[Gasification] "tube in tube" hearth design pictures

[jim mason]

here are some pictures of the previously discussed "tube in tube"
hearth design, finally built and in operation.
http://www.flickr.com/photos/jesshobbs/sets/72157600913638462/

remember, the idea here is a bit of an elaboration on the swedish
inverted V hearth design, trying for a similar "self-insulating with
char" design, but without the need to fabricate the tapered V.  tubes
cut to various lengths, sealed at the bottom with welded rings, seemed
an easier way to get something similar.  actually, it probably has
better insulation in the combustion area than the inverted V hearth,
as there are multi steel walls to prevent convection air flow.  my
anecdotal running of it says "works great", but i have no hard data to
make claims or compare with other designs.  about all i can say
definitively is that it works vastly better than the open firetube
stratified downdraft designs of before.

but after building this, i can no longer claim this is an easy way to
create a well insulated constriction type hearth.  the many rings at
the bottom were not trivial to make.  if one has access to a cnc
plasma or water jet, or just a good hand compass for a plasma cutter
the rings are tolerable to make.  but any free hand circle cutting is
far from easy, and the fit of these rings between the tubes is ratther
precise.

i'm currently bringing the air down from the top, with an adjustable
1.5" pipe and side hole nozzles.  i want to see if the "easy" top air
in scenario is adequate, as it is much easier to adjust for different
combustion zone sizes, as well as easier than the side nozzles
plumbing.

also, i'm interested in adding a venturi pinch in the pipe, using
regular plumbing reducers, at the correct place in the hopper so as to
create tar "recycling" or "scavenging" from the pyrolysis zone, into
the air pipe, and directly into the hot combustion zone.  most tar
recyling i've seen does this with a hopper tap that is rerouted around
to the side air inlets, using a fan to drive it.  seems to me we can
do this with a venturi in the air inlet, which is well self-contained
if we are doing a top down through hopper air in system.  some
experimentation will be needed to get the neck down/up and side
opening in the correct size and location.  but well sized and
positioned, it seems such an air inlet venturi would do much to
scavenge tars as they generate, and force them into the hottest area
of the combustion zone for cracking.

this hearth is now in the cafe racer truck.  photos of the truck are here:
http://www.flickr.com/photos/laughingsquid/sets/72157600218339882/

we are currently making a glass fuel hopper for the top of the
gasifier vessel so one can see the fuel, steam and tar smoke through
the glass.  big metal tanks make little sense to civilians unschooled
in the gasifaction arts.   i'm trying to expose the workings wherever
possible.

jim



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jim mason
website: www.whatiamupto.com
email: jimmason at whatiamupto.com
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current project: mechabolic (http://whatiamupto.com/mechabolic/index.html)