Modeling and nonlinearity studies of low density polyethylene (LDPE) tubular reactor

Abstract

One of the constraints in developing a successful model based control scheme is the selection of an appropriate model structure. Typically, the selected model should be able to capture the dynamics and nonlinearity behavior of the process. However, the model selection task can become challenging when the nature and behavior of the process is not fully comprehended. The aim of this study is to observe the nonlinearity behavior of Low Density Polyethylene (LDPE) Process in a Tubular Reactor. In order to study these behaviors, several nonlinearity tests based on Pearson [1] work have been adopted. The tests are asymmetric response, harmonic response, input multiplicity and output multiplicity. These tests have been conducted on steady state and dynamic simulation model of the process, which was developed using Aspen Plus software. Based on these tests, the LDPE process shown the existences of asymmetric response, super-harmonic response, input multiplicity and output multiplicity. It is shown that the process could be classified as strong nonlinearity system. Therefore, the application of nonlinear model is suggested to be more feasible for model based control application in the LDPE tubular reactor.