Desalination Plants To Produce Fresh Water In Lakshwadeep

The thermal gradient (temperature difference between sea surface water and deep sea water) of about 15⁰C required for desalination plants as this, is found near the Lakshadweep coasts only as of now. Three LTTD plants have been successfully commissioned in the country, one each at Kavaratti, Minicoy, and Agatti islands of the Union Territory of Lakshadweep. In addition, work has been initiated to set up a prototype LTTD plant with a capacity of generating 2 million litres of potable water per day (2 MLD) at the Tuticorin Thermal Power station, Tamil Nadu.

Sea water desalination is attaining increasing attention of present day policy makers, especially with the growing demands that urbanization, population explosion, irregular rainfall and ground water contamination place on the fragile natural resources. Low temperature thermal desalination (LTTD) is one process that uses the availability of a temperature gradient between two water bodies or flows to evaporate the warmer water at low pressures and condense the resultant vapour with the colder water to obtain fresh water. While ocean, with its temperature variation across its depth presents one such scenario of two water bodies, a coast-based thermal power plant discharging huge amounts of condenser reject water into the nearby ocean represents an alternate scenario. The simplicity of the LTTD process also enables to control the quality of product water in order to provide either good quality drinking water or boiler makeup water as the situation warrants.

The successful demonstration of an LTTD plant with the existing temperature gradient of mere 8oC at the NCTPS provides another new area for its application. Since most power plants discharge the condenser reject water at 8o-10oC above the ambient sea water temperature, any increase in the available temperature difference or the provision of additional process steam from power plant will increase the efficiency of the LTTD process, resulting in the generation of huge quantity of fresh water. If implemented in the design stages further optimization of the power consumption is also possible. Newer power plant projects are also coming up all over the country, most along the coast. Thus, the LTTD technology, if applied to power plants, would be useful in providing high quality freshwater for boilers, while reducing the thermal pollution.