CCS and CCUS

Carbon capture and storage (CCS) is the capture and storing of carbon dioxide (CO2) before it is released into the atmosphere.

It involves a three-step process, consisting of

1.       Capture. The separation of CO2 from other gases produced during electricity generation and industrial processes such as steel and cement production, as well as fertiliser production;

2.       Transport. Once captured, the CO2 is compressed and transported by ship, road or pipeline to a storage site;

3.       Storage. CO2 is placed in underground geologic formations, like depleted coalbeds or oil and gas reservoirs or deep saline aquifers suitable for long-term storage.

A related concept is CCUS, which stands for Carbon Capture, Utilisation and Storage. The difference is that instead of storing carbon, it could be re-used in industrial processes by converting it into, for example, plastics, concrete or biofuel.

There are three main technologies for capturing CO2. They are post-combustion, pre-combustion, and oxy-fuel combustion.

1. Post-combustion method, mainly used at power plants, separates CO2 from the flue gas, by using a chemical solvent for instance, after the fuel is burnt. This type of technology can be incorporated in new as well existing power plants.

2. Pre-combustion methods involve converting the fuel into a gas mixture consisting of hydrogen and CO2 by way of partially oxidizing it. Once the CO2 is separated, the remaining hydrogen-rich mixture can be used as fuel. Typically used in the fertiliser, chemical, gaseous fuel and power generation industries, this method of carbon capture is best incorporated into new builds.

3. Oxy-fuel combustion technology involves burning a fuel with almost pure oxygen to produce carbon dioxide and steam, with the released CO2 subsequently captured. This method of carbon capture can be retrofitted to existing facilities as well as new plants.