Today, 39%of all the fresh water taken from rivers, lakes,and reservoirs is ear marked for the cooling needs of power plants, that use fossil fuels, or nuclear power. The problem? A large portion of that water ends up floating away in clouds of vapor. In other words, hundreds of billions of gallons of clean, otherwise usable water, are lost each year. But now, a new system, devised by a team of MIT engineers could provide an efficient, low-cost way to capture a substantial amount of that lost water, ultimately making power plants less wasteful and more self sustaining, and the water collected could become a source of potable water for parched cities around the world.
The motivation to develop this new system stems directly from the inefficiencies of current natural fog harvesting systems. Existing systems, which generally consist of a plastic or wire mesh,hung vertically in the path of fog banks, only capture about one to three percent of the water droplets that pass through them. The reason for such a tiny percentage is the result of aerodynamics. As a stream of air passes an obstacle, such as the wires in these mesh fog catching screens, the air flow naturally deviates around the obstacle.
Thus, carrying droplets that were heading toward the wire off to the side. The researchers found that once they zap the fog with a beam of electrically charged particles know as ions, the opposite effect happens. Not only do all the droplets that are in the path of the wires land on them, but even droplets that were aiming for the holes in the mesh get pulled toward the wires, due to the charge. The droplets then collect on that mesh, drain down into a collecting pan, and can be reused in the power plant or sent to a city’s water supply system. The team is currently building a full scale test version of their system, to be placed on the cooling tower of MIT’s central utility plant.
A natural gas, co-generation power plant, that provides most of the campus’s electricity, heating and cooling. In a series of experiments,the researchers demonstrated the concept, by building a small lab version of a stack emitting a plume of water droplets. They then place their ion beam and mesh screen on it. When the condenser is off, a thick plume of fog droplets rise form the device. Once the condenser is turned on, the plume almost instantly disappears and liquid can be seen condensing on the wire dome. The equipment is simple,and the amount of power required is minimal. And the result is something priceless.
Access to free, clean water. The researchers say this could be a great solution to the global water crisis, by offsetting the need for about 70% of new desalination plant installations,in the next decade. For example, a typical 600 megawatt power plant could capture 150 million gallons of water a year, representing a value of millions of dollars. The researchers aim to test the system at MIT’s central utility plant in the fall. The campus’s power plant tests will not only the risk the technology, but will also help the MIT campus improve it’s water footprint.