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发表于 2010-5-13 11:28
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来自： 中国山东济南
Osmosis is a naturally occurring phenomenon without which life itself would be impossible. It is by osmotic processes that plants can extract nutrition from the soil, or that our kidneys can remove waste products from the blood stream.
Although osmosis was discovered and studied as far back 1850, its practical use for the desalination of water became only possible in the early 1960's when the first useable osmotic membranes were produced. Since then, the technical and commercial development of this desalination process has been nothing less but explosive.
The name "reverse osmosis" stems from the fact that is contrary to "normal" osmosis. If two liquids with different saline concentrations are separated by a semi-permeable membrane, a difference exist between the pressures on the two sites of the membrane related to the difference in concentrations. The water passes through the membrane from the less concentrated compartment to the more concentrated compartment, where the pressure tends to rise.
The difference between the solutions of different concentrations is the osmotic pressure. It can reach high values, for example 25 bars for sea water containing 35 g/l of salts.
In case water has to be desalinated, the natural osmotic pressure has to be overcome, and a additional pressure difference has to be maintained to achieve a proper flow through the membranes.
Water that is pumped to the desalination unit should first be filtered and conditioned before desalination with the precious membrane technique can be used. The membranes are designed to handle water that is free of suspended solids.
The process scheme relevant for the desalination unit, can be found on the next page of this manual. The process consists of the following steps, pre-filtration, scale inhibiting and desalination. In this chapter these process steps are explained. |
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