The process variables are as follows:
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Input variables |
Manipulated |
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Disturbance |
Measured |
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Unmeasured |
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Output variables |
Measured |
Primary |
All flows and temperatures |
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Secondary |
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Unmeasured |
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Fig. I.3(a) : A process of Continuous Stirred Tank Reactor |
The coolant flow rate (Fc) can be manipulated to control the temperature (T) . Inlet temperatures of reactant and coolant (Ti,Tci) are disturbances which can be measured, however concentration of reactant (CAi) is an unmeasured disturbance. Flow rates and temperatures can be measured and can be regarded as primary output whereas volume of the liquid inside the tank can be estimated by measuring its level. Hence it is a secondary output. Outlet concentration of product is an unmeasured output unless there is an on-line concentration analyzer in place.
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Fig. I.3 (b) : A process of Continuous Stirred Tank Reactor (with different arrangement of valve)
The position of valve in the reactant/product line decides the identity of Fi and F. If valve is placed at inlet, Fi is the manipulated input and F is the measured primary output. If the valve is placed at the outlet line, F is the manipulated input and Fi is the source of measured disturbance.