Reverse Osmosis Desalination Driven By Organic Rankine Cycle Modeling Research

Currently under the situation of freshwater, energy crisis and environmental pollution, the exploit of efficient desalination technology driven by clean energy becomes a hot topic. Organic rankine cycle (ORC), due to its advantages in the use of low grade heat source, is able to couple industrial waste heat, solar energy, biomass energy and geothermal energy with reverse osmosis desalination (RO).In this paper, the technology of reverse osmosis desalination driven by organic rankine cycle is researched. First of all, regenerative organic rankine cycle is modeled, by means of the first and the second law of thermodynamics. Then the method of pinch temperature coupling heat source is used to calculate and compare the general ORC and the regenerative ORC. It comes that regenerative cycle has higher exergy efficiency and lower operation pressure, and with regenerative equipment output power can increase by 5.1% and expander inlet pressure can decrease by 17%. It is mainly because that regenerative cycle has much lower exergy loss in condenser. Based on the conclusion, heat transfer enhancement in condenser is researched. The internal phase separation heat transfer enhancement tube is modeled with the theory of multiphase flow. It is proved that the tube can modulate the flow pattern and then enhance the heat transfer of condensation. The results of the model are in good agreement with experimental data and it comes to the conclusion that under the condition of low gas velocity and high liquid velocity, the tube can achieve the optimal flow regime for heat transfer enhancement, which is called the second operating condition.For RO desalination, the classic theory of reverse osmosis desalination is used to establish the mathematic model of membrane element. And the model is verifed by experimental data and desalination plants data from multiple perspectives. The conclusion is that for improving the performance of membrane element, it is recommended to increase supply pressure, reduce the supply salinity and choose the appropriate supply water volume flow. Based on the membrane element model, the economy mathematical model for RO desalination plant driven by ORC is built. The comparison between conventional desalination plant and ORC coupled RO desalination plant is analyzed. It comes to conculsion that measures to improve the economical efficiency of desalination plant include introducing the organic rankine cycle, improving the energy efficiency, increasing plant capacity and locating the plant in low salinity sea area.