What is Direct Air capture?
Direct air entrapment is the process of drawing air out of the atmosphere and using a chemical reaction to separate carbon dioxide (CO2) gas. The recovered CO2 can be stored underground or used to make durable materials such as cement and plastic. The purpose of direct air capture is to use technical modifications to reduce the total CO2 concentration in the atmosphere. Thus, direct air entrapment can work with other initiatives to help mitigate the already devastating impact of the climate crisis.
According to the International Energy Agency, an energy modeling organization, 15 direct air recovery units are in operation in the United States, Europe, and Canada. These plants currently capture over 9,000 tons of CO2 annually. The United States is also developing a direct air capture plant capable of removing 1 million tons of CO2 from the air annually.
The United Nations Intergovernmental Panel on Climate Change (IPCC) warns that global CO2 emissions must be reduced by 30–85% by 2050 to keep atmospheric CO2 levels below 440 ppm. Earth temperature due to more than 2 degrees Celsius (3.6 degrees Fahrenheit) rise. Can direct air entrapment help reduce them?
IPCC scientists and economists agree that slowing climate change requires long-term measures to reduce anthropogenic greenhouse gas emissions. Direct air capture has been widely criticized as insufficient to reduce the number of harmful CO2 in the atmosphere on its own. In addition, it is more expensive per 21 tonnes of CO recovered than other mitigation strategies for the climate crisis.
How Does Direct Air Capture Work?
Direct air capture uses two different methods to remove CO2 directly from the atmosphere. The first process uses so-called solid adsorbents to absorb CO2. An example of a solid adsorbent is a basic chemical that resides on the surface of a solid. When air passes through the solid adsorbent, a chemical reaction takes place and the acid gas CO2 binds to the main solid. When the solid adsorbent is filled with CO2, it is heated to a temperature of 80 ° C to 120 ° C (176 ° F to 248 ° F), or a vacuum is used to absorb the gas from the solid adsorbent. The solid adsorbent can then be cooled and used again.
Another type of direct air recovery system uses liquid solvents and is a more complex process. It begins with a large container in which a basic liquid potassium hydroxide (KOH) solution flows over a plastic surface. When a large fan draws air into the container and the air containing CO2 comes into contact with the liquid, the two chemicals react to form a type of carbon-rich salt.
The salt flows into another chamber, where another reaction takes place, producing a mixture of solid calcium carbonate (CaCO3) and water (H2O) granules. The mixture of calcium carbonate and water is then filtered and separated. The final step in the process is to heat the solid calcium carbonate pellets to 900 ° C (1652 F) using natural gas. This produces high-purity CO2 gas, which is collected and compressed.
The remaining material is returned to the system for reuse. Once CO2 is recovered, it can be continuously pumped into underground rocks to revive dilapidated wells or to be used in the production of durable products such as plastics and building materials.
Direct Air Capture vs. Carbon Capture and Storage
Many experts believe that both direct air capture and carbon capture and storage (CCS) systems are integral to the climate crisis mitigation puzzle. At a basic level, both technologies reduce the amount of CO2 that can enter the atmosphere and exacerbate climate change.
However, unlike direct air capture, CCS uses chemicals to capture CO2 directly at the source. This prevents CO2 from being released into the atmosphere. For example, CCS can be used to capture and compress all CO2 in chimney emissions from coal-fired power plants. On the other hand, direct air entrainment collects CO2 that has already been emitted into the atmosphere by coal-fired power plants or other fossil fuel combustion operations.
Both direct air capture and CCS use basic chemicals such as potassium hydroxide and amine solvents to separate CO2 from other gases. After recovering CO2, both processes require the gas to be compressed, transferred, and stored. CCS is a slightly older process than direct air capture, but both are relatively new technologies and may benefit from further development.
Since CCS removes CO2 from its sources, it can only be used in places where fossil fuels burn, such as industrial facilities and power plants. In theory, direct air capture can be used anywhere, but placement near a power source or where CO2 can be stored improves efficiency.
Pros and Cons
The most obvious benefit of direct air capture is the ability to reduce CO2 concentration in the atmosphere. Not only is it more widely used than CCS, but it also takes up less space to capture the same amount of carbon as other carbon sequestration technologies. In addition, direct air entrapment can be used to create synthetic hydrocarbon fuels. But to be effective, the technology must be sustainable, cheap, and scalable. Until now, direct air capture technology has not made sufficient progress to meet these requirements.
Companies specializing in direct air capture technology are currently developing new, larger direct air capture plants capable of capturing up to 1 million tonnes of CO2 annually. If small enough direct air capture plants are built, they can capture up to 10% of anthropogenic CO2. By pumping and storing CO2 underground, carbon is permanently removed from the cycle.
Direct air recovery works independently of power plants and other fossil fuel-fired power plants, as it is based on capturing CO2 from the atmosphere rather than directly on fossil fuel emissions. This allows for more flexible and ubiquitous placement of direct air inlet plants.
Compared to other carbon capture methods, direct air capture requires less land per 21 tonnes of CO to be removed. This requires only 0.003 km2 to 0.77 km2 (0.0012 to 0.31 sq mi) compared to forests that require 333 km2 (130 sq mi) to capture the same amount of CO2.
Direct air capture can reduce the need to extract fossil fuels and also reduce the amount of CO2 released into the atmosphere by combining the captured CO2 with hydrogen to produce synthetic fuels such as methanol. It can be further reduced.
Direct air capture is more expensive than other carbon captures technologies such as reforestation and plantations. Some direct air capture plants currently cost between $ 250 and $ 600 per ton of CO2 removed, with estimates ranging from $ 100 to $ 1,000 per ton. According to researchers at the RFF-CMCC Institute for European Economic and Environmental Research, the future cost of direct air capture is uncertain as it depends on the speed of technological progress. Conversely, the cost of reforestation is only $ 50 per tonne.
The high value of direct air capture is due to the amount of energy required to remove CO2. The heating process to directly capture both liquid solvents and solid adsorbents requires chemical heating to 900 ° C (1652 F) and 80 to 120 ° C (176–248 F), respectively, which is very high. If a direct air recovery unit does not solely rely on renewable energy sources to generate heat, it still uses some fossil fuels, even if the process ultimately negatively impacts carbon.