Capture it, if you can't reduce it
While the world is fighting a pandemic but another crisis is still looming: the climate change. As global temperature continue to rise, the effects of it are increasingly felt through more severe storms, wildfires and flooding. The latest climate science indicates that it is pertinent to keep temperature rise below 1.5–2 degrees C (2.7–3.6 degrees F), which would prevent the worst impacts of climate change. Efforts to reduce green-house gases (GHG) emissions should always take priority to meet the climate goals as per Paris Agreement. But current visible efforts and tangible policies of the governments around the world doesn’t seem much focused on the impending disaster. Hence the saying, if we can’t reduce the emissions, we might need to capture it. Direct Air Capture (DAC) is gaining traction as a promising carbon removal approach that will likely be a necessary part of a larger carbon removal portfolio, at the billion-tonne scale by mid-century.
What is DAC ?
Direct air capture (DAC) is a carbon-dioxide removal (CDR) process directly from the ambient air, by passing it through an liquid solvents or solid sorbents. Subsequently CO2 is stripped from the chemical through the application of heat, resulting in a CO2 stream that can undergo dehydration and compression, while simultaneously regenerating the chemical media for reuse.
Sounds interesting? Yet not many players in the field
Climeworks, Global Thermostst and Carbon Engineering are the leading companies working on direct-air-capture. A brief about them is below:
What is done with the CO2 ?
The captured carbon dioxide can then be stored, or reused as a raw material. Climeworks has partnered with another company, Carbfix, to permanently store captured CO2 beneath the earth. The gas is mixed with water and pumped deep underground. Here it reacts with basalt rock and itself becomes stone “within a few years”.
If it isn't stored, then potential uses include as building materials or for fuel and energy, according to a Columbia University blog. Carbon Engineering, for example, has a process to turn the CO2 into synthetic crude. This can then be turned into petrol, diesel and jet fuel for sectors where electrification remains a challenge — marine and air travel.
The company says this process adds little or no new emissions to the atmosphere, compared to traditional fuels. The fuels release captured CO2 when they’re burned, simply returning levels to where they were. Or, if the CO2 is recaptured, you create a circular system of emissions.
What are the energy needs for DAC ?
The two main direct air capture systems in use today have very different temperature requirements, which impacts the types of energy required to operate them. Liquid solvent systems require 900 degrees C (1652 degrees F) to release captured CO2, whereas solid sorbent systems require 80 degrees C to 120 degrees C (176 to 248 degrees F). This means that solid sorbent systems can use lower-grade waste heat.
Recent research shows that coupling solid sorbent DAC with geothermal or nuclear power producers could be the first step to reaching the billion-tonne scale of removal necessary, as doing so could accelerate direct air capture deployment — potentially capturing up to millions of tonnes of CO2 per year. Early research is also looking into the possibility of coupling DAC to curtailed renewable energy.
How much does DAC Cost ?
Depending on the technology choice, energy source and the scale of deployment, the range of cost for DAC vary between $250-$600. For comparison, reforestation costs less than $50/tonne. Fundamentally, DAC is expensive because of the following reasons:
- the concentration of carbon dioxide in the air is still very dilute and requires lots of energy to separate out.
- there are not very many companies or projects yet — developing more projects will provide learning that could reduce costs.
- the markets for CO2 are limited and cannot provide enough revenue to offset the cost of capture.
Recent commercial engagement:
On March 2021, Canada’s most valuable online retail platform Shopify, inked a deal with Carbon Engineering to capture 10,000 metric tons of carbon dioxide and store it permanently underground. This is in addition to a previous 5,000-tonne commitment to Climeworks.
Shopify’s latest sustainability report shows the company has purchased enough carbon offsets over the years to offset all the emissions associated with its operations and energy use dating back to its 2004 founding.
