Thermo-economic analysis of combined transcritical CO2 power cycle based on a novel liquefied-biomethane energy storage system

Abstract

The Chinese government has been encouraging to accelerate the development of energy storage systems to support the rapid growth of renewable energy power generation. For the purpose of achieving flexible and economic energy storage, in this study, a combined transcritical CO2 power cycle is added to biomethane plants to form a liquefied-biomethane energy storage system. A mathematical model that includes terms of energy, exergy, and economy is established to assess the performance of the combined transcritical CO2 power cycle. The effects of critical parameters on the thermo-economic performance are studied. A sensitivity analysis is used to evaluate the extent of the influence of critical parameters. According to the simulation results, the characteristics of the liquefied-biomethane energy storage system are calculated and evaluated. The results show that at a liquefied-biomethane mass flow rate of 1 kg/s, the maximum net power output of the combined transcritical CO2 power cycle reaches 909.81 kW by adjusting the pressure and temperature. High turbine inlet temperature, pump pressure ratio, and methane purity have positive effects on system performance. Among these, the inlet temperature of turbine 2 is the most sensitive factor. Simultaneously, the maximum energy storage density and round-trip efficiency of the liquefied-biomethane energy storage system are 106.8 Wh/L and 52.7 %, respectively. Benefiting from less upfront equipment investment, the lowest power capital cost of the liquefied-biomethane energy storage system is 885.3 $/kW. In conclusion, the liquefied-biomethane energy storage system integrated with a combined transcritical CO2 power cycle exhibits good performance in terms of power output and economy.