Applications – Continuous Chemical Reactor

As mentioned in my previous blogs on the book Control Loop Foundation – Batch and Continuous Processes, the application examples included in Chapter 16 illustrate the various ways single loop and multi-loop control techniques may be used automate plant control. The third workshop exercise in this chapter allows the reader to explore the different features of continuous chemical reactor control.

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. The control loops and measurements commonly found on a continuous chemical reactor are shown below.

Any changes in the composition of the feedstock streams will impact the rate of chemical reaction and the composition of the product stream. To compensate for this type of change, the feed stream ratio may be automatically regulated based on an on-line analysis of the product. If the measurement provided by this analysis deviates from setpoint, then the analytic controller will adjust the feed stream ratio to bring the product composition measurement back to setpoint. If the product is analyzed offline in a lab, then the lab results may be used by the operator to manually adjust the feed stream ratio setpoint. The control module provided for continuous chemical reactor control workshop is shown below.

By accessing the book’s web site, you may complete the continuous chemical reactor control workshop using your web browser. The viewer below may be used to see the solution to this exercise.