Desalination drinking water plants on anvil

Foreseeing acute shortage of drinking water in near future, Ministry of Earth Sciences, through its National Institute of Ocean Technology, has embarked upon a very unique programme of making desalination drinking water plants near various coastal cities in the country. Worldwide, 13,080 desalination plants produce more than 12 billion gallons of water a day, According to the International Desalination Association.
Water is desalinated in order to be converted to freshwater suitable for human consumption or irrigation. It is used on many seagoing ships and submarines. Most of the modern interest in desalination is focused on developing cost-effective ways of providing freshwater for human use in regions where the availability of freshwater is limited.
Most of the plants are being made on Low Temperature Thermal Desalination (LTTD) process, informs Dr. Shailesh Nayak, Secretary, Ministry of Earth Sciences.
According to Dr. Shailesh Nayak, “LTTD is one process that uses the availability of a temperature gradient between two wter bodies or flows to evaporate the warmer water at low pressure and condense the resultant vapour with the colder water to obtain freshwater. While ocean, with its temperature variation across its depth, presents one such scenario of two water bodies, a coast based thermal power plan discharging huge amounts of condenser based thermal water in to the nearby ocean represents an alternate scenario. The simplicity of LTTD process also enables to control the quality of product water in order to provide either good quality drinking water or boiler grade water as the situation warrants.”
It can be seen from these LTTD plants that a temperature difference and adequate vacuum levels should be sufficient for the generation of freshwater. Thermal power plants discharge warm water from their condensers. The process that involves transfer of tremendous levels fo energy usually includes heat recovery systems like cooling towers or heat dissipating open channels before the condenser reject water at acceptable temperatures is discharged back into the surrounding environment. Consequently, the resultant termal pollution by the power plants is a serious issue today. An efficient way to utilize the heat available in the condenser reject water would reduce the load on the cooling towers and in turn the resultant thermal pollution. One of the aspects of LTTD is that it transfers the available heat from warmer water to the colder water while generating freshwater from the warm water. This aspect could therefore be aptly used in thermal power plants resulting in the double benefits of cooling the condenser reject water and generating the freshwater. A small temperature gradient of about 8-10 degrees celcius, as is the case with most power plants, would be sufficient to utilize the concept.
Dr. Nayak informed that the Ministry of Earth Sciences targets to cover all 10 major habited islands of Lakshadweep with plants of capacity of one lakh litres each per day by the end of 2010. Two plants have already come into operation at Kavaratti and Chennai. LTTD technology is being used at all places.