Tom,
Thanks for that clarification about the hemicelluloses. I should add that I am
somewhat of a practitioner myself, but with (a lot) more experience on the
biochar side. If you would aid me with a couple more doubts:
- When I conduct a volatile matter test at 950 C (the ASTM standard method), is
the fraction lost still only equivalent only to celluloses?
- We are working with a large, i would call it “institutional” TLUD which with
some feedstocks experiences pyrolysis front temperatures of up to 900 C! Are
other (non-cellulostic) fractions being gasified? I am interested in this point
for later effects on carbon stability and effects in the soil, but don’t have
access at the moment to advanced analytical tools to know the answer.
- What about so-called “resins” or heavy-weight compounds from such as from
pine bark (here our pyrolysis front temp. was measured at 825 C)? Do you think
these might remain in/on the char or be volatilised?
Thanks for any thoughts, -EM
Evan
Good question, "Why do TLUDs (Toplit updraft combustors) exclude hemicellulose
and lignin?" First, I think they do burn the hemicellulose along with the
cellulose. Maybe I should have said "celluloses". (The hemicellulose is only
a few % of wood! and is even more volatile than the cellulose. )
You are correct. The cellulose (and hemicellulose) become volatile at about
330C,
C6H10O5 + 1/2 O2 ===> 6 CO + 5 H2 Delta H = (2829 - 3080) -260
ENDOTHERMICl
and generates the gas we see burning in the match (for instance). The same
temperature converts the lignin to charcoal, and if there is a choice between
cellulose (in the next lower layer for TLUDS) and this charcoal, the flame
moves to the cellulose gas from the next layer, leaving the charcoal behind,
protected by the oxygen free gas left from cellulose combustion.
The WWII (Imbert) gasifiers injected air below the unburned wood and above the
charcoal as it formed. This keeps the air in balance, since it too much
charcoal was momentarily consumed, more wood fell in front of the air nozzles
and balance was restored.
<><><>
Today we have an alternate use for the charcoal, Biochar, to improve soil
fertility and reduce global warming, so by consuming only the celluloses, we
produce ~ 20% charcoal from our wood supply. So the TLUD gasifier is a simple
alternative to Imbert. It also produces a gas that is easier to clean for
engine use.
It is surprising that, with all the dependence on wood burning for heat, this
wasn't discovered centuries earlier. If you make a vertical pile of fireplace
logs and light ON TOP, they will burn down at a steady rate, the embers of each
layer lighting the next layer, no matter how high the pile.
Try it, and send comments.
Tom Reed
Dr. Thomas B Reed
280 Hardwick Rd
Barre, MA 01005
508 353 7841
> On Feb 7, 2014, at 4:00 PM, Evan Marks <yarmarks at gmail.com> wrote:
>
> A question to Tom Reed:
>
> Just wanted to get some clarity on the statment that TLUDs only burn
> cellulose. If we are contrasting for instance WWII sytems and TLUDs, and
> therefore limitation to only the cellulose fraction, is the primary
> difference temperature? Why do TLUDs exclude hemicellulose and lignin? Is the
> cellulose fraction equivalent to the volatile fraction?
>
> Thanks, -EM
>
>
>
>
>
> Dear Tom Miles and all
>
> WWII gasification converted all the fuel into a low quality (150Btu/scf) gas
> that required considerable cleanup. Before use in engines.
>
> Now that we recognize the value of biochar as
>
> O. A soil amendment
>
> O. Reducing global warming
>
> a second option is more attractive.
>
> In the TLUD stove and larger (eg 33 gal garbage can) only the cellulose
> burns, giving a cleaner gas
>
> C6H10O5 + 1/2 O2 ===>
> 6O + 5 H2
>
> Plus. biochar for addition to the soil.
--
Evan Marks, PhD
Grup de Protecció i Restauració de Sols
Centre de Recerca Ecològica i d'Aplicacions Forestals
Edifici C, Campus de la UAB
08193, Bellaterra (Cerdanyola del Vallès)
Spain
Tel (+34) 93 581 4850
e.marks[at]creaf.uab.es
www.creaf.uab.es
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