EssentialsofFluidizationTechnology
Editedby JohnR.Grace
XiaotaoBi
NaokoEllis
Editors
Prof.JohnR.Grace
UniversityofBritishColumbia ChemicalandBiologicalEngineering VancouverCampus 2360EastMall
Canada
V6T1Z3NK
Prof.XiaotaoBi
UniversityofBritishColumbia ChemicalandBiologicalEngineering VancouverCampus 2360EastMall
Canada
V6T1Z3NK
Prof.NaokoEllis UniversityofBritishColumbia ChemicalandBiologicalEngineering VancouverCampus 2360EastMall
Canada
V6T1Z3NK
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Contents
Preface xix Acknowledgement xxi
1Introduction,History,andApplications 1 JohnR.Grace
1.1DefinitionandOrigins 1
1.2Terminology 2
1.3Applications 3
1.4OtherReasonsforStudyingFluidizedBeds 4
1.5SourcesofInformationonFluidization 8 References 8 Problems 9
2Properties,MinimumFluidization,andGeldart Groups 11 JohnR.Grace
2.1Introduction 11
2.2FluidProperties 11
2.2.1GasProperties 11
2.2.2LiquidProperties 12
2.3IndividualParticleProperties 12
2.3.1ParticleDiameter 12
2.3.2ParticleShape 12
2.3.3DensityandInternalPorosity 13
2.3.4SurfaceRoughness 14
2.3.5TerminalSettlingVelocity 14
2.3.6CoefficientsofRestitution(Particle–Particleand Particle–Wall) 15
2.3.7DielectricConstantandElectricalConductivity 16
2.3.8ThermalProperties 16
2.4BulkParticleProperties 16
2.4.1MeanParticleDiameterandParticleSizeDistribution 16
2.4.2BulkDensity,Voidage,and“Flowability” 16
2.5MinimumFluidizationVelocity 18
2.5.1Measuring U mf Experimentally 18
2.5.1.1PressureDropvs.SuperficialVelocityMethod 18
2.5.1.2OtherExperimentalMethodsofDetermining U mf Experimentally 20
2.5.2Predicting U mf BasedonParticleandFluidProperties 20
2.5.3OtherFactorsInfluencingtheMinimumFluidizationVelocity 23
2.6GeldartPowderClassificationforGasFluidization 24
2.7VoidageatMinimumFluidization 27
SolvedProblem 28
Notations 28
References 29
Problems 31
3LiquidFluidization 33
RenzoDiFeliceandAlbertoDiRenzo
3.1Introduction 33
3.2FieldofExistence 33
3.3OverallBehaviour 35
3.4SuperficialVelocity–VoidageRelationship 37
3.5ParticleSegregationandMixing 40
3.6LayerInversionPhenomena 41
3.6.1PredictingtheLayerInversionVoidage(viatheParticleSegregation Model) 43
3.6.2LayerInversionVelocity 46
3.7HeatandMassTransfer 46
3.7.1InterphaseTransfer 46
3.7.2Bed-to-SurfaceTransfer 47
3.8DistributorDesign 48
SolvedProblems 48 Notations 51 References 52 Problems 53
4GasFluidizationFlowRegimes 55 XiaotaoBi
4.1OnsetofFluidization 55
4.2OnsetofBubblingFluidization 55
4.3OnsetofSluggingFluidization 57
4.4OnsetofTurbulentFluidization 58
4.5TerminationofTurbulentFluidization 62
4.6FastFluidizationandCirculatingFluidizedBed 62
4.7FlowRegimeDiagramforGas–SolidFluidizedBeds 64
4.8GeneralizedFlowDiagramforGas–SolidVerticalTransport 65
4.9EffectofPressureandTemperatureonFlowRegime Transitions 68
SolvedProblems 70
Notations 71 References 72 Problems 74
5ExperimentalInvestigationofFluidizedBed Systems 75 NaokoEllis
5.1Introduction 75
5.1.1DesignGoals 75
5.1.2PurposeofExperiments 76
5.2ConfigurationandDesign 76
5.2.1ColumnMaterial 78
5.2.2DistributorPlate 79
5.2.3PlenumChamber 81
5.2.4FeedingSystem(SeeAlsoChapter11) 81
5.2.4.1HopperDesign 82
5.2.5AuxiliaryComponents 83
5.2.5.1SecondaryInjectionofFluid 84
5.3FluidizabilityandQualityofFluidization 84
5.3.1CharacterizationofFlowabilityofParticles 84
5.3.2ParticlePropertiesandFluidizability 86
5.3.3QualityofFluidization 86
5.4InstrumentationandMeasurements 87
5.4.1PressureMeasurements 87
5.4.2ThermalSensors 89
5.4.3OpticalProbes 89
5.4.4Non-invasiveMeasurements 90
5.4.5VisualizationMeasurements 91
5.4.6AcousticEmissionMeasurements 92
5.4.7SolidsCirculationFlux 92
5.4.8GasorSolidsSampling 92
5.4.9MixingandResidenceTimeDistribution 93
5.5OperationofFluidizedBeds 93
5.5.1Start-UpandShutdown 94
5.5.2Steady-StateOperation 94
5.6DataAnalysis 95
5.6.1FrequencyAnalysis 95
5.6.2BivariateTimeSeries 96
5.6.2.1JointProbabilityDensityFunction 96
5.6.2.2Cross-CorrelationFunction 96
5.6.2.3Cross-SpectralDensityFunction 97
5.6.3OtherSignalAnalyses 98 SolvedProblem 98 Notations 98 References 100 Problems 104
6ComputationalFluidDynamicsandItsApplicationto Fluidization 109 TingwenLiandYupengXu
6.1Two-FluidModel 110
6.1.1GoverningEquations 110
6.1.2KineticGranularTheory 112
6.1.3FrictionalModel 114
6.1.4LimitationsofTFM 115
6.2DiscreteParticleMethod 115
6.2.1GoverningEquations 116
6.2.2LimitationsofCFD–DPM 119
6.3Gas–SolidInteraction 119
6.3.1Gas–SolidDrag 119
6.3.2Gas–SolidHeatTransfer 121
6.4BoundaryConditions 122
6.5ExampleandDiscussion 123
6.5.1TFMSimulationofaBubblingFluidizedBedwithTube Bundle 123
6.5.2CFD–DPMSimulationofaSmall-ScaleCirculatingFluidized Bed 124
6.5.3Discussion 125
6.6ConclusionandPerspective 126 SolvedProblem 126 Notations 127 References 128
7HydrodynamicsofBubblingFluidization 131 JohnR.Grace
7.1Introduction 131
7.2WhyBubblesForm 133
7.3AnalogyBetweenBubblesinFluidizedBedsandBubblesin Liquids 134
7.4HydrodynamicPropertiesofIndividualBubbles 135
7.4.1RisingVelocityofSingleBubbles 135
7.4.2BubbleWakes 135
7.4.3BubbleBreakupandMaximumStableSize 137
7.4.4InterphaseMassTransferandCloudFormation 137
7.5BubbleInteractionsandCoalescence 139
7.6FreelyBubblingBeds 139
7.6.1FlowofGasbyTranslationofBubbles 139
7.6.2MeanBubbleDiameterasaFunctionofHeightandGas Velocity 140
7.6.3RisingVelocityofBubblesinFreelyBubblingBed 142
7.6.4BubbleVolumeFraction(Holdup) 142
7.6.5BedExpansion 142
7.6.6RadialNonuniformityofBubblesandItsEffectonMixing 143
7.6.7TurnoverTime,SolidsMixing,andParticleSegregation 144
7.6.8GasMixing 145
7.7OtherFactorsInfluencingBubblesinGas-FluidizedBeds 146 SolvedProblem 147 Notations 147 References 148 Problems 152
8SlugFlow 153
JohnR.Grace
8.1Introduction 153
8.2TypesofSlugFlow 153
8.3AnalogyBetweenSlugsinFluidizedBedsandSlugsinLiquids 155
8.4ExperimentalIdentificationoftheSlugFlowRegime 155
8.5TransitiontoSlugFlow 156
8.6PropertiesofSingleSlugs 156
8.7HydrodynamicsofContinuousSlugFlow 158
8.7.1SlugRisingVelocity 158
8.7.2SlugSpacingandLength 158
8.7.3TimeBetweenSuccessiveSlugsandSlugFrequency 159
8.7.4BedExpansion 159
8.7.5UniformityandSymmetryofFlow 159
8.8MixingofSolidsandGasinSluggingBeds 159
8.9SluggingBedsasChemicalReactors 160
SolvedProblem 160
Notations 161 References 161
9TurbulentFluidization 163
XiaotaoBi
9.1Introduction 163
9.2FlowStructure 165
9.2.1AxialandRadialVoidageDistribution 165
9.2.2LocalVoidSizeandRiseVelocity 166
9.2.3VoidPhaseVolumeFraction,VoidPhase,andDensePhaseSolids Holdup 167
9.3GasandSolidsMixing 168
9.3.1GasMixing 168
9.3.2SolidsMixing 171
9.4EffectofColumnDiameter 172
9.5EffectofFinesContent 173
SolvedProblem 173 Notations 175 References 176 Problems 180
10EntrainmentfromBubblingandTurbulentBeds 181 FarzamFotovat
10.1Introduction 181
10.2Definitions 182
10.2.1TransportDisengagementHeight(TDH) 182
10.2.2Elutriation 184
10.3EjectionofParticlesintotheFreeboard 184
10.4EntrainmentBeyondtheTransportDisengagementHeight 185
10.5EntrainmentfromTurbulentFluidizedBeds 190
x Contents
10.6ParametersAffectingEntrainmentofSolidParticlesfromFluidized Beds 191
10.6.1PropertiesofParticles 191
10.6.2GeometryandShapeofFreeboard 192
10.6.3DenseBedHeight 192
10.6.4Internals 192
10.6.5PressureandTemperature 193
10.6.6ElectrostaticCharges 194
10.7PossibleMeansofReducingEntrainment 195 SolvedProblem 195
Notations 196 References 197 Problems 201
11StandpipesandReturnSystems,SeparationDevices, andFeeders 203
TedM.KnowltonandSuryaB.ReddyKarri
11.1StandpipesandSolidsReturnSystems 203
11.1.1PackedBedFlow 206
11.1.2FluidizedBedFlow 206
11.1.3TypesofStandpipes 206
11.1.3.1OverflowFluidizedStandpipe 207
11.1.3.2UnderflowPackedBedStandpipe 208
11.1.3.3UnderflowFluidizedStandpipes 210
11.2StandpipesinRecirculatingSolidsSystems 212
11.2.1AutomaticSolidsRecirculationSystems 212
11.2.2ControlledSolidsRecirculationSystems 213
11.2.3FunctionofaStandpipe 215
11.3StandpipesUsedwithNonmechanicalSolidsFlowDevices 216
11.3.1NonmechanicalSolidsControlModeOperation 216
11.3.2AutomaticSolidsFlowDevices 219
11.3.2.1CycloneDiplegs 219
11.4SolidsSeparationDevices 222
11.4.1Cyclones 222
11.4.1.1CycloneTypes 223
11.4.1.2FlowPatternsinCyclones 225
11.4.1.3CyclonesinSeries 226
11.4.1.4CyclonesinParallel 226
11.4.1.5Internalvs.ExternalCyclones 227
11.4.1.6CycloneInletDesign 227
11.4.1.7EffectofSolidsLoading 227
11.4.1.8GasOutletTube 228
11.4.1.9InletGasVelocity 228
11.4.1.10CycloneDimensionsandDesign 228
11.4.2OtherSeparationDevices 229
11.4.2.1ParticulateScrubbers 229
11.4.2.2FabricFilters 229
11.4.2.3GranularBedFilters 230
11.4.2.4ElectrostaticPrecipitators 230
11.4.2.5U-Beams 230
11.5SolidsFlowControlDevices/Feeders 230
SolvedProblem 232 Notations 233 References 235 Problems 237
12CirculatingFluidizedBeds 239
ChengxiuWangandJesseZhu
12.1Introduction 239
12.1.1WhatIsaCirculatingFluidizedBed? 239
12.1.2KeyCharacteristicsofCirculatingFluidizedBeds 240
12.2BasicParameters 241
12.3AxialProfilesofSolidsHoldup/Voidage 243
12.4RadialProfilesofSolidsDistribution 246
12.5TheCirculatingTurbulentFluidizedBed 249
12.6Micro-flowStructure 250
12.7GasandSolidsMixing 256
12.8ReactorPerformanceofCirculatingFluidizedBeds 258
12.9EffectofReactorDiameteronCFBHydrodynamics 261 Notations 262 References 263 Problems 268
13OperatingChallenges 269
PoupakMehraniandAndrewSowinski
13.1Electrostatics 269
13.1.1MeasurementandPredictionofElectrostaticCharge 271
13.1.2MitigationTechniques 272
13.1.3Summary 273
13.2Agglomeration 273
13.3Attrition 274
13.3.1ModellingAttrition 276
13.4Wear 278
SolvedProblems 280 Notations 286 References 287 Problem 290
14HeatandMassTransfer 291 DeningEricJia
14.1HeatTransferinFluidizedBeds 291
14.1.1InterphaseHeatTransfer 293
14.1.2Bed-to-SurfaceHeatTransfer 294
14.1.2.1GeneralConsiderations 294
14.1.2.2ParticleConvectiveComponent 294
14.1.2.3GasConvectionComponent 298
14.1.2.4MaximumHeatTransferCoefficient 299
14.1.3HeatTransferCorrelationsforFluidizedBeds 302
14.1.3.1CorrelationsforBed-to-SurfaceHeatTransfer 303
14.1.4HeatTransferBetweenFluidizedBedandImmersedSurfaces 304
14.1.4.1CorrelationsforVerticalTubes 306
14.1.4.2Martin’sCorrelationsforHeatTransfertoImmersedSurfaces 309
14.1.4.3FinnedTubesandNon-cylindricalTubes 312
14.1.4.4TubesinFreeboardRegion 313
14.1.4.5MethodsofAugmentingBed-to-SurfaceHeatTransfer 314
14.1.5RadiativeHeatTransfer 314
14.1.6HeatTransferinFastandCirculatingFluidizedBeds 316
14.2MassTransferinFluidizedBeds 318
14.2.1ParticleandFluidMassTransferintheDensePhase 318
14.2.2BubbletoDense-PhaseInterphaseMassTransfer 320
SolvedProblem 320
Notations 323 References 325 Problem 329
15CatalyticFluidizedBedReactors 333 AndrésMahecha-Botero
15.1Introduction 333
15.2ReactorDesignConsiderations 334
15.2.1SuitabilityofFluidizedBedsforCatalyticProcesses 334
15.2.2ReactorTypesbyFlowRegimeandPhase 334
15.3ReactorModelling 334
15.3.1ModelDevelopment 337
15.3.2ModelStructureandReactionConsiderations 338
15.3.2.1FlowRegimeConsiderations 338
15.3.2.2ReactionEquilibriumConsiderations 339
15.3.2.3ReactionKineticsConsiderations 340
15.4FluidizedBedCatalyticReactorModels 342
15.4.1Mass/MoleandEnergyBalances 345
15.4.2ReactionRateExpressions 345
15.4.2.1Single-PhaseModels 346
15.4.3ModelsBasedonStandardTwo-PhaseTheory 349
15.4.3.1DivisionofFlowandCalculationofFluidizedBedParameters 349
15.4.4MoreSophisticatedModels 352
15.4.4.1ComprehensiveReactorModelling 352
15.4.4.2ComputationalFluidDynamics(CFD)ModelsforFluidizedBed CatalyticReactors 353
15.4.5ModelVerificationandValidation 353
15.4.6RecommendationsforProgrammingandNumericalSolutionof ReactorModels 356
15.5Conclusions 356 Notations 357 References 358 Problems 361
16FluidizedBedsforGas–SolidReactions 363
JaberShabanianandJamalChaouki
16.1Introduction 363
16.2Gas–SolidReactionsforaSingleParticle 364
16.2.1ReactionModelsforNon-porousParticles 365
16.2.1.1ShrinkingParticle 366
16.2.1.2ShrinkingUnreactedCoreModel 369
16.2.2ReactionModelsforPorousParticles 373
16.2.2.1ReactionsofCompleteConsumptionoftheParticle 373
16.2.2.2ReactionsforPorousParticlesofUnchangingOverallSize 374
16.2.3ReactionModelsforSolid–SolidReactionsProceedingThrough GaseousIntermediates 377
16.3ReactionsofSolidParticlesAlone 377
16.4ConversionofParticlesBathedbyUniformGasCompositionina DenseGas–SolidFluidizedBed 378
16.5ConversionofBothSolidsandGas 381
16.5.1ReactorPerformanceCalculationforaBedofFineParticles (CaseI) 382
16.5.2ReactorPerformanceCalculationforaBedofCoarseParticles (CaseII) 385
16.6ThermalConversionofSolidFuelsinFluidizedBedReactors 386
16.7FinalRemarks 390 SolvedProblems 391 Acknowledgments 398 Notations 398 References 401 Problems 403
17Scale-UpofFluidizedBeds 405
NaokoEllisandAndrésMahecha-Botero
17.1ChallengesofScale 405
17.2HistoricalLessons 407
17.3InfluenceofScaleonHydrodynamics 408
17.3.1BubblingFluidization 408
17.3.2TurbulentFluidizationFlowRegime 410
17.3.3FastFluidization 411
17.4ApproachestoScale-Up 412
17.4.1FramingQuestions 412
17.4.2GeneralApproaches 412
17.4.3DimensionalSimilitude(ScalingModels) 413
17.4.4OtherModels 414
17.5PracticalConsiderations 415
17.5.1PurposeofPilot-ScaleUnits 415
17.5.2Pilot-ScaleUnits 416
17.5.2.1BiomassCombinedHeatandPower(CHP)GüssingCase 416
17.5.2.2DualGasifierwithCO2 Capture 417
17.5.2.3CalciumLoopingTechnologies 419
17.6Scale-UpandIndustrialConsiderationsofFluidizedBedCatalytic Reactors 419
17.6.1ChallengesofScale-UpofFluidizedBedCatalyticReactors 419
17.6.2PracticalRecommendationsforIndustrialImplementationof ReactorSystems 422 SolvedProblems 424 Notations 426 References 426 Problems 429
18BafflesandAidstoFluidization 431 YongminZhang
18.1IndustrialMotivation 431
18.2BafflesinFluidizedBeds 432
18.2.1ClarificationofBafflesinLow-VelocityDenseFluidizedBeds 432
18.2.2GeometricCharacteristicsofBaffles 432
18.2.2.1HorizontalBaffles 432
18.2.2.2VerticalBaffles 435
18.2.2.3FixedPackings 436
18.2.3BafflesinLow-VelocityDenseFluidizedBeds 439
18.2.3.1EffectofBafflesonBedHydrodynamics 439
18.2.3.2PerformanceofBafflesinIndustrialFluidizedBedReactors 445
18.2.3.3OtherFindingsandApplications 446
18.2.4BafflesorInsertsinHigh-VelocityFastFluidizedBeds 446
18.2.5DesignofBafflesforIndustrialFluidizedBeds 447
18.3OtherAidstoFluidization 449
18.3.1BriefIntroduction 449
18.3.2ElectricalFields 450
18.3.3MagneticFields 450
18.3.4PulsationsandVibrations 451
18.3.5GlidantsandAntistaticAgents 451
18.4FinalRemarks 452
Notations 452
References 452
Problem 455
19JetsinFluidizedBeds 457 CedricBriensandJenniferMcMillan
19.1Introduction 457
19.2JetsatGasDistributors 457
19.2.1CriterionforUniformGasDistribution 459
19.2.1.1“Dry”DistributorPressureDrop 461
19.2.1.2ActualDistributorPressureDrop 461
19.2.2DefluidizedZones 462
19.2.3ErosionofInternals 464
19.2.3.1PenetrationofUpwardVerticalJets 465
19.2.3.2PenetrationofHorizontal,Inclined,andDownwardVertical Jets 466
19.2.3.3AngleofUpwardJets 466
19.2.3.4MergingandCoalescence 466
19.3MassTransfer,HeatTransfer,andReactioninDistributorJets 467
19.4ParticleAttritionandTribochargingatDistributorHoles 467
19.5JetsFormedinFluidizedBedGrinding 469
19.5.1Mechanisms 469
19.6Applications 471
19.7JetPenetration 471
19.8SolidsEntrainmentintoJets 471
19.9NozzleDesign 472
19.9.1NozzleInclination 472
19.9.2ImpactofBedHydrodynamics 473
19.9.3OpposingJets 473
19.10Jet-TargetAttrition 473
19.10.1PredictionofAttritionRates 474
19.11JetsFormedWhenSolidsAreFedintoaFluidizedBed 475
19.11.1Mechanisms 475
19.11.2Applications 475
19.11.3JetPenetration 476
19.11.4SolidsEntrainment 476
19.11.5InjectionSystemDesign 476
19.11.6NozzleInclination 476
19.11.7ImpactofBedHydrodynamics 476
19.12JetsFormedWhenLiquidIsSprayedintoaGas-Fluidized Bed 477
19.12.1PureLiquidJets 477
19.12.2MechanismforGas–LiquidJets 477
19.12.3Applications 478
19.13JetPenetration 478
19.13.1SolidsEntrainment 478
19.13.2InjectionSystemDesign 479
19.13.2.1UpstreamPipingDesign 479
19.13.2.2SprayNozzleDesign 480
19.13.2.3LaboratoryNozzles 480
19.13.2.4Non-rodableCommercialNozzles 480
19.13.2.5RodableCommercialNozzles 480
19.13.2.6DownstreamAttachments 481
19.13.2.7ImpactAttachments 481
19.13.2.8Shrouds 481
19.13.2.9GasJets 482
19.13.2.10DraftTubes 482
19.13.3NozzleInclination 482
19.13.4InteractionsBetweenSprayJets 483
19.13.5ImpactofBedHydrodynamics 483
SolvedProblems 483
Notations 487 References 488 Problem 497
20DownerReactors 499
ChangningWuandYiCheng
20.1DownerReactor:ConceptionandCharacteristics 499
20.2Hydrodynamics,Mixing,andHeatTransferofGas–SolidFlowin Downers 501
20.2.1BasicHydrodynamicBehaviour 501
20.2.2MixingBehaviourofSolidsinDowners 503
20.2.3HeatTransferinDowners 506
20.3ModellingofHydrodynamicsandReactingFlowsinDowners 508
20.3.1ReactionEngineeringModel 509
20.3.2Eulerian–EulerianModel 509
20.3.3Eulerian–LagrangianModel 511
20.4DesignandApplicationsofDownerReactors 514
20.4.1InletDesign 514
20.4.2FastSeparationofGasandSolidsatDownerExit 517
20.4.3High-DensityDowner 518
20.4.4Downer–RiserCoupledReactors 518
20.4.5ApplicationCase1:FCC 519
20.4.6ApplicationCase2:Gasification 521
20.4.7ApplicationCase3:CoalPyrolysisinPlasma 521
20.5ConclusionsandOutlook 523 SolvedProblem 523
Notations 525 References 526 Problems 528
21Spouted(andSpout-Fluid)Beds 531
NormanEpstein
21.1Introduction 531
21.2Hydrodynamics 532
21.2.1ConstraintsonFluidInletDiameterandConeAngle 532
21.2.2MinimumSpoutingVelocity 533
21.2.3MaximumSpoutableBedHeight 534
21.2.4FluidFlowinAnnulus 535
21.2.5FluidFlowinSpout 536
21.2.6PressureDrop 536
21.2.7BehaviourofSolidParticles 537
21.3HeatandMassTransfer 538
21.4ChemicalReaction 538
21.5Spoutingvs.Fluidization 539
21.6Spout-FluidBeds 540
21.7Non-conventionalSpoutedBeds 543
21.8Applications 546
21.9MultiphaseComputationalFluidDynamics 547
SolvedProblem 547
Notations 548 References 549
22Three-Phase(Gas–Liquid–Solid)Fluidization 553 DominicPjontek,AdamDonaldson,andArturoMacchi
22.1Introduction 553
22.1.1GeneralDescriptionandClassification 553
22.1.2Applications 554
22.2ReactorDesignandScale-up 556
22.2.1ReactorDesign 556
22.2.2ReactorScale-up 558
22.3CompartmentalFlowModels 558
22.3.1PlenumandFluidDistributor 560
22.3.2FluidizedBed 561
22.3.3Freeboard 562
22.4FluidDynamicsinThree-PhaseFluidizedBeds 562
22.4.1FlowRegimes 562
22.4.1.1MinimumFluidization 562
22.4.1.2BubblingRegimes 564
22.4.2PhaseHoldups 565
22.4.2.1Modelling:Global(BedVolumeAveraged) 565
22.4.2.2BedContractionvsExpansion 568
22.4.2.3ParticleEntrainment 568
22.5PhaseMixing,MassTransfer,andHeatTransfer 569
22.5.1PhaseMixing 569
22.5.2Surface-to-BedHeatTransfer 570
22.5.3InterphaseGas–LiquidandLiquid–SolidMassTransfer 571
22.5.3.1Gas–LiquidMassTransfer 572
22.5.3.2Liquid–SolidMassTransfer 572
22.6Summary 574
SolvedProblems 574
Notations 582 References 585 Problems 587
Index 591
Preface
Wearepleasedtopresentthefirstcomprehensiveteachingbookon fluidized beds tobepublishedinnearlythreedecadessincethesecondeditionoftheKunii andLevenspiel, FluidizationEngineering bookin1991andthe GasFluidizationTechnology bookeditedbyGeldart,publishedin1986.Duringtheinterveningperiod,therehasbeenconsiderableprogress,leadingtonewunderstanding insuchareasasmultiphasecomputationalfluiddynamics(CFD),interparticle forces,electrostatics,jets,downers,andadvancedexperimentalmethodologies (suchasparticletracking,MRI,andvarioustypesoftomography).Thesenew areasare,toadegree,coveredinthisbook,whilewehavealsodrawnheavily onthe“moreclassical”fluidizationliterature.Wehavealsoincludedchapterson liquidandthree-phasefluidization,spoutedbeds,CFD,anddowners,topicsnot includedinpreviousfluidizationbooksintendedaseducationaltexts.
Therehavealsobeenanumberofnewfluidizedbedapplicationsand processesinrecenttimes,mostnotablyinchemicallooping,processingof silicon-containingmaterialsforsolarapplications,extractionofadvancedmaterials,thermochemicalconversionofbiomassresiduestoenergyandbiofuels, andeffortstoproduceorutilizenanoparticles.Whilethesenewprocesses arenotdealtwithexplicitlyindepthinthebook,theyhaveinfluencedthe fluidizationresearchcommunityandtopicsofresearcharticles,henceaffecting theknowledgereflectedinthisbook.Theauthorswhohavecontributedtothe bookcombinesomewhohavebeenengagedinthisfieldformanydecadeswith anewgenerationoffluidizationexperts,eagertoadvancetheunderstanding andapplicabilityoffluidizedbeds.
Inchoosingthematerialtobeincludedinthebook,wehavebeenguided bytheword“Essentials”inthetitle.Thuswehavehadtoleaveoutmaterial,which,whileinteresting,isnotessentialformostbeginnersandgeneral readers.However,readersshould,afterclosereadingofthechapters,beable todelveintotheextensivespecializedresearchliteraturewithagoodgeneral background.Ourbookwillhaveserveditspurposeifithelpsreaders,whether thesebeyoungengineersworkinginindustryorgraduatestudentsundertaking researchprojectsrelatedtofluidization,becomefamiliarwiththebroadareas
xx Preface offundamentalandpracticalknowledgeunderlyingthefield.Incorporationofa smallnumberofsolvedproblemsandunsolvedproblemexercisesisintended tofurthertheunderstandingofthetopicscovered.Inadditiontosingle-reader usage,weintendthatthisbookbeavailableasatextbookforcoursesrelatedto fluidizationandmultiphasesystems.
Vancouver 31October2019
JohnGrace NaokoEllis XiaotaoBi
Acknowledgement
Wethanktheauthorsforrespondingwithenthusiasmtoourproposaltowrite chaptersofthebookandfortheirhelpinpreparingandrevisingthematerial.We thankZezhongJohnLiforassistancewithfigures,logistics,andadministrative details.WearegratefultotheNaturalSciencesandEngineeringResearchCouncil ofCanadaforfundingsomeoftheexpensesrelatedtothepreparationofthis book,aswellasforcoveringthecostsofanumberofstudiesthathavecontributed toourexperienceandexpertiseinfluidizationandrelatedareas.
Introduction,History,andApplications
JohnR.Grace
UniversityofBritishColumbia,DepartmentofChemicalandBiologicalEngineering,2360EastMall, Vancouver,CanadaV6T1Z3
1.1DefinitionandOrigins
Fluidizationoccurswhensolidparticlesaresupportedandallowedtomoverelativetoeachotherasaresultofverticalmotionofafluid(gasorliquid)ina definedandcontainedvolume.Mostcommonly,thefluidisagasblownupwards byablowerorcompressorthroughaperforatedflatplateoraseriesoforifices, butmanyotherconfigurationsarepossible.Onceanassembly(“bed”)ofparticles hasbeenactuatedinthismanner,itissaidtobea“fluidizedbed.”
Theoriginoffluidizedbedsisunclear,butliquid-fluidizedbedslikelypreceded gas-fluidizedbeds.Forexample,earlyfluidizationhasbeenattributedtoAgricola[1]whenhedescribedandillustratedhandjiggingfororedressing.Thefirst industrialapplicationsoffluidizedbedswerelikelybedsoforeparticlesfluidized byliquidsinordertoclassifythembysizeordensityinanoperationknownas “teetering”[2].
Thefirstwidespreadapplicationofgas-fluidizedbedswasinthe1920sin GermanywhenWinkler[3]patentedanovelgasifier.However,theterms “fluidization”and“fluidbed”didnotemergeuntilabout1940whenresearchers intheUnitedStatesdevelopedgas-supportedbedsforcatalyticcrackingof heavyhydrocarbons[4,5].Aplaquecommemoratingthedevelopmentofthe fluidbedreactoratalocaloilrefinerywaserectedattheLouisianaArtand ScienceMuseuminBatonRougein1998.
Theterm“circulatingfluidizedbed”(or“CFB”)hasbeenusedsincethe1980s tocoverconfigurationswherethereisnoupperbedsurface,withparticlessupportedbyfluidcontainedinequipmentthatincorporatesoneormoregas–solid separator(usuallycyclones),aswellasrecirculationpipingasanintegralpart ofthesystem.Thesehavebecomepopular,mostlyforcalcination,energy,and metallurgicaloperations[6].
Commercialfluidizedbedreactorsarenowamongthelargestchemicalreactorsintheworld.Forexample,inChinafluidizedbedcombustorshavereached apowercapacityof660MWe [7].
EssentialsofFluidizationTechnology, FirstEdition.EditedbyJohnR.Grace,XiaotaoBi,andNaokoEllis. ©2020Wiley-VCHVerlagGmbH&Co.KGaA.Published2020byWiley-VCHVerlagGmbH&Co.KGaA.
1.2Terminology
Asinotherfields,specializedterminologyisusedbythefluidizationcommunity. Definitionsofthefollowingtermsmaybehelpfulforthosenewtothefield:
Agglomeration:Particlesstickingtogethertoformassemblies(agglomerates).
Attrition:Break-upofparticlesduetocollisionsorotherinteractionsand stresses.
Bedexpansion:Heightofoperatingfluidizedbeddividedbystaticbedheightor bedheightatminimumfluidization.
Bubbles:Voidscontainingfew,ifany,particles,risingrelativetotheparticles abovethemandbehavinginasomewhatanalogousmannertobubblesinliquids.
Choking:Collapseofdilutegas–solidsuspensionintodensephaseflowwhen decreasingthegasvelocityatconstantsolidsflow.Fordifferentmodesofchoking,see[8].
Circulatingfluidizedbed:Fluidandparticlesinrelativemotioninaconfigurationwherethereisnodistinctupperbedsurfaceandentrainedparticlesare continuouslyseparatedandreturnedtothebaseofariser.
Cluster:Groupofparticlestravellingtogetherduetohydrodynamicfactors.
Densephase:Gas–solidregionwheretheconcentrationofparticlesissufficientlyhighthattherearesignificantparticle–particleinteractionsand contacts.
Dilutephase:Regionwhereparticleconcentrationislowenoughthatinterparticlecontactsarerelativelyrare.
Downer:Vesselinwhichparticlesarecontactedwithafluidwhiletheyfalldownwards.
Distributor:Horizontalplatewithperforations,nozzles,orotheropeningsor othermeansofintroducingafluidizingfluidtosupporttheweightofparticles andcausethemtomovewhilealsosupportingthedeadweightoftheparticles whentheflowoffluidisinterrupted.
Elutriation:Progressiveselectiveremovaloffinerparticulatesbyentrainment.
Fines:Relativelysmallparticles,typicallythosesmallerthan37or44 μmindiameter.
Fluid:Eithergasorliquid,usuallytheformerinthecontextoffluidization.
Freeboard:Regionextendingfromdensefluidizedbeduppersurfacetotopof vessel.
Geldartpowdergroup:SeeChapter2.
Grid:Alternatenameforgasdistributorsupportingthefluidizedbedandassuringuniformentryofgasatitsbase.
Loopseal:Commonconfiguration(seeChapter11)forrecirculatingsolidstothe bottomofafluidizedbedorriserwithoutreverseflowofgas.
Membranewalls:Containingwallconsistingofverticalheattransfertubes connectedbyparallelfins,commonlyusedincombustionapplications(see Chapter14).
Membranereactor:Reactorcontainingsolidsurfaces(“membranes”)thatare selectivelypermeabletooneormorecomponentofthegasmixture.
1.3Applications 3
Plenumchamber:Pressurizedchamberbelowthedistributorofafluidization columnfromwhichfluidizingfluidisfedintothebedabovethedistributor.
Riser:Tallcolumninwhichparticlesarecarried,onaverage,upwardsbyan ascendingfluid.
Segregation:Tendencyforparticlesofdifferentphysicalcharacteristics(e.g.differentsize,density,and/orshape)topreferentiallybecomemoreconcentrated indifferentspatialregions.
Solids:Generictermreferringtosolidparticles.
Superficialvelocity:Volumetricflowrateoffluiddividedbytotalcolumn cross-sectionalarea.
Voidage:Fractionofbedvolumeorlocalvolumeoccupiedbyfluid.
Windbox:Sameasplenumchamber,butonlywhenthefluidizingfluidisagas.
Othertermsareintroducedanddefinedasneededinthetext.
1.3Applications
Gas-fluidizedbedsaccountformostofthecommercialapplicationsoffluidized beds.Relativetopackedbeds,gas-fluidizedbedscommonlyofferthefollowing advantages:
➢ Temperatureuniformity(withvariationsseldomexceeding10 ∘ Cinthedense bedandeliminationof“hotspots.”)
➢ Excellentbed-to-surfaceheattransfercoefficients(typically1orderofmagnitudebetterthaninfixedbedsand2ordersofmagnitudebetterthaninempty columns.)
➢ Abilitytoaddandremoveparticlescontinuously,facilitatingcatalystregenerationandcontinuousoperation.
➢ Relativelylowpressuredrops(essentiallyonlyenoughtosupportthebed weightperunitcross-sectionalarea.)
➢ Scalabletoverylargesizes(e.g.therearecommercialfluidizedbedreactors hundredsofsquaremetresincross-sectionalarea.)
➢ Excellentcatalysteffectivenessfactors(i.e.verylowintra-particlemasstransferresistances):Withparticles1orderofmagnitudesmallerthaninfixed beds,i.e.catalystparticlessmallerthan100 μm,effectivenessfactorsusually approach1.
➢ Goodturndowncapability:Thegasflowratecanbevariedoverawiderange, typicallybyatleastafactorof2–3.
➢ Abilitytotoleratesomeliquid:Forexample,inanumberofprocesses,suchas fluidcatalyticcracking,liquidsaresprayedintothecolumnwheretheyvaporizeandthenreact.
➢ Wideparticlesizedistributions(typicallywitharatioofuppertolowerdecile particlediameter, d p90 /d p10 ,of10:20).
Theseadvantagesmustbesignificantenoughtocompensateforsomesignificantdisadvantagesofgas-fluidizedbeds:
❖ Substantialvertical(axial)mixingofgas:Gasisdraggeddownwardsby descendingparticlesresultingin“backmixing”andlargedeviationsfromplug flow,withtypicalaxialPecletnumbersoforder5–10.
❖ Substantialaxialdispersionofsolids:Vigorousmotionofparticlesandtheir clustersresultsinsubstantialaxialdispersionandbackmixingofsolids.Asa result,incontinuousprocesses,someparticlesspendverylittletimeinthe bed,whileothersspendmuchlongerthanthemeanresidencetime.
❖ Bypassingofgas:Gasassociatedwithalower-densityphase,e.g.risingas bubbles,passesthroughthebedmorequicklyandwithlessaccesstoparticlesthangasassociatedwithadenserphaseinwhichthereisbettergas–solid contacting.
❖ Limitationsonparticlesthatcanbesuccessfullyfluidized:Particlesof extremeshapes(e.g.needleorflatdiscshapes)orsmallerthanabout30 μm inmeandiameteraredifficult,orevenimpossible,tofluidize.
❖ Entrainment:Particles,especiallyfineones,arecarriedupwardsbythe exhaustorproductgasandleavethecolumnthroughtheexit.Tominimize theirlosses,entrainedparticlesmustnormallybecontinuouslycapturedand returnedtothebottomofthevessel.
❖ Attrition:Particlescanbreakorbeabradedwhentheycollide/interactwith eachotherandwithfixedsurfaces.
❖ Wearonsurfaces:Particlemotiontendscauseserosion/wastageoffixedsurfaces.
❖ Complexityandrisk:Fluidizedbedsaremorecomplextodesign,operate, andmodelthancomparablefixedbedreactors.Asaresult,thereisgreater riskofproblemsandlessthandesiredperformance.
Theadvantagesidentifiedabovehavebeenfoundtooutweighthedisadvantagesinanumberofindustriallysignificantprocesses.Themostimportantof theseprocessesarelistedinTable1.1.Usefulreviewsoftheearlyyearsofthese processeswereprovidedbyGeldart[9–11].
PracticalinformationrelatedtomanyoftheprocesseslistedinTable1.1was summarizedbyYerushalmi[12].Forinformationonarecentlycommercialized process,seeTianetal.[13].Forapplicationsrelatedtofoodprocessing,seeSmith [14].ThetypicaloperatingrangeforcatalyticfluidizedbedreactorsaresummarizedinTable1.2.Particlestendtobelargerandgassuperficialvelocitiestobe higherinthecaseofphysicaloperationsandforgas–solidreactionsthanforcatalyticprocesses.
Applicationsofliquid-fluidizedbeds,spoutedbeds,andgas–liquid–solid(i.e. three-phase)fluidizedbedsarecoveredinChapters3,21,and22,respectively.
1.4OtherReasonsforStudyingFluidizedBeds
Inadditiontobeingusefulinmanycommercialapplications,assummarized aboveandasoutlinedinlaterchapters,thereareotherreasonsforinterestin thebehaviouroffluidizedbeds:
Table1.1 Industrialapplicationsofgas-fluidizedbeds.
PhysicaloperationsSolid-catalyzedreactionsGas–solidreactions
DryingofparticlesFluidcatalyticcrackingCombustionandincineration
GranulationAcrylonitrileGasification
Coatingofsurfacesby
ChemicalVapour
Deposition
EthylenedichloridePyrolysis
Particlemixing/blendingCatalyticcombustionTorrefaction
PreheatingandheatingEthanoldehydrationRoastingofores
SteamraisingEthylenesynthesisReductionofironoxide
FreezingMaleicanhydridePolyolefinproduction
Quenching/temperingFischer–TropschsynthesisFluidcokingandflexicoking
Carburizing,nitridingAnilineCalcination
Constanttemperature baths
MethanoltoolefinsCatalystregeneration
FilteringofparticlesMethanoltogasolineChlorination,fluoridation
FeedingofparticlesOxidative dehydrogenation
Hydrochlorinationofsilicon
SorptionofharmfulgasesPhthalicanhydrideSilanedecomposition → pureSi
TreatmentofburnvictimsCatalyticreformingCarbonnanotubesviaChemical VapourDeposition
TarcleaningGas–solidfermentation
SteamreformingMelamineproduction
MethanationTitaniumdioxidepigment
Table1.2 Usualoperatingrangesforsolid-catalyzedgas-phase reactors.
VariableRangeandcomments
Sautermeanparticlediameter50–100 μm
ParticlesizedistributionBroad,e.g.0–200 μm
ReactordiameterUpto ∼7m
PressureUpto ∼80bars
TemperatureUpto ∼600 ∘ C
Superficialgasvelocity ∼0.3–12m/s
Staticbeddepth1–10m
ImmersedsurfacesMaycontainhorizontalor verticalheattransfersurfaces
Gas–solidseparationHeavilyreliantongascyclones
Table1.3 SummaryofproceedingsofmajorfluidizationandCFBconferences.
YearDesignationConferencelocationEditor(s)Publisher
1967International Symposiumon Fluidization Eindhoven,NetherlandsDrinkenburgNetherlandsUniversityPress
1975Fluidization Technology Asilomar,CaliforniaKeairnsandDavidsonHemisphere
1978FluidizationCambridge,UKDavidsonandKeairnsCambridgeUniversityPress 1980FluidizationHenniker,NH,USAGraceandMatsenPlenumPress 1983FluidizationKashikojima,JapanKuniiandToeiEngineeringFoundation 1985CFBIHalifax,CanadaBasuPergamonPress 1986FluidizationVLyngby,DenmarkOstergaardandSorensenEngineeringFoundation 1988CFBIICompiègne,FranceBasuandLargePergamonPress 1989FluidizationVIBanff,CanadaGrace,Shemilt,BergougnouEngineeringFoundation 1990CFBIIINagoya,JapanBasu,Horio,HasataniPergamonPress 1992FluidizationVIIGoldCoast,AustraliaPotterandNicklinEngineeringFoundation 1993CFBIVHiddenValley,USAAvidanAIChE 1995FluidizationVIIITours,FranceLargeandLaguérieEngineeringFoundation 1996CFBVBeijing,ChinaKwaukandLiSciencePress,Beijing 1998FluidizationIXDurango,USAFanandKnowltonEngineeringFoundation 1999CFBVIWürzburg,GermanyWertherDECHEMA 2001FluidizationXBeijing,ChinaKwauk,Li,YangUnitedEngineeringFoundation
2002CFBVIINiagaraFalls,CanadaGrace,Zhu,deLasaCanadianSocietyforChemical Engineering
2004FluidizationXIIschia,ItalyArena,Chirone,Miccio,SalatinoEngineeringConferencesInternational 2005CFBVIIIHangzhou,ChinaCenInternationalAcademicPublishers 2007FluidizationXIIHarrison,CanadaBi,Berruti,PugsleyEngineeringConferencesInternational 2008CFBIXHamburg,GermanyWerther,Nowak,Wirth,HartgeTuTechInnovation 2010FluidizationXIIIGyeong-ju,KoreaKim,Kang,Lee,SeoEngineeringConferencesInternational 2011CFB10Sunriver,Oregon,USAKnowltonEngineeringConferencesInternational 2013FluidizationXIVNoordwijkerhout,NetherlandsKuipers,Mudde,vanOmmen,DeenEngineeringConferencesInternational 2014CFB11Beijing,ChinaLi,Wei,Bao,WangChemicalIndustryPress 2016FluidizationXVMontebello,CanadaChaoukiandShabanianVol.316ofPowderTechnology,Elsevier 2017CFB12Krakow,PolandNowak,Sciazko,MirekJournalofPowerTechnologiesand ArchivumCombustionis 2019FluidizationXVIGuilin,ChinaWangandGeAmericanInstituteofChemical Engineering 2020CFB13Vancouver,CanadaBi,Briens,Ellis,WormsbeckerGLAB
⬩ Theyareinherentlyfascinatingtoobserve,evenfindingtheirwayintokinetic art.
⬩ Duetotheircomplexflowpatternsandthemanyfactorsinvolved,fluidized bedsarechallenginganddifficulttomodel,withsomesurprisingfeatures.
⬩ Theymayberelatedtosomenaturalphenomena,inparticularavalanches, pyroclasticflowsassociatedwithvolcaniceruptionsandatmosphericconvectionofwaterdrops,snowflakes,andhailstones[15,16].Therehasevenbeen speculationthatsomecratersonthesurfaceofthemoonmayberelatedto eruptionoffluidizationbubbles.
1.5SourcesofInformationonFluidization
Thousandsofpapershavebeenpublishedinthescientificandengineering literature(journalsandbooks)onfluidizationfundamentalsandapplications. Duetolengthrestrictionsanditsscope,thisbookcitesonlyasmallfraction ofthesearticles.Inadditiontothemanyresearcharticlesthatappearin journalslike PowderTechnology, Particuology, AdvancedPowderTechnology, and theInternationalJournalofMultiphaseFlow,manyrelevantpapersappear inthemajorchemicalengineeringjournalssuchas ChemicalEngineering Science, IndustrialandEngineeringChemistryResearch,and AmericanInstitute ofChemicalEngineers(AIChE)Journal ,aswellasawidevarietyofother engineering-andphysics-relatedjournals.Inaddition,therearemanypublished proceedingsofconferencesandsymposiaonfluidization.Themostusefulof theseforthoseinterestedinfundamentalsoffluidizedbedshaveappearedin refereedproceedingsoftri-annualFluidizationconferences,coordinatedfor manyyearsbytheEngineeringFoundationandthenbyEngineeringConferences International,andtri-annualCFBconferences(recentlyrenamed“International ConferenceonFluidizedBedTechnology.”)Informationontheseproceedings issummarizedinTable1.3.Lessrigorouslyrefereedproceedingsoffluidized bedcombustion,originallycoordinatedandpublishedbytheAmericanSociety ofMechanicalEngineersattwo-yearintervals,andmorerecentlyeverythree years,alsocontainmanyappliedandfundamentalfluidizationarticles.Periodic China–JapanConferencesonFluidizationhavealsoledtoaseriesofwell-edited volumes.
References
1 Agricola,G.(1556). DeReMetallica (trans.H.C.HooverandL.H.Hoover), 310–311.NewYork,1950:Dover.
2 Epstein,N.(2005).Teetering. PowderTechnol. 151:2–14.
3 Winkler,F.(1922).VerfahrenzumHerstellenWassergas.GermanPatent 437,970.
4 Jahnig,C.E.,Campbell,D.L.,andMartin,H.Z.(1980).Historyoffluidized solidsdevelopmentatExxon.In: Fluidization (eds.J.R.GraceandJ.M. Matsen),3–24.PlenumPress.
5 Squires,A.M.(1986).Thestoryoffluidcatalyticcracking:thefirst“circulating fluidbed.”.In: CirculatingFluidizedBedTechnology (ed.P.Basu),1–19.New York:PergamonPress.
6 Reh,L.(1971).Fluidbedprocessing. Chem.Eng.Prog. 67:58–63.
7 Cai,R.,Ke,X.W.,Lyu,J.F.etal.(2017).Progressofcirculatingfluidizedbed combustiontechnologyinChina:areview. CleanEnergy 1(1):36–49.https:// doi.org/10.1093/ce/zkx001.
8 Bi,H.T.,Grace,J.R.,andZhu,J.(1993).Typesofchokinginverticalpneumaticsystems. Int.J.Multiph.Flow 19:1077–1092.
9 Geldart,D.(1969).Physicalprocessingingasfluidisedbeds. Chem.Ind. 33: 311–316.
10 Geldart,D.(1967).Thefluidisedbedasachemicalreactor:acriticalreview ofthefirst25years. Chem.Ind. 31:1474–1481.
11 Geldart,D.(1968).Gas-solidreactionsinindustrialfluidizedbeds. Chem.Ind. 32:41–47.
12 Yerushalmi,J.(1982).Applicationsoffluidizedbeds,Chapter8.5.In: HandbookofMultiphaseSystems (ed.G.Hetsroni),8-152–8-216.Washington,DC: HemispherePublishing.
13 Tian,P.,Wei,Y.,Ye,M.,andLiu,Z.(2015).Methanoltoolefins:Fromfundamentalstocommercialization. ACSCatal. 5:1922–1938.
14 Smith,P.G.(2007). ApplicationsofFluidizationtoFoodProcessing .Oxford, UK:BlackwellScience.
15 Wilson,C.J.N.(1984).Theroleoffluidizationintheemplacementofpyroclasticflow:experimentalresultsandtheirinterpretation. J.Volcanol.Geotherm. Res. 20:55–84.
16 Horio,M.(2017).Fluidizationinnaturalphenomena,referencemodule.In: Chemistry,MolecularSciencesandChemicalEngineering (ed.J.Reedijk). Waltham,MA:Elsevierhttps://doi.org/10.1016/B978-0-12-409547-2.12185-7.
17 Gullichsen,J.andHarkonen,E.(1981).Mediumconsistencytechnology. TAPPIJ. 64:69–72.and113–116.
Problems
1.1 GullichsenandHarkonen[17]appliedtheterm“fluidization”tothecreation ofafluid-likestateinpulpfibreaqueoussuspensionsduetorapidcentrifugalmechanicalmixing.Isthisuseofthetermconsistentwiththedefinition offluidizationgiveninthischapter?
1.2 Imagineareactorofcross-sectionalarea100m2 containingcatalystparticlesofdiameter60 μmanddensity1600kg/m3 .Thevoidfractionofthe staticmaterialis0.52.Howmanyparticlesareneededtofillthereactorto astaticbeddepthof6m?Whatisthetotalmassoftheseparticles?
Properties,MinimumFluidization,andGeldartGroups
JohnR.Grace
UniversityofBritishColumbia,DepartmentofChemicalandBiologicalEngineering,2360EastMall, Vancouver,CanadaV6T1Z3
2.1Introduction
Thischapteridentifiesthekeyparticleandfluidpropertiesthataffecttheabilitytofluidizeparticlesandthatplayamajorroleindeterminingtheproperties offluidizedbeds.Itisimportanttocharacterizetheseproperties,oratleastto considerwhethereachcouldberelevant,whendecidingwhetherornotagiven processmightbenefitfromfluidization,aswellaswhendesigning,operating, andmodellingfluidizedbedprocesses.Thechapteralsoconsidersdifferentmethodsofmeasuringandpredictingboththeminimumfluidizationvelocityandthe bedvoidageatminimumfluidization,twoveryimportantquantitiesaffectingthe propertiesoffluidizedbeds.Finally,weintroducethefourGeldartpowdergroups forparticlesfluidizedbygases.Thisclassificationiswidelyusedindiscussing, characterizing,andexplaininggasfluidization.
2.2FluidProperties
2.2.1GasProperties
Gaspropertiesthatinfluencethepropertiesofgas-fluidizedbedsare:
Density:Highergasdensityleadstoincreaseddragonparticlesandhenceearlier andmorevigorousfluidization.Gasdensityincreaseswithincreasingpressure anddecreaseswithincreasingtemperature.Idealgasbehaviourcanusuallybe assumedasagoodapproximationwhenassessingtherolesoftemperatureand pressureongas-fluidizedbeds.
Viscosity:Highergasviscositycausesgreaterdragforsmallparticles,butplays onlyasmallroleforlarger(e.g.GeldartD)particles(seeSection2.6).Gas viscosityisalmostindependentofpressure,butincreaseswithincreasing temperature.
