Trapping the Toxin

In the previous article we had discussed various aspects of Carbon Capture and Sequestration (CCS). A similar Carbon Dioxide Removal (CDR) technology is that of Direct Air Capture (DAC), where carbon dioxide is literally plucked from the air using various tools and techniques. Let us discuss this in more detail.

Direct Air Capture

While CCS is used mostly in industry and oil and gas installations, DAC can be implemented anywhere. Moreover, DAC removes the carbon dioxide already present in the air, as opposed to CCS, which captures the carbon dioxide at the source of emission and prevents it from being released into the air. The commonality between DAC and CCS is that both capture carbon dioxide and transport it to be stored in underground reservoirs.

DAC involves the pulling in of large amounts of air using giant fans or pumps, which is then passed through chemicals. The chemicals react with air in such a manner that carbon dioxide is trapped and the other air is released. There are typically two types of DAC systems: Solid DAC (S-DAC) and Liquid DAC (L-DAC). In S-DAC, the solid adsorbents (solid materials that absorb the carbon dioxide) are used to trap carbon dioxide, while in L-DAC, the adsorbent is a liquid chemical, for the same purpose. In both S-DAC and L-DAC, the carbon dioxide is released from the liquid/solid adsorbents by applying heat at low pressure. The pure stream of carbon dioxide is then carried to underground reservoirs for storage.

The International Energy Agency (IEA) reports that there are 27 DAC projects in the world and another 130 projects are in various stages of planning. Most of the DAC plants under operation are small operations. The only DAC plants capturing 1000 tonnes of CO2 per year or more are: the Climeworks Orca plant in Iceland (removes 4000 tonnes per year) and Mammoth Plant in Iceland (with a capacity to remove 36000 tonnes per year), the Global Thermostat plant in Colorado (removes 1000 tonnes per year) and Heirloom’s plant in California (removes 1000 tonnes per year). Heirloom is building two large DAC plants in Louisiana, USA with a capacity to remove 3,20,000 tonnes of carbon dioxide per year. In addition, the US Government also set aside funding of US$3.5 billion for developing four DAC hubs. In August, 2023, US$1.2 billion was released to develop the Project Cypress Hub in Louisiana and the South Texas Hub in Texas. While Project Cypress will have the capacity to remove One Million tonnes of carbon dioxide per year, the South Texas Hub will be built to remove 30 million tonnes of carbon dioxide per year. Another large DAC plant is being built by the company 1PointFive in Texas, with a capacity to remove half a million tonnes of carbon dioxide per year. Such large DAC plants are also being planned in the UK (in North East Scotland by Storrega and Carbon Engineering).

While DAC is now recognised to be a part of any technological pathway to achieving Net Zero, it has its own challenges.

• DAC plants are highly capital intensive and typically require state support. Moreover, the cost of capturing per tonne of carbon dioxide is much higher than other mitigation measures.
• Large DAC plants require an unending steady flow of clean renewable energy: something that Climework’s Orca and Mammoth plants enjoy. They are situated next to the ONPower’s geothermal power facility in Iceland. Similarly, the South Texas Hub and the Louisiana plants have access to renewable energy and low carbon energy.
• The other challenge for DAC plants is that they require a large underground space to store the carbon dioxide.
• Most large DAC plants are located in Europe and the USA and are yet to be tested in other environments.

Conclusion

Even with the challenges that DAC faces, it is a worthwhile technology and needs to be supported by governments in the form of outright project finance, tax breaks and subsidies. As the DAC bandwagon grows, its project cost will also begin to fall as is the case with most technologies (solar and wind technologies, for example). The other advantage is that DAC is actually providing a public good in terms of putting away carbon dioxide forever and needs to be supported.

The writer is the Additional Chief Secretary, Department of Cooperation, Government of West Bengal