Simulation Analysis of Double-effect Seawater Desalination System Using Compression Heat Pump

Abstract

The lack of freshwater resources has become the biggest obstacle to the sustainable development of the world economy with the expansion of population and the impact of climate change. Seawater desalination is recognized as the most effective means to alleviate water scarcity. A double-effect seawater desalination system using compression heat pump is proposed by combining a compression heat pump and a double-effect desalination system. Performances of the proposed system are simulated using Aspen simulation software. Based on the simulation results, the influence of heat pump evaporating/condensing temperature, temperature difference between the two effects and the brine circulation ratio on the system Performance Ratio (PR) and freshwater production are analysed. It is concluded that the value of PR increases but the freshwater production reduces with the increase of evaporating temperature of the heat pump. Both the value of PR and the freshwater production decreases with the condensing temperature of the heat pump. An optimal temperature difference between the two effects exits to get the highest PR and freshwater production for a constant heat pump operation condition. The freshwater production can increase slightly with the increase of the brine circulation ratio. When the mass flow rate of feed seawater is 80kg/h and the evaporation temperature of primary effect evaporator is 40°C, the PR of the system reaches 40.07 with an evaporating/condensing temperature of 20°C/50°C. The freshwater production is 39.76kg/h with an evaporating/condensing temperature of 10°C/50°C.