Fresh water is an essential requirement of mankind for drinking, agriculture & Industrial purpose & is amongst one of the most important input for man’s survival. The rapid increase of world’s population and non uniform distribution of potable water has forced mankind to develop new techniques to generate potable water. Fresh water rivers, lakes & other natural sources are not able to meet the over growing demand of potable water forcing the scientists to look towards the sea to fulfill the need of fresh water. Sea water is available in abundance; however, its conversion to fresh water is limited & restricted due to high cost of conversion. The salt content in the sea water is very high making it unfit for human consumption and industrial use. Various processes are being developed to reduce the salinity of sea water so as to make it fit for human consumption and use. The most popular processes presently being used are Distillation, Reverse Osmosis & Electro dialysis. The selection of the right process depends upon the initial capital investment, plant capital, operation and maintenance costs etc.Scientists all over the world are constantly working on developing economical process so as to generate fresh water on large and economical sales. In this article the focus is primarily on the new process developed by Indian Scientists known as the process of “Low Temperature Thermal Desalination” (LTTD).
0.1 Million Litres per day pilot plant on LTTD process has already been commissioned and is in operation since May 2005 which was designed, fabricated & installed by Indian Scientists at Kavaratti in Lakshadweep. The plant has been working since then, generating fresh water from the sea water to meet the drinking water needs of people of Kavaritti Island, part of Lakshadweep. Sea water contains dissolved salts having a concentration of about 35,000 ppm which is too high for use by human beings. This level must be reduced below 500 ppm before it can be used. Distillation is the oldest and the most commonly used method of desalination, where sea water is evaporated and vapours then condensed giving clean water. The latent heat of water is about 540 kcal/kg making the process highly energy intensive and conventional distillation columns prove uneconomical for production due to high input energy requirements. Various techniques are being used to recover the latent heat like multi effect evaporators, which can lower the energy requirement costs drastically. In LTTD method the energy requirement for the evaporation of water are taken from sea which makes the process eco-friendly and uses renewable source of energy. LTTD uses the temp difference which exists between the surface layer water 28°-30°C) & deep sea layer water (7°-10°C) existing in an ocean to produce potable water.
Everest has been proud to be associated with this project. Vacuum experts at Everest have designed and manufactured complete vacuum system capable of handling total non condensable & carry over water vapour load maintaining system pressure of 25 mbar. Everest leaders in Vacuum technology and manufacturers of Dry Mechanical Vacuum Boosters once again proved their capability to design, manufacture and deliver a vacuum system to meet the stringent needs of Indian scientists. We wish to thank our scientists for putting into actual use of concept, known for a long time but neverattempted before.
A 10 times larger project of 1.0 Million Litres per day (10 MLD) based on the above LTTD concept is already in advanced stage of erection & commissioning in the costal waters of T.N. Here, Everest has once again extended its expertise & has undertaken the complete design, manufacture & supply of the vacuum system. To improve, additional technique of de-aeration of sea water prior to its admittance in the flash chamber is planned which should result in higher efficiency, yield and low power consumption. All the Vacuum pumping system for de-aerator has also been designed and supplied by Everest. 1 MLD project based on LTTD technique is in the advance stage of erection & commissioning and hope by the time the article is published, final trials would be through. The above technology can extensively be used in many chemicals plants for treatment of effluent. In fact a project on similar lines is already in commissioning stage for concentration of Sodium Chloride solution in one of the large pesticide manufacturing units in India. The technical team at Everest, after being exposed to revolutionary technique of LTTD, gained valuable information and practical experience which has been put into commercial use by chemical and pharmaceutical Industry to economize production.