Heat Removal from Gas-Phase Polyethylene Reactors in the Supercondensed Mode

Abstract

For gas-phase fluidized bed polyethylene reactors, heat removal is one of the controlling factors that limits the production rate. Since the invention of condensed mode operation, several process improvements for enhancing heat transfer have been discovered. In the current article, a nonequilibrium model for multicomponent condensation in vertical heat exchangers described by Jiang et al. has been used to simulate supercondensed mode operation and to test other new designs for heat removal from polyethylene reactors. It appears that a larger heat exchanger or a significant change in the inlet conditions of cooling water is not required for supercondensed operation, in which substantially higher amounts of heat are removed and substantially higher production rates are achieved. It is found that operating at higher reactor temperatures can lead to a 1.1%/°C increase in both heat removal and production rates. Decreasing the operating pressure of the heat exchanger inhibits heat transfer. Makeup ethylene should be added after the heat exchanger, and makeup hexene should be added before the exchanger to maximize heat removal.