[Stoves] Edinburgh biochar

ajheggie at gmail.com ajheggie at gmail.com
Sat May 28 07:22:22 CDT 2011


On Friday 27 May 2011 14:46:25 Ron Larson wrote:
>
>
>     [RWL -  This last (few negatives) is very good news.  (Alex means
> Alex English?) 

Yes Alex English in Ontario, he's a plantsman as well as a pyromaniac ;-)

> I understand the issue with 'soil-speak'. I have looked 
> up a lot of strange words.]

I left one extremely important bit out, The American guy that is working 
at a Welsh University had access to some Carbon14 data from Rothamsted, 
where they have some trials running for over 100 years. Apparently there 
is no "priming" ( which I take to mean causing or catalysing CO2 release 
from soil organic carbon) of the long lived element of SOM, the humic 
fraction, when biochar is used, so biochar does not affect this very long 
lived SOM.

It looks like we are going to see a lot more results as the non-fixed 
portion of biochar degrades and then effects will only be related to 
fixed carbon char. Lehman pointed out the CEC potential of biochar has 
not been seen yet as it takes much longer to develop.

>
>        [RWL-  I believe Biochar to be superior to burial, though,
> because of the out year benefits possible.  Same comment re last
> sentence re lost energy in next paragraph.  Sorry to lose energy value
> when you create Biochar - but we get more energy back in out-years (if
> done right).  Too few get this.

I agree but for a quick fix...

Anyway if humanity is here for the long game it begins to look like from a 
sequestration perspective on the 100 year plus scale a higher temperature 
char may be better, which means you forego less energy in the conversion 
in an energy recovery combined biochar plant.
>
> > The interesting points were the life of the labile or non fixed
> > carbon portions of the char ( tars etc) this varied for 2-500 years
> > but the fixed char potentially thousands of years. There will be
> > interesting studies to do with how their labile portions contribute
> > to the biochar effect ( they are touted as food for bugs) compared
> > with the long term benefit of fixed carbon. Also the business of how
> > high a temperature to char at, essentially the fixed carbon of a
> > woodchar sample is always ~15% no matter what the pyrolysis
> > temperature and it will be less for feedstocks with low lignin.
>
>     [RWL -  This last sentence doesn't sound right.  Can you clarify
> fixed?]

See above also but basically if you make biochar with wood we know the 
total carbon content decreases with the temperature of reaction, However 
at the lower temperatures the char consists of a carbon portion ( mostly 
contributed by the lignin fraction) and higher temperature resisting tars 
plus a small amount of tars that have been cracked to sooty particles 
deposited inside the char ( this is why charring large sections has a 
higher yield than smaller where the volatiles vent before they can inter 
react). As the temperature increases the tar portions continue to 
pyrolyse ( split) and be given off. In a simple system, like a stove, 
these higher temperatures will not be reached and the small sections of 
wood will not retain the vapours within the wood particles for much 
secondary reactions. Also as the temperature increases the fractions of 
the wood that were chainlike molecules of hemicellulose and cellulose 
morph into carbon rings. I saw the term turbostratified used but it still 
looks much the same as I thought previously, instead of amorphous carbon 
the "turbostratified" carbon has formed into non cohesive clumps of 
graphene like groupings of a few carbon rings [1]. I think this may be 
what is happening in a hot sooty secondary flame. We know from the mishap 
at Windscale that graphite ( sheets of graphene stacked on top of each 
other) resists oxidation to quite high temperature,  and that even 
diamond morphs to graphite before it burns (I think my brother said 
heated to 400C and dropped into liquid oxygen was the lowest temperature  
he had burned diamond but he's richer than I ;-)). Back to the point 
before mission creep: it is only this fixed carbon proportion ( probably 
plus the turbo stratified soot) that is very long term in the surface 
layers of soil, because bugs attack the higher tars. Note even at the 
highest temperatures there is always some O and H associated with the 
fixed carbon. So after some years the low temperature char has been 
eroded to  just its fixed carbon element and this is then the same amount 
as if the high temperature char had been deposited and aged similarly.

My thought on this is that chars made from lower lignin feedstock will not 
have a high proportion of fixed carbon and will be subject to attrition 
by bugs and air over time. Presumably not the case at great depths of 
undisturbed soil.

For stoves I cannot see an immediate way around but on the more technical 
side it would be possible to combine high pressure and high temperature 
to force cracking, turbostratification and deposition of volatile 
fractions from lignin, hemicellulose and cellulose.

> >
> > Now here is the nub for me, all talk of rewarding the subsistance
> > farmers over the whole globe for sequestrating the emissions of us
> > rich few are gone. Talks of offsets and carbon trading was missing,
> > chiefly because this was a gathering of soil scientists.
>
>       [RWL -  And maybe no abstracts sent in.  And it's been said
> before, largely.  But agreed we have to keep talking about the
> ethics/morals and urgency and the validity and need for funding.]

For the purposes of this [stoves] list it is the most likely means by 
which a subsistence farmer ( what proportion of the 2billion people 
cooking with biomass are directly involved in farming?) could 
economically benefit from biochar. I guess an exception would be a poor 
soil ( ferosol was mentioned as an acid depleted soil that benefits) and 
lots of stranded residues which would normally largely be incinerated in 
situ but could be charred instead. I wonder if the economic benefit would 
cover the operating cost in the absence of a cash incentive from someone.

>
> > The delegate who stated that we would reach a global population of 9
> > billion and a temperature rise of 4C was not doubted.

I missed out that he seemed to imply the 385 ppm CO2 concentration 
mentioned at Newcastle two years ago had moved up a surprising number of 
parts but I forget the figure.

>
> > There was little at the conference to upset my friend Kevin C and
> > nothing to worry people that don't see a problem with
> > anthropologically enhanced CO2 levels in the atmosphere.
>
>    [RWL - Hmm.  That's OK, as long as they believe and act
> differently.]

It's plain to me that at an individual  level wealthy people will not 
unless they believe the CO2 level should be reduced, most of my wealthy 
acquaintance, and I work for one who is energy profligate, either deny 
there is a problem, assume they will afford to find a means of living 
with the consequences, because the mitigation is too expensive, or trust 
in their deity. Governments are making plans but is it just lip service? 
Poorer peoples tend not to have large carbon footprints and I don't wish 
poverty on anyone.
>

>     [RWL  -  I fixed most, I hope.  Thanks a lot for picking out some
> items to look for in the video tapes (which are better done than a lot 
> - and can be found by googling "UKBRC").  Ron

Thanks Ron, the sound system went down for the first couple of hours of 
day 2. I cannot simultaneously post to [stoves] and biochar lists.

It looks like IBI are pulling their horns in and not running conferences 
as there are enough national ones coming along, I did feel a bit of a 
pariah amongst the erudite throng and I don't think I was alone amongst 
the elderly interested gents.
>
[1] Another thing I left out was concerns about Polycyclic Aromatic 
Hydrocarbons in the char. It was not clear how speakers considered they 
are formed but this turbo-stratification does seem a route as they are 
compounds of a few joined carbon rings  with oxygen joined at the points 
they would be attached to other carbon rings in a sheet of graphene. The 
presence of PAHs in biochar ( as opposed to smoke I think) increases with 
temperature, so I suspect they are formed in the cracking and 
redeposition. The only significant PAH mentioned was naphthalene ( an 
insecticide used in mothballs I think, it is only 2 benzene rings 
siamesed with oxygen around the outside so possibly formed earliest in 
cracking??). The PAH cited as being the carcinogen e.g. in cigarette 
smoke, benzo(a)pyrene which has 5 rings and presumably takes longer to 
grow, was not in the list as being measurable. PAHs act by forming bonds 
between the two strands of the DNA helix. I think they are only a problem 
if digested and as they are reactive they shouldn't last long in the 
soil, I would like to learn more.

AJH




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