Ever since it was determined by present-day scientists that native people incorporated charcoal into soils in the Amazonian Basin for thousands of years to increase soil fertility, biochar has fallen under the spotlight. There are many sites on the internet that are devoted to biochar and a search will get you a great deal of information. Nevertheless, the chief advantages of converting biomass into biochar can be summarized as follows (for more click here).
1. is considered a stable form of carbon in soil that effectively sequesters atmospheric carbon for long periods. (Carbon-negative)
2. in the form of sequestered carbon has a potential value on carbon markets.
3. displaces fossil fuel use as a result of partial combustion of biomass feedstocks.
4. as a soil amendment, helps to improve crop yields and productivity, raise soil pH, and reduce the need for some chemical and fertilizer inputs.
5. helps retain nutrients, thereby inhibiting leaching.
6. is but one product; syngas, bio-oils and energy are other potential products.
7. can be produced in pyrolytic or gasification systems that are scalable in output.
The technology to covert solid carbonaceous feedstocks to gaseous and liquid higher heating value products is well developed. Even so, research continues into refinements that are feedstock-specific. Many corporations and companies are involved and there are numerous products on the market that serve a variety of applications. Systems that produce biochar also have the advantage of dealing well with high-ash fuels because the temperatures in the reaction chamber are low enough to prevent ash sintering or agglomeration. Also, the stream of syngas that is produced following gasification can be cleaned up as necessary before it is used in combustion or bio-oil production. In contrast, combustion in an “excess-air” environment releases pollutants that must be filtered out at the tail–end of the process in order to meet air quality standards.
With all of these points in its favor, what is there not to like? It really comes down to what one’s objectives are. When many of us first became interested in using grass for bioenergy, our overarching principle was that we should squeeze the most useable energy out of our renewable, but finite, energy crops. To do this, we should reduce losses from processing and transportation to a minimum. We should conserve as much of that good photosynthetic chemical energy as possible. I feel that this principle remains valid, but the urgent need to pull carbon out of the atmosphere has risen in importance. This means that it is not enough to merely offset the use of fossil carbon using bioenergy crops; we must also actively sequester carbon in a cost-effective and practical manner.
The future of biochar, it seems to me, hinges on determining its monetary value. How valuable is it as a soil amendment? How valuable will it be on carbon markets? One convenient thing is that there is no ambiguity about how much carbon has been sequestered (unlike other carbon offsets that rely on assumptions and verification schemes). A tonne of biochar is essentially comprised of carbon and ash. If you know the ash content, you know the carbon content. It is directly measurable. What you see is what you get.
When it comes to bio-energy, the value of biochar will determine whether we will try to oxidize all of the photosynthetic carbon for energy or only a fraction, saving the remainder as a hedge against climate change.
This is a big topic. I do not pretend to be an authority on it and welcome comments.