Operation mode and working fluid selection for organic Rankine cycle coupled with reverse osmosis desalination

In view of the problems of water shortage and energy waste,the optimization design of organic Rankine cycle(ORC)coupled with reverse osmosis(RO)desalination was presented in this paper.The high pressure pump was driven by expander,and seawater entered the condenser cooling from the organic fluid out of the expander which can improve the recovery rate of desalination.The paper analysed effects of the pure working fluid,ratio of mixture components,seawater inlet temperature and seawater flow rate on the cycle performance by the method of thermodynamic analysis.In the same heat absorption,working fluid and seawater temperature,the results showed the water production of the system that seawater is heated by the condenser is80%higher than the system that is not preheated.Then fresh water production of zeotropic mixtures is greater than pure fluid because of the temperature slip.Aiming at water production function,R134a/R245fa(0.5/0.5)is the best working fluid.It is10.01%higher than R245fa at12℃and25.04%higher than R245fa at18℃.In the operation of the system,when the high-pressure pump seawater inlet temperature less than40℃,the water flow depends on the power of high-pressure pump.When the water temperature exceeds the working temperature of the reverse osmosis membrane,the system need to open the drain valve and increase the water flow of the condenser and the excess water discharged from the drain valve.At the same time,the advantage of zeotropic mixtures is better than pure working fluid.