Detailed steady-state simulation of tubular reactors for LDPE production: Influence of numerical integration accuracy

Abstract

Simulators are widely used for analyzing and optimizing the production of low density polyethylene in tubular reactors under steady state conditions. This steady state is in practice often simulated by chemical engineers using a series of CSTRs type model due to its stable behavior with respect to spatial discretization and smooth convergence for the underlying stiff model equations. Although already a large number of CSTRs is used, this number appears to be too low for the physical reality. Here, this traditional cascaded CSTR approach is compared with a plug flow type approach for a highly detailed reaction model describing the free radical copolymerization. Additionally, the influence of the discretization is rigorously investigated and quantified. It is shown that the discretization does not significantly affect the temperature and the conversion profile, but has a major impact (deviations up to 30%) on the properties which determine the end product. However, this impact of discretization is in practice often overlooked.