Thermo-economic analyses and evaluations of small-scale dual-pressure evaporation organic rankine cycle system using pure fluids

Thermo-economic performance of small-scale (<1 MW) dual-pressure evaporation organic Rankine cycle (DPORC) system using pure fluids was studied. The effects of heat source conditions (flow rate and temperature), pinch point temperature differences (PPTDs), and heat sink condition on the thermo-economic performance of DPORC system were analyzed. The distribution characteristics of component costs were given. Traditional single-pressure evaporation ORC (SPORC) system was selected as the compared object to evaluate the thermo-economic performance of DPORC system. Results show that the minimized specific investment cost (SIC) of DPORC system substantially decreases with increasing flow rate and temperature of heat source. The DPORC system can obtain a better thermo-economic performance compared with SPORC system. For R245fa, the minimized SIC of DPORC system can be 0.6% lower than that of SPORC system, meanwhile its net power output also increases by 21.9%. The substantial increase of heat absorbers cost generally results in the minimized SIC of DPORC system is higher. Furthermore, the DPORC system has a larger application potential at the working conditions of the large flow rate of heat source and PPTD during heat absorption process. The working fluid with a high critical temperature is more suitable to adopt the DPORC system.