fluidized bed reactors

8/18/2019 Fluidized Bed Reactors

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FLUIDIZED BED REACTORS

Fluidized bed reactors (FBR) are catalytic reactors in which the catalyst is fluidized within the reactor.

(Copyright Envirogen Technologies nc.! "ingwood! T#)

GENERAL INFORMATIONFluidized bed reactors are heterogeneous catalytic reactors in which the $ass of catalyst is fluidized. This allows for e%tensive$i%ing in all directions. & result of the $i%ing is e%cellent te$perature stability and increased $ass'transfer and reaction rates.

Fluidized bed reactors are capable of handling large a$ounts of feed and catalyst. ictured below is an FBR used for treatinganiline'and nitrobenzene'conta$inated wastewater.


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EQUIPMENT DESIGNThe $ovie below shows the operation of a fluidized bed reactor. Before the reactor is started the catalyst pellets lie on a grateat the botto$ of the reactor. Reactants are pu$ped into the reactor through a distributor continuously! causing the bed tobeco$e fluidized. The beds behavior after initial fluidization depends on the state of the reactant. f it is a li*uid the bed

e%pands unifor$ly with increased upward flow of the reactant. This is called ho$ogenous fluidization. f the reactant is a gas thebed will be non'unifor$ because the gas for$s bubbles in the bed! resulting in aggregative fluidization. +o$eti$es these bubblesin coarse $aterials can grow larger than two'thirds of the beds dia$eter! which can cause slugging. +lugging can result invariable pressures! vibrations in the bed! and heat transfer reductions. ncreasing the velocity of the gas leads to a turbulentregi$e! as shown below. n the fast fluidization regi$e the bed surface starts to disappear. ncreasing the gas velocity furtherresults in pneu$atic transport! in which the bed is co$pletely re$oved and the particles are unifor$ly spaced in the fluid.,uring this process the reactants react due to the presence of the catalyst pellets! for$ing products that are re$ovedcontinuously.


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(Copyright Che$ical Engineering! &ccess ntelligence! --C)

Fluidized bed reactors are generally very large. They $ust be designed so that the fluid flowrate is sufficient to suspend thecatalyst particles. The particles typically range in size fro$ / ' 0// $icrons.

1hen designing a fluidized bed reactor! the catalyst life $ust also be ta2en into account. 3ost fluidized bed reactors! such as theone shown here have a separate co$part$ent to regenerate the catalyst.


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USAGE EXAMPLESFluidized bed reactors are co$$only used in catalytic crac2ing processes. They are also used in the o%idation of naphthalene tophtalic anhydride! roasting of sulfide ores! co2ing of petroleu$ residues! and the calcination of li$estone. They are often usedwhen there is a need for large a$ounts of heat input or output! or when closely controlled te$peratures are re*uired.

The fluidized bed reactors below are used in 4&+&s 5et ropulsion -aboratory for the re$oval of perchlorate and chlorinatedsolvent fro$ groundwater. The syste$ can re$ove perchlorate fro$ up to 06/ gallons of groundwater per $inute.


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ADVANTAGES

• Even te$perature distribution eli$inates hot spots.

• Catalyst is easily replaced or regenerated.

• &llows for continuous! auto$atically controlled operations.

• 3ore efficient contacting of gas and solid than in other catalytic reactors.

fluidized bed reactors

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