Optimization of Multilayer Standby Mechanisms in Continuous Processes under Varying Loads

Abstract

In modern chemical plants, there is a class of continuous processes operated under varying loads. In these processes, the standby mechanisms are needed to ensure that the downstream demand is always satisfied during the operations. Although a few related studies have been reported in literature, a comprehensive analysis of multilayer standby mechanisms in processes under varying loads has not been carried out. In this paper, a generalized mathematical model is developed to automatically generate the optimal standby mechanisms for any given processes by minimizing the total expected lifecycle expenditure. A Matlab code has been developed to perform these optimization tasks via genetic algorithm. The feasibility and effectiveness of the proposed model are demonstrated with the case study concerning a fan system for providing instrument air in a typical chemical plant. From the optimization results, one can determine the optimum configurations of the standby mechanisms, which include: (1) the number of protection layers, (2) the number of both online and spare sensors in the measurement channels, (3) the corresponding voting-gate logic in each channel, (4) the inspection intervals of switch and (5) the number of spares for switch.