Study On The Effect Of System Parameters On The ORC System Performance

At present,human society is facing great challenges due to the rapid deterioration of energy and environmental problems.Therefore,it is urgent to save energy,reduce the use of traditional energy sources and develop new energy sources.China is rich in low-grade waste heat resources,but the utilization of waste heat resources is relatively low,and it can't effectively alleviate the energy and environmental pressures.The Organic Rankine Cycle(ORC)can be used to recover the low-grade waste heat resource and realize the reutilization of the waste heat resource,which can effectively improve the energy and environment condition of our country.The heat exchanger pinch point temperature difference is an important parameter affecting the heat transfer performance.Rational and effective allocation of the evaporator and condenser pinch point temperature difference can significantly improve the ORC system performance.This paper established the thermodynamic model and economic model of ORC system which recover the low-grade waste heat.Through the comprehensive evaluation and analysis of the ORC system,the most suitable operating condition of ORC system is obtained.The thermodynamic performances of the ORC system are studied.And the variation of ORC system thermodynamic performance with the evaporation temperature,the condensation temperature and the pinch point temperature difference assignment are acquired.Based on the results,the optimal evaporation temperature,the condensation temperature and the pinch point temperature difference assignment parameters are determined according to the thermodynamic standard;Secondly,the economic performance of the ORC system is studied,and the heat exchanger area per unit net output power(APR)is taken as the economic evaluation index to analyze the effect of the pinch point temperature difference assignment scheme on ORC system economic performance.And the change of the optimal pinch point temperature difference distribution scheme with the system economic performance as the evaluation standard is obtained under the condition of changing the system working condition;Finally,the thermal and economic performances of the ORC system are considered comprehensively.The ORC system is evaluated and analyzed by the AHP-entropy method,and the change of the comprehensive evaluation index ? with the pinch point temperature difference ratio k is obtained,so as to obtain the best pinch point temperature difference matching scheme.By comparing and analyzing the comprehensive evaluation index ? of different working fluids,the optimal organic working medium of ORC system is chosen.The results show that the pinch point temperature difference ratio k between the evaporator and condenser is between 1.25 and 1.5 for the subcritical ORC system,and the optimal organic fluid is R11.