EFFECTS OF OPERATING-CONDITIONS ON HEAT REMOVAL FROM POLYETHYLENE REACTORS

A one-dimensional nonequilibrium model for multicomponent condensation is used to simulate a vertical single-pass shell-and-tube heat exchan ger in an industrial gas-phase polyethylene reactor system. Starting t he calculation at the top of the exchanger, the model can predict temp eratures at the bottom of the exchanger within an accuracy of +/- 5 K as compared to three sets of industrial data. Sensitivities of model p redictions were analyzed, including uncertainties associated with phys ical and transport property estimates, step size, and convergence crit erion. Model predictions are not particularly sensitive to the estimat ion errors of physical and transport properties if K values are calcul ated using an equation of state applicable to both liquid and vapor ph ases. Effects of operating conditions on heat removal from polyethylen e reactors were investigated for an existing process. It was quantitat ively demonstrated why and how severely noncondensable gases impede co ndensation hear transfer. The level of noncondensable gases and the co oling wafer temperature are the two most important factors influencing the heat-removal rate. Replacing a portion of noncondensable gas, suc h as N-2, with a condensable fluid that is inert to polymerization rea ctions can substantially increase the heat-removal rate from the react or, thereby allowing for an increase in polymer production rate.