Carbon Capture and Storage (CCUS) is an integral tool in combating climate change. CCUS captures carbon dioxide emissions produced by burning fossil fuels before it enters the atmosphere, then stores it permanently underground in geological formations like depleted oil fields, coal seams or salt formations.
What is CCS?
CCS involves extracting and storing carbon dioxide (CO2) generated from industrial processes and fossil fuel power plants into a form that can be transported and stored underground.
Capture technologies range from chemical transformation before fossil fuel combustion occurs to physicochemical separation of flue gas emissions. Once captured, CO2 is transported to a storage site where it will be permanently stored within deep geological formations.
Numerous large-scale commercial CCS projects exist today; however, most were not intended for climate purposes and do not need to operate in such a way that minimises CO2 emissions or maximises how much of it they store.
These projects typically use an organic-chemical system called an “amine scrubber”, known for binding CO2, to separate CO2 from natural gas. Often powered by biomass or coal, some projects use captured CO2 for enhanced oil recovery (EOR), which allows oil companies to release trapped petroleum by injecting it back into depleted wells.
Capturing CO2
Carbon capture requires significant electricity use; thus making it no stand-in solution to climate change; rather, carbon capture must be combined with other emissions reduction technologies and natural climate solutions to be effective.
After being separated from power plant emissions, CO2 is transported by pipelines, ships or trains to a storage site where it will be permanently stored underground geological formations with higher temperature and fluid pressure levels than those found in earth’s atmosphere. Once there, supercritical CO2 becomes trapped deep beneath ground where its temperatures and fluid pressures allow it to become supercritical and remain trapped under ground.
Thirty commercial scale CCS projects are already operational worldwide and another 153 projects are in various stages of development. While certain plants (e.g. Boundary Dam project) have experienced technical hurdles, such problems tend to be temporary when early testing of new technology takes place and should eventually be resolved in later plants.
Transporting CO2
CO2 captured from power plants and other industrial processes must be transported to CCS storage facilities where it will be stored. As more CCS sites open up, pipeline networks may need to expand.
Compressing and cooling CO2 into liquid form takes considerable energy, necessitating special pipelines with special designs capable of withstanding both high pressures and extreme cold temperatures that could render their materials fragile and make transportation of this gas difficult.
At a storage site, CO2 is injected deep underground into geological formations such as depleted oil and gas reservoirs or saline aquifers. Monitoring is used to ensure that any CO2 that enters is contained in its intended storage formation rather than seeping into shallower formations or even the atmosphere.
The Alberta Carbon Trunkline serves as an impressive example of large-scale carbon capture pipelines. At 240 km long, this shared pipeline transports carbon from fertiliser plants and refineries to the Weyburn Oil Field for enhanced oil recovery purposes.
Storing CO2
To reduce greenhouse gases and limit temperature rise, we need to implement CCS at scale. This will require existing technologies to operate with greater capacity and be deployed for different gas compositions – leading to new engineering challenges and higher costs.
Carbon storage involves injecting CO2 underground in suitable formations, such as depleted oil and gas reservoirs, saline formations or unmineable coal areas. A key requirement is that storage sites possess an ample pore space within permeable rocks to hold large volumes of CO2. Furthermore, these formations must feature confining zones or sealing layers above them that prevent CO2 leakage.
Quest in Illinois provides an example of such an endeavor by using autothermal reforming to separate CO2 from hydrogen gas, transport it up to 150km, and injecting it since 2015 into Snohvit storage site at Snohvit storage site in order to reduce emissions. Quest was one of the first global projects designed specifically to store CO2 at large scale for emissions reduction purposes.