Thermodynamic analysis and optimization of four organic flash cycle systems for waste heat recovery

The basic organic flash cycle (BOFC) system has difficulty in achieving the high system efficiency due to the great exergy destruction of the throttling process. To reduce the energy loss and increase the BOFC system's efficiency, three improved systems including the regenerative organic flash cycle (ROFC) system and two novel organic flash Rankine cycle (OFRC) systems were presented in this work. Thermodynamic analysis including energy, exergy and economic analysis were conducted to evaluate the performance of the system, and system optimization based on the particle swarm optimization (PSO) algorithm was performed to indicate the development potential of the system. In addition, performance comparison between four OFC systems and the basic organic Rankine cycle (BORC) system was also carried out. Obtained results showed that the largest exergy destruction of both the BOFC system and the ROFC system was caused by the throttling process, while the biggest energy loss of the two OFRC systems was caused by the heat transfer process in the heat recovery unit. Compared with the ROFC system and the OFRC-I system, the OFRC-II system was considered to be the most promising solution in enhancing the performance of the BOFC system. Finally, optimization results showed that the OFRC-II system had the higher global thermal and exergy efficiencies, compared to the BORC system.