GAS-L: Why won't my gas light?

["Joel Florian" <joflo@yifan.net>]

Dear Tom, Alex, Peter, John and the rest of the list,

Thank you for your contributions to my Science Fair Project.  Last night I
started on my proof of concept gasifier.  Those of you who look down on
"garage mechanics" please give me a chance:  I'm trying to prove that
gasification of sawdust is a viable way to produce heat and power.  This
little Science Fair Project could release at least $10,000 from the local
sawmill to get started on a cogen plant utilizing sawmill waste.  I'd be
interested in quotes from those of you who can make that sort of thing. (off
list, of course)

I was trying to replicate Alex English's "Pyrolyser with Horizontal Burner"
of March 24, 2000.  I made a few modifications to accomodate my needs and
materials.  I need you to tell me which modifications made it not work.

Instead of a 5 gallon metal bucket (I couldn't find one in decent shape) I
used an old 4 gallon army gas tank.  Instead if wood pellets, I substituted
sawdust (approximately 1/4" x 1/4" x 1/8").  For an air inlet, I punched a
hole in the side of the tank and welded a  1" pipe with many 1/8" holes
punched at  intervals (similar to an oven burner) Reduced that down to 1/8"
and put a small valve and gauge on the inlet and a quick disconnect for
compressed air hose.  (too bad I don't have my digital camera yet.)    At
the top I inserted a similar pipe for the gasses to escape.

I filled the bucket 3/4 of the way full with sawdust through the filler cap
(the 3" hole might be fine for gasoline, but it sure is inconvenient for
sawdust) The only way I could get it started was to let a little hiss of air
in the bottom and light it with a propane torch through the filler hole.  (I
guess the 3" hole doesn't let enough oxygen in to support combustion).  I
let it run for a few minutes with the cap off and experimented with varying
the air volume.   That was fun.   If I opened the valve all the way (port in
the valve smaller than 1/8")  I could get a 10 foot flame.  Buring hot like
that, a lot of tiny sparks flew out with the flame (carbon? ash?)  With the
air turned down, I could look inside and  see the what looked like an
incandescent sponge -- some spots were black and others were glowing red and
burrowing into the pile.  So far so good, right?

With some difficulty, I got the cap threaded into the hot gasifier so that
the fumes were directed out of the port I had made at the top.  Fumes is the
right word.  Acrid, irritating smoke filled the shop in about 20 seconds (or
as long as it took me to get the roll up door open and get the behemoth
outside.  But then I couldn't get the fumes to ignite.  I tried varying the
air supply, I tried different sized outlet ports, I tried running the fumes
through a propane torch.  All I ever got was flash  that would usually put
out the propane torch -- that may have just been due to the way I was
holding the torch.   What am I missing?  Is my gas to rich in CO2?  Does it
need to be hot to burn?

Anyway, my primary objective was to build a gasifier that would produce gas
that I could burn 10 or 20 feet away in a propane burner.  If I succeeded in
that objective, I have a couple of old generators  with worn out gas
engines....  If I can't get this gasifier working, I may change gears and
try pyrolysis (ie plug the ports in the tank I made  and put in on top of a
stove so the sawdust cooks in the absence of oxygen)

Please correct me where I'm wrong.  A lot hinges on this experiment.




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