| Waste heat power generation system based on organic Rankine Cycle(ORC)is considered to be one of the most effective ways to recover low-grade energy.In order to improve the thermal efficiency of the system,the paper selected different working fluids.Mathematical models programmed by REFPROP 8.0 and MATLAB 2010 a are used to analysis the thermal performance of the system.Frist of all,according to physical properties,isentropic properties,environment protection and safety,the 84 kinds of working fluids provided by REFPROP 8.0 were initial selected.Taken the net output power and thermal efficiency as the evaluation index,to analysis initial working fluids’ optimal evaporation and condensation temperature with the establishment of basic ORC system.The results show that dry working fluid is more suitable for the ORC system than wet working fluid,each of working fluid has its own optimal evaporation temperature.R245 fa and R152 a have better comprehensive performance than others,and their optimal evaporation temperatures are 148 ℃ and 105 ℃.Then,the author analyzed respectively the thermodynamic performance of recuperation ORC system,steam extracted ORC system and reheating ORC system.And found the law governing changes under the condition of different regenerator effectiveness,extraction pressure ratio and reheating pressure ratio.The results show that,compared with the basic ORC system of thermal efficiency,recuperation ORC system improved about 1.5 percentage points;steam extracted ORC system improved about 3 percentage points,R245 fa and R152 a have their optimal extraction pressure ratios are 0.4,0.55;reheating ORC system has a significantly improvement in net output power,R245 fa and R152 a have their optimal reheating pressure ratios are0.42,0.52.And then,this paper selected R245 fa and R152 a as the component of mixed fluid to established model for reheating-regenerative-internal regenerative organic Rankine cycle.By analyzing the thermal efficiency and exergy destruction factor withdifferent mixed fluids,the optimal composition was ascertained.The results show that when the mass ratio of R245 fa to R152 a in the mixed fluid equaled 0.85:0.15,the system has the maximum thermal efficiency of 18..52%,and the minimum exergy destruction factor.Finally,multi-objective function was built to study the optimization model considering C-ORC system extraction pressure ratio and reheating pressure ratio,the thermal efficiency and the investment cost of the unit net output power were chosen as the objective functions.To analyze the law governing changes in objective function and get the minimum value of the function.The results show that when extraction pressure ratio and reheating pressure ratio are 0.45 and 0.44,the C-ORC system has better thermal performance and economic performance at the same time. |
