Chapter_5_-_Fluidization - Chapter 5 Fluidization...

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Chapter 5 Fluidization Instructor: Dr. Rami Jumah Department of Chemical Engineering Jordan University of Science and Technology
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JUST Department of Chemical Engineering ChE 362 Unit Operations Chapter 5- 2 The Phenomenon of Fluidization Increasing fluid velocity Increasing fluid velocity
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JUST Department of Chemical Engineering Ch E 362 Unit Operations Chapter 5- 3
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JUST Department of Chemical Engineering ChE 362 Unit Operations Chapter 5- 4 When a fluid is pumped upward through a bed of fine solid particles at a very low flow rate the fluid percolates through the void spaces without disturbing the bed. The particles are in direct contact with each other, supporting each other’s weight. This is a fixed bed process. At an intermediate flow rate the bed expands and is in what we call an expanded state. In the expanded bed the particles have a mean free distance between the particles and the particles are supported by the drag force of the fluid. The expanded bed has some of the properties of a fluid and is called a fluidized bed . There is a minimum fluidization velocity, V oMF , at which the bed just begins to fluidize. If the upward velocity is very large the bed mobilized pneumatically and may be swept out the process vessel. Fixed Bed, no movement of particles (V o < V oMF ) Batch Fluidization, particles stay in bed (V oMF < V o < u t ) Mobilized bed, particles entrained (V o > u t )
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JUST Department of Chemical Engineering ChE 362 Unit Operations Chapter 5- 5 Definition Fluidization is the operation by which solid particles are transformed into fluidlike state through suspension in a gas or liquid. Particle size: 10 m 6 mm Bed diameter: 0.1 m 10 m Bed height: few cm 10 m Superficial velocity: 0.01 m/s 10 m/s
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JUST Department of Chemical Engineering Ch E 362 Unit Operations Chapter 5- 6 Liquidlike Behavior of a Fluidized Bed Light objects float on top of the bed (i.e., objects less dense than the bulk density of the bed) The surface stays horizontal even in tilted beds The solids can flow through an opening in the vessel just like a liquid Levels between two similar fluidized beds equalize their static pressure heads The beds have a “static” pressure head due to gravity, given by ρgh
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JUST Department of Chemical Engineering Ch E 362 Unit Operations Chapter 5- 7 Advantages of Fluidization Smooth, Liquid like behaviour of particles easy to control and automate Rapid and well mixing of solids: Uniform temperature and concentrations Resists rapid temperature changes, hence responds slowly to changes in operating conditions and avoids temperature runaway with exothermic
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