Research On Refinery Production Scheduling Problems

Scheduling is the key of Manufacturing Executing System (MES), which links process control system and business management system in process industry. It determines whether production process is running smoothly, influences production cost and reasonable utilization of resources. It is oil refinery that is one of the typical representatives of process industry. The refineries have to make great efforts to increase profits while decrease costs under market competition. The optimal solution of refinery production scheduling can reduce the costs of purchase, transportation, storage, and make the best of production capacity, improve efficiency of resource utlization and capacity ratio, meet demands and maximize profits, the refinery production scheduling problem receives significant attention in recent year. However, the refinery scheduling problem is difficult to solve for its complexity, uncertainty, nonlinearity, multi-objectives and multi-contraints. In many literatures, scheduling object was one section of production process in refinery such as tank farm storage, production unit process, crude oil or products blending, but entire refinery were not considerd as the scheduling target. It is obvious that local production optimization does not achieve global refinery optimization.The main works of this dissertation are as follows:(1) Based on the supply chain management and demands of products in market, the scheduling model of entire refinery is developed to make maximum profit and the strategy of decomposition and coordination of overall refinery scheduling problems is proposed. Moreover, according to oil refinering principle and material flows, the scheduling model of total refinery is decomposed into blending scheduling model, production unit scheduling model and crude oil scheduling model. By available constraint conditions, the scheduling target of entire refinery coincides with the sum of the scheduling targets of three forenamed submodels. Different mathematical motheds are used to solve the submodels while using heuristic motheds to simplify. Thus thesolution of entire refinery production scheduling is obtained to achieve the global optimization.(2) As blending scheduling being constrainted nonlinear optimization problem, it is difficult to obtain optimum solution by general methods. In this dissertation, based on the particle swarm optimization (PSO) algorithm, which is able to solve the nonlinear optimization problem with both continuous and discrete variables, the algorithm for the blending scheduling model is proposed and to obtain solution of the blending scheduling problem under uncertainty. The effectiveness of the proposed algorithm is experientally confirmed by the example of gasoline blending.(3) The production unit scheduling problem is very difficult since complex structures among production units. To get the minimum of total process cost of units, satisfy the main constraints and consider runuing and storage of units, take the blending components of blending scheduling model for production targets of units, the production unit scheduling model is developed. A heuristic-based mathematical programming algorithm is introduced to obtain the optimum solution of such model to arrange production reasonably. The results of an example illustrate that it is effective.(4) Crude oil scheduling problem includes vessel unloading, storage in port and refinery tanks, delivery from port to refinery tanks, blending of crude oils, delivery from charge tanks to distillation units. To take the blending crude oil of production unit scheduling model for target of crude oil scheduling, the crude oil scheduling model is developed. An algorithm based heuristic mothed is proposed to solve the crude oil scheduling model, which may decrease the size and complexity of the problem. The results of an example illustrate that the crude oil scheduling model is effective.(5) The association and restriction are among the process of storage, transportation, demand and distribution of products. Without reasonable solution, shortage of product storage and imperfect vehicle arrangement would happen, and the cost of transportation, distribution and mamgement would increase dramatically. Consider these factors, the scheduling model of the storage and transportation network which is from refinery to depot to gas station is developed to instead of the model only betweendepot and gas station. A mothed combined heuristic and directed graph is proposed to solve this model and is proved to be valid.Finally, a summary is concluded and the future scheduling study directions are indicated in this dissertation.