Impact of Superheat and Reheat on the Thermal Efficiency of Regenerative Organic Rankine Cycle (R-ORC) with Optimized Operating Conditions

Abstract

[Abstract]: Organic Rankine cycle is a mature technology for recovering energy form a waste heat source of medium temperature. Internal heat exchanger, superheat and reheat, in order to use additional heat load, are three improvement-performance modifications of Rankine cycles. Organic Rankine cycles including these three modifications have been optimized and analyzed in this paper: Regenerative-ORC (R-ORC), Reheat-Regenerative-ORC (RR-ORC), and with/without superheating. The performance of the four configurations has been compared, and the effects of superheat and reheat has been analyzed. In the reheated configurations, the heat load supplied in the reheating stage comes from a separate stream independent of that used in the evaporator. Based on their thermodynamic, and safety properties, ten working fluids were selected: R1234ze(Z), Butane, Cis-butene, Trans-butene, Isobutane, Pentane, Isopentane, R245fa, R1336mzz(Z) and R1233zd(E). The main operation conditions are optimized for each cycle configuration and fluid to maximize the thermal efficiency using the Particle Swarm Optimization algorithm. A robust thermodynamic model has been developed for this purpose, enabling energetic, exergetic, and economic analyses. The model allows for the calculation of heat exchanger areas and pressure losses, and updates the thermodynamic states based on the corrected pressures. The best thermal efficiency, with superheating, in R-ORC is 17.64% and 19.78% for RR-ORC for Trans-butene. Without superheating stage, the highest thermal efficiencies are 12.22% (Isopentane)for R-ORC and 17.67% (Pentane) for RR-ORC. Integrating superheating with reheating improve the thermal efficiency and net power output of the regenerative cycle. Whereas, the exergetic efficiency depends more strongly on the working fluid used.