Removing Carbon From Our Atmosphere With Carbon Capture Technology
Climate change is a topic gaining more and more relevance as time goes on. This is because we have measured an increase in carbon within our atmosphere because of burning fossil fuels. Worldwide emissions of carbon dioxide “total about 34 billion tonnes per year. About 45% of this is from coal, about 35% from oil, and about 20% from gas” (World Nuclear Association). A way to mitigate this is by carbon capture, utilization, and storage (CCUS).
CCUS is a set of technologies that capture carbon dioxide emissions, utilize them for various applications, or store them underground to prevent them from being released back into the atmosphere. CCUS technologies are typically installed at existing plants that emit large amounts of carbon dioxide rather than in any location. This technology is critical for reducing greenhouse gas emissions and mitigating climate change. So, how does it work?
There are three main methods for capturing CO2 from our atmosphere: post-combustion, pre-combustion, and oxy-fuel combustion. Post-combustion “separates CO2 from the flue gas, by using a chemical solvent for instance, after the fuel is burnt”. Pre-combustion involves “converting the fuel into a gas mixture consisting of hydrogen and CO2 before it is burnt. Once the CO2 is separated, the remaining hydrogen-rich mixture can be used as fuel”. Lastly, oxy-fuel combustion “involves burning a fuel with almost pure oxygen to produce CO2 and steam, with the released CO2 subsequently captured” (The London School of Economics and Political Science). The main difference between these three is the fitting to plants. Both pre and oxy-fuel combustion can be installed in new plants or pre-existing facilities. Pre-combustion, however, “requires larger modifications to the operation of the facility and are therefore more suitable to new plants” (The London School of Economics and Political Science).).
You might be thinking, why not capture carbon from the air in neighborhoods or in areas where there may be little development? This is because there is a much lower concentration of CO2 in the atmosphere than in flue gas. Not to mention the high energy consumption those machines would have as they need fans to draw air in. It doesn’t make sense to have it in this stage of development due to cost, policy, and efficiency.
Once CO2 is captured, it must be stored or transported to be used in some sort of application. For some applications, captured CO2 can be used for synthetic fuels, enhanced oil recovery (EOR), and building materials such as concrete. Synthetic fuels are a solution for reducing emissions in the aviation and shipping sectors because they are hard to electrify due to energy density requirements. The process combines CO2 with green hydrogen (produced through water electrolysis using renewable electricity) to create hydrocarbons such as methanol, synthetic gasoline, diesel, or jet fuel. These types of fuels are carbon-neutral, which means the CO2 released during combustion is equal to the amount captured during production.
Enhanced oil recovery is the process of extracting additional oil from underground reservoirs that are no longer productive through conventional methods. There are a few ways to enhance oil recovery, one of the more sustainable options being gas injection. This approach uses gases such as CO2 “that expand in a reservoir to push additional oil to a production wellbore” (U.S. DOE). This reduces the oil’s viscosity, making it easier to push toward production wells. This provides a way to monetize captured CO2 by increasing oil production as “EOR can extract 30% to 60% or more of a reservoir’s oil, compared to 20% to 40% using primary and secondary recovery” (Helig E’).
Another way that CO2 is being repurposed is by injecting it into concrete during the production process. “Carbon mineralization technologies, such as CarbonCure, are a relatively new but proven solution” (CarbonCure). Carbon mineralization is a method in which “captured CO2 is injected into fresh concrete while it’s being mixed. Immediately upon injection, a chemical reaction takes place between the calcium oxide in the product’s cement and the CO2 that is introduced by the CarbonCure system. This reaction creates nano-calcium carbonate (CaCO3) minerals that become permanently embedded” (CarbonCure). This method is both a utilization and storage of captured carbon, limiting the amount of carbon re-introduced to the atmosphere.
If the captured carbon isn’t used for some type of application, it must be stored as a supercritical fluid. “Supercritical CO2 means that the CO2 is at a temperature in excess of 88 degrees Fahrenheit and a pressure in excess of 1,057 psi” (National Energy Technology Laboratory). This allows CO2 to have some properties like a gas and some like a liquid, which lowers the required storage volume. CO2 would have to be injected below 2,600 feet to remain in supercritical condition. Four main mechanisms trap the injected CO2 underground: structure trapping, residual trapping, solubility trapping, and mineral trapping.
Structural trapping is the mechanism that traps the largest percentage of CO2. The rock layers and faults around the storage formation where the CO2 is injected act as seals that prevent the CO2 from escaping. Residual trapping traps CO2 in the pore space between the rock grains as the CO2 plume migrates through the rock. When the CO2 is injected into the site, it displaces existing fluids and moves through the porous rocks. As the CO2 moves, small portions are left behind in the pore spaces, rendering it immobile. Solubility trapping relies on a chemical reaction with brine water that is present in pore spaces within a rock. Some CO2 molecules will dissolve into the brine water, allowing it to combine with available hydrogen atoms to form HCO3-. Lastly, mineral trapping also relies on a reaction that can occur when the CO2 dissolved in the brine water reacts with the minerals in the rock. The acid produced “can react with the minerals in the surrounding rock to form solid carbonate minerals, permanently trapping and storing that portion of the injected CO2” (National Energy Technology Laboratory). It’s important to note that leaks can happen, and measures must be in place to monitor these sights.
Currently, 43 carbon capture storage facilities are in place, with many more in development. Capturing carbon from industrial facilities will help reduce the amount of carbon dioxide released into the atmosphere, allowing cleaner air and a way to recycle CO2. It is important to note that CCUS is part of a more extensive solution to address climate change rather than a single solution for emission reduction. This technology aims to work toward achieving new-zero emission targets for a cleaner, more sustainable world.
Works Cited
“Carbon Capture.” Center for Climate and Energy Solutions, 30 Aug. 2023, www.c2es.org/content/carbon-capture/#:~:text=Carbon%20capture%2C%20use%2C%20and%20storage,power%20plants%20and%20industrial%20facilities.
“Carbon Dioxide Emissions from Electricity.” World Nuclear Association, world-nuclear.org/information-library/energy-and-the-environment/carbon-dioxide-emissions-from-electricity#:~:text=Worldwide%20emissions%20of%20carbon%20dioxide,and%20about%2020%25%20from%20gas. Accessed 18 Oct. 2024.
“Enhanced Oil Recovery | Department of Energy.” Office of Fossil Energy and Carbon Management, www.energy.gov/fecm/enhanced-oil-recovery. Accessed 18 Oct. 2024.
E’, Helig. “Enhanced Oil Recovery (EOR).” Journal of Petroleum & Environmental Biotechnology, www.walshmedicalmedia.com/open-access/enhanced-oil-recovery-eor.pdf. Accessed 18 Oct. 2024.
“What Is Carbon Capture and Storage?” Netl.Doe.Gov, netl.doe.gov/carbon-management/carbon-storage/faqs/carbon-storage-faqs. Accessed 18 Oct. 2024.
“What Is Carbon Capture, Usage and Storage (CCUS) and What Role Can It Play in Tackling Climate Change?” Grantham Research Institute on Climate Change and the Environment, 16 Aug. 2024, www.lse.ac.uk/granthaminstitute/explainers/what-is-carbon-capture-and-storage-and-what-role-can-it-play-in-tackling-climate-change/.
