Re: GAS-L: gasifying green wood (fwd)

[Reedtb2@cs.com]

Dear Eric and all Gasifier Afficianados:

(What should we call ourselves, those infected with the Gazogene disease?)

VERY interesting, and the concept of putting logs in a gasifier is new and
non-intuitive to me.  However, I have an open mind and if it works let's look
for an explanation.  

(Why be rational if you can't rationalize?)

Downdraft gasifiers have a full charge of fuel and a small amount of air at
the top.  As the reaction proceeds the fuel goes to 5-10% of the original
mass (? of volume), so could occupy much less diameter, hence the choke on
the Imbert.  We at CPC call this the "virtual taper" of the fuel.  So, the
image of a single tree being converted in a gasifier is just barely possible.
 

The absolute objection in the stratified downdraft is that there is no way
for air to get to the reaction zone.  However, in the Imbert gasifier the
nozzles would be blasting away at the perimeter of the log, reducing it's
diameter like a pencil sharpener.  

Dream on...

Tom Reed



In a message dated 2/17/01 9:12:29 AM Mountain Standard Time,
ericbj@club-internet.fr writes:

I have looked at contemporary cut-away diagrams put out by Imbert's company
and one shows very short lengths of wood, of the nature of blocks, while
another shows longer lengths, maybe 30 cm (12"), but no full length logs.
However, in speaking to my neighbour again this afternoon, he said that, in
his experience, full length - 1 metre or so - logs were inserted in the
gazogènes, the length depending upon the height of the gazogène ; a
practice in line with that mentioned by "renertec" in respect of stationary
equipment.  Maybe the design of gasifier had something to do with it?  
Imbert gasifiers were the most common, and the most highly thought of
(according to my book on Imbert gasifiers) but they were not the only ones.
 My neighbour has no idea of  the internal construction of those he saw.  
But he mentioned again that it was said in those times that "beech produces
the best gas". I realize now that the moisture in wood cannot produce
water-gas (H2 + CO) in an updraught gasifier, since the evaporating water
will be carried away from the hot coals, and not through them.  Imbert
appears to have taken out a patent on a downdraught gasifier in 1933 -
French patent #765369 - so it is not clear to me why his firm continued
making updraught gasifiers. By the way, I see from the book "Le gazogène à
bois Imbert" that in Sweden in the early forties there were several hundred
motorcycles fitted with gazogènes.  There are photographs of them. Am still
trying to contact the person whose family (name: Chevet) built gazogènes.
Joacim Persson a écrit:

> The logs were approximately 10 to 15 cm (4" to 6") in diameter and from
1
> metre to 1 metre 80 (3' to 6') long.  The gasifiers were very tall,
> making possible insertion of long logs, and usually mounted just behind
> the cab. But this was not plain Imbert gasifiers?  The form of the fuel
vessel
allows sticking small logs in it, but I can't imagine the regular Imbert
hearth operate properly with logs. A V-hearth would be even worse I should
think. Later during the war, around 1944 or so, they begun modifying the
Imbert
gasifiers by turning the upper half of the outer mantle into a condenser.
(Actually, this was invented earlier, but for some obscure reason,
ignorance perhaps, or patents? it wasn't put to practise in the early
40's.) Now, if we stick a metre long log into such a gasifier, the log
will be
heated from the lower end, near the hearth, and release water and steam by
the upper end, near the condenser. Why then the gasifier burns sticks in
roughly the same way as when I put green sticks on a camp fire then. ;)
And just like the man says, the fire on a dry log would perhaps spread
across the length of it too fast, while on a damper log the oxidation zone
would stay by the nozzles. I've never heard of small vehicle gasifiers
running on logs before. It
could be something worth developing further. It could also be that they
got
better operation with green logs than dry ones, when using logs, but would
have gotten even better operation with regular block wood. Slicing up logs
to block wood is a lot of work though, particulary if electric circular
saws aren't available (or too expensive to use). Maybe they were
too shorthanded to have block wood as an option in the fuel economy. I'm
sure they must have been aware of that block wood was used elsewehere.
This doesn't explain why `my reference' suggested green birch though. I
tested it, and the gasifier runs on it, but poorly. The fuel consumption
goes up significantly (about doubles), and I can't put too much load on
the
gasifier or I get problems (fuel hangs, poor gas -- have to stop and let
it
rest with the lid open and charify for a while). Green fir is worse
though.
I think that must be the worst possible gasifier fuel there is. But one of
these days... A friend of mine, another gasifier tinkerer, told me some
time ago he had
had a weird dream were I and him were firing up a gasifier we had designed
that ran on full length logs (whole tree sticking out - hilarious). In the
dream, it had some sort of turbine whizzing down the hearth. He thought
that was a big laugh. ;) Wait till he hears of this.