Performance Analysis Of Zeotropic Mixture Orc Applied To Generate With Mid-low-Grade Waste Heat Source

Industrial energy consumption accounts for 70% of national total energy consumption based on the structure of energy consumption in China,and 60%~65% of industrial energy consumption is converted into different forms of waste heat resources with various temperatures,among them,the proportion of mid-low-temperature waste heat is about 40%~50%,which has not yet been fully used,it is one of the main reasons resulting in low energy efficiency in our country.With advantages of simple structure,environment friendly,strong adaptability to the mid-low-temperature heat source,and so on,Organic Rankine Cycle(ORC)is becoming the preferred technique for the utilization of mid-low-temperature waste heat.This paper presents the study of ORC power generation system using zeotropic mixture as working fluid.In the first part of this paper,the thermodynamic and economic model of ORC is built,and mixtures R227ea/R245 fa,Butane/R245 fa and RC318/R245 fa are selected as working fluids.Based on set above,the system thermodynamic and economic performance are analyzed and compared with pure fluid ORC.In addition,the impact of key parameters such as heat source inlet temperature,cooling water temperature difference and pinch point temperature difference on ORC system are also studied.The result indicates that maximum thermal efficiency and exergy efficiency can be achieved when the temperature difference of cooling water is near the temperature glide of zeotropic mixture in the condenser,and thermal efficiency,exergy efficiency and the net power output all increase compared to corresponding pure fluid cycles;the net power output per unit UA becomes worst while the net power output is best,in other words,the economic performance of this system becomes worse in some degree;the larger the cooling water temperature difference is,the poorer the thermal performance of this system achieves;thermal efficiency and exergy efficiency increase with the increase of the pinch point temperature difference of the evaporator,while the trend of economic performance is in inverse.In the last part of this paper,the dual loop model applied to recover multi-grade waste heat from internal combustion engine is established,and mixtures RC318/R1234 yf,Butane/R1234 yf and RC318/R245 fa are selected as working fluids in the Low Temperature Loop(LTL).Whether the system aggregate performance will be improved in such a dual-loop system with mixture as working fluid is explored,and the impact of condensation temperature in High Temperature Loop(HTL)on system performance is also investigated.The conclusion is summarized as follows: the mixture RC318/R1234 yf can recover nearly 17.3% of the waste heat form jacket cooling water,which is more than all the four pure working fluids researched,it reveals that the mixture do perform better in the aspect of matching two heat sources of different grades.The condensing temperature in HTL has an important impact on the position of pinch point of Evaporator 1,which will affect system performance.Therefore,selecting suit condensing temperature in HTL and taking the position of pinch point of Evaporator 1 into account adequately during the designing and operation process in a dual-loop system are significant.