[Gasification] W-Gas and P-Gas defined

Sun Dec 11 16:41:31 CST 2011

Dear Dr. Reed

You raise some very interesting points and issues!

----- Original Message ----- 
From: "Thomas Reed" <tombreed2010 at gmail.com>
To: "Discussion of biomasspyrolysis and gasification" 
<gasification at lists.bioenergylists.org>; "Hugh McLaughlin" 
<hmcLaughlin at alternabiocarbon.com>; "Paul Anderson" <psanders at ilstu.edu>; 
"William Ayres" <waayres at gmail.com>; "Kathy Nafie" <kathynafie at yahoo.com>; 
"Jim Fournier" <jim.fournier at gmail.com>; "Mukunda HS" <hsm.cgpl at gmail.com>
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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