A continuous chemical reactor process is characterized by the continuous feed of two or more chemical reactants and a continuous output flow of product. To achieve the desired product specifications, the proportions of each reactant must be tightly maintained at a target value using ratio control. The chemical reaction that occurs within the reactor is often exothermic. In such cases, the reactor temperature may be maintained at setpoint by automatically regulating coolant flow through an external heat exchanger. Any gases and vapors that are created as a by-product of the chemical reaction are vented to maintain the reactor overhead pressure at setpoint. Any imbalance between the feed stream input flows and the product flow from the reactor is reflected by changes in the reactor level measurement. Thus, the product flow rate is automatically regulated to maintain the reactor level at setpoint.
From Terry Blevins at Modeling & Control