Improvement Research Of Condensing System In Organic Rankine Cycle

At present,energy-saving and emission reduction have become the key target of national support and development,and organic Rankine cycle(ORC)is one of the hot spots.Condensing equipment has become an important part of the low-temperature ORC power generation system because it can provide a lower outlet pressure for the steam turbine and increase the power generation of the system.In the present study,two ORC models of different cooling towers are established by Engineering Equation Solver(EES): In the first model,the predicted performance of the opening cooling tower(OCT)for ORC systems is studied and compared with the experimental measurement for a 500 kW ORC system.In the second model,because of the high mass flow of the cooling water and high energy consumption of the cooling water pump for the OCT,the predicted performance of the closed wet cooling tower(CWCT)to replace the OCT for ORC systems is studied.The models are capable of predicting the variation of the pressure loss of heat exchangers,the temperature of heat source,evaporation and condensation temperatures.R123,R227 ea,R245fa,R600 and R600 a are tested as working fluids.The results show that for using R227 ea,two models have the largest net power generation and net generation efficiency,and for using R123,two models have the minimum net power generation and net generation efficiency.Pressure drop and heat losses of heat exchangers have a great effect on the system net power generation and net generation efficiency.The effect of condenser pressure drop is much greater than evaporator pressure drop.The effect of pressure drop on the systems is reduced with the increase of the heat source temperature and evaporation temperature,but the effect of pressure drop on the systems is increased with the increase of condensation temperature.Comparing the two models,it can be found that when the CWCT pressure drop varies between 0.06-0.1 MPa,only for using R227 ea,the net power generation and net generation efficiency of the CWCT-ORC system are higher than the OTC-ORC system.For using working fluids,the net power generation and net generation efficiency of the CWCT-ORC system are higher than the OTC-ORC system under different CWCT pressure drop.In addition,when the pressure drop of CWCT is set to be 0.06 MPa,the difference between net power generating and net generating efficiency of two systems decrease with the increase of heat source temperature when using R123.For using other working fluids,the difference between net power generating and net generating efficiency of two systems increase first and then decrease with the increase of heat source temperature.The CWCT-ORC system reduces the energy consumption of cooling water pumps by about 80 % for all five working fluids.For the CWCT-ORC system,CWCT has the best cooling effect in winter,the second in spring and autumn,and the worst in summer.Among them,the energy consumption of cooling water pump and fan in spring and autumn is 43.4 % less than that in summer;the energy consumption of cooling water pump and fan in winter is 21.6 % less than that in spring and autumn.In summary,using CWCT can effectively reduce the energy consumption of the cooling water pump of the ORC power generation system.For each working fluid,there is a design pressure drop of CWCT that makes the CWCT-ORC system perform better than the OCT-ORC system.