The Research On Solar Desalination System With Evacuated Tube Collectors

Conventional seawater desalination technology could solve the problem of fresh water shortage, but consumed a large amount of fossil fuel, leading to the environmental problems such as global warming, acid rain, etc. The increasingly serious of the fresh water scarcity, energy exhaustion and environment pollution made many researchers focus on renewable energy desalination technology. This paper reviewed the documents about renewable energy desalination technology domestic and foreign, showed the advantages of various renewable energies coupled with seawater desalination technologies, and put the emphasis on solar desalination technology (heat). Detailed discussion was made on application, region, scale, technology and cost, etc, about different forms of solar collectors and solar desalination technology (heat). At last, evacuated tube collectors coupled with multi-effect distillation was chose for thermal and economic performance analysis.Mathematical and economic models were established based on mass and energy conservation, which concluded evacuated tube collector mathematical model, thermal storage tank mathematical model, flasher tank mathematical model, multi-effect distillation mathematical model, electrical heating and cooling system model. Meanwhile, the fresh water cost model was also made in this paper. All these models were established and solved by MATLAB software.While the load of collector added from "Valley Value" to "Peak Value", the fresh water yield increased, but the fresh water cost had an optimal value.When the system was on "designed load", the increasing of collector area also added the fresh water yield, volume of thermal storage tank and area of evaporator, decreasing the cost of fresh water. But the fresh water cost was almost constant when the collector area exceeded 4000m2. The increasing of outlet temperature of collector slightly reduced the fresh water cost, but it basically had no effect on area of evaporator and fresh water yield. And there was an optimal heating vapor temperature of the first effect in this paper which was about 68℃to guarantee the fresh water cost to be the lowest, though the heating vapor temperature basically had no effect on the yield of fresh water. Also, when the effects of multi-effect distillation system exceeded 8, the decline of cost of fresh water would not evident.When the area of collector equaled to 8716m2, the outlet temperature of collector was 95℃, the temperature of the heating vapor in the first effect was 68℃and the number of the effects of multi-effect distillation system equaled to 8, the calculated results is that performance ratio was 6.75, the yield of system was 300t/d and the fresh water cost was 37.6￥/t. What's more, the investments part constituted 80% of the total cost, during which the land cost counted 35.3% is the biggest one, proving the ETC solar desalination project was cost intensive.The decreasing of land and collector cost could reduce the fresh water cost, so the economical efficiency of system could be enhanced if appropriate site existed and prefect ETC was developed.