A Multiperiod Nonlinear Programming Approach for Operation of Air Separation Plants with Variable Power Pricing

Cryogenic air separation processes consume a large amount of electricity producing significant quantities of high purity gases. Rather than operating at a fixed steady state, it may be profitable to switch among different operating conditions because of variability of electrical prices and product demands. This article addresses the problem of determining the optimal daily multiperiod operating conditions for an air separation process under variable electricity pricing and uncertain product demands. The multiperiod nonlinear programming formulation includes a rigorous nonlinear model of the highly-coupled process, and decision variables include the operating conditions within each period, as well as the transition times. Demand uncertainty is treated using the loss function included in the objective function and constraints on customer satisfaction levels. Solutions are obtained with high computational efficiency, allowing management to make informed decisions regarding operating strategies while considering the trade off between profitability and customer satisfaction levels. (C) 2010 American Institute of Chemical Engineers AIChE J, 57: 2421-2430, 2011