Numerical investigations of polymer sheet breakup and secondary phase change processes in steam contactors

Abstract

Polymer devolatilization or steam stripping involves removing any unwanted substances, such as volatiles and solvents, from the polymer mixture. This is achieved via mixing with superheated steam and breakup into smaller droplets followed by phase change, resulting in dry polymer crumb. The objective of the current study is embodied in two steps. The first step involves the development of a computational fluid dynamics (CFD)-based multiphase model that solves for the initial breakup of the liquid polymer mixture by steam. As part of this effort, detailed parametric studies are conducted to determine the effects of different contactor geometries on the initial sheet breakup, and the potential impact on the final polymer product quality. The second step then uses the resulting diameter distribution to model the multiphase heat and mass transfer of the polymer mixture including evaporation of the solvent. Specifically, 3D CFD calculations are carried out using a Eulerian-Lagrangian approach, where the superheated steam is modelled as the continuous phase and tracked in a Eulerian frame, while the cement droplets are treated using a Lagrangian tracking method, thereby providing distributions of particle sizes, temperatures, and solvent content in the contactor. Results can help optimize the devolatilization process in terms of steam savings and volatile content in the final polymer.