Fluidized Bed Reactor

Group Members:

Nabeel Shabbir Siddique-2k13-33Aun Muhammad-2k13-40Qaiser Mehmood-2k13-41 Amir Sohail-2k13-34Usman-2k11-71

Table of content :

Introduction to Fluidized Bed Reactor.Description and Flow Regimes.Advantages and disadvantages.Industrial Current Applications.Working of (FBR) at molecular level.Designing of (FBR).

“ Judging a Person Does not define who they were ……..

Actually ! It defines who you are . ”

What Is Fluidization …….

The Operation by which Fine Solids are Transformed into Fluid-Like State, through Contact with the Gas or Liquid.

Some Size Reduction Processes used in Fluidization Process:

Attrition

Compression

Impact

Shear

Why is size Reduction process important in (FBR)?

Smaller the size of the particles greater is its surface area and greater will be its efficiency.

In this case smaller the size the solid catalyst greater is the number of active sides that are available for reactions.

How Fluidization Occurs??

When the flow of gas is introduced from the bottom of the reactor.

The gas exerts drag force on the solid particles.The solid exerts gravitational force due to its natural weight.A time comes when the drag force (Fd) becomes equal to the

gravitational force (Fg).And the Bed of solid particles become suspended the process

is known as fluidization.

Example

A simplified every-day-life example of a gas-solid fluidized bed would be a hot-air popcorn popper. Because of the intense mixing of the particles, a uniform temperature of the kernels throughout the chamber is maintained, minimizing the amount of burnt popcorn.

After popping, the larger popcorn particles encounter increased aerodynamic drag because of there low density which pushes them out of the chamber and into a bowl.

Flow Regimes Observed in (FBR):

Fixed Bed Condition.Fluidized Bed Condition.Aggregative Bubbling.Slugging Process.Pneumatic Conveying.

Fixed Bed Operation:

When the drag force exerted by the fluid on the solid particles is less then the gravitational force exerted by the solid particles in the downward direction the fluid passes through void and this is known as fixed bed operation

A time comes when the drag force exerted by the fluid become equal to the gravitational force (due to weight of particles) the condition is known as fluidization.

Fluidized Operation

On further increasing the gas velocity bubbles of gases are formed a turbulent mixing starts of fluid and catalyst.

Aggregative bubbling:

As the superficial velocity of air is further increased slugs are formed and the gas phases escapes through the channels

Slugging Operation

Further increasing the fluidization velocity pneumatic transport starts and it is used only for transportation not for fluidization reactions other wise catalyst will come out the reactor tube.

Pneumatic conveying

(FBR) is a type of reactor that can be used to carry out a variety of multiphase chemical reactions. In this type of reactor, a fluid (gas or liquid) is passed through a granular solid material (usually a catalyst possibly shaped as tiny spheres) at high enough velocity to suspend the solid.

Fluidized bed reactor

Advantages

Capacity

larger processing capacity then other

type of reactors

gives a larger production

Easier in catalyst Replacement:

One of the advantages of fluidized bed reactor is that the catalyst can easily be replaced.

And the exhausted Catalyst can be regenerated.

Uniform Particle Mixing:

Due to the intrinsic fluid-like behavior of the solid material. fluidized beds do not experience poor mixing as in packed

beds. The complete mixing allows for a uniform product that can

often be hard to achieve in other reactor designs.

Uniform Temperature

Many chemical reactions produce or require the addition of heat.

Local hot or cold spots within the reaction bed, often a problem in packed beds, are avoided in a fluidized situation such as a FBR.

In other reactor types, these local temperature differences, especially hotspots, can result in product degradation. Thus FBR are well suited to exothermic reactions.

Researchers have also learned that the bed-to-surface heat transfer coefficients for FBR are high.

Disadvantages

Increased Reactor Vessel Size

Because of the expansion of the bed materials in the reactor, a larger vessel is often required than that for a packed bed reactor.

This larger vessel means that more must be spent on initial startup costs.

Pumping Requirements and Pressure Drop

The requirement for the fluid to suspend the solid material necessitates that a higher fluid velocity is attained in the reactor.

In order to achieve this, more pumping power is required Higher energy costs are needed. In addition, the pressure

drop associated with deep beds also requires additional pumping power.

Erosion of Internal Components

The fluid-like behavior of the fine solid particles within the bed eventually results in the wear of the reactor vessel. This can require expensive maintenance and upkeep for the reaction vessel and pipes.

Lack of Current Understanding

Current understanding of the actual behavior of the materials in a fluidized bed is rather limited.

It is very difficult to predict and calculate the complex mass and heat flows within the bed.

Due to this lack of understanding, a pilot plant for new processes is required.

Even with pilot plants, the scale-up can be very difficult and may not reflect what was experienced in the pilot trial.

Particle Entrainment

The high gas velocities present in this style of reactor often result in fine particles becoming entrained in the fluid.

These captured particles are then carried out of the reactor with the fluid, where they must be separated. This can be a very difficult and expensive problem to address depending on the design and function of the reactor.

This may often continue to be a problem even with other entrainment reducing technologies.

FBRs are everywhere in the Process Industries. They find broad use in the petroleum and petrochemical industries, as well as numerous chemical industries.

Current Applications for Fluidized Bed Reactors

· Acetone Recovery· Aniline· Aniline from Nitrobenzene· Ethanol from Butadiene· Polyethylene· Hydrogen from Steam· Coal Gasification· Styrenes from Hydrocarbons· Cracking of Methylcyclohexane· Maleic Anhydride· Maleic Anhydride from Benzene and Butylenes· Vinyl Chloride· Vulcanization of Rubber

Here are some other applications of FBR technology.

· Fertilizers from Coal· Oil Decontamination of Sand.· Industrial and Municipal Waste Treatment.· Radioactive Waste Solidification.

Kunni and Levenspeil ModelGas flows up in bubble.Mass transfer takes place in and out bubble,Reactions takes place on the active sides of the solid catalyst.E.g.: Any reaction A BMass Transfer of the products takes place through the

bubble.All bubble are of same sizes.Gas void fraction is nearly equal to void fraction at minimum

fluidization velocity.In Wakes concentration of solid is maximum.

Factors:Mass transferBubble residence time which is a function of superficial

velocity.Rate of Reaction.

Parameters Needed in the Designing of Fluidized bed Reactor:

Porosity of the bed (Emf).Velocity of the Bubble rising through the column.Minimum and maximum fluidization velocity for different

cases.Diameter of Bubbles and Various others.

•References:

. Fluidization Technology, vol. I and II. Washington, D.C.: Hemisphere Publishing Co. in association with McGraw-Hill I(1975), II(1976). 7. Kunii, D., O. Levenspiel, Ind. Eng. Chem. Process Design Devel., 7, 481 (1968). 8. Kunii, D., and O. Levenspiel, Fluidization Engineering, 2nd Ed., (Boston: Butterworth, 1991).Coulson and Richardson volume 2,Chp:6 Fluidization.