[Gasification] Universal tar catalyst

[jim mason]

basic biomass composition question.

the rule of thumb is biomass is 20% fixed carbon and 80% volitiles. i
have never heard of your 30% volitiles number below.  can you clarify
this tom?  coal can range all over the place, but as an approximation
is considered 20% volatiles, 80% fixed carbon.  i assume these are by
weight percentages, but am not sure.

when slow pyrolysed, all the carbon stays, and all the volitiles go,
thus the around 20% yield of charcoal making.  but then again, as
charcoal yield can go up to 25% and higher, maybe the fixed carbon
number is actually  higher.

the figures i have never heard clearly are the relative amounts of
energy in the fixed carbon vs volatiles.  we can easily get an energy
number for combusting the carbon, but what about the volitiles?  they
are a huge mixed collection of things.  i'd imagine experiment would
be the best way to determine the energy available in them.

so, is there a rule of thumb of energy content in biomass carbon vs
volatiles?  assume that all the volatiles come off as primary tars, as
actual fragments of the original biomass, but now as gaseous forms.

my guess is that it is  about 40% energy in fixed C and 60% energy in
volatiles by weight.

jim






On Dec 9, 2007 5:16 PM, Thomas Reed <tombreed at comcast.net> wrote:
> Dear All:
>
> "Tars" sure are the Achilles Heel of biomass gasification,
> since biomass
> is typically >30% volatiles with slow pyrolysis.  Those
> volatiles formed
> the basis of the development of organic chemistry from
> 1850-1950.  There
> are over 50 compounds at greater than 1% in the liquors and
> tars.  Great
> for chemistry but bad for gasification.
>
> In the 1980s many people pursued "catalytic tar destruction"
> and we made
> tests on a number of catalysts while developing our oxygen
> gasifier at
> SERI/NREL.  (Reported in our book "Air-Oxygen Stratified
> Downdraft
> Gasification" at woodgas.com).
>
> Dolomite was claimed by many Europeans to be a great and
> cheap catalyst
> for tar destruction.  It was the bottom of our list of half
> a dozen
> catalysts we tried.  I was very puzzled.  Is European
> Dolomite different
> from US?
>
> I haven't heard much about dolomite recently.
>
> Any updates?
>
> TOM REED          BEF
>
>
>
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-- 
--------------------------------------------------------------------------------
jim mason
website: www.whatiamupto.com
current project: mechabolic (http://www.mechabolic.org)
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