Optimal Scheduling for Decoking Operation of Ethylene Cracking Furnace System
Qiang Xu, Ph.D.
Professor
Industrial ethylene cracking process employs multiple cracking furnaces in parallel to convert various hydrocarbon feedstocks to multiple smaller-molecule hydrocarbon products. The operation is also a typical semi-continuous dynamic process, where a cracking furnace has to be periodically shut down for decoking. Given the data of multiple feed characteristics, different furnace performances, various manufacturing costs, and specified operational constraints, an optimal decoking policy for the entire cracking system can be determined to achieve the best economic performance of an ethylene cracking furnace system. In practice, because of the feed supply and maintenance uncertainties, furnace decoking activities are better to be conducted in a dynamic and reactive way, by which the furnace system operations can be timely rescheduled once an uncertainty is identified. Thus, the feeds from the new delivery and the leftover inventories can be timely, feasibly, and optimally allocated to different furnaces for processing to obtain the maximum average net profit per day.
Our research team has developed a series of novel scheduling models to generate optimal decoking strategy for the entire furnace system. They can cyclic or dynamic optimize multiple-feed assignments, running length of each batch operation, and decoking sequence for every furnace in the system based on the new feed deliveries, the leftover feeds, and current furnace operating conditions. It also simultaneously addresses major scheduling issues for real cracking furnace operations, such as non-simultaneous decoking, secondary ethane cracking, cold maintenance, seamless rescheduling, or environmental conscious decoking. The developed MINLP (mixed-integer nonlinear programming) model is applicable to any cracking furnace system and can be easily extend to any real ethylene plants. The real applications of decoking scheduling work can also be commercialized as an excel tool to help real industries.
Selected References
- Chen, M., Xu, Q.*, “Upset-conscious Scheduling for Continuous Parallel-process and Performance Decaying Unit System”, Chemical Engineering Science, 195, 828-840, 2019. (2019 Best Paper Award of AIChE Process Development Division)
- Chen, M., Xu, Q.*, “Optimal Scheduling for Olefin Plant Furnace System with Consideration of Inherent Process Upset Reduction”, Computers & Chemical Engineering, 126, 157-167, 2019.
- Zhang, S. J., Wang, S. J. Xu, Q.*, “Emission Constrained Reactive Scheduling of Ethylene Cracking Furnace System”, Industrial & Engineering Chemistry Research, 56(5), 1327-1340, 2017.
- Zhao, C. Y., Liu, C. W., Xu, Q.*, “Dynamic Scheduling for Ethylene Cracking Furnace System”, Industrial & Engineering Chemistry Research, 50(21), 12026 -12040, 2011.
- Zhao, C. Y., Liu, C. W., Xu, Q.*, “Cyclic Scheduling for Ethylene Cracking Furnace System with Consideration of Secondary Ethane Cracking”, Industrial & Engineering Chemistry Research, 49(12), 5765-5774, 2010. (2011 Best paper award of AIChE Process Development Division)
- Liu, C.W., Zhang, J., Xu, Q.*, Li, K. Y., “Cyclic Scheduling for Best Profitability of Industrial Cracking Furnace System”, Computers & Chemical Engineering, 34(4), 544-554, 2010.
- Xu, Q.* and Zhao, C. Y., “Dynamic Scheduling for Optimal Decoking Operation of Cracking Furnace System”, the 24th Ethylene Producers' Conference, Houston, TX, April 2-5, 2012.
- Zhao, C. Y., Fu, J., Xu, Q.*, “Emission Considered Cyclic Scheduling for Ethylene Cracking Furnace System”, Proceedings of FOCAPO 2012, paper #71, Savannah, Georgia, USA, 2012.