A coal-fired power plant that emits almost no CO₂? In the not-too-distant future, it could be a reality. There are already three promising methods for capturing CO₂ for low-emission coal-fired power generation: post-combustion capture, pre-combustion capture, and oxyfuel combustion.

In post-combustion capture, CO₂ is chemically washed out of flue gas. In pre-combustion capture, coal is first transformed into a gas called syngas; CO₂ is then removed from the syngas prior to combustion. In oxyfuel combustion, coal is burned in pure oxygen instead of air, which results in a significantly higher concentration of CO₂ in the flue gas. The flue gas must then be scrubbed of its remaining components such as oxygen, sulfur dioxide, and nitrous oxides.

Post-combustion capture is the only capture method that can be retrofitted onto existing power plants without significant modifications.

But no matter which capture method is used, it's essential that we find efficient and safe ways to transport and store CO₂. Porous, geological formations called aquifers represent a particularly promising solution for storing CO₂ deep underground. Strata of nonporous cap rock above the aquifer ensure that the CO₂ doesn't escape.