If biochar is still in larger chunks after pyrolysis, it may need to be processed into smaller pieces or even into a powder before further uses. There is an ongoing debate in the biochar community as to how far down in size these pieces need to be crushed, and whether or not it is really necessary to further grind them down to a fine powder. Some people think this is not necessary, and that it is fine to use the smaller pieces when applying to soil. Natural processes such as the freeze-thaw cycle and plant root intrusion may already break down the pieces over time.
Typical biochar processing steps after pyrolysis include crushing, screening, adding liquids (such as fertilizer, e.g. urine and microbes, e.g. from compost tea). The Crusher could be an important technology for The Biochar Economy, although it remains to be seen how important.
Proposed Solution: Open Source Biochar Crusher
The proposal is to design and build an open source char 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)
Important Design 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 steel surfaces are involved. This can 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. However, most chars are soft and easy to crush.
- Biochar may be somewhat abrasive.
- Char dust exposure is a problem for human health, and good machine design should minimize it.