Total-site scheduling for better energy utilization

Improving energy efficiency is one of the most important issues for clean production. In a chemical production site, production and utility plants are highly interactive and are all required to perform preventive maintenance to reduce production losses and accidents due to equipment failures. To minimize its impact on production and utility systems during routine maintenance, maintenance scheduling has to be done carefully with consideration of site-wide utilities and material balances. In this paper, a multi-period mixed integer linear programming model, namely a site model, is proposed for generating optimum long-term schedules for plant maintenance as well as production. The model simultaneously takes into account product demands, plant and equipment capacities, site-wide material and utility balances, etc., to optimize a maintenance schedule for a period of two years. The model can be used to maximize site-wide energy efficiency during normal and shut-down maintenance periods, optimise long-term electricity contracts, inventory strategies and purchasing of intermediate materials. A site model contains eight production plants and a utility plant with two boilers and three turbines is used for case studies.