By Laura Martin
It’s a classic catch-22. Desalination is becoming increasingly necessary due to drinking water scarcity, but the practice requires electricity, created by power plants that need large amounts of water.
The solution: side-by-side power and desalination plants that work together to efficiently utilize resources and create potable water, said Veera Gnaneswar Gude, a professor and researcher from Mississippi State University.
“There is a mutual benefit for both in combining these two processes together,” Gude explained. “It’s the ideal fit. “
Gude and his research team have spent the last eight years working on a new system that makes the desalination-power generation partnership possible.
Instead of using water for cooling purposes, Gude’s technique incorporates a power plant refrigeration system that produces cold air. This system is run by waste heat already being produced in the power plant, and does not require any outside energy resources. The waste heat is also used to power a neighboring low-temperature desalination (LTD) plant.
The partnership works because LTD is significantly less energy intensive than conventional desalination. LTD separates the salt by condensing water at a lower pressure point and temperature (40 to 50 degrees Celsius) than conventional desalination. The LTD process also doesn’t require any mechanical pumping or cooling, which saves even more energy.
“This kind of system is useful for places that are in need of power but don’t have access to water,” Gude said. “It avoids using up a precious resource.”
A thermal energy storage system is also incorporated into Gude’s system, which holds any waste heat created by the power plant that isn’t needed immediately. The stockpiled heat can then be used anytime additional energy is needed at the desalination or power plant.
“That is assuring that demand and supply stay consistent,” said Gude.
This type of power/desalination plant combination could conceivably desalinate 250,000 to 500,000 gallons of water per day using only 500 megawatts of power.
“This process could be as much as 50 percent more economical than current practices,” Gude predicted.
But energy efficiency isn’t the only benefit. By taking water out of the cooling equation at power plants, Gude’s system avoids potential damage that can result from releasing water that is still too warm into the environment.
“Adding heat to the water is just as bad as polluting the water,” Gude said. “It can be very dangerous to fish and plant life.”
On the desalination side, LTD means lower corrosion and scaling rates, as the temperatures required are well below the saturation limits of problem scalants like calcium sulfate.
Gude and his team have a patent in the United States for this process and several pending internationally. They have done small-scale testing and are working on acquiring funding to conduct larger-scale testing and go to market. A demonstration project is planned in the near future in Saudi Arabia.
“We have a lot of interest with industry partners, and everything is moving forward,” Gude said. “Probably within five years we should be able to market this.”
There are currently around 15,000 desalination plants worldwide, according to International Renewable Energy Agency. Most use either membranes or high-temperature evaporation techniques. LTD plants are still rare — the first opened in 2005 in India. This plant, located on the shore in Kavaratti, uses vacuum pumps to create a low-pressure, low-temperature environment where water can evaporate and salt can be removed. Cold water is extracted from deep in the ocean and used for cooling purposes. Gude feels this style of LTD process uses more energy than is necessary to desalinate water.
Regardless of which method is determined to be the most energy efficient, desalination is the future of water, Gude said.
“Our water has to come from somewhere, and we are using up a lot of our freshwater,” he said. “The seriousness of water scarcity will only increase, and desalination is the solution.”
For more on the relationship between energy and water check out this featured article on Water Online.