The Quest To Capture Greenhouse Gases And Bury Them

Is there a better way to handle the greenhouse gas emissions that come from electric power plants?

Right now, that question has a lot of “maybe” answers.

Those answers matter because greenhouse gases like carbon dioxide have been blamed for trapping sunlight in the atmosphere, artificially causing the Earth’s climate to heat up.

One proposal for controlling those gases is a two-part scheme that involves capturing the carbon dioxide (CO2) that forms when coal is burned, then storing that byproduct underground.

If that sounds complicated, it is. But is it a realistic solution?

Engineers and geologists right here in Kentucky are testing this new idea to see if it is practical.

How the capture part works
Known as “carbon capture and storage” or “carbon capture and sequestration,” this proposal for handling greenhouse gas emissions is very easy to describe.

The first step is to install equipment at a coal-fired power plant that will trap the carbon dioxide as it comes out of the plant, to keep the gas from going into the air. The second step would move the CO2 through pipes, then pump the invisible gas far underground for permanent storage. This step will “sequester” the gas indefinitely, keeping it apart from the atmosphere.

The description is easy. But taking the ideas from the drawing board to a power plant is harder. A lot harder.

At the University of Kentucky’s Center for Applied Energy Research (CAER) north of downtown Lexington, Program Manager Kunlei Liu and Senior Research Engineer Jim Neathery are testing carbon capture equipment that might be useful at existing coal plants.

One device they’ve built in their laboratory is a 20-foot-tall piece of equipment that resembles the kinds of flue gas desulphurization (FGD) scrubbers that are already in use at many coal-fired power plants. Those existing scrubbers are huge devices that remove tiny particles of trace gases such as sulfur oxides. The experimental device in the CAER lab is just a very small working model; one that would be built for a real coal-fired plant would likely be 100 feet tall. The carbon dioxide scrubber vessels would be two to three times the size of current FGD scrubber devices.

Neathery notes that one of the major problems with developing ways to capture carbon dioxide is the difference in the proportion of the emissions.

“With other gases over the years,” Neathery says, “we’ve been working on things that are just traces, gas molecules that are measured as tiny parts per million. But with carbon dioxide, it is a major component that occurs as up to 15 percent of the emissions. Tons and tons of invisible carbon dioxide go out the stacks every day. That huge volume of gas must be physically and chemically captured, then compressed in order to be able to handle it for transportation to a storage site.”

Investigators in labs throughout America have already determined that capturing that much carbon dioxide takes a lot of extra energy. Most technologies being investigated today would require using about 30 percent of the energy produced at the power plant to do this new job. In practical terms, it means that for every 100 megawatts of power generated, 30 megawatts would be used to operate the new carbon capture equipment—and that means only 70 megawatts would be available to go into the grid for customers.

One way to look at that huge additional use of electricity is that adding carbon capture equipment would mean a decrease in plant efficiency—less usable energy from every ton of coal. And it would mean an increase in what it costs to produce every megawatt that eventually goes to the consumer.

Neathery says, “The massive amount of material we’d have to remove is one of the major hurdles we’ve come across. And the power requirements mean that we’d have to build more power plants to help run the other plants—and that doesn’t make a lot of sense. So a major focus of our research here is trying to lessen the amount of energy required to remove each pound of CO2.”

Exploring storage
Meanwhile, in mid-town Lexington at UK’s main campus, geologist James Drahovzal spends his workdays looking into the practical details of storing carbon dioxide deep underground here in Kentucky. Retired head of the Energy and Minerals section of the Kentucky Geological Survey and an adjunct professor at the University of Kentucky, Drahovzal’s been involved in carbon sequestration research for eight years.

Pumping carbon dioxide deep underground is not a new idea. In fact, it’s been going on for more than 30 years elsewhere, but for a completely different purpose. In some areas, pumping compressed carbon dioxide gas into wells is used to enhance the amount of oil that can be removed from deep underground sources. This technology has been working very well in the Permian Basin in Texas and New Mexico. Injecting the carbon dioxide under pressure forces the remaining tiny bits of oil to move to places where they can be more easily pumped to the surface. Some of the carbon dioxide stays underground while most is recycled as part of the process.

It’s possible that carbon dioxide could be used in this way in some of Kentucky’s older oil wells to boost production, but those kinds of underground areas are relatively small.

Under much of Kentucky, the situation is quite different because we have different kinds of rock formations here. Most of Kentucky’s potential storage areas are deep saline formations, although some deep coal seams might be usable as well.

Early research by the Kentucky Geological Survey estimates that our rock formations may have the potential to store 32.5 billion metric tons of carbon dioxide. That would be enough for about 370 years’ worth of CO2 at the current rate of power plant emissions in our state.

But whether these underground areas really are suitable for the long-term storage of carbon dioxide depends on several things.

The physical characteristics of a potential storage area must be just right. The rock that will contain the CO2 must be porous and large enough to hold substantial amounts of carbon dioxide. Whatever’s already in the pores, usually brine, must be something that we aren’t likely to need for some other purpose later. That’s because injecting the carbon dioxide will change the physical and chemical properties of what’s there at the beginning.

The boundaries of the storage area are important, too. The storage area must be capped by a rock formation that’s sturdy enough to prevent the carbon dioxide from escaping upward; fluids must not move through this cap. The storage area must also be quite separate from and much deeper than underground freshwater aquifers. To further complicate the investigation, concerns about fractures or faults from earthquakes could put some regions of our state out of the running as storage sites.

Another concern involves practical matters of working at such great depths.

Drahovzal says, “The characteristics of carbon dioxide mean that to sequester it underground we’ll have to go at least 2,500 feet below the surface.” Drahovzal and his team have started working out on paper how they think the carbon dioxide will behave that far underground. They’ve also made rather detailed predictions and maps about what the rock formations are like at various depths throughout Kentucky.

Drahovzal says, “In the second phase of a joint research project with a utility company, we are going to drill a test well and inject a small amount of CO2 to find out what happens. In Boone County, we plan to inject one to three thousand tons of CO2 between 3,200 to 3,500 feet below the surface.”

The Kentucky Consortium for Carbon Storage, established in 2007 as part of Kentucky’s House Bill 1, plans additional deep drilling tests in both eastern and western Kentucky within the next few years.

Drahovzal notes that similar small-scale underground storage test projects are going on in seven different regions of the United States. Carbon storage technology will move from this research and development stage into the deployment phase during the next 10 years. Drahovzal expects these large-scale commercial level projects to inject up to one million tons of carbon dioxide per year in each region within the United States.

Today’s carbon capture and storage experiments and test designs for existing coal plants, although initially expensive and not very energy efficient, may yet play a valuable role over the long term. They could make it possible to continue to use the fleet of coal plants we already have, while other, different emissions reduction technologies and strategies become practical and affordable.

CO2 STORAGE STUDIES GO GLOBAL

While this month’s column focuses on Kentucky research into capturing and storing carbon dioxide greenhouse gas emissions, related work is going on around the United States, and the world.

The experimental “carbon capture and storage” idea has been identified as one of the most significant ways to reduce carbon dioxide emissions, which have been blamed for global warming.

It’s also one of the most complicated and expensive solutions.

Basin Electric Power Cooperative, based in North Dakota, has been making commercial use of the technology for nearly 10 years. A Basin Electric Co-op plant that converts coal into synthetic natural gas ships excess carbon dioxide to Canada, where it is injected permanently into underground oil fields to bring more oil to the surface.

Closer to Kentucky, a more ambitious project is having trouble getting off the drawing board.

That five-year-old effort would test the technology by building an experimental coal-fired electric power plant in Mattoon, Illinois. FutureGen, as the project is known, would have had almost no harmful emissions and combined many different functions into a single large plant. But in February, the U.S. Department of Energy withdrew its support. Skyrocketing budget estimates (from its original $950 million to $1.8 billion) and changing energy priorities made the project seem unworkable. Parts of the FutureGen design may be incorporated into other projects.

There are two other projects storing carbon dioxide underground, one in Norway and the other in Algeria. But experts agree the expense and complexity of the technology make it “not ready for prime time.”

U.S. and international scientific groups studying carbon capture and storage have urged that governments around the world spend more to develop the technique.

Among the electric co-op efforts to test the technology is North Dakota’s Basin Electric, which is exploring plans to adapt the methods from its synfuels plant to a nearby electric generating station. And Arizona Electric Power Cooperative based in Benson, Arizona, plans to join with other utilities to be one of seven initiatives around the country to receive major funding from the U.S. Department of Energy.

Several other carbon capture and storage projects are envisioned by loan guarantees from the Department of Energy. Among those projects are joint efforts by the DOE and the Environmental Protection Agency to study environmental effects of storing carbon dioxide underground.

Next month: The efficiencies of hybrid electric cars