Economic Incentive for Intermittent Operation of Air Separation Plants with Variable Power Costs

This article presents a simplified economic analysis of the effect of hourly variations in power costs on energy and capital costs of cryogenic air separation plants. The objective is to see what ratio of peak-to-minimum energy costs is required to make intermittently operated air separation plants economically attractive. The study focuses on super-staged argon-column air separation plants producing both gaseous and liquid oxygen and nitrogen, along with high-purity liquid argon. Preliminary results indicate that power price ratios between about 2 and 7 are required, depending on the process and economic assumptions. The analysis uses thermodynamic ideal-work calculations to predict energy requirements for plants that produce varying amounts of liquid and gaseous products. These products must be provided to customers even when the plant is not running, so excess liquid oxygen and nitrogen must be produced and stored during the period when the plant is running. The actual power consumption of the base 24-...