1. Fluidization

2. What is Fluidization?
The operation by which fine solids are transformed into a fluidlike state through contact with a gas or liquid.

3. Some Key Terminology Attrition: breakdown of particles
Choking: collapse of a dilute-phase suspension into a dense-phase flow as the gas velocity is reduced at constant solids flow
Circulating fluidized bed: configuration intended to send particles around in a loop continuously, with no upper interface within the bed

4. Some Key Terminology
Downer: column where particles are made to fall through under gravity, usually with cocurrent gas flow
Distributor or Grid: support plate at bottom which introduce the gas to the bottom of the bed and supports the weight of the bed when it is shut down
Elutriation: tendency for fine particles to be preferentially entrained from the reactor

5. Some Key Terminology
Fast fluidization: flow regime whereby there is a relatively dense suspension, but no distinct upper surface, and a superficial velocity generally at least 3 m/s
Fines: generally particles smaller than 37 µm in diameter (smallest regular sieve size)
Freeboard: region extending from top of bed surface to top of reactor vessel

6. Some Key Terminology
Interstitial gas: gas between the particles in dense suspension
Porosity: fraction of gas in bed/given region as a whole or only inside the particles; sometimes used interchangeably with voidage
Riser: column where particles are carried upwards by the gas, with no distinct bed surface

7. Some Key Terminology
Segregation: tendency for particles to gather in different zones according to their size and/or density
Solids: used synonymously with particles
Superficial velocity: gas flow rate divided by total column surface area

8. Some Key Terminology
Transport disengaging zone: region in freeboard beginning at bed surface in which particle flux decreases with height and above which the entrainment is independent of height
Voidage (or void fraction): fraction by volume of suspension or bed which is occupied by the fluid

9. Elements of Fluidized Bed Reactors

10. Contacting Methods
Batch, cocurrent, backmix, crossflow, countercurrent
Solids may often be represented by backmix flow
By using proper baffling and staging of units, and with negligible entrainment of solids, the contacting in fluidized beds can be made to approach closely the usually desirable extreme of cuntercurrent plug flow
For good design, proper contacting of phases is essential

14. Advantages of Fluidized Beds
The smooth, liquid-like flow of particles allows continuous automatically controlled operations with ease of handling.
The rapid mixing of solids leads to nearly isothermal conditions throughout the reactor, hence the operation can be controlled simply and reliably.
It is suited to large-scale operations.

15. Advantages of Fluidized Beds
The circulation of solids between two fluidized beds makes it possible to transport the vast quantities of heat produced or needed in large reactors.
Heat and mass transfer rates between gas and particles are high when compared with other modes of contacting.
The rate of heat transfer between a fluidized bed and an immersed object is high, hence heat exchangers within fluidized beds require relatively small surface areas.

16. Disadvantages of Fluidized Beds
The difficult-to-describe flow of gas, with its large deviation from plug flow and the bypassing of solids by bubbles, represents an inefficient contacting system.
The rapid mixing of solids in the bed leads to nonuniform residence times of solids in the reactor.
Friable solids are pulverized and entrained by the gas.
Erosion of pipes and vessels from abrasion by particles.
For noncatalytic operations at high temperature the agglomeration and sintering of fine particles can necessitate a lowering in temperature of operation, reducing the reaction rate.

17. Commercial Applications
Solid-Catalysed Gas-Phase Reactions:
Fluid catalytic cracking, reforming
Fischer-Tropsch synthesis
Phthalic and maleic anhydride
Acrylonitrile and aniline
Chlirination and bromination of hydrocarbons
Polyethylene and polypropylene
Oxidation of SO2 to SO3

18. Commercial Applications
Gas-Solid Reactions:
Roasting or ores (ZnS, Cu2S, nickel sulphides, etc.)
Combustion and incineration
Gasification, coking and pyrolysis/carbonization
Calcination (limestone, phosphates, aluminium hydroxide)
Flurination of uranium oxide
Fluid coking
Reduction of iron oxide
Catalyst regeneration

19. Commercial Applications
Gas-Phase Non-Catalytic Reactions:
Natural gas combustion
Gas-Liquid-Solid:
Hydrotreating, hydroprocessing
Biochemical processes

20. Commercial Applications
Physical Processes:
Drying of particles
Coating of surfaces
Granulation (growing particles)
Heat treatment (e.g. annealing, quenching)
Medical beds
Filtration
Back-purging of filters
Blending
Classification

21. Flow Regimes for Upward Flow of Gas through Solid Particulate Materials

22. Various Kinds of Contacting of a Batch of Solids by Fluid

23. Classification of Fluidized Beds

24. Classification of Dense-Phase Fludized Beds

25. Industrial Applications of Fluidized Beds

26. Winkler Gas Generator

27. Large Scale Fluid Bed Catalytic Cracking Pilot Plant

28. Two-Stage Fluidized Salt Dryer

29. Pilot Plant for Fluidized Drying of Air with Adsorbent
The drying of air by circulation of large (3.2 to 4.8 mm) silica gel beads of multistage fluidized adsorption.
To reduce the humidity from to kg/kg pilot plant uses a five-stage fluidized absorber 1.2 m square in cross section, 6.1 m high, a pressure drop of 127 cm H2O.
A perforated plate distributor with rubber flaps at the lower end of the downcomers to assure steady flow of particles from stage to stage.

30. Typical Flow Regimes Observed

31. Qualitative Fluidization Map for Fine Solids

32. Solids Mixing by a Single Rising Bubble in a Bed of Small Particles

33. Solids Mixing by a Single Rising Bubble in a Bed of Large Particles