Different configurations of bioreactor

Seminar by,Urmila .N.Pai

6th semSCET

- 1. Stirred tank

The continuous stirred-tank reactor, also

known as vat- or backmix reactor, is a common ideal

reactor type in chemical engineering.

A CSTR oftenrefers to a model used to estimate

the key unit operation variables when using a

continuous agitated-tank reactor to reach a specified

output.

Mixing method: Mechanical agitation

•Baffles are usually used to reduce vortexing

• Applications: free and immobilized enzyme reactions

•High shear forces may damage cells

•Require high energy input

- 2. Bubble column

• Mixing method: Gas sparging

• Simple design

• Good heat and mass transfer

• Low energy input

• Gas-liquid mass transfer coefficients depend largely

on bubble diameter and gas hold-up.

- 3. Airlift reactor

Air-lift bioreactors are similar to bubble column

reactors, but differ by the fact that they contain a draft

tube.

The draft tube is always an inner tube (this kind of

air-lift bioreactor is called "air-lift bioreactor with an

internal loop) or an external tube (this kind of air-lift

bioreactor is called "air-lift bioreactor with an external

loop) which improves circulation and oxygen transfer and

equalizes shear forces in the reactor

• Mixing method: airlift

• Compared to bubble column reactors, in an airlift

reactors, there are two liquid steams: up-flowing and

down-flowing steams. Liquid circulates in an airlift

reactor as a result of density difference between riser

and downcomer.

4. Packed-bed reactor

• Packed-bed reactors are used with immobilized or

particulate biocatalysts.

• Medium can be fed either at the top or bottom and

forms a continuous liquid phase.

• In packed bed reactors, cells are immobilized on large

particles. These particles do not move with the liquid.

Packed bed reactors are simple to construct and

operate but can suffer from blockages and from poor

oxygen transfer.

• Continuous packed bed reactors are the most widely

used reactors for immobilized enzymes and

immobilized microbial cells. In these systems, it is

necessary to consider the pressure drop across the

packed bed or column, and the effect of the column

dimensions on the reaction rate.

• There are three substrate flow possibilities in a

packed bed and they are illustrated below:

• 1. Downward flow method

• 2. Upward flow method

• 3. Recycling method

• The recycling method is advantageous when the

linear velocity of the substrate solution affects the

reaction flow rate. This is because the recycling

method allows the substrate solution to be passed

through the column at a desired velocity.

• For industrial applications, upward flow is generally

preferred over downward flow because it does not

compress the beds in enzyme columns as downward

flow does. When gas is produced during an enzyme

reaction, upward flow is preferred.

• A continuous packed bed reactor has the following

advantages over a batch packed bed reactor:

• 1. Easy, automatic control and operation

• 2. Reduction of labor costs

• 3. Stabilization of operating conditions

• 4. Easy quality control of products

-5. Trickle-bed reactor

• The trickle-bed reactor is another variation of the

packed bed reactors.

• Liquid is sprayed onto the top of the packing and

trickles down through the bed in small rivulets.

A trickle-bed reactor (TBR) is a chemical

reactor that uses the downward movement of a liquid

and gas over a packed bed of catalyst particles. It is

considered to be the simplest reactor type for

performing catalytic reactions where a gas and liquid

(normally both reagents) are present in the reactor and

accordingly it is extensively used in processing plants.

Typical examples are liquid phase hydrogenation

in refineries (three phase hydrotreater) and oxidation of

harmful chemical compounds in wastewater streams.

- 6. Fluidized bed reactor

• When the packed beds are operated in upflow mode,

the bed expands at high liquid flow rates due to

upward motion of the particles.

Fluidized bed reactor (FBR) is a type of reactor device

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 velocities to suspend

the solid and cause it to behave as though it were a fluid.

This process, known as fluidization, imparts many

important advantages to the FBR. As a result, the

fluidized bed reactor is now used in many industrial

applications.