(190h) Combined Dynamic Simulation and Scheduling Optimization of Shutdown Procedures of Ethylene Plants

Shutdown and startup procedures are important operations for maintenance of olefin plants. Both procedures involve complicated facility operations, take long time and may produce huge amount of flare emissions. Optimize shutdown procedures could shorten duration time, reduce flare emissions and decrease cost by saving intermediate materials.

In this presentation, a new shutdown methodology for olefin plants is proposed. The key issue is to recover remaining liquid and vapor materials in facilities during the shutdown procedure. To achieve that, CGC (Charge Gas Compressors) must be kept running during recovering, and recovered hydrocarbon is sent to other plants as feed. Dynamic simulations of the whole procedure are used to determine possibility and to provide necessary operation data.

Moreover, the shutdown procedure can be considered as a scheduling problem. Thus, an MIP (Mixed-Integer Programming) model is developed to get an optimized shutdown schedule for facilities. By optimizing shutdown arrangements for facilities, the overall shutdown time could be reduced by 25%. Combining with the new shutdown methodology, over 90% of hydrocarbon could be saved, and flare emissions could also be reduced by 90%.