. Washed and dried biodiesel samples were tested for properties such as density, kinematic viscosity and flash point.
Figure 4 - Unit Arrangement of the Biodiesel Pilot Plant 3.2 Reaction Set-up A 250 ml reagent glass bottle with a stopper and a magnetic stirrer were used as a laboratory scale reactor for all the lab-scale studies. A thermometer was inserted to the bottle through a stopper to measure the temperature of the reaction mixture. This complete system was placed on a heating magnetic stirrer to provide heating and mixing. All pilot-scale studies were done using the fabricated 50 L reactor system.
3.4 Biodiesel Production in Pilot-Scale As in the lab-scale studies, low FFA containing palm oil was directly subjected to transesterification in pilot scale studies. However, acid esterification was done prior to alkali-catalyzed transesterification for WCO with a high FFA content.
3.3 Biodiesel Production in Lab-Scale Among the feedstock materials tested, only coconut oil had a low content of FFA and hence, directly subjected to transesterification. Acid esterification was done prior to alkali-catalyzed transesterification as a pre-treatment step to reduce FFA content to a value below 2% for the rest of the oils which had a high FFA content.
Oil pre-treatment AV of the WCO was measured and the amounts of H2SO4 and methanol to be used were estimated based on the FFA present as 0.10 g of H2SO4/g of FFA and 2.5 g of methanol/g of FFA. The same procedure followed in lab-scale oil pre-treatment was adapted and the remaining FFA amount was estimated after settling.
Oil pre-treatment Acid value (AV) of the oil samples was measured according to ASTM D 1980-67 and the FFA of oils were calculated. The amounts of H2SO4 and methanol to be used were estimated based on the initial amounts of FFA present in the samples [7]. In all esterification reactions done in laboratory scale work, 0.05 g of H2SO4/g of FFA and 2.5 g of methanol/g of FFA were used. Oil samples were preheated and H2SO4-methanol mixtures were introduced. Then the reaction was carried out at atmospheric pressure for 30 min by maintaining the temperature at 55°C while mixing. After the reaction time, samples were allowed to settle for 2 h and then the layers were separated. The
Alkali-catalyzed transesterification Alkali-catalyzed transesterification studies were done in the 50 L reactor unit as pilot-scale studies for palm oil and pre-treated WCO samples of 25 litres each. The required KOH and methanol amounts were estimated as in the lab-scale studies. The oil samples were then
28
reacted with methanol-KOH mixtures for 1.5 h. The top layers were separated after 24 h of settling, and pure biodiesel samples were obtained after washing and drying. Produced biodiesel samples were then tested for properties such as density, kinematic viscosity and flash point.
All six feedstock materials tested have reached ASTM and/or EN standards of the flash point. The required density level was also achieved by all biodiesel samples except coconut and jatropha oils. Although coconut oil and RSO derived biodiesel were within the standard values of kinematic viscosity, WCO, Jatropha and Neem derived biodiesel have higher viscosities. However, there is a high viscosity reduction in all biodiesel samples when compared with the respective original oils. All the kinematic viscosity readings were measured at room temperature (i.e. within 27-30°C) and a low values can be expected if these measurements were done at the standard measuring temperature of 40°C. Further, incomplete transesterification reaction could be another reason for this high viscosity.
3.5 Engine Testing and Road Testing Biodiesel was tested for its performances using 70 kW “Toyo” AC diesel generator and road testing was carried out using an unmodified “Piaggio” diesel three-wheeler.
4.
Results and Discussion
4.1
Biodiesel Production in Lab-Scale
The properties of biodiesel produced using six different oil/fat feedstocks are given in Table 1.
Table 1 - Properties of Biodiesel Produced in Lab-Scale using Different Feedstock Materials Property Point Density
Unit
Coconut RSO
°C
110
g/cm3
0.835
Feedstock material WCO Jatropha
126
172
0.877 0.877
cSt 4.9* 5.7* Viscosity * Measured at room temperature
10.26*
4.2 Biodiesel Production in Pilot-Scale The properties of biodiesel produced using WCO and palm oil are given in Table 2. According to the results obtained, flash points and densities were compatible with ASTM and EN standards. However, kinematic viscosities have shown higher values than the standards, as observed in the lab-scale studies. When the properties of biodiesel produced in pilot-scale and lab-scale are compared, no significant difference was observed. This confirms that scaling up has been successful with minimum product deviations.
°C g/cm3
WCO derived biodiesel 179 0.868
Palm oil derived biodiesel 192 0.869
cSt
8.06
8.63
Unit
Flash Point density Kinematic Viscosity
Lard
155
160
179
> 130/110
0.955
0.881
0.868
0.86-0.9
17.12*
8.51*
-
1.9-6.0
4.3
Energy Consumption for Biodiesel Production The energy consumption in biodiesel production in the pilot-scale unit is reported here as it is an important parameter which affects the production cost when produce in commercial-scale. The total energy requirement of the unit is equal to its electrical energy requirement, since it is completely powered by electricity. The energy consumption was measured using the rated power consumptions and the running times of process equipment. Reasonable rated powers were assumed for equipment whenever rated powers were not available. The summary of assumed/used rated powers of process equipment is given in Table 3. Table 3 – Rated Power Summary of Process Equipment
Table 2 - Properties of Biodiesel Produced using WCO and Palm Oil in Pilot-Scale Property
ASTM/EN Neem
Process Equipment Circulation pump Control system Heaters (per unit) Mixing motor Air/Oxygen pump Solenoid valve
29
Rated Power (W) 370 50 2,000 25 30 20
The material cost for the production of biodiesel using WVO was estimated based on the results of both lab-scale and pilot-scale studies. The price of WVO was taken as Rs. 20.00 per litre and the cost of the rest of the chemical required were their bulk market price. According to the estimation, cost of material was Rs. 53.51 for WVO with 5.595% of FFA (Table 5). However, the price will vary with the FFA content of the oil.
According to the estimation, the energy required to produce 35 litre biodiesel batch was 8.702 kWh (Table 3). Hence, the energy required to produce one kg of biodiesel is 0.287 kWh (1,032 kJ/kg), and is at an acceptable level when compared with the calorific value of biodiesel (which is 35-40 MJ/kg).
4.4
Raw Material and Chemical Cost
Table 4 - Electrical Energy Consumption for Biodiesel Production per Batch Production stage
Equipment
Number of units
Oil Pre-treatment Stage H2SO4 and Mixing motor Control system methanol mixing Electrical heaters Circulation pump Oil preheating Solenoid valves Control system Electrical heaters Circulation pump Reaction stage Solenoid valves Control system Solenoid valves Layer separation Control system Biodiesel Production Stage Methoxide Mixing motor reaction Control system Electrical heaters Circulation pump Oil preheating Solenoid valves Control system Electrical heaters Circulation pump Reaction stage Solenoid valves Control system Circulation pump Solenoid valves Layer separation Control system Biodiesel Purification Stage Oxygen pump Biodiesel washing Solenoid valves Electrical heaters Circulation pump Biodiesel drying Solenoid valves Control system
Running Rated time (min) Power (W)
Electrical energy consumption (kWh)
1 1 3 1 2 1 3 1 2 1 2 1
5 5 7 7 7 7 10 30 30 30 5 5
25 50 2,000 370 20 50 2,000 370 20 50 20 50
0.002 0.004 0.700 0.043 0.005 0.006 1.000 0.185 0.020 0.025 0.003 0.004
1 1 3 1 2 1 3 1 2 1 1 2 1
5 5 7 7 7 7 30 90 90 90 5 5 5
25 50 2,000 370 20 50 2,000 370 20 50 370 20 50
0.002 0.004 0.700 0.043 0.005 0.006 3.000 0.555 0.060 0.075 0.031 0.003 0.004
1 2 3 1 2 1
30 5 20 20 20 20
60 20 2,000 370 20 50
0.030 0.003 2.000 0.123 0.013 0.017
Total Energy Consumption 4.5 Engine Testing and Road Testing The load profile obtained from engine testing of WVO derived biodiesel is in accordance with
0.006
0.754
1.230 0.008 1.997
0.006
0.754
3.690
0.038
0.033
2.153 2.186 8.702
the results of fossil diesel for the tested 2.5 - 3.5 kW range. The results are shown in Figure 5. The road testing done using 100% WCO and
30
Fuel consumption (m/kW hr)
neem derived biodiesel in unmodified diesel engine showed similar engine ignition as fossil diesel and was able to drive the vehicle smoothly. However, it is not recommended to use pure biodiesel in engines without identifying long-run effects.
1200 Biodiesel
Conventiona l Diesel
1000 800 600 400 200 0 0
0.5
1
1.5
2
2.5 3 3.5 Power (kW)
4
4.5
5
5.5
6
Figure 5 – Load Profile for Biodiesel and Fossil Diesel Table 5 – Material Consumption for Biodiesel Production per Litre Production stage
Material
Unit
Quantity
Unit price (Rs.)
1.1080 0.2074 0.0055 1.0526 0.2105 0.0200
20.00 125.00 80.00 0.00 125.00 260.00
Cost (Rs.)
Material usage Oil Pre-treatment Biodiesel production
WVO Methanol H2SO4 FFA reduced WVO Methanol KOH
lit lit kg lit lit kg
Water for washing
lit
Methanol (50% of total)
lit
22.16 25.92 0.44 0.00 26.32 5.19
48.52
31.51
Purification 5
0.10
0.50
0.50
Material recovery 0.2089
Cost of material
5.
125.00
(26.12) (26.12) 54.01
scaling up. Studies also showed that the material cost and the energy requirement for biodiesel production in pilot-scale is Rs. 53.51 (for WCO) and 0.287 kWh/kg (1,032 kJ/kg), respectively. Apart from biodiesel production studies, road testing proved the ability of using biodiesel in unmodified engines even as a pure fuel.
Conclusions
Lab-scale and pilot-scales studies showed the potential of using locally available oils and fats such as coconut, palm, RSO, neem, jatropha, lard and WCO in biodiesel production. The properties of biodiesel produced using different feedstock materials were up to the level of ASTM and/or EN standards in their flash point and density. However, kinematic viscosity has shown a considerable deviation from the standards, though the biodiesel produced using coconut and RSO were within the limits. The reasons for higher kinematic viscosity are assumed to be the incompletion of transesterification reaction and incorrect temperature at viscosity measuring.
References
A 50 litre pilot plant which could handle pretreatment, processing and washing of biodiesel was designed and fabricated. The studies done in pilot-scale showed that the quality of biodiesel produced in pilot-scale is same as in the lab-scale, and no significant corrections are required for the process when
31
1.
Scholl, K. W. and Sorenson, S. C., "Combustion of soybean oil methyl ester in a direct injection diesel engine”. SAE International, 1993.
2.
Vellguth, G., "Performance of vegetable oils and their monoesters as fuels for diesel engines", SAE International, 1983.
3.
Lotero, E., Liu, Y., Lopez, D. E., Suwannakarn, K., Bruce, D. A. and Goodwin, J. G., "Synthesis of biodiesel via acid catalysis". Industrial & Engineering Chemistry Research 44(14): 5353-5363, 2005.
4.
Noiroj, K., Intarapong, P., Luengnaruemitchai, A. and Jai-In, S., "A comparative study of koh/al2o3 and koh/nay catalysts for biodiesel
production via transesterification from palm oil". Renewable Energy 34(4): 1145-1150, 2009. 5.
Ma, F. and Hanna, M. A., "Biodiesel production: A review". Bioresource Technology 70: 1-15, 1999.
6.
Addison, K. (2008), "Biodiesel processors". http://journeytoforever.org/biodiesel_processo r.html. Accessed on 11th March 2009.
7.
Walpita, D. R. S. H., Gunawardena, S. H. P., Ismail, F. M., Sampath, P. R. A. U. and Samarakoon, S. P. A. G. L., Quantification of reactants required in the conversion of free fatty acids (FFA) present in vegetable oils and animal fats into fatty acid methyl ester, Sri Lanka Patent Pending, 2011.
32
Annual Transactions of IESL, pp. [33-37], 2012 © The Institution of Engineers, Sri Lanka
The Development of a Process to Synthesize Carbon Nanotubes from Biogas Komathy Vamathevan, Manisha Gunasekera and Ajith de Alwis Abstract: Carbon nanotubes represent one of the most important materials in nanoscience and nanotechnology. The unique properties of carbon nanotubes open new fields in science and technology. This paper explains a simple process developed towards synthesizing carbon nanotubes from biogas by the method of chemical vapour deposition. In this process, Ni/SiO2 was used as catalyst at 550 OC temperature. The biogas was supplied to the reactor for one hour continuously. The final sample was investigated by means of scanning electron microscope (SEM). Key Words: Biogas, Carbon nanotubes, Chemical Vapour Deposition, Catalyst.
1.
250$ (32,500 LKR) per gram and it varies with the purity and quality of the product [6]. The high price is due to the fact that CNT could be produced so far only on a laboratory scale, through different gas-phase processes (flame synthesis, catalytic chemical vapour deposition, electrical arc discharge, laser ablation, etc), and requires a complex cleaning and separating procedures. Another main reason is the difficulty in transferring of the molecular properties to macroscopic materials which is a complex process and still at research level. Some examples are the dispersion of CNT in composite matrices or spinning of CNT to macroscopic fibers.
Introduction
Carbon nanotubes (CNTs) are molecular-scale tubes of graphitic carbon with outstanding mechanical, electrical, chemical and thermal properties [1, 2]. They are among the stiffest and strongest fibres known, and have remarkable electronic properties and many other unique characteristics [3]. Due to these reasons they have attracted huge academic and industrial interest, with thousands of papers on nanotubes being published every year. It is considered as the most researched material of the 21st century. Commercial applications have been rather slow to develop, however, primarily because of the high production costs of the best quality nanotubes [4]. The continuous production of CNT’s is a challenging target.
Compared with arc discharge and laser ablation methods Chemical Vapour Deposition (CVD) is the cheapest and need less intensive technology [5, 7]. But the major problem of this method is catalyst deactivation within a short time period. Thus, catalyst development is also an end goal in process development.
The objective of this research is to develop a process to synthesize CNTs from biogas by catalytic deposition method. This method is known to be the cheaper method to produce carbon nanotubes than the other two methods namely Arc Discharge and Laser ablation [5].
Direct catalytic decomposition of methane at moderate temperature is synthesizing carbon nanotubes [8]. The rate of carbon deposition is controlled by isothermal carbon diffusion through the metal particle [9].
In this local development of the process to synthesize carbon nanotubes from biogas, the research focuses on the preparation of a catalyst, designing and fabricating of a suitable reactor, and subsequent scaling-up. The paper presents the results from the initial phase of work.
2.
Eng. (Ms.) Komathy Vamathevan , B.Sc. Eng. (Moratuwa) , M.Sc. (Moratuwa), Lecturer of Mechanical Engineering, Department of Mechanical Engineering, Jaffna Regional Centre , The Open University of Sri Lanka. Eng. (Dr.).(Ms) Manisha Gunasekera, B.Sc. Eng. (Moratuwa), M.Eng. (Moratuwa), Ph.D. (Loughborough), Senior Lecturer, Department of Chemical and Process Engineering University of Moratuwa, Sri Lanka.
Background
2.1
Challenges of Producing Carbon Nanotubes At present, technical application of CNT based materials is slow due the very high price of CNT. Particularly for single wall CNT (99wt%), which amounts to approximately
Prof. Ajith de Alwis, , B.Sc. Eng. (Moratuwa), MBA (PIM-SriJ), Ph.D. ( Cambridge ), Professor, Department of Chemical and Process Engineering , University of Moratuwa, Sri Lanka.
33
The catalyst is deactivated because of the active surface blocking by carbon deposits. Therefore to avoid this issue and find a processing method with long catalyst lifetime despite carbon is deposited in large quantity is necessary for large scale production.
biogas containing methane and carbon dioxide over a catalyst. The research focuses on Preparation of the catalyst Design and fabrication of the equipment for decomposition of methane on the catalyst The use of reactor and catalyst to synthesize carbon nanotubes from biogas.
Nagayasu, et al (2006) has explained the mechanisms of deactivation of catalyst [10]. According to their explanation part of carbon atoms which remain on the front surface of the nickel particles, gradually develop into graphite sheets. Therefore, the catalyst is rapidly deactivated at a certain carbon yield in the decomposition of pure methane. This is because the partial pressure of hydrogen in the catalyst bed affects the development of graphite sheets. In the decomposition of pure methane, the rate of carbon decreases by gradual development of the graphite sheets on the nickel particles. Simultaneously, the partial pressure of hydrogen in the catalyst bed gets decreased, which diminishes the reaction rate of surface carbon species with gas-phase hydrogen molecules thus causing rapid deactivation of the catalyst. Methane is decomposed to carbon species on both Ni particle and acid site of the support. Carbon dioxide is also activated on both Ni particles and the support. Methane decomposition on Ni particles takes place much faster than removal of the carbon species by reaction with surface oxygen species on Ni. Compared with pure methane decomposition the time taken is long to deactivate the catalyst while using carbon dioxide with methane [10].
3.
Experimental Procedure
3.1 Catalyst Preparation Nickel as the catalyst material and SiO2 as a support material were selected for this reaction. Availability of material to prepare Ni/SiO2 in the Sri Lankan market is higher than other support materials such as Al2O3, TiO2, and ZrO2. Also, Ni/ SiO 2 catalyst can be prepared by using Sol – Gel method and for this method advanced equipment is not necessary as in the case of impregnation method. A nickel precursor was prepared by hydrolysis of the ammonia complex produced by dissolving nickel nitrate in aqueous ammonia solution [11, 12]. The precipitate was filtered out and washed with water in order to remove ammonium nitrate. The specific surface area of the prepared hydroxide Ni(OH)2 was 460m2/g after drying in air at 110 OC. Nonstoichiometric nickel oxide is prepared by calcining nickel hydroxide in flowing air at 250OC. There by, the specific surface area of the oxide could be further reduced. Next, the texture of this nickel oxide was varied by calcination at 350, 450 and 700 OC, thus the moisture capacity of nickel oxides was from 6 to 0.8 ml/g.
Effect of carbon dioxide co-feed on decomposition of methane over Ni catalysts has studied by Akinori, et al [10, 11]. They have used carbon dioxide and methane as two separate supply material in their experiments [10, 11]. However, biogas consists of these two materials together and composition ratio of methane to carbon dioxide is approximately 3: 2.
To prepare 90% NiO–10% SiO2 systems, the sample of nickel oxide was modified with silica by mixing them with alcosol containing silica in amount of 10%. The Alcosol was prepared by mixing 50 ml of Tetra Ethyl Ortho Silicate (TEOS), 40 ml of ethanol, 2ml of water and 0.5 ml of 40% HCl. The content of silica in the alcosol is 0.147 g per 1ml, and could be varied by dilution with ethanol.
Biogas is a renewable carbon substrate for this process and as such quite promising. Sri Lanka has a very high potential to produce biogas in large scale. Currently, lots of plants are operating in small scale to produce biogas. Therefore, biogas is selected in this research work to synthesize carbon nanotubes.
The mixture of NiO and alcosol was dried in flowing air at room temperature. Then the temperature was elevated to 150 OC and the sample was allowed to stand at this temperature for an hour.
2.2 Objective The objective of this research is to develop a process to synthesize carbon nanotubes from
34
3.2 Reactor Design The reactor was designed and fabricated in the workshop using available reactor fabricating material in Sri Lankan markets (shown in Figure 1). Stainless steel was used as the main material to fabricate the cylinder vessel, inlet and outlet tubes and inside holder. Mild steel was used to make the supporting legs.
temperature of the reactor, and power is supplied through the inverter to maintain the constant temperature. Gas In
P-1
V-1
Thermo Couple TT
P-3
Reactor Heating Element
TIC Relay
Temperature Indicating Controller Catalyst Holder
Inverter
Catalyst Holder
E-2
P-2
P-2
V-2
Gas Out
Figure 2 - Process Control Diagram
The power is supplied to the relay and it is connected to the temperature controller. It is then transmitted through the inverter and supplied to the heating element. Here, the relay is used to control the circuit by a lowpower signal. The temperature sensor (Thermo Couple), located near the top of the vessel senses the temperature. It is connected to the temperature indicating controller (TIC). The transmitter reports the process variable that is the temperature of the reactor to the controller using digital bits of information.
Figure 1 - Fabricated Reactor
Accordingly the size requirement, stainless steel tube was selected for the cylinder part of the reactor and the fitting top cap cut with the lathe machine was welded permanently using an arc discharge. A slightly thicker bottom cap was prepared with the fitting thread and fitted to the bottom of the cylinder. A Catalyst holder was made from stainless steel rod and placed inside the cylinder. The design parameters are as follows:
3.4 Experiments with Biogas A 2.54 g sample of the catalyst material was kept in the holder and the holder was fixed inside the cylinder for the synthesis of carbon nanotubes from biogas. Then, the argon gas was sent into the reactor and an inert environment inside the reactor cylinder was obtained. The reactor was heated up to 550 0C and at this temperature the biogas was sent in to the reactor for one hour [10-13]. The one hour was selected based on the experimental results of reaction time vs carbon yield reported by Nagayasu, et al [10].
Internal pressure – 1.55 kg/cm2 ( 1.5 atm) Design pressure – 2.07 kg/ cm2 (2 atm) Material – stainless steel (ASTM / ASME SA 312 GR. TP 316L) Outside diameter – 0.051 m Allowable stress – 8.8 kilograms (force) per square inch
At the end of one hour, the gas supply was stopped and the reactor was allowed to cool down to the room temperature. The reaction product sample is taken out of the reactor at room temperature. This sample was checked for the morphologies of the carbon thus
3.3 Process Control The control system developed to ensure that the chemical solution inside the reactor vessel is maintained at isothermal conditions (shown in Figure 2). A heater band transfers heat to the reactor. The control system maintains a constant temperature by measuring the
35
deposited by the biogas, using a Scanning Electron Microscope (Hitachi SU6600).
4.
Observations, Discussion
Results
diffusion of carbon through the Ni metal particle followed by deposition of carbon graphite layers on the rear side of the Ni particle [14].
and
In this research for developing a process to synthesize carbon nanotubes using biogas has been carried out using the catalysts with nickel particles anchored on the support surface to prevent expulsion of the nickel particles from the support. It is recognized that the present work aimed at synthesis of CNTs should be continued with modification to the process parameters.
The SEM images of the sample produced in argon atmosphere with reactor temperature at 550 0C are shown in Figure 3. Carbon nanotubes were not found in the above sample. Therefore, it is understood that the continuation of further testing experiments with some modification to process parameters is necessary to promote CNTs formation.
5.
Conclusion
The designed and fabricated reactor can be used for methane decomposition on the Ni/SiO2 Catalyst prepared by the Sol-Gel method. However, further work needs to be done in the development of the process to synthesize carbon nanotubes from biogas. The microscopy imaging had indicated the portential and next phase of work will report on CNT production and optimization of the system.
Acknowledgment The staff of workshop unit at the Open University of Sri Lanka is gratefully acknowledged for their support in making the reactor and help in carrying out the experimental work. The analytical service of Sri Lanka Institute of Nanotechnology is also gratefully acknowledged.
References 1.
Hone J., Carbon Nanotubes: Thermal Properties, Dekker Encyclopedia of Nanoscience and Nanotechnology, pp.603-610, 2004.
2.
Rodney S. Ruoff , Dong Qian , Wing Kam Liu, Mechanical properties of carbon nanotubes: theoretical predictions and experimental measurements, C. R. Physique 4, 993–1008, 2003.
3.
Valentin N. Popov, Carbon nanotubes: properties and application, Materials Science and Engineering R 43, 61–102, 2004.
4.
Carbon nanotube field-effect transistor, Available from:< http://en.wikipedia.org/ wiki/Carbon_nanotube_field-
Figure 3 - SEM Image of Carbon Deposited on SiO2 and Ni Sample at 550 0C
The factors which influence the above reactions are feed gas flow rate, catalyst material, and catalyst support material, temperature of the catalyst reaction, morphology of the catalyst support material and partial pressure of the reaction gas. It is generally accepted that in the methane decomposition on Ni catalysts, carbon nanotubes are formed by the dissociation of methane on the Ni metal surface, dissolution of the surface carbon into the Ni particles and
36
effect_transistor#cite_note-park10-27>. [3 July 2012]. 5.
Stephanos F. Nitodas, and Theodoros K. Karachalios, Nanothinx S.A, Low-cost Production and Applications of High Purity Carbon Nanotubes.
6.
Helix Material Solutions, Available from: < http://www.helixmaterial.com/Ordering.ht ml> . [25 July 2012].
7.
Daenen M., The Wondrous World of Carbon Nanotubes - a review of current carbon nanotube technologies, Eindhoven University of Technology, 2003.
8.
Mordkovich V.Z., Dolgova E.A., Karaeva A.R., Kharitonov D.N., Synthesis of carbon nanotubes by catalytic conversion of methane: Competition between active components of catalyst. ScienceDirect, Carborn 45, pp. 62-69, 2006.
9.
Carole E. Baddour, and Cedric Briens, Carbon Nanotube Synthesis: A Review. International journal of chemical reactor engineering, volume 3, Review R3, 2005.
10.
Yoshiyuki nagayasu, Akinori nakayama, Eriko Yagasaki, Kouta Asai, Masshi Inoue, and, Shinji Iwamoto, Effect of Carbon Dioxide Cofeed on decomposition of Methane over Ni Catalysts. Journal of the japan Petroleum Institute, 49, pp.186-193, 2005.
11.
Akinori nakayama, Eriko Yagasaki, Masshi inoue, Shinji Iwamoto, Syunsuke Kurasawa and Yoshiyuki nagayasu, Influence of Catalyst Support and Reaction Gas of Decomposition of Methane over Ni Catalysts. Journal of the japan Petroleum Institute, 48, pp.301 – 307, 2004.
12.
Ermakov, D.Yu. and Ermakova, M.A., Ni/SiO2 and Fe/SiO2 catalysts for production of hydrogen and filamentous carbon via methane decomposition. Catalyst Today, 77, pp.225-235, 2002.
13.
Ermakova MA, Ermakov DYu, Plyasova LM, Kuvshinov GG. XRD studies of evolution of catalytic nickel nanoparticles during synthesis of filamentous carbon from methane. Catal Lett 1999; 62(2–4):93–7.
14.
Baker R.T.K, Barber M.A., Feates, F.S., Harris P.S. and Waite R.J ; Nucleation and growth of carbon deposits from the nickel catalyzed decomposition of acetylene , Journal of the catalyst, 1972: Vol. 26, pp.51 – 62.
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Annual Transactions of IESL, pp. [38-45], 2012 © The Institution of Engineers, Sri Lanka
Design of a Solar Hybrid Dryer for Copra Drying H. P. K. Udana and A.D.U.S. Amarasinghe Abstract: A small scale, forced convection, solar-biomass hybrid dryer for drying copra has been designed, fabricated and tested for drying copra. The dryer is consisted with a solar air heater, a biomass-stove heat exchanger and a drying chamber. The biomass consumption of the dryer was found to be reduced by more than 60% when the solar air heater was in operation. The reduction of moisture content of copra from 50% to 7% was recorded after 32, 35 and 37 hours at drying temperatures of 72°C, 60°C and 55°C, respectively. The highest percentages of brown copra (13.33%) and low grade copra (1.67%) were recorded at 72°C and the remaining copra was either white or light brown. More than 75% of white copra could be produced by maintaining the drying temperatures below 60°C. Colorless coconut oil with good quality could be extracted mechanically by using both white copra and light brown copra obtained from hybrid drying. Keywords:
1.
Hybrid dryer, Copra, Drying, Coconut oil
deposition of impurities like dusts [6], [7]. The poor quality copra always results in bad quality coconut oil. The PAH deposited in the copra can easily be transferred to the coconut oil and brown colour copra always provides brown coloured oil which can be easily adulterated with other low quality oils [3]. To overcome these problems, use of hybrid hot air dryer which consists of a solar collector and a biomass stove heater is a good alternative for dying copra. It is an indirect heating dryer in which the consumption of biomass can be minimized under good weather conditions. Furthermore, it can be used during nights and rainy or cloudy days which is a major advantage over solar dryers. Several experimental studies have been carried out on development of hot air dryers for copra drying [6], [8], [9]. However, variation of the quality of copra and coconut oil with the drying behaviour was not reported. In this study the drying characteristics and the quality of copra produced in a solar-biomass hybrid dryer were investigated. The effect of drying behaviour on the quality of coconut oil was also examined.
Background
Copra is a primary product which is produced by drying of coconut kernel. The drying operation reduces the moisture content in the kernels from around 50% to 6% [1]. Copra is considered as an intermediate product of the coconut oil manufacturing process since a major portion of the world’s copra production is utilized for coconut oil production. Several methods for copra making have been developed throughout the world. Among them, traditional kiln drying is the widely used method and sun drying is also practiced in small scale. In Sri Lanka, Ceylon-copra-kiln has been using extensively by both large scale commercial copra manufacturing mills and small scale copra manufactures. Several modifications were done for the Ceylon-copra-kiln after that it first introduced in early 50s [1], [2]. In the Ceylon-copra-kiln, coconut cups are spread on a platform in an open space as a single bed and coconut shells are burnt underneath. Hot air and combustion gases are flown up through the copra bed by natural convection to remove the moisture of coconut meat. Direct contact of smoke and burnt gases with copra in kiln drying process produces poor quality copra due to deposition of polycyclic aromatic hydrocarbons (PAH) on the kernel of copra and makes colour of copra to brown [3], [4], [5]. Sun drying process produces cleaner copra than kiln drying process. But sun drying process requires more days to dry copra and favourable weather conditions, is more labour intensive and allows some quality deterioration due to
2.
Materials and Methods
2.1 Hybrid Dryer The hybrid dryer was consisted with solar collector, biomass stove-heat exchanger unit
H.P.K. Udana, B.Sc. Eng. (Moratuwa), Research student, Department of Chemical & Process Engineering, University of Moratuwa. Eng. (Dr.) A D U S Amarasinghe, B.Sc. Eng. (Moratuwa), PhD (Cambridge), MIE (Sri Lanka), Head of the Dpt., Department of Chemical & Process Engineering, University of Moratuwa.
1
38
and drying chamber. A picture of the hybrid dryer is shown in Figure 1. The drying chamber and heat exchanger were connected through a 1hp centrifugal blower to provide necessary air flow to the drying chamber. The preheated air by the solar collector was further heated by the stove-heat exchanger unit to the required temperature prior to send into the drying chamber.
fabricated with L-iron (38.1 mm x 38.1 mm). A 25 mm thick glass wool insulation was provided to all outer areas and to the duct at air outlet. The angle of the solar collector was kept as 10° to the horizontal which is considered to be an optimum angle for Sri Lanka [10]. The collector was oriented to face south to maximize incident solar radiation. 1
The temperature was controlled with an accuracy of ± 5 C by incorporating a bypass line for supplying ambient air in between the drying chamber and the heat exchanger. Further, a gate valve was fixed at the outlet of heat exchanger to regulate air flow rate through the dryer. 3
2
1. Solar air heater 2. Heat exchanger 3. Drying chamber
3 2
1. Glass cover 2. Baffles 3. Air inlet Figure 2 - Solar Air Heater 1
B) Biomass stove-heat exchanger The stove was consisted with a grate covered by fire bricks. The primary air inlet was located in the door of the stove and secondary air was allowed to flow through the grate. The flame intensity could be controlled by varying the primary air supply. Ash generated during the combustion process was collected underneath of the stove across the grate. This eliminated the accumulation of ash inside the effective burning area in the stove. The stove is shown in Figure 3.
Figure 1 - A Picture of Hybrid Dryer A) Solar collector A corrugated flat plate solar collector with a single glass cover was developed to preheat air as shown in Figure 2. A V-corrugated 1 mm thick sheet coated with dull black paint was used as the absorber plate of the solar collector. The area of the solar collector was 2 m2. The area of the absorber plate was 2.31 m2 since its corrugated shape. The glass cover was made of normal 5 mm thick window glass. Rectangular shape air gap (25 mm) was provided between glass cover and the absorber plate to facilitate air flow. Five V-shaped baffles made out of copper were fixed between glass cover and absorber plate to increase the turbulence of air flow. A 50 mm gap between the absorber and bottom outer plate was filled with sand as heat storage for night and to reduce heat losses. The outer box was made by 1 mm thick iron sheets and the supporting frame and legs were
4
2
1
3
1. Fire bricks 2. Grate 3. Primary air inlet 4. Door Figure 3 - Biomass Stove The heat exchanger was fixed on the top of the stove to facilitate the flue gas flow through the 2
39
heat exchanger. Since the air-to-air heat transfer is very low, the retention time of flue gas in the heat exchanger was increased to gain the maximum heat transfer with minimum loss of heat to the environment. This was achieved by designing the heat exchanger with three sections; center, middle and outer (Figure 4). With this arrangement, the heat exchanger was operated as a three pass shell and tube heat exchanger. Heat was transferred by radiation in the center section while convective heat transfer was dominant in other sections. The outer area of the heat exchanger was insulated by glass wool with a thickness of 25.4 mm.
1
meshes and trays could be replaced with desired meshes according to the size of the material to be dried. Each compartment was provided a door with locking arrangement in one side for loading and unloading of materials. A trapezoidal plenum chamber was fixed below the first drying compartment to maintain the proper distribution of inlet air. The outlet of the drying chamber was also fitted with trapezoidal chamber to guide the exhaust air properly into the atmosphere. The outer box of the chamber was made out of 1 mm thick iron sheets and covered with 25 mm glass wool insulation. The supporting frame was made with L-iron (38.1 mm x 38.1 mm). Hollow Aluminium tubes of diameter 10 mm were inserted through the walls of the chamber to measure the temperatures in each compartment using glass thermometers. Even though three compartments were available in the drying chamber only one was used in the present study.
2
3 1. Center section 2. Middle section 3. Outer section Figure 4 - Arrangement of Tubes in the Heat Exchanger
2
4
1
3 1. Doors 2. Compartments 3. Trays 4. Measurement points Figure 6 - Drying Chamber 2.2
Experimental Procedure
2.2.1 No Load Experiments No-load tests were carried out to examine the performance of the hybrid dryer. Those experiments were designed to find the required biomass feeding rate to the stove in order to keep the outlet temperature of the heat exchanger at 60°C, 70°C and 80°C with and without preheating of air by solar collector. The stove was fired for at least one hour before the measurements were taken in order to allow the shell and tubes of the heat exchanger reach steady state. Since coconut shells could be obtained as by product in the copra drying process, coconut shells were used as the fuel.
Figure 5 - Heat Exchanger C) Drying chamber A vertical drying chamber (600 x 600 x 1350mm) was used to store copra in three compartments through which the hot air was allowed to pass from the bottom compartment to the top compartment. A picture of the drying chamber is shown in Figure 6. The chamber was designed to store around 420 coconut halves in three compartments. Drying trays were made out of 25.4 mm x 25.4 mm iron 3
40
The additional energy requirement fulfilled by using firewood.
����� =��
was
�
3.
A) Moisture content The moisture content on wet basis was calculated by the following equation. �0 −���
�× 100
Results and Discussion
3.2 Drying Experiments The temperature of hot air varied while passing through the copra bed and hence, an average
…. (1)
where, ���� = Percentage of moisture content on wet basis, �0 = Initial weights of the sample, ��� = Final weights of the sample B) Thermal efficiency The thermal efficiency of the dryer is defined as the ratio of energy used to evaporate moisture from the material to the amount of energy supplied to the dryer.
…. (2)
3.1 Operation of the Hybrid Dryer Constant feeding of biomass to the stove was required to maintain the outlet temperature of the heat exchanger at steady levels. The biomassfeeding rate to achieve outlet temperatures at 60°C, 70°C and 80°C were investigated. As expected, the biomass consumption was at higher levels when the dryer was operated only with biomass. The results are shown in Table 1. The time period of 9.00 am to 5.00 pm was considered for evaluating the hybrid operation. Feeding rate was not uniform during that time; less in around the noon and high in the morning and the afternoon. The results given in Table 1 indicate an average value of biomass feeding rate for the entire time period. The results suggested that more than 60% reduction in biomass consumption could be achieved by hybrid operation.
Data Analysis
�0
×
D) The instantaneous moisture content Following equation was used to compute the instantaneous moisture content of copra at any given time. � �� –(� − � …. (3) ��= � � � � ) � �� where, ��� = Mass of material at any given time, ��� = Initial mass of material, ��� = Moisture content of material at given time, ��� = Initial moisture content of material
in a convective electrical oven (A Griffin 1/200) which was maintained at temperature of 105°C till the samples achieved constant weight. Firing started around 1 hour before the circulation of air through the drying chamber. The air flow through the drying chamber was adjusted to around 0.6 ms-1. The air velocity through the drying bed was measured using a velometer (Alnor). The wet and dry bulb temperatures of inlet and outlet air flow of the drying bed and the ambient air were recorded at one hour time intervals. The weights of six selected coconut cups were measured in hourly basis to find the reduction of moisture level during the drying process. Drying process was stopped when a constant weight was recorded and dried copra was examined for its quality. After 24 - 26 hours of continuous heating, copra was allowed to cool for 4 hour interval in order to avoid case hardening effect. The scooping of shells was also done during this period. The average final moisture content of copra was also determined by a similar method as used in finding the initial moisture content.
���� = �
�� + �
where, ��� = Amount water evaporated during the drying process (kg), ���� = Amount of energy consumed by the blower (kJ), � = Amount of biomass fuel used (kg), � =Calorific value of particular biomass. (kJ/kg)
2.2.2 Drying Experiments Three copra drying experiments were performed at different drying temperatures to find out the drying characteristics of the copra. In each experiment, exactly 120 coconut halves were loaded into the first compartment of the drying chamber. Fully matured coconuts were used for experiments. Three samples of 10 g each were prepared from randomly selected ten cups to find out the average initial moisture content of the coconut. The samples were kept
2.2.3
���
C) Specific moisture extraction rate Specific moisture extraction rate is the amount of water evaporated per unit of energy.
4
41
drying temperature, which is the mean of inlet and outlet to the dryer at a given time, was defined as the operating temperature of the dryer. The variation of average drying temperatures with time for each of the drying experiments is shown in Figure 7. The outlet temperature of the heat exchanger was highly dependent on burning rate and type of biomass in the furnace and was not an easily controllable parameter. As a result, the outlet temperature of the heat exchanger was fluctuated during the drying process and this
42
Table 1 - Fuel Consumption by Hybrid Dryer Biomass Consumption (kg/hr) Coconut shells Firewood 0.18 0.36 0.40 1.20 0.30 0.52 0.79 2.00 0.40 0.75 1.10 2.60
Operation mode Hybrid Biomass only Hybrid Biomass only Hybrid Biomass only
60 70 80
Relative Humidity (%)
Temperature (°C)
Temperature ( °C )
was more significant at higher operating temperatures. The outlet temperature from the dryer was found to be significantly lower than the inlet temperature during the initial drying period. The operating temperature was gradually increasing and reached to a steady value after about 4 hours. Experiment 1 was carried out at the highest operating temperature with an average of 73°C, while experiment 2 and 3 were having average operating temperatures of 55°C and 60°C respectively. The discontinuity of the graph was attributed to the four hour cooling period.
90 80 70 60 50
Experiment 1 Experiment 2 Experiment 3
40 30 20 10 0 0
10
20 Drying Time (h)
30
40
Figure 8 - Variation of Relative Humidity
90 80 70 60 50 40 30 20 10 0
Variation of moisture content of copra with drying time is shown in Figure 9. The final moisture contents were recorded as 6.6%, 7% and 6.75% for experiments 1, 2 and 3, respectively. Nearly a constant initial drying rate could be observed in all 3 experiments due to the evaporation of surface moisture. After that, the drying process was continued with a falling rate until the end of drying process. The falling rate period is corresponding to internal migration of moisture from inner layers to the surface. The reduction in drying rate may due to the shrinkage of the cell structure and the reduction in water concentration of copra kernel which result in a lower diffusion coefficient. These effects were more significant in Experiment 1 due to high drying temperatures.
Experiment 1 Experiment 2 Experiment 3
0
10
20 30 Drying Time (h)
40
Figure 7 - Variation of Average Drying Temperature with Time The variation of the relative humidity of outlet air from the drying chamber with time is shown in Figure 8. In all 3 experiments, the relative humidity (RH) had decreased with time and became constant after the drying process was completed. Similar to the notable variation of the operating temperature, RH was considerably high within the first 4 hours due to the removal of unbound moisture from copra. Final relative humidities were 15.64 %, 18.93 % and 18.53 % in experiments 1, 2, and 3, respectively and these values were exactly corresponding to RH values of ambient air at respective drying temperatures. Therefore, the measurement of RH may be used as an indicator of the level of drying in the copra bed.
Shortest drying time was observed in the experiment 1 which was 32 hours. The drying time of experiment 2 was 37 hours which was longer than the drying time of experiment 3 by two hours. Results of the three experiments are summarized in Table 2. The results suggest that the drying temperature has a significant effect on the drying time of copra. The drying time for copra to reach the final moisture level was comparable with the previous studies. Mohanraj et al. (2008) recorded a higher drying time and also higher
43
Moisture Content (%)
final moisture content than the present study for copra drying with a flat plate solar collector. However, there were few differences between the two studies. They used a drying chamber with two compartments to dry 300 nuts of coconut to produce 60 kg of copra A drying time of 71 hour was recorded by Thanaraj et al. (2007) in a solar–biomass hybrid dryer to reduce the moisture content of coconut from 50% to 7%. Even though, the drying time was higher than the present study, they produced 147 kg of copra within one batch.
60 Experiment 1 Experiment 2 Experiment 3
50 40 30 20 10 0 0
3.3 Quality of Copra and Coconut Oil The quality of copra was analyzed by considering mainly the colour, oil content and presence of low grade copra. Low grade copra included scorched copra, slimy copra and mouldy copra.
10
20 30 Drying Time (h)
40
Figure 9 - Variation of Moisture Content with Drying Time
Table 2 - Results of Copra Drying Experiments Experiment
Average Drying Temperature(°C)
Drying Time (Hrs)
1 2 3
72 55 60
32 37 35
No scorched or mouldy copra were resulted from drying in all 3 experiments. Case hardening which is the formation of a hard layer on the outer surface of the product that restricts the passage of moisture movement from the interior to the surface is common in copra drying at high temperatures. However, case hardening was not observed even at Experiment 1.
Moisture Content (% wet.) Initial Final 49.13 6.60 49.81 7.00 50.41 6.75
Copra Production (kg) 11.94 12.06 12.24
in colour with a total percentage of 74.68%. Brown copra was produced only in experiment 1 with a percentage of 13.33%. The comparison of colours of white copra and light brown copra obtained from experiments with kiln dried brown copra are shown in Figure 10. The production of low grade copra was very low in all 3 experiments. The oil contents of copra produced in all 3 experiments were nearly the same with a value of around 60% by mass. A notable difference in smell and or taste was not observed among the copra produced in each experiment.
The results of all the quality variations are summarized in Table 3. The percentages of white copra produced from experiments 2 and 3 were 82% and 76%, respectively. The remaining copra in those two experiments was either light brown or pale yellow in colour. Thanaraj et al. (2007) were also able to produce white copra with a percentage slightly above 70% at drying temperature around 60°C. Even though the white copra production in the first experiment was as low as 10.32%, the majority of copra was either light brown or pale yellow
Usually pairing is removed in the production process of virgin oil as it may impart a yellowish colour. However even with the pairing, the coconut oil obtained by mechanical extraction from the white and light brown copra was almost colourless and the oil was very similar to virgin coconut oil by appearance.
Table 3 - Analysis of Copra Quality Experiment
White copra (%)
Light Brown copra (%)
Brown copra (%)
Other copra (%)
Oil content (% by weight)
1 2 3
10.32 82.00 76.00
74.68 16.40 23.17
13.33 0 0
1.67 1.60 0.83
60.33 60.18 60.44
6
44
(a) White copra (b) Light brown copra (c) Brown copra
Figure 10 - Colours of Copra A comparison of colours of coconut oil obtained from white and light brown copra with coconut oil obtained from kiln dried brown copra is shown in Figure 11.
values and iodine values of all the oil samples were in the specified range for coconut oil. The moisture contents were also in the range for good quality coconut oil. Free fatty acid contents were in the range for white coconut oil. More importantly colours of coconut oil from both white copra and light brown copra were in the range of virgin coconut oil. 3.4 Performance of the Dryer The thermal efficiency of the dryer was examined for each experiment. The efficiency values were calculated using a similar method as used by Thanaraj et al. [9].
(a) From white and light brown copra (b) Kiln dried copra Figure 11 - Colours of Coconut Oil
The calculated thermal efficiencies for experiments 1, 2 and 3 are 4.23%, 4.05% and 4.18%, respectively. These values are comparatively lower than the values recorded in previous studies on copra drying (around 10%).
The oils obtained from each experiment were tested for psychochemical properties according to SLS 32:2002 standards for coconut oil and the results are given in Table 4. The relative densities, refractive index values, saponification
Table 4 - Physicochemical Properties of Coconut Oil Oil Samples
Property Colour (25-mm cell on the Lovibond colour scale) Relative density at 30°C Moisture & other matter (Volatile at 105°C) Free fatty acids (as lauric Acid, per cent by mass) Saponification value Iodine value Refractive Index Oil samples;
1: From white copra
1 0.8 0.919 0.34 0.71 252 8.53 1.4489
2: From light brown copra
7
45
2 1.0 0.919 0.37 0.63 255 7.99 1.449
3 3.1 0.918 0.38 0.68 258 8.65 1.449
3: Brown copra
However, most of these dryers were having natural draft. Consequently, the final moisture contents were as high as 14% for a similar time period to the present study. In the present study, significantly low moisture content (6% 7%) was achieved when compared to the conventional copra drying (about 12% - 15%). The considerably low thermal efficiencies recorded in the present study may be attributed to following reasons.
to be low but can be increased by improving the thermal efficiency of the dryer.
notably high amount energy is required for removing the bound moisture from about 12% - 15% to 6% - 7%. energy required by the blower to maintain the forced draft. heat loss to the environment was high from the walls of stove since it was made up with mild steel. Fabricating the stove with less conductive material like firebrick or normal brick would decrease the heat loss and increase the efficiency of the dryer. loss of flue gas from the grate was noted during all the experiments. Since the flue gas was circulated through the heat exchanger by natural draft, it may escape through the grate due to possible pressure drop in the flow path. possibility of accumulating soot in the flow path might have affected the heat transfer from flue gas to air.
1. Thiruchelvam Thanaraj, Nimal, D.A. Dharmasena, Upali Samarajeewa (2007), Comparison of quality and yield of copra processed in CRI improved kiln drying and sun drying, Journal of Food Engineering 78, pp. 1446– 1451. 2. Thiruchelvam Thanaraj, Nimal, D.A. Dharmasena, Upali Samarajeewa (2007), Comparison of drying behavior, quality and yield of copra processed in either a solar hybrid dryer on in an improved copra kiln. International journal of food science and technology 42. pp.125-132. 3. Roberto C. Guarte, Werner Mfihlbauer, Manfred Kellert, (1996), Drying characteristics of copra and quality of copra and coconut oil, Postharvest Biology and Technology 9, pp.361-372. 4. Rodrigo, M. C. P., Arnarasiriwardene, B. L. and Samarajeewa, U. (1996), Some observations on copra drying in Sri Lanka, COCOS (1996) 11, pp.21 -31. 5. Wijerathna, M. C. P., Samarajeewa, U., Rodrigo, M.C.P. (1996), Polycyclic aromatic hydrocarbons in coconut kernel products, J. Natn. Sci. Coun. Sri Lanka 24, pp.285-297. 6. Mohanraj, M., Chandrasekar, P. (2008), Comparison of drying characteristics and quality of copra obtained in a forced convection solar dryer and sun drying. Journal of scientific and industrial research 67, pp.381-385. 7. Mohanraj, M., Chandrasekar, P. (2008), Drying of copra in a forced convection solar dryer, Biosystems Engineering, 99, pp.604 – 607 8. Satter, M. A. ( 2003), Design and development of a portable copra dryer, Proceedings of the International Conference on Mechanical Engineering. 26- 28 December 2003, Dhaka, Bangladesh. 9. Thanaraj, T., Dharmasena, N.D.A., Samarajeewa, U. (2004), Development of a rotary solar hybrid dryer for small scale copra processing, Tropical Agricultural Research, 16, pp.305-315. 10. Ekechukwu, O.V., Norton, B. (1999), Review of solar-energy drying systems II: an overview of solar drying technology, Energy Conversion & Management 40, pp.615-655.
-
-
-
-
Acknowledgements The authors express their sincere gratitude to the Coconut Development Authority, Sri Lanka for their support
References
The specific moisture evaporation rates (SMER) were found to be 0.168 kg/kJ, 0.154 kg/kJ and 0.162 kg/kJ for experiment 1, 2 and 3, respectively. These values are lower than the SMER values reported in previous studies. This may be due to the lower thermal efficiency of the dryer.
4.
Conclusion
Clean and white copra could be able to produce from the hybrid dryer. The amount of white copra that can be obtained is mainly dependent on the drying temperature. The production of brown copra could be minimized by maintaining drying temperatures below 70°C. Low quality copra such as, scorched copra and mouldy copra were not observed in hybrid drying. Good quality coconut oil which was similar to virgin coconut oil by appearance could be extracted from the copra produced in the hybrid dryer. The colour of the oil was comparable to virgin oil even with the light brown copra which could be produced at temperatures lower than 70°C. The specific moisture evaporation (SMER) rates were found
8
46
Annual Transactions of IESL, pp. [46-52], 2012 © The Institution of Engineers, Sri Lanka
Development of a Water Processing Plant to Reduce Fluoride and Hardness in Drinking Water W.M. Jayawardhane and J.P. Padmasiri Abstract: Quality of drinking water from ground sources in the dry zone of Sri Lanka, is sometimes below desirable limits. Presence of Fluoride in excess in drinking water is causing health problems in the community. Total hardness far in excess of the desirable limit, makes the water less palatable. A simple and sustainable method for reducing Fluoride and Total hardness is discussed in this paper. The plant discussed here is based on electrocoagulation, where no chemicals are added to the raw water, and electricity is used to cause coagulation. The dissolved contaminants which have to be removed combine with the insoluble sludge, and the sludge is separated from the water by settling and filtration techniques. A pilot plant which was set up in 2010 continues to operate to date. In addition several other plants with certain improvements are in operation. A multi-disciplinary effort involving Civil, Mechanical, and Electrical Engineering along with Chemistry and water quality monitoring was applied in this project. Keywords:
1.
Electrocoagulation, Sludge, Potable water, Fluoride, Hardness
Introduction
According to the annual report of the National Water Supply & Drainage Board (NWS&DB) for the year 2009, 52% of their water supply connections are in the Western Province where the population according to the 2001 Census is only 28.6% [1, 2]. In the rest of the country too, where the majority live, water is supplied to the population by the NWS&DB through their large schemes, as well as Rural Water Supply Schemes. Some rural water supply schemes are funded by INGOs. These rural schemes are operated by Community Based Organizations (CBOs). Where there are no water supply schemes, the communities depend on shallow wells, tube wells, irrigation reservoirs, irrigation canals etc. for their water, for house hold use. Some of these sources are not hygienic. Water supplied by several CBOs, to their consumers, has been tested for Total Hardness and Fluoride, by the authors, as well as Institute of Fundamental Studies (IFS). It has been found that, quality of water in some schemes, does not fall within the desirable limits set by Sri Lanka Standards Institute (SLSI) [3]. In the absence of alternative sources, some consumers continue to
1
47
drink sub-standard pipe borne water, while others go back to unhygienic sources. In the dry zone of Sri Lanka, paddy and highland crop cultivation are the main sources of income. During the dry months when people are engaged in their routine work, they consume large quantities of water. When the drinking water is contaminated with chemicals such as Fluoride, this causes health problems [4]. Hardness is felt in the mouth and therefore water with very high hardness is rejected by the consumer. Fluoride is colourless and tasteless, and the consumer cannot detect its presence in drinking water. A good example is Mihindu Prajamoola Sanvidhanaya of Asokamalagama, a CBO, in Mahavilachchiya Irrigation Scheme, which was supplying pipe borne water with a Fluoride content of 5.5 mg/l and hardness of 180 mg/l. This level of hardness is tolerated by the consumers. Pipe born water is used for many purposes in addition to cooking and drinking. Eng. W.M. Jayawardhane, C.Eng. B.Sc.Eng. MIE(Sri Lanka) , MBA, Civil Engineer (Retired). J.P. Padmasiri, B.Sc.(Hons), M.Phil, C.Chemist. Visiting Scientist, Institute of Fundamental Studies, Kandy.
As an interim measure, at least the water requirement for drinking and cooking has to be made safe. This can be done by processing only the quantity required for the purpose and making it available to the consumer. The aim of this project is to develop a unit for reducing Fluoride and Hardness in drinking water for community use.
2.
100 years. Yet its full potential is not used in water treatment [8]. Water from ground sources contains several dissolved minerals and salts, and these ions affect the EC process making it very complicated [9]. Malkootian et al [5] have studied the efficiency of removing hardness from water using EC. Cocke et al [10] have studied the use of EC for waste water treatment. Mollah et al [11] in their study of Science and Applications of EC, state that while EC is used successfully for treatment of contaminated water, its full potential is yet to be realized.
Literature Review
There are many methods used for water treatment. The scope of this presentation is limited to reducing hardness and Fluoride in ground water for drinking.
Fluoride
2.1 Electrocoagulation Electrocoagulation is an electrochemical process where a current is passed through the liquid to be treated using suitable electrodes. In the process the anode is sacrificed, and the ions from the anode react chemically causing coagulation. The choice of anode material depends on the application.
Adsorption eg. Activated Alumina Chemical coagulation & precipitation Electrodialysis Reverse Osmosis etc.
The following chemical reactions explain the electrocoagulation process when Aluminium is used for the anode. At the anode,
Well known processes used for removal of hardness include; a. Ion exchange b. Reverse Osmosis c. Lime soda-ash method etc. Similarly include; a. b. c. d.
processes for
removing
Each of the above processes has its own advantages and disadvantages. Reverse Osmosis, which is very widely used for desalination, uses a membrane. Contaminated water is forced through the membrane, which allows only water to pass through. When the membrane gets blocked it has to be backwashed using filtered water, and this consumes a good part of filtered water.
Al Al+3 + 3e2H2O + 2e4H+ + O2 + 4e-
(1) (2)
At the cathode, 2H2O + 2e-
H2
+
2OH-
(3)
The metal ions react with the hydroxyl ions to produce metal hydroxides. Aluminium ions in water will produce Aluminium hydroxides or poly-hydroxides. At pH values 6-8, these compounds adsorb Fluoride forming Al(OH)3-xFx, thus removing the Fluoride from water. Calcium Bicarbonate causing hardness in water is converted to insoluble Calcium Carbonate as given by Eqns. (4) and (5).
Chemical methods where dosing of chemicals are involved, can be hazardous in a rural setting. A Fluoride filter for domestic use where brick pieces are used for adsorption, has been developed and introduced by Padmasiri et al [7]. This is not very popular because the brick pieces have to be replaced every three months.
HCO3 - + OHCO 32- + Ca2+
Ion exchange is very effective in removing cations such as Ca+, Mg+ where regeneration is done with brine, but consequently the Na+ ion concentration increases.
CO32- + H 2O CaCO3
(4)
(5)
Similarly, CO32- + Mg2+ MgCO3 (6) While Aluminium Hydroxides precipitate with Fluoride, the Carbonates get deposited on the cathode surface. The Hydrogen and Oxygen
Electrocoagulation (EC) is an electrochemical process that has been discovered over the last
47
gases help the precipitate to float to the surface [8].
developing a continuous flow unit to handle at least 100 l/h. with a Fluoride content < 1.0 mg/l.
3.
A unit with a tubular Aluminium anode 1500mm long, surrounded by a stainless steel tubular cathode was tried out. To give a longer reaction time 10 such units were connected in series (Figure 3).
Methodology
A small cell of capacity 500 ml and four Aluminium electrodes 100 mm x 100 mm were used for the early trials. A DC power source, a rheostat and an ammeter were used as the variable power supply. (Figure 1) The electrodes were connected in monopolar mode. Water samples with a high Fluoride content from different parts of the country were used in the trials. A current of 1A was sent through the water for duration of 30 minutes. The sludge produced was allowed to settle overnight and the supernatant liquid was decanted and tested for Electrical conductivity, Total hardness and Fluoride content.
Figure 2 - 5 l Cell with Plate Electrodes
A few results of early trials are shown in Table 1. Once the results were found to be promising, a 5l capacity vessel with plate electrodes was used for the trials. By varying the current and the reaction time, several trials were conducted. Results of four trials with the 5 l capacity vessel and 6 Aluminium electrodes (Figure 2) and a current of 1A for 30 minutes are shown in Table 2.
IN
OUT
J2
790
482
J5
1189
J9
1510
IN
OUT
IN
OUT
250
125
0.9
0.3
200
125
0.3
0.1
684
425
150
1.6
0.2
1046
400
150
6.4
0.74
J1
Legend: J1 Polpithigama J2 Handapanagala
Figure 1 - First Unit used for Trials The need for a water processing plant to serve a community was recognized in March 2010, when a CBO supplying water with a Fluoride content of 5.5 mg/l to the community, was detected. Thereafter efforts were directed at
48
Fluoride (mg/l)
Conductivity (us/cm)
Sample No.
For ease of removal of electrodes for cleaning, they were connected in bipolar mode.
Total Hardness (mg/l)
Table 1 - Results of Early Trials
J5 Wellawaya J9 Dambulla
Residual Fluoride (
5 4 3 2 1 0 0
2
4
6
8
Age of electrodes (Hours)
Figure 4 - Residual Fluoride vs. Time with Tubular Electrodes Analysis of these results revealed that, as the concentration of the contaminant reduced, higher energy had to be applied, for removal of the balance. The charge given in the table is a measure of the energy supplied, and is in Coulombs. The findings are shown in Table 3 and Figure 5.
Figure 3 - EC Unit with 10 Tubular Electrodes
Fluoride( mg/l)
Total Charge C
Residual Fluoride g/l
Fluoride removed mg/l
Fluoride removed %
0
0
0
5.30
0
0
1
2
116
116
2.00
3.30
62
Each tube had its own DC supply unit and the current was maintained at 2A. The aim was to check whether the unit was capable of handling 100 l/h. of raw water with a Fluoride content of 5.5 mg/l. This unit was installed at Asokamalagama in August 2010. The results of a trial with tubular electrodes are shown in Figure 4.
2
2
116
232
1.94
3.36
63
3
2
116
348
1.43
3.87
73
4
2
116
464
1.30
4.00
75
5
2
116
580
1.27
4.03
76
6
3
174
754
0.97
4.33
82
7
3
174
928
0.58
4.72
89
8
3
174
1102
0.76
4.54
86
The Fluoride content came down only to 1.5mg/l. In an attempt to solve this problem, the number of electrodes was increased to 15 thus increasing the contact time, with no success. During the subsequent attempt, instead of giving the same current to all 15 electrodes, the power supply was changed as shown in Table 3.
9
4
232
1334
0.89
4.41
83
10
5
290
1624
0.80
4.50
85
11
6
348
1972
0.74
4.56
86
12
6
348
2320
0.70
4.60
87
13
6
348
2668
0.60
4.70
89
14
6
348
3016
0.52
4.78
90
15
6
348
3364
0.35
4.95
93
IN
1 2 3 4
OUT
IN
OUT
2340 1940 800
OUT
375
2.4
0.38
1545
930
IN
610
270
1.9
0.08
1550 1290 300
125
2.1
0.19
970
100
1.4
0.03
745
250
Tube No.
Charge C
Table 3 - Results of a Trial using Different Currents in Tube Electrodes Current A
Sample No.
Conductivity( us/cm)
Total Hardness( mg/l)
Table 2 - Results of Trials with Plate Electrodes
Water flow was adjusted to 100 l/h and samples were collected from each tube. The samples were tested for Fluoride content immediately after vacuum filtration using a hand operated vacuum pump.
49
Residual Fluoride (mg/l)
Fluoride removed %
and a flow rate of 150 l/h are shown in Figure 7.
100 80 60 40 20 0 0
1000 Total ch2a0r0g0e C
3000
4000
6 5 4 3 2 1 0 0
2
4
6
8
10
Age of electrode( hours)
Figure 5 - Total Charge vs. Fluoride Removed as a Percentage of Initial Fluoride Content
Figure 7 - Residual Fluoride vs. Age of Plate Electrodes
At 100 l/h, time of contact with a single electrode is 58 sec. It is seen that the Fluoride content can be reduced by 90%. It was also found that Total hardness could be reduced by 70%. These efficiencies can vary with the quality of the raw water.
It can be seen that the Fluoride level is maintained below 1.0 mg/l even after 9 hrs. This arrangement is now being used in the new plants with the flow rate increased to 200 l/hr. The number of reactors in decided upon the Fluoride content of the raw water.
Use of tubular electrodes posed problems mainly in sealing the ends. The anode tubes had to be removed periodically for cleaning and reassembled. Leaks at the end caps continued to be a problem. For this reason, plate electrodes were re-introduced. Three vessels with plate electrodes were connected in series. The current supplied was changed to 2A, 4A & 6A for the three reactors, respectively. This arrangement is shown in Figure 6. At the same time an attempt was made to increase the flow rate.
Passivation of the electrodes is the major problem. The anode surface gets oxidized and gets coated with Aluminium oxide. The cathode surface gets coated with Calcium and Magnesium Carbonates. At present, the electrodes are cleaned manually when the coating starts obstructing the passage of electric current. After EC the sludge is separated by settling and filtration. Arrangements are provided for backwashing of the sand filter.
4.
Discussion
By using the electrocoagulation technique, it has been possible to reduce Fluoride content by 90% and Total hardness by 70%. Malakootiyan et al [5] have reported a hardness reduction of 80.6% with a contact time of 60 min. Emamjomeh et al [12] have achieved a Fluoride reduction of 99% with a flow rate of 150 ml/min which is 9 l/hr in a continuous reactor.
Figure 6 - Three Reactors with Plate Electrodes in Series Results of a trial with Asokamalagama water using three vessels with plate electrodes in series
50
In comparison, the flow rate in this plant is 200l/hr with a contact time of 20 minutes. In areas where, even after EC the hardness is high, an ion exchange resin is used to bring down the hardness further. The other issue of concern is the residual Aluminium in the finished product. The residual Aluminium is kept below 0.2 mg/l which is the upper limit as per SLS.614 of 1983.
electrodes is giving consistent results. All plants are being periodically monitored for quality.
5.
Conclusions
The CBO at Asokamalagama, delivering pipe borne water with a Fluoride content of 5.5 mg/l and Total hardness above 180 mg/l was spotted in March 2010. By August 2010, a unit which could bring down the Fluoride to 1.5 mg/l at a flow rate of 100 l/h was installed at this site. By April 2011, it was improved to the present level, delivering water with Fluoride below 1.0 mg/l, and Hardness below 100 mg/l, at a flow rate of 200 litres per hour.
Ten water processing plants, each of capacity 200 l/h are now in operation, nine in Anuradhapura District and one in Kurunegala District. Eight plants in Anuradhapura District were funded by the Ministry of Technology and Research. For quality control, samples are drawn daily from specified points and are tested at IFS for Total Hardness, Fluoride and also residual Aluminium. The plants are operated mostly by village girls who have been trained, and the water is sold to their own members and the public at Rs. 2.00 per litre. The cost is around Rs.1.10 per litre.
Electrocoagulation as a feasible method for reducing excess Fluoride and Hardness in drinking water is therefore established. The benefits of using water with low Fluoride cannot be assessed by Engineering means, but listening to the consumers, it can be seen that early symptoms of Fluorosis could be reversed just by consuming water with low Fluoride.
A photograph of the plant is shown in Figure 8.
Acknowledgements The authors are grateful for the logistical support received from Link Natural Products (pvt) Ltd, and Atlas Machine Components (pvt) Ltd. Institute of Fundamental Studies, and in particular Prof. C.B. Dissanayake, Director has been of immense help throughout. Spectra Industries Lanka (pvt) Ltd was of invaluable help in improving the plant in every possible way, even when such improvements cost them a share of their profit. Authors are grateful to Bandula Prematileka for sharing with them, all the hardships during the surveys, as well as during testing, installation and commissioning of the plants.
Figure 8 - Part of a Complete Plant The plant at Kadawathgama in Medawachchiya is operating at full capacity, because of the high demand.
References
Sustainability of the method is proven by the fact that Asokamalagama Plant which has been in operation since April 2011, with plate
51
1.
National Water Supply & Drainage Board, Annual Report 2009.
2.
Census of Population and Housing 2001Department of Census and Statistics.
3.
SLS 614 – 1983 Sri Lanka Standard for Potable Water.
4.
Dissanayake C.B., -“Water Quality in the Dry Zone of Sri Lanka-Some Interesting Health Aspects” J. National Science Foundation, Sri Lanka 2005, 33(3).
5.
Malkootian M., Yousefi N.,” The Efficiency of Electrocoagulation Process using Aluminium Electrodes in Removing Hardness” Iran. J. Environ. Health. Sci. Eng., 2009, Vol. 6, No. 2, pp. 131-136.
6.
Feenstra L., Vasak L., Griffioen J., “Fluoride in Ground Water-Overview and Evaluation of Removal Methods” International Groundwater Resources Assessment Centre Report no SP 2007-1.
7.
Padmasiri J.P. & Dissanayake C.B., “A Simple Defluoridator for Removing Excess Fluoride from Fluoride Rich Drinking Water”-International J. Environment Health research 5 1995.
8.
Christos Comninellis, Guohua Chen, Electrochemistry for the Environment, 1st ed., Springer, 2010, p.245.
9.
Hu C.Y., Lo S.L. and Kim W.H., “Effects of Co-existing Ions on Fluoride Removal in Electrocoagulation Process using Aluminium Electrodes”- Water Research 37 (2003).
10.
Cocke D.L., Mollah M.Y.A., and Parga J.R., “Electrocoagulation, an Evolving Electrochemical Technology for Waste Water Treatment”- Symposia paper presented before the division of environment chemistry, American Chemical Society, 18-22 Aug 2002.
52
11.
Mollah M.Y.A., Schennach Robert, Jose R. Parga, David L. Cocke “ElectrocoagulationScience and Application”- J. of Hazardous Materials B84 (2001), pp.29-41.
12.
Emamjomeh Mohammmad M., Sivakumar Muttucumaru ”Fluoride Removal by a Continuous Flow Electrocoagulation Reactor” J. of Environmental Management Vol. 90, Issue 2, pp. 1204-1212.
Annual Transactions of IESL, pp. [53- 60], 2012 © The Institution of Engineers, Sri Lanka
Development of a Methodology for Assessing Inherent Environmental and Safety Hazards S. Warnasooriya and M.Y. Gunasekera Abstract: At early stages of chemical process plant design and development it is necessary to identify environmental and safety hazards involved in the process. This paper proposes a methodology for assessing a chemical process route to manufacture a chemical based on inherent environmental and safety hazards. The method developed in this work can be used during early design stages. It considers the potential toxicological impact on the environment and the potential chemical and process safety impacts associated within the plant. A chemical process plant at its ongoing operational condition is looked at. An index called Inherent Chemical Process Route Index (ICPRI) is proposed. The lower the ICPRI the more inherently environmentally friendly and inherently safer the route is. The methodology developed is applied on cumene oxidation process which is one of the routes to produce acetone. Keywords:
1.
Inherent safety, Environmental hazard, Chemical process design
ways. They are by considering possible environmental impacts associated with a
Introduction
Assessing environmental and safety hazards during early design stages of a chemical process plant development is an important action needs to be done in achieving an inherently environmentally friendly and safer plant. It is easier to make changes to a plant design during early stages of plant development. Changes to a plant at this stage are less costly compared to costs involved in making changes once the plant is built [1].
catastrophic failure condition and considering impacts due to day to day plant operation condition [3]. To assess inherent environmental friendliness of a chemical process route in the condition catastrophic failure of a chemical process plant, Environmental Hazard Index (EHI) has been developed by Cave et al. [3]. EHI estimates the maximum environmental harm to the aquatic and terrestrial ecosystems due to a total loss of chemical containment and alternative chemical process routes can be ranked or screened using EHI. The EHI is a dimensionless number which indicates the potential environmental hazard of a route in such a manner that the hazard increases with increase in EHI value. The chemical process route is the raw material and the sequense of reaction steps that convert them to the desired products [1]. The Atmospheric Hazard Index (AHI) devised by Gunasekera et al. [4] assess
The concept ‘Inherent’ used in this study means which is intrinsic to a chemical process plant. An inherently safer design based on plant environment and plant safety avoids or reduces hazards rather than controlling them by adding protective equipments [2]. The concept of Inherently Safer Design (ISD) is well described in Kletz’s publication on plant design for safety [2]. Several research works have been reported to assess environmental and safety hazards at early design stages. These works propose methodologies to assess a plant based on the two hazard categories, plant safety and plant environment hazards separately. However, studies available to assess a plant based on both issues together are lacking. The environmental friendliness of a plant can be assessed in two
Mrs. S. Warnasooriya, B.Sc. Eng.(Hons) (Moratuwa), Research Student, Department of Chemical & Process Engineering, University of Moratuwa, Sri Lanka. Eng. (Dr.) (Ms) M. Y. Gunasekera, B.Sc. Eng.(Hons) (Moratuwa), M. Eng. (Moratuwa), PhD. (UK), CEng., MIE(Sri Lanka), Senior Lecturer, Department of Chemical & Process Engineering, University of Moratuwa, Sri Lanka.
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the atmospheric environmental impacts of a particular chemical process route considering toxicity impact. Gunasekera et al. [5] later published an improved version of AHI with a different evaluating technique while considering various other atmospheric impact categories along with toxicity such as photochemical smog, acid deposition, global warming and stratospheric ozone depletion. This method is applicable for a catastrophic release case and the assessment doesn’t depend on the characteristics of the plant location. An index called Inherent Environmental Toxicity Hazard (IETH) devised by Gunasekera et al. [6], estimates the potential impact of chemicals involved in a chemical process route on atmospheric, aquatic and terrestrial environment. Elliot et al. [7] have developed an index method which is also a quantitative environmental impact assessment tool. This assesses both short-term and long-term effects of new processes as well as in redesigning of existing processes where continuous operational conditions are observed.
considering the hazards associated with daily plant operation conditions. An integrated index called Inherent Chemical Process Route Index (ICPRI) is developed to assess combined issues of inherent environmental and safety hazards.
2.
Development of Inherent Chemical Process Route Index (ICPRI)
This methodology is developed using the limited data available on equipment and plant layout at the early design stages of the chemical process plant and hence this work begins with the construction of simple Process Flow Diagram (PFD) and material balance of the chemical process route. The maximum possible impacts on environment and safety considering the daily plant operational conditions are estimated through the ICPRI, which is a dimensionless number. Higher ICPRI indicates a higher hazard and a low ICPRI value indicates a lower hazard on the environment and safety. Figure 1 shows the procedure for the ICPRI calculation.
There are number of research works that have been reported to assess inherent safety. Using the data available at the chemical route selection stage, Edwards et al. [1] have listed 17 parameters that might affect inherent safety and developed a prototype index called Inherent Safety (PIIS). Using their work Gupta et al. [8] have presented a graphical approach for evaluating inherent safety. Further works have been developed by Heikkilä et al. [9], Khan and Abbasi [10] and Khan and Amyotte [11] to assess chemical process routes based on their inherent safety. The i-Safe index developed by Palaniappan [12], [13] compares process routes by using sub-index values developed based on the inherent safety index (ISI) [9] and PIIS [1].
Construct simple PFD with material balance
Assess Environmental hazard (IETHI)
Assess Safety hazard (CRISI)
Calculate ICPRI Figure 1 – Schematic Diagram for ICPRI Development 2.1 Assessing the Environmental Impacts Among the number of environmental impacts that can result in due to operations of a chemical process plant, toxicological impact was selected to assess inherent environmental hazard in this work. It is assumed that environmental implications of daily chemical emissions of a plant are mainly due to toxic effects. Further, the data on toxicity estimation can be found readily at the preliminary design stage of the plant [3]. Therefore in this methodology, an index called “Inherent Environmental Toxicity Hazard Index (IETHI)” is developed. Here, the methods proposed by Cave et al. [3] and Gunasekera et al. [4] are used
Although there are methodologies developed to assess chemical process routes during early design and development stages based on safety and environmental factors separately, studies on routes assessment based on these factors together are found to be few. Further, the studies of this assessment considering the plant operation condition scenario are also lacking. Therefore, this work proposes a methodology to assess inherent environmental and safety hazards of a chemical process route during early plant design and development stage while
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with some modifications. Figure 2 shows the development of IETHI for a chemical route. The Inherent Environmental Toxicity Hazard Index for a chemical process route is calculated by considering aquatic, atmospheric and terrestrial ecosystems’ hazard indices. These are calculated based on Predicted Environmental Concentration (PEC) and Acute Toxicity data Lethal Concentration (LC50), Lethal Dose (LD50) inhalation Lethal Concentration (inhLC50). The IETHI is developed in the way that when higher the index value higher the environmental hazard is.
and therefore, inputs by emission are balanced exactly by reactions. Chemicals are degraded in the environment by reactions according to first order reaction kinetics. All the phases are behaving like individual CSTRs.
PEC of each chemical emission resulting from plant operations is calculated considering the model environment “Unit world” proposed by Mackay et al. [15]. Figure 3 shows a cross section of the ‘unit world’ which has 1 km 2 cross-sectional area and 6 km atmospheric height.
Calculate Predicted Environmental Concentration (PEC) Air 6 × 109 m3
Calculate Chemical Water Hazard Index (CWHI), Chemical Terrestrial Hazard Index (CTHI), Chemical Atmospheric Hazard Index (CAHI) for each chemical present in the route
Soil 4.5 × 104 m3 Water 7 × 106 m3
Determine Water Hazard Index (WHI), Terrestrial Hazard Index (THI), Atmospheric Hazard Index (AHI) of the process route
Biota 7 m3
Suspended Sediment 35m3 Sediment 2.1 × 104 m3
Figure 3 – Cross Section – Unit World 2.1.2 Toxicity Data When assessing aquatic toxicity, LC50 of a species that represent aquatic life is used. For assessing terrestrial and atmospheric toxicity, LD50 and inhLC50 of animals are used. The LC50, inhLC50 and LD50 values of the most sensitive species in the environment are considered [16]. Toxicity data such as LC50, inhLC50 and LD50 are used in this study because these data are available in literature for many known chemicals [16].
Calculate IETHI Figure 2 – Schematic Diagram for IETHI Development 2.1.1 Predicted Environmental Concentration In order to estimate the environmental impacts due to daily emissions of chemicals from the plant, the distribution of these emitted chemicals in different environmental compartments such as air, soil, water and sediments should be estimated. Therefore, Predicted Environmental Concentration (PEC) which interprets the concentration of chemicals in different environmental compartment is estimated using fugacity level II model proposed by Mackay [14]. The fugacity level II model is applied in this study with the following assumptions. No advective inflows and outflows of chemicals on the selected environment
2.1.3
Inherent Environmental Toxicity Hazard Index Using the estimated PEC and acute toxicity data, three indices were developed for aquatic, atmospheric and terrestrial ecosystems using Eqns. (1), (2), and (3) called Chemical Water Hazard Index (CWHI), Chemical Atmospheric Hazard Index (CAHI) and Chemical Terrestrial Hazard Index (CTHI) respectively. Eqns. (1)
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and (3) are based on Cave et al. [3] work with their same assumptions. The food and water intake of all the species are from the contaminated area. The concentration of the chemical in the food is assumed to be equal to that in the soil. LD50 can be used to estimate a total lethal dose over a 4 day period. CWHI i
PEC wi LC 50i
PEC ai CAHI i inhLC50 i
approach has been adopted by Edwards et al [1] in their work on PIIS.
WHI max (CWHI i )
... (4)
THI max (CTHI i )
... (5)
AHI max (CAHI i )
... (6)
i 1..n
i 1..n
i 1..n
Using WHI, THI and AHI values the Inherent Environmental Toxicity Hazard Index (IETHI) for a chemical process route is calculated as shown in Eq. (7).
… (1)
… (2)
IETHI WHI THI AHI
TDI wx PEC wi TDI fx PEC si w s M … (3) CTHI i d i LD50 xi
… (7)
2.2 Evaluation of Inherent Safety To assess inherent safety of a chemical process route, an index called Chemical Route Inherent Safety Index (CRISI) is proposed. This index value also gives a higher hazard when the value is high. The CRISI is developed by considering two aspects namely chemical safety and process safety based on previous research works [1, 9, 17].
where, i n d Mi PECsi PECwi PECai
= chemical i involved with the route. = number of chemicals in the route = Time period, days = Molecular weight of chemical, g/mol = PEC in soil compartment, mol/m3 = PEC in water compartment, mol/m 3 = PEC in air compartment, mol/m 3 ρw = Density of water kg/m 3 ρs = Density of soil kg/m3 TDIwx = Daily fluid intake of animal species x, g/ kg body weight /day TDIfx = Daily food intake of animal species x, g/kg body weight/day LC50 = LC50 for aquatic life, mol/m3 inhLC50 = Inhalation LC50 of chemical, mol/m3 LD50 = Lethal Dose of chemical that kills 50% of the test population of species x. mg/kg body weight CTHIi = Chemical Terrestrial Hazard Index CWHIi = Chemical Water Hazard Index CAHIi = Chemical Atmospheric Hazard Index
The safety assessing parameters selected in this study are listed in Table 1. The data on these parameters are available during the preliminary process design stage for most chemicals. Evaluation of CRISI in this study is based on the work of Sirinivasan et al. [17]. Table 1 - Parameters Used to Evaluate CRISI 1 2 3 4 5 6 7
Process Temperature Process Pressure Process Yield Reactivity Flammability Explosiveness Heat of Reaction
While reactivity, flammability and explosiveness were chosen to assess chemical safety aspects, heat of reaction, process yield, temperature and Pressure were considered to assess process safety [17] of the chemical process route.
Using Eqns. (1), (2) and (3), chemical hazard indices of each chemical involved in the route are calculated. Then, the chemical for which the maximum value was observed for each CWHI, CTHI and CAHI in the route are taken as the WHI, THI and AHI, respectively as shown in Eqns. (4), (5) and (6), respectively. Therefore, the maximum possible impact on environmental compartments is assumed to be due to the impact of this chemical. Similar
2.2.1
Calculation of Chemical Route Inherent Safety Index (CRISI) To determine CRISI of a process route, selected safety assessing parameters are scored and scaled from zero to one range according to the
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method presented in the work of Sirinivasan et al. [17]. Scores of a chemical for reactivity (Ri) and flammability (Fi) are given based on the National Fire Protection Association (NFPA) rankings which takes a value from zero to four [18]. These values are then transformed to the range zero to one using Eqns. (8) and (9), respectively [17]. A ‘‘0’’ in the scale means not hazardous and ‘‘1’’ represents the most hazardous level.
R si Fsi
Ri 4
… (8)
Fi 4
… (9)
As cited in Sirinivasan et al. [17] work, heat of reaction (∆Hj), pressure (Pj), process temperature (Tj) are converted to scaled heat of reaction score (∆Hsj), scaled pressure score (Psj) and scaled temperature score (Tsj) respectively using functions listed in Eqns. (13), (14), and (15). These scaling functions are based on the frequency distribution of these parameters for common reactions and scores are converted to the range from zero to one. 1 H sj 1 b a 4.47E 05, b 2 1 aH j
1 e a ( p j 1) a 0.03 for p j 1atm Psj ..(14) 1 e a ( Pj 1) a 5.00otherwise
Explosiveness of a chemical (Ei) is taken as the difference of upper and lower explosive limits and is scaled (Esi) from zero to one from its range of 0 to 100 using Eq. (10).
E si
Ei 100
1 e ( aT j b ) 0 a 0.005,b 0.125 forT j 25 C ..(15) Tsj ( aT b ) 1 e j a 0.020,b 0.500 otherwise
… (10)
Then, the chemical that has the highest scale value in each of these individual parameters is selected as the relevant safety hazard index of the process route. For example Reactivity Index (RI) of the route is equal to the maximum scaled reactivity score (Rsi) present in the route as shown in Eq. (11).
RI max ( Rsi ) i 1..n
The process safety hazard indices, Yield Index (YI), Heat of Reaction Index (ΔHI), Pressure Index (PI) and Temperature Index (TI) are then determined by taking the maximum of scaled scores of Ysj, ∆Hsj, Psj and Tsj out of the m reaction steps present in the route. As an example, YI is determined according to the Eq. (16).
… (11)
Flammability Index (FI) and Explosiveness Index (EI) are also determined in a similar way by taking the maximum values of scaled flammability score (Fsi) and scaled explosiveness score (Esi), respectively.
YI max (Y sj ) j 1..m
… (16)
In this methodology, safety indices represent the maximum possible chemical and process hazard of the chemical process route.
Process safety hazards present in the route are assessed according to the reaction steps present in the route and scored on to the range zero to one [0,1] according to the description given below. The notation “j” is used to represent a reaction step and “m” denotes number of reaction steps present in the route.
Then, CRISI for a chemical route is calculated by adding individual safety hazard indices together as shown in Eq. (17). This concept is applied in Sirinivasan’s work [17] as well when they calculated a cumulative index of each route.
CRISI RI FI EI YI HI PI TI ..(17)
Yield of a reaction step j (Yj) values from 0 - 100 is transformed as scaled yield score (Ysj) which is varied from zero to one using Eq. (12) to account for the fact that a smaller yield is more hazardous.
100 Y j Ysj 100
... (13)
2.3
Inherent Chemical Process Route Index (ICPRI) The Inherent Chemical Process Route Index (ICPRI) is obtained by combining IETHI, and
… (12)
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3.1 IETHI Calculation Table 2 shows CWHI, CTHI and CAHI of each chemical present in the cumene oxidation route.
CRISI. Since all of these indices are build up with dimensionless individual indices in [0,1] range, ICPRI of each Chemical Process route can be determined by adding these individuals as shown in Eq. (16). Aggregation of dimensionless scores by addition has also been used by other researchers [1],[5],[17] by assuming additive effect of impacts.
ICPRI = IETHI + CRISI
Table 2- CWHI, CTHI and CAHI for Cumene Oxidation Route Chemical Cumene Cumene HydroPeroxide Dimethylphenylm ethanol Acetophenone Dicumylperoxide Acetone Phenol α-Methylstyrene Sulfur Dioxide
… (16)
The outcome of ICPRI is a summation of 10 parameters in the range [0, 1]. Accordingly, the maximum of ICPRI will be 10, which interprets the highest hazard based on inherent environment and safety assessment and the minimum will be 0 which interprets the lowest hazard.
3.
CWHI
CTHI
CAHI
0.3875 0.0105 0.0246 0.1360 0.0272 0.0000 0.0000 0.0000 0.0000 0.1846 0.0000 0.8754 0.8192 0.0000 0.0000
0.0190 0.0000 0.0030 0.0647 0.0000 0.0000
0.0001 0.0000 0.0005 0.0024 0.0000 0.0000
Example & Discussion The maximum of CWHI, CTHI, CAHI in the route is shown in bold values in Table 2. From Eq. (7), IETHI of the route is equal to 0.9647. According to the results obtained in this example of cumene oxidation route to produce acetone, aquatic compartment is subjected to a higher toxic hazard as the maximum value of CWHI, 0.8754 is closer to one in the scale which represents the highest hazard. The terrestrial and atmospheric compartments’ hazards are closer to zero which represents the lowest hazard.
The methodology described above to assess inherent environmental and safety hazards of a chemical process route has been applied on cumene oxidation process route to produce Acetone. In this study, target acetone production capacity selected was 150000 t/yr with 8000 h/year operating time. Hence, the target acetone production rate was 18.75 t/h. Cumene oxidation process mainly consists of two reaction steps and in step 1, 99.9% minimum purity Cumene is oxidized by air to cumene hydroperoxide. In step 2, cumene hydroperoxide from step 1 is cleaved in the presence of an acid catalyst. Phenol and acetone produced in the process are recovered by distillation.
3.2 CRISI Calculation As described in the methodology, the chemical having the maximum scaled score of flammability, reactivity and explosiveness of the route separately were taken as the chemical safety hazard indices for arriving at the CRISI.
Step 1:
Scores for the process safety assessing parameters for two reaction steps in cumene oxidation route are shown in Table 3.
Step 2:
Table 3- Scaled Scores for Process Safety Parameters Reaction Step 1 Reaction Step 2 Tsj 0.31 0.20 Psj 0.00 0.02 Ysj 0.65 0.05 ∆Hsj 0.38 0.74
Figure 4 - Cumene Oxidation Reaction Steps
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Similar to the chemical safety hazard indices, process safety hazard indices are also taken as the maximum scaled scores out of the two reaction steps.
4.
Conclusions
The Inherent Chemical Process Route Index (ICPRI), developed in this study interprets the inherent environmental and safety hazard associated with a chemical process route quantitatively. This assessment is suitable for hazards posed by emissions from daily plant operations. The method developed is simple and uses data available during early stages of a chemical process plant design and development.
Therefore for cumene oxidation route, chemical and process safety hazard indices are as follows. RI = 1.00 FI = 0.75 EI = 0.10 TI = 0.31 PI = 0.02 YI = 0.65 ∆HI = 0.74 By adding these seven safety indices CRISI is found to be equal to 3.572.
Although in this work the ICPRI is tested on one route to produce acetone, it is recognised that this method could be used to test on other routes to manufacture acetone as well. Therefore, the comparison of alternative routes to produce acetone could be considered as a possible future study. Further, since this method is generic it could be used on other chemical processes as well.
3.3 Interpretation of ICPRI According to the equation (16), ICPRI value for producing 18.75 t/h Acetone with cumene oxidation route is equal to 4.53. The ICPRI varies between a minimum value of zero and a maximum value of ten. The ICPRI for cumene oxidation route obtained in this example is close to the middle of the ICPRI range. Therefore, environmental and safety hazards due to daily chemical emissions of this route to produce acetone can be thought to be considerable.
Acknowledgement This research project was supported by University of Moratuwa Senate Research Grant Number SRC/LT/2011/13.
When evaluating ICPRI, the indices IETHI and CRISI were developed based on several assumptions. In the development of IETHI the hazard due to the most toxic chemical on aquatic, terrestrial and atmospheric environmental compartments were considered in arriving at the respective hazards posed by the route. Further, the CRISI has also been developed by considering the most hazardous chemical in the case of chemical safety and the most hazardous reaction step in the case of process safety of the process route. However, it is recognised that the impact due to other chemicals involved in the route could also have a contribution to the overall impact when considered collectively along with the most toxic chemical. Although the methodology is tested on cumene oxidation route to manufacture acetone based on estimated data available during early design stages authors would like to highlight that further work needs to be done to validate this methodology using data from existing chemical manufacturing plants to confirm its applicability.
References
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Kletz T. A., Plant Design for Safety. A UserFriendly Approach. New York, USA: Hemisphere Publishing Corporation, 1991.
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Gunasekera M. Y. and Edwards D. W., "Chemical process route selection based upon the potential toxic impact on the aquatic, terrestrial and atmospheric environments," Journal of Loss Prevention in the Process Industries, vol. 19, p. 60, 2006.
Srinivasan R. and Nhan N. T., "A statistical approach for evaluating inherent benignness of chemical process routes in early design stages," Process Safety and Environmental Protection, vol. 86, pp. 163174, 2008.
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Khan F. I. and Abbasi S. A., "Multivariate hazard identification and ranking system," Process Safety Progress, vol. 17, pp. 157-170, 1998.
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Khan F. I. and Amyotte P. R., "I2SI: A comprehensive quantitative tool for inherent safety and cost evaluation," Journal of Loss Prevention in the Process Industries, vol. 18, pp. 310-326, 2005/11// 2005.
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Palaniappan C., "Expert system for design of inherently safer chemical processes ". vol. MEng: National University of Singapore, 2002.
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Palaniappan C., Srinivasan R., and Tan R., "Selection of inherently safer process routes: a case study," Chemical Engineering and Processing, vol. 43, pp. 641-647, 2004.
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Mackay D., Multimedia Environmental Models; The Fugacity Approach, 2 ed.: Lewis Puplishers, 2001.
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Mackay D. and Paterson S, "Fugacity Models. in Karcher, W. & Deviller, J. (ed.). Practical Applications of Quantitative Structure-Activity Relationships (QSAR) in Environmental Chemistry and Toxicology," Kluwer, London, 1990, pp. 433-460.
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Annual Transactions of IESL, pp. [61- 69], 2012 © The Institution of Engineers, Sri Lanka
Evaluation of Landscape along a Tropical Expressway based on Landscape Components: Case Study Based on Southern Expressway D. Gunawardhana, G.N. Samarasekara, K. Fukahori and H.A.C. Chaminda Abstract: As many other developing countries Sri Lanka is also trying to develop an extensive set of transportation corridors which are intended to be visually attractive. Creating such attractive roads should begin with comprehensive understanding of user perception followed by comprehensive evaluation of the landscape. Yet at present there are no proper criteria for assessment of visual qualities along roads. By taking the landscape of Southern Expressway as a case study this study attempted to understand how the users perceive a tropical expressway landscape in a developing country. A semi structured questionnaire was distributed among 500 expressway users where the users were requested to describe about the landscapes that they perceive as good or bad. 379 users returned the completed questionnaire which was answered while travelling along the road. Instead of a traditional statistical analysis, a content analysis based on grounded theory was conducted to identify factors behind highway experience. Vegetation, mountain, road side plantations, and view of cultural elements like Buddha statues were among the mostly enjoyed landscapes. Untended vegetation, concrete structures, under-maintained roadside landscapes, exposed rock faces and corps of animals’ were among the disliked landscapes. The results could be utilized to identify and preserve the existing landscape resources while taking steps to improve negative views via suitable proposals. Keywords:
1.
Highway Landscape, Scenic Routes, Southern Expressway, Visual Elements
Introduction officials have an obligation provide a spectrum of travel experiences and to help protect and preserve those highway qualities that are valued. Thus the development of scenic qualities of a route should begin with a proper assessment of visual resources and problems as perceived by the highway users. This study forms the first part of such an aim by attempting to identify what kind of landscapes are perceived as visual resources and what are perceived as visual problems by the road users. Such identification can make way for a proper assessment process and can also be utilised to propose landscape treatment methods.
According to the future plans of Road Development Authority, the Sri Lankan transportation network would be expanded extensively [1]. In addition to their core function of facilitating the vehicle movements, these transportation corridors are intended to be visually attractive to have a good travel experience and to encourage more tourism. Improving the scenic qualities along transportation corridors is becoming important worldwide [2]. Movements like Americas Scenic Byways are encouraging people to travel along scenic routes simply to enjoy the landscape along the route [2]. Visually attractive routes can relieve the stresses of users while bringing economic benefits to the local area. Study on Americas Scenic Byways has found that designated scenic routes lead to increase in traffic, visitor spending per day, increase in miles travelled and increase of jobs [3]. According to Brown [4] the landscape along a highway is not a mere collection of physical resources, but something shaped by the natural and human forces existing in the landscape as well as by the perception of the viewers. Further Brown has suggested that if the highway landscape is an important concern, the highway
2.
Background of the Study
The highway landscapes in developed countries like USA, Japan or England have extensively D. Gunawardhana, BA(Hons), Instructor, Department of Interdisciplinary Studies, University of Ruhuna. Dr. (Ms.) G.N. Samarasekara, PhD, MEng., BSc. Eng. (Hons), AMIE(Sri lanka), Senior Lecturer, Department of Civil and Environmental Engineering, University of Ruhuna. Dr. K. Fukahori, Associate Professor, Division of Environmental Science & Infrastructure Engineering, University of Saitama, Japan. Eng. H.A.C. Chaminda , MEng., BSc. Eng. (Hons), MIE(Sri Lanka), Highway Design Engineer, Engineering Consultant Limited.
1
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been studied by many pioneer researchers like Appleyard, Sheppard or Smardon. [5].
questions were prepared both in Sinhala and English languages and the respondents had the option of answering in either of the languages. 379 users returned the completed questionnaire which included 98 questionnaires consisting only of demographic data, which were excluded from further analysis. This resulted in 281 questionnaires leading to a response rate of 56%. This paper mainly focuses on data for the second question related to the general opinion about the landscape. The related demographic and usage data is also presented to relate the context.
Yet if the landscape experience is influenced by the natural and human forces existing in the landscape as well as by the users, neither the outcomes of their studies nor the parameters used in such studies can directly be applied to the Sri Lankan context where the landscape is dominated by tropical weather and the users represent eastern cultural groups. Thus in order to understand the landscape experience along Sri Lankan expressways a separate study should be conducted. This research intends to cover such research gap by identifying rationale behind aesthetically positive and negative landscapes. For this purpose the landscape along the Southern Expressway was selected as a case study route and the data of real landscape experience of Expressway users were obtained. Researchers, who attempt to understand the human perception independent of previous theories, often use approach of Grounded Theory in which the results would be grounded on the real observations and not on the previous theories. In assessing the natural landscape cognition Ohta (2001) [6] has used this approach, in which he derived the phenomena behind cognition of natural landscapes based on interviews of a semi structured open ended questionnaire. Thus in trying to understand the preference for landscape without being influenced by theories of other countries this study adopted a method similar to what has been used by Ohta (2001) [6] to understand the natural landscape cognition.
4.
4.1 Demographic and Usage Data The first part of the questionnaire intended to get demographic and usage data of the respondents. The respondents consisted of 47% Car users, 27% Bus users, 23% Van users and 2% Truck or other vehicle users. Among them 54% were males and 46% were females. Their age distribution was 1% below 15 years; 16% between 15 – 24 years; 31% between 25 – 34years; 26% between 35-44 years; 17% between 45 – 54 years; 6% between 55 – 64 years and 3% 65years and above. In terms of their user frequency, 34% were first time users of the expressway, 22% used less than once in a month, 24% were monthly users, 17% were weekly users and 3% were daily users. The above demographic and usage data indicates that the questionnaire respondents sufficiently represented different demographic characteristics and usage levels. 4.2
3.
Data Analysis and Results
General Opinions about the Landscape of the Southern Expressway This section consisted of two open ended questions which required them to describe what kinds of landscapes make the Expressway aesthetically positive and what kinds of landscapes make it aesthetically negative. The respondents have given lengthy descriptions about the types of landscapes they liked and disliked. The descriptions given in Sinhala were translated in to English and all further analysis were conducted based on the descriptions available in English. These descriptions were then analysed using the standard qualitative research method of content analysis as described by Putton[7]. Ohta(2001) [6] work on natural landscape cognition illustrates how the standard content analysis can be used to analyse a set of cognitive descriptions using coding at multiple levels. The authors in this work adopted a similar approach to analyse perception of expressway landscape. Two separate analyses
Methodology
The data was collected using a semi structured questionnaire, distributed among 500 expressway users who volunteered to participate up on a verbal request made at the expressway entrance. The questionnaire were distributed at the Pinnaduwa and Makumbura entrances and collected at the Makumbura and Pinnaduwa exists respectively. This facilitated a stretch of 95km one way so that a significant length of landscape is exposed to the participants. It was answered by the passengers while travelling along the road. The questionnaires were distributed on a Friday and a Saturday. The questionnaire consisted of three components each requesting demographic and usage data, data about their general opinion on Southern Expressway landscape and data about the specific landscapes which they perceived as either being positive or as negative. The 2
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5.2.
General Opinions about the Landscape of the Southern Expressway 5.2.1. Positive Landscape Experiences along the Southern Expressway From the descriptions about the positive landscapes, 508 remarkable segments were coded. This has led to 49 level III themes 8 level II themes and 3 level I themes. The frequent occurrence of any theme within the remarkable segments reflects that Southern Expressway is aesthetically valued for the presence of that theme. The three themes at level I were Landscape Elements, Landscape configurations/ characteristics and composition and Psychological constructs.
were conducted to analyse descriptions about aesthetically positive and aesthetically negative landscapes. Accordingly, the first two authors carefully examined each of the descriptions and identified the key themes For this purpose the descriptions were re-examined to identify the important remarks and each such remark was coded using the most suitable theme or themes from the list of themes. A list of key themes were made thereby. These key themes composed the level III (see Appendix) key themes as shown in Table 1 and Table 2. Based on similarity of meaning among level III themes, these were then grouped in to several groups. By studying the meaning within the themes of a group, a new themes which reflected the level II themes were obtained. A similar procedure was adopted to obtain a set of level I themes from level II themes. Based on the above a hierarchical conceptual model was obtained to describe the landscape preference of the Southern Expressway in a qualitative manner.
Most enjoyable landscapes The level III themes suggest detailed levelled themes and indicate individual aspects that can directly contribute to visual appearance. Vegetation, paddy fields and landcover – rock were the three most frequently mentioned themes. Thus these three elements are the most important visual elements that make the expressway aesthetically attractive. Thus any landscape preservation efforts should first be focused towards these.
Further observations about relative importance of parameters in the above model were made based on the frequency of usage of individual themes at all three levels. Accordingly, number of times a theme was mentioned was counted to obtain the frequency related to that aim. As an example the 117 in Table 1 represents that among all positive landscape explanations, there were 117 remarkable segments in which vegetation was the theme. Similarly the counts related to level II themes were obtained by summing up the counts of level III themes related to that particular level II theme. The level I counts were obtained similarly by summing up the relevant level II themes.
5.
The observations of relevant landscape elements themes described the preference due to the presence of an individual physical element such as trees, a plantation or a Buddha Statue. As an example one respondent rationalised his preference about the Expressway as “The palm trees either sides make a highway beautiful”. Descriptions on Landscape configurations/ characteristics and composition, revealed the preference for Southern Expressway not merely which resulted due to the enjoyment of a landscape composition, configuration or a characteristic. As an example many comments mentioned that they prefer the Southern Expressway for its “Green color” which reflected the landscape characteristic of colour. The Psychological constructs reflected the feelings about landscape. Almost all the psychological constructs were related their feelings about the overall landscape. Majority of such comments mentioned that Southern Expressway is beautiful which reflected their feeling about the route as a whole.
Discussion
5.1. Demographic and Usage Data In selecting the participants, researchers studying landscape cognition (Ohta, 2001) [6] adopt the method of recruiting volunteers up on request. The participants of this research were actual road users who volunteered to participate. Although a strictly random sample was not used due to the difficulties of getting such a sample under a strictly regulated environment at expressway entrance, the statistics shows that sample is represents different demographic characteristics and also gender and age distributions reflect the general demographic trends in Sri Lanka.
The landscape elements Among the 508 coded segments, 462 comments (91%) were in terms of landscape elements where as Landscape configurations/ characteristics and composition and Psychological constructs were included only in 3
63
6% and 3% of the comments. In an expressway where the vehicles traverse at higher speeds, perceived landscape generally consists of longer views, patterns and colour. Noticing landscape elements is not very frequent. But the above results suggest that a significant number of observations were in terms of landscape elements. Accordingly, any landscape treatment in terms of individual elements, would be noticed highly in comparison to any treatment to the landscape composition which may be costly and complicated.
manner to highlight the limited number of mountain views. Irrespective of being a primary landscape element, only few participants mentioned water as a reason for their preference for this route. The expressway crosses multiple water bodies of different scale. Unfortunately the bridge design has been done in such a way that the visibility of the water is limited to the users of taller vehicles such as the bus. Also the bridges have adopted very economical designs, in which even the presence of a bridge is hard to noticed unless for the short parapet walls. But if the bridges were designed to be more conspicuous along with more conspicuous indication of the approach to the bridge, then people will be able identify the bridge. This can make them to appreciate the presence of water leading to a richer landscape experience.
The landscape elements observed consisted of four, level II themes. Those were natural landscape elements, agricultural elements, manmade elements and cultural elements. Among them natural landscape elements were most frequently mentioned.
Agricultural elements: Among the landscape elements the second most frequently mentioned theme at level II was the agricultural elements. It represented a set of level III themes, such as paddy fields, rubber, tea, palm, farm lands, animals and cinnamon. These described a set of key agricultural practices in Sri Lanka. In considering the road side land use of the expressway, the initial stretches closer to Makumbura side have many rubber and paddy cultivation. The intermediate segments have palm oil trees, rubber and paddy cultivation. The latter segments closer to the Pinnaduwa are characterised by rubber, tea and some cinnamon. Such variation of roadside land use along with the above observations about frequent mentioning of multiple agricultural practices only within 95 km, highlights the capability of southern expressway landscape to communicate about the multiple agricultural practices in Sri Lanka to tourists. Such communication can be enhanced by creating a good interpretation master plan for the expressway.
Natural Landscape Elements: Within the theory of landscape perception, water, vegetation and land cover are identified as primary landscape elements, the presence of which creates a preferred landscape [8]. The results here confirms this point whereby the presence of vegetation had strongly (54% among natural landscape elements; 23% among all remarkable segments) contributed to the preference for this expressway. The other themes land cover rock and mountains also represent another primary landscape element namely the land cover. The theme land cover rock referred to exposed rock surfaces by road side. While they received higher level of positive perception, among the list of negative themes were the two themes rocks and rocky mountains which have been mentioned in relatively fewer occasions. This divided opinion on similar elements could have resulted either due to the individual differences in opinions or due to the comments referring to differently appearing rock faces. While the treatment to the individual differences is beyond the highway planner’s scope, improvement possibilities lie with the latter. Along the expressway there are many places where the rock surface appears to be disorderly due to rock blasting which might have received the foresaid negative comments. The planners can take some measures to improve the appearance of such rock faces to ensure they appear natural.
Manmade elements: Some of the man made elements were also perceived as positive elements. Among them most frequent perceptions included bridges, lighting, slope and the monument of the bird as well as the road itself. Bridges due to their functional meaning and the architectural appearance are one of the most enjoyed landscape elements in highway landscapes. While the bridges have received highest number of comments among man made elements, this perception level could be increased if they were more conspicuous as mentioned earlier. Adding public art with a landscape theme, making the parapet walls taller or adding some attractive landscape elements in
Unlike the hill country, which is known for scenic beauty of mountains, the Southern region in Sri Lanka is characterised by flatter terrains or low altitude mountains. But the frequent mentioning of mountains shows that the highway alignment had been done in an optimum 4
64
5.2.2. Negative Landscape Experiences along the Southern Expressway From the descriptions about the negative landscapes, 226 remarkable segments were coded. This has led to 43 level III themes 7 level II themes and 3 level I themes. If any of the above theme is frequently mentioned within the remarkable segments, such theme is likely to influence the Southern Expressway negatively.
the approach to the bridge could make the bridge more noticeable. The slopes have also been noted their positive contribution along with lighting and fences. Also the monument of a bird near Welipenna rest area have also been noticed and appreciated by many showing a higher landscape potential. Cultural elements: Buddha statue, village and temple were some frequently mentioned elements with a cultural meaning. Among them the Buddha Statue had received the highest number of comments followed by village and temple. Although the best observable Buddha statues by the expressway are two in number, they are well appreciated as mentioned by one participant “Buddha statues makes our mind happy. We want more creations like this”. For most of its parts the expressway traverses through plantations in which the landscape is inactive. Perception of well placed cultural elements as discussed above can bring some lively feeling and thereby break the monotonous landscape experience of the expressway.
Most negative landscapes Concrete structures, corps of animals and grass were the three most frequently mentioned negative themes at level III. These indicate individual aspects that can directly contribute to the negative visual appearance. Thus it is important for the officials to treat these aspects in order to make the expressway more visually attractive. The three themes at level I were Landscape Elements, Landscape composition and Psychological constructs. These three themes showed a higher degree of similarity to the level I themes of positive landscape in content. Also the relative frequency of mentioning showed the same order with landscape elements being mentioned in 94% of the remarkable segments.
Landscape configurations/ characteristics and composition Three level II themes have emerged under the above which were landscape characteristic, landscape composition and road geometry.
Landscape elements The level II aims of the above consisted of negative man made elements, negative natural elements, negative due to maintenance and negative by practice. Negative man made elements: The majority of the negative landscape elements consisted of man made elements especially related to the road infrastructure. Among them concrete structures was frequently mentioned followed by bridges, Houses, Building, Fences, Wires, Cuts and Drain. As discussed above with respect to bridge noticeability, in finalising the designs based on economic grounds, the room for architectural appearance might have to be compromised. But the results here suggest that such decisions may lead to the creations of a landscape that is not aesthetically pleasing. Another element mentioned as negative were billboards and political cut outs that were facing the road. Although a decision has been taken to not to allow such along the road, occasional breaching of such practices can be observed. But with the above observation confirming that even occasional breaching does not go unnoticed the officials should take more care to ensure 100% adherence to the rule.
Landscape characteristics: These reflected comments about inherent qualities about the expressway which will be helpful to form the image of the expressway. Among the level III themes only green had been mentioned frequently as a landscape characteristic. Thus the users are likely to imagine and remember this route as a place of green. Landscape compositions: The level III themes under landscape compositions identified some perceived patterns in which the landscape is composed of. But the themes were scattered and infrequent indicating that this route is not highly memorable in terms of landscape compositions. Road geometry: This was mentioned by one respondent in describing the positive contribution of the bends to the aesthetic appearance. Psychological constructs Instead of rationalising the preference for expressway landscape using the foresaid objective aspects, some participants have expressed their preference in a gross manner using psychological constructs like beautiful, clean or unique.
Negative due to maintenance issues: The next most frequently mentioned themes of negative landscape related to lack of maintenance which included Badly maintained vegetation, Buildings 5
65
underconstruction, Broken Fences, Garbage, Defects of road, Broken rocks, Grass land, Broken Houses, Broken Road, Broken Structures, Grass dried, Structures broken. Although vegetation has a universal acceptance as an aesthetically attractive element, untended vegetation is a cause for negative landscape (Kaplan, 1986). The data here confirms the above point. The other frequently mentioned elements mentioned above such as broken elements, structures, under construction or garbage confirms the importance of proper maintenance and construction. This confirms that officials should pay sufficient attention to the maintenance of expressway.
grass, this data suggests that higher preference for mountain landscape instead of open areas. Psychological constructs Only three elements were mentioned to describe the feelings towards the expressway. The theme monotonous which described the lack of a good sequential landscape highlights an important point. Irrespective of being visually attractive, a similar landscape continues in most of the parts. Such monotonous appearance may make the drivers feel bored which may lead to negative consequences like accidents. Therefore it is important to establish some conspicuous visual elements at regular intervals to break monotony. Landmarks like Buddha statue or monuments could be used for this purpose.
Negative natural elements: The negatively perceived elements included some natural elements, namely Grass, Rocky mountains, Soil, Forest, Rocks, Coconut trees, Rubber and Stones. Among those grass was frequently mentioned as a negative element. One element under negatively perceived landscape compositions was empty areas. But preference for vegetation confirms that taller trees were perceived as positive. Also the mountains received higher preference levels. The totality of above suggests that empty areas or grass areas without trees are perceived as negative in the context of this landscape of mountainous appearance.
6.
Conclusion
Through a content analysis of a set of landscape preference descriptions this research was able to identify a set of factors that describe the preference for a tropical expressway. In the absence of previous knowledge that matches the context, this research adopted a bottom up approach whereby some basic factors behind the preference for a tropical expressway was elicited. The methodology did not allow statistically significant identification of what is the best factor. Instead a set of potential factors were identified which can be studied to depth and more quantitatively in future studies. Based on the above results following recommendations can be made in order to improve the landscape of a tropical expressway of similar context.
Negative by practice: Three other elements namely, cloths hung, corps of animals and animals on the road highlighted some practices which may need regulation. The road side occupants may hang cloth without realising the visibility of such to the road user. In the perception of the road user, cloths hung by the road side symbolises lack of attention or even displeasure of road side occupants towards the existence of the road. The data here confirms such a point. Most of such hanging has been done on the fence belonging to the expressway. If the road side dwellers are made aware of this negative practice, the issue may be resolved. The corps of animals killed by hitting with vehicles is another frequently mentioned negative element. Thus it is important for the expressway authority to establish a method to remove such immediately to avoid disgusting appearance of corps on road.
Landscape treatments should focus more on above identified individual elements instead of composition/ configuration or characteristic Preserving views of traditional agriculture Creation of an interpretation master plan to communicate the values of landscape Improving the appearance of blasted rocks Making the bridges more attractive and bridge approaches more conspicuous Introducing a mechanism to remove corps Increasing appearance of concrete elements Ensuring the adherence to no billboard policy Regular maintenance to roadside landscape, removal or garbage and repairing the broken elements like fences Planting trees in empty and barren areas Educating people to refrain from hanging clothes within road vicinity Introducing more landmark elements and cultural elements like Buddha statue
Landscape composition Showing a similar trend to the positive elements, only few themes were mentioned to describe the landscape composition. Among these empty areas were frequently mentioned as being negative. As discussed above with respect to the element
6
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Acknowledgements This research was funded by research grants received under project for Internationalization of University of Ruhuna. The authors would also like to acknowledge the help extended by the officials of Southern Expressway Maintenance Authority, the staff policemen attatched to the Pinnaduwa and Makubmbura exchanges in conducting the questionnaire.
References 1) 2) 3)
http://www.rda.lk, Visited, 15th September 2011. http://byways.org/ Visited, 15th September 2011. Petraglia, L & Weisbrod, G, A Review of Impact Studies Related to Scenic Byway Designation, A report submitted to Scenic Byway Resource Center, March 2011, Downloaded on 26th March, 2006.
4)
Brown, G., A method for assessing highway qualities to integrate values in highway planning, Journal of Transport Geography Vol. 11 (2003) pp 271–283. Smardon, R.C. amd Karp, J.P. (1993). The legal Landscape, Van Nostran Reinhold, New York. Patton, M. Q. (1980). Qualitative Evaluation Methods. Beverly Hills, U.S.A.: SAGE Publications. Ohta, H. A phenomenological approach to natural Landscape cognition. Journal of Environmental Psychology 21, (2001). Pp 387- 403 Kaplan S., Aesthetics, affect and cognition: Environmental preference from an evolutionary perspective. Environment and Behavior, . 19, (1987) pp 3-32.
5) 6)
7)
8)
7
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Table 1 - Themes of Positive Landscapes Level I Themes
Counts of level I themes
Percentag e within Level I
462
91
Landscape Element
Landscape configurat ions/chara cteristics/c ompositio n
Psycholog ical construct
29
17
6
3
Level II Themes
Count of level II themes
Percenta ge within Level II
Primary Landscape Elements
215
47
Agricultura l elements
162
35
Manmade elements
59
13
Cultural Element
26
6
Total Characterisi tic
462 20
67
Compositio n
9
30
Road geometry Total Evaluation Total
Total
1
3
Level 3 Themes
Vegetation land cover rock Mountain Water land cover coloured soil sky Paddy field Rubber Tea Palm Farms Coconut Animals Cinnamon Total Bridge Lighting slope Fence Bird monument Road Channel embankment exit Cut fly over houses Concrete work entrance factory landscaping steps Structures Total Buddha Statue Village Temple Habitation Total Total green biodiversity enroute change Total view country side Flat Landscape footpath to village tropical landscape Total bend
117 47 40 8 2 1 66 37 22 14 8 7 5 3 162 8 8 8 5 5 4 3 3 3 2 2 2 1 1 1 1 1 1 59 10 8 7 1 26 215 18 1 1 20 5 1 1 1 1 9 1
Total
1 10 4 2 1 17
30
17
100
508
Count of level III themes
beautiful clean Unique Sri Lankan culture Total
8
68
Percenta ge within Level III
54 22 19 4 1 0 41 23 14 9 5 4 3 2
Percent age among all comme nts 23.0 9.3 7.9 1.6 0.4 0.2 13.0 7.3 4.3 2.8 1.6 1.4 1.0 0.6
14 14 14 8 8 7 5 5 5 3 3 3 2 2 2 2 2 2
1.6 1.6 1.6 1.0 1.0 0.8 0.6 0.6 0.6 0.4 0.4 0.4 0.2 0.2 0.2 0.2 0.2 0.2
38 31 27 4
2.0 1.6 1.4 0.2
90 5 5
3.5 0.2 0.2
56 11 11 11 11
1.0 0.2 0.2 0.2 0.2
100
0.2
59 24 12 6
2.0 0.8 0.4 0.2
Table 2- Themes of Negative landscapes Level I Themes
Landscape Elements
Count of level I themes
Percent age within Level I
212
94
Landscape Composition
11
5
Psychologica l Constructs
3
1
Total
226
Level II Themes
Count of level II themes
Percenta ge within Level II
Level III themes
45.8
Concrete Structures Bridges Houses Building Fences Wires Cuts Drain Bill board and political cut outs Exits Overhead bridges Channel Signage Tunnel Village Walls Total Badly maintained vegetation Buildings underconstruction Broken Fences Garbage Defects of road Broken rocks Grass land Broken Houses Broken Road Broken Structures Grass dried Structures broken Total Grass Rocky mountains Soil Forest Rocks Coconut trees Rubber Stones Total Corps of animals Clothes hung Animals on road Total
33 12 9 6 6 6 5 5 4 3 3 1 1 1 1 1 97 12 11 10 9 3 2 2 1 1 1 1 1 54 13 8 8 4 3 1 1 1 39 15 6 1 22 9 1 1 11 1 1 2 2
Negative man made elements
97
Negative due to maintenance issues
54
25.5
Negative natural elements
39
18.4
Negative by practice
22
10.4
Total Landscape Composition
212 11
100
Empty areas Disorderly trees Gaps
33.3
Ugly
Total Evaluation
11
Count of level III themes
Total 1
Total Sequence Total
2 3
66.7
Monotounous Total
69
Percent age within Level III 34 12 9 6 6 6 5 5 4 3 3 1 1 1 1 1
Percentage among all negative comments 14.6 5.3 4.0 2.7 2.7 2.7 2.2 2.2 1.8 1.3 1.3 0.4 0.4 0.4 0.4 0.4
22 20 19 17 6 4 4 2 2 2 2 2
5.3 4.9 4.4 4.0 1.3 0.9 0.9 0.4 0.4 0.4 0.4 0.4
33 21 21 10 8 3 3 3
5.8 3.5 3.5 1.8 1.3 0.4 0.4 0.4
68 27 5
6.6 2.7 0.4
82 9 9
4.0 0.4 0.4
100
0.4
100
0.9
Annual Transactions of IESL, pp. [70-75], 2012 © The Institution of Engineers, Sri Lanka
Effectiveness of Bio-filter for Removal of Ammonia, Hydrogen Sulphide and Phenolic Compounds Emanating from Agricultural Sources W. R. K. Fonseka and D. M. H. S. Disssanayake Abstract: Bio-filtration of odorous gases possesses several advantages over conventional treatment methods. The technology utilizes a solid media to absorb and adsorb compounds in the air stream (influent) and retains them for subsequent biological oxidation. This is a cost effective, environmental friendly technique. Eventhough interest in bio-filtration is growing; literature about this technology is not specific about the applications or gas streams that can be effectively treated. This project aims at studying the effectiveness of bio-filter technology for removal of ammonia, hydrogen sulphide and phenolic compounds emanating from agricultural sources. In this study a mobile bio-filter pilot unit designed by Industrial Technology Institute (ITI) was installed, in a poultry rendering plant utilizing locally available low cost materials (coir fibre, coir pith, pieces of tile and compost) as the filter media. Measurements were taken weekly to study percentage reduction of ammonia, hydrogen sulphide and phenolic compounds emanating from the rendering plant by using Industrial Scientific’s Portable VOC Detector. The results indicated that high reduction efficiency (>99.5%) can be achieved in removal of those compounds by the combine action of humidification and biodegradation of the bio-filter unit using locally available filter media. Keywords: efficiency
Bio-filter, Ammonia, Hydrogen Sulphide, Phenolic compounds, Reduction
Alternatively, Bio-filtration possesses several advantages over above mentioned conventional APC technologies. The most attractive features among them are lower capital costs, lower operating costs, low chemical usage and no combustion source. Water re-circulating pump of the humidifier and centrifugal fan that moves air through the system are the only two energy sinks in this system.
1. Introduction A major challenge in the area of air pollution control (APC) is finding cost effective ways of treating emissions of volatile organic compounds (VOCs) and odour causing inorganic gases. Although several techniques such as thermal and/or catalytic oxidation, adsorption (by activated carbon), absorption (scrubbing), adsorptive oxidation etc. is available in Sri Lanka for controlling emissions of odorous compounds/VOCs, most industries are reluctant to adopt these technologies due to high capital and operating costs. On the other hand, most of these conventional techniques require end-of-pipe treatment as only phase transfer of contaminants occurs (transfer of air pollutants, which is in gaseous phase to liquid or solid phase/s during treatment). For example; if adsorption technology is used, spoiled activated carbon has to be disposed as a solid waste after reaching the saturation condition (gas-solid transfer takes place) and if scrubbing technology is used, air pollutants are transferred into the scrubbing liquid (gas-liquid transfer takes place) , which has to be treated separately in a wastewater treatment plant.
Bio-filters have been recognized by several states as Best Available Control Technology (BACT) for the treatment of VOCs and odour (ex: Australia, Canada, Europe). [1] The technology utilizes a solid media (filter media) to absorb and adsorb compounds in the air stream (influent) and retains them for subsequent biological oxidation. The filter
Eng. W. R. K. Fonseka, B.Sc. (Hon.) Chemical Eng. (Moratuwa), M.Sc. (Env. Scie. & Tech.) (Delft) AMIE(Sri Lanka), Senior Research Engineer, Industrial Technology Institute. Eng. (Ms.) D. M. H. S. Dissanayake, B.Sc. (Hon.) Chemical & Process Eng. (Moratuwa), AMIE(Sri Lanka), Research Engineer, Industrial Technology Institute.
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media is simply a bed of organic material, typically a mixture of compost and bulking agent that provide acceptable voidage and surface properties (ex: wood chips, coir, gravel etc.). The influent air humidity should be around 100% RH (saturated air) and air temperature should be less than 35°C to maintain optimum moisture content and temperature in the bio-filter system. [2] An adequate moisture level is very important for proper functioning and efficiency of a bio-filter as the degradation processes are exothermic and tend to dry the filter beds. [3] Moreover, bio-filter systems are particularly effective when used with systems that generate large quantities of air containing low concentrations of biodegradable VOCs (4600 >4600 >4600 [ppm] Mean Conc. after Humidification 104.03 126.63 7.13 [ppm] Mean Conc. after Bio-Filtration 9.2 19.55 4.37 [ppm]
Figure 5 - Comparison Bio-Filter Inlet and Outlet (Pilot Study Results)
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Further reduction can be observed at the biofilter outlet. This is a result of biodegradation of odorous gases in to CO2, H2O and microbial biomass, which carried out by naturally occurring microorganisms in the bio-filter medium (refer Figure 5 and Table 3). Moreover, after bio-filtration step mean concentration of H2S, NH3 and Phenol is below the respective TLV (refer Table 2).
combine action of humidification biodegradation of the bio-filter unit.
and
Figure 7- % Reduction of H2S, NH3 and Phenol Concentrations Over 6 Weeks
5. Conclusions
Results of the study indicated that high reduction efficiencies (>99.5 %) can be achieved by combine action of humidification and biodegradation of the bio-filter unit in removing ammonia, hydrogen sulphide and phenolic compounds emanate from agricultural sources.
This type of air pollution control technique is cost effective as the capital cost of the unit is comparatively less, since locally available filter media is utilized.
This technique can be developed to apply as a low cost air pollution control option in small and medium scale agricultural industries for odour control.
Further investigations in the field of microbiology will assist to optimize this technology.
Figure 6 - % Reduction of H2S, NH3 and Phenol Concentrations in the Bio-Filtration Step Over 6 Weeks High percentage reduction efficiencies at initial stage of the measurements (refer Figure 6) are due to absorption of the gases into the filter media rather than biodegradation of them. Sudden decrease in percentage reduction in between initial-middle stages (refer Figure 6) may be either due to individual or combined result of 1) toxic inhibition; as the raw gas contains a mixture of VOCs and/or inorganic odourous gases, the microbial degradation rate of individual components is often influenced by other components in the mixture 2) reduced filter effectiveness, since the filter materials tend to pack over time 3) lack of moisture or nutrients 4) starvation of microbes 5) saturation of filter media due to overloading of smoke etc. At final stage of measurements, percentage reduction of H2S and NH3 seems stable (refer Figure 6). Acclimatization of specific microorganisms and biodegradation of H2S and NH3 as a result of their optimum activity may be the reason for this. However, percentage reduction of Phenol continued to decrease with time. Toxic inhibition may be responsible for this kind of behavior.
Acknowledgements Grateful appreciation to National Foundation for financial assistance
Science
Specific thanks to the staff of Maxies Farm, Bujjampola for invaluable support throughout the pilot study Staff of ITI for continual and timely assistance in project activities
Referring to Figure 7, high reduction efficiencies (>99.5%) can be achieved by
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References 1.
Dal-Hoon Lee, Development of An Alternative Biofilter System for Odour Treatment, A Thesis Submitted in Partial Fulfillment of The Requirements for The Degree of Doctor of Philosophy, The Faculty of Graduate Studies, Chemical/BioResources Engineering, The University of British Columbia, December 1998, p. 2-3
2.
Paige Hunter & S. Ted Oyama, Control of Volatile Organic Compound Emissions, Chapter 9-Biodegradation, 2000, p. 147-151
3.
Edward C. Moretti, Reduce VOC and HAP Emissions, Baker Environmental, Inc., [URL: www.cepmagazine.org], June 2002, p. 35,
4.
Gary D. McGinnis, Principle Investigator, Final Project Report, Coupled Physical/Chemical and Biofiltration Technologies to Reduce Air Emissions from Forest Products Industries (DE-FC0796ID13440), December 31, 2001, p. 5
5.
Eszenyiova, V. Bilska & Rajnohova H., Removal of VOC from Waste Gases by Biofiltration Technology, Petroleum and Coal, Vol 43, 1, 2001, p. 22-26
6.
Choi J. H., Kim Y. H., Joo D. J., Choi S. J., Ha T. W., Lee D. H., Park I. H. & Jeong Y. S., Removal of Ammonia by Biofilters: a Study with Flow Modified System and Kinetics, J. Air Waste Manage. Assoc. 53 (2003), p. 9210
7.
Nicolai R. E. & Janni K. A., Biofilter Media Mixture Ratio of Wood Chips and Compost Treating Swine Odours, Water Science and Technology, Vol 44 No 9, 2001, p. 261-267
8.
ergosphere.files.wordpress.com/2007/04/c wt_naturalgastechconf2_11_04.pdf visited, 24th February 2009
9.
www.epa.gov/ttn/chief/ap42/ch09/final/ c9s05-3.pdf visited, 24th February 2009
10. Respirator Selection Guide, 3M Occupational Health and Environmental safety Division, 1996
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Annual Transactions of IESL, pp. [76-84], 2012 © The Institution of Engineers, Sri Lanka
Quantitative Risk Assessment of Ancient Earth Dams in Sri Lanka: Preliminary Assessment of Nachchaduwa Dam as a Case Study S. Premkumar and L. I. N. De Silva Abstract: Nachchaduwa is an ancient tank, which was built 17 centuries ago to supply water for irrigation purposes. It was restored in 1906 and improved in 1917 by the Irrigation Department of Sri Lanka. According to an investigation carried out by Dam Safety and Water Resource Planning Project (DSWRPP), Nachchaduwa dam is selected as one of the dams with a higher risk of failure with some signs of excessive seepage and slope instability along the dam embankment. Risk assessment can provide valuable information on the risk reduction measures and benefits of structural and nonstructural risk reduction options. In addition, risk assessment outcomes can strengthen the case for funding capital improvements, additional investigations, and on-going dam safety activities, such as monitoring and surveillance and emergency management. In view of the above, a standard risk assessment framework for safety evaluation of ancient earthen dams in Sri Lanka was proposed in the companion paper. The above framework was employed to conduct an initial level risk assessment on Nachchaduwa Dam in the present paper. This paper summarizes the risk assessment process, results, findings and recommendations for Nachchaduwa dam. Keywords:
1.
Load state, Failure mode, Probability of failure, Consequences, Risk
suitable assumptions were made with proper judgement.
Introduction
Nachchaduwa dam is owned by the Irrigation Department (ID) and is situated some 15 km southeast of Anurathapura. It is an ancient tank built to supply water to the city tanks, and was restored in 1906 and improved in 1917. The dam is built across Malwathu Oya and its tributary Maminiya Oya. There are four medium tanks and hundreds of minor tanks in the catchment. The area consists of jungle, paddy fields, hamlets and chena with moderate slope.
The initial level risk assessment process is divided into eight sections, as follows: inspection of dam and inundation area, identifying the hazards, identifying failure modes, evaluating the load states, estimation of probability of failure, estimation of consequences, estimation of risks, and evaluation of risks, as explain in the sections below.
2.
A risk assessment was done under Dam Safety and Water Resources Planning Project (DSWRPP) for Sri Lankan earth dams. According to their report, there are 32 critical dams in Sri Lanka and Nachchaduwa is one of them.
Inspection of Inundation Area
Dam
and
Nachchaduwa dam is believed to be an essentially homogenous earthfill dam with associated spillway and sluice structures. There is no known zoning of fill materials [1]. Originally the dam is being constructed based on the bund of an ancient tank which has been restored several times to give the present dam.
In this paper, the initial level quantitative risk assessment is selected, considering the availability of data. In this case study the priority is given to the life safety consequences. Critical failure modes were identified for Nachchaduwa dam based on the comprehensive facility review (CFR) done at Nachchaduwa dam.
The upstream slope of initially 1(v):2.5(h) is generally protected with a riprap. The slope is grassed above the riprap line. There is
Eng. S. Premkumar, BSc. Eng (Moratuwa), Research Assistant, AMIE (Sri Lanka) Department of Civil Engineering, University of Moratuwa, Sri Lanka.
Here, the risk is estimated for possible failure scenarios and unacceptable risks of life were reported. In the estimation of consequences,
Eng. (Dr.) L. I. N. De Silva, BSc. Eng (Moratuwa), M. Eng (Tokyo), PhD (Tokyo), Senior Lecture (II), Department of Civil Engineering, University of Moratuwa, Sri Lanka.
1
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significant tree growth along the dam crest and upstream slope; many trees are of large size and considerable age.
4.
The following failure modes were included in the study, considering the data gathered from Comprehensive Facility Review (CFR):
The dam crest is around 3.5 to 4 m wide and carries an unsurfaced road on the centreline. The profile is reasonably regular and no major settlement was identified.
Normal operating load:
The downstream slope is initially given as 1(v):2(h). Upper areas of the slope are generally grassed but in the toe zone there is a considerable number of large trees. There are areas which are settled and eroded by pedestrian and animals crossing the slope. There are three piezometers located downstream of the dam.
At the right hand end of the main spillway, a three bay masonry faced sluice to supply water to the low-level Nuwarawewa transfer canal is constructed. The sluice is called “right bank sluice”. An abandoned central sluice at ch 01+250 m is an old sluice and has been plugged with concrete at the upstream end. At the left abutment of the dam, a two gated concrete/natural stone (masonry) outlet which discharges into a pond from which high and low level canals are fed. The necessary data of Nachchaduwa dam are given in Table 1.
Internal erosion and piping through the embankment – along and into the conduit;
Internal erosion and piping through the weathered foundation;
Downstream slope instability.
Embankment overtopping;
Internal erosion and piping through the embankment – in the dam;
Internal erosion and piping through the embankment – along and into the conduit;
Internal erosion and piping through the weathered foundation.
5.
Evaluating the Load States
A representative critical load state from the normal operating load and flood load was selected for the analysis. The loading states selected under normal operating load and extreme flood load are discussed in the following sections.
104.32 m MSL 101.68 m MSL 3.5 – 4.0 m 1 (v): 2.5 (h) 1 (v): 2 (h) 1650 m Earth fill Clayey sand
5.1 Normal Operating Loads Since this is an initial level risk assessment, it was assumed that the reservoir is always at Full Supply Level (FSL). So the probability of loading state is taken as 1.0 under normal operating load.
Identifying the Hazards
According to the developed guidelines, the following hazards were categorized as obvious hazards for Nachchaduwa dam:
Internal erosion and piping through the embankment – in the dam;
Other failure modes such as internal erosion and piping form embankment to the foundation, Spillway and spillway energy dissipation scour, and overtopping of spillway chute wall, are excluded from the current study, since there are no sufficient investigation data to carry out the analysis.
Table 1 - Tank Data
3.
Extreme flood load:
The dam is with gated and ungated spillways and three sluices. The main ungated spillway (length 142 m) is a mass concrete structure buttresses build on a massive outcrop of rock in the bed of the river. Adjacent to the ungated weir, at its left-hand end, is the gated auxiliary spillway built with concrete with six vertical gates, each of 2.77 m (w) ×2.29 m (h) [1].
Crest level Full supply level Crest width Upstream slope Downstream slope Length Nature Fill material
Failure Mode Analysis
5.2 Flood Loads The extreme flood level was assumed as 103.6m MSL with the Annual Exceedance Probability (AEP) of 1:1000.
Normal operating load (the storage water); Flood load.
2
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6.
6.1.1
Probability of Failure under Normal Operating Load The estimated probabilities of failure for each branches of the event trees for internal erosion and piping, through embankment-in dam, through embankment-along or into conduit, and through foundation are given in Figure 1, Figure 2 and Figure 3, respectively. The conditional probability of failure, for internal erosion and piping, through the embankmentin dam, through the embankment-along or into conduit, and through foundation are estimated as; 9.7x10-5, 6.44x10-4, and 2.5x10 -12, respectively.
Estimation of Probability of Failure
Probabilities of failure were estimated using both event tree method and historic performance method. An event tree is a graphical representation of a series of events, which form failure or accident scenarios for a dam, while the historic performance methods use the historic performance of dams similar to the dam being analysed to assess a historic failure frequency, and assumes that the future performance of such dams will be similar.
6.1.2
Probability of Failure under Extreme Flood Load The factors influencing on the likelihood of internal erosion and piping is same for both normal operating load and extreme flood load. But the reservoir level changes under, normal operating load and flood loading condition. Reservoir water level is recognized as an important factor on the likelihood of a concentrated leak forming, pipe enlargement and of the formation of a breach mechanism.
6.1 Internal Erosion and Piping The probability of failure of internal erosion and piping was estimated by engineering judgement using both event tree method and historic performance method. Different even trees were prepared for each failure modes of internal erosion and piping. In this paper the probabilities for each braches of the event tree was estimated by engineering judgement based on Foster et al (1999) [2] and Rabin Fell and Chi Fai Wan (2005) [3]. The engineering judgement was made using “verbal descriptors” scheme given in Table 2.
So it was assumed that the likelihood of initiation, pipe enlargement and the formation of breach mechanism under extreme flood loading, increase by the percentage given below: Initiation - 30 % Pipe enlargement - 20 % Formation of breach mechanism - 50 %
The “verbal descriptors” scheme given in the first two columns of Table 2, was developed for use in dams risk assessment, by Barneich et al (1996) [4] from Military Standard (1993), using Baysian theory to assess historical data. Here, five different levels of likelihood ranges were included additionally as shown in 3rd column to simplify the judgement.
Under extreme flood load, the conditional probability of failure, for internal erosion and piping, through the embankment - in dam,
Table 2 - Mapping Scheme Linking Description of Likelihood to Quantitative Probability with Included Likelihood Ranges
Description of condition or event
Occurrence is virtually certain. Occurrences of the condition or event are observed in the available database. The occurrence of the condition or event is not observed, or is observed in one isolated instance, in the available database; several potential failure scenarios can be identified. The occurrence of the condition or event is not observed in the available database. It is difficult to think about any plausible failure scenario; however, a single scenario could be identified after considerable effort. The condition or event has not been observed, and no plausible scenario could be identified, even after considerable effort. 3
78
Order of Magnitude of Probability Assigned 1
Likelihood Range Very High
10-1
High
10-2
Average
10-3
Low
10-4
Very Low
through the embankment – along or into conduit, and through foundation are estimated as; 2.724x10-4, 1.807x10-3, and 7.02x10-12.
Concentra ted leak or Suffusion Pd = 0.2 In dam
No erosion
Ability to limit flow
Pd = 0.01
Pd = 0.4
Some erosion Pd = 0.09
Breach initiate
Non erodible soil
Support a roof
Pd = 0.99
Pd = 0.5
Continuing erosion
Inability to limit flow
Pd = 0.9
Pd = 0.6
No leak
Not support a roof
Pd = 0.8
Pd = 0.5
Early intervention
Pd = 0.4
unsuccessful
Pd = 0.5 Erodible soil Pd = 0.009
Breach not initiate Pd = 0.6 Early intervention successful Pd = 0.5
Figure 1 - Event Tree for Internal Erosion and Piping Through Embankment-in Dam
Concentra ted leak or Suffusion Pf = 0.5 Conduit
No erosion
Ability to limit flow
Pf = 0.001
Pf = 0.35
Some erosion Pf = 0.009
Non erodible soil
Support a roof
Pf = 0.98
Pf = 0.5
Continuing erosion
Inability to limit flow
Pf = 0.99
Pf = 0.65
No leak
Not support a roof
Pf = 0.5
Pf = 0.5
Early intervention
Breach initiate Pf = 0.4
unsuccessful
Pf = 0.5 Erodible soil Pf = 0.02
Breach not initiate Pf = 0.6 Early intervention successful Pf = 0.5
Figure 2 - Event Tree for Internal Erosion and Piping Through Embankment - Conduit
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Concentrated leak or Suffusion or Blow out P = 0.001
In foundation
No leak P = 0.999
No erosion
Erosion restricted
P = 0.2
P = 0.996
Some erosion
Support a roof
P = 0.3
P = 0.0005
Breach initiate Early intervention unsuccessful
P = 0.005
P = 0.5
Continuing erosion
Erosion not restricted
P = 0.5
P = 0.004
Not support a roof P = 0.9995
Breach not initiate Early intervention successful
P = 0.995
P = 0.5
Figure 3 - Event Tree for Internal Erosion and Piping Through Foundation 6.3 Embankment Overtopping The assumed high flood level is 103.6 m MSL. But the average embankment crest elevation is at 104.32 m MSL. Therefore, there won’t be any overtopping failure under this flood loading. So the probability of failure is zero.
6.2 Downstream Slope Instability In this paper, the probability of failure for downstream slope instability was estimated based on the plot given in Figure 4, which shows the relationships between factor of safety and annual probability of failure based on actual engineering projects and developed through quantified expert judgment. This plot is an updated version of the one originally presented by Lambe (1985) and Baecher and Christian (2003) [5, 6].
6.4 Combining the Probabilities The annual probabilities of different failure modes under normal operating load and extreme flood load are given in Table 3 and Table 4. Under extreme flood load, the modes of failures were taken as mutually exclusive since they occur due to same load state. Here, since the probabilities are of small value they can be added directly. Under normal operating load, since these failure modes occurs at previously experienced water levels (except on first filling), the four modes of failures were taken to be mutually exclusive and probabilities are added directly.
7.
Estimation of Consequences
In this case study, the load states under full supply level and expected extreme flood was included. Also the probabilities and the consequences are calculated for the whole dam embankment, without considering different components. Here, in this case study we have given priority to the life safety consequences.
Figure 4 - Factor of Safety Versus Annual Probability of Failure [5] It was assumed that the Nachchaduwa dam comes under category III and from the geoslope model, the factor of safety of downstream slope stability under full supply level is estimated at 1.8. So the probability of failure by slope instability is estimated as 7.5x10 -4.
7.1
Estimating the Life Safety Consequences According to the information provided by resident engineer, the inundation area under
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“no failure” condition doesn’t have any population. So the population at risk is zero under “no failure” condition. Therefore, the incremental consequences are equal to the failure consequences. In the following section, consequences under failure condition are estimated.
that Anuradhapura town, Nachchaduwa division and 25% of Mahavilachchiya division will be flooded under the entire failure scenarios. In this paper, the most critical time category is considered and assumed that the area flooded is be same for all the failure modes included in
Table 3 - Combined Probabilities of Failure Modes Initiated by Normal Operating Load Annual probability of reservoir level state (1)
1.0
Conditional probability of failure (3)
Annual probability of failure (4) = (1) x (3)
Piping through the embankmentin dam
9.7x10-5
9.7x10-5
Piping through the embankmentalong or into the conduit
6.44x10-4
6.44x10-4
Piping through the foundation
2.5x10-12
2.5x10-12
Downstream slope instability
7.5x10-4
7.5x10-4
Failure Mode (2)
Total for normal operating conditions
1.49x10-3
Table 4 - Combined Probabilities of Failure Modes Initiated by Extreme Flood Load Annual probability of Extreme flood load (1)
0.001
Failure Mode (2)
Piping through the embankment- in dam Piping through the embankment-along or into the conduit Piping through the foundation Embankment overtopping
Conditional probability of failure (3)
Conditional probability of failure for flood load (4)
Annual probability of failure for flood scenario (5) = (1) x (4)
2.079x10-3 (U) 1.807x10-3 (L)
2.079x10-6(U) 1.807x10-6 (L)
2.724x10-4 1.807x10-3 7.02x10-12 zero 2.079x10-6(U) 1.807x10-6 (L)
Total for flood conditions 7.1.1 Estimating the Loss of Life The loss of life is estimated using the method proposed by Graham (1999) [7]. In this paper, four failure modes under normal operating load and four failures under extreme flood load were included. The whole dam embankment was considered as one component and the probabilities are estimated under critical condition. Here, it was assumed that the dam break flood conditions same for all the locations by considering a constant downstream condition. The overall dam failure scenarios are given in Table 5.
the study. According to the available data, the population of the selected areas are as follow:
Anuradhapura town Nachchaduwa division Mahavilachchiya division
– 40000 – 25464 – 22258
According to the above information, the Population at Risk (PAR) in the dam-break zone is estimated at 71029. The loss of life was estimated as multiplying the Population at Risk by the conditional probability of fatality (fatality rate). Here, the fatality rate is the fractions of people expected to die. The factors influencing on the estimation of fatalities are flood severity, amount of warning and a measure of whether people
In this case study, the most critical category out of day and night is included. Since this is an initial level risk assessment, it was assumed
816
understand the severity of the flooding [7]. The Graham method for estimating LOL gives conditional probability of fatality directly.
8.
Estimation of Risk
In this case study, the life safety risks is estimated in terms of individual risk and societal risk. Generally, risk is estimated by the combined impact of all triplets of scenario, probability of occurrence and the associated consequences. The Risk is estimated as multiplying the annual probability of overall dam failure scenario by consequences. Here, the overall dam failure scenarios are comprised of two key sub- scenarios;
The flood severity is assumed as low for normal operating conditions and medium for extreme flood conditions, considering the distance to the populated area, dam height and reservoir water level during the failure. The warning time is taken as the most critical range. The warning time for all the failure scenarios comes under no warning category as per the assumptions.
Table 5 – Included Overall Dam Failure Scenarios Failure Scenario 1 2 3
Load Scenario
Dam Component
Failure Mode
Normal operating load at full supply level
Embankment
Piping through the embankment- in dam Piping through the embankmentalong or into the conduit Piping through the foundation
4 5 6
Exposure Scenario
Downstream slope instability Natural extreme flood load
Embankment
Piping through the embankment- in dam
Piping through the foundation
8
Embankment overtopping
Here, it was assumed that the warning issuers do not comprehend the true magnitude of the flooding. The estimated conditional probability of fatalities (fatality rates) and number of life loss for different failure scenarios are given in Table 6.
(Fraction of people at risk expected to die)
0.0075
533
2
0.0075
533
3
0.0075
533
4
0.01
711
5
0.04
2842
6
0.04
2842
7
0.035
2487
The annual probability of failure; Exposure factor.
The exposure factor refers to exposure of different group of people to the dam-break flood. Here, the residents of the dam-break zone were considered for the risk estimation and exposure factor is taken as 1.0. In the above, it was assumed that these residents are continuously in the dam-break zone.
Number of Life Loss
1
The scenario “at the dam”; The “downstream” scenario.
The annual probability of overall dam failure scenario is computed as the product of [8]:
Table 6 - Fatality Rate and Number of Life Loss for Different Failure Scenarios Fatality Rate
district
Piping through the embankmentalong or into the conduit
7
Failure Scenario
Residents of Anuradhapura
The annual probability of different overall dam failure scenarios are given in Table 7.
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Table 7 - Annual Probability of Overall Dam Failure Scenarios Failure Scenario
Annual Probability of Failure
Exposure Factor
aggregated, before computing the complementary cumulative distribution function (the “F” values). The Calculated “f,N” and “F,N” pairs for identified overall failure scenarios are given in Table 9.
Annual Probability of Overall Dam Failure Scenario
1
9.7x10-5
1.0
9.7x10-5
2
6.44x10-4
1.0
6.44x10-4
3
2.5x10-12
1.0
2.5x10-12
4
7.5x10-4
1.0
7.5x10-4
5
2.724x10-7
1.0
2.724x10-7
6
1.807x10-6
1.0
8.124x10-7
7
7.02x10-15
1.0
7.02x10-15
Table 9 - Cumulative Distribution Function and Number of Life Loss Failure Scenario
9.
Conditional Probability of Fatality
9.7x10-5
0.0075
7.27x10-7
2
6.44x10-4
0.0075
4.83x10-6
3
2.5x10-12
0.0075
1.88x10-14
4
7.5x10-4
0.01
7.50x10-6
5
2.724x10-7
0.04
1.09x10-8
6
8.124x10-7
0.04
7.23x10-8
7
7.02x10-15
0.035
2.46x10-16
(N)
Cumulative Probability Function F (>=N)
3
2.5x10-12
533
1
9.7x10-5
533
2
6.44x10-4
533
4
7.5x10-4
7
7.41x10-4
1. 49x10-3
711
7.50x10-4
7.52x10-4
7.02x10-15
2487
7.02x10-15
2.08x10-6
5
2.724x10-7
2842
6
1.807x10-6
2842
2.08x10-6
2..08x10-6
Risk Evaluation
In case of societal risk, the F-N lines method was followed with included negligible level of risk developed by New South Wales Dam Safety Association (NSWDSC) [9]. If the risks are under broadly acceptable level, then there is no need for any risk reduction measures.
Individual Risk
1
Aggregated “f”
In the following sections, the tolerability of the life safety risk has been tabulated. Here, individual risk was evaluated based on the tolerable level of risk proposed by ANCOLD guidelines on risk assessment, 2003 [8].
Table 8 - Individual Risk for Different Failure Scenarios Annual Probability of Overall Dam Failure Scenario
Number of Life Loss
Scenario
8.1 Individual Risk of Life In this paper, the individual risk of life was calculated for the residents of the dam-break zone. Here, it was assumed that all the residents in the dam-break zone bear the same amount of risk. Since the conditional probabilities are low, the individual risks of life contributed by each of the failure scenarios are aggregated by simple addition. The individual risk of life for the residents of the dam-break zone, under each of the identified failure scenarios are given in Table 8.
Failure Scenario
Annual Probability of Overall Dam Failure
The term ALARP arises from UK legislation, particularly the Health and Safety at Work etc. Act 1974, which requires "Provision and maintenance of plant and systems of work that are, as far as is reasonably practicable, safe and without risks to health". ALARP is the key determinant of tolerable risk [8]. Determining that ALARP (As Low As Reasonably Practicable) is satisfied is a matter for judgement by the dam owner, subject to any regulatory requirements that must be met. Tables 10 and 11 show the tolerability of individual risk and societal risk for included failure scenarios.
8.2 Societal Risk of Life The societal risks are reported as an “F-N” plot. There are number of scenarios with the same “N” value, so the annual probability of failure scenario (“f”) for those scenarios was
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Table 10 - Tolerability of Individual Risk Failure Scenario
Individual Risk
1
7.27x10-7
2
4.83x10-6
3
1.88x10-14
4
7.50x10-6
5
1.09x10-8
6
7.23x10-8
7
2.46x10-16
should be considered. In this case study, only one loading state is selected for each loading domains and it should be modified with number of loading states for detailed studies.
Tolerability of Risk Broadly acceptable level Acceptable if ALARP is satisfied Broadly acceptable level Acceptable if ALARP is satisfied Broadly acceptable level Broadly acceptable level Broadly acceptable level
From the case study of Nachchaduwa dam, individual risks of life are under broadly acceptable level for most of the failure scenarios except, piping through the embankment – along or into conduit and downstream slope instability. Also, societal risks of life are unacceptable under all four failure scenarios considered under normal operating load, while the societal risks of life under extreme flood load need to satisfy ALARP.
References 1. Dam Safety and Water Resources Planning Project (DSWRPP), Nachchaduwa Dam: Inspection and Conceptual Design Report, August, 2010. 2. Foster, M.A., & FELL, R., “A framework for estimating the probability of failure of embankment dams by piping using event tree methods” UNICIV Report No. 377., The University of New South Wales, Sydney 2052, Australia. July, 1999.
Table 11 - Tolerability of Societal Risk Failure Scenario
Number of Life Loss (N)
3 1
533 533
2
533
4
711
7
2487
5
2842
6
2842
Cumulative Probability Function F (>=N)
Tolerability of Risk
1. 49x10-3
Risk are unacceptable
7.52x10-4
Risk are unacceptable
2.08x10-6
2..08x10-6
3. Fell, R., & Wan, C. F., “Methods for Estimating the Probability of Failure of Embankment Dams by Internal Erosion and Piping in the Foundation and from Embankment to Foundation” UNlClV Report No. R- 436., the University of New South Wales, Sydney 2052, Australia, January, 2005. 4. Barneich, J., Majors, D., Moriwaki, Y., Kulkarni, R. And Davidson, R., “Application of Reliability Analysis in the Environmental Impact Report (EIR) and Design of a Major Dam Project” Proceedings of Uncertainty 1996, Geotechnical Engineering Division, ASCE, August, 1996.
Risk are tolerable if they satisfy the ALARP Risk are tolerable if they satisfy the ALARP
5. Baecher, G. B., and Christian, J. T., “Reliability and Statistics in Geotechnical Engineering”, Wiley, Chichester, U.K., pp. 319–322, 2003.
6. Silva, F., Lambe, W. T., &
10.
Marr, W. A., “Probability and Risk of Slope Failure” J. Geotechnical and Geoenvironmental Eng., ASCE, Vol. 134, No. 12, December, 2008, pp. 1691-1699.
Conclusions
For initial level studies, the conservative assumption that the reservoir is always full under normal operating conditions analyses may be reasonable in some cases, but this position should not be taken without consideration of how representative it is of the annual operating cycle for the reservoir.
7. Graham, W. J., “A Procedure for Estimating Loss of Life Caused by Dam Failure” U.S. Department of the Interior, Bureau of Reclamation, September, 1999, DSO-99-06, Dam Safety Office. 8. ANCOLD., “Guidelines on Risk Assessment” October 2003. 9. Premkumar, S., & De Silva, L. I. N., “Development of a Risk Assessment Framework for Safety Evaluation of Earthen Dams in Sri Lanka” Annual transaction of the IESL, October, 2012 (companion paper).
Here, in terms of flood loading, only the natural extreme flood was included for the case study of Nachchaduwa dam. In detailed studies, other scenarios such as flooding due to, upstream dam failure, wind effect, etc, also
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Annual Transactions of IESL, pp. [85- 94], 2012 © The Institution of Engineers, Sri Lanka
Development of a Risk Assessment Framework for Safety Evaluation of Earthen Dams in Sri Lanka S. Premkumar and L.I.N. De Silva Abstract: Sri Lanka has a rich history of earth dam construction with over 300 large and medium scale dams and over 12,000 small scale earth dams currently in service. According to ICOLD (International Commission of Large Dams) classification, there are 76 large dams in Sri Lanka. A vast majority of those earth dams were built several centuries ago. After serving the nation for centuries, a large number of ancient earth dams are suffering partial failures due to excessive seepage, piping and slope instability. The failure of an earth dam may involve a number of modes. The quantitative risk assessment seeks to enumerate the risk in terms of likelihood (probability) and consequences. The probability of failure for each mode involves engineering assessment of the particular failure mechanisms, and looking for solutions that can reduce the probability of those failure modes or minimize the consequences of a failure. There is no standard framework adopted in Sri Lanka for the risk assessment process of earth dams. The objective of this paper is to propose a standard quantitative risk assessment framework for safety evaluation of earth dams in Sri Lanka. Here critical loading conditions which are relevant to Sri Lanka will be considered. Keywords:
1.
Risk assessment, Probability of failure, Event tree, Load state, Failure mode
Fully quantitative risk assessment seeks to enumerate the risks in terms of probability of failure and consequences. With the move to a risk based approach to dam safety there has been a concomitant focus on estimating the probability of failure of dams.
Introduction
In Sri Lanka, regular monitoring schemes were not frequently implemented to investigate the mechanisms of earth dam failures. The national mechanism and standard for dam safety assessment and management in the country can be further modified to meet the international standard. Currently, it seems that, constructing berms and repairing cracks based on previous experience is the main solution adopted by the governing organizations to address the underlying geotechnical issues.
Here, in this paper the quantitative risk assessment framework was proposed by considering the condition of earth dams in Sri Lanka. The suitable methodologies for estimating probabilities and consequences for given failure modes of a dam under different loading conditions are discussed. In the current study, priority was given to the life safety consequences.
The origins and evolution of dam safety risk assessment can be traced back to a variety of engineering, societal considerations; and public policy and business issues. Currently, different risk assessment frameworks are in practice for safety evaluation of dams.
2.
Quantitative Risk Assessment Framework
The risk assessment process can be sub divided into two sections as risk analysis and risk evaluation, where risk analysis is the combination of risk identification and risk estimation. The framework of quantitative risk assessment comprises the steps such as risk identification, estimation and evaluation of risk
By the middle of the 1990s, the Australian Committee on Large Dams (ANCOLD 1994) published guidelines on dam safety that explicitly addressed tolerable life loss risk criteria based on nuclear power and industrial facility risk practices, mirroring similar work that had been published by BC Hydro (but was subsequently abandoned in 1997). Starting in 1995, USBR developed risk assessment procedures and is currently one of the largest users of risk based methodologies. In 2003, the Australian Committee on Large Dams [1] has upgraded the guideline published in 1994.
Eng. S. Premkumar, BSc. Eng (Moratuwa), Research Assistant, AMIE (Sri Lanka), Department of Civil Engineering, University of Moratuwa, Sri Lanka. Eng. (Dr.) L. I. N. De Silva, BSc. Eng (Moratuwa), M. Eng (Tokyo), PhD (Tokyo), Senior Lecture (II), Department of Civil Engineering, University of Moratuwa, Sri Lanka.
1
85
details of planning restrictions, expected future developments, areas of heritage or special environmental value and to establish contact for later inquiries.
as discussed in the following sections. A flow chart of the proposed risk assessment frame work is shown in Figure 1.
Hazard identification is primarily related to quantitative analysis. The selected obvious hazards for Sri Lankan earth dams are;
The storage water is itself a hazard, given that the dam is an imperfect container (hence the need to consider failure modes under normal operating conditions);
Floods.
Data on earthquakes felt in Sri Lanka suggest that earthquakes of magnitude 4 have not occurred in Sri Lanka during historical times for which records are available. However, the possibility of earthquakes of magnitude greater than 4 occurring at these dam sites cannot be ruled out [2]. However, in this paper, based on the studies and present status of ancient earth dams in Sri Lanka, earthquake loading is considered as less obvious. 2.2 Failure Mode Analysis The failure modes to be analysed should be identified. A failure mode is a sequence of system response events, triggered by an initiating event, which could culminate in dam failure. Failure modes analysis can be undertaken using systematic and comprehensive process such as FMEA (Failure Modes and Effects Analysis) or FMECA (Failure Modes, Effects and Criticality Analysis) [1]. In quantitative risk assessment, the usual process is FMEA; because the criticality will be defined under consequences. FEMA is a quantitative technique by which the effects of individual component of failures are systematically identified.
Figure 1 - Flow Chart of the Proposed Risk Assessment Framework 2.1
Inspection of Dam and Inundation Area and Hazard identification The dam and the inundation area should be inspected before going in to the risk assessment process. In preparation, inspection checklist can be prepared and necessary arrangements should be made. Furthermore an initial list of hazards and failure modes should be prepared. During the inspection, systematically work through the inspection checklist and make an on-site record against each item. Apart from these, key dimensions should be measured and necessary information should be gathered.
ANCOLD (Australian National Committee on Large Dams) guidelines divide the FMEA into nine steps as [1]; Establish the basic principle and corresponding documentation in performing the analysis; Define the system which may be defined at various levels; for example, the dam, which would be broken down into sub-systems, which do not overlap in function; such as, reservoir, spillway, outlet works; Define the components of each sub-system; Identify the causes of the failure modes and operating conditions under which the failure can occur; Identify the failure modes;
Inspect the dam-break inundation area, with the task of estimating consequences in mind. The consequences sub-team should visit local authorities and interest groups to find out 2
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Identify the effects of the component failure on system considering local and global effects; Identify the failure detection method; Identify compensating or mitigating provisions including isolation and redundancy; Assign the severity classification.
2.3 Evaluation of Load States Loading on the dam needs to be partitioned over the full range of possible loads. The amounts of partitioning of the load states should take account of the type of analysis and the system response to the loads. Preliminary studies will use less partitioning, or may not formally partition the loads.
Most important failure modes to be considered for embankment dams are embankment slope instability, settlement and loss of freeboard, internal erosion and piping, and embankment overtopping.
Most of the Sri Lankan dams are interconnected and failure of an upstream dam may cause other dams failure. But, the failure of upstream dams should not be considered as loading conditions in a risk analysis [4]. The risk of multiple dam failures/incident are addressed by assigning the cause of failure to the most upstream dam failure and including the resulting dam failures as consequences for that dam [4].
Failure modes should be listed in sufficient detail to capture all of the significant failure scenarios. For example, if internal erosion and piping is considered, based on the failure path, the failure mode can be sub divide as; internal erosion and piping through the embankment, through the foundation and from embankment to foundation. Furthermore piping through the embankment can be sub-divided into; internal erosion and piping in the dam and internal erosion and piping along or into conduit [3] (see Figures 2 to 4).
2.3.1 Normal Operating Loads A reservoir level-duration relationship is used to estimate the likelihood that normal operating loads will occur in a specified range [5]. This relationship should be based on a continuous record of water levels, and not peak water levels. It is important that this relationship be representative of operating conditions for the period of time for which the risk analysis is to be carried out. If operating rules, inflow characteristics, or reservoir release patterns have changed over the life of the reservoir, the historical record should be adjusted, using reservoir simulation, to represent future conditions before the reservoir level-duration relationship is developed [5].
Figure 2 - Internal Erosion and Piping Through the Embankment
2.3.2 Flood Loads ANCOLD guidelines on risk assessment divide the flood load evaluation into three tasks as [1];
Figure 3 - Internal Erosion and Piping Through the Foundation
i.
Production of event magnitude versus frequency/probability curves to define a loading domain.
ii.
Partitioning of the loading domains into load states that will be used in the risk analysis.
iii. Identify the load scenarios. One or more load states define a load scenario. The term loading domain is used to refer to the total range in magnitude of loads, together with their associated probability of occurrence, expressed as a continuous relationship – peak flood discharge versus annual exceedance probability (AEP). Figure 4 - Internal Erosion and Piping from Embankment into Foundation 3
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An example partitioning of an inflow flood domain for quantitative analysis is given in Table 1.
b) Event tree method Event tree methods have the advantage that the mechanics of the failure, from initiation to breach can be modelled; the details of the dam and its foundation and the ability to intervene to prevent breaching. In this paper it is discussed about the event tree method to estimate the probability of failure of internal erosion and piping.
Table 1 - Manual Portioning of Inflow Flood Domain Partition Point Peak Inflow Discharge (m3/s)
Partition Point Annual Exceedance Probability
250
1 in 1
3200
1 in 500
5750
1 in 3500
9000
1 in 35000
12000
1 in 3500000
13500
1 in 1000000
Represent ative Inflow Discharge (m3/s)
Annual Probability of Flood with Peak Inflow in Partition
1725
9.980E-01
4475
1.714E-03
7375
2.571E-04
10500
2.571E-05
12750
1.857E-06
13500
1.000E-06
Total
2.4.1 Internal Erosion and Piping The event tree method involves the decomposition of the failure process into a sequence of events, starting from initiating events through to breaching. Conditional probabilities are assigned to each branch of the event tree, often by a panel of "experts". These are generally judgmental probabilities and are based on the expert’s experience, review of information on the design, construction, and performance of the dam, and the reading of selected dam incident and performance case histories from the literature. In this paper the event tree for internal erosion and piping through embankment and foundation is presented based on Foster et al (1999) [3] and Robin Fell and Chi Fai Wan (2005) [6]. The event tree for internal erosion and piping through the embankment is given in Figure 5.
0.9999993
2.4 Estimation of Probabilities There are two broad categories of methods for estimating probabilities of failure: a) Historic performance methods These methods use the historic performance of dams similar to the dam being analysed to assess a historic failure frequency, and assumes that the future performance of such dams will be similar. Foster et al (1999) [3] explained the historic performance method to estimate the probabilities in the branches of event trees for internal erosion and piping.
Similarly in the event tree for internal erosion and piping through foundation, branches are almost same as for internal erosion and piping through the embankment. The limitation of flows is less influential for limiting the enlargement of the pipe in piping through the foundation compared to piping through the Ability to limit flow
No erosion Concentrated leak or Suffusion
Some erosion
Non erodible soil
Support a roof
No leak
Early intervention unsuccessful
Inability to limit flow
Continuing erosion
Not support a roof
Breach initiate
Erodible soil
Breach not initiate Early intervention successful
Figure 5 - Event Tree for Internal Erosion and Piping Through the Embankment 4
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2.4.2 Slope Instability Probability of slope failure can be estimated using historical data, mathematical modelling and quantification of expert judgement. In this paper, it is discussed about the method based on quantification of expert judgement.
embankment [3]. However, the factors influences the limitation of flow is contribute by restricting erosion [3]. Therefore, the flow limitation and soil erodibility are combined in to one branch as “restricting erosion”. Factors influencing on the likelihood of each branches of an event tree are slightly different for piping through embankment and piping through foundation depending on the material type and filter conditions. The probability of each branches in the event tree of internal erosion and piping can be calculated by engineering judgement based on historic performance of similar earth dams and by incorporating mapping scheme developed by Barneich et al (1996) [6].
Figure 6 presents the relationships between factor of safety and annual probability of failure based on actual engineering projects and developed through quantified expert judgment [8]. This plot is an updated version of the one originally presented by Lambe (1985) and Baecher and Christian (2003) [8]. Figure 6 classifies earth structures into four categories based on the level of engineering, ranges from best Category (I) to poor Category (IV). The level of engineering can be established by examining the practices followed for design, investigation, testing, analyses and documentation, construction, and operation and monitoring. The four categories correspond to the following types of facilities [8]:
Here, in this paper, an extra column with different likelihood ranges was added to the mapping scheme developed by Barneich et al (1996) [7] as given in Table 2, in order to estimate the probability of failure related to their range of likelihood of occurrence in addition to verbal descriptors of likelihood. Table 2 Mapping Scheme Linking Description of Likelihood to Quantitative Probability [7] with Included Likelihood Ranges Description of condition or event
Occurrence is virtually certain. Occurrences of the condition or event are observed in the available database. The occurrence of the condition or event is not observed, or is observed in one isolated instance, in the available database; several potential failure scenarios can be identified. The occurrence of the condition or event is not observed in the available database. It is difficult to think about any plausible failure scenario; however, a single scenario could be identified after considerable effort. The condition or event has not been observed, and no plausible scenario could be identified, even after considerable effort.
Order of Magnitude of Probability Assigned
Likelihood Range
1
Very High
10-1
High
i.
Category I—facilities designed, built, and operated with state-of-the-practice engineering. Generally these facilities have high failure consequences;
ii.
Category II—facilities designed, built, and operated using standard engineering practice. Many ordinary facilities fall into this category;
iii. Category III—facilities without site-specific design and substandard construction or operation. Temporary facilities and those with low failure consequences often fall into this category; iv. Category IV—facilities with engineering.
10-2
Average
10-3
Low
10-4
Very Low
little or no
Figure 6 - Factor of Safety Versus Annual Probability of Failure [8] 5
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PUB = 1- (1-P1). (1-P2)....... (1-Pn)
The factor of safety of embankment slopes can be estimated by conducting a slope stability analysis.
where, PUB
2.4.3 Embankment Overtopping The probability of failure is calculated from the reservoir level vs. AEP, and a system response curve, that is, probability of failure versus depth of water over the dam crest, which is developed for that dam. Selection of the response relationship is subjective, with factors such as material type, compaction and inherent susceptibility to erosion influencing the choice.
P1 to Pn =
... (1)
= the estimated upper bound conditional probability of failure the estimates of the several individual mode conditional probabilities of failure.
This computation must be made on the estimated conditional probabilities of failure before multiplying by the annual probability of the loading scenario [1]. The lower bound estimate is the maximum individual conditional probability.
Most studies seem to accept that the probability of failure approaches 1.0 when the depth of overtopping is between 0.5 m and 1 m for a modern compacted rockfill dam or a wellgrassed cohesive earthfill dam [1].
2.5.3 Combining Probabilities of Failure Modes Initiated by Flood The annual likelihood or probability of occurrence of the load state or scenario needs to be multiplied by the estimated conditional probability of failure, in order to find the annual likelihood of failure for each failure mode.
2.5 Combining the Probabilities In quantitative analysis, annual probability of failure should be estimated from the estimation of probabilities previously made. Here, the estimation of failure per annum by load states is discussed.
If likelihood of failure is to be aggregated over several failure modes that are not mutually exclusive, it is necessary to apply de Morgan’s rule to compute the estimated upper bound conditional probability before multiplying by the annual likelihood of the load state or scenario [1]. It should be noted that the simple addition approximates de Morgan’s rule, if the conditional probabilities are low in value.
2.5.1 Common Cause of Failures Common cause failure modes are failure modes that can occur simultaneously at a single dam section due to a single initiating event, and failure modes that can occur simultaneously at multiple sections of a dam due to a single initiating event. The total probability of dam failure is some combination of the probabilities of dam failure that are associated with each of the possible modes.
An example computation of combining the probabilities of failure modes initiated by flood load is given in Table 3. Table 3 - Combining Probabilities of Failure Modes Initiated by Flood Load
For this case, there is no practicable way of computing the estimated overall probability of failure, given the several individual failure mode conditional probabilities of failure. Following the theory of uni-modal bounds the upper and lower bounds can be determined [1]. 2.5.2 Uni-Model Bound Theorem The conditional probabilities for the failure modes that are not mutually exclusive can be adjusted for common cause occurrence by using the uni-modal bounds theorem [1]. Following the theory of uni-modal bounds, the bounds are determined as upper bound and lower bound.
2.5.4 Combining Probabilities of Failure Modes Initiated by Normal Operating Load The annual probability of the maximum reservoir level being in each level state is multiplied by the conditional probabilities of failure, typically found from event trees. Here, the level state affects the conditional probabilities.
The upper bound is the union of the events, the several failure modes. From de morgan’s rule, the estimated upper bound conditional probability is;
6
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analysis. Route the selected dam–break flood through the downstream channel. Record such outcomes as inundation limits, peak flow depths, peak mean velocities and flood wave travel time at representative sections along the channel [9].
2.6 Estimation of Consequences Potential consequences resulting from an uncontrolled release of a reservoir have several different dimensions. In addition to the economic losses related to lost project benefits and potential damage to property in the inundated area, there is a potential for loss of life, alteration of the habitat and environment, social impact on local community and loss of confidence in the dam owner and operators. The consequences of failure and the circumstances surrounding a failure (advance warning, detection possibilities, impact of the failure, etc.) should be addressed for each potential failure mode since these factors play a role in assessing the significance of the potential failure mode. Incremental consequences are defined as the difference in consequences between those due to dam failure, and those due to the same routed through the dam without its failure.
The zone affected by a dam break flood may be defined by experienced judgement as an initial assessment or by inundation mapping for more comprehensive assessments. An inundation map provides a description of the areal extent of flooding which would be produced by a dam-break. It should be plotted on a scaled plan to show the maximum extent of a dam failure flood as it travels downstream, regardless of the time after failure occurred. The output from a dam break analysis should include the following:
2.6.1 Identifying Dam Break Scenarios Dam-break scenarios which are adequately representative of all of the overall dam failure scenarios should be identified. The term overall dam failure scenario refers to the total suite of states and conditions that defines each dam failure case that is analysed in the study [1].
Hydrograph at each section (Flow versus time); Depth at each section at appropriate time intervals; Velocities at each section at time intervals; Flood peak arrival times at each section; The first rise in water level at each section; Recession time of the dam break flood.
Several computer programs are available to carry out dam break analysis.
For example, an overall dam failure scenario could be defined by: A loading scenario (such as concurrent reservoir level); A dam component (e.g.: embankment); A failure mode; Downstream conditions; An exposure scenario.
2.6.3
Estimation of Life Safety Consequences In quantitative risk analysis, estimation of life safety consequences can be divided into two steps as follows [1]: Loss of life (LOL) for both the “failure” and “no failure” cases, for each overall failure scenario (needed to estimate societal life safety risks); Conditional probability of fatality (fatality rate) for the person or group most at risk, given dam failure, for each overall failure scenario and the complementary “no failure” case (needed to estimate individual risk to life).
In quantitative risk analysis, every overall dam failure scenario, of which there may be thousands in complex analyses, has an estimated probability of occurrence with failure of the dam, and there is a complementary probability of occurrence of the scenario with no failure [1]. Because of practical considerations of cost and time, only a relative few dam breach, dam – break and consequences analysis are normally undertaken.
Note that the currently available empirical models developed for estimating LOL due to dam-break are not suitable for estimating LOL for the case without dam failure. The model of Graham (1999) [10] is considered the most suitable of the empirical approaches to estimate the loss of life.
2.6.2 Estimation of the Downstream Inundation Characteristic For quantitative analyses, undertake breach analyses to estimate the outflow flood hydrograph for each representative dam breach/break scenario, using methods appropriate to the level of detail of the risk
The Graham method estimates loss of life based on data taken from every documented U.S. dam failures that resulted in more than 50 fatalities and every documented dam failures that 7
91
occurred after 1960 resulting in at least one fatality. Graham found that loss of life resulting from dam failure is highly influenced by three factors: (1) the number of people occupying the dam failure floodplain; (2) the amount of warning that is provided to the people exposed to dangerous flooding; and (3) the severity of the flooding [10].
they change the PAR at particular times [1]. For example, if there are a number of large schools in the dam-break zone, the population at risk may reduce significantly outside school hours. Other kind of exposure factors can be defined by proper judgement. Exposure factors should be in the range of 0 to 1.0 [1]. 2.8 Estimation of Risks In the general case, risk is estimated by the combined impact of all triplets of scenario, probability of occurrence and the associated consequences. The annualised risk can be estimated as the product of the probability of overall dam failure scenario and the consequences. Risk to life can be reported as, the individual risk to life for the person or group most at risk and societal risk to life.
The Graham method for estimating LOL gives conditional probability of fatality directly. The loss of life was estimated as multiplying the Population at risk by the conditional probability of fatality. Here, the fatality rate is the fractions of people expected to die. The factors influencing on the estimation of fatalities are flood severity, amount of warning and a measure of whether people understand the severity of the flooding [10]. 2.7
Estimation of Probability of Overall Dam Failure Scenario
2.8.1 Individual Risk of Life The assessment of individual risk to life is based on the person or group most at risk. Usually it is a small group, such as the occupants of a single house or a small hamlet, because it is not practicable to say that any one member of that group bears a higher risk than the any other member. All members are taken to bear the same risk and it is this risk that is computed as the individual risk.
the
The estimation of probability of overall dam failure scenarios should consider the downstream conditions. The overall dam failure scenarios are comprised of two key subscenarios; The states and conditions that contribute to or attend the dam failure mechanism leading to breach of the dam - the scenario “at the dam”; The states and conditions that exist in the dam-break affected zone the “downstream” scenario.
For each failure scenario, the contribution to individual risk is computed as the product of [1]: The annual probability of the overall failure scenario; and The conditional probability of fatality, given dam failure.
Probability of the overall dam failure scenario is estimated by multiplying the probability of the dam failure by the exposure factor – dam failure at a time when that exposure scenario applies.
2.8.2 Societal Risk of Life The primary outcome of a quantitative risk analysis is a series of estimated probability of failure and estimated consequences pairs, one pair for each specified overall failure scenario. These are termed “f,N” pairs (for risk to life), and should be reported to the decision maker, since they represent potential dam failure outcomes.
In each failure scenario, there is the corresponding “no failure” scenario, in which all states and conditions are the same, except that the dam does not fail. The annual probability of the “no failure” scenario is 1.0 minus the annual probability of the failure scenario.
These pairs show a decision maker the failure scenarios that could occur, the likelihood that they will occur, and the best estimate of loss of life if they do occur. It is helpful to report them in both tabular and graphical format. It is conventional to have “f” on the vertical axis using a log scale, and “N” on the horizontal axis using a log scale [1]. The pairs will plot as a cloud of points, generally with no pattern to them.
2.7.1 Exposure Factor Population at risk and their vulnerability vary according to time of day, day of week and season of the year, as a minimum. This fact gives rise to the concept of exposure scenario and exposure factor. Such exposure factors directly affect the risk imposed on particular individuals (individual risk), but only affect the estimation of LOL if 8
92
Expected value of life loss (lives per annum) is the product of “f” and “N”. The product “f ×N” aggregated over all scenarios, is often given as the correct measure of risk, but in reality is a special case of the general definition of risk. ANOCOLD guidelines on risk assessment [1], prefers the way of presenting the societal risk is the use of F–N plots, where “F” is the complementary cumulative distribution function, the estimated annual probability of a failure expected to result in the loss of “N” or more lives.
value and broadly acceptable value level) determined in accordance with the ALARP principle. The average/broadly acceptable individual risk to the person or group is 10-6 per annum.
2.9.2 Evaluation of Societal Risks There are two main approaches to societal risk criteria; • F-N lines; • Expected annual life loss values. ANCOLD follows the F-N lines approach while the USBR (1997) follows the expected value approach. ANCOLD guidelines on risk assessment [1] propose that for existing dams, a societal risk that is higher than the limit curve shown in Figure 7 is unacceptable, except in exceptional circumstances. Also the risks are to be lower than the limits of tolerability to an extent determined in accordance with the ALARP principle.
F, probability of failure per dam per year with expected loss of life > N
2.8.3 Uncertainty in the Risks In quantitative analysis, uncertainty of both probability and consequences should be reported. This need to report uncertainty may be less critical for studies that simply aim to rank the relative risk. In risk analysis the estimates of probability incorporate many of the uncertainties. In consequence analysis, uncertainty needs to be dealt with separately for each type of consequence.
The horizontal truncation of Figure 7 is without precedent, but represents ANCOLD’s present judgement of the lowest risks that can be realistically assured in light of [1]; Present knowledge and dam’s technology; Methods available to estimate the risks.
2.9 Risk Evaluation The determination of tolerable levels of risk is fraught with difficulty. If the dams cannot be made absolutely risk free, then we need to know the tolerable risks. Risk assessment typically requires tolerable risk policies and criteria. It is the responsibility of the dam owner to ensure that the policies and criteria are set, and to endorse them. The dam owner needs to decide what risks are tolerable. The tolerable risk to life should be identified if the dams are not absolutely risk free. In any particular case, all three guidelines on tolerability of life safety risk are to be satisfied; that is: The individual risk guideline; The societal risk guidelines; The ALARP (As Low As Reasonably Practicable) requirement. The tolerability of life safety risks are discussed in the following sections.
N, number of fatalities due to dam failure
Figure 7 - Revised ANCOLD Societal Risk Guideline for Existing Dams [1]
2.9.1 Evaluation of Individual Risks The tolerable risk criteria accepted by ANCOLD was considered as suitable for ancient Sri Lankan earth dams.
For societal risk, the New South Wales Dam Safety Committee has adopted a negligible level, which is two orders lower than (one hundredth of) the limit of tolerability. The DSC regards the negligible level of risk as usually acceptably low. So it can be taken that the risk is negligible if it is two orders lower than the limit of tolerability. ALARP should be satisfied for risk in between limit value and negligible value.
For existing dams, ANCOLD guidelines on risk assessment propose that [1]; The limit for individual risk to the person or group, which is most at risk, is 10-4 per annum, except in exceptional circumstance; The risks are to be lower than the limits of tolerability to an extent (between the limit 9
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The principal condition in the USBR’s [1997] two-tier public protection (societal risk) guidelines is that expected (i.e., average annual or annualized) incremental life loss, n, due to dam failure should be less than 0.001 lives per annum for each loading type (e.g., flood, earthquake, and normal operating conditions). Specifically, Reclamation’s Tier1 Guideline is summarized as follows [11]:
n > 0.01—“Strong justification for taking actions to reduce risks for both long-term and short-term (5 years or less) continued operations.”
0.01 > n > 0.001—“Strong justification for taking actions to reduce risks under continued long-term operations.”
n < 0.001—“Justification for reducing risk decreases (diminishes); evaluate (cost) effectiveness (i.e., ALARP) and public trust responsibilities.”
estimated with care, because it will likely to vary depending upon the time of year, day of week and time of day during which the failure occurs.
References 1. ANCOLD, “Guidelines on Risk Assessment” October 2003.
2. Welikala, D.L.C., “Assessing the Likelihood
of Failure of Old Homogeneous Earth Embankment Dams by Piping” Coffey Mining Pty Ltd, Notting Hill, Victoria, Australia.
3. Foster, M.A., & FELL, R., “A Framework for Estimating the Probability of Failure of Embankment Dams by Piping using Event Tree Methods” UNICIV Report No. 377., The University of New South Wales, Sydney 2052, Australia. July, 1999. 4. USBR., “Dam Safety Risk Analysis Methodology” US Bureau of Reclamation, US Department of the Interior, Technical Service Centre, Denver, Colorado, Version 3.3, September, 1999.
2.9.3
ALARP (As Low As Reasonably Practicable) Principle ALARP is the key determinant of tolerable risk. Determining that ALARP is satisfied is a matter for judgement by the dam owner, subject to any regulatory requirements that must be met. Some statements of the ALARP principle are [1]: Risk is tolerable only if risk reduction is impracticable or if its cost is grossly disproportionate to the improvement gained (Health and Safety Executive, 1992);
3.
5. Fell, R., Bowles, D.S., Anderson, L.R., & Bell, G., “The Status of Methods for Estimation of the Probability of Failure of Dams for Use in Quantitative Risk Assessment”, Proc. International Commission on Large Dams 20th Congress, Beijing, China, 2000. 6. Fell, R., & Wan, C. F., “Methods for Estimating the Probability of Failure of Embankment Dams by Internal Erosion and Piping in the Foundation and from Embankment to Foundation” UNlClV Report No. R- 436., the University of New South Wales, Sydney 2052, Australia, January, 2005. 7. Barneich, J., Majors, D., Moriwaki, Y., Kulkarni, R. And Davidson, R., “Application of Reliability Analysis in the Environmental Impact Report (EIR) and Design of a Major Dam Project” Proceedings of Uncertainty 1996, Geotechnical Engineering Division, ASCE, August, 1996.
Residual risk is tolerable only if further risk reduction is impracticable or requires action that is grossly disproportionate in time, trouble and effort to the reduction in risk achieved (HSE, 1999a).
8. Silva, F., Lambe, W. T., & Marr, W. A., “Probability and Risk of Slope Failure” J. Geotechnical and Geoenvironmental Eng., ASCE, Vol. 134, No. 12, December, 2008, pp. 1691-1699.
Discussion and Conclusions
In this paper, a quantitative risk assessment framework for safety evaluation of earth dams is presented considering the conditions of earth dams in Sri Lanka. Here, the methods that are applicable to earth dams with available data and proper investigation are discussed.
9. ANCOLD “Guidelines on Assessment of the Consequences of Dam Failure” May, 2000b. 10. Graham, W. J., “A Procedure for Estimating Loss of Life Caused by Dam Failure” U.S. Department of the Interior, Bureau of Reclamation, September, 1999, DSO-99-06, Dam Safety Office. 11. Bowles, D. S., “Evaluation and Use of Risk Estimates in Dam Safety Decision making” Proc., ASCE, In Risk-Based Decision-Making in Water Resources IX, August, 2001, pp.17-32.
Since the embankment instability and loss of freeboard is mainly occurs under earthquake loading, it has been omitted from discussion. When using the “mapping scheme” to estimate the probabilities, engineering judgement should be taken with care. Otherwise, it would result in overestimation or underestimation of the probabilities. In estimation of life safety consequences population at risk should be 10
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Annual Transactions of IESL, pp. [95- 103], 2012 © The Institution of Engineers, Sri Lanka
Comparison of Performance against Predictions in a Water Distribution Network W. K. Illangasinghe Abstract: Kandy South Water Supply Project was planned in 2003 and commissioned in 2010. The project consists of 403 km newly laid pipes and 160 km existing pipes scattered in 19 subzones with their own storage reservoirs. Projected population and water demand for the year 2029 was 350,000 people and 58,000 m3/day including 20% average water loss. A study had been carried out in September to November 2011 in Panabokka, Maligatena and Angunawala, subzones using onsite measurements, GIS and commercial database. This study focused on evaluating the number of consumers, quantity and pattern of water demand and water losses in the system. Nodal pressure at control points were compared with design pressures. The study has revealed that the number of consumers at present is lesser than the expected. Consequently, a lesser water demand is recorded. The assumed hourly peak demand of 2.0 was confirmed. However, a slight variation in the demand pattern was observed. Water losses are varying from 6.9 % to 59.8%. The nodal pressures are tallying with the designed values. Lesser number of consumers is probably due to the cost constrains. Higher water losses reflect the higher percentage of old pipes. Inaccuracy of water meters and service water contributes to the losses. Study emphasizes the importance of rehabilitations, improvements and good maintenance of a pipe network to ensure minimum losses. Similar regular observation would be helpful for monitoring and improvement of the system. Keywords: Sub Zones, Head works, Water demand, Demand Pattern, Nodal Pressure, Non Revenue Water (NRW)
1.
The project was implemented from May 2006 to January 2010 as a design and built contract. 32,000 m3 capacity Meewatura Treatment Plant located at Peradeniya is the largest plant constructed under the Project.
Introduction
Pipe borne water supply coverage in Kandy District was 38%in year 2003. Safe water coverage was 53% including the deep wells. The population growth rate of the Divisional Secretary Divisions within the District varies from -0.3% to 1.5% during the period 1981-2001. DS divisions in the suburbs of Kandy town show a high growth rate. Projected population density map for year 2025 shows a high density area to the north and south of Kandy Town.
Establishing the service area and forecasting the population and water demand in year 2029, were made using Census and Statistics Records [1, 4], Data bases of Divisional Secretariat’s, Socio Economic Survey of 1060 families in the service area [6], demand criteria established with past records [1] and DS division layer, GN division layer, of GIS data set. A water distribution pipe network of 403 km was laid by the project within the service area. 160 km of existing pipes were connected with the new pipes and 55 km of existing pipes were abandoned. Due to unavailability of data related to the existing pipe network and consumer connections increase in water leaks and “no water” complaints from consumers were encountered during the transition period from old system to new system.
The water supply to southern area of Kandy city was covered by five existing water supply schemes. The service hours are varying from few hours per day to few days per week. A waiting list of about 7500 was maintained since 1998 by the National Water Supply & Drainage Board (NWSDB). Due to water quality and quantity restrictions it was not possible to give new connections from the existing schemes. Towns South of Kandy Water Supply Project was planned in year 2003 to meet the water demand of the people living in five DS divisions situated to the south of Kandy Town.
Eng. (Ms.) W.K. Illangasinghe, B.Sc. Eng. (Hons) (Peradeniya), C. Eng., M. Eng. (Yokohama,), Project Director, Towns South of Kandy Water Supply Project, National Water Supply & Drainage Board.
951
Twenty months after commissioning of the scheme, a study was carried out in three selected subzones to evaluate the accuracy in predicting number of consumers, water demands, water losses and design pressure and flow of pipes.
area had also been accounted for computing the future water demand in the area. Relevant details have been gathered from related organisations. Figure 2 shows the Kandy District Development plan prepared by the Urban Development Authority (1998) [5].
This paper presents the details of planning and design of the Project and the post evaluation of the system. The paper will give recommendations to improve future design and construction of distribution pipe networks.
2.
Service Area and Population Predictions in Project Planning
In planning a potable water supply scheme the first step is to establish the service area. Collection of data on existing population, population growth patterns, water demand, current water supply facilities etc. is required for this. The Grama Niladari (GN) division was the macro unit considered in the project planning. [3]
Figure 2 - Kandy District Development Plan UDA, 2001 The project area is divided into three zones Urban, semi-urban and rural based on the available information of population, future developments and geographic locations of GN divisions. Considering the general trend in population growth and predicted developments a growth pattern is assumed for the forthcoming 25 years as shown in Figure 3.
The Census and Statistics data of years 1981 and 2001 was used to evaluate the population growth patterns in the Kandy District (Figure 1). The average growth rate in Central Province was 0.97% and the growth rate in Kandy District was 0.9%. However a substantial variation in growth rates (-0.3% to 1.5%) has been observed in individual DS divisions. A high growth rate was seen in all the DS divisions surrounding Kandy City. Apparently, the migration of people towards the town centre and the suburbs is the reason for this. The lands in the Kandy City Limit were already occupied thus showing a low growth rate.
The projected population was then calculated. Figure 4 shows the spatial distribution of population densities of GN divisions in 2025. Overlaying the density map with the contour map and the existing water supply facility map the service area for Kandy South Water Supply Project was demarcated [2] (Figure 5).
The population records of the GN divisions for year 2004, prepared by each DS division were then used for further planning. The commercial, institutional and industrial developments in the 2
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Table 1 - Outcome of Socio-Economic Survey Average household size 4.3 Building type (domestic/Non 85%/ 15% domestic) Water Supply (pipe born or 15% / 85% tube well(safe)/ other) Average expenditure for electricity as a % of mean 4.2% income Need for a water supply and 98% willing to pay Table 2 Assessment Figure 4 - Predicted Population Density Map 2025
Norms
for
Design period years Service level and hours/day Average household size Daily domestic consumption litres per capita per day Non domestic demand as a percentage of domestic Non revenue water
Water
Demand
25 100% and 24 5 120 10% 15%- 25%
Table 3 - Water Demand in each DS Division DS
%*
Populat ion 2029
Gangawata 161,395 17 49,965 Udunuwar 98,879 100 158,315 Yatinuwara 96,946 89 89,120 Gangaihala 50,706 57 17,821 Udapalatha 131,238 39 34,779 Total 539,164 350,000 * % GNDs covered by the project
Figure 5 - Selected Service Area of the Project
3.
Populati on 2001
Socio-Economic Survey and Water Demand Predictions
4.
A socio economic survey is carried out within the demarcated project area using cluster sampling method. A random sample of 1060 households was selected from 73 GN divisions out of the total of 255 GN divisions in the selected service area. They were surveyed to identify the household population, present water source and usage, need of a new water supply system, sanitary facilities in the households, economic condition of the families, affordability and willingness to pay for a new water supply system. Table 1 gives a summary of the outcome of the socio economic survey relevant to this paper. [2]
Water demand m3 2029 8729 24,933 16,711 2598 4955 57,926
Establishment of Water Supply Strategy
Establishing a suitable strategy for the water supply is mainly based on water demand, water service area, water source with adequate yield and suitable water quality. The location of water source with respect to the service area is an important parameter which will contribute to the cost effectiveness of the proposed water supply scheme. A good quality water source will reduce the costs involved in water treatment. Centrally located water extraction points and the possibility of gravitating the water throughout the service area will reduce the costs involved in water transmission system from treatment plant to service reservoirs (headworks).
Water demand calculations were carried out based on the outcome of socio-economic survey and the established norms using past records. [3] (Table 2). Table 3 gives the water demand predicted within the project area. 3
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After a careful study of available water resources using the GIS maps and past flow measurement records, the water supply strategy for the project was established. Four sub schemes were identified within the total project area; Kandy South, Gampola, Ulapane and Elpitiya. Table 4 & Figure 6 give the proposed water supply strategy.
to feed the service area. Existing Nilambe water supply scheme with capacity 10,500 m3/day and proposed new plant at Meewatura by producing 32,000 m3/day from Mahaweli River water. The project has constructed 12 new storage reservoirs of capacity ranging from 300 m31750m3. The existing reservoir at Maligatenna was augmented by adding another 356 m3 storage volume. Each ground reservoir has its own distribution sub zone with attached distribution pipe network.
Table 4 - Water Supply Strategy of the Project Scheme
Population covered
Demand m3
Kandy South
196,169
32,000
Gampola
37,510
6000
Ulapane
15,090
8000
Elpitiya
35,515
7000
Nilambe (Existing)
65,720
10,500
Water source
Mahaweli River Paradeka Oya Ulapana Oya Shallow wells Nilambe Oya
6.
Design criteria used in the design of water transmission pipes and the distribution network is given in Table 5 [8]. Table 5 - Design Criteria Water Transmission Pipes Pipe type DI/ HDPE or PVC based on pressure Max/ Min. Velocity of pipes 6-3/0.6* m/s Maximum working pressure 100 m Water distribution pipes Pipe type PVC., Diam. Above 280 mm- DI Minimum residual pressure 10 m Maximum static pressure 60 m * Depending on pipe type The treated water transmission network of the Meewatura system consists of 33.3 km of water conveyance pipes from the treatment plant at Meewatura (474 m MSL) to the reservoirs. (542740 m MSL). The highly undulating terrain of the project area necessitated installing 9 booster pump stations to boost up the water to its final destination. Booster pump stations are located such that the maximum pressure in the transmission pipelines are maintained at a range of 80-100 m.
Figure 6 - Proposed Water Supply Strategy
5.
Water Supply Scheme Kandy South Area
Detail Designs
for
Using the topography, existing storage reservoirs, existing service pipe network, residential and commercial inhabitations, the new reservoir locations, water conveyance strategies within the system etc. were formulated. Special attention was given to locate distribution reservoirs at the correct levels and locations in order to distribute water to consumers with pressure not exceeding 60m and conveyance pipes with minimum length. However, due to the special nature of the terrain in the area at some places water pressure had to be raised up to about 80 m to economise the project cost by limiting the number of booster pump stations and storage reservoirs. The Kandy South scheme consists of 19 distribution sub-zones. Two sources are used
Figure 7 - Location of Headworks 4
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HDPE, PVC and DI pipes were used with diameter ranging from 100 mm to 450 mm (see Figure 7). The distribution pipe network was designed to incorporate the existing pipes with rezoning of service area to accommodate the new distribution model. Computer software is used for modelling the headworks as well as individual distribution sub-zones. The computer model was run for an extended period of 72 hours in designing the head works and an extended period of 24 hours for distribution subzones. The hourly demand of the service area is assumed as given in Figure 8 considering the water usage pattern of present consumers. Figure 9 - Distribution Network
7.
Commissioning of the System
The project was commissioned in January 2010 after the successful completion of new constructions. Transfer of existing pipes and the consumers to the new system is made in two ways. One method is connecting the existing distribution pipe to new trunk mains. The consumers attached to the existing pipe will be automatically fed by the new system with this pipe connection. When the condition of existing pipe does not match with the new re-zoning design, each consumer is connected individually to the new pipe laid along the route.
Figure 8 - Demand Pattern of Domestic Consumers Assumed in the Design 55 km existing old Asbestos Concrete and Cast Iron pipes were to be replaced with new pipes in order to reduce the water losses in the system.
8. Methodology of Post Evaluation of the Distribution Network
Nilambe system was re-zoned to have four distribution sub-zones including the newly constructed reservoir at Hiddaula with 62.6km of existing pipes and 74.2 km of new pipes.
During commissioning period, several problems were encountered. Due to unavailability of drawings, or other details related to the existing system the transfer was a trial and error process. Prior to commissioning the new and old systems had to be run parallel for a period of about two months to avoid prolonged water cuts to the existing consumers until their connection details could be established for the needful transferring to the new system.
Meewatura system was re-zoned to have a total of 15 distribution sub-zones, including 3 existing reservoirs and augmented Maligatenna reservoir with 95.2km of existing pipes and 270.7 km of new pipes. The pipe type used is PVC. DI pipes were used at special locations such as culvert crossings and bridge crossings. Pipes were of diameters ranging from 63 mm to 280 mm.
This created water leaks appearing in the old pipes due to increased pressure as per new rezoning design, unexpected pipe bursts due to
The overall distribution network of Kandy South scheme is depicted in Figure 9.
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inadequate pipe depth of some existing pipes, etc.
Table 6 gives the details of the selected three sub-zones and the control points.
Considering the above problems faced at the commissioning stage, it was decided to carry out a post evaluation of the system. In 2011 September, i.e, 20 months after commissioning a post evaluation was carried out in the distribution system. Three distribution subzones out of the 15 sub-zones of Meewatura system was selected for the post evaluation.
Table 6 - Details of the Selected Sub-Zones Description Design Water demand m3 (2025) Reservoir cap. m3
The three zones were selected giving due consideration to pipe length, proportion of existing and new pipes, number of consumers, and location of the distribution sub-zone. It was decided to evaluate following parameters in the study; 1. Number of consumers 2. Water consumption 3. Water consumption pattern 4. Water losses 5. Nodal Pressure
Panabo ka
Maligat ena
Angun awala
1200
3118
6564
536
1750
Location
Rural
Elevation m MSL Existing pipes m New pipes m % existing pipes No. Of control points
655.4 310 14,762 2
916 Semi Urban 594.8 5830 48,970 10.6
10
10
9.
Urban 588 37,236 35,196 51.4 10
Results of the Field Study
At the site reconnaissance survey, few discrepancies were found between the actual site situation and the sub-zone pipe network model. The computer model is updated to depict the exact site situation.
The methodology of the study is depicted below. At first a site reconnaissance had been carried out to verify that the pipe network operating at site is as same as the designed pipe network. Number of control points was identified by a careful study of the distribution map to cover new consumers areas, existing consumer areas, different elevations, system mid points and extreme ends. The pipe flows and nodal pressures were measured on site using the control points. To establish water consumption and consumption pattern, monthly records of the bulk meter at reservoir outlet and hourly readings of the bulk meter for a period of 24 hours had been recorded.
Figure 10 - Theoretical & Actual Demand Patterns at 3 Reservoirs
The consumers in the three sub-zones were coordinated using GPS. The GPS readings were taken by the study team together with the meter readers covering the monthly meter reading cycles of the zones. By this method, it was ensured that all the consumers who are in the commercial data base of the NWSDB were mapped to the GIS. The water consumption was planned to be obtained from the commercial database, established by onsite monthly consumer consumption readings recorded by meter readers.
Figure 10 shows the average water demand pattern of the three reservoirs. The layout maps of the three sub-zones including the consumers are shown in Figures 11, 12 and 13. In all 3 sub-zones, it has been found that the commercial database does not match with the actual site situation. Some consumers who are actually being served by other sub-zones are entered incorrectly to the study zones and some
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Table 7 - Number of families/ consumers
consumers relevant to study zones are found to be recorded in other areas. The water consumption of the sub-zones was re-evaluated with the consumers assigned to their correct sub-zones. Table 7 gives the outcome of the consumer mapping.
As per pop. survey
As per commercial DB (Aug)
Panabokka
817
461
408
Maligatenna
2473
2088
2146
Angunawala
4673
5885
5817
Reservoir
After GIS (Aug)
Figure 11 - Layout Map of Panabokka The predicted water demand, water demand calculated with actual average number of consumers using the same design criteria used for predictions with an NRW of 15% and the average consumption calculated using four months actual water meter readings are tabulated in Table 8.
Figure 13 - Layout Map of Angunawala Table 8 - Water Demand Predicted and Actual (m3/d)
Table 9 gives the calculated water loss of each sub-zone during three months study period considering different sets of data.
Predicted domestic water demand 2011
Calculat ed 2011 (Avg)
Measured consumpt ion (Avg)
Panabokka
547
290.6
128.1
Maligatenna
1881
1731.7
943.6
Angunawala
3678.4
4396.3
2939.9
Reservoir
Table 10 gives the nodal pressures at the control points. The installation of bulk meters to measure the flow could not be carried out as planned.
10.
Analysis of Results
The expected number of consumers as per the design has not been achieved in the rural areas. This may be due to cost constrains. In semi urban areas number of consumer connections has reached about 87% of the expected value and in urban areas consumer number has exceeded the predictions. The water demand of the zone varies in correlation with the number of consumers. The demand calculated using the number of consumers is from 53%-92% of predicted. The measured water demand is 23%-80% of the predicted. This necessitates further studies to
Figure 12 - Layout Map of Maligatenna 7
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verify the assumption of per capita demand and percentage NRW assumed in the system. The possibility of having pipes related to adjacent sub-zones being connected with the incorrect sub-zone shall also be checked. The minimum average monthly consumption per connection varies from 0.25-0.46 m3/d (10.4-19.2 l/h). Assumed peak factor 2, has been justified for the system. A slight variation in the assumed demand pattern is seen with respect to each reservoir and the relevant consumer base. This could be due to varying consumer behaviour in the sub-zones.
Figure 14 - Flow Error Curve of Water Meter
Table 9 - Calculated Water Losses NRW% Sep Calculated with onsite bulk meter measurement Calculated with onsite minimum night flow
Angunawala Oct Nov
Sep
Maligatenna Oct Nov
July
Panabokka Aug Sept
44.2
48.07
39.61
41.3
54.5
37.2
26.7
52.3
30
39.2
42.05
NA
59.8
46.6
25.6
6.9
13.2
27.6
Table 10 - Pressure at Control Points Control point 1 2 3 4 5 6 7 8 9 10
Angunawala
Maligatenna
Design 20.3 34.1 45.4 50.5 55.5 69.4 76.4 86.3
Onsite 36 28 40 58 52 42 66 78
Design 26.14 34.75 48.35 62.66 70.06 80.46 83.96 79.49
Onsite 22 32 50 60 62 50 62 78
90.2
80
93.39
60
91.5
48
64.75
The NRW is varying from 26.7% - 54.5% in the three subzones. The minimum night flow has been varying from 6.9%-59.8%. Upon checking the water leak records of the sub-zones it is noted that most of the leaks are occurring in the service connections.
Panabokka 15.08. 2011, 12.30-15.30 Design Onsite 23.4-28.3 28.0 33.7-36.5 40.0 25.2-42.2 48.0 47.0-47.5 45.0 42.2- 48.9 54.0 49.9-50.8 46.0 72.0-73.6 74.0 74.0-86.8 90.0 88.9-90.7
85.0
58 74.0-88.3 92.0 4. Delay in reporting and attending the water leaks creating high water losses 5. Water meter errors. 6. Low leakage rate and long duration of leaks in service connections.
The water meters used in the system are rotary piston type water meters. As per the manufacturers catalogue the main technical data (Table 11) and the flow error curve (Figure 14) [7], when the consumption per connection is less than the recommended minimum flow of the water meter, errors could occur in the meter readings. Old water meters in the system will give erroneous meter readings.
High NRW recorded in the system could be due to several reasons; 1. The commercial database does not match with the real number of consumers relevant to the respective sub-zone. 2. The billing cycle could be varying. 3. Percentage of existing pipes in the system is high.
Presenting water losses as a percentage of production fails to take into account the main 8 102
inherent losses in the systems especially in the service connections shall be developed. Introducing zonal valves in the system will help to reduce service water losses.
local influences such as operating pressure, length of mains, pipe material, frequency of leaks, type of soil etc [9]. Table 11 - Technical Data of Water Meters Description Model No. & Class Size mm Max. Flow m3/hr Nominal flow m3/hr Transitional flow l/hr Minimum flow l/h
Inaccuracy of water meters also contributes to the losses. Random field trials shall be done to assess the accuracy of water meters. Continuous field monitoring of water meter accuracy and proper maintenance of pipe network and doing needful rehabilitation and improvements to distribution pipe systems on appropriate time will ensure reduced water losses in the system. Developing a suitable plan for pipe improvements and rehabilitation is recommended. Technical performance indicators (litres /service connection/day) can be used to calculate real losses in a system [9]. Similar regular observation would be helpful for monitoring and improvement of the system.
Data LXH-15A, Class C 15 3 1.5 22.5 15
The pipe pressures at most of the control points are tallying with the design. However, variations are observed in some points. These may be due to the flow in the pipes being less than the final design flow. Another cause is unknown cross connections in the pipe network. Where there is an excessive difference the system shall be re-checked to ensure the designed system is on site.
11.
Acknowledgement The author wishes to acknowledge the contributions of Engineers and Engineering Assistance, of TSK Project, Operation and Maintenance Division and NRW unit and meter readers and other field staff, Commercial Officers and the GIS analyst in doing this evaluation.
Conclusions
Number of consumers in the three sub-zones differs from the predictions of the population survey. The difference in predictions of population survey and the site situation can be due to cost constrains, migration of population to areas with improved infrastructure and other facilities.
References 1. Design Manual D2, Urban Water Supply and Sanitation, National Water Supply & Drainage Board, March 1989 pp. 3/1- 3/8. 2. Feasibility Report, Towns South of Kandy Water Supply Project, National Water Supply & Drainage Board., March 2003 pp. 9-20. 3. Procedure Manual P1 for Project Planning and Preparation of Feasibility Reports, Nat. Water Sup. & Drainage Board, Sept. 1988. 4. Census of Population and Housing, Dept. of Census and Statistics 1981 and 2001. 5. Environmental and Infrastructure Action Plan for Central Province, Ministry of Urban Development and Housing, 1998. 6. Household Income and Expenditure Survey 1995/1996, Dept. of Census and Statistics. 7. Product Catalogue, Rotary Piston Water Meters, Ningbo water meters Co. Ltd, China 5. 8. Tender Documents Vol. 2, Design and Construction of Towns South of Kandy Water Supply Project, April 2005, pp.5/16- 5/18. 9. W.H.O., Leakage Management and Control, A Best Practise Training Manual, 2001.
Mapping of existing consumers as well as all the new connections in a regular manner is essential to identify the correct distribution subzones and also to maintain a realistic consumer record. The commercial database has to be updated to the exact site condition using the GIS consumer layer. The measured water consumption is less than the design water demand. The assumed peak factor and the recorded peak factor are tallying. However, slight variations are seen in the hourly patterns. Further onsite water consumption studies shall be carried out to assess the real per capita demand of domestic and non-domestic consumers and water demand pattern. With the help of the studies the demand criteria as well as the demand pattern can be modified in future project planning. Considerable difference is seen in the assumed and measured water losses. The amount of existing pipes and old water meters in a system has a significant effect to the water losses. Considering high water losses recorded with night flow, a strategy to find and repair 9
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Annual Transactions of IESL, pp. [104-111], 2012 © The Institution of Engineers, Sri Lanka
Ecological Design Considerations in High-Rise Buildings with References to CO2 Levels R.U. Halwatura, G.H.E. Silva, H.A.D. Mahanama, P.M.S. Jayamanna and A.G.T.N. Jayaweera Abstract: Rapid development coupled with urbanization has been identified as the main cause of environmental and social imbalances. This will lead to the increment of population as well as the pollutants in cities. This scenario results in limited space, there-by giving more room to high-rise buildings, which lack proper ecological design considerations. An urban area with buildings arranged densely will result in not just poor ventilation but also a strong heat island effect. Less vegetative urban areas do not have a proper mechanism to absorb the green-house gas emissions, which are increasing at an alarming rate. In a high-rise building, this effect can differ with location and also with the elevation. An in-depth analysis of Carbon Dioxide (CO2) concentrations, Relative Humidity (RH) and temperature can be used to evaluate indoor air quality, which should be acceptable in terms of both health and comfort of people. A densely populated urban area located along the Galle road in the City of Colombo was chosen for the research to analyze the effect of the sea-breeze on the variation of CO2 level, RH and temperature. They were obtained in each floor of selected high-rise buildings on either side (sea-side and land-side) of Galle road. Analysis of data provides evidence that the dispersion of CO2 and temperature is uniform and considerably low in sea-side buildings throughout the day, where as in land side, the variation is significant. However, the variation of humidity is significant in sea-side buildings. Even though both categories of buildings experience the same heavy traffic condition of the main road data provide evidence that sea-side buildings were successful in maintaining a better indoor air quality than the land-side buildings. That implies a better indoor air quality can be achieved in properly ventilated buildings. Therefore, it concludes that ecological design consideration plays an important role in making the urban cities sustainable over a long period. Keywords: Indoor air quality, Carbon dioxide (CO2) level, Urbanization, High-rise building, Thermal comfort
1.
priority list. This is understood as the factor for nurturing both man and environment [3].
Introduction
Urbanization and industrialization are dynamically linked with the urban environment [7]. Human behaviour is the main cause of ecological patterns, processes and subtle variances [6]. Therefore, it is best fit for the planners to reason out all these factors to build cities that will be resilient with the ecological system.
In particular, urban and industrial growth and the implied environmental changes have caused the urban environment to deteriorate and have modified urban climate [7]. It is largely accepted that urban design with climatic formation deals with holistic morphology of the city and with urban details, such as street width, formation, orientation, building heights, city compactness or dispersion, urban open spaces and other related issues [3]. As a result of a study, the following urban design issues have been identified [1]. Lack of fresh air paths, tall bulky buildings put up closely causing unwanted wind breaks to urban fabric, uniform building heights resulting
The technicality that links human and ecological processes is the key to control the dynamics and evolution of the human-eco cycle. Furthermore, change could be highlighted as an inherent property of the ecological system. Hence, in view of adding sustainability to cities over a long period of time it is quite necessary for the urban ecosystem to fall in line with the changes that are required to build cities [6].
Eng. (Dr.) R.U. Halwathura, B.Sc.Eng.(Moratuwa), Ph.D.(Moratuwa), C.Eng., MIE(Sri Lanka), AMSSE, Senior Lecturer, Department of Civil Engineering, University of Moratuwa. Ms. G.H.E. Silva (EC), H.A.D. Mahanama, P.M.S. Jayamanna, A.G.T.N. Jayaweera, Dept. of Civil Engineering, University of Moratuwa.
Dana Raydon believes that a new symbol system is needed for the sustainability of cities because sustainability is rated at the top of the 1
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in wind moving over the top of the buildings and not being re-routed into the fabric; packed narrow streets not aligned with prevailing wind with tall buildings resulting in urban canyons; minimal gaps between buildings forming wind barriers; projections from buildings and blockades on narrow streets and lack of soft landscaping shading and greenery contributing to poor ventilation and environmental quality in high-rise, compact built areas [1]. Moreover, discomfort to the urban population due to the rise of temperature, wind tunnel effects in streets and unusual wind turbulence due to imperfectly designed high-rise buildings are very common [11].
settlements, indoor air quality is inadequate in 30% of the buildings around the world [2]. A variety of techniques are available to determine building ventilation and indoor air quality, which include the measurement and analysis of indoor carbon dioxide concentrations. A number of relationships could be used to analyze and interpret carbon dioxide and indoor air quality, which includes the relationship between CO2 concentrations and occupant perceptions, level of other indoor contaminants and outdoor air ventilation rates [8]. Due to green-house gas emissions, it was identified that the global mean surface temperature will increase by 1.40C - 5.80C [4]. The major parameters that affect thermal comfort are air temperature, humidity, air velocity and environment temperature [5]. Natural ventilation is a more effective tool to improve indoor air quality in urban areas. Proper ventilation in urban buildings can contribute enormously to reduce the concentration of indoor air pollutants, improve indoor thermal comfort and decrease the energy consumption of buildings [2].
All inadvertent climate changes occur as a result of the concept of urban ‘heat island effect’ and ‘urban street canyon effect’. The aspect of the heat island always increases the energy consumption and exceedingly increases thermal discomfort. Beyond this the heat island also increases smog production [7]. The concept of ‘street canyons’ can be defined as the standard unit of reference at local scales in urban studies. The variation of pollutants within the street canyon depends on the presence or absence of vortex [10]. Height to width ratio of buildings plays an important role in identifying the local modification to wind flow patterns. As buildings get closer to the other buildings, one structure interferes with the patterns produced by the surrounding structures. Finally the obstacles become so close that the majority of the flow moves over the surface and there is limited penetration from wind flows above into the urban canopy [10]. Geographical features such as land sea-breeze in urban areas can have an important effect on spread of pollutants.
This research focuses on the effective methods in reducing the indoor CO2 concentrations, temperature and relative humidity, and improving indoor air quality in high-rise buildings, providing more room for a better living coupled with the construction industry.
2.
Objective
This research was carried out to evaluate the indoor air quality with references to Carbon Dioxide (CO2) level, relative humidity (RH) and temperature. Their variation with time and height was analyzed in different locations (seaside and land-side). The objective of the research was to identify whether the presence of sea-breeze could make a difference in the indoor air quality.
Another study shows that 75% of pollution is caused by urban environments. Roughly 45% from buildings and 30% from transport [3]. As the public has become more aware of air quality problems in recent years, building operators have begun to ensure that air quality is acceptable in terms of both health and comfort of people [9].
3.
Methodology
Measurements were taken in terms of CO2, humidity and temperature of selected high-rise buildings located on either side (sea-side and land-side) of the Galle road, to evaluate the indoor air quality with the presence of the seabreeze. Buildings on either side of the Galle road were identified to have the same traffic condition. Two categories of buildings were identified, one set of buildings (sea-side buildings) experiencing a large amount of seabreeze and the other set (land-side buildings) poorly ventilated. Measurements were obtained
The indoor environment quality of urban buildings is seriously impacted by the concentration of harmful pollutants in the indoor environment. However, the presence of indoor pollutants can be two to five times higher than outdoor pollutants [2]. According to United Nations Centre for Human
2
105
in the buildings marked in Figure 2. Measurements were obtained every half an hour (e.g. 1st session from 8.00 - 8.30 a.m., starting from the ground floor to the roof top. Thereafter, the routine is continued every half an hour till 5 p.m.) in each floor of selected buildings. Measured CO2, RH and temperature were plotted against time and building height. Then the variation of CO2, RH and temperature was analyzed to understand their behaviour with respect to location and also the elevation. With the analyzed data effective methods were identified in reducing indoor CO2 concentrations, RH and temperature, in order to improve indoor air quality.
surrounded by all the houses and it is also open to the sky.
3.1 Site Description Wellawatte, is located in the City of Colombo. It is known to be dense in population with a compact surrounding minus vegetation. Highrise buildings on either side along the Galle road were selected as the perimeter. This is the main road along the coastal belt, which is within 1 km of the sea-shore and is common place for heavy traffic.
Photographs show how the readings were obtained, with the help of the CO2 meter.
Photographs showing the surrounding area
Apartment with the central courtyard open to the sky, separated from the car park. (Building 4)
In the selected sea-side buildings, the presence of sea-breeze is enormous where as in the landside buildings, it is restricted due to a wind barrier that is created by the sea-side buildings. However as a whole, buildings in both sides experience the same traffic condition. Bird’s eye view of the selected location is shown in Figure 2. Here, buildings 1 and 3 represent the sea-side buildings, 2 and 4 represent the land-side buildings. ‘A2’ marked in green colour represents the main road (Galle road). Buildings 1, 2 and 3 have the same design concept. It was noticeable that in above buildings, an open space was kept and it runs from the car park (ground floor) to the roof top through all the floors of the houses. This is covered in the rooftop and this roof was designed in order to prevent rain water coming inside, but keeping a small space between the roof and the wall for ventilation purposes. Heated fuel emissions from the vehicles in the car park tend to rise up and it takes the only path available, through the open space. Therefore, all the houses in the floors experience heated and polluted air.
Apartment with an open space covered in the roof top, exposed to the car park. Figure 1 - Site Photographs
4.
Results and Discussion
Readings were obtained in two sea-side and two land-side buildings shown in bird’s eye view of Figure 2. All the readings were plotted using CO2, RH and temperature of each building (sea-side and land-side) and the variation with respect to time and height was compared and analyzed. Buildings 1 and 3 (sea-side) gave the same result. But the variation of building 2 (landside) was considerably different. Therefore, the respective graphs of buildings 1, 2 are presented and discussed below. Even though building 1 (sea-side) and building 2 (land-side) has the same design concept, it was noted that there is a considerable difference of the results.
But in building 4, it was noted that all the floors were separated from the car park. Therefore, these houses will not experience the fuel emissions of the car park. A court yard was placed in the middle which runs from the 1st floor to the roof top. This courtyard is 3
106
well. However, in land-side buildings there is a decrement in CO2 level after 12 noon.
Figure 2 - Bird’s Eye View 4.1
CO2 Variation with respect to Time Figure 4 - CO2 Variation in a Land-Side Building with respect to Time 4.2
CO2 Variation Building Height
with
respect to
Figure 3 - CO2 Variation in a Sea-Side Building with respect to Time Figure 3 and 4 When comparing the CO2 variation with respect to time, sea-side buildings shows a uniform and relatively low CO2 concentration throughout the day. This is shown in Figure 3. When considering the CO2 variation in land-side, it was understood that the variation is significant as shown in Figure 4. A heavy traffic can be observed in the Galle road from 8-10 a.m. and also in the evening from 3-5 p.m. In sea-side buildings, the effect of the fuel emissions was controlled by the sea-breeze and is capable of maintaining a CO2 level between 410-425 ppm, but in land-side CO2 variation is between 405470 ppm, which is considerably high. Same situation can be observed in the evening as
Figure 5 - CO2 Variation in a Sea-Side Building with respect to Building Height Figure 5 & 6 Figure 5 shows that the indoors in sea-side buildings maintain almost the same CO2 level as the CO2 level in roof top and ground floor, which represents the outdoor environment. Also it was noted that it is relatively low and does not vary with the elevation. But, the landside buildings show a significant variation with the height (Figure 6). Even though in land-side buildings, the CO2 level in roof top and ground floor (which are exposed to outdoor) maintain a 4
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370C. Roof top temperature (exposed to outdoor) is relatively high in the land-side. The presence of the wind in sea-side buildings was able to keep the outdoor temperature at a considerably low level.
low CO2 level, indoors of other floors failed to maintain the same CO2 level. Also the CO2 level in land-side is relatively high.
Figure 6 - CO2 Variation in a Land-Side Building with respect to Building Height 4.3
Figure 8 - Temperature Variation in a LandSide Building with respect to Time
Temperature Variation with respect to Time
4.4
Temperature Variation with respect to Building Height
Figure 7 - Temperature Variation in a Sea-Side Building with respect to Time Figure 7 & 8 In general, there is an increment of the temperature in outdoor environment between 11 a.m. to 3 p.m. In land-side buildings, there is an increment in indoors between the same period of time (Figure 8). But as shown in Figure 7, sea-side buildings are capable of maintaining a uniform and a relatively low temperature throughout the day. Variation of temperature in sea-side buildings is between 28 – 33 0C, where as in land-side it is between 27 –
Figure 9 - Temperature Variation in a Sea-Side Building with respect to Building Height Figure 9 & 10 When comparing the behaviour of the temperature with the elevation, it was noted that sea-side buildings do not show a considerable variation and almost all the floors experience a relatively low temperature according to Figure 9. However, land-side 5
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building shows a tremendous increment of the temperature from the 4th floor to roof top. Therefore, people in the upper floors will experience a thermal discomfort.
of humidity in sea-side is between 63% - 73% and in sea-side it is 63% - 77%.
Figure 12 - Humidity Variation in a Land-Side Building with respect to Time
Figure 10 - Temperature Variation in a LandSide Building with respect to Building Height
4.6 4.5
Relative Humidity Variation with respect to Time
Relative Humidity Variation respect to Building Height
with
Figure 13 - Humidity Variation in a Sea-Side Building with respect to Building Height Figure 11 - Humidity Variation in a Sea-Side Building with respect to Time
Figure 13 & 14 Humidity in sea-side buildings does not vary with the elevation, but in land-side buildings there is a decrement.
Figure 11 & 12 Humidity varies significantly both in land-side and sea-side buildings with the time. Variation
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live in top floors will experience a thermal discomfort. Humidity variation: Humidity varies significantly with time, in both categories of buildings. In sea-side buildings, all the floors have almost the same humidity percentage, where as in land-side buildings, lower floors will experience a high humidity level. Even though both categories of buildings experience the same traffic condition, it was found that sea-side buildings were successful in maintaining a better indoor air quality than the land-side buildings. The analyzed data provide evidence that the presence of the sea-breeze can reduce the effect of the heavy traffic on the Galle road. It was concluded that ecological design considerations plays an important role in constructing buildings, in order to make the urban cites sustainable over a long period.
Figure 14 - Humidity Variation in a LandSide Building with respect to Building Height
5.
5.2 Recommendations Based on the results obtained the following recommendations can be adapted to have a better indoor air quality of high-rise buildings.
Conclusions and Recommendations
5.1. Conclusions This research was carried out to evaluate the indoor air quality with references to CO2 level, relative humidity and temperature. Effect of the sea-breeze on the variation of CO2 level, RH and temperature was analyzed. With the analyzed data the following conclusions can be highlighted.
CO2 variation: In sea-side buildings, CO2 level does not vary with the time or with the building height and almost all the floors maintain the outdoor CO2 concentration, which is considerably low. In land-side buildings, CO2 varies significantly with the time and also with the height.
Temperature variation: In general, there is an increment of the temperature from 11 a.m. to 3 p.m. But sea-side buildings maintain uniform and relatively low temperature throughout the day. In sea-side buildings all the floors maintain almost the same temperature level. In land-side buildings, there is an increment of the temperature from the 4th floor to roof top, therefore, people
A building should be properly ventilated in order to reduce smog products circulating inside the building. It could be designed to have cross ventilation and large openings to get the maximum sunlight into the building. All the floors of a high-rise building can be designed to face a central courtyard open to the sky. This will help the indoors to maintain the same outdoor CO2 level which is relatively low and also the circulation of indoor heated air will be at a much lower volume. A car park should be built separately from other floors in order to prevent the heated fuel emissions entering the other floors. Green roofs and green beds for balconies to reduce the indoor CO2 level. Develop a set of rules and regulations in order to construct more ecologically designed high-rise buildings. Rules for the minimal gaps between buildings, building heights and etc.
References 1.
7
110
Belinda Yuen, Anthony, G. O, ‘High-Rise Building Living in Asian Cities’, 2011.
Cristian Ghiaus, Francis Allard, ‘Natural Ventilation in the Urban Environment’, 2005. 3. Dana Raydon and Koen steemers ‘Environmental Urban Design’. 4. Dareeju, B.S.S.S, Meegahage,J.N., Halwatura, R.U., ‘Green Roof Performance Against the Global Warming Effects’. 5. John D. Spengler, Jonathan M. Samet, John F. McCarthy, ‘Indoor Air Quality Handbook’, 2000. 6. Marina Alberti, ‘Advances in Urban Ecology’, 2008. 7. Matheos Santamouris, ‘Environmental Design of Urban Buildings: An Integrated approach, 2006. 8. Persily, A.K, ‘The Relationship between Indoor Air Quality and Carbon Dioxide, Evaluating Building Air Quality and Ventilation with Indoor Carbon Dioxide’, 1997. 9. Reardon, J.T, Shaw, C.Y, Vaculik, ‘Air Change Rates and CO2 Concentrations in High-Rise Office Buildings’, 1993. 10. Ronald E. Hester, Roy M. Harrison, ‘Air Quality in Urban Environments’, 2009. 11. StavroulaKaratusou, Mat Santamouris and Vassilios Goros, ‘Urban Building Climatology’. 2.
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Structural Effects on Existing Buildings due to Installation of Rooftop Towers Nadira Gunathilaka Abstract: Lots of roof top telecommunication towers are available on multi-storey buildings and in most of the cases, towers are installed on existing buildings which had not been designed for dead and wind loading of a telecommunication tower. The main objective of this research is the identification of structural effects caused by installation of towers on existing buildings. Identification of ways and means of reducing additional loads on columns due to installation of roof top towers and checking the possibility of tolerating the erection of a rooftop tower on typical building which was not originally designed for tower loading considering strength of columns are critically analyzed in this research. According to results of this analysis, it was observed that generally installation of shorter telecommunication towers (tower having heights less than 15 m) could be tolerated even if building had not been designed for tower loading initially. The methodology adopted for the analysis, outcome and recommendations with respect to the above objective are discussed in this paper. Keywords:
1.
Rooftop Towers, Telecommunication Towers
structural drawings throughout the life time of building is lacking in most of the building owners especially with low rise buildings.
Introduction
Large number of roof top towers is a common sight in most of the urban and sub urban areas of the country. This is due to the consideration of urban and sub urban areas as their potential business target areas by telecommunication operators. The construction of a green field tower in a populated area is not a simple task due to scarcity of lands, very high market price of lands and difficulties of obtaining various clearances from the relevant authorities. As a result of this, telecommunication operators start to install roof top towers as an alternative to green field towers.
Hence, the objective of this research was the identification of structural effects caused by installation of roof top towers on existing buildings. As per the above objective, following aspects were analyzed;
However, roof top towers are relatively new concept in this country, even though there are few roof top towers which have been installed about 30 years ago. Hence, a scientific research regarding structural effects caused by the installation of these towers has not been carried out yet in Sri Lanka. Even in world context, very few researches have been done in this regard.
2.
1.
Variation of additional column loads with height and base width of the towers, size of the panel on which tower is installed.
2.
Identification of the optimum size and amount of reinforcement requirements for a column under different tower conditions and it’s variation from without tower case.
3.
Analysis
In this analysis, it was decided to consider four leg lattice towers installed on rectangular or square roof panels only. A separate analysis was carried out using different base dimensions and bracing types to identify the optimum towers in cost wise in both 15 m and 20 m height cases. Generally , the cost of a tower is totally depends on self weight of the tower and therefore, the tower having least
Objectives
Most of the roof tops that are used to install roof top towers have not been initially designed considering additional moments and forces develop as a result of installation of towers and also, structural details of such buildings are not available in most of the instances, since importance of keeping
Eng. Nadira Gunathilaka ,Bsc.Eng (Hons), M.Eng. (Structural), C.Eng., MIE(Sri Lanka), Engineer /Civil Planning , Sri Lanka Telecom PLC.
1
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weight becomes the optimum tower in cost wise as well. Following towers were identified as the optimum towers under respective base dimensions (or H/B ratios) from the above analysis; 15 m towers;
Critical support reactions under ultimate limit state of the above cases 1 to 3 are as 208 kN, 144kN and 108 kN, respectively and cases 4 to 6 are as 410 kN, 267 kN and 227 kN, respectively and these are tensile and compressive forces in respective supporting points as marked in Figure 3.
Case 1 - H/B ratio is 15, Base dimension is 1 m & K bracing type Case 2 – H/B ratio is 10, Base dimension is 1.5 m & XBX bracing type Case 3– H/B ratio is 7, Base dimension is 2.05 m & XBX bracing type 20 m towers; Case 4 - H/B ratio is 13, Base dimension is 1.5 m & K bracing type Case 5– H/B ratio is 9, Base dimension is 2.25 m & K bracing type Case 6– H/B ratio is 7, Base dimension is 2.85 m & K bracing type
As expected, these loads are considerably large and hence, structural elements such as slabs and beams of an existing building which has not been designed for such loads cannot be used to transfer these loads to columns. This scenario is observed in almost all practical occasions. Therefore, telecommunication operators usually install a new set of beams usually out of concrete or steel on top of the roof slab and tower loads are directly transferred to the columns through that system without considering the structural strength of existing beam slab system. However, usually strengthening of columns or foundation would not be carried out. It is assumed that those components have adequate capacity to withstand under these additional loads without a proper analysis due to non availability of structural details of existing structures for such analysis.
All of the above towers are designed for wind speed of 42.5 m/s corresponding to wind zone 2 –normal structures condition of Sri Lanka with open country with no obstruction condition. Wind shield areas for antennas are selected as 10m2 for 15 m towers and 12 m2 for 20 m towers. It was assumed that the tower was installed on a four storey building having an overall height of 15 m. The wind calculations were done according to CP3: Chapter V: Part 2 (1972) [1] and IS 875 Part 1: (1975) [4], which is the Indian Code of Practice for wind load calculations. Based on the results obtained from the 3D models, the lattice towers were designed according to IS 802 [3], which is the Indian Code of Practice for permissible stresses in Lattice towers.
As per objective of this research, analyzing the effect on columns due to tower loads was carried out based on the support reaction of above mentioned tower cases.
X
a
Legs of the tower
Y
b
p Existing columns
y
x
p
Figure 1 - Base Beam Arrangement for Four Legged Roof Top Towers
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Figure 2 - Steel Base Beams of a Roof Top Tower The most widely used beam arrangement for installation of roof top towers is shown in Figure 1. Hence, it was decided to carry out this analysis based on this arrangement. Additional loads from towers on columns varies with the parameters a, b, p, x and y.
3. Self weight + Wind from Y direction 4. Self weight + Wind from diagonal direction It is observed that support reactions at the base level of the tower under load case 1 (Self weight only) were very small when compared with other load cases during the tower analysis. Therefore, the loads that were transferred to columns under this load case were found to be comparatively very small and it was decided to neglect that load case from the analysis. Other three load cases can be schematically represented as shown in Figure 3.
To study this effect of parameters mentioned before, the behaviours of base beam arrangement under following different load cases of tower were studied; 1. Self weight only 2. Self weight + Wind from X direction
-R
R-RD
-R R Y X
R=0
R=0
R
-RD
Reactions under load case 2
Y
X Reactions under load case 4
R R Y
-R X
-R
Reactions under load case 3
Figure 3 – Graphical Representation of Critical Load Cases
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Even though, it has used the same magnitudes of R as support reactions at all four legs under load cases 2 and 3, it was observed that some variation would occur between magnitudes of support reactions under practical conditions. However, for the simplicity of the analysis, above assumption was made and it had not caused any significant effect on the results since these variations were negligibly small when compared with magnitude of support reactions. Also, support reactions along one diagonal are marked as zero under load case 4 in Figure 3. However, actual reactions at those locations were not exactly zero and it would have a very small value.
Support reaction on any column = ±RDp( b + x - y) or ±RDp(x-y) ab ab ±RDp(b + x -a –y ) or ±RDp(a + y- x ) ab ab
±RDp( x + a + p) ab
or
±RDp(a-p-y-x) ab
(3)
However in practical cases, the common practice is to install the tower at the middle of the panel. In order to get equal design loads for all the columns, tower has to be placed at center of the panel and if not, some of the columns of the panel experience greater loads than others. Hence, that condition was selected as the suitable case for the analysis. When a tower is located at the center of a panel, the expressions for design column loads can be simplified as Eq. (4); Design column load from tower
= ±Rp or ± Rp a b ±RDp(a + b) ab
or (4)
Using the Eq. (4) and support reactions obtained from tower analysis, additional column loads were calculated for following panel sizes. Dimensions of panels that were considered in analysis ; 1. 3 m X 3 m 2. 3 m X 4 m 3. 3 m X 5 m 4. 3 m X 6 m 5. 4 m X 4 m 6. 4 m X 5 m 7. 4 m X 6 m 8. 5 m X 5 m 9. 5 m X 6 m 10. 6 m X 6 m
Expressions for support reactions under different load cases are given as Eqns. (1), (2) & (3); Under load case 2,
(1)
Under load case 3, Support reaction on any column = ±Rp(2a -2x - p) or ±Rp(2x+p) ab ab
or
±RDp(x-b + p +y ) or ±RDp(a-x +b-p-y) or ab ab
Expressions can be obtained for support reactions on columns for above load cases by analyzing above beam arrangements by using simple structural analysis theories. It assumed that secondary beams on which the tower is installed were connected to the main beams by pin connections. It also assumed that the connection between main beams and columns were as pin connections. These assumptions match well with the practical situation. If steel beams are used as supporting beams, moment transferring joints are not practically used during construction in this type of work. Also, with concrete beams, it would be difficult to achieve moment transferring joint especially near existing columns since it has to be connected to the beams and already casted columns. Further, if secondary beams are connected to main beam with moment transferring joints, the main beam has to be designed for torsional moments as well.
Support reaction on any column = ±Rp(2y+p) or ±Rp(2y+p-2b) ab ab
or
Design column load from tower (additional load from tower for structural reassessment) for 15 m tower case and 20 m tower case for different panel sizes are given in Tables 1 and 2, respectively.
(2)
Under load case 4,
From the above analysis, it was found that RDp(a+b)/ab is the governing expression (i.e.
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load case 4) to obtain addition design load on columns due to installation of towers. Hence, if it is necessary to reduce the additional design column load, panel should be selected in such a way, so that it reduces the value of (a + b )/ab for any tower case. Usually, (a+b)/ab reduces with increase of “ a” and “b” (i.e. the size of the panel ), but this cannot always be guaranteed.
installation on columns, a hypothetical building was selected having following characteristic. However, dimension of column grid of building was changed in each case as per the panel sizes considered for analysis. 1. Building that is used for the analysis is a four storey building 2. Live load for all floors is 2.5 kN/m 2 (including roof floor)
Another important observation from this analysis is the effect of the base dimension of towers on additional loads applied on columns. The minimum additional design column loads in 15 m height tower case was observed when H/B ratio is 15 and for 20 m case, it was observed for H/B ratio of 9. Hence, it is quite evident that additional loads on the columns cannot be reduced by increasing the base dimensions as in green field towers. As per the result of the above tables, base dimension of a roof top tower causes a minimum effect on additional column load and maximum variation between minimum additional design column load and maximum case is always less than 12% and about 15 kN in numerical terms.
3. Slab thickness of floor slabs; i.. If the smallest dimension of panel 4m, slab thickness = 150 mm 4. Characteristic strength 25 N/mm2
of
concrete is
5. Additional dead loads considering finishes, partition etc, is 2.25 kN/m2 6.
Panel that is selected for the analysis is considered as an internal panel; therefore it does not have brick walls along the edges of panel.
For the purpose of analyzing the effects of the additional design load due to tower Table 1 - Design Column Loads for 15 m Towers De sign Column loads of 1 5 m tow e rs pannel Size a (m) b (m) x (m) y (m) p (m) Wper reaction (kN)
3m x 3m 3 3 3 3 0.475 0.75 0.475 0.75 2.05 1.5 112 144
Mini.coulmn load (kN) variation of loads (kN) % variation of loads
3m x 5m
3m x 6m
4m x 4m
4m x 5m
4m x 6m
5m x 5m
5m x 6m
6m x 6m
3 3 3 4 5 5 1 0.475 0.75 1.5 1.475 1.75 1 2.05 1.5 208 112 144
3 3 3 5 6 6 1 0.475 0.75 2 1.975 2.25 1 2.05 1.5 208 112 144
3 4 4 6 4 4 1 0.975 1.25 2.5 0.975 1.25 1 2.05 1.5 208 112 144
4 4 4 4 5 5 1.5 0.975 1.25 1.5 1.475 1.75 1 2.05 1.5 208 112 144
4 4 4 5 6 6 1.5 0.975 1.25 2 1.975 2.25 1 2.05 1.5 208 112 144
4 5 5 6 5 5 1.5 1.475 1.75 2.5 1.475 1.75 1 2.05 1.5 208 112 144
5 5 5 5 6 6 2 1.475 1.75 2 1.975 2.25 1 2.05 1.5 208 112 144
5 6 6 6 6 6 2 1.975 2.25 2.5 1.975 2.25 1 2.05 1.5 208 112 144
6 6 2.5 2.5 1 208
354
354
245
354
192
245
354
192
245
354
192
354
354
245
354
192
245
354
192
245
354
131 123 118 115 107 103 105 98 118 103.25 94.4 13 4.5 0 12 3.9 0 11 3.6 11 3.8 0 11 3.8 0 11 3.8
94
98
92 88.5 0 9.9 3.4 0 11 3.8
89
98
92 88.5 0 9.9 3.4 0 11 3.8
89
89
83 80 82 77 74 79 74 79.65 73.75 70.8 0 8.9 3 0 8.2 2.8 0 7.9 2.7 0 11 3.8 0 11 3.8 0 11 3.8
71
72
67 64.9 0 7.3 2.5 0 11 3.8
65
66
61 59 0 6.6 2.3 0 11 3.8
59
Wdig reaction(kN) Design column load (kN)
3m x 4m 3 3 3 3 4 4 1 0.475 0.75 1 0.975 1.25 1 2.05 1.5 208 112 144
192
245
192
245
192
245
192
245
192
0 0
Table 2 – Design Column Loads for 20 m Tower De sign Column loads of 2 0 m tow e rs Panel Size a (m) b (m) x (m) y (m) p (m) Wper reaction (kN) Wdig reaction(kN) Design column load (kN) Mini.coulmn load (kN) variation of loads (kN) % variation of loads
3m x 3m
3m x 4m
3m x 5m
3m x 6m
4m x 4m
4m x 5m
4m x 6m
5m x 5m
5m x 6m
6m x 6m
3 3 3 3 3 3 3 3 3 3 3 3 4 4 4 4 4 4 4 4 4 5 5 5 5 5 5 6 6 6 3 3 3 4 4 4 5 5 5 6 6 6 4 4 4 5 5 5 6 6 6 5 5 5 6 6 6 6 6 6 0.075 0.375 0.75 0.075 0.375 0.75 0.075 0.375 0.75 0.075 0.375 0.75 0.575 0.875 1.25 0.575 0.875 1.25 0.575 0.875 1.25 1.075 1.375 1.75 1.075 1.375 1.75 1.575 1.875 2.25 0.075 0.375 0.75 0.575 0.875 1.25 1.075 1.375 1.75 1.575 1.875 2.25 0.575 0.875 1.25 1.075 1.375 1.75 1.575 1.875 2.25 1.075 1.375 1.75 1.575 1.875 2.25 1.575 1.875 2.25 2.85 2.25 1.5 2.85 2.25 1.5 2.85 2.25 1.5 2.85 2.25 1.5 2.85 2.25 1.5 2.85 2.25 1.5 2.85 2.25 1.5 2.85 2.25 1.5 2.85 2.25 1.5 2.85 2.25 1.5 129 157 252 129 157 252 129 157 252 129 157 252 129 157 252 129 157 252 129 157 252 129 157 252 129 157 252 129 157 252 227
267
410
227
267
410
227
267
410
227
267
410
227
267
410
227
267
410
227
267
410
227
267
410
227
267
410
227
267
410
216 200 205 189 175 179 173 160 164 162 150 154 162 150 154 146 135 138 135 125 128 129 120 123 119 110 113 108 100 103 200 175 160 150 150 135 125 120 110 100 15 0 4.8 13 0 4.2 12 0 3.8 12 0 3.6 12 0 3.6 10 0 3.2 9.6 0 3 9.2 0 2.8 8.5 0 2.6 7.7 0 2.4 7.7 0 2.4 7.7 0 2.4 7.7 0 2.4 7.7 0 2.4 7.7 0 2.4 7.7 0 2.4 7.7 0 2.4 7.7 0 2.4 7.7 0 2.4 7.7 0 2.4
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Other than above building loads, maximum loads on columns due to erection of 15 m or 20m towers obtained from Tables 1 and 2 were also considered to select a suitable column with appropriate reinforcement to withstand under each condition. The optimum column section with appropriate reinforcement was obtained for both at foundation level and roof level for each panel by using structural design according to BS8110: Part I :1985 [2]. When, the columns were checked, both uplift and compressive cases were considered, since some of the columns were always subjected to tension while other columns were under compression due to additional tower design loads.
- Area of concrete
As
- Area of reinforcement
Therefore, tensile carrying capacity of column (under SLS) = 1.31 x { Ac + (m-1) x As}/103 kN For the design of columns for compression, loading at both roof level and foundation level were considered, since additional compressive load transferred from tower was an additional load to the existing compressive loads in the columns. Also, maintaining the same column size and amount of reinforcements throughout the column height (from foundation level to roof level) does not give an optimum solution. Design checking of columns was done using equation 39 of BS 8110: Part 1:1985 [2] assuming that columns were short braced columns. This is an appropriate assumption, since most of the buildings in Sri Lanka are having masonry infill walls and also satisfy the slenderness limit in most of the cases.
When the tensile stresses that develop in columns due to installation of roof top towers are considered, critical level of column that should be considered for analysis is the top most level of the column (i.e. Roof top level of the column). In lower levels, downward forces transferred from slabs diminishes out the tensile stress in the column. Therefore, if the column is found be safe at the roof level under tensile stresses, it can guarantee that the column is safe throughout its length due to induced tensile stresses. The columns were checked under both ultimate and serviceability limit states. Under ultimate limit state, the column was checked assuming zero tensile capacity of concrete and whole of the tensile resistant were provided by the reinforcement as per the method given in BS8110: Part I : 1985 [2]. Under serviceability limit state, tensile carrying capacities were calculated using limiting stress values for uncracked condition. In the BS codes, it has not given allowable stresses for concrete in direct tension without cracking. Therefore, Indian code IS 456: 2000 [5] is used for this purpose. According to that;
At the end of the above analysis for both compression and tension, optimum column sections at roof level and foundation level were indentified for each of the panel sizes considered in the analysis and these are tabulated in Table 3. Table 3 can be used as a guideline for selection of column details for given grid size if there is an intension to install a 15 m or 20 m tower. Accordingly, installation of 15 m tower is possible even if columns are having minimum size (225 mm x 225 mm) with nominal reinforcement at roof level in any column grid sizes considered in this analysis. But for 20 m tower case, it is possible only with large panel sizes. When it considers about compressive condition of columns, columns are safer (without modifying the size or amount of reinforcements of columns) under additional loads due to 15 m tower in most of the cases, unless if very marginal design have been adopted for column design under normal condition (without tower case). However, if a 20m tower is considered, columns have to be modified in most of the cases to cater for additional loads due to tower installation. Structural feasibility of foundation of columns due to tower installation has not been checked in this analysis. A behaviour similar to columns can be expected in foundations as well.
Permissible maximum direct tensile stress for concrete without cracking = 1.31 N/mm2 (For Grade 25 concrete according to Clause 44.1.1 of IS 456) Equivalent area of concrete (considering equivalent area of concrete for reinforcements) = Ac + (m-1) x As where, m
Ac
- modular ratio (this is assumed as 15)
117 1
Table 3- Details of Optimum Column Sections
4.
However, considerable reduction of additional column loads on building can be achieved by changing panel size.
Conclusion
This analysis was carried out with two main objectives as variation of additional column loads with height and base width of the towers, size of the panel and Identification of optimum size and amount reinforcement requirements for a column under different tower conditions and it’s variation from without tower case.
Lowest column loads can be expected in panel which having lowest value of (a+b)/ab. Usually, above value will reduce with the increase size of the panel, but it cannot be always guaranteed. Hence, if the freedom is available to select a panel out of different panel sizes in a particular case, it better to select the panel having lowest (a+b)/ab ratio for tower erection to reduce the additional loads on column due to tower installation.
According to results of the analysis, it is shown that achieving considerable variation of additional loads in column due to installation of roof top towers by changing base dimension (base width) of tower is not possible. Therefore, increasing base dimension of a roof top tower is not advisable with the intension of reducing loading on columns from tower as in green field towers. (Generally in green field towers, foundation loads reduce with the increase of base dimension of tower.)
The data in Table 3 can be used to find the optimum column section for particular panel size to allow 20 m or 15 m tower installation on a typical four storey building. According to results of Table 3, it seems that normally a installation of 15 m tower on a building, which has not been initially designed for such tower load, can be tolerated if the columns have not
118 1
been optimized up to its extreme limit during design. For 20 m tower case, it is not possible to allow such installation in most of the cases, even if there is some additional capacity in columns, since additional loads from the tower are considerably large. However, it is always advisable to carry out individual analysis case by case prior to installation of roof top tower on existing building, if the structural details of the building are available.
References 1.
CP3: Chapter V: Part 2 (1972): Code of basic data for design of buildings- Wind loads.
2.
BS 8110: Part 1: 1985: Structural use of concrete - Code of Practice for design and construction.
3.
IS 802 Part 1: (1978) Code of Practice for permissible stresses in Lattice towers Indian standard.
4.
IS 875 Part 1: (1975) Code of Practice for wind loads Indian Standard.
5.
IS 456 : 2000 Code of Practice for Plain and Reinforced concrete Indian Standards
6.
Brain. W. Smith, Communication structures Thomas Telford Ltd, London, 2007, pp.72-80.
7.
Dayaratnam P., Design of Steel Structures, S. Chand & Company Ltd, New Delhi, India, 2008, pp. 101-108.
8.
Suagnthan S., Widanagama K.N., Diawakara A.J. L., “Study on telecommunication towers”Undergraduate final year research project report, University of Moratuwa, 2006.
9.
http://www.masterower.com, visited, on 20th Dec. 2011.
10. http://www.utlnepal.com, visited, on 10th Dec. 2011.
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Mitigating the Scale of Urban Heat Island Effect in Cities with Implementation of Green Roofs S.N. Wijerathne and R.U. Halwatura Abstract: Variations of the urban heat island effect is different from city to city. To understand the variations in the heat island effect, in the center of the Colombo City the capital of Sri Lanka, with the locations of buildings and roads, the temperature and humidity was measured with the height. A detailed analysis was done to find the specific height of which the heat island effect prevails and the temperature variations with height. With that a theoretical model was developed to identify the possibilities of controlling the heat island effect. The model was developed with replacing existing flat roof areas with green roofs, in randomly selected area (0.5 Km²) in the Colombo City. These findings were coupled with the energy balance in the selected area and with a computer simulation. The reduction in the temperature in the canopy air layer in the roof level was calculated. The results show that there is a variation in the heat island effect with height. When, the vertical distance increases from the heating surfaces, the heat island effect is lesser. The heat island effect can be reduced with the implementation of green roofs in the Colombo City. Key Words:
1.
Heat island effect, Green roofs, Sensible heat, Energy balance, Computer simulation deteriorate our living environment, increase energy requirement, elevate ground-level ozone and even increase mortality rates [6]. Installing green roofs is now widely considered as an effective strategy to solve these problems. With the major benefit of green roofs, which is mitigating the urban heat island (UHI) effect, it has other benefits namely improving the energy efficiency of buildings, reducing storm water runoff, increasing biodiversity, purifying water and air, as well as elongating the life span of roofs.
Introduction
Large areas that modern cities occupy, their structure, materials and the general lack of vegetation have altered the climatic characteristics of urban spaces [1]. According to the Population Reference Bureau 50% of the world population (3.4Billion) is settled in urban areas [2]. Massive building construction is under way to respond to this overwhelming dwelling demand. This excessive and unplanned growth of urbanization has caused undesired side effects around the world. Urban Heat Island (UHI) as a consequence of urbanization was first documented by Howard in 19th century [3].
Because of the benefits mentioned above, green roofs have become the focus of the current research [7]. This study was carried out to analyze the role of green roofs, on the city temperature in the tropical climatic conditions. For the analysis, building energy balance with the surrounding was used [8]. To compensate this condition a considerably large area was chosen in the city.
The urban heat island effect is the temperature increase in urban areas compared that with surrounding rural areas. This is caused by the increased use of impervious land surfaces covered by anthropogenic material, the complexity of the three dimensional structures of the surface, and the coincident decrease of vegetation coverage, as well as anthropogenic heat discharge due to human activities [4]. Also due to the lower wind speeds in urban areas, less convective heat losses and less evapotranspiration, yields more energy for surface warming [5].
Many different types of surfaces that make up an urban environment affect the heat balance of
Eng. S.N. Wijerathne, B.Sc.Eng(Moratuwa), AMIE(Sri Lanka), CIMA Passed Finalist, Engineer in RDA, No:115 CE Office, Dharmapala Mw.,Colombo 07. Eng. (Dr.) R.U. Halwatura, PhD(Moratuwa), B.Sc .Eng (Moratuwa), C.Eng, MIE(Sri Lanka), AMSSE, Senior lecturer Department of Civil Engineering, University of Moratuwa.
Urban heating causes many problems for the inhabitants of cities, in particular those with a tropical environment. Urban heating could
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cities. Roof surfaces are key interfaces in the volumetric exchange of energy because they constitute a large fraction of urban surface areas, and due to their exposure, they receive considerable solar radiation [9]. Therefore, it is important to understand the heat storage capacities to understand the effect on the air temperature of the city canopy air layer. The study mainly concentrated on the temperature variation with height in a canopy layer and of four different types of roofs namely asbestos, tile, flat slab and green roofs. The temperature variation is calculated with the varied properties of these roofs.
the canopy air layer), rc (air resistance between canopy and building roof level). Eq.(2) [11] comes after applying the energy balance model to the roof level where QEC is absent due to the hypothesis of dry building surfaces. Denotation c is given to represent the building surface level. QC* + QFC = ΔQSC + QHC
(2)
In the study QFC is neglected with compared to the radiative heat flux (Q*) from the sun which is then simplifies as follows. QC* = ΔQSC + QHC
(3)
2. Theory ΔQSC is found by the DEROB (Dynamic Energy Response of Buildings LTH) modeling values where DEROB is a design tool used to explore the complex dynamic behavior of buildings for different designs. The behavior is expressed in terms of temperatures, heating- and cooling loads and different comfort indices [10] QC* is also found by the climatic data file generated by DEROB software. The sensible heat flux is calculated by using the Eq. (3) with the calculated QC *and ΔQSC. The found sensible heat flux is then related to the canopy air layer temperature with the Eq. (4) [11]. Where, TC values are obtained from the DEROB simulation, rc is the air resistance, r is the air density, Cp is the specific heat capacity of the dry air and T1 is the temperature of canopy air layer [11].
The urban surface energy balance is expressed as: Q* + QF= QH + QE +ΔQS +ΔQA
(1)
where, Q* is the net all wave radiation, QF the anthropogenic heat release, QH and QE the sensible and latent heat fluxes, respectively, ΔQS the net storage flux, and ΔQA the net horizontal heat advection (representing the net gain or loss due to the transport associated with the spatial heterogeneity of sources and sinks, as well as heat advection associated with local and mesoscale circulation) [1]. The term ΔQS is of particular relevance in the urban environment, because it accounts for almost half of the daytime net radiation in highly urbanized sites. The UHI can develop only under favorable synoptic weather conditions (in a radiative scenario, in presence of light wind), in which the term ΔQA is negligible [6].
(4)
3.
The energy balance model is applied to the building roof level and the parameters which are measured and unknown are shown in the diagram.
The main objective of this research is to identify the existence of heat island effect in different elevations from ground and to compare the temperature difference of the city canyon air layer by replacing the existing flat roof slabs with green roofs in the Colombo city center. The following methodology was used for achieving the above objectives:Roof Level Taking the temperature and humidity measurements of the physical models built, The actual different roof areas in the selected city area in Colombo district in Sri Lanka were measured, Temperature and humidity at different heights from ground were measured,
Resistance measuring tool
TC rc
Objective and Methodology
T1
Building Ground Level Figure 1 - Simulation Scheme A system of independent equations are necessary to relate three variables Tc (skin temperature of the building), T1 (temperature in
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The experiment was carried out in a chosen city in tropical climate, which is situated in the Colombo district in Sri Lanka. It is a highly dense area with less vegetation. An area of 0.5km2 was chosen for the experiment to simulate the city canyon. The average height of the city canyon is 6m. The picture of the chosen area is shown in the Figure 4. Two high rise buildings with natural ventilation were chosen from the area near by city canopy. The temperature and humidity was measured with time in the 8 floor levels with an electronic meter. The measurements were taken from 8.30am to 5.00 pm because the net all wave radiation is positive only in that period. The temperature and humidity measurements were taken for every half an hour in all the eight floors. Sunny days were chosen to take the measurement.
Identifying the existence of heat island effect in different heights and comparing the temperature difference of the city canyon air layer by replacing the existing flat slabs with green roofs, Identifying the patterns of energy storage of different roof types during different time periods in a day.
3.1 Measurements on Real Scale Model The best suitable soil cover thickness is 50mm in terms of the thermal performance and the growing characteristics [12]. And also, It was noted that the temperature reductions in slab top and the soffit are in the same scale for both having 50 mm and 75 mm soil covers and compared that with unprotected slab, the thermal performance can improved drastically by growing grass over the slab [12]. To measure the top surface temperature of roof slab arrangements with and without grass cover and the amount of heat stored in the system, small scale models were created. Experimental set up it shown in Figure 2. The measured slab soffit and outdoor temperature variation for soil layer of 50 mm and uncovered slab are shown in the Figure 3 [12]. This shows that the flat roof slab is a heating body which emits long waves after heating to the atmosphere.
When investigating the area three roof types were identified as Tile roofs, Asbestos Roofs, Flat Slabs. The areas of all the roofs in the chosen area were measured through the Google Earth Pro. When measuring the areas, the altitude of the Google Earth is set to zero. The image of measured flat slab roof areas is shown in the Figure 5.
Figure 2- Small Scale Physical Model Created Figure 4 - Selected Area for the Experiment The simulation temperature values from the DEROB model were obtained for each hour from 7 am to 5 pm. DEROB-LTH is a software, which was well proven to do thermal simulation. This is well tested by many researchers and it has a high usage in comparative studies [10, 13, 14]. For each roof type a DEROB model was simulate, with a house of average dimensions in the area, to obtain the surface temperatures. The simulated models are shown in Figures 6 and 7.
Figure 3 - Temperature Variation of the Slab Soffit in Two Cases with Compared to the Outdoor Temperature 3.2 Energy balance and heat island effect
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Figure 6 - Simulated Model with Asbestos Sheet Roof
.
Figure 5 - Measured Roof Areas With the obtained temperatures the energy stored in each existing roof types were calculated separately. To calculate the total energy stored by the roofs in the selected area, the energy stored in each roof, which was calculated previously from the simulations, were multiplied by the area of the distinct roof and was added. When calculating the energy stored in the green roofs the fact of 1.2% of energy out of the total solar radiation is stored in soil plant system of the green roof was used [7]. According to the actual temperature data obtained from the metrological department the radiative flux by the sun was obtained by using the climatic file for each hour, and was multiplied by the total sample area to calculate the total radiative flux to the area [15].
Figure 7- Simulated Model with Green Roof
4.
4.1 Temperature Variation with Height The temperature values obtained on different elevations within different time intervals are shown in the Figure 8. From the figure, it’s clearly evident that generally up to 9 m from ground the temperature is decreasing and from there the temperature is increasing with height. But at the height of 27 m the temperature reduces than the temperature at the height of 25m except in the time interval from 1.00 pm to 3.00 pm.
The sensible heat flux was obtained by subtracting the energy stored from the total flux. The canopy air temperature was calculated by the equation 4 where [16].
Results and Discussion
Cp was 1.01kJ/kgK , r was 1.29kg/m3 , rc was 15 sm-1
The same procedure was followed by replacing all the flat slabs in the considered area with properties of green roofs. The temperatures of the two situations were compared.
Figure 8 - Temperature Variation with Height at Different Time Intervals The Reduction in the temperature up to 9 m could be due to the reduction of the effect of the
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heated road in the canyon. The reflective radiations from road warm up the air up to a 9m from ground. Figure 9 shows the temperature variation with height form 1.00 pm to 3.00 pm. From the Figure 10, it’s clear that the maximum solar radiation occurs at 1.00 pm. With that it can be stated that the maximum temperature should be occurred after 1.00pm. From Figure 9, it’s clear that within this selected time interval the temperature is increasing after 9 m from ground. It’s clear at 27 m the air temperature reaches to its highest within the time interval of 1.00 to 3.00 pm and that is at 2.15 pm.
Figure 9 -- Temperature Variation with Height at Selected Time Intervals
4.2
Ambient Air Temperature Reduction with Implementation of Green Roofs
Figure 10 - Comparison of Temperature Variation with Radiation Flux Temperature of the air varies with the solar radiation magnitude. According to the Figure 10, the maximum solar flux occurs at 12.00 pm and the maximum air temperatures take place at 1.00 pm. It can be clearly stated that the maximum temperature of the canyon air occurs just after one hour from the maximum solar radiation taking place.
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Figure 11 - Temperature Variation of the City Compared to the Rural Area Air Temperature The magnitude of the canyon air temperature varies with time. From the Figure 11, it’s evident that the air temperature is comparatively high in the city canopy in the case 1 than the normal air temperature. There, the case 1 represent the air temperatures of the canyon under the prevailing conditions of the city and case 2 represent the canyon air temperatures when all the flat slabs in the area are replaced with green roofs. This value is maximized at 1.00 pm. The canyon air temperature in that hour is 34.47°C where the normal air temperature (ambient air temperature) is only 31.3°C and the difference is more than 3°C. This is a further evidence of prevalence of heat island effect, in the compacted cities.
Figure 12 - The Temperature Variation with Time in Two Cases The air temperatures obtained for each case in considered time period are shown in the Figure 12. The considered time period was from morning 7.00 am to evening 5.0 pm because the net all wave radiation is positive only in that period. According to the Figure 12, the temperatures of the canyon air is high under the prevailing condition compared to that the flat slabs replaced with green roofs. When the flat slabs are replaced with green roofs the canyon air
temperatures reduces approximately by 1.5 °C than the prevailing condition. This reduction of the temperature can be seen throughout the considered time period.
5.
Canyon temperature is increasing with height after 9 m from ground during 1.00 pm - 3.00pm. When all the flat slabs are replaced with green roofs it can be stated that this increasing canyon air temperature can be reduced by 1.5°C. This reduction can be maintained throughout the day time with implementation of green roofs on existing flat roof slabs. The findings are very important when considered the future development to be made. If the future constructed buildings are coupled with green roofs, the temperature issues that would have aroused due to impervious surfaces can be reduced. Other than the temperature benefits the visual benefits are also there with the increased greenery in the city.
References
2.
3.
4.
Robert L Wilby, Construction climate change scenarios of urban heat island intensity and air quality, Department of Geography, Lancaster University, Farrer Avenue, Lancaster LA 4YQ,England, 2008.
6.
Rizwan Ahmed Memon, Dennis Y.C. Leung , Chun-Ho Liu., An investigation of urban heat island intensity (UHII) as an indicator of urban heating Department of Mechanical Engineering, The University of Hong Kong, Hong Kong, China, 2009.
7.
Chi Feng, QinglinMeng, Yufeng Zhang., Theoretical and experimental analysis of the energy balance of extensive green roofs Building Environment and Energy Laboratory (BEEL), State Key Laboratory of Subtropical Building Science, South China University of Technology, Wushan, Guangzhou, PR China, 2009
8.
Francisco Sánchez de la Flor, Servando Alvarez Dom´ınguez., Modelling microclimate in urban environments and assessing its influence on the performance of surrounding buildings E.S. Ingenieros, Grupo de Termotecnia, Avda. de los descubrimientos s/n, 41092 Seville, Spain, 2004.
9.
Stephanie K. Meyn, T.R. Oke., Heat fluxes through roofs and their relevance to estimates of urban heat storage Dept. of Geography, University of British Columbia, 1984 West Mall, Vancouver, BC, Canada V6T 1Z2, 2009.
Conclusion
Due to the impervious faces the city temperature is increased compared to the temperature in rural areas. Green roofs are identified as a solution for the above mentioned problem.
1.
5.
10. Smeds , M. Wall., Enhanced energy conservation in houses through high performance design Division of Energy and Building Design, Department of Architecture and Built Environment, Lund University, P.O. Box 118, SE-221 00 Lund, Sweden, 2006.
Eleftheria Alexandria, Phil Jones., Temperature decreases in an urban canyon due to green walls and green roofs in diverse climates Mantzakou 2-6, 114 73 Athens, Greece,Welsh School of Architecture, Cardiff University, King Edward VII Avenue, Cardiff CF10 3NB, UK, 2006.
11. V. Bonacquisti, G.R. Casale, S. Palmieri, A.M. Siani ., A canopy layer model and its application to Rome University of Rome “La Sapienza”, Department of Physics, Italy, 2006.
Parham A. Mirzaei, Fariborz Haghighat ., Approaches to Study Urban Heat Island – Abilities and limitations Department of Building Civil and Environmental Engineering Concordia University, Montreal, Quebec, Canada H3G, 2010.
12. B.S.S.S. Dareeju, J.N. Meegahage, R.U. Halwatura ., Influence of Grass Cover on Flat Reinforced Concrete Slabs in a Tropical Climate, Department of Civil Engineering, University of Moratuwa, Moratuwa, Sri Lanka, 2010.
X. X. Zhanga, P. F. Wub B. Chena ., Relationship between vegetation greenness and urban heat island effect in Beijing City of China Key Lab of Soil & Water Conservation and Desertification Combating & Ministry of Education, College of Soil and Water Conservation, Beijing Forestry University, Beijing, 100083, 2010.
13. Francisco Arum'i-Noi~ and David O. Northrup ., A Field Validation of the Thermal Performance of a Passively Heated Building as Simulated by the DEROB System Numerical Simulation Laboratory, School of Architecture, The University of Texas, Austin, Texas (U.S.A.), 1979.
Soushi Kato, Yasushi Yamaguchi Estimation of storage heat flux in an urban area using ASTER data, Department of Earth and Environmental Sciences, Graduate School of Environmental Studies, Nagoya University, Furo-cho, Chikusaku,Nagoya, Aichi, 464-8601, Japan, 2007.
14. Francisco Arumi and Mo Hourmanesh, ., Energy Performance of Solar Walls: A Computer Analysis Numerical Simulation Laboratory, School of Architecture, The University of Texas, Austin, Texas (U.S.A.), 1977.
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15. S. Oxizidis , A.V. Dudek , A.M. Papadopoulos ., A computational method to assess the impact of urban climateon buildings using modeled climatic data Laboratory of Heat Transfer and Environmental Engineering, Department of Mechanical Engineering, Aristotle University of Thessaloniki, University Campus, Egnatia Street, 54124, PO Box 483, Thessaloniki, Greece Norwegian Institute for Air research, Kjeller, Norway, 2008. 16. D. Troutleau, J.P. Lhomme, B. Monteny, Sensible heat flux and radiometric surface temperature over sparse Sahelian vegetation( An experimental analysis of the kB-l parameter) CEMAGREF-ENGREF, Remote Sensing Laboratory, Maison de la T~l EdEtection, 500 rue J.F. Breton, 34093 Montpellier Cedex 5, France ORSTOM, Laboratoired'Hydrologie, BP 5045, 34032 Montpellier, France, 1997.
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Annual Transactions of IESL, pp. [127-132], 2012 © The Institution of Engineers, Sri Lanka
Simulation of Air Movement in a Cinnamon Chips Dryer using Computational Fluid Dynamics B.D.G.P. Nandadeva, A.D.U.S. Amarasinghe and P.G. Rathnasiri Abstract: Non uniformity of final moisture content of the product being dried is the main drawback of tray dryers. The difficulty in maintaining the uniform air velocity throughout the drying chamber had been identified as the main reason for this non uniform drying. A CFD model was developed to analyse the velocity and temperature profiles of a cinnamon chips dryer by using STAR CD. The modelled data for air velocities had been experimentally verified for velocity distribution within the drying chamber. The CFD analysis revealed the presence of non uniform air re-circulating zones at the inlet air duct and drying chamber, which results in non uniformity of air velocities. Previously reported variations of moisture level in dried cinnamon chips at different tray locations were compared with modelled velocity distributions of the present study. The results indicated that the variations in the moisture level of dried cinnamon chips were directly attributed to the non uniform air distributions at different tray locations Keywords:
1.
Computational Fluid Dynamics, CFD, Cinnamon, Drying, Simulation
Measuring the air velocity at various locations in a tray dryer is a tedious work and redesigning the dryer to achieve uniform air flow requires fabrication of several units. Computational Fluid Dynamics (CFD) is a powerful tool for predicting the flow characteristics and it can be effectively used to understand the flow behaviour in a tray dryer. Some of the examples for application of CFD in modelling the dryers to predict flow characteristics include; spray dryers [4], ovens [5], [6], [7], [8], [9].
Introduction
Cinnamon (Cinnamomum Zeylanicum or Cinnamomum verum) which is popularly known as “Kurundu” in Sri Lanka is widely used as a spice for many food items. Cinnamon chips are the rough bark which cannot be scraped off from thicker stems of the tree and widely used to produce cinnamon bark oil. Since the initial water content of cinnamon bark is high (typically 70%), it is dried prior to extraction of oil. Main disadvantages of the conventional drying had been identified as long processing times, dependency on climatic conditions, high labour cost and damages to product quality due to dust, fungus and insects. Chandra et al. (2011) fabricated a biomass driven batch type tray dryer to mitigate those drawbacks and it was capable of drying 4.8 kg of wet cinnamon chips within 3 hours [1]. The experimental results suggested that optimum drying temperature to obtain high quality cinnamon oil is 35 qC. However, achieving a uniform drying condition throughout the dryer had become the major challenge as product was over dried in some trays and under dried in some others.
In most of the cases, dryers had been modelled through CFD and then the experimental data were validated with CFD results. Amanlou and Zomorodian found good correlation between the experimental data and the CFD analysis with correlation coefficients of 99.9% and 86.5%, respectively for the temperature and velocity of drying air [10]. Commercial CFD packages had been used to analyse and modify the tray dryers which were used to dry various food items [10], [11], [12], [13]. Mathioulakis et al. carried out both experimental and CFD B.D.G.P Nandadeva, B. Sc. Eng. ( Morat uwa), Research student, Department o f Chemical & Process Engineering, University of Moratuwa. Eng. (Dr.) A.D.U.S. Amarasinghe, B. Sc. Eng. ( Moratuwa) , PhD (Cambridge) , MIE (Sri Lanka ), Head of the Dpt., Department of Chemical & Process Engineering, Uni versity of Moratuwa. Eng.(Dr.) P.G Rathnasiri, B.Sc. Eng. (Morat uwa), PhD (Norwegian University of Science and Technol ogy), Senior Lecturer, Department of Chemical & Process Engineering, University of Moratuwa.
Main reasons for the variation of final moisture content were identified as change in velocity, temperature and humidity of the air while passing through the trays. Experimental studies had revealed that drying rate is a strong function of air velocity [2] whereas baffles could reduce the variation of air flow [3]. 1
127
analysis and found a strong correlation between the drying rate and the air velocity [11]. By applying CFD to analyse seven different geometrical configurations, Amanlou and Zomorodian were able to obtain even distribution of air velocity and temperature throughout the dryer [10]. Margaris and Ghiaus were able to optimize the drying space and improve the quality of the dried product together with considerable reduction in energy consumption [13].
the trays. The hot air is passed through the drying chamber and leaves through the two outlet air vents. The first air vent is located at the top with an opening angle of 10q and the other one is opened with an angle of 15q as indicated in Figure 1.
The main focus of the present study was to simulate the velocity distribution of a tray dryer originally used to dry cinnamon chips by using STAR CD. The simulation results of velocity distribution was then compared with the experimentally found final moisture contents of cinnamon chips at different tray locations to examine the relationship of drying rate and the air velocity.
The volume available for the air flow in the drying chamber has a total length of 1 m, width of 0.53 m and total height of 0.53 m. Inlet velocity of air was measured using an anemometer (Dwyer, model 471 digital thermo anemometer) and the average velocity was calculated by taking the mean value of air velocity measured at five different locations. Further, an anemometer was used to measure the air velocity inside the drying chamber above each tray at a distance of 5, 10, 15 and 20 cm away from the wall. The locations of measuring air velocity near the wall are shown in Figure 1.
2.
2.2
Materials and Methods
2.1 Analyse the Cinnamon Chips Dryer A schematic diagram of the tray dryer used for drying cinnamon chips is depicted in Figure 1. The dryer consists of two main parts; drying chamber and combustion chamber. Hot air generated in the combustion chamber is blown through a pipe by a centrifugal blower (240V2A), in to the drying chamber. The eight trays in the dryer were made of iron grid so that the product is being dried by means of convective heat transfer occurring in both above and below
Basic Governing Equations for the Tray Dryer STAR-CD uses basic mass and momentum conservation equations (the ‘Navier-Stokes’ equations) for general incompressible and compressible fluid flows. ߲ߩ
μ
൫ǒ—൯ ൌ • ߲ ݐμš ୨ ୨ ߲ ߩ �ݐ ߲ ߲ݐ
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Figure 1 - Schematic Diagr2am of Cinnamon Chips Dryer
128
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The standard ݉ ൌ ߝ model is based on transport equations for turbulent kinetic energy (k) and its dissipation rate (ߝ). The transport equations for the turbulent kinetic energy are as follows [14]. Ǎ� ߲ ݉ ߲ ߲ ߩ݉ ߩ ݉ �ݐൌ ߲ݐ ߲ �ݐ ൰ ߲ ൬ߤ � ǔ୩ ݐ ൌ Ǎ� ݉ ݉� ൌ ߩߝ ʹ ߲ݐ ߲ݐ ൌ ൬Ǎ� � � ͵ � ݉൰ ߲ݐ ߲ݐ
where,
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Depending on the Re number, standard kEpsilon/High Reynolds number model was selected as the turbulent model for the present study.
�
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standard (Amanlou and Zomorodian, 2010).
Ǎ� ݉ே ͵
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2.3 Numerical Simulation x CFD analysis was performed on a simplified model which simulates the geometrical configuration presented in Figure 1, using the commercial CFD code STAR CD v.3.2, based on finite volume method. The computational mesh is an unstructured three-dimensional mesh of 22,225 tetrahedral cells.
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129
The air flow pattern of the empty dryer was determined by assuming incompressible,
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Newtonian and steady flow behaviour. Boundary conditions: o Mean inlet air velocity was found to be -1
20.5 ms and the direction of air flow
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was normal to the inlet. Turbulent intensity (I) and turbulent length scale (L) at the inlet were calculated in alternate to calculating
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130
x
x
x
x
of the pipe at the inlet was taken as turbulent length scale. o At the outlet, gauge pressure was assumed to be zero. The other required information at the outlet was extrapolated by STAR CD from the interior section of the drying chamber. Since the dryer is symmetrical along the width, a longitudinal view of the dryer was taken as the model where the cutting plane was defined as a symmetry plane to reduce the number of cells. It was assumed that the trays were fully filled with the product and the volume of voids had been neglected. Single precision solver was used and the model was allowed to be solved in steady state, SIMPLE solution algorithm. Velocity and temperature profiles of the model were obtained and the results were compared with the experimental data.
4.
Results and Discussion
The simulation results for the velocity distribution throughout the drying chamber were in good agreement with the experimental data. Since the velocity was measured at 40 different locations using the anemometer the model can be considered as a representation of the real system. Simulation results of velocity and temperature profile of the empty dryer over the symmetrical plane is shown in Figure – 2. Even though, Figure 2(a) shows a maximum velocity of 21.78 ms-1, the actual velocity inside the drying chamber was found to be lesser than 2 ms-1 and hence a new velocity range had been defined by taking maximum velocity as 1.5 ms-1 (Figure - 2(b)) to obtain comparable results. The temperature profile indicates that there is no significant difference in temperature throughout the dryer (Figure 2(d)). When the convective heat and mass transfer during drying is neglected, only possible heat transfer is the heat loss to the environment and the change in temperature can be neglected once
Figure 2 - Simulation Results (a) - Velocity Profile, (b) - Scaled Velocity Profile, (c) – Velocity Magnitude, (d) - Temperature Distribution throughout the Dryer.
131
the flow reaches the steady state. With reference to previous studies, it can be concluded that the drying chamber is quasiisothermal where re-circulating velocity is resulted from thermal homogenization of the flow [10], [11], [12], [13]. An enlarged arrangement of the simulation results of the velocity at the inlet area is shown in Figures 3 and 4. Figure 3 indicates the occurrence of reverse flow in both of the inlet air duct and the drying chamber. A zone of air recirculation is observed in Figure 4. As a result of this air recirculation, the upcoming inflow is forced towards the bottom side of the dryer. Therefore when air leaves the dryer from the air vents, majority of fresh inlet air will not be passed through the upper trays as shown in Figure 2(b). If the dryer has to be modified for maximum operating conditions, reverses flow and the re-circulating zones have to be minimized and uniform flow of air throughout the drying chamber should be enabled.
Figure 3 - Reverse Flow at the Inlet Air Duct
Figure 4 - Air Re-circulating Zones at the Inlet Air Duct
Hence, it can be concluded that the final moisture content of the cinnamon chips depend not only on the location of the tray, but also with the distance from the wall within the same tray as indicated in Figure 5.
Figure 5 – Contours of Velocity Magnitude along the Width A previous work was reported on drying of cinnamon chips using the same dryer [1]. The results of this work indicated that the final moisture content was non uniform. These results were used to analyse the relationship between moisture content of the dried product and the air velocity below and above a tray. Figure 6(b) gives the experimental results of the final moisture content of the cinnamon chips at the symmetry plane in each tray, whereas Figure 6(a) visualizes the simulation results of air velocities inside the drying chamber along the axis of symmetry. The results of experimental and CFD analysis indicates that the lowest drying rate and lowest velocity can be observed at the tray number 1B which is in the top right side of the dryer. Similarly both indicate that the maximum air velocity and the maximum drying rate were attributed to the tray number 3A. In the previous studies on various products, the drying rate was found to be a strong function of air velocity [11]. The results of the present study confirm that the drying rate of cinnamon chips also attributed to the air velocities below and above the trays.
5.
The contours of velocity magnitudes (Figure 2(c)) indicate that there is a considerable variation of velocity magnitude along the width of the dryer where the velocity increases at the middle plane of the dryer and gradually reduce near the wall. This may be due to the fact that when air enters the system through small diameter pipe, it will not spread properly along the width of the air duct. Further, the velocity profile indicated a reverse flow near the wall.
Conclusions
Experimental results for velocity distribution being in agreement with the CFD results suggest that CFD can be effectively used to describe flow patterns in various equipments. As the velocity profiles indicate the areas which lack the spatial homogeneity, it can be used to determine the most optimum geometrical configuration which would minimize the variations of air flow at the design stage.
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Figure 6(a) – Velocity Profile at the Middle Plane 6(b) – Experimental Results of the Final Moisture Content of the Dried Cinnamon Chips The air re-circulating zones in the inlet air duct is the main cause of non-uniformity of air velocity as the air tends to flow downwards before it enters the drying chamber. Hence if modifications are to be done, the geometry of the inlet air duct has to be modified to enable uniform air flow to the drying chamber. The air velocity of the current geometry varies along the cross sectional and longitudinal directions resulting in severe variation of final moisture content of the product in different trays as well as within the same tray.
6.
7.
8.
Acknowledgement This MSc research project was supported by University of Moratuwa Senate Research Grant Number SRC/LT/2011/11 “.
References 1.
2. 3.
4.
5.
Chandra, K. A., Walpolage, S. and Amarasinghe, A. D. U. S., "Performance analysis of a dryer design for drying cinnamon chips", Annual Transactions of The Institution of Engineers, Sri Lanka (IESL) 1(B): pp.362-368, 2011. Mulet, A., Berna, A., Borras, M. and Pinaga, F., "Effect of air flow rate on carrot drying", Drying Technology 5(2): pp.245-258, 1987. Adams, R. L. and Thompson, J. F., " Improving drying uniformity in concurrent flow tunnel dehydrators", Transactions of ASAE 28(3): pp.890-892, 1985. Roustapour, O. R., Hosseinalipour, M., Ghobadian, B., Mohaghegh, F. and Azad, N. M., "A proposed numerical-experimental method for drying kinetics in a spray dryer", Journal of Food Engineering 90(1): pp.20-26, 2009. Therdthai, N., Zhou, W. and Adamczak, T., "Two-dimensional cfd modelling and simulation
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10.
11.
12.
13.
14.
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of an industrial continuous bread baking oven." Journal of Food Engineering 60(2): pp.211-217, 2003. Therdthai, N., Zhou, W. and Adamczak, T., "Three-dimensional cfd modelling and simulation of the temperature profiles and airflow patterns during a continuous industrial baking process", Journal of Food Engineering 65(4): pp.599-608, 2004. Wong, S.-Y., Zhou, W. and Hua, J., "Cfd modeling of an industrial continuous breadbaking process involving u-movement", Journal of Food Engineering 78(3): pp.888-896, 2007. Mondal, A. and Datta, A. K., "Two-dimensional cfd modeling and simulation of crustless bread baking process", Journal of Food Engineering 99(2): pp.166-174, 2010. Smolka, J., Nowak, A. J. and Rybarz, D., "Improved 3-d temperature uniformity in a laboratory drying oven based on experimentally validated cfd computations", Journal of Food Engineering 97(3): pp.373-383, 2010. Amanlou, Y. and Zomorodian, A., "Applying cfd for designing a new fruit cabinet dryer", Journal of Food Engineering 101(1): pp.8-15, 2010. Mathioulakis, E., Karathanos, V. T. and Belessiotis, V. G., "Simulation of air movement in a dryer by computational fluid dynamics: Application for the drying of fruits", Journal of Food Engineering 36(2): pp.183-200, 1983. Mirade, P. S., "Prediction of the air velocity field in modern meat dryers using unsteady computational fluid dynamics (cfd) models", Journal of Food Engineering 60(1): pp.41-48, 2003. Margaris, D. P. and Ghiaus, A.G., "Dried product quality improvement by air flow manipulation in tray dryers", Journal of Food Engineering 75(4): pp.542-550, 2006. STAR-CD Version 3.20 Methodology Manual, Chapter 13, CD-adapco, UK, 2004.
Annual Transactions of IESL, pp. [133-139], 2012 © The Institution of Engineers, Sri Lanka
Seismic Demand Prediction of Eccentrically Loaded Steel Bridge Piers Subjected to Moderate Earthquakes K.A.S. Susantha and H.H.M. Gunasoma Abstract: This paper presents numerical results of displacement and stress demands of eccentrically loaded steel bridge piers subjected to moderate ground accelerations along in-plane transverse direction. The columns considered are of box sections having sixteen longitudinal stiffeners. The time series analyses were conducted to predict maximum transverse deflection and stresses at plates near the column base. The analyses involved linear elastic material behaviour. The level of eccentricity and the magnitude of axial load are considered to be the main variables. Level of eccentricity is represented by the ratio of eccentric distance to the height of the column (e/h ratio) while axial load is represented by the ratio of axial load to squash load (P/Py). Two columns having almost equal slenderness but different geometry were designed for the analysis according to the Japanese Design Specification for highway bridge piers. Twenty cases were considered for one column which includes five eccentricity levels where each level has four axial load ratios. The results are presented for two past earthquake records. The effects of eccentricities and axial load ratios were found to be different when distinct earthquake records are used. In most of the cases, the maximum stress decreases with decreasing axial load. The results clearly showed that the peak ground acceleration is not the sole influencing factor of seismic demands. Keywords: Eccentrically loaded columns, Seismic demand, Steel columns, Dynamic analysis, Finite element analysis
1.
Introduction
Concentrically loaded columns are the most commonly found bridge pier type in all over the world. Meanwhile, the use of eccentrically loaded columns is found to be very useful in situations where serious space restrictions are encountered, especially in urban transportation networks. There are a large number of eccentrically loaded columns built in elevated highway systems in developed countries. The technique is equally important in rapidly developing transportation infrastructures in countries like Sri Lanka. The columns under eccentric axial loads will have extra stresses at eccentric side due to the additional moments when in-plane transverse loadings are considered. When out-of-plane loadings are considered the stress condition becomes more complex as torsional moments come into action. The most serious transverse loading occurs due to the earthquake induced ground vibrations.
Figure 1 - Example of Eccentrically Loaded Bridge Pier in Highway System
2.
Literature Review
There are number of studies conducted on static pushover and lateral cyclic analysis of eccentrically loaded steel piers. In a study by Gao et al. [4] ultimate strength and ductility correlation between centrally loaded and eccentrically loaded steel columns subjected to
This study deals with dynamic behaviour of eccentrically loaded steel columns subjected to base acceleration in longitudinal (in-plane) direction. Several past studies are available on seismic demand evaluation of concentrically loaded steel/concrete/steel-concrete composite columns (e.g., Elnashai and Elghazouli [1], Ge et al. [2], Madas and Elnashai [3]).
Eng. (Dr.) K. A. S. Susantha,, C. Eng., MIE(Sri Lanka), B.Sc. Eng. (Peradeniya), M.Eng. (AIT), D. Eng. (Nagoya), Senior Lecturer, Department of Engineering Mathematics, University of Peradeniya, Sri Lanka. Eng. H.H.M. Gunasoma, B.Sc. Eng. (Hons) (Peradeniya), AMIE(Sri Lanka), Civil Engineer, Central Engineering Consultancy Bureau, Colombo 07.
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cyclic transverse loads at column top were investigated using finite element analysis involving material and geometrical nonlinearity.
observed that the columns with well distributed longitudinal reinforcement laterally supported by closely spaced transverse reinforcement showed extreme ductile behaviour.
Hsu and Liang [5] conducted an experime ntal investigation to find out the performance of hollow composite members subjected to eccentric lateral loading. The effects of combined bending and torsion on member capacities and ductility were found to be significantly reduced when subjected to torsion. The magnitudes of torsion and section aspect ratios were studied to evaluate the torsional effects on the member performances. It was revealed that the strength ratios of concrete and steel need to be adequately proportioned to maximize the ductility of members.
3.
In elastic dynamic analysis of eccentrically loaded steel bridge piers modelled as single degree of freedom system was conducted by Lie et al. [6]. The in-plane horizontal capacity and hysteretic behaviour of eccentrically loaded piers become unsymmetrical due to extra bending moment. In this study, the yield load and yield displacement in the positive and negative directions are defined as shown in Figure 2. The yield displacement and yield load in the positive direction are smaller than those in the negative direction. Their analyses showed that the bridge piers with intermediate eccentricity under Level 2 accelerograms are susceptible to highest maximum displacements.
3.2 Design of Steel Columns The columns are designed according to the seismic design specifications of Japanese Road Association (JRA 2002) [8]. The columns are of stiffened steel box sections. The parameters governing the ductility performance of stiffened columns are; flange plate slenderness, RR, stiffener plate slenderness, RF, slenderness ratio, λ, and rigidity ratio, γl/γ*. The equations for the above parameters are;
Dynamic Columns
Analysis
of
Steel
3.1 General Time series analyses of two stiffened steel columns are carried out to check the displacement demands and stresses induced due to dynamic loads at the vicinity of the column base. Columns are modelled using finite element method. Static axial load at column top and lateral dynamic load in terms of ground accelerations at the base are applied to the model.
RR
b y 12(1 2 ) t E 2k R
(1)
RF
b y 12(1 2) 2kF t E
(2)
where b=plate width, t=plate thickness, y=yield stress, E=Young’s modulus, =Poisson’s ratio, kR and kF=buckling coefficients of simply supported plate and stiffened plate, respectively. Parameter l is given by; 12(1 2 )I l (3) l bt 3 where, Il is the moment of inertia of the Tsection consisting of a longitudinal stiffener and the effective width of the plate to which it is attached. The expression for the optimum rigidity of stiffeners, l*, is given as follows: ( 2 1) 2 l * 4 2 n(1 n l ) for 0 (4) n 1 * l [2n 2 (1 n l ) 1]2 1 for 0 (5) n where, n=number of sub panels in a stiffened plate, l=area ratio of a longitudinal stiffener to plate. (=a/b)=aspect ratio, a being the spacing
(a) (b) Figure 2 - Yield load and Yield Displacement; (a) Positive Direction, (b) Negative Direction In a work by Saatcioglu et al. [7], the characteristics of confined concrete columns under two levels of end eccentricities were investigated by testing twelve column specimens. The effects of parameters such as arrangement, spacing, and volumetric ratio of confinement reinforcement were checked. They
2
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between diaphragms. Critical aspect ratio, 0 is given by
0 4 1 n l
designed to withstand the axial load given by 0.15 times its yield axial load [10]. Under concentric axial load the section will undergo uniform strain resulting in uniform stress distribution across the section. In contrast, when axial load has some eccentricity the stress distribution is not uniform and the maximum stress, max, occurs in extreme fibres at one end of the section, and is given by,
(6)
Detailed information on the above parameters is available in Chen and Duan [9]. In addition, slenderness parameter , which has a great effect on overall instability of a column, is defined as follows: 2h 1 y r E where, h=column height gyration of cross section.
(7) and r=radius
max
of
for
Two columns, namely SEC-1000 and SEC-1250, having a value of = 0.3 were designed keeping the values of other parameters within the ranges given in Table 1. The yield strength of steel was taken as 355 MPa, Young’s modulus as 2.05 x 105 N/mm2, and Poisson’s ratio as 0.3. The dimensions and values of structural parameters of two columns are listed in Table 2. The general cross section of columns is shown in Figure 3. Table 2 - Dimension Parameters of Columns Section No h / (mm) b / (mm) bs /(mm) t /(mm) ts /(mm) n RR RF γl/γ*
SEC-1000 4250 1000 130 10 14 5 0.438 0.303 2.117 0.307
and
(8)
where, A is the cross sectional area, P is the axial load and Py is the yield axial load. Other parameters are as explained earlier. For a given eccentricity and value of max, the value of P can be calculated and for higher eccentricities the value of P will be smaller. Therefore, it will be unrealistic to follow the same concept practiced in concentrically loaded columns to decide the value of P in eccentrically loaded columns. As such, when stress at b/4 distance away from the neutral axis reaches 0.15 times the yield strength, the corresponding P is taken to be the design axial load for that eccentricity. The values of P calculated according to the above concept for five values of eccentricities are given in Table 3. The eccentric distance is usually in the range of 0.1h to 0.5h in practical designs of eccentrically loaded columns in countries where severe earthquakes are expected [4]. Even though the maximum limit of eccentric distance higher than 0.5h is feasible in the case of moderate earthquakes, 0.5h limit was chosen in this study considering economical aspects of the design. The interval of 0.1h is considered to be adequate to monitor the trend of performance.
For the best seismic resisting performance in terms of ductility, JRA 2002 [8] recommends ranges of values for RR, RF and γl/γ* given in Table. 1. The value of parameter γl/γ* should be greater than one. A value of around 3.0 has been found to offer the best ductility performance. Table 1 - Recommended Values Parameters RR, RF and γl/γ* Parameter Range RR 0.2-0.5 RF 0.3-0.5 γl/γ* >1
P Peb A 2I
Table 3 - Variation of P/Py with Eccentricity
Structural
SEC-1250 5350 1250 157 12 14 5 0.456 0.322 2.048 0.300
e/h
P/Py
0.1 0.2 0.3 0.4 0.5
0.084 0.058 0.044 0.036 0.030
b
ts t
b bs
3.3 Axial Load and Eccentricity In seismic design of steel piers, columns subjected to concentric axial loads are usually
Figure 3 - Details of the Cross Section 3
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3.4 Finite Element Model Two columns were modelled using finite element method with the help of SAP2000 program [11]. The basic shape of the mesh is shown in Figure 4. The lower part of the model consists of shell elements while the upper part is modelled using frame elements. This kind of combined usage of shell and frame elements is very economical when dynamic time series analysis is conducted using sophisticated material models involving large deformation finite element formulations. However, the present analyses are linear elastic, hence computational advantage is not significant. Several analyses were carried out to check the mesh sensitivity of shell elements. With the use of the optimum shell element mesh the portion of column (h1) where frame elements are assigned was decided using another set of analyses.
h1
earthquake and 0-component of Cape Mendocino 1992 earthquake, were selected for this study. The peak ground acceleration of Georgia 1991 and Cape Mendocino 1992 earthquakes are 0.117g and 0.229g, respectively, where g is the acceleration of gravity. They can be considered as moderate earthquakes. The analyses were repeated for several past earthquake data but only these two representative cases are presented in this paper.
4.
Results and Discussion
The outcome of the time series analyses of eighty (80) cases (i.e., two models subjected to the above two earthquakes under four axial loads where each axial load contains five eccentricities) are summarized in this section. A representative case of displacement versus time for the model SEC-1000 with e/h=0.1 and P/Py of 0.084 is shown in Figure 5. 4.1 Maximum Lateral Displacement The maximum lateral displacement at column top obtained for all the cases under Georgia-X and Cape Mendocino earthquakes are shown in Figures 6 and 7, respectively. In each figure, two curves are shown for models SEC-1000 and SEC-1250. The maximum displacement of SEC1250 is slightly less than that of SEC-1000 for all the axial load ratios and eccentricities under Georgia earthquake. When Cape Mendocino earthquake is considered, in some cases, SEC1250 gives higher maximum displacement than that of SEC-1000. Nevertheless, the difference between maximum displacements obtained from the two models is very small (i.e, around 1.0 mm) for all the cases. The effect of e/h on displacement demand varies with the change of axial load. It is observed from Figures 6 and 7 that when axial load increases the maximum displacement demand increases under Georgia earthquake but it is the opposite in the case of Cape Mendocino earthquake. An interesting
Frame elements
h
Shell elements
Figure 4 - Finite Element Mesh 3.4 Ground Acceleration Data A large number of past ground acceleration records are freely available in Pacific Earthquake Engineering Research Centre (PEER) data base [12]. Two earthquake records, namely, X-component of Georgia 1991
Figure 5 - Displacement versus Time for SEC-1000 Column with e/h=0.1 and P/Py=0.084
4
136
influencing the displacement demand of the columns. In fact, frequency content of the selected ground accelerations should be studied together with PGA to understand the reason for different behaviour under different earthquake records.
observation is that among all the cases under Georgia earthquake, the case of P/Py = 0.084 and e/h = 0.5 gives the maximum value. On contrary, P/Py = 0.036 and e/h = 0.1 gives the maximum value under Cape Mendocino earthquake. This implies that peak ground acceleration (PGA) of the input ground motion is not the only factor
Figure 6 - Maximum Displacement versus e/h Ratio for Different Axial Load Ratios-Georgia Earthquake
Figure 7 - Maximum Displacement versus e/h Ratio for Different Axial Load Ratios-Cape Mendocino Earthquake
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4.2
Maximum Stresses
However, the effective working stress would be higher than the 355 MPa because stresses due to static loads such as dead weights and live loads are not included in the results of time series analysis. The effects of e/h ratio on the maximum stresses seem to be not significant when comparatively low axial load ratios are maintained. This is evident from the case of P/Py of 0.036.
The maximum stresses induced in steel plates near the bottom of the column are monitored for each case and plotted as shown in Figures 8 for Georgia earthquake. It is observed that the maximum stress of model SEC-1000 occurs at e/h ratio of 0.5 and axial load ratio of 0.084. The value is about 320 MPa which is less than the yield strength of the steel (y=355 MPa).
Figure 8 - Maximum Stress versus e/h Ratio for Different Axial Load Ratios- Georgia Earthquake
Figure 9 - Maximum Stress versus e/h Ratio for Different Axial Load Ratios- Cape Mendocino Earthquake 6
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and Structural Dynamics, Vol. 22, pp. 315-345, 1993.
The stresses recorded using Cape Mendocino earthquake are shown in Figure 9. The difference between the maximum stress at e/h of 0.1 and e/h of 0.5 for the model SEC-1250 is around 150 MPa in the case of P/Py of 0.036. This means that, unlike the results of Georgia earthquake, when comparatively low axial loads are considered, the effect of eccentricity becomes significant. It is evident from the results that the trend of the maximum stress with increasing axial loads differs when different e/h ratios are considered. For example, the maximum stress increases with increasing axial loads with e/h ratio of 0.5 but decreases with e/h ratio of 0.1.
5.
Ge, H. B., Susantha, K. A. S., Satake, Y., & Usami, T., “Seismic demand prediction of concrete-filled steel box columns”, Engineering Structures, Vol. 25, pp. 337-345, 2003.
3.
Madas, P, & Elnashai, A. S., “A new passive confinement model for the analysis of concrete structures subjected to cyclic and transient dynamic loading”, Earthquake Engineering and Structural Dynamics, Vol. 21, pp. 409-431, 1992.
4.
Gao, S. Usami, T., & Ge, H. B., “Eccentrically loaded steel columns under cyclic in plane loading”, J. of Structural Engineering, Vol. 126, No. 8, pp. 964-972, August 2000.
5.
Hsu, H. L., & Liang, L. L., “Performance of hollow composite members subjected to cyclic eccentric loading”, Earthquake Engineering and Structural Dynamics, Vol. 32, pp. 443-461, 2003.
6.
Lie, Q, Usami, T., & Kasai, A., “Inelastic seismic response analysis of eccentrically loaded steel bridge piers”, J. of Structural Mechanics and Earthquake Engineering, JSCE, No 654/I-52, 2000.
7.
Saatcioglu, M., Salamat, H., & Razvi, S., “Confined columns under eccentric loading”, J. of Structural Engineering, Vol. 121, No. 11, 1995.
8.
Japan Road Association (JRA 2002). Design specifications for highway bridges, Part V, Seismic design, 2002.
9.
Chen, W. F., & Duan, L., Bridge Engineering Handbook, CRC Press, Boca Raton, FL., 2000.
10.
Susantha, K.A.S., Aoki, T., & Kumano. T., “Strength and ductility evaluation of steel bridge piers with linearly tapered plates.” J. of constructional steel research, 62, pp 906-916, 2005.
11.
SAP2000 Advanced 10.1, Structural Analysis Program, Computers and Structures Inc. Berkeley, CA.
12.
Pacific Earthquake Engineering Research Centre (PEER) Database, http://peer. berkeley.edu/nga/flatfiles.html.
Conclusions
Dynamic time series analyses were conducted using several past earthquake acceleration records to examine the effect of eccentricity on the dynamic behaviour of eccentrically loaded steel bridge piers under different axial loads. The maximum displacement at column top and the maximum stress at a critical location of column were discussed for two earthquake records having peak ground accelerations of 0.119g and 0.229g. The performance of columns varies with different eccentricities and axial load ratios. When Georgia earthquake is concerned, the maximum displacement occurs with highest axial load and highest eccentricity but in the case of Cape Mendocino earthquake it was with the lowest axial load and lowest eccentricity. Hence, the trend observed under one earthquake record could not be noticed with the other. Thus, there was no consistent correlation between the peak ground acceleration and the results (i.e., displacement and stress demands). It was clear that the combined effects of peak ground acceleration, frequency content and the duration of selected earthquake records have affected the results. Therefore, the finding of these analyses cannot be generalized for all ground acceleration records but the procedure and observations of this study will be useful in future studies.
References 1.
2.
Elnashai, A. S. & Elghazouli, A. Y., “Performance of composite steel/concrete members under earthquake loading. Part I: Analytical Model”, Earthquake Engineering
7
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Annual Transactions of IESL, pp. [140-145], 2012 © The Institution of Engineers, Sri Lanka
Characterization of Locally Available Montmorillonite Clay using FTIR Technique S.U. Adikary and D.D. Wanasinghe Abstract: Montmorillonite (MMT) is a layered silicate clay which belongs to the smectite clay group with a wide range of applications in medicine, polymer industry, ceramic industry and nano materials. This research is focused on the use of Fourier Transform Infrared Spectroscopy (FTIR) technique to identify and characterize Montmorillonite clay deposits available in the dry zone of Sri Lanka. Apart from identification, FTIR can be used to discover the family of minerals to which the specimen belongs, the nature of isomorphic substituent and the distinction of molecular water from constitutional hydroxyl. Clay samples obtained from several locations within the dry zone of Sri Lanka were purified, treated and subjected to FTIR, X-ray Diffraction (XRD) and Differential Thermal Analysis (DTA). To further strengthen the findings, specimens of commercially available MMT and Bentonite were subjected to the same tests. Peaks of the resultant spectrum were analyzed and compared with published literature. Results revealed that the specimens subjected to the tests contained MMT with Kaolinite. In-depth study of absorbance level of each specimen was useful in identifying the exchangeable cations present in MMT. Further study of the spectrum could pave the way for quantitative analysis of these clay minerals. Keywords:
1.
Montmorillonite, FTIR, Clay minerals, Smectite clay
(XRD) and other methods used to investigate clays and clay minerals. It is an economical, rapid and common technique because a spectrum can be obtained in a few minutes and the instruments are sufficiently inexpensive (Madejova et al., [9]). A FTIR spectrum can serve as a fingerprint for mineral identification, but it can also give unique information about the mineral structure, including the family of minerals to which the specimen belongs and the degree of regularity within the structure, the nature of isomorphic substituents, the distinction of molecular water from constitutional hydroxyl, and the presence of both crystalline and non-crystalline impurities (Madejova, [4]).
Introduction
Montmorillonite is the well-known smectites which is most commonly used in the preparation of polymer nanocomposites. Raw formula of MMT is (Na,Ca)0.3(Al,Mg)2Si4O10(OH)2,nH2O. MMT has the wider acceptability for use in polymer nanocomposites because of its ease availability, well known intercalation/ exfoliation chemistry, high surface area and high surface reactivity. Polymer-clay composites synthesized with MMT are known to have superior mechanical, thermal and gas-barrier properties (Olad, [5]). Recently there has been a growing interest for the development of polymer-clay nano composites due to their improved properties compared to the conventional polymer composites. Polymer clay nano composites received intense attention because of their unique properties which can never be attained by micro size fillers or by other nano fillers. The enhancement of properties by the addition of Montmorillonite clay, without sacrificing the pure polymer processability, mechanical properties and light weight, make this clay more and more important in modern polymer industry (www.sigmaaldrich.com, [10]). Fourier Transform Infrared Spectroscopy (FTIR) has a long and successful history as an analytical technique. It is mainly a complementary method to X-ray diffraction
Published literature has shown the presence of MMT in clay deposits located mainly in the dry zone of Sri Lanka (Herath, [3]). The identification of MMT from deposits has been conducted extensively using XRD analysis. The growing interest in MMT in the nano engineering applications has given the need of a rapid and user-friendly identification and Eng. (Dr.) S.U. Adikary, B.Sc. Eng (Hons) (Moratuwa), M.Sc., PhD. (Hong Kong), AMIE (Sri Lanka), Senior Lecturer, Department of Materials Science and Engineering, University of Moratuwa. Eng. D.D. Wanasinghe, B.Sc. Eng (Hons) (Moratuwa), AMIE (Sri Lanka), Research Assistant, Department of Materials Science and Engineering, University of Moratuwa.
1
140
characterization technique which can be used repeatedly. FTIR technique has the ability to fulfill these requirements adequately.
period of one hour. Resultant powder is then subjected to FTIR, XRD and DTA. FTIR tests were carried out by using Bruker alpha-T instrument employing KBr pellet method for frequency range of 4000-500 cm-1. Specimens were subjected to XRD using Siemens D5000 X-ray diffractometer to ensure the presence of MMT and to verify the results of FTIR. Specimens were first spread on a flat surface in a desiccator and ethylene glycol was added to the bottom of the desiccators. The entire desiccator was then put into the oven and heated to 60 0C and kept at that temperature for one hour. Then it was kept for 24 hours before being subjected to XRD analysis. DTA and TGA test were done by Differential Thermal Analyzer, Rigaku Thermoflex TG 8110, by heating the specimens from room temperature to 9900C.
Therefore this research was focused on the use of FTIR to identify and characterize MMT from locally available clay deposits which are known to be rich in MMT.
2.
Methodology
Studies done previously revealed MMT is abundant in the dry zone of Sri Lanka (Herath, [3]). Therefore, the selection of sites to obtain specimens was done in that region. Clay samples were collected from four sites located in Anuradhapura region. Exact locations of these sites are as follows, Clay 1 - Kalathirappane Tank Clay 2 - Galkulama Tank Clay 3 - Illanthagahawewa Tank Clay 4 - Pallankulama Tank Collection of samples was done at a depth of 3 ft from the surface. Collected samples were then wet sieved from 53 μm to remove any organic and coarse particles present in clay. Then, each specimen were dried in the oven at 1200C, ground using mortar and pestle to make them powder again and sieved again from 53 μm sieve. In order to remove organic materials, the specimens were heated up to 3000C for a
3.
Results and Discussion
Resultant FTIR spectrums for specimens tested are given in Figure 1. In addition to the four specimens, MMT, Bentonite (BT) and Kaolinite were tested using the FTIR technique, since Kaolinite is found in almost all the clay deposits in Sri Lanka. The FTIR spectrums reveal a vast similarity between the clays analyzed and the commercial MMT and BT. Table 1 summarizes the absorption bands found in the spectrum.
Figure 1- FTIR Spectrum of Different Clay Specimen
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Absorption bands that are common to tested specimens are as follows,
MMT has different phases of SiO 2 (Madejova, et al. [9]).
1 - OH stretching of structural hydroxyl groups 2 - OH stretching of structural hydroxyl groups 3 - OH stretching of water 5 - OH deformation of water 7 - Si–O stretching of cristobalite 8 - Si–O stretching 10 - AlAlOH deformation 11 - Si–O stretching of quartz and silica 14 - Coupled Al–O and Si–O, out-of-plane 15 - Al–O–Si deformation
Band 13 is again present in all the specimens tested except in the commercial MMT and BT. This band is a result of perpendicular vibration of Si-O present in kaolinite, indicating again the presence of kaolinite in specimens (Madejova, et. al. [9]). Most important bands needed for the identification of MMT in the tested range are 2, 3, 8, 10 and 15, which are all present in tested specimens (Madejova, et al. [9]). Presence of other bands reveals the impurities and/or other minerals that are present in these specimens. The splitting of the first band indicates the presence of more than one type of hydroxyl bonds, due to their different absorption frequencies. This in turn shows the presence of more than one clay fraction in the specimen (Madejova, [4]). The exact absorption frequency reveals the presence of MMT and kaolinite. Furthermore these spectrums can be used to identify the different phases of SiO 2 present in the mineral.
The presence of band 1 can be seen for all the tested specimens except in MMT and bentonite. Comparison with values from literature indicates that this band is a result of presence of kaolinte in the specimen. The deposits used in this study are known to be a mixture of kaolinite and MMT. Band 7 indicates the presence of cristobalite and its stretching due to the absorption of infrared radiation indicating that the commercial grade of
Table 1 - Absorption Bands in the FTIR Spectrum Absorption Band
Clay 1
Clay 2
Clay 3
Clay 4
MMT
Bentonite
1
3698
3697
3698
3698
2
3624
3622
3622
3623
3626
3626
3
3437
3442
3443
3446
3450
3450
3755
4 1635
6
1398
1634
1634
7 1037
1035
1036
1633
1637
1636
1101
1067
1075
1037
1031
1033
9
1633
1093
1010
10
915
915
915
916
918
918
11
790
787
788
783
797
795
12 13
3451 1851
5
8
Kaolinite
805 729
694
695
14
647
15
537
694
536
142
696 646
620
538
529
546
568
Van Olphaen et a!. (7(; Cintron Alvarado et a!. (8[). Table 2 summarizes all the interplaner spacing values (d values) that are present in the specirrens and d values of MMT fromliterature.
The finding; in the FTIR analysis are corrq> atible with the XRD analysis. The XRD pattern shown in Figure 2 shows the presence of both MMT and kaolinite. Peaks that are characteristics of MMT are 13.6 A, 4.47 A, 3.13 A, and 2.56 A (Peter, (6(; MMT
M
·j• 1ro >
°
._
Q
Cia 4
=n
·• '" > c
''
""
=
·• ... > c
"'
... 0
·•
>
c
11S:Z
M
- ""
·• > c
...
Q
=
M
... .>
0
, ..
10
2 Theta
M· Monnnorillonile K· Kaolil\ite
Q·Quartz
P- l')'rophylli1e
Fig2u-e XRD Patterns ofDiffe entClay Specimen Tested
143
The presence of other peaks is due to the inclusion of kaolinite (4.478 Å, 3.847 Å, 3.745 Å, 3.376 Å and 3.155 Å), quartz (3.342 Å, 4.257 Å and 2.457 Å) and other clay types which belong to the smectite group. The intensity of each peak in XRD analysis is proportional to the amount present in each mineral and the intensities of other peaks change when the intensity of the main peak varies. Due to this reason, some peaks may not be visible and difficult to detect in the XRD analysis.
As shown in Figure 3, DTA and TGA curves were used to analyze and confirm the findings of FTIR. The resultant peaks and calculated weight loss values are given in Table 3. The first peak associated with DTA is as a result of evaporation of physically bonded water in the clay mineral and in the TGA graph the weight loss will differ depending on the amount of water present in each clay specimen. The endothermic peak in the range of 525-575 0C is due to the loss of hydroxyls in kaolinite (Bergaya, et al. [1]). Endothermic peaks in the range of 650-700 0C are as a result of hydroxyl of MMT. This reaction will cause the crystal structure of MMT to disintegrate as it removes the hydroxyl from it.
Table 2 - d Values of XRD Patterns of specimen Clay Type
d Values of XRD Peaks (Å)
MMT
13.6, 4.47, 3.13, 2.56
Clay 1
13.48, 4.4394, 3.1921, 2.5476
Clay 2
4.2034, 3.7642, 3.1414, 2.5476
Clay 3
13.48, 4.4394, 3.1921, 3.4694
Clay 4
According to the source of the MMT specimens, the exchangeable cation can vary which will have an influence on the removal of hydroxyl ion. If the specimen includes a large amount of kaolinite, peaks created by MMT will not appear as it will consume all the hydroxyl present in the mineral (Fajnor, et al. [2]).
4.4394, 3.8372, 3.3243, 3.1921
5 Figure 3 - DTA and TGA Graphs of Clay Specimen
144
Therefore, it is difficult to assess the presence of one mineral by using DTA and TGA data alone. Exothermic peaks that occur due the presence of MMT and quartz will be present after 1000 0C. Due to the limitations of the instrument used in this experiment the maximum temperature was limited to 9900C. However, the data obtained from this test also confirm the presence of MMT. Table 3 - DTA and TGA Peaks of Tested Specimen (Note: Endo- Endothermic reaction, Exo- Exothermic reaction) DTA TGA Clay Peak Temperature Weight Type type (0C) loss % Endo 120 11.99 Endo 160 BT Endo 700 3.52 Exo 920 Endo 90 7.12 Clay 1 Endo 508 6.00 Exo 880 Endo 100 1.06 Clay 2 Endo 504 5.39 Exo 886 Endo 108 7.69 Clay 3 Endo 516 5.55 Exo 880 Endo 92 4.68 Clay 4 Endo 508 3.69 Exo 890 Endo 120 10.99 MMT Endo 680 3.90
4.
Conclusions
Specimens tested using FTIR shows the presence of MMT while exposing the presence of kaolinite and other impurities. These results were compared with data obtained from XRD which showed a direct correlation with the findings from FTIR analysis. Intensities of the peaks in the XRD analysis change as the intensity of the main peak change, making it difficult to detect other peaks. Since MMT content of tested clay samples is relatively low, detection of MMT using XRD is difficult. This problem is not encountered in FTIR analysis as it uses the energy absorbed by different bonds present in the mineral. DTA and TGA analysis indicated that the specimen contained kaolinite. Therefore, it can be concluded that
145
the analysis of MMT using FTIR is more reliable and economical technique than conventional methods.
References 1.
Bergaya, F., Theng, B.K.G., and Lagaly, G., Handbook of Clay Science, 1st ed, Elsevier Publications, 2006, pp. 289-309. 2. Fajnor, V.S., and Jesenak, K., Differential Thermal Analysis of Montmorillonite, Volume 46, Journal of Thermal Analysis, 1996, pp. 489-493. 3. Herath, J.W., Industrial clays of Sri Lanka, Economic bulletin no.1, Geological Survey Dept., Ministry of Industries and Scientific Affairs, Republic of Sri Lanka (Ceylon), 1973, p. 49. 4. Madejova, J., FTIR techniques in clay mineral studies, Vibrational Spectroscopy, Elsevier Publications, 2003, pp. 1-10. 5. Olad, A., Polymer/Clay Nanocomposites InTechOpen Publications, 2011, p. 113. 6. Peter, B., “Mineral Powder Diffraction File, Search manual, Data book, Joint Committee on Powder diffraction Standards data cards (JCPDS), JCPDS International Center for Diffraction Data”, U.S.A, 1986, (card no.33-1161, 2-45, 29733, 34-166, 16-613). 7. Van Olphaen, H., Fripiat, J., “Data hand book for Clay materials and other Non-Metallic minerals”, 1st edition, William Clowes and sons Ltd, London, 1979, (pp.13-63, 69-119, 243-281). 8. Cintrón Alvarado, I.A., Glotch, T., Che, C., XRAY Characterization of Clay Minerals and Their Thermal Decomposition Products, American Geophysical Union, Fall Meeting, 2008. 9. Madejova, J., and Komadel, P., Baseline Studies of the Clay Minerals Society SourceClays: Infrared Methods, Institute of Inorganic Chemistry, Clays and Clay Minerals, Vol. 49, No. 5, pp. 410–432, 2001. 10. http://www.sigmaaldrich.com/materialsscience/nanomaterials/nanoclaybuilding.html, Visited October 2011.
Annual Transactions of IESL, pp. [146-150], 2012 © The Institution of Engineers, Sri Lanka
Influence of Plasticity Index on Sub-base Material: Experimental Review D.G.S. Tharaka, B. Suvetha and W.K. Mampearachchi Abstract: Major parts of the Eastern and Northern Provinces of Sri Lanka are covered with cohesionless soil. These locally available cohesionless soils have been utilized for construction of subbase in road constructions. Recently cracks, settlement and outward movement have been observed in the certain pavements constructed in the north and east. It is suspected that the poor plastic properties of locally available soil would have caused this failure. Objective of this paper is to identify the influence of Plasticity Index on sub-base material properties and review the applicability of the current specifications for selection of low plasticity soil as Sub-base material. Based on the collected information, a comprehensive laboratory tests program was formulated to investigate the interrelationships between the soil properties such as grading, maximum dry density, CBR value, Plasticity Index, and Liquid Limit by mixing different type of clays with pure coarse sand (River Sand). Relationships between CBR Vs Plasticity Index and MDD Vs Plasticity Index have been established for a fine grade sub-base material. It was found that CBR is low at both low and high plasticity soil. ICTAD specification specified upper limit for Plasticity Index has been verified in the experimental study. Experimental results emphasised the need of establishing a lower limit for the Plasticity Index in selection of sub-base material. Keywords:
1.
PI, CBR, Grading such as: cracks, settlement and outward movement have been observed in the road pavement within short period after allowing traffic. Failure locations of an arterial road in Eastern Province are shown in Figure 2. It is suspected that the Cohesionless soil used for the sub-base construction could be one of the contributory factors for the above failures. In this paper, improvements for sub-base specification given in specification for road and bridges [1] of The Institute for Construction Training and Development (ICTAD) have been discussed.
Introduction
Large number of infrastructure development projects is currently being built in Sri Lanka and major portion of that development drive is in the highway sector. The infrastructure development projects related to highway sector can be categorized into two: construction of new expressways and upgrading of existing roads to standard road. Since highway construction is an expensive task, locally available materials have been widely used in the recent past for the upgrading of existing roads. In addition to the economical benefits, use of locally available material reduces the adverse environmental impacts. Locally available cohesionless soils have been used as a sub-base material in certain road improvement projects in the Northern and Eastern regions of Sri Lanka. Some sections of the A9 (Mulative- Mankulam Rd) and A15 (Trincomalee- Batticloa) have used road side borrow pits to mine Sub-base material. Figure 1 shows a photograph of the Kadiraweli borrow pit at Vakarie, Batticloa. Sandy nature of the soil is shown in the photograph. Usually borrow pits in other parts of the country are located above ground level. However, the borrow pits used for A15 and A9 roads located in below ground level. Table 1 shows the properties of selected borrow pit material collected from North – East region. Problems
Figure 1 - Kadiraweli Borrow Pit in Batticloa D G S Tharaka , B.Sc( Hons) in Engineering, Dept. of Civil Engineering, University of Moratuwa. Ms. B. Suvetha B, B.Sc (Hons) in Engineering, Dept. of Civil Engineering, University of Moratuwa. Eng. (Dr.) W.K. Mampearachi B.Sc.Eng., MSCE (South Florida), Ph.D. (Florida), CEng, MIE(Sri Lanka), CMILT (UK), Senior Lecturer, Dept. of Civil Engineering, University of Moratuwa.
1
146
Table 1 - Borrow Pit Properties of Sub-base Material Liquid Plasticity MDD Borrow pit Index kg/m3 limit Kadiraweli, 26 8 2.090 Kayankani 25 8 2.028 Thanadi (1) 26 7 2.004 Thanadi (2) 27 3 2.018
soil being compacted. Therefore, Sub-bases constructed using cohesionless soil found to be vulnerable against flooding, storms and disturbance during service [3, 4, 5, and 6].
2.
Objective and Methodology
ICTAD specifications do not specify a lower bound for the plasticity Index of soil to be used for sub-bases. This research focuses on finding the requirement on an acceptable lower bound for the Plasticity Index for soil used for subbase. Soil samples with varying plasticity were prepared, while maintaining the particle size distribution within the ICTAD specification. Atterberg Limits, CBR and Proctor Compaction tests [7] were conducted on prepared soil samples and the results were compared with the ICTAD specifications to understand the requirement of defining a lower limit for the Plasticity Index. Plasticity of the soil was varied by mixing varying proportions of pure Bentonite, Dolamite, Kaoline and Red clay with coarse sand. The percentage of clay in the prepared soil was varied at 5, 10, 15, and 20. According to the ICTAD Specification, 0.075 mm particle fraction (Sieve no 200) should be maintained within limit of 5% to 25%. So that selection of clay percentage was maintained in the range of 5% to 20 %. Natural soil samples collected from construction sites in the University (University of Moartuwa) premises were used to represent samples with high clay content and high plasticity.
Figure 2 - Failure Locations of a Road in Eastern Province Sub-base is a secondary load spreading layer in the pavement structure and acts as a working platform as well. Sub-base should be free from excessive settlement, cracks, and outward movements and should have adequate bearing strength for smooth functioning of the road surface. The ICTAD specification for road and bridges allows cohesionless material to be used as Sub-base material. According to the ICTAD Specifications, selected sub-base material should satisfy following criteria [1].
3.
Results and Discussion
Figure 3 shows typical Particle size distribution of coarse sand with clay mixture, which strictly maintained within bounds as ICTAD specified for sub-base.
1- Liquid limit 30 However, it is found that when cohesionless soil is used as a sub-base material, it is difficult to achieve the required compaction and bearing strength [3]. It was observed that during the compaction process, maintaining moisture content is a very difficult task due to the absence of absorption effect and plasticity of the
In order to obtain the worst condition for the prepared samples in terms of sub-base material, coarse particle size and its percentage were maintained at finer [2].
2
147
Typical plot of the proctor compaction test for soil prepared by mixing Bentonite is shown in Figure 5. It shows that optimum moisture content increases as the clay percentage increases. Similar behaviour is observed for other clay types as well. Further, it can also be observed that the maximum dry density of soil is increasing with clay percentage up to 10% of clay and decreases as further increase of clay.
Figure 3 - Particle Size Distribution for Prepared Soil with Bentonite Clay at all Percentages Table 2 shows summary of Atterberg limit test results for the prepared samples. It shows that the liquid limit and plasticity Index values increase as clay percentage increases. In order to validate above findings, activity diagram was plotted. Figure 4 shows a plot of Plasticity Index against clay percentage from the above data. Extension of each line goes through the origin, this shows the accuracy of the tests, and from the gradient of each line it can be observed that, Bentonite and dolomite are having consecutively highest and lowest plasticity Indexes. Kaoline is having plasticity Index little higher than Dolamite and plasticity Index of red clay is in between Bentonite and Kaoline.
Figure 4 - Activity Diagram for Prepared Samples For Dolamite and Kaoline clay, maximum dry density value is increasing with clay percentage. Red clay achieved the maximum dry density at 15% of clay mixture.
Table 2- Summary of Atterberg Limit Test Clay Type
% of Clay
Liquid limit
Plasticity Index
CBR, %
Red Clay Red Clay Red Clay Red Clay Kaoline Kaoline Kaoline Kaoline Bentonite Bentonite Bentonite Bentonite Dolamite Dolamite Dolamite Dolamite Natural 1 Natural 2 Natural 3
5% 10% 15% 20% 5% 10% 15% 20% 5% 10% 15% 20% 5% 10% 15% 20% 45% 38% 40%
28.40 40.25 50.98 57.15 15.50 21.94 29.98 31.40 29.80 42.25 52.12 59.15 12.80 19.40 23.50 27.32 64 59 64
5.00 12.56 21.08 26.71 4.16 7.28 12.31 13.31 7.90 15.61 23.12 28.91 2.42 5.89 7.10 10.32 27 21 24
10.4 20 10.2 9.1 11 17 10.2 13 7 13.2 21 8.9 8.5 6.3
Figure 5 - Proctor Compaction Curves for Soil Mixed with Bentonite at all Percentages In order to check the variation of maximum dry density with Plasticity Index, relationship between Plasticity Index and MDD were estimated. Figure 6 shows a plot of maximum dry density against Plasticity Index. In order to increase the accuracy of the plot, compaction data for natural soil (soils found from vicinity of the University of Moratuwa) were also included to the graph. It can be observed that maximum dry density value is increasing up to certain value of Plasticity Index and it starts to reduce with increment of Plasticity Index and almost all the maximum dry density values are 3
148
greater than 1750 kg/m3. It means that all the samples are satisfying the maximum dry density requirement given in the ICTAD specification.
experimental study. Further, optimum moisture content increases as clay percentage increases. Maximum dry densities of the all the mixers satisfy ICTAD specification. It can be seen that there is an optimum MDD at Plasticity Index of 10%. It also shows that MDD decreases as the Plasticity Index decreases. According to ICTAD specifications CBR of upper sub-base should be greater than 30. The experimental study was conducted for a poor aggregate gradation within the specification limit. Lack of coarser particles greater than 10mm and the higher amount of fines has been used for the prepared samples. None of the prepared sample achieved the required CBR. It is clear that gradation and the Plasticity Index are equally important to achieve the required support condition.
Figure 6 - Maximum Dry Density against Plasticity Index for Soils Mixed with Various Clay Types and Natural Soil Figure 7 shows the plot of CBR values against Plasticity Index values. Results presented in Figure 6 indicate that, CBR is increasing with the increment of Plasticity Index up to a certain value and starts to reduce with further increase in the Plasticity Index. It gives the similar behaviour as maximum dry density varies with Plasticity Index.
The relationship of the CBR and Plasticity Index clearly emphasised the requirement of defining a lower boundary for the Plasticity Index to maintain the CBR of the soil. An upper limit of 15% for the Plasticity Index in the ICTAD specification has verified with the data obtained from the experimental study. With the limited test results from the present study, it may be concluded that the lower limit for the Plasticity Index should be above 8 to maintain the same level of strength obtained with 15% of Plasticity Index (ICTAD Plasticity limit for Sub-base material). It is recommended that this value should be further verified by further testing on natural soil samples.
Acknowledgements The authors would like to convey the heartiest gratitude to Prof. Saman Thilakasiri for his valuable comments and the relevant officers at Road Development Authority, National Building and Research Organization and Ceylon Pottery Centre for helping to collect samples.
Figure 7 - CBR Percentage against Plasticity Index Plot for Natural and Soil Mixed with Various Clay Types
4.
References
Conclusion
1.
Experimental investigation shows that there is a strong correlation among type of clay, percentage of clay and Plasticity Index. It can be seen that Plasticity Index increases as the clay percentage increases. Highest Plasticity Index has been observed with Bentonite clay while the lowest with Dolomite clay. The Plasticity Index of Red clay is higher than Kaoline in the
Standard Specifications for Construction and Maintenance of Roads and Bridges (SSCM 2005), Institute for Construction Training and Development, Sri Lanka, 2005.
2. AASHTO, “Standard Specifications for Transportation Material and Methods of Sampling and Testing”, 25th edition, (AASHTO) AASHTO Provisional Standards, 2005 Edition.
4
149
3.
Yesim, Gurtug ; Sridharan, A. (2004) Compaction Behaviour and Prediction of its Characteristics of Fine Grained Soils with Particular Reference to Compaction Energy Soils and Foundations, 44 (5). pp. 27-36. ISSN 0038-0806.
4.
Zelalem Worku Ferede, “Prediction of California Bearing Ratio (CBR) Value from Index Properties of Soil”, Masters Thesis Addis Ababa University.
5.
Jegede G., “Effect of Soil Properties on Pavement Failures along the F209 Highway at Ado-Ekiti, South-Western Nigeria” Construction and Building Materials, Volume 14, Number 6, September 2000 , pp. 311-315(5).
6.
Al-abdul Wahhab H. I., Asit I. M., “Improvement of Marl Dune and Sand for Highway Constructions in Arid Area” Building and Environment Volume 32, Issue 3 , May 1997, Pages 271-279.
7.
Yucel Guney , Aydilek Ahmet H., Demirkan M. Melih ”Geo Environmental Behavior of Foundry Sand Amended Mixtures for Highway Sub-Bases” Waste Management 26 (2006) 932–945.
5
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Annual Transactions of IESL, pp. [151-159], 2012 © The Institution of Engineers, Sri Lanka
Causes and Effects of Delays in Construction of Medium Scale Drinking Water Supply Projects in Sri Lanka W.D.A. Perera and R.U. Halwatura Abstract: Most of the infrastructure developments are carried out on project basis. Construction projects frequently suffer from delay, though there are many sophisticated tools and techniques available for construction project management. This paper presents the results of a questionnaire survey conducted to identify and rank the causes and effects of delays in construction of medium scale drinking water supply projects in Sri Lanka. Both Severity Index (SI) and Frequency Index (FI) were used to rank the importance of the factors and the findings of the study indicate that inclement weather conditions, contractors’ financial difficulties, shortage of labour, rules and regulations of road authorities, delays in sub contractors’ work, material import delays and ineffective planning and scheduling of projects by contractors are among the most important factors causing delay in construction of medium scale drinking water supply projects. Moreover, time overruns, cost overruns, funding difficulties, development of unfair relationships among the parties and disputes are the most important effects due to delay. Delays are costly for both clients and contractors and often result in disputes and claims. Therefore in order to improve the situation and avoid /mitigate delays in construction of medium scale water supply projects, several prescriptions are recommended for clients and contractors. Keywords:
Water supply projects, Causes and effects of delays, Ranking of delay factors
tasks to be performed and a defined time frame and also every construction contract considers time as the essence of the project. Delay is a situation when the contractor and the project owner jointly or individually contribute to the non-completion of the project within the original or the stipulated or agreed contract period [2]. Delays in construction projects are frequently expensive, as they are usually involved with construction loans which charges interest, management staff dedicated to the project whose costs are time dependent and ongoing inflation in wage and material prices [3].
1. Introduction In Sri Lanka, a considerable amount of the national budget on infrastructure development is channelled to water supply sector and at present only around 37 percent of the population have access to pipe borne water [1]. The demand for pipe borne water is growing continuously with the increased level of urbanization, change in lifestyles and expansion of commercial and industrial activities. National Water Supply & Drainage Board is responsible for supplying pipe borne drinking water to the nation. The operation and maintenance of existing water supply schemes and the implementation of projects to construct new schemes to meet the growing demand due to urbanization are among the major tasks of it. In recent past, number of water supply projects that had been planned to supply water to developing areas in and around major cities of the country has failed to meet the time targets due to various reasons and affected the socio-economic development of the country.
Some projects are susceptible to delay due to their nature and water and sewerage projects are in this category with several influential factors causing delays. These factors include; the projects are taken place in public roads and streets where special precautions are required, high uncertainty associated as they require Eng. W D Anuruddha Perera, B.Sc.Eng.(Hons), M.Sc.(CPM), C.Eng., MIE(Sri Lanka), Chief Engineer, National Water Supply & Drainage Board, Avissawella. Eng. (Dr.) R U Halwatura, BSc Eng. (Hons), PhD, CEng., MIE(Sri Lanka), AMSSE, Senior Lecturer, Civil Engineering Department, University of Moratuwa.
Most of the infrastructure developments are carried out on project basis. Every construction project has a defined goal or objective, defined
1 151
excavation and trenching works in varied soil and site conditions, works are heavily dependent on equipment and machineries, which are susceptible to repairs and need to get approvals from various authorities [4]. Further, the procedures in issuing of approval certificates for excavation for trenching from government authorities are complex and time consuming due to lack of coordination and various other reasons [5]. There are different perceptions among the major parties involved in projects regarding the causes of project delays. Both contractors and consultants agree that owner interference, inadequate contractor experience, financing and payments, labour productivity, slow decision making, improper planning and sub-contracting are among top ten causes of construction delays in traditional contracts [6]. In most of the developing countries, infrastructure development projects are implemented through the major government authorities that still act as traditional organizers and strictly bound to follow government rules and regulations on procurement. There are a lot of criticisms on the inefficiencies of these government institutions regarding project implementation.
site, changes in specifications and labour disputes and strikes were found to be the major causes of schedule delay in road construction projects in Zambia [10]. Both the project owners and contractors suffer from the delays. The owner loses his money due to increased overheads for supervision, contract administration and also delaying the use of the final product or result of the project [4]. On the other hand, the contractor losses may be the lost opportunities for new projects, increased overheads, etc. But, most of the construction projects suffer from delay, though there are many tools and techniques available for project management. However, there are only few previous studies available on this topic and related to our construction projects. Therefore, there is a need for more efforts to identify the causes and effects of delays in different types of construction projects in Sri Lanka and made awareness of the relevant parties involved to avoid or minimize them and complete the projects successfully.
2. Objectives of the Study The Contractor’s improper planning is the major cause of delay in Malaysian construction industry [7]. According to this study, contractors often fail to come out with a practicable and workable “work program” at the initial planning stage and this failure is interrelated with lack of systematic site management and inadequate contractor’s experience towards the projects. On the other hand, the significant factors causing delays in Hong Kong construction projects are: ‘poor site management and supervision’, ‘unforeseen ground conditions’, low speed of decision making involving all project teams’, ‘ client – initiated variations’ and ‘necessary variations of work’ [8]. Further, the most significant problems causing construction project delays in Thailand includes lack of resources, poor contractor management, shortage of labour, design delays, planning and scheduling deficiencies, change orders and contractors' financial difficulties[9]. Moreover, delayed payments, financial processes and difficulties on the part of contractors and clients, contract modification, economic problems, materials procurement, changes in drawings, staffing problems, equipment unavailability, poor supervision, construction mistakes, poor coordination on
To identify and rank causes and effects of delays in construction of medium scale drinking water supply projects in Sri Lanka.
To study the difference in perceptions of the two major parties involved in construction of drinking water supply projects namely clients and contractors on causes and effects of delays in construction of medium scale drinking water supply projects.
Propose measures to mitigate delays in construction of medium scale drinking water supply projects.
3. Research Methodology A detailed literature review was carried out to identify the previous studies in the research area and found the major causes and effects of delays in projects in Sri Lanka and other counties. Then, a careful identification of the factors related to the study were done and a survey questionnaire was developed to assess
152
the perceptions of contractors and clients who were involved in construction of medium scale water supply projects on the relative importance of causes and effects of construction delays. The questionnaire consisted of four parts; part I- respondents’ details, part II–causes of delays, part III–effects due to delays, part IV– mitigation actions. The first part of the questionnaire requested the respondents’ general details while the second part of the questionnaire consisted of thirty nine causes of delay that were categorized under seven major groups: i. Project related: Inadequate project duration, Improper contract formulation (large Nos. of contracts for a single project, intake civil construction work included in a pump contract, etc.),type of project bidding and award (tendency in awarding the contracts to lowest bidder) ii. Owner/consultant related: Delay in progress payments by owner, delay in handing over the site to the contractor, delay in approval of shop drawings and samples, delay in inspection and testing of works, Inadequate Liquidated damages, too many change orders, slow decision making, poor contract management of owner/consultant. iii. Contractor related: Contractors financial difficulties, mistakes during construction and rework, shortage of project staff with required experience, Poor coordination/communication by the contractor with other parties, Ineffective planning and scheduling of project by contractor, improper construction methods implemented by contractor, delays in sub contractors’ work, insufficient delegation of power to the site management team. iv. Design related: Delays in producing construction drawings, unclear and inadequate details in drawings, mistakes and discrepancies in drawings and bills of quantities, inadequate specifications for materials. v. Materials related: Shortage of construction materials in market, changes in material types and specifications during construction, restrictions on issuing permits to transport materials, rejection of imported materials due to non-compliance with the contract specifications. vi. Equipment and Labour related: Frequent equipment breakdown, shortage of equipment and hiring delays, low productivity and efficiency of equipment,
vii.
low productivity level of workers, shortage of labour, labour union actions. External factors: Inclement weather conditions, delay in obtaining permits, services, etc. from local authorities and other organizations such as electricity board, traffic/security problems, changes in government regulations and laws, rules and regulations of Road Development Authority(RDA), Provincial Road Development Authority (PRDA) and local government authorities (PS) on road excavation work approvals.
The third part of the questionnaire consisted of the effects due to delay checklist: Time overrun cost overrun, dispute, arbitration, litigation, total abandonment, funding difficulties, delay in commissioning other related projects and develop unfair relationships with other organizations such as RDA, PRDA, PS, etc. The last part of the questionnaire is for getting the respondents prescriptions to reduce delays in construction of medium scale water supply projects. For each cause/effect two questions were asked: what is the frequency of occurrence for this cause? and what is the degree of severity of this cause on project delay? Both frequency of occurrence and degree of severity were categorized on a four point scale. Frequency of occurrence was categorized as: Rarely, Sometimes, Often and Always. Similarly, degree of severity was categorized as: Little, Moderate, Great and Extreme. In Sri Lanka, almost all the medium scale drinking water supply projects are carried out by the National Water Supply and Drainage Board and the contractors are involved in these developments. The questionnaire was distributed among the professionals of the above two groups and the sampling method used in this study was convenience and snowball sampling that comes under the class of non-probability sampling techniques [7].
3.1 Ranking of delay factors The ranking of causes and effects of delays from the viewpoints of three parties involved in construction projects; owners, contractors and consultants can be done using three indices; frequency index, severity index and importance index [11]. The similar method was applied in the study and the following equations were used for the calculation of three indices. Frequency index (FI) is a formula
153
4.2 Data Analysis The responses to the questionnaires were analyzed from client’s, contractor’s and overall perspectives based on severity and frequency of occurrence of the causes and effects to identify the most important causes and effects of delays. The ranking indices were calculated using the three formulas stated under methodology and are presented in Tables 3 and 4. Table 2 - Respondent’s Qualifications
used in the study to rank causes of delay based on frequency of occurrence as identified by the participants. : (FI) (%) = ∑a (n/N)*100/4
(1)
where, a is the constant expressing weighting given to each response (ranging from 1 for rarely up to 4 for always), n is the frequency of the responses, and N is total number of responses. Severity Index (SI) is a formula used in the study to rank causes of delay based on severity as identified by the participants. (SI) (%) = ∑a (n/N)*100/4
Category
(2)
Client
where a is the constant expressing weighting given to each response (ranges from 1 for little up to 4 for severe), n is the frequency of the responses, and N is total number of responses. Importance Index (IMPI) of each cause is calculated as a function of both frequency and severity indices. (IMPI) (%) = (FI) (%) *(SI) (%)
Contractor
Total
(3)
Nos. of participants Nos. of respondents Response rate% Nos. of participants Contractor Nos. of respondents
Response rate% Nos. of participants T otal
Nos. of Respondents Response rate %
12
77.78
80.00
35
15
3
43
14.29 59.70 20
70
6
40
30
4
85.71
26.67
30.00 57.14
71
30
41 142
58
16
81.69
53.33
9
25.6
B.Sc.
20
46.5
M.Sc.
12
27.9
Ph.D.
0
0.0
Dip.
10
25.0
B.Sc.
25
62.5
M.Sc.
5
12.5
Ph.D.
0
0.0
Dip.
21
25.3
B.Sc.
45
54.2
M.Sc.
17
20.5
Ph.D.
0
0.0
Severe delay factors The results of the analysis show that the clients’ ranked ineffective planning and scheduling of the project by contractor (SI=87.79), contractor’s financial difficulties (SI=84.30) and rejection of imported materials (SI=83.72) as the most severe causes of delay while the contractor considers weather conditions (SI=90.00), delays in sub contractors’ work (SI=89.38) and delay in progress payments by owner (SI=88.13). This shows that there is a disagreement between the two parties regarding the most severe causes of delays. In Sri Lanka, almost all the medium scale water supply projects are implemented through National Water Supply & Drainage Board and funded by either the capital budget or foreign donor funds.
Hand Regualr Via Total delivery mail Internet 36 15 21 72 28
11
5.1 Causes of Delay The importance of the identified thirty nine causes of delay in construction of medium scale water supply projects were depended on both the severity and frequency of occurrence.
Table 1- Questionnaire Response Rate
Client
%
Dip.
This section discusses the results obtained in the analysis. First, the results obtained by analyzing the causes of delay in construction of medium scale water supply projects were discussed and compared the client, contractor and overall perspectives. Then, the results obtained by analyzing the effects due to delay were discussed.
4.1 Sample Characteristics The questionnaires were distributed to a sample of professionals of the two major parties (clients and contractors) involved in the construction of medium scale water supply projects by hand delivery, regular mail and also via internet. The survey was carried out over the period from August 2010 to October 2010, and the response rate and the basic qualifications of the sample were as shown in the Tables 1 and 2.
Questionnaire sent
No. of Res pondents
5. Discussion of Results
4. Data analysis
Category
Bas ic Qualification
83
21.95 58.5
154
Project related 1 Inadequate Contract duration
64.5 47.1 30.4 22 86.9 84.4 73.3 5 75.3 65.1 49.0 16
2 Improper contract formulation
63.4 34.9 22.1 34 60.0 42.5 25.5 36 61.7 38.6 23.8 35
3 Tendency in awarding the
51.7 77.9 40.3 18 68.1 76.9 52.4 21 59.6 77.4 46.2 17
1 2 3 4 5
contracts to lowest bidder Owner/cons ultant related 4 Delay in progress payments by 5 6 7 8 9
owner Delay in handing over the site to the contractor Delay in approval of shop drawings and samples Delay in inspection and testing of works Inadequate application of Liquidated damages Too many change orders
76.2 56.4 43.0 16 88.1 84.4 74.4 4 81.9 69.9 57.3 11 77.3 72.1 55.7 8 81.3 78.1 63.5 19 79.2 75.0 59.4
9
59.9 66.3 39.7 19 56.9 38.8 22.0 38 58.4 53.0 31.0 31
62.2 37.2 23.1 33 83.1 82.5 68.6 13 72.3 59.0 42.7 21
84.3 83.1 70.1 2 79.4 86.9 69.0 11 81.9 84.9 69.6
2
13 Mistakes during construction and 52.3 54.1 28.3 27 56.9 51.9 29.5 31 54.5 53.0 28.9 32
rework 14 Shortage of project staff
63.4 74.4 47.2 12 64.4 56.9 36.6 27 63.9 66.0 42.1 23
15 Poor coordination/
64.0 79.7 50.9 11 64.4 46.3 29.8 30 64.2 63.6 40.8 24 87.8 92.4 81.2 1 73.8 56.9 41.9 25 81.0 75.3 61.0
Rank
FI Imp. Index
32.5 6 79.7 34.3 27.32 8 81.0 36.7 29.77 7
6 Total abandonment
96.9 28.8
27.9 8 94.8 29.1 27.55 7 88.6 28.9 25.61 8
7 Funding difficulties
83.8 81.3
68.0 3 66.3 75.0 49.71 3 72.9 78.0 56.86 3
41.9 42.5
17.8 9 48.8 37.8 18.46 9 45.5 34.9 15.89 9
69.4 65.6
45.5 4 60.5 72.1 43.59 4 59.0 69.0 40.72 4
Frequent delay factors Frequency of occurrence of delay factors is also a significant aspect, which uses to determine the importance of causes of delay. The client ranked Ineffective planning and scheduling of project by contractor (FI 92.44) as the most frequent factor causing delays in construction of medium scale water supply projects while it is ‘inclement weather conditions’ for both contractor’s (FI 91.25) and overall (FI 88.6) rankings. The inclement weather conditions badly affect the construction of water supply projects and in sometimes it will cease the construction activities until the weather becomes normal [12]. This supports the findings of the research and reconfirms that inclement weather is a frequent cause of delay in construction of water supply projects and the project teams should draw special attention to the inclement weather conditions at the planning, design and construction stages of the medium scale water supply projects.
54.7 55.2 30.2 23 58.1 45.6 26.5 34 56.3 50.6 28.5 33 75.6 77.3 58.4 7 89.4 88.8 79.3 2 82.2 82.8 68.1
5
the site Des ign related 20 Delays in producing construction 70.3 43.6 30.7 21 73.1 67.5 49.4 22 71.7 55.1 39.5 26
drawings 55.8 50.6 28.2 28 87.5 80.0 70.0 9 71.1 64.8 46.0 18 52.3 85.5 44.7 14 78.1 90.0 70.3 7 64.8 87.7 56.8 12 56.4 34.3 19.3 37 57.5 51.3 29.5 32 56.9 42.5 24.2 34
24 Shortage of construction materials 66.9 43.6 29.2 26 55.6 65.0 36.2 28 61.4 53.9 33.1 28 25 Material import delays (Pipes,
35.3 5 63.4 47.1 29.84 6 70.5 51.8 36.51 6
82.5 39.4
7
19 Insufficient delegation of power to 56.4 52.9 29.8 24 59.4 60.6 36.0 29 57.8 56.6 32.7 29
drawings 22 Mistakes and discrepancies in drawings and BOQ 23 Inadequate specifications for materials Materials related
30.8 7 34.9 89.5 31.23 5 44.0 88.6 38.94 5
68.1 51.9
There is a high competition in the industry and most of the contracts are awarded to lowest bidders who are normally having a little profit margin. There are delays in monthly progress payments to the contractors due to the financial difficulties faced by the client. Hence, the work progress can be delayed.
owner/consultant Contractor related
21 Unclear and inadequate details in
69.1 2 79.7 76.2 60.66 2 81.9 78.9 64.65 2
36.3 85.0
8
62.8 41.3 25.9 30 78.1 89.4 69.8 10 70.2 64.5 45.2 19
18 Delays in sub contractors’ work
70.9 1 80.2 86.6 69.50 1 82.8 88.3 73.10 1
84.4 81.9
Source: calculated from survey data 72.7 75.6 54.9 9 80.6 83.8 67.5 16 76.5 79.5 60.8
11 Poor contract management of
communication 16 Ineffective planning and scheduling of project 17 Improper construction methods
78.8 90.0
Delay in commissioning other related projects Develop unfair relationships with 9 other organizations such as RDA, PRDA, PS,etc.
52.9 44.8 23.7 32 80.0 85.0 68.0 14 66.0 64.2 42.3 22
10 Slow decision making
12 financial difficulties
Time overrun Cost overrun Dispute Arbitration Litigation
8
51.7 50.0 25.9 31 76.9 88.1 67.7 15 63.9 68.4 43.7 20
Overall view SI
SI
Causes of delay
Client's View FI Imp. Index Rank
Effects due to delay
Index Rank
No
FI Imp.
Contractor's view Rank
FI Imp. Inde
SI
Overall Rank
FI Imp. Inde
SI
Contractor Rank
SI
FI Imp. Inde
Client Factor Description
Table 4 - Ranking of Effects due to Delay
SI
Table 3 - Ranking of Causes of Delay
76.7 78.5 60.2 6 81.9 86.3 70.6 6 79.2 82.2 65.1
6
fittings, etc.) 26 Changes in material types and 59.9 35.5 21.2 36 57.5 44.4 25.5 35 58.7 39.8 23.4 37 specifications 27 Restrictions on issuing permits to 56.4 80.2 45.2 13 77.5 85.6 66.4 17 66.6 82.8 55.1 13 transport materials. 28 Rejection of imported materials 83.7 44.2 37.0 20 81.9 53.8 44.0 24 82.8 48.8 40.4 25 Equipment and Labour related 29 Equipment breakdown
55.8 79.1 44.1 15 72.5 81.3 58.9 20 63.9 80.1 51.2 15
30 Shortage of equipment and hiring
52.3 56.4 29.5 25 65.6 74.4 48.8 23 58.7 65.1 38.2 27
delays 31 Low productivity and efficiency of 47.7 55.8 26.6 29 61.9 61.3 37.9 26 54.5 58.4 31.9 30 equipment 32 Low productivity level of workers 57.6 73.8 42.5 17 78.8 87.5 68.9 12 67.8 80.4 54.5 14 33 Shortage of labour
80.2 84.3 67.6 3 82.5 85.0 70.1 8 81.3 84.6 68.8
34 Labour union actions
51.2 28.5 14.6 39 56.3 31.3 17.6 39 53.6 29.8 16.0 39
3
Further, the delay factors such as RDA, PRDA, and PS rules and regulations on road excavation work approvals, material import delays (pipes, fittings, etc.) that occur due to the nature of water supply projects are identified by clients as well as contractors as frequent causes of delay and ranked within first ten positions. Moreover, both the clients and the contractors ranked the delay factors
External factors 35 Inclement weather conditions
72.7 86.0 62.5 4 90.0 91.3 82.1 1 81.0 88.6 71.8
36 Delay in obtaining permits,
64.0 84.9 54.3 10 75.6 85.0 64.3 18 69.6 84.9 59.1 10
1
services, etc. 37 Traffic/security problems
44.2 48.3 21.3 35 51.3 51.9 26.6 33 47.6 50.0 23.8 36
38 Changes in government
51.7 31.4 16.2 38 62.5 38.1 23.8 37 56.9 34.6 19.7 38
regulations and laws 39 RDA, PRDA, PS. rules and regulations
75.0 82.6 61.9 5 83.8 90.6 75.9 3 79.2 86.4 68.5
4
155
‘labour union actions’ and ‘changes in government regulations and laws’ as very rare causes of delay in construction of medium scale water supply projects although in some other sectors in Sri Lanka ‘union actions’ are very frequent. One of the reasons for this is less opportunities in the construction industry to organize for bargaining for their benefits. But in the recent past the union actions of clients professional staff had been affected project activities and there had been delays in extra work approvals, tender evaluations, tender awarding, and etc., which caused delays in construction of water supply projects.
Table 5 - Important Delay Factors Contractor’s Client’s view view 1
2
3
The construction of water supply projects requires getting various types of approvals from government institutions. Due to improper coordination with these organizations, it has been facing difficulties in getting these approvals on time. The delays in getting approvals for road excavation that requires for pipe laying in public roads have been identified as a frequent causes of delay in construction of water supply projects. Further, the introduction of new rules and regulations of Road Development Authority (RDA) on road reinstatement after trenching has severely affected the implementation of water supply projects, as it requires some time to adjust to new requirements and take necessary policy decisions to develop relevant systems to carry out the works. Therefore early attention should be drawn in this regard and develop some effective and efficient systems to handle RDA requirements and provide necessary provisions in contracts to do the temporary as well as permanent road reinstatement.
Delays in sub contractors’ work RDA, PRDA, and PS rules and regulations on road excavation work approvals Delay in progress payments by owner
Contractors financial difficulties Shortage of labour
5
RDA, PRDA, PS. rules and regulations on road excavation work approvals Material import delays (Pipes, fittings, etc.)
Inadequate contract duration
7
Delays in sub contractors’ work
Mistakes and discrepancies in drawings and bills of quantities
8
Delay in handing over the site to the contractor Too many change orders
Shortage of labour
Delay in obtaining permits, services, etc. from local authorities and other organizations such as Electricity Board.
Slow decision making
10
156
Inclement weather conditions
Inclement weather conditions
9
Contractors ranked inclement weather conditions first, whereas the clients ranked it fourth. The construction of medium scale water supply projects normally includes construction of head works, laying of transmission and distribution systems and construction of office, stores and other facilities.
Inclement weather conditions
4
6
Important delay factors The results of the analysis show that there are several important factors underlying causes of delay in construction of medium scale water supply projects in Sri Lanka. Ten most important delay factors as identified by clients, contractors and overall view are presented in Table 5.
Ineffective planning and scheduling of project by contractor Contractors financial difficulties Shortage of labour
Overall view
Material import delays (pipes, fittings, etc.)
Unclear and inadequate details in drawings
RDA, PRDA, PS. rules and regulations on road excavation work. Delays in sub contractors’ work Material import delays (Pipes, fittings, etc.) Ineffective planning and scheduling of project by contractor Too many change orders Delay in handing over the site to the contractor Delay in obtaining permits, services, etc.
medium scale water supply projects due to many reasons, the relevant organizations have taken measures to complete the projects without abandonment. Further, the clients and contractors agreed that time overruns and cost overruns are among the most severe effects due to delay. These effects may lead to other effects such as disputes, funding difficulties, delay in commissioning related projects, etc.
The inclement weather affects most of these works, and especially for pipe laying works and intake construction works. Contractor’s ineffective planning and scheduling of the project will make worse the situation if he does not consider or fails to predict the weather pattern at the initial planning. Skills and experience of workforce, management, job planning, workers motivation, and material availability were the major drivers of productivity of water and waste water treatment plant construction works [13]. It is essential to draw special attention to these factors and apply in construction of medium scale water supply projects as this will help to speed up of the works and also help to expedite the delayed works due to various causes identified in this study.
On the other hand, both clients and contractors agreed that time overruns, cost overruns and disputes are the most frequent effects due to delay in construction of medium scale drinking water supply projects in Sri Lanka. Most of the delay factors, which were categorized under seven sections in this study, affect the completion of the projects and cause time overrun, cost overrun and disputes. Similar effects have been identified as the most frequent effects due to delays in Nigerian construction industry through a study carried out concentrating the building construction industry [15]. This study mainly recommended providing sufficient contingency provisions in total cost estimates to handle the project uncertainties. As the construction of water supply projects also faces a lot of uncertainties due to their nature [4], it is better to consider this recommendation and decide contingency percentages wherever necessary after carefully considering the requirements rather than providing fixed percentages from the contract value.
Agreement among groups The degree of agreement between the clients and contractors on causes of delays in construction of medium scale water supply projects was calculated using spearman’s rank correlation coefficient. The equation, rs = 1(6∑d2/N(N2-1)) was used to calculate this coefficient when there are no tied links [14]. Where rs = Spearman’s rank correlation coefficient, d = the difference in ranking between the clients and the contractors and N = the number of variables. The spearman’s correlation coefficient calculated was 0.55 for the causes of delays ranked by the clients and contractors. Spearman’s rank correlation coefficient equals to +1 means that two variables are having perfectly positive correlation while -1 gives perfectly negative relationship. The somewhat low value of rank correlation coefficient (0.55) indicates low agreement between clients and contractors on the ranking of the factors. This low agreement has created disputes between the parties and the most delays occur at the project construction phase.
The importance of the effects due to delay the same as the importance of causes of delay is determined by considering both severity and frequency of occurrence. Hence some effects due to delay, which were having higher frequency indices with low severity indices, were ranked as the lesser important factors. As an example, “Disputes” has the highest frequency index of 88.6% and the least severity index of 44.0% as per the overall view, were ranked at 5th as per the importance with 38.94% importance index. Therefore the identification of these effects due to delay based on the above three indices will help the project management to select the causes of delay, which requires more attention based on their consequences.
5.2 Effects due to Delay Clients as well as contractors ranked, total abandonment as the most severe effect due to delay in construction of medium scale water supply projects and the severity indices calculated for them are 94.8 and 96.9, respectively. But they ranked it as a very rare effect due to delay and the frequency indices are 29.1 and 28.8, respectively. This depicts that though there are delays in construction of
157
6. Conclusions and Recommendations
construction of medium scale drinking water supply projects.
There are delays in construction of medium scale drinking water supply projects in Sri Lanka. As per the overall view inclement weather conditions, contractors’ financial difficulties, shortage of labour, rules and regulations of road authorities and delays in sub contractors’ work are the first five important factors causing delays in construction of medium scale water supply projects. Further, both clients and contractors agree that rules and regulations of road authorities and inclement weather conditions are among the most important delay factors. On the other hand, as per the overall view inclement weather conditions, mistakes and discrepancies in drawings and bills of quantities, rules and regulations of road authorities, delay in obtaining permits services, etc. and contractor’s financial difficulties are the most frequent causes of delay while rejection of imported materials due to noncompliance with contract, delay in subcontractors ‘ work, delay in progress payments by owner, contractors financial difficulties and shortage of labour are ranked as the most severe causes of delay.
Prescriptions for Contractors
Contractors must consider their financial capabilities before bidding projects and should employ a qualified staff for the financial management of projects. Contractors should not take up the job in which they do not have sufficient expertise. Contractors should employ qualified and well experienced site staff during the project period. The planning and scheduling of the project should be done properly and the revision of the schedules has to be done as required. When employing sub-contractors it has to be done after considering his capabilities and by entering into a formal agreement. Contractors should keep site records properly. Contractors should submit their claims as per the requirements given in the contract.
Prescriptions for Clients
On the other hand, time overruns, cost overruns, funding difficulties, disputes, arbitration, litigation, delay in commissioning related projects, total abandonment and develop unfair relationships with road authorities are the effects due to delay in construction of medium scale water supply projects. Both clients and the contractors felt that time overruns, cost overruns, funding difficulties and develop unfair relationships with other organizations appear to be the most important effects due to delay in construction of medium scale water supply projects. As per the overall view, disputes and time overruns are the most frequent effects while total abandonment and time overruns are the most severe effects due to delay.
A proper understanding of these causes of delays and their consequences will help the relevant project professionals to better manage delay situations in construction of medium scale water supply projects.
Further, based on the study, the following prescriptions are recommended for clients and contractors to avoid/mitigate delays in
158
Contractors should not be selected based only on the lowest bid. The client should consider contractor’s experience in similar works and his technical and financial capabilities, before awarding the contracts. It is necessary to decide realistic project durations by the client considering various aspects. The client should take necessary measures to use qualified and experienced professionals for planning and designs of projects. The clients must take necessary actions to handover the possession of site to the contractors without delay. The client should employ a capable and well experienced project staff for the construction stage. They have to closely monitor the progress of work and propose necessary steps to expedite the works to the contractor if the progress is behind the schedule. Appropriate total cost estimates should be prepared at the initial stage of projects and the client should settle the contractors’ claims without delay. Enforcing liquidated damage clauses and offering incentives for early completion.
Minimize change orders during construction to avoid delays. The client should coordinate with other organizations such as local authorities, road authorities and various other government organizations at various stages of projects.
6.1 Recommendations for Future Studies Similar study can be conducted for other types of infrastructure development projects such as road development projects, telecommunication projects, power generation projects, etc. and compare the similarities and differences of causes and effects of delays in these projects.
10.
Chabota Kaliba, A, Cost escalation and schedule delays in road construction projects in Zambia. International Journal of Project Management, pp.522-531, 2009.
11.
Assaf, S., & Al-Hejji, S., Causes of delay in large construction projects. International Journal of Project Management, pp.349-357, 2006.
12.
Frimpong, Y., Oluwoye, & Crawford, L., Causes of delay and cost overruns in construction of ground water projects in developing countries; Ghana as a case study. International Journal of Project Management, pp.321-326, 2003.
13.
Mojahed, S., & Aghazadeh, F., Major factors influencing productivity of water and waste water treatment plant construction: Evidence from the deep South USA. International Journal of Project Management, pp.195-202, 2008.
14.
Dowdy, S., & Wearden, S., Statistics for research. New York: John Wiley & Sons, pp.233-247, 1985.
15.
Aibinu, A., & Jagboro, G., The Effects of Construction Delays on project delivery in Nigerian Construction Industry. International Journal of Project Management, pp.593-599, 2002.
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Report, C. B. (2010), Central Bank Report, pp.23-45.
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Levy, S. M. (1994), Project Management in Construction. Mgraw-Hill Inc.USA, pp. 54-65.
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Trauner, T.J., Construction Delays, Publisher, Butterworth Heinemann, pp.126-143, 2009.
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Al-Khalil, M., & Al-Ghafly, M., Delay in public utility projects in Saudi Arabia. International Journal of Project Management, pp.101-106, 1999.
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Luu, V., Kim, S., Tuan, N., & Ogulana, S., Quantifying schedule risk in construction projects using Baysian belief networks. International journal of project management, pp.425-437, 2008.
6.
Odeh, A., & battaineh, H., Causes of construction delay: traditional contracts. International Journal of Project Management, pp.67-73, 2002.
7.
Sambasivan, M., & Soon, Y., Causes on effects of delays in Malaysian Construction Industry. International Journal of Project Management, pp.517-527, 2007.
8.
Chan, D., & Kumaraswamy, M., A comparative study of causes of time overruns in Hong Kong construction projects. International Journal of Project Management, pp.55-63, 1997.
9.
Toor, S., & Ogunlana, S., Problems causing delays in major construction projects in Thailand. Construction Management & Economics, pp.395-408, 2008.
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Annual Transactions of IESL, pp. [160-168], 2012 © The Institution of Engineers, Sri Lanka
Study of Northern Province Medium Voltage Network Interconnection with the Sri Lankan Power Grid A. Ananthasingam, R. Shailajah, N. Yoganathan, S. Arunprasanth, A. Atputharajah and M.A.R.M. Fernando Abstract: Interconnection of power systems will strengthen the power grid due to its inertia addition. However, interconnection of long distanced large loads and generating plants causes problems like voltage drops, line overloading, power fluctuation and difficulties in black start up. The literature survey resulted that the Flexible AC Transmission System is a proven technology as solution. In Sri Lanka, the Jaffna Peninsula MV network is planned to be re-connected to the main grid network in 2013. This paper discusses about reliable and efficient operation of the Sri Lankan power grid as whole after this interconnection. In this study the present, 2016 predicted Sri Lankan transmission network and Northern MV networks were modelled. Growth rate of the Jaffna Peninsula was calculated using the 2007 to 2011 recorded historical data. Simulated results on load flow and fault analysis were similar to the operational data, thus validated the modelled network. In Sri Lankan power system, the longest transmission line will interconnect the loads and generators at Northern Province with main grid. Solutions to the problems related to this interconnection were studied with an optimally placed Static VAr Compensator. This study has proven better performance in reducing overloading, improving voltage profile and easy black start up. Keywords: Sri Lankan Transmission network, Jaffna Peninsula, Growth rate calculation, Reactive power compensation, Static VAr Compensator
1.
point of this interconnection the load centre (Northern part of Sri Lanka) is located far from the generation (Central part of Sri Lanka). Therefore, after the connection using long AC transmission lines (about 224 km long) may bring numerous technical challenges which are on the system reliability, stability and power quality.
Introduction
In Sri Lankan existing power system, Jaffna peninsula is operated as islanded mode generation since 1990. Until 1990 Jaffna Peninsula was operated with the national grid by a 132 kV double circuit transmission line from Anuradhapura to Chunnakam. In that period, there was a diesel power plant of 15 MW at Chunnakam grid. During the civil war, the Killinochchi grid and the transmission line to Chunnakam were damaged and Jaffna MV network was isolated. But in a developing small country like Sri Lanka, further islanded operation makes power networks smaller in size and causes problems. Problems related to thermal generation are high generation costs, environmentally harmful gas emission and high replacement cost of the machines [1 and 2]. Therefore, Ceylon Electricity Board (CEB) has already planned to re-connect the Jaffna peninsula with the Sri Lankan transmission network by 2013.
Therefore, a study on these issues is timely Ms. A. Ananthasingam, B.Sc. Eng. (Peradeniya)-reading, Student Member IESL, Department of Electrical & Electronic Engineering, University of Peradeniya. Ms. R. Shailajah, B.Sc. Eng. (Peradeniya)-reading, Student Member IESL, Student Member IEEE, Department of Electrical & Electronic Engineering, University of Peradeniya. Ms. N. Yoganathan, B.Sc. Eng. (Peradeniya)-reading, Student Member IESL, Department of Electrical & Electronic Engineering, University of Peradeniya. Eng. S. Arunprasanth, B.Sc. Eng. (Peradeniya), AMIE(Sri Lanka), MIEEE, Lecturer, Department of Electrical & Electronic Engineering, University of Peradeniya. Eng. (Dr.) A. Atputharajah, C.Eng., MIE(Sri Lanka), SMIEEE, B.Sc. Eng. (Peradeniya), PhD (UMIST), Senior Lecturer, Department of Electrical & Electronic Engineering, University of Peradeniya.
This Interconnection is targeted to strengthen the existing system while transmitting the power to the northern part. To make sure the efficient interconnection, several factors have to be considered at the planning stage; such as power quality and reliability issues. In the view
Eng. (Prof.) M.A.R.M. Fernando, C.Eng., MIE(Sri Lanka), SMIEEE, B.Sc. Eng. (Peradeniya), Tech. Lic., PhD (Chalmers), Associate Professor, Department of Electrical & Electronic Engineering, University of Peradeniya.
1
160
effort. Reactive power compensation is chosen as a suitable option to satisfy these challenges [2-7]. There are different types of reactive power compensators such as Static VAr Compensator (SVC), Static Compensator (STATCOM), Unified Power Flow Controller (UPFC), and Dynamic Voltage Restorer (DVR) [4].
Lanka and the generation voltages are around 12.5 kV, 13.8 kV. Total installed capacity is 3141 MW and the number of power stations 139. Peak demand is about 2163 MW. Total energy generation is about 29.35 GWh/day and 60% is thermal power generation and the rest 40% is hydro power generation [9 and 10]. Hydro power plants are divided into 5 Groups. Mahaweli complex-plants operated by the water from Mahaweli River, Laxapana Complex-plants operated by the water from Kelani River, Samanala Wewa, Kukule Ganga and other small hydro. The thermal plants classified into two, those are CEB thermal and IPP thermal.
There was an SVC in Galle which is already connected to the transmission network. However, it is not in operation at the moment. According to the CEB plan the SVC Galle will be in operation by 2013. Therefore, this paper propose one of the solution which is another SVC in Northern Province by considering the reactive power compensation, improvement of the voltage profile, damping power fluctuation, easy black start up and mainly long term usage.
Existing Jaffna power system consist an islanded diesel operated generations and MV network [10]. But with this generation, system is not cost effective [1 and 2]. According to the CEB plan, interconnection of the Jaffna Peninsula with the national grid is the best solution [9 and 10]. However, as the interconnection is made through long transmission line which is about 224 km there will be some issues on power quality, system reliability and stability.
This study was focused to (i) find 2016 load in Northern Province, (ii) check any overloading or under voltage problem in the interconnection at 2016 and (iii) propose an optimum placement of SVC in the Sri Lankan transmission network to make the Northern power system reliable and stable after the interconnection with the consideration of cost and advantages of SVC. As a result, the effort mainly involves with demand and generation forecast, modelling of Sri Lankan transmission network as in 2016 and several case studies on Sri Lankan transmission network as in 2016. The reason for selecting year 2016 model of transmission network is according to CEB plan the major plants such as Puttalam coal power last two steps (600 MW) and Trinco coal power plant (500 MW) will be connected to the network by this year.
2.
2.3
Improving Power System Reliability and Stability Power electronics based FACTS device technology allows to increase loading possibility, improve the system reliability and stability, provides voltage control with the great advantage of having high speed response to disturbances. It can also control line impedance, line voltage, active and reactive power flows in the line [5]. In long transmission lines, voltage stability is the main issue. The load variations, switching of system elements such as transmission lines, reactors, capacitor banks and transformers affect the voltage significantly. Increase of load may cause voltage collapse or light load may cause voltage rise. For these problems, the SVC is proven as the best power system voltage control device. Reactive power compensation is normally used in the transmission systems to improve network voltages and power transfer capability. It is also used in the distribution networks to compensate large amount of reactive power [4-7 and 11].
Literature Review
2.1 Network Modelling Modelling of power system network is the foundation of a power system analysis. Modelling consume the most attention as it is the backbone for all the power system analyses. Ongoing system operational directions, future plans on expansion of the power system such as new additions of generations/transmissions are done through the power system modelling [8]. 2.2
Sri Lankan Transmission Network2011 and Jaffna Power System-2011 Sri Lankan transmission system consists of two different transmission voltages 220 kV and 132kV. Hydro and thermal generations are the main generation technologies followed in Sri
SVC is a shunt-connected device, which absorbs or injects reactive power to maintain or control specific parameters of the electrical power system. Its operations can be made for voltage control, power factor control, damping of 2
161
power fluctuation, etc [13]. SVCs are based on Thyristor Switched Capacitors (TSCs) or Breaker Switched Capacitors (BSCs), and Thyristor Controlled Reactors (TCRs) with the dynamic on-off capability [4 and 5].
As the next step, several case studies were done using the modelled Sri Lankan power system network as in 2016, with night and day peak scenarios. Study of Northern Province Medium Voltage Network Interconnection with the Sri Lankan Power Grid
Literature review
Carrying out the load flow analysis Upgrading
TCR
TSC
2016 Sri Lankan Transmission network forecast without Jaffna. 1. Generation (CEB) 2. Major loads (CEB)
Figure 1 - Single Line Diagram of SVC Advantages of using an SVC are fast response to change in system voltage, dynamic reactive power supply and absorption capability damping capability and more reliable. SVC is considered as the lower cost alternative device to the STATCOM and UPFC [4 and 5]. Further, it has long life time. Therefore, it is selected as better solution in this study.
3.
2016 Jaffna Demand forecast 1. Generation 2. Major loads 3. Load Demand (MW & MVAr)
Interconnecting Jaffna with SL Transmission network
2016 Sri Lankan Transmission network connected with Northern Province MV network
Methodology
This study was carried out through the steps shown in Figure 2. Initially, the present Sri Lankan transmission network-2011 and Jaffna MV network-2011 were modelled using Integrated Power System Analysis (IPSA) simulation tool. Load flow analysis was done on each model for different scenarios and the results were observed.
Case studies on 2016 Sri Lankan transmission network.
Selection of significant case studies on 2016 Sri Lankan transmission network.
Optimum placement of the SVC
In the second step, the modelled Sri Lankan Transmission network was upgraded to 2016 with the consideration of future load demands and generation according to the CEB plan. Future demand and generation of the Jaffna peninsula were calculated separately, because the growth rate in Jaffna peninsula is different from other part of the island as a result of the civil war. A method was also developed to find the growth rate of Jaffna peninsula [Section 3.3A]. From that two growth rates were calculated and the highest one was selected. Then the complete Sri Lankan 2016 transmission network was modelled with the newly predicted Jaffna demand.
Finding Optimum capacity of SVC
Figure 2 – Methodology Followed The highest power generation observed in night peak around 8 p.m. All the industrial and domestic electricity usages are high at this time. But in the day peak which is the second highest generation, most of the industries are involved and it is around 11 a.m. Those case studies were analysed mainly into two different sets: (i) with all the CEB predicted reactive power compensators and (ii) By removing some of the reactive power compensators at Jaffna peninsula and instead placing the SVC at 3
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According to the available data, there were 436 distribution transformers. This Jaffna MV network was modelled using IPSA software tool. The main difficulty was to find the load demand of each transformer for the night & day peak scenarios.
different locations. In this analysis, the following cases were considered, (i) with and without the Trincomalle coal power plant (500 MW), (ii) with and without Nuracholai coal power plant (600 MW) and (iii) with and without Chunnakam (30 MW) power plant. The Trincomalle coal power plant and Nuracholai coal power plant were considered because, both the Trincomalee -500 MW (completion date July 2016) and Nuracholai-600 MW (completion date April 2014) plants will be in operation by the year of 2016 [12]. These two plants will have major role in Sri Lankan power generation by the year of 2016 because of the higher capacity and the main target of this study is the interconnection of the Jaffna MV network with the national grid. Therefore, the Chunnakam plant was also considered in the above case studies. Then, the worst cases were considered based on the result on violations of operating conditions. For those worst cases placement of SVC was studied in different locations. Then optimum placement of the SVC was found to solve those violations.
Table 1 - Power Distributor Details of Jaffna Power distributors Contract power/MW No of generator No of transformers
Modelling of 2011 Transmission Network The 2011 power transmission network was modelled by IPSA. Here, the Jaffna peninsula is isolated from the transmission network. To study about the Sri Lankan power network three cases such as (i) Day peak, (ii) Night peak and (iii) Off peak, as shown in Figure 3, were considered with thermal maximum scenario.
IPP1
IPP2
CEB
18
15
13
7
18
14
2x(11/33 kV)
6x(0.4/11 kV) 2x(11/33 kV)
14x(0.4/33 kV)
3.1
Figure 4 - Physical Arrangement of the Jaffna MV Network
Figure 5 – Arrangement Figure 3 - Daily Electricity Load Curve in Sri Lanka (Source CEB)
Chunnakam Power Station
Different approaches were used to give the load demand for each transformer. In usual practice, using measured active and reactive power generation data of each generator units and load demand data of each distribution transformer at a particular day and time is used. However, the measured load demand for all the distribution transformers was not received. Therefore, the load demand of the each feeder was taken and it was divided by the number of distribution transformers, connected
3.2 Jaffna MV Network Modelling The Jaffna MV network modelling was done from few officially collected raw data. Jaffna MV network refers the 33 kV and 11 kV. In the existing Jaffna MV network available power generation is thermal. Power station is located at Chunnakam. Table 1 shows the details about the all three power distributers. 4
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to that particular feeder. Load flow study on the modelled Jaffna MV network was carried out successfully for both the day and night peak scenarios.
Figure 6 shows the plot of generation data with years by taking an assumption that there were no power cuts during this five year period. Since there is no linearity found in the plot, 2016 demand was predicted by using selected two gradients in a graph as shown in Figure 6.
3.3
Modelling of 2016 Transmission Network Already available model of the Sri Lankan Transmission network was upgraded to 2016 using the data given in the CEB guidelines [9]. The Jaffna peninsula demand was predicted with the calculated growth rate.
A.2 Prediction of Major Load Demand From the collected data (required MVA for the sectors) of the major loads, the demand for the major loads was calculated separately with the assumption of the power factor is 0.8.
A Prediction of Jaffna Load Demand Typical growth rate of Sri Lanka is about 6% per year [9]. When it comes to Jaffna, it varies because of different reasons such as war, displacement of people during and after the war and also last two year changes are due to several developments carried out. This irregular variation directed to do a separate study on this topic. Here, total demand was calculated by the addition of the predicted domestic demand and major loads demand.
3.4
A.1 Prediction of Domestic Load Demand The possible methods to predict the domestic MW, MVAr demands are (i) from the consumer records and monthly electricity usage, (ii) calculation from the load curve, (iii) calculation using measured data of the generation and (iv) calculation using measured demand in each transformer. Last five years data were collected from CEB to carry out this task. Since in recent past no any major loads were recorded, this domestic demand was calculated without considering the major loads. This paper explains demand prediction according to the (ii) and (iii) ways.
Table 2 - Different Generation Units
Important Cases Considered in this Study Different cases were studied on the 2016 modelled transmission network to check the reliability. Initially, studies were conducted with Mechanically Switched Capacitors (MSC) at Chunnakam according to the CEB load prediction. Table 2 shows 8 cases considered with different combinations of generation units and all of them were studied for two scenarios such as day and night peaks.
Cases 1 2 3 4 5 6 7 8
Jaffna On On On On Off Off Off Off
Combinations Puttalam On On Off Off On On Off Off
of
Trinco On Off On Off On Off On Off
As the next level of the study above mentioned different generation combinations were studied with the placement of SVC in the Killinochchi and Vavuniya grid separately. Two different predicted demand of Jaffna were calculated as mentioned in Figure 6. Study cases were analysed using the maximum predicted demand. Total of 48 cases were studied for finding the optimum placement of SVC.
4.
Results
The following results are obtained by the load flow study by using IPSA simulation tool. 4.1
Study on Jaffna MV Network-2011
Table 3 - Violated Buses in Load Flow Study Scenario Day peak
Figure 6 – Load Increase with Years to Calculate the Growth Rate in Jaffna Peninsula
Night peak
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Over loaded transformer Punkankulam (G014) and Kanagaratnam sub no-2 (G003) Punkankulam (G014)
4.2
Study on Sri Lankan Transmission Network - 2011 Voltage violation criteria (132 kV: -10% to +5% and 33 kV: ± 2%) practiced in Sri Lanka [9] was used to identify the voltage violated buses.
4.4
Case Studies
A
Result of Base Case Studies - with all MSCs according to the CEB Plan Table 9 - Base Case Studies - with all MSC
Busbar Case No Chunnaham- 132 kV Chunnaham- 33 kV Killinochchi- 132 kV Killinochchi- 33 kV Vavunia- 132 kV
Table 4 - Results of Load Flow Study
Day Peak
Galle and New Anuradhapura
Night Peak
Galle, New Anuradhapura and Ampara
Transmission line Over Loading PolpitiyaKiribath kumbura 132 kV line Colombo(E)Colombo(F) 132 kV Cable
Off Peak
-
-
Day Peak
-
PolpitiyaKiribath kumbura 132 kV line and KollonnawaPannipitiya 132 kV line
Night Peak
Galle, New Anuradhapura, Ampara and Valachchennai
Colombo(E)Colombo(F) 132 kV line
Loading Condition
Day
21/08/2011 (Sun day)
19/08/2011 (Week day)
Off Peak
4.3
Voltage Violated Grid Sub Station -
Table 5 - Results from the Load Curve 2016 Night Peak 49
Predicted MW value
Day Peak 24.5
B
Table 6 - Results from the Collected Data Year Loading Condition Growth Rate Predicted Active power demand/MW Predicted reactive power demand (A)/MVAr
2016 (using gradients 1 and 2) Day peak Night peak 1 2 1 2 32.5
43.2
12.2
43
13.539
8.88
Total
Apparent power/MVA 28.23
Active power/MW 22.584
53.867
23.859
Reactive power/MVAr 16.929
C
0.993
1.005 0.902
0.919
SVC
Placement
in
Day Peak 5 0.904 1.015 0.924 1.006 0.929
1
Night Peak 2
1.02 0.980
Result of SVC Placement in Vavuniya
Table 11 - Results with a 25 MVAr SVC Placed in Vavuniya 33 kV Busbar Case No Chunnaham- 132 kV Chunnaham- 33 kV Killinochchi- 132 kV Killinochchi- 33 kV Vavunia- 132 kV
2016 Day peak 1 2
Result of Killinochchi
Busbar Case No Chunnaham- 132 kV Chunnaham- 33 kV Killinochchi- 132 kV Killinochchi- 33 kV Vavunia- 132 kV
Table 8 - Total Predicted Demand at Jaffna at 0.4 kV Year Loading condition Growth rate Active/ Total MW predicted Reactive power /MVAr
1.000
Table 10 - Results with a 25 MVAr SVC Placed in Killinochchi (33 kV)
Table 7 - Predicted Future Major Loads Demand
Night Peak 1 2
In the simulation carried out with the day peak scenario for cases 1, 2, 3, 4, 6, 7 and 8, no voltage violations (except case 5 as shown in Table 9, where under voltage conditions are highlighted) were observed, but all the simulation cases were converged in IPSA load flow analysis, which used the fast decoupled Newton-Raphson method. Similarly a study was carried out for the night peak scenario and it was observed only case 3 succeed without any voltage violations. It is important to notify that the cases 4, 5, 6, 7 and 8 were diverged even with less number of iterations. This is mainly because of the disconnection of two large power plants together (n-2 contingency criteria), therefore they did not converge. This confirmed that one of these two power plant project should complete before providing the predicted load demand. In cases 1 and 2 had some violation as shown in Table 9, but those cases converged.
Demand Prediction of Jaffna (2016)
Year
Day Peak 5
Night peak 1 2
55.084
65.784
65.584
76.451
29.120
30.468
25.800
40.788
6
165
Day Peak 5 0.900 1.007 0.915 0.996 0.941
1
Night Peak 2
1.018
0.900
D
Selection of Worst Case
damping control as an added advantage, which will be helpful in the future, when the long transmission line is loaded much with the developments in northern part of Sri Lanka.
Out of the possible 3 cases (cases 1, 2 and 5) the worst case was case 2 at night peak. This has shown that it is possible to succeed the simulation if it has some variable reactive power compensation to boost the voltage. Therefore, this case 2 night peak was selected to analysis with the SVC and to find the optimum solution of it.
With SVC
1.0
0.8
0.6
E
Without SVC
Optimum Solution 0.4
The case 2 night peak was simulated with many possible solutions by changing the size of Kilinochchi SVC (25 MVAr) and the results show that it is not enough to improve the voltage profile. Then according to the CEB plan the MSC value is increased from 0 MVAr to 60 MVAr. Finally the optimum solution was found when placed a 25 MVAr SVC at Kilinochchi33kV and a 60 MVAr MSC at Chunnakam. Table 12 shows the results.
0.2
0.0 0
2
4
6
8
t/s
Figure 7- Voltage Variation at Kilinochchi 132 kV Busbar with & without SVC 4.6 Easy Black Start Figure 8 shows the contribution from the SVC on the voltage control during the black start-up.
Table 12 – Results with Optimum Solution
1.2
Chunnaham-132 kV Chunnaham-33 kV Killinochchi-132 kV Killinochchi-33 kV Vavunia-132 kV
Optimum Solution
Witho ut SVC
Vavuniya
Busbar
Killinochchi
With SVC in With SVC
1.0
0.8
0.6
0.906 0.984 0.901 0.980 0.900
Without SVC
0.4
0.2
4.5 Further Studies-Transient Analysis In IPSA, the equivalent circuit for the whole network at the New-anuradhapura grid was modelled without considering Chunnakam, Kilinochchi, Vavuniya and Mannar grids. Then the above four grids were connected. Then the below studies were carried out with and without SVC.
0.0 0
5
10
15
t/s
Figure 8-Black Start Voltage Profile of Kilinochchi 132 kV Busbar during Transient Simulation at 1 second of run, the line connecting Kilinochchi-132kV and Chunnakam-132kV grids was disconnected and then reconnected at 4 second. During this period, only the generation and load at Chunnakam, were disconnected. It was notified that the over voltage (greater that 1.05 pu) when load is disconnected and under voltage (lower that 0.9pu) when loads were connected without MSC. Therefore, this proves during black start-up process the busbars will have chances to get over voltage and under voltage. This may keep on tripping and black start-up will be difficult. Therefore, a dynamic voltage compensator such as SVC will help to the black start up process also.
Figure 7 shows the observed waveform of voltage variation on IPSA at Kilinochchi 132 kV busbar with & without SVC, when a threephase-ground fault was applied at Kilinochchi 132 kV busbar and the fault was removed after 200ms. SVC model in IPSA simulation package (Ver. 1.6) does not have control for damping power fluctuations. Therefore, the waveform in Figure 7 doesn’t show oscillation damping. But it has been proven in [13] that the SVC works perfectly for power oscillation damping if the relevant control is incorporated. Small oscillations in the voltage may result larger voltage in power. Placement of SVC brings 7
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Another option is using Chunnakam power station and do the restoration with few loads in islanded mode and finally connected to the main grid. However, synchronisation should be done between two systems carefully. Dynamics of this operation need to be studied further. This paper discussed the SVC application with many functions including black start up.
5.
compensation for smooth voltage control and fast reactive power control for black start up. Optimum placement of SVC has been suggested to avoid violations to bring the power system efficient and reliable. All the observed problems were solved by the placement of the 25MVAr SVC at Killinochchi and 60 MVAr as the total MSC placement at Jaffna.
Discussion
Authors of this paper strongly believe that this paper will be a supportive document to CEB planning engineers as an independent study, which suggests using SVC as a solution to the reactive power compensation. Further studies can be made to minimum possible capacity of the SVC with some cost analysis.
According to the Long Term Transmission Plan (2011-2020) released by the CEB, the predicted night peak active and reactive power demands of the Jaffna Peninsula are 64.4 MW and 13.1 MVAr, respectively. But this study results predicted the Jaffna Peninsula demands as 76.45 MW and 40.78 MVAr. The reason for this variation is the consideration of the actual system and the ongoing growth rate prediction. CEB has proposed the predicted reactive power compensation for the Jaffna peninsula as 30 MVAr. The study explained in this paper proposed an additional reactive power compensation of 25 MVAr at Kilinochchi or Vavuniya to supply the predicted demand. But from the case studies, it was proved that Kilinochchi is the best place for the system reliable and efficient if the reactive power compensator includes SVC also. From the results it was observed that 25 MVAr reactive power compensation is not enough to keep the system with the best solution. Therefore, further analyses were conducted. As the result of them addition of 30 MVAr MSC to the CEB predicted MSC at Jaffna Peninsula together with the 25 MVAr SVC at Killinochchi is the best solution for the efficient and reliable Sri Lankan power system. With this compensation Northern power system grid will be efficient and reliable.
6.
Acknowledgements First of all, we sincerely thank Eng. Rohana Ekanayake, Transmission Engineer (CEB) for providing his IPSA model of Sri Lankan transmission network as in 2007. We are heartily thankful to, Assistant General Manager, Deputy General Manager (DGM) and the Chief Engineer of Transmission Planning of CEB. DGM, Planning Engineer, Electrical Engineers and Electrical Supernatants of Northern Province are to be thanked for providing their fullest support to use their resources. Finally our thanks go to the Department of Electrical and Electronic Engineering, University of Peradeniya for providing the platform for our research and to CEB for helping us in various circumstances.
References
Conclusions
This research yields an accurate model of the predicted Sri Lankan transmission network, which includes Northern part of Sri Lanka. Addition to that, this study explains the growth rate calculation using historical data and consideration of the future Jaffna developments (explained in Section 3.3-A). Further, this paper proposes integration of FACTS devices to improve the power system performance in terms of voltage boosting, damping power fluctuations and easy black start-up. SVC has been proposed to achieve static and dynamic control for steady state and transient operations such as continuous reactive power 8
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1.
Dolezal J., Santarius P., Tlusty J., Valouch V., Vybiralik F., “The Effect of Dispersed Generation on Power Quality in Distribution System”, Quality and Security of Electric Power Delivery Systems, 2003. CIGRE/PES 2003. CIGRE/IEEE PES International Symposium, 8-10 Oct. 2003, pp: 204 – 207.
2.
Zhu Dan, “Power System Reliability Analysis with Distributed Generators”, Thesis, Virginia Polytechnic Institute and State University, May, 2003.
3.
Papadopoulos M.P., Peponis G.3. and Ilatziargyriou N. D., “Distribution Network Reconfiguration to Minimize Resistive Line Losses”, Proceedings of the Joint International Power Conference, Sep 1993, Vo. 2, pp. 601–605.
4.
Hingorani Narain G., Gyugyi Laszlo, “Understanding FACTS Concepts and Technology of Flexible AC Transmission Systems”, (book), IEEE Press, New York NY, ISBN 0-7803-3455-8, 2000, Wiley.
5.
Hingorani N. G., “FACTS Technology - State of the Art, Current Challenges and Future Prospects”, IEEE Power Engineering Society (PES) General Meeting, June 2007, pp. 1-4.
6.
Laszlo Gyugyi, “Power Electronics in Electric Utilities: Static VAr Compensators”, Proceedings of the IEEE, Vol. 76, No. 4, April 1988, pp. 483–494.
7.
Ekanayake J. B., “An Investigation of an Advanced Static VAr Compensator”, PhD Thesis, University of Manchester Institute of Science and Technology (UMIST), September, 1995.
8.
de Vos A. and Rowbotham T., “Knowledge Representation for Power System Modelling” 22nd IEEE Power Engineering Society (PES) International Conference, 2001, pp. 50 – 56.
9.
Long Term Transmission Development Plan (2008-2016), (2011-2020) and MV Distribution plan (2010-2019)-Region 1, Ceylon Electricity Board (CEB).
10.
Hammad A.E., “Analysis of Power System Stability Enhanced by Static VAR Compensators”, IEEE Transactions on Power Systems, Vol. 1, No. 4, November 1986, pp. 222-227.
11.
Kundur P., “Power System Stability and control”, McGraw-Hill Inc. 1994.
12.
Ceylon Electricity Board (CEB), Sri Lanka, official website. http://www.ceb.lk/.
13.
Arulampalam A., Saha T.K., “Static VAr Compensator for Damping Power Fluctuation with Locally Measured Parameters - Hybrid Control Technique using Power, Rate of Change of Power and Phase Angle”, IEEE 20th Australasian Universities Power Engineering Conference (AUPEC 2010), December 2010, pp. 1-6.
9
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Annual Transactions of IESL, pp. [169-175], 2012 © The Institution of Engineers, Sri Lanka
Viability of Grid Connected Small Wind and Solar Photovoltaic Home Systems in Sri Lanka Mahinsasa Narayana Abstract: According to the present energy scenario in Sri Lanka, out of whole electricity generation 65% is generated by fossil fuel and it is a large fraction of the total imports. In this situation, utilization of renewable energy for electricity generation is very important to reduce the requirement of foreign currency. Wind and solar energy has been identified as promising available renewable energy resources and then small-scale grid connected wind and solar systems are being promoted and hope to introduce encouraging net-metering in-feed tariff rates. The focal point of this study is evaluation of the economic viability of the solar and wind home power systems to verify suitable in-feed tariff rates. The current market price of the systems and operational cost mainly depend on the size and type of the model. In this study, the capacities 1kW p solar and 2.4 kW wind systems were considered. The hourly based energy generations were evaluated by the power curve of the small wind system and performance of the solar system for available solar and wind resource data in different locations in the country. The total cost expenditures within life time of the systems were evaluated by considering net present value of capital cost, operational cost and salvage cost. Keywords:
1.
Small Scale wind and solar, Net-metering, Cost of energy generation
to be evaluated in residential areas with netmetering facility. In this study, hourly based energy generations were considered by using the power curve of a commercially available small wind system and performance of the solar PV system for available solar and wind resource data in Colombo suburbs and Hambantota. Then viability of solar and wind systems in different two locations of the country was reviewed in this study. The total cost expenditures within life time of the systems were evaluated by considering netpresent value of the investment cost, operational cost and salvage cost.
Introduction
Hydropower is the major renewable energy contribution to the network in Sri Lanka. However, it is limited for further developments and the demand for electricity is estimated to rise at an annual pace of 8% - 10% [1]. Wind and solar energy have also been identified as promising available renewable energy resources to generate electricity in Sri Lanka[2]. Due to recent developments in the power electronic sector, controllability of grid power quality has been improved and distributed micro power generations are being encouraged throughout the world. Therefore, small-scale renewable energy based power generation can be absorbed and transmission losses can be reduced as a result of localized distributed generations. This smart grid technology is capable to harness more renewable and improves energy efficiency. Presently, smallscale grid connected wind and solar systems are being promoted in Sri Lanka and hope to introduce encouraging net-metering in-feed tariff rates. Cost of energy is the critical factor rather than capacity or plant factor and conversion efficiency in renewable energy generations. That is mainly depends on investment cost of the plant and available resources. The current market price of the systems and operational cost mainly depend on the size and type of the model. Grid connected solar and wind power micro generations need
2. Solar and Wind Energy Resources in Sri Lanka 2.1 Solar Resources Solar resource assessment results show availability of good annual global radiation levels all over the country, in the range of 5.0 to 6.0 kWh/m2/day on flat plate collector tilted at the latitude [3]. Thus, there is lot of potential for flat plate collectors based solar heating systems and all the applications of solar photovoltaic. The variability in global horizontal solar resource is relatively small across most of the
Eng. (Dr.) Mahinsasa Narayana. C. Eng., MIE(Sri Lanka), B.Sc. (Eng,), MPhil (.Eng.) , PhD, Senior Lecturer, Department of Chemical and Process Engineering, University of Moratuwa, Sri Lanka.
1
169
of 600 W/m2 and above) [5]. If one also includes sites with moderate wind resources, then this potential increases to 51350 MW [5].
country. The highest resources are in the northern and southern regions, and the lowest resources are in the interior hill country [3]. During the southwest monsoon the northeast portion of the country shows quite high solar resources. During the northeast monsoon, the southern and western portions of the country show higher resources. However, the highest resources occur during the hot dry period from March and April. However, annual direct normal radiation levels are low, ranging from 3.5 to 4.5 kWh/m2/day [3].
Generally small scale wind turbines are installed at lower heights in constricted areas. Therefore in this study, the logarithmic profile (or log law) assumes that the wind speed is proportional to the logarithm of the height above ground. The following equation gives the ratio of the wind speed at hub height to the wind speed at anemometer height [6]:
7 6
Daily radiation (kWh/m2/day) Clearness index
0.7
0.5 3
0.4 0.3
2
WRAM wind map was predicted 50 m height wind speeds [5]. Practical maximum hub height of small scale wind turbines is around 20 m. The typical surface roughness length in Colombo suburbs is assumes as z0=1.5 m [7]. The surface roughness length for many trees and few buildings, which is applicable to Hambantota, is z0= 0.25 m [7]. Estimated wind speeds at 20 m height by considering the logarithmic profile in a location of Colombo suburbs and near Hambontota are shown in Table 1.
0.2 1
0.1 0
Daily radiation (kWh/m2/day)
0 Jan Feb Mar Apr May Jun
Jul Aug Sep Oct Nov Dec
6
Daily radiation (kWh/m2/day)
1
Clearness index
0.9 0.8
5
0.7
Clearness Index
Figure 1 - Daily Radiation at Colombo
7
0.6
4
........ (1)
the hub height of the wind turbine [m] the anemometer height [m] the surface roughness length [m] wind speed at the hub height of the wind turbine [m/s] vanem = wind speed at anemometer height [m/s] ln(..) = the natural logarithm
0.6
4
h ln hub z 0 h anem ln z0
where, hhub= hanem= Z0 = vhub =
1 0.9 0.8
5
vhub v anem
Clearness index
Daily radiation (kW/m 2/day)
Latitude value at Colombo and Hambantota is used to calculate average daily radiations from the clearness index and vice-versa [3,4]. Annual average tilted at latitude radiation in Colombo is 4.81kWh/m2/day and in Hambantota is 5.31kWh/m2/day[3]. Daily radiation in Colombo and Hambantota are shown Figure 1 and 2.
0.5 3
When hourly wind speed measurements are not available, hourly data can be generated synthetically from monthly averages. Generate a first-order autoregressive sequence for wind data with the desired degree of autocorrelation [8-10]. Following first-order autoregressive model (see Equation 2) was used to generate hourly based wind data from WRAM wind map wind data [9]. As general rules of thumb, the lower the autocorrelation factor the higher the value of wind power. Autocorrelation factor is assumed in the location at Colombo suburbs is 0.99 and near Hambantota is 0.97 [11, 12].
0.4 0.3
2
0.2 1
0.1
0
0 Jan Feb Mar Apr May Jun
Jul Aug Sep Oct Nov Dec
Figure 2 - Daily Radiation at Hambantota 2.2 Wind Resources As per the Wind Resource Assessment Model (WRAM), total wind electric potential (on land only) is about 20750 MW for large scale wind power generations, if one considers only those sites that have wind resources in the category of either `good’ (Wind power density of 400 – 500 W/m2) or `excellent’ (Wind power density
wt awt 1 f (t) 2
170
.........
(2)
where, wt = wt-1 = a= f(t) =
The International standard ISO 9845-1:1992 is defined for terrestrial use of solar PV. The AM1.5G global spectrum is designed for flat plate modules and has an integrated power of 1000 W/m2. Then energy output per day of a PV panel is given by;
the wind speed value in time step t the wind speed value in time step t-1 the autoregressive parameter a 'white noise' function that returns a random number drawn from a normal distribution with mean of zero and a standard deviation of 1
Energy Output per day (kWh / day) System size(W p ) Solar insolation (kWh / m 2 / day)
Table 1 - Monthly Average Wind Speeds at 20 m Height Monthly average wind speed at 20m height (m/s) Months Colombo Hambantota suburbs Jan 3.0 5.7 Feb 2.0 5.0 Mar 2.5 4.3 Apr 2.8 3.2 May 4.9 6.0 Jun 5.3 6.2 Jul 5.0 6.5 Aug 5.3 7.0 Sep 4.7 4.7 Oct 3.8 5.4 Nov 2.8 2.4 Dec 3.0 2.9 Average 3.9 4.8
3. Solar and Wind Generations
AM1.5G(1000W / m 2 )
...... (4) For grid connection, a grid tied inverter is used to convert DC power from the solar PV to AC power with correct frequency, phase angle and voltage, which are compatible with the grid power quality. Generally, grid tied inverter has conversion efficiency of 80-90%, which was considered for energy calculations. In this study, system capacity of 1 kW p PV panel is used to evaluate energy generation in locations of Colombo suburbs and near Hambontota. According to the solar resources data in each location, a solar system of 1kW p capacity can generates 1726 kWh/year in Colombo suburbs and 1866kWh/year near Hambantota (see Equation 4). 3.2 Wind Energy Generations A grid connected variable speed type smallscale wind turbine system consists of a wind turbine, a DC/DC converter for power control and a grid tied inverter. All conversion efficiencies were considered for energy calculations. Schematic of a grid connected small wind turbine is shown in Figure 3.
Energy Micro
3.1 Solar Energy Generations Air Mass (AM) is the measure of how far sun light travels through the Earth's atmosphere. One air mass, or AM1, is the thickness of the Earth's atmosphere. Air mass zero (AM0) describes solar irradiance in space, where it is unaffected by the atmosphere. The power density of AM1.5 light is about 1000 W/m2; the power density of AM0 light is about 1360 W/m2, which is considered to be the solar constant [13]. 1 AM ..... (3) cos where,
Generally for net-metering purpose, capacities of 25W to 10 kW range of wind turbines are used. In some countries, small rooftop wind turbines are also becoming popular in urban areas. For this study capacity of 2.4 kW commercially available small wind turbine (SW-Skysream3.7) was selected and the power curve of the wind turbine is shown in Figure 4 [14].
: Zenith angle (=48.20 for AM1.5) AM1 : Sun directly overhead AM1.5G : “Conventional” G(Global): Scattered and direct sunlight D(Direct): Direct sunlight only AM0 : Just above atmosphere (space applications) Figure 3 - Schematic of a Grid Connected Small Wind Turbine
3
171
i(1 i)N CRF (i, N ) N (1 i) 1
Power (kW)
2.5
where; Ccap Crep CRF() i
2
1.5
1
0.5
N
........... (9)
= Initial investment (Rs.) = Replacement cost (Rs.) = Capital recovery factor = Real interest rate (reflects inflation and bank loan interest rate) = Project life time
0 0
3
6
9
12
15
18
21
A Capital Recovery Factor (CRF) converts a present value into a stream of equal annual payments over a specified time, at a specified real interest rate. Preset real interest rate in Sri Lanka is around 7%, which is reflected the inflation and nominal bank interest [15]. Annualised replacement cost of a system is the annualised value of the all the replacement cost occurring throughout the lifetime of the project minus the salvage value at the end of the project. Generally maintenance cost (CO&M) is increasing with the price increasing of spare parts and labour cost. It is assume that this variation is in accordance with the inflation and interest rates.
Wind speed (m/s)
Figure 4 - Power Curve of a Commercially Available Small Scale Wind Turbine Annual energy output of the wind turbine system was evaluated based on hourly wind speed data for 20 m hub height in locations of Colombo suburbs and near Hambontota. According to the wind resources data in each location, this wind turbine can generate 987 kWh/year in Colombo suburbs and 3048 kWh/year near Hambantota.
4. Cost of Energy Generation
4.1 Cost of Solar Energy Generation The cost of photovoltaic systems has fallen rapidly. Over the last 30 years, researchers have watched as the price of capturing solar energy has dropped exponentially. The price per Watt of solar modules has dropped from $22 in 1980 down to under $1.5 today [16]. Presently cost of 1kW solar PV module and grid tied inverter installation is less than $2300 [17,18]. However, initial investment cost per 1 kW installation depends on module size. Generally higher capacities can be installed with lower cost per 1 kW installation. Surface area of 8 m2 is required for 1 kW p PV module and then 1 kW p capacity is appropriate for domestic installation in Sri Lanka for the net-metering application. Therefore, in this study 1kW p grid connected solar PV module was considered for cost of energy calculation in different locations in the country. Solar PVs are maintenance free and life time is around 20 years. Replacement cost is considered equal to initial cost of the system and then salvage cost is neglected. The cost of solar energy generation in each location was evaluated (see Equation 4) by considering annualised cost and annual energy generations.
Analysts are frequently interested in the capacity factor for power generation systems. It is definitely not desirable to increase the capacity factor for a renewable energy based power generations, as it would be for technologies where the fuel is not free! Cost of energy and initial cost of the system are the most important parameters to evaluate and compare the each renewable energy based power generation systems and possible locations with resources data.
COE
C ann,tot E
.......
(5)
where; COE = Cost of energy (Rs./kWh) Cann.tot = Total annual cost (Rs.) E = Annual Energy Generation (kWh)
Cann,tot Cann.cap Cann.rep CO&M ...... (6) Total annual cost of the system (Cann,tot) is the sum of the annualised capital cost (Cann,cap), the annualised replacement cost (Cann,rep) and the annual operation and the maintenance cost(CO&M).
Cann,cap Ccap .CRF (i, N )
.......... (7)
Cann, rep Crep .CRF (i, N )
.......... (8) 4
172
Cost of Energy Geneartion (Rs./kWh)
costs are between 1.5% and 2% of the turbine cost but increase with time as the turbines get older [17, 20]. Life time of the system is taken as 20 years. Replacement cost is considered equal to initial cost of the system and then salvage cost is neglected. The cost of wind energy generation Vs initial investment cost in a location at Colombo suburbs is shown in Figure 7 and a location near Hambantota is shown in Figure 8. If the initial investment cost of a small wind turbine is around Rs. 500,000 per 1 kW installation [19], cost of wind energy in a location at Colombo suburbs is 115.25 Rs./kWh and near Hambantota is 37.30 Rs./kWh.
25 20 15 10 5 0 0
100000
200000
300000
400000
500000
Investment cost of 1kW PV system (Rs.)
Figure 5 - Cost of Solar Energy Generation Vs Investment Cost of 1kWp PV System in Colombo Suburbs
5. Conclusions In this paper, initial cost of systems are indicated in $US, as presently these components need to be imported from foreign countries. Present value of energy cost noted in the local currency, which should be reasonable with local in-feed tariffs. Cost of Energy Generation (Rs./kWh)
Cost of Energy Generation (Rs./kWh)
The cost of solar energy generation Vs initial investment cost of a 1 kW system in a location at Colombo suburbs is shown in Figure 5 and a location near Hambantota is shown in Figure 6. These graphs show cost of solar energy generations with the variation of market value (or initial investment) of equipments. If the initial investment of 1 kW grid connected solar home system is around Rs. 275, 000, cost of solar energy generation in a location at Colombo suburbs is 15Rs./kWh and near Hambantota is 14 Rs./kWh. 25 20 15 10
200 180 160 140 120 100 80 60 40 20 0
5
100000 200000 300000 400000 500000 600000 700000 Investment cost per 1kW installation ( Rs.) 0
Cost of Energy Generation (Rs./Kwh)
0 100000 200000 300000 400000 500000 Investment cost of 1kWp PV system (Rs.)
Figure 7 - Cost of Wind Energy Generation Vs Investment Cost per 1 kW Installation in Colombo Suburbs
Figure 6 - Cost of Solar Energy Generation Vs Investment Cost of 1 kWp PV System in Hambantota 4.2 Cost of Wind Energy Generation Cost of typical small wind system in the world is $3,000 - $5,000 per 1 kW capacity installed [19]. In this study, sensitivity analysis of cost of energy generation and investment cost was done by considering performance of 2.4 kW small wind turbine system (SW-Skysream3.7) and wind resources data in two different locations in the country. A small wind turbine requires periodic, usually annual maintenance such as oiling, regular safety inspections check electrical connections, check wind turbines for corrosion and the guy wires supporting the tower for proper tension, etc. The maintenance
60 50 40 30 20 10 0 100000 200000 300000 400000 500000 600000 700000 Investment cost per 1kW installatiom ( Rs.)
Figure 8 - Cost of Wind Energy Generation Vs Investment Cost per 1 kW Installation in Hambantota
5
173
Small scale wind turbines are possible to manufacture in Sri Lanka. Presently locally manufactured small wind turbines are used for off-grid applications [21-23]. This study was based on an imported wind turbine and cost of energy depends on initial cost of that system. This study shows that cost of wind energy generation is not competitive with other sources of generations. However, there is a option to produce grid connected small wind turbines locally with less initial investment to tally with appropriate cost of energy generation. Small scale wind turbines, which are used for net-metering applications, are restricted to install in residential areas, where the wind speed potential is not much high due to high surface roughness value of terrain conditions. However, large scale wind generations are much cheaper than small scale wind power generations as well as these can be sited in best locations [24]. In this study, WRAM wind map data is used and the logarithmic profile is assumed to predict wind speeds at the turbine hub height. Therefore, proper micro sitting with ground measurements should be carried out to estimate more accurate energy productions in each location in the country.
metering applications same power applied for sell back power and then feed tariff rate (15Rs./kWh) does promote the grid feeding of solar micro power generations.
prices are present innot much and wind
This study shows that in-feed tariff rates must be varied with the location and system size to encourage the grid feed micro electricity generations for net-metering.
References 1.
2.
3.
4.
5.
The less solar power costs, the more favourably it compares to conventional power, and the more attractive it becomes to utilities and energy users around the globe. Presently solar PV is not manufactured in Sri Lanka and hence, foreign currency is spent on purchase of equipment for solar energy generation. However, this study shows that cost of solar energy generation is competitive with present in-feed tariff rates for other renewable in Sri Lanka [25]. At the producing stage of PV, it requires large amount of energy for silicon process. Still the energy payback period of solar PV is around 2-3years [26], which is comparatively high with other source of energy generations.
6.
7.
8.
9.
10.
Annual average household electricity consumption in urban areas is around 1200 kWh per year [27] and then this amount can be fulfilled by a small solar or wind home system. The tier type tariff mechanism is applied in Sri Lanka for grid electricity sales [28] and then for typical house mean electricity flat rate is around 15 Rs./kWh [29]. For net-metering connections in Sri Lanka the consumer is not paid for export of energy, but is given credit (in kWh) for consumption of same amount of energy later [30]. Therefore, presently for net
11.
12.
6
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CEB. 2010 [cited; Available from: http://www.ceb.lk/sub/publications/stati stical.aspx. Solar and Wind Energy Resource Assessment; Sri Lanka Country Report: Energy Status and Renewable Energy Deployment, 2003, National Engineering Research and Development Centre, Sri Lanka: Ekala, Jaela. Schillings, C., R. Meyer, and F. Trieb, High Resolution Solar Radiation Assessment for Sri Lanka. 2004, Deutsches Zentrum für Luftund Raumfahrt (DLR). Umanand, L. and R. Kumar, Estimation of Global Radiation using Clearness Index Model for Sizing Photovoltaic System, Renewable Energy, 2005. 30: pp. 2221–2233. Elliott, D., et al., Wind Energy Resource Atlas of Sri Lanka and the Maldives, 2003, National Renewable Energy Laboratory, USA. Tennekes, H., The Logarithmic Wind Profile. Journal of Atmospheric Sciences, 1973. 30(02): pp. 234-238. Manwell, J.F., J.G. McGowan, and A.L. Rogers, Wind Energy Explained: Theory, Design and Application, 2002: John Wiley & Sons. Suomalainen, K., et al., A Method for Including Daily Patterns to Synthetic Wind Speed Data for Energy Systems Planning: Validation in the Azores Islands, Journal of Renewable and Sustainable Energy 4(2): p. 15. Aksoy, H., et al., Stochastic generation of hourly mean wind speed data. Renewable Energy, 2004, 29(14): pp. 2111–2131. Fidan, M., F.O. Hocaoğlu, and Ö.N. Gerek, Improved Synthetic Wind Speed Generation using Modified Mycielski Approach, International Journal of Energy Research, 2011. Cancino-Solórzano, Y., A.J. GutiérrezTrashorras, and J. Xiberta-Bernat, Analytical Methods for Wind Persistence: Their Application in Assessing the Best Site for a Wind Farm in the State of Veracruz, Mexico. Renewable Energy, 2010, 35(12): pp. 28442852. Sahin, A.D. and Z. Sen, First-order Markov Chain Approach to Wind Speed Modelling.
13.
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24.
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27.
Journal of Wind Engineering and Industrial Aerodynamics, 2001. 89(34): p. 263-269. Myers, D.R. and K. Emery, Revising and Validating Spectral Irradiance Reference Standards for Photovoltaic Performance, in ASES/ASME Solar 2002, 2002: Reno, Nevada. Southwest Windpower, I., Power Performance Measurement on the Skystream 3.7 according to IEC 61400-12-1 and BWEA. 2009. Central Bank of Sri Lanka, 2010 [cited; Available from: http://www.cbsl.gov.lk/ htm/english/_cei/ir/i_1.asp. Scientific American. 2012 [cited; Available from: http://blogs.scientificamerican.com/guestblog/2011/03/16/smaller-cheaper-fasterdoes-moores-law-apply-to-solar-cells/. New Energy. 2012 [cited; Available from: http://www.dcac-powerinverter.com/products.html. navitron. 2012 [cited; Available from: http://www.navitron.org.uk/. Small Wind Systems. 2012 [cited; Available from: http://www.seco.cpa.state.tx.us/ re_wind_smallwind.htm. Forsyth, T., P. Tu, and J. Gilbert, Economics of Grid-Connected Small Wind Turbines in the Domestic Market, in AWEA Wind Power 1999: Burlington, Vermont. Narayana, M., Micrositing of Small-Scale Wind Turbines is Economically Viable For Rural Electrification in Sri Lanka, in The International Technical Conference, 8th German Wind Energy Conference. 2006: Bremen, Germany. Dharmakeerthi, C.H., A. Arulampalam, and J.B. Ekanayake. Field Experience with an islanded micro wind power plant, in IEEE International Conference on Sustainable Energy Technologies (ICSET). 2008, SMU conference center, Singapore. Binduhewa, P.J., et al. Design and Implementation of a Novel Controller for Autonomous 2.5 kW Wind Power Plant in EEE first International Conference on Industrial and Information Systems, 2006, University of Peradeniya, Sri Lanka. Narayana, M., Validation of Wind Resource Assessment Model (WRAM) map of Sri Lanka, using Measured Data, and Evaluation of Wind Power Generation Potential in the Country, Energy for Sustainable Development, 2008, 12: p. 64-68. CEB. Non conventional Renewable Energy Tarff Announcement, 2010 [cited 2012/05/20]; Available from: http://www.ceb.lk/download/db/ncre_ta riff.pdf. NREL. What is the energy payback for PV? 2004 [cited; Available from: http://www.nrel.gov/docs/fy04osti/35489 .pdf. Study on Requirement of Prospective Electricity Consumers and Fuel Poverty (Electricity) &
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29.
30.
7
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Affordability. 2010, Social Policy Analysis and Research Centre, University Of Colombo: Colombo. CEB. Tariff Plan. [on-line] 2012 [cited 2012 29th July]; Available from: http://www.ceb.lk/sub/residence/tariffpl an.html. CEB. Bill Calculator. 2012 [cited 2012 04/08/2012]; Available from: http://www.ceb.lk/sub/business/billcalcu lator.aspx. CEB. What is Net Metering. 2012 [cited; Available from: http://www.ceb.lk/sub/db/readmore.htm l.
Annual Transactions of IESL, pp. [176-184], 2012 © The Institution of Engineers, Sri Lanka
Condition Assessment of Current Transformers - Chemical and Electrical Analysis of Transformer Oil M.A.A.P. Bandara, B.S.H.M.S.Y. Matharage, M.A.R.M. Fernando and G.A. Jayantha Abstract: This paper presents condition assessment of current transformers based on electrical and chemical analysis on field-aged and laboratory-aged transformer oil samples. The electrical analysis included the measurement of breakdown voltage and frequency dielectric spectroscopy covering frequency variation of the loss tangent, the permittivity and the conductivity. The chemical analysis represents measurements of dissolved fault gases, acidity, inter-facial tension and moisture content. In the laboratory ageing, 12 virgin transformer oil samples were continuously aged at 120°C inside an oven. The samples sets were divided into four categories: dry sealed, wet sealed, dry unsealed and wet unsealed, to represent the sealed and unsealed transformers as well as ageing with and without moisture. The three samples in each category were aged with different ageing times of 2, 4 and 7 weeks. In addition, Cu, Al, Fe and Zn metal substances were added to each sample to see the catalytic effect of the materials used in real transformers. In comparison, 16 field-aged oil samples were taken from current transformers selected in three power stations covering 25-50 service years. Both field-aged and laboratory aged oil samples were analysed by visual inspection (colour), electrical and chemical tests. It was found that the chemical and electrical analysis provide useful information about condition of the tested oil samples. Keywords:
1.
Transformer oil, Current transformer, Electrical tests, Chemical tests
average life time of such transformers ranges from 20 to 30 years, provided that an assessment of the condition of the insulation is done at regular interval. It is therefore, essential the use of maintenance techniques that protect such important and high value investments. Extensive studies have been conducted on analysing the transformer insulation condition using different evaluation techniques [3-9].
Introduction
Current transformers (CTs) are one of the most important high voltage apparatus installed at power stations and substations for both measuring and protection purposes [1]. Failures of high voltage (HV) CTs with porcelain housings can be catastrophic and usually lead to severe explosions. Hence, condition monitoring of the CTs in switchyards and transformers has become utmost important. For example, severe explosion of a 132 kV, CT recently reported from Rantambe Power Station resulted loss of life of one of the technical personnel, indicated how fatal was the accidents of HV CTs.
At present, Ceylon Electricity Board (CEB) adopts methods to monitor the condition of CTs which are in service. They are the measurement of dissipation factor from primary terminal to test-tap and test-tap to
The CT failures occur due to different types of reasons such that insulation failures, open circuit on secondary, open circuit in capacitive test tap, oil leakages etc. The reliability of a CT mainly depends on its insulation condition. Normally, the insulation system of a CT consists of mineral oil, cellulose paper and pressboard. However, when the transformers are exposed to different stresses over their life time, their insulation may deteriorate causing reduction of the dielectric strength of the insulation and increase of the probability of insulation failure [2]. It is noteworthy that the
Eng. M.A.A.P. Bandara, B.Sc. Eng. (Peradeniya), AMIE(Sri Lanka), Operation Engineer, Kotmale Power Station, Ceylon Electricity Board. Eng. B.S.H.M.S.Y. Matharage, B.Sc. Eng. (Peradeniya), AMIE(Sri Lanka), Temporary Instructor, Department of Electrical and Electronic Engineering, University of Peradeniya. Eng. (Prof.) M.A.R.M. Fernando, C.Eng., IntPE, MIE(Sri Lanka), B.Sc. Eng., Tech Lic. PhD, SMIEEE, Associate Professor, Electrical and Electronic Engineering Department, Department of Electrical and Electronic Engineering, University of Peradeniya. Eng. G.A. Jayantha, B.Sc. Eng. (Peradeniya), C.Eng., MIE(Sri Lanka), Deputy General Manager (Generation Projects) , Ceylon Electricity Board.
1
176
earth at 10 kV and 2.5 kV voltages, respectively. Measurement of capacitances and internal pressure are also included in those tests. However, oil analysis together with the above tests would give easy and detailed information about the condition of the CT. Unlike larger ventilated type power transformers, CTs have limited oil capacity and removal of 1-2 l of oil for testing is a considerable amount and may affect to the operation of the CT. Since the procedure required for oil sampling and refilling is complicated, utilities are reluctant to perform oil testing very frequently. It is therefore, important of consider tests which require very small amounts of oil as well as provides useful information about the condition of the oil. Frequency Dielectric Spectroscopy (FDS) measurement covering frequency variation of the loss tangent, the permittivity and the conductivity is good in this respect. It also gives good correlation with other tests such as Dissolve Gas Analysis (DGA), acidity, moisture content etc.
Figure 1 – Failure of Current Transformer When condition assessment of CTs is considered, basically DGA and moisture content (MC) are the major analysing tools used by most utilities.
3.
DGA has been used for many years as an effective and reliable tool to detect incipient faults in mineral oil filled transformers. This method is based on the analysis of the concentration and rate of gases generated and dissolved in transformer oil, and associates the kind of failures with the presence of those gases [10]. There are mainly seven types of dissolved fault gases namely Hydrogen (H2), Carbon monoxide (CO), Carbon dioxide (CO2), Methane (CH4), Ethane (C2H6), Ethylene (C2H4), Acetylene (C2H2).
This paper presents condition assessment of CTs in Sri Lanka. Electrical and chemical tests were conducted on field-aged and laboratoryaged oil samples to show the potential of monitoring the condition of the oil-filled CTs.
2.
Current Faults
Transformers
Dissolved Gas Analysis (DGA)
and
3.1 DGA Evaluation Techniques The IEC 60599 gives typical values of fault gases used for CTs. Two evaluation methods are commonly used to evaluate DGA in transformers namely Basic Gas Ratio and Duval triangle Method [10]. The IEEE analysis method uses the concept of key gases. For example, low intensity PD or corona produces mainly H 2. Same way, the key gas C2H2 is for arcing; C2H4 for overheating oil and CO is for overheating of cellulose [11].
The CTs belonging to the group of instrument transformers has a basic function of measuring high currents which can’t be measured with normal measuring equipments. Insulation of CTs consists of solid (paper, pressboard) and liquid (mineral oil) insulations. Mainly solid insulation is used to provide the insulation for the primary and secondary windings whereas the liquid insulation provides transformer insulation as well as cooling the windings. The CT failures can be severe since they are often followed by explosions. Figure 1 illustrates this effect. The consequence of such a failure is not only net disturbances, but also a high risk of personnel injuries and damage to surrounding equipment due to the possible launching of porcelain splinters [1]. The main factors for oil-paper insulation ageing can be listed as; 1) Degradation due to the development of ionization processes, 2) Thermal Ageing, 3) Degradation caused by oxidation processes in oil, 4) Moistening of the insulation [1]. Mainly there are five types of faults identified in CTs [10].
4.
Sample Preparation and Test Procedure
4.1 Laboratory Aged Samples Twelve virgin transformer oil samples were prepared according to the details given in Table 1 and Table 2. The sample sets were divided into four categories: dry sealed, wet sealed, dry unsealed and wet unsealed, to represent the sealed and unsealed transformers as well as ageing with and without moisture. In addition, Cu, Al, Fe and Zn metal substances were added to each sample to see the catalytic effect of the 2
177
materials used in real transformers [12]. The total ageing period was about seven weeks which gives satisfactory ageing [4].
years, 15 years). Sampling were done under very dry condition in mid day time (around 300C and humidity less than 50%). The details of the oil samples are shown in Table 3.
Table 1 – Details of the Oil Samples Table 3 – Details of Field Aged Oil Samples Aging Sample Volume Time Temperature No. [ml] [hours] NT New Transformer Oil (NT) Unsealed Wet Transformer Oil (UWT) 1200C for UWT1 200 1000 upto 200 UWT2 438 1000 hours then between UWT3 640 1100 1100C-1300C Unsealed Dry Transformer Oil (UDT) UDT1 200 1000 1200C for upto 200 UDT2 438 1000 hours then between UDT3 640 1100 1100C-1300C Sealed Wet Transformer Oil (SWT) SWT1 336 1000 1200C SWT2 840 1000 SWT3 1176 1000 Sealed Dry Transformer Oil (SDT) SDT1 336 1000 1200C SDT2 840 1000 SDT3 1176 1000
Power Station
Voltage [kV]
KOT/01 UKU/01 UKU/02 UKU/03 UKU/04 UKU/05 UKU/06 UKU/07 UKU/08 UKU/09 UKU/10 UKU/11 UKU/12 UKU/13 UKU/14 UDW/01
Kotmale Ukuwela Ukuwela Ukuwela Ukuwela Ukuwela Ukuwela Ukuwela Ukuwela Ukuwela Ukuwela Ukuwela Ukuwela Ukuwela Ukuwela Udawalawe
220 132 132 132 132 132 132 132 132 132 132 132 132 33 33 33
Ageing Time [Years] 26 35 35 35 34 34 34 33 33 33 35 35 35 26 26 49
4.3 Ageing Procedure Sealed oil samples were aged inside a drying oven for a temperature of 120 0C up to 1176 hours continuously. Pressboards were added to wet samples and kept for whole ageing period.
Table 2 – Materials Added to Each Sample Transformer Material Aluminium (Al) Zinc (Zn) Copper (Cu) Iron (Fe) Press board
Sample No.
Quantity [g/l] 0.5 0.5 2.5 2.5 100
Unsealed oil samples were aged inside the drying oven initially for 200 hours at 1200C, and then for 1200 hours as a cyclic manner (nearly half a day ageing and a half day resting) at between 1100C and 1300C. Pressboards were added to wet samples and kept initially for 40 hours.
For unsealed samples six stainless steel containers of 1500 ml and for sealed samples six auto clave glass bottles of 1 000 ml were taken. First, they were rinsed and washed with hot water (1000C) and then, washed by methanol and dried. Afterwards, containers and bottles were washed by transformer oil.
The three samples in each category were aged with different ageing times of 2, 4 and 7 weeks. The empirical 10 degree rule which states the ageing rate is doubled in every increment of 10°C was used to recalculate the equivalent ageing time for laboratory aged samples [4].
4.2 Field Aged Samples Sixteen field-aged oil samples were taken from CTs selected in three power stations covering 25-50 service years. Samples were taken from the CTs immediately after they have been removed from the service. Sampling has been done according to the specification given by IEC. There are test lugs provided in CTs to take oil samples for evaluation after long service (10
4.4 Test Procedure Both field-aged and laboratory-aged oil samples were analyzed by visual inspection (colour), electrical and chemical tests. The electrical study included the measurement of breakdown voltage and frequency dielectric spectroscopy covering frequency variation of the loss tangent, the permittivity and the conductivity. The chemical analysis represents
3
178
oil increases with increasing temperature and neutralization value [13]. Moisture content was determined only on field aged oil samples due to the amount of laboratory aged oil was limited.
dissolved fault gases, acidity, inter-facial tension and moisture content measurements. 4.4.1 Visual Inspection The removed laboratory aged samples were carefully checked for any reduction of oil level. Significant reduction of oil level was observed in unsealed samples confirming the evaporation. All laboratory and field aged sample colours were recorded. 4.4.2
4.4.2.4 Dissolved Gas Analysis (DGA) Dissolved gases are analyzed using the MYRKOS Transformer Fault Gas Analyzer. Selected field and laboratory aged samples were subjected to this analysis.
Chemical Testing 4.4.3
4.4.2.1 Interfacial Tension (IFT) IFT measures the surface tension at the interface between two liquids (in our case oil and water) which do not mix. The interfacial tension between oil and water provides a means of detecting soluble polar contaminants and products of deterioration [13].
Electrical Testing
4.4.3.1 Breakdown Voltage Breakdown voltage is an indicator of dielectric strength i.e. the ability to withstand electrical stresses without failure. Breakdown voltage was tested using MEGGER OTS 80AF/2 test equipment across a sphere gap of 2.5 mm. BS148:1984 standard is used for this test.
The IFT of the samples were measured from Easy Dyne measuring device which used the du Noüy ring method to find the IFT. The IFT was measured five times and the average value was taken as the IFT value.
4.4.3.2 FDS Measurements FDS measurements were conducted by Insulation Dielectric Analyzer (IDA 200) and a three terminal oil test cell (geometric capacitance of 70 pF). FDS measurements were done from 1 kHz to 1 mHz for a voltage of 50 V. 75 ml samples were taken and FDS tests were conducted in two different temperature levels for each sample. i.e. at room temperature about 27 0C and high temperature about 700C.
4.4.2.2 Acidity (Neutralization number) Acids are usually formed from oil oxidation or from atmospheric contamination. In the presence of water, acids may cause corrosion in the transformer. So that acidity of oil is important in the condition assessment. As the process of oxidation progresses in, the amount of sludge increases reducing the heat transfer capacity of the mineral oil [13].
The frequency variation of the capacitance of the oil samples can be written as; C f
In the process of acidity measurements, 50 mg of analytical grade NaOH flakes were dissolved in 500 ml of de-ionized water in a volumetric flask to make 0.1%w/v lye solution. One ml of oil was dissolved in 10 ml of pure commercial grade isopropyl alcohol (IPA) in a titration flask. The flask was gently warmed and stirred until all the oil was completely dissolved in the alcohol and turned clear. Two drops of phenolphthalein was added to the solution in the titration flask. Then, the sample was titrated with 0.1% w/v lye solution until the colour turned to pink (magenta). The acid value (AV) of the oil was estimated as in [2] and acidity was expressed in KOH mg/Oil g by using KOH equivalents and density values obtained in IFT.
C ' jC" C0 ' j " C0
(1)
The permittivity is given b;
' " ' j
0
"
(2)
where, is the conductivity and is the susceptibility. Usually the variation of susceptibility with respect to frequency is negligible oil and the relative permittivity ’ can directly be obtained from ’ at 1 kHz i.e. at our case. The loss tangent can be obtained as,
tan
C" f " f C ' f ' f 0
(3)
The loss tangents at 50 Hz were used for the analysis. The conductivity was obtained at -1 gradient of the log-log plot of tan Vs frequency. The conductivity is temperature dependent and follows Arrhenius law as;
4.4.2.3 Moisture Content (MC) Water may originate from the atmosphere or be produced by the deterioration of insulating materials. The solubility of water in transformer 4
179
E KT 0
e
(4)
and wax in transformer oil. It can be noted that decreasing IFT with the unsealed condition is higher than the sealed condition.
From the conductivity values obtained for room temperature (200 C-300 C) and high temperature (700 C), the activation energy E was obtained. From this activation energy, conductivity at 90°C was estimated.
5.
Results and Discussion
5.1
Laboratory Aged Samples
5.1.2.3 Acidity Acidity of laboratory aged oil samples is shown in the Figure 3. Acidity level of all transformer oil samples increased in first few days and then came to a stable level. Lowest acidity values show in sealed dry samples compared to other samples confirming lower contact with oxygen and moisture.
5.1.1 Visual Inspection (Colour) Table 5 shows the colour variations of oil samples. Colour changes in unsealed transformer oil were high compared to those of sealed samples. The reason could be when the unsealed transformer oil was exposed to air the oxidization with sufficient oxygen from surrounding may produce substances with colour changes. 5.1.2
Figure 3 –Variation of Acidity with Aging Time
Chemical Testing
5.1.2.1 Dissolved Gas Analysis (DGA) Table 4 shows the DGA of some of the selected oil samples. SWT3 shows excess C2H6 indicating oil overheating. Basic Gas Ratio method gives correct diagnosis for this case while duval triangle method gives wrong interpretation for SWT3 sample. CO represents basically paper overheating and wet samples shows more CO due to adding of pressboards. It can be assumed that produced CO in unsealed samples not appears in the results due to unsealed condition.
5.1.3
Electrical Testing
5.1.3.1 Breakdown Voltage (BDV)
5.1.2.2 Inter Facial Tension (IFT) Figure 4 – Variation of BDV with Aging Time Figure 4 show the variation of breakdown voltage with respect to ageing time of the laboratory aged samples. According to the figure, the breakdown voltage for unsealed samples initially increased proving that the oil had been gone through a purification process rather than the ageing. However, the values reduced at 600 hours of ageing time confirming a deterioration of the oil samples. The sealed samples showed a different behaviour by first by reducing and then increasing of the breakdown voltage. The reason could not be clear.
Figure 2 – Variation of IFT with Aging Time Figure 2 shows the variation of IFT with aging time for laboratory aged oil samples. IFT values usually reduce due to the presence of moisture or any other substances. Fast deterioration of IFT normally indicates the formation of sludge
180 5
Table 4 – Test Results of Dissolved Gas Analysis, Basic Gas Ratios and Duval Triangle Method Sample Name
Dissolved Gases in ppm
H2
CH4
C2H6
C2H 4
C2H 2
Basic Gas Ratios
CO
CO2
C2H 2
CH4
C2H 4
C2H 4
H2
C2H 6
Diagnosis Basic Gas Ratio
Duval Triang le
UWT3
15
0
0
0
0
13
452
-
0
-
PD
-
UDT3
21
0
0
0
0
14
483
-
0
-
PD
-
SWT3
26
79
204
0
0
573
2784
-
3.038
0
T1
PD
SDT3
28
0
0
0
0
68
919
-
0
-
PD
-
-
-
0
T1
PD
T1
PD
28.418 0.002
T1
PD
KOT/01
0
4
6
0
0
0
1357
UKU/01
439
22961
7757
31
32
134
760
UKU/02
1232 35011
9172
15
12
84
541
UKU/05
1084 25741
6938
12
10
88
718
0.833 23.746 0.002
T1
PD
UKU/06
727
9
6
114
924
0.667 53.121 0.001
T1
PD
UKU/09
1009 29141
9794
11
11
81
900
1
UKU/11
140
0
73
0
0
143
1205
-
UKU/13
0
1
130
1750
1090
0
UKU/14
0
4065
146
900
907
UDW/01
0
4410
28
0
0
38619 10652
1.032 52.303 0.004 0.8
T1
PD
0
0
PD
-
10180 0.623
-
13.46
D2
D2
0
5426
1.008
-
6.164
D1
D1
0
8020
-
-
0
T1
PD
5.1.3.2 Frequency Dielectric Spectroscopy Figures 5, 6 show variation of conductivity, loss tangent at 50 Hz for laboratory aged samples. Recommended conductivity level for new transformer oil at 900C is 16.5 pS/m [13]. Unsealed conditions have higher conductivity than sealed conditions. However, the conductivity levels for unsealed samples reduced after 600 hr.
28.881 0.001
first few days [2]. Unsealed transformer oil has started to age before sealed transformer oil. The variation of permittivity was comparatively lower as expected for insulating materials than other two parameters (loss tangent and conductivity). However, slight decrease could be noted [see Table 5]. Decreasing in permittivity in first few days proved that the oil had been gone through a purification process.
Figure 5 – Variation of Conductivity at 90 oC with Aging Time Figure 6 – Variation of Tan δ at 50 Hz at 70 oC with Aging Time
Also an unsealed wet condition shows the highest value of conductivity in transformer oil. Decomposition of Pressboard/paper in presence of air and metal substances such as Fe and Cu would be the reason for it.
5.2
Field Aged Samples
5.2.1 Visual Inspection (Colour) Table 5 shows that the colour of field aged samples. In general, field-aged samples shows limited changes in colour compared to those of laboratory aged ones. Oxidization process
Figure 6 shows that in first few days loss tangent reduced in transformer oil. This implies that all samples had undergone purification in
181
5.2.3
seems to be weaker in field-aged samples. However, they get worst with the increasing of acidity and decreasing of IFT. 5.2.2
Electrical Testing
5.2.3.1 Breakdown Voltage (BDV) For CTs greater than 170 kV voltages recommended minimum BDV value is 50 kV and for other voltages minimum of 40 kV [13]. So in our case, the minimum breakdown voltage is 40 kV.
Chemical Testing
5.2.2.1 Dissolved Gas Analysis (DGA) Table 4 shows the contents of disslove gasses of field-aged oil samples and the evaluated faults under Basic gas ratio and Duval triangle methods. UKU/01, 02, 05, 06, 09 indicate excess of H2, CH4, C2H6 and C2H2. UKU/13 shows excess of CO2, C2H4 and C 2H2. For UKU/14 oil sample, CO2, CH4, C2H6, C2H4 and C2H2 are in excess amounts. UDW/01 indicates excess of CO2 and CH4. IEEE key gas analysis gives interpretation of paper overheating for UKU/11 and oil overheating with arcing for UKU/13, 14 while fails to interpret about other samples. It could be noted that for UKU/13, 14 samples, all Basic Gas Ratio, Duval Triangle and key gas analysis methods give same diagnosis but for other cases they are different to each other.
Figure 8–BDV Values of Field Aged Samples According to the Figure 8 UKU/05, 06, 12, 13, KOT/01 and UDW/01 showed very poor breakdown voltage values. 5.2.3.2 Frequency Dielectric Spectroscopy Maximum conductivity value for CTs voltages higher than 170 kV is 1000 pS/m and 1428.5 pS/m for voltages less than 170 kV at 90 oC [13]. Table 5 shows that only UKU/08 violates the acceptable limit of conductivity.
5.2.2.2 Moisture Content (MC) Figure 7 shows the MCs at 20oC for field aged samples. The limits of MC for CTs are ≤ 20 ppm for >170 kV and ≤ 30 ppm for 170 kV) and maximum of 0.3%( 1dBm).
7
223
6.
Tharranetharan S., Saranraj M., Sathyaram S., and Herath V.R., A Performance Comparison of Nonlinear Phase Noise Tolerant Constellation Diagrams, 2011 6th International Conference on Industrial and Information Systems, ICIIS 2011, Sri Lanka, Aug. 16-19, 2011.
7.
Constraint Based Routing Due to Physical Impairments in Automatically Switched Transport Networks, Stephan Pachnicke.
8.
Alan Pak Tao Lau and Joseph M. Kahn, ``Signal Design and Detection in Presence of Nonlinear Phase Noise”. Journal of Lightwave Technology, Vol. 25, No. 10, pp. 3008-3016, October 2007.
Annual Transactions of IESL, pp. [224-233], 2012 © The Institution of Engineers, Sri Lanka
Socio-Economic Impacts of Rural Electrification R.K.P.S. Gunatilake and R.U. Halwatura Abstract: Electricity is very important in uplifting rural socio-economic conditions from poverty lines. Its application in rural projects aimed at integrated infrastructure development and poverty alleviation. Well planned, carefully targeted and effectively implemented rural electrification programs provide enormous benefits to rural people. In 100% electrification of the country with a massive investment, it is important to investigate the effectiveness and the impact on the rural areas and come up with suitable solutions to maximize the benefits. Therefore, in this research the impacts of grid electricity on sustainable rural development were carefully analyzed from electricity consumption data and a detail questionnaire survey. The most effective benefit from access to electricity is better quality lighting, savings on fuel, improved security, clean and hazard free environment, extended evenings and ability to study at night. Rural electrification has a significant impact on the quality of life of the rural people, which brings them closer to the comforts enjoyed by the urban people. Increased household income due to extended hours of working causes the economic development of the country. Impact on rural to urban migration and the improvement in quality of life is considerable. However, rural electrification does not have a considerable impact on the nurturing, growth or diversification of income generating small commercial/industrial activities. Keywords:
1.
Electricity, Rural electrification, Socio-economic impact
Introduction
Electricity is a very important component in uplifting rural socio-economic conditions from poverty lines. Being a safe and clean form of energy that is efficient and easy to transmit, electricity finds application in abundance of rural projects aimed at integrated infrastructure development and poverty alleviation.
Electricity generally promotes agriculture and animal husbandry schemes, agro based and other industries and increases the earning power of villagers alleviating their poverty (Hisaya Oda, 2011). Poverty is a major obstacle for sustainable development of a country. (Kanagawa Makoto, 2008) Nowadays poverty is defined as low attainment of social conditions, for example education, health and nutrition in addition to economic deprivation. One way to cope with this multi dimensional aspect of poverty is to promote opportunity (World Bank, 2001) and one of the opportunities is access to modern energy such as electricity.
Electrification of rural areas could reduce the poverty index to a very great extend through the following mechanisms. Failure to electrify has stagnated development. It has forced villages to adopt more costly energy supply options. Electrification would remedy this situation. Electrification provides more facilities in schools and households for education. Villagers would be served with better communication facilities enhancing their knowledge inducing them to participate in community and social activities.
The influence of energy on socio-economic conditions of developing countries is shown in Figure 1. Eng.(Mrs) R.K.P.S. Gunatilake, C.Eng.,MIE(Sri Lanka), BSc Eng (Peradeniya), PGDip EPCEng (Peradeniya), MBA PM (Moratuwa), Chief Engineer (Station Performanc & Engineering Quality) Mahaweli Complex, Ceylon Electricity Board. Eng. (Dr.) R U Halwatura, BSc Eng. (Hons), PhD, CEng., MIE(Sri Lanka), AMSSE, Senior Lecturer, Civil Engineering Department, University of Moratuwa.
Electricity driven water supply schemes can provide better sanitation. Electricity would make household chores of women very much easier.
1
224
Figure 1 - Link between energy and components of poverty (Kanagawa Makoto, 2008) 1.1 Background Only 80% of the population in Sri Lanka has the direct access to grid electricity. (Ceylon Electricity Board, 2008) Out of total of 35,697 villages that existed from ancient times, several villages were urbanized over the years and many villages have been electrified under the Rural Electrification Projects by the Ceylon Electricity Board (CEB) with the assistance of the Government of Sri Lanka and lending agencies. Approximately 264 million US$ have been spend on rural electrification form 1983 to 2007. However, still many villages remained needing electrification and development. Another 65.8 million US$ is to be invested under the Rural Electrification Project 8. (Ceylon Electricity Board, 2008) 1.2 Objective of the Research Well planned, carefully targeted and effectively implemented rural electrification programs provide enormous benefits to rural people. The main objective of this research is to examine the impacts of extension of national grid electricity on sustainable rural development and focused on following aspects.
Review the effectiveness of rural electrification programs implemented in the recent past. Investigate the limitations on this impact. Special emphasis will be placed on the economic benefits, creation of income
225
generating entrepreneurial activities and improvement of the quality of life. To come up with suitable recommendations to overcome the existing barriers in using electricity for income generating activities.
1.3 Methodology Proposed methodology for the research involves extensive literature survey on rural electrification published on international research publication journals, especially focused on developing countries and South Asia. As well as literature survey on local publications, by the Ceylon Electricity Board, Ministry of Power and Energy, Sustainable Energy Authority of Sri Lanka, Central Bank of Sri Lanka and Department of Census and Statistics. Carrying out a survey of rural households connected to the national grid before two years in a selected sample in Kalutara District encompassing the economic, social and environmental aspects of rural life. Collect billing data for newly electrified rural areas from Ceylon Electricity Board billing system. Analyzing survey results and billing data, placing emphasis on measures aimed at improved quality of life, economy and environmental benefits. Conclusions are drawn on grid electricity penetration among rural communities in terms of their contribution to sustainable development. Deriving conclusions on electricity demand growth among the rural areas in relation to the uplifting of quality of life. Making recommendation to improve the provision of supporting services, particularly those associated with micro-financing, training, technical support from the point of view of rural communities of using electricity for income generating small industrial and commercial activities. 1.4 Importance of the Study In the process of 100% electrification of the country with a massive investment, it is important to investigate the effectiveness and the impact on the rural areas and come up with suitable solutions and programs for the
maximum benefits for the rural people from grid extensions. 1.5 Limitations of the Study This study was limited to Kalutara District and primary data was collected from recently electrified areas. Some villagers were reluctant to disclose their monthly expenditure and their future expectations. Limited number of villagers had to be interviewed from a particular scheme as most of the adults were away from their houses during day time. Sample size had to be limited to 50 due to the limited time available for the survey.
2.
The Survey
2.1 General The survey was carried out with the intension of obtaining relevant information on the use of grid electricity in rural areas. For this purpose a questionnaire is designed to address the following issues.
The main reason for the selection of Kalutara District is that it is the only district which is not 100% electrified in Western Province and also relatively underdeveloped region where any social and economic improvements can be readily observed. The main sources of income for the recently electrified rural areas of Kalutara District are Tea and Rubber. Almost all the villages have their own cultivated land, and a house to live. The average size of the household is four. Most households use at least a motor bicycle, as the means of transport. 2.3 Secondary Data Collection The secondary data of electricity consumption was collected for few rural villages electrified recently and couple of years ago from the billing centre of Western Province South 1, of Ceylon Electricity Board. The billing data was obtained for the following schemes. Diganna Athweltota
General information
Illukpotha Atahaulhena
The impact of electricity in terms of social and economic development:
Galahitiya Molkawa Palenda Ukkowita Illukpotha Hingurakandagama
Purposes for electricity is using at present;
Ownership of durable electrical assets. Use of electricity for activities related to income generation. Ways of using electricity in order to achieve sustainable development in rural households.
This information was collected through personal visits by the author. 2.2 Sample Selection A random sample of 50 households was selected for the research in Kalutara District of Western Province. These households were electrified at least two years before the month of October 2011. The sample was picked from the following rural electrification schemes in Palindanuwara Divisional Secretary Division. Athweltota Ambegoda Galahitiya Molkawa Ihala Hewessa Hallindola Hedigalla Dikhena
Illukpotha Palindanuwara The number of electricity consumers for the billing data sample was obtained for 381 household electricity accounts. Other socioeconomic data was obtained from the publications of Department of Census and Statistics, Central Bank of Sri Lanka and World Bank web site.
3.
Survey Results and Analysis
3.1 General Electricity consumption data from the date of electrification were analyzed for 3 rural electricity schemes for 255 households to get the correlation between the energy consumption pattern and improvement in quality of life. The answers to the questionnaire were tabulated and statistical analysis was done to investigate the economic and social benefits to the rural community after electrification. The analysis was emphasized on impact of grid electricity in terms of social and economic development, agriculture and other entrepreneurial activities.
226
Total units (kWh)
3.2 The Pattern of Demand for Electricity From the analysis of electricity consumption data for 255 households, it was observed that there is a clear incremental pattern from the day of electrification. Initially the total electricity consumption was exclusively for lighting and
subsequently used for other household activities. Especially for entertainment having a television set, for ironing of clothes and refrigeration of food items. The incremental growth for three year period for three rural electrification schemes is shown in Figure 2.
5000 4000 3000 2000 1000 0 240 Bill cycle
250 Sch 1
260 Sch 2
270
280
Sch 3 Average fuel cost before electrification (Rs)
230
Figure 2 - Incremental Demand Growth for 3 Schemes If small home based industries and small commercial activities could be promoted among the rural electricity consumers the above trend in demand for electricity would be increased adding more economical and social benefits to the community. 3.3 Impact of Grid Electricity in Terms of Social and Economic Development Immediately after electrification of rural villages, the usage of kerosene for domestic lighting has greatly been reduced. All solar home system users have switched to grid electricity due to the efficiency, capacity and multi usability of grid electricity. Thus, the immediate economic benefit is the saving on imported fuels. After electrification of the households the expenditure on kerosene was dropped to zero for 17 households out of the sample of 50. Only very small quantities of kerosene are being still used for easy lighting up of the firewood stove. Usage of kerosene for emergency lighting purposes during electricity failure is very much limited due to the higher content of soot and hazardousness of bottlelamps used in the rural households. Instead paraffin candles are being used for emergency lighting. Figure 3 shows the fuel costs before and after electrification.
1600 1400 1200 1000 800 600 400 200 0 0
less than less than less than 100 200 500
Present fuel cost (Rs) Average fuel cost before electrification Figure 3 - Fuel Cost before Electrification and Fuel Cost after Electrification Disposable income is a good measurement to determine the economic development of a family. According to the Department of Census and Statistics of Sri Lanka, the official poverty line for Kalutara District for the month of September 2011 is Rs. 3373/= per head. From the survey results it is evident that only 4 households have an average monthly
227
Average monthly elec (Rs)
expenditure less than Rs 10,000 /=. This is 8% of the sample.
600 500
The average percentage saving on fuel for lighting is 22% for the surveyed sample. This saving on fuel increases the disposable income. More disposable income in other words means higher family income. Therefore the economic development in the sense of enhanced family income is obvious.
400 300 200 100 0
Figure 4 shows the present average monthly expenditure or the disposable income of the surveyed sample households.
Median expenditure per month (Rs) Average electricity bill
Average monthly household expenditure (Rs)
Figure 5 - Distribution of Average Monthly Electricity Bill
8% 20%
All the black and white television sets which have been used by battery power, before electrification have been replaced with colour television sets. 94% of the sample households have a colour television set. Apart from this other electrical appliances such as water heaters, smoothing irons, fans and refrigerators are commonly used by the households. Usage of electricity for cooking is limited due to the abundance availability of firewood. But use of rice cookers for cooking rice is considerable. Figure 6 shows the percentage use of electrical appliances within the survey area.
30% 26%
More than 25000 Figure 4 - Average Monthly Household Expenditure
94% 96%
100% 90%
Percentage
electricity is shown in Figure 5. As per the CEB tariff structure (published by Public utilities Commission of Sri Lanka for the period 1 st. January 2011 to 30 th. June 2011), the maximum billed amount for 30 kWh for a period of 30 days would be Rs.120.00. For a consumer of 60 kWh the maximum is Rs 291.00. Therefore, it clearly shows that the lower expenditure households use lesser electricity solely for lighting. The middle level expenditure group of the sample and the higher expenditure group spend more on electricity by using other electrical equipment for entertainment, water heating, cooking, refrigeration and ironing of clothes.
70% 60% 50% 40% 30% 20%
62% 58% 40% 32% 24% 20%
44%
6%
0%
Electrical appliance
Figure 6 Appliances
Most of the villagers use compact florescent lamps for their domestic lighting. Use of several other electrical equipment, which makes the life easy and comfortable also significant among the rural communities.
Percentage use of
Electrical
228
Iron
electric…
television
fan
kettle/he…
hotplate
The ownership of durable electrical assets is an indication of the quality of life or the social and economic development. When compared with the country data for percentage distribution of blender
Less than 25000
refrigerat…
Less than 20000
other
Less than 15000
rice cooker
Less than 10000
water…
16%
percentage
households own television, washing machine, refrigerator, electric fan and personal computer, the sample lags only for washing machine and personal computer. Figure 7 shows that television, refrigerator and electric fan percentages are more than the country percentage for 2009/10 data. 100 90 80 70 60 50 40 30 20 10 0
migration to urban areas searching for employment is significantly reduced after electrification. 68% of the households have been upgraded, improved or added extra rooms. It was observed that majority of the houses are well built and with modern tiled floors. 3.5 Impact of Grid Electricity on Agriculture and Other Income Generating Activities Due to the highly favourable weather conditions prevailing in the survey area, none of the villagers use electricity for pumping water for their cultivated land. No electricity is used for agro-based industries such as tea, rubber processing or food processing. Nobody is engaged in livestock or poultry farming using electricity. Figure 8 shows the percentage of usage of electricity for different activities.
94 86.5 76.3
78.2 58.3
58 44
42.5
32.9
27
16.6 8.7
5.7
2
Urban % 2009/10
2
Rural % 2009/10
Sample % 2011 Figure 7 - Ownership of Durable Electrical Assets (Department of Census and Statistics of Sri Lanka, 2009/10) The study time at home of all school children are tremendously improved due to the electrification of these rural households. Elimination of inefficient unsafe and hazardous kerosene oil lit bottle lamps has made a significant change in the evening studies. The average increment in study time of children is 3 hours. This will result higher standards of education.
100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0%
% usage of electricity for sample Figure 8 - Percentage Usage of Electricity for Different Activities It was observed that only one small rice mill was running with electric motors. But all the retail shops operated were using refrigerators and some of them using deep freezers for commercial activities. Only one barber salon and small garment workshop within the house used electrically powered equipment. But use of electricity for local carpentry work and painting was common. Therefore, no significant development in small scale industries and commercial activities took place due to electrification as expected at the beginning. This will result a very poor load profile of the power system. But, those who involved in entrepreneur activities using electricity were able to increase
Every household is equipped with a CDMA land telephone connection or a hand held telephone set after electrification improving the communication needs of the villages. Eventually saving their time for engaged in income generating activities and other social activities. 3.4 Impact of Migration to Urban Areas Due to the fertile cultivated land with tea and rubber and the high income from the crop, the villagers are motivated to stay in the village. The availability of electricity has made the village life much comfortable. As the cost of living is considerably low and their needs are simple and could be fulfilled from the surrounding
229
their income by an average of 30% after electrification.
for the sample before 2 years and for August 2011 is shown in Table 1, according to the CEB categorization of electricity usage. The percentage of low consumption below 30 kWh has been reduced from 51 to 33%.
Only 6% of the sample has obtained a formal training for their trade out of which 20% are self employed in other income generating activities other than tea/rubber cultivation. None of the sample had got any technical assistance from outside parties or any micro financing or credit facilities for carrying out their business.
It was clear that, more than 30 kWh but less than 60 kWh users have increased by 6% and less than 90 kWh users have increased from 11% to 20%. Hence it was confirmed that the quality of life of the rural people is improved tremendously over a short period of time. The trend is towards the island wide consumption pattern. This phenomenon is shown in Figure 9. The migration from lower electricity consumption which was used solely for lighting soon after electrification of the household, to higher consumption of electricity for other uses is shown in Figure 10.
percentage
3.6 Impact on Quality of Life Soon after the electrification of the village, electricity was used only for the domestic lighting. From billing data analysis of 381 households which connected to the grid recently, it was observed that the new customers were moving gradually from lower energy consumption to higher energy consumption category. The percentage consumption pattern 60 50 40 30 20 10 0
percentage difference reference to month 1
-10 0
1
2
3
4
Unit blocks % present (sample)
% Country
5
6
7
% 2 Yrs ago (sample)
Figure 9 - Electricity Consumption Pattern in Unit Blocks 15 10 5 0 -5 0
1
2
3
4
5
6
-10 -15 LT 30
period of 6 months interval LT 90 LT 120
Figure 10 - Percentage Difference of Percentage Consumers using Electricity in Unit Blocks – Reference to Month-1 of Electrification
230
Table 1 - Percentage Consumer Consumption Pattern for the Sample Data
Unit Blocks
Consumption (kWh) Unit Blocks
Consumer % in August 2009
Consumer % in August 2011
1
Units n) , w ≤ 3 To date, the exact mechanism of setting and hardening of the geopolymer material is not clear, as well as its reaction kinetics and it is believed that the chemical reaction may comprise the following steps [3].
2.3. Alkaline Solutions It has been identified that the type of alkaline liquid also plays an important role in the polymerisation process. The most common alkaline liquid used in geo-polymerisation is a combination of Sodium Hydroxide (NaOH) or Potassium Hydroxide (KOH) along with Sodium Silicate (Na2SiO3) or Potassium Silicate (K2SiO3). Generally NaOH causes a higher extent of dissolution of minerals than KOH while addition of Na2SiO3 to the NaOH solution as the alkaline liquid enhances the reaction between the source material and the solution [5].
Dissolution of Si and Al atoms from the source material through the action of hydroxide ions Transportation or orientation or condensation of precursor ions into monomers Setting or polymerization of monomers into polymeric structures
3.
Experimental Investigation
Experiments were carried out starting from fly ash based geopolymer paste, mortar and concrete to find out the behaviour and properties of each type in order to derive an optimum mix proportion. Throughout the research, the composition of all constituents such as NaOH, Na2SiO3 and class ‘F’ fly ash were kept constant. Tables 1, 2 & 3 show the chemical composition of the above three materials mentioned above.
2.2. Types of Fly Ash There are two main types of fly ash, namely Class F and Class C fly ash which are waste products of combusted coal in thermal power plants. Fly ash is collected in electrostatic precipitators, and then transferred to large silos for shipment. When needed, fly ash is classified by precise particle size requirements, thus assuring a consistent quality product. Class F fly ash is the most commonly found type where it is generally low in lime, usually under 15 % and contains a greater combination of Silica, Aluminium and Iron (greater than 70 per cent) than class C fly ash.
Table 1- Composition of the NaOH
Class C fly ash normally comes out of coal power plants with higher lime content generally more than 15 % often as high as 30 %. Elevated levels of Calcium Oxide (CaO) may give class C unique self-hardening characteristics [3]. It is also revealed that the Calcium content in fly ash plays a significant role in strength development and final compressive strength. Higher Calcium content results in faster strength development and higher compressive strength. However, in order to obtain the optimal binding properties of the material, fly ash as a source material should have low Calcium content and other characteristics such as unburned material lower than 5%, Fe2O3 content not higher than 10% [4]. It is also stated that the presence of Calcium in fly ash in significant quantities could interfere with the polymerisation setting rate and alters the microstructure [4]. Therefore, it appears that the use of low Calcium (Class F) fly ash is more
Component
%
NaOH (with 98 % purity)
40.00
Sodium Carbonate
1.00
Chloride
0.005
Sulphate
0.0005
Phosphate
0.0005
Silicate
0.001
Total Nitrogen
0.0003
Heavy Metals (such as Pb)
0.0005
Nickel
0.0005
Iron
0.0005
Aluminium
0.0005
Calcium
0.0005
Potassium
0.005
Table 2- Composition of the Na2SiO3 Component SiO2-Na2O
2.0
SiO2 by weight
35.7
Na2O by weight
17.8
H2O by weight
46.5
Specific Gravity
1.7
Tolerance +2% to -2%
268
%
observe the strength development at room temperature.
Table 3 - Composition of the ‘Class F’ Fly Ash Component
%
SiO2
60.41
Al2O3
28.97
CaO
1.60
Fe2O3
3.67
SO3, Chlorides,Na2O & others
5.35
As one of the objectives of this experimental study was to develop a High Volume Fly Ash (HVFA) product, the following trials were carried out keeping the NaOH and fly ash ratios constant while varying the Na2SiO3 proportions to find the best ratio between SiO 2to-Na2O (known as Ms modulus).
3.1 Fly Ash based Geopolymer Paste Trial tests were carried out to develop fly ash based geopolymer paste with fly ash and alkaline solution made out of NaOH and Na2SiO3 along with some additional water (Figures 1 and 2). Constituent materials were thoroughly mixed using the Hobart Mixture and cubes of 70 mm x 70 mm x 70 mm were cast.
Varying the Na2SiO3 mass ratio from 2 to 6 while keeping the NaOH to fly ash ratio as 1:40 Varying the Na2SiO3 mass ratio from 2 to 6 while keeping the NaOH to fly ash ratio as 1:30 Varying the Na 2SiO3 mass ratio from 2 to 6 while keeping the NaOH to fly ash ratio as 1:15
To achieve a desirable workability, trials were carried out varying the additional amount of water added keeping the ratio of NaOH: Na2SiO3: fly ash at 1:4:15 which was found by earlier trials. The task was to find the minimum water quantity that will not affect the compressive strength negatively but enhance workability. Trials were carried out starting from zero additional water and increased up to 50 ml per one cube having dimensions of 70mm x 70 mm x 70mm.
Figure 1 - Process of Making Fly Ash based Geopolymer Paste
A series of tests were carried out to study the effect of alkalinity on compressive strength by changing the concentration of NaOH from 8mol/dm3 to 20 mol/dm 3 while keeping the NaOH, Na2SiO3 and fly ash as at 1:4:15 ratio and with the optimum additional water content found in the earlier test series. Heat curing substantially assists the geo polymerization chemical reaction that occurs within the geopolymer paste. According to the literature [6], as both curing time and temperature influence the compressive strength, a series of tests were done by varying curing temperature by leaving it in the ambient (room) temperature and elevated temperatures inside the oven.
Figure 2 - Pouring Geopolymer Paste into the Moulds After pouring the paste into the mould, any entrapped air was removed by tamping with a rod. The moulds were placed inside an oven for almost 5 hours at 800C. A separate set of samples were kept at room temperature to
Compressive strengths of samples were determined after 7 days of casting and for the witnessed optimum paste, compressive strength gain with time was observed. This optimum mix was used as the base to produce optimum mix for the alkali activated fly ash based geopolymer mortar and the concrete.
269
3.2 Fly Ash based Geopolymer Mortar To produce geopolymer mortar, sieved fine sand was used with the geopolymer paste. Washed sea sand sieved through the 0.60 mm standard sieve was mixed with fly ash before adding it to the alkaline solution to produce mortar. The proportion of sand in the mortar mix was changed as given in Table 4. Table 4 - Mix Proportions for Geopolymer Mortar NaOH
Na2SiO3
Fly ash
Sand
1 1 1 1
4 4 4 4
15 15 15 15
7.5 15 22.5 30
Figure 5 - Length Comparator and Standard Invar Bar for Measuring Drying Shrinkage of Geopolymer Mortar Specimen 3.3 Fly Ash based Geopolymer Concrete Finally, trials were carried out for geopolymer concrete with the addition of 10 mm coarse aggregate (known as ‘chips’). The coarse aggregate content was increased starting from the initial value of one and a half times the fine aggregate content and the compressive strength was measured at 7 and 28 days after casting.
Similar heat curing procedure as used in geopolymer past was carried out in producing geopolymer mortar and the noticeable fact was that the cohesion of the mortar made it very hard to compact as mortar adhered to the compacting rod.
To assist the polymerization reaction concrete samples were heat cured similar to that of geopolymer paste and mortar.
After identifying the optimum ratio, another series of tests for both heat cured and air cured samples were carried out to measure the strength gain with time. Samples were tested at 3,7,14 and 28 days after casting. In order to identify and understand more about the properties of fly ash based geopolymer mortar, tensile strength (Figure 3 and 4) and drying shrinkage (Figure 5) of the optimum mix proportion was also measured similar to that of OPC mortar testing procedure.
3.4
Solid Block for Load Bearing Masonry Work A solid block (see Figure 6) was cast using the optimum concrete mix proportion with chips being substituted by an equal weight of quarry dust. A simple ‘Cinva ram’ mechanism was used where the mix was compressed from the bottom and the block was taken out from the top. The mix used to cast the solid block had to satisfy to two main conditions. Firstly, it should be dry enough so that it does not collapse when it is de-moulded, while it should have sufficient consistency to compact. Quarry dust used in the experiment was air dried to remove excess moisture. Heat curing at 800C for 5 hours was carried out to assist the geo polymerization chemical reaction within the solid block.
Figure 3 - Sample Specimen used to test the Tensile Strength of Geopolymer Mortar
Figure 6- Casting a Solid Block having dimensions of 290 mm (length) x 135 mm (width) x 135 mm (height) using the Cinva Ram
Figure 4 - After the Sample being tested in the Tensile Testing Machine
270
3.5 Interlocking Paving Block Using the optimized mix of geopolymer concrete, an interlocking block with a surface area of 26,551 mm 2 was cast using vibrating paving block making machine (see Figures 7 and 8). The mix was loaded to the paving machine where it was first vibrated and then compressed using a heavy plate and produced a 70 mm thick interlocking paving block. The heat curing process lasted for 5 hrs at 800C and checked the compressive strength after 7 days.
4.1 Fly Ash based Geopolymer Paste Table 5 gives the compressive strength of geopolymer paste for different proportions of NaOH: Fly ash. Table 5 - Average Compressive Strength for varying Na2SiO3 ratios from 2 to 6 Avg. strength Category N/mm2 NaOH : Fly ash ratio at 8.00 1 : 40 NaOH : Fly ash ratios at 11.00 1 : 30 NaOH : Fly ash ratios at 14.40 1 : 15
The top surface of the paving block was made smooth by applying Plaster of Paris and was placed between two plywood plates before they were being tested in the Amsler machine.
When it comes to the minimum additional water quantity required, the test results for the 20 ml of additional water for a 70 mm x 70 mm x 70 mm test cube gave the maximum strength of 28.20 N/mm2 (see Table 6). The exact amount of additional water needed for the paste depends on the desired workability and the water contribution from the Na2SiO3 itself should be considered. Table 6 - Compressive Geopolymer Paste Samples Na2SiO3: Fly ash ratios at 1:4:15
Figure 7 - Making of the Interlocking Paving Block in Progress
Water per 70 mm x 70 mm x 70 mm test cube (ml)
Compressive Strength (N/mm2)
0
Unsuccessful in casting
10
27.63
20
28.20
30
24.40
40
20.40
50
16.20
Remarkable increase in compressive strength was not gained with the increase of NaOH concentration from 8 mol/dm3 (resulting in 35N/mm2) to 20 mol/dm 3 (resulting in 36N/mm2).
Figure 8 - Interlocking Paving Block
4.
Strength of for NaOH:
Results and Discussion
Test results corresponding to the compressive strengths of geopolymer paste, mortar and concrete with time, NaOH concentration, additional water content and other parameters were analyzed to study the effect of each parameter on compressive strength.
Table 7 shows the results of compressive strength of geopolymer paste with age for both air cured and heat cured specimens. When analysing the results obtained for compressive strength with age, it was observed that a rapid increase in strength within the first two weeks in the heat cured sample relative to air cured samples.
271
Table 7 - Age vs. Compressive Strength of Geopolymer Paste Age (days) Heat cured (N/mm2) Air cured (N/mm2)
3
7
14
5.2 10.8 16.1 1.1
2.3
8.7
28
120
18.2
22.8
11.4
seen that compressive strength increases with the increase of the coarse aggregate content and the maximum strength obtained was 33.4N/mm2 at 28 days. Table 10 - Variation of Compressive Strength with Coarse Aggregate Content for Geopolymer Concrete
13.1
Coarse aggregate content
4.2 Fly Ash based Geopolymer Mortar Average compressive strength obtained for a heat cured fly ash based geopolymer mortar after 7 days of casting was 37.0 N/mm2 and it was recorded for the mix proportion of 1:4:15:15 for NaOH: Na2SiO3: Fly ash: Sand.
2
3
Tensile Strength (N/mm2)
1.30
1.17
1.39
Avg. strain measured throughout the week (x 10-4)
1st
7.095
2nd
6.392
3rd
7.424
4th
6.732
5th
6.030
6th
7.526
7th
5.792
8th
6.426
9th
7.186
23.32
33.37
30
18.09
28.14
Solid Block for Load Bearing Masonry Work Table 11 gives strength results of solid blocks with and without heat curing. As results indicated heat curing for the solid block for load bearing masonry work is essential in order to obtain a reasonable compressive strength. Table 11 - Compressive Strength of Heat and Air Cured Solid Blocks
Table 9 - Drying Shrinkage of Geopolymer Mortar Week
27.5
4.4
Table 8 - Tensile Strength of Fly Ash based Geopolymer Mortar 1
28 day strength (N/mm2) 31.16
(Note - NaOH: Na2SiO3: Fly ash: Sand kept constant at 1:4:15:15)
Table 8 gives tensile strength of geopolymer mortar 1:4:15:15 (NaOH: Na2SiO3: Fly ash: Sand) mix while Table 9 shows the results of the drying shrinkage. It can be seen that some scattering of the results but there was no indication of increase in drying shrinkage during the period tested.
Sample
22.5
7 day strength (N/mm2) 21.11
Block type
Heat cured
Air cured at room temperature
Compressive Strength (N/mm2)
24.15
2.01
4.5 Interlocking Paving Block Compressive strength of 48 N/mm2 was achieved for the interlocking paving block made out of geopolymer concrete. This can be easily manufactured using a normal paving block machine. Higher cohesiveness of the geopolymer concrete mix is an added advantage in producing paving blocks because low workability is desirable to retain the shape of the block during demoulding. 4.6 Excess Alkali in Geopolymer Products Even though the polymerization process needs a high pH value it may cause an irritating sensation to humans when it’s touched due to some non-reacted alkaline content in the geopolymer products. Therefore, it is important to use correct amount of alkaline content so that at the end polymerization process no excess alkali materials will be left in the product.
4.3 Fly Ash based Geopolymer Concrete Testing procedure was similar to that of OPC concrete. The difficulty encountered during batching was compaction due to the high cohesiveness of the mixture. A flat end compaction rod was much effective than the standard round end compacting rod and vibration was not effective. Compressive strength results are given in Table 10. It can be
272
4.7 Optimum Mix Proportions After analysing all the test results and experimental observations, the following optimum mix proportions were obtained for each phase of geopolymer (Tables 12, 13 & 14).
This may be due to the slow speed of polymerization at low temperatures. 3. Fly ash based geopolymer concrete can be
efficiently used to manufacture relatively high strength interlocking paving blocks.
Table 12 - Geopolymer Paste (Weight per m3) 4. Drying
Constituent material
kg per m3
NaOH 8mol/dm3
110
Na2SiO3
465
Fly ash
1750
Additional water
30
shrinkage of fly ash based geopolymer mortar was in the range of 6.7 x 10-4
References 1.
Table 13-Geopolymer Mortar (Weight per m3) Constituent material
kg per m3
NaOH 8mol/dm3
70
Na2SiO3
280
Fly ash
1020
Sand
1020
Additional water
45
2. Davidovits, J. (1988). “Soft Mineralogy and Geopolymers.” Proceedings of the Geopolymer 88 International Conference, the Université de Technologie. Compiègne, France.
Table 14 - Geopolymer Concrete (Weight per m3)
5.
Constituent material
kg per m3
NaOH 8mol/dm3
36
Na2SiO3
87
Fly ash
510
Sand
545
10 mm aggregate
932
Additional water
90
Mehta, P.K., “Reducing the Environmental Impact of Concrete”, Concrete International, Vol 23, No: 10, pp 61-66, 2001.
3.
Davidovits, J. (1999). Chemistry of Geopolymeric Systems, Terminology. Geopolymer ’99 International Conference. France: Geopolymer Institute.
4.
http://www.yourbuilding.org/Article/News Detail.aspx?p=83&id=1570, Visited, 10th October 2010
5. XuH., Van Deventer J.S.J., (2000), The Geopolymerisation of alumino–silicate minerals, Int. J. Miner, Process, 59247-266. 6.
Concluding Remarks
According to the experimental results of geopolymer paste, mortar and concrete, the following observations can be made. 1. A rapid strength development during first 3
days of heat cured geopolymer samples was witnessed. 2. The time taken for strength gain in ambient
cured samples was much higher than that of the heat cured samples. Approximately half of the strength achieved by heat curing after 28 days can be also achieved by keeping it at room temperature for the same time period.
273
Djwantoro Hardjito, Steenie E. Wallah, Dody M.J. Sumajouw, and B.V. Rangan, “Factors Influencing the Compressive Strength of Fly Ash-Based Geopolymer Concrete”, Civil Engineering Dimension, Vol. 6, No: 2, pp 88–93, September 2004.
Annual Transactions of IESL, pp. [274-280], 2012 © The Institution of Engineers, Sri Lanka
Regression Models for Proportioning of Selfcompacting Concrete mixes and Estimating Their Rheological Properties in Terms of Bingham Constants H.M.G.U. Karunarathna, H. Abeyruwan, H.H.M. Gunasoma and S.D.J.M.T. Situge Abstract: Proportioning self-compacting concrete (SCC) normally involves a lengthy iterative procedure. The work reported herein deals with establishing regression based models for the design of SCC mixes in order to shorten the process. Regression based models for estimating rheological properties of SCC are also presented. Rheological characteristics of concrete are expressed by using the Bingham model. A range of the combinations of yield shear stress and plastic viscosity, which are the two material constants included in the model, was identified within which the concrete is likely to be self-compactable. To determine the self-compactability of a concrete three index properties were determined by experiments. Self-compactability was judged by criteria given in the European Guidelines for Self Compacting Concrete (EFNARC publications). Large coaxial cohesiometer was used to vary and measure the rotational speed and the corresponding torque on fresh concrete, for the purpose of obtaining data to calculate the material constants. Regression models are established from the results of slump flow diameter, V-funnel flow time, T50cm Slump flow time, J-ring height difference, V-funnel at T5min, yield shear stress and plastic viscosity as functions of relative water content (w), water-cement ratio (w/c), water-powder ratio (w/p) and the superplasticizer dosage. Keywords: Bingham Constants, Filling Ability, Passing Ability, Rheological Characteristics, Segregation Resistance, Self-Compacting Concrete.
1.
water-powder (cement and filler taken together is called powder) ratio and by adding Superplasticizer (High-Range Water-Reducing Admixture) the workability can be increased [4,5]. The workability of ordinary concrete is commonly measured by standard slump test by recording the vertical slump of a formed concrete frustum of a cone, whereas for SCC the horizontal spread or slump flow is measured instead. But for SCC, slump flow which is an index or test specific parameter alone is not adequate to judge the suitability of a fresh mix [6].
Introduction
Self-compacting concrete (SCC) is a special kind of concrete which is able to flow under its own weight and completely fill the restricted sections as well as the congested reinforcement cages while maintaining homogeneous composition without the need of any external energy source. There are several advantages of SCC over conventional concrete. It is environmental friendly because no additional energy input is needed in placing, and there is no associated noise pollution. It helps to accelerate the pace of construction by making simple to place concrete even in complicated formwork. Achievability of a homogeneous quality of concrete over the entire member is an added advantage [1,2,3].
1.1 Rheology Two SCC mixes showing the same slump flow
Eng. H.M.G.U. Karunarathna, B.Sc. Eng. (Hons) (Peradeniya), AMIE(Sri Lanka), Civil Engineer, Central Engineering Consultancy Bureau, Sri Lanka. Mr. H. Abeyruwan, B.Sc. Eng. Sri Lanka, MPhil Hong Kong, C.Eng. MICE, MIEAust, CPEng, MIEEE, Senior Lecturer, Department of Civil Engineering , University of Peradeniya, Sri Lanka. Eng. H.H.M. Gunasoma, B.Sc. Eng. (Hons) (Peradeniya), AMIE(Sri Lanka), Civil Engineer, Central Engineering Consultancy Bureau, Sri Lanka. Eng. S.D.J.M.T. Situge, B.Sc. Eng. (Hons) (Peradeniya), AMIE(Sri Lanka), Civil Engineer, Maga Engineering Pvt. Ltd., Sri Lanka.
SCC was first developed in Japan in 1988 and later in 1990’s in European countries as a one solution for the lack of skilled labour to place concrete in construction. Workability requirement of SCC include high filling ability, passing ability and segregation resistance [2]. By reducing the coarse aggregate content, increasing the paste content which consists of a mix of cement, filler and water, lowering the 1
274
value may behave differently when used to fill a formwork with spaces of different shapes and sizes and containing reinforcement. Therefore, the flow characteristics are studied in a broader perspective under the discipline called rheology which is the science dealing with the flow and deformation of matter.
Regression models are established from the experimental data to express slump flow diameter, V-funnel flow time, T50cm Slump flow time, J-ring height difference, V-funnel at T5min, yield shear stress and plastic viscosity as functions comprising relative water content, i.e. the ratio between the water content and the typical water content of 200 l/m3 (w), watercement ratio (w/c), water-powder ratio (w/p) and the superplasticizer (HRWR) dosage.
1.2. Bingham model Newtonian fluids like water start to flow even under infinitesimal shear stress. However, materials like cement paste, fresh mortar, and fresh concrete fall into a category called thick suspensions and behave differently. They begin to flow only upon reaching the shear stress a significantly large critical value. Such materials are categorized as visco-plastic materials. SCC also falls into that latter category.
1.3 Three key properties of fresh SCC The three key properties of fresh SelfCompacting Concrete are: [1] Filling ability – The ability of SCC to flow into and fill completely all spaces within the formwork, under selfweight. Passing ability – the ability of SCC to flow through tight openings such as spaces between steel reinforcing bars without segregation or blocking. Segregation resistance – The ability of SCC to remain homogeneous in composition during transport and placing.
Bingham model [4,7] is a simple relationship adequately representing the flow characteristics of visco-plastic materials. It has two material parameters which are called yield shear stress (τ0) and plastic viscosity (μ). Those parameters are considered as intrinsic flow properties [7]. The model can be used for numerical analysis of the behaviour of SCC under different boundary conditions.
1.4
Acceptable regions of flow parameters for SCC There are acceptable ranges for index properties of a concrete mixture to behave as self-compactable concrete. Typical acceptance ranges for self-compacting concrete with a nominal maximum aggregate size of 20mm are shown in Table 1[4].
The Bingham model is usually expressed mathematically as:
τ τ0 μ D
Rate of shear , D
τ = τ0 + μD D= 0 = = = =
if τ ≥ τ0 if τ < τ0
… (1) … (2)
Shear stress (Pa) Yield stress (Pa) Plastic viscosity (Pa.s) Rate of change shear strain (1/s)
Table 1 – Acceptable Ranges of Index Flow Parameters for SCC[4]. Typical range of values Method Unit Minimum Maximum Slump flow by mm 650 800 Abrams cone s 2 5 T50cm slump flow J-ring mm 0 10 V-funnel s 6 12 Time increase, Vfunnel at s 0 +3 T5minutes
Slope μ μμ τo
Stress, τ
Figure 1 – The Bingham Model μ
1.5 Mix design There is several mix design procedures applied in the world. The most common of those is the ACI method of proportioning [13]. Nevertheless, for the special requirements of SCC, several modifications to that method are needed [4].
In this paper, the domain of Bingham constants within which a concrete mix possesses selfcompatability is established. The plastic viscosity and yield shear stress of a concrete mix is measured using coaxial type rheometer.
2
275
1.6
2.
Typical ranges of proportions [1]. Water/powder ratio by volume of 0.80 to 1.10 Total powder content - 160 to 240 litres (400-600 kg) per cubic meter. Coarse aggregate content normally 28 to 35 percent by volume of the mix. Water/cement ratio is selected based on requirements in EN 206-1 [8]. Typically water content does not exceed 200 l/m3. The sand content occupies the balance volume.
increase the cohesiveness of concrete. A polycarboxylate formulation (concentration 20g/l) was used as the superplasticizer to obtain the desired flow properties at reduced water content The maximum size of the aggregate depends on the particular application and in this study it was limited to 20 mm. Table 2 – Mix Compositions
Objectives and scope of the study
2.1 Objectives The first objective of this study is to establish relationships between the index flow properties and mix parameters based on regression analysis, for application in mix proportioning process; and the second one is to relate the Bingham constants to the mix parameters using the same approach, for application in numerical modelling processes; and the third is to verify the existence of any domain of combinations of Bingham constants within which a concrete mix likely to possesses self-compactability. 2.2 Scope of study The mix compositions used in the experiment are given in Table 2.
3.
Methodology
The concrete mixtures will be prepared according to specifications given in literatures, which were introduced as self-compactable. The ranges of amount of materials selecting so that the concrete mixtures are willing to be possess self-compactability. After preparation the mixes they are tested for self-compactability by several test methods as given in the specifications. Then the rheological properties are measured and determine the ranges within which the concrete mix possesses selfcompactability.
Mix No
water ( l / m 3)
1 2 3 4
180 180 180 180
watercement ratio (by mass) 0.40 0.40 0.40 0.40
waterpowder ratio (by volume) 0.90 0.80 0.76 0.71
5 6 7 8 9 10
180 190 200 195 190 190
0.40 0.40 0.40 0.40 0.60 0.50
0.73 0.80 0.80 0.80 0.80 0.80
2.50 2.00 2.50 2.50 2.50 2.50
11 12 13 14 15 16
190 190 190 190 190 190
0.50 0.50 0.45 0.45 0.45 0.55
0.70 0.90 0.85 0.80 0.90 0.90
2.50 2.50 2.20 2.30 2.10 2.90
17 18 19 20 21 22 23 24
190 190 190 190 190 190 190 190
0.55 0.55 0.50 0.50 0.45 0.45 0.55 0.50
0.85 0.8 0.85 0.75 0.75 0.70 0.85 0.80
2.70 2.50 2.70 2.20 2.40 2.40 3.00 2.40
25 26 27
190 190 190
0.45 0.50 0.55
0.90 0.75 0.75
2.40 2.50 2.30
HRWR (l/100kg of cement) 1.30 1.80 2.00 2.25
3.2 Mix design procedure In the study, the water content was varied between 180 l/m3– 200l/m3 [4]. Initially, 180 l/m3 was selected as the water content. Then for the purpose of obtaining the selfcompacting mixes, water content was increased to 190 l/m3. Water-cement ratio was varied between 0.4 and 0.6 by mass. Adhering to the EFNARC [1] specified range of 28% - 35%, coarse aggregate content used in the investigation was maintained at 28% by volume. Fine aggregate content was chosen to fill the balance volume[1].
3.1 Selection of ingredients General conformity of cement to EN 197-1[9] was verified, in the first round using cement from different sources, and finally a commercially available cement of EN type CEM II/A-LL42.5 N, was selected for the programme. Dolomite powder which finer than 0.075 mm was used as the filler material to 3
276
Finally concrete was mixed and the properties were measured. Based on the results obtained, necessary modifications were carried out according to Trouble shooting Guide of EFNARC guidelines [1]. There are 27 mix design proportions by varying the watercement ratio, water-powder ratio and the superplasticizer dosage.
� � 2 −�2 �� � � � � � � = 0 R 4��h ln �c � 1
1
1
… (4)
Rb
Where;
S Rb Rc h
3.3 Testing of concrete To determine the filling ability of the concrete slump flow test, T50cm and the V-funnel tests were used. To measure the passing ability Jring apparatus was used. V-funnel test at T5min is used to measure the resistance to the segregation of the concrete.
4.
= Ω/T = Radius of inner cylinder = Radius of outer cylinder = height of the cylinder
Results and discussion
Summary of workability indices of the test mixes are summarised in the Table 3. Table 3 – Summary of Workability Indices of the Test Mixes
3.4 Measuring rheological properties Coaxial type rheometer shown in Figure 2 was used to determine Bingham constants experimentally. Concrete mixture was poured into the gap between the inner cylinder and the outer cylinder up to a specified height. Then the outer cylinder was rotated in varying speed and the torque on the inner cylinder was measured. Then the graph of the variation of the torque on the inner cylinder with the rotational speed was plotted. Plastic viscosity and the yield shear stress were calculated by using the gradient and the intercept of the graph.
Mix No
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27
Figure 2 – Rheometer 3.4.1
Equations for the determination of Bingham constants The slope of the graph of Torque (T) against the rotational speed (Ω) is 1/S. Then the following equations give the yield stress and plastic viscosity [7]. 1 1 1 1 � 2 − 2� … (3) �= 4�ℎ �� �� �
Slump flow T50cm by slump Abram’s flow cone (s) (mm)
445 678 720 600 635 690 715 775 675 740 740 795 655 715 620 740 715 715 750 725 730 725 690 673 720 645 490
6.40 3.13 5.47 5.20 4.05 4.24 3.35 2.99 2.10 2.38 1.90 3.53 3.00 2.64 1.69 3.28 2.24 2.01 2.41 3.35 3.65 2.02 3.51 2.06 4.04 -
Vfunnel time (s)
16.59 16.90 14.59 13.97 30.50 14.52 5.53 17.91 7.37 8.24 17.34 4.33 6.97 8.67 5.12 4.95 6.77 6.22 7.15 7.80 10.56 10.53 6.36 10.27 7.81 11.91 21.38
J ring height differ ence
Vfunnel at T5min
(mm)
(s)
24.29 6.22 23.81 6.78 24.68 4.24 20.60 6.48 23.50 12.50 16.50 3.04 55.00 0.56 24.25 0.34 23.50 4.70 9.50 1.65 6.00 11.59 3.25 0.72 9.75 2.93 6.75 2.55 5.75 1.73 13.50 1.16 6.50 2.44 5.75 1.70 4.00 15.30 9.25 2.84 12.75 4.49 10.50 4.21 9.75 0.63 6.75 0.72 5.00 2.59 10.00 2.80 21.50 7.09
Qual ificat ion as SCC
DQ DQ DQ DQ DQ DQ DQ DQ DQ Q DQ DQ Q Q DQ DQ Q Q DQ Q DQ DQ Q Q Q Q DQ
DQ –Disqualified Q – Qualified
4.1
Guidance for the interpretation of the index flow properties of SCC Larger the diameter of the slump flow, the greater is the ability of the concrete to fill the formwork.
4
277
4.3.1 Slump flow Slump flow = [37.190(w) − 19.605(w) 2 + 1.058(w⁄c) − 1.853(w⁄c)2 + 5.384(w⁄p) − 3.196(w⁄p)2 + 0.673(HRWR) − 0.105(HRWR)2 − 20.083] ∗ 795 … (5)
4.2
4.3.2 V-funnel flow time V funnel flow time = [83.105(w) − 45.154(w)2 − 27.765(w⁄c) + 27.991(w⁄c)2 − 0.296(w⁄p) + 2.317(w⁄p)2 − 0.304(HRWR) + 0.065(HRWR)2 − 27.944] ∗ 30.5 … (6)
Yield shear stress (Pa)
Smaller the V-funnel flow time, the greater is the filling ability. Smaller the value of T50cm slump flow time, the greater is the filling ability. Smaller the value of J-ring height difference, the higher is the passing ability. Larger the time increase in V-funnel at T5min, the greater is the tendency for segregation. Combinations of yield shear stress and plastic viscosity for selfcompactability 300 250 200
SCC (Author's )
4.3.3 T50cm slump flow time T50cm slump flow time = [−86.069(w) + 44.827(w)2 − 8.838(w⁄c) + 8.294(w⁄c)2 + 6.938(w⁄p) − 4.791(w⁄p)2 − 0.545(HRWR) + 0.093(HRWR)2 + 42.381] ∗ 6.4 … (7)
non SCC (Authors ) SCC
150
non SCC
100
non SCC
50 0 0
50
100
150
Plastic viscosity ( Pa s)
4.3.4 J-ring height difference J ring height difference = [−327.949(w) + 175.712(w)2 − 17.446(w⁄c) + 18.485(w⁄c)2 − 0.272(w⁄p) − 0.136(w⁄p)2 − 0.266(HRWR) + 0.036(HRWR)2 + 157.948] ∗ 55 … (8)
Figure3 – Domain of Shear Stress and Plastic Viscosity of Self-Compacting Concrete Shaded area in Figure 3 is the domain of the combinations of yield shear stress and plastic viscosity of concrete mixes which are having the self-compacting properties. The range of plastic viscosity and yield shear stress within which concrete mixes demonstrated selfcompactability, according to the EFNARC criteria [1] is given in Table 4. It is to be noted that the criteria are not unique but typical.
4.3.5 V-funnel at T5min V funnel at T5min = [−44.507(w) + 21.947(w)2 + 24.122(w⁄c) − 25.045(w⁄c)2 − 8.916(w⁄p) + 4.711(w⁄p)2 − 1.143(HRWR) + 0.257(HRWR)2 + 22.310] ∗ 15.3 … (9)
Table 4 – Range of Yield Shear Stress and Plastic Viscosity for Self-Compactability Parameter
Range
Yield shear stress (Pa)
8-80
Plastic viscosity (Pa s)
40-108
4.3.6 Yield shear stress Yield shear stress = [−109.756(w) + 56.468(w)2 − 20.963(w⁄c) + 21.327(w⁄c)2 − 5.907(w⁄p) + 3.684(w⁄p)2 + 1.179(HRWR) − 0.316(HRWR)2 + 60.010] ∗ 276.52 … (10)
4.3 Regression model for mix design Regression models are obtained from the experiment for slump diameter, V-funnel flow time, T50cm Slump flow time, J-ring height difference, V-funnel at T5min, yield shear stress and plastic viscosity as functions of relative water content(w), water-cement ratio (w/c), water-powder ratio (w/p) and superplasticizer dosage (HRWR) and their square terms. The expressions are listed as Equations 5 through 11. The comparison of measured values with the calculated ones using the regression models are given in Figures 4 through 10.
4.3.7 Plastic viscosity Plastic viscosity = [22.165(w) − 11.775(w)2 − 22.280(w⁄c) + 23.975(w⁄c)2 − 16.351(w⁄p) + 9.102(w⁄p)2 + 0.681(HRWR) − 0.234(HRWR)2 + 2.211] ∗ 141.26 … (11)
5
278
Measured value (s)
Measured value (mm
800 2
R = 0.5177 750 700
6 5 4
650
3
600
2
550
Line of equality
Line of equality
1
500 0
450
0
450
500
550
600
650
700
750
1
2
800
3
4
5
6
Calculated value (s)
Calculated value (mm)
Figure 7 – Variation of Measured Value with Calculated Value for J-ring Height Difference Measured value (s)
Measured value (s)
Figure 4 – Variation of Measured Value with Calculated Value for Slump Diameter 25 2
R = 0.5882 20 15
12 2
10 8 6
10
Line of equality
Line of equality
5 2
0 0
5
10
15
20
0
25
0
2
4
Calculated value (s)
8
10
12
Calculated value (s)
Figure 5 – Variation of Measured Value with Calculated Value for V-funnel Flow Time
Figure 8 – Variation of Measured Value with Calculated Value for V-funnel at T5min Measured value (Pa)
Measured value (mm
6
35 R2 = 0.825 30 25
350 300 250
20
200
15
150 100
10
Line of equality 50
5
0
0 0
5
10
15
20
25
30
0
35
50
100
150
200
250
300
350
Calculated value (Pa)
Calculated value (mm)
Figure 6 – Variation of Measured Value with Calculated Value for T50cm slump Flow Time
Figure 9 – Variation of Measured Value with Calculated Value for Yield Shear Stress
6
279
Measured value (Pa s)
160 2
R = 0.7292
140
References
120
1.
100 80
Line of equality
60
2.
40 20 0 0
20
40
60
80
100 120 140 160
3.
Calculated value (Pa s)
Figure 10 – Variation of Measured Value with Calculated Value for Plastic Viscosity
5.
4.
Conclusions
5.1.
Estimation of mix properties by using regression models It is possible to establish regression models with reasonable reliability to estimate the index flow properties and Bingham constants by inputting mix parameters
5.
6.
5.2. Qualified mix proportions as SCC The test mixes which are qualified to be SCC according to EFNARC guidelines [1] are given in the Table 5.
7.
Table 5 – Qualified Mix Proportions as SCC w/c (by w/p (by HRWR / (L/100kg mass) volume) of cement) 0.45 0.80-0.90 2.2-2.4
9.
0.50
0.75-0.80
2.2-2.5
0.55
0.80-0.85
2.5-3.0
8.
10. 11.
5.3.
Range of yield shear stress and plastic viscosity for SCC The investigation shows that the existence of a region of combinations of plastic viscosity and yield shear stress, where the mixes are highly likely to be self-compactable.
12.
The region is bounded by the inequalities 12 to 15. �0 > 2.57� − 94.7 … (12) �0 < 2.64� − 205.6 … (13) ��0 > 0.05� − 12.0 … (14) ��0 < −0.13� − 94.2 … (15)
13.
7
280
Specifications and Guidelines for Self Compacting Concrete., (Electronic database). EFNARC, Association house, Surrey GU9, February 2002. http://www.efnarc.org Hwang, S.D., Khayat, K.H., & Bonneau, O., “Performance based specifications of SelfConsolidating Concrete used in Structural applications.” ACI Materials Journal, Vol. 103, No 2, March-April 2006, 121-129. Okamura, H., & Masahiro, O., “Self Compacting Concrete.” Journal of Advance Concrete Technology, (online serial), Vol 1, No 1, April 2003, 5-15. http://www.j-act.org Specifications and Guidelines for Self Compacting Concrete., Specification Production and Use, (Electronic database). EFNARC, May 2005. http://www.efnarc.org Okamura, H., “Self Compacting High Performance Concrete.” Concrete International, July 1997, 50-54. Brower, L.E., & Ferraris, C. F., “Comparison of Concrete Rheometers.” Concrete International, Vol 25, No 8, August 2003, 4147. Tattersall, G.H. (1976), “The Workability of Concrete.” View Point Publication, Cement and Concrete Association, UK. European Standard for Concrete – Part 1: Specification, performance, production and conformity. EN 206-1: 2000. European Standard for Cement – Part 1: Composition, Specifications and Conformity Criteria for Common Cements. EN 197-1: 2000. European Standard for Aggregates for Concrete. EN12620: 2002. Saak, A.W., Jennings, H.M., & Shah, S.P., “New Methodology for Designing SelfCompacting Concrete.” ACI Materials Journal, Vol 98, No 6, November-December 2001, 429430. Application of Self Compacting Concrete in Japan Europe and United States., Bridge Technology, (Electronic database). Federal Highway Administration, Washington DC USA., 2006. http://www.fhwa.dot.gov/bridge/scc ACI Committee 211 (1991) Standard Practice for Selecting Proportions for Normal, Heavyweight and Mass Concrete (ACI 211.191 – Reapproved in 2009), American Concrete Institute, Detroit
Annual Transactions of IESL, pp. [281-289], 2012 © The Institution of Engineers, Sri Lanka
Service Life Evaluation of Reinforced Concrete Structures in Sri Lanka B.H.J. Pushpakumara, G.S.Y. De Silva and G.H.M.J. Subashi De Silva Abstract: Sri Lanka is an island surrounded by Indian Ocean. Most of structures near to costal region are corroded due to Chloride attack. Because of the Chloride attack, the structures near to the coastal region do not often achieve their design service life. By periodically repairing, the service life of the existing structures can be increased. Evaluation of service life of reinforced concrete (RC) structures is essential for the identification of the required repairing level. Objective of this study is to evaluate the service life of RC structures by using numerical calculation method and crack observation method. In the numerical calculation method, service life was calculated by finding the values for parameters. The initial corrosion time, de-passivation time and propagation time were calculated by using Fick’s second law and Bazant methods. The tensile stress, diffusion coefficient, rust production and surface chloride concentration were used as parameters for numerical calculation method. In the crack observation method, the service life was evaluated by developing a relationship of the time taken to reach the allowable crack width (i.e., 0.2 mm) between actual environmental condition and laboratory experimental condition. For crack observation method, RC beams were prepared with different concrete grades (G20 and G40), different cover depths (10 mm and 20 mm) and different r/f bar diameters (12 mm and 16 mm). Crack width was measured with the time for RC beams, which were corroded by using Accelerated Corrosion Test Method (ACTM) and actual environmental conditions. The time to reach the allowable crack width (0.2 mm) was defined as the service life for RC structures in crack observation method. The numerical calculation method was applied to predict the service life of an actual reinforced concrete structure. It was found that, numerical calculation method provides an accurate prediction. Keywords: Reinforced concrete, Chloride attack, Corrosion, Service life
1.
initiation of reinforcing steel are the ingress of chloride ions and carbon dioxide to the steel surface. After initiation of the corrosion process, the corrosion products (iron oxides and iron hydroxides) are usually deposited in a restricted space in the concrete around the steel. Their formation within this restricted space sets up expansive stresses, which split and spall (Figure 1) the concrete cover (Veerachai et al. [9]). This results in progressive deterioration of the concrete, and affects significantly on the reduction of the service life of the structures.
Introduction
Sri Lanka is an island surrounded by Indian Ocean. Most of structures near to costal region are corroded due to Chloride attack. When reinforcement steels corrode, signs of deterioration, such as rusting, cracking and spalling, usually appear on the concrete surface. Once these signs appear, it may be too late to prevent further deterioration through repair work. Evaluation of service life of reinforced concrete (RC) structures is essential for the identification of the required repairing level.
Eng.B.H.J.Pushpakumara,B.Sc.Eng.(Hons)(Ruhuna), AMIE(Sri Lanka), Rresearch Student, Department of Civil and Environmental Engineering, Faculty of Engineering, University of Ruhuna, Sri Lanka, Eng. (Dr.) G.S.Y. De Silva, PhD(Saitama), M.Eng (Saitama), PG.Dip(Strut.), B.Sc.Eng.(Hons)(Moratuwa), C.Eng., MIE(Sri Lanka), Member-JCI(Japan),Senior Lecturer, Department of Civil and Environmental Engineering, Faculty of Engineering, University of Ruhuna, Sri Lanka, Eng. (Dr.) (Mrs).G.H.M.J. Subashi De Silva, PhD (Saitama), B.Sc.Eng.(Hons)(Moratuwa), C.Eng., MIE(Sri Lanka), Senior Lecturer, Department of Civil and Environmental Engineering, Faculty of Engineering, University of Ruhuna, Sri Lanka,
Figure 1- Corrosion in Structures Corrosion of reinforcing steel in concrete is a very complex phenomenon that involves many factors. The most important causes of corrosion 1
281
Corrosion induced da
Corrosion consists of an oxidation reaction and a reduction reaction at the surface of the corroding material. The oxidation reaction generates metal ions and electrons; the electrons are then consumed in the reduction reaction. For environments with the presence of water, including moisture in the air, the electrons are consumed by converting oxygen and water to hydroxide ions. In iron and many iron alloys, these hydroxide ions in-turn combine with iron ions to form a hydrated oxide (Fe(OH)2). Subsequent reactions form a mix of magnetite (Fe3O4) and hematite (Fe2O3). This red-brown mixture of iron oxides is rust (Hansson et al. [4]).
timeand t is the service life of corrosion process for RC strcutures.
The higher the ionic conductivity, the quicker this reaction takes place. As a result water containing electrolytes, such as salt, is far more damaging. In addition, reducing the amount of dissolved oxygen in solution can inhibit corrosion directly. However, many other reduction reactions can consume the electrons.
Figure 2- Service Life of RC Structures affected by Corrosion (Martin et al. [6]) Initiation time (tc) can be predicted using Fick’s Second law (Ming et al. [7]);
The corrosion process consists of three major time periods: Initiation time (tc), De-passivation time (tp) and Propagation time (tcorr) as shown in Figure 2 (Ming et al. [7] and Tsuyoshi et al. [8]). The initiation stage is the phase during which chloride ions penetrate into the concrete cover and reach the reinforcing steel in sufficient quantities to de-passivate it, therefore initiating the process of corrosion. The time taken to initiation of the corrosion is the time when the chloride concentration at the reinforcement level has reached the threshold value (Martin et al. [6]). The de-passivation time is defined as de-passivation normally provided to the steel by the alkaline hydrated cement matrix locally leading to pitting corrosion. The propagation time is the time started from corrosion products form to the stage where they generate sufficient stress to disrupt the concrete cover by cracking or
Bazant established two classical formulae for calculating the de-passivation time (tp) and propagation time (tcorr).
� (� � � � , ��) = � � (2) 0 � � � � � � � 4� � � � �� � Where C (x,t) is the chloride concentration at depth x after time t, C0 is the concentration of chloride ions in pores of concrete at the surface, erfc is the complementary error function, x is the concrete cover at various times t relevent to required design life, tc is the initiation time and Dc is the diffusion coefficient.
De-passivation time can be calculated by averaging the values of Bazant method (Equation 3) and Ming’s Proposed method (Equation 4) (Ming et al. [7]); 2
⎡ ⎤ 1 � ⎢ � � � ⎥ = 12��� ⎢ �∗ ⎥ 1−� � � ⎣ 0⎦
spalling, or when local attack on the reinforcement becomes sufficiently severe to impair its load-carrying capacity. Based on the mathematical modelling, the corrosion process could be formulated based on the above three stages.
2
⎡ ⎤ 1 � ⎢ � � � ⎥ = 4�� � �⎢ 1−� ∗ ⎥ � � ⎣ 0⎦
The total service life of RC structure can be expressed as (Ming et al. [7]); t = ��� + ��� + ��������
(1)
Where tc is the initiation time, tp is the depassivation time, tcorr is the propagation
(3)
2
282
(4)
Where tp is the depassivation time, Dc is the diffusion coeffision, L is the cover thickness C* is the threshold value of the chloride concentration and Co is the concentration of chloride ions in pores of concrete at the surface. Parameters defined in Equations (3) and (4) are
the same. However in Ming’s Proposed method, it was proposed to consider three times of the tp compared with Bazant method.
Propagation time (tcorr) can be calculated by using modified Bazant method (Ming et al. [7]); � ∆��∗ � � �� � � � � = � � � �� � � � � Where∆��∗ is ; � � �
∆D* =fl l � 2 �+ 1��δPP Where δPP is; 2��3 � δPP = (1 + ��) + 2 � �� � � � � � � � �
2.
(5)
method and crack observation method. Forty test beams having a size of 400 mm x 100 mm x 150 mm were prepared with changing the cover depth (10 mm and 20 mm), concrete grade (Grade 20 and Grade 40) and reinforcement diameter (12 mm and 16 mm tor steel bars). The on laboratory experiments.
(6)
(7)
The pH of concrete has a significant influence on the corrosion of steel in concrete. It is generally believed that, the lower the pH of concrete, the higher the probability of corrosion. Due to the high concentration of alkalis in the pore water and soluble calcium hydroxide in concrete, the pH is usually well above 12 and the passivation on the steel surface is thermodynamically stable as long as the pH of concrete (pore water) remains above 11.5 (Jerzy [5]). In Sri Lanka, most of the structures, including reinforced concrete (RC) and pre-stressed concrete (PC) bridges, are situated in the coastal region. These structures are exposed to a severe environment all the time. However, any of the prevention method to minimize the corrosion of the reinforcement in existing structures has rarely been considered. This was resultant to spend large amount of money for repairing the structures when they were severely corroded and came to the critical condition. Objectives of the present study were;
Methodology
The service life of reinforced concrete elements were studied by using numerical calculation
Where, ρcor is the density of the corrosion product, s is the space of the steel bar, D is the steel diameter, jr is the rate of rust production per unit area of plane, ft’ is the tensile strength, L is the cover thickness, δpp is the bar hole flexibility, � is the Poisson’s ratio (� � =0.18) and ����� is the effective elastic modulus.
To evaluate the effectiveness of parameters that dominate the corrosion To evaluate the service life of existing reinforced concrete structures based on the laboratory experiment and field inspections.
To identify the parameters that effect on the corrosion of reinforced concrete structures. To evaluate the service life of RC structures for different concrete grades, cover depths and r/f diameters based 3
283
stirrup were prepared by using 6 mm diameter mild steel bars and placed at 100 mm interval. Eight specimens were kept in a laboratory environment while other 32 specimens had being placed on suitable location at the coastal region near to Galle town. From the specimens kept in laboratory environment, the crack width was measured by using a crack gauge. Eight of specimens kept in actual environment were used to find the service life by using crack observation method while other 24 specimens were used to find service life by the numerical calculation method. From these 24 specimens, rate of rust production per unit area was determined for every 60 days. 2.1
Numerical Calculation Method
Evaluation of the service life by using numerical calculation method, the calibration of total time for the corrosion process was done by calculating the initiation time by using Fick’s Second law (Equation 2), de-passivation time by using Bazant method and Proposed method (Equations 3 and 4) and propagation time by using Modified Bazant method (Equation 5). In the numerical calculation method, four parameters were monitored using laboratory experiments. These parameters were concentration of chloride ion (Cl ) on concrete surface (Co), tensile strength of concrete (ft’), rate of rust production per unit area of the plane (jr) and diffusion coefficient of concrete (Dc).
284
2.1.1
Strength Properties of Concrete
concrete surface, by using titration method. In this method, firstly 25 ml of sea water (NaCl(aq)) was mixed with 1 ml of 5% K 2CrO4 (aq). Then, it was titrated against known AgNO3 (aq) and required volume of AgNO 3 (aq) was measured at the end point. Using the measured volume of AgNO3, concentration of chloride ions in the sea water was calculated and considered as concentration of chloride ions on concrete surface.
Tensile strength and compressive strength of concrete were investigated according to the BS 1881-part 117 [2]. Tensile strength of concrete was investigated by using splitting tensile test of 150 mm x 300 mm concrete cylinder for both G20 and G40 concrete after 28 days curing. Three specimens were prepared for each concrete grade and the tensile strength values were averaged.
2.1.3 (a)
Rust Production (jr)
Rust product per unit area of the plane was found using two methods. In first method, weight of rust product on reinforcement steel of concrete specimens was measured by demolition and removing rust at an interval of 60 days.
(b)
Figure 3- (a) Tensile Strength and (b) Compressive Strength test Compressive strength of concrete was investigated (BS 1881 part 116 [1]) using cubes having the size of 150 mm x 150 mm x 150 mm after 28 days curing. Three cubes were prepared for each concrete grade and the compressive strength values were averaged.
Figure 4- RC Beams were Placed in Tidal Zone In second method, volume of rust product was determined by calculating volume reduction of reinforcement bar due to rust. It was calculated by measuring initial diameter (12 mm and 16 mm) (before preparing concrete specimens) of reinforcement bar and measuring diameter of reinforcement bar after every 60 days (diameter was measured after removing rust product by scrapping). For these methods, eight specimens were used at every 60 days to measure rust product per unit area of the plane (Figure 4).
The modulus of elasticity was obtained by using Equation 8;. ��� = 4700(�� ′)1/2
(8)
Where Ec is the Modulus of Elasticity and fc’ is the average compressive strength. The effective elastic modulus (Eef) was obtained by using equation 9; ��� ����� = 1 + ���
2.1.4
Diffusion Coefficient (D c)
Diffusion coefficient of concrete was found by Rapid Chloride Permeability Test (RCPT).
(9)
Where φcr is creep coefficient of concrete. It was considered as 0.2 mm. The effective elastic modulus (Eef) was used in Equation 7 for the calculation of bar hole flexibility (δpp).
2.1.2
100mm
50mm
Concentration of Chloride Ions (Co)
(b) (a) (a) Schematic diagram (b) Actual specimens, piled on each other Figure 5- Specimens for RCPT
Concentration of chloride ions on concrete surface is equal to concentration of chloride ions in sea water because of specimens were placed in tidal zone. Therefore, concentration of chloride ions in sea water was determined, instead of concentration of chloride ions on
The concrete specimens(Figure 5b), on completion of moist curing period of 28 and 90 4
285
solution (mol/cm3), and dc/dt is the steady state migration rate of chloride ion (mol/cm 3.s).
days, were used for RCPT as according to ASTM C1202 (Ganesan et al. [3]) (Figure 6). 60 V DC supply
2.2
mA
Crack Observation Method
(a)
PVC pipe
(b)
Copper electrode NaOH 0.3 M
NaCl 2.4 M
Figure 7aCrack Locations were Identified
100 mm dia. X 50 mm concrete specimen Figure 6- RCPT set up
Figure 7b- Crack Width Measured by Using Microscope and Crack
In the crack observation method, the service life was evaluated using the measured crack width. The beams were tested at laboratory experimental condition and actual environmental condition. For the laboratory experiment, the Accelerated Corrosion Test Method (ACTM) was conducted for eight specimens to accelerate the corrosion process. Crack widths were measured at an interval of three days using a crack gauge (Figure 7b). The crack width was tabulated with days and variation of crack width with the age was plotted. Using the graph, the time required to reach allowable crack width (i.e., 0.2 mm) was calculated. It is equal to the service life of specimens. Simultaneously, time to appear a very first crack in eight specimens kept in the actual chloride environment was counted. It is equal to the actual service life of these specimens.
The positive reservoir of the cell was filled with 0.30 M NaOH solution while the negative reservoir was filled with 3.0% NaCl solution as shown in Figure 6. Two identical Copper Substrate Insoluble Anodes (CSIA) mesh were used as anode and cathode. A direct current (DC) with 60 ± 0.10 V was applied across the specimen faces, and the current across the specimens were recorded at every 30 minutes interval, for a period of 6 hrs. By knowing the current and time history, the total charge passed (CP) through the specimen was computed by Simpson’s rule (Equation 10) as given in the ASTM 1202 (Ganesan et al. [3]). ��� = 900[��0 + 2��30 + 2� � 60 + 2�� � + ⋯ + 2� � 330 + 2� � (10) 360 ] Where CP is total charge passed in coulombs, I0 is initial current in Ampere (A) and It is Ampere (A) at time t measured in minutes.
2.2.1 Accelerated Corrosion Testing Method (ACTM)
The chloride diffusion coefficient was calculated as per the equation (11) (Ganesan et al. [3]), � � � � � � � �� �� �� ��� = � �� � � � � � �
(11)
Where Dc is the diffusion coefficient (given in cm2/s), β is the corrosion factor for ionic interaction (varies from 1.22 to 1.7 based on the chloride concentration from 0.1 M to 0.5 M NaCl), k is the Boltzman constant (1.38 x 10-16 ergs/k/ion), T is the temperature (K), Z is the chloride valance (Z is 1 for NaCl), e is the charge of proton (4.8 x 10-10e.s.u), E is the applied electrical potential (V), L is the specimen thickness (cm), V is the volume of chloride collecting tank (cm 3), C is the initial
chloride
5
286
concentration
in
chloride
source
Figure 8- ACTM set up This test was based on electrochemical polarization principle. The experimental test setup essentially consisted of anon-metallic container, in which the concentration of Cl- in sea water was improved to 5% and filled to the required level. In this container, the concrete specimens with reinforcement bars were placed
287
centrally. The reinforcement bar of the concrete specimen was connected to a DC power supply to the positive terminal (+ve) and the copper electrode to the negative terminal (-ve). This set up formed an electrochemical cell with reinforcement bar acting as anode and copper electrode as cathode. Number of such units can be made and connected to a DC power supply of multi-channel system. A constant voltage of 5.0 V was applied from the DC Power Pack. Current was monitored with respect to time up to the propagation period.
concentration in sea water was obtained as 34.8kgm-3.
Crack widths at an interval of three days were measured and tabulated with the age of the specimens (i.e., time). Time required to reach allowable crack width (0.2 mm) was calculated from a graph that was plotted with crack width and the age of specimens. It is equal to service life of specimens.
Table 2- Rust Production Measurements
Results
3.1
Numerical calculation method
B1 B2 B3 B4 B5 B6 B7 B8
3.1.4
Strength properties of concrete
2.79 3.06
Cover (mm) 10 10 20 20 10 10 20 20
12 16 12 16 12 16 12 16
7.515 18.59 21.48 100.9 6.227 17.29 18.72 85.58
Diffusion coefficient (D c)
Elastic modulus-Ec (GPa) Effective elastic modulus-Eef (GPa)
Current(A)
0.7 0.6 0.5 0.4 0.3 0.2 0.1
22.457 30.259
18.714 25.216
0
Concentration of chloride ions (Co)
Grade 40-1 Grade 40-2 Grade 40-3
The concentration of chloride ions in sea water sample was determined by applying titration to the sample against the AgNO3. The volume of AgNO3 was measured and the chloride ions concentration was calculated. The chloride ions
Time (min.) Grade 20-1 Grade 20-2 Grade 20-3
Figure 9- Current Across Specimens at Different Time Intervals (RCP Test)
6
288
0 30 60 90 120 150 180 210 240 270 300 330 360
3.1.2
Average compressive strength- fc’ (MPa) Average tensile stress-ft’ (MPa)
Concrete grade
Table 1- Strength Properties with Concrete Grade
22.83 41.85
20 20 20 20 40 40 40 40
Jr (g/m2.s) x10-8
The diffusion coefficient was investigated by using Rapid Chloride Permeability Test (RCPT). The current across the specimens at different time intervals are presented in Figure 9.
Table 1 presents compressive strength, tensile strength, Modulus of Elasticity of concrete specimens.
20 40
Concrete grade
Specimen Identification No
Rust productions generated in different specimens are shown in Table 2. Specimens were varied with concrete grade, size of the cover and diameter of reinforcement bars. It can be seen from Table 2 that with the increase of the size of bar diameter, the amount of rust production was increased.
To determine service life using Numerical calculation method, concentration of chloride irons on the surface of concrete (Co), strength properties of concrete, rust production (jr), and diffusion coefficient (Dc) were determined 3.1.1
Rust production (jr)
r/f diameter (mm)
3.0
3.1.3
The steady state migration rate of chloride ions (dc/dt) was evaluated based on Figure 9. Diffusion coefficient, which was determined by adding the averaged dc/dt values to the Equation 11, is presented in Table 3. The grade of the concrete is mainly affected for the chloride ions diffusion. It can be seen from Figure 9 that with the lower concrete grade (G20), the current passes across the specimen was increased. That means the chloride ions concentration was higher.
From Figure 10, it can be identified that the beam number B09 (G20, cover 10 mm, bar diameter 12 mm) reached to the crack width of 0.2 mm at the shortest time period. Therefore, the B09 was having the lowest service life. Moreover, the beams with the cover depth of 10 mm reached to the allowable crack width (0.2 mm) earlier compared with the time taken to form a crack in other beams. By comparing the beam number B09 (cover-10 mm, -12 mm) and B11 (cover-20 mm, Ф-12 mm), the lower cover depth beam (B09) reached to crack width of 0.2 mm at the less time period compared with the B11. The bar size (i.e., diameter) for both B09 and B11 was the same. Therefore, it seems that the bar diameter of the reinforcement did not significantly effect on the service life compared to the cover depth.
1 2 3 1 2 3
20
40
3.2
dc/dt ( mol cm-3s-1) x 10-9 2.219 2.394 2.252 1.288 1.345 1.178
Diffusion coefficient (mm2/year) Average Diffusion coefficient (mm2/year)
Test No. Concrete grade
Table 3- Diffusion Coefficient Values
18.71 20.18 18.98 10.86 11.34 9.93
19.29 By comparing the specimens B09 and B13, the time period to reach 0.2 mm crack width was less with the B09. The only difference between these beams was concrete grade. With the lower concrete grade, the time period was lower. Therefore, the permeability of chloride ions was increased with the lower of concrete grade.
10.71
Crack observation method
Crack Width (mm)
To evaluate the service life of RC specimens by using Crack observation method, crack width was measured for the crack formed from accelerated corrosion test. 3.2.1
Accelerated corrosion test
4.0
Discussion
4.1
Numerical calculation method
The service life of the test specimens was calculated by substituting the measured data to the Equations 1 to 5. Table 4 shows the calculated Initiation time, De-passivation time and Propagation time with relevant to the specimen numbers.
0.6
0.4
Table 4- Service Life Numerical Method
Calculations for
7
289
Propagation time (years)
Service life (years)
Figure 10- Variation of Crack Width with the Age of Specimen (ACTM test)
De-passivation time (years)
43 49 55 61 67 73 79 85 91 97 103109 Times (Days) B09(G20,cover 10, =12mm) B10(G20,cover 10, =16mm) B11(G20,cover 20, =12mm) B12(G20,cover 20, =16mm) B13(G40,cover 10, =12mm) B14(G40,cover 10, =16mm) B15(G40,cover 20, =12mm) B16(G40,cover 20, =16mm)
Initiation time (years)
0
Specimen Identification No.
0.2
B1 B2 B3 B4 B5 B6 B7 B8
2.52 2.52 9.80 9.80 4.53 4.53 18.17 18.17
8.23 8.23 32.92 32.92 14.82 14.82 59.29 59.29
3.6 3.34 4.27 3.86 3.13 2.92 3.98 3.71
14.35 14.09 49.99 46.58 22.48 22.27 81.44 81.17
According to both numerical calculation method and crack observation method (from accelerated corrosion test data), the cover depth is the predominant factor for the corrosion process of RC structures. The concrete grade also effect on the corrosion process, although it is not as significant as the effect of cover. While keeping suitable size of cover depth for the structures, which are located near to coastal region, the corrosion initiation can be delayed. It helps to increase the service life of the RC structures.
The only difference between specimen B1 (G20, cover depth- 10 mm, – 12 mm) and B2 (G20, cover depth- 10 mm, – 16 mm) was reinforcement diameter. According to the Table 4, the B1 and B2 achieved nearly an equal service life value. Therefore, there is no significant effect of changing the reinforcement bar diameter on the service life. The final calculations show that the clear cover of concrete and the grade of concrete are directly affect to the service life of RC structures. Moreover, according to the Table 4, the clear cover is the most critical factor for the service life of RC structures. 4.2
The service life prediction by crack observation method is still continuing.
Crack observation method 4.3 Applying the Numerical Calculation Method for Existing RC Structures
The service life prediction from crack observation method was conducted by measuring the corrosion crack width of natural condition and accelerated corrosion condition test beams. Because of the actual environmental RC beams are still testing, the accelerated corrosion conditions were discussed in this section.
A reinforced concrete building which was located near to the Galle (close to the coastal belt), constructed in 1960 and isolated from 2007, was selected for applying numerical calculation method to predict service life of the structure. Core samples that were taken from existing slab of the structure were used to find rust product (measured per unit area) and chloride concentration. The rebound hammer test was used to evaluate the concrete compressive strength. The average concrete strength was taken as 20 N/mm2 for the building. Cover for reinforcement steel was considered as 20 mm for calculations. From the visual inspections, locations of corroded steel reinforcements were identified in slabs, beams and columns. The concrete cover of the steel reinforcements was cracked, spalling and delaminated.
Time (Days)
The time taken to expand the crack to the allowable crack width (0.2 mm) of accelerated corrosion test was graphed for test specimens B09 to B16 (Figure 11). The test specimens were cast with concrete grade of G20 and G40, cover depth of 10 mm and 20 mm and the r/f bar diameter of 12 mm and 16 mm. 150 100 50 0
(a)
(b)
Specimen number Figure 11- Times (Days) for the Allowable Crack Width of ACTM
(a) A view of the selected building (b) Process of Cutting Core Samples Figure 12- Selected Existing Structure:
B16
B15
B14
B13
B12
B11
B10
B09
Among the changing parameters of concrete beams, there was no significant effect from the bar diameter on the time taken for reaching of allowable crack width. The cover depth and concrete grade governed the initial cracking process. According to the Figure 11, the test specimens which were having 10mm cover depth (B09, B10, B13 and B14) reached to the allowable crack width (0.2 mm) within lower time period. Therefore, cover depth is the critical factor for the corrosion of RC structures.
8
290
9.8
Depassivation time (Years) Propagatio n time (Years)
Initiation time (Years)
Table 5- Service Life Calculation for the Selected Structure
32.92
6.64
technical assistance for carrying out research work presented in this paper.
References
Service life (Years)
1. British Standard 1881-part 116: 1983, Method for Determination of Compressive Strength of Concrete Cubes
49.36
2. British Standard 1881-part 117: 1983, Method for Determination of Tensile Splitting Strength
From the calculation, it was found that the service life of the building was 49.36 years and it should be year 2009. However, the structure was attacked by the tsunami in 2004 and abandoned from 2007. Therefore, the calculated service life is approximately equal to actual service life of the building. From the result it can be concluded that numerical calculation method gives reasonably accurate prediction of the service life of RC structures.
5.0
the
3. Ganesan K., Rajagopal K. and Thangavel K., “Chloride Resisting Concrete Containing Rice Husk Ash and Bagasse Ash”, Indian Journal of Engineering & Materials Sciences, Vol.14, June 2007, pp.257-265 4. Hansson C.M., Poursaee a. and Jaffer S.J., “Corrosion of Reinforcing Bars ibn Concrete”, R & D Serial No. 3013, Portland Cement Association, Skokie, Illinois, USA, 2007 5. Jerzy Z., “Modelling the Time to Corrosion Initiation for Concretes with Mineral Admixtures and/or Corrosion Inhibitors in Chloride- Laden Environments”, Virginia Polytechnic Institute and State University, Blacksburg, Virginia, January 1998
Conclusions
The prediction of service life of reinforced concrete structures is important to improve the durability and service life of structures. With the knowing of corrosion initiation time of a structure, the adopting of corrosion preventing, minimizing and repairing methods can be used effectively. Evaluation of service life of RC structures was investigated using numerical calculation method and crack observation method.
6. Martin-Perez.B and Lounis.Z, “Numerical Modelling of Service Life of Reinforced Concrete Structures”, Proceedings of 2 nd International RILEM Workshop on Life Prediction and Aging Management of Concrete Structures, Paris, France, May 2003, pp.71-79 7. Ming-Te L., Ran H., Shen-An F. and Chi-Jang Y., “Service Life Prediction of Pier for the Existing Reinforced Concrete Bridges in Chloride-Laden Environment”, Journal of Marine Science and Technology, Vol.17, No.4, 2009, pp.312-319
It was found that the numerical calculation method predict reasonably accurate service life of RC structures exposed to chloride environment. Based on the both numerical calculation data and accelerated corrosion test data, cover depth of concrete structures is the critical parameter, among the parameters that drive the corrosion process. Concrete grade also affects to the corrosion process, although it is not as significant as the cover depth.
8. Tsuyoshi M., Kailin H., Hitoshi T. and Somnuk T., “Numerical Modelling of Steel Corrosion in Concrete Structures due to Chloride Ion, Oxygen and Water Movement”, Journal of Advanced Concrete Technology, Vol.1, No.2, July 2003, pp.147-160 9. Veerachai L., Toshimitsu S., Yuichi T. and Masayasu O., “Estimation of Corrosion in Reinforced Concrete by Electrochemical Techniques and Acoustic Emission”, Journal of Advanced Concrete Technology, Vol.3, No.1, February 2005, pp.137-147
The numerical calculation method was applied to predict the service life of an actual structure. It was found that, numerical calculation method provides an accurate prediction.
Acknowledgement The authors wish to express their special thanks to Research Grant of Transforming University of Ruhuna to International Level for providing necessary funds and Faculty of Engineering, University of Ruhuna for providing necessary
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Annual Transactions of IESL, pp. [290-296], 2012 © The Institution of Engineers, Sri Lanka
The Effect of Silica to Carbon Black Ratio on Properties of a Tubeless Tyre Inner Liner Compound Prepared with a Blend of Chlorobutyl Rubber and Natural Rubber T. A. A. I. Siriwardane, S. M. Egodage and D. G. Edirisinghe Abstract: Inner liner of a tubeless tyre is currently constructed using a specialty synthetic rubber called chlorobutyl rubber (CIIR). Blending of CIIR with natural rubber (NR) will enable to achieve improvement in physico-mechanical properties with a reduced compound cost. The property increase is enhanced by addition of a combined filler of carbon black and silica. Finally this blending provides an increase in NR market potential. In this present study, different series of compounds were prepared; one is with CIIR alone by varying the carbon black to silica ratio at 10 phr intervals; other is with CIIR/NR blends by varying NR loading from 0 to 100% at 20% intervals for selected carbon black to silica ratios. Total filler loading was kept constant at 60 phr. Melt viscosity, hardness, tensile strength, modulus, and tear strength increased with silica loading while scorch time, cure time, abrasion volume loss and permeability decreased above silica loading of 30 phr. When replacing CIIR with NR, cure rate index increased significantly from 40% NR, and hence the cure time decreased. Mechanical properties and air permeability varied significantly. Results in overall showed optimum properties for the 20:80 CIIR/NR blend at 50:10 silica:carbon black ratio. Keywords: silica
1.
Inner liner, Chlorobutyl and Natural rubber blends, Combined filler carbon black and
between the inner liner and the carcass could be improved if a diene rubber like NR is blended with IIR in inner liner compounds [5]. The blends of NR either with BIIR [6-8] or CIIR [2] have been already used for inner liners. These blends showed higher air permeability compared to 100% BIIR or CIIR. NR compared to IIR exhibited at least 8 times lower values as air pressure loss in passenger car tyres [3]. The difference in air permeability constants for BIIR and CIIR is negligible, but it is 8, 10 and 18 times greater at 23 0C for NR, SBR and BR, respectively [7]. Although the air permeability of CIIR/NR blends is generally increased, this increase does not have an effect on the practical use of these blends for inner liners.
Introduction
The inner liner is a thin rubber sheet applied to the interior of a tubeless tyre to keep high pressure inflation inside the tyre by minimizing air migration from the inflation chamber into the carcass body of the tyre [1]. Any reduction in pressure causes deflection, heat build up and a reduction in performance [2]. This air migration is controlled by the air permeability of the rubber compound and by the thickness of the inner liner. Butyl rubbers (IIR) due to their gas impermeability are generally used as the base rubber for inner liners [3]. At present, halobutyl rubbers such as bromobutyl rubber (BIIR) and chlorobutyl rubber (CIIR) with enhanced reactivity, and compatibility to their unsaturated rubbers, are used in inner liner compounds. Approximately more than 80% of the worldwide usage of butyl rubbers is for tyres, inner tubes and inner liners [1, 3].
Carbon black and silica are the most widely
Eng. (Dr.) (Mrs.) S. M. Egodage, BSc Eng(Moartwa) , MSc(SL) , Mphil(SL), PhD(Loughborough) C Eng, MIE(Sri Lanka), Senior Lecturer, Department of Chemical and Process Engineering, University of Moratuwa. T. A. A. I. Siriwardane, BSc (Open Uni) , Chemist Technical Assistant, Puttalum Coal Fired Power Plant, Ceylon Electricity Board. Mrs. D. G. Edirisinhghe, BSc (Colombo) , MSc(SL) , Mphil(UK), Senior Research Officer, Department Rubber Technology and Development, Rubber Research Institute of Sri Lanka.
The carcass of the tyre is constructed with unsaturated rubbers, such as natural rubber (NR), styrene butadiene rubber (SBR) and butadiene rubber (BR) [4], which are not compatible with butyl rubbers. The adhesion 1
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used reinforcing fillers in rubber industry. Carbon black improves strength, toughness, tear resistance, abrasion and flex cracking and some other properties of rubber [9]. Silica is difficult to incorporate to hydrocarbons, due to its polar surface [9], but silica in presence of a coupling agent provided enhancement in physical properties [10]. Therefore silica is partially or even completely replaced carbon black filler in different rubbers and in rubber blends [10-12]. However, the use of silica and carbon black as combined filler is not reported for CIIR/NR blends.
to carbon black were used. Silica to carbon black ratio of 50:10 showed best combined properties for the first series of compounds and hence it was selected. Silica loadings lower than 30 phr did not show improved properties. However, silica to carbon black ratio of 10:50 was selected to compare the properties of CIIR/NR blends having high silca loading. Other ingredients, in phr, were added according to the formulation: Si 69-4, sulfur-1, ZnO-5, stearic acid- 2, MBTS-2, IPPD-1, DEG-2 and oil -10. These compounds were mixed in two stages: firstly rubber and other ingredients, except the vulcanizing system, in an internal mixer for 7 minutes, and secondly the vulcanizing system in a two roll mill for 3 minutes.
Sri Lanka is a NR producing country and produced 152,900 MT of NR in 2010 [13]. Of that, 51,500 MT (34%) is exported in raw form without value addition. CIIR is an imported rubber and is costly compared to NR. Blending of NR with CIIR will reduce the cost of the inner liner compound and will also increase NR market potential. Therefore a detailed study on the use of carbon black-silica combined filler in a CIIR/NR blend is important especially to Srilankan rubber industry.
The important characteristic properties of a tyre inner liner were measured. Those properties include cure characteristics such as minimum torque, maximum torque, cure time and scorch time and physico-mechanical properties. Air permeability was also measured for selected compounds.
This paper presents first the effect of silica loading in a combined filler of carbon black and silica on the properties of CIIR inner liner compound, and second the effect of NR loading on properties of CIIR/NR blends.
2.
Cure characteristics of the compounds were determined using a moving die rheometer (MDR 2000) at 160 0C, according to BS 5738. The test specimens were prepared by vulcanizing with respect to their cure times. Tensile properties and tear strength of the rubber vulcanizates were determined using Hounsfield tensile testing machine according to the BS ISO 37:2010 and BS ISO 34-1:2010, respectively. Dumbbell tensile specimens and angle test tear specimens were used. Hardness of vulcanizates was determined using a dead load hardness tester according to BS ISO 48:2010. De Mattia flex cracking abrasion volume loss, rebound resilience and compression set were determined according to BS ISO 132:2011, DIN 53516, BS ISO 4662:2009, and BS ISO 815-1:2008, respectively. Tan 60 0C, as an indication of rolling resistance, was determined using MDR 2000 at 60 0C. Air permeability was determined according to IS 3400 (Part 21) -1980/Constant Pressure Method. Results were produced as average values of six, with standard deviations.
Experimental
NR (SLR 20) and CIIR were kindly supplied by the Rubber Research Institute of Sri Lanka and D. Samson Industries (DSI), Galle, respectively. The coupling agent, bis-3-triethoxysilylpropyl tetrasulfane (Si 69,) was supplied by Elastomeric (Pvt.) Ltd, Pliyandala. The two fillers carbon black (N 660) and Silica (Ultrasil VN3), the vulcanizing agent sulphur, the activators zinc oxide (ZnO) and stearic acid, the accelerator di benzothiazal di sulphide (MBTS), the antioxidant N- phenyl, N’ isopropyl paraphenylene Diammine (IPPD), diethyl glycol (DEG) and the white paraffinic processing oil were of industrial grade and were purchased from the local market. At first, a series of rubber compounds were prepared with CIIR alone by varying silica loading in the combined filler of silica and carbon black from 0 to 60 phr at 10 phr intervals. Total filler loading was kept constant at 60 phr. Secondly, a series of CIIR/NR blends were prepared by varying the NR loading from 0 to 100% at 20 % intervals. Two ratios of silica
3.
Results and Discussion
3.1 CIIR compounds Cure characteristics of the CIIR compounds prepared with different carbon black to silica ratios against the silica loading are given in 2
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Figure 1. Minimum torque (ML) and maximum torque (MH) did not vary until silica loading of 30 phr, but increased thereafter significantly. Cure time (t90) and scorch time (ts2) also showed no effect until silica loading of 30 phr, but decreased thereafter. Silica has finer particles compared to carbon black. With replacing carbon black by silica above 30 phr melt viscosity of the compound increased, and hence the torque increased. Finer and polar silica particles develop greater friction and hence a greater heat within the rubber compound to complete cure at a shorter time. This effect is enhanced may be when the matrix filler phase converted to silica above 30 phr. However, the cure rate index, which indicates the cross-link insertion rate, did not vary with the silica loading. This suggests that no effect of filler type on cross-link formation.
any pin hole even after 80,000 flex cycles. This is a requirement for an inner liner compound. 3.2 CIIR/NR blends Maximum and minimum torques, and scorch and cure times, of the CIIR/NR blends against NR loading at silica to carbon black ratios of 10:50 (10phr) and 50:10 (50 phr) are given in Figure 3 and Figure 4, respectively. With replacement of CIIR by NR at silica to carbon black ratio of 10:50, minimum and maximum torque did not vary. However, the torques were significantly increased with the NR loading when silica to carbon black ratio was 50:10. With the addition of higher levels of fine silica particles, melt viscosity and hence minimum torque increased drastically. This effect is enhanced with the replacement of low molecular weight CIIR by higher molecular weight of NR. The presence of natural accelerators in NR also enhanced cross-link formation and hence maximum torque increased with NR loading. Due to this acceleration process, both scorch time and cure time decreased with NR loading.
Tensile strength (TS) and elongation at break (%Eb) of CIIR vulcanizates against silica loading are given in Figure 2, while tear strength, modulus at 300% elongation (modulus @300%), hardness, rebound resilience, compression set, abrasion volume loss and Tan 60 0C are given in Table 1.
Tensile properties of the CIIR/NR blends against NR loading at silica to carbon black ratios of 10:50 and 50:10 are given in Figure 5. Other physico-mechanical properties of the said blends are given in Table 2. 100% NR compound showed a higher tensile strength than that of 100% CIIR compound and is associated with strain induced crystallisation nature of NR. All blends showed lower strengths than pure NR compound, but blend having 80% NR showed somewhat similar values to that of pure CIIR compound. Negative deviation of the tensile strength of blends from the addition rule is due to formation of partially compatible two phase blends. Elongation at break is high for pure CIIR compound, and that of the blends showed lower values due to the two phase system. Test specimen may be broken at early stages due to non ability of load transfer from one rubber phase to the other. Due to this two phase system, tear strength also showed a similar trend.
Tensile strength of the CIIR compound up to silica loading of 30 phr remained constant, and gradually increased thereafter with the silica loading. This increase in tensile strength is associated with the increase in reinforcement with the matrix filler phase change to silica due to presence of larger quantities of finer particles. However, no effect of silica loading on elongation at break was exhibited indicating there is no effect of particle size on the elongation at break. However, CIIR compound with silica alone, compared to that with carbon black alone, showed low elongation at break. Tear strength also showed a variation similar to variation of tensile strength and is associated with the degree of reinforcement. With increase of the surface area of the filler associated with presence of finer silica particles, compound hardness increased and hence modulus at 300% elongation increased. This is confirmed by the increase in maximum torque with the silica loading above 30 phr. Rebound resilience and compression set also increased accordingly. Abrasion volume loss and Tan 60 0C (indicates a low rolling resistance) showed lower values with the silica loading suggesting a good CIIR compound could be prepared with silica loading above 30 phr. Flex cracking was good for all compounds, which did not show
CIIR is softer than NR and showed hardness and modulus at 100% elongation for pure CIIR compound. All blends showed higher values than pure rubber compounds. With release of deformation, NR due to its coil structure, exhibited greater compression set. These set values varied with increase in NR loading. In relating to coil nature, rebound resilience 3
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increased with NR loading while abrasion volume loss decreased. These results suggest that the wear resistance, which is also an important property of a tyre inner liner to be comparable with the rest of the parts of a tyre, is increased with NR loading. However, Tan 60 0C increased with increase in NR loading indicating increase in rolling resistance with increase in NR loading. None on the CIIR/NR blends also show any pin hole even after 80,000 flex cycles. Of the two silica to carbon black ratios studied, 50:10 ratios showed greater physico-mechanical properties of the CIIR/NR blends compared to the ratio of 10:50. This property variation was comparable with the property variation observed for CIIR compounds.
time with NR loading due to its high molecular weight and presence of natural crosslink promoters, respectively. Most of the physicomechanical properties improved with the addition of NR, but they showed a negative deviation from the linear increment. These results indicate that the CIIR/NR blend is a two phase system. The air permeability, and Tan 60 0C increased with NR loading. High rolling resistance of the tyre inner liner resulted a low overall rolling resistance performance of a tyre. Flex cracking was good for all CIIR compounds and CIIR/NR blends. The optimum properties were obtained with the 20:80 CIIR/NR blend at silica to carbon black ratio of 50:10. 100% NR compound showed relatively greater physicomechanical properties. However, Tan 60 0C, which is an indication of the rolling resistance, was high. Air permeability, which is the most important property of the tyre inner liner, was exceptionally high.
Air permeability of pure CIIR compound having silica loading of 10 phr was 2.06 E -12 m2/Pa.s while that of pure CIIR compound and pure NR compound having silica loading of 50 phr were 1.29 E-12 m2/Pa.s and 9.05 E -12 m2/Pa.s, respectively. Further, the permeability of blends having 40%, 60% and 80% of NR were 1.35 E-12, 2.62 E-12, and 5.94 E-12 m2/Pa.s, respectively. The latter permeability values are for NR/CIIR blends prepared with silica loading of 50 phr. These results clearly showed that CIIR is less permeable than NR. Further, the air permeability increased with increase in NR loading while decreased with silica loading. 100% NR compound showed very high air permeability compared to other blends. However, air permeability values of all blends are within the acceptable levels for a tyre inner liner compound.
4.
References 1.
2.
3.
Conclusions
CIIR inner liner compounds were successfully prepared with a combined filler of carbon black and silica at different ratios. Replacement of carbon black by silica over 30 phr significantly increased melt viscosity, hardness, modulus at tensile strength, 300% elongation, tear strength and compression set, while decreased scorch time, cure time, rebound resilience, due to its fine particle structure, and when matrix filler phase was converted from carbon black to silica. Abrasion volume loss, Tan 60 0C and permeability also decreased explaining high silica loading is favour for enhanced physicomechanical properties of the CIIR compound. The best overall properties for CIIR compounds were showed at silica to carbon black ratio of 50:10. Replacement of CIIR by NR increased melt viscosity, and decreased scorch and cure 4
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Coddington D M, “Halogenated butyl tubeless tire innerliner background”, US patent 3769122, 1973. . Turturro A, Falqui L, Laprevite M, Giuliani G, Mowdood S and Serra A “Tubeless tyre inner liners morphology and physical properties of elastomer blends”, Elastomers and Plastics, Vol. 1, No. 2, pp 36-42, 2001. Fusco J V and Hous P in Rubber Technology, 3rd Ed, Morton M Ed, Van Nostrand Reinhold, New York, 1987, pp 288-362.
4.
Datta R N, “Rubber curing systems”, RAPRA review reports, Vol. 1, No. 1, p 36, 2001.
5.
Yasuhusa M, Akihiro N and Takashi I, “Dynamic vulcanization of halogenated butyl rubber/natural rubber blend”, Journal of the Society of Rubber Industry, Vol. 73, No., pp 62-69, 2000.
6.
Waddell W H, Napier B and Rouckhourt DR, “Polymers for innerliner applicationsnew developments”, Raw materials and applications, pp 483-488, 2010.
7.
Polysar company, Polysar Butyl Handbook, Ryerson Press, Toronto, 1966, pp 319-324.
8.
Rodgers B, Webb R N and Weng W, “Advances in tire innerliner technologies”, Rubber World, June, 2006.
9.
Schaal S, Coran A Y and Mowdood S K, “The effects of certain recipe ingredients and mixing sequence on the rheology and
processability of silica and carbon black filled tire compounds”, Rubber Chemistry and Technology, Vol. 73, p 240, 2000. 10.
Brinke J W, “Coupling agents in silica filled tyre rubbers”, Natural Rubber, Vol. 23, 1st quarter, 2003.
11.
Zhang Y, Ge S, Tang B, Kogo T, Rafailovich M H, Sokolov J C, Pieffer D G, Li Z, Dias K, McElrath K O, Lin M Y, Sajita S K, Urquhart SG, Ade H and Nguyen D, “Effect of carbon
black and silica fillers in elastomer blends”, Macromolecules, Vol. 34, pp 7056-7065, 2001. 12.
Waddell W H, Tracey D S, Botfild S W, “Select elastomeric blends and their use in articles”, US patent 7696266, 2010.
13.
Ministry of Plantation Industries, Rubber Sector (Chapter 3), “Statistical Information on Plantation Crops – 2010”, Plantation Sector Statistical Pocket Book – 2010, Colombo: State Printing Corporation, 2011.
Figure 1-Cure Characteristics of CIIR Compounds Against Silica Loading
Figure 2-Tensile Properties of CIIR Compounds Against Silica Loading
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Silica loading, phr
Tear Strength, N/mm
Modulus @300%, MPa
Hardness IRHD
Rebound Resilience, %
Compression set,%
Abrasion volume loss, mm3
Tan 60 0C
Table 1 -Physico-mechanical Properties of CIIR Compounds Against Silica Loading*
0 10 20
33.6(0.4) 32.5(0.6) 32.1(0.2)
4.9(0.1) 5.5(0.3) 4.8(0.3)
47(1) 49(1) 48(1)
24(2) 24(1) 28(0)
13.2(0.1) 14.2(1.0) 13.7(0.3)
430(09) 274(08) 265(14)
0.30 0.30 0.33
16.7(0.3) 17.9(0.7) 19.1(0.1) 19.3(0.9)
325(02) 258(09) 283(03) 259(02)
0.28 0.32 0.26 0.20
12
30 ML@10phr
ML@50phr
MH@10phr
MH@50phr
10
25
8
20
6
15
4
10
2
5
0
Maximum toque, dNm
28(1) 23(1) 23(1) 23(0)
Minimum torque, dNm
30 33.1(0.1) 4.8(0.4) 48(2) 40 45.0(0.1) 6.6(0.2) 62(1) 50 44.0(0.1) 6.0(0.4) 63(2) 60 48.5(0.3) 6.8(0.4) 63(1) * Standard deviations are given in brackets
0 0
20
40 60 NR loading, %
80
100
12
50 ts2@10phr
ts2@50phr
t90@10phr
t90@50phr
10
40
8 30
Cure time, min
Scorch time, min
Figure 3-Minimum and Maximum Torque of CIIR/NR Blends Against NR Loading at Silica to Carbon Black Ratios of 10:50 and 50:10
6 20 4 10
2 0
0 0
20
40 60 NR loading,%
80
100
Figure 4-Scorch and Cure Time of CIIR/NR Blends Against NR Loading at Silica of Carbon Black Ratios of 10:50 and 50:10
297
800 TS@10phr
TS@50phr
Eb@10phr
Eb@50phr
40
600
Elongation at break, %
Tensile Strength, MPa
50
30 400 20 200
10
0
0 0
20
40 60 NR loading,%
80
100
Figure 5-Tensile Strength and Elongation at Break of NR/CIIR Blends Against NR Loading at Silica of Carbon Black Ratios of 10:50 and 50:10
1.7(0.2) 2.5(0.1) 2.8(0.2) 2.6(0.1) 2.6(0.1) 1.9(0.1)
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Tan 60 0C
32.5(0.6) 30.0(0.9) 28.0(0.9) 28.4(0.8) 31.2(0.5) 34.1(0.9)
Abrasion volume loss, mm3
Silica : Carbon black = 10:50 49(1) 14.2(1.0) 55(1) 22.6(0.7) 59(1) 20.3(1.6) 58(1) 19.7(1.3) 56(1) 18.0(1.6) 50(1) 33.0(1.4) Silica : Carbon black = 50:10 0 44.0(0.1) 1.5(0.1) 63(2) 19.1(0.1) 20 30.8(0.7) 2.7(0.1) 72(1) 25.2(1.7) 40 30.4(0.8) 3.6(0.0) 75(1) 28.9(1.5) 60 32.5(0.8) 2.6(0.1) 73(1) 24.5(0.5) 80 72.4(2.6) 2.2(0.1) 70(2) 21.4(0.3) 100 101.7(4.0) 2.1(0.0) 70(1) 25.5(2.9) * Standard deviations are given in brackets 0 20 40 60 80 100
Rebound Resilience, %
Compression set,%
Hardness IRHD
Modulus @100%, MPa
Tear Strength, N/mm
NR %
Table 2-Physico-mechanical Properties of CIIR/NR Blends Against NR Loading at Silica:carbon Black Ratios of 10:50 and 50:10*
24(1) 27(1) 34(1) 43(1) 47(1) 58(1)
274(08) 339(13) 227(01) 165(13) 141(33) 134(05)
0.30 0.30 0.33 0.41 0.42 0.43
23(1) 33(1) 37(1) 40(1) 46(1) 47(2)
283(03) 211(12) 149(02) 136(02) 136(03) 116(04)
0.26 0.29 0.31 0.34 0.36 0.38
Annual Transactions of IESL, pp. [297- 304], 2012 © The Institution of Engineers, Sri Lanka
Some Important Legal Aspects Relevant to Dispute Resolution in Construction Contracts U.G. Mallawaarachchi Abstract: Practice of dispute resolution through Dispute Adjudication Boards (DABs) or Arbitration in Construction Contracts has increased substantially in the recent past and hence, adjudication and arbitration play a major role in the construction industry. In many situations, a DAB or an arbitrator would be required to extend his analysis of a dispute beyond the interpretation of the conditions of contract. Application of common law principles would be essential in reaching conclusions in such cases. The author attempts to describe some legal aspects raised during DAB proceedings of a Construction Contract with the arguments brought forward by the parties in connection with such aspects. Reference to resolved cases has been made to discuss underlying legal principles. The main areas discussed in the paper are: existence of a dispute referable to adjudication and jurisdiction of the adjudicator arising wherefrom, legal aspects related to enforcement of DAB decisions, representations made by the parties before entering into the Contract and their significance including legal concepts such as waiver, estoppels, collateral contracts and their applicability. The discussion would be useful to those involved in dispute resolution process in construction contracts, especially who are outside the legal profession. It would help parties to disputes to frame their arguments and members of DABs to make informed decisions. Further, certain areas where refinement of the available legal and administrative procedures or training is required can be identified through the analysis given in the paper. Keywords: Adjudication, arbitration, Dispute, Common law, Representations, Waiver, Estoppels, Collateral contracts
1.
Introduction
2.
Importance of speedy dispute resolution in the construction projects has been identified by all those involved in construction industry in the last decade. With the introduction of provisions for Dispute Adjudication Boards (DAB) in the FIDIC Conditions of Contract (1999 edition), similar provisions were included in widely used ICTAD Conditions of Contract as well. Consequently, many construction professionals were compelled to get involved in adjudication process as members of DABs or claims specialists.
Existence of a Dispute
2.1 Significance of the Issue It is a fundamental requirement that the DAB to have jurisdiction to give a decision on a matter referred to them by a party to a construction contract, such matter should have been developed to a dispute between the parties referable to DAB. This requirement is generally known as ‘crystallization of a dispute.’ There had been a large number of decided court cases in UK where DAB decisions were set aside by the Courts for the reason that ‘a dispute referable to DAB had not been in existence’ [3]. Hence, it is of paramount importance that the parties should make sure that a dispute exists, before referring any matter to DAB. If any party ignores this aspect and refers the matter to DAB, other party may challenge the jurisdiction of the DAB based on ‘non existence of a referable dispute’. Giving a ruling on the objection raised is vested with the DAB.
Parties in a construction contract as well as the DAB are faced with the challenge of understanding the essential legal aspects associated with the DAB process, in addition to usual understanding of the contractual framework defined by the contract documents. This situation is particularly evident when a root of a dispute extends to the pre contract period, i.e. tender receiving, evaluation and acceptance process.
Eng. U.G.Mallawaarachchi, C. Eng., FIE(Sri Lanka), MICE (UK), MIHT(UK), AMCIArb(UK), B.Sc. Eng. Hons (Peradeniya), M.Eng. (Moratuwa), MBA (Sri.J.) . PG Dip .H& Tr Eng. (Moratuwa), Dip.Com.Arb (ICLP). Contract Specialist, Outer Circular Highway Project (Phase 1).
Some of the common situations where knowledge on legal interpretation is highly important are treated in detail in this paper. 1
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A thorough understanding on a test to be followed in determining on the existence of a dispute is important in any of the above situations. As the primary and essential requirement, there should be a claim, request, complaint or allegation of some kind raised by one party which has not been addressed or has been rejected by the other party. However in most practical situations, the determination on existence of a dispute is not straight forward and hence, a rational approach should be adopted based on past judicial decisions.
notified to some agent of the respondent who has a legal duty to consider the claim independently and then give a considered response, a longer period of time may be required before it can be inferred that mere silence gives rise to a dispute. P6. If the claimant imposes upon the respondent a deadline for responding to the claim, that deadline does not have the automatic effect of curtailing what would otherwise be a reasonable time for responding. On the other hand, a stated deadline and the reasons for its imposition may be relevant factors when the court comes to consider what is a reasonable time for responding. P7. If the claim as presented by the claimant is so nebulous and ill-defined that the respondent cannot sensibly respond to it, neither silence by the respondent nor even an express nonadmission is likely to give rise to a dispute for the purpose of arbitration or adjudication. “
2.2
Guidelines on Crystallization of a Dispute Many judicial decisions delivered by Technology and Construction Court (TCC), UK are available on this aspect. However, the ‘flexible approach’ used by a panel of judges headed by Mr Justice Jackson in the case AMEC Civil Engineering Ltd v. The Secretary of State for Transport in 2004 has been accepted in most of the subsequent cases. Jackson, J. derived seven propositions after review of the authorities on the subject, of which five useful guidelines are reproduced below [7]:
The above propositions provide a very useful guideline to the practitioner in deciding whether a dispute exists or not. Two situations are described in Table 1, where the respondent party used those guidelines (as in the Remarks column) to argue that a dispute does not exist.
“ P3. The mere fact that one party (whom I shall call ‘the claimant’) notifies the other party (whom I shall call ‘the respondent’) of a claim does not automatically and immediately give rise to a dispute. It is clear, both as a matter of language and from judicial decisions, that a dispute does not arise unless and until it emerges that the claim is not admitted. P4. The circumstances from which it may emerge that a claim is not admitted are protean. For example, there may be an express rejection of the claim. There may be discussion between the parties from which objectively it is to be inferred that the claim is not admitted. The respondent may prevaricate, thus giving rise to the inference that he does not admit the claim. The respondent may simply remain silent for a period of time, thus giving rise to the same inference. P5. The period of time for which a respondent may remain silent before a dispute is to be inferred depends heavily upon the facts of the case and the contractual structure. Where the gist of the claim is well known and it is obviously controversial, a very short period of silence may suffice to give rise to this inference. Where the claim is
Table 1 – Some Examples on Application of Guidelines to Identify Existence of a Dispute Situation Remarks Contractor proposed a From the rate of Rs A for a new Contractor’s work item; Engineer subsequent did not accept this rate conduct, it can and fixed Rs B as the be inferred that suitable rate. he does not Subsequently believe firmly Contractor proposed that the rate two options Rs C and should be Rs A. Rs D, both of which the Hence, there Engineer rejected. can’t be a claim Contractor referred the for Rs A, and claim for Rs A to DAB. hence a dispute may not exist with regard to Claim for Rs A (Ref P3 in the guidelines above).
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Contractor submitted a claim for extension of time which does not specifically mention how much extension he is entitled to. According to the calculations submitted in the claim, the work would be completed before contractual completion. Engineer replied that a claim does not exist and hence no determination is made. This was submitted to the DAB, but the basis of the claim was highly unclear.
“…The decision shall be binding on both Parties, who shall give effect to it unless and until it shall be revised in an amicable settlement or an arbitral award as described below….”
As the claim is unclear, Engineer’s response may not result in a dispute (Ref: P7).
“If the DAB has given its decision as to a matter in dispute to both Parties, and no notice of dissatisfaction has been issued by either Party within 28 days after it received DAB’s decision, then the decision shall become final and binding upon both Parties.” The above Sub Clause leads to the proposition that when a notice of dissatisfaction has been issued, the decision has not become final, but it should be binding until it is revised later according to the contractual provisions. This would be a situation with temporary binding effect on the parties. Action to be taken when a party does not implement the decision when a notice of dissatisfaction has been issued, has not been clearly indicated in the FIDIC Conditions (1999 edition). The general practice is that the party giving notice of dissatisfaction (often the Employer) would wait without implementing the decision, expecting that the other party (the Contractor) would refer the matter to arbitration.
Contractor submitted a claim notice and then substantiated within the stipulated time frame. Contractor had inserted a deadline of 28 days for the Engineer to respond. Engineer did not respond within a period of 28 days.
FIDIC (1999 edition) specifies 42 days or any other time agreed by the parties as the time to respond. 28 days target set by the Contractor may be inadequate. (Ref. P5). (The above examples have been simplified for demonstration purposes. Actual application would depend on the material facts of each case and the relevant legal system).
To improve the situation, in FIDIC Conditions (MDB Harmonized Edition – March 2006), the wordings of Sub Clause 20.4 and 20.5 have been changed so that the party giving notice of dissatisfaction should indicate its intention to commence arbitration on the dispute.
Sub Clause 3.5 of the FIDIC Conditions (1999 edition) has been included to minimize the complexities arising from referral of a matter to DAB before crystallization of a dispute. Engineer shall give notice of determination made under this Sub Clause to each Party, so that any disagreement can then be a dispute in unequivocal terms.
3.
3.2
Present Situation regarding Implementation There are practical difficulties in the implementation of DAB decisions in a temporary binding situation, especially in relation to the Public Sector Employer organizations.
There are no clear provisions in Financial Regulations and other statutory documents governing the use of public funds regarding the authority of public officers to spend public funds for a temporary binding situation. Hence, an accountability issue would arise;
If the amount involved is substantial, and there would be a shortage of funds to meet the total construction costs, an
Enforcement of a DAB Decision
3.1
Contractual Provisions on Implementation of a DAB Decision The contractual provisions regarding implementation of DAB decisions are available under Sub Clause 20.4 and 20.7 of FIDIC Conditions (1999 Edition). The following section of Sub Clause 20.4 relating to DAB decisions has created much controversy:
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elaborate time consuming procedure needs to be followed by the officer concerned to obtain required funds;
However, the following arguments can be put forward by the responding parties: Non implementation of a DAB decision should not be regarded as a dispute within the interpretation of Sub Clause 20.4, as it arises from a decision of DAB itself;
Possibility of recovering the amounts spent is available only through amicable settlement or if no settlement is reached, through arbitration. The amicable settlement and arbitration processes are to be initiated by the public officer concerned. This has not been a common practice in Sri Lanka, and the officer concerned would face numerous procedural problems in the process.
Owing to the above situation, the general tendency in public sector projects is to refrain from implementing the decision when a notice of dissatisfaction has been issued. Long term desirability of such a tendency should be reviewed by the higher authorities of the government and practical solutions to the situation should be sought. 3.3 Legal Procedure for Enforcement In several cases where the Employer has not taken action to implement the DAB decision, contractors have sought the assistance of DAB to get the decision implemented. The arguments in support of taking such step are:
According to Sub Clause 20.4 of FIDIC (1999 edition) or any equivalent Clause in any other Conditions of Contract, any dispute between the parties in connection with or arising out of the Contract or execution of the Works may be referred to the DAB for its decision;
Non implementation of a DAB decision by a party to the Contract is a violation of a provision in Sub Clause 20.4, and it can be referred to as a dispute in connection with or arising out of the Contract. Hence, the DAB has the jurisdiction to give its decision;
A basic principle adopted in the judicial systems worldwide is that a decision taken by a lower court cannot be enforced by the same court. It has to be referred to a higher court for enforcement;
Sub Clause 20.7 of FIDIC Conditions (1999 edition) stipulates that the failure to comply with DAB decision when a notice of dissatisfaction has not been served by either party, should be referred to arbitration for enforcement. A case where notice of dissatisfaction has been issued by one or both party/(ies) is a more severe situation where the DAB decision has been challenged. In such a situation, DAB cannot have jurisdiction to give a ruling on implementation of its own decision;
DAB’s decision to implement its own decision would not produce any fruitful result as a notice of dissatisfaction can be served on the second decision too. If the same principle is adopted as for the first decision, then the second decision should also be referred to the DAB, which would lead to a non ending process.
3.4 Recent Decisions of Singapore Courts Decision of the Singapore Appeal Court in the case PT Perusahaan Gas Negara (Persoro) TBK v CRW Joint Operation (PGN v CRW) has added a new dimension to the issue of enforcement of a DAB decision [6].
Parties to the Contract are not permitted to refer a dispute directly to arbitration without referring the same to DAB first. The dispute in this case is the non implementation of the DAB decision. Arbitrator’s jurisdiction to hear the case will be derived from application of provisions of Sub Clause 20.5 or 20.7 to the dispute of non implementation of DAB decision.
In this case, original dispute referred to DAB consisted of 13 variation order proposals related to a pipeline construction project. The DAB decision consisted of several payments out of which payment on one variation order proposal (to an amount of US $ 17,298,834.57) was not accepted by PGN. The Conditions of Contract applicable was FIDIC (1999 edition). PGN issued a Notice of Dissatisfaction under 4
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the Contract and refused to pay the amount in dispute.
4.
CRW referred to ICC International Court of Arbitration for arbitration on the second dispute arisen from non payment of the amount above. The arbitral tribunal issued a final award to direct PGN to pay the amount decided by DAB promptly to CRW. While issuing the award, the tribunal observed that PGN has the right to commence a separate arbitration if it so wished. However, payment of the amount should be made immediately.
Representations by the Parties and their Significance
As commonly known even among the non legal professional, a Contract is formed when an offer by one party is accepted by another. In traditional construction contracts, the tender (bid) submitted by the Contractor is the offer, and the Contract is formed when the letter of Acceptance is issued. Tender documents consist of submission of not only duly completed tender form, priced BOQ and other documents issued by the Employer, and also other supporting information requested from the tenderers.
Singapore High Court set aside the award on the basis that, in making a final award without opening up the merits of the DAB’s decision, the tribunal has made the DAB’s decision “final and binding”, thereby exceeding the tribunal’s powers under the arbitration agreement. The main reason behind the position of the High Court has been that the FIDIC (1999 edition) does not expressly allow arbitrations of an award which is “binding but not final”. According to the judgment, what the correct course of action the arbitral tribunal would have taken is to issue an interim award and then proceed to issuing of final award after reviewing the whole DAB decision.
Such information includes work programmes, method statements, information on resources, analysis of tendered rates etc. Further, it is important to note that there can be negotiations between the parties during the period from receiving the tender and issuing of the Letter of Acceptance. During these negotiations many other supplementary information would be exchanged between the parties. This additional or supporting information supplied by parties until acceptance of the tender are known as “representations” in legal terms. When a construction dispute arises from the representations made by the parties, investigation whether such representation is a term of the Contract is vital in the dispute resolution process.
An appeal to the High Court decision was made by CRW in the Court of Appeal. The position of the Court of Appeal was that, even though Sub Clause 20.4 stipulates that each party is bound to give effect to the DAB decision (which will be binding but not final), the decision to pay the amount can only be enforced by an interim or partial award in an arbitration commenced under Sub Clause 20.6. The Court noted “In other words, Sub Clause 20.6 contemplates a single arbitration where all the existing differences between the parties arising from the DAB decision concerned will be resolved”.
The FIDIC Conditions (1999 Edition), in its standard form for Contract Agreement the following documents have been listed as forming the Contract. The Letter of Acceptance The Letter of Tender The Addenda The Conditions of Contract The Specifications The Drawings The Completed Schedules
Although these Court decisions have been criticized by some legal professionals, they give us insight to the difficulty in enforcing a binding and not final decision of DAB. Subsequent addition regarding “intention to commence arbitration” in Sub Clause 20.4 and 20.5 in FIDIC Conditions (MDB Harmonized Edition – March 2006) would be a step forward in resolving this uncertainty.
Priority of the documents for interpretation purposes is prescribed in Sub Clause 1.5 as follows: “ (a) the Contract Agreement, (b) the Letter of Acceptance, (c) the Letter of Tender, (d) the Particular Conditions, (e) these general Conditions, (f) the Specification, (g) the Drawings, and
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(h) the Schedules and any other documents forming part of the Contract. “
the conditions agreed when submitting the tender may be valid during the execution of construction contract.
4.1
Distinguishing Mere Representations and Terms However, those contractual provisions would not be adequate to determine the level of significance of any of the supporting document (or supplementary information) in interpretation of the Contractual obligations of the parties, especially when an important supporting document has not been listed in the Agreement. The following four tests would be useful in deciding whether a representation is in fact would become a term of the Contract [4].
Table 2 - Practical Applications of the Guidelines to distinguish Representations and Terms Situation Remarks Contractor argues that Contractor should the mark up indicated in prove that the the rate analysis award of the submitted with the Contract was based tender as a supporting strongly on rate document has a binding analysis if it were to effect between the become a term of parties and hence the the Contract. Engineer should use the Otherwise there same mark up when may not be any fixing rates for binding effect. (Ref variations. The rate Principle 2 and 3). analysis has not been listed in the Agreement as a constituting document. Contractor agrees to If there is proof that reduce a tendered rate at such agreement was the last stages of the reached, the negotiations. This was reduced rate may done in order to make become a contract his tender competitive. rate, even if there are restrictions mentioned elsewhere in the Contract, to change the tendered rates. (Ref: Principles 2, 3 and 4). (The above examples have been simplified for demonstration purposes. Actual application would depend on the material facts of each case and the relevant jurisdiction).
1. Relative knowledge Whether the party has sufficient expertise on the subject matter of the representation. 2. Reliance Has the other party actually relied on the representation made, in entering into the Contract? 3. The strength of the statement If the statement is strong, it is more likely to be a term of the Contract. 4. Timing If the statement has been made immediately before entering into the Contract, it is more likely to be a term. There are many court cases mostly outside construction industry, where courts have used the above four principles to determine whether a representation has actually become a term. Certain situations involving construction contracts, where the above principles are applicable are given in Table 2. It would always be a good practice to incorporate the significant agreements made during the negotiations in the documents in clear terms. In the absence of clarity, it has to undergo the difficult process as discussed above.
4.2 Waiver There are different meanings given to the term waiver as a legal concept. The following meanings are much relevant to the construction contract situations: (1) Abandonment of a right: a party entitled to a right forgoes or gives up the right expressly or implicitly;
The Instructions to Tenderers contain many conditions which the tenderers are subject to in submission of a tender. When submitting a tender in anticipation of entering into the Contract for construction, each tenderer accepts those conditions laid down in the Instructions to Tenderers. Hence, even though the Instructions to Tenderers are not listed as a document forming the construction contract,
(2) A promise by one party to the other, either express or implied that the party will release the other party from performance in the future of a term of the contract [1].
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claiming the higher rate included in his original tender, even if the reduction of rate is not formally documented.
A disclaimer, when accepted would become a waiver. Applicability of the concept of waiver largely depends on jurisdiction and hence the examples may be over simplified [8].
4.4
For illustration purposes, one example of the application of this principle is given below: The Instructions to Tenderers of a certain contract contains a statement “The Contractor specifically agrees that it shall have no entitlement to any claim which relies upon information provided in Supplementary Information provided with the tender”.
Collateral Contracts
The concept of collateral contracts has emerged from the principles described in 4.1 above for distinguishing mere representations from terms of Contract. A collateral contract is a contract which co-exists side by side with the main contract, where the consideration of the former is the entering into the latter. However, the collateral contract is not included as a term of the Contract.
Contractor, in execution of the subsequent Contract, claimed that, he is entitled for a x% mark up on all variations, as Rate Analyses submitted with the tender as part of the Supplementary Information indicated a mark up of x%.
A collateral contract can exist between one party to the Contract and a third party, or between the parties of the Contract [2]. One example for such a contract between one party and a third party is as follows:
In this situation, the clause of the Instructions to Tenderers preventing the use of Supplementary Information in subsequent claims may be regarded as a waiver of type (1) and this position may be used in rejecting the Contractor’s claim.
A has entered into a contract with B to purchase some finished goods made by B to C. The decision to purchase from B was made based on the assurance given by C regarding the quality of the goods. In this case A and C can be considered to have formed a collateral contract.
4.3 Rule of Estoppel Estoppel is an important legal principle connected with representations by parties and their effect during execution. The general meaning of estoppel as described in literature is that “a rule of evidence whereby a party is barred from denying the truth of a fact that has already been settled.”[4].
A collateral contract can exist between the parties to a construction contract based on certain promises made during negotiations. However, negotiations do not always lead to collateral contracts.
Estoppel may be applicable where: (1) A clear and unequivocal promise or representation was made which was intended to affect the legal relations of the parties;
The test to identify whether a collateral contract exists in a given situation consists of four main sections, namely: (1) The agreement should be promissory in nature;
(2) The promise or representation has been relied upon by the promise or representee (possibly to his detriment); (3) It would be inequitable to allow the promisor or representor to go back on his promise or representation.
(2) It should have been made with the intention to induce the other party’s entry into the Contract; (3) Must be consistent with the terms of the main contract;
There are many types of estoppels as defined in law which vary with different jurisdictions [5]. But however, discussion of a simple example would be adequate for the construction professionals to understand its relevance.
(4) Made before or at the time of formation of the Contract. The following example application of this test:
Example: A Contractor offers a reduction of a rate quoted in his tender before acceptance of the tender. The Employer, relying on his offer, accepts the tender and enters into the Contract. The Contractor may now be estopped from changing his mind and
illustrates
the
The contractor of the contract in first example in Table 2 brought an argument that a collateral contract has been formed due to agreement by the parties to the x% mark up in the rate analysis submitted as supplementary information with the 7
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tender. Pages of the rate analysis document had been signed by both parties and contractor used this fact in support of his position.
differences in application of those concepts in different jurisdictions. However, awareness of those concepts is essential for those involved in the dispute resolution process. It is highly recommended that these concepts should be included in training courses on dispute resolution. The paper would have provided some insights useful in such situations.
We can investigate whether the above situation passes the test for the existence of a collateral contract as follows: There is no evidence that the mark up figure has been a decisive factor in entering into the Contract. Tendered rates and amounts have been a major consideration but individual rate analyses have not been so. Further, Instructions to Tenderers stated that the supplementary information were intended for checking of the quality of the tender only, and Contractor cannot have a claim based on the information provided. The above facts can be put forward as arguments against Contractor’s position. Based on these arguments, it may be deduced that mark up of x% has not been a consideration for entry to the Contract. In this situation sections (1) and (2) of the test may fail.
Acknowledgements Author wishes to express his gratitude to Eng MKCP Manamperi, Document Specialist of Oriental Consultants Ltd, who assisted in preparation of this paper.
References 1.
Arjunan, Kris, “Waiver and estoppel – A Distinction without a Difference?”, Australian Business Law Review, 2, p.86, April 1993.
2.
http://en.wikipedia.org/wiki/ Collateral_contract. Visited, 11th April 2012.
3.
The document has been signed by the two parties after issuing the Letter of Acceptance. Hence the section (4) would fail.
www.constructionlawhandbook.com. Visited, 10th April 2012.
4.
www.e-lawresources.co.uk. April 2012.
5.
Hence, by applying the test as above, there is a possibility to reject the argument for existence of a collateral contract.
http://en.wikipedia.org/wiki/estoppel. Visited, 11th April 2012.
6.
Megens, P., “Singapore Arbitration and the Courts: Quo Vadis?”, J. The International Journal of Arbitration, Mediation and Dispute Management, Vol.78, Number 1, pp.26-33, February 2012.
7.
Ndekguri, I., Russell,V., “Disputing the Existence of a Dispute as a Strategy for Avoiding Construction Adjudication”, J. Engineering, Construction and Architectural Management, Vol. 13 No.4, pp 380-395, 2006.
8.
http://en.wikipedia.org/wiki/Waiver Visited, 16th April 2012
5.
Conclusion
As dispute resolution through Dispute Adjudication Boards has become a common practice in the construction industry, involvement of non legal professionals in the process has increased significantly. However, as discussed in the above sections, certain legal aspects cannot be ignored in reaching a fair decision through DABs. “Existence of a dispute referable to adjudication” is of paramount importance as making referrals before crystallizing a dispute would not only be a wastage of resources but also it disturbs the contract administration system. Legal position regarding enforcement of DAB decisions is in a confused state at present, and intervention of policy making levels is a current need. Relevant sections in the paper can be used as a basis for finding solutions to the related issues. The legal concepts related to representations such as waiver, estoppels and collateral contracts are highly relevant in many common disputes taken up before DABs. There are 8
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Web Based Information Systems for the Construction Industry A.A.D.A.J Perera Abstract: Information systems are now gradually getting converted to web based systems which allows users to access the information system using an internet connection. Construction industries of many countries use company specific web based information systems as well as common information systems such as price books. The research was carried out with the aim of establishing the readiness, feasibility, cost and benefits to the construction industry from web based systems. The literature review established the available technology and similar systems that operate in other countries. The field survey among contractors revealed that many use information systems including MS Project, Primavera, Excel and other systems but hardly any use of web based systems. The features of information systems related estimating planning, store management, accounts, and procurement are presented. The costs of web based systems are fast becoming affordable to organizations of the construction industry and benefits are exceptionally attractive. The information systems developed using open source platforms are less in costs, but benefits are similar or higher than proprietary systems. The benefits can be more than costs within a three year period. The main challenges are the people factor, top management support, IT support, telecommunications and security. Keywords:
1.
Information Systems, Construction Management, Estimating, Cost Control
process risks, technology risks, implementation issues and maintenance issues [5].
Introduction
Web based information system (WBIS) can be defined as “A system that uses internet web technologies to deliver information and services, to users or other information systems or applications.” The time period from 1992 to today is considered as the “Enterprise Internet Era” [1]. The main characteristics of the Enterprise Internet Era are company wide information systems, the use of a central database, access through internet, and information security.
Therefore, it is important to establish the readiness, feasibility, cost and benefits to the construction industry in Sri Lanka for web based information systems. Further it is important to identify the best suited web based information systems for organizations in the construction industry.
2.
By 1998, most of the fortune 500 companies had already installed web based enterprise systems, and by 2009, most of mid-size companies in the developed countries have installed web based systems. The current trend in developed countries is the implementation of web based systems in small organizations [2]. The trend in Sri Lanka is similar and more than 5 large companies have implemented web based information systems and the trends are continuing in large and mid sized organizations [3]. Surveys conducted among organizations related to the construction industry revealed that most organizations use computer for their daily work, but none use web based enterprise information systems [4]. Many web based information systems have run into difficulties due to various reasons such as people factor,
Literature Review
The long-term survival of construction organisations is dependent upon meeting market needs through a long-term value creation process. Information is the cornerstone of any business process. It is not surprising, therefore, for IT to emerge as a key enabler to change the way business is conducted [6]. The literature review was carried out to identify trends in WBIS, the types of WBIS suitable for the construction industry, the factors that affect the feasibility and establish the challenges for implementations.
Eng. (Prof.) A.A.D.A.J. Perera, C. Eng., MIE(Sri Lanka), B.Sc. Eng. (Moratuwa), M.Sc (Lough), PhD(Lough), Professor of Civil Engineering, Department of Civil Engineering, University of Moratuwa
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2.1 The Types of WBIS The main types of enterprise information systems are identified as Sales and Marketing, Manufacturing and Production, Finance and Accounting, and Human Resource Management [1]. The first two types can be defined for the construction industry as Estimating and Tendering, and Construction. Before the “Enterprise Internet Era” the organization had independent, nonrelated systems for major business operations. Construction industry too had the same characteristics where independent estimating and tendering systems, independent accounts and finance systems, independent human resource systems were present. The main challenge was the integration of systems. The system integration was successfully achieved by Enterprise Resource Planning Systems known as ERP ( [5]. Therefore, the application of ERP in the construction industry need to be explored.
The risks and benefits of WBIS (ERP and others) are now established by many researchers. A comprehensive analysis of tangible and intangible benefits is given by Leon[5] The tangible benefits are quantifiable and given in Table 1 [5]. The main intangible benefits are information visibility, new improved business process, customer responsiveness, integration, standardization, flexibility, globalisation, business performance and supply chain management. Table 1- Tangible Benefits of WBIS Item Benefit 1. Reduced inventory costs At least 20% 2. Reduced inventory carrying 25–30% costs 3. Reduced manpower costs 10% or more 4. Reduced material costs 5% or more 5. Improved sales 10% or more 6. Improved customer service 5% or more 7. Efficient financial 18% or more management
The estimating and tendering system are continued to be present. The first estimating and tendering system were introduced as early as 1980 [7]. The construction industry had price books probably for more than 100 years and most of those have been now converted to web based systems; i.e. web based price books [8]. Therefore systems related ERP, and price books are need to be analysed.
2.3 The Technology of WBIS The 7 components of WBIS systems are given by Loudon and Loudon [1]. They are: 1. Computer hardware platforms include client machines and server machines 2. Operating system platforms include platforms for client computers, dominated by Windows operating systems, and servers, dominated by the various forms of the UNIX operating system or Linux. 3. Enterprise and other software applications include SAP, Oracle, and PeopleSoft, and increasing open source systems. 4. Data management and storage is handled by database management software and storage devices. 5. Networking and telecommunications platforms LAN and many wide area networks (WANs) use the TCP/IP standards for networking. 6. Internet platforms, internet explorer. 7. Consulting and system integration services It is important to study the availability of these components for WBIS for organizations in Sri Lanka.
The third type WBIS for the construction industry is the project management systems. Up to 1990 the project management was based on a single project but with availability of information system such as MS Project Server and Primavera web based project management systems have become available. 2.2 Why WBIS “During the last decade or so, significant productivity improvements experienced by a wide range of industries have been associated with IT implementation. IT has provided these industries with great advantages in speed of operation, consistency of data generation, accessibility and exchange of information” [6]. Further the same authors have found “However, construction organisations rarely recognise the value IT adds to the process of project information management because they are too narrowly focused on financial figures and functional level performance such that they fail to capture long-term IT-induced business success.”
2.4 Available WBIS The available WBIS for the construction industry is given in many publications ( [9], [10]). All leading ERP systems such SAP,
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Oracle, SAGE, and open source systems etc., can be used by the construction industry. There are more than 130 WBIS for project management [10] and more than 90 propriety and more than 20 open source ERP systems [9]. The suitability of WBIS for the construction industry is an important research. The feasibility need to be performed by evaluating the 7 technological factors.
3.
organization which is valid for construction organizations. 1. Approximately 85 % of the respondents use ICT for financial management, 60% for human resource management and 52% for inventory management in their day to day back office operational activities. 2. Approximately 94% of the organizations use the internet for communication purposes, 55% for business activities with customers followed by 45% for research purposes. 3. Use of proprietary operating systems and productivity tools is very high in all sectors with an average of 96%. Free and open source software is also commonly used in all sectors with an overall average of 30%. 4. It is observed that 37% of the organizations use 2 Mbps ADSL connectivity followed by 32% of the organizations using 512 Kbps ADSL connectivity. 5. Nearly 1/3rd of organizations have wide area networks (LAN/WAN). The findings confirm that organizations in Sri Lanka generally have a satisfactory level of computer usage by senior and middle management and required infrastructure for web based information systems.
Research Methodology
The research was performed with the objective of establishing the readiness, feasibility, cost and benefits to the construction industry for web based systems. The feasibility was established by comparing the requirements and availability of infrastructure within and outside of construction organizations. The feasibility was established by cost benefit analysis and technical evaluation. Several field surveys were carried out to obtain technical data ( [4], [11], [12], [13]). The field surveys were conducted to the guidelines given by Zikmund [14].
4.
Data Collection and Analysis
Three main surveys were carried out to collect data. Firstly, the usage of computers by organizations and availability of infrastructure were performed, followed by evaluation. Secondly data related to contractors were established based on published data for the performance of cost benefit analysis. Thirdly survey was conducted to identify the implementation issues related WBIS mainly ERP systems.
The construction sites are scattered all over the island, and it is important to analyse the availability of internet connection and level of service. A survey was carried out among the service providers using the facility provided by Telecommunications Regulatory Commission of Sri Lanka web site [16]. Table 2 and Table 3 below gives details and these tests were carried out in October 2011 from two locations, one at Colombo and one at Kiribathgoda. These tests were carried out between 10.00AM to 12.00noon.
4.1 The Computer usage and Current Infrastructure The availability of infrastructure was established based on the information provided by telecommunication service providers. The computer usage of the construction industry was established using available secondary data and related field surveys of research work.
Table 2 - Downloading Speed Test of Fixed lines
The survey conducted by ICTA [15] has found Over 50% of all senior and middle level staff in all the sectors use computers for more than 75% of day to day activities. The research conducted by Nimashinie [11] confirmed this considering the use of computers in Planning and monitoring of construction projects. Nimmashinie [11] reported that among the contractors 75% use MS Project, 8% Primavera, 14% MS Excel and 2% other software for planning and scheduling work. The ICTA [15] further reported the use of ICT facilities in an
Service Provider
512kbps
2Mbps
USA DE* USA SLT 380 440 1200 Suntel 280 320 400 Lanka Bell 280 220 333 Dialog 320 380 1,533 Average 315 340 866 * Germany (Internet Abbreviation)
DE* 5,500 4,500 5,500 5,000 5,125
The speed test show satisfactory level connections for WBIS. However, the specific
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WBIS demand of speed for connectivity will vary and need to be checked. Some of those aspects are presented later.
general analysis for the Industry. The main type of WBIS is ERP. Therefore a detail analysis was performed for the use of ERPs in the construction industry. As such a model was developed based on published information and for five values of total revenue per year the cost and benefit were calculated. The total revenue values were Rupees 50, 100, 200, 500 and 1000 million. The breakdown of the capital as given Harris and McCaffer [7] was used. The breakdown given relative to total revenue is: 1. Material stock - 1.67% 2. Management staff cost - 6.67% 3. Total material cost - 48.33% The balance sheets of two contractors, one with around Rs. 200million and the other with over Rs.2.0 billion confirm the accuracy of the breakdown. Further, a contractor or any organization can re-calculate the cost benefits calculated here based on their last balance sheet.
Table 3 - Downloading Speed Test of 3G Mobile
Service Provider Air Tel Dialog Mobitel Etisalat Average
Kiribathgoda USA 100 100 100 300 150
DE* 200 200 100 900 150
Colombo 5 USA 200 300 400 100 250
DE 600 2,990 1,290 1,500 1,595
* Germany (Internet Abbreviation)
It is reasonable to expect all the benefits stated in Table 4 since benefits from reduced material inventory, reduced manpower (management) cost and reduced material costs were considered. The benefits that can be expected for different revenues are given in Table 5.
Figure 1 -The Speed of internet Connection from USA
The next aspect is the coverage of internet connection in Sri Lanka. Mobitel [17] and Dialog [18] have given this data too and show in Figure 2.
Table 4 -Weighted Cost Savings for ERP Item % of % Cost Weighted Revenue Saving cost saving % Material 1.67 20 0.33 stock Management 6.67 10 0.67 staff cost Total 48.33 5 2.42 material cost Table 5 -Benefits of ERP Total Revenue per year in Rs. millions Item 50 100 200 500 1000 Material 0.17 0.33 0.67 1.67 3.33 stock Manageme 0.33 0.67 1.33 3.33 6.67 nt staff cost Total material 1.21 2.42 4.83 12.08 24.17 cost Total Benefit per 1.71 3.42 6.83 17.08 34.17 year Rs. Millions
Mobitel3G Dialog 3G Figure 2- 3G Coverage of Mobile operators
The Figure 2 shows that there are some locations where Mobile coverage will not be available as well as the fixed line connections. If construction site offices are located in these locations it will not be possible to use WBIS from construction sites.
The benefits stated in Table 5 will not materialize unless certain conditions are met. The material stock reduction will be usually achieved. However, cost savings through management staff efficiency improvement or reduction will take some time, and most probably will occur after one or two years. The
4.2 Cost and Benefits of WBIS It is possible to calculate cost and benefits of WBIS for a contractor but difficult to perform a 4
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benefit of material cost reduction will occur due to low wastage, and one could argue it may not achieve 5% level. Therefore, further analysis was carried out for three possible scenarios, optimistic(all three benefits as indicated), average (material stock benefit and half of total material cost benefit) and most pessimistic (only material stock benefit) and given in Table 6.
It is difficult to perform financial feasibility of WBIS due numerous variables. However, a reasonable assessment can be performed by comparing total cost for a period three years. Yeo and Qiu [21] has given an improved method of analysis. Suggestions given by Yeo and Qiu were considered in this study. In this analysis, it will be possible to determine whether investments in WBIS can be recovered with a period of three years. Table 9 and Table 10 give the information.
Table 6 -Range of Benefits of ERP Total Revenue per year in Rs. millions Item 50 100 200 500 1000 Optimistic 1.71 3.42 6.83 17.08 34.17 benefits Average 0.94 1.88 3.75 9.38 18.75 Benefits Pessimistic 0.17 0.33 0.67 1.67 3.33 benefits
The comparison of the two tables gives the following conclusions. 1. For contractors with revenue more than Rs.500 million per year, the implementation of ERP will be profitable. However, the right type ERP system is required to be implemented. 2. It is not profitable to implement high end ERP for construction organizations. This will lead to a cost higher than benefits. 3. For contractors with revenue between Rs.200 to Rs.300 millions cost and benefits can have mix results. Therefore for positive benefits the installation and its use should be monitored and controlled. 4. It will not be profitable to implement ERP for contractors with revenue less than Rs.200 millions.
The leading WBIS is the ERP and first analysis are performed for ERP. The cost of ERP is wide varying, and vendors generally do not give cost of ERP. Two vendors ( [19], [20])have indicated the general cost their ERP specially for contractor organization in Sri Lanka. The cost indicated is between Rs.3.00 million to Rs. 5.0 Million. Further the leading commercial ERP systems, SAP, Oracle, SAGE and Microsoft Dyamics costs around Rs.10 million to Rs. 100.0 million for contractor organization [3]. The cost of WBIS will vary depending on the number of access points, number of users, type of technology etc. Further the general licence fees will be around 10% to 20% of installation cost. The likely implementation cost for contractors based on above implementation costs is given in Table 7
Table 9 -Total Cost of WBIS for a period of three years Total Revenue per year in Rs. millions Item 50 100 200 500 1000 Lowest End 0.9 1.45 2.9 4.35 7.25 ERP Average Leading 13.0 26.0 39.0 52.0 65.0 ERP High End 39.0 65.0 84.5 104.0 130.0 ERP
Table 7- Installation cost of ERP for Contractors Item Lowest End installation Average Leading ERP High End ERP
Total Revenue per year in Rs. millions 50 100 200 500 1000 0.60
1.0
2.0
3.0
5.0
10.0
20.0
30.0
40.0
50.0
30.0
50.0
65
80.0
100.0 Table 10 - Benefits of ERP for three year period Total Revenue per year in Rs. millions Item 50 100 200 500 1000 Optimistic 5.1 10.2 20.4 51.2 102.5 Average 2.8 5.6 11.2 28.1 56.2 Pessimistic 0.5 1.0 2.0 5.0 10.0
Table 8 - Annual Maintenance cost of ERP for Contractors Item Lowest End ERP Average Leading ERP High End ERP
Total Revenue per year in Rs. millions 50 100 200 500 1000 0.10
0.15
0.30
0.45
0.75
1.0
2.0
3.0
4.0
5.0
3.0
5.0
6.5
8.0
10.0
The second type of WBIS for construction organizations is related to estimating and tendering. The online price books are available and being used in developed countries, and 5
309
BCIS [8] of UK is one such example. Online price books are now offered in Sri Lanka too and cost is less Rs.50,000 per year [19]. Therefore, WBIS related to estimating and tendering can be used by any organization in the construction industry.
computer facilities are available. Organizations have the option to use rented virtual severs or cloud computing. Reliable virtual server can be rented from Rs.4,000/= per month [23] while purchase cost and maintenance of a server could be around Rs.52,000 per month. The cost of Rs.52,000 month was derived for sever cost of Rs.1.2 million and room air-conditioning and maintenance cost of Rs.18,000 per month. Yet again the right technology needed to be selected and cost and benefits calculated earlier will not be valid.
The third type of WBIS that can be used by an organization is related to project management. The leading WBIS related project management is MS Project Sever and Primavera. The benefits of MS Project Sever are well established which includes [22] unified project and portfolio management, drive accountability and control with governance workflow, standardize and streamline project initiation, select the right portfolios that align with strategy, easily build Web-based project schedules, intuitively submit time and task updates, gain visibility and control through reports and dashboards, simplified administration and flexibility, gain additional value from the Microsoft platform, and extensible and programmable platform. Nimashanie [11] has found that preparation of time schedules by contractors as required by ICTAD conditions as 37% of all projects, 39% except a few projects, 14% only a few projects, and 10% very rarely. Further Nimashanie [11] reported that only 23% personal is aware of key performance indicators of project management, the earn value technique. As such, it is important to study and apply project management tools and techniques before applying web based project management systems.
4.4 Features of WBIS The author together with other researcher carried out an analysis of features of WBIS which can be summarised as given below ( [10], [9], [19], [12]). Manufacturing – Engineering resource and capacity planning, material planning, work flow management, shop floor management, quality control, bills of material, manufacturing process. Financial – Accounts payable, account receivable, fixed assets, general ledger, cash management and billing. Human Resource – Recruitment, benefits, compensation, training, payroll, time and attendance, labour rules, people management. Supply-chain management – Inventory management, supply chain planning, supplier scheduling, and claim processing, sale order administration, procurement planning, transportation and distribution. Projects – Costing, billing, activity management, time and expenses. Customer relationship management – Sales and marketing, service, communications, customer contacts, and after sales support.
4.3 Technology of WBIS The fist division of technology comes related to software development. The main divisions are open source software and proprietary systems such as Microsoft windows. The high end WBIS systems generally use propriety operating systems such windows server and databases such Oracle or SQLSever. The open source systems use Linux operating system and Mysql database. One of the main reasons of high annual fee of ERP systems stated in Table 8 is the high cost associated to propriety operating systems and databases. This is one variable that need to be considered in the selection of WBIS for contractors.
4.5 Implementation of WBIS Two studies were carried out by the author together with other researchers in the area of implementation issues [24] and WBIS complexities [3]. The key contributing factors for the complexity of ERP systems are product dimension, people factor, project dimension and company business processes and there is a strong correlation among variables. Complexity analysis survey results revealed that SAP and Oracle records higher complexity index and Microsoft Dynamics and WebERP records lower complexity indexes. Further secondary data revealed that SAP and Oracle records highest ERP per user cost. ERP’s such as IFS Applications, Dynamics GP, and Sage Accpacc records less ERP per user cost compared to SAP and Oracle. As per the
WBIS require computer servers to be purchased. The purchase and maintenance of computer servers are of high cost and today options such as renting a virtual server, cloud 6
310
research analysis, customization of ERP system is another key concern apart from the above mentioned complexity and cost analysis in the ERP selection process for medium scaled businesses. 5
5.
Conclusions 6
It is feasible to implement web based information systems for construction organizations in Sri Lanka. The infrastructure is available in Sri Lanka including the internet connection. The availability of computers and skills of personnel in contractor organizations for the implementation of web based information systems is yet another positive factor. The benefits are more than the cost for contractor organizations with an annual turnover of more than Rs.500 million while mix situations exist for annual turnover between Rs.200 and Rs.500 millions. It is not profitable to employ web based ERP systems for contractors with less than Rs.200 million annual turnover. The software and infrastructure required for web based information systems need to be selected by evaluating the available options. If not a profitable potential could become unprofitable. The available web based systems for estimating and tendering can be used by all organizations of the construction industry. The available web based systems related to project management too can be used by all organizations in the construction industry provided that they first use correct project management tools and techniques.
7
8 9
10
11
12
13
Acknowledgements The author would like to acknowledge the assistance provided by Ms. M.M.K. Manike, technical officer and Mr. A. Wethasinghe, Mr. V. Wickramsekera and Mr. S. Senanayake for their work towards field surveys and tests.
14
15
References 1
2
3
4
Loudon, K. C., Loudon, J. P.,Management Information Systems, 11/E,: Prentice Hall, New York, 2010. Monk, E. F., Wagner, B. J., Enterprise Resource Planning, Cengage Learning India Private Limited, New Delhi, 2009. Ratnayake, L. S. “The influence of Complexities of ERP for Effective Implementation at Medium sized Companies in Sri Lanka,” MBA Thesis, Department of Civil Engineering, University of Moratuwa, Moratuwa, 2012. Wetthasinghe, W. A. S. A., Wickramasekera, I. V., Senanayake, G. H.
16 17 18
19 20 21
7
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H. S., “Feasibility of Web Based Information Systems for Construction Industry,” Undergraduate Thesis, Department of Civil Engineering, University of Moratuwa, Moratuwa, 2011. Leon, A., Enterprise Resource Planning, Tata McGraw Hill Education Private Limited, New Delhi, 2008. Stewart, R. A. and Mohamed, S., “Evaluating web-based project information management in construction: capturing the long-term value creation process,” Automation in Construction, Elsevier B.V, Amsterdam, 2004, p. 469–479. Harris, F., McCaffer, R., Modern Construction Management, BSP Professional Books, Oxford, 1989. http://www.bcis.co.uk/bcispriceboo Visited 30 April 2012. http://en.wikipedia.org/wiki/List_of_ERP software_packages. Accessed 30 April 2012. http://en.wikipedia.org/wiki/ Comparisonof_project_management_ software, Visited 30 April 2012. Nimashanie, T. W. M., “Application of Earned Value Management in Sri Lankan Construction Projects,” MBA Thesis, Department of Civil Engineering, University of Moratuwa, Moratuwa, 2012. Perera, P. I. , “Return on Investment of Implementing an ERP System in Health Sector in Sri Lanka,” MBA Thesis, Department of Civil Engineering, University of Moratuwa, Moratuwa, 2012. Vidanapathirana, U., “Success of Information Systems Implementation in Sri Lanka Business Organizations,” MBA Thesis, Department of Civil Engineering, University of Moratuwa, Moratuwa, 2012. Zikmund, W. G., Business Research Methods, 8th Edition, South-Western College Pub, New York, 2009. MG Constants Pvt Ltd, “National ICT Workforce Survey,” ICTA, Colombo, 2010. http://www.trc.gov.lk/. Visited 14 October 2011. http://www.mobitel.lk/en/web/ mobitel/coverage. Visited 30 April 2011. http://www.dialog.lk/support/mobile/ coverage-service-points/3g-coveragemap/. visited 30 April 2012. http://arpmservices.com/your-cost.html. visited 25 April 2012. http://www.htnsys.com/services/ construction/. Accessed 25 April 2012. K. Yeo and F. Qiu, “The Value of Management Flexibility—A Real Option
Approach to,” International Journal of Project Management, vol. 21, 2003, p. 243– 250. 22 http://www.microsoft.com/project/enus/project-server-2010-benefits.aspx. Visited 29th April 2012. 23 http://www.godaddy.com/hosting/virtualdedicated-servers.aspx?ci=9013. Accessed 30 4 2012. 24 V. Vidanapathirana, “Success of Information Systems Implementation in Sri Lankan Business Organizations,” MBA Thesis, Department of Civil Engineering, University of Moratuwa, 2011.
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Annual Transactions of IESL, pp. [313-319], 2012 © The Institution of Engineers, Sri Lanka
Study on the Delays in Construction Projects in Water Sector in Sri Lanka S.B.Wijekoon and S.B. Uduweriya Abstract: The objectives of this study are to identify various causes for delays in construction projects in water sector in Sri Lanka, to categorize the identified significant delays according to the general classification of delays and to propose methods to overcome the identified significant delays in the future projects. A structured questionnaire was developed to gather project participants’ opinions on delays and the information were used to identify significant factors contributing to delays in construction projects. Frequency of Occurrence Index (FOI) and Standard Deviation (SD) were used to rank the delay factors according to their significance. The difference in perception between the owner and the contractor was also examined by using Rank Agreement Factor (RAF), Percentage Agreement (PA) and Percentage Disagreement (PD). The results show that: evaluation of bid documents by the Engineer, reviewing and approving of bid documents and designs by the Employer, acquisition of land, errors in bid documents and decision making by the Engineer are most significant factors contributing to project delays during pre-construction phase; and procurement of imported materials, variation orders, shortage of skilled labour, poor planning and scheduling and government restrictions for mining and transporting of material are the corresponding ones contributing to project delays during construction phase. In conclusion, methods are proposed to overcome the identified significant delays in the future projects. Keywords:
1.
Delays, Water Sector, Construction Projects
Introduction
In construction, a delay means a time overrun either beyond completion date specified in a contract, or beyond the date that the parties have agreed upon for delivery of a project [1]. In the project owner’s point of view, a project delay could result in loss of revenue through lack of production facilities or having to depend upon the present facilities on rent to the owner. In Contractor's point of view, delay normally means extra overhead costs, and sometimes additional labour and material costs due to inefficiencies and inflation [2]. “A delay is the time during which some part of the construction project has been extended or not performed due to an unanticipated circumstance”[3]. An incident of delay can originate from within the contractor’s organization or from any of the other factors interfacing upon the construction project. Delays are very common in construction projects in any country. Although Sri Lanka is rich in natural water resources compared to other countries, only around 77% of the population has access to safe drinking water, of which 32% is through piped water supply systems [5]. Government had set a target of providing safe drinking water for 85% of the population by 2015 and 100% by 2025,
respectively [8]. In line with this objective, a number of water supply projects have been planned and implemented.
Figure 1- Capital Investment on Water and Sewerage Sector (Source: NWS&DB Annual Report 2007) Figure 1 shows capital investment on water and sewerage sector in Sri Lanka during the last few years [6]. Eng. S. B.Wijekoon, Int. PEng.(SL), C. Eng., FIE(Sri Lanka),MIE(SL),MIPM(SL), B.Sc. Eng. (Peradeniya), M. Eng., MBA, Senior Lecturer, Industrial Training & Career Guidance Unit, Faculty of Engineering, University of Peradeniya. Eng. S.B. Uduweriya, C. Eng., MIE(Sri Lanka), MSSE(SL), However, it was reportedUDS that most of(Pvt.) the water B.Sc. Eng.(Hons), Consultant, Engineering Limitedprojects are not completed within the sector
313
agreed time periods due to various delays during project execution.
2.
Literature Review
Delays are generally classified into three main categories such as excusable delays, nonexcusable delays and concurrent delays. Furthermore, excusable delays can be subdivided into two categories; they are compensatory delays and non-compensatory delays [3]. Figure 2 shows the classification of delays in a chart.
equipment, shortage of qualified staff, shortage of skilled and unskilled labour. Such delays are within the contractor’s control and therefore, the contractor is not entitled for additional time or money. According to the condition of contract, employer is entitled to claim liquidated damages against the contractor, if the contractor prolonged the contract beyond the contract period due to this delay [3]. 2.4 Concurrent Delays When two or more incidents of delay occur at the same time or overlap to some degree, such combined delays are called concurrent delays. These delays can occur when both the owner and the contractor are at fault. These delays can occur at Pre-construction stage and Construction stage of the project [3]. Pre-construction delays can occur during bidding, bid evaluation and contract awarding stages of the project. The bidding stage delays are occurred due to the errors in preparation of drawings, specifications, bill of quantities (BOQ) and other contract documents.
Figure 2 - Classifications of Delays 2.1 Excusable / Compensatory Delays Excusable and compensatory delays normally occur when extra work orders are issued by the employer. It can also occur due to the suspension or interruption to all or part of the work due to the actions by the employer. In this situation, contractor is entitled to get an extension of time and additional payment depending on the circumstance [3]. 2.2 Excusable / Non-Compensatory Delays Excusable and non-compensatory delays are caused due to the unforeseeable factors; may be due to unforeseen ground condition, unexpected weather condition and strikes. In this situation, neither the Employer nor the Contractor are responsible for that delay and both parties share the impact of the delay. In this case, the contractor is entitled to extension of time without cost [3]. 2.3 Non-Excusable Delays The contractor is fully responsible for nonexcusable delays. This can be due to the action and inaction of the contractor, sub contractor, materials suppliers and other parties working for the contractor. These delays could be the result of mismanagement of resources, low productivity and lack of planning and programming, rework, breakdown of
314
It is noticed that, most of the delays in the contract awarding stage may be due to the funding issues, land acquisition issues [2]; political influences [7] during the preconstruction stage and all these delays are mainly due to the shortcomings of the Employer. During the construction stage, contractor’s involvement is higher than that of the employer; hence the contractor is responsible for most of the delays during this phase. But employer also has a responsibility for certain matters during construction phase; for example, not settling the contractor’s invoices in time [2], [7]. Most common causes of delays that the contractor is responsible are: slow mobilization at site [4],[7], shortage of construction materials and machineries, lack of qualified professional staff, shortage of skilled labour [2], unforeseen ground conditions, bad weather conditions [4], poor resource management, poor planning and scheduling, cash flow difficulties [1],[4],[7]. Some of the project delays for which the Employer is responsible are: handing over of the possession of site, releasing of mobilization advance in time [2], issuing instructions, approving interim payments, issuing variation orders, extra works [4], decision making and design changes during construction[2].
3.
Objectives
The objectives of this study are: to identify various causes for delays in construction projects in water sector in Sri Lanka; to categorize the most significant delays identified according to the general classification of delays and propose methods to overcome the identified significant delays in the future projects.
4.
which has a lower SD has high priority, while high SD indicates low priority. Eqns. (1) and (2) are used to calculate FOI and SD, respectively. The FOI is simply a weighted average of scores given by the respondents on each factor of project delays. Eq. (1) presents the formulation of FOI of each cause of delays from the weighting given by the respondents. The relative importance index method is best suited to determine the significant delay factors [4].
Research Methodology
n
A structured questionnaire was developed by focusing the delays identified during literature review and the authors’ extensive construction experience earned from construction projects in Sri Lanka. The questionnaire was divided into two stages: namely, Pre-construction stage and Construction stage. Data were collected by distributing this questionnaire among project managers, design engineers and project engineers who are working in water sector construction projects including Employer Organizations, Consulting Organizations and Contractor organizations. Interviews were conducted during site visits and over the phone to realize the current issues faced by the project managers, design engineers and project engineers. Total of sixty five questionnaires were distributed and forty four were received. The details of the questionnaires distributed and responses received are shown in Table 1. Table 1 - Distribution and Receiving of Questionnaire Organization NWS&DB* Consulting Firms Contractors Organizations Total
Distributed
13 06
28
25
65
44
i
FOI =
, (0 index
i
AxN
1)
.... (1)
where, Fi = Weightage given to each factor by the respondents and ranges from 1 to 5 where, 1 is ‘adverse effect’ and 5 is ‘no effect’ A = highest frequency (i.e. 5 in this case) N = total number of respondents
... (2) In order to quantify the agreement in ranking between two different groups of participants, the Rank Agreement Factor (RAF) given in Eq. (3) is used. For any two groups, let the rank of the ith items in Group 1 be Ri1 and in Group 2 be Ri2, N be the number of items and j = N – i + 1.
N Ri1 Ri 2 i 1 RAF = N
.... (3)
The maximum RAF is calculated using Eq. (4).
N R i1 R j 2 i 1 RAFmax = N
Received
20 17
F
.... (4)
The Percentage Disagreement (PD) is calculated using Eq. (5).
* National Water Supply & Drainage Board
R N
i1
PD =
5.
Data Analysis
i 1 N
R
i1
Frequency of occurrence index (FOI) and Standard Deviations (SD) were used to prioritize delay factors according to their impact on the project delays. SD is used to prioritize the delay factors which have the same FOI. A delay factor
315
i 1
Ri 2 x 100
Rj 2 )
.... (5)
The “Percentage Agreement (PA)” is calculated using Eq. (6).
PA = 100 - PD
... (6)
Higher value of RAF suggests a weaker agreement between any two groups [4]. A rank agreement factor of zero would mean perfect agreement.
6.
Results and Discussion
Table 2 - Five Delay Factors (according to the FOI Values Based on Employer, Engineer and Contrctor responses)
Evaluation of Bid documents by Employer
FOI 0.5227
FOI
Rank
0.4947
1
0.5053
2
Acquisition of Land
0.5474
3
Errors in Bid documents
0.5684
4
Awarding of Contract and issuing of Letter of acceptance
0.6211
5
Reviewing and approving of Bid documents and designs by employer Evaluation of Bid documents by employer
Rank 1
Reviewing and approving of Bid documents and designs by Employer
0.5273
2
Acquisition of Land
0.5364
3
Errors in Bid documents
0.5636
4
0.5727
5
Delay in decision making by Engineer
Table 3 - Five Delay Factors (According to the FOI Values Based on the Employer and Engineer responses) Factor
6.1 Delays during Pre-Construction Phase Table 2 shows how the Frequency of occurrence index (FOI) is used to rank top five significant delay factors as postulated by the respondents. FOI values in Table 2 are calculated using responses of all three parties, namely employer, engineer and contractor.
Factor
bidders occur due to inadequate time period given by the employer for the bidders to prepare and submit tenders. .
Reviewing and Approving of Bid documents and Designs by Employer is the second ranked factor as shown in Table 2. This could happen due to incomplete bid documents and designs prepared by the Engineer and the Employer, mainly due to inadequate time period provided for the preparation of documents and design.
FOI values in Table 3 shows ranking of five significant delay factors based on the responses of Employer and Engineer only. Evaluation of Bid documents by employer is the top ranked delay factor according to the Table 2. On most of the occasions, bidding stage delays have been reported due to the errors in submitted bill of quantities (BOQ), inadequate details in pre-qualification documents and it will take considerable delay in correcting those errors and awarding the contract. Also submission of large amount of disqualified bids would increase the time period required for bid evaluation. The errors in submitted bids by
316
Delay in acquisition of lands for the construction site is ranked at third position according to FOI. This is a common issue in water sector projects in Sri Lanka and it is mainly due to long period taken to complete the acquisition process. In water projects, pipes are generally laid along the roads and it is a mandatory requirement to obtain permission from the road authority to which the particular road belongs. The approval process usually takes a long time and result a project delay. To avoid these delays, it is necessary to develop an effective coordination between the Water Authority and the other relevant authorities. Errors in Bid Documents are ranked at fourth position according to FOI. This will happen due
to incomplete bid documents submitted by bidders. It was revealed during the discussions that those delays are mainly due to inadequate time given for the preparation of bids. The fifth ranked factor in Table 2 is the delay in decision making by the Engineer. In order to resolve this issue, adequate authority should be delegated to the Engineer to enable him to make decisions. 6.2 Delays during Construction Phase Table 4 shows the frequency of occurrence index (FOI) values used to rank top ten delay factors as postulated by the respondents. Table 4 - Top Ten Delay Factors based on Frequency of Occurrence Values Factor
FOI
Rank
Procurement delay in imported materials
0.386
1
Variation orders
0.441
2
Shortage of Skilled Labour
0.477
3
Poor planning and scheduling
0.491
4
0.500
5
Government restrictions for mining and transportation of materials Aggressive weather conditions Material Price Increase Shortage of Resources Break down of equipment
0.505
6
0.509
7
0.509
8
0.514
9
Variation orders are the second ranked delay factor in construction stage according to FOI. This includes issuing of variation orders by employer, preparing of variation orders by the contractor, recommending them by the engineer and approving of the variation orders by the employer. Shortage of skilled labour force is the third ranked delay factor according to FOI. This has a significant impact on the construction industry. In order to improve the skilled labour force, government has to expand vocational training centers to the village level and provide sufficient training for the young generation. On the other hand, increasing labour wages according to their performance and providing high job security are the other approaches for addressing this issue. Poor planning and scheduling of the project by the contractor is the fourth ranked delay factor according to FOI. This may be due to contractor’s inadequate project management experience. To avoid this, contractor’s project management skills are to be improved by introducing educational and training programmes on construction management. This can be implemented through Institute for Construction Training and Development (ICTAD) and National Construction Contractors Association of Sri Lanka (NCCASL). The fifth ranked factor according to FOI is the Government restrictions for mining and transportation of material. This largely affects the construction projects because materials such as sand, gravel, borrowed soil, pebbles, and filter materials are heavily used in water sector construction projects.
Shortage of qualified Professional staff in 0.523 10 Contractor's organization Procurement delay in imported materials is the highest ranked delay in water sector construction projects during construction stage. In order to avoid this delay, it is proposed to separate the Material Supply contract and the Construction Contract. The former can be awarded early and after the materials are brought to Sri Lanka, the construction contract can be awarded.
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The sixth ranked delay factor according to FOI is bad weather conditions. This kind of event cannot be avoided, but proper planning of construction works may partially resolve the delays due to bad weather. The seventh ranked delay factor is shortage of resources for construction works. This represents the capacity of Sri Lankan contractors and could occur due to financial capability of contractors and especially the amount of funds used to purchase reliable and appropriate plant and machinery. This may lead to the eighth ranked delay factor in the Table 4. i.e. breakdown of equipment. Contractors are trying to purchase used or poor quality equipment and machinery instead of new ones due to their
limited financial capacity. It is very important to improve contractor’s financial capability especially by providing more funds to purchase new or reliable equipment.
Table 5 -Different Participants
Factors Material price increase has been identified as the ninth factor according FOI. In general, provisions for price escalation are provided in almost all construction contracts and this issue can be resolved partially utilizing that provision. Shortage of qualified professional staff in Contractor's organization is ranked at tenth position according to the FOI. Attractive salaries and other benefits should be offered to the qualified staff by the contractors to retain them in the organization especially when there is a high demand for qualified and experienced staff in the construction industry. Table 5 shows the different perceptions between the Employer & the Engineer and the Contractor during the construction phase.
7.
Conclusions
Delays are unavoidable in any construction project and through this study an effort was made to categories the identified significant delay factors according to the general classification of delays, and propose methods to overcome the identified significant delay factors in future projects. Five significant factors contributing to delays during the pre-construction phase are: evaluation of Bid documents by the Employer; reviewing & approving of bid documents & designs by the Employer; acquisition of lands; errors in bid documents and delay in decision making by the Engineer. All these five delays can be categorized as “Concurrent Delays”. It is the responsibility of the employer to take actions at early stage of the project to minimize these delays by providing reasonable time for evaluation of bid documents, reviewing them by experienced professionals before approving them. Also actions should be taken to identify the land acquisition issues very early in the project and develop an efficient mechanism to complete the acquisition process in time. It is also necessary to delegate a reasonable authority to the Engineer who is administering the projects to avoid delays in decision making.
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Perceptions of Project Employer & Engineer's view
Contractor’s view
FOI
FOI
Rank
Rank
Procurement delay in imported 0.42 1 0.36 3 materials Contractor's cash 0.46 2 0.70 54 flow difficulties Extra work given 0.47 3 0.35 1 by employer Delay in approving of 0.47 4 0.36 2 variation orders by employer Poor planning and scheduling of 0.48 5 0.50 16 contractor Shortage of 0.50 6 0.46 8 skilled Labour Shortage of 0.51 7 0.54 25 qualified professional staff Weather 0.51 8 0.50 18 conditions Variation orders 0.52 9 0.45 5 of Contractor Shortage of 0.53 10 0.50 15 Resources Lack of supervision and 0.53 11 0.52 20 direction for labour Delay in certifying 0.54 12 0.40 4 variation orders by Engineer Note: Ranks in bold indicate the strong disagreement on the perceptions between the Employer & Engineer and the Contractor. Remaining delay factors were identified as moderate and with less disagreement on the perceptions between project participants. Five significant factors contributing to delays during the construction phase are: procurement delay in imported materials, variation orders, shortage of skilled labour, poor planning & scheduling, and government restrictions for mining and transportation of materials. Delay in procurement of imported materials can be categorized as an “Excusable Delay” and depending on who is responsible for this work
the delay can be further categorized as either “Compensatory Delay” or Non Compensatory Delay”. Issuing Variation orders is the responsibility of the Employer and the Engineer and therefore this delay can be categorized as an “Excusable, Compensatory Delay”. Delays due to shortage of skilled labour, poor planning & scheduling can be categorized as “Non Excusable Delays as the contractor is responsible for these delays. Delays due to government restrictions for mining and transportation of materials can be categorized as “Excusable, Compensatory Delay”. It is revealed that the contractor’s performance has the most significant impact on delays in construction phase. It is a good practice to award a separate contract to supply imported materials or supply these materials by the employer. An effective and clear procedure should be included in the contract to prepare and approve variation orders in all contracts to minimize delays due to variations. It is essential to employ skilled labour in all construction activities to avoid delays and improve performance. Providing formal and on the job training play a vital role in this regard. Also it is important to train all staff on construction management, especially on planning and scheduling of construction activities. It is also important to make submissions to the government ministries to relax some of the restrictions imposed on mining and transportation of construction materials. This can be done through the National Contractor Association of Sri Lanka, Institute for Construction Training and Development and other relevant bodies.
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AUTHOR INDEX Abeyratne S.G. Abeyruwan H. Adikary S.U. Alwis T.T. Alahakoon A.M.S.D. Amarasinghe A.D.U.S. Ananthasingam A. Anuradha H.B.B. Arunprasanth S. Atputharajah A. Auttanat T. Bandara H.M.D.N. Bandara M A A P Chaminda H.A.C. Dasanayaka D.R.D.H. Dhananjaya H.R.K. de Alwis Ajith De Silva G.H.M.J. Subashi De Silva G.S.Y. De Silva L. I. N. Dissanayake D M H S Edirisinghe D G Egodage S M Ekanayake M.P.B. Fernando M.A.R.M. Fonseka W R K Fukahori K Gajananan A. Gajanayake C. Goddaliyadda G.M.R.I. Gunarathne R.M.D.S. Gunasekera Manisha Y Gunasoma H.H.M. Gunathilaka Nadira Gunatilake R.K.P.S. Gunawardena S.H.P. Gunawardhana D Hewa Walpita D.R.S. Halwatura R U Herath V.R. Illangasinghe W. K. Ismail F.M. Jayamanna P. M. S. Jayantha G.A. Jayasekara B.B.K.J. Jayathilaka S.M.R.A. Jayathilake D.W.A. Jayawardhane W.M. Jayaweera A. G. T. N. Jongpatiwut S. Kalpage C.S. Karunarathna C. A. B. Karunarathna H.M.G.U. Kithalawa Arachchi J.N.J.
211 274 140 9 250 9, 38, 127 160 9 160 160, 234 20 211 176, 241 61 9 211 33 281 281 76, 85 70 290 290 193, 250 160, 176, 234, 241 70 61 234 234 193, 250 14 33, 53 133, 274 112 224 25 61 25 104, 120, 151, 224 217 95 25 104 176, 241 193 193 211 46 104 20 241 234 274 267
Kodagoda K.G.H. Kulathunga Gamini Madhubhashini H.P.N. Mahanama H. A. D. Mallawaarachchi U G Mampearachchi W.K. Matharage B S H M S Y Nanayakkara S.M.A. Nandadeva B.D.G.P. Narampanawe K M M W N B Narayana Mahinsasa Nelundeniya S. W. Nissanka N. A. C. R. Olwa Joseph Padmasiri J. P. Perera A A D A J Perera Kulupanage Upuli Chathurika Perera W D A Premkumar S. Punchibanda D.M. Pushpakumara B.H.J. Randeniya D.I.B. Rathnasiri P.G. Ratnayake H. M. I. C. Rupasinghe B.W.H.A. Samarasekara G.N. Saranraj M. Sathyaram S. Shailajah R. Silva G. H. E. Silva S.V.A. Siriwardane T A A I Situge S.D.J.M.T. Soysa W.N.M. Susantha K. A. S. Suvetha B Tharaka D G S Tharanga M.A. Tharranetharan S. Udana H. P. K. Uduweriya S.B. Vamathevan Komathy Wanasinghe D.D. Warnasooriya S Wickramasinghe A.S. Wijayakulasooriya J.V. Wijekoon S.B. Wijerathne S.N Wijewardena C.L. Yoganathan N.
320
20 1 250 104 297 146 176, 241 259, 267 127 211 169 259 259 1 46 305 1 151 76, 85 14 281 202 127 259 185 61 217 217 160 104 267 290 274 250 133 146 146 9 217 38 313 33 140 53 185 193, 250 313 120 267 160
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