How to: make a carbon-negative fuel
LinkMy colleague Jer Faludi has written up the best overview I've yet read about how biochar/gasification systems work. Given that there is at least the theoretical potential here to create a carbon-negative energy source (that is, an energy source that over the course of normal operation actually *removes* carbon dioxide from the atmosphere), the char/gas combo has a lot of people, um, fired up.
(Though it's important to remember that when dealing with complex systems like climate, topsoil and farm subsidies, no bullet is as silver as it looks from afar.)
Snip:
"We've mentioned terra preta before: it's a human-made soil or fertilizer. "Three times richer in nitrogen and phosphorous, and twenty times the carbon of normal soils, terra preta is the legacy of ancient Amazonians who predate Western civilization." Although we don't know how it was made back then, we do know how to make it now: burn biomass (preferably agricultural waste) in a special way that pyrolisizes it, breaking down long hydrocarbon chains like cellulose into shorter, simpler molecules. These simpler molecules are more easily broken down by microbes and plants as food, and bond more easily with key nutrients like nitrogen and phosphorus. This is what makes terra preta such good fertilizer. Because terra preta locks so much carbon in the soil, it's also a form of carbon sequestration that doesn't involve bizarre heroics like pumping CO2 down old mine shafts."
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The 'special process' is to heat the material in the absence of oxygen (or minimal oxygen) to drive off the volatile components and make charcoal.
The volatile components can then be fed into a totally stock gasoline engine and burned to produce energy.
That reaction does produce CO2, but as long as you don't burn the charcoal you have a net reduction in carbon.
This is the 'gasification'/syngas/wood gas/city gas process...see:
http://en.wikipedia.org/wiki/Syngas
It works, and is a proven technology. Early street lights burned 'city gas,' and a million cars ran on it during WWII...
Jim Mason and friends have been doing a lot with this:
http://www.whatiamupto.com/gasification/index.html
and
http://www.whatiamupto.com/mechabolic/index.html
Chicken John is running his truck on it (at least some of the time :-) during his mayoral campaign
http://voteforchicken.com/
It is all stunningly cool stuff.
The quoted summary has some inaccuracies. Terra Preta isn't the same thing as simple soil with charcoal. It is not fertilizer, nor is char, and the char is not broken down by microbes and plants for food.
Simply adding char to soil at rates from 4 to 20 tons per acre (sometimes up to 160 t/a) can increase crop productivity, in some cases up to 4 times. The char helps to improve soil conditions but is not consumed in the process. Research indicates that the char itself is fairly stable in the soil, lasting for hundreds to thousands of years. This is why it is useful as a way to sequester carbon, perhaps making it possible to produce carbon-negative biofuel (but not if you use fossil diesel to deliver the biofuel!)
Amazonian Terra Preta seems to be more than just soil with a high carbon content. There is speculation that the original formula for it's creation involved food scrap, human and/or animal waste and perhaps a particular balance of soil microbes.
You may visit the Terra Preta site hosted by bioenergylists.org for more details.
http://terrapreta.bioenergylists.org/
There are also a couple of good books about Terra Preta soil and research. If you'd like to do some research of your own, be sure to report your results!
One thing I wonder about the terra preta research: why aren't any of them talking with the prairie soil researchers? Prairie earth is black, and part of the reason is that it burned every year (or nearly) for millenia, and it's ludicrously rich in nutrients. Or was.
A few months ago, I asked one of these people (Mike Miller from Argonne) about terra preta, and he was somewhat skeptical about the claims. In his prairie soil research, the carbon from charcoal doesn't get much about 10% of carbon in the soil. In prairies, plants dump a lot of carbon compounds into the soil as part of their normal working processes, so that drowns out the charcoal signal.
In any event, I do find myself wishing that the terra preta group would reach out to other soil researchers more, particularly in North America. The evidence that the Indians burned their lands is overwhelming and massively understudied from a soils point of view. While I believe Dr. Miller's numbers, I find myself wondering if the famous farm soils of the Midwest weren't originally built partially on char. If so, there are a lot of things we can do in the US to restore soil fertility.
Check out this US Carbon Footprint Map, an interactive United States Carbon Footprint Map, illustrating Greenest States to Cities. This site has all sorts of stats on individual State & City energy consumptions, demographics and much more down to your local US City level...
http://www.eredux.com/states/
This is pseudo-science of the worst order. Global warming is being accelerated by the amount of carbon dioxide gas in our atmosphere, and carbon sequestration is a popular short-hand phrase for carbon dioxide sequestration. Burying charcoal in surface soil does not remove CO2 from our environment, CO2 is released when charcoal is made.
Basic high school physics - the principal products of combustion are CO2 and water vapor. There is no free lunch in physics, you don't get to have your cake and eat it too.
Woodgas is very interesting technology, but it is definitely a niche item. Brazil is already way ahead of the rest of the world with ethanol usage, which does not release fossilized CO2 that has already been sequestrated.
Burying charcoal in surface soil does not remove CO2 from our environment, CO2 is released when charcoal is made.
It isn't necessary to burn all of the carbon contained in the plant into CO2. The plants grow, using solar energy (that's your 'free lunch' right there, the solar input) to convert (for example) 1000lbs of atmospheric CO2 into the various carbon compounds making up the plant's structure.
We harvest the plant and burn it, yielding 400lbs of charcoal, about 80% of which is carbon. This is applied to the soil where it stays, reducing total atmospheric carbon by about 300lbs (which represents about 800lbs of CO2) and increasing soil productivity for subsequent crops (for soil that has not yet been treated).
It is important to consider the products of the combustion (wood gas), some of them are potent greenhouse gases (methane, carbon monoxide). These can either be simply flared off or used for heating.
In practice it isn't simple, there are many factors to consider and screwing any of them up can eliminate any gains. For example, if you have to truck in and out material for any distance you may well end up with a positive carbon balance because of fossil fuels used by the trucks.