Re: flash carbonization of biomass

[AJH <andrew.heggie@dtn.ntl.com>]

On Mon, 07 Jan 2002 13:00:38 -0600, "Paul S. Anderson"
<psanders@ilstu.edu> wrote:

>Note:  This refers to the primary combustion of the fuel in the IDD 
>"gasifier" stove.
>
>AND note to Ron and Tom:  Ron prefers the word "pyrolyzer" 
>("PIE-row-lie-zer", right?) instead of "gasifier".  

I think I miss heard you, say that again :-) but I think you've got
it.

My use of the terms is:

Pyrolysis comes from a classical root (Greek I think) where pyro means
fire and lysis means to split. Hence it means to split the biomass, in
this case into char and offgas, by use of fire. I guess thermolysis is
the same with the heat being derived without a fire, in which case a
retort may involve thermolysis? or perhaps they are both the same.

See also electrolysis.

I take gasification to mean the reduction of the solid to gas, again
in this case by heat and chemical reactions, normally the producer and
water gas reactions. Gasification of biomass inevitably involves
pyrolysis, pyrolysis tries to avoid gasification  as it reduces the
char yield.


>>Tom Reed wrote:    However, in order to move DOWN to the next layer  [in 
>>the pyrolisizer, the low flame ] needs to ignite [the next lower material] 
>>and if it is wet it needs additional heat to move down.  Therefore, the 
>>wetter the fuel the more charcoal is also burned.  With bone dry wood we 
>>get 25% charcoal yield;  with 30% moisture we get 5% charcoal yield.  But 
>>the gases for cooking burn remarkably similarly across this range.
>Tom,  I read this to mean that "greener or wetter or lesser quality" fuels 
>will yield the desired gases are about the same, and the only loss is in 
>the reduced yield of charcoal.  (And some people are not interested in the 
>charcoal anyway if we get good heat from the pyrolysis/gasification  process.
>
>In other words, IF the user is stuck with using wet or higher moisture 
>fuel, then "no big problem" with the pyrolysis/gasification process, 
>assuming acceptance that less charcoal is produced.

It is accepted that some moisture in the fuel optimises the burning in
some way. I have done few tests on this but I do not appear to be able
to sustain and idd burn with moisture contents >30%dwb. From Tom's
postings it does seem possible, using forced draught, to cause an idd
burn to consume all its charcoal. My feeling is there should be some
measurable loss of thermal efficiency because of mass flow
implications.
>
>OR:  Do NOT make a fire for the purpose of drying the damp fuel for later 
>burning (in a gasifier stove), because the only gain would be a bigger pile 
>of charcoal.

I have posted previously (and in the light of previous recent postings
I may well be wrong) that I see no drawback in char left at the end of
a burn. Ron feels it is a saleable product, if not, I suggest it can
be recycled into the next burn.
>
>I would think that this is rather important (?).
>
Probably, now I'm off to bed.
AJH


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