Improved Regulatory Control of Industrial Gas-Phase Ethylene Polymerization Reactors

Abstract

This paper investigates the application of two techniques to improve the proportional-integral (PI) control performance when implemented to stabilize the operation of gas-phase polyethylene reactors around an optimal operating point which is open-loop unstable. The first technique deals with improving the performance of a single input-single output control loop through employing an on-line adaptive tuning strategy. The purpose of the tuning strategy is to force the closed-loop response to fit inside a desired time-domain specification envelope by automatically adapting the PI setting values. The second technique deals with improving the multiple input-multiple output control performance by simple selection of the proper control structure design. The objective of the proposed control design is to avoid the procedure of screening various control structure candidates. Moreover, because there are more inputs than outputs, a splitrange configuration is used to utilize all available manipulated variables. This configuration allows for tight control. Simulation results demonstrated the success of the proposed methods to provide a better regulatory control performance when compared to those that have been reported in earlier work.

A review on modeling and control of olefin polymerization in fluidized-bed reactors

“…The authors found that a multi-loop control scheme must be used to improve the feedback response and they did so using an NLMPC controller. The authors, in another study, tried to overcome the PI shortcomings in SISO and MIMO cases by on-line adaptive tuning and finding proper control structures (Ali and Abasaeed 1999). Ghasem (2000) also studied the dynamics of a UNIPOL ® process using their model a PI controller.…”

Dynamic process modeling and hybrid intelligent control of ethylene copolymerization in gas phase catalytic fluidized bed reactors

“…Dadebo et al 2 controlled the temperature and showed that the nonlinear error trajectory controller (ETC) displayed better performance when compared with an optimally tuned proportional-integral-differential (PID) controller and that nonlinear controllers have an advantage as they are more capable of rejecting disturbances and ensuring stability. Ali et al 14 have tried to control monomer concentration and reactor temperature using improved single-input/single-output (SISO) and multi-input/multi-output (MIMO) PI-based controllers by manipulating the catalyst feed rate, U 0 /U mf ratio and feed temperature. Sato et al 15 designed a model inverse optimal MIMO servo controller with integral actions plus an attached nonlinear compensator to control MFI and polymer density by altering the fresh hydrogen and butene feed concentrations.…”

Multivariable Control of a Simulated Industrial Gas-Phase Polyethylene Reactor

“…[1][2][3][4] Stabilization of polyethylene reactors is therefore a challenging problem and needs to be addressed through good control. Dadebo et al 5 and Ali et al 6,7 have addressed the stabilization of the reactor temperature through different approaches. Recently, Seki et al 8 have also studied the stabilization of gas-phase polyethylene reactors through an adequate tuning of the proportionalintegral-derivative controller.…”