Environmental Impact Analysis And Multi-objective Optimization Of Organic Rankine Cycle System

Energy shortage and environmental pollution are the main factors restricting economic and social development.The key to reduce the huge consumption of traditional energy by economic and social development is to improve energy efficiency,develop and utilize new energy and low-grade energy.Organic Rankine Cycle（ORC）is a promising technology and has been widely studied.Carbon footprint（CF）and water footprint（WF）models are established based on exergoenvironmental method for Organic Rankine Cycle（ORC）.Sensitivity study is performed.For the case of equal criteria weight and unequal criteria weight,multi-objective decision framework under equal and unequal criteria weight are built respectively to determine the optimal working fluid and operating conditions of organic Rankine cycle（ORC）.R1233zd（E）,R600a and R245fa and R245fa/R600a（0.5/0.5）are selected as the working fluids.The results show that the main methods to decrease CF and WF of ORC system are not the same from both exergoenvironmental analysis viewpoint and sensitivity study aspect.The differences lie in（i）from exergoenvironmental analysis viewpoint,reducing the CF cost of exergy destruction of evaporator and condenser is necessary;While reducing the WF costs rate of condenser is indispensable for WF reduction;（ii）regarding sensitivity study,the increase of evaporating temperature and decline of pinch point temperature difference in evaporator can be adopted to reduce the carbon emission;While increasing evaporating temperature and pinch point temperature difference in evaporator is effective to decrease the water consumption.Under the multi-objective decision-making framework of equal criteria weight,the optimal working fluid of the system is R245fa/R600a,the optimal evaporation temperature,the pinch point temperature difference in the evaporator and superheat are 119.47^oC,6.87K and 1.1K respectively,and the corresponding net output work,CF cost of unit net output work and WF cost of unit net output work are 10.04k W,134.35kg CO₂eq/GJ and 69.54kg H₂O/GJ,respectively.While in the case of that of unequal criteria weight,the optimal working medium of the system is R600a,and the optimal operational parameters are 117.81^oC,5.03K and1.78K,respectively;the corresponding criteria are 9.54k W,131.51kg CO₂eq/GJ and61.22kg H₂O/GJ,respectively.