Fluidization

Fluidization operation

1. Fluidization

2. What is Fluidization? “The operation by which fine solids are transformed into a fluid like state through contact with a gas or liquid.” The terms fluidization and fluidized bed are used to describe the condition of fully suspended particle, since the suspension behave as a dense fluid. Fluidization refers to those gas-solids and liquid-solids system in which the solid phase is subjected to behave more or less like a fluid by the upwelling current of gas or liquid stream moving through the bed of solid particles.

3. Types of fluidization Particulate fluidization:- This occurs mainly with liquid-solid fluidized system. eg, when peas are fluidized by brine solution during bleaching. Aggregative fluidization:- This occurs with gas-solid fluidized system. As gas velocity increases, a fraction of the gas will pass through the bed in the form of bubbles. The velocity at which the bubble first form is known as the minimum bubbling velocity( ).  

4. Condition for fluidization

5. Once the bed is fluidized the pressure drop across the bed stays constant, but the bed height continues to increase with increasing flow. The superficial velocity need to support a bed of particles is much less than the terminal velocity for individual particles. The final bed height may be greater than the initial value for the fixed bed . For fast fluidization flow regime where by there is a relatively dense suspension, but no distinct upper the surface, and a superficial velocity generally at least 3 m/s. For fluidization the particles size are in range of 30 to 300 μ m.

6. Application of fluidization Most of the fluidization applications use one or more of three important characteristics of fluidized beds: Fluidized solids can be easily transferred between reactors. The intense mixing within a fluidized bed means that its temperature is uniform. There is excellent heat transfer between a fluidized bed and heat exchangers immersed in the bed.

7. Gas-Solid Reaction:- Fluid catalytic cracking, reforming Fischer- tropsch synthesis Oxidation of to Fluid cooking Catalyst regeneration  

8. Physical Process:- Drying of particles Coating of surfaces Granulation (growing particles) Filtration Blending

9. Advantage of fluidization The chief advantage of fluidization are that the solid is vigorously agitated by the fluid passing through the bed, and the mixing of the solid ensures that there are practically no temperature gradients in the bed even with quite exothermic or endothermic reactions. The smooth, liquid-like flow of particles allows continuous automatically controlled operations with easy of handling.

10. The rapid mixing of solids leads to nearly isothermal conditions throughout the reactor, hence the operation can be controlled simply and reliably. It is suitable to large-scale operation.

11. Disadvantage of fluidization The main disadvantage of gas-solid fluidization is the uneven contacting of gas and solid . Erosion of vessel and pipes from abrasion by particles. Attrition of solids. Because of attrition, the size of the solid particles is getting reduced The rapid mixing of solids in the bed leads to non uniform in the reactor.

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