Monday, March 23, 2015

The Various Forms Of Seawater Technologies

By Lelia Hall


In the recent past there has been an increase in the population. Living standards have changed and in the industrial and agricultural sector expansion has been exhibited. The trend is expected to continue in the future. This has called for more demand of fresh aqua making it a rare commodity. Focusing on the seawater technologies has been of assistance to combat this shortage.

Statistically the marine makes up 97% of the global aqua storage. Whereas the locked amount by the glaciers and ice caps amount to 2% of the total supply. The percentage available for human use is about 0.5%. Supplied by lakes and rivers. Water from the sea is neither suitable for consumption by humans nor industrial use. There by desalination being considered as an important alternative for sourcing out fresh water.

The process comprises division of the commodity into two. Fresh stream containing little concentration of salts dissolved while the other is heavily concentrated brime. Forms of energy are required for the above process and there by different inventions are being used. Various technologies have come up based on different platforms such as freezing, electro dialysis etc. But the two mostly used and have a promising future are the MSF and RO. Together with MED, they are predicted to be the dominant methods in future.

So what are some of the technologies used? Multiple-stage flash distillation is one of them. This one is based on the principle of flash evaporation. The resource is evaporated by reducing the pressure as opposed to raising temperature. The economies of the MSF heating technology are achieved by regenerative heating where the sea water flashing in each flash chamber or stage gives up some of its heat to its counterpart going through the flashing process.

Another form of distillation in the multiple effect, also the MED. Is considered very efficient thermodynamically. It occurs through a series of evaporators known as effects. And applies the principle of lowering the pressure in the different effects. Its economic level is dependent on the number of effects. There are different tubes used. Some submerged, horizontal and others vertical. Has been applied in the Middle East. Its utilization is still low as compare to the MSF but gradually increasing.

Another form of distillation is the vapor compression. Where compression of vapor is the means of heating the incoming aqua. This is made possible by application of two methods. Use of mechanical compressor hand in hand with steam jet. It is built in the principle that boiling point is reduced with reduction of pressure. In small scale units of desalination this method is highly used.

RO, also known as reverse osmosis, is highly used. Where osmotic pressure is overcome through application of outer pressure which is more compared with the sea water osmotic pressure. It therefore flows in reverse direction in respect to direction of the natural flow. Dissolved salts are left behind as it concentration increases. Previous development have come up in aiding the reduction of cost operation of RO plants. They include development of efficient membranes that also last longer and energy recover devices.

Methods such as solar evaporation, freezing and potabilization are used but not as often as the ones described above.




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