Combustion And Gasification in Fluidized Beds

by Basu; Prabir

• ISBN13: 9780849333965
• ISBN10: 0849333962
• Edition: 1st
• Format: Hardcover
• Copyright: 2006-02-17
• Publisher: CRC Press

Summary

Besides being one of the best Clean Coal Technologies, fluidized beds are also proving to be the most practical option for biomass conversion. Although the technology is well established, the field lacks a comprehensive guide to the design and operating principles of fluidized bed boilers and gasifiers. With more than 30 years of research and industrial experience, Prabir Basu answers this pressing need with Combustion and Gasification in Fluidized Beds.This book is a versatile resource that explains how fluidized bed equipment works and how to use the basic principles of thermodynamics and fluid mechanics in design while providing insight into planning new projects, troubleshooting existing equipment, and appreciating the capabilities and limitations of the process. From hydrodynamics to construction and maintenance, the author covers all of the essential information needed to understand, design, operate, and maintain a complete fluidized bed system. It is a must for clean coal technology as well as for biomass power generation.Beginning with a general introduction to fossil or biofuel conversion choices, the book surveys hydrodynamics, fundamentals of gasification, combustion of solid fuels, pollution aspects including climate change mitigation, heat transfer in fluidized beds, the design and operation of bubbling and circulating fluidized bed boilers, and various supporting components such as distributor grates, feeding systems, and gas-solid separators.

Table of Contents

Introduction	1	(20)
Background	1	(3)
Fluidized Bed Equipment	4	(6)
Applications	4	(1)
Fluidized Bed Gasifiers	5	(1)
Fluidized Bed Boilers	6	(3)
Application in Cement Industries	9	(1)
Features of Fluidized Beds	10	(3)
Advantages of Fluidized Bed Boilers	10	(2)
Features Specific to CFB Boiler	12	(1)
Fluidized Bed and Other Technology Options	13	(8)
Technological Options for Generation of Power from Solid Fuels	13	(2)
Improved Firing	15	(1)
Combined-Cycle Plants	16	(2)
Cost Implications	18	(1)
References	19	(2)
Hydrodynamics	21	(38)
Regimes of Fluidization	21	(14)
Packed Beds	25	(1)
Bubbling Fluidized Beds	25	(4)
Slugging	29	(1)
Turbulent Beds	29	(1)
Bubbling to Turbulent Transition	29	(2)
Terminal Velocity of a Particle	31	(4)
Freeboard and Furnace Heights	35	(1)
Fast Fluidized Bed	35	(7)
Characteristics of Fast Beds	35	(2)
Transition to Fast Fluidization	37	(5)
Dense Suspension Up-Flow	42	(1)
Hydrodynamic Regimes in a CFB	42	(1)
Difference in Operating Regimes of CFB Boilers and Reactors	43	(1)
Hydrodynamic Structure of Fast Beds	43	(9)
Axial Voidage Profile	43	(5)
Lateral Distribution of Voidage in a Fast Bed	48	(4)
Gas--Solid Mixing	52	(1)
Gas--Solid Slip Velocity	52	(1)
Dispersion	52	(1)
Scale-Up	53	(6)
Circulating Fluidized Bed	53	(1)
Bubbling Fluidized Bed	54	(1)
Cyclone	54	(1)
Nomenclature	55	(1)
Greek Symbols	56	(1)
Dimensionless Numbers	56	(1)
References	57	(2)
Fluidized Bed Gasification	59	(44)
Types of Gasifiers	60	(3)
Entrained Bed	61	(1)
Fluidized Bed	62	(1)
Spouted Bed	62	(1)
Fixed/Moving Bed	62	(1)
Theory	63	(6)
Pyrolysis or Devolatilization	64	(2)
Combustion	66	(1)
Gasification	66	(1)
Composition of Gas Yield	67	(2)
Effect of Operating Parameters on Gasification	69	(2)
Boudouard Reaction	69	(1)
Water--Gas	69	(1)
Methanation	69	(2)
Effect of Feed Properties on Gasification	71	(3)
Fuel Reactivity	71	(1)
Volatile Matter	72	(1)
Ash	73	(1)
Moisture	73	(1)
Fluidized Bed Gasification	74	(3)
Comparison of Bubbling and Circulating Fluidized Bed Gasifiers	75	(1)
Types of Fluidized Bed Gasifiers	75	(2)
Examples of Some Fluidized Bed Gasifiers	77	(6)
Winkler Gasifier	77	(2)
KRW Gasifier	79	(1)
Spouted Bed Partial Gasifier	79	(1)
Foster Wheeler Atmospheric CFB Gasifier	80	(1)
Battelle/Columbus Indirect Gasifier	81	(1)
Halliburton KBR Transport Reactor	82	(1)
Carbon Dioxide Acceptor Process	82	(1)
Gas Cleaning	83	(2)
Sulfur and Other Chemical Contaminants Removal	83	(1)
Tar Removal	84	(1)
Particulate Removal	85	(1)
Design Considerations	85	(11)
Gasifier Efficiency	85	(1)
Equivalence Ratio	86	(2)
Gas Composition	88	(1)
Energy and Mass Balance	89	(1)
Bed Materials	89	(1)
Gasifier Sizing	90	(5)
Alternative Design Approach	95	(1)
Modeling of Fluidized Bed Gasification	96	(7)
Appendix 3A	97	(1)
Estimating Equilibrium Gas Composition	97	(2)
Appendix 3B	99	(1)
An Example of a Fluidized Bed Biomass Gasifier	99	(1)
Nomenclature	99	(1)
Greek Symbols	100	(1)
References	100	(3)
Combustion	103	(32)
Stages of Combustion	103	(14)
Heating and Drying	103	(1)
Devolatilization	104	(2)
Volatile Combustion	106	(1)
Char Combustion	107	(2)
Burning Rate of Char in Fluidized Beds	109	(6)
Communition Phenomena during Combustion	115	(2)
Factors Affecting Combustion Efficiency	117	(3)
Feed Stock	117	(2)
Operating Conditions	119	(1)
Combustion in Bubbling Fluidized Bed Boilers	120	(2)
Recirculation of Fly Ash	120	(1)
Effect of Design Parameters on Combustion Efficiency	120	(2)
Combustion in Circulating Fluidized Bed Boilers	122	(5)
Combustion of Char Particles	123	(2)
Effect of Cyclone Design on Combustion Efficiency	125	(1)
Some Combustion Design Considerations	125	(2)
Performance Modeling	127	(1)
Biomass Combustion	127	(8)
Agglomeration	129	(1)
Fouling	130	(1)
Corrosion Potential in Biomass Firing	130	(1)
Nomenclature	130	(1)
Greek Symbols	131	(1)
Dimensionless Numbers	132	(1)
References	132	(3)
Emissions	135	(38)
Air Pollution	135	(6)
Pollutants	136	(5)
Emission Standards	141	(1)
Sulfur Dioxide Emission	141	(18)
Chemical Reactions	142	(4)
Reactions on Single Sorbent Particles	146	(2)
Reactivity of Sorbents	148	(2)
Sulfur Capture in Fluidized Beds	150	(4)
Simple Model for Sulfur Capture in CFB Boilers	154	(3)
Selection of Sorbent	157	(2)
Nitrogen Oxide Emission	159	(3)
Sources of NOx	159	(1)
Methods of Reduction of NOx Emissions	159	(2)
NOx Emission from CFB	161	(1)
Nitrous Oxide Emission	162	(2)
Mechanism of Formation of N2O in CFB	162	(1)
Effects of Operating Parameters on N2O	163	(1)
Reduction of N2O	164	(1)
Mercury Emission	164	(1)
Sorbent Injection	164	(1)
Electro-Catalytic Oxidation	164	(1)
Precombustion Technologies	165	(1)
Carbon Monoxide Emission	165	(1)
Carbon Dioxide Emission	165	(1)
Emission of Trace Organies	166	(1)
Particulate Emission	166	(7)
Ash Characteristics	166	(2)
Nomenclature	168	(1)
Greek Symbols	169	(1)
References	169	(4)
Heat Transfer	173	(38)
Gas-to-Particle Heat Transfer	173	(5)
Gas-to-Particle Heat Transfer Equations	173	(3)
Heating of Gas and Solids in the Fast Bed	176	(2)
Heat Transfer in Circulating Fluidized Beds	178	(11)
Mechanism of Heat Transfer	178	(1)
Theory	179	(5)
Experimental Observations in a CFB Boiler	184	(3)
Effect of Vertical Fins on the Walls	187	(2)
Heat Transfer in Bubbling Fluidized Bed	189	(12)
Mechanistic Model	190	(5)
Experimental Observations in Bubbling Fluidized Beds	195	(2)
Heat-Transfer Correlation in Bubbling Beds	197	(1)
Use of Design Graphs	197	(3)
Calculation Based on Tables	200	(1)
Freeboard Heat Transfer in Bubbling Fluidized Beds	201	(1)
Heat Transfer in Commercial-Size CFB Boilers	202	(9)
Heat Transfer to the Walls of Commercial CFB Boilers	202	(1)
Wing Walls	202	(1)
Heat-Transfer Variation along the Furnace Height	203	(1)
Circumferential Distribution of Heat-Transfer Coefficient	203	(2)
Nomenclature	205	(2)
Greek Symbols	207	(1)
Dimensionless Numbers	207	(1)
References	207	(4)
Bubbling Fluidized Bed Boiler	211	(42)
Description of a BFB Boiler	211	(4)
Feedstock Preparation and Feeding	211	(2)
Air and Gas Handling	213	(1)
Ash and Emission Systems	213	(2)
Steam Generation System	215	(1)
Combustion Chamber	215	(1)
Features of BFB Boilers	215	(1)
Advantages	215	(1)
Limitations	216	(1)
Thermal Design of Bubbling Fluidized Bed Boilers	216	(12)
Overall Heat Balance of the Boiler	216	(3)
Boiler Efficiency	219	(2)
Energy Balance in Dense Bubbling Bed	221	(2)
Heat Balance of Boiler Components	223	(3)
Mass Flow Rates of Fuel and Air	226	(1)
Gas-Side Heat Balance	226	(2)
Combustion in Bubbling Fluidized Bed	228	(6)
Coal Combustion in BFB Boilers	228	(2)
Minimization of Combustible Losses in BFB Combustors	230	(4)
Furnace Design	234	(8)
Basic Design of Furnace	235	(3)
Part-Load Operations	238	(2)
Other Operating Conditions	240	(2)
Start-Up Procedure and Control	242	(4)
Start-Up Procedure	243	(1)
Control of BFB Boiler	243	(3)
Some Operational Problems and Remedies	246	(2)
Erosion of In-Bed Components	246	(2)
Design of Feed Systems for BFB Bed Boiler	248	(5)
Nomenclature	249	(2)
Greek Symbols	251	(1)
References	251	(2)
Circulating Fluidized Bed Boiler	253	(46)
General Arrangement	253	(4)
Air System	253	(2)
Flue Gas Stream	255	(1)
Solid Stream	255	(1)
Water--Steam Circuit	255	(2)
Types of CFB Boilers	257	(2)
Boilers without Bubbling Bed Heat Exchangers	257	(1)
Boilers with Bubbling Fluidized Bed Heat Exchanger	258	(1)
Boilers with Inertial or Impact Separators	259	(1)
Boilers with Vertical, Noncircular Cyclones	259	(1)
Other Types	259	(1)
Non-CFB Solid Circulation Boilers	259	(4)
Circo-Fluid Boilers	259	(1)
Low-Solid Circulation Boiler	260	(1)
Circulating Moving Bed Boiler	260	(3)
Combustion in a Circulating Fluidized Bed Furnace	263	(1)
Design of CFB Boilers	264	(7)
Combustion Calculations	264	(1)
Heat Balance	264	(2)
Mass Balance	266	(1)
Flow Split	266	(1)
Control of Bed Inventory	267	(3)
Some Operating Issues	270	(1)
Furnace Design	271	(6)
Furnace Cross-Section	273	(1)
Width and Breadth Ratio	273	(3)
Furnace Openings	276	(1)
Design of Heating Surfaces	277	(10)
Effect of Fuel Type on Furnace Heat Load	278	(2)
Heat Absorption in the External Heat Exchanger	280	(1)
Heat Absorption in the Furnace and Rest of the Boiler	280	(5)
Heat Balance around a CFB Loop	285	(2)
Auxiliary Power Consumption	287	(1)
Control of CFB Boilers	287	(4)
Part-Load Operation	287	(2)
Load Control Options	289	(2)
Supercritical CFB Boiler	291	(8)
Supercritical Operation	292	(1)
Vertical vs. Wrapped Tube Arrangement	292	(1)
Low Heat Flux	293	(1)
Cost Advantage	293	(1)
Nomenclature	293	(3)
Greek Symbols	296	(1)
References	296	(3)
Material Issues	299	(38)
Material Selection Criteria	299	(2)
Structural Requirements	299	(1)
Heat-Transfer Duty	300	(1)
Erosion Potential	301	(10)
Basics of Erosion	301	(3)
Types of Erosion	304	(1)
Erosion in Bubbling Fluidized Beds	304	(2)
Options for Reduction of Erosion in Bubbling Beds	306	(1)
Erosion in CFB Boilers	307	(4)
Corrosion Potentials	311	(7)
Corrosion Mechanisms	312	(1)
Examples of Fire-Side Corrosion	312	(1)
Chemistry of Fire-Side Corrosion of Heating Surfaces	313	(2)
Chlorine Corrosion	315	(1)
Vanadium Corrosion	316	(1)
Prevention of High-Temperature Corrosion	316	(1)
Erosion--Corrosion	317	(1)
Fouling and Deposit Formation	318	(1)
Steels Used in Fluidized Bed Boilers	318	(2)
Carbon and Alloy Steels	318	(2)
Refractory and Insulations	320	(13)
Importance of Lining	320	(1)
Properties of Refractory	320	(1)
Types of Refractory	321	(1)
Types of Insulation	322	(2)
Anchors	324	(1)
Design Considerations of Lining	325	(1)
Areas of Refractory Use in Fluidized Bed Boilers	325	(4)
Failure Analysis	329	(2)
Refractory Maintenance	331	(2)
Expansion Joints	333	(4)
Nomenclature	334	(1)
Greek Symbols	334	(1)
References	334	(3)
Solid Handling Systems for Fluidized Beds	337	(22)
Solid Handling Systems	337	(4)
Fossil Fuel Plants	337	(2)
Municipal Solid Waste	339	(2)
Biomass Handling Systems	341	(1)
Feeding of Harvested Fuels	341	(1)
Feeding of Nonharvested Fuels	341	(1)
Feed System for Bubbling Beds	342	(10)
Types of Feeders	342	(5)
Mode of Feeding in Bubbling Beds	347	(3)
Feed Point Allocation	350	(2)
Feed System for Circulating Fluidized Beds	352	(1)
Fuel Feed Ports	352	(1)
Limestone Feed System	353	(1)
Design of Pneumatic Transport Lines for Solids	353	(6)
Pressure Drop in a Pneumatic Transport Line	353	(2)
Design of a Pneumatic Injection System	355	(1)
Fuel Splitter	355	(2)
Nomenclature	357	(1)
Greek Symbols	357	(1)
References	357	(2)
Air Distribution Grate	359	(22)
Distributor Plates	359	(7)
Plate-Type Distributor	360	(2)
Nozzle-Type Distributor	362	(1)
Sparge Pipe Distributor	363	(1)
Distributor Grids for CFB	364	(1)
Distributor Grids for Bubbling Beds	365	(1)
Operation of Distributors	366	(2)
What Causes Nonuniform Fluidization	366	(2)
Design Methods	368	(3)
Design Procedure for Bubbling Fluidized Beds	368	(2)
Design Procedure for Circulating Fluidized Beds	370	(1)
Practical Considerations	371	(10)
Plenum or Air Box	372	(1)
Sealing of Distributor	373	(1)
Attrition	374	(1)
Back-Flow of Solid	375	(2)
Opening and Closing of Nozzles	377	(1)
Erosion and Corrosion of Nozzles	378	(1)
Nomenclature	379	(1)
Greek Symbols	379	(1)
References	380	(1)
Gas--Solid Separators	381	(36)
Cyclones	381	(24)
Types of Cyclone	382	(3)
Theory	385	(1)
Critical Size of Particles	385	(5)
Working of Cyclones for CFB Combustors or Gasifiers	390	(2)
Pressure Drop through a Cyclone	392	(2)
Cyclone Collection Efficiency	394	(5)
Reentrainment of Solids	399	(1)
Cyclone Geometry	400	(1)
Effect of the Vortex Finder	400	(2)
Practical Considerations for CFB Cyclones	402	(3)
Impact Separator	405	(5)
Features and Types	405	(1)
Separation through Impaction	406	(1)
Separation through Interception	407	(2)
Grade Efficiency of Impingement Collectors	409	(1)
Some Types of Impact Separators	409	(1)
Inertial Separators	410	(7)
Separation through Gravity Settling	411	(1)
Cavity Separator	411	(1)
Design Steps	411	(2)
Nomenclature	413	(2)
Greek Symbols	415	(1)
References	415	(2)
Solid Recycle Systems	417	(22)
Types of Nonmechanical Valves	417	(4)
Loop-Seal	418	(2)
L-Valve	420	(1)
V-Valve	420	(1)
Principles of Operation	421	(5)
Solid Flow from Standpipe to Recycle Chamber	422	(2)
Flow of Solids through Recycle Chamber	424	(2)
Design of Loop-Seal	426	(5)
Pressure Balance	426	(1)
Size of Loop Seal	427	(1)
Air-Flow through Loop Seat	428	(3)
Design of L-Valve	431	(2)
Maximum Solid Flow Rate	432	(1)
Additional Design Considerations	433	(1)
Practical Considerations	433	(6)
Plugging of Loop-Seal	433	(1)
Pressure Surge	434	(1)
Avoiding Loop-Seal Plugging	434	(1)
Nomenclature	435	(1)
Greek Symbols	436	(1)
References	436	(3)
Appendix 1 Characteristics of Solid Particles	439	(6)
Solid Particles	439	(3)
Equivalent Diameters	439	(1)
Sphericity (φ)	440	(1)
Mean Particle Size and Its Measurement	440	(2)
Packing Characteristics	442	(1)
Particle Classification	442	(3)
Group C	443	(1)
Group A	443	(1)
Group B	444	(1)
Group D	444	(1)
Nomenclature	444	(1)
References	444	(1)
Appendix 2 Stoichiometric Calculations	445	(8)
Chemical Reactions	445	(1)
Air Required	446	(1)
Sorbent Requirement	446	(1)
Solid Waste Produced	446	(1)
Gaseous Waste Products	447	(1)
Carbon Dioxide	447	(1)
Water Vapor	448	(1)
Nitrogen	448	(1)
Oxygen	448	(1)
Sulfur Dioxide	448	(1)
Fly Ash	448	(1)
Heating Value of Fuels	448	(5)
Nomenclature	450	(1)
Reference	451	(2)
Appendix 3 Simplified Model for Sulfur Capture	453	(2)
Nomenclature	454	(1)
Appendix 4 Tables of Design Data	455	(6)
Index	461