In-situ partial reduction of biochar by overlaying a syngas stream

This work focuses on the partial reduction of a hot biochar by a hot syngas coming out of the partial oxidation zone in the Ariane® pyrolysis prototype. The patented geometry of this pyrolyser, with separate pyrolysis and partial oxidation zones, enables easy management of biochar and syngas flows. The aim is to increase the specific surface area of the biochar to achieve more agronomic specifications, while maintaining a high carbon content in the biochar. The experimental implementation of this partial reduction is achieved by adding a partial reduction zone at the bottom of the reactor, enabling direct contact between biochar and syngas. This part now enables biochar and syngas streams to be mixed in a high-temperature zone ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mo>></mml:mo> <mml:msup><mml:mn>500</mml:mn> <mml:mo>∘</mml:mo></mml:msup> <mml:mi>C</mml:mi></mml:mrow> </mml:math> ). The addition of this part increased the specific surface area of the biochar by <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mn>250</mml:mn> <mml:mspace></mml:mspace> <mml:msup><mml:mrow><mml:mi>m</mml:mi></mml:mrow> <mml:mn>2</mml:mn></mml:msup> <mml:mo>/</mml:mo> <mml:mi>g</mml:mi></mml:mrow> </mml:math> and preserved the carbon content of the biochar regardless of the biomass flow rate. Around <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mn>20</mml:mn> <mml:mspace></mml:mspace> <mml:mo>%</mml:mo></mml:mrow> </mml:math> of the carbon in the biochar is consumed by the reduction and transferred from the biochar to the syngas. The syngas is thus enriched in particular in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>H</mml:mi> <mml:mn>2</mml:mn></mml:msub> </mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>C</mml:mi> <mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> </mml:mrow> </mml:math> and depleted in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>C</mml:mi> <mml:msub><mml:mi>H</mml:mi> <mml:mn>4</mml:mn></mml:msub> </mml:mrow> </mml:math> , which opens up a wider range of development opportunities for this gas (biomethane, biohydrogen, biokerosene, cogeneration, etc.). Thanks to this activation method, a better compromise has been achieved (compared with the previous version of the prototype) between quality (specific surface area and carbon content) and quantity of biochar produced (anhydrous yield).