1. G.H.PATEL COLLEGE OF ENGINEERING AND TECHNOLOGY Subject : mechanical operation Subject code : 2150505 TOPIC : fluidization guided by : prof V.B Patel Prof Rajesh Triphthy

2. Submitted By : MAYUR KASODARIYA130110105011 KAUMIL PANCHAL 130110105012 KOSHA DESAI130110105013 KRUPESH PATEL130110105014 MAYANK VITHALANI 130110105015

3. Content : Introduction Fluidization regimes Minimum fluidization velocity Fluidized bed Design of bed Expansion of fluidized bed Application of fluidization Reference

4. Introduction : Fluidization is a process similar to liquefaction whereby a granular material is converted from a static solid-like state to a dynamic fluid- like state. This process occurs when a fluid (liquid or gas) is passed up through the granular material. Fluidized beds are used widely in chemical processing industries for separations, rapid mass and heat transfer operations, and catalytic reactions. A typical fluidized bed is a cylindrical column that contains particles and through which fluid, either gaseous or liquid flows. The velocity of the fluid is sufficiently high to suspend, or fluidize, the particles within the column, providing a large surface area for the fluid to contact. which is the chief advantage of fluidized beds

5. As shown in Figure 1, fluidized beds range in size from small laboratory- scale devices to very large industrial systems. which is the chief advantage of fluidized beds. As shown in Figure 1, fluidized beds range in size from small laboratory-scale devices to very large industrial systems. fig : 1

6. A simplified every-day-life example of a gas-solid fluidized bed would be a hot-air popcorn popper. The popcorn kernels, all being fairly uniform in size and shape, are suspended in the hot air rising from the bottom chamber. Because of the intense mixing of the particles, akin to that of a boiling liquid, this allows for a uniform temperature of the kernels throughout the chamber, minimizing the amount of burnt popcorn. After popping, the now larger popcorn particles encounter increased aerodynamic drag which pushes them out of the chamber and into a bowl. The process is also key in the formation of a sand volcano and fluid escape structures in sediments and sedimentary rocks.

7. FLUIDIZATION REGIMES : When the solid particles are fluidized, the fluidized bed behaves differently as velocity, gas and solid properties are varied. It has become evident that there are number of regimes of fluidization, as shown in Figure 2. When the flow of a gas passed through a bed of particles is increased continually, a few vibrate, but still within the same height as the bed at rest. This is called a fixed bed. If the particles are fluidized at a high enough gas flow rate, the velocity exceeds the terminal velocity of the particles.

8. The upper surface of the bed disappears and, instead of bubbles, one observes a turbulent motion of solid clusters and voids of gas of various sizes and shapes. Beds under these conditions are called turbulent beds as shown in Figure With further increases of gas velocity, eventually the fluidized bed becomes an entrained bed in which we have disperse, dilute or lean phase fluidized bed, which mounts to pneumatic transport of solids.

9. MINIMUM FLUIDIZATION VELOCITY : An equation for the minimum fluidization velocity can be obtained by setting the pressure drop across the bed equal to the bed per unit area of cross section, allowing for the buoyant force of the displaced fluid After the drag exerted on the particles equals the net gravitational force exerted on the particles, that is, Now term minimum fluidization Vs introduced

10. Fluidized bed : A fluidized bed is formed when a quantity of a solid particulate substance (usually present in a holding vessel) is placed under appropriate conditions to cause a solid/fluid mixture to behave as a fluid. This is usually achieved by the introduction of pressurized fluid through the particulate medium. This results in the medium then having many properties and characteristics of normal fluids, such as the ability to free-flow under gravity, or to be pumped using fluid type technologies. The resulting phenomenon is called fluidization.

11. Fluidized beds are used for several purposes, such as fluidized bed reactors (types of chemical reactors), fluid catalytic cracking, fluidized bed combustion, heat or mass transfer or interface modification, such as applying a coating onto solid items. This technique is also becoming more common in aquaculture for the production of shellfish in integrated multi-trophic aquaculture systems. The property of bed is it consists of fluid-solid mixture that exhibits fluid-like properties. As such, the upper surface of the bed is relatively horizontal, which is analogous to hydrostatic behaviour The bed can be considered to be a heterogeneous mixture of fluid and solid that can be represented by a single bulk density.

12. TYPES OF FLUIDIZED BED Circulating fluidized beds (CFB), where gases are at a higher velocity sufficient to suspend the particle bed, due to a larger kinetic energy of the fluid. As such the surface of the bed is less smooth and larger particles can be entrained from the bed than for stationary beds. Entrained particles are recirculated via an external loop back into the reactor bed. Depending on the process, the particles may be classified by a cyclone separator and separated from or returned to the bed, based upon particle cut size.

13. Vibratory fluidized beds are similar to stationary beds, but add a mechanical vibration to further excite the particles for increased entrainment. Transport or flash reactor (FR). At velocities higher than CFB, particles approach the velocity of the gas. Slip velocity between gas and solid is significantly reduced at the cost of less homogeneous heat distribution. Annular fluidized bed (AFB). A large nozzle at the centre of a bubble bed introduces gas as high velocity achieving the rapid mixing zone above the surrounding bed comparable to that found in the external loop of a CFB.

14. APPLICATION OF FLUIDIZED BED Fluidized beds are used as a technical process which has the ability to promote high levels of contact between gases and solids. In a fluidized bed a characteristic set of basic properties can be utilised, indispensable to modern process and chemical engineering, these properties include: Extremely high surface area contact between fluid and solid per unit bed volume High relative velocities between the fluid and the dispersed solid phase. High levels of intermixing of the particulate phase. Frequent particle-particle and particle-wall collisions.

15. APPLICATION OF FLUDIZATION 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.

16. In 1920s, the Winkler process was developed to gasify coal in a fluidized bed, using oxygen. It was not commercially successful. The first large scale commercial implementation, in the early 1940s, was the fluid catalytic cracking process, which converted heavier petroleum cuts into gasoline. petroleum

17. REFERENCES Unit operations of chem. Engg. By W. McCabe & J Smith. www.Fundamentalsofchemical.com www.wikipedia.com/fluidization www.wikipedia.com/fluidizedbed

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