Analysis and assessment of a novel organic flash Rankine cycle (OFRC) system for low‐temperature heat recovery

In this paper, a novel organic flash Rankine cycle (OFRC) system for low-temperature heat recovery is analyzed and optimized using the 3E (energy, exergy, and economic) analysis method and particle swarm optimization algorithm, respectively. Five environmentally friendly organic fluids and three typical heat source conditions are simultaneously discussed during the parametric analysis and optimization process, to obtain a comprehensive understanding of the thermo-economic characteristics of this novel system. The main analysis results show that the biggest exergy loss of the OFRC system is caused by the condenser, followed by the evaporator. About 70% of the specific power cost is caused by the capital investment of the system, and more than 60% of the capital investment is spent on purchasing the high-pressure and low-pressure expanders. Under the same operating conditions, the working fluids with high critical temperatures can achieve higher cycle thermal efficiency and lower specific power costs than those with low critical temperatures. The optimization results show that the OFRC system is able to achieve a better thermodynamic performance than the organic Rankine cycle (ORC) and organic flash cycle (OFC) systems, and when the heat source's inlet temperature is set to 100 degrees C, 120 degrees C, and 140 degrees C, R245fa, R290, and R152a are, respectively, recommended as the best working fluid for the OFRC system. Besides this, it is found that the OFC system has the worst thermo-economic performance, and the ORC system can achieve the lowest specific power cost. A new finding is that, for all three systems, the higher the critical temperature of the working fluid, the lower the specific power cost of the system.