Photos: The technology turning agricultural waste into 'sticky' bio-oil for permanent carbon storage

• The company, Charm, captures thousands of tons of carbon by transforming CO2-rich plant waste into bio-oil before storing it geologically through injection wells.
• Businesses like Microsoft, Shopify, and Stripe are already paying the company 600 dollars for each tonne of carbon it buries underground.
• IE discusses the questions and concerns regarding how reliable, scalable, and economical this approach will prove.

Somewhere at the edge of Kansas, there's a crew of employees from a San Francisco startup called Charm Industrial working in corn fields, transporting branches and bushes to a diesel-powered semi-trailer. Yet, this is no regular clean-up- the company intends to lock away the carbon stored in these crops for thousands to millions of years by turning them into a sticky tar-like mix of biochar and bio-oil.

The approach does make sense, considering how experts describe such a build-up of carbon, in the form of bio-waste, as a supercharged fuel. We know that if left to decay or burn, either naturally from a wildfire or through conventional waste management practices such as incinerators or landfills, the plant waste from the crops will eventually release carbon dioxide into the atmosphere.

Still, while businesses like Microsoft, Shopify, and Stripe are willing to offset their carbon use by compensating Charm with 600 dollars for each tonne of carbon it buries underground, the question remains as to how dependable, scalable, and economical Charm's technique will prove to be.

So, how does Charm's technique work?

Leveraging photosynthesis that captures CO2 in plant biomass

In an interview with Charm, spokesperson Harris Cohn explains to IE that "Charm Industrial removes carbon from the atmosphere by leveraging photosynthesis that captures CO2 in plant biomass."

The company's technique ultimately converts plant biomass into a bio-oil and permanently sequesters (stores) that bio-oil underground in geological storage. Geological storage is basically rock formations located deep underground, which are sealed by impermeable rock layers and geochemical trapping mechanisms (to prevent any escape).

"The agricultural biomass residues (e.g., corn stover, wheat straw) and forestry residues that Charm uses would otherwise decompose or burn," explains Harris Cohn. This results in releasing embodied carbon dioxide into the atmosphere- a problem the startup is trying to solve.

Addressing the misconception that "offsetting" emissions are sufficient to keep climate change to manageable levels

Harris Cohn tells IE that, "these customers [such as Microsoft, Shopify, and Stripe] are actively working to correct the misconception that "offsetting" emissions are sufficient to keep climate change to manageable levels."

Cohn explains to IE that "avoidance offset" pays someone not to emit carbon; therefore, avoidance offsets do not impact the carbon already in our atmosphere.

"We need removals to reduce the amount of carbon in our atmosphere to safe levels," asserts Cohn.

Pyrolysis and 500°C heat break down the biomass

According to the company, Charm uses fast pyrolysis to heat the biomass to around 500°C, which breaks down the biomass into a carbon-rich bio-oil in the absence of oxygen. This liquid is then transported in a truck and injected into rocks for permanent sequestration. "Surprisingly, the carbon value of the bio-oil is higher than the energy value!" Cohn adds.

The specifics of how this biomass is transformed into bio-oil have yet to be revealed. Moreover, a recent report by BBC also shares that the startup did not allow them to record the process, prompting one Youtube user to comment, "where does the energy they are using for their "secret process" come from? Coal?" The company has not disclosed this information.

According to the firm's internal carbon math, as reported in a MIT technology review, the process typically removes 0.85 tonnes of carbon dioxide for every tonne of biomass when the company employs its own pyrolyzers.

Last year, the company announced on its website that the process has safely removed the equivalent of 5,000 tons of CO2- its largest amount of long-term carbon removal to date (for the company). But, this amount may appear tiny compared to the millions of tons of carbon dioxide per year that companies like CarbonCapture Inc. claim to be sucking up.

How much net carbon the process stores, is complicated

The amount of net carbon the process stores depends on what would have occurred to the plant material without human intervention. For instance, crops that are trampled down and trees that are harvested for their wood can both temporarily store carbon.

Charm could also improve its pyrolysis process by adopting a more carbon-neutral transport approach. By opting for diesel trucks to transport the bio-oil, the company essentially generates its own emissions. Could electric-powered trucks improve the math? It is unclear, but it could be intriguing to find out.

On that note (that is, transport), we also don't know how economic it is to move bio-oil between farms to storage locations.

Refilling wells: an approach similar to reverse oil drilling

According to the company website, Charm prepares the bio-oil and then injects it into EPA (Environmental Protection Agency)-regulated injection wells, which are certified for use as industrial wells or salt caverns. Many of these voids in Earth's subsurface have been left behind by oil and gas companies.

In short, the process is similar to reverse oil drilling, with the same infrastructure of pumps, filters, and injection units pumping the bio-oil underground and refilling the wells. Ultimately, the bio-oil sinks and solidifies (hardens) in place for permanent storage.

Plant-based bio-oil is a different chemistry from that's found in salt caverns- will this be feasible on a large scale?

According to Prof. Saeed Salehi, quoted in the MIT technology review, there may not be enough data to say this injection will be 100% safe. Saheli is a petroleum and geological engineering professor specializing in geological carbon storage and well integrity at the University of Oklahoma.

The professor suggests that years of research may be necessary to show that plant-based bio-oil can be securely and permanently sequestered in these spaces. This is because the bio-oil has a different chemistry than the petroleum and natural gas already being stored in salt caverns.

Additionally, numerous questions and concerns about the risk of leakage in geological storage exist. We only need reminding of the many failed carbon capture projects of the past- including the 2.7 billion-dollar carbon capture Salah project in Algeria. Due to worries about the integrity of the seal and strange movements of the trapped carbon dioxide underneath, injection (which had begun in 2004) was suspended in 2011.

While the problems encountered at the Salah project were related to carbon dioxide and not bio-oil, they are still typical issues associated with the use of depleted oil and gas reservoirs. Therefore, they serve as examples of what could also be encountered at the US salt caverns.

Injection wells at scale have induced earthquakes in the past

Other concerns relate to the triggering of earthquakes when carbon sequestering is done at scale- as a University of California Santa Cruz study argues.

Still, in the same MIT tech review, the company asserts that most of its technical effort has been focused on carbon sequestration. This includes analyses to find the subsurface chemistry and geology most suitable for locking away and solidifying the bio-oil.

Charm also highlight on their website how their approach differs from those high volume water injection wells that could result in an induced seismic hazard. This is because Charm injects its bio-oil at much lower volumes and rates.

Competing demands for the crops Charm relies on could be a challenge

Corn farmers actually depend on large quantities of agricultural waste. They plow it under to reduce erosion and return nutrients to the soil or selling it for use as bedding or supplemental feed for cattle. If companies like Charm buy up a lot of these 'leftover', farmers could be encouraged to grow additional crops, further contributing to the problem of global warming.

Therefore, this raises the issue of whether Charm's strategy will be scalable in the long run, since farmers already use and sell a significant amount of their 'waste' crops.

Moreover, companies such as LanzaJet, Schlumberger New Energy, and Chevron already use these crops and crop waste to produce energy. Such a growing demand for corn and similar crops could increase the price of agricultural waste, which would be a challenge for a relatively small company like Charm.

Still, the innovation continues toward carbon-negative steel

Still, the innovation doesn't end with geologically-stored bio-oil for Charm. In fact, it's quite the opposite. The company reveals to IE that it is currently commercializing a technique to gasify the bio-oil. So, from solid to liquid to now gas- how much energy will this process require? We simply don't know the details (yet).

According to Cohn, Charm intends to create a 'syngas stream' that could be used to make carbon-negative steel. We'll keep you posted on that one!