Carbon Capture Utilization and Storage (CCUS) has been proposed and endorsed by numerous scientific, academic, and corporate actors as an essential component in the transition into clean energy. It has been backed by climate experts such as the Intercontinental Panel on Climate Change as a key component of achieving net zero emissions in CO2 by 2050. It has been identified as a potentially strong mitigator of CO2 emissions in hard-to-abate sectors such as fertilizers, aluminum, steel, and cement, a bridge to emerging net zero technologies, and a bridge for renewable energy sources.

CCUS technology currently exists in various types and can be divided into two sub-groups of point-source capture and direct air capture. Point-source capture aims to capture carbon directly from industrial processes that would emit CO2 into the atmosphere. Point-source capture technologies can be observed alongside power generation facilities or industrial sectors that heavily emit CO2. The process occurs through the chemical separation of CO2 from streams of gas or synthetic gas, upon which the separated CO2 is stored or used as fuel for the production of industrial or consumer goods. Point-source capture can be further divided into three separate technologies: pre-combustion, post-combustion, and oxy-fuel. Pre-combustion technology entails the removal of carbon at the synthetic gas stage, in which the feedstock (carbon or natural gas) is transformed by oxidation processes into synthetic gas. Under this process, the synthetic gas - consisting of hydrogen, carbon monoxide, and CO2 - is broken down, in which the CO2 is separated, captured, transported, and stored. By contrast, post-combustion technology separates CO2 from flue gases following the combustion stage using a chemical solvent. The flue gas is released through equipment that separates and captures the CO2 within it. Post-combustion capture is the most commonly employed method for industrial emitters of fossil fuels such as cement and steel producers or power generation sites, which can retrofit their facilities to include post-combustion equipment. The final method of point-source capture, oxy-fuel combustion, is the least developed of the three methods. It entails the combustion of fossil-fuel in nearly pure oxygen rather than air, which produces flue gas which is primarily composed of CO2 and water. Capturing the CO2 through oxy-fuel can be easier than standard combustion processes, as the gas holds lower nitrogen content than pre- or post-combustion methods. However, separating oxygen from air demands higher levels of energy than other combustion methods, an obstacle which developers of oxy-fuel technology are attempting to mitigate through technological advancements. Point-source capture plays a central role in reducing the carbon footprints of industries and individual corporations which emit high levels of COin their operations. However, despite its efficacy in preventing the emission of additional carbon into the atmosphere, point-source technology offers little in reducing the amount of CO2 already present in the atmosphere.

Direct air capture (DAC) technology, also known as carbon dioxide removal (CDR) technology, offers the capacity to directly remove existing CO2 from the atmosphere, presenting a more proactive mechanism in the net zero project. Although companies are developing multiple different technological methods, DAC technologies mainly employ solid sorbent filters which chemically link with CO2 and subsequently release captured CO2 into storage or containers to be transported for further use.

Once captured, CO2 can be stored or employed for various purposes. Captured CO2 is stored primarily underground. It is often stored in deep saline formations, which consist of rock formations that are layered with brine. Other common storage areas are coal beds, basalt formations, and shale basins. Captured CO2 can also be stored in oil and gas reservoirs, in which CO2 infusions can be employed to extract more oil and gas from the sites. This process is known as Enhanced Oil Recovery (EOR). Beyond the extraction of additional oil, captured CO2 can be used as fuel for manufacturing goods. Examples of uses for captured CO2 involve outcomes such as jet fuel, automobile seats, biofuel, and building materials.

CCUS is touted by numerous experts as an essential piece in the transition to clean energy. It is especially deemed important in commercial sectors where de-carbonization will require more time to develop, such as aviation, aluminum, or steel. It is also identified as a potential bridge for renewable energy sources such as blue hydrogen, which can be produced from technologies that can separate natural gas into hydrogen and CO2. Moreover, some net zero technologies such as clean fuels and bioenergy are related to CCUS technology, in which strengthening CCUS infrastructure could simultaneously strengthen the scalability of net zero technologies.

However, there also exist several barriers for CCUS technology which impede it from occupying a larger role in achieving net zero emissions. The technology remains in early stages of development, with high figures for both fixed costs for installation and variable costs for operations. For instance, fixed cost estimates for very concentrated CO2 streams such as ethanol and natural gas are approximately USD $15-25/t CO2, and between $40-120/t CO2 for dilute gas streams such as cement and power. Although point-source technologies such as post-combustion offer lower fixed costs as many fossil fuel facilities can be retrofitted into carbon capture sites, it simultaneously demands higher variable costs to operate the technology and extract the CO2. DAC technology, meanwhile, is currently the most expensive of all existing CCUS technologies, priced at between $250-600/t CO2. In comparison, reforestation efforts would cost on average below thresholds of $50/t CO2. Although CCUS technologies continue to become more efficient and cost-efficient with simultaneous public and private sector support, the technology has not yet reached a point in which it is widely affordable for widespread use and implementation. Another point of concern is that point-source carbon capture technology - currently the most scalable version of CCUS - only addresses scopes 1 and 2 of CO2 emissions. Scopes 1 and 2 of emissions are limited to emissions produced at the industrial production and power generation. Limited to the first two scopes of emission, point-source capture does not work to reduce a company’s scope 3 emissions, which accounts for the indirect emissions resulting from the activities of a company’s capital goods, purchased goods and services, or owned assets. Given that scope 3 emissions account for more than 90% of total CO2 emissions for numerous companies, currently prominent CCUS methods may not have as broad of an impact in emissions reductions as argued by proponents of CCUS.  

For a more in-depth look at how CCUS technology operates, visit the following resources:

Financial Times | Carbon capture: the hopes, challenges and controversies

New York Times | Carbon Capture Explained | How It Happens

FreeThink | Carbon Capture Technology Explained

Real Engineering | Carbon Capture - Humanity's Last Hope?

Sources:

Carbon Capture From Flue Gas and the Atmosphere: A Perspective

CCS explained - Carbon Capture

Pre-Combustion Capture

Direct Air Capture