Clean water could be zapped out of power plant steam

Approximately 39 percent of all water drawn from US rivers, lakes and reservoirs is used to cool electric power plants. Much of that water, in turn, ends up going out those plants' cooling towers in the form of steam. A new system created at MIT, however, could convert that steam into clean drinking water.

Developed by a team led by Dr. Maher Damak and associate professor Kripa Varanasi, the system is a variation on existing fog net technology, which involves using vertically-hanging fine mesh nets to collect water droplets from moist air passing through them. Those collected droplets subsequently trickle down the mesh, and are collected in a trough at the bottom.

One of the problems with these nets is the fact that the air naturally tends to flow around objects in its path – such as the wires that make up the mesh – taking the droplets through the gaps between those wires. As a result, most fog nets only capture around 1 to 3 percent of the droplets that go through them.

In the new MIT system, the net is replaced with a window screen-like apparatus (that still contains a wire mesh), and the moist air is zapped with a beam of ions before it passes through. This causes the water droplets in that air to become electrically charged, so they're actually drawn onto the wires. As a result, a much higher percentage of them are captured.

If applied to power station cooling towers, the system (which requires little electricity) would be collecting water that was already distilled, meaning it could be used as drinking water. That said, the water could also be reused at the plant, allowing operators to save money.

Additionally, at coastal power plants that use seawater for cooling, the technology could be an alternative to conventional desalination plants. The scientists figure that adding the system to an existing power plant would cost about one third as much as building a stand-alone desalination plant, and the operating costs would be around one fiftieth. In fact, Varanasi estimates that "it could offset the need for about 70 percent of new desalination plant installations in the next decade."

The researchers are now planning on installing a full-scale test version of the system on the cooling tower of MIT's Central Utility Plant. It is believed that if integrated into a typical 600-megawatt power plant, the technology could collect 150 million US gallons (567.8 million l) of water annually, representing around 20 to 30 percent of water currently lost as steam.

The system is currently being developed by spinoff company Infinite Cooling, and is described in a paper published this Friday in the journal Science Advances.

Source: MIT