Instructables

Backyard BBQ Biochar

Picture of Backyard BBQ Biochar
Your beautiful and well maintained lawn can be one of the best carbon sequestration devices in existance. Lawn grass, because of its abundance, captures more ambient CO2 than any existing or proposed technology. The plants in home landscaping are well watered, well fed and well cared for (generally) and grow at optimum rates, which means optimum carbon dioxide uptake. If this captured carbon dioxide can be diverted and sequestered the power of this resource can be realized. Well now it can.

How? By converting your weekly yard waste into biochar using your backyard BBQ. Once your yard waste has been reduced to its native carbon it can be bagged and disposed of ease with the trash, added to your compost heap or buried in that old family Cold War era bomb shelter.

Now that summer is here most of will be mowing the grass and firing up the BBQ. For those of us with a charcoal BBQ the leftover coals can be put to good use. I haven't tried with a gas grill yet, but I will. What we're going to do is make a simple biochar reactor and use the BBQ, some charcoal and a small fan to turn it into biochar.

Here's some helpful hints:
hint #1: Don't be an idiot. Make sure you produce more charcoal than you burn.
hint #2: Check your local burning regulations
hint #3: This stuff is hot, really hot, be careful
 
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jimvandamme2 years ago
According to what I've read about biochar tossed in the garden, the carbon in the soil won't get released for hundreds or thousands of years. Meanwhile, it loosens soil, and soaks up water and nutrients. So it's better than throwing it in a landfill, and more lasting than composting it where it creates methane and complex carbohydrates which will turn into CO2 in a few years.
egbertfitzwilly (author)  jimvandamme2 years ago
I agree its useful in a ground but buried is buried...
Ronyon3 years ago
Your use of a paint can was very instructive.
Thank you for your Instructible.
JohnBonitz4 years ago

Thanks for making this Instructable.  And good for you, for emphasizing the importance of the "energy input vs output" question.

However, please note that there is an additional problem here and that is production of VOCs. This method of charcoal production might NOT be climate-friendly.  Any combustion process that releases un-burned gases will actually exacerbate the greenhouse-effect.  The simple pyrolysis/gasification effect created in this paint-can-on-the-BBQ will release gases called "volatile organic compounds" or VOCs, including methane.  This looks like smoke or fumes, and may be gray or yellowish in color. 

Methane is a gas that is 20 to 25 times more potent than CO2 in trapping heat in the atmosphere.  In other words, the effect of the gases you create while making biochar could exceed the carbon-capture benefit of biochar in soils.

To fix this, you have two options:
1) make certain that any gases you create (i.e., "smoke" or "fumes") are burned or flared, thus reducing the VOCs to CO and CO2 (less potent GHGs than methane).
2) even better, engineer a system to make use of these gases for thermal energy.  Waste-not-want-not!

Cheers!
egbertfitzwilly (author)  JohnBonitz4 years ago
Actually this is a common misconception. Since any materials released by the biomass (either the raw biomass or the fuel) must have come originally from ambient the absolute worst case would be a zero sum game IF all consumed carbon were released back into the atmosphere. However only a tiny percentage of consumed carbon gets re-released (much of which is consumed by the carbon fabrication process), most is retained as complex organic or inorganic compounds.
With all due respect, this is not a misconception, it is good science.  And science I have just this morning re-confirmed with Dr Julie Major of the International Biochar Initiative.  Here is confirmation from another source:
http://biochar.pbworks.com/Gases
"If 3% Methane-CH4 is emitted, then there is more damage done to the atmosphere by increasing the Methane-CH4 content than could ever be recovered, even if all of the carbon from the original biomass could be captured and sequestered."

What you say about 'zero-sum' would be the true IF all VOCs are reduced to CO2 or CO through flaring or total combustion.  Pyrolysis is inherently incomplete combustion, because you are starving the process of oxygen in order to produce char. 

As GHGs come, methane is 20 to 25 times more potent than CO2.  There is no escaping the atmospheric physics.  Incomplete combustion is worse for the climate than any potential benefit from storing carbon in the soil as biochar. 

If you want to help the climate, don't make biochar unless you can be sure to flare the resulting VOCs.
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egbertfitzwilly (author)  JohnBonitz3 years ago
I hear this claim made a great deal but I no one presents any science to support it. Bad science repeated on the internet is still bad science.

Secondly you will note that the gases vent into fire, flaring the methane so that CO2 is emitted (as noted in your references).

Lastly methane breaks down, explosively, in the presence of lightning producing 1M of CO2 for each mole of methane (and H2O). So how 1M of the methane is 20x worse than 1M of CO2 escapes me completely.
dchall85 years ago
I can't be overly positive on this. Sorry. You're burning off carbon brickettes to supposedly capture CO2 from...where again? CO2 is a gas at room temperature. It never will become a black solid at any temperature. What you are doing with this is burning away minerals (including carbon) that would otherwise have been used by the microbes in your soil had you left the clippings in the lawn. You end up with a net loss of carbon to the atmosphere. On the other hand, live grass will absorb CO2 from the air, convert the carbon to sugar (which does not evaporate), and release the oxygen to the air for animals to breathe. To my thinking the best use of grass is to let it get as tall as you can stand it and grow it on every inch of bare ground you have for as much of the year as you can. When you mow it, leave the clippings in place so the soil microbes can decompose the clippings and produce plant food. There's nitrogen in those clippings.
Carbon Dioxide is a gas yes, but carbon its self need not be a gas. The Black matter at the bottom is largely carbon, what is being burned off is largely water. Though I'm dubious about how much you'll sequester using briquettes as fuel.
egbertfitzwilly (author)  steveo_mcg5 years ago
I agree about the need to make sure one produces more charcoal by weight than is consumed, otherwise there's not much point. Although that's not actually hard. The Mark II model is significantly improved, I'll put that up this week...maybe..
egbertfitzwilly (author)  dchall85 years ago
You are correct, the whole point is to create a net loss of carbon to the atmosphere. That would be whole point of this instructable. By taking in CO2 and isolating the carbon for long term storage your lawn becomes a carbon sequestration engine. When the grass clippings are reduced to carbon the carbon portion of the CO2 is isolated and may be permanently sequestered.