ABSTRACT

 

This research work presents the design concept, construction and performance evaluation of a 10kg capacity portable crucible furnace which uses charcoal as fuel. The 10kg crucible furnace was designed, constructed using locally available engineering materials mild steel sheet of 3 mm, mild steel (angle iron) of 5 mm, scrap aluminum, asbestos, clay sand, stainless steel sheet of 2 mm, stainless steel pipe of 2 mm and wood charcoal. An electrical kitchen scale with model No ek5055 and thermocouple with model No Kane-may km 340 were used to measure the fuel consumption and heat generated respectively. The furnace produced the total heat QT = 67,943.16 kJ, and supplied the heat required to melt 10 kg of aluminum from room temperature to melting temperature QT = 35,859.13 kJ in a duration of 1hr 33min, the total heat absorbed by the furnace components was QFC = 25,425.44 kJ and the heat transferred to the crucible was QC = 14,118.72
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kJ. The efficiency of the furnace was achieved at 76% dividing heat used by total heat supplied and multiplied by 100. The furnace is suitable for use both in the rural and urban areas for casting of different types of aluminum. The furnace is environmental friendly without health hazards to the workers and can be moved from one place to another unlike the local one. The results of the test of the furnace performance show that it consumes 3kg of charcoal in 1hr 33mins to melt 10kg of aluminum.

 

TABLE OF CONTENTS

Title Page —————————————————————————————————- i Approval Page ———————————————————————————————— iii Acknowledgements —————————————————————————————— iv Dedication —————————————————————————————————– v Declaration ————————————————————————————————— vi Certification ————————————————————————————————- vii Table of Contents —— ———————————————————————————– viii List of Tables———————————————————————————————— xvi List of Figures———————————————————————————————- xvii List of plates ———————————————————————————————–xviii List of Abbreviations————————————————————————————– xix Abstract —————————————————————————————————- xxii CHAPTER ONE
1.0 INTRODUCTION————————————————————————————-1
1.1 BACKGROUND OF THE WORK—————————————————————-1
1.2 Statement of Research Problems——————————————————————- 3
1.3 Aim and Objectives————————————————————————————3
1.4 Significance of the Study——————————————————————————3
1.5 Justification of the Work—————————————————————————–4
1.6 Scope of the Work————————————————————————————-4
CHAPTER TWO 2.0 LITERATURE REVIEW—————————————————————————- 5 2.1 Crucible—————————————————————————————————6
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2.2 Furnace————————————————————————————————— 7 2.2.1 Types of furnace—————————————————————————————- 7 2.2.2 Classification of furnace——————————————————————————–8 2.2.3 Crucible furnace—————————————————————————————–8 2.3.0 Fuels——————————————————————————————————-9 2.3.1 Types of fuels——————————————————————————————-10 2.4.0 Review of the past work on charcoal————————————————————-10 2.4.1 The charcoal fuel—————————————————————————————11 2.4.2 Types of charcoal————————————————————————————– 11 2.4.3 Uses of charcoal—————————————————————————————-11 2.5.0 Aluminum and aluminum alloys—————————————————————— 12 2.5.1 Aluminum———————————————————————————————–13 2.5.2 Cast Aluminum—————————————————————————————–13 2.5.3 Aluminum casting alloy——————————————————————————-13 2.6.0 Mode of heat Transfer—————————————————————————— 14 2.6.1 Conduction———————————————————————————————-15 2.6.2 Convection———————————————————————————————-17 2.6.3 Radiation————————————————————————————————18 CHAPTER THREE 3.0.0 Material and methodology————————————————————————- 20 3.1.0 Materials and Material selections—————————————————————–20 3.1.1 Materials for the furnace unit————————————————————————-20 3.1.2 Materials for Blower———————————————————————————–21 3.1.3 Material for air pipe———————————————————————————– 21 3.1.4 Material used for insulators————————————————————————– 21 3.1.4.1 Asbestos———————————————————————————————- 21 3.1.4.1a Types of Asbestos———————————————————————————-21 3.1.4.1b Use of Asbestos———————————————————————————— 22
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3.1.4.1c Asbestos health hazards————————————————————————— 22 3.1.4.2 Clay sand——————————————————————————————— 22 3.1.4.2 Uses of clay soil————————————————————————————- 23 3.1.5 The charcoal fuel————————————————————————————– 23 3.1.5.1 Calorific value of the charcoal——————————————————————– 23 3.2 Methodology——————————————————————————————- 24 3.2.1 Engineering design———————————————————————————–24 3.2.2 Design consideration———————————————————————————25 3.2.3 General layout of the furnace———————————————————————–25 3.3.0 Design Criteria and theories———————————————————————-25 3.3.1 Determination of the minimum thickness of the furnace wall——————————— 25 3.3.2 Determination of the maximum allowable working pressure for the furnace—————-25 3.3.3 Determination of the stresses setup in the furnace———————————————–26 3.3.4 Determination of the thermal stress set-up in the furnace wall——————————– 26 3.3.5 Investigation of the effect of internal pressure on the furnace dimension——————–26 3.3.6 The change in length of the furnace—————————————————————-26 3.3.7 The change in diameter of the furnace————————————————————-26 3.3.8 Change in volume of the crucible—————————————————————— 27 3.4.0 Combustion chamber——————————————————————————-27 3.4.1 The amount of fuel burnt per hour—————————————————————–27 3.4.2 Determination of the distance between the fire grate and the crucible port——————28 3.4.3 The thermal load of the combustion chamber—————————————————-28 3.4.4 Thermal load of the fire grate———————————————————————- 28 3.4.5 Determination of the design height of the combustion chamber—————————— 28 3.5 Chemical Analysis of the fuel———————————————————————–29 3.5.1 The amount of air required per kg of the fuel for complete combustion——————— 29 3.5.2 Determination of the mass of the products of combustion ————————————-30 3.5.3 Determination of the CO2 content of the flue gas ———————————————–30
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3.6 Determination of the required Fan capacity—————————————————- 30 3.6.1 Determination of the power required to drive the fan——————————————-31 3.6.2 Determination of the peripheral discharge velocity——————————————— 31 3.6.3 Determination of the discharge velocity pressure ———————————————–31 3.6.4 Total dynamic head developed by the fan ——————————————————- 31 3.7 Fan Design———————————————————————————————-31 3.7.1 Determination of the fan major diameter——————————————————— 31 3.7.2 Determination of the fan minor diameter ——————————————————– 32 3.7.3 Determination of the fan blade width major —————————————————–32 3.7.4 Determination of the fan blade width minor —————————————————– 32 3.7.5 Determination of the fan blade inlet angle ——————————————————- 32 3.7.6 Determination of the fan casing outlet velocity ————————————————- 32 3.7.7 Determination of the fan casing outlet area ——————————————————32 3.8 Fan casing design calculation———————————————————————– 32 3.8.1 Fan casing inlet area ———————————————————————————32 3.8.2 Determination of the fan casing outlet diameter ————————————————-33 3.8.3 Determination of the fan casing inlet diameter ————————————————– 33 3.8.4 Determination of the fan case width ————————————————————– 33 3.9.0 Belt and pulley ————————————————————————————– 33 3.9.1 Pulley ————————————————————————————————–33 3.9.2 Types of pulley system —————————————————————————– 34 3.9.3 Belt —————————————————————————————————- 34 3.9.4 Uses of belt drive ————————————————————————————35 3.9.5 Types of belts —————————————————————————————- 35 3.9.6 Belt and pulley calculation ————————————————————————-36 3.9.7 Determination of the length of a open belt ——————————————————- 36 3.9.8 Determination of the angle of contact or lap —————————————————- 36 3.9.9 Determination of the velocity ratio of a belt drive ———————————————–36
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3.9.10 Determination of the peripheral velocity of the belt on the driving pulley——————37 3.9.11 Determination of the speed ratio —————————————————————– 37 3.9.12 Determination of the house power ————————————————————– 37 3.9.13 Determination of the torque ———————————————————————–37 3.9.14 Determination of the initial tension ————————————————————- 37 3.10.0 Thermal insulators for the furnace————————————————————37 3.10.1 Determination of the effectiveness of insulators ———————————————- 38 3.11.0 Determination of the melting heat————————————————————–39 3.11.1 Determination of the sensible heat of the metal ———————————————– 39 3.11.2 Determination of the enthalpy of fusion ——————————————————– 39 3.11.3 Determination of the super heat value ———————————————————–39 3.11.4 Heat transferred to the wall of the furnace ——————————————————39 3.11.5 Determination of the heat transferred to the crucible furnace ——————————–40 3.11.6 Determination of the total heat absorbed by the furnace components ———————–40 3.11.7 Determination of the total heat required for a melt ——————————————- 40 3.11.8 Determination of the total heat required to be supplied by the furnace ———————41 3.11.9 Determination of the total useful heat ———————————————————–41 3.11.10 Efficiency of the furnace ————————————————————————-41 3.12.0 Determination of the heat losses in the furnace———————————————-41 3.12.1 Loss from the heat carried by dry flue gas ——————————————————41 3.12.2 Loss due to evaporation of hydrogen ————————————————————41 3.12.3 Loss from the evaporation of fuel moisture —————————————————–42 3.12.4 Loss from moisture in the air ——————————————————————— 42 3.12.5 Loss due to unconsumed fuel ———————————————————————42 3.12.6 Radiation loss in the furnace ———————————————————————-42 3.13.0 Performance of the furnace———————————————————————-42 3.13.1 Theoretical thermal efficiency of the furnace ————————————————–42 3.14.0 The energy Balance——————————————————————————–43
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3.14.1 Heat balance in the furnace ———————————————————————–43 3.15.0 Design Calculations——————————————————————————–44 3.15.1 Calculation of minimum thickness of the furnace ———————————————44 3.15.2 Calculation of maximum working pressure of the furnace ———————————–44 3.15.3 Calculation of thermal stresses set up in the furnace walls ———————————–45 3.15.4 Calculation of change in the furnace dimension ———————————————–45 3.15.5 Calculation for Combustion chamber ———————————————————– 47 3.15.6 Calculation for the distance between fire grate and crucible ———————————48 3.15.7 Calculation for the thermal load of the combustion chamber ——————————–48 3.15.8 Calculation for the thermal load of the fire grates ———————————————48 3.15.9 Calculation for the height of the combustion chamber ————————————— 49 3.15.10 Calculation for the amount air required for complete combustion ———————— 49 3.15.11 Calculation for the mass of the products of combustion ————————————49 3.15.12 Determination of the total air flow required in the furnace ———————————50 3.15.13 Calculation of fan air discharge capacity —————————————————– 51 3.15.14 Calculation for the power required to drive the fan —————————————– 51 3.15.15 Calculation of the fan peripheral discharge velocity —————————————- 52 3.15.16 Calculation for the fan discharge velocity pressure —————————————– 52 3.15.17 Total dynamic head developed by the fan —————————————————–52 3.16.1 Calculation for the fan major diameter —————————————————— 52 3.16.2 Calculation for the fan minor diameter ———————————————————-52 3.16.3 Calculation for the fan blade width major —————————————————— 53 3.16.4 Calculation for the fan blade width minor ——————————————————53 3.16.5 Calculation for the fan blade inlet angle ———————————————————53 3.17.1 Calculation for the fan casing outlet velocity ————————————————54 3.17.2 Calculation for the fan casing outlet area ——————————————————- 54 3.17.3 Calculation for the fan casing inlet area ———————————————————54 3.17.4 Calculation for the fan casing outlet diameter ————————————————–54
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3.17.5 Calculation for the fan casing inlet diameter ————————————————– -54 3.17.6 Calculation for the fan casing width ————————————————————-55 3.18.1 Calculation for the belt pitch ——————————————————————-55 3.18.2 Calculation for the angle of contact or lap ——————————————————55 3.18.3 Calculation for the velocity ratio of a belt drive ———————————————– 55 3.18.4 Calculation for the speed ratio ——————————————————————–56 3.18.5 Calculation for the initial tension in the belt —————————————————-56 3.18.6 Calculation for the torque transmitted ———————————————————–56 3.19.0 Calculation for the effectiveness of the insulator ——————————————-57 3.20.1 Calculation for heat required for melt of aluminum ——————————————-58 3.20.2 Calculation for heat required for melt of kilograms of aluminum —————————61 3.21.0 Calculation for the heat transfer to the furnace ——————————————–63 3.21.1 Calculation for the heat transferred to the crucible ——————————————–64 3.21.2 Total heat absorbed by furnace components ————————————————— 64 3.21.3 Heat for melt of nkg of aluminum ————————————————————— 64 3.21.4 Total heat supplied by the furnace ————————————————————— 65 3.21.5 Total used heat ————————————————————————————- 65 3.21.6 Number of calories needed for the melt ———————————————————65 3.21.7 Number of grams needed to give number calories of energy ——————————– 65 3.22.1 Heat supplied to the furnace by fuel ———————————————————-65 3.22.2 Heat output of the furnace ————————————————————————-66 3.23.0 Calculation of heat losses————————————————————————-66 3.23.1 Calculation for the loss of heat carried by dry flue gas —————————————-66 3.23.2 Calculation for loss of heat from evaporation of fuel moisture ——————————66 3.23.3 Calculation for loss of heat due to moisture in the air —————————————- 66 3.23.4 Calculation for loss of heat due to unconsumed fuel ——————————————67 3.23.5 Radiation heat loss in the furnace —————————————————————-67 3.23.6 Calculation for the uncounted heat loss ———————————————————67
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3.23.7 Calculation for the furnace efficiency ———————————————————–68 3.24.0 Construction —————————————————————————————–70 3.25.0 Fabrication process———————————————————————————–7 3.26.0 Components assembling process—————————————————————-78 3.27.0 Comparison of the designed crucible furnace and conventional type———————–81 3.28.0 Testing of the furnace and operating procedure ————————————————82 3.28.1 Measurements of kilograms and temperature ————————————————– 82 3.28.2 The charcoal fuel ———————————————————————————- 82 3.28.3 Scrap aluminum ———————————————————————————— 82 3.28.4 Temperature Measurements ——————————————————————–82 3.29.0 Experimental procedure ————————————————————————-83 3.29.1 The environment ————————————————————————————83 3.29.2 Sequence of the testing process ——————————————————————-84 3.29.3 Starting the furnace———————————————————————————84 3.29.4 Furnace on testing ———————————————————————————-85 3.30.0 The amount of heat generated———————————————————————85 3.31.0 The amount of fuel used ————————————————————————– 85 3.32.0 Duration for complete melting of aluminum ————————————————— 86 3.33.0 Cost Analysis—————————————————————————————-87 CHAPTER FOUR 4.1.0 Experimental Results ——————————————————————————–88 CHAPTER FIVE 5.0 Discussion of results————————————————————————————94 5.1 No – load ————————————————————————————————94 5.2 With load test ——————————————————————————————-94 5.3 Continuous test method ——————————————————————————- 94 CHAPTER SIX 6.0 Conclusion——————————————————————————————— 98
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6.1 Recommendations———————————————————————————— 99 6.2 References——————————————————————————————– 100 6.3 Appendix I furnace pictures————————————————————————-103 6.4 Appendix II experimental results tables———————————————————–106 6.5 Appendix III working drawing ——————————————————————– 107

 

 

CHAPTER ONE

1.0 INTRODUCTION
1.1 BACKGROUND. Foundry technology is practiced in both urban and rural areas of Nigeria; the local foundry man digs a hole on the ground to take the shape of an oven, using coal or charcoal as fuel and makes use of a clay or metal pot as the crucible. A blower is used to supply the air needed for the combustion process. Plate 1.1 shows the shape of the local furnace used in local foundries.
PLATE 1.1 A typpical furnace. Source: Muchia market 4/11/2011 The local foundry people use the crucible furnace for making of casting of different objects such as machines parts, domestic cooking pots of different sizes, serving spoons, fraying pans, etc. The foundry people were having problems working with local type of crucible furnace such as excessive fuel consumption, excessive heat radiation to the operator, time consuming for operation and excessive heat lost in the system. An attempt has been made to improve on the local method of melting being practiced by local foundry men in Nigeria, considering availability of materials, high demand of their products, reduction of cost of production and attraction of youth to foundry practice.
Kulla (2007) pointed out that due to inefficient burning and poor heat transfer; fuel wood that would have been sufficient for 10-33 years is consumed annually. Based on this and other reasons he conducted research on how to reduce the wood consumption in domestic cooking, this has indicated the need to improve the efficiency of the crucible furnace used in local foundries,
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thus reducing the quantity of charcoal consumed. Another serious problem is the emission of combustion products which result in respiratory diseases (Kulla, 2004). Komolafe, (1992) improved on the crude method of melting by foundry men by designing and constructing a gas fired crucible type furnace making use of locally sourced materials. It is noticed that gas as a source of energy can be very hazardous and is not as common as coal or charcoal in use. The gas furnace is found in big industries only and ordinary foundry men do not know much about gas, and gas is not readily available and cheap in every part of the country compared to charcoal. The Industrial Development Centre Zaria foundry uses a gear driven blower to supply air needed for combustion to the coal or charcoal oven but since the oven or furnace is not covered, much heat is lost, as in the case of those used by local foundry men. Therefore there is need for improvement in the combustion efficiency and conservation of the heat generated. Charcoal is available in all parts of the country and is cheap. An improved furnace can be designed and fabricated to improve on the locally used furnaces. The charcoal fired crucible furnace will use a manually operated pulley driven blower. The crucible furnace is the oldest form of foundry technology which has been used and has varied with time. The designs reflect the purposes for which they are used and there are regional variations. The earliest crucible form derives from the sixth/fifth millennium B.C. (Roberts et al; 2009). A typical local crucible furnace is shown in Plate 1.2
PLATE 1.2 a typical old type crucible furnace used in the foundries. Source: Muchia Market 4/11/2011
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1.2 STATEMENT OF THE PROBLEM The major problems associated with the old type open crucible furnaces used in the local foundries are:-
i. The foundry man is exposed to heat and combustion products which are harmful to his health.
ii. More than half of the heat escapes due to the open nature of the local furnace.
iii. These open crucible furnaces contribute to ecological problems, global warming and environmental degradation due to high demand of wood for charcoal production.
iv. The process consumes large quantities of fuel (charcoal) due to its low combustion efficiency and high heat loss.
1.3 AIM AND OBJECTIVES OF THE WORK The aim of the work is to improve on the technology of local foundry men in the melting of aluminum. The research is expected to come up with a portable, safe and economical crucible furnace, which is going to be used in small scale casting industries with maximum efficiency (i.e. efficient use of heat energy with minimum loss of heat energy). Specific objectives of this research are as follows:
i. To design a portable charcoal fired crucible type furnace that can melt 10Kg of aluminum.
ii. To construct the furnace using local materials.
iii. To test the furnace constructed.
iv. To carry out performance evaluation of the furnace.
1.4 SIGNIFICANCE OF THE STUDY The design and construction of a charcoal fired crucible furnace is significant in the following ways
i. It will contribute significantly to the effort to convert scrap aluminum into useful products
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ii. It will also contribute significantly to the effort in the development of indigenous technology especially in the production industries,
iii. It will contribute significantly in the training of students in casting practice.
iv. It will improve working conditions of foundry men and encourage youths to venture into the foundry work.
1.5 JUSTIFICATION OF THE RESEARCH This field of research is very important to small scale industries, considering the number of people in the industry. Each shop has the capacity of 10 to 15 people in the industry. It is important to work on this topic to improve the working environment and provide safety to the operator (foundry man) by designing and constructing a safer crucible furnace. 1.6 SCOPE OF THE WORK The scope of the research work will be limited to:
i. Designing of the essential components that make up the charcoal fuel crucible furnace for melting 10 kg of aluminum and these include;
a. Crucible
b. Furnace
c. Safety cover
d. Frame
e. Blower and rotating mechanisms
ii. Construction of these components.
iii. Assembly of the various components including accessories.
iv. Testing of the device on a load of 10 kg of aluminum and observing working conditions and the duration of the work.
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