Compression scheme comparison for a carbon dioxide energy storage system

The gas-liquid type compressed carbon dioxide energy storage is an emerging potential energy storage technology to stable the renewable power output. The trying improvements that this paper is focused on are effective realization of the gas-liquid conversion of the high pressure CO2 without utilizing extra cold sources and efficient allocating the pressure ratio in the compression/expansion lines. Two self-condensing systems with qual pressure ratio and equal outlet temperature arrangements are proposed and evaluated. Numerical simulations to the considered systems are conducted on an in-house code that is compiled with the established energy, exergy and economic mathematical models. Results indicate that the equal outlet temperature system is more suggested due to its lower levelized cost of storage at the optimized operating conditions, being 0.11329 $/kWh when the high-pressure cooler cold-side temperature difference is 11 °C, liquid CO2 temperature is 16 °C and throttling pressure is 7.8 MPa. In the component level, the gas holder and liquid CO2 tank constitute the highest portion to the overall system purchase cost. The compressors, turbines, evaporator and condenser account for the largest share of thermodynamic inefficiencies in sequence. The pinch temperature difference of the condenser and evaporator should not be higher than 8 °C.