How to produce biogas and biochar through the pyrolysis of plants

October 3, 2022

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Carbon neutrality
Clément Georget

Clément Georget

Chief Product Officer

How do we produce biochar and biogas through pyrolysis?

How does a plant pyrolysis work? What is the process?

The process of plant pyrolysis is ultimately quite simple but extremely effective in producing many good things from organic matter with initially low plant waste usage.

The steps are as follows:

  • Harvest organic biomass waste.
  • Dry organic materials.
  • Grind them.
  • Conduct pyrolysis, which is combustion without oxygen.
biochar process explain how it works

The co-products of plant pyrolysis include biochar and biogas but not only

The benefits of exploiting these renewable energies are numerous, resulting in a reduction of greenhouse gas emissions. Many highly useful products can be separated from this process:

  • Biochar : solid carbon stabilized, capable of storing carbon for hundreds of years.
  • Biogas: energy replacing natural gas, but with a significantly lower carbon impact.
  • Bio-oils: low-carbon substitution products usable in various industrial applications.
  • Heat and electricity usable on-site or connectable to a network.

Biogas, a very low-carbon energy and useful against climate change.

By nature, biogas is a low-carbon energy.

The biogas sector fully contributes to the objectives of energy transition for green growth, namely the development of renewable energies, the reduction of greenhouse gas emissions, and the development of a circular economy with the valorization of digestates from methanization in agriculture. The basis of biogas is the valorization of organic waste, and its use presents several immense advantages:

  • The gas used is extracted from a short carbon cycle, which would have been emitted anyway, so its valorization does not emit more GHGs than the current scenario.
  • It replaces a polluting energy source, usually natural gas, with local production and equivalent effect.
  • Finally, burning the methane in biogas transforms it into CO2 (a greenhouse gas 25 times less potent) and therefore reduces the greenhouse effect!

Biogas, an excellent versatile energy for substituting fossil fuels.

Biogas, a clean means of producing energy, can replace several uses:

  • Replace natural gas, very useful in many industrial applications and for heating buildings.
  • Replace mobility fuels by transforming it into bio-LNG.
  • Produce electricity in production peaks, with gas-fired power plants being the most efficient means of responding to a rapid increase in demand.

As shown in the graph below, regardless of the use, biogas remains a low-carbon energy compared to others:

energy biogas

Objective of biogas

The global consumption of biogas, natural gas (often in the form of biomethane), has increased on average by 3.5% per year from 1965 to 2000, while the overall demand for primary energy increased by "only" 2.4% per year. It's an energy that needs to be maximized for its efficiency. The SNBC therefore sets between 30% and 65% the consumption of gas by biogas in 2050, compared to less than 1% today, due to the lack of large-scale installations (the price of natural gas still being "relatively" cheap, even though recent events are pushing for change). The only constraints on biogas lie in the quantity of agricultural waste and available biomass.

Biochar and charcoal, what are the differences?

Biochar: an excellent means of carbon sequestration.

Biochar, this new black gold for the climate, is now positioned as a viable solution to replace charcoal. The term 'biochar' is short for 'bio-charcoal', from the prefix "bio" meaning biological origin and the English word "charcoal." This green coal not only avoids emissions associated with the combustion of non-renewable biomass but also the large amounts of methane (CH4) generated by traditional charcoal production.

Recently, biochar has been used as a means of carbon storage. Indeed, during pyrolysis, carbon is captured and fixed in the form of biochar. Its manufacturing process, by pyrolysis, also allows for the local and decentralized production of renewable energies. Furthermore, carbon is trapped in the soil, so biochar acts as a "carbon sink." However, depending on certain factors, the quality of carbon capture can vary greatly. The main factor to monitor is the production of the raw material. Indeed, the quality of biomass and how it is cultivated are two factors that can modify the sequestration rate.

Characteristics of sustainable biochar

To ensure that biochar is produced sustainably (and not by burning down growing forests, for example), several elements must be taken into account:

  • The raw materials used must be sustainable biomass, ideally biomass waste.
  • The biochar must be stable in the long term to ensure that carbon remains well stored (H2 content vs. carbon content > 0.2).
  • Pyrolysis must be carried out without using only fossil fuels, and with valorization (or at least combustion) of the gases produced during the process.

Objective of biochar

Still marginally used today, although known for millennia, biochar is a major tool in the fight against global warming:

  • The IPCC estimates its potential at 0.66 GtCO2 by 2050 (vs 32GtCO2 emitted in 2020, i.e., 2%).
  • The Drawdown study, listing the 100 major weapons against global warming, even establishes its potential at 2GtCO2 in 2050 (6.25% of the 32GtCO2!).

Naoden: the perfect example of a plant producing both biogas and biochar

Naoden allows industries to replace natural gas - used for heat or electricity - with biogas produced directly on-site, with a simple and modular methanization unit.

Naoden's LCA illustrates its impact: waste valorization has led to a 93% reduction in GHG emissions. This means that for every MWh produced, around 212.3 kgCO2 are avoided. Moreover, Naoden uses digestate to produce biochar, which is a by-product of fermentation. Thus, for every MWh, biochar allows industries to capture 60 kgCO2. Finally, for every MWh of primary energy produced, around 270 kgCO2e are avoided. A single Naoden module produces approximately 2400 MWh each year, while avoiding 2545 tCO2 by 2026 and capturing 700 tCO2 with biochar.

Naoden biogas site

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