Direct Air Capture: is Time Travel possible?

At COP 21 in 2015 the Paris Agreement was born, a document that set out goals and a framework for international climate action. One of the goals, one that everyone should be familiar with, is limiting global warming to well below 2°C, preferably 1.5°C, compared to pre-industrial levels. To achieve this, industries are moving to innovate and explore ways in which they can ‘decarbonise’ in order to reach the ultimate goal: net zero or even negative emissions.  

One of the most exciting emerging technologies from the last decade or so is Direct Air Capture (DAC), which could very well prove to be a crucial complimentary industry for the path towards our species living in equilibrium with the planet. In a nutshell it will mean drawing carbon dioxide directly from the air, which will not only offset present and future emissions, but also those we’ve emitted in the past. Sounds amazing right? Elon Musk has been bitten by the carbon capture bug too, recently tweeting: “Am donating $100M towards a prize for best carbon capture technology. Details next week”. 

In the aviation world, United Airlines have jumped onboard the carbon capture train by committing to a multi-million-dollar investment towards a DAC plant and pledging to be carbon neutral by 2050. Up until now, carriers have used the Carbon Offsetting and Reduction Scheme for International Aviation (CORSAIR) and sustainable liquid fuels to reduce their emissions. CEO of United, Scott Kirby believes that “the math just doesn’t come close to adding up,” and that “the only way we can truly make a dent in the levels of atmospheric carbon is through direct air capture and sequestration.”  

One of the main players in the world of DAC is Carbon Engineering, a company founded in Canada in 2009 by Harvard Professor David Keith. They have been capturing carbon dioxide from the atmosphere since 2015 at their small-scale pilot plant in Squamish, British Columbia. In partnership with a development company aptly named 1Point5, they will be building the world’s largest DAC plant (funded in part by United) in the Permian Basin in Texas. This facility will capture up to one million tons of carbon dioxide from the air per year and sequester it underground in geological formations. This is equivalent to the photosynthesis of 40 million trees.  

CE Pilot Plant, photo source: Carbon Engineering

The way Carbon Engineering extracts carbon dioxide from the air has 4 stages: 

  1. Air Contractor: Pulls atmospheric air in using giant fans and passes it over thin plastic surfaces with a potassium hydroxide solution flowing over them. The solution chemically binds with the CO2, trapping them in the liquid as carbonate salt, then the CO2 is concentrated, purified and compressed using a series of chemical processes. 
  2. Pellet Reactor: The carbonate salt is separated from the solution, forming small pellets. 
  3. Calciner: The pellets are heated so that the CO2 is released as a gas. 
  4. Slaker: Any pellets left behind are hydrated and recycled back into the system to produce more CO2. 

Inputs to this process are water, electricity from renewables and natural gas. You may be thinking: “But natural gas is a fossil fuel, how does this not result in a huge carbon footprint?” Well, all emissions from the combustion of the natural gas are fed back into the cycle and the carbon dioxide is captured and sequestrated, making the whole operation emissions free. In fact, if enough renewable energy is available at a location, natural gas is not needed at all. Another bonus is that DAC plants can use non-potable water, be built on non-arable land, so they will not compete with food production, and the chemicals needed are kept in a closed loop, meaning they can be used over and over again.   

Carbon Engineering is also working with UK company Pale Blue Dot Energy (PBDE) to deploy DAC plants across the UK. One of the locations being considered is in Aberdeenshire in North East Scotland close to PBDE’s Acorn Project, a proposed off-shore hydrogen generation and carbon capture and storage (CCS) facility, due to begin operations in 2024. It will do what a lot of CCS facilities will probably end up doing – use existing fossil fuel infrastructure like natural gas pipelines to transport hydrogen and carbon dioxide. 

Another pioneer in this field is a Swiss company called Climeworks who are busy building a DAC plant in Iceland. Named ‘Orca’, the plant will be ideally placed, using geothermal energy from the Hellisheiði power plant to capture CO2 in a similar process to Carbon Engineering. An Icelandic company called Carbfix, will then mix the CO2 with water and pump it deep underground, where it will react with basalt rock and turn into stone, a natural mineralisation process which can take a few years.  

‘Orca’, photo source: Climeworks

Which brings us onto the next issue. Where will all this captured CO2 be stored? One solution has already been mentioned – basaltic geological formations. It is estimated that around 7,000 Gigatons of CO2 could be stored offshore Iceland, 1 Gigaton being equal to 1 billion tons. Other geological storage options include using depleted oil and gas reservoirs, deep saline solution reservoirs or by enhanced fossil fuel recovery, meaning fossil fuels are extracted and during the process CO2 is pumped in to replace it. Ocean storage is another option, by directly injecting CO2 into water where it will either dissolve or form a ‘lake’ on the seabed depending on how deep it’s piped in. The third option is turning the CO2 into a solid through mineral carbonation, which can then be stored.  

Appropriate risk management should be carried out on all storage sites chosen as there are obvious hazards which spring to mind. How will leakage be mitigated? Will there be subterranean pressure build ups? How will the local chemical environment of ocean storage areas be altered? Mineral carbonation requires metal oxides – will they be mined without harming the environment? As this industry grows it should be strictly regulated to make sure that we’re not solving one problem and unwittingly causing another.  

One further development worth noting is Air-to-Fuel technology – synthetic liquid fuels made from nothing more than hydrogen and CO2. First CO2 is captured using DAC, then water is split into hydrogen and oxygen via electrolysis using renewable electricity, and finally the CO2 and hydrogen are reacted together to form hydrocarbons, which can then be refined into Jet A1. This process is still very expensive, but as DAC and Green Hydrogen are scaled up, and the cost of renewables goes down, Air-to-Fuel could become commercially viable.  

United’s pledge to be Net Zero by 2050 sets a more ambitious goal than the industry wide target of reducing net CO2 emissions to half of what they were in 2005, by 2050, and matches the U.K. aviation industry’s pledge announced earlier this year. Along with renewable sources of electricity and sustainable fuels, this is why many are calling this phase in human history a new energy revolution. A step further is carbon capture, thereby removing historical carbon dioxide from the atmosphere to undo what has been emitted during the energy revolutions of past. Time travel isn’t real, but this may be the closest we’ll get.  

Lead Image Source: Climeworks

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