Eco-friendly thermal desal unit planned in Tuticorin power plant

CHENNAI: Thermal power plants are major water guzzlers, exerting tremendous pressure on fresh water resources. So, to find a solution to this complex problem in which one can’t decide between power and water, the Union Ministry of Earth Sciences (MoES) is advocating the concept of producing their own water with the help of a cheaper and reliable Low Temperature Thermal Desalination (LTTD) technology developed by the Chennai-based National Institute of Ocean Technology (NIOT).

M Rajeevan Nair, secretary, MoES, told Express that the government was planning to use the LTTD technology in all thermal plants located close to the coast. The first such desalination plant with a capacity of 2 mld (million litres per day) will be set up in 1,050-MW Tuticorin Thermal Power Plant.

This assumes significance as the Tuticorin power plant was recently accused of depleting the Tamirabarani water by drawing fresh water from the Srivaikuntam dam. The Southern Bench of the National Green Tribunal has also restrained the Tamil Nadu Water Supply and Drainage (TWAD) Board from supplying water to the power plant.

Nair said the LTTD technology had been used successfully in the projects being implemented in the Lakshadweep Islands. Also, an experimental 1-mld plant was also set up in the North Chennai Thermal Plant, which has established its utility in a power plant. “Shortly, tender process will commence for the desalination plant in Tuticorin,” he said.

NIOT director Satheesh C Shenoi said thermal power plants discharged large quantities of warm water, which was an environment threat. The conventional desalination processes such as reverse osmosis leave behind high concentration of membrane which again contributes to environment degradation.

“So, what the LTTD does is 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 benefits of cooling the condenser-rejected water and generating freshwater without using chemicals. A small temperature gradient of about 10°C, as is the case with most power plants, would be sufficient,” he said.

Also, NIOT officials said this Tuticorin desalination plant was designed to produce boiler quality water, which is the purest water. “Usually, drinking water is required to have less than 500 ppm, but the boiler quality water needs 1 ppm. So, it’s an advanced technology,” a senior scientist said.

Number crunching

• A thermal power plant discharges 32,000 cubic metres of water every hour. One cubic metre of water is equal to 1,000 litres
• According to the 2011 Planning Commission report, India’s annual rainfall is 4,000 trillion litres, of which only 1,869 trillion litres are usable. Of this, less than 1,123 million litres are actually put to use
• Groundwater, which accounts for 433 million litres, contributes 70-80% of that used in farms, around 80% of the supply in rural areas, and about half of that used in cities and by industry in India
• The conventional desalination processes such as reverse osmosis, multi-state flash desalination (MSF), multi-effect desalination (MED) are too expensive and not environment-friendly