采用涡轮膨胀机的有机朗肯循环系统优化

Optimization of an Organic Rankine Cycle System with Turbo-Expander

针对采用涡轮膨胀机的低温亚临界有机朗肯循环(Organic Rankine cycle,ORC)系统,以R245fa为循环工质,基于EES(Engineering Equation Solver)软件建立了数学模型。在给定的冷热源参数条件下,以单位净发电量所需的总传热面积和循环热效率为目标函数,采用共轭方向法对ORC系统进行多目标优化,并在此基础上研究了冷热源参数变化对综合目标函数的影响规律。结果表明:存在最优的换热器夹点温差和涡轮膨胀机转速使ORC系统的综合目标函数最小;当换热器夹点温差和涡轮膨胀机转速恒定为优化值时,ORC系统的综合目标函数随着热水进口温度的升高而降低,随着冷却水温度、热水和冷却水进出口温差的升高而逐渐升高。

Using R245fa as working fluid,a mathematic model for subcritical organic Rankine cycle(ORC)system with turbo-expander driven by low-temperature heat source was built based on Engineering Equation Solver software.Under specific working conditions,with total heat transfer area per unit net power output and thermal efficiency as objectivefunctions,the ORC system was multi-objectively optimized by the conjugate directions method.Based on the optimization,the influence of hot and cooling water parameters on the objective functions was also investigated.The result shows that there is an optimum pinch point temperature difference in the heat exchangers and an optimum turbo-expander rotationalspeed that can minimize the combined objective function of ORC system.Under the optimum pinch point temperature difference and turbine rotational speed,the increase in the hot water inlet temperature will reduce the ORC system’s combined objective function,but the rise in the cooling water temperature and the temperature difference between the inlet and outlet of hot water as well as cooling water will enlarge the combined objective function.