Making freshwater from its saline cousin
The Vice-Chancellor of Karunya Deemed University A.E. Muthunayagam, has designed a pioneering system
Karunya's desalination project
CHUGGING OUT of the harbour is a little tugboat hauling a large empty bag made of toughened plastic. Some distance from the shore, the boat draws alongside a floating barge with a metallic structure upon it.
This is a desalination plant that has turned seawater into freshwater, and stored it in a large plastic bag that is now almost full.
For a few minutes, the crew on board the tugboat are busy detaching the freshwater bag from the plant and replacing it with the empty bag they have brought with them. After a quick inspection to ensure that the plant is working normally, the crew turn the tugboat towards the shore, drawing the freshwater bag behind them.
Desalination system
This scenario could become commonplace at port cities in the country, if the desalination system based on `low pressure distillation' is widely adopted for commercial use.
The Vice-Chancellor of Karunya Deemed University, A. E. Muthunayagam, has designed a pioneering system to turn seawater into water vapour, and condense the vapour into freshwater.
To demonstrate that his idea was feasible, Muthunayagam built an experimental plant at Karunya Deemed University in Coimbatore, under a research project sponsored by the Department of Science and Technology (DST).
Saltwater from a tank entered a metallic container called vaporiser, maintained at low pressure by a vacuum pump.
Offshore and onshore
Owing to the low pressure, a portion of the saltwater turned into water vapour and moved into a container called condenser, kept cool by circulating cold water around it.
In the condenser, the water vapour condensed into freshwater, and flowed into a storage receptacle from where it could be periodically removed.
Muthunayagam said that in an offshore unit, warm water from the upper layers of the ocean could be sent into the vaporiser, and cold water from the ocean depths to constantly cool the condenser.
He said that the system could be installed as an onshore unit, to use the warm water discharged into the sea by thermal power stations.
Thermal stations drew water from the sea at about 30 degrees Celsius, and used it for cooling. This raised the temperature of the seawater to 40 degrees Celsius, and it was then allowed to flow back into the sea. In this situation, Muthunayagam planned to use the heated water in the low-pressure vaporiser, and cold seawater in the condenser, which was also maintained at low pressure.
Demonstration unit
Using the Karunya plant, he was able to show that his method of low-pressure distillation was feasible. He demonstrated the system using an experimental desalination plant at the Tuticorin Thermal Power Station last month.
This was in association with M/s AEM Ocean Technologies and Services Pvt. Ltd., and M/s Koushic Pressure Vessels Pvt. Ltd. The plant had a production capacity of 100 litres of freshwater per hour.
All the hardware was commercially available, and there were no high technology elements like membranes and fine filters. Moreover, the operations were very simple and there was no need for highly skilled workers. Above all, it did not harm marine life.
Superior system
Low-pressure distillation required external energy for injecting water into the vaporiser, circulating cooling water around the condenser, and running the vacuum pump. He said that the system was superior to `reverse osmosis' that required pre-treating the water by filtering it to remove floating substances, and adding chemicals to prevent micro organisms growing on the membrane and damaging it.
When designing the plant, Muthunayagam drew upon knowledge gained in space science as well as ocean development. He said that low-pressure distillation was better than the two major systems of desalination used nowadays.
These were the multi-stage flash system and the reverse osmosis system.
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Karnataka
Chennai
Coimbatore
Hyderabad
Madurai
Tiruchirapalli
Vijayawada
Visakhapatnam
