REFINERY SCHEDULING OPTIMIZATION USING GENETIC ALGORITHMS AND COOPERATIVE COEVOLUTION / OTIMIZAÇÃO DA PROGRAMAÇÃO DA PRODUÇÃO EM REFINARIAS DE PETRÓLEO UTILIZANDO ALGORITMOS GENÉTICOS E CO-EVOLUÇÃO COOPERATIVA

AUTOR(ES)
DATA DE PUBLICAÇÃO

2004

RESUMO

This work investigates the use of Genetic Algorithms and Cooperative Coevolution in refinery scheduling optimization. Oil refineries are one of the most important examples of multiproduct continuous plants, that is, a continuous processing system that generates a number of products simultaneously. A refinery processes various crude oil types and produces a wide range of products, including LPG (liquefied petroleum gas), gasoline, kerosene and diesel. It is a complex optimization problem, mainly due to the number of different tasks involved and different objective criteria. In addition, some of the tasks have precedence constraints that require other tasks to be scheduled first. For example, in order to schedule a task that transfers one of the yields of a certain crude distillation unit, both the task that feeds the crude oil into the unit and the task that sets the unit`s current operation mode must already be scheduled. Therefore, applying traditional evolutionary models, like the order- based ones, can create many infeasible solutions that will have to be corrected or rejected later on, thereby jeopardizing the algorithm performance and feasibility. The main goal was the development an evolutionary model satisfying well-defined objectives, which would optimize production scheduling and address the various constraints entailed in the problem, thus generating only feasible solutions. This work consisted on three main steps: a survey on crude oil refining and refinery scheduling; the development of a cooperative coevolutionary model to optimize the refinery scheduling and the development of a software tool for case studies. The study about refining and scheduling involved gathering information about the existent processes in a refinery, starting from the arrival of crude oil, its distillation and transformation into several products and, finally, the delivery of these products to their respective destination. The levels of decision making in a refinery were surveyed too, in order to identify the main goals for each one, and how the scheduling level fits into the structure as whole. Then, all the routine scheduling tasks and their roles in a refinery were carefully studied. The decision of when and how to assign those tasks is the final output of the scheduling task, so it must be the main output of the algorithm too. The development of the evolutionary model consisted of a survey on some of the most common evolutionary approaches to scheduling. The adopted coevolutionary model breaks the problem down into two parts, thus using two species with different responsibilities: One is responsible for deciding when a task should be scheduled, while the other is responsible for assigning a resource for this task. The first species representation was based on a model used for the Dial-a- Ride (Moon et al, 2002) kind of problems, and uses a graph to help the fitness evaluation function find the right order in which to schedule the tasks. This representation was devised in such a way that the precedence constraints were satisfied and no infeasible solutions were generated. The representation of the second species, which assigns resources for the tasks, let genetic operators change the selection order when picking a resource for a task. Finally, a software tool was developed to be used for implement this model and for performing a case study. This case study should comprise all the needed characteristics, in order to test the quality of the representation as well as evaluate the results. A simple refinery was designed, containing all equipment types, tasks and constraints found in a real-world refinery. The constraints mentioned are the precedence constraints, handled by the graph used by the first species, plus other operational constraints found in refinery scheduling. It was possible, then, to see the decoding of chromosomes into feasible solutions, always satisfying all the constraints. Several tests

ASSUNTO(S)

scheduling petroleum algoritmos geneticos co-evolucao cooperativa industry refinery refinaria evolutionary computation petroleo industria genetic algorithms programacao da producao cooperative coevolution computacao evolucionaria

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