Study On Multiple-effect Falling Film Seawater Desalination Using Solar Energy

The proportion of the world’s freshwater is quite low. The distribution of water resources also is very uneven. By the way the water pollution problem has been increasing. As a result global water situation has been increasing serious and seawater desalination has become an important means to obtain fresh water. At the same time conventional desalination technology is a high-energy-consuming industry. Nowadays, because of shortage of fossil fuels supply, soaring energy prices and the deterioration of environment quality, the utilization of clean and renewable energy for desalination will become an important development direction. Especially in the areas which lack of fresh water such as offshore islands, ships and remote areas withour power supply, the utilization of natural solar energy for desalination has profound practical significance.Multiple-effect vertical plate falling film seawater desalination technology using solar energy was put forward in this paper. This method of desalination can overcome traditional basin type still’s shortcomings such as large water thickness, big heat capacity, difficult to warming up and no latent heat reutilization. On the other hand this thchnology use solar energy for desalination and it can avoid using any other power-consuming appliance.Established a mathematical model of single effect vertical plate falling film desalination and accomplished the model’s calculation. The fresh water production was estimated when device under different water feeding rate and input energy flux. Device’s water production rate has a first increases then decreases tendency with the increase of water flow rate, so the still has a best water flow rate for a fixed input energy flux. Multi-effect falling film evaporation mathematical model was set up on the basis of single effect model. Water production rate with different series of multi-effect falling film desalination was calculated. The result showed that water production rate increased with the increase of the series. The extent of the increase of water production rate is smaller with the series of desalination device increase.A multi-effect vertical plate falling film evaporation desalination experiment system was set up after simulation was finished. The set was consisted of multiple partition plates of0.27m wide,0.44m high with a evaporation area reached0.1188m2. The single effect and six effect vertical plate falling film evaporation experimental research was accomplished on the experiment system. Water production rate variation tendency with different water feeding rate and input energy flux had a good agreement between the mathematical model and the experimental result. The experimental result showed that evaporation surface will not appear dry point and the device had a relatively high fresh water production rate and coefficient for single effect when seawater feeding rate is4.0×10-4kg.s-1.m-1. The single falling film distill’s water production rate can reach4.77kg.m-2.d-1with an average input energy flux of600W.m-2, and its coefficient of performance can reach0.53. It increased by77%compared with basin type still. At the same time six effect falling film evaporation experimental research was accomplished, it showed that evaporation surface will not appear dry point and the device had a relatively high fresh water production rate and coefficient for single effect when seawater feeding rate is4.0×10-4kg.s-1.m-1. The distill’s water production rate can reach16.62kg.m-2.d-1with an average input energy flux of600W.m-2, it’s5-6times of traditional basin type still.Hangzhou’s total solar radiation intensity was measured in the whole day of July5,2012. The relationship between water production rate and input energy flux was fitted according to experimental result of six effect vertical plate falling film evaporation desalination. This paper coupled the actual solar radiation intensity which was measured outside to the relationship between water production rate and input energy flux. Then the relationship between fresh water production rate with the change of time in July5,2012was acquired, then integrate fresh water production rate to the time in the day, water production in this day can reached15kg. It’s about five times of basin type solar still. As a new seawater desalination technology, it is proved that multi-effect vertical plate falling film evaporation solar desalination technology has certain practical research significance.