What if it were possible to just suck all the harmful pollutants out of the air so that they wouldn’t be such a nuisance and we wouldn’t be so worried about their effect on the planet? This is the basis of Carbon Capture, a relatively new concept where carbon dioxide would be captured at point sources, such as factories, natural-gas plants, fuel plants or any other big source of CO2 emissions. This CO2 can then be stored for future use, or simply put back into the Earth so that it doesn’t enter the atmosphere. Like many other recent developments, carbon capture is part of a new set of procedures that are collectively known as geoengineering, the purpose of which is to alter the climate to counteract the effects of global warming by targeting one of the chief greenhouse gases. The technology has existed for some time, but it has only been in recent years that it has been proposed as a means of combatting climate change as well.
Currently, carbon capture is most often employed in plants that rely on fossil fuel burning to generate electricity. This process is performed in one of three basic ways – post-combustion, precombustion and oxy-fuel combustion. Post-combustion involves removing CO2 after the fossil fuel is burned and is converted into a flue gas, which consists of CO2, water vapor, sulfur dioxides and nitrogen oxide. When the gases travel through a smokestack or chimney, CO2 is captured by a “filter” which actually consists of solvents that are used to absorb CO2 and water vapor. This technique is effective in that filters can be retrofitted to older plants, avoiding the need for a costly power plant overhaul.
In the case of precombustion, CO2 is trapped before the fossil is even burned. Here, coal, oil or natural gas is heated in pure oxygen, resulting in a mix of carbon monoxide and hydrogen. This mix is then treated in a catalytic converter with steam, which then produces more hydrogen and carbon dioxide. These gases are fed into flasks where they are treated with amine (which binds with the CO2 but not hydrogen); the mixture is then heated, causing the CO2 to rise where it can be collected. In the final process (oxy-fuel combustion), fossil fuel is burned in oxygen, resulting in a gas mixture of steam and CO2. The steam and carbon dioxide are separated by cooling and compressing the gas stream, and once separated, the CO2 is removed.
The results of these processes have so far been encouraging, with up to 90 % of CO2 being removed from emissions. The worry however is that some these processes add to the overall cost and energy consumptions of power plants. However, researchers are developing new techniques which they hope will reduce both costs and consumption.
We’ve also recorded an episode of Astronomy Cast all about planet Earth. Listen here, Episode 51: Earth.