The Comparison Between WRC and ORC in Moderate Temperature Gas Heat from Exhaust Gases

• 1、School of Mechanical,TianJin University,Education Ministry Key Laboratory of High Efficiency Utilization of Low and Moderate Grade Heat, 300072

Abstract：The performance of Organic Rankine Cycle(ORC) is much better than Water Rankine Cycle (WRC) in low-temperature heat recovery area. That's why ORC has replaced WRC in low-temperature heat recovery. This paper compares the performance of ORC and WRC in mid-temperature(230oC-600oC) gas waste heat recovery with net power per unit mass as the objective function. By calculating cycle performance of 18 organic working fluids, we find that working fluids with a critical temperature higher than 200oC is better than low critical temperature working fluids, and better than water.When the gas temperature is 300oC or 400oC, the optimal working fluids are benzene and toluene respectively. The difference in heat transfer pinch point distribution between mid-temperature ORC and low-temperature ORC has been analyzed .When the temperature of gas is about 470oC and isentropic efficiency of turbine and working fluid pump is 0.8 and 0.9, WRC's net power per unit mass is higher than ORC with toluene as the working fluid. The efficiency of turbine and pump greatly impact the comparison between ORC and WRC. The higher the gas temperature is, the more obvious the WRC's advantage is.

Keywords： moderate temperature waste heat ORC comparison of cycles pinch point of temperature difference