Application of Repetitive SA Method to Scheduling Problems of Chemical Processes

Abstract

One of the predominant characteristics of chemical batch processes is that the material leaving a batch unit is fluid. Therefore, the starting times of jobs at each unit must be determined by taking into account the availability of storage between two units. In this paper, for such chemical processes, a scheduling algorithm using simulated annealing (SA) method is proposed. In the proposed method called repetitive SA method, in order to reduce the probability of being trapped in a : bad local optimum, the scheduling using SA method is executed repeatedly, and a best schedule is selected at the final stage of repetition. The problem is how to determine the number of repetitions of scheduling and the number of schedules searched in a round of scheduling. In order to find out the best combination of those two numbers, first the probability distributions of the performances of the schedules are calculated for various cases where the number of schedules searched in a round of scheduling is different from one another. Then, the best combination of those numbers is selected using the derived probability distributions. The results of applying the repetitive SA method to scheduling problems of chemical processes suggest that the proposed method is effective typically in reducing the deviation of the performances of the schedules.