ABSTRACT
Majority of farmers in Nigeria harvest a large proportion of maize under conditions of high
humidity, and sadly enough, they lack equipment for drying the grains. The farmers store the
grains at conditions of high moisture and humidity which results in growth of organisms that
cause deterioration. One of the most important operations carried out for the preservation of
maize is dehydration. It helps to reduce the moisture content of the grains to a level in which
spoilage organisms are less active or inactive. Maize has high moisture content (between 30%
and 40% w.b.) as at the time of harvest. This amount of moisture present does not support
immediate storage, hence the need for dehydration.
Dehydration can be carried out in various ways. The conventional method of dehydration is
basically by sun drying. However, the limitations to the use of this method which includes
variation in drying temperature, no control over the source of drying as well as change in
climatic conditions has led to the fabrication of machines that could carry out drying operations
efficiently and without the above limitations.
This project focuses on the design, fabrication and evaluation of the characteristics of a C-class
fire-in-tube boiler. The design is carried out to specification with a design objective to deliver
high pressure steam that performs useful work in synchronization with the dehydration unit of
the existing pilot tray dryer for the dehydration of maize products from a moisture content of
23% to 10% and also for the study of the drying kinetics of the grains. The fabricated boiler
was capable of generating steam at a pressure of about 4 bar and temperature of about 150oC.
The throughput of the boiler is 40.5 litres/hr with a thermal efficiency of 71.64%.
TABLE OF CONTENTS
DEDICATION............................................................................................................................... iii
ACKNOWLEDGEMENT ............................................................................................................. iv
TABLE OF CONTENTS................................................................................................................ v
LIST OF TABLES......................................................................................................................... ix
LIST OF FIGURES ........................................................................................................................ x
ABSTRACT................................................................................................................................... xi
CHAPTER ONE ............................................................................................................................. 1
INTRODUCTION .......................................................................................................................... 1
1.1 Background ...................................................................................................................... 1
1.2 Objectives......................................................................................................................... 3
1.3 Scope of the Project Work ............................................................................................... 3
CHAPTER TWO ............................................................................................................................ 5
LITERATURE REVIEW ............................................................................................................... 5
2.1 Maize................................................................................................................................ 5
2.1.1 Importance and Uses of Maize ................................................................................. 7
2.1.2 Maize Drying ............................................................................................................ 8
2.1.3 Storage .................................................................................................................... 10
2.2 Boilers............................................................................................................................ 12
2.2.1 Fundamentals of Steam Generation ........................................................................ 16
2.2.2 Classification of Boilers.......................................................................................... 21
2.2.3 Types of Boilers...................................................................................................... 22
2.2.4 Working Pressure and Temperature........................................................................ 37
2.2.5 Fuel Type ................................................................................................................ 37
2.2.6 Key Components of Boilers.................................................................................... 38
2.2.7 Superheaters............................................................................................................ 39
2.2.8 Safety Issues............................................................................................................ 43
2.2.9 Best Practices for Efficient Operation .................................................................... 44
CHAPTER THREE....................................................................................................................... 47
METHODOLOGY........................................................................................................................ 47
3.1 Design Considerations.................................................................................................... 47
3.2 Components of the Fire-tube Boiler............................................................................... 47
3.3 Design Calculations........................................................................................................ 49
3.3.1 The Tube ...................................................................................................................... 49
3.3.2 The Shell ...................................................................................................................... 52
3.3.3 Fixed Tube Plate .......................................................................................................... 55
Design of the Fixed Tube Plate................................................................................................. 55
3.3.4 The Superheated Steam Chamber................................................................................ 56
3.4 Materials of Construction............................................................................................... 57
3.5 Lagging Materials .......................................................................................................... 57
3.6 Pressure Testing ............................................................................................................. 57
3.7 Product Selection............................................................................................................ 60
3.8 Moisture content determination of maize grains............................................................ 60
3.9 Determination of Physical properties of maize grains................................................... 60
3.10 Performance Evaluation of the Boiler ........................................................................ 61
3.10.1 Boiler Evaluation Using Gas...................................................................................... 61
3.10.2 Boiler Evaluation Using Biomass (Charcoal)............................................................ 62
3.10.3 Throughput of the Boiler............................................................................................ 62
3.10.4 Thermal Efficiency of the Boiler ............................................................................... 62
3.11 Performance Evaluation of the Pilot tray dryer ................................................................ 63
3.12 Cost Estimate .................................................................................................................... 67
CHAPTER FOUR......................................................................................................................... 69
RESULTS AND DISCUSSIONS................................................................................................. 69
4.1 Moisture Content............................................................................................................ 69
4.2 Determination of Some Physical Properties of the maize grains................................... 69
4.3 Thermal Efficiency of the Boiler ................................................................................... 71
4.4 Throughput of the Boiler................................................................................................ 71
4.5 Pressure Variation in the Boi0ler ................................................................................... 71
4.5.1 Pressure Variation during Gas-Firing .......................................................................... 71
4.5.2 Pressure variation during Charcoal-fired evaluation ................................................... 71
4.6 Temperature variations during Evaluation..................................................................... 79
4.6.1 Temperature variation in the Boiler during Gas-Fired Evaluation .............................. 79
4.7 Temperature variation in the pilot tray dryer during drying .......................................... 88
4.8 Drying Kinetics of the maize grains in the Pilot Tray Dryer ......................................... 92
4.9 Discussions..................................................................................................................... 95
CHAPTER FIVE........................................................................................................................... 97
CONCLUSION AND RECOMMENDATION............................................................................ 97
5.1 Conclusion...................................................................................................................... 97
5.2 Recommendations.......................................................................................................... 98
REFERENCES.............................................................................................................................. 99
APPENDIX I............................................................................................................................... 102
APPENDIX 2.............................................................................................................................. 103
APPENDIX 3.............................................................................................................................. 104
APPENDIX 4.............................................................................................................................. 105
APPENDIX 5.............................................................................................................................. 106
APPENDIX 6.............................................................................................................................. 107
APPENDIX 7.............................................................................................................................. 108
APPENDIX 8.............................................................................................................................. 109
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