Chapter 1 Introduction ......................................... 1
1.1 Background ................................................. 1
1.2 Fluidized Bed Equipment .................................... 4
1.2.1 Applications ........................................ 4
1.2.2 Fluidized Bed Gasifiers ............................. 5
1.2.3 Fluidized Bed Boilers ............................... 6
1.2.4 Application in Cement Industries .................... 9
1.3 Features of Fluidized Beds ................................ 10
1.3.1 Advantages of Fluidized Bed Boilers ................ 10
1.3.2 Features Specific to CFB Boiler .................... 12
1.4 Fluidized Bed and Other Technology Options ................ 13
1.4.1 Technological Options for Generation of Power
from Solid Fuels ................................... 13
1.4.2 Improved Firing .................................... 15
1.4.3 Combined-Cycle Plants .............................. 16
1.4.4 Cost Implications .................................. 18
References ................................................ 19
Chapter 2 Hydrodynamics ....................................... 21
2.1 Regimes of Fluidization ................................... 21
2.1.1 Packed Beds ........................................ 25
2.1.2 Bubbling Fluidized Beds ............................ 25
2.1.3 Slugging ........................................... 29
2.1.4 Turbulent Beds ..................................... 29
2.1.5 Bubbling to Turbulent Transition ................... 29
2.1.6 Terminal Velocity of a Particle .................... 31
2.1.7 Freeboard and Furnace Heights ...................... 35
2.2 Fast Fluidized Bed ........................................ 35
2.2.1 Characteristics of Fast Beds ....................... 35
2.2.2 Transition to Fast Fluidization .................... 37
2.2.3 Dense Suspension Up-Flow ........................... 42
2.3 Hydrodynamic Regimes in a CFB ............................. 42
2.3.1 Difference in Operating Regimes of CFB Boilers
and Reactors ....................................... 43
2.4 Hydrodynamic Structure of Fast Beds ....................... 43
2.4.1 Axial Voidage Profile .............................. 43
2.4.2 Lateral Distribution of Voidage in a Fast Bed ...... 48
2.5 Gas-Solid Mixing .......................................... 52
2.5.1 Gas-Solid Slip Velocity ............................ 52
2.5.2 Dispersion ......................................... 52
2.6 Scale-Up .................................................. 53
2.6.1 Circulating Fluidized Bed .......................... 53
2.6.2 Bubbling Fluidized Bed ............................. 54
2.6.3 Cyclone ............................................ 54
Nomenclature .............................................. 55
Greek Symbols .......................................... 56
Dimensionless Numbers .................................. 56
References ................................................ 57
Chapter 3 Fluidized Bed Gasification .......................... 59
3.1 Types of Gasifiers ........................................ 60
3.1.1 Entrained Bed ...................................... 61
3.1.2 Fluidized Bed ...................................... 62
3.1.3 Spouted Bed ........................................ 62
3.1.4 Fixed/Moving Bed ................................... 62
3.2 Theory .................................................... 63
3.2.1 Pyrolysis or Devolatilization ...................... 64
3.2.2 Combustion ......................................... 66
3.2.3 Gasification ....................................... 66
3.2.4 Composition of Gas Yield ........................... 67
3.3 Effect of Operating Parameters on Gasification ............ 69
3.3.1 Boudouard Reaction ................................. 69
3.3.2 Water-Gas .......................................... 69
3.3.3 Methanation ........................................ 69
3.4 Effect of Feed Properties on Gasification ................. 71
3.4.1 Fuel Reactivity .................................... 71
3.4.2 Volatile Matter .................................... 72
3.4.3 Ash ................................................ 73
3.4.4 Moisture ........................................... 73
3.5 Fluidized Bed Gasification ................................ 74
3.5.1 Comparison of Bubbling and Circulating Fluidized
Bed Gasifiers ...................................... 75
3.5.2 Types of Fluidized Bed Gasifiers ................... 75
3.6 Examples of Some Fluidized Bed Gasifiers .................. 77
3.6.1 Winkler Gasifier ................................... 77
3.6.2 KRW Gasifier ....................................... 79
3.6.3 Spouted Bed Partial Gasifier ....................... 79
3.6.4 Foster Wheeler Atmospheric CFB Gasifier ............ 80
3.6.5 Battelle/Columbus Indirect Gasifier ................ 81
3.6.6 Halliburton KBR Transport Reactor .................. 82
3.6.7 Carbon Dioxide Acceptor Process .................... 82
3.7 Gas Cleaning .............................................. 83
3.7.1 Sulfur and Other Chemical Contaminants Removal ..... 83
3.7.2 Tar Removal ........................................ 84
3.7.3 Particulate Removal ................................ 85
3.8 Design Considerations ..................................... 85
3.8.1 Gasifier Efficiency ................................ 85
3.8.2 Equivalence Ratio .................................. 86
3.8.3 Gas Composition .................................... 88
3.8.4 Energy and Mass Balance ............................ 89
3.8.5 Bed Materials ...................................... 89
3.8.6 Gasifier Sizing .................................... 90
3.8.7 Alternative Design Approach ........................ 95
3.9 Modeling of Fluidized Bed Gasification .................... 96
Appendix 3А ............................................... 97
Estimating Equilibrium Gas Composition ................. 97
Appendix 3В ............................................... 99
An Example of a Fluidized Bed Biomass Gasifier ......... 99
Nomenclature .............................................. 99
Greek Symbols ......................................... 100
References ............................................... 100
Chapter 4 Combustion ......................................... 103
4.1 Stages of Combustion ..................................... 103
4.1.1 Heating and Drying ................................ 103
4.1.2 Devolatilization .................................. 104
4.1.3 Volatile Combustion ............................... 106
4.1.4 Char Combustion ................................... 107
4.1.5 Burning Rate of Char in Fluidized Beds ............ 109
4.1.6 Communition Phenomena during Combustion ........... 115
4.2 Factors Affecting Combustion Efficiency .................. 117
4.2.1 Feedstock ......................................... 117
4.2.2 Operating Conditions .............................. 119
4.3 Combustion in Bubbling Fluidized Bed Boilers ............. 120
4.3.1 Recirculation of Fly Ash .......................... 120
4.3.2 Effect of Design Parameters on Combustion
Efficiency ........................................ 120
4.4 Combustion in Circulating Fluidized Bed Boilers .......... 122
4.4.1 Combustion of Char Particles ...................... 123
4.4.2 Effect of Cyclone Design on Combustion
Efficiency ........................................ 125
4.4.3 Some Combustion Design Considerations ............. 125
4.4.4 Performance Modeling .............................. 127
4.5 Biomass Combustion ....................................... 127
4.5.1 Agglomeration ..................................... 129
4.5.2 Fouling ........................................... 130
4.5.3 Corrosion Potential in Biomass Firing ............. 130
Nomenclature ............................................. 130
Greek Symbols ......................................... 131
Dimensionless Numbers ................................. 132
References ............................................... 132
Chapter 5 Emissions .......................................... 135
5.1 Air Pollution ............................................ 135
5.1.1 Pollutants ........................................ 136
5.1.2 Emission Standards ................................ 141
5.2 Sulfur Dioxide Emission .................................. 141
5.2.1 Chemical Reactions ................................ 142
5.2.2 Reactions on Single Sorbent Particles ............. 146
5.2.3 Reactivity of Sorbents ............................ 148
5.2.4 Sulfur Capture in Fluidized Beds .................. 150
5.2.5 Simple Model for Sulfur Capture in CFB Boilers .... 154
5.2.6 Selection of Sorbent .............................. 157
5.3 Nitrogen Oxide Emission .................................. 159
5.3.1 Sources of NOx .................................... 159
5.3.2 Methods of Reduction of NOx Emissions ............. 159
5.3.3 NOx Emission from CFB ............................. 161
5.4 Nitrous Oxide Emission ................................... 162
5.4.1 Mechanism of Formation of N2O in CFB .............. 162
5.4.2 Effects of Operating Parameters on N2O ............ 163
5.4.3 Reduction of N2O .................................. 164
5.5 Mercury Emission ......................................... 164
5.5.1 Sorbent Injection ................................. 164
5.5.2 Electro-Catalytic Oxidation ....................... 164
5.5.3 Precombustion Technologies ........................ 165
5.6 Carbon Monoxide Emission ................................. 165
5.7 Carbon Dioxide Emission .................................. 165
5.8 Emission of Trace Organics ............................... 166
5.9 Particulate Emission ..................................... 166
5.9.1 Ash Characteristics ............................... 166
Nomenclature ............................................. 168
Greek Symbols ......................................... 169
References ............................................... 169
Chapter 6 Heat Transfer ...................................... 173
6.1 Gas-to-Particle Heal Transfer ............................ 173
6.1.1 Gas-to-Particle I leal Transfer Equations ......... 173
6.1.2 Heating of Gas and Solids in the Fast Bed ......... 176
6.2 Heat Transfer in Circulating Fluidized Beds .............. 178
6.2.1 Mechanism of Heat Transfer ........................ 178
6.2.2 Theory ............................................ I79
6.2.3 Experimental Observations in a CFB Boiler ......... 184
6.2.4 Effect of Vertical Fins on the Walls .............. 187
6.3 Heat Transfer in Bubbling Fluidized Bed .................. 189
6.3.1 Mechanistic Model ................................. 190
6.3.2 Experimental Observations in Bubbling Fluidized
Beds .............................................. 195
6.3.3 Heat-Transfer Correlation in Bubbling Beds ........ 197
6.3.4 Use of Design Graphs .............................. 197
6.3.5 Calculation Based on Tables ....................... 200
6.4 Freeboard Heat Transfer in Bubbling Fluidized Beds ....... 201
6.5 Heat Transfer in Commercial-Size CFB Boilers ............. 202
6.5.1 Heat Transfer to the Walls of Commercial CFB
Boilers ........................................... 202
6.5.2 Wing Walls ........................................ 202
6.5.3 Heat-Transfer Variation along the Furnace
Height ............................................ 203
6.5.4 Circumferential Distribution of Heat-Transfer
Coefficient ....................................... 203
Nomenclature ............................................. 205
Greek Symbols ......................................... 207
Dimensionless Numbers ................................. 207
References ............................................... 207
Chapter 7 Bubbling Fluidized Bed Boiler ...................... 211
7.1 Description of a BFB Boiler .............................. 211
7.1.1 Feedstock Preparation and Feeding ................. 211
7.1.2 Air and Gas Handling .............................. 213
7.1.3 Ash and Emission Systems .......................... 213
7.1.4 Steam Generation System ........................... 215
7.1.5 Combustion Chamber ................................ 215
7.2 Features of ВFB Boilers .................................. 215
7.2.1 Advantages ........................................ 215
7.2.2 Limitations ....................................... 216
7.3 Thermal Design of Bubbling Fluidized Bed Boilers ......... 216
7.3.1 Overall Meat Balance of the Boiler ................ 216
7.3.2 Boiler Efficiency ................................. 219
7.3.3 Energy Balance in Dense Bubbling Bed .............. 221
7.3.4 Heat Balance of Boiler Components ................. 223
7.3.5 Mass Flow Rates of Fuel and Air ................... 226
7.3.6 Gas-Side Heat Balance ............................. 226
7.4 Combustion in Bubbling Fluidized Bed ..................... 228
7.4.1 Coal Combustion in BFB Boilers .................... 228
7.4.2 Minimization of Combustible Losses in BFB
Combustors ........................................ 230
7.5 Furnace Design ........................................... 234
7.5.1 Basic Design of Furnace ........................... 235
7.5.2 Part-Load Operations .............................. 238
7.5.3 Other Operating Conditions ........................ 240
7.6 Start-Up Procedure and Control ........................... 242
7.6.1 Start-Up Procedure ................................ 243
7.6.2 Control of BFB Boiler ............................. 243
7.7 Some Operational Problems and Remedies ................... 246
7.7.1 Erosion of In-Bed Components ...................... 246
7.8 Design of Feed Systems for BFB Bed Boiler ................ 248
Nomenclature ............................................. 249
Greek Symbols ......................................... 251
References ............................................... 251
Chapters 8 Circulating Fluidized Bed Boiler .................. 253
8.1 General Arrangement ...................................... 253
8.1.1 Air System ........................................ 253
8.1.2 Flue Gas Stream ................................... 255
8.1.3 Solid Stream ...................................... 255
8.1.4 Water-Steam Circuit ............................... 255
8.2 Types of CFB Boilers ..................................... 257
8.2.1 Boilers without Bubbling Bed Heal Exchangers ...... 257
8.2.2 Boilers with Bubbling Fluidized Bed Heat
Exchanger ......................................... 258
8.2.3 Boilers with Inertial or Impact Separators ........ 259
8.2.4 Boilers with Vertical, Noncircular Cyclones ....... 259
8.2.5 Other Types ....................................... 259
8.3 Non-CFB Solid Circulation Boilers ........................ 259
8.3.1 Circo-Fluid Boilers ............................... 259
8.3.2 Low-Solid Circulation Boiler ...................... 260
8.3.3 Circulating Moving Bed Boiler ..................... 260
8.4 Combustion in a Circulating Fluidized Bed Furnace ........ 263
8.5 Design of CFB Boilers .................................... 264
8.5.1 Combustion Calculations ........................... 264
8.5.2 Heal Balance ...................................... 264
8.5.3 Mass Balance ...................................... 266
8.5.4 Flow Split ........................................ 266
8.5.5 Control of Bed Inventory .......................... 267
8.5.6 Some Operating Issues ............................. 270
8.6 furnace Design ........................................... 271
8.6.1 Furnace Cross-Section ............................. 273
8.6.2 Width and Breadth Ratio ........................... 273
8.6.3 Furnace Openings .................................. 276
8.7 Design of Heating Surfaces ............................... 277
8.7.1 Effect of Fuel Type on Furnace Heat Load .......... 278
8.7.2 Ileal Absorption in the External Heat Exchanger ... 280
8.7.3 Heat Absorption in the Furnace and Rest of the
Boiler ............................................ 280
8.7.4 Heat Balance around a CFB Loop .................... 285
8.8 Auxiliary Power Consumption .............................. 287
8.9 Control of CFB Boilers ................................... 287
8.9.1 Part-Load Operation ............................... 287
8.9.2 Load Control Options .............................. 289
8.10 Supercritical CFB Boiler ................................. 291
8.10.1 Supercritical Operation ........................... 292
8.10.2 Vertical vs. Wrapped Tube Arrangement ............. 292
8.10.3 Low Heat Flux ..................................... 293
8.10.4 Cost Advantage .................................... 293
Nomenclature ............................................. 293
Greek Symbols ......................................... 296
References ............................................... 296
Chapter 9 Material Issues .................................... 299
9.1 Material Selection Criteria .............................. 299
9.1.1 Structural Requirements ........................... 299
9.1.2 Heat-Transfer Duty ................................ 300
9.2 Erosion Potential ........................................ 301
9.2.1 Basics of Erosion ................................. 301
9.2.2 Types of Erosion .................................. 304
9.2.3 Erosion in Bubbling Fluidized Beds ................ 304
9.2.4 Options for Reduction of Erosion in Bubbling
Beds .............................................. 306
9.2.5 Erosion in CFB Boilers ............................ 307
9.3 Corrosion Potentials ..................................... 311
9.3.1 Corrosion Mechanisms .............................. 312
9.3.2 Examples of Fire-Side Corrosion ................... 312
9.3.3 Chemistry of Fire-Side Corrosion of Heating
Surfaces .......................................... 313
9.3.4 Chlorine Corrosion ................................ 315
9.3.5 Vanadium Corrosion ................................ 316
9.3.6 Prevention of High-Temperature Corrosion .......... 316
9.3.7 Erosion-Corrosion ................................. 317
9.3.8 Fouling and Deposit Formation ..................... 318
9.4 Steels Used in Fluidized Bed Boilers ..................... 318
9.4.1 Carbon and Alloy Steels .......................... 318
9.5 Refractory and Insulations ............................... 320
9.5.1 Importance of Lining .............................. 320
9.5.2 Properties of Refractory .......................... 320
9.5.3 Types of Refractory ............................... 321
9.5.4 Types of Insulation ............................... 322
9.5.5 Anchors ........................................... 324
9.5.6 Design Considerations of Lining ................... 325
9.5.7 Areas of Refractory Use in Fluidized Bed
Boilers ........................................... 325
9.5.8 Failure Analysis .................................. 329
9.5.9 Refractory Maintenance ............................ 331
9.6 Expansion Joints ......................................... 333
Nomenclature ............................................. 334
Greek Symbols ......................................... 334
References ............................................... 334
Chapter 10 Solid Handling Systems for Fluidized Beds .......... 337
10.1 Solid Handling Systems ................................... 337
10.1.1 Fossil Fuel Plants ................................ 337
10.1.2 Municipal Solid Waste ............................. 339
10.2 Biomass Handling Systems ................................. 341
10.2.1 Feeding of Harvested Fuels ........................ 341
10.2.2 Feeding of Nonharvested Fuels ..................... 341
10.3 Feed System for Bubbling Beds ............................ 342
10.3.1 Types of Feeders .................................. 342
10.3.2 Mode of Feeding in Bubbling Beds .................. 347
10.3.3 Feed Point Allocation ............................. 350
10.4 Feed System for Circulating Fluidized Beds ............... 352
10.4.1 Fuel Feed Ports ................................... 352
10.4.2 Limestone Feed System ............................. 353
10.5 Design of Pneumatic Transport Lines for Solids ........... 353
10.5.1 Pressure Drop in a Pneumatic Transport Line ....... 353
10.5.2 Design of a Pneumatic Injection System ............ 355
10.5.3 Fuel Splitter ..................................... 355
Nomenclature ............................................. 357
Greek Symbols ......................................... 357
References ............................................... 357
Chapter 11 Air Distribution Grate ............................. 359
11.1 Distributor Plates ....................................... 359
11.1.1 Plate-Type Distributor ............................ 360
11.1.2 Nozzle-Type Distributor ........................... 362
11.1.3 Sparge Pipe Distributor ........................... 363
11.1.4 Distributor Grids for CFB ......................... 364
11.1.5 Distributor Grids for Bubbling Beds ............... 365
11.2 Operation of Distributors ................................ 366
11.2.1 What Causes Nonuniform Fluidization .............. 366
11.3 Design Methods ........................................... 368
11.3.1 Design Procedure for Bubbling Fluidized Beds ...... 368
11.3.2 Design Procedure for Circulating Fluidized Beds ... 370
11.4 Practical Considerations ................................. 371
11.4.1 Plenum or Air Box ................................. 372
11.4.2 Sealing of Distributor ............................ 373
11.4.3 Attrition ......................................... 374
11.4.4 Back-Flow of Solid ................................ 375
11.4.5 Opening and Closing of Nozzles .................... 377
11.4.6 Erosion and Corrosion of Nozzles .................. 378
Nomenclature ............................................. 379
Greek Symbols ......................................... 379
References ............................................... 380
Chapter 12 Gas-Solid Separators ............................... 381
12.1 Cyclones ................................................ 381
12.1.1 Types of Cyclone .................................. 382
12.1.2 Theory ............................................ 385
12.1.3 Critical Size of Particles ........................ 385
12.1.4 Working of Cyclones for CFB Combustors or
Gasifiers ......................................... 390
12.1.5 Pressure Drop through a Cyclone ................... 392
12.1.6 Cyclone Collection Efficiency ..................... 394
12.1.7 Reentrainment of Solids ........................... 399
12.1.8 Cyclone Geometry .................................. 400
12.1.9 Effect of the Vortex Finder ....................... 400
12.1.10 Practical Considerations for CFB Cyclones ........ 402
12.2 Impact Separator ......................................... 405
12.2.1 Features and Types ................................ 405
12.2.2 Separation through Impaction ...................... 406
12.2.3 Separation through Interception ................... 407
12.2.4 Grade Efficiency of Impingement Collectors ........ 409
12.2.5 Some Types of Impact Separators ................... 409
12.3 Inertial Separators ...................................... 410
12.3.1 Separation through Gravity Settling ............... 411
12.3.2 Cavity Separator .................................. 411
12.3.3 Design Steps ...................................... 411
Nomenclature ............................................. 413
Greek Symbols ......................................... 415
References ............................................... 415
Chapter 13 Solid Recycle Systems .............................. 417
13.1 Types of Nonmechanical Valves ............................ 417
13.1.1 Loop-Seal ......................................... 418
13.1.2 L-Valve ........................................... 420
13.1.3 V-Valve ........................................... 420
13.2 Principles of Operation .................................. 421
13.2.1 Solid Flow from Standpipe to Recycle Chamber ...... 422
13.2.2 Flow of Solids through Recycle Chamber ............ 424
13.3 Design of Loop-Seal ...................................... 426
13.3.1 Pressure Balance .................................. 426
13.3.2 Size of Loop-Seal ................................. 427
13.3.3 Air-Flow through Loop-Seal ........................ 428
13.4 Design of L-Valve ........................................ 431
13.4.1 Maximum Solid Flow Rate ........................... 432
13.4.2 Additional Design Considerations .................. 433
13.5 Practical Considerations ............................ 433
13.5.1 Plugging of Loop-Seal ............................. 433
13.5.2 Pressure Surge .................................... 434
13.5.3 Avoiding Loop-Seal Plugging ....................... 434
Nomenclature ............................................. 435
Greek Symbols ......................................... 436
References ............................................... 436
Appendix 1 Characteristics of Solid Panicles ................. 439
A1.1 Solid Particles ................................... 439
A1.1.1 Equivalent Diameters ...................... 439
A1.1.2 Sphericity (ø) ............................ 440
A1.1.3 Mean Particle Size and Its Measurement .... 440
A1.2 Packing Characteristics ........................... 442
A1.3 Particle Classification ........................... 442
A1.3.1 Group С ................................... 443
A1.3.2 Group A ................................... 443
A1.3.3 Group В ................................... 444
A1.3.4 Group D ................................... 444
Nomenclature ............................................ 444
References .............................................. 444
Appendix 2 Stoichiometric Calculations ....................... 445
A2.1 Chemical Reactions ................................ 445
A2.2 Air Required ...................................... 446
A2.3 Sorbent Requirement ............................... 446
A2.4 Solid Waste Produced .............................. 446
A2.5 Gaseous Waste Products ............................ 447
A2.5.1 Carbon Dioxide ............................ 447
A2.5.2 Water Vapor ............................... 448
A2.5.3 Nitrogen .................................. 448
A2.5.4 Oxygen .................................... 448
A2.5.5 Sulfur Dioxide ............................ 448
A2.5.6 Fly Ash ................................... 448
A2.6 Healing Value of Fuels ............................ 448
Nomenclature ............................................ 450
Reference ............................................... 451
Appendix 3 Simplified Model for Sulfur Capture ............... 453
Nomenclature ............................................ 454
Appendix 4 Tables of Design Data ............................. 455
Index ......................................................... 461
|
