Petri Net Modeling And Short-Term Scheduling Analysis Of Crude Oil Operations In Refinery Under Hybrid Oil Feeding Mode

Manufacturing systems can be divided into two categories:process industry and discrete manufacturing one. As one of the process industries, oil refinery is chatercterized as high energy consumption, high cost, and low labor productivity. It is known that a well-operated refinery can effectively reduce the product cost and energy consumption. It can also ensure the quality of products. Scheduling optimization plays an important role in operating a refinery.The scheduling of a refinery can be divided into long-term refining scheduling and short-term scheduling. A long-term scheduling is called planning. Depending on different refineries, the horizon of a long-term scheduling can be a quarter, a month, and so on. Based on the existing research results for the long-term scheduling, linear programming method can be applied such that the requirements of practical production can be satisfied. With linear programming techniques, commercial software tools have been developed to optimize a long-term schedule. To formulate the short-term scheduling problem of a refinery, there are a large number of discrete and continuous variables and it belongs to a hybrid system. For such a system, there is no suitable method and technique. Thus, in practice, short-term scheduling is still done by planners in a try-and-error way. This not only imposes heavy workload on the planners and reduce the labor efficiency, but also makes scheduling optimization impossible.Limited by the resources, such as the number of storage tanks and charging tanks, short-term scheduling sould be obtained with resource constraints being taken into account. In addition, since the operation of a refinery involves different kinds of production devices, there are variety of process constraints. Ignoring any of them leads to an infeasible schedule.In some of the existing research, the two types of constraints above are fully considered and schedulability conditions are established such that a feasible schedule can be obtained. However, these studies consider just a single oil feeding mode. By this mode, a charing tank feeds just one distiller at a time. However, in many cases, there are not enough charging tanks for feeding distillers in this way. In this situation, some distillers need to feed two distillers simultaneously. This makes the short-term scheduling problem very complicated.This thesis studies the short-term scheduling problem for crude oil operations in a refinery under a hybrid oil feeding mode in a control theory perspective. First, the process of crude oil operations under such a hybrid oil feeding mode is modeled by a Petri net. With this model, the effect of the number of charing tanks and distillers, the capacity of charging tanks, the flow rates of the pipleline on the existence of a schedule are analyzed, and schedulability conditions are obtained. With these conditions, given a refining schedule, if it is schedulable, a feasible short-term schedule can be easily obtained. The obtained results are verified by an industrial case.