August 14, 2021. By Kolemann Lutz
Fog fences have been used for decades to collect the water droplets from dew and fog, some of which have been designed to be up to 45-meters in height. These fences are typically located at higher elevations near coastal regions where moisture is carried in by winds that blow over a cold ocean current during the early morning hours.
MIT Professor of Mechanical Engineering, Kripa Varanasi, originally envisioned developing efficient water recovery systems (WRS) by collecting water droplets from natural fog and plumes from power plant cooling towers. The project started as a doctoral thesis research project lead by Maher Damak PhD ’18 to improve the efficiency of fog-harvesting systems like the ones used in some arid coastal regions as a source of potable water. Typical fog harvesting systems consist of plastic or metal mesh hung vertically in the path of fogbanks and only capture about 1 to 3 percent of the water droplets that pass through them.
In 2018, Varanasi and Damak found that vapor collection could be made much more efficient by first zapping the tiny droplets of water with a beam of electrically charged particles, or ions, to give each droplet a slight electric charge. The stream of droplets passes through a wire mesh that holds an opposite electrical charge, which causes the droplets to be strongly attracted to the mesh. After the water particles accumulate in size, they soon fall and are collected in trays placed below the mesh.
Because the two hydrogen atoms (slightly positive) and one oxygen atoms (slightly negative) are free to move around in aqueous phase, they can easily be affected by a static electrical charge.
About 40% of H2O withdrawn from lakes, rivers, and wells in the U.S. is used to cool power plants. As nuclear power plants are typically built near large bodies of water to provide enough cooling water to dissipate waste heat, most fission power plants do not reuse and recycle the water vapor that is produced as a byproduct of cooling the reactor core. Of the 442 operational reactors, 96% are water cooled reactors that push water past the core with electrically driven pumps
Over 65 percent of these power plants use evaporative cooling, leading to huge white plumes that billow from their cooling towers, which can be a nuisance and, in some cases, even contribute to dangerous driving conditions.
The researchers cofounded a startup, Infinite Cooling, with Damak as CEO, Khalil as CTO, and Varanasi as chairperson and immediately went to work setting up a test installation on one of the cooling towers of MIT’s natural-gas-powered Central Utility Plant. After installing their water vapor collection system above one of the nuclear power plant’s four cooling towers, they found that the collected water was more than 100 times cleaner than the feedwater coming into the cooling system. Furthermore, the mesh screens were installed and mounted vertically or parallel to the vapor steam to improve efficiency.
While Infinite Cooling is Varanasi's second startup, his pioneering work at MIT focuses on nano-engineered surface, interface, and coating technologies. Already, he has co-founded two other startups, LiquiGlide to commercialize super-slippery coatings, and DropWise, to commercialize an advanced coating material that increases efficiency in power plant desalinization and refrigeration systems.
The system is essentially a distillation process, and the pure water it produces could go into power plant boilers — which are separate from the cooling system — that require high-purity water.
Infinite Cooling secured arrangements for the first two installations on operating commercial plants, which should begin before the beginning of 2022.
In many locations power plants have to pay for the water they use for cooling, Varanasi says, and the new system is expected to reduce the need for water by up to 20 percent. For a typical 600 MW power plant, the water collection system could capture 150M gallons of H2O and recover around one million dollars saved in water costs per year.
Water used in power plant cooling systems typically measures 3,000 microsiemens per centimeter, while the water supply in the City of Cambridge is typically around 500 or 600 microsiemens per centimeter. “The water captured by this system typically measures below 50 microsiemens per centimeter.”, Karim Khalil, Co-Founder & CTO explains.
The system could eliminate a significant amount of water used by the plants and then lost to the sky, potentially alleviating pressure on local water systems, which could be especially helpful in arid regions.
Novel water capture technology would essentially add a water desalination capability to the power plants cooled with seawater in arid coastal areas with the potential to offset the need for about 70% of the new plant desalinations by 2030, alleviating water constraints in local communities.
On the Moon and Mars, there is no air to cool radiators similar to those used in automobiles, and no readily available large body of liquid water to pump water into water-cooled reactors. Thus, a space reactor power plant can use conduction or convection cooled reactor systems with a waste-heat radiator that cools the hot fluid coming from the energy-conversion unit. The waste heat can then be pumped to the settlement for thermal heat, into the local environment, or back into empty space.
Further research in reduced gravity experiments will help improve efficiencies of wire mesh nanoscale geometry, materials, and coatings, pore space architecture, integrated dust filtration, electrolysis, higher quality water, and even thermal water ice mining via tent-induced sublimation on celestial bodies.
The electrical mesh wiring approach holds great potential to improve ionized vapor collection systems and Environmental Control and Life Support Systems to improve water quality by orders of magnitudes and to electrically extract liquid vapor and atmospheric water on Mars, Moon, Venus, and other planetary bodies.