What is Carbon Capture?
Carbon capture and storage (CCS) or carbon sequestration, is the name given to a combination of technologies that captures carbon dioxide emissions and stores these emissions in geological rock formations that are deep below the surface of the earth which prevents the carbon emissions release into the atmosphere.
​
There are three different types of carbon capture systems suitable for deployment in power stations:
1. Post-combustion
In this post-combustion, CO2 is separated from the flue gas of the power station by bubbling the gas through an absorber column packed with liquid solvents such as ammonia. In the most widely used system, once the chemicals in the absorber column have become saturated, a stream of superheated steam, at around 120 degrees Celsius, is passed through the chemicals. This releases the trapped CO2, which then can be transported for storage. An experimental technique to scrub CO2 from flue gas without the two-step process include using seawater to absorb the gas and then returning the mixture back to the ocean for long-term storage but so far, this method has proved less efficient and reliable.
CO2 capture approaches Source: WorleyParsons, 2009 [1]
​
2. Pre-combustion
The pre-combustion method is normally applied to coal-gasification combined-cycle power plants. The coal is gasified to produce a synthetic gas made from carbon monoxide and hydrogen. The mixture of carbon monoxide and hydrogen is reacted with water to produce CO2, which is captured, and hydrogen. The hydrogen can be diverted to a turbine where it can be burned to produce electricity. Alternatively, some of this gas can be bled off to feed hydrogen fuel cells for cars.
​
3. Oxyfuel
When coal, oil or natural gas is burned in normal air, CO2 makes up around 3-15% of the waste gas and separating the CO2 out of the waste gas is difficult and energy-intensive. An alternative method is to burn fuel in pure oxygen to create a mixture. In this environment, virtually all the waste gas will be composed of CO2 and water vapor. The water vapor can be condensed and taken out of the mixture while the CO2 can be piped or transported directly to a storage facility. In the oxyfuel system, the challenge that arises is the aspect of separating large volumes of air into liquid oxygen, gaseous nitrogen, argon, and other trace gases. This process can use up to 15% of the power produced at the station.