Chennai: The technology behind desalination plants may appear simple extract seawater, remove salt, make freshwater but operating such plants is power intensive and can also pollute the environment through toxic brine (salts) effluents.
After it was realized that the solution to tackling water scarcity lay in seawater and the Sun, a team has now set up the country’s first solar-powered desalination plant, with a capacity to generate 10,000 litres of freshwater a day, on 120sqm near Vivekananda Memorial at Kanyakumari. The solar-powered lo- temperature flash desalination system is locally available, time-tested and marries both technologies. The ministry of earth sciences-funded Rs 1.22 crore experimental project will be soon inaugurated.
At the plant, Prof A Mani of the refrigeration and airconditioning lab at IIT-M’s department of mechanical engineering said, surface seawater is pumped in and a collector that traps sun’s radiation converts it into heat. This is used to heat seawater, which is around 37 C, to 70 C and above. The hot water is pushed into a flash chamber under vacuum and around 1% turned into vapour. The vapour is sent to a condenser and cooled with sea surface water to generate freshwater.
The sun’s energy is used to heat water and generate power through photovoltaic panels to operate the plant. “It requires about 15kv power a day to function. We have installed panels that each generate around 324 watts. Since the plant is completely solar powered, it can be operated only during the day i.e for 6-7 hours between 9am and 4pm,” he said. The generated power, converted from DC to AC through an inverter, is stored in 14 batteries to provide 30-minute power backup.
Five solar-powered motors operate the plant. “We also replaced a mechanical vacuum pump to maintain vacuum pressure with a low maintenance ejector,” Prof Mani said. The freshwater generated has only 2ppm of dissolved salts. “For drinking, WHO recommends water with 500ppm. So, we mix this water with local municipal water,” he added.
M A Atmanand, director of NIOT which has provided technical assistance, said “Solar desal plant has a lot of potential in coastal areas. This technology can be replicated and technology transfer can be done through NIOT to be used in other areas.”
Four faculty members and nine PhD students from IITM have been collecting data, like effects of weather and if the desired capacity is generated, from the plant for the last 18 months. Researchers said scaling up the technology to generate 10MLD or 100MLD can be technically challenging as PV panels are space consuming.