The U.S. produces half its electricity from burning coal—and pumps out more than 40 percent of its carbon dioxide (CO2) emissions in the process. Vattenfall—the enormous Swedish electric company—has a similar problem, though it sources most of its electricity in that Nordic country from dams and nuclear power plants.

The company also owns a slew of dirty, old coal-fired power plants in the former East Germany. These plants burn the dirtiest form of coal, lignite (a.k.a. brown coal), which is soft because it’s still damp and produces much more polluting soot when burned.

With the onset of a new CO2 emissions trading scheme in the European Union, Vattenfall decided to build a demonstration project at its lignite-burning power plant in Schwarze Pumpe. The technology is called oxyfuel, and it basically relies on burning coal in pure oxygen and CO2 rather than normal air.

By stripping out the nitrogen and other gases, the burning coal produces mostly water vapor and nearly pure carbon dioxide. After condensing the water, the CO2 can be bottled and pumped underground (in this case, into an old natural gas field to get even more methane out of the ground).

The problem is that stripping nitrogen out of air requires a good chunk of the energy produced by the burning of the coal in the first place. After all, nitrogen makes up 78 percent of the air we breathe.

But such oxyfuel technology is common in other energy-intensive industries such as steel or aluminum production and, if it can be scaled up to conventional 1,000 MW power plant scale, it might even become economically attractive. After more than two-and-a-half years of construction costing $100 million, the plant will begin demonstrating the feasibility of this technology on September 9.

“As a user of fossil fuels, Vattenfall is one of the owners of the climate change issue,” said Lars Josefsson, the president and CEO in a statement. “Our ambition is that this technique should become fully commercialized by 2020 and that the cost of capture and storage should be cut to EUR 20 per [metric ton] of carbon dioxide.”

Capturing and storing permanently the CO2 from fossil fuel burning is the promise of clean coal—and many scientists, experts and politicians argue that it is key to a clean energy future that avoids catastrophic climate change. Of course, it remains unclear how safe and permanent such geologic storage is and the phrase “clean coal” begs the question: how clean can an energy source be that requires leveling mountains?

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