Multiperiod refinery optimization for mitigating the impact of process unit shutdowns

Process unit shutdowns, whether planned or unplanned, disrupt the normal operation of process plants. The negative impact of such disruptions can often be mitigated by the strategic use of material inventories, coupled with redistribution of material flows. In this paper, an optimization framework is proposed for a multiperiod refinery planning model in which a system of inventory tanks is used to mitigate the impact of process unit shutdowns. An economic objective is optimized over a planning horizon, subject to operating, design, and product quality constraints. Two formulation paradigms are considered - an operating problem in which optimal material flow trajectories are determined in response to a shutdown scenario, and a retrofit design problem in which the optimal location and sizing of inventory tanks are determined, the latter formulated as a two-stage stochastic programming problem. The utility of the formulation to shutdown planning is shown through case studies of the operational and design problems applied to a simple refinery scheme.