Exergy analysis and optimization of a CCHP system composed of compressed air energy storage system and ORC cycle

Cogeneration systems are getting more attention due to their high efficiency. These systems can provide different commodities with lower energy consumption; therefore their utilization has decreased fossil fuel consumption throughout the world. In this paper, a new cogeneration system is proposed which is composed of a compressed air energy storage system (CAES), an ORC cycle and an ejector system. The proposed system is capable of producing power, heating and cooling energy. The CAES system is used to produce electricity during the peak hours. The system has been evaluated thermodynamically and effect of different parameters on the system performance has been studied. Finally an optimization process is carried out to find system's optimum performance. The results show that under design condition, the system can produce almost 34 kW power, 25.5 kW heating and 0.3 kW cooling with 68% round trip efficiency. The results of exergy analysis show that approximately half of the plant's total exergy destruction occurs in the combustion chamber. Finally optimization shows that round trip efficiency of the system could increase up to 71.87% which is 5.7% higher than the base case efficiency. It is also indicated that there is an optimum value for ORC turbine inlet pressure and ejector inlet pressure which leads to maximum efficiency of the plant.