(440f) Optimal Front-End Crude Scheduling for Refinery with Consideration of Proactive Unit Maintenance

The front-end crude scheduling (FECS) has been well studied and convincingly proven very effective for the scheduling of crude supply process [1,2]. It can be used to tackle crude movement problems from crude importing by vessels, unloading through berths, temporarily storing at port-side storage tanks, transferring via long-distance pipeline, blending at refinery-side charging tanks, to continuously feeding to refineries. Through FECS, optimal crude transfer schedules in terms of profitability and operability can be determined. In previous studies, most works were developed based on the assumption that all processing units were under normal working status without consideration of any possible abnormal performance. In reality, however, the performance of every processing unit will be inevitably decaying along with the processing time and load. Thus, regular maintenance operations have to be scheduled in advance to restore unit performing efficiency and more importantly to prevent potential unit failures [3,4]. Meanwhile, the unit maintenance schedule needs to be proactively integrated with the crude movement schedule to ensure the real operability as well as the minimization of the overall cost. Some research works did deal with maintenance issues by identifying post remedial strategies for unit failures [5,6]. However, the reactive response will unavoidably and stiffly disrupt the original schedule, resulting in higher operating expense and even infeasible operations. Therefore, proactive scheduling of regular unit maintenance is a promising opportunity to further improve and significantly benefit the crude supply process.

In this study, a novel continuous-time FECS model combined with proactive scheduling of unit maintenance has been developed. It involves a large-scale mixed-integer nonlinear programming problem, covering all crude movements from shipping all the way to the refinery processing. Through this model, the optimal schedule for both crude supply and unit maintenance operations will be simultaneously identified for the minimal operating cost. It can not only determine when and how to isolate the designated unit(s) from the process system for the maintenance preparation (i.e., how to discharge the leftover inventory in units), but also identify the best opportunity for the maintenance-completed unit(s) to rejoin the system for continuous production during the scheduling time horizon. In addition, real process requirements, including tank inventory, transfer flowrate, blending specifications are all taken into account to guarantee the obtained schedule is practical. The efficacy and performance of the proposed model has been tested and demonstrated through various unit(s) and maintenance scenarios.

References

[1] Zhang, S., & Xu, Q., (2015) Refinery continuous-time crude scheduling with consideration of long-distance pipeline transportation. Computer and Chemical Engineering, 75, 74-94.

[2] Li, J., Misener, R., & Floudas, C., (2012) Continuous-time modeling and global optimization approach for scheduling of crude oil operations. AIChE Journal, 58, 205-226.

[3] Amaran, S., Sahinidis, N., Sharda, B., Morrison, M., Bury, S., Miller, S., & Wassick, J., (2015) Long-term turnaround planning for integrated chemical sites. Computer and Chemical Engineering, 72, 145-158.

[4] Vieira, M., Varela, T., Povoa, A., (2017) Production and maintenance planning optimization in biopharmaceutical processed under performance decay using a continuous-time formulation: A multi-objective approach. Computer and Chemical Engineering, 107, 111-139.

[5] Zhang, S., Xu, Q., (2014) Reactive scheduling of short-term crude oil operations under uncertainties. Industrial & Engineering Chemistry Research, 53, 12502-12518.

[6] Zhang, S., Wang, S., & Xu, Q., (2015) A new reactive scheduling approach for short-term crude oil operations under tank malfunction. Industrial & Engineering Chemistry Research, 54, 12438-12454.