Good Thinking

Clean water could be zapped out of power plant steam

There's potable water in that thar steam
There's potable water in that thar steam
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A lab testing setup of the system
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A lab testing setup of the system
There's potable water in that thar steam
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There's potable water in that thar 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

7 comments
sugamari
please don't tell nestle - their water is cheap enough
Roger Garrett
The article starts off with "Approximately 39 percent of all water drawn from US rivers, lakes and reservoirs is used to cool electric power plants." I call BS on that. Utter BS. If there's one industry that uses the most water from those sources it's agriculture. And water for drinking is likely the second highest use of that water.
Roger Garrett
The SECOND sentence states, "Much of that water, in turn, ends up going out those plants' cooling towers in the form of steam." No, no, no. That's WATER VAPOR coming out of those towers, not steam. Can't these people get anything right?
Roger Garrett
And more. The articles says, "the water could also be reused at the plant, allowing operators to save money." So they're proposing that the water that's intended to remove heat from the power plant can be captured and used again and again to remove heat. So, where exactly does the heat go? How would that work from a thermodynamic standpoint?
piperTom
Like Mr. Garrett, I am suspicious of the 39% figure for power plant water usage -- but not for the same reason. By far, the cheapest thing a power plant can do with the water they have drawn from a lake or river is -- put it back into the lake or river. So, even if the 39% figure is accurate, it's not relevant to the current topic. As to the thermodynamics, the answer is easy. In the open cycle sort of cooling tower where this technology would useful, the main point of cooling is in that evaporation of the coolant water. Evaporation transfers heat from the water to the air. The heat goes into the air! The scheme described in the article would effectively transform an open cycle cooling tower into a closed cycle (or partial). Closed cycle towers are already used in places without adequate water.
ljaques
It bodes ill that an article like this could come out of MIT. All the mistakes the article makes re: steam/vapor, % of fresh water used, and captured water reuse. One last thought: don't we want extra water vapor going into the atmosphere to create clouds which help defeat the AGWK with which humankind is killing its world? <g>
Gannet
Capturing humidity from the air is hardly new,OK, the big dealis that they've made one method more efficient. And a bit late, these dinosaur power plants are disappearing at a rapid rate that this technology will soon be useless.