Thermodynamic assessment of a geothermal power and cooling cogeneration system with cryogenic energy storage

Abstract

Geothermal energy is one of the main renewable energy sources for power generation and district cooling, and liquid air energy storage is an emerging technology suitable for both power and cold storages. Accordingly, a combined power and cooling cogeneration system with cryogenic energy storage is proposed in this paper, which is powered by geothermal energy and connected with the grid. The system is formed by integrating a turbine ejector cogeneration cycle with an air liquefaction cycle, a liquid air direct expansion cycle and a cryogenic organic Rankine cycle. In normal operation mode, only the turbine ejector cogeneration cycle works in the system based on the cooling load requirement. In charging operation mode, all the power produced in the system is used to liquefy air in the air liquefaction cycle owing to cheap electricity tariff. In discharging operation mode, the additional electricity is provided to meet peak time energy requirement by the direct expansion cycle and cryogenic organic Rankine cycle. A geothermal source at 180 °C with a flow rate of 100 kg/s is used as the heat source in this study, the cogeneration system has the ability to produce 15,470 kW of power and supply 4800 kW of cooling simultaneously, the system round trip efficiency is 41.07%, and the exergy efficiency of cryogenic energy storage is 60.43%. Also, the effects of geothermal energy temperature, system size, turbine mass split ratio and normalized mass flow rate on the system performance are clarified.