The government launched its largest water desalination project, located on a barge off the coast of Chennai, which promises to generate nearly a million litres of potable water per day.
The project has been executed by the National Institute of Ocean Technology in Chennai. Said S.R. Kaitholi, the director of the institute: “As of now, the plant has a capacity of about one million litres a day, but if we can scale it up 10 times, we could easily produce the water at less than four paise a litre.”
Without factoring in the cost of the project, to which the government refused to put a number, the cost of producing a litre of water is currently about six paise. Moreover, the water is claimed to have dissolved solids of 10 parts per million (ppm) compared with 200-300 ppm in bottled mineral water. The underlying technology exploits one of the oldest principles in chemistry, of lowering pressure, to reduce the boiling point of a liquid. This desalination plant consists of two chambers—the flash chamber and a condenser. A vacuum is created within the flash chamber which draws sea-surface water.
The resultant steam now passes into the condenser, which uses cold water pumped from the sea and drawn by a 600-metre deep pump. The steam cooled by this water is condensed into potable water. Special nylon bags with a capacity of two lakh litres can be used to store the water, and transported by fishing boats to the shore.
Though the technology has been indigenously developed by the government, and there are no buyers yet, science and technology minister Kapil Sibal is confident of the technology’s feasibility and success. “We intend to scale this up using the public-private partnership model. We’ve developed the technology and now it’s up to the industry to bring it to the people. We are in talks with some companies,” he said. However, the major thrust of the technology is its implication, once integrated with power plants. Using the cold water from the sea, Sibal said power plants in the city could be configured to meet over 25% of the city’s fresh water requirement.
Project leader Purnima Jalihal’s reasoning is that the sea water used for cooling purposes by thermal power plants attains temperatures of 42-44 degrees Celsius and can be used as warm water for evaporation in the flash chamber of desalination plant.
Sea-surface water at 28-30 degrees can be used for cooling the vapour in condensation plants. However, this system can work, and be cost effective, only if desalination plants can be integrated with thermal power plants.
The government had launched a one-lakh-litre-per-day plant at Kavarathy, in Lakshadweep in 2005. “It’s the success of that project that has encouraged us to go ahead with this project,” said Sibal. The minister claimed that the project at Kavarathy has generated over 50 million litres of pure water since theplant’s launch. However, this project is a land-based one meaning the condensation chambers are located on the ground. “The sea-based plant is working fine, in a few months we will know how well it compares to the Kavarathy project,” said Kaitholi.
Desalination at sea (Graphic)