(160a) Reactive Production Scheduling for Ethylene Cracking Furnace System

Thermal cracking furnace system is the most critical section of an ethylene plant, where multiple furnaces in parallel are used to break various hydrocarbon feedstock (e.g. naphtha, ethane, and propane) into smaller-molecular hydrocarbon products.  Due to its performance-decaying operational characteristic, the cracking furnace system has to experience periodic hot and cold maintenance, which consequently upset the furnace system operation and the downstream process operations.  Also, in practice, because the feed supply conditions change constantly, it is necessary to implement a reactive scheduling strategy which can smartly reschedule the furnace operations with respect to any new feed delivery. 

The previously published works are either focused on simulation and control aspects, or simply scheduling the furnace for maximum average daily profits without incorporating some realistic operational constraints.  In the proposed scheduling model, most of the major scheduling issues concerning a cracking furnace system have been addressed, such as multiple feedstock, multiple furnaces, hot shutdowns for decoking operations, cold shutdowns for mechanical maintenance, decaying cracking performance, non-simultaneous shutdowns, split cracking and recycled C2/C3 cracking.  Specially, to mitigate the flow rate upsets caused by furnace shutdowns to the downstream operations, the developed scheduling model considers different measures commonly applied in industry, such as additional furnace capacity makeup.  Furthermore, the scheduling model is constructed in a reactive and iterative way to seamlessly make transitions from current schedule to reschedule under any delivery of new feeds and on a rolling forward scheduling horizon.  The efficacy of the developed scheduling model is demonstrated by some case studies.