A Two-Phase Approach To Short-Term Scheduling Of Crude Oil Operations In Refinery

Integrated automation takes vitally important role in process industries. It has great effect on production costs and resource utilization. Manufacturing execution system (MES) in process industries is the core of the middle layer in operating a process industry. In fact, MES is also the bottleneck of the integrated automation. In MES, the key is scheduling optimization. For this reason, scheduling determines whether the production process is running smoothly and effectively. Oil refinery is a typical process industry. For profit gain and competitiveness in the global market, efforts have to be made reduce costs and increase resource utilization. Since a refinery process is a typical hybrid system with both discrete event and continuous variable when modeling it. The short-tem scheduling problem of such a system is more complex than a discrete event system or a continuous one. Thus, it is challenging to schedule such a system. This dissertation conducts a study on this problem and the work done is as below.Propose the mathematic description of the shor-term scheduling problem for crude oil operations in refineries. The goal of crude oil operations system is to effectively allocate the resources such that to maximum profit can be gained. Hence, to effectively operate the system is to find an optimal short-term scheduling such that resources are optimally allocated and all rigid constraints are satisfied as well. After analyzing the problem, the mathematic description for the problem is presented.In order to analyze scheduling problem of the crude oil operations, we define the system state and equivalent state for the process. With such definitions, if one state that is equivalent to the initial one is reachable after a period of time, we think that the system is schedulable. Then, the schedulability problem for the distiller refining process is discussed under different cases with different number of available tanks.To operate the system effectively, it is necessary to have a good scheduling mode. In this paper, a hybrid scheduling mode is presented by integrated the push and the pull strategies by reasonably selecting the boundary of them.Due to the structure and characteristics of crude oil operations, the pipeline is considered as the boundary to the scheduling problem of the entire system. In this way, the scheduling problem is decomposed into two sub-problems such that the complexity of the problem is greatly reduced.In the process of scheduling distiller refining based on the schedulability condition, the push strategy is adopted to obtain the crude oil transportation requirements for the pipeline.With transportation requirements for the pipeline known, mathematical model for scheduling the crude oil operations at the dock is developed by uising the information of initial inventory of oil in the tanks at the dock and tanker arrivals. Finally, to solve the model more effectively, some valid inequalities are added to the model as constraints.