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Design, Construction And Simulation of Maize Cobs Fluidized Bed Combustor

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Design, Construction And Simulation of Maize Cobs Fluidized Bed Combustor.

ABSTRACT

This study adopts the theory of fluidisation to design a combustor suitable for use in the ruralcommunities of Nigeria.

The Combustor, which will use sand particles as bed material, will burnmaize cobs supplied at 5kg/h to generate heat energy for thermal applications including steamgeneration.

Like most African countries, lack of adequate electricity supply in Nigeria has hamperedeconomic activities, with less than 40% of the rural community connected to the national griddue to high cost of rural electrification exercise.

Furthermore, the rural population continuouslyrely on direct burning of solid biomass (like fuel wood) as means of obtaining much needed heatenergy for basic applications like cooking and heating, constituting an environmental nuisance.

The study contends that using a bubbling fluidised bed combustor, it is possible to reduce energypoverty 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 fluidisedbed combustion including its history, principle of fluidization and advantage of fluidized bedsover conventional methods of burning biomass.

TABLE OF CONTENTS

Title Page…………………………………………………………………………………………………………………….i
Declaration………………………………………………………………………………………………………………….ii
Certification……………………………………………………………………………………………………………….iii
Dedication………………………………………………………………………………………………………………….iv
Acknowledgements …………………………………………………………………………………………………….. 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 fluidised bed combustor ……………………………………………………………………..8
2.4.2 Pressurized fluidised bed combustor ………………………………………………………………………8
2.4.3 Bubbling fluidised bed………………………………………………………………………………………….9
2.4.4 Circulating fluidised 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 fluidisation 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 fluidised 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 modelling 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 rapid depletion of non-renewable energy resources (fossilfuels). This demand, along with high crude oil prices are key factors driving renewable energydevelopment and utilisation (Omer, 2013).

Renewable energy is the energy which comes from natural sources such as the sun, wind, waterand plant or animal organic matter. It is replenished by natural processes at a rate equal to orfaster than the rate at which it is consumed.

Biomass, a renewable energy source, refers tobiological material from living or recently living plants and animals. It can either be useddirectly, or converted into other energy products such as biofuel .

While the discovery of fossilfuels has led to a decline in the use of biomass, recent data has indicated renewed efforts towardsconversion of biomass to bioenergy either by combustion, gasification, conversion of biomass tobiofuels or biomass briquettes.

Biomass resources include dedicated energy crops, forestresidues, municipal, animal and agricultural waste (DOE, 2007).Combustion of solid biomass fuels accounts for over 90% of the energy generated from biomassworldwide.

This is mostly common in developing countries, where biomass combustion providesbasic energy for cooking and heating in rural households (ECN, 2006). These traditionalapplications are relatively inefficient and promote environmental degradation.

REFERENCES

Amitin, A. V., Matyushin, I. G., and Gurevic, D. A. (1968). Dusting in the Space above theBed In Converters with a Fluidized Catalyst Bed. Chemistry and Technology ofFuels and Oils Volume 4, Issue 3, pp 181-184.

Basu, P. (2006). Combustion and Gasification in Fluidised Beds.Retrieved June 14, 2012, fromnet library database.

Biomass energy conversion overview [Image].2012. Retrieved from http://www.globalproblemsglobalsolutionsfiles.org/gpgs_files/pdf/UNF_Bioenergy/UNF_Bioenergy_5.pdf

Bird, R.B., Stewart, W.E. and Lightfoot, E.N. (1960). Transport Phenomena. John Wiley &Sons, New York, Chapter 6: Interphase Transport in isothermal Systems(2002).

Bontoux, L. (1999). The Incineration of Waste in Europe: Issues and Perspectives. Institute forProspective Technological Studies Seville w.t.c., Isla de la Cartuja, s/n, E-41092 Sevilla

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.

Den Hartog, J. P.(1952). Strength of Materials Cylinders and Curved Bars.Pp 136Department of Energy. (2007). Biomass Basics: The Facts About Bioenergy. EERE InformationCenter 1-877-EERE-INF (1-877-337-3463) eere.energy.gov/informationcenter

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.

CSN Team.

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