Heirloom Carbon ($54M 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.

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.


Heirloom Carbon Direct Air Capture technology (ref. US20220347650A1)
Heirloom Carbon Direct Air Capture technology (ref. US20220347650A1)

The overall system comprises a feedstock source, a grinding system, carbonization plots, a conveyor system, calciners, and a CO₂ post-processing system.

  • Feedstock source

Heirloom uses limestone (CaCO₃) feedstock. The feedstock is processed in a grinding system and heated in renewable electricity-powered calciners to produce CaO powders which are hydrated to form Ca(OH)₂ to capture CO₂ from the air.

Global limestone resources stand at 90 trillion metric tons. Limestone is a sedimentary rock that is primarily composed of calcium carbonate (CaCO₃) and is commonly used in the construction industry as a building material and as a raw material for cement production. The largest reserves of limestone are found in China, followed by the United States, India, and Russia.

  • Grinding system

The grinding system grinds the limestone to a desired average particle size about 20 μm. Small particles of limestone have a large surface area exposed to the air, allowing for more efficient CO₂ capture. The operation of the grinding system emits CO₂, which is collected by the CO₂ post-processing system.

  • Carbonization plots

Carbonation plots contain limestone or Ca(OH)₂ particles. These particles are laid out as a thin layer onto a large area tray. The layer is about 10 cm thick. The carbonation plots are arranged so that Ca(OH)₂ particles can capture CO₂ directly from the air.

Carbonation plots are stacked vertically and are clustered into a group. The clustered carbonation plots enable modular operation of the overall system. The overall system includes a sufficient number of carbonation plots to hold a sufficient amount of the Ca(OH)₂  to sequester a desired amount of CO₂.

  • Calciners

Renewable-electricity powered calciners heat CaCO₃ at around 900 ºC for a duration between 30 minutes and 2 hours to replenish CaO from CaCO₃, which is then returned to carbonation plots. The CO₂ evolved from the calciners is collected by the CO₂ post-processing system.

  • Conveyor system

The conveyor system transports CaCO₃-rich carbonation plots to calciners and returns Ca(OH)₂-rich composition to carbonation plots.

  • CO₂ post-processing system

The CO₂ post-processing system collects CO₂ streams from the grinding system and calciners. CO₂ can be stored underground or used to make “net zero” carbon products, such as CO₂-added concrete and air-to-fuels.

How does Heirloom Direct Air Capture technology work?

Heirloom DAC technology involves two essential steps.

In the initial step, CaCO₃ powders in the carbonation plots are sent into a 900 ºC calciner which is powered by renewable electricity. In the calciner the CaCO₃ decomposes into calcium oxide (CaO) and CO₂ at high temperature for less than 2 hours, as depicted in the diagram below. A high-purity stream of CO₂ directly from the calciners is captured by the CO₂ post-processing system.

Regeneration of sorbents in Heirloom Carbon DAC process
Regeneration of sorbents in Heirloom Carbon DAC process.

In the second step, CaO is hydrated to form Ca(OH)₂. The exothermic nature of the hydration reaction affords an opportunity for heat recovery. Ca(OH)₂ is used as the sorbent in the CO₂ capture to reform the CaCO₃, as shown in the diagram below. A 10 cm thick layer carbonates to 85% in less than 3 days. The consistent fast rate attained by the Heirloom process corresponds to 630 g  CO₂ removed per 1 m² of exposed carbonation area every 2.5 days.

CO2 captured by sorbents in Heirloom Carbon DAC process
CO2 captured by sorbents in Heirloom Carbon DAC process.

Once the material is saturated with captured CO₂, it is sent back to the calciners and decomposed once more to form CaO and CO₂. The process continues cyclically.

After repeated calcination, the pores in the particles of the composition begin to clog, deactivating sorbents. Studies have demonstrated that the reaction capacity of CaO diminishes by greater than half the original capacity after 45 cycles. A grinding process is used to periodically produce new sorbents.

The cost of CO₂ net removed

Using current costs of grid and solar electricity ($0.06 kWh⁻¹), Heirloom has estimated that the cost of CO₂ net removed ranges from $46 – $159 tCO₂⁻¹, while the cost of CO2 produced ranges from $29 – $79 tCO₂⁻¹. Using future cost projections for solar electricity ($0.03 kWh⁻¹) yields $43 – $149 tCO₂⁻¹ net removed and $25 – $77 tCO₂⁻¹ produced. Currently, DAC technologies have been demonstrated on industrial and pilot scales with costs of CO₂ net removed reported between $500 and $600 tCO₂⁻¹.

Heirloom Carbon Patent

  • US20220347650A1 Systems and methods for enhanced weathering and calcining for CO2 removal from air

Heirloom Carbon Technology Applications

Carbon dioxide removal projects

Heirloom’s scalable Direct Air Capture (DAC) technology leverages the natural power of limestone to remove carbon dioxide from the atmosphere. The company’s technology accelerates the natural process of carbon mineralization, where CO₂ from the atmosphere binds to minerals and permanently turns to rock, from years to just a few days.

The company’s approach is also environmentally friendly, with facilities capable of removing 50 tons of CO₂ per square meter and can be sited on non-arable land.

Heirloom is operating the first commercial DAC facility in the United States, which is actively capturing atmospheric CO₂ and sequestering it in concrete through a partnership with CarbonCure Technologies.

Heirloom Carbon Products

The market for Direct Air Capture technology is growing rapidly, and it is expected to reach $6.86 billion by 2029 with a CAGR ( Compound Annual Growth Rate).

Heirloom has conducted many tests and prototypes to validate its direct air capture technology, and it has raised $53 million in a Series A funding round. The company has a facility in Brisbane, California that captures CO₂ from the atmosphere which is then embedded permanently in concrete.

The company also sells carbon credits to allow companies to offset their own CO₂ emissions, and its buyers include Microsoft, Stripe, Shopify, and Klarna. Heirloom’s carbon removal credits will cost less than $100 per ton of CO₂ by 2035.

Heirloom Carbon Funding

Heirloom has raised a total of $54.3M in funding over 4 rounds, including

Their latest funding was raised on Apr 22, 2022 from a Grant round.

The funding types of Heirloom Carbon.
The funding types of Heirloom Carbon.
The cumulative raised funding of Heirloom Carbon.
The cumulative raised funding of Heirloom Carbon.

Heirloom Carbon Investors

Heirloom is funded by 18 investors, including

XPRIZE and Musk Foundation are the most recent investors.

The funding rounds by investors of Heirloom Carbon.
The funding rounds by investors of Heirloom Carbon.

Heirloom Carbon Founder

Shashank Samala and Noah McQueen are Co-Founder.

Heirloom Carbon CEO

Shashank Samala is CEO.

Heirloom Carbon Board Member and Advisor

Alice Newcombe-Ellis is Board Member.

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