In November 2023, Heirloom Carbon Technologies, a US-based climate company, unveiled its direct air capture facility in Tracy, California. The plant will remove up to 1,000 tonnes of carbon dioxide (CO2) from the atmosphere annually. While early in operation, the facility and its technology represent exciting advancements in the field of carbon capture, a critical part to preventing passing the 1.5C global warming threshold.
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Carbon Capture and Storage
Direct air capture (DAC) is a rapidly developing field and is one of three main methods for carbon capture, usage, and storage (CCS or CCUS). The two more established CCS methods are pre-combustion and post-combustion capture.
Pre-combustion capture separates carbon dioxide from a refined gas mixture prior to its combustion and use for energy production. Pre-combustion capture is more expensive than post-combustion capture and is harder to retrofit existing plants, however, it produces a more concentrated stream of CO2 and prevents carbon dioxide combustion pollutants from being released. Post-combustion carbon capture involves capturing CO2 from flue gas, also called “Stack” or exhaust gas, before it exits a plant and is released to the atmosphere. Post-combustion capture technology is much easier to retrofit to existing plants, though the recovery of CO2 is much more inefficient and requires higher energy inputs to achieve storage.
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Direct Air Capture
Direct air capture (DAC) removes CO2 from the atmosphere, compared to pre- and post-combustion, which prevents its release, and makes it available for storage or reuse. DAC often uses chemically absorbent materials for CO2. However, these often have significantly high costs, anywhere from $7,000 to $100,000 per metric tonne, according to an operational report from Heirloom.
Heirloom’s California plant uses a natural process that uses limestone, calcium carbonate (CaCO3), and recurring cycles of heating and carbonation to achieve cost effective atmospheric carbon dioxide capture, resulting in significantly lower costs for absorbent material. Limestone can be purchased for as low as $10 per tonne.
Flowchart summarizing the limestone-based process of atmospheric CO2 removal used in Heirloom’s California facility. Graph: Michael Chase. Data: Heirloom (2022).
The flowchart above shows how calcium carbonate in limestone can be reused in a naturally occurring cyclical pattern, reducing the need for new material, and greatly reducing waste from the process.
Heirloom’s new process has accelerated carbonization of Ca(OH)2 from the literature benchmark of two weeks down to three days. Heirloom’s facility also uses modularity, or separated units of CO2 collection stacks, allowing for extraction to continue even if a unit experiences a disruption or difficulty.
Heirloom has partnered with another climate startup, CarbonCure Technologies, to store the CO2 extracted in its facility in long-term infrastructure materials like concrete. The new facility is also carbon negative, as the facility itself and the kiln used in heating are running off of 100% renewable energy.
The current average cost for carbon capture credits is between US$600-$1,000 per tonne. Heirloom is aiming for their carbon credits to cost only $100 by 2035, supported by recent investments into direct air capture from subsidies and tax credits through the US government.
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The Future of Direct Air Capture
Following investments that came as part of the 2023 Infrastructure Investment and Jobs Act, the US Department of Energy announced funding for two DAC facilities capable of removing 1 million tonnes of CO2 annually. This removal capacity would be 1,000 times higher than Heirloom’s California facility and represents the removal capacity that will be needed at several more facilities across the globe by mid-century to meet current climate goals.
While investment into DAC is important to achieve project scaling and substantial increases in extraction capacity worldwide, direct air capture and other carbon capture technologies alone will not deliver the net zero carbon future we need. Global decarbonization and drastically cutting greenhouse gas emissions is still the main way to reach a more sustainable system. DAC alone would not be able to compensate for the rising amount of greenhouse gas emissions.
There are also concerns with some of the funding and storage aspects of DAC. Without strong policies to regulate the use of carbon removal credits, some conservationists fear that rather than lower their emissions, emitting companies will just buy removal credits to “offset” their emissions, which achieves little to no progress towards translational shifts of net zero operations.
There are also fears over the long-term geologic impacts of injecting extracted CO2 into geologic reserves underground for sequestration. With more development DAC, however, can be a highly impactful assisting technology that could turn back the greenhouse gas “timetable,” and reduce global atmospheric CO2 levels, once net zero has been reached. Advancements in direct air capture represent how ingenuity and dedication above all, are the strongest tools we have in the fight against climate change and its impacts.
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