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THE COPPERBELT UNIVERSITY SCHOOL OF TECHNOLOGY CHEMICAL ENGINEERING DEPARTMENT
HYDROCHLORIC ACID PLANT DESIGN
i
THE COPPERBELT UNIVERSITY SCHOOL OF TECHNOLOGY CHEMICAL ENGINEERING DEPARTMENT
HYDROCHLORIC ACID PLANT DESIGN
PREPARED BY: 1.
MUTAMBANSHIKU LYASHI ARREN
98715747
2.
ROMANSHI EMMY
3.
SHIMOONJE HANS K
99229633
4.
SICHALI RONNY KAPYELA
98611062
SUPERVISED BY: Mr J.J. KANYEMBO
This paper is prepared in partial fulfilment leading to the award of a Bachelor of Engineering (BEng) in Chemical Engineering.
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LETTER OF TRANSMITTAL The projects co-coordinator, Chemical Engineering department, Copperbelt University, P.O BOX 21692, Kitwe. 25th November 2005
Dear Sir, RE: SUBMISSION OF DESIGN PROJECT. We refer you to your request for a report on the design of a Hydrochloric acid plant as partial fulfillment for the award of a degree in Chemical Engineering. We submit this report with the view that it meets the standards necessary for the assessment of this course (CE-500). It is our sincere hope that this report will meet your expectations.
Yours faithfully, Sichali Ronny Kapyela
.......................... ....................................... ....................... ..........
Mutambanshiku Lyashi Arren
.......................... ....................................... ..................... ........
Romanshi Emmy
.......................... ....................................... ....................... ..........
Shimoonje Hans
.......................... ....................................... ......................... ............
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DECLARATION I Sichali Ronny having read the University Regulations on cheating plagiarism, do by here declare that to the best of my knowledge the work contained in this presentation is of my own working and that all material used print, electronic and verbal have been dually acknowledged. The examiners cannot, however, be held responsible for the views expressed, nor the factual accuracy of the contents.
Sichali Ronny Kapyela ……………………………………………..
Mr J.J Kanyembo (Supervisor) …………………………………………………….
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DECLARATION I Mutambanshiku Lyashi Arren having read the University Regulations on cheating plagiarism, do by here declare that to the best of my knowledge the work contained in this presentation is of my own working and that all material used print, electronic and verbal have been dually acknowledged. The examiners cannot, however, be held responsible for the views expressed, nor the factual accuracy of the contents.
Mutambanshiku Lyashi Arren ……………………………………………..
Mr J.J Kanyembo (Supervisor) …………………………………………………….
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DECLARATION I Romanshi Emmy having read the University Regulations on cheating plagiarism, do by here declare that to the best of my knowledge the work contained in this presentation is of my own working and that all material used print, electronic and verbal have been dually acknowledged. The examiners cannot, however, be held responsible for the views expressed, nor the factual accuracy of the contents.
Romanshi Emmy ……………………………………………..
Mr J.J Kanyembo (Supervisor) …………………………………………………….
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DECLARATION I Shimoonje Hans having read the University Regulations on cheating plagiarism, do by here declare that to the best of my knowledge the work contained in this presentation is of my own working and that all material used print, electronic and verbal have been dually acknowledged. The examiners cannot, however, be held responsible for the views expressed, nor the factual accuracy of the contents.
Shimoonje Hans ……………………………………………..
Mr J.J Kanyembo (Supervisor) …………………………………………………….
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ACKNOWLEDMENTS RONNY SICHALI’S ACKNOWLEDGEMENT
I would like to take this opportunity to thank the almighty Jehovah GOD, without who non-this would have been possible. To my project supervisor, Mr J.J Kanyembo, for the guidance and patience during the duration of this project, to you sir, I say thank you very much. To my mum, Karen Sichali-Sichinga for the encouragement and believing in me. Thanks a million, love you. I would also like to thank the Sichali family for moral and financial support. And to my sponsors, GRZ through the bursaries department. A big thank you to some very good friends; Kabuswe Bwalya, Simon Bwalya and family, Elias, Mr and Mrs C Bwembya, Lumbwa Kafwimbi, and to all my friends thanks for being there. MUTAMBANSHIKU’S ACKNOWLEDGEMENT
My thanks to the project supervisor Mr.J.J.Kanyembo a nd staff in the Chemical Engineering Department. Thank you to the project team; Ronny, Hans, Emmie and myself for the intellectual and fruitful arguments. My thanks go to my classmates whose suggestions added value to this work. My special thanks go to my family the driving force to this mission. My special, special thanks to Jehovah God for the vision that He rekindles each new day. SHIMOONJE HANS’ ACKNOWLEDGEMENTS
Firstly I would like to give thanks to the almighty God for blessing me with my abilities and for carrying me this far. I would also like to give passionate acknowledgements firstly to my mother, Mrs. R.J Shimoonje, for her unconditional and undying support and love in all my endeavors, and to my late father, Mr. J.M Shimoonje for laying a solid
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educational foundation on my life and for all the inspirational and motivational words that I still carry deep within me. To my brothers Hector, Shachillu and Mbaze, thank you for your love, it keeps me going. To my sister Trina thanks for your love and financial support, I will never forget! To my group members, Arren, Ronny and Issa, your criticism has added to my intellectual growth and working with you has opened my mind to new ideas, to you I say thank you and job well done. To my friends T.K, Martin, Yanda, Gilbert, Davies Z,Goli, Luke and Maimbo, the memories we share I hold close to my heart, thank you for everything. Last but not least , to our supervisor Mr. J.J Kanyembo thank you for all the guidance and criticism which played a key role in shaping this report.
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ABSTRACT The aim of this project is to design a plant that will be producing 150 tons a day of Hydrochloric acid, with a quality of 20 ºBe´. Given Sodium Chloride NaCl (Common salt) and Sulphuric Acid H2SO4 of 60 ºBe´ quality as raw materials. This will include determining whether the project is viable or not through costing and equipment sizing. As the country currently has no HCl plant this project is worth carrying out as it may provide not only local source for HCl required in Chemical and allied industries, but also employment for the local people. The production will be carried though the reacting of raw materials given, by heating them to a required temperature and subsequent absorption of the gas
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TABLE OF CONTENT Item
age number
Letter of transmittal
..............
I
Declarations
..............
ii
Acknowledgments
..............
vi
Abstract
..........
vii
Table of contents
...........
ix
List of tables
...........
xii
List of figures and diagrams
............
xii
1.0 Introduction
..............
1
1.1 Process of design
..............
2
1.2 Uses of HCl
..............
4
2.0 Reactor (furnace design)
...................
5
2.1 Design objectives
....................
6
2.2 Process design
.................
6
2.2.1 Physical properties
..................
6
2.2.2 Process description
..................
8
................
10
..................
11
..................
12
2.4.1 Operating conditions
......................
12
2.4.2 Reaction kinetics
....................
12
.................
16
Chapter one
Chapter two
2.3 Material balance 2.3.1 Component balance 2.4 Muffle furnace
2.5 Energy balances around the furnace
2.5.1 Heat of reactions conversion for furnace duty.....
16
2.5.2 Furnace duty and fuel quantity
....................
17
2.5.3 Air and fuel analysis
..................
19
ix
item
page number
2.6 Selection of fuel
....................
20
2.7 Type of fuel
...................
21
2.8 Process control
..................
22
2.9 Mechanical design (muffle furnace)
..................
22
2.10 Costing of muffle furnace
.................
23
3.0 cooling of hydrogen chloride gas
..................
25
3.1 Introduction
....................
26
Chapter three
3.1.1 Advantages of the Trombone Cooler …………..
27
3.1.2 Industrial Applications
28
…………..
3.2 Process design
…………
28
3.2.1 Heat Flow through A Trombone Cooler
…………
28
3.2.2 Calculation of Outside Film Coefficient
……….
29
3.2.3 Heat load
………..
30
3.2.4 Pressure drop
………….
35
3.3 Summary of process design
………….
36
3.4 Mechanical design
…………..
37
3.5 Unit Costing of Cooler
……………
38
4.0 Absorption column design
……………
40
4.1 Introduction
……………
41
4.2 Process Design
……………
43
4.2.1 Column diameter
……………
43
4.2.2 Selection of plate type
……………
43
4.3 Material balance
…………….
45
4.4 Equation of the operating line
…………….
47
……………..
50
Chapter four
4.4.1 Column diameter Calculation
x
item
age number
4.5 Unit Costing and Evaluation
…………….
53
5.0 site selection and safety
…………….
55
5.1 Occurrences of raw materials
……………
55
5.2 Site selection
……………
55
5.4 Safety factors
……………
56
6.0 project evaluation and cost
.................
58
6.1 Introduction
...............
58
6.2 Fixed and installation cost
…………..
59
6.2.1 Physical plant cost (PPC)
………….
60
6.2.2 Fixed capital cost (FCC)
…………..
60
6.2.3 Cost (expenditure)
…………..
60
6.2.4 Income per year
…………..
60
Conclusion
………….
64
Recommendations
…………..
67
Reference
…………….
69
Appendix
……………
71
Chapter five
Chapter six
xi
List of tables Item
Page number
Properties and composition of fuel selected table 2.1
18
Fuel air combustion analysis table 2.2
18
Fuel air combustion analysis table 2.3
19
Hydrocarbon fuel cost table 2.4
21
Furnace dimensions summary table 2.5
23
Solubility of HCl in water at 760mmHg table 4.1
41
Mechanical description table 4.2
52
Summary table cost evaluation table 6.1
61
Process design summary table 6.2
62
Mechanical design and costs summary table 6.3
63
LIST OF FIGURES AND DIAGRAMS Item
page number
Overall material balance diagram 2.1
10
Component material balance around the furnace fig 2.1
11
Energy balance around the furnace diagram 2.2
16
Trombone cooler Diagram 3.1
27
Falling film absorber Diagram 4.1
42
Summary of outcome of calculations diagram 4.2
47
Dimensions diagram 4.3
52
xii
CHAPTER ONE 1.0 INTRODUCTION Basilius Valentinus is credited with the production of hydrogen chloride in the fifteenth century. Its commercial production awaited the Leblanc process for sodium carbonate in which hydrogen chloride and salt cake are co products. For a time, the gas was merely vented to the atmosphere, but legislation was enacted prohibiting its indiscriminate discharge, and thus necessitating its recovery. The developed world today describes this era as the information age following successes of industrialization age; however, this idea has landed the least developed countries on an unfair field of play. Though the theory of quantum leap do apply in certain quotas but its not so in other quotas. There are no short cuts to credible achievement or success as success should have a traceable root thus has to be worked for. The labor of industrialization has built strong economies in the developed countries. In particular, the chemical and allied industries have been described to be the backbone of these successful economies. The need for industrialization in developing countries and Zambia in particular is therefore very obvious. Since 1964, Zambian industrialization process has suffered a lot of set backs because of changes in both the political and economic development. This has been seen by the closure of many manufacturing industries and mines in particular. The few existing manufacturing plants driving the Zambian economy are now being recapitalized by foreign investment and others are still calling for recapitalization whose operations are far below their capacity for instance Nitrogen Chemicals of Zambia (NCZ) plant. The status quo of the industrialization crusade in Zambia is a challenge to the technocrats. The need for new and viable projects in chemical and allied industries should be regarded not only as a challenge but as an opportunity for economic growth. This is report is on a project whose objective is to design a plant to produce 150 tones per day of hydrochloric acid (20oBe’) from sodium chloride and sulphuric acid (60oBe’).There is no existing plant in Zambia produc ing hydrochloric acid
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despite its wide application in both local and regional industries This report will discuss the plant design of the commercial production of hydrochloric acid. What is hydrochloric acid? Hydrochloric acid is a solution of hydrogen chloride (HCl) in water. In industry it is referred to as the spirit of salt where it attracts a wider application which will be discussed in detail later in the report. There are four major known processes used commercially to produce hydrogen chloride and hydrochloric acid. (1) the salt-sulphuric acid process, (2) the Hargreaves process-salt, sulphur dioxide, air and water-vapor used as reactants, (3)synthetic process or thermal process- combustion of hydrogen and chloride mixture, (4)the by-product of organic chlorinations such as methane and benzene. 1.1 Process of design The design approach to the stated objective will be the salt-sulphuric acid process because of the specified raw materials in the design question. The HCl plant will have three (3) main units and service equipment namely the furnace (reactor), the cooler and the absorber and a compressor as a service unit. The report will consider discussing each unit as an individual chapter. However, each unit chapter will adopt the same outline of detailed discussion under the subsections namely; the process design, mechanical design and unit costing. The furnace which will be the reactor, the heart of the plant will be discussed in chapter two. The physical properties of raw materials and products will be discussed. The process description, the reaction chemistry, the reaction kinetics, the material and energy balances, the type and analysis of fuel and its choice will all be discussed in this chapter. Product gas temperature will be expected to exceed that allowable for absorption. Methods of cooling do vary with temperature volume of gas to be processed. Chapter three discusses in detail the suitable type of cooling for the duty. Chapter four discusses in detail the absorption of HCl gas in the absorber to produce the final product HCl acid. Hydrogen chloride exerts a destructive action on the mucous membrane and skin. For instance, exposure to HCl gas or acid may result in chemical burns or
2
dermatitis. Chapter five discusses safety, health and environment (SHE) in detail. In order for the process to produce the HCl (20 oBe’) with consistence, raw materials and operating conditions must be adhered to. This important aspect would be possible with a process control in place. Chapter six discusses briefly the process control and the loop will be indicated on the overall plant design flow sheet. The overall plant costing versus the projected sales volume of the product and the by product to ascertain the viability of the project will be discussed in detail in chapter seven. As earlier mentioned HCl attracts a wider industrial application, chapter eight will discuss in detail its uses. The occurrence of raw materials and factors influencing site selection will be discussed in detail in chapter nine. It is the hope of the design project team that the report will have a conceptual approach to provide workable solution to the design question.
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1.2 Uses of HCl A s t r o n g i n o r g a n i c a c i d u s e d i n m a n y i n d u s t r i a l p r o c e s s e s .
Regeneration of ion exchangers resins.
pH control in food, pharmaceutical, drinking water and neutralizing waste streams. It is used to control the pH of the process streams.
Pickling is an essential step in metal surface treatment, to remove rust or iron oxide scale from iron or steel before subsequent processing, such as extrusion, rolling and galvanizing among many other techniques.
In the production of inorganic compounds such as flocculants and coagulants useful in wastewater treatment, drinking water production, and paper production.
Production of organic compounds; vinyl chloride for PVC and other pharmaceutical products.
Leather processing, household cleaning and building construction.
Diluted to 10% to 12% strength is recommended for household purposes, mostly cleaning.
Used as a form improver in the production of washing detergents.
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CHAPTER TWO 2.0 REACTOR (FURNACE DESIGN) NOMENCLATURE volume of solid, m ν s
h
height of reactor,m
d
diameter of reactor,m
ν NaCl
volumetric flow rate of sodium chloride, m 3 /s
ρNaCl mNaCl ө
density of sodium chloride, kg/m
3
mass flow rate of sodium chloride, kg/s uncorrected residence time, s
к
correcting factor for particles of nominal diameter 53-63microns
t r
corrected residence time for a single particle, s
r A
reaction rate for reactant A,
К
reaction rate constant
C AO
initial concentration of reactant A, kmol/m 3
C BO
initial concentration of reactant B, kmol/m 3
C A
final concentration of reactant A, kmol/m 3
C B
final concentration of reactant B, kmol/m 3
ν H2SO4
volumetric flow rate of sulphuric acid, m 3 /s
ρH2SO4 mH2SO4 X A
density of sulphuric acid, kg/m 3 mass flow rate of sulphuric acid, kg/s fractional conversion of reactant A
F AO
Initial molar flow rate, kmol/s.
τ
residence time for the reaction mixture, s
Q
heat added by fuel, kW
mf
mass flow rate fuel,kg/s
CV
calorific value of fuel, MJ/kg
5
2.1 design objective
To design a plant to produce 150 tones per day HCl (20 oBe’) from NaCl and H 2SO4 (60oBe’).
This section of the project deals with the sizing of a furnace in which the raw materials solid sodium chloride and liquid sulphuric acid will react to produce hydrochloric acid gas the desired product and solid sodium sulphate a byproduct. The sizing will be based on reaction kinetics and the material balance. The reaction requires a long reaction time and a high temperature. This is achieved in a muffle furnace with a body of hearth which is heated with oil burners to 550-660oC. 2.2 process design ASSUMPTIONS
The process is a steady state flow
The process is endothermic and adiabatic.
The reactor is a non-catalytic CSTR.
The reactants are uniformly mixed.
The system is homogeneous on this basis.
The muffle furnace efficiency is 100%.
2.2.1 Physical Properties Sulphuric Acid (H2SO4), Colorless, viscous liquid, specific gravity of 1.835 and boiling point is 270 oC. It is a strong acid. Feed conditions Temperature = 20oC Quality = 60oBe’ Specific gravity = 1.705 Flow rate = 3174.13kg/h Enthalpy = -887.13kJ/mol
6
Sodium chloride (NaCl) Ionic crystal, colorless and has closed packed lattices. Specific gravity, 1.1978. Specific heat, 12359 Cal/mol. Lattice energy, 182 Cal/mol. Solubility in water, 35.7g/100g in water at 0 oC, 39.8g/100g in water at 100 oC. Temperature = 50oC Flow rate = 3789.52kg/h Enthalpy = -411.38kJ/mol Product conditions from the furnace Hydrochloric (HCl) gas, Colorless or slightly yellow, fuming gas, suffocating odor, very soluble in water; in alcohol and ether and its non-flammable Specific gravity = 1.16. Melting point = -114 oC Boiling point = -85 oC Solubility= 72g/100g in water (20 oC) Temperature = 537oC Quality = 20oBe’ Specific gravity = 1.16 Flow rate = 2364.4kg/h Enthalpy = -92.31kJ/mol
Sodium sulphate (Na2SO4) (s) Temperature = 527oC Specific gravity = Flow rate = 4599.24kg/h
7
Enthalpy = -1382.81kJ/mol Reaction Chemistry Common salt, sodium chloride and 60 oBe’ sulphuric acid react readily to form hydrogen chloride and the acid sulphate, NaHSO4, at temperatures in the range of 148.9oC and finally the normal salt, Na 2SO4 at 527.8 oC. The reactions are endothermic and are represented as follows:
NaCl (s) + H2SO4 (l) →NaHSO 4(s) + HCl (g) NaCl (s) + NaHSO4(s) →Na2SO4(s) + HCl (g) 2NaCl (s) + H2SO4 (l) →Na2SO4 (s) + 2HCl (g)
2.2.2 Process description The sodium chloride is ground in a mill, mixed with current of hot compressed air to 50oC and liquid sulphuric acid are charged through a feed inlet through the cover of the furnace. This is an externally heated furnace in which the process stream is heated primarily by radiactive and conductive heat transfer from the flame and hot gases and is known as Continuous Mechanical Muffle furnace. This furnace as it is referred to comprise the combustion chamber, the work space, the stationary circular muffle with a bottom concave pan and a domed cover separated by a cylindrical mantle or steel column and the plough mounted on rotating arms fixed to a central under driven shaft. The combustion chamber is where the fuel/air combustion takes place to produce combustion gases, CO2 and H2. Hot flue gases are circulated around the muffle. The work space which is sufficiently tight to keep out contaminants is where the actual decomposition of the reactants takes place to produce HCl gas and solid Na2SO4.This is an externally heated furnace in which the process stream is
8
heated primarily by radiative and conductive heat transfer from the flames and hot gases (combustion gases) above the dome and the pan transmit the required heat for the reaction by radiation from the cover and by conduction through the pan (there is no direct contact between the combustion gases and the reactants/products). The reaction mass is agitated by the ploughs. The rotating ploughs move the reacting mass toward the periphery of the pan where the salt cake, sodium sulphate is discharged. Hydrogen chloride (30- 36% by weight) and air are withdrawn from an outlet in the cover and transferred to coolers and absorbers. Combustion chamber temperatures of about 1202oC (1475K) are used for heating. The reaction between sodium chloride and sulphuric acid takes place at temperatures ranging 500 to 550oC. The product hydrogen chloride gas is discharged at temperature 537oC and the byproduct sodium sulphate is discharged from the hearth at about 527 oC.
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2.3 Material balance Overall material balance diagram 2.1
OVERALL MATERIAL BALANCE H2SO4 (l)
HCl(g)
NaCl (s)
Na2SO4 (S)
2NaCl(s) + H2 SO4 (l) (98)
→
Na2SO4 (s) + 2HCl (g)
(117)
(142)
(73)
Basis: 150t/day of HCl (20 oBe’) (150 x 1000) / 24 = 6250kg/h HCl acid But the amount of HCl gas which is leaving the reactor (furnace) to be absorbed with water at 95% efficiency is obtained by: Consider solubility ratio of 0.561: 1 that is HCl/water ratio (0.561/1.561) x 6250 = 2246.15kg/h HCl to be absorbed in water Therefore at 95% efficiency of the absorber, this implies that 95% HCl acid leaving the absorber = 2246.15kg/h giving 35.9% by wt HCl acid 100% HCl gas entering the absorber = x x = (100 x 2246.15)/95 = 2364.4kg/h This value serves as a basis for the material balance at the reactor
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2.3.1 component balance Component material balance around the furnace fig 2.1
NaCl
(s) HCl (gas)
H2SO4(l)
Na2SO4(s)
Basis: 2364.4kg/h of HCl gas Feed: H2 SO4 (l): (98/73) x 2364.4 = 3174.13kg/h NaCl (s): (117/73) x 2364.4 = 3789.52kg/h Product: HCl (g): 2364.4kg/h % wt: [2364.4/ (3174.13 + 3789.52)] x 100 = 33.95% (It is within the expected value ranging between 30-36% for the conventional sulphate process) By-product Na2SO4 (s): (142/73) x 2364.4 = 4599.24kg/h
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2.4 Muffle Furnace 2.4.1 Operating Conditions C o m b u s t i o n c h a m b e r :
Temperature = 1202oC Pressure = 6.8atm Work space:
Temperature = 500-550oC Pressure = 1.5atm Reaction kinetics
Diameter of the reactor = 3m
Height of the reactor = 6m
Average particle diameter of NaCl(s) NaCl(s) = 53-63 microns.
Residence time, volume of solid in the reactor , s
d 2 h 4
3 2 6 4
0.01 0.424m 3
volumetric feed feed rate of NaCl
Nacl
m
3789.52 3600 1197.8
8.788 10 -4 m 3 / s
s 0.424 482 s 4 v 8 . 788 10 residence time, t r for particl particles es of average diameter 53 63microns, t r 482 0.6 289 s 4min min where is the reaction time factor factor for NaCl particl particles es
2.4.2 Reactor kinetics H2 SO4 (l) + 2NaCl(s) → Na2SO4 (s) + 2HCl
(g)
12
Since sulphuric acid is more expensive than sodium chloride (natural salt), it is taken as a limiting reagent and the basis for the calculations in reactor kinetics, Let A, and B represent sulphuric acid and sodium chloride respectively.
r kC C A
C Ao
A B
H SO 2
4
M H SO 2
C Bo
2
Na C l
M Na Cl
1705 98
17.39kmol / m3
4
1197.8 58.5
20.48kmol / m3
13
C A C Ao 1 X A 17 .39 1 0.98 0.3478 kmol / m 3 C B C Bo 2C Ao X A
20 .48
2 17 .39 0.98 0.9277 kmol / m 3
r A 0.005 0.3742 0.2984 2
r A 0.0001665 kmol / m s 3
Ao
3174 .13 3600 98
F Ao 8.997 10 3 kmol / s V o
V o
F Ao C Ao
8 .997 10
4 .809 10
V F Ao
3
18 .71
4
m 3 / s
X A 0 . 98 8.997 10 3 0 . 0001665 r A
14
The conversion of the reaction is at 0.98 C A C Ao 1 X A 17 .39 1 0.98 0.3478kmol / m 3 C B C Bo 2C Ao X A
20 . 48 2 17 .39 0 .98
0.9277 kmol / m
3
r A 0.005 0.3742 0.2984 2
r A 0.0001665 kmol / m s 3
F Ao
3174 .13 3600 98
F Ao 8.997 10 3 kmol / s V o
V o
F Ao C Ao
8 .997 10
4 .809 10
V F Ao
3
18 .71
4
m 3 / s
X A 0 .98 8.997 10 3 r A 0 .0001665
V 52 .9 m 3
V V o
52 .9 0 .01 4 .809 10
4
18 .3 min
15
2.5 Energy balance around the furnace energy balance around the furnace diagram 2.2
ENERGY BALANCE AROUND THE FURNACE 2NaCl(s) + H2SO4 (l)
HCl(g) + Na2SO4 Qin
( ΔH) H2SO4 (l)
( ΔH) Flue gas ( ΔH) HCl(g)
( ΔH) NaCl(s)
( ΔH)Na2SO4(s)
heat products feeds added enthalpy enthalpy The reference state is 22oC and 1atm
2.5.1 Heat of reactions conversion for furnace duty evaluation….. 2NaCl(s) + H2 SO4 (l) → Na 2SO4 (s) + 2HCl (g) -411.38kJ/mol
-887.13kJ/mol
-1382.81kJ/mol
-92.31kJ/mol
H2 SO4 (l): [3174.13/3600]/98*[-887.13*103] = -7981.48kW.
16
2NaCl(s): [3789.52/3600]/58.5*[-822.73*103] = -14804kW. Na2SO4: [4599.24/3600]/142*[-1382.81*103] = -1248.87kW. 2HCl: [2364.4/3600]/36.5*[-184.62*103] = -3322.04kW. 2.5.2 Furnace duty and fuel quantity ….. Furnace duty = Heat added by fuel Heat added by fuel, Q
= (Heat in Products)-(Heat in Reactants) = -4570.91-(-22785.48) = 18214.57kW
Therefore, quantity of HFO required for this duty is: Q = CV*mf Where mf = mass flow rate of fuel (HFO), kg/s CV = calorific value of fuel, kJ/kg mf = 18214.57kJ/s*[1/42.9*103kJ/kg] = 0.425kg/s (1528.49kg/h) or 63.68tpd Volumetric flow = [1528.49kg/h]/[960kg/m 3] = 1.59m 3/h (1592.18l /h)
17
Table Showing Properties and Composition of Fuel Selected table 2.1
Composition % by Fuel
Relative Density
mass C
Calorific value (MJ/Kg)
H
O
N
S
Ash
Gross Net
Heavy Fuel Oil
0.96
85.4 11.4
2.8
1.0
0.5
1.5
42.9
40.5
table 2.2
FUEL AIR COMBUSTION ANALYSIS Component element
C H O N S Ash TOTAL
Oxygen required
Products per Kg
Mass / kg fuel
Combustion equation
Per Kg of fuel
0.854
C(s)+ O2(g)
CO2(g)
2.28
3.13
0.114
2H2(g)+ 02(g)
2H2 0(l)
0.912
1.026
0.028
_
0.01
_
0.005 0.025
S(S)+ 02(g)
_
- 0.028
_ S02(l)
0.005
_
of fuel
_ 0.01 0.01 0.025
3.169
18
FUEL AIR COMBUSTION ANALYSIS
Kmol per
% by Vol.
% by Vol.
Kg Fuel
By MASS
Kg/Kmol
Kg Fuel
Wet basis
Dry basis
12.0
13.31
CO2
3.13
18.2
44
0.071
H2 O
1.026
6.0
18
0.057
02
0.601
3.5
32
0.018
N2
12.43
72.3
28
0.4444
S02
0.01
0.0006
64
0.0002
total
Wet:17.20
100.0
PRODUCT
Mass per
%
M
9.7
Wet:0.5906
Dry:16.17
3.0
3.37
75.3
83.28
0.03
0.04
100.0
100.0
Dry: 0.5336
table 2.3 2.5.3 Air and fuel analysis
Assume 20% excess o f Air is suplied.
3.169 Air requir ed per Kg of Fuel 13.49 kg air/kg fuel 0.233 stoichiome tric A/F r atio
13.39 1
Actual A/F stoic A/F ratio %excess stioc A/F ratio
13.99 20% 13.49 16.19 Kg air / Kg fuel Therefore , Air fired to furnace 16.96 Kg air / kg fuel 1528.49 Kg / h fuel
25923.19 Kg / h flue gas given out 16.17 Kg flue / Kg fuel 1528.49 Kg fuel / h
24715.68 Kg / h 19
2.6 Selection of fuel For selecting a particular type of fuel, the following factors are taken into consideration:1. Suitability to process. 2. Supply position. Supply position with regard to availability in sufficient quantity will be considered. Reliability of supply is also taken into consideration. Factors which may affect the reliability of fuel supply are: life of reserves, international politics, wars, labor difficulties and weather disturbances. 3. Cost of fuel. Cost of fuel depends on the following factors:(i) Cost of fuel per unit of calorific value (C.V.). (ii) Cost incurred in its tapping and transport. (iii)Efficiency of utilization . A fuel may be utilized efficiently only with a particular
set of equipment. For example efficiency of the fuel in the furnace can be achieved if heat recovery equipment is incorporated in the plant. (iv) Maintenance of equipment . Cost of maintenance, storing, handling and
burning of fuel must be considered. Such cost is higher in the case of coal than in case of oils. (v)Labor and convenience. For example, labor is required for moving the fuel
when the coal is burnt while no such labor is required for gaseous and liquid fuels. (vi) Refuse handling and burning quality . When coal is burnt some labor is
required to remove ash. No such labor is required when oil or gas is burnt. Whether it burns efficiently and without smoke. (vii) Auxiliary power . Cost of auxiliary power required with a particular type of fuel
is taken into consideration. For example, power is required for conveying coal or for pulverizing or pumping coal; power is required for supply of air or steam for atomization of oil, and for supplying air of combustion.
20
2.7 Types of fuel Basically there are three types of fuel to select from namely coal, diesel or heavy fuel oil (HFO).
Hydrocarbon fuel cost table 2.4
FUEL
CV
DENSITY COST
COST
MJ/t
Kg/l
ZM K
US $
Diesel 51700 0.87
509.04 2,063,027.13
HFO
42400 0.96
265.00 1,073,986.70
Coal
30400 1.10
135.29
548,300.61
Muffle furnace does not favor the use of coal because of its ash accumulation nature. Therefore, the choice is reduced to either HFO or diesel but despite the higher CV of diesel than HFO, the cost implications disadvantage its choice for a suitable fuel. HFO is a residue fuel from the refinery and costs less and able to meet the energy demand for the design.
21
2.8 Process control
The salt is dosaged by means of a belt weigher, the quantity of acid is measured by flow measurement and controlled by an electropneumatic positioner. Based on raw material analyses, the quantity ratio of the materials is then
controlled by a human operator.
The reaction between sulphuric acid and potassium chloride requires a long reaction time and a high temperature.
Producing sulphate that is free of sulphuric acid and hydrochloric acid requires equivalent amounts of acid and salt.
The furnace will have both the temperature and pressure sensors installed to ensure operating conditions are monitored and adhered to.
2.9 Mechanical design (muffle furnace) The continuous mechanical muffle furnace is primarily a stationary circular muffle comprising a bottom concave pan (hearth). It consists of a circular refractory hearth, up to 6m in diameter, with a silicon carbide hearth. And a domed cover separated by a cylindrical mantle. The external structure has a steel shell with two main access doors. The muffle furnace consists of basically two apartments. The 1st apartment is the combustion chamber where the fuel/air combustion takes place. The 2 nd apartment is the work space where the reaction between the reactants (sodium chloride and sulphuric acid) to produce desired product (HCl gas) and by-product (Na2SO4) takes place. The 1st apartment- combustion chamber is has an acidic refractory lining to protect the steel shell high temperature combustion gases and their acidic nature. The 2nd apartment- work space comprises a circular refractory hearth with a silicon carbide hearth. The acidic refractory lining is used because of the acidic nature of the feed material and the product material.
22
The muffle would be cast iron with refractory lining and steel enclosure supported on steel columns. The internal diameter of the furnace is 3m with a refractory lining of thickness 10cm. Muffle thickness is 3cm. The combustion chamber spacing 1.5m and shell thickness of 3cm (includes corrosion allowance). The overall shell diameter is 3.34m. The depth of the reaction volume is 6m. The overall height of the furnace is 10.78m.
Furnace dimensions summary table 2.5 ITEM
DIAMETER HEIGHT (m) (m)
Work space (depth)
1x 3.0
1 x 6.0
Refractory thickness
6 x 0.1
6 x 0.1
Muffle thickness
4 x 0.03 4 x 0.03
Support (columns)
0.5 x 2
0.5 x 2
Combustion space
1.5 x 2
1.5 x 2
Shell thickness
0.03 x 2 0.03 x 2
OVERALL
7.28
10.78
23
2.10 COSTING OF MUFFLE FURNACE The cost of furnace is based on the furnace energy demand. Furnace duty = Heat added by fuel = 18214.57kW Ce = CSn Where Ce = purchased equipment cost, ₤. S = characteristic size parameter, KW. C = constant taken from table. n = index for the type of equipment = 220 x 18214.57 0.77 = 419,695.958 = ₤ 419,695.96 (ZK 292,347,614.90)
Exchange rate as at 23.11.05 ZK 6,969.57 is equivalent to £ 1.00 (British Pound) ZK 4,052.78 is equivalent to $ 1.00 (US Dollar)
24
CHAPTER THREE 3.0 COOLING OF HYDROGEN CHLORIDE GAS NOMENCLATURE
Q
heat load ,W
U
overall heat transfer coefficient,W/m C
A
effective heat transfer area,m
T
temperature , C
F T
temperature correction factor
Өln
log mean temperature difference
G,G
mass velocity
H
heat transfer coefficient,W/m C
h i
inside(tube-side) heat transfer coefficient,W/m C
h o
outside heat transfer coefficient
D o
outside diameter ,m
D i
Inside diameter ,m
2o
2
o
2o
2o
C PH 2O heat capacity of water,Kj/KgK C PH 2O heat capacity of hydrochloric acid gas,Kj/KgK o
Өcorr
corrected temperature , C
m
mass flowrate ,Kg/s
Re
Reynolds’s number
µ
viscocity,Ns/m
M
mass flowrate ,Kg/s
Ρ
density,Kg/m
∆P
pressure drop, Kpa
U
velocity, m/s
j f
W L ,I
2
3
dimensionless friction factor m
- viscosity correction factor length m
25
3.1 I n t r o d u c t i o n Product gas temperatures from the reactor (furnace) exceed those allowable for absorption. The method used for absorption varies with the temperature and volume of the gas being processed. Some cooling is achieved in the pipeline carrying the gas from the generating unit to the cooler or cooler-absorber. In the cast-iron or steel flue carrying the high-temperature gas from the salt-sulphuric acid process, some heat is removed by radiation to the atmosphere. In synthesis plants using impervious graphite or silica coolers, the pipe may be cooled with external water sprays. Generally, the high-HCl low-volume gases are cooled in tubular equipment, and the low-HCl high-volume gases by heat interchange with concentrated hydrochloric acid in packed towers. For this design particular design the cooling was achieved by a tubular exchanger known as the Trombone Cooler. Other names for the trombone cooler include trickle coolers or cascade coolers. Trombone coolers are S-shaped bends, consisting of a bank of standard pipes one above the other in series and over which water trickles downward, partly
26
evaporating as it travels (see diagram below)
Trombone cooler Diagram 3.1 Tubes are made out of impervious ceramic material for cooling corrosive gases at atmospheric pressure, such as HCl and NO 2 that may be cooled by exterior water or may be jacketed. Trombone coolers are also available in cross-flow types and banks of impervious graphite tubes have been used which are submerged in running water. Packed columns may also be used for the low volume gases.
3 .1 .1 A d v a n t a g e s o f t h e T r o m b o n e C o o l e r
Its pipes are made of ceramic material which offers a very good resistance to high temperature corrosive gases.
It does not consist of a lot of components hence it is easier to design than most other types of coolers.
27
It’s relatively cheaper to design compared to other types of coolers.
3.1.2 Ind us trial Ap plication s
Trombone coolers have been used extensively in the following industries
heavy chemical
brewing
Coke
petroleum and
ice-making industries.
3.2 Process design 3.2.1 Heat Flow Throug h A Tromb on e Cooler
When calculating the heat flow through ceramics the resistance of the pipe wall must be included. The basic design equation is
Q = UA∆T Where,
Q = heat load,W U = overall heat transfer coefficient,W/m 2oC A = the effective heat transfer area,m 2 The trombone cooler presents two problems: (1) the evaluation of the outside film coefficient and (2) calculation of the cross flow true temperature.
T em p e r at u r e d i f f e r en c e i n t h e T r o m b o n e C o o l e r
Bowman, Mueller, and Nagle have prepared correction factors F T by which the true temperature difference ∆ t can be obtained as the product
F T x
LMTD
for both the return-bend and helical types of trombone arrangement. 28
3.2.2 Calculatio n of Outs ide Film Coefficient
In calculating the outside film coefficients, the following assumptions are made: (1) no evaporation occurs from the surface of the water although it is exposed to the atmosphere. (2) half of the liquid flows down each side of the pipe in streamline flow. The criterion of streamline flow is a Reynolds’s number,
4G '
, of less than
2100, where G =
m , m is the water rate in kilograms per hour, and L is the length 2 L
of each pipe in the bank in meters. The equation for the transfer coefficients within ±25% is given by the dimensional equation
G' 1/3 h = 65 Do where Do is the outside diameter of the pipe in meters. When the value of the Reynolds’s number exceeds 2100,it is to be expected that the rates will be
somewhat higher. Any appreciable evaporation will also increase the film coefficient. Large fouling factors and low outlet-water temperatures are recommended, particularly when the water has a large mineral content.
29
3.2.3 Heat load It is desired to cool gaseous hydrochloric acid from the reactor temperature of 5370C to 60OC before it is fed into the absorption column. The mass flowrate of the gaseous HCl is 2364 Kg/hr. In cooling the gas, the temperature of water is raised from 20oC to 90oC.The process design was carried out as follows:
537 60 CHcl @Tav = = 0.84Kj/Kg 2 90 20 CH20 @ tav = = 4.2 Kj/Kg 2 Heat load o f coo ler,
Q = m H O x Cp H O x ∆T 2
=
2
2364 3600
x 0.84 x (537 – 60)
= 263.1KW
C o o l i n g w a t e r f lo w ,
Q
mH2O =
mhcl (t 2 t 1 )
=
263.1 4.2(90 20)
= 0.89 Kg/s = 3204 Kg/hr Lo g Mean Tem perature Difference(LMTD),
Өln =
=
(T 1 t 2 ) (T 2 t 1 ) (T t ) ln 1 2 (T 2 t 1 )
(500 90) (60 20) (500 90) ln (60 20)
30
=
410 40 410 ln 40
= 159oC
C o r r e c t i o n f a c t o r F T ,
R =
500 60 60 20
= 6.3
This value is out of range of fig.20(Kern pg728) so the reciprocal is used, 1
R
= 0.16
S=
@(
900 20 500 20 1
R
= 0.15,use RS = 0.95
, RS) F T = 0.9
Corrected temperature,
Өcorr = F T∆Ө ln
= 0.9 x 159OC = 143.1oC
Tube-Side Coefficient:
Using 3in. IPS pipes (Kern Table11 Pg 844), Flow area per pipe , a t
= 7.38 in2
All pipes in series therefore , Total flow area =
7 .38 144
= 0.052ft 2 (0.0048m2 )
31
Mass velocity , Gt =
m a
t
=
2364 0.0048
D = 3.068in x 0.0254m/in = 0.078 m @ Tav = 280oC, hcl = 0.25 x 10 -4Nsm-2 {fig 15,p825}
Reynolds’s number , Re =
DG t
Friction factor jH = 790 Thermal conductivity Khcl = 0.12W/oC
c k
{kern table 5,p801}
1/ 3
= (0.84 x 0.25 x 10 -4 / 0.12)1/3 = 0.06
inside coefficient , 1/ 3
k c hi = j H at k
0.12 2o = 790 x x0.06= 72.9 W/m C 0.078
outside coefficient ,
hio= hi x
ID 3.068 = 72.9 x = 63.9 W/m2oC OD 3.50
Overall heat transfer coefficient without fouling ,
Uclean =
hi hio hi
hio
=
(72.9 x63.9) (72.9 63.9)
= 34.1 W/m2oC
32
Allowing a dirt coefficient of R d = 0.01,overall coefficient with fouling becomes ,
hd =
1 0 .01
= 100
overall coefficient with dirt is given by , (U clean xhd )
Udirt =
(U clean hd )
=
(34.1 x100) (34.1 100)
= 25.4 W /m 2o C Overall heat transfer area is given by A =
=
Q (U d x corr )
263.1 x10 3 (25.4 x143.1)
= 72.4m2 (779ft 2 )
from table 11 Kern p844 ,
external surface/lin ft = 0.917
therefore,
number of pipe lengths =
779 ft 2 (0.917 x8in)
= 106t u b e s
O u t s i d e C o e f f ic i e n t :
m H 0 = 2988Kg/hr = 6587lb/hr 2 H O @ 55oC= 0.00034lb/ftsec = 1.22lb/fthr 2
33
Mass velocity ,
m H O
G=
2
2 L
=
6587 (2 x8)
= 411.7 kg/hrm2
Reinhold’s number,
Re =
=
4G '
4 x 411.7 1.22
= 1350 (streamline flow ) Outside diameter,
Do =
3 .5 12
{1in. 12 ft }
= 0.292 ft
Coefficient given as ,
G ' ho = 65 D o
1/ 3
411.7 = 65 0.292
1/ 3
= 729W/m2oC
34
3.2.4 Pressure drop Tube-Side Pressu re Drop
The pressure drop suffered by the gas in flowing through the entire tubular length of the cooler is given as,
∆Pt =
8jf Ld i' ρ
u
2 t
2
w
m
Where,
∆Pt = pressure drop in tubes, Pa
jf = dimension friction factor = 1.7 L’ = effective pipe length = 8 in x 90tubes
di = tube inside diameter= 3.068 in
ρ = density of fluid,kg/m 3 ≈ 600kg/m3 2
u t = tube-side velocity, m/s =
w
G
= 0.0058m/s
m
= viscosity correction factor ,m= -0.14 for turbulent flow.
Therefore,
0.0058 2 90 x8 x ∆Pt = 8 x 1.7 x x 600 x 2 3
0.25 x10 4 4 0 . 215 x 10
0.14
≈ 0.03 K p a
35
3.3 S u m m a r y o f p r o c e s s d e s i g n :
2o
Overall heart transfer coefficient = 25.4W/m C 2
Heat transfer area , A =72.4m
2o
Tube-side coefficient, h i =72.9w/m C 2o
Outside coefficient, h o =729W/m C Total number of tubes required =106 Reynolds’s number, Re =1350
36
3.4 Mechanical design Stoneware ceramic has the following physical properties which make it the best
choice for this particular construction:
Tensile strength = 28.6 Kp si Compressive strength = 325kp si o r 2241 -6 Young’s modulus = 45 x 10 -6 Mpa Shear Modulus=45 x10
Fracture toughness= 3.7Mpa m Hardness = 1160 kg /mm 2
With these properties the heat exchanger will have the following notable attributes:
High durability
H i g h r e s i s t an c e t o c o r r o s i o n
L o w m a i n t en a n c e c o s t s
37
3.5 Unit Costing The material chosen to construct the tubes of the cooler is ceramic material known as stoneware. From chemical engineering vol.6 ,table …, cost per unit volume, m 3 , of stoneware = £ 620, The cost of construction the equipment was performed as follows, V o l u m e o f 1 t u b e = p i
(d 2 d 1 ) 2 4
l
Where ,
l = length of one tube = 8in = (8 x.0.0254) m therefore, v o l u m e o f 1 t u b e= 3.142 x
(0.078) 2 4
x (8 x 0.0254)
= 1.5m3 3
T o t a l v o l u m e = 1.5m / tube x 106tubes
= 159m3 Purchase cost = 159m 3 x £620 = £98,580 therefore,
Cost of construction = purchase cost x material factor = 98,580 x 0.03 = £2957.40
38
The exchange rate for the pound by mid-1998 was taken as, 1£ = K6969.57 Hence, Cost of construction = 2957.40 x 6969.57 = K20, 611, 806 ≈ K 21, 000,000
39
CHAPTER FOUR 4.0 ABSORPTION COLUMN DESIGN Nomenclature
A
Heat transfer area
at
Area of the tubes
a’t
lin surface area of a tube
L(b)
Baffle spacing
Cp
Heat capacity at constant pressure
Ds
Shell diameter
di
Tube inside diameter
do
Tube outside diameter
g
Gravitational acceleration
Hgf
Sensible heat of vapour
ho
Heat transfer coefficient
j
Heat transfer factor
Nb
Number of baffles
N
Number of tubes
P
Total pressure
ΔPs
Shell pressure drop
ΔPr
Tube pressure drop due to tube resistance
ΔPt
Tube pressure drop due to fluid flow
Q
Heat transfer in unit time
Vv
Vapour velocity
Vl
Liquid velocity
W
Mass flow rate of fluid
μ
Viscosity of bulk fluid
ρ
Fluid density
40
4.1 Introduction Absorption or gas absorption is a unit operation used in chemical industry to separate gases by washing or scrubbing a gas mixture with a suitable liquid. One or more of the constituents of the gas mixture will dissolve or be absorbed in the liquid and can thus be removed from the mixture. In some systems this gaseous constituents forms a physical solution with the liquid or the solvent and in other cases, it reacts with the liquid chemically the purpose of such scrubbing operations may to the following: i)
gas purification
ii)
product recovery
iii)
production of solution of gases for various purposes
Gas absorption is carried out in vertical countercurrent columns. The solvent is fed at the top of the absorber. Whereas the gas mixture enters from the bottom Hydrochloric acid can be produced to any specification, ranging from technical or chemical quality to foodstuffs quality. Weak acid can be fed into the absorber as absorbing liquids and brought up to the required acid concentration. Solubility of HCl in water HCL is a relatively stable compound with slight evidence of dissociation at temperatures above 1500°c it is completely miscible with water foaming a max building azeotropic that boils at 108.58°c at 1 atm and contains 20.22% Solubility of HCl in water at 760mmHg table 4.1 Temp
0
30
40
50
60
Solubility, g HCl / 100g H2O 82.31 67.30 63.07 59.59 56.10 The classical equipment for hydrogen chloride absorption was a system of cellarius focrills or woulfe modern time’s use cooled – absorption towers.
The cooling – absorber is essentially a vertical shell and tube heat exchanger of impervious graphite or glass such as the one shown below.
41
Diagram 4.1 Falling film absorber
Production of hydrochloric acid in a concentration of 1 to 40 % HCl acid from chlorine and hydrogen, using water or weak hydrochloric acid as the absorbing liquid. System of failing – film cooler – absorbers has been used for recovering hydrogen chloride from gases as dilute as 5 – 10 % HCl. This is accomplished by increasing the mass – transfer surface, by adding one or two absorbers and possibly increasing the length of the tubes. The absorption of HCl in water however generates heat as the process is highly exothermic. This makes the falling firm cooler – absorber ideal. However there is not enough information available for the design of the type of absorber. Therefore a sieve plate water cooled tower will be opted for.
42
4.2 Process Design Plate spacing The overall height of the column will depend on the plate spacing. Plate spacing from 0.15m (6in) to 1m (36in) are normally used. The spacing chosen will depend on operating conditions. Closed spacing is used with small – diameter columns and where head room is restricted as it will be when a column is installed in a building. 4.2.1 Column diameter The principal factors that determine the column diameter is the vapor from rate. The vapor velocity must be below that which would cause excessive liquid entrainment or a high pressure drop. The equation given which is based on the well known sounders and Brown equation Lowenstein (1961) can be used to estimate the maximum allowable superficial vapor velocity and hence the column area and diameter. U v
( l v) 1 (0.171l 2 0.27lt 0.047) 2 v t
Uv - must allowable vapor velocity Lt – plate spacing D – diameter D
4Vw pvUu
4.2.2 Selection of plate type Principal factors to consider when comparing the performance of bubble cup, sieve and valve plates are cost, capacity, operating, efficiency and pressure drop. Cost.
43
Bubble cup plates are appreciably more expensive than sieve or valve plates the relative cost will depend on the material of construction used for mild steel the ratio is; Bubble – cup: sieve: valve plates 3.0: 1.5: 1.0 Capacity. There is little difference in capacity rating of the three types (the diameter of the column required for a given flow rate) the ranking is sieve, valve and bubble.
Operating. By operating range it means the range of vapor and liquid rate over which the plate will operate satisfactorily (this is the most significant) some flexibility will always be require in an operating plant to allow for changes in production rate and to cover start – up and shut down conditions. The ratio of the highest to the lowest is termed as the turn down ratio. Bubble – Cups have a partial liquid seal and can therefore operate efficiently at very low vapor rates. Sieve plates rely on the flow of vapor through the hole to hold the liquid on the plate and can not operate at very low vapor rates. But with good design sieve plates can be designed to give a satisfactory operating range typically from 50 – 120% Valve plates are intended to give greater flexibility than sieve plates at a lower cost than bubble – cups. Efficiency. The Murphree efficiency of the three types of plates will be virtually the same when operating over their design flow range and no real distribution can be made between them. Pressure drop. The pressure drop for the design of columns. The plate pressure drop will depend on the detailed design of the plate but in general. Sieve plates give the
44
lowest pressure drop followed by valve plates with bubble – cup giving the highest. Summary Sieve plates are the cheapest and are satisfactory for most applications.
4.3 Material balance For an inlet temperature of 60°c the solubility is 56.10g HCl / 100g H2O Overall material balance around. Given that the amount of product is 150 ton/day 150ton *1000kg / ton 24hrs / day
6250kg / hr
As the basis and at a temperature of 60°c
45
Water X kg/hr HCl.2H2O (6250 kg/hr) HCl Y kg/hr
Ratio since the solubility at 60°c is 56.10g HCl/ 100g water. HCl: H2O 56.1: 100 0.561: 1 HCl in (y kg/hr) Total ratio = 1+ 0.561 = 1.561 y
0.561
* 6250 1.561 y 2246.2kg / hr
H2O into absorber (x kg/hr) x
1
* 6250 1.561 x 4003.84kg / hr
Assuming an efficiency of 95% for the HCl y will be as follows, 0.95 y 2246.2 y
2246.2
095 y 2364.4kg / hr
The HCl loss in the out let purge will therefore be.
46
2364.4 2246.2 118.2kg / hr
Summary of outcome of calculations diagram 4.2
4.4 Equation of the operating line Assuming is solubility
47
Lyn 1 Gxn 1 Gxn 1 Lyn Lyn 1 Lyn Gxn Gxn 1 L( yn 1 yn) G ( xn xn 1) L G
xn xn 1 yn 1 yn
48
Material balance Vyo Bx1 Lx1 B L
Based on the figure above Gy 0 Lxn 1 Gyn Lx1 Gyn Gy 0 Lxn 1 Lx1 Gyn Lxn 1 Gy 0 Lx1
Equation of the absorber is them and by Dividing through out by G
L L yn xn 1 y 0 x1 G G yn
L G
( xn 1 xn) y 0
Therefore equation of the operating line becomes yn
L G
x1 y 0
Were liquid L = 6250kg/hr and gas G = 2364.4 kg/hr Therefore the equation reduces to
6250 yn x1 y 0 2364 . 4 yn 2.64 x1 0.35
Values obtained from the above equation. And these are plotted on a graph. X
0.1
0.5
Y
0.389
0.546
49
The above graph gives two stages Mechanical design Based on the vapor flow rate of 2364.4kg/hr Therefore basis = 2364.4 kg/hr 4.4.1 Column diameter Calculation Most of the above factors that affect column operation are due to vapor flow conditions: either excessive or too low. Vapor flow velocity is dependent on column diameter. Weeping determines the minimum vapor flow required flooding determines the maximum vapor flow allowed, hence column capacity. Thus if the column diameter is not sized properly, the column will not perform well. Not only will operational problems occur, the desired operational duties will not be achieved.
50
State of Trays and Packings. Since actual number of trays required for a particular separation duty is determined by the efficiency of the plate and the packings, if packings are used. Thus any factors that cause a decrease in tray efficiencies are affected by fouling wear and tear, corrosion and the rates at which these occur depends on the properties of the liquid being processed. Thus appropriate material should be specified for tray construction. Weather Conditions. Most distillation columns are open to the atmosphere, although many of the columns are insulated, changing weather conditions can still affect the operation. Thus the reboiler must be appropriately sized to ensure that enough vapors can be generated during cold or windy spells and that it can be turned down sufficiently during hot seasons. The same applies to condensers. These are some of most important factors that can cause poor distillation column performance. Other factors include changing operating conditions and throughputs, brought about in changes in up stream conditions and changes in the demand of the products. All these factors including associates control systems should be considered at design stage because once a column is built and installed nothing much can be done to rectify the situation without incurring significant costs. The control of distillation column will be looked at later Column diameter Were Vm – is the maximum allowable flow pL – liquid density UL – vapor calculated Therefore the column diameter will be Column height (m) It is given by the number of plates x spacing + 2 x spacing The number of plates is 2
51
h 2 1.2 2 1.2 h 2.4 2.4 h 4.8m
dimensions diagram 4.3
Mechanical description table 4.2 Item
Actual calculated value Nearest number estimation
Column diameter (m) 0.9605m
1m
Column height (m)
4.8m
5m
Number of plates
2
2
4.5 Unit Costing and Evaluation 52
Ce = CSn Where Ce – purchased equipment cost C – cost constant from appendix 1 S – characteristic size diameter appendix 1 n – index for that type of equipment Data (adsorption column) Dc – 0.96309 m Hc – 4.8m Area of column therefore A (m2) A A
dh 4 0.96309 4.8 4
A 3.631m
2
Cost of shell Material factor at (s.s) stainless steel = 2.5 Cost = 7.5 x 1000 = $ 7 500 Therefore cost = 7500 x 2.5 = $ 18 750 Cost of the two plates From appendix 2 (fig 6.7) Bare cost = $ 1 600 Material factor – 1.7 Installed cost = bare cost + material factor = 1600 x 1.7 = $ 2 720 / plate = $ 2 720 x 2
53
= $ 5 440 Total cost for the absorption column will be Cost of shell + cost of plates = 18 750 + 5 440 = $ 24 190 Conversion in Kwacha based Bank Of Zambia exchange rate obtained from The Time of Zambia news paper dated 02/11/2005 $1 – K4 321.11 = 43211.1 x 24190 = K 104,527,650.9 = K 104.53 million
54
CHAPTER FIVE 5.0 SITE SELECTION AND SAFETY 5.1 Occurrences of raw materials
Sodium chloride occurs in solution in sea water.
Also occurs in dry deposits as rock salt and brine.
There are sodium chloride deposits in Kaputa and Mkushi districts in Zambia It can be acquired from neighboring Congo D.R., Mozambique and Angola.
Sulphuric acid can be obtained from Mbwana Mkubwa acid plant in Ndola or KCM acid plant in Kitwe.
5.2 Site selection The plant will best be located in Ndola, because of the following factors ;
It is a central town in terms of the acquisition of factors of production; raw materials, labor and transport net work.
Sulphuric acid will be acquired from Bwana Mkubwa and Konkola Copper (Kitwe) mines.
Sodium chloride deposits in Kaputa and Mkushi districts in Zambia are accessible and easily are transported to Ndola.
The energy source electricity, coal, diesel or oil is easily accessible because of the already existing national power grid and both the rail and road network.
It will be located near Kafubu River as source industrial water and for treated wastewater disposal.
S i n c e N d o l a i s a c en t r a l t o w n , o u r p r o d u c t a n d b y p r o d u c t c a n f i n d r e a d y market in the following indu stries:
The main product hydrochloric acid will find market in the mines, cement industry, textile industry, and leather industry.
The by-product, sodium sulphate which is used in glass manufacturing, for example the coming back into life of Kapiri glass factory.
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Sodium sulphate is used by detergent manufacturing companies as a ‘builder’ and in dyeing to standardize dyes, therefore Ndola is nearby for
marketing. 5.4 SAFTY FACTORS A report prepared By: U.S. Office of Air Quality Planning and Standards, Air Quality Strategies and Standards Division, Integrated Strategies and Economics Group, Research Triangle Park, North Carolina out lines the hazardous associated with HCl gas and acid. There are Regulatory issues such as national emission standards for hazardous air pollutants (NESHAP) for hydrochloric acid (HCl) production facilities, including HCl production at fume silica facilities. The EPA has identified these facilities as major sources of hazardous air pollutant (HAP) emissions; primarily HCl. Hydrochloric acid is associated with a variety of adverse health effects. These adverse health effects include chronic health disorders (e.g., effects on the central nervous system, blood, and heart) and acute health disorders (e.g., irritation of eyes, throat, and mucous membranes and damage to the liver and kidneys). The production processes NESHAP affect are processes that routes a gaseous stream that contains HCl to an absorber, thereby creating a liquid HCl product. Among these various processes are: i) Organic and inorganic chemical manufacturing processes that produce HCl as a byproduct; ii) The reaction of salts and sulfuric acid (Mannheim process); iii) The reaction of a salt, sulfur dioxide, oxygen, and water (Hargreaves process); iv) The combustion of chlorinated organic compounds; v) The direct synthesis of HCl through the burning of chlorine in the
presence of hydrogen It is important to note that most HCl production is as a by-product of other processes such as aliphatic and aromatic hydrocarbon chlorination, the
56
phosgenation of amines for isocyanates, and halogenations for making chlorofluorocarbons. Only about 5 percent of HCl is produced as primary product. Production from the U.S. HCl industry is roughly 4.2 million tons/year as of 1997. Most of the production is captive capacity; that is, the HCl is produced as an intermediate product to be used in final output. Given that about 5 percent of HCl produced in the U.S. is as primary product, this means that only about 200,000 tons of primary HCl output is generated in a typical year. It’s therefore imperative that safety attire be emphasized at all times, it the
responsibility of there company as well as the workers for such a plant to ensure that safety attire are worn, in addition to the regulatory bodies assigned to the tusk.
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CHAPTER SIX 6.0 PROJECT EVALUATION AND COST 6.1 Introduction The use of HCl in the production of other chemicals is the major way in which HCl is used in the U.S. Thirty percent of HCl produced in the U.S. goes into production of other chemicals. The next most common uses of HCl are steel pickling (20 percent), oil well acidizing (19 percent), and food processing (17 percent). Other uses for HCl include semiconductor production and regeneration of ion-exchange resins for water treatment. The U.S. imports and exports very little HCl. In 1997, the U.S. imported 85,000 tons of HCl, or only 2 percent of U.S. capacity. During that same year, the U.S. exported 60,000 tons of HCl or only 1.5 percent of U.S. production capacity. 3 hence, the U.S. imports as much or more HCl as it exports, but the trade balance is negligible compared to the output consumed within the U.S. Most of this trade is with Canada. The growth in U.S. HCl production averaged about 4.2 percent per year from 1993 to 1998. Growth has averaged roughly 3 percent per year from 1985 through 1998, so there has been some increase in production growth in the decade of the 1990's.4 Prices for HCl have increased considerably from 1992 to 1998. These prices generally ranged from $40/ton to $57/ton in 1992 and 1993, but rose to over $90/ton in 1998 due to railroad disruptions that occurred late in 1997 and continued into 1998. Projected growth is expected to be about 2.5 percent per year through 2003, though this amount could be an underestimate if continued strength in oil drilling leads to additional demand for HCl. As of 2003 the price of HCl acid stood at $92.25 /ton therefore the estimated revenue from the sales of HCl acid is about $92.25 /ton x 150 ton/day x 350 days/year = $4, 843, 125. /year In kwacha $4, 843, 125 X K4, 052.00 = K19, 624, 342, 500. /year
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6.2 Fixed and installation cost Using the factorial method of overall project estimation we can estimate the cost of this project and determine of it’s viable or not . This is based on the following,
Taking into consideration of the PCE at $ 36,340.87 item
PCE
f 1 – equipment erection
0.4
f 2 – Piping
0.7
f 3 – instrumentation
0.2
f 4 – Electrical
0.1
f 5 – Building process
0.15
f 6 – Utilities
0.5
f 7 – storage
0.15
f 8 – site development
0.05
f 9 – ancillary building
0.15
Total
3.40
PCE which is the purchased cost is total of cost of all the major units PCE = $ 36,340.87 PCE = K 417.88m 6.2.1 Physical plant cost (PPC) PPC = PCE (1+ f 1 + …. + f 9) PPC = 36,340 x 3.40 PPC = $ 123,556 6.2.2 fixed capital cost (FCC) Item
PPC
f 10 – design and engineering
0.3
f 11 – constructor’s fee
0.05
f 12 – contingency
0.1
Total
1.45
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FCC = PPC x 1.45 FCC = 123,556 x 1.45 FCC = $ 179,156.2 Simple mathematics 6.2.3 Cost (expenditure) Cost (expenditure) = $ 179,156.2 Or = 179,156.2 x 4053 = K 726,119,268. K 726.12m This is what it will cost just the project to start running and buy all the equipment needed. Plus variable cost which are about 10% of FCC = $ 17,215.62 Therefore total cost for one year = $ 196,371.82 6.2.4 Income per year From HCl sold in one year = $4, 843, 125. /year The by product sold in one year will be Na2SO4 = $ 60 / ton Production is at = 4.6 ton/hr or 39,744 ton/year Therefore 39744 ton x $ 60 = $ 2,384,640/ year Total income is $ 7, 227, 765/year The pay back time for this project will be in the first month of sales and production. See summary table below.
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Summary table cost evaluation table 6.1 Expenditure for given month Month/year Fixed cost $ 1m 2m
19,259.34 104,297.0
sales or income for given month
Variable cost $ Sales $
Operating cost $
963
0
0
10,430
0
0
3m
36,340.87
3,634
0
0
4m
50,800.00
25,343
602,313.75
12,046.28
5m
0
25,343
602,313.75
12,046.28
6m
0
25,343
602,313.75
12,046.28
2y
0
433,665.9
7,227,765
72,277.65
3y
0
433,665.9
7,227,765
72,277.65
4y
0
433,665.9
7,227,765
72,277.65
5y
0
433,665.9
7,227,765
72,277.65
6y
0
433,665.9
7,227,765
72,277.65
7y
0
433,665.9
7,227,765
72,277.65
45,173,531.25
469,804.74
Total cost
210,696.34
2,693,052.
Grand total Expenditure = $ 3,373,553.08 Profit
Up to year 7
Income = $ 45,173,531.25 $ 41,799,977.92
The pay back time for this project is 4 months just in the first month of sales and production. with the total investment being $ 263,112.62 for the plant to be complete and start running. Therefore it’s a viable project with a good pay back time .
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Process design summary table 6.2
FLOWRATE(kg/h)
ENERGY (kW)
TEMP. o C)
PRESSURE (atm)
Sodium chloride
3774.13
-14804
50
1.0
Sulphuric acid
3174.13
-7981.48
20
1.0
HCl(gas)
2363.4
-3322.04
537
1.5
Sodium sulphate
4599.2
-1248.87
527
1.0
FUEL (HFO)
1528.49
18214.57
FURNACE
6.5
COOLER Process Stream:
-
HCl (gas) (inlet)
2363.4
-
537
1.5
HCl (gas) (outlet)
2363.4
-
60
1.4
H2O (inlet)
3204
-
22
1.0
H2O (outlet)
3204
-
90
1.0
HCl (gas) in
2363.4
-
60
1.4
HCl (gas) out
2363.4
-
61
1.5
HCl(gas)
2363.4
-
60
1.5
H2O
4003.98
-
22
1.0
HCl (vent)
118.2
-
62
1.1
HCl(aq)
6250.0
-
60
1.5
Service Stream:
COMPRESSOR
ABSORBER
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Mechanical design and costs summary table 6.3
Item/ units
units
Diameter
m
7.28
Height
m
10.78
Length
m
-
0.02032
-
Area
m
-
72.4
-
# Tubes
Nil
-
106
-
# Plates
Nil
-
-
Material of
Nil
Refractory
Stone ware
Stainless
brick & steel
ceramics
steel
6,969.57
5,181.3
292.35
21.0
Construction
Furnace
Cooler
Absorber
0.0078
0.9605 4.8
2
Cost of unit
$
24,190
Cost of unit
K (m)
Sales HCl
K / year
19,629,185,625m
Sales Na2SO4
K / year
9,664,945,920m
Total sales
K
104.53
29,294,131,545m
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CONCLUSION To design a plant which will be producing 150tpd HCl (20 oBe’) from sodium chloride and H2SO4 (60oBe’), the salt -sulphuric acid process has been adopted because of the specified raw materials in the question. Although there are three other methods used to produce HCl but there use in the question is not favored because of other raw materials used in other processes. The design process adopted for this design question uses three (3) main units and service equipment namely the furnace (reactor), the cooler and the absorber and a compressor as a service unit. The muffle furnace is operated at 500 to 550oC in the work space heated by indirect heat from the combustion chamber operating at temperature as high as 1205 oC. The furnace is operated at 1atm. Heavy fuel oil is suitable for the muffle furnace. The reaction volume of the reactor is 52.8m3 and the residence time is 18.3minutes. The duty of the furnace is 18214.57kW. The cost of the furnace based on the energy demand is £419,695.96 (ZK 292,347,614.90). HCl gas leaves the furnace at 537oC temperature which exceeds that suitable absorption temperature of 60oC. For this particular design the cooling has been achieved by a tubular exchanger known as the Trombone Cooler and operates at atmospheric pressure. Total heat transfer area for the trombone cooler is 72.4m2 giving a total number of 106 tubes. The cost of the trombone cooler is £ 2,957.40 (ZK 21,000,000.00). At the cooler there is a pressure drop in the flow of HCl gas and therefore a compressor has been used to compensate for pressure loss prior to absorption form 1.4atm to 1.5atm. Gas absorption is carried out in a vertical countercurrent column. The solubility of HCl in water at 60°C is 56.10g HCl/ 100g water. The column diameter is 0.96m and height of the absorber is 4.8m and the number of plates is 2. The cost for the absorption column is K 104.53 million. Plant location has been influenced by raw material availability, other factors of production and main product and by-product market forecast. Other than importing sodium chloride from Congo DR, Mozambique and South Africa, it can
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also be sourced locally form Kaputa and Mkushi districts. Sulphuric acid will be sourced from Mbwana Mkubwa acid plant in Ndola or KCM acid plant in Kitwe. The plant will best be located in Ndola, because it central to sources of raw materials and product market. Environmental, safety and health (SHE) issues have been considered for instance plant location is far from the residential areas because of the dangers hydrogen chloride gas and acid pose on human tissue, potentially damaging respiratory organs, eyes, skin and intestine. Plant location near the stream which provides service water through out the year makes it possible to treat waste streams before they are disposed to the environment. Quality assurance of the project has been taken into account by incorporating a process control system to monitor that specific operating conditions are adhered to, namely, raw material flow rates, operating temperature and pressure at the furnace, the temperature of process and service streams at the cooler and the flow rates and temperatures of water and HCl gas at the absorber. HCl acids attracts a wider application in industry among these include; Regeneration of ion exchangers resins. pH control in food, pharmaceutical, drinking water and neutralizing waste streams. It is used to control the pH of the process streams. Pickling is an essential step in metal surface treatment. The byproduct sodium sulphate also attracts a wider application in industry among these include glass manufacturing, detergent manufacturing used as form builder and in some types of cement it is used for cement setting property a substitute for gypsum. Using the factorial method the overall project cost has been estimated taking into account the costs for equipment erection, piping, instrumentation, electrical, building process, utilities, storage, site development and ancillary building, to determine its viability. The total investment cost is $ 251,066.34 (ZK 1,017,320,809.68) and operating cost for plant start up is $12,046.28 (ZK 48,811,526.56). The plant grand total cost is $263,112.62 (ZK 1,066,132,336.24) The unit price of HCl is $92.25 /ton and the total HCl sold in one year is $4, 843, 125. /year (ZK 19,624,342,500.00/year). The unit price of Na 2SO4 (by-product) is
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$ 60 / ton and the total Na 2SO4 is $ 2,384,640/ year (ZK 9,662,561,280.00/year). The projected sales volume gives a grand total income of $ 7, 227, 765/year (ZK 29,286,903,780.00/year) . The pay back time for this project is 4 months just in the first month of production and sales. Therefore, this project is viable.
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RECOMMENDATIONS A detailed analysis of this report reveals that the costs of implementation of this project are outweighed by the various benefits that it has to offer hence the project team recommends this project as a viable project and worth undertaking. This project has the potential to add major growth to the Zambian economy. Therefore, if this project were to be undertaken, the project team recommends a subsidy, by government, on certain materials of construction. This can be achieved by reduction of import duty on those materials that have to be imported from outside the country. Additionally the team also recommends that government makes available research scholarships for Zambian chemical engineers to expose them to heavily industrialized countries where technology such as HCl production is a practical reality. This would result in highly competent Zambian engineers and hence get rid of the dependency on expatriates. As with any other plant design, this undertaking is heavily material dependent hence special factors pertaining to site selection have to be considered in order to optimize on transportation costs. The plant must be centrally located in terms of easy access to market as well as easy access to raw materials and thus Ndola has been recommended. Safety factors, however, should also to be observed as pertaining to the location of the plant, bearing in mind that hydrochloric acid is a hazardous air pollutant (HAP) associated with a variety of adverse health effects. Therefore, the plant must be located at a healthy distance away from residential areas to allow for dilution in case of accidents and effluent and emission standards should strictly be observed.
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To the department, we would first of all like to commend you for a job well done on the supervision and guidance of the projects, and at list we are now seeing an increase in the number of project the are practical and an involvement of industries in the projects, this is good as it will increase cooperation between the University and the industry. We would like to recommend the following; i) Some of the small scale projects done by students are manageable financially; the department should try and actually do some of these projects for income generation. ii) We recommend that the projects done by previous students be made available to the student by means of a department library or the library it self, after all what power does knowledge have if it can’t be shared.
All in all we commend you for job well done given the conditions.
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REFERENCE Chattopadhyah P, (1998) Unit Operations Of Chemical Engineering vol. 1. New Delhi: Khanna publishers.
Chattopadhyah P,(2001) Unit Operations Of Chemical Engineering vol. 2 New Delhi: Khanna publishers.
Corporate author, (2005) Chemical Engineering resource page , www.chemiresouces.com. Extracted 11/10/2005, 14:36. Corporate author , Energy Regulation Board news letter 2004 , government publishers. Lusaka Zambia. Corporate author, (2005), GRAPHITE HYDROCHLORIC ACID (HCL ACID) SYNTHESIS UNIT, http://www.ptcexports.com/index.htm, extracted 10/11/2005. 17:08 Corporate author Ministry of Energy, (2004), ZAMBIA ENERGY POLICY DOCUMENT 1994. Government publishers. Lusaka Zambia.
Corporate author, (2005), GRAPHITE FALLING FILM ABSORBERS, http://www.ptcexports.com/index.htm, extracted 10/11/2005. 17:56 Corporate Author, (1965) Encyclopedia Of Chemical Technology, New York 2nd Inter-science publishers, a division of John Wiley & sons Publishers inc, Consultant Michael J. Ervin and Associates and published in, (2005), FUEL FACTS .www.mjervin.com , Visit M.J. Ervin and Associates' website extracted 2710/2005 17:30
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Coulson and Richardson, (1999) Chemical Engineering vol. 2. 3rd edition, Butterworth: Oxford Heinemann, Jordan hill. Coulson and Richardsons, (1999) Chemical Engineering vol. 6. 3rd edition, Butter worth: Oxford Heinemann, Jordan hill. Kern Donald Q, (1997) Process Heat Transfer . 2nd edition, New Delhi: Tata McGraw – hill publishing company. Perry Robert H, (1999) Perry’s Chemical Engineers’ Handbook 7th edition, New York: McGraw-Hill Companies, Inc.
Tasmin Huda, Evaluation of the Design and Implementation of Training Programs, (a case study of Barclays Bank (Zambia) Thesis), C.B.U, school of business. Smith C, Julian (1976) Unit Operations Of Chemical Engineering , 3rd Edition, New York: McGraw-Hill Companies Inc.
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APPENDIX Appendix 1 Muffle Furnace
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