Evaluation of organic Rankine cycle by using hydrocarbons as working fluids: Advanced exergy and advanced exergoeconomic analyses

Abstract

Hydrocarbons (HCs) are characterized by extremely low global warming potential (GWP) and are promising working fluid for organic Rankine cycle (ORC). A comprehensive advanced evaluation model is developed to study the energetic, advanced exergy and economic performance of ORC system by using twelve HCs, considering the heat recovery from geothermal, low-temperature solar, engine waste gas heat, and high-temperature solar applications. The results show that cyclohexane obtains the highest value of thermal efficiency for high-temperature solar energy. The exergy efficiency of ORC is improved by about 20% after the system optimization through the advanced exergy analysis. In addition, the recoverable effect for the four major components can be ranked as expander, evaporator, condenser, and pump. Exergetic improvement potential ratio of expander by employing propyne and isopentane obtains the highest value of 12.41% and 12.60% at the heat source temperature of 115 and 140 °C, respectively. The lowest value of levelized energy cost are propyne, pentane, cyclohexane, and cyclohexane, which are 1.46, 1.28, 1.05, and 0.95 USD/kWh. Isobutene, isopentane, cyclohexane, and cyclohexane obtain the highest endogenous avoidable cost corresponding to the four heat sources. The endogenous avoidable cost is relatively sensitive to the heat source temperature, and it is reduced by 28% with the heat source temperature increasing from 100 to 150 °C, while it is insensitive to the expander efficiency.