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Exergy-Based and Economic Evaluation of Liquefaction Processes for Cryogenics Energy Storage

Hamdy, Sarah; Moser, Francisco; Morosuk, Tatiana; Tsatsaronis, George

FG Energietechnik und Umweltschutz

Cryogenics-based energy storage (CES) is a thermo-electric bulk-energy storage technology, which stores electricity in the form of a liquefied gas at cryogenic temperatures. The charging process is an energy-intensive gas liquefaction process and the limiting factor to CES round trip efficiency (RTE). During discharge, the liquefied gas is pressurized, evaporated and then super-heated to drive a gas turbine. The cold released during evaporation can be stored and supplied to the subsequent charging process. In this research, exergy-based methods are applied to quantify the effect of cold storage on the thermodynamic performance of six liquefaction processes and to identify the most cost-efficient process. For all liquefaction processes assessed, the integration of cold storage was shown to multiply the liquid yield, reduce the specific power requirement by 50–70% and increase the exergetic efficiency by 30–100%. The Claude-based liquefaction processes reached the highest exergetic efficiencies (76–82%). The processes reached their maximum efficiency at different liquefaction pressures. The Heylandt process reaches the highest RTE (50%) and the lowest specific power requirement (1021 kJ/kg). The lowest production cost of liquid air (18.4 €/ton) and the lowest specific investment cost (<700 €/kWchar) were achieved by the Kapitza process.