Cascade PID Control of a Reactive Distillation Process for Biodiesel Production: A Comparison with Conventional PID Control

Abstract

The combination of chemical reaction and distillation, which is analogous to inserting a chemical reactor into a distillation column, is a phenomenon that can be accomplished using a single piece of equipment known as a reactive distillation column, and the phenomenon is, thereby, referred to as reactive distillation process. Because of this combination, a lot of benefits such as improving reaction conversion, suppressing side reactions and utilizing heat of reaction for mass transfer operation can be achieved. However, this combination has made the control of this process a little bit challenging because of some disturbances that normally affect its smooth running. Therefore, cascade control method, being a type that can be used to handle any disturbance before it affects the main process, is applied in this work to carry out the control of a biodiesel reactive distillation process using proportional-integral-derivative (PID) control algorithm. The responses of the process towards the applications of step changes to the input variable (reboiler duty) of the process revealed that it was stable because it could attain steady states. Also, the closed-loop simulations showed that cascade PID controller was better for the control of the process than the conventional PID controller owing to the fact that the responses of the cascade PID control system, upon the application of step changes to the set-point value of the controlled variable, were found to get to the desired setpoint faster and in a better way than those of the conventional PID control system. Moreover, the superiority of the cascade PID controller over the conventional one was demonstrated by the estimation of the integral absolute error (IAE) and integral squared error (ISE) of the cascade control system, which were obtained to be less than those of the conventional PID control system.