Stepping up from its ongoing initiative of providing potable water in six islands of Lakshadweep using Low Temperature Thermal Desalination (LTTD) technology, the Chennai-based National Institute of Ocean Technology (NIOT) is working at making this process free of emissions.
What is Low Temperature Thermal Desalination (LTTD) technology?
- It is based on Ocean Thermal Energy Conversion (OTEC) principle.
- It is one process that uses the availability of a temperature gradient between two water 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 plant discharging huge amounts of condenser reject water into the nearby ocean represents an alternate scenario.
Note: Near Lakshwadeep there is a difference of about 15 – 20 degree Celsius between sea surface water and deep sea water.
- Warm surface sea water is flash evaporated at low pressure and the vapour is condensed with cold deep sea water.
- LTTD exploits the difference in temperature (nearly 15°C) in ocean water at the surface and at depths of about 600 feet.
- This cold water condenses water at the surface, that is warmer but whose pressure has been lowered using vacuum pumps.
- Such de-pressurised water can evaporate even at ambient temperatures and this resulting vapour when condensed is free of salts and contaminants and fit to consume.
Note: Sea water is salty. When water evaporates, it leaves the salts behind. Those vapours when get condensed, are transformed into pure fresh water.
- The LTTD technology does not require any chemical pre and post-treatment of seawater and thus the pollution problems are minimal and suitable for island territories.
- Since no effluent treatment is required, it gives less operational maintenance problems compared to other desalination processes.
- The LTTD technology is completely indigenous, robust and environment friendly.
- The cost per liter of desalination would depend on the technology used and cost of electricity which varies from place to place.
Existing issue: Currently the desalination plants, each of which provides at least 100,000 litres of potable water everyday, are powered by diesel generator sets — there being no other source of power in the islands. However, the need for diesel power to reduce the water pressure means that the process is not fossil-fuel free and also consumes diesel, a precious commodity in the islands that has to be shipped from the mainland critical for powering the electric grid.