Putting Carbon Dioxide In Its Place
A large hole in West Virginia may help keep the world from heating up. In late May, a group of scientists and engineers began drilling a well 2,800 meters down into a deep aquifer beneath an American Electric Power Co. (AEP ) coal-fired power plant. Now the hole is finished, and researchers are analyzing the samples they have brought up from each layer in the earth. The aquifer, along with other geological formations, may someday provide a home for millions of tons of carbon dioxide that are now being spewed into the atmosphere by the burning of coal, oil, and gas. Sequester enough greenhouse emissions, and it may be possible to slow global warming.
It's a controversial plan -- and not just because global warming is still questioned in some circles. If capturing and storing carbon is feasible, environmentalists fear that nations may ease up on efforts to boost energy efficiency and develop renewable resources. "We can't allow it to be a substitute for reducing emissions," says Philip Clapp, president of the National Environmental Trust.
Yet economic models show that carbon sequestration is cheaper than most emission-cutting strategies. So even many environmentalists view it as a vital strategy. And power-industry executives say that it's virtually inevitable. Whether or not you believe that global warming is occurring, regulations restricting the release of CO2 are coming, says Dale E. Heydlauff, AEP senior vice-president for governmental & environmental affairs. "We are going to live in a carbon-constrained world."
Several nations already have imposed carbon taxes or limits, and more will come if the Kyoto Protocol goes into effect across much of the world. At the same time, there's little prospect of weaning the world from fossil fuels such as oil and coal. "Put the two together and we need to figure out how to use coal more efficiently -- and we need to capture CO2 and store it permanently," says Heydlauff. "That is the dream."
The dream is closer to reality than most people realize. "Every single major component is being done," says Howard J. Herzog, professor of chemical engineering at Massachusetts Institute of Technology and program manager for MIT's Carbon Sequestration Initiative. "There's no doubt it is technically feasible."
Indeed, since the 1970s, oil companies have pumped CO2 down many oil wells to make oil more fluid and easier to bring to the surface. Now, they're also testing the idea of sealing the gas underground. Three years ago, for instance, an international group began pumping CO2 into the Weyburn oil field in Saskatchewan. So far, the results are promising. After all, the CO2 is merely displacing oil and natural gas that had been locked beneath the earth for millions of years. "What this offers is a solution to the greenhouse gas problem in the oil and gas industry's backyard," says geochemist Bill Gunter of the Alberta Research Council. The hole in West Virginia is expected to show that similar storage is available near coal-fired power plants.
Geologists calculate that depleted oil and gas fields, aquifers, and other underground formations could store trillions of tons of CO2. That's plenty of space, given that the world's current emissions of the gas from fossil fuel use are about 22 billion metric tons a year. And economists peg the burial cost at a relatively affordable $1 to $8 per ton of CO2.
More expensive is capturing the gas in the first place. The standard way is to bubble the stuff spewing out of power plant smokestacks through a liquid solvent. The solvent dissolves the CO2, then heating the solvent releases the gas. The process is well understood but takes lots of energy. As a result the cost is high. That's why energy companies launched a research effort two-and-a-half years ago to lower the cost by half to three quarters. "We've gone a long way to identifying the technologies," says Vello A. Kuuskraa, chair of the project's advisory board.
According to most experts, though, the best approach would be to grab the CO2 out of fossil fuel before it's burned. In a process called gasification, coal is converted into hydrogen and carbon monoxide. The hydrogen can then be used to make electricity or to power cars, and the CO is easily reacted with oxygen to make CO2. U.S. utility companies and the Energy Dept. are planning a $1 billion coal gasification project, called FutureGen, to generate power and store carbon.
Proponents are hoping the plant will demonstrate that the approach works in time to get the technology into power plants that will be built in China and elsewhere in coming decades. "It's absolutely critical that we develop methods of burning coal cleanly. That means both gasification and sequestration," says Clapp. The companies have pledged $200 million for FutureGen, but Congress has yet to appropriate funds for the rest.
To environmentalists who would prefer to reduce emissions in the first place, the idea of capturing and storing carbon is a bit unsavory -- like tackling obesity by developing yet more low-calorie foods instead of cutting excessive consumption. But inelegant as it may be, carbon sequestration appears to be the quickest and cheapest route to fighting global warming.
By John Carey in Washington