Process Flow Diagram for Portland Cement Manufacturing

The Cement Industry Members of Group H, for CHE 581 Supervised By

Engr. Dr. C.N. Owabor

B.Eng Chemical Engineering, 500L University of Benin, Benin City, Nigeria March 20, 2012

1

MEMBERS OF GROUP H

S/N

NAME

MAT. NO

1

AKINBULUMA TOSIN

ENG0701650

2

EMEBU SAMUEL

ENG0701685

3

NSAKA ESTHER

ENG0701728

4

ONWUEMENE O. FAITH

ENG0604576

5

OSARUMWENSE EGHOSA SAMUEL

ENG0701767

6

OLADIMEJI ISAAC

ENG0701745

7

IGHODALO .E. HENRIETTA

ENG0701704

8

UMANAH EMEMOBONG

ENG0601047

9

ABIA EMEM PETER

ENG0701642

10

EHIMWENMA BELLO

ENG0701668

11

2

Contents List of figures Abstract Acknowledgements 1. Introduction………………………………………………………………………… 4-7 1.1 A brief history of portland cement 1.2 Uses of Portland cement 1.2.1 Rapid-Hardening cement 1.2.2 Moderate-Heat cement 1.3 The chemistry of cement function 1.4 Environmental implication 1.4.1 Dust emission 1.4.2 CO2 emission. 1.4.3 Quarry and plant water runoff 1.4.4 Chrome bricks 2. Portland cement manufacturing…………………………………………………….. 2.1 process description 3. Cement production process route……………………………………………………

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12-13

4. Benefit of cement industry to the Nigerian economy………………………………… 14 4.1 challenges in the cement industry 5. Emerging trends in the global and Nigerian cement industry………………………..

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6. Local content initiative in the emerging trends of the Nigeria cement industry…….. 6.1 Raw material input 6.2 Employment 6.3 output 6.4 Improvement of imported technology

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7. Corporate social responsibility of cement industry…………………………………… 20 8. Conclusion…………………………………………………………………………….

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9. Recommendation………………………………………………………………………

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10. Reference……………………………………………………………………………..

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LIST OF FIGURES 1. Block diagram for portland cement production 2.Block diagram for the processing of cement

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SUMMARY Despite an impressive performance of the Nigeria cement industry in the sub-saharan region of Africa the price of cement in Nigeria still remains expensive and unaffordable by the common man. This is majorly attributed to poor power supply, poor transportation network, importation of raw material for cement production and government policies encouraging the importation of cement into the country. In spite of the challenges facing the Nigeria cement industry. The sector has been able to contribute to the Gross Domestic Product (GDP), create employment and provide social infrastructure and responsibility for communities within and outside its location of operation. Regardless of the lapses in the Nigeria cement industry, one can not totally ignore its presence in the Nigeria economy as this sector has immensely contributed to the growth of the Nigeria economy through the government-private partnership.

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Acknowledgement

It is factual that without the immense contribution of some dynamic people this assignment would not have been a success .But above all the largest part of the glory must go to the almighty God for his assistance. A very big well done goes to every members of this group most especially to Tosin Akinbuluma,Emebu Samuel and Nsaka Esther for making their computers available for use. Also we must say a very big thank you to Godwin Bassey of group G and every members of room 193 hall 4 unit 1 for helping us with internet connection and accommodating us respectively during the course of this research. we jointly commend them and appreciate their kind gesture. Finally we are very grateful to everybody that has in one way or the other contribute to the success of this project. we say God bless you all…

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1.0

INTRODUCTION

Cement is a fine grey powder which when reacted with water hardens to form a rigid Chemical mineral structure which gives concrete its high strengths. Cement is in effect, the glue that holds concrete together. Concrete is an extremely versatile material, being used in the production of anything from Nuclear radiation shields to playground structures and from bridges to yachts. It is able to be Used in such a wide variety of applications because it can be poured into any shape Reinforced with steel or glass fibres, precast, coloured, has a variety of finishes and can even Set under water. Modern concrete is made by mixing aggregate (sand, stones and shingle) with Portland cement and water and allowing it to set. Of these ingredients, the most Important is Portland cement. 1.1 A brief history of Portland cement The credit for cement discovery is given to the Romans, who mixed lime (CaCO3) with volcanic ash, producing a cement mortar which was used during construction of such impressive structures as the Colosseum. When the Roman Empire fell, the information on how to make cement was lost and was not rediscovered until the 16th century. Cement has been made since Roman times, but over time the recipes used to make cement have been refined. The earliest cements were made from lime and pozzolana (a volcanic ash containing significant quantities of SiO2 and Al2O3) mixed with ground brick and water. This cement was not improved upon until 1758, when Smeaton noticed that using a limestone that was 20 - 25 % clay and heating the mixture resulted in a cement that could harden under water. He called this new cement 'hydraulic lime'. When the mixture was heated, a small quantity of it was sintered. Normally this was discarded as waste, but in the 1800s Aspdin and Johnson discovered that when the entire batch was sintered and then ground, a superior cement was formed. This substance became designated Portland cement (after the region in which they were working) and is the most common cement in use today. Portland cement was first produced commercially in New Zealand in 1886 by James Wilson and Co., and has been produced here ever since. There are currently two companies producing cement in New Zealand: Golden Bay Cement Ltd. in Whangarei and Milburn New Zealand Ltd. in Westport. Production has increased from aound 5 000 t/annum in 1900 to in excess of 500 000 t/annum in 1991 and a New Zealand market demand in 1996 in excess of 800 000 t/annum. 7

Portland cement is currently defined as a mixture of argillaceous (i.e. clay-like) and calcaneous (i.e. containing CaCO3 or other insoluble calcium salts) materials mixed with gypsum (CaSO4⋅2H2O) sintered and then pulverised into a fine powder. The precise definition of Portland cement varies between different countries, and in New Zealand are controlled by New Zealand's Standard Specification (NZS) 3122. Portland cement differs from its precursors primarily in the fact that it is sintered. 1.2 Uses of Portland cement Cement is produced in three main grades: ordinary Portland cement, rapid hardening cement and moderate-heat cement. 1.2.1  

Rapid-hardeningcement: used in precast concrete pipes and tiles. It is finer ground so that it hydrates more . 1.2.2 Moderate-heat cement:  used for the construction of hydro-electric dams  as the heat produced by ordinary cement creates uneven expansion and hence cracking when such a large volume of concrete is used.

1.3 The chemistry of cement function Concrete mix is a mixture of cement and aggregate - sand and gravel. When water is added to this the cement undergoes a series of chemical reactions to form a "gel" (a colloidal system). The fine cement particles are broken down into even smaller particles (thus increasing the reactive surface) by crystallizing out from the supersaturated solution formed. A series of immensely strong Si-O-Si bonds form between the particles, making a network in which the aggregates are trapped. In addition, bonds are formed to the aggregates, but these are much weaker, especially for smooth, inert, hard aggregates: because they have a smaller surface area than rough aggregates, a smaller area can be involved in bonding. These reactions continue to take place for some time (depending on the exact composition of the cement), and after the initial brief expansion of the cement the material shrinks as unreacted water is lost. It is rare for all the cement to react:usually after five months the grains are only hydrated to a depth of 6-9μm, while cement grains range up to 100μm in diameter. Of these compounds, C3S and C3A are mainly responsible for the strength of the cement. High percentages of C3S (low C2S) results in high early strength but also high heat generation as the concrete sets. The reverse combination of low C3S and high C2S develops strengths more slowly (over 52 rather than 28 days) and generates less heat. C3A causes undesirable heat and rapid reacting properties, which can be prevented by adding CaSO4 to the final product. C3A can be converted to the more desirable C4AF by the addition of Fe2O3 before heating, but this also inhibits the formationof C3S. C4AF makes the cement more resistant to seawater and results in a somewhat slower reaction which evolves less heat. The balance of the formed compounds versus the performance characteristics required from the cement is a chemically controlled parameter. For this reason considerable efforts are 8

made during the manufacturing process to ensure the correct chemical compounds in the correct ratios are present in the raw materials before introduction of the materials to the kiln. Breaking the reaction processes into a number of simple zones means we can make some approximations about the cement formation process. Zone 1: 0 - 35 min, 800 - 1100oC Decarbonation. Formation of 3CaO•Al2O3 above 900oC. Melting of fluxing compounds Al2O3 and Fe2O3. CaCO3 → CaO + CO2 (heat) Zone 2: 35 - 40 min, 1100 - 1300oC Exothermic reactions and the formation of secondary silicate phases as follows: heat 2CaO + SiO2 → 2CaO•SiO2 Zone 3: 40 - 50 min, 1300 - 1450 - 1300oC Sintering and reaction within the melt to form ternary silicates and tetracalcium aluminoferrates: heat + time 2CaO•SiO2 + CaO → 3CaO•SiO2 heat + time 3CaO•Al2O3 + CaO + Fe2O3 → 4CaO•Al2O3 •Fe2O3 Zone 4: 50 - 60 min, 1300 - 1000oC Cooling and crystallisation of the various mineral phases formed in the kiln.[1] 1.4 ENVIRONMENTAL IMPLICATIONS Many of the aspects of the cement making process are potentially environmentally damaging, although these risks can be minimised. The areas of potential concern are listed below. 1.4.1 Dust emissions The manufacture of cement generates large quantities of dust. These must be prevented (both on environmental and economic grounds) from escaping to the atmosphere. The two areas where dust has the potential to escape are via air streams that have been used to carry cement (e.g. the mills or kiln) and directly from equipment used to transport cement (e.g. the various conveyor belts). Thus to prevent dust emissions all transport equipment is enclosed, and the air both from these enclosures and from the kiln and mills is treated in an electrostatic precipitator to remove its load of dust. 1.4.2 CO2 emissions Cement manufacture is an energy intensive process. One of the most significant challenges facing the industry into the 21st century is a requirement to reduce CO2 emissions. CO2 is produced during the calcination phase of the manufacturing process and also as a result of burning fossil fuels. Opportunity to reduce emissions through increased energy efficiency is only possible on the latter of the CO2 emissions. 1.4.3 Quarry and plant water runoff Runoff of storm water and treatment of waste water from quarries is a problem for almost all quarry operations. Usually this is trapped in wetland areas where the water is treated in a controlled manner. Within the factory runoff can be contaminated by oils and lubricants, but the runoff is monitored and training programmes are reguarly undertaken to ensure this does not happen. 9

1.4.4 Chrome bricks Kiln bricks used to be made of hexavalent chrome, which is a carcinogen and causes dermititus in some people.

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2.0

Portland Cement Manufacturing

2.1 Process Description Portland cement is a fine powder, gray or white in color, that consists of a mixture of hydraulic cement materials comprising primarily calcium silicates, aluminates and aluminoferrites.More than 30 raw materials are known to be used in the manufacture of portland cement, and these materials can be divided into four distinct categories: calcareous, siliceous, argillaceous, and ferrifrous. These materials are chemically combined through pyroprocessing and subjected to subsequent mechanical processing operations to form gray and white portland cement. Gray Portland cement is used for structural applications and is the more common type of cement produced. White portland cement has lower iron and manganese contents than gray portland cement and is used primarily for decorative purposes. Portland cement manufacturing plants are part of hydraulic cement manufacturing, which also includes natural, masonry, and pozzolanic cement. A diagram of the process, which encompasses production of both portland and masonry cement, is shown in figure 1 below, the process can be divided into the following primary components: raw material acquisition and handling, kiln feed preparation, pyroprocessing, and finished cement grinding. Each of these process components is described briefly below. The initial production step in portland cement manufacturing is raw materials acquisition.Calcium, the element of highest concentration in portland cement, is obtained from a variety of calcareous raw materials, including limestone, chalk, marl, sea shells, aragonite, and an impure limestone known as "natural cement rock". Typically, these raw materials are obtained from open-face quarries, but underground mines or dredging operations are also used. Raw materials vary from facility to facility. Some quarries produce relatively pure limestone that requires the use of additional raw materials to provide the correct chemical blend in the raw mix. In other quarries, all or part of the noncalcarious constituents are found naturally in the limestone. Occasionally, pockets of pyrite,which can significantly increase emissions of sulfur dioxide (SO2), are found in deposits of limestone,clays, and shales used as raw materials for portland cement. Because a large fraction of the mass of this primary material is lost as carbon dioxide (CO2) in the kiln, Portland cement plants are located close to a calcareous raw material source whenever possible. Other elements included in the raw mix are silicon, aluminum, and iron. These materials are obtained from ores and minerals such as sand, shale, clay, and iron ore. Again, these materials are most commonly from open-pit quarries or mines, but they may be dredged or excavated from underwater deposits.Either gypsum or natural anhydrite, both of which are forms of calcium sulfate, is introduced to the process during the finish grinding operations. These materials, also excavated from quarries or mines, are generally purchased from an external source, rather than obtained directly from a captive operation by the cement plant. The second step in portland cement manufacture is preparing the raw mix, or kiln feed, for the pyroprocessing operation. Raw material preparation includes a variety of blending and sizing operations that are designed to provide a feed with appropriate chemical and physical properties. The raw material processing operations differ somewhat for wet and dry processes.Cement raw materials are received with an initial moisture content varying from 1 to more than 50 percent. If the facility uses dry process kilns, this moisture is usually reduced to less than 1 percent before 11

or during grinding. Drying alone can be accomplished in impact dryers, drum dryers,paddleequipped rapid dryers, air separators, or autogenous mills. However, drying can also be accomplished during grinding in ball-and-tube mills or roller mills. While thermal energy for drying can be supplied by exhaust gases from separate, direct-fired coal, oil, or gas burners, the most efficient and widely used source of heat for drying is the hot exit gases from the pyroprocessing system.Materials transport associated with dry raw milling systems can be accomplished by a varietyof mechanisms, including screw conveyors, belt conveyors, drag conveyors, bucket elevators, air slide conveyors, and pneumatic conveying systems. The dry raw mix is pneumatically blended and stored in specially constructed silos until it is fed to the pyroprocessing system. In the wet process, water is added to the raw mill during the grinding of the raw materials in ball or tube mills, thereby producing a pumpable slurry, or slip, of approximately 65 percent solids. The slurry is agitated, blended, and stored in various kinds and sizes of cylindrical tanks or slurry basins until it is fed to the pyroprocessing system. The heart of the portland cement manufacturing process is the pyroprocessing system. This system transforms the raw mix into clinkers, which are gray, glass-hard, spherically shaped nodules. The chemical reactions and physical processes that constitute the transformation are quite complex, but they can be viewed conceptually as the following sequential events: 1. Evaporation of free water; 2. Evolution of combined water in the argillaceous components; 3. Calcination of the calcium carbonate (CaCO3) to calcium oxide (CaO); 4. Reaction of CaO with silica to form dicalcium silicate; 5. Reaction of CaO with the aluminum and iron-bearing constituents to form the liquid phase; 6. Formation of the clinker nodules; 7. Evaporation of volatile constituents (e. g., sodium, potassium, chlorides, and sulfates); and 8. Reaction of excess CaO with dicalcium silicate to form tricalcium silicate. This sequence of events may be conveniently divided into four stages, as a function of location and temperature of the materials in the rotary kiln. 1. Evaporation of uncombined water from raw materials, as material temperature increases to 100°C (212°F); 2. Dehydration, as the material temperature increases from 100°C to approximately 430°C (800°F) to form oxides of silicon, aluminum, and iron; 3. Calcination, during which carbon dioxide (CO2) is evolved, between 900°C (1650°F) and 982°C (1800°F), to form CaO; and 4. Reaction, of the oxides in the burning zone of the rotary kiln, to form cement clinker at temperatures of approximately 1510°C (2750°F). Rotary kilns are long, cylindrical, slightly inclined furnaces that are lined with refractory to protect the steel shell and retain heat within the kiln. The raw material mix enters the kiln at the elevated end, and the combustion fuels generally are introduced into the lower end of the kiln in 12

a countercurrent manner. The materials are continuously and slowly moved to the lower end by rotation of the kiln. As they move down the kiln, the raw materials are changed to cementitious or hydraulic minerals as a result of the increasing temperature within the kiln. The most commonly used kiln fuels are coal, natural gas, and occasionally oil. The use of supplemental fuels such as waste solvents, scrap rubber, and petroleum coke has expanded in recent years. NOTE: Five different processes are used in the portland cement industry to accomplish the pyroprocessing step: the wet process, the dry process (long dry process), the semidry process, the dry process with a preheater, and the dry process with a preheater/precalciner. Each of these processes accomplishes the physical/chemical steps defined above. However, the processes vary with respect to equipment design, method of operation, and fuel consumption. Generally, fuel consumption decreases in the order of the processes listed. The paragraphs below briefly describe the process, starting with the wet process and then noting differences in the other processes. In the wet process and long dry process, all of the pyroprocessing activity occurs in the rotary kiln. Depending on the process type, kilns have length-to-diameter ratios in the range of 15:1 to 40:1.While some wet process kilns may be as long as 210 m (700 ft), many wet process kilns and all dry process kilns are shorter. Wet process and long dry process pyroprocessing systems consist solely of the simple rotary kiln. Usually, a system of chains is provided at the feed end of the kiln in the drying or preheat zones to improve heat transfer from the hot gases to the solid materials. As the kiln rotates, the chains are raised and exposed to the hot gases. Further kiln rotation causes the hot chains to fall into the cooler materials at the bottom of the kiln, thereby transferring the heat to the load. Dry process pyroprocessing systems have been improved in thermal efficiency and productive capacity through the addition of one or more cyclone-type preheater vessels in the gas stream exiting the rotary kiln. This system is called the preheater process. The vessels are arranged vertically, in series, and are supported by a structure known as the preheater tower. Hot exhaust gases from the rotary kiln pass countercurrently through the downward-moving raw materials in the preheater vessels.Compared to the simple rotary kiln, the heat transfer rate is significantly increased, the degree of heat utilization is greater, and the process time is markedly reduced by the intimate contact of the solid particles with the hot gases. The improved heat transfer allows the length of the rotary kiln to be reduced. The hot gases from the preheater tower are often used as a source of heat for drying raw materials in the raw mill. [2] BLOCK DIAGRAM FOR CEMENT PROCESSING

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3.0 Cement Production Process Route. Portland cement (the only type of cement in common use today) is manufactured in a four step process. Step 1 - Quarrying Limestone and a 'cement rock' such as clay or shale are quarried and brought to the cement works. These rocks contain lime (CaCO3), silica (SiO2), alumina (Al2O3) and ferrous oxide (Fe2O3) - the raw materials of cement manufacture. Step 2 - Raw material preparation To form a consistent product, it is essential that the same mixture of minerals is used every time. For this reason the exact composition of the limestone and clay is determined at this point, and other ingredients added if necessary. The rock is also ground into fine particles to increase the efficiency of the reaction. Step 3 - Clinkering The raw materials are then dried, heated and fed into a rotating kiln. Here the raw materials react at very high temperatures to form 3CaO•SiO2 (tricalcium silicate), 2CaO•SiO2 (dicalcium silicate), 3CaO•Al2O3 (tricalcium aluminate) and 4CaO•Al2O3 •Fe2O3 (tetracalcium alumino-ferrate). Step 4 - Cement milling The 'clinker' that has now been produced will behave just like cement, but it is in particles up to 3 cm in diameter. These are ground down to a fine powder to turn the clinker into useful cement. Cement production has several quite serious environmental hazards associated with it: dust and CO2 emissions and contaminated run-off water. These production steps are streamlined into:  Preparing raw materials: Mixing/homogenising, grinding and preheating (drying) produces the raw meal.  Burning of raw meal to form cement clinker in the kiln: The components of the raw meal react at high temperatures (900-1500 °C) in the precalciner and in the rotary kiln, to give cement clinker.  Finish grinding of clinker and mixing with additives: After cooling the clinker is ground together with additives. Two types of kilns are distinguished: rotary kilns and shaft kilns. The former is mainly used in industrialized countries, while the latter is more in use in China.

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BLOCK DIAGRAM FOR PORTLAND CEMENT PRODUCTION CORRECTIVE MINERALS

LOCAL ROCK LIMESTONE

RAW MIXTURE MILL

RAW MIXTURE SILO

ROTATING KILN

CLINKER SILO

CEMENT MILL

ADDITIONAL MATERIAL FLY ASH, BLAST FURNANCE

PARKING AND TRANSPORT OF CEMENT TO CONSUMER 16

Fig 3.0

4.0 BENEFITS OF CEMENT INDUSTRY TO NIGERIAN ECONOMY    



The cement industry has served as a major employer of both the skilled and unskilled labour in Nigeria. Cement has contributed massively in the completion of most Engineering works such as road construction,as well as the building of houses. The cement has created an avenue for competitive advantage. The cement industry has contributed to the aspect of encouraging private sector to play pivotal role in the industrial development of the country.This can be seen by various industries like WESTCOM TECHNOLOGIES AND ENERGY SERVICE LIMITED which is presently into terminal operation of bagging of cement;IBETO CEMENT COMPANY in port Harcourt having a capacity of 1.5m metric tonnes per annum and some other companies which also engage in manufacturing of cement (like the dangote cement) The industry has helped in the growth of the real gross domestic product (GDP) of Nigeria economy.

However,the aboved mentioned benefits has not fully taken shape in our Nigerian economy today as a result of the following reason : 4.1 challenges  

High cost of road transportation Demand is high and supply is low hence leading to bridging by importation.

 The prices of cement in Nigeria today have risen drastically due to factors of inflation, deficient infrastructure challenges and supply bottleneck. An average price of cement has moved from N625 in 2002 to N2000 in 2008.As a result of such increase in price, the federal government has issued license to some manufacturer and bagging plants to import cement.

 Poor power supply.  importation of raw materials such as gypsum.

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5.0 EMERGING TRENDS IN THE GLOBAL AND NIGERIAN CEMENT INDUSTRY 

   

               

Indian cement industry has been very proactive in adopting various technological advancements taking place all over the world. This was particularly triggered by the partial decontrol of cement industry in 1982 followed by full decontrol in 1989 giving the resultant free market competition an opportunity for growth in production and productivity. The share of energy inefficient wet process plants had slowly decreased from 94.4% in 1960 to 61.6% in 1980. Thereafter as a result of quantum jump in production capacities through installation of modern dry process plants as well as conversion of some of the wet process plants, the share of wet process has reduced to less than 5% today. During the last two decades (80's and 90's), major technological advancements took place in design of cement plant equipment/systems basically in the following major areas : a) Pre-calcination b) High pressure grinding c) Automation in process control d) High efficiency particle separation e) Clinker cooling These resulted in sea change developments globally and the Indian cement industry followed the international trend. The special features noticeable were: (i) Standard size of the new plants neared a million tonnes per annum (ii) Large areas of limestone even in remote areas exploited by cluster of plants (iii) Active search made for the latest type of technology and equipment to continually bring down the energy costs (iv) Large number of old wet process plants closed down or converted into dry process on account of high cost of operation (v) Introduction of multiple grades of cement on strength parameters surpassing the Bureau of Indian Standards (BIS) specifications (vi) Many plants taking to automation, computer controlled systems and man power reduction (vii) Improvement in packaging with the use of HDPE/PP/paper bags in place of conventional jute bags (viii) Shift in the marketing strategy with specific emphasis on quality associated with brand.[3]

The trends used in Indian industries as explained above is based on best global practices and hence also applicable to the Nigerian cement factories.

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6.0 LOCAL CONTENT INITIATIVE IN THE EMERGING TREND OF THE NIGERIAN CEMENT INDUSTRY 6.1 Raw materials Input The primary input for the production of cement is limestone. Secondary materials are gypsum, shale or clay, and fuel oil or coal. More than 95% of the sector's materials are obtained locally (most companies import the gypsum). One company now operates with 100% locally sourced materials, and CMAN is making efforts to ensure the local sourcing of all materials. Nkalagu Cement and Ashaka Cement Company have captive plants dedicated to satisfying their paper-bag needs. However, the Nigerian Paper Mill in Jebba is the main supplier. The bag manufacturers have a total installed capacity of 230 × 106 bags per annum, and the seven main cement producers require 104 × 106 bags per annum. There is, therefore, an excess capacity of 55% in the bag-manufacturing industry. 6.2 Employment Employment categories in the cement industry range from the professional grades (the works, mechanical, production, electrical, and process engineers), to the skilled grades (the machinists, plant mechanics, pipefitters and welders, kiln mechanics, and kiln burners), to administrative staff, to unskilled labour. All the cement-manufacturing firms in operation in Nigeria were set up with a foreign technical partner. These partners furnished the initial expertise needed for operations, so the proportion of expatriate personnel in most of the cement companies was initially high. However, with the implementation of the Nigeria Enterprises Promotion Decrees of 1972 and 1977 and determined efforts to train Nigerians, the cement industry now has many Nigerians in its management and professional cadres. The present estimated number of staff at the seven firms in the cement industry is 9000. About 10% of these people are in the professional and management categories. The rest are supervisory, clerical, and other junior workers. The expatriate staff constitute about 2% of the total work force. 6.3 Output Although there have been seven cement companies operating in Nigeria since 1978, there are eight cement works (WAPCO has two, at Ewekoro and Shagamu). The combined installed capacity of the cement factories is about 5.3 × 106 t/year. Table 3 shows the local production of cement by the individual companies in Nigeria from 1981 to 1990 and gives the capacity utilization for the industry as a whole. The output in 1990 was estimated at 3.05 × 106 t, representing 61% capacity utilization. The industry's advantage in local sourcing has led to a

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fairly stable trend in the level of capacity utilization, so the capacity underutilization shown in the table must be attributed to other factors. 6.4 Improvement of imported technology WAPCO commissioned its first works at Ewekoro in 1960/61, when the first kilns were built. Subsequent kilns followed until the full complement of three kilns at Ewekoro and two kilns at Shagamu was reached. Both works operate with the relatively old wet-process technology, although two of the kilns at Ewekoro were converted in 1981 to the semiwet process. Over the years, major refurbishment and improvement projects have been carried out at both works. Ewekoro Works is one of the oldest successfully operating cement works in the world. Because of its obsolescence, it has a high maintenance-demand factor and a more complex mix of machinery and equipment than its sister works at Shagamu. It has a complete quarry unit; five 12 HP raw mills (1 HP = about 745 W); five cement mills; a set of silos for ground clinker and cement; a filter press for the two semiwet kilns; and three kilns. Over the years, Ewekoro has had many improvement and refurbishment projects: rebuilding of the grate cooler structure; conversion of the long wet kiln to the semiwet process by the introduction of the filter press unit and the Lepol grate; refurbishment of the electrostatic precipitator unit to reduce dust loss and improve the environment; complete change of the chain system in the kiln; civil engineering works on the preheater system; and repairs and refurbishment of the back-end kiln-seal system. Shagamu Works was designed with the benefit of the experience gained at Ewekoro and is newer and more robust. It also is less complex; it has a big quarry; two big crushers (for rocks); three raw mills (3000 HP each); two wet kilns (60 t/h each); two cement mills (each with 3000 HP and a cement capacity of 100 t/h); and two cement-packing units (about 100 t/h). The major refurbishment projects at Shagamu include the improvement of fuel-consumption efficiency; and dust insufflation to minimize dust-loss problems. Case 1: Improvement to the Davies preheater system: At commissioning, Ewekoro Works consisted of three long kilns using the wet process. However, in the late 1970s, a conversion of the works was carried out so that two of the kilns could use the semiwet process. Concomitant with this conversion was a change in the process technology. The slurry is now subjected to further processing before it is let into the kiln proper. The slurry is first filtered in a reactor, where the moisture content of the slurry is drastically reduced. The slurry exits from the filter in a cake form. The cake material then passes to the nodulizer, which is essentially a horizontal plate rotating and vibrating on its axis. The effect of the movement of the nodulizer is to turn the cake into neat spherical balls. The nodules then pass to the Davies preheater, where, as the name implies, they are preheated before they pass into the kiln. Passing the nodules through the Davies preheater reduces energy consumption. In the Davies preheater, nearly all the moisture in the nodules evaporates before they go into the kiln, where calcination takes place to produce the cement clinker. 20

The Davies preheater is a patented technology, introduced to WAPCO by BCI. It consists of three main parts: the dome, the bowl, and the floor. Surrounding the floor are two slanting coaxial cylinders. The outer one (the bowl) is mounted to a stationary, rigid steel frame so that it can rotate independently on its axis, which is a shaft connected to a bearing arrangement at the top. At the bottom of the dome there is space above the floor to give clearance. These cylinders (i.e., the bowl and the dome) are sealed at the outer and inner edges with an annular top cover and hood, respectively, which confine the nodules between the cylinders but leave open to the atmosphere the upper side of a roof that spans and closes the dome. The underside of the roof slopes upward and inward and remains static. It has an inlet through which the nodules are fed and an outlet for exhausting gas. The dome, bowl, and floor rotate independently about their respective axes. Only the floor is power driven, and this is by an auxiliary motor. There are no mechanical links between the bowl, dome, or floor. The rotation of the bowl and dome is due to the friction of the nodules. The nodules move through the annulus to the floor chamber and then exit into the front end of the kiln. Going counter to the flow of the nodules is hot air from the kiln, which preheats the nodules while they are in the preheater. Water seals are used to keep the whole arrangement air tight. There are three water seals: the bottom seal and the inner and outer top seals. However, after the preheater was in operation for some time at Ewekoro, problems were encountered. There were leaks in the top seals, allowing water into the nodules. Furthermore, the water leakage caused frequent seizures of the whole unit. A project team, set up to study the problem, came up with a solution: converting the wet seal to a dry seal at the top level. The seal chamber was given a heat-resistant rubber–teflon seal. A spring was also mounted so that the constant motion of the parts helped to reinforce the seal. This solution was arrived at after much experimentation. Another output of the industry is decorative products, on which WAPCO has monopoly. Portland Paints and Products Division (PPPD) was established in 1972, when WAPCO acquired Cement Paints Nigeria. At inception, the division manufactured only cement-based decorative products, known as Snowcem, Cemwash, and Color-crete. Between 1974 and 1979, Sandtex products, manufactured in the United Kingdom by BCI, were introduced by PPPD. In 1980, the division commenced the local manufacture (under licence) of Sandtex trowel, Sandtex matt, and Sandtex textured. Other PPPD products has introduced to the Nigerian market include a rollertextured decorative coating (Bluetex) and a high-quality emulsion paint (vinyl matt emulsion). Case 2: Improvement to the cooler-drive system: The clinker exits at the back end of the kiln at a temperature of > 200°C. In this state, it cannot be fed into the mills for grinding. A cooler is, therefore, incorporated at the end of the kiln. In the original cooler assembly at Ewekoro, the cooler drive is mounted at the front end. The power to drive the cooler is transmitted via a V-belt pulley to a gear box, then to the drive shaft of the cooler. Thus, the drive is eccentric to the cooler. However, it the machinery and components were too compact, making access for maintenance very difficult. 21

In 1985, the staff improved this unit by mounting the drive on the side. This arrangement was similar to the original, but the drive was mounted at the centre of the moving frame of the cooler, rather than being eccentric. Case 3: Improvement to the cement-milling system: After cooling, the next unit operation in cement manufacture is milling. At this stage, the clinker, dosed with gypsum, enters the mill, where it is ground. Cement emerges at the end of this operation. The milled material is sent to the separator, where it is discharged onto a vibrating, electrically controlled screen. Coarse rejects fall off the surface of the screen, and the fine dust is sent to the silos for storage. The pumping unit, submerged in a pit, pumps the cement up against gravity to the silos. The vibrating screen is also at underground level, in the pump pit. However, water logging of the pit, especially during rainy seasons, hampered production and made maintenance more difficult. The screening mechanization is now a mechanically driven rotary screen, which rotates at the same speed as the mill. As well, the pump was brought up to ground level, eliminating all the problems.[4]

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7.0 CORPORATE SOCIAL RESPONSIBILITY OF CEMENT INDUSTRY IN NIGERIA Corporate Social Responsibility or CSR has been defined by Lord Holme and Richard Watts in The World Business Council for Sustainable Development’s publication ‘Making Good Business Sense’ as “…the continuing commitment by business to behave ethically and contribute to economic development while improving the quality of life of the workforce and their families as well as the local community and society at large"[5]. From the explanation of corporate social responsibility the dangote cement company have played their part and are still contributing in CSR across Africa and specifically in Nigeria, both nation-wide and in host communities of cement factories, for which the company has spent a total of #15.5 billion in the 2011 as explained by the executive director of Dangote Foundation Mr. Ahmed Iya. The foundation has covered wide sectors which includes: health, community service, education, empowerment e.t.c across Nigeria. Typical scenarios of CRS carried out by the company in Nigeria includes: (i).Education In August 2011 #100 million,#18 million and #50 million was donated to the proposed Otuoke University in Bayelsa state, University of Nigeria and Port Harcourt respectively for various developmental projects. (ii).Security The dangote group denoted #50 million to Lagos sate’s security fund in March 2011. (iii).Succour for Victims of Natural Disaster/violence #100 and #60 million was denoted to Lagos state in July 2010 and Ibadan flood victims for rehabilitation purposes. #400 million was donated to victims of post-election violence in Kaduna, Bauchi and Gombe. (iv).Price reduction programs Dangote cement factories have been distributed in zones nation-wide and there is an ongoing plan to construct rail lines to all of these factories to increase the availability of the product and reduction of the cost of product through reduce cost of transportation. This rail line will also serve for the mass transportation of humans and other goods and services in interstate basis nation-wide hence reducing cost of other products in the country and alternative for human transport. Other CSR includes construction of school blocks, bore holes, roads and electrification in host communities.[6]

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8.0 CONCLUSION The rising investment in infrastructure in developing countries of the world like Nigeria had led to an increase in the demand for cement. Nigeria cement industry estimated value grows from about 26 billion in 2004 to 134 billion in 2008. Statistics has shown that Nigeria has the largest demand for cement in Sub-Saharan Africa and about 95% of the inputs for cement production are sourced for locally. The Dangote group is by far the biggest player in Nigerian cement production; others are the Lafarge WAPCO which dominates the south-west market, Ashaka control sales in the northern region. The Dangote Cement company has witnessed appreciable growth in the cement industry which raised its share capital to about 20% but has not been able to cover the gap of consumption of cement in Nigeria. The consumption of cement in Nigeria is determined by factors influencing the level of housing and industrial constructions, irrigation projects, roads, laying of water supply pipes, drainage pipes, establishment of new universities by Federal government and private individuals. Growth in population and level of urbanization in major cities like what we are currently experiencing In Lagos, Port Harcourt, Benin are also factors that confirm the imminent demands for cement in Nigeria and other parts of Africa. All these including the supply gap of cement in Nigeria show that the future investments in Nigeria Cement industry will be a viable venture. Investigation has shown that road transportation of cement with trucks beyond 200km is not economically viable for movement of cement within the country. So we implore the federal government to fast track construction of new railways and rehabilitation of the existing ones and provision of many wagons for transportation of cement within the country. These may relax the pressure on price of cement.

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9.0 Recommendations Based on this study, the following recommendations are made: 1. Government should develop an incentive system to encourage entrepreneurs to invest in more foundries, forges, machine shops, etc., as these provide inputs to large firms and are the "missing link" in the Nigerian industrial sector. 2. The government and the cement manufacturers should together make efforts to establish local sourcing of gypsum. 3. The government and the cement manufacturers should together make efforts to establish rail lines for cost effective transportation of raw materials and products 4. Government should provide a dynamic link between national research and development institutions and industry, thus ensuring a sustained generation of technical change. 5. Government through private partnership should supply constant power .

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References

1.Article written by Heather Wansbrough from the article in the previous edition by G. Slocombe (Tikipunga High School) and D. Gallop (Wilsons (N.Z.) Portland Cement Ltd. with advice from Martyn Compton (Golden Bay Cement), Murray Mackenzie (Milburn New Zealand Ltd.) and Tim Mackay (The Cement and Concrete Association of New Zealand) and with reference to: 100 years helping build a nation; Milburn Cement; 1988 and Bogue, Robert Herman; The Chemistry of Portland Cement (2nd. edition); Reinhold Publishing Corporation; 1955) 2.

The Manufacture of Portland Cement, The Cement and Concrete Association of New Zealand; 1989 3. Mr. G. Jayaraman. Technological Trends In Cement Industry-Energy And Environmental Impact 4. Esubiyi, Chapter 18. Technical Change in the Nigerian Cement Industry

5. en.wikipedia.org/wiki/social_responsibility. 6 Dangote Spends #15.5bn on Social Responsility, http;//nnn.com.ng/?p=3693

• Lea, F. M.; The Chemistry of Cement and Concrete (3rd edition); Edward Arnold (Publishers) Ltd.; 1970

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