New Idea of geothermal power that will lock away unwanted CO2
Researchers are developing a new kind of geothermal power plant that will lock away unwanted carbon dioxide, CO2, underground – and use the greenhouse gas in liquid form as a tool to boost electric power generation 10-fold in geothermal power plants.
Teams of researchers at the University of Minnesota, Ohio State University and Lawrence Livermore National Laboratory are collaborating on using CO2 in its liquid form as a supplemental fluid in geothermal power plants. The CO2 would otherwise be emitted to the atmosphere and contribute to climate change.
The design contrasts with that of conventional geothermal plants, explained study co-author Jeffrey Bielicki, assistant professor of energy policy in the Department of Civil, Environmental and Geodetic Engineering and the John Glenn School of Public Affairs at Ohio State University.
“Typical geothermal power plants tap into hot water that is deep under ground, pull the heat off the hot water, use that heat to generate electricity, and then return the cooler water back to the deep subsurface. Here the water is partly replaced with CO2 or another fluid – or a combination of fluids that extract heat more efficiently than water alone.
This approach – using concentric rings that circulate multiple fluids – builds upon the idea to use CO2 originally developed by Martin Saar and others at the University of Minnesota, and can be at least twice as efficient as conventional geothermal approaches, computer simulations show.
At relatively low temperatures and pressures CO2 becomes “supercritical,” a phase in which it has the density of a liquid but flows as easily as a gas, resulting in high mobility.
“CO2 would go supercritical during injection, after it gets about 800 meters deep,” says Saar. “It would stay supercritical underground.”
The CO2 would be injected into a sedimentary basin filled with impotable salty water and capped by a layer of impermeable rock. The supercritical CO2 would float on top of the brine and displace it as more CO2 was added. Its high mobility would allow it to rapidly transport the heat it picks up, through the hot geologic formation and up a production well to the surface. There, the release of its heat and pressure would drive a turbine to generate electricity.
The cooled and expanded CO2 would then be pumped back into the ground, along with fresh CO2 captured at the fossil fuel power plant, to repeat the cycle.
“As a result, no CO2 is released to the atmosphere, and, in fact, all of the CO2 is eventually, permanently stored underground,” explained Saar. “This results in a geothermal power plant with a negative carbon footprint.”
Published date, Dec 27, 2013