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 this is not necessary, and that it is fine to use the smaller pieces when applying the biochar to soil. Natural processes such as freeze-thaw cycles and plant root intrusion may 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 Crusher could be an important technology for The Biochar Economy, although it is not clear how important.
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 below)
- meatgrinder-type (see second video below)
- ball mill
- roller mill (counter-rotating drums that crush the pieces between them)
- 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 of the machine.
- Biochar consistency will vary with feedstock: char made from dense wood or nut hulls will have different properties than char made from straw. Most chars are soft and easy to crush though.
- Biochar may be somewhat abrasive.