The Research On A New Solar Desalination System With Natural Vacuum Desalination Technology

Small desalination technology could solve the shortage of freshwater resources in remote areas, islands, offshore platforms. Combined with solar technology, small desalination system can reduce the use of non-renewable resources like coal and oil, which is important in terms of energy saving and environmental protection.A new solar desalination system with natural vacuum desalination (NVD) and mechanical vapor compression (MVC) technology has been designed in this paper. This new system has combined the character of NVD technology saving electricity with the character of MVC technology with high thermal efficiency. Physical and mathematical models of this new NVD-MVC system are established, including collecting process models, storage/heating process models, seawater supplement process models, preheating process models, evaporation process models, condensation process models and compression process models. And the mathematical models are programmed and solved under MATLAB environment.Performance parameter of monthly representative day and a year has been analyze under different heating water flow and height difference between brine pipe and seawater pipe. When the height difference between brine pipe and seawater pipe is fixed and the heating water flow increases, fresh water productivity and specific productivity for the collector area both increase, specific power lows firstly and increases later, and there is a optimal heating water flow for the lowest specific power. And specific module area for the heat exchanger lows. When the heating water flow is fixed and height difference between brine pipe and seawater pipe increases, fresh water productivity and specific productivity for the collector area both low, specific power and specific module area for the heat exchanger both increases.An optimum operation mode of the NVD-MVC system has been obtained based on optimal heating water flow and height difference between brine pipe and seawater pipe of every monthly representative day. When the area of collector is 200 m2, and the volume of thermal storage tank is 70 m3, the average fresh water productivity is 9.33t/d, and the average specific power is 11.52kW·h/t under the optimum operation mode. Comparing with the operation mode with fixed heating water flow and height difference between brine pipe and seawater pipe in all the year, the optimum operation mode could produce more water of 277.4t per year, and save 715.14kW·h electricity energy per year under its productivity.Performance of this NVD-MVC system and the traditional solar assisted NVD system are compared and analyze. Under the calculation conditions of this paper, NVD-MVC system could produce more water, and use less heat source, but its average specific power is higher. Finally a concept of specific stand coal consumption was proposed, and specific stand coal consumption of NVD-MVC system was smaller, which means better energy performance. Meanwhile, Performance of this NVD-MVC system and the traditional solar assisted MVC system are compared and analyze. Under the calculation conditions of this paper, NVD-MVC system could save more power.