Economic Cost Function Design and Grade Change Optimization for a Gas Phase Polyethylene Reactor

Gas phase polyethylene reactors are able to produce several different grades of polymer. Adapting to market conditions requires grade transitions, associated with costs in terms of raw material and temporary production of lower priced off-specification products. In this paper, both stationary production and dynamic grade transitions are optimized to maximize profit, i.e., economic process optimization. A cost function for transitions that utilizes product quality variable intervals, specifying premium priced products, and that also gives incentives to produce products having quality variables on target, i.e., equal to a defined grade, is designed. A previously published reactor model is extended with quality variable models and several grade transitions are optimized and shown