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Chemical Engineering And Processes

Plant and machine operation (processing) /Particle Technology

Plant and (machine operation processing)

FLUIDIZATION

Learning Outcome

Learning Outcome 1:To be able to interpret the particulate interactions with fluids,equipment used for the separation of particles by fluid i.e Fluidization,Filtration, Sedimentation.Learning Outcome 2:To be able to apply various law’s and calculate the energy of eqipument’s used in the particle processing and seperation e.g fluidization, sedimentation, filteration.In This Presentation we will focus on Fluidization

In the end quiz for given topic is available to check learning outcome attainment.

FLUIDIZATION

The term fluidization and fluidized bed are used to describe the condition of fully suspended particles, since the suspension behave like dense fluid

Fluidization PhenomenonTypes of FluidizationErgun EquationApplicationsQuiz/Problem

1

Fluidization

FluidizationPhenomenon

Fluidization Principle

If the velocity is steadily increased, the pressure drop and drag on individual particles increases and eventually particles start to move and become suspended in the fluid. When fluid pass through bed of solid particles at low velocities and the particle do not moves the pressure drop is given by Ergun equation.

Process

Pressure drop and bed height vs Superficial Velocity

Beds of solids that are fluidized with air usually exhibit what is called “Aggregative or Bubbling Fluidization”, since as the velocity is increased beyond minimum fluidization velocity, most of the gas passes through the bed in the form of bubbles or voids that are free of solids and only a small fraction of gas flows through the channel between the particles. (when dealing with problems including mass and heat transfer through these beds, this is termed as Two-Phase theory of fluidization).

When fluidizing sand with water, the particles move farther apart and their motion becomes more vigorous as the velocity is increased, but the average bed density at a given velocity is same in all the sections of the bed, this is called as “ Particulate Fluidization”, characterized by large expansions of the bed.

Types of Fluidization

When superficial velocity increases to values much above minimum fluidization velocity, there is a transition from bubbling fluidization to what is called “Turbulent Fluidization”

As the gas fluidization velocity through tube is increased, successive bubbles then travel up the column separated by slugs of solids, this is called as “Slugging”, and is usually undesirable due to pressure fluctuations in the bed.

Types of Fluidization

Ergun Equation

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Applications

The industrial fluidized bed process ranges from simple applications like drying, cooling, pneumatic transport of powders, etc.to more complex chemical reactors such as FCC for oil cracking, CVD coating of solids in a fluidized bed, combustion or gasification of coal or biomass, etc.

Numerical Problem

START

Question 1

A packed bed of solid particles of density 2500 kg/m3, occupies a depth of 1 m in a vessel of cross-sectional area 0.04m2. The mass of solids in the bed is 50 kg and the surface volume mean diameter of the particles is 1 mm. A liquid of density 800 kg/m2 and viscosity 0.002 Pa-s flows upwards through the bed. (a) Calculate the voidage (volume fraction occupied by voids) of the bed. (b) Calculate the pressure drop across the bed when the volume flow rate of liquid is 1.44m3/h. (c) Calculate the pressure drop across, the bed when it becomes fluidized.

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