[Gasification] W-Gas and P-Gas defined - and redefined

Tom Miles tmiles at trmiles.com
Sun Dec 11 13:33:16 CST 2011

Useful predictions: gas and char quality


If TLUD gas and char are different than gas and char from updraft or
downdraft gasifiers, or pyrolyzers operated in different conditions it would
be useful to characterize their properties. I would expect the gas from TLUD
to be higher in CO2, N2 and lower in condensable tars, CO and H2 than the
others. If so is it similar to a downdraft gas that simply has a higher
equivalence ratio (say closer to 0.4 than 0.2)? That is useful to know for
designing combustors for the gas for various uses. 


I think the chars have been described as similar to the oxidative chars from
downdraft gasifiers. Is there any consistency with regard to the extent of
carbonization (% fixed carbon) or other physical or chemical qualities of
TLUDD chars compared with the downdraft chars? Are there any distinctive
qualities of TLUD chars from agronomic trials? What do soils and plants
like/dislike about TLUD chars? Do they have more affinity to chemicals than
other chars?


Tom MIles   


From: Hugh McLaughlin [mailto:hmcLaughlin at alternabiocarbon.com] 
Sent: Sunday, December 11, 2011 7:52 AM
To: Tom Miles; Discussion of biomass pyrolysis and gasification; Paul
Anderson; William Ayres; Kathy Nafie; Jim Fournier; Mukunda HS
Cc: Hugh McLaughlin
Subject: RE: [Gasification] W-Gas and P-Gas defined - and redefined



Hello everyone,

At BEF Stove and CHAB camps, we have used the following logic:

Wood burns in two steps: Wood, when heated, converts to char and char, when
exposed to available oxygen and sufficiently hot, converts to ash.

Conditions that convert the wood to char generate "wood gas" and leave
behind the char.

Conditions that convert char to ash generate "char gas" and leave behind

Conditions that do both, by converting wood to char and char to ash in the
same regime, produce both wood gas and char gas - as in most open campfires.

This set of parallels has the advantage that students seem to get is better
than the set of definitions Tom suggested.

It is clear that the gas composition will be a function of both the starting
fuel and the conditions of transformation, which makes me uncomfortable
trying to predict a gas composition from just the conversion process. Making
things worse, the relatively wide range of conditions present within any
class of conversion processes means that a wide range of gas compositions
are anticipated - an essentially impossible to predict.

I am actively trying to get out of the "impossible predictions business".

- Hugh McLaughlin

Hugh McLaughlin
Director of Biocarbon Research
Alterna Biocarbon
P: 250-649-2460
F: 250-563-1880
P. O. Box 2250
Prince George, BC  V2N 2J8

-----Original Message-----
From: Tom Miles [mailto:tmiles at trmiles.com]
Sent: Sat 12/10/2011 6:26 AM
To: 'Discussion of biomass pyrolysis and gasification'; Hugh McLaughlin;
'Paul Anderson'; 'William Ayres'; 'Kathy Nafie'; 'Jim Fournier'; 'Mukunda
Subject: RE: [Gasification] W-Gas and P-Gas defined

Tom Reed,

For a start, has a laboratory characterized the gas and charcoal from
pyrolytic gasification and compared it to "wood gas" or char from pyrolysis
or gasification? I have not seen data plots from a gas analyzer on a TLUD or
full characterization of the gases, tars or chars.


Tom Miles

-----Original Message-----
From: gasification-bounces at lists.bioenergylists.org
[mailto:gasification-bounces at lists.bioenergylists.org] On Behalf Of Thomas
Sent: Saturday, December 10, 2011 5:34 AM
To: Discussion of biomasspyrolysis and gasification; Hugh McLaughlin; Paul
Anderson; William Ayres; Kathy Nafie; Jim Fournier; Mukunda HS
Subject: [Gasification] W-Gas and P-Gas defined

Dear Gasification list

Well defined terminology is fundamental to a discussion of the science and
praxis of any subject.   I am proposing two new words for the different
gases we make.  They will help clarify  discussions we have and will have
here at the "Discussion of biomass pyrolysis and gasification " list. 

These are proposals, and I hope they will spark a discussion of this and
other terms that have grown up helter skelter.  We welcome alternate


WOODGAS is a term I have been using for thirty years.  In German it is
Holzgaz, an exact translation, holz being the German name for wood.  It
refers to the gas made in gasifiers that completely convert wood to
combustible gas, often for use in IC engines.  It is the name of our website
where we sell books on gasification and Woodgas cookstoves.

For this discussion and others, I propose the abbreviation "W-Gas".

Wood is composed of ~20% lignin and ~80% cellulose (cellulose plus
hemicellulose). On heating in the absence of air, the cellulose produces
mostly the Woodgas, while the lignin is converted to charcoal.  Since the
lignin is the principal source of tars in Woodgas (up to 2% by weight of the
wood) tar removal is a very big problem for using W-gas in engInes. 


More recently (starting in 1985)  we have developed a new form of "PYROLYTIC
gasification" in which air is admitted to a dense bed of wood pellets, chips
or sticks, forming an auto pyrolysis zone passing up or down through the bed
and burning a small fraction of the pyrolysis gas to convert the remaining
cellulose to a combustible gas which can be used for cookstoves and charcoal
generation. Paul Anderson has dubbed the stoves "TLUD, Toplit Updraft"

The TLUD gas composition has not been well characterized yet, but I'm hoping
someone will do so soon (possibly me). ( In an attempt to measure tar, I
condensed about 1/2 % of a non sticky grey soot in a four foot X 4"
galvanized stove pipe.).

I propose the name "P-Gas" for the gas made from mostly the cellulose in
this process.

(Incidentally, the charcoal made in this 600-800C process is significantly
different from conventional charcoal, and has much less tar and much higher
absorption properties.  It could be called PG- (PYROLYTIC gasification)
charcoal. )


I hope that this will spark a discussion of this and other terminology used
in this list.  Since Tom Miles is the moderator of this list, I'd like to
appoint him as the final arbiter of terminology for the list.

Dr Thomas B Reed
The Biomass Energy Foundation
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