Optimal Scheduling of Air Separation with Cryogenic Energy Storage

The idea of cryogenic energy storage (CES), which is to store energy in the form of liquefied gas, has gained increased interest in recent years. Although CES at an industrial scale is a relatively new approach, the technology used for CES is well-known and essentially part of any cryogenic air separation unit (ASU). In this work, we assess the operational benefits of adding CES to an existing air separation plant. Three potential new opportunities are investigated: (1) increasing the plant's flexibility for load shifting, (2) storing purchased energy and selling it back to the market during higher-price periods, (3) creating additional revenue by providing operating reserve capacity. We develop a mixed-integer linear programming (MILP) scheduling model for an ASU-CES plant and apply a robust optimization approach to model the uncertainty in reserve demand. Results from an industrial case study show that the amount of wasted products can be considerably reduced and significant cost savings can be achieved by utilizing the CES.