2 October 2008

Scrubber captures greenhouse gases

It is possible to capture the greenhouse gas carbon dioxide directly from the air, using near-commercial technology.

Carbon dioxide (CO2) is the main greenhouse gas that contributes to global warming, and by using a relatively simple machine, it is possible to capture the trace amount of CO2 present in the air at any place on the planet, said David Keith, University of Calgary (U of C) climate change scientist.

"At first thought, capturing CO2 from the air where it's at a concentration of 0.04% seems absurd, when we are just starting to do cost-effective capture at power plants where CO2 produced is at a concentration of more than 10%," said Keith, Canada research chair in Energy and Environment. "But the thermodynamics suggests that air capture might only be a bit harder than capturing CO2 from power plants. We are trying to turn that theory into engineering reality."

The research is significant because air capture technology is the only way to capture CO2 emissions from transportation sources such as vehicles and airplanes. These diffuse sources represent more than half of the greenhouse gases emitted on Earth.

"The climate problem is too big to solve easily with the tools we have," said Keith, director of the Institute for Sustainable Energy, Environment and Economy's (ISEEE) Energy and Environmental Systems Group and a professor of chemical and petroleum engineering at U of C.

"While it's important to get started doing things we know how to do, like wind power nuclear power, and regular carbon capture and storage, it's also vital to start thinking about radical new ideas and approaches to solving this problem," he said.

Energy-efficient and cost-effective air capture could play a valuable role in complementing other approaches for reducing emissions from the transportation sector, such as biofuels or electric vehicles, said David Layzell, ISEEE's executive director.

"That is a major step in advancing air capture as a solution to a very pressing problem," Layzell said.

Air capture is different than the carbon capture and storage (CCS) technology, which is a key part of the Alberta and federal governments' strategies to reduce greenhouse gas emissions. CCS involves installing equipment at a coal-fired power plant to capture carbon dioxide produced during burning of the coal, and then pipelining this CO2 for permanent storage underground in a geological reservoir.

Air capture, on the other hand, uses technology that can capture the CO2 present in ambient air everywhere.

"A company could, in principle, contract with an oil sands plant near Fort McMurray to remove CO2 from the air and could build its air capture plant wherever it's cheapest-China, for example-and the same amount of CO2 would be removed," Keith said.

Keith and his team showed they could capture CO2 directly from the air with less than 100 kilowatt-hours of electricity per metric tons of carbon dioxide. Their custom-built tower was able to capture the equivalent of about 20 metric tons per year of CO2 on a single square meter of scrubbing material, the average amount of emissions that one person produces each year in the North American-wide economy.

"This means that if you used electricity from a coal-fired power plant, for every unit of electricity you used to operate the capture machine, you'd be capturing 10 times as much CO2 as the power plant emitted making that much electricity," Keith said.

The U of C team has devised a new way to apply a chemical process derived from the pulp and paper industry to cut the energy cost of air capture in half, and has filed for two patents on their end-to-end air capture system.

The technology is still in its early stage, Keith said. "It now looks like we could capture CO2 from the air with an energy demand comparable to that needed for CO2 capture from conventional power plants, although costs will certainly be higher and there are many pitfalls along the path to commercialization."

Nevertheless, the relatively simple, reliable, and scalable technology that Keith and his team developed opens the door to building a commercial-scale plant.