Dear Ron
Quoting "Ronal W. Larson" <[email protected]>:
Tom - see notes below. I have little time for a few more weeks,
but will try to get back to this, if others haven’t already supplied
enough of a response.
On Dec 23, 2013, at 4:36 PM, Tom Miles <[email protected]> wrote:
Ron,
I didn’t mean anything quite so personal. :-/
[RWL1: See next response to Mark Ludlow. I was mostly trying
to get some humor injected - about my own “cult”.
Most of the biochar research has focused on pyrolitic char and not
on combustion or gasification char. There is a clear bias toward
pyrolysis, or low temperature char. Can anyone really say this is
the way that the Amazonians, or anyone else, created the charcoal
that we find in the terra preta soils? Or was it smoldering
combustion, staged combustion (a la Alex English), or a combination
of pyrolysis, gasification and combustion? I know that I have had a
lot of bad slash and straw burns that have left a lot more char on
the ground than ash. Are there “signatures” in the terra preta char
that point specifically to pyrolysis, gasification or combustion?
[RWL2: I just spent half an hour trying to find something
definitive. I found one Ppt by three friends on this topic, but
not enough words to go with the pictures. I will check after Xmas.
I hope someone on this list has looked at efforts to mimic the
Terra Preta soils.
# KC: This seems to be "The Unspoken Elephant in the Room." Just how
did the Terrapretians actually make Terra Preta??? Did they actually
make it on purpose, OR did it just happen, when they disposed of
wastes, either ``jungle wastes`` or ``domestic wastes``? What is the
difference between making "Terra Preta" and the Milpa Agriculture, as
practised in Belize?
It seems clear they did much more than just put
out ash - which seems to have been what the vast majority of
aboriginal slash and burn cultures did.
# KC: The inorganic fraction of the char remaining from "slash and
burn" could be one possible explanation for the presence of charcoal
in the soil.
I favor an argument that the
char came from what happened during and after cooking (If wood is
easy to come by, you can make a lot of char in a 3-stone arrangement.
# KC: Certainly, there was an excess of wood available.... a "jungle
full of wood." However, it was certainly not easily available... there
would be an enormous labour content requirement to cut down trees and
prepare the wood for use as a fuel, with only "Stone Age Implements
and Technology." The ``Amazonian Terrapretians`were no doubt just as
smart and just as lazy as Modern Day Men. Those who have chopped down
a hardwood tree with a sharp axe can appreciate the difficulty of
chopping down jungle trees with a relatively blunt stone age axe.
I have seen one argument for an approach like HTC.
# KC: The possibility of using the nutritious ``black goop`` from the
bottom of the Òxbow Lakes that are very common along the Amazon River
has been suggested as a source of fertiliing nutrients for Terra Preta
on this list in the past, and the concept was received with extreme
disinterest. I would suggest that the ``black goop``was made by the
`LTAHTC Process``, ie, the ``Low Temperature Anaerobic HydroThermal
Carbon Process``
I see biochar production growing in stages. For the time being a
large quantity of char that is sold as Biochar is actually char
from gasification. As biochar markets grow we might expect to find
more pyrolytic char made “for purpose” but now we have some
pyrolitic char and byproducts of gasification (including TLUDs) and
combustion.
[RWL3: I wouldn’t couple the words “TLUDs” and “gasification”.
TLUDs look like pyrolysis to me.
# KC: Also in the past on one of these lists
(Biochar...Gasification... Stoves...) were extensive discussions on
the subject of whether a TLUD was a `Gasifier Stove`or not. The
conclusion at the time seems to have been that the TLUD was indeed a
gasifier, that was close coupled to a stove . Given that gases are
produced in pyrolysis, it would seem fair to accept as a fact that
pyrolysis is a `gasification process.
The “high temperature” gasifier char performs very well and in some
applications better than pyrolytic char. Several studies (and some
commercial producers) have found that conditioning the char through
partially oxidation (to higher temperature) enhances nutrient
retention. These products are for improving soil fertility , not
necessarily to replace activated carbon. So why not consider CO2
gasification as a possible process step?
[RWL4: I need help on this. I am assuming that adding CO2 to
hot char is designed to leave little char. Doesn’t sound like a
major help for producing a biochar.
# KC: The ``Pillar of Agricultural Biochar`` seems to be Terra Preta.
Perhaps someone could provide evidence of some sort showing how the
Amazonian Terrapretians controlled their char making temperatures.
One major producer of char in California uses a downdraft gasifier.
In a downdraft gasifier wood devolatilizes at or above the
oxidation zone. Volatile carbon is oxidized by the air injected
from nozzles to make CO2. The hot CO2 reacts with the char to form
CO and H2. This occurs in the “reduction zone”. The reduction zone
is often shown as a deep bed of carbon but in fact it is usually
only a couple of inches thick. Large chips reduce to powdered char
in less than 2 inches where gas temperatures are 800-900C. The
resultant producer gas is a mixture of this CO from reducing char
and the devolatilized gas. Taking CO2 and reacting it with charcoal
at 800-900C as Purdue has done is not a lot different so the
qualities of the char should be similar.
[RWL5: Still need help (not knowing enough about the term
“gasification”). In downdraft gasifiers, I have been assuming that
the injected air was reacting mostly with the char, not with the
already produced gases. The intent was to get rid of as much char
as possible (and I assume the same for the Purdue researchers). I
understand that Purdue is inputting CO2 and not air (in a second
stage), but the intent in both cases is (I presume) to leave as
little char as possible. I just don’t see how that fits into this
list - interested in getting a lot of char. I understand that part
of the processing is to maximize CO and H2. I’ll try to get back
to this.
# KC: The problem seems to be when those interested in producing
``Biochar`` for Agricultural Purposes get into conflict with those who
want to produce ``Biochar```for ``Climate Change Purposes``, or other
purposes. A clear definition of ``The Various Biochars`` would indeed
be helpful
I think we need to explore all avenues of producing char and energy
1. Slow pyrolysis – 25%-30% char; 30% oil+gas
2. Fast pyrolysis – 15% char; 60% oil
3. Gasification – 5%-25% char; 75%-95% energy
4. Combustion – 1-5% char; 95% heat
[RWL: Tom - the bottom two total near 100%, but not the top
two; can you add some more components?. I am surprised also to see
gasification char as high as 25%; who is getting this high - and
how?.
# KC: There are indeed a lot of different kinds of chars that are
produced by various means, for various purposes, from various
feedstocks, and at various temperatures. It seems that there are still
a lot of ``loose ends`` associated with ``Char``, ``Biochar``, etc.
Adding to this list might be the work of Mike Antal (and
Mantria) with added pressure. Also Cool Planet uses pressure and
catalysts with the term “fractionator”. Retort char (zero oxygen)
could be a little different from your four - all of which involve
some O2?. Maybe same for char made with microwaves (heating from
the inside of particles being different)? Certainly HTC
(hydrothermal carbonization) is very different. Is the approach by
Alex English different from any of these (I think it is close to
slow pyrolysis). Nat Mulcahy with World Stove has a different
approach with no oxygen flowing through the fuel bed. Jim Mason’s
BEK will be called gasification?
# KC: You make a very good case for the need for the IBI to clean up
their definition of ``Biochar``.
I heat my home partly with wood (mostly solar (except when cold
and cloudy), no gas) - and have pulled copious amounts of char out
of my (open front) stove - a lot more than 5%. I believe that has
to be called interrupted combustion - just the same as the whiskey
maker Jack Daniels does - combustion interrupted at the end of the
pyrolysis stage and before much gasification can have occurred. The
difference seems to be whether an O2 molecule can reach a hot char
surface or not - because of still-exiting pyrolysis gases getting
oxidized first (mainly to CO and H2O).
# KC: With all this char being available to you, it would be
interesting to see your comments on tests that you have probably done,
using this kind of char as a soil additive for improving plant growth.
All in all I think it great that there are so many
carbonization approaches - hopefully enough for every combination of
soil and plant species. The big divider will be process
temperature, it seems.
# KC: It would be very interesting to see your comments on which
kinds of chars are best for the various end uses to which the various
chars can be put.
Best wishes, for ``Biochar Clarification`in 2014``.
Kevin
Ron
Tom
From: [email protected] [mailto:[email protected]] On
Behalf Of Ronal W. Larson
Sent: Monday, December 23, 2013 2:53 PM
To: Biochar; Tom Miles
Cc: Crispin Pemberton-Pigott; Gasification-Request
Subject: Re: [biochar] Pine char gasification
Tom etal:
1. I’m not sure I want to accept the “philia” part of this
message (“philia” goes with “abnormal” and pedophilia at one
google site). I found the word agape - but that sounds
presumptuous. But I do admit to being at the non-sensical end of
the char spectrum. Maybe charphilia is apt.
2. I know close to zero about any part of gasification, but I
can understand why one would promote the idea of recycling the CO2
to get more gas (eventually the Purdue group wants liquid, it
seems). But that has to result in less char - and apparently
leaves much higher temperature char. Eventually it is almost all
CO2, for gasification, but I worry that the char produced this
(high temperature) way might only be suited to replace AC =
activated carbon.
3. Since Alex English name came up today, we should note that he
also recycles CO2.
4. The dogma of the cult I am in says more char beats more heat,
gas or liquid, so I will look forward to some proof that is not
correct.
Good luck to the Purdue folk.
Ron
On Dec 23, 2013, at 12:58 PM, Tom Miles <[email protected]> wrote:
Ron,
This work is very important for both the biochar and gasification
lists. Biochar will be produced at the large, or even small, scale
as a co-product of energy (liquid fuels and/or power). The most
efficient way to generate power from the gases and vapors from slow
pyrolysis (50% of the energy) is probably through charcoal
gasification (e.g. run the pyrolysis gases through a charcoal
gasifier). There are commercial systems under development to make
char and power in this way. There are also commercial systems under
development to make liquid fuels through combinations of pyrolysis
and gasification. The char products from these and fast pyrolysis
processes run from 0% to about 15% of fuel input. I don’t know the
fuel or char yield for Cool Planet.
This particular study prepared the char with high temperature (826
C) nitrogen. Wood particles (chips, sawdust) and resultant char
particles in this study are larger than for other char studies. Obs
ervations about BET surface area, particle size and the char
morphology are very interesting. The char morphology looks
different than the SEM images that we typically see. From
gasification and pyrolysis we know that pine carbonizes differently
than hardwood so it is interesting to see the shredded fibrous
appearance of the pine char in this study compared to the neat
geometric structures that we often see, which is probably from
hardwood chars. The authors observe that the macropore volume is
significantly greater than the mesopore or micropore volume of the
char. They observe “numerous wide tunnel protruding into the char
particles. . . [that] may provide pathways for bulk transport of
CO2 into the particle.”
Char conversion numbers are interesting. Only 10-12% of the char
was gasified at 726 C (BET 391 m3/g) while 98-100% was converted at
896 C. Surface area increased with conversion but not much greater
than the 35-47% conversion at 776 C so CO2 gasification could be
used to increase surface area at the expense of half of char (660
m3/g). Meso and micro pore volume doubles at the higher rate but
stays pretty constant above 776 C. Researchers conclude that a
significant proportion of the pore volume is within macro pores
although the majority of the internal surface area is within micro
pores. They point out that the mass loss with surface gasification
occurs within the smaller pores leading to pore widening.
Researchers explain that the char gasification process involves
three steps: (1) adsorption of the gas-phase species to the char
surface, (2) surface reactions, and (3) desorption of the
gasification products from the surface. The latter is the rate
limiting process.
Recycling CO2 from gasification to gasify the char is an
interesting concept that may apply to modifying char properties
(e.g. increase surface area) from pyrolysis or recovering energy
(heat, power, syngas) in an industrial setting.
There is very little information about gasification or combustion
chars. Sometimes it helps to step back from our char-philia (and
gaso-phobia) to see what products combined pyrolysis and
gasification can produce.
Tom
RL> don’t see any relevance to the biochar list. (Except if this
work shows that char is more valuable in the ground and/or that an
approach like Cool Planet’s is more efficient.) On the biochar
list, we should want BOTH high value fuels and charcoal.
This Purdue work is all about gasification of char - not
pyrolysis. I am not sure whether the topic is appropriate for
“gasification” either, since that list seems to want gases for
engines, not liquids.
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