December 13, 2013
Generating Electricity May Utilize Otherwise Unwanted Carbon Dioxide
Brett Smith for redOrbit.com - Your Universe Online
A team of American researchers has designed a novel geothermal power plant that would sequester large amounts of carbon dioxide underground as part of its operations.
According to a report being presented on Friday at the American Geophysical Union meeting in San Francisco, carbon dioxide can be used to boost power generation from geothermal sources by at least 10 times compared to conventional means.
“Typical geothermal power plants tap into hot water that is deep underground, 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,” said Jeffrey Bielicki, assistant professor of energy policy at The Ohio State University.
Computer simulations have shown that this new design might sequester as much as 15 million tons of carbon dioxide annually – roughly equivalent to the amount generated by three medium-sized, coal-fired power plants in the same time span.
The novel design is based on a series of concentric rings of horizontal wells deep underground. In the design, carbon dioxide, nitrogen and water all circulate independently within the rings to extract heat from deep in the ground and draw it up to the surface, where it can be used to generate electricity. According to computer simulations, the design can be at least twice as effective as traditional geothermal approaches.
“When we began to develop the idea to use CO2 to produce geothermal energy, we wanted to find a way to make CO2 storage cost-effective while expanding the use of geothermal energy,” said Jimmy Randolph, an earth science researcher at the University of Minnesota.
"We hope that we can expand the reach of geothermal energy in the United States to include most states west of the Mississippi River," Bielicki said.
Currently, most geothermal power plants are located in California and Nevada, where hot water can be found close to the surface. However, the novel design’s efficiency could change that by drawing significant heat from smaller-scale “hotspots” found in and around West Virginia.
The research team said their design could also enable the new geothermal power plants to stock up on energy for days or months, and release it when demand is high. This would be done by storing hot, pressurized carbon dioxide and nitrogen deep underground, then releasing the heat to the power plant as needed.
“What makes this concept transformational is that we can deliver renewable energy to customers when it is needed, rather than when the wind happens to be blowing, or when spring thaw causes the greatest runoff,” said Tom Buscheck, a scientist from the Lawrence Livermore National Laboratory (LLNL).
The researchers noted that their power plant would probably have to be physically connected to a source of carbon dioxide – such as a coal-fired power plant that is scrubbing the CO2 from its own emissions. Buscheck said the plant could run without carbon dioxide, and a nitrogen-only pilot plant could help to determine the economic viability of using carbon dioxide.
“We built this concept of public outreach into our efforts not just to communicate our work, but also to explore new ways for scientists, engineers, economists and artists to work together,” Bielicki said.