Is there an optimal wood chip size for the Biochar feedstock?

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Lee Swain

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Mar 19, 2018, 10:31:52 AM3/19/18
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Trying to research the whole process.

Can anyone tell me what the premium size of the input wood peices would be for the highest quality/highest value final Biochar product? Or does it not really matter?

Thank you!!

Nando Breiter

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Mar 19, 2018, 10:51:41 AM3/19/18
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Hello Lee,

Sorry, it took me a few days to approve your first message. 

What matters is the consistency of the chip size and density, and also the consistency of the heat distribution methodology. 

As an analogy, when baking cookies, you bake the same size together, and if you have an oven with multiple racks, there is a circulation fan so they all get evenly heated. 

Ideally what you want for soil fertility are carbon molecules with a high percentage of aliphatics, the randomly structured combinations you get of O, H and C when biomass decomposes in soil, humic substances. That's what plant life evolved with and therefore needs. The functional OH functional groups that form on the surfaces of these carbon based molecules provide cation exchange capacity and redox signaling potential, the equivalent of a nervous system between roots and microbial life forms in soil. 

The lower the temperature and shorter the processing time, the more aliphatics and overall carbon is left behind. The higher the temperature and longer the processing time, the less aliphatics and less overall carbon is left behind, and the more carbon is immediately vented to the atmosphere as CO2.

That said, for animal feed, a higher processing temperature is better, more toward activated carbon than a biochar ideal for soil fertility. We would want to ensure all potential residues are driven out the char pores, particular any tars and residual PAH. 

Hope that helps.

Nando



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