Can Carbon Sequestration Solve Global Warming?

Dissatisfied with the long-term potential of most current technologies for carbon sequestration, Klaus Lackner, Ewing-Worzel Professor of Geophysics at Columbia University, has designs for new power plants that would capture carbon dioxide before it leaves the facility, as well as for "synthetic trees" that would pluck carbon from the air, mix it with magnesium silicate, and store the carbon in the "rocks" that would result from the chemical interaction between the elements.

"Injecting carbon underground is a short-term solution," Lackner said. "The oil industry has done this with 20 million tons a year in West Texas, but that is not the scale we're talking about here. We need to find a way to put away 20 billion tons." The Intergovernmental Panel on Climate Change has estimated that worldwide carbon dioxide emissions could more than triple over the next 100 years, from 7.4 billion tons of carbon per year in 1997 to approximately 20 billion tons per year by 2100. Lackner argued that large-scale carbon sequestration would allow the continued use of carbon-based fuels during the time needed to develop alternative sources of energy.

Encouraged by preliminary reports indicating the feasibility of carbon sequestration in coal seams and deep saline reservoirs, the U.S. Department of Energy recently announced it will fund public-private ventures to explore the capture of carbon, but researchers say there are considerable barriers to be overcome before the technology can be widely implemented. Injecting carbon into coal seams, for example, would force millions of gallons of salty water to the Earth's surface, substantially greater amounts than the briny water produced during recovery of natural gas.

"This is not a trivial problem," said Curt White, Carbon Sequestration Science Focus Area Leader at the National Energy Technology Laboratory, Pittsburgh, PA, who will report on new findings regarding the physical and chemical phenomena that take place when carbon dioxide is injected into coal seams, and discuss the projected storage capacity of coal seams.

White will detail some of the technological obstacles to performing sequestration of carbon dioxide in deep unmineable coal beds, as well as parallel efforts to identify and recover the methane gas that is found in some of those sites. The valuable gas offers hope that the cost of capturing carbon can be covered.

Water disposal is a challenge because high concentrations of salts and other dissolved solids can be toxic to some organisms, White said. "Development of technologies to properly dispose of huge amounts of produced water is a problem area that needs further research." White and his colleagues are studying surveys conducted by the U.S. Bureau of Mines to determine which coal seams in the United States might contain the most methane. The researchers are also exploring the long-term impact of pumping carbon into coal seams and brine fields.

"We now have a much better understanding of what we think is going to happen," White said. "I think that with the proper research and the right resources, the problem areas can be overcome."

The capture of carbon will not become routine, however, until steps are taken to reduce greenhouse gas emissions, according to Howard Herzog, principal research engineer at Massachusetts Institute of Technology Laboratory for Energy and the Environment.

"Unless the economic incentives are in place, the technology is not going to go anywhere," said Herzog, who studies the economics of carbon sequestration. "Right now, the price of emitting carbons is almost free. If it goes up to about $100 per ton of carbon produced, you'd begin to see some significant scale of capture and storage."