Carbon capture and storage (CCS) can permanently store huge amounts of CO2, which makes it an essential part of climate action worldwide. It also has the potential to create "negative emissions", which is actually a good thing!
CCS is a key tool for reducing emissions from industries, such as cement, steel, chemicals and fertilisers. These industries create CO2 as part of their processes and for thermal energy (heat) generation. CCS is currently the only technology that can realistically reduce process emissions and those from high temperature generation by mid-century at scale.
CO2 capture works by separating the greenhouse gas from the exhaust gases of industrial processes. This separation can be achieve through the use of CO2-absorbing chemicals, pressure changes or membrane filters. Capturing CO2 also uses energy and investments in the technology are quite considerable, but work is ongoing by companies, universities and research institutes to reduce this energy use and the costs associated with capture technologies. New innovative industrial processes are tying CO2 separation and capture into the heart of industrial manufacturing, thereby cutting costs and increasing efficiency.
CO2 transport: As a gas, CO2 is commonly transported by steel pipeline, similar to how we transport the natural gas used to heat our homes. CO2 can also be transported by truck, train or ship. In this case, the CO2 is cooled and compressed into liquid form to take up less space and allowing more to be transported in each batch. Most people are familiar with CO2 as an ingredient in fizzy drinks, and CO2 is already being transported across Europe for various uses. Since most of Europe’s emitters are clustered in industrial hubs close to major transport waterways, an efficient and flexible way of transporting CO2 from source to offshore storage site is by ship and river barge. Existing oil and gas industry infrastructure facing decommissioning can even be repurposed to transport CO2 to geological storage sites.
CO2 storage takes place in porous and permeable rock layers at a depth of several thousand metres. The storage sites are located beneath a non-permeable barrier rock that prevents the CO2 from expanding upwards. Wells, akin to those used for oil and gas production, are accurately drilled to access the porous layers through which the CO2 is injected. Once injection has finished, the well is removed and ‘plugged’ using cement, which prevents the CO2 from escaping. The CO2 eventually binds with the surrounding salty water molecules and remains stored between impermeable layers of rock indefinitely.
The potential for CO2 storage is greatest in offshore saline aquifers and depleted oil and gas fields. Effectively, this represents a return of carbon into formations from where carbon-intensive fossil fuels had been extracted before. Demonstrating that CO2 storage can work, every year since 1996, one million tonnes of CO2 have been stored in the Sleipner field beneath the North Sea off Norway. Since 2008, another 4 million tonnes of have been stored at Norway’s Snøhvit CCS project. The SCCS joint industry project, CO2MultiStore, created this animation to illustrate offshore geological CO2 storage. Watch it here.
What are negative emissions? An organic material, such as biomass (trees), absorbs CO2 from the air during its lifetime through the natural process of photosynthesis. When it is burned to generate heat or power this CO2 is released. If the gas is then captured and stored, this actively removes it from the atmosphere. Negative emissions are likely necessary to achieve the deep emission cuts as required under the Paris agreement. Having a CO2 transport and storage infrastructure in place is an enabler for this climate option.