Carbon dioxide capture and storage (CCS) is a way of mitigating the contribution of fossil fuel emissions by capturing and subsequently storing the carbon dioxide (CO₂).

Global climate change is caused by such emissions, and it is an increasingly important and pressing issue for the world. In 2015, countries agreed to limit warming to well below 2°C and aim for 1.5°C, and the Intergovernmental Panel on Climate Change (IPCC) and International Energy Agency (IEA) say that CCS is key in achieving the goals. In the pursuit of net-zero emissions by 2070 the International Energy Agency says that CCS should contribute around 15% of the effort, and 25% of the effort if 2050 is the target (IEA, Energy Technology Perspectives, 2020).

CO₂ makes up 74% of global greenhouse gas emissions according to Climate Watch, with 89% of this CO₂ coming from the use of fossil fuels in power generation, industry and transportation. Each regular power plant is capable of emitting several million tonnes of CO₂ every year. Other industrial processes, such as oil refineries, cement works and metal production, also emit large amounts of CO₂ from each plant. These emissions could be reduced to close to zero by capturing and storing the CO₂.

The process of CCS is a suite of existing, proven technologies that make up three main components; the capture of CO₂ from ‘sources’, the transport of the CO₂ to ‘sinks’ and the permanent, safe storage of the CO₂ deep underground in geological formations.

Capture

There are four main ways to capture CO₂ from power plants:

1. Directly where the plant process produces pure CO₂ streams, such as ammonia and ethanol plant.
2. Post-combustion – which takes place after the normal combustion process has taken place (so after the fuel has been burnt to produce electricity) and uses a solvent to ‘wash’ the exhaust gases of CO_2.
3. Pre-combustion – is done by removing the CO₂ from the raw fuel.
4. Oxyfuel combustion – which burns the fossil fuels in oxygen to produce water and CO₂, which are separated and removed from the flue gas.

The methods used for the capture of CO₂ use well-known technologies that can effectively stop the amount of emissions that would normally be released into the atmosphere.

Transport

The transport of CO₂ can be done by pipelines or by shipping. The CO₂ that has been captured from the power plants is compressed and turned into a fluid state, known as supercritical CO₂. It is then moved via thick carbon steel pipelines or taken in a specially-equipped ship to the chosen site of storage.

storage

Geological storage formations are chosen for the storage of CO₂ depending on their physical properties. To safely store CO₂ the formation must have a suitable ‘reservoir’ rock to receive the CO₂ and an impermeable ‘caprock’ on top of the reservoir to prevent the CO₂ from rising upwards underground. The reservoir rock is porous, which means that there are tiny little spaces between the grains that the CO₂ gets trapped in; the caprock is non-porous, so this means there are no spaces at all in between the rock grains, so the CO₂ cannot enter this top, capping rock.

These geological formations are either deep saline formations, depleted oil and gas reservoirs, or deep unmineable coal seams.

The geological storage formations are not just a few metres under the ground; they are always at depths greater than 800 metres. This is not only for security of storage, but also because the effectiveness of CO₂ storage increases with depth and this means that the captured CO₂ can be permanently stored in these geological formations. The underground storage of CO₂ has actually been taking place for many decades already in the oil and gas industry, for ‘enhanced oil recovery’ and this practice, along with many large-scale and research projects doing CO₂ storage, shows that CO₂ CAN be stored safely and permanently underground.

wHAT IS THE CURRENT STATUS OF CCS?

As of 2020, there are 51 large-scale CCS facilities all over the world. Work is also ongoing at smaller, pilot-scale locations to help us learn even more about the important technologies in CCS that are needed to help combat the amount of emissions entering the atmosphere. So far, over 260 million tonnes of human-induced CO₂ has been safely stored which goes to show that CCS can really make a difference to helping combat climate change.

If you have any questions about CCS or the IEAGHG programme, please contact one of our Technology Analysts, Samantha Neades at This email address is being protected from spambots. You need JavaScript enabled to view it..