Chemical Engineering Department Faculty of Engineering Technology And Research A Presentation on Open Ended Project Topic:- Fluidization Subject:- Fluid Flow Operation Prepared by:- (1)Kakadiya Rajan(140840105016) (2)Dangariya Milan(140840105005) (3)Vasoya Parth(140840105059) (4)Dudhat Mayur(140840105009) (5)Ghodhani Digjay(140840105010) Chemical Engineering Department

FLUIDIZATION Introduction of fluidization Fluidized bed. Topics Introduction of fluidization Fluidized bed. Fluidization Regimes. Geldart’s powder classification Application of fluidization

Introduction of fluidization Definition:- Fluidization is a process in which solids are caused to behave like a fluid by blowing gas or liquid upwards through the solid-filled reactor Fluidization is widely used in commercial operations; the applications can be roughly divided into two categories, i.e.,   •Physical operations, such as transportation, heating, absorption, mixing of fine powder, etc. and •Chemical operations, such as reactions of gases on solid catalysts and reactions of solids with gases etc.

Continued….. Fluidization in vertical column

Fluidized bed In a packed bed of small particles, when a fluid enters at sufficient velocity from the bottom and passes up through the particles, the particles are pushed upward and the bed expands and becomes fluidized.

Continued….. The Graph:(01)Superficial velocity VS Pressure drop (02)Superficial velocity VS Bed Height

Continued….. Pressure drop across fluidized bed:- Upward force on the bed =ΔPA If the height of the bed at this point is and the void fraction is Lε, we can write Volume of particles =(1-ε)AL If the acceleration due to gravity is , the net gravitational force on the particles (net weight) is Net Weight of the particles = Balancing the two yields:

Continued….. Significance of Fluidized beds:

Continued….. Fluidized beds layout:

Advantages and Disadvantages of Fluid bed:- Fluidization column in industry:

Fluidization Regimes (01) (02) (03) (04) (05) (06)

Continued….. 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. (01) With increasing gas velocity, a point is reached where the drag force imparted by the upward moving gas equals the weight of the particles, and the voidage of the bed increases slightly: this is the onset of fluidization and is called minimum fluidization.(02) Increasing the gas flow further, the formation of fluidization bubbles sets in. At this point, a bubbling fluidized bed occurs.(03)

Continued….. If the ratio of the height to the diameter of the bed is high enough, the size of bubbles may become almost the same as diameter of the bed. This is called slugging.(04) If the particles are fluidized at a high enough gas flow rate, the velocity exceeds the terminal velocity of the particles. 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.(05) 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 amounts to pneumatic transport of solids. (06)

Geldart’s powder classification

Geldart’s powder classification Class A •Aeratable •Characterized by a small Dp and small ρp •Large bed expansion before bubbling starts •Gross circulation of powder even if only a few bubbles are present •Large gas backmixing in the emulsion phase •Examples: FCC, milk flour Class B •Bubbling •Umb and Umf are almost identical •Solids recirculation rates are smaller •Less gas backmixing in the emulsion phase •Example: sand

Geldart’s powder classification continue… Class C •Cohesive •Difficult to fluidized, and channeling occurs •Interparticle forces greatly affect the fluidization behaviour of these Powders •Example: flour, cement Class D Spoutable •Either very large or very dense particles •Bubbles coalesce rapidly and flow to large size Examples: Coffee beans, wheat, lead shot

Application of fluidization Extensive use of fluidization started in petroleum industry as fluid catalytic cracking. It is used in catalytic processes.such as synthesis of acrelo nitrile,solid gas reaction,coal gasification. It is also used as rosting ores,drying fine solid,adsorption of gases. Solid is vigorously agitated by fluid passing through bed,this ensure that there is no temperature gradient to bed. FCC convert heavier petroleum fraction into smaller. In 1950,it was applied to mineral&metallurgical process such as drying & rosting. In 1970, it was used to produce most useful polyethelene, which is reduced the cost of it very much.

Summary When a liquid or a gas is passed at very low velocity up through a bed of solid particle,the partical do not move, and the pressure drop is given by Ergun equation. If the fluid velocity is steadily increased,the pressure drop and the drag on individual particles increased,the pressure drop and the drag on individual particles increase,and eventually the particle start to move and become suspended in the fluid.   The term fluidization and fluidized bed are used to describe the condition of fully suspended paricles,since the suspension behave as a dense fluid.  If the bed is tilted,the top surface remains horizontal and large objects will either float or sink in the bed depending on their density relative to the suspension.  The fluidized solid can be drained from the bed through pipes and valves just as a liquid can, and this fluidity is one of the use of fluidization for handling solids.

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