Dear Dr. Reed
You raise some very interesting points and issues!
----- Original Message -----
From: "Thomas Reed" <[email protected]>
To: "Discussion of biomasspyrolysis and gasification"
<[email protected]>; "Hugh McLaughlin"
<[email protected]>; "Paul Anderson" <[email protected]>;
"William Ayres" <[email protected]>; "Kathy Nafie" <[email protected]>;
"Jim Fournier" <[email protected]>; "Mukunda HS" <[email protected]>
Sent: Saturday, December 10, 2011 9:34 AM
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
suggestions.
# There have been a number of attempts in the past to define stoves and
gases in the past, sadly with more heat and acrimony, than clarity. I hope
that this attempt will be more fruitful.
<><><>
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".
# The chemical analysis, Higher Heating Value, the tar content, carbon
particle content, and ash content, of "gas that is made in a gasifier that
completely converts wood to a combustible gas" can vary tremendously,
depending on the size and nature of wood fuel used, its moisture content,
hearth loading and the specific design of the gasifier. One could define
wood gas as "W-Gas" but the definition would be generally unhelpful to a
designer who was attempting to design equipment, or a process, to use it.
Consider, for example, the FEMA Gasifier, and the Imbert Gasifier. The FEMA
Gasifier is generally known as a "tar producer, generally not suitable for
engine use," while a well designed and operated Imbert Gasifier can
generally be considered as suitable for producing woodgas of a quality
suitable for fueling an IC engine on a reasonably sustained basis.
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.
Some gasifiers, such as the GEK produced and sold by Allpower Labs, run on
wood, and can produce an "Engine Grade Gas" with no provisions for tar
removal. Their kind of W-Gas has virtually no tar, while te stratified
downdraft gasifiers that I sell produce W-Gas with significant tar
quantities.
<><><><>
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" stoves.
# I believe that in your original work, you coined the term "inverted
downdraft gasifier", which was subsequently clarified as a "top lit up
draft". The "inverted downdraft" gasifier is basically a "stratified
downdraft gasifier", known for its tar producing tendancies, and direct
unsuitability for use fueling engines without subsequent gas cleaning.
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.).
# Would not TLUD gas analysis be virtually identical to the analysis of gas
from a "Stratified downdraft" gasifier, with similar hearth loading, and
feed characteristics?
I propose the name "P-Gas" for the gas made from mostly the cellulose in
this process.
# Given that "Wood" is an intimate mixture of lignin and cellulose, how can
one make gas from the cellulose in the process in a way that it is separate
from the lignin in the process?
# Consider a case where a "Bottom Lit Up Draft" gasifier was fed with pure
cellulose: would the product gas also be labeled "P-Gas" I would propose
that such tarry gases be called "T-Gas", to describe them as "Thermal Gases,
or "HF-Gases", to describe them as "Heating Fuel Gases" This contrasts with
"E-Gas", which is a gas with sufficiently low ash, char, and tar, and a high
enough calorific value to be used as an Engine Gas Fuel"
(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. )
# As far as is known, all the charcoal used in the famous Terra Preta, which
most people seem to wish to duplicate, was "low temperature charcoal". Less
tar, and more absorption capability may, or may not, lead to a superior
Terra Preta.
<><><>
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.
It would indeed be helpful to clarify the situation.
Best wishes,
Kevin Chisholm
Dr Thomas B Reed
The Biomass Energy Foundation
www.Woodgas.com
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