Sustainable Energy

The Quest to Sequester

One way to continue using coal and other fossil fuels without promoting catastrophic climate change would be to capture the carbon dioxide released by burning them and then pump it underground for permanent storage, a process called carbon sequestration.

This strategy has been demonstrated in a few places. But for it to make a significant impact on carbon emissions, researchers must find economical ways to capture the gas, plus practical ways to liquefy and bury billions of tons of it each year–and keep this up for decades. The need is staggering: coal accounts for 20 percent of all greenhouse-gas emissions worldwide. In the United States, for example, 600 coal-fired power plants emit two billion tons of carbon dioxide annually. China’s coal emissions are roughly double that amount and growing rapidly.

The first problem is capturing the gas. Right now, retrofitting existing power plants with carbon dioxide scrubbers will eat up a quarter of the energy the plant produces. Jared Ciferno, who specializes in carbon capture technology at the U.S. Department of Energy’s National Energy Technology Laboratory, says this loss needs to be cut to 18 percent to make post-combustion carbon dioxide capture economically viable.

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Alternative processes exist: coal can be turned into a combustible gas, which produces a purer stream of easier-to-capture carbon dioxide when it’s burned. However, gasification plants cost more than coal-burning ones. A few of these are under construction in Indiana, Pennsylvania, and Tianjin, China, but they would not be cost-effective without government incentives.

Then there’s the problem of burying the carbon dioxide. Here, there is some good news: many major coal-burning countries and regions, including the United States and China, are believed to have geological features suitable for sequestration, especially deep saline aquifers that sit beneath multiple layers of rock to keep carbon dioxide safely trapped. What’s more, where sequestration has been tried, geologists report that the carbon dioxide hasn’t leaked, even in regions where decades of oil drilling have perforated underground rocks.

However, there are still no financial or regulatory incentives for power producers to pursue carbon sequestration. It’s unlikely that the technology will get very far without, for example, a tax or other mechanism for putting a price on carbon. Says Julio Friedmann, director of Lawrence Livermore National Laboratory’s Carbon Storage Initiative, “We need incentives to get the sequestration market moving.”

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