Water-Repellent Coating Could Make Power Plants Greener

Applying a novel coating to part of the machinery in power plants could significantly reduce carbon dioxide emissions. Applying it at just one coal plant would reduce yearly emissions as much as taking 4,000 cars off the road, says Kripa Varanasi, a professor of mechanical engineering at MIT who helped develop the new coating, which is being commercialized by a startup called DropWise.

The coating improves the efficiency of a key part of a power plant, the steam condenser. In power plants, fuel is burned to produce steam that spins a turbine. As the steam emerges from the turbine, it needs to be cooled down and condensed back into water—doing so creates a suction force that helps spin the turbine.

The coating helps increase that suction force. The condenser is a series of pipes, and when steam hits them, it turns to water. Ordinarily, water builds up on the walls of the pipes and slows down the cooling process. The new coating repels water, keeping it from building up.

Researchers have been attempting to develop such coatings for decades, but existing methods for depositing them—such as spraying—have trouble producing the correct thickness. Depending on the method and material, they were either so thick that they themselves slowed cooling, or too thin to withstand the harsh steam, says Jonathan Boreyko, a Virginia Tech professor and expert on heat transfer, who did not participate in the work.

To get the right thickness, MIT researchers invented a new process that involves flowing two gases past heated filaments. The gases react and form a polymer coating that is “just thin enough to still be much more efficient, but thick enough to be durable,” Boreyko says.

So far the coating technology has been tested only in the lab. DropWise is working on deals to test the technology in power plants. While the technology could help with emissions, the main incentive for power plants to use the technology would likely be fuel savings—power plant operators could save nearly half a million dollars per year.