ABSTRACT
This study adopts the of fluidization to design a combustor suitable for use in the rural communities of Nigeria. The Combustor, which will use sand particles as bed material, will burn maize cobs supplied at 5kg/h to generate heat for thermal applications including steam generation.
Like most African countries, the lack of adequate electricity supply in Nigeria has hampered economic activities, with less than 40% of the rural connected to the national grid due to the high cost of rural electrification exercises.
Furthermore, the rural continuously relies on the direct burning of solid biomass (like fuelwood) as means of obtaining much-needed energy for basic applications like cooking and heating, constituting an environmental nuisance.
The study contends that using a bubbling fluidized bed combustor, it is possible to reduce energy poverty in the rural areas of Nigeria while complying with the sustainable development goals.
Chapter one discusses the background of the study, identifying the objectives, research problems, justification, and scope of the work.
Chapter two reviews the previous documentation on fluidized bed combustion including its history, principle of fluidization, and advantage of fluidized beds over conventional methods of burning biomass.
TABLE OF CONTENTS
Title Page…………………………………………………………………………………………………………………….i
Declaration………………………………………………………………………………………………………………….ii
Certification……………………………………………………………………………………………………………….iii
Dedication………………………………………………………………………………………………………………….iv
Acknowledgments…………………………………………………………………………………………………….. v
Abstract…………………………………………………………………………………………………………………….. vi
Table of Contents ……………………………………………………………………………………………………..viii
List of Tables…………………………………………………………………………………………………………….xii
List of Figures…………………………………………………………………………………………………………..xiii
List of Plates……………………………………………………………………………………………………………. xiv
List of Appendices…………………………………………………………………………………………………….. xv
Nomenclature…………………………………………………………………………………………………………… xvi
1.0 INTRODUCTION…………………………………………………………………………………………………1
1.1Background …………………………………………………………………………………………………………..1
1.2Statement of the Problem……………………………………………………………………………………….2
1.3Justification of the Research…………………………………………………………………………………..3
1.4Aim and Objectives of the Study …………………………………………………………………………….4
1.5 Scope…………………………………………………………………………………………………………………….5
2.0 LITERATURE REVIEW ……………………………………………………………………………………..6
2.1Background History……………………………………………………………………………………………….6
2.2Renewable Solid Fuels……………………………………………………………………………………………6
2.3Characteristics of Fluidised Bed Combustion………………………………………………………….7
2.4Types of Fluidised Bed Combustors………………………………………………………………………..8
2.4.1Atmospheric fluidized bed combustor ……………………………………………………………………..8
2.4.2 Pressurized fluidized bed combustor ………………………………………………………………………8
2.4.3 Bubbling fluidized bed………………………………………………………………………………………….9
2.4.4 Circulating fluidized bed……………………………………………………………………………………….9
2.5 Advantages of Fluidised Bed Combustion…………………………………………………………….10
2.6 Applications of Fluidised Bed Combustion …………………………………………………………..10
2.7Principle of Fluidisation ……………………………………………………………………………………….11
2.8Fluidisation Regimes…………………………………………………………………………………………….11
2.9Review of Related Works……………………………………………………………………………………..12
2.10 Theoretical Background…………………………………………………………………………………….14
2.10.1 Thermal stress analysis……………………………………………………………………………………..14
2.10.2 Geldart’s Classification……………………………………………………………………………………..15
2.11Energy Potential in Maize Cobs ………………………………………………………………………….17
2.12Brief Description of ERGUN 6.2 Software …………………………………………………………..18
3.0 MATERIALS AND METHOD ……………………………………………………………………………19
3.1 Description of Bubbling Fluidised Bed Combustor……………………………………………….19
3.2Materials……………………………………………………………………………………………………………..20
3.2.1 Maize cobs………………………………………………………………………………………………………..20
3.3 Material Selection ……………………………………………………………………………………………….20
3.3.1 Fluidised bed cylinder…………………………………………………………………………………………21
3.3.2 Distributor…………………………………………………………………………………………………………21
3.3.3 Cyclone …………………………………………………………………………………………………………….21
3.3.4 Feed hopper……………………………………………………………………………………………………….21
3.3.5Insulator …………………………………………………………………………………………………………….22
3.4Design Analysis…………………………………………………………………………………………………….22
3.4.1 Bed temperature …………………………………………………………………………………………………22
3.4.2 Bed depth ………………………………………………………………………………………………………….23
3.4.3 Bed material and particle size ………………………………………………………………………………23
3.4.4 Minimum fluidization velocity …………………………………………………………………………….24
3.4.5 Terminal velocity……………………………………………………………………………………………….24
3.4.6 Superficial velocity …………………………………………………………………………………………….25
3.4.7 Gas viscosity ……………………………………………………………………………………………………..26
3.4.8 Gas density………………………………………………………………………………………………………..26
3.4.9 Bed voidage ………………………………………………………………………………………………………26
3.4.10 Design of gas distributor……………………………………………………………………………………27
3.4.11 Distributor grids for bubbling fluidized beds………………………………………………………..27
3.4.11.1 Pressure drop…………………………………………………………………………………………………28
3.4.11.2 Orifice velocity ……………………………………………………………………………………………..28
3.4.11.3 Orifice number………………………………………………………………………………………………29
3.4.12 Distributor thickness…………………………………………………………………………………………29
3.4.13 Plenum chamber……………………………………………………………………………………………….29
3.4.14 Bed expansion design ……………………………………………………………………………………….30
3.4.15 Bubble velocity ………………………………………………………………………………………………..31
3.4.16 Bubble diameter……………………………………………………………………………………………….31
3.4.17 Volume fraction of bubbles in the bed…………………………………………………………………32
3.4.18 Transport disengagement height (TDH)………………………………………………………………33
3.4.19 Cylinder thickness…………………………………………………………………………………………….34
3.4.20 Insulation thickness…………………………………………………………………………………………..34
3.4.21 Entrainment……………………………………………………………………………………………………..35
3.4.21.1 Design of cyclone ………………………………………………………………………………………….35
3.4.21.2 Cyclone diameter …………………………………………………………………………………………..35
3.5Design Consideration……………………………………………………………………………………………37
3.5.1 Calorific value……………………………………………………………………………………………………37
3.5.2 Combustion temperature……………………………………………………………………………………..37
3.5.3 Minimization of combustible losses ……………………………………………………………………..37
3.5.4 Gravity chute feed hopper……………………………………………………………………………………38
3.5.5 Bed material and bed height ………………………………………………………………………………..38
3.5.6 Power Requirement…………………………………………………………………………………………….38
3.6Design Calculations………………………………………………………………………………………………39
3.7 Equipment ………………………………………………………………………………………………………….39
3.8Construction ………………………………………………………………………………………………………..40
3.8.1 Cylinder…………………………………………………………………………………………………………….40
3.8.2 Distributor grid…………………………………………………………………………………………………..41
3.8.3 Cyclone …………………………………………………………………………………………………………….41
3.8.4 Feed hopper……………………………………………………………………………………………………….42
3.8.5 Blower………………………………………………………………………………………………………………42
3.8.6 Insulation…………………………………………………………………………………………………………..42
3.9Simulation of Fluidised Bed ………………………………………………………………………………….42
3.9.1 Introduction……………………………………………………………………………………………………….42
3.9.2 Parameters for fluidized bed simulation ………………………………………………………………..44
3.9.3 Data requirement………………………………………………………………………………………………..46
4.1Ignition/Testing Procedure …………………………………………………………………………………..49
4.2Bed Temperature …………………………………………………………………………………………………49
4.3 Flue Gas Temperature…………………………………………………………………………………………51
4.4Volume Flow Rate………………………………………………………………………………………………..53
4.5 Results Of Simulation………………………………………………………………………………………….54
4.5.1 Particle ……………………………………………………………………………………………………………..54
4.5.2 Grid ………………………………………………………………………………………………………………….55
4.5.3 Bubbling……………………………………………………………………………………………………………56
4.5.4 Reh diagram………………………………………………………………………………………………………57
4.5.5 Entrainment……………………………………………………………………………………………………….58
4.5.6 Cyclone …………………………………………………………………………………………………………….59
4.5.7 Fluidised bed modeling and expert analysis………………………………………………………….60
4.5.8 Comparing calculated and simulated values…………………………………………………………..61
4.5.9 Estimated Cost of a Fluidised Bed System…………………………………………………………….61
5.0 SUMMARY, CONCLUSION AND RECOMMENDATION…………………………………63
5.1Summary……………………………………………………………………………………………………………..63
5.2Conclusion …………………………………………………………………………………………………………..63
5.3 Recommendation…………………………………………………………………………………………………64
REFERENCES…………………………………………………………………………………………………………65
APPENDICES………………………………………………………………………………………………………….72
INTRODUCTION
Background
Global demand for energy has led to the rapid depletion of non-renewable energy resources (fossil fuels). This demand, along with high crude oil prices are key factors driving renewable energy development and utilization (Omer, 2013).
Renewable energy is the energy that comes from natural sources such as the sun, wind, water, and plant or animal organic matter. It is replenished by natural processes at a rate equal to or faster than the rate at which it is consumed.
Biomass, a renewable energy source, refers to biological material from living or recently living plants and animals. It can either be used directly or converted into other energy products such as biofuel.
While the discovery of fossil fuels has led to a decline in the use of biomass, recent data have indicated renewed efforts towards the conversion of biomass to bioenergy either by combustion, gasification, conversion of biomass to biofuels, or biomass briquettes.
Biomass resources include dedicated energy crops, forest residues, municipal, animal, and agricultural waste (DOE, 2007). Combustion of solid biomass fuels accounts for over 90% of the energy generated from biomass worldwide.
This is most common in developing countries, where biomass combustion provides basic energy for cooking and heating in rural households (ECN, 2006). These traditional applications are relatively inefficient and promote environmental degradation.
REFERENCES
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Basu, P. (2006). Combustion and Gasification in Fluidised Beds.Retrieved June 14, 2012, fromnet library database.
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Darton, R.C., LaNauze, R.D., Davidson, J.F. and Harrison,D.(1977). Bubble Growth Due toCoalescence in Fluidised Beds. TransInstChem Eng. 55:274-280.
Davidson, J.F. and Harrison, D.(1963).Fluidised Particles. Cambridge University Press,Cambridge.
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Dibofori-Orji, A.N. and Braide S.A. (2013). Emission of Nox, Sox and Co from the Combustionof Vehicle Tyres in an Abattoir. Journal of Natural Sciences Research Vol.3, No.8, 2013.
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