Writer: Allison Cui
The Impact of Carbon Emissions
As we all know, the increasing volume of carbon emissions continues to threaten not only our planet but also our lives as a whole, for the amount of carbon emissions trapped in our atmosphere causes global warming which ultimately leads to climate change. The rates of carbon being emitted had not shown significant signs of slowing down (before 2020) as the gross total U.S. greenhouse gas emissions has increased by 3.7% since 1990, despite a few fluctuations every year due to changes in the economy and other factors. 2020, of course, is a unique case: there has been an incredibly sharp decline in CO2 emissions due to the pandemic in which emissions dropped 17% globally. Without the extensive use of primary sources of greenhouse gas emissions everyday, such as transportation, industry, and air travel, daily CO2 emissions have decreased by approximately 18.7 million tons compared to last year. However, experts speculate that these conditions won’t last unless the government follows through with a movement towards cleaner energy. Air capture technology aims to combat climate change from a different perspective.
What is Air Capture Technology?
Direct air capture technology is a process by which machines are used to suck carbon dioxide out of the atmosphere. This is an example of “negative emissions technology,” which includes a wide variety of approaches such as planting trees. Direct air capture technology (DAC) specifically uses a chemical scrubbing process that directly removes CO2 from the outside air in order to gradually lower the world’s global temperature—the goal is to lower it to just 1.5 or 2 degrees Celsius above pre-industrial levels. A recent study found that DAC is a relatively easy task when compared to the other several ways pursuing removal of CO2 from the atmosphere due to the easier-to-scale-up technology involved. When the CO2 captured is stored underground, the process is also referred to as direct air carbon capture and storage (DACCS). DAC technologies are being developed by numerous startup companies around the world that are tackling the different ways to absorb greenhouse gases from the air. One method, piloted by Carbon Engineering, uses a hydroxide solution that is heated to high temperatures to release the CO2. It then can be stored and the hydroxide can be reused. This process utilizes existing technology and currently encompasses the lower cost of the two primary technologies. The second method employs amine adsorbents in small, modular reactors that are being developed by Climeworks.
Design and Mechanisms
The Canadian company Carbon Engineering (CE) has created an innovative design and vision in order to trap CO2 from the atmosphere. As I mentioned before, CE uses a hydroxide solution to capture atmospheric CO2 and manage about 60% of emissions. It does this by functioning like a plant and takes in carbon dioxide while giving out oxygen. The company sets up these plants in environments where trees cannot survive. The technology’s design includes two processes: first, an air contractor, and then a regeneration cycle whose purpose is ensuring the ongoing atmospheric CO2 capture and generation of pure CO2. The air contractor device is composed of arranged, corrugated PVC sheets so that when CO2 is pulled in through the fans, it will come in contact with an alkaline hydroxide solution that naturally absorbs CO2. This solution has been altered by specifically chosen additives and concentration to optimize the amount of carbon dioxide absorbed. A cost effective air contractor will not only engage in minimal land but it will also help to trap large scale quantities of CO2 with both low solution pumping and energy inputs for fans. On the other hand, the regeneration cycle is the process in which the air contractor’s CO2 laden chemical solution is treated to release pure, compressed CO2. The pure CO2 can be further combined with hydrogen to create more fossil fuels while the original chemical solution can be restored. It can also be stored underground in geological formations. In the future, designers plan to use renewable and clean sources of energy (solar, thermal, wind, or nuclear) for the air capture plant.
The Significance of Direct Air Capture Technology
The prototype plant in British Columbia currently has the capability to capture almost 14 to 15 vehicles’ greenhouse gas emissions. If this whole set up were to be scaled up by 20,000 times, it is predicted that that the CO2 emitted from up to 300,000 vehicles can possibly be captured. Furthermore, direct air capture technology can eliminate more CO2 per acre of land footprint than what plants can do. It is one of the more inexpensive and economically attractive methods in combatting global warming.
Unexplored Concepts and Limitations
One of the main concerns is that even though direct air capture technology seems promising in regards to extracting atmospheric CO2, it is still extremely unlikely that environmental problems will be solved. In order to have a significant impact on global concentrations of CO2, direct air capture would need to be rolled out on a vast scale. However, professor of chemical engineering at Worcestor Polytechnic Institute Prof. Jennifer Wilcox warrants caution: “Is the rate of scale-up even feasible? Typical rules of thumb are increase by an order of magnitude per decade [growth of around 25-30% per year]. [Solar] PV scale-up was higher than this, but mostly due to government incentives…rather than technological advances.” As a result, serious questions are raised about the amount of energy required, the levels of water usage, and the impact of toxicity from the chemical sorbents involved.
Furthermore, issues regarding long-term CO2 storage are relevant due to the high uncertainty in maintaining safe conditions and minimizing leakages. DAC’s large requirement for of energy input, about up to 45 gigajoules per tonne of CO2 extracted, some geoengineering promoters have suggested the use of “small nuclear power plants” connected to DAC installations. This however could introduce several more complications and environmental impacts. Likewise, DAC also has a high demand for water input. One study estimates that with implementation levels that would remove 3.3 gigatonnes of carbon per year, it is expected that the DAC would use approximately 300 cubic kilometers of water per year. This number is equivalent to 4% of the water used for crop cultivation every year. Other risks include breaching Paris temperature limits, leading to a global temperature overshoot of up to 0.8 degrees Celsius.
Negative emissions technology poses one final challenge: ocean rebound. Ocean rebound means that oceans will absorb a significant portion of human-caused CO2 emissions each year. Thus, even if large quantities of CO2 is removed with DAC, these amounts could be offset by the oceans release of CO2 back into the atmosphere, which reduces their supposed efficacy.
As climate change’s presence in our world gradually becomes more prominent, researchers and scientists have turned to direct air capture technology as a short-term solution. Despite the several difficulties in execution and practicality, the net impact is beneficial for areas where clean energy technologies are lacking.
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