Regarding cascade control
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This is cascade control, but why is the steam measurement point located before the control point? In cascade control, the secondary loop should be closed; however, in this case, when there are fluctuations in steam flow, control through valves can only affect the steam that enters the reboiler – the incoming steam cannot be controlled. Can this still be considered a closed loop? It seems that the flow measurement point should be placed behind the control valve; in this way, if the measured flow rate is high, the valve can be closed, which ultimately results in a lower measured flow rate, which seems to better reflect the characteristics of the circuit. I need a solution.
The fluid is continuous, and the flow rate before and after is the same (assuming equal pressure); generally, the measurement point should be located upstream of the control valve. This design is fine.