Terra preta: a fuel that could be also carbon negative?
This looks nice enough to make it a fertilizer, but what does this have to be with fuel? Well, the pyrolising process happens to actually produce energy. The chemical reactions that break the cellulose chains results in gasification, giving off hydrogen gas, methane and other flammable gases, as well as CO2 and tars. When tar levels are low, the gases can be used to power an engine. See, for example, the Mechabolic.
Gasification is not a new thing; syngas is obtained with a similar process with coal. Using this process on biomass - creating terra preta and using the released gases - does put some CO2 in the air, but the terra preta will still contain the CO2 the crops captured while growing. When this is then used as a fertilizer to grow more crops, it yields more biomass and then more terra preta. And the whole thing might be carbon negative.
I suppose that there are many things missing from the concept, and even the original author couldn't provide actual data on the carbon capture result of the process. Still, Worldchanging points out there is some government investment in terra preta going on in India. Perhaps they'll be able to tell us.
[Source: World Changing]
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