CCS is associated with three activities: CO2 capture, transport and storage. Each of these activities can be conducted using a range of technologies characterised by various maturity levels, costs and applicabilities. The purpose of CCS is to prevent CO2 from enter-ing (or staying) in the atmosphere where it contributes to global warming, which in turn causes climate change with its catastrophic consequences. 

Capture 

The objective of CO2 capture is to prevent CO2 resulting from a production or combustion process from being emitted into the atmosphere, or to remove CO2 from the air. There are multiple CO2 capture technologies varying in terms of their maturity, costs and energy requirements. The choice of the capture technology for an individual industrial site will depend on the design and pro-cess conditions of that site. 

Capture technologies can be classified into three main categories, depending on the stage of the process during which they are put to work. The first group, post-combustion, is characterised by the capture of CO2 from the flue gas stream resulting from fuel com-bustion or from the chemical processes associated with the treatment of carbon-containing raw materials. Due to the low content of CO2 in flue gases, its capture requires additional energy, which increases the operating costs of the manufacturing process. It is the most common type of CO2 capture technology today. Post-combustion CO2 capture can be achieved via different capture media and processes. Importantly, existing industrial sites can be retrofitted in order to apply post-combustion CO2, as opposed to catego-ries of CO2 capture which need to be part of the original design of the plant.

In the second group, pre-combustion, CO2 is removed from the fuel or raw material, before it is combusted or processed. Finally, oxyfuel combustion is the third category of CO2 capture and is based on the use of oxygen in the combustion process, which yields a CO2-rich gas stream. 

There is a growing number of existing plants and planned projects applying all above mentioned CO2 capture technologies, including the production of ammonia, cement, power generation and waste incineration plants.

Transport

CO2 can be transported in various phases (solid, gaseous, liquid and dense/supercritical) and by multiple modes (pipeline, ship, train, truck or barge, or a combination thereof), depending on the CO2 volume, the location of the capture and the storage or utilisation sites, the topography of the terrain and the distance between these sites. 

Most of the CO2 transport today is associated with the well-established traditional applications of CO2 utilisation, predominantly Enhanced Oil Recovery (EOR), mainly located in the USA, and conducted by CO2-dedicated onshore pipelines. Offshore systems are in use too, including in Europe. There is also a potential, albeit limited, to repurpose parts of the existing gas transmission infrastruc-ture for CO2 transport.

Pipelines can move larger volumes of CO2 than alternative modes of transport over the same distance and in the same time; this favours large emitters and industrial clusters as the main candidates for CO2 pipelines. However, this advantage limits the flexibility of transport routes, and requires large volumes to keep operational costs low.

Ship, truck and rail transport of CO2 are limited to commercial applications of CO2 in the food and drink industry, but could be scaled up and compete with or complement the pipeline networks. They could also be used as part of multi-modal systems, such as the planned Longship project connecting a cement and a waste-to-energy plant in Norway via a road, ship and pipeline-based transport network. In both cases, CCS is the only solution that can reduce most of the carbon footprint of both plants.

For offshore storage and intermediate maritime connections within a larger CO2 transport network, ships can offer more flexibility than pipelines. Transport by ship can also better adapt to scaling up CO2 volumes. 

Storage

Storage is the final stage of the CCS value chain and an ultimate way to keep captured CO2 away from the atmosphere in a perma-nent manner. In most cases, CO2 is injected into geological formations such as saline aquifers. Alternatives to aquifers include de-pleted oil and gas fields, igneous rocks or coal beds. Most of the injection today is associated with EOR, but storage projects moti-vated by climate action are also in place and are gaining more ground, including storing CO2 captured directly from the air.

When it comes to CO2 storage, the key to success is to map, model and evaluate the specific site for storage in terms of its ability to contain the required volumes of injected CO2 in a stable state over centuries and millennia.

In a well-regulated environment, the risks of leakage are very small, and manageable, as attested by storage projects in Norway. The overall conclusion is that CO2 storage is a safe climate change mitigation option. Also, the storage potential is big enough, both in Europe and globally, to significantly contribute to mitigating further global warming.

Source: Bellona Europa’s report, Current state of CCS technologies and the EU policy framework, October 2021

https://ccs4cee.eu/current-state-of-ccs-technologies-and-the-eu-policy-framework/