Carba, an American climate tech company founded in 2021, develops carbon removal technology using low-temperature pyrolysis (torrefaction) to convert biomass waste into biochar, which can then be buried to seal carbon in place for generations. This process is energy neutral, requiring near zero additional power.
Challenges: carbon emissions and biochar carbon removal
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.
Biochar carbon removal
Biochar removes CO₂ from the atmosphere by sequestering carbon.
It begins with plants absorbing atmospheric CO₂ and converting it into biomass during photosynthesis. Waste biomass is converted to a stable solid biochar at high temperatures and in the absence of oxygen.
When biochar is buried underground, it acts as a carbon sink, storing the carbon that was previously in the atmosphere. This long-term carbon storage contributes to the reduction of CO₂ in the atmosphere, helping to mitigate climate change.
In addition to its role in carbon sequestration, biochar improves soil performance by enhancing the retention and diffusion of water and nutrients.
Carba has developed a low-temperature pyrolysis (torrefaction) method for converting biomass waste into biochar. This process involves heating the biomass at a low temperature and transforming cellulose and hemicellulose molecules into a stable solid carbon. The biochar produced is then buried underground, effectively sequestering the carbon for thousands of years. The company’s method is energy neutral, requiring almost no additional energy, and is regarded as the most energy- and material-efficient use of biomass waste.
Carba biochar technology
The diagram below depicts the Carba’s low-temperature torrefaction system.
The torrefaction reactor is ideally located at or near the burial sites. Biomass waste is transported to the location of the torrefaction reactor. Once inside the reactor, the biomass is initially dried, followed by the decomposition and dehydration of the internal biopolymers at 425 ºC, resulting in the production of stable solid carbon. Torrefied carbon is deposited underground to achieve carbon sequestration.
- Carbonaceous feedstock
Carbonaceous feedstocks for low-temperature torrefaction are diverse and widely distributed. Among these feedstocks, lignocellulosic materials, which contain branched lignin polymer integrated with hemicellulose and cellulose, are abundant and easily accessible as waste, amounting to gigatons of potential resources.
These lignocellulosic materials exist in various forms, such as landscape waste (e.g., lawn and brush clippings), agricultural waste (e.g., hulls and shells), industrial waste (e.g., paper packaging), forestry management residues (e.g., branches and wood chips), municipal solid waste (e.g., waste paper), construction and demolition waste, and food waste (e.g., rotting agricultural products).
- Low-temperature torrefaction process
The biomass feedstock is initially dried at a lower temperature. After the drying phase, biomass particles are heated further in the absence of oxygen until biopolymer thermolysis commences. The torrefaction process lasts less than an hour.
The yield of the solid carbon product is determined by the temperature of the biomass during reaction. Controlling the heat transfer into the biomass is crucial, and this can be accomplished through reactor design. To maximize the yield of the solid carbon product, torrefaction reactors are designed with many geometries and mechanisms of biomass flow to rapidly heat biomass particles to temperatures below 425 ºC. Over this temperature, cellulose rapidly fractures and depolymerizes into volatile products.
During torrefaction, biomass loses oxygen and hydrogen and produces a carbon-rich solid (biochar). The biochar has a high degree of unsaturated carbon–carbon bonds and aromaticity. These changes in chemical properties significantly reduce the ability of fungi and bacteria to degrade biochar into volatile products, resulting in a solid that can sequester carbon long-term.
During the torrefaction process, syngas is produced. Syngas exits the reactor and is redirected to an oxidizer to generate heat, which is then transferred back into the reactor.
- Burial of torrefied carbon
Torrefied carbon that is buried underground will be stable for tens of thousands of years.
Carba locates their reactors at or near the burial sites to reduce carbon emissions from transportation, digging, and churning of soil. Appropriate burial sites include existing holes from abandoned mines, aggregate pits, or landfills.
For example, mines are frequently abandoned without reclamation, which can lead to environmental problems. Landfills produce leachate-containing toxins including perfluoroalkyl “forever” chemicals (PFAS), heavy metals, and hydrocarbons. While torrefied carbon is buried in a mine or landslide, it can absorb environmental contaminants.
Carba technology cost
Based on its existing pilot facility design (not disclosed), the average total capital cost for the 60 ton-per-day reactor and ancillary equipment (e.g., hoppers and conveyors) is $675,000.
The cost of generating and burying one ton of CO₂ equivalent is estimated to be $130, which is dominated by the average cost of biomass and delivery ($34 per ton-biomass), diesel ($19.9 per ton-biomass), trucking ($12.8 per ton-biomass), and burial ($11.6 per ton-biomass).
Biochar market for carbon removal
Biochar is a solid material with high levels of carbon, made from feedstock biomass that offers compelling climate benefits. According to the IPCC 6th Assessment Report, soil carbon management in agriculture, like biochar projects, can reduce about 1.8 to 4.1 gigatons/year of CO₂. The market value of biochar for carbon removal can be assessed in terms of its price as a carbon credit and its overall market size.
The global biochar market size was valued at $184.90 million in 2022 and is projected to grow from $204.69 million in 2023 to $365.0 million by 2028 at a CAGR of 12.1% in the 2021-2028 period. In the U.S., the biochar market size was estimated at $125.3 million in 2020 and is expected to expand at a CAGR of 16.8% from 2021 to 2028.
Biochar carbon credits are typically priced in the range of $20+ per mtCO₂e, with some biochar projects selling credits for as high as $110 per mtCO₂e. For example, Puro Earth, a marketplace listing 23 biochar projects, lists prices for biochar-based carbon removal credits ranging from $98 to $200 per mtCO₂e.
Carba provides a CO₂ removal and permanent storage solution for B2B applications. The company’s carbon removal technology collects CO₂ directly from biomass waste, converts the biomass into biochar, and sequesters the carbon underground for thousands of years. This technology is energy neutral, requiring near zero additional power, and is considered the most energy-efficient and material-efficient use of biomass waste.
Demos Capital is the investor.
Andrew Jones is CEO.