Here's a few biochar companies you might find interesting:

http://www.biocharsolutions.com/

https://www.biocarbontech.com/

http://blackcarbon.dk/

https://www.carboculture.com/

http://fullcirclebiochar.com/

(list is from AirMiners, index of companies mining carbon from the air, plus lots of other sequestration tech: http://airminers.org)

The tricky thing is that most (possibly all) of these cos are basically dormant. None has production-ready tech.

Interesting! How are you evaluating "dormant"? Curious to know, their sites look fairly active to me, perhaps I missed something.

Yes absolutely. I think that is one of the most promising solutions next to direct-air-capture

Have you checked out Drawdown [0]? Biochar was #72 out of 80 solutions for magnitude of emissions reduction by 2050 emissions. I haven't gone through their numbers, but they found that biochar could displace only 0.81 GT of CO2 equivalent between now and 2050. Compare that to recycled paper (0.90 GT) [1].

[0] http://www.drawdown.org/the-book/ [1] http://www.drawdown.org/solutions-summary-by-rank

Drawdown focuses on use of crop residues as feedstock for biochar. Specifically they cite a figure that represents 50% of the crop residues burned annually as being potentially available for biochar feedstock. For reasons I don’t understand, they ignore forestry waste. It is actually much more efficient to make biochar from forestry residue than crop residue.

Huh. Thanks for the clarification. Have you reached out to them to clarify their thinking here?

What are the efficiency gains of burning forestry waste vs. crop residue? Also, what is the relative size of forestry waste vs crop residue, and how much more/less impact does it have on CO2 displacement by 2050?

I have not reached out to them. Their book was already published so they probably don’t care.

I don’t know the actual difference in efficiency, but from experience I can tell you that:

1) forestry waste is much easier to load into a reactor and handle in an automated way than crop waste. I’ve actually not seen a functional materials handling system for crop residues at the 1 ton per day or greater scale. These are common in forestry waste.

2) Feedstock needs to be bone dry before it will pyrolyze into biochar. It takes more energy to dry crop waste than forestry residue.