instrumentation and control of chemical reactor

INDUSTRIAL PROCESS CONTROL:INSTRUMENTATION AND CONTROL OF CHEMICAL REACTORNikhilbinoy.CAssistant Professor, ICE Department, N.S.S. College of Engineering, Palakkad.

Temperature Control

Reaction temperature is the control variable in reaction control.

Variables sensitive to temperature are: Reaction rate. Side reactions. Distribution of side products. Polymer molecular weight distribution.

Many reactions are exothermic.

The released heat must be removed from the system as it is liberated by the reactants to control the reaction temperature.

TICM

TT

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HeatTransferMediumSupply

Unsatisfactory for large number of installations. Under throttled

conditions, the flow of heat transfer medium can be inadequate to maintain a good heat transfer coefficient.

Can result in localized temperature differences within the reactor (hot and cold spots). Due to different heat

transfer area of the jacket.

Due to temperature gradient.

Both are uncontrollable and undesirable.

TICM

TT

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HeatTransferMediumSupply

Reactor TemperatureSetpointReactor Temperature with localized temperature differences

Temperature gradient problem is reduced.

This system has time lags in the response of the loop of the heat transfer medium in adjusting the temperature of the cooling medium. Due to reactant mass and

by the relatively large quantity of heat which must be removed to bring a small change in reactant temperature.

Overcompensation, upset, cycling, etc. will occur before the controller compensated for the system disturbances.

TICM

TT

Return

HeatTransferMediumSupply

Time lag of previous systems can be reduced by using cascade controller. Reactor batch

temperature is the primary variable. Slow to changes in the

heat transfer medium flow.

Jacket temperature is the secondary variable. Response to changes in

process load is rapid.

TICM

TT

HeatTransferMediumSupply

TT

SP

Certain chemical reactors require pressure control.

Oxidation and hydrogenation.

Reaction rate is also a function of pressure in gas phase reaction.

Pressure Control

PRC

M

PT

FT

FR

Processgas

PRC

PTFT

FRC

Vent

VentCondenser

CoolingMedium

Processgas

Optimization

Maintains the reaction at high rate.

The reactor is controlled to maintain a feed rate high enough that polymerization will occur as rapidly as the cooling system can remove the reaction heat.

Two feed streams are on feed ratio. Charging feed A at

high rate to achieve maximum optimization.

Using conventional cascade controller, the coolent temperature is maintained at low temperature to maintain the jacket temperature as low.

OIC is used to maintain 90% cooling load.

TRC

TT

SPFT

FRC

TT

FTFRC

FYFY RC RA

PIC

OIC

SP

Cascade Controller

RatioController

Cascade Controller

Thank You