Essentials of Fluidization Technology E-Book
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- Herausgeber: Wiley-VCH Verlag GmbH & Co. KGaA
- Kategorie: Fachliteratur
- Sprache: Englisch
A concise and clear treatment of the fundamentals of fluidization, with a view to its applications in the process and energy industries.
Das E-Book Essentials of Fluidization Technology wird angeboten von Wiley-VCH und wurde mit folgenden Begriffen kategorisiert:
fluidized; bed; particle; packed; gas; liquid; CFD; computational; fluid; dynamics; regime; turbulent; bubbling; entrainment; heat; mass; transfer; spouted; circulating; cyclone; CFB
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Seitenzahl: 1043
Veröffentlichungsjahr: 2020
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Table of Contents
Cover
Preface
Acknowledgement
1 Introduction, History, and Applications
1.1 Definition and Origins
1.2 Terminology
1.3 Applications
1.4 Other Reasons for Studying Fluidized Beds
1.5 Sources of Information on Fluidization
References
Problems
2 Properties, Minimum Fluidization, and Geldart Groups
2.1 Introduction
2.2 Fluid Properties
2.3 Individual Particle Properties
2.4 Bulk Particle Properties
2.5 Minimum Fluidization Velocity
2.6 Geldart Powder Classification for Gas Fluidization
2.7 Voidage at Minimum Fluidization
References
Problems
Note
3 Liquid Fluidization
3.1 Introduction
3.2 Field of Existence
3.3 Overall Behaviour
3.4 Superficial Velocity–Voidage Relationship
3.5 Particle Segregation and Mixing
3.6 Layer Inversion Phenomena
3.7 Heat and Mass Transfer
3.8 Distributor Design
References
Problems
4 Gas Fluidization Flow Regimes
4.1 Onset of Fluidization
4.2 Onset of Bubbling Fluidization
4.3 Onset of Slugging Fluidization
4.4 Onset of Turbulent Fluidization
4.5 Termination of Turbulent Fluidization
4.6 Fast Fluidization and Circulating Fluidized Bed
4.7 Flow Regime Diagram for Gas–Solid Fluidized Beds
4.8 Generalized Flow Diagram for Gas–Solid Vertical Transport
4.9 Effect of Pressure and Temperature on Flow Regime Transitions
References
Problems
5 Experimental Investigation of Fluidized Bed Systems
5.1 Introduction
5.2 Configuration and Design
5.3 Fluidizability and Quality of Fluidization
5.4 Instrumentation and Measurements
5.5 Operation of Fluidized Beds
5.6 Data Analysis
References
Problems
6 Computational Fluid Dynamics and Its Application to Fluidization
6.1 Two-Fluid Model
6.2 Discrete Particle Method
6.3 Gas–Solid Interaction
6.4 Boundary Conditions
6.5 Example and Discussion
6.6 Conclusion and Perspective
Notations
References
7 Hydrodynamics of Bubbling Fluidization
7.1 Introduction
7.2 Why Bubbles Form
7.3 Analogy Between Bubbles in Fluidized Beds and Bubbles in Liquids
7.4 Hydrodynamic Properties of Individual Bubbles
7.5 Bubble Interactions and Coalescence
7.6 Freely Bubbling Beds
7.7 Other Factors Influencing Bubbles in Gas-Fluidized Beds
References
Problems
8 Slug Flow
8.1 Introduction
8.2 Types of Slug Flow
8.3 Analogy Between Slugs in Fluidized Beds and Slugs in Liquids
8.4 Experimental Identification of the Slug Flow Regime
8.5 Transition to Slug Flow
8.6 Properties of Single Slugs
8.7 Hydrodynamics of Continuous Slug Flow
8.8 Mixing of Solids and Gas in Slugging Beds
8.9 Slugging Beds as Chemical Reactors
References
Note
9 Turbulent Fluidization
9.1 Introduction
9.2 Flow Structure
9.3 Gas and Solids Mixing
9.4 Effect of Column Diameter
9.5 Effect of Fines Content
References
Problems
10 Entrainment from Bubbling and Turbulent Beds
10.1 Introduction
10.2 Definitions
10.3 Ejection of Particles into the Freeboard
10.4 Entrainment Beyond the Transport Disengagement Height
10.5 Entrainment from Turbulent Fluidized Beds
10.6 Parameters Affecting Entrainment of Solid Particles from Fluidized Beds
10.7 Possible Means of Reducing Entrainment
Solved Problem
References
Problems
11 Standpipes and Return Systems, Separation Devices, and Feeders
11.1 Standpipes and Solids Return Systems
11.2 Standpipes in Recirculating Solids Systems
11.3 Standpipes Used with Nonmechanical Solids Flow Devices
11.4 Solids Separation Devices
11.5 Solids Flow Control Devices/Feeders
References
Problems
12 Circulating Fluidized Beds
12.1 Introduction
12.2 Basic Parameters
12.3 Axial Profiles of Solids Holdup/Voidage
12.4 Radial Profiles of Solids Distribution
12.5 The Circulating Turbulent Fluidized Bed
12.6 Micro-flow Structure
12.7 Gas and Solids Mixing
12.8 Reactor Performance of Circulating Fluidized Beds
12.9 Effect of Reactor Diameter on CFB Hydrodynamics
References
Problems
13 Operating Challenges
13.1 Electrostatics
13.2 Agglomeration
13.3 Attrition
13.4 Wear
References
Problem
14 Heat and Mass Transfer
14.1 Heat Transfer in Fluidized Beds
14.2 Mass Transfer in Fluidized Beds
References
Problem
15 Catalytic Fluidized Bed Reactors
15.1 Introduction
15.2 Reactor Design Considerations
15.3 Reactor Modelling
15.4 Fluidized Bed Catalytic Reactor Models
15.5 Conclusions
References
Problems
16 Fluidized Beds for Gas–Solid Reactions
⋆
16.1 Introduction
16.2 Gas–Solid Reactions for a Single Particle
16.3 Reactions of Solid Particles Alone
16.4 Conversion of Particles Bathed by Uniform Gas Composition in a Dense Gas–Solid Fluidized Bed
16.5 Conversion of Both Solids and Gas
16.6 Thermal Conversion of Solid Fuels in Fluidized Bed Reactors
16.7 Final Remarks
Acknowledgments
Notations
References
Problems
Note
17 Scale-Up of Fluidized Beds
17.1 Challenges of Scale
17.2 Historical Lessons
17.3 Influence of Scale on Hydrodynamics
17.4 Approaches to Scale-Up
17.5 Practical Considerations
17.6 Scale-Up and Industrial Considerations of Fluidized Bed Catalytic Reactors
References
Problems
18 Baffles and Aids to Fluidization
18.1 Industrial Motivation
18.2 Baffles in Fluidized Beds
18.3 Other Aids to Fluidization
18.4 Final Remarks
References
Problem
19 Jets in Fluidized Beds
19.1 Introduction
19.2 Jets at Gas Distributors
19.3 Mass Transfer, Heat Transfer, and Reaction in Distributor Jets
19.4 Particle Attrition and Tribocharging at Distributor Holes
19.5 Jets Formed in Fluidized Bed Grinding
19.6 Applications
19.7 Jet Penetration
19.8 Solids Entrainment into Jets
19.9 Nozzle Design
19.10 Jet-Target Attrition
19.11 Jets Formed When Solids Are Fed into a Fluidized Bed
19.12 Jets Formed When Liquid Is Sprayed into a Gas-Fluidized Bed
19.13 Jet Penetration
References
Problem
20 Downer Reactors
20.1 Downer Reactor: Conception and Characteristics
20.2 Hydrodynamics, Mixing, and Heat Transfer of Gas–Solid Flow in Downers
20.3 Modelling of Hydrodynamics and Reacting Flows in Downers
20.4 Design and Applications of Downer Reactors
20.5 Conclusions and Outlook
References
Problems
21 Spouted (and Spout-Fluid) Beds
21.1 Introduction
21.2 Hydrodynamics
21.3 Heat and Mass Transfer
21.4 Chemical Reaction
21.5 Spouting vs. Fluidization
21.6 Spout-Fluid Beds
21.7 Non-conventional Spouted Beds
21.8 Applications
21.9 Multiphase Computational Fluid Dynamics
References
22 Three-Phase (Gas–Liquid–Solid) Fluidization
22.1 Introduction
22.2 Reactor Design and Scale-up
22.3 Compartmental Flow Models
22.4 Fluid Dynamics in Three-Phase Fluidized Beds
22.5 Phase Mixing, Mass Transfer, and Heat Transfer
22.6 Summary
References
Problems
Index
End User License Agreement
List of Tables
Chapter 1
Table 1.1 Industrial applications of gas-fluidized beds.
Table 1.2 Usual operating ranges for solid-catalyzed gas-phase reactors.
Table 1.3 Summary of proceedings of major fluidization and CFB conferences.
Chapter 2
Table 2.1 Typical sphericities for common materials.
Table 2.2 Terminal settling velocity correlations for spheres
Table 2.3 Particle properties and gasrelative humidities (RHs) that generally...
Table 2.4 Effects of increasing temperature and pressure on minimum fluidizat...
Chapter 4
Table 4.1 Major characteristics of gas–solid fluidization and adjacent flow r...
Table 4.2 Flow regimes and corresponding flow patterns in a vertical tube wit...
Chapter 5
Table P5.1 Experimental data and conditions.
Chapter 7
Table 7.1 Other influences on bubbles in gas-fluidized beds.
Chapter 8
Table 8.1 Factors that tend to favour each of the three modes of slugging.
Chapter 9
Table 9.1 Some commercial turbulent fluidized bed reactors.
Chapter 10
Table 10.1 Selected correlations for elutriation rate constant.
Chapter 12
Table 12.1 Operating conditions of CFB combustors and FCC risers.
Table 12.2 Typical advantages and disadvantages of turbulent and circulating ...
Table 12.3 Experimental studies on characteristics of particle aggregates in ...
Table 12.4 Summary of solids aggregation forms in CFB risers.
Chapter 13
Table 13P.1 Particle and fluid properties.
Table 13P.2 Attrition testing conditions and Sauter mean diameter results.
Chapter 14
Table 14.1 Regimes of heat transfer for different particle sizes.
Table 14.2 Accumulation coefficients for common gases at room temperature.
Table 14.3 Heat transfer performances between two different types of finned t...
Table 14.4 Radiation percentages of overall heat transfer.
Table 14P.1 Particle sieving analysis result.
Chapter 15
Table 15.1 Some requirements of fluidized bed catalytic reactors.
Table 15.2 Comparison of typical fluidized bed catalytic reactors and gas–sol...
Table 15.3 Comparison of major fluidization flow regimes for most reactor app...
Table 15.4 How to identify apparent and intrinsic kinetics.
Table 15.5 Comparison of simple and sophisticated reactor models.
Chapter 16
Table P16.1 Results of Solved Problem 16.3.
Chapter 17
Table 17.1 Atmospheric combustor modelled by a bed fluidized at ambient condi...
Chapter 20
Table 20.1 Representative inlet design for downers.
Table 20.2 Comparison of DCC process in commercial riser and hot downer.
Table 20.3 Summary of key features of riser and downer reactors.
Chapter 21
Table 21.1 Significant differences between gas-spouted beds and gas-fluidized...
Chapter 22
Table 22.1 Parameters that affect bed transport phenomena.
Table 22.2 Qualitative effect of changes of operating conditions and physical...
Table 22.3 Qualitative effect of varying operating conditions and physical an...
Table 22P.1 Operating conditions and phase physical properties for worked exa...
Table 22P.2 Heavy oil conversion reactions and kinetic parameters.
Table 22P.3 Minimum fluidization velocity, particle terminal velocity, and ga...
Table 22P.4 Gas and liquid superficial velocities in the ebullated bed region...
Table 22P.5 Ebullated bed and freeboard region phase holdups.
Table 22P.6 Reactions rates and heavy oil conversion estimates for H ...
List of Illustrations
Chapter 2
Figure 2.1 Graphical identification of the minimum fluidization velocity,
U
m
...
Figure 2.2 Minimum fluidization velocity,
U
mf
, for spherical particles of di...
Figure 2.3 Geldart powder classification group boundaries for fluidizat...
Chapter 3
Figure 3.1 Limits of existence for a liquid-fluidized bed of spherical parti...
Figure 3.2 (a) Homogeneous expansion of a liquid-fluidized bed. (b
1
–b
3
) Snap...
Figure 3.3 Parameter
n
as reported by Richardson–Zaki as a function of
Re
t
....
Figure 3.4
U
i
/
v
t
ratio reported by Richardson–Zaki as a function of
Re
t
.
Figure 3.5 Layer inversion observed in a small-scale pseudo-2D geometry simu...
Figure 3.6 Layer inversion of lab-scale water-fluidized bed containing
x
1
= ...
Figure 3.7 Region of possible occurrence of layer inversion characterized by...
Chapter 4
Figure 4.1 Flow patterns in gas–solid fluidization systems, modified from ...
Figure 4.2 Standard deviation of absolute pressure fluctuations in a 0.1 m
I
...
Figure 4.3 Instantaneous spatial distribution of voids in a gas–solid fluidi...
Figure 4.4 Standard deviation of pressure fluctuations at three heights in a...
Figure 4.5 Comparison of simulated amplitude of local pressure fluctuations ...
Figure 4.6 Simulated standard deviations of differential pressure fluctuatio...
Figure 4.7 Schematic of a bottom-restricted circulating fluidized bed system...
Figure 4.8 Flow pattern transitions in a circulating fluidized bed system.
Figure 4.9 Fluidization flow regime diagram of Bi and Grace, extended from G...
Figure 4.10 Schematic of nonrestricted vertical transport line with gas flow...
Figure 4.11 Flow regime diagram for nonrestricted vertical transport lines. ...
Figure 4.12 Flow regime map for batch gas–solid fluidization together with l...
Chapter 5
Figure 5.1 2D column with glass beads depicting gas bubbles.
Figure 5.2 Basic components of a gas–solid fluidized bed system. (1) fluidiz...
Figure 5.3 Some examples of distributor plates: (a) top view and (b) side vi...
Figure 5.4 Side view of the effect of shroud on jets: (a) diverging jet, (b)...
Figure 5.5 Schematic diagram of an air-supply system for a gas–solid fluidiz...
Figure 5.6 Depiction of angle of repose of particles.
Figure 5.7 Depiction of angle of internal friction (
α
) indicated by par...
Figure 5.8 Piston set-up for measuring angle of internal friction.
Figure 5.9 Typical axial distribution of time-average gauge pressure.
Figure 5.10 Top view of optical probe tips in relation to particle size and ...
Figure 5.11 Tip of an optical fibre probe with one light-emitting and two li...
Figure 5.12 Coherence function and standard deviation vs. superficial gas ve...
Figure P5.1 Time-average pressure drop plotted against
U
.
Figure P5.2 Simplified schematic of acrylonitrile fluidized bed reactor.
Figure P5.3 Grid hole discharge coefficient design chart.
Figure P5.4 Schematic of experimental set-up.
Figure P5.5 Time-average radial voidage profile.
Chapter 6
Figure 6.1 Different CFD models for gas–solid flows.
Figure 6.2 Regime map for granular flow rheology. (a) Quasi-static regime, (...
Figure 6.3 Schematic of soft-sphere model of particle collision.
Figure 6.4 TFM simulation of a bubbling fluidized bed with immersed tube bun...
Figure 6.5 CFD–DPM simulation of a small-scale circulating fluidized-bed sys...
Chapter 7
Figure 7.1 Shapes of isolated bubbles, viewed by X-rays, rising in fully...
Figure 7.2 Tracing of images of a pair of vertically aligned bubbles in late...
Figure 7.3 Tracings from photographs of a bubble splitting into two smaller ...
Figure 7.4 Bubble rising in a thin “two-dimensional” fluidized bed showing w...
Figure 7.5 Wake volume fraction and wake angle as functions of particle size...
Figure 7.6 Nitric oxide bubble rising in a two-dimensional fluidized bed sho...
Figure 7.7 View of bubbles rising in a two-dimensional (thin) fluidized bed ...
Figure 7.8 Schematic showing development of characteristic nonuniform spatia...
Chapter 8
Figure 8.1 Profiles of types of slug flow in vertical columns. (a) Round-nos...
Figure 8.2 Cloud formation for a single slug in a column of circular cross s...
Figure 8.3 The assumed sequence of slugs is portrayed in Figure 8.3, with th...
Chapter 9
Figure 9.1 Axial voidage profiles in turbulent fluidized beds.
Figure 9.2 Radial profiles of solids holdup and particle velocity in turbule...
Figure 9.3 Bubble/void diameter and its rise velocity as a function of super...
Figure 9.4 Radial profiles of local void fraction in bubbling and turbulent ...
Figure 9.5 Axial gas dispersion coefficient as a function of superficial gas...
Figure 9.6 Axial gas dispersion coefficient in dense emulsion phase and dilu...
Figure 9.7 Radial gas dispersion coefficient as a function of superficial ga...
Figure 9.8 Axial solids dispersion coefficient as a function of superficial ...
Figure 9.9 Normalized radial voidage profiles in turbulent fluidized beds of...
Figure 9.10 Effect of fines content on axial and radial dispersion coefficie...
Chapter 10
Figure 10.1 Solids concentration profiles in different zones of a gas–solid ...
Figure 10.2 Transport disengagement height (TDH) graphical correlation.
Figure 10.3 Normalized entrainment flux vs. electrostatic-to-gravity-force r...
Chapter 11
Figure 11.1 Schematic drawing of FCC process solids circulation loop.
Figure 11.2 Standpipe relative gas velocity flow cases.
Figure 11.3 (a) Overflow and (b) underflow standpipe configurations.
Figure 11.4 Operation of an overflow fluidized standpipe. (a) low pressure d...
Figure 11.5 Operation of an underflow packed bed standpipe. (a) underflow st...
Figure 11.6 Adding aeration prevents defluidization in underflow fluidized s...
Figure 11.7 Why aeration is added uniformly in group A underflow fluidized s...
Figure 11.8 Fluidized bed two-stage cyclone recirculation system.
Figure 11.9 Gas–solid flow in an angled standpipe.
Figure 11.10 Pressures around an FCC unit.
Figure 11.11 Most common types of nonmechanical valves used for solids contr...
Figure 11.12 Gas flows around an L-valve bend. (a) Gas flow down standpipe a...
Figure 11.13 L-valve in a CFB loop configuration.
Figure 11.14 Automatic (a) L-valve, (b) seal pot, and (c) loop seal.
Figure 11.15 Relative solids flow rates in primary and secondary diplegs.
Figure 11.16 (a) Trickle valve and (b) counterweighted flapper valve.
Figure 11.17 Gas flow direction in a dipleg as a function of solids mass flu...
Figure 11.18 (a) Uniflow and (b) reverse-flow cyclones.
Figure 11.19 (a) Volute, (b) tangential, and (c) axial inlet reverse-flow cy...
Figure 11.20 Effect of loading on cyclone pressure drop.
Figure 11.21 (a) Tangential and (b) volute inlet operation at high solids lo...
Figure 11.22 Schematic drawing of top view of U-beam separator.
Figure 11.23 Control valve/feeders for particulate solids. (a) Slide valve, ...
Chapter 12
Figure 12.1 Typical configuration for a circulating fluidized bed (CFB).
Figure 12.2 Typical solids holdup profiles along circulating fluidized bed: ...
Figure 12.3 Typical radial profile of solids holdup.
Figure 12.4 Radial profiles of (a) particle velocity and (b) corresponding s...
Figure 12.5 Schematic of circulating turbulent fluidized bed.
Figure 12.6 Comparison of solids concentration distribution in three fluidiz...
Figure 12.7 Photographs of particle clusters in risers: (a) images of cluste...
Figure 12.8 Sequences of clusters in CFB riser: (a) cluster on wall side; (b...
Figure 12.9 Illustration of proposed particle aggregation processes.
Figure 12.10 Axial gas dispersion at different superficial gas velocities....
Figure 12.11 Concentrations along CFB reactor: (a) ozone concentration; (b) ...
Figure 12.12 Ozone concentration in axial direction for very high density co...
Figure 12.13 Distribution of the ozone concentration inside a CFB riser, (a)...
Figure 12.14 Effects of reactor diameter on solids concentration and particl...
Figure 12.15 Effects of reactor geometry on solids holdup distribution.
Chapter 13
Figure 13.1 Change of particle size distribution from different modes of att...
Figure 13.2 Cross section of horizontal heat transfer tube after being immer...
Figure 13P.1 Single charged polyethylene particle adhering to a fluidization...
Chapter 14
Figure 14.1 Relative orders of magnitude of heat transfer coefficients for e...
Figure 14.2 Temperature profile in a fluidized bed combustor with heavily co...
Figure 14.3 Schematics of unsteady-state gas convective heat transfer: (a) s...
Figure 14.4 Different temperature profiles between heating surface and surro...
Figure 14.5 Simultaneous measurement of local bed voidage and local heat tra...
Figure 14.6 Effect of gas flow rate and particle size on heat transfer.
Figure 14.7 Dependence of maximum heat transfer coefficient on particle size...
Figure 14.8 Effect of pressure on heattransfer.
Figure 14.9 Measurements (symbols) of heat transfer coefficients and predict...
Figure 14.10 Experimental instantaneous heat transfer coefficient near a hor...
Figure 14.11 Polar plot of local heat transfer coefficient vs. angle around ...
Figure 14.12 Common tube bundle configurations in fluidized beds and paramet...
Figure 14.13 Dimensionless correction factor for heat transfer coefficients ...
Figure 14.14 Comparison between predictions of Martin's model and heat trans...
Figure 14.15 Key dimensions of a finned tube.
Figure 14.16 Comparison of predicted and experimental heat transfer coeffici...
Figure 14.17 Modified emissivity vs. surface temperature.
Figure 14.18 Schematic diagram of circulating fluidized bed with heat transf...
Figure 14.19 3D and sectional view of part of membrane water–wall assembly....
Figure 14.20 Schematic of the bubbling bed approach to mass transfer calcula...
Figure 14P.1 Heat transfer measurement in a rectangular fluidized bed....
Figure 14P.2 Dimensions of the fluidized bed particle heat exchanger.
Chapter 15
Figure 15.1 Design workflow for selection of process alternatives and reacto...
Figure 15.2 Steps for model development and validation.
Figure 15.3 Equilibrium reactor simulation for NO and SO
2
oxidation. System ...
Figure 15.4 Basic formulation of mass/mole and energy balances.
Figure 15.5 Schematic of flow division among phases.
Figure 15.6 Schematic of comprehensive two-phase reactor models.
Figure 15.7 Example of a model assessment study for a fluidized bed catalyti...
Figure 15.8 Example of a logic diagram for model programming and solution.
Chapter 16
Figure 16.1 Steps in reaction of a single solid particle with a gas.
Figure 16.2 Steps in shrinking particle reaction. Solid and gaseous reactant...
Figure 16.3 Steps in shrinking unreacted core particle reaction. Solid conve...
Figure 16.4 Schematic representation of grain model for gas–solid reaction w...
Figure 16.5 Schematic representation of fluidized bed reactor treating parti...
Figure 16.6 Schematic representation of (a) CLC, (b) iG-CLC, and (c) CLOU pr...
Chapter 17
Figure 17.1 General development scheme of fluidized bed process.
Figure 17.2 Effect of column diameter on voidage for Sasol Advanced Synthol ...
Figure 17.3 Effect of column diameter and superficial gas velocity on bubble...
Figure 17.4 Effect of column diameter on transition velocity,
U
c
.
Figure 17.5 Conceptual diagram of the Biomass CHP Plant Güssing.
Figure 17.6 Schematic diagrams of pilot plants at TU Vienna depicting design...
Figure 17.7 Conceptual diagram of the sorbent-enhanced biomass gasification ...
Figure 17.8 Photograph of the sorbent-enhanced biomass gasification at the U...
Chapter 18
Figure 18.1 Mesh grid.
Figure 18.2 Perforated plate.
Figure 18.3 Different types of louver baffles. (a) louver baffle; (b) single...
Figure 18.4 Crosser grid.
Figure 18.5 FCC external catalyst cooler (KBR).
Figure 18.6 Pagoda-shape (a) and ridge-shape internals (b).
Figure 18.7 Various fixed packings used as catalyst stripper baffles. (a) KF...
Figure 18.8 KBR's fixed packing for FCC regenerators.
Figure 18.9 Diagram of dilute region immediately underneath a horizontal lou...
Figure 18.10 Effect of louver baffle on axial profile of solids holdup. FCC ...
Figure 18.11 Effect of louver baffle on magnitudes of pressure fluctuations....
Figure 18.12 Effect of different baffles on bed expansion in a two-dimension...
Figure 18.13 Effect of baffles on transition from bubbling to turbulent flow...
Figure 18.14 Effect of baffles on axial gas dispersion coefficients in fluid...
Figure 18.15 Comparison of simulated transient vertical solids flux in baffl...
Figure 18.16 Typical baffles for fast fluidized bed risers. (a) ring baffle;...
Figure 18.17 Typical transient stresses on an inclined slat under different ...
Figure 18.18 Particle behaviour in a freely bubbling bed: (a) without electr...
Figure 18P.1 Schematic of an industrial FCC regenerator wall.
Chapter 19
Figure 19.1 Perforated plate.
Figure 19.2 Windbox.
Figure 19.3 Sparger.
Figure 19.4 Cross-sectional view of sparger pipe.
Figure 19.5 Bubble flow patterns with a good and a poor distributor.
Figure 19.6 PIV measurements in a 2-D fluidized bed.
Figure 19.7 MRI measurements in a 3-D fluidized bed.
Figure 19.8 Design to avoid defluidized zones (pyramidal additions in red)....
Figure 19.9 Punched plate distributor with details of one hole.
Figure 19.10 Slotted distributor (slots at a 45° angle).
Figure 19.11 Expansion cycle of a pulsating vertical gas jet.
Figure 19.12 Magnetic resonance imaging of a pulsating vertical jet. Images ...
Figure 19.13 X-ray picture of the merging of two jets.
Figure 19.14 Attrition processes.
Figure 19.15 Shrouded jet design.
Figure 19.16 Jet milling mechanisms.
Figure 19.17 Particle velocities within the first part of the jet formed by ...
Figure 19.18 Particle velocity on jet centreline (glass spheres with a Saute...
Figure 19.19 Typical attrition nozzle.
Figure 19.20 Solids distribution in a fluidized bed with three opposing jets...
Figure 19.21 X-ray picture of jet cavity created by gas–liquid spray in a bu...
Chapter 20
Figure 20.1 Four quadrants of gas–solid two-phase flows.
Figure 20.2 Diagrams of downer reactors: (a) essential concept design and (b...
Figure 20.3 Basic hydrodynamic behaviour in downers with force balance analy...
Figure 20.4 Solid volume fraction at different axial positions in a downer: ...
Figure 20.5 Typical radial profiles of solid volume fraction, gas velocity, ...
Figure 20.6 Typical solids RTDs and Péclet numbers (
Pe
) in riser ...
Figure 20.7 Typical radial profiles of heat transfer coefficient and solid v...
Figure 20.8 Simplified reaction scheme of FCC process: four-lump reaction ki...
Figure 20.9 Comparison of model predictions and experimental data in downers...
Figure 20.10 CFD predictions of scale-up effect of downers.
Figure 20.11 Schematic of Eulerian–Lagrangian model for simulation of reacti...
Figure 20.12 CFD–DEM simulation of hydrodynamics in downer.
Figure 20.13 Comparison of reacting flow simulation results between riser an...
Figure 20.14 Representative outlet designs for downers.
Figure 20.15 Schematic diagrams of coupled downer-to-riser reactors (DTRR) f...
Chapter 21
Figure 21.1 Schematic diagram of a spouted bed. Arrows indicate direction of...
Figure 21.2 Flow regime map for wheat particles (prolate spheroids: 3.2...
Figure 21.3 Calculated and tracer-observed gas streamlines for a 0.24 m diam...
Figure 21.4 Typical pressure drop vs. flow rate curves for the onset of whea...
Figure 21.5 Schematic diagram of a multiple spouted bed.
Figure 21.6 (a) Schematic of a two-compartment slot-rectangular spouted bed....
Figure 21.7 Schematic diagram of a top-sealed spouted bed with draft tube an...
Chapter 22
Figure 22.1 Three-phase fluidization examples: (a) Co-current gas and liquid...
Figure 22.2 (a) LC-FINING unit schematic.(b) Grid schematic with plenum ...
Figure 22.3 Length and time scales in multiphase reactor modelling.
Figure 22.4 Schematic diagram of fluidized reactor development.
Figure 22.5 (a) Bed dynamic pressure drop as function of
U
L
at constant
U
g
. ...
Figure 22.6 Schematic diagram of flow regimes observed for an air-water-1.5...
Figure 22.7 Gas–liquid–solid fluidized bed dynamic pressure profiles in an a...
Figure 22.8 Impact of particle–bubble interaction on sharpness of bed–freebo...
Figure 22.9 Species concentration gradients across phase boundaries for a so...
Figure 22P.1 Gas–liquid–solid fluidized bed reactor sizing and design proced...
Figure 22P.2 Heavy oil conversion as a function of ebullated bed height.
Guide
Cover
Table of Contents
Begin Reading
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Essentials of Fluidization Technology
Edited by
John R. Grace
Xiaotao Bi
Naoko Ellis
Editors
Prof. John R. Grace
University of British Columbia
Chemical and Biological Engineering
Vancouver Campus
2360 East Mall
Canada
V6T 1Z3 NK
Prof. Xiaotao Bi
University of British Columbia
Chemical and Biological Engineering
Vancouver Campus
2360 East Mall
Canada
V6T 1Z3 NK
Prof. Naoko Ellis
University of British Columbia
Chemical and Biological Engineering
Vancouver Campus
2360 East Mall
Canada
V6T 1Z3 NK
Cover Credit: iStock # 1153898634/ DamienGeso.
All books published by Wiley-VCH are carefully produced. Nevertheless, authors, editors, and publisher do not warrant the information contained in these books, including this book, to be free of errors. Readers are advised to keep in mind that statements, data, illustrations, procedural details or other items may inadvertently be inaccurate.
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All rights reserved (including those of translation into other languages). No part of this book may be reproduced in any form – by photoprinting, microfilm, or any other means – nor transmitted or translated into a machine language without written permission from the publishers. Registered names, trademarks, etc. used in this book, even when not specifically marked as such, are not to be considered unprotected by law.
Print ISBN: 978-3-527-34064-4
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Cover Design: Adam-Design, Weinheim, Germany
Preface
We are pleased to present the first comprehensive teaching book on fluidized beds to be published in nearly three decades since the second edition of the Kunii and Levenspiel, Fluidization Engineering book in 1991 and the Gas Fluidization Technology book edited by Geldart, published in 1986. During the intervening period, there has been considerable progress, leading to new understanding in such areas as multiphase computational fluid dynamics (CFD), interparticle forces, electrostatics, jets, downers, and advanced experimental methodologies (such as particle tracking, MRI, and various types of tomography). These new areas are, to a degree, covered in this book, while we have also drawn heavily on the “more classical” fluidization literature. We have also included chapters on liquid and three-phase fluidization, spouted beds, CFD, and downers, topics not included in previous fluidization books intended as educational texts.
There have also been a number of new fluidized bed applications and processes in recent times, most notably in chemical looping, processing of silicon-containing materials for solar applications, extraction of advanced materials, thermochemical conversion of biomass residues to energy and biofuels, and efforts to produce or utilize nanoparticles. While these new processes are not dealt with explicitly in depth in the book, they have influenced the fluidization research community and topics of research articles, hence affecting the knowledge reflected in this book. The authors who have contributed to the book combine some who have been engaged in this field for many decades with a new generation of fluidization experts, eager to advance the understanding and applicability of fluidized beds.
In choosing the material to be included in the book, we have been guided by the word “Essentials” in the title. Thus we have had to leave out material, which, while interesting, is not essential for most beginners and general readers. However, readers should, after close reading of the chapters, be able to delve into the extensive specialized research literature with a good general background. Our book will have served its purpose if it helps readers, whether these be young engineers working in industry or graduate students undertaking research projects related to fluidization, become familiar with the broad areas of fundamental and practical knowledge underlying the field. Incorporation of a small number of solved problems and unsolved problem exercises is intended to further the understanding of the topics covered. In addition to single-reader usage, we intend that this book be available as a textbook for courses related to fluidization and multiphase systems.
Vancouver31 October 2019
John Grace
Naoko Ellis
Xiaotao Bi
Acknowledgement
We thank the authors for responding with enthusiasm to our proposal to write chapters of the book and for their help in preparing and revising the material. We thank Zezhong John Li for assistance with figures, logistics, and administrative details. We are grateful to the Natural Sciences and Engineering Research Council of Canada for funding some of the expenses related to the preparation of this book, as well as for covering the costs of a number of studies that have contributed to our experience and expertise in fluidization and related areas.
1Introduction, History, and Applications
John R. Grace
University of British Columbia, Department of Chemical and Biological Engineering, 2360 East Mall, Vancouver, Canada V6T 1Z3
1.1 Definition and Origins
Fluidization occurs when solid particles are supported and allowed to move relative to each other as a result of vertical motion of a fluid (gas or liquid) in a defined and contained volume. Most commonly, the fluid is a gas blown upwards by a blower or compressor through a perforated flat plate or a series of orifices, but many other configurations are possible. Once an assembly (“bed”) of particles has been actuated in this manner, it is said to be a “fluidized bed.”
The origin of fluidized beds is unclear, but liquid-fluidized beds likely preceded gas-fluidized beds. For example, early fluidization has been attributed to Agricola [1] when he described and illustrated hand jigging for ore dressing. The first industrial applications of fluidized beds were likely beds of ore particles fluidized by liquids in order to classify them by size or density in an operation known as “teetering” [2].
The first widespread application of gas-fluidized beds was in the 1920s in Germany when Winkler [3] patented a novel gasifier. However, the terms “fluidization” and “fluid bed” did not emerge until about 1940 when researchers in the United States developed gas-supported beds for catalytic cracking of heavy hydrocarbons [4, 5]. A plaque commemorating the development of the fluid bed reactor at a local oil refinery was erected at the Louisiana Art and Science Museum in Baton Rouge in 1998.
The term “circulating fluidized bed” (or “CFB”) has been used since the 1980s to cover configurations where there is no upper bed surface, with particles supported by fluid contained in equipment that incorporates one or more gas–solid separator (usually cyclones), as well as recirculation piping as an integral part of the system. These have become popular, mostly for calcination, energy, and metallurgical operations [6].
Commercial fluidized bed reactors are now among the largest chemical reactors in the world. For example, in China fluidized bed combustors have reached a power capacity of 660 MWe [7].
1.2 Terminology
As in other fields, specialized terminology is used by the fluidization community. Definitions of the following terms may be helpful for those new to the field:
Agglomeration
: Particles sticking together to form assemblies (agglomerates).
Attrition
: Break-up of particles due to collisions or other interactions and stresses.
Bed expansion
: Height of operating fluidized bed divided by static bed height or bed height at minimum fluidization.
Bubbles
: Voids containing few, if any, particles, rising relative to the particles above them and behaving in a somewhat analogous manner to bubbles in liquids.
Choking
: Collapse of dilute gas–solid suspension into dense phase flow when decreasing the gas velocity at constant solids flow. For different modes of choking, see [
8
].
Circulating fluidized bed
: Fluid and particles in relative motion in a configuration where there is no distinct upper bed surface and entrained particles are continuously separated and returned to the base of a riser.
Cluster
: Group of particles travelling together due to hydrodynamic factors.
Dense phase
: Gas–solid region where the concentration of particles is sufficiently high that there are significant particle–particle interactions and contacts.
Dilute phase
: Region where particle concentration is low enough that interparticle contacts are relatively rare.
Downer
: Vessel in which particles are contacted with a fluid while they fall downwards.
Distributor
: Horizontal plate with perforations, nozzles, or other openings or other means of introducing a fluidizing fluid to support the weight of particles and cause them to move while also supporting the dead weight of the particles when the flow of fluid is interrupted.
Elutriation
: Progressive selective removal of finer particulates by entrainment.
Fines
: Relatively small particles, typically those smaller than 37 or 44 μm in diameter.
Fluid
: Either gas or liquid, usually the former in the context of fluidization.
Freeboard
: Region extending from dense fluidized bed upper surface to top of vessel.
Geldart powder group
: See
Chapter 2
.
Grid
: Alternate name for gas distributor supporting the fluidized bed and assuring uniform entry of gas at its base.
Loop seal
: Common configuration (see
Chapter 11
) for recirculating solids to the bottom of a fluidized bed or riser without reverse flow of gas.
Membrane walls
: Containing wall consisting of vertical heat transfer tubes connected by parallel fins, commonly used in combustion applications (see
Chapter 14
).
Membrane reactor
: Reactor containing solid surfaces (“membranes”) that are selectively permeable to one or more component of the gas mixture.
Plenum chamber
: Pressurized chamber below the distributor of a fluidization column from which fluidizing fluid is fed into the bed above the distributor.
Riser
: Tall column in which particles are carried, on average, upwards by an ascending fluid.
Segregation
: Tendency for particles of different physical characteristics (e.g. different size, density, and/or shape) to preferentially become more concentrated in different spatial regions.
Solids
: Generic term referring to solid particles.
Superficial velocity
: Volumetric flow rate of fluid divided by total column cross-sectional area.
Voidage
: Fraction of bed volume or local volume occupied by fluid.
Windbox
: Same as plenum chamber, but only when the fluidizing fluid is a gas.
Other terms are introduced and defined as needed in the text.
1.3 Applications
Gas-fluidized beds account for most of the commercial applications of fluidized beds. Relative to packed beds, gas-fluidized beds commonly offer the following advantages:
Temperature uniformity (with variations seldom exceeding 10 °C in the dense bed and elimination of “hot spots.”)
Excellent bed-to-surface heat transfer coefficients (typically 1 order of magnitude better than in fixed beds and 2 orders of magnitude better than in empty columns.)
Ability to add and remove particles continuously, facilitating catalyst regeneration and continuous operation.
Relatively low pressure drops (essentially only enough to support the bed weight per unit cross-sectional area.)
Scalable to very large sizes (e.g. there are commercial fluidized bed reactors hundreds of square metres in cross-sectional area.)
Excellent catalyst effectiveness factors (i.e. very low intra-particle mass transfer resistances): With particles 1 order of magnitude smaller than in fixed beds, i.e. catalyst particles smaller than 100 μm, effectiveness factors usually approach 1.
Good turndown capability: The gas flow rate can be varied over a wide range, typically by at least a factor of 2–3.
Ability to tolerate some liquid: For example, in a number of processes, such as fluid catalytic cracking, liquids are sprayed into the column where they vaporize and then react.
Wide particle size distributions (typically with a ratio of upper to lower decile particle diameter,
d
p90
/
d
p10
, of 10: 20).
These advantages must be significant enough to compensate for some significant disadvantages of gas-fluidized beds:
Substantial vertical (axial) mixing of gas
: Gas is dragged downwards by descending particles resulting in “backmixing” and large deviations from plug flow, with typical axial Peclet numbers of order 5–10.
Substantial axial dispersion of solids
: Vigorous motion of particles and their clusters results in substantial axial dispersion and backmixing of solids. As a result, in continuous processes, some particles spend very little time in the bed, while others spend much longer than the mean residence time.
Bypassing of gas
: Gas associated with a lower-density phase, e.g. rising as bubbles, passes through the bed more quickly and with less access to particles than gas associated with a denser phase in which there is better gas–solid contacting.
Limitations on particles that can be successfully fluidized
: Particles of extreme shapes (e.g. needle or flat disc shapes) or smaller than about 30 μm in mean diameter are difficult, or even impossible, to fluidize.
Entrainment
: Particles, especially fine ones, are carried upwards by the exhaust or product gas and leave the column through the exit. To minimize their losses, entrained particles must normally be continuously captured and returned to the bottom of the vessel.
Attrition
: Particles can break or be abraded when they collide/interact with each other and with fixed surfaces.
Wear on surfaces
: Particle motion tends causes erosion/wastage of fixed surfaces.
Complexity and risk
: Fluidized beds are more complex to design, operate, and model than comparable fixed bed reactors. As a result, there is greater risk of problems and less than desired performance.
The advantages identified above have been found to outweigh the disadvantages in a number of industrially significant processes. The most important of these processes are listed in Table 1.1. Useful reviews of the early years of these processes were provided by Geldart [9–11].
Practical information related to many of the processes listed in Table 1.1 was summarized by Yerushalmi [12]. For information on a recently commercialized process, see Tian et al. [13]. For applications related to food processing, see Smith [14]. The typical operating range for catalytic fluidized bed reactors are summarized in Table 1.2. Particles tend to be larger and gas superficial velocities to be higher in the case of physical operations and for gas–solid reactions than for catalytic processes.
Applications of liquid-fluidized beds, spouted beds, and gas–liquid–solid (i.e. three-phase) fluidized beds are covered in Chapters 3, 21, and 22, respectively.
1.4 Other Reasons for Studying Fluidized Beds
In addition to being useful in many commercial applications, as summarized above and as outlined in later chapters, there are other reasons for interest in the behaviour of fluidized beds:
Table 1.1 Industrial applications of gas-fluidized beds.
Physical operations
Solid-catalyzed reactions
Gas–solid reactions
Drying of particles
Fluid catalytic cracking
Combustion and incineration
Granulation
Acrylonitrile
Gasification
Coating of surfaces by Chemical Vapour Deposition
Ethylene dichloride
Pyrolysis
Particle mixing/blending
Catalytic combustion
Torrefaction
Preheating and heating
Ethanol dehydration
Roasting of ores
Steam raising
Ethylene synthesis
Reduction of iron oxide
Freezing
Maleic anhydride
Polyolefin production
Quenching/tempering
Fischer–Tropsch synthesis
Fluid coking and flexicoking
Carburizing, nitriding
Aniline
Calcination
Constant temperature baths
Methanol to olefins
Catalyst regeneration
Filtering of particles
Methanol to gasoline
Chlorination, fluoridation
Feeding of particles
Oxidative dehydrogenation
Hydrochlorination of silicon
Sorption of harmful gases
Phthalic anhydride
Silane decomposition → pure Si
Treatment of burn victims
Catalytic reforming
Carbon nanotubes via Chemical Vapour Deposition
Tar cleaning
Gas–solid fermentation
Steam reforming
Melamine production
Methanation
Titanium dioxide pigment
Table 1.2 Usual operating ranges for solid-catalyzed gas-phase reactors.
Variable
Range and comments
Sauter mean particle diameter
50–100 μm
Particle size distribution
Broad, e.g. 0–200 μm
Reactor diameter
Up to ∼7 m
Pressure
Up to ∼80 bars
Temperature
Up to ∼600 °C
Superficial gas velocity
∼0.3–12 m/s
Static bed depth
1–10 m
Immersed surfaces
May contain horizontal or vertical heat transfer surfaces
Gas–solid separation
Heavily reliant on gas cyclones
Table 1.3 Summary of proceedings of major fluidization and CFB conferences.
Year
Designation
Conference location
Editor(s)
Publisher
1967
International Symposium on Fluidization
Eindhoven, Netherlands
Drinkenburg
Netherlands University Press
1975
Fluidization Technology
Asilomar, California
Keairns and Davidson
Hemisphere
1978
Fluidization
Cambridge, UK
Davidson and Keairns
Cambridge University Press
1980
Fluidization
Henniker, NH, USA
Grace and Matsen
Plenum Press
1983
Fluidization
Kashikojima, Japan
Kunii and Toei
Engineering Foundation
1985
CFB I
Halifax, Canada
Basu
Pergamon Press
1986
Fluidization V
Lyngby, Denmark
Ostergaard and Sorensen
Engineering Foundation
1988
CFB II
Compiègne, France
Basu and Large
Pergamon Press
1989
Fluidization VI
Banff, Canada
Grace, Shemilt, Bergougnou
Engineering Foundation
1990
CFB III
Nagoya, Japan
Basu, Horio, Hasatani
Pergamon Press
1992
Fluidization VII
Gold Coast, Australia
Potter and Nicklin
Engineering Foundation
1993
CFB IV
Hidden Valley, USA
Avidan
AIChE
1995
Fluidization VIII
Tours, France
Large and Laguérie
Engineering Foundation
1996
CFB V
Beijing, China
Kwauk and Li
Science Press, Beijing
1998
Fluidization IX
Durango, USA
Fan and Knowlton
Engineering Foundation
1999
CFB VI
Würzburg, Germany
Werther
DECHEMA
2001
Fluidization X
Beijing, China
Kwauk, Li, Yang
United Engineering Foundation
2002
CFB VII
Niagara Falls, Canada
Grace, Zhu, de Lasa
Canadian Society for Chemical Engineering
2004
Fluidization XI
Ischia, Italy
Arena, Chirone, Miccio, Salatino
Engineering Conferences International
2005
CFB VIII
Hangzhou, China
Cen
International Academic Publishers
2007
Fluidization XII
Harrison, Canada
Bi, Berruti, Pugsley
Engineering Conferences International
2008
CFB IX
Hamburg, Germany
Werther, Nowak, Wirth, Hartge
TuTech Innovation
2010
Fluidization XIII
Gyeong-ju, Korea
Kim, Kang, Lee, Seo
Engineering Conferences International
2011
CFB 10
Sunriver, Oregon, USA
Knowlton
Engineering Conferences International
2013
Fluidization XIV
Noordwijkerhout, Netherlands
Kuipers, Mudde, van Ommen, Deen
Engineering Conferences International
2014
CFB 11
Beijing, China
Li, Wei, Bao, Wang
Chemical Industry Press
2016
Fluidization XV
Montebello, Canada
Chaouki and Shabanian
Vol. 316 of Powder Technology, Elsevier
2017
CFB 12
Krakow, Poland
Nowak, Sciazko, Mirek
Journal of Power Technologies and Archivum Combustionis
2019
Fluidization XVI
Guilin, China
Wang and Ge
American Institute of Chemical Engineering
2020
CFB 13
Vancouver, Canada
Bi, Briens, Ellis, Wormsbecker
GLAB
They are inherently fascinating to observe, even finding their way into kinetic art.
Due to their complex flow patterns and the many factors involved, fluidized beds are challenging and difficult to model, with some surprising features.
They may be related to some natural phenomena, in particular avalanches, pyroclastic flows associated with volcanic eruptions and atmospheric convection of water drops, snowflakes, and hailstones [
15
,
16
]. There has even been speculation that some craters on the surface of the moon may be related to eruption of fluidization bubbles.
1.5 Sources of Information on Fluidization
Thousands of papers have been published in the scientific and engineering literature (journals and books) on fluidization fundamentals and applications. Due to length restrictions and its scope, this book cites only a small fraction of these articles. In addition to the many research articles that appear in journals like Powder Technology, Particuology, Advanced Powder Technology, and the International Journal of Multiphase Flow, many relevant papers appear in the major chemical engineering journals such as Chemical Engineering Science, Industrial and Engineering Chemistry Research, and American Institute of Chemical Engineers(AIChE) Journal, as well as a wide variety of other engineering- and physics-related journals. In addition, there are many published proceedings of conferences and symposia on fluidization. The most useful of these for those interested in fundamentals of fluidized beds have appeared in refereed proceedings of tri-annual Fluidization conferences, coordinated for many years by the Engineering Foundation and then by Engineering Conferences International, and tri-annual CFB conferences (recently renamed “International Conference on Fluidized Bed Technology.”) Information on these proceedings is summarized in Table 1.3. Less rigorously refereed proceedings of fluidized bed combustion, originally coordinated and published by the American Society of Mechanical Engineers at two-year intervals, and more recently every three years, also contain many applied and fundamental fluidization articles. Periodic China–Japan Conferences on Fluidization have also led to a series of well-edited volumes.
References
1
Agricola, G. (1556).
De Re Metallica
(trans. H.C. Hoover and L.H. Hoover), 310–311. New York, 1950: Dover.
2
Epstein, N. (2005). Teetering.
Powder Technol.
151: 2–14.
3
Winkler, F. (1922). Verfahren zum Herstellen Wassergas. German Patent 437,970.
4
Jahnig, C.E., Campbell, D.L., and Martin, H.Z. (1980). History of fluidized solids development at Exxon. In:
Fluidization
(eds. J.R. Grace and J.M. Matsen), 3–24. Plenum Press.
5
Squires, A.M. (1986). The story of fluid catalytic cracking: the first “circulating fluid bed.”. In:
Circulating Fluidized Bed Technology
(ed. P. Basu), 1–19. New York: Pergamon Press.
6
Reh, L. (1971). Fluid bed processing.
Chem. Eng. Prog.
67: 58–63.
7
Cai, R., Ke, X.W., Lyu, J.F. et al. (2017). Progress of circulating fluidized bed combustion technology in China: a review.
Clean Energy
1 (1): 36–49.
https://doi.org/10.1093/ce/zkx001
.
8
Bi, H.T., Grace, J.R., and Zhu, J. (1993). Types of choking in vertical pneumatic systems.
Int. J. Multiph. Flow
19: 1077–1092.
9
Geldart, D. (1969). Physical processing in gas fluidised beds.
Chem. Ind.
33: 311–316.
10
Geldart, D. (1967). The fluidised bed as a chemical reactor: a critical review of the first 25 years.
Chem. Ind.
31: 1474–1481.
11
Geldart, D. (1968). Gas-solid reactions in industrial fluidized beds.
Chem. Ind.
32: 41–47.
12
Yerushalmi, J. (1982). Applications of fluidized beds, Chapter 8.5. In:
Handbook of Multiphase Systems
(ed. G. Hetsroni), 8-152–8-216. Washington, DC: Hemisphere Publishing.
13
Tian, P., Wei, Y., Ye, M., and Liu, Z. (2015). Methanol to olefins: From fundamentals to commercialization.
ACS Catal.
5: 1922–1938.
14
Smith, P.G. (2007).
Applications of Fluidization to Food Processing
. Oxford, UK: Blackwell Science.
15
Wilson, C.J.N. (1984). The role of fluidization in the emplacement of pyroclastic flow: experimental results and their interpretation.
J. Volcanol. Geotherm. Res.
20: 55–84.
16
Horio, M. (2017). Fluidization in natural phenomena, reference module. In:
Chemistry, Molecular Sciences and Chemical Engineering
(ed. J. Reedijk). Waltham, MA: Elsevier
https://doi.org/10.1016/B978-0-12-409547-2.12185-7
.
17
Gullichsen, J. and Harkonen, E. (1981). Medium consistency technology.
TAPPI J.
64: 69–72. and 113–116.
Problems
1.1
Gullichsen and Harkonen [
17
] applied the term “fluidization” to the creation of a fluid-like state in pulp fibre aqueous suspensions due to rapid centrifugal mechanical mixing. Is this use of the term consistent with the definition of fluidization given in this chapter?
1.2
Imagine a reactor of cross-sectional area 100 m
2
containing catalyst particles of diameter 60 μm and density 1600 kg/m
3
. The void fraction of the static material is 0.52. How many particles are needed to fill the reactor to a static bed depth of 6 m? What is the total mass of these particles?
2Properties, Minimum Fluidization, and Geldart Groups
John R. Grace
University of British Columbia, Department of Chemical and Biological Engineering, 2360 East Mall, Vancouver, Canada V6T 1Z3
Keywords: properties; minimum fluidization velocity; voidage at minimum fluidization; fluidizability; pressure drop; Geldart classification;
2.1 Introduction
This chapter identifies the key particle and fluid properties that affect the ability to fluidize particles and that play a major role in determining the properties of fluidized beds. It is important to characterize these properties, or at least to consider whether each could be relevant, when deciding whether or not a given process might benefit from fluidization, as well as when designing, operating, and modelling fluidized bed processes. The chapter also considers different methods of measuring and predicting both the minimum fluidization velocity and the bed voidage at minimum fluidization, two very important quantities affecting the properties of fluidized beds. Finally, we introduce the four Geldart powder groups for particles fluidized by gases. This classification is widely used in discussing, characterizing, and explaining gas fluidization.
2.2 Fluid Properties
2.2.1 Gas Properties
Gas properties that influence the properties of gas-fluidized beds are:
Density
: Higher gas density leads to increased drag on particles and hence earlier and more vigorous fluidization. Gas density increases with increasing pressure and decreases with increasing temperature. Ideal gas behaviour can usually be assumed as a good approximation when assessing the roles of temperature and pressure on gas-fluidized beds.
Viscosity
: Higher gas viscosity causes greater drag for small particles, but plays only a small role for larger (e.g. Geldart D) particles (see
Section 2.6
). Gas viscosity is almost independent of pressure, but increases with increasing temperature.
Humidity
: As discussed in
Chapters 10
and
13
, the humidity (water vapour content) of a gas can affect the electrostatic charges on particles, thereby affecting the properties of, and entrainment from, gas-fluidized beds.
Adsorptivity
: The presence of gaseous components that adsorb on the surface of particles can affect van der Waals interparticle forces, thereby influencing the properties of fluidized beds, especially if the particles are relatively fine.
2.2.2 Liquid Properties
Liquid properties that affect the properties of liquid- and three-phase fluidized beds are:
Density
: Higher liquid density leads to both higher buoyancy and increased drag on particles and hence promotes earlier and more vigorous fluidization. Liquid density is virtually independent of pressure and generally (except for water in the 0–4 °C range) decreases slightly with increasing temperature.
Viscosity
: Higher viscosity causes greater drag on particles. Liquid viscosity is almost independent of pressure, but, contrary to the behaviour for gases, decreases with increasing temperature.
Contact angle
: The contact angle of a liquid on the surface of particles determines the extent to which the liquid wets particles, thereby affecting capillary forces.
Surface tension
: When gas is present in addition to the liquid, the surface tension of the liquid affects the formation and properties of drops and bubbles.
2.3 Individual Particle Properties
2.3.1 Particle Diameter
Particle size is profoundly important in fluidization processes. The size is expressed as a diameter, usually based on sieve (screening) analysis, as the mean of the opening sizes of the last screen through which the particle passed and the sieve through which it did not pass. For nonspherical particles, this corresponds approximately to the maximum dimension (or chord length) in the second of three principal (orthogonal) directions. Various sphere-equivalent diameters are also widely used, such as a volume-equivalent diameter (diameter of a sphere with the same volume as the particle). Of these equivalent diameters, the most appropriate average for fluidization is the Sauter mean:
where Vp
