CFD analysis of micromixing effects on polymerization in tubular low-density polyethylene reactors

A novel multi-environment CFD micromixing model is used to describe the sma ll-scale mixing of chemical species inside a tubular low-density polyethyle ne (LDPE) reactor under different operating conditions. The model is couple d with a comprehensive kinetic scheme describing ethylene polymerization th at includes kinetic mechanisms describing polymer properties and ethylene d ecomposition. The simulation results show that imperfect mixing between ini tiator and monomer reduces monomer conversion and increases the polydispers ity index. Insufficient micromixing also causes local hot spots, which may lead the reactor to thermal runaway. Thus, the small-scale mixing has a sig nificant impact on the reactor stability. The study not only illustrates th e importance of mixing effects on LDPE polymerization but also provides imp ortant insights into the physical phenomena occurring inside the reactor, w hich are extremely helpful in evolving a criteria for stable operation of t he reactor while controlling the product quality in the plant-scale tubular LDPE reactor. Compared to full probability density function (PDF) methods used in the literature for similar studies, the multi-environment CFD micro mixing model offers a computationally highly efficient description of the t urbulent reacting flow inside the LDPE reactor. (C) 1999 Elsevier Science L td. All rights reserved.