Heirloom Carbon ($204 million to develop Direct Air Capture technology using low-cost limestone)

Heirloom Carbon (Heirloom), an American cleantech company founded in 2020, uses Direct Air Capture (DAC) technology to capture carbon dioxide (CO₂) from the atmosphere using limestone and store CO₂ safely and permanently. By 2035, Heirloom aims to remove 1 billion tons of CO₂. The company also sells carbon credits to allow companies to offset their own CO₂ emissions.

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Challenges: Carbon emissions and Direct Air Capture

Carbon emissions

Since the early 1900s, carbon dioxide (CO₂) levels in the atmosphere have increased by 50% due to human activities. When fossil fuels (such as coal, oil, and natural gas) are burned for energy production, transportation, and industrial processes, CO₂ is released into the atmosphere. This excess CO₂ acts as a greenhouse gas, trapping heat and causing the air and ocean temperatures to rise. CO₂ emissions play a crucial role in driving climate change.

This warming effect has caused the global average temperature to rise by about 1.1 ºC since the pre-industrial period. This has led to rising in the frequency and intensity of extreme weather events, melting of polar ice caps and glaciers and rising sea levels, shifts in species ranges and increased risk of species extinction, agriculture and food security,  and ocean acidification.

To mitigate these impacts, the Paris Agreement aims to limit global warming to well below 2 ºC above pre-industrial levels. The Intergovernmental Panel on Climate Change (IPCC) estimates that a “carbon budget” of about 500 GtCO₂, which corresponds to about ten years at current emission rates, provides a 66% chance of limiting global warming to 1.5 ºC.

Direct Air Capture

Direct Air Capture (DAC) is a technology that uses chemical or physical processes to extract CO₂ directly from the atmosphere. DAC technology includes two main types of systems: liquid solvent systems and solid sorbent systems. Liquid solvent systems use a chemical solution to absorb CO₂ from the air, whereas solid sorbent systems use a solid material. The extracted CO₂ can be stored in deep geological formations, achieving CO₂ removal.

DAC technology is considered a feasible option for achieving net-zero emissions by 2050, and it is expected to capture nearly 60 Mt CO₂/year by 2030.

DAC advantages

DAC technology offers several benefits, including reducing atmospheric CO₂, being space-efficient, and having a smaller land footprint compared to other carbon capture technologies.

DAC is also location-flexible, meaning it can be built in any location that has low-carbon energy and CO₂ storage. DAC plants can be constructed on non-arable land, which does not add further pressure on land use. DAC and storage plants offer an affordable solution for removing CO₂ from the air at megaton-scale.

DAC disadvantages

However, DAC is more costly per ton of CO₂ (tCO₂⁻¹) removed than many mitigation approaches and natural climate solutions, as separating dilute CO₂ from ambient air is an energy-intensive process. Currently, DAC technologies have been demonstrated on the industrial and pilot scales, with reported net CO₂ removal costs between $500 and 600 tCO₂⁻¹.

DAC system costs could be lowered significantly with commercialization in the 2020s followed by massive implementation in the 2040s and 2050s. Cost of DAC deployment affects climate outcomes, and low-cost DAC decreases the amount of total energy used, which can reduce the deployment costs and improve climate outcomes.

Heirloom Carbon Technology

Heirloom uses limestone (CaCO₃) instead of synthetic sorbents to capture CO₂ from the air and store it safely and permanently. Limestone is heated in renewable-energy powered calciners to remove CO₂ and produce Ca(OH)₂ sorbents from the hydration of CaO powders. Ca(OH)₂ sorbents are placed on vertically stacked trays, and algorithms are used to optimize their capacity to absorb CO₂ in different environmental conditions. Heirloom's DAC technology accelerates the natural property of limestone, reducing the time it takes to absorb CO₂ from years to just three days. The company claims that its technology has the lowest peer-reviewed, at-scale cost of any direct air capture technology on the market.

Heirloom Carbon Direct Air Capture technology

The diagram below depicts the system of Heirloom DAC technology.