[Gasification] Cellulose Gas and Biochar option

Evan Marks e.marks at creaf.uab.es
Fri Feb 7 18:37:07 CST 2014

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


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)
Tel (+34) 93 581 4850

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