Biochar Crusher

Problem Statement

After pyrolysis, biochar, especially when made from wood, is often made up of larger chunks. These are often too big for use as a soil amendment and will need to be crushed. There is an ongoing debate in the biochar community as to how far down in size these pieces need to be crushed, and whether it is necessary to further grind pieces down to fine powder or not. A lot of people think it's not necessary, and that it's fine to use the smaller pieces when applying the biochar to soil. Natural processes such as freeze-thaw cycles and plant root intrusion already break down the pieces. Typical biochar processing steps after pyrolysis include crushing, screening, adding liquids (such as fertilizer, e.g. pee and microbes, e.g. from compost tea). The biochar crusher is one of the technologies that enables The Biochar Economy.

Proposed Solution: Open Source Biochar Crusher

The proposal is to design and build an open source biochar crusher (alternative names: pulverizer, grinder). Possible technical approaches are:

• shredder-type (see first video link below)
• meatgrinder-type (see second video link below)
• tamper
• ball mill
• counter-rotating drums that crush the pieces between them (what is that called?)

Important Considerations

• charcoal dust, when mixed with air, can lead to a flammable gas-like mixture. The crushing process can therefore potentially result in a "coal dust explosion" (!), especially when moving metal surfaces are involved. This could be avoided by wetting the biochar before it goes into the crusher, although this may necessitate changes in the design.
• char consistency will vary with feedstock: char made from dense wood or nut hulls will have different properties than char made from straw; that said, most chars are soft and easy to crush
• biochar may be somewhat abrasive

Video collection

• https://youtu.be/2YH1UOI8ulg
• https://youtu.be/Meaaaq7O80Y

Link collection: crush or not?

• To crush or not?
• Appropedia: Corn Cob Charcoal Crusher