[Terrapreta] Flaring the more potent GHG in the off gas from a charcoal kiln?

[Sean K. Barry]

Hi Andrew,

You say, 99% fixed carbon char with ~15% yield (= ~15% of the original biomass carbon) or 78% fixed carbon char at ~45% yield (= ~35% of the original biomass carbon) ...

Does the production (without flaring) of either material exhaust more high potency GHG than the other?

Un-flared "producer gas" from pyrolysis of wood into charcoal has a constituency like (~50%-N2(inert), ~29%-CO(not GHG), ~14%-H2(not GHG), ~4.5%-CO2, ~2%-CH4, <1%-others)).  Methane (CH4) is the most potent of those GHG in the producer gas.  It and CO2 are the only GHG of any significance.  Assuming your numbers are good, then 15% to 35% of the original biomass carbon is left in the char.  That sounds about right to me, too.  This means, 65% to 85% (you darn near burned it all up!?) of the carbon from the biomass is pyrolyzed and burned, made available as possible carbon in any of the exhaust producer gas.

At most then, 0.02*0.85 = ~1.7% of all the carbon in the original biomass will go into the methane (~2%-CH4) released.  The least carbon into methane would be 0.02*0.65 = ~1.3%.  Okay?  99% fixed carbon char with ~15% yield will release more methane.  That answers the question above.

The global warming potential (GWP) of methane is 62 in the first 20 years, 23 in the first 100.  The GWP of CO2 is 1 for all time.  So, for the first 20 years, 0.017*62 = 105.4%, or 0.013*62 = 80.6% and releasing the un-flared ~2%-CH4 into the atmosphere is as bad as burning (full combustion into CO2) ~81% to ~105% of the original carbon in the biomass.  Then 0.017*23 = 39.1%, or 0.013*23 = 29.9%, and the ~2%-CH4 let into the atmosphere is only as bad as burning up ~30% to 39% of the original biomass carbon.  

So, producing any type of charcoal and NOT FLARING the off gas is bad!  The effect of releasing the only ~2%-CH4 into the atmosphere as a green house gas does go down over time,  but it isn't offset by the reduction in atmospheric carbon that was achieved by burying the charcoal in the soil (for at least the first 100+ years anyway).  It definitely would be creating another problem to NOT flare off the the ~2%-CH4.

However charcoal is produced, the off gas from the kiln must be "flared off".

I backed up your argument with my analysis, Andrew.  My analysis assumes your numbers and my numbers are relatively accurate and that my analysis isn't flawed (any of you can judge that?)  I actually think it could easily be a worse problem, if for instance the producer gas was ~4%-CH4 or ~5%-CH4?!

I am now trying harder (with less amusement for you), to "EDIT YOUR BLOODY IRRELEVANT QUOTES!!!", as my buddy Kurt says.


SKB
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