The things we can do with hydrochar
Hydrothermal carbonization uses ubiquitous wet biomass and turns it into a coal-like substance. But what can we do with this substance in order to achieve a carbon neutral or negative economy?
In the last two newsletters we tackled inputs (carbon, not carbon dioxide) and processes (biochar or hydrochar), but to conceive a carbon-neutral or carbon-negative economy we still have to find uses for our carbonization end product that are economically feasible, scalable, and contribute to a net reduction of carbon emissions.
Luckily hydrothermal carbonization creates a range of outputs, from a substitute brown coal (lignite) via humus to liquid and gaseous fuel substitutes.
Long-term and irreversible sequestration
The ultimate and most pressing goal is to come up with economically feasible, scalable, and decentrally deployable ways to remove carbon once and for all.
Conversion of biomass into difficult-to-degrade / unassailable elementary carbon.
Deep-storage carbon sequestration: We can simply put coal back where it came from, by refilling deep underground mines.
Bioaccumulation of toxic substances in plants, transformation to hydrochar and sequestration by means of deep-storage.
Mid-term and reversible sequestration
Not all carbon sequestration has to be irreversible. In part because we expect irreversible sequestration to be more costly and energy intensive than reversible sequestration strategies. “Mid-term” in this context captures a time frame of some fifty to a few hundred years, similar to the time horizon of a reforestation programme.
Surface sequestration by refilling open pit mines, terraforming (moor reconstruction), and wastewater treatment.
Restoration of farmland by using biochar as a durable soil ameliorant.
Filler for construction and substitute building materials (carbon concrete).
Carbon-neutral fuel substitutes and other immediate uses
The use of hydrothermal carbonization for biofuels as replacement in power plants might be the most well-known and best-research application. After all, the original Bergius process was conceived to create a coal substitute. Other uses include:
Cement production.
Metal production (metallurgical furnaces) e.g. iron.
Steam reforming for hydrogen production.
Upcycling of waste biomass into high-end carbons such as supercapacitors.
Over the next weeks we will spend some time detailing these use cases. The point of this short survey was to show that just like hydrothermal carbonization can take in a wide range of input materials, the outputs can be channeled into numerous uses, from carbon neutral to carbon negative.
While research activity is thriving, it has yet to capture the public imagination. A major step forward would be the establishment of negative carbon credits, going beyond the current cap-and-trade model based on pollution allowances. Key is a reliable tracking of biomass, formation of the hydrochar and sequestration for a defined time to establish valid and tractable proofs of carbon removal.
Further readings
Fang et al “Minireview of potential applications of hydrochar derived from hydrothermal carbonization of biomass” Journal of Industrial & Engineering Chemistry (2018).
Sharma et al “A comprehensive review on hydrothermal carbonization of biomass and its applications” Chemistry Africa (2020).
Masomui et al “Hydrochar: A review on its production technologies and applications” Catalysts (2021).
Zhang et al “Insights into biochar and hydrochar production and applications: A review” Energy (2019).
Don’t forget to follow us on Twitter @hydrochar.
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