A Comparison of Strategies for the Control of a Polypropene Reactor

Abstract

The paper discusses various structures for the control of the reactor in an industrial polypropene plant. The basic reactor variables which are controlled are: level in the reactor, level in the reflux accumulator and pressure in the reactor. Of these, the pressure determines the conversion. The basic inputs that are manipulated in order to control the plant are: monomer feed rate, the removal of energy in an external reflux heat exchanger, and the reflux of liquid monomer from the accumulator. In the present structure of single loop PI controllers, monomer feed controls the reactor level, removed energy in the heat exchanger controls the reactor pressure, and refluxed liquid controls the accumulator level. In a suggested new structure, refluxed liquid is used to control the pressure while removed energy in the heat exchanger controls the accumulator liquid level. In addition, a multivariable PID controller is investigated in addition to a decoupling structure. The different structures are compared with regards to set point tracking, disturbance rejection and suppression of varying process parameters. Overall, the multivariable PID controller yields the best result. The present structure may also give a satisfactory result if properly tuned.