Reactors

A chemical reactor is a process equipment used in transforming raw materials to desired products. The vessels themselves can be simple mixing tanks or complex flow reactors. In all cases, a reactor must provide enough time for chemical reaction to occur.


Types of Reactors
1- Batch Reactor
2- Continuous Stirred Tank Reactor (C.S.T.R)
3- Plug Flow Reactor (P.F.R)
4- Semi-Batch Reactor
5- Fluidized Bed Reactor


1- Batch Reactor

DESCRIPTION:
A batch reactor, a non-continuous type of reactor, is a closed vessel in which reactions happen. The material is placed in the reactor before the reaction begins, and all materials are removed after the reaction is completed. There is no addition or withdrawal of materials during the reaction process. The vessel contains an agitator to mix the reactants thoroughly so that the contact makes them react together efficiently and produce products. In order to handle exothermic reactions, the batch reactor is often equipped with cooling coils. In order to work with endothermic reactions, it has provisions for heating the reaction mixture.



CLASSIFICATION:
The batch reactor, one of the five primary reactor configurations, is the oldest reactor scheme.

ADVANTAGES:
- Concentrations are not averaged over time. Initially, when concentrations are at their highest, the corresponding rates of reaction are also high. This gives the greatest amount of conversion in the shortest time.
- It is extremely flexible compared with continuous reactor configurations.

DISADVANTAGES:
- The hold-up time between batches.
- It requires lots of labor force to constantly charge reactants, discharge products and then to clean the reactor for the next batch.



2- Continuous Stirred Tank Reactor (C.S.T.R)

DESCRIPTION:
It is also often called a mixed flow reactor (M.F.R). In this reactor also the reaction occurs in a closed tank. The tank also has an agitator to mix the reactants thoroughly. It is different from batch reactor in the sense that the name itself indicates it is a continuous type of equipment. The reactants enter the reactor at a certain mass flow rate, the react inside the vessel for some time dictated by the space time of the reactor and then they form products.


CLASSIFICATION:
It is one of the two primary types of ideal flow reactors.

ADVANTAGES:
- Steady-state operation.
- Economical operation when large volumes require high contact time.
- Enhancement of heat transfer by mixing.

Disadvantage:
- Larger reactor volumes are usually required, compared with other reactor schemes, and that energy for agitation is required in the tank, increasing operating costs.


3- Plug Flow Reactor (P.F.R)

DESCRIPTION:
It is also sometimes called a continuous tubular reactor (C.T.R). This reactor has continuous input and output of material through a tube.


CLASSIFICATION:
It is the second primary type of ideal flow reactor.

ADVANTAGES:
- Steady-state operation.
- Minimum reactor volume in comparison with CSTR.
- No requirement for agitation and baffling.

DISADVANTAGES:
- More complex than the continuous-stirred tank alternative with regard to operating conditions.
- For highly viscous reactants, problems can develop due to high-pressure drop through the tubes and unusual flow profiles.


4- Semi-Batch Reactor

DESCRIPTION:
It is a semi-flow reactor. It is a modification of batch reactor. The semi-batch reactor is a cross between a batch reactor and a CSTR; one of the reactants is charged completely initially in the reactor and the other reactant is charged continuously in the reactor as the time progresses.


CLASSIFICATION:
It is one of the primary ideal reactor types since it cannot be accurately described as either a continuous or a batch reactor.

ADVANTAGES:
- This reactor is extremely useful when we are doing an exothermic reaction as the continuous flow of the other reactant can be varied to better control the exothermic reaction.

DISADVANTAGES:
- The temperature conditions and the batch nature of this reactor are the primary operational difficulties and make the reactor impractical for most reactions, even for computer-controlled systems.


5- Fluidized Bed

DESCRIPTION:
Fluidization occurs when a fluid is passed upward through a bed of fine solids. The reactor configuration is usually a vertical column. The fluidized solid may be either a reactant, a catalyst, or an inert. The solid may be considered well mixed, while the fluid may be either plug flow or well mixed depending on the flow conditions.


CLASSIFICATION:
Fluidized reactors are the fifth type of primary reactors configurations.

ADVANTAGES:
- The small particle sizes used in the bed allow high surface area per unit mass for improved heat and mass transfer characteristics.
- The fluidized configuration of the bed allows catalyst removal for regeneration without disturbing the operation of the bed.

DISADVANTAGES:
- The equipment tends to be large.
- Gas velocities must be controlled to reduce particle blowout
- Deterioration of the equipment by abrasion occurs.
- Improper bed operation with large bubble sizes can drastically reduce conversion.

Resources:

Foutch, Gary L., and Arland H. Johannes. "Reactors in process engineering." Encyclopedia of Physical Science and Technology (2003)