Can We Turn Unwanted Carbon Dioxide Into Electricity?


New power plant design to expand use of geothermal energy in the U.S.

SAN FRANCISCO—Researchers are developing a new kind of geothermal power plant that will lock away unwanted carbon dioxide (CO2) underground—and use it as a tool to boost electric power generation by at least ten times compared to existing geothermal energy approaches.

The technology to implement this design already exists in different industries, so the researchers are optimistic that their new approach could expand the use of geothermal energy in the U.S. far beyond the handful of states that can take advantage of it now.

At the American Geophysical Union Meeting on Friday, Dec. 13, the research team debuted an expanded version of the design, along with a computer animated movie that merges advances in science with design and cognitive learning techniques to explain the role that energy technologies can have in addressing climate change.

The new power plant design resembles a cross between a typical geothermal power plant and the Large Hadron Collider: it features a series of concentric rings of horizontal wells deep underground, inside which CO2, nitrogen, and water circulate separately to draw heat from below ground up to the surface, where the heat can be used to turn turbines and generate electricity.

The design contrasts with 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 The 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,” he said.

CO2, extracts heat more efficiently than water, he added.

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, according to computer simulations. “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, postdoctoral researcher in the Department of Earth Sciences 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.

The current research team includes Ohio State, the University of Minnesota and Lawrence Livermore National Laboratory, where geoscientist Tom Buscheck came up with the idea to add nitrogen to the mix.

He and his colleagues believe that the resulting multi-fluid design will enable geothermal power plants to store energy away—perhaps hundreds of gigawatt hours—for days or even months, so that it is available when the electricity grid needs it. The underground geothermal formation could store hot, pressurized CO2 and nitrogen, and release the heat to the surface power plant when electricity demand is greatest; it could also suspend heat extraction from the subsurface during times of low power demand, or when there is already a surplus of renewable power on the grid.

"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,” Buscheck said.

In computer simulations, a 10-mile-wide system of concentric rings of horizontal wells situated about three miles below ground produced as much as half a gigawatt of electrical power—an amount comparable to a medium-sized coal-fired power plant, and more than ten times bigger than the 38 megawatts produced by the average geothermal plant in the United States.

The simulations also revealed that a plant of this design might sequester as much as 15 million tons of CO2 per year, which is roughly equivalent to the amount produced by three medium-sized coal-fired power plants in that time.

Bielicki noted the possibility of expanding the use of geothermal energy around the country. Right now, most geothermal power plants are in California and Nevada, where very hot water is relatively close to the surface. But the new design is so much more efficient at both storing energy and extracting heat that even smaller-scale “hotspots” throughout the western U.S. could generate power.

The eastern U.S. is mostly devoid of even small hotspots, so geothermal power would still be limited to a few particularly active areas such as West Virginia, he said.

Another caveat: the geothermal plant would probably have to be connected to a large CO2 source, such as a coal-fired power plant which was scrubbing the CO2 from its own emissions. That connection would likely be made by pipeline.

Buscheck added, however, that the study showed that this design could work effectively with or without CO2, and a pilot plant based on this design could initially be powered solely by nitrogen injection, in order to prove the economic viability of using CO2. The research team is currently working on more detailed computer model simulations and economic analyses for specific geologic settings in the U.S.

The project is unusual in part because, as they were refining their ideas, the engineers joined with Shannon Gilley, then a master of fine arts student at the Minneapolis College of Art and Design. Bielicki worked with Gilley for more than a year to create the computer animated video, “Geothermal Energy: Enhancing our Future.” Part of Gilley’s task was to communicate the more complex details of climate change, CO2 storage, and geothermal energy to the general public.

“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.

Co-authors on the presentation also included Mingjie Chen, Yue Hao, Yunwei Sun, all of Lawrence Livermore National Laboratory. Work at the University of Minnesota and The Ohio State University has been funded by the National Science Foundation, while work at Lawrence Livermore National Laboratory has been funded by the U. S. Department of Energy’s Office of Energy Efficiency and Renewable Energy.





Turning unwanted carbon dioxide into electricity



By Anne Stark

SAN FRANCISCO —Researchers are developing a new kind of geothermal power plant that will lock away unwanted carbon dioxide (CO2) underground—and use it as a tool to boost electric power generation by at least 10 times compared to conventional geothermal power.

The technology for this design already exists in different industries, and the researchers, led by Tom Buscheck, earth scientist from Lawrence Livermore National Laboratory, are hopeful that their new approach to the technology will expand the use of geothermal energy in the U.S. far beyond the small handful of states that can take advantage of it now. Heat Mining Company, LLC, a startup spun off from the University of Minnesota, expects to have an operational project based on an earlier form of this new approach in 2016.

At the American Geophysical Union Meeting on Friday, Dec. 13, Buscheck and his colleagues from Ohio State University, the University of Minnesota and Lawrence Livermore, will debut an expanded version of the design and explain the role that this new approach to geothermal energy production and grid-scale energy storage can have in addressing climate change.

The new power plant design resembles a cross between a geothermal plant and the Large Hadron Collider: it features a network of subsurface concentric rings of horizontal wells inside which CO2, nitrogen, and water circulate to draw heat from deep below ground up to the surface, where it can be used to turn turbines and generate electricity. “This well arrangement encircles the injected fluids with a subsurface hydraulic dam, functioning much like a hydroelectric dam. The intent is to recover the maximum energy benefit from fluid injection operations, a major improvement over conventional geothermal power systems,” Buscheck noted.

The design contrasts with conventional geothermal plants in a number of important ways, explained study co-principal investigator Jeffrey Bielicki, assistant professor of energy policy in the Department of Civil, Environmental, and Geodetic Engineering at The 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 and/or another fluid” he said.

“There are benefits to using CO2, because it mines heat from the subsurface more efficiently than water,” he continued. “This combined approach, originally developed by Martin Saar and others at the University of Minnesota, can be at least twice as efficient as conventional geothermal approaches, and expand the reach of geothermal energy in the United States to include most states west of the Mississippi River.”

The research team used computer simulations to design the system. In the simulations, a system of four concentric rings of horizontal wells about three miles below ground, with the outer ring being a little more than 10 miles in diameter, produced as much as a half a gigawatt of electrical power — an amount comparable to a medium-sized coal-fired power plant, and more than 10 times bigger than the 38 megawatts produced by the average geothermal plant in the U.S.

The simulations also revealed that a plant of this design might sequester as much as 15 million tons of CO2 per year, which is roughly equivalent to the amount produced by three medium-sized coal-fired power plants in that time.

“One of our key objectives when we began developing the CO2 plume geothermal technology was to find a way to help make CO2 storage cost effective while expanding the use of geothermal energy,” said Jimmy Randolph, postdoctoral researcher in the Department of Earth Sciences at the University of Minnesota.

During the past year, Buscheck added another gas — nitrogen — to the mix, resulting in a design that he and his colleagues believe will enable highly efficient energy storage at an unprecedented magnitude (at least hundreds of gigawatt hours) and unprecedented duration (days to months), provide operational flexibility, and lower the cost of renewable power generation.

“Nitrogen has several advantages.” Buscheck explained. “It can be separated from air at lower cost than captured CO2, it’s plentiful, it’s not corrosive, and will not react with the geologic formation in which it is being injected. And because nitrogen is readily available, it can be injected selectively. Thus, much of the energy required to drive the hot fluids out of the deep subsurface to surface power plants can be shifted in time to coincide with minimum power demand or when there is a surplus of renewable power on the electricity grid.”

“Because we are storing energy in the form of pressurized fluids, we can further improve on this concept by selectively producing hot fluids when power demand is high, as well as reduce or stop that production when power demand is low. 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.”

The technology could possibly be used to expand the use of geothermal energy around the country. Right now, most geothermal power plants are in California and Nevada, where an especially strong geothermal gradient heats water underground. But the new design is so much more efficient at storing energy and extracting heat that even smaller-scale “hotspots” throughout the western U.S. could generate power. (The eastern U.S. is mostly devoid of even small hotspots, so geothermal power would still be limited to a few particularly active areas such as West Virginia, Bielicki said.)

Another caveat: the geothermal plant would probably have to be connected to a large CO2 source, such as a coal-fired power plant which was scrubbing the CO2 from its own emissions. That connection would likely be made by pipeline. Buscheck added, however, that a pilot plant based on this design could initially be powered solely by nitrogen injection, in order to prove the economic viability of using CO2. The study also showed that this design can work effectively with or without CO2, broadening where this approach could be deployed. The research team is currently working on more detailed computer model simulations and economic analyses for specific geologic settings in the U.S.

Co-authors on the presentation included Mingjie Chen, Yue Hao, Yunwei Sun, all of Lawrence Livermore. Work at the University of Minnesota and The Ohio State University is funded by the National Science Foundation, while work at Lawrence Livermore National Laboratory is funded by the U. S. Department of Energy’s Office of Energy Efficiency and Renewable Energy.