Carbon Capture VS Direct Air Capture: How We Can Tackle Rapid Climate Change
Earth has been experiencing extreme weather conditions over the last decade and climate induced disasters have been increasing in magnitude and frequency. These extremities in Earth’s climate are being observed and studied by scientists across the world. The Intergovernmental Panel on Climate Change (IPCC) released a report in early August, 2021, sounding a red alert for humanity. Prepared by 234 scientists from 66 countries, the report details the present scenario of climate change and highlights the importance of immediate action.
The UN Secretary-General, António Guterres, in his reaction to the report, noted that the soaring temperature levels are perilously close to the internationally-agreed threshold of 1.5 degrees above pre-industrial levels of global heating. The only way to prevent exceeding this threshold, is by urgently stepping up our efforts, and pursuing the most ambitious path. He added that ahead of the crucial COP26 climate conference in Glasgow in November, all nations — especially the advanced G20 economies — needed to join the net zero emissions coalition, and reinforce their promises on slowing down and reversing global heating.
The IPCC report highlights that human influence has warmed the climate at a rate that is unprecedented in at least the last 2,000 years. In 2019, atmospheric CO2 concentrations were higher than at any time in at least 2 million years, and concentrations of methane and nitrous oxide were higher than at any time in the last 800,000 years. Emissions of greenhouse gases from human activities are responsible for approximately 1.1°C of warming between 1850–1900, and averaged over the next 20 years, global temperature is expected to reach or exceed 1.5°C of heating.
Given that carbon emissions have been a major source of excessive heating on Earth, oil and gas industries around the world are required to adopt carbon capture technologies to reduce carbon concentrations in the atmosphere. Biological approaches, like planting trees, can offer a start to controlling carbon dioxide. But in the long-term, they may not be able to keep up with human activity. Two technologies that can curb carbon emissions are Direct Air Capture (DAC) and Carbon Capture and Storage (CCS), also known as Carbon Capture, Utilisation and Storage (CCUS). This article compares these two popular technologies
Direct Air Capture
1. What is DAC?
Direct air catch is an innovative strategy that utilizes chemical reactions to catch carbon dioxide (CO2) from the climate. At the point when air moves over these chemicals, they specifically respond with and eliminate CO2, permitting remaining components of air to go through. These chemical compounds can appear as either fluid solvents or strong sorbents, which make up the two sorts of DAC frameworks being used today.
When the carbon dioxide is caught from the air, heat is regularly applied to set it free from the solvent or sorbent. Doing so regenerates the solvent/ sorbent for another cycle of capture. The captured CO2 can be infused underground for long-lasting storage in certain geologic developments or utilized in different items and applications. Super durable storage can bring about the greatest environmental advantage.
2. Cost of DAC
DAC is an expensive process. Even though the concentration of carbon dioxide is increasing, it is still very dilute and requires a lot of energy to separate out. DAC is more costly per tonne of CO2 captured compared to most mitigation approaches and most natural climate solutions. This technology is still in its initial stages and requires a lot of study to find ways to reduce costs. Depending on the rate of deployment, which can accelerate through supportive policies and market development, costs for DAC could fall over the next 5–10 years.
3. Advantages of DAC
- Can be employed in a wide variety of locations — DAC plants can be deployed in a larger variety of locations. DAC does not need to be attached to an emissions source such as a power plant in order to remove CO2. In fact, by placing DAC facilities close to locations where the captured CO2 can then be stored in geologic formations, the need for extensive pipeline infrastructure is eliminated. Without a long network of pipelines, the potential for CO2 leaks is greatly reduced
- Requires a smaller footprint — The land use requirement for DAC systems is considerably small. DAC plants only require between 0.5 and 15 square feet of land.
4. Disadvantages of DAC
- Requires large amounts of energy — In order to drive air through the part of a DAC plant that contains the sorbent materials that capture the CO2, large fans are used. These fans require large amounts of energy to operate. High energy inputs are also necessary to produce the materials required for DAC processes and to heat sorbent materials for reuse.
- Environmental risks — CO2 from DAC must be transported and then injected into geologic formations to be stored. There is always a risk of leakage from the transport infrastructure. The groundwater may get polluted in the process of injection, or the disruption of geologic formations during injection will trigger seismic activity.
- Can enable enhanced oil recovery — CO2 is injected into the oil well to aid in the extraction of oil that would otherwise be inaccessible. If the amount of CO2 injected is not less than or equal to the amount of CO2 released when the recovered oil is burned, then employing CO2 for enhanced oil recovery will not result in carbon neutrality.
Carbon Capture and Storage
1. What is CCS?
Carbon dioxide (CO2) capture and storage (CCS) is a process consisting of the separation of CO2 from industrial and energy-related sources, transport to a storage location and long-term isolation from the atmosphere.
There are three steps to the CCS process:
- Capture — CO2 is separated from other gases produced in industrial processes, such as those at coal and natural-gas-fired power generation plants or steel or cement factories.
- Transport — CO2 is then compressed and transported via pipelines, road transport or ships to a site for storage.
- Storage — Finally, CO2 is injected into rock formations deep underground for permanent storage.
2. Cost of CCS
CCS is currently the cheapest option for reducing emissions in the production of some important chemicals such as ammonia, which is widely used in fertilisers. The estimated costs of CCS-equipped ammonia and methanol production based on natural gas are around 20–40% higher than their unabated counterparts, while the cost of electrolytic hydrogen routes is estimated to be 50–115% higher.
3. Advantages of CCS
- Can reduce emissions at the source — Most of the greenhouse gas emissions come directly from energy production or industry. The biggest advantage of CCS is its ability to capture CO2 from these point sources and then permanently store it in geological formations.
- CO2 is easier to remove at point sources — It is relatively difficult to capture CO2 through DAC due to its low concentrations. In the CCS process of oxyfuel combustion, oxygen is used to combust the fuel and the leftover exhaust gas also has a very high concentration of CO2. This makes it much easier for the CO2 to react with the sorbent in the CCS process and then be separated.
- Other pollutants can be removed at the same time — During oxyfuel combustion, high concentrations of oxygen used for combustion leads to a significant reduction of nitrogen oxide (NOx) and sulfur dioxide gases. Particulates created by oxyfuel combustion CCS can be removed with an electrostatic precipitator.
4. Disadvantages of CCS
- Cost of adopting CCS is high — In order to equip existing industry and electric generation plants with CCS technology, the cost of the product being generated must increase if no subsidies are provided. There are currently no regulatory drivers in most places to incentivize or require the use of CCS, so the cost of equipment and materials to separate CO2, build infrastructure to transport it, and then store it may be prohibitively high.
- CO2 Transport and Storage Sites Could Be Dangerous — While accident rates during the transport of CO2 are relatively low, the potential for a dangerous leak still exists. According to IPCC, if CO2 were to leak from a pipeline, a concentration between 7% and 10% in the ambient air could pose an immediate threat to human life.
- Public perception of storing CO2 near them is negative — Storing carbon from CCS has several perceived risks that are not popular among the public. Large-scale implementation of CCS technology will require a place to store the CO2.
How can the Captured Carbon be used?
The most common use of captured carbon is enhanced oil recovery, where CO2 is pumped into oil fields to push more oil to the surface. Four other uses listed by The Earthbound Report are:
- Building materials — CO2 is being used in industrial processes that mimic the natural formation of limestone, thereby speeding up the process. Certain waste products can be reacted with CO2 to make materials for plasterboard, cement and bricks.
- Fertilizer — A commercial air capture plant in Switzerland draws CO2 from the air, and pumps it across a field to a farm where it is used in their greenhouses. Additionally, CO2 can be combined with waste straw and methane from a landfill site, to create a crumbly soil enriching fertilizer.
- Plastic — CO2 can be used as a feedstock for plastic. This has two benefits. First, it replaces half of the oil normally used as a feedstock, and second, it locks up that CO2 in a durable plastic item.
- Gas — A certain single celled organism, called Methanogenic Archaea, consumes CO2 and produces methane as waste. This is being used to turn carbon emissions into natural gas.
References:
https://news.un.org/en/story/2021/08/1097362
https://crsreports.congress.gov/product/pdf/IF/IF11501/3
https://www.iea.org/reports/direct-air-capture
https://www.iea.org/fuels-and-technologies/carbon-capture-utilisation-and-storage
https://www.treehugger.com/direct-air-capture-pros-and-cons-5119399
https://www.ipcc.ch/site/assets/uploads/2018/03/srccs_wholereport-1.pdf
https://www.treehugger.com/carbon-capture-and-storage-ccs-pros-and-cons-5120005
https://earthbound.report/2017/11/21/five-uses-for-captured-co2/
