Thermodynamic performance analysis of a novel integrated energy cascade system of liquid air energy storage and two-stage organic Rankine cycles

Abstract

Liquid air energy storage can enhance the absorptive capacity for renewable energy due to its high energy storage density and extensive application scenarios. This paper proposes an integrated cascade energy system including liquid air energy storage, two-stage organic Rankine cycle, organic Rankine cycle, liquid natural gas regasification and absorption heat pump/chiller to use waste heat and liquid natural gas's cold energy fully and improve the round-trip efficiency. The waste heat of liquid air energy storage and the cold energy of liquid natural gas could increase the temperature and condense the working fluid of organic Rankine cycles. The system's thermodynamic model in design and off-design conditions are established. The charge and discharge minimum loads of liquid air energy storage are 82.5 % and 33.5 %, respectively. The round-trip efficiency of liquid air energy storage obtains a maximum of 49.6 % and a minimum of 29 % in the load ranges. Based on the load changes, the effects on the organic Rankine cycle are discussed, and four control strategies are proposed to absorb the waste heat and cold energy efficiently under off-design conditions. Besides, the organic Rankine cycles are affected by the mass flow of liquid natural gas and split ratio, which are discussed, and its underlying causes are analyzed. The results show that the integrated cascade energy system's round-trip efficiency reaches a maximum of 80.3 % in design conditions and a minimum of 62.7 % in off-design conditions, increasing by 61.9 % and 116.2 %, respectively.