[Gasification] the "tube within tube" hearth design

[Robert Deutsch]

I like your idea a lot.... but hows about you only weld the inner most tube 
to said plate and then fix the rest of the concentric tubes with removable 
tuyauteries?  Then you could take it apart if need be.

R-


----- Original Message ----- 
From: "jim mason" <jimmason at whatiamupto.com>
To: "A Gasification" <gasification at listserv.repp.org>
Sent: Friday, April 27, 2007 1:14 AM
Subject: [Gasification] the "tube within tube" hearth design


> here's an idea i'm working on for an "easy-to-build" hearth design in the
> fixed combustion zone with restriction tradition.  i'm calling it the 
> "tube
> within tube" hearth.  this is offered open source for anyone who might 
> like
> to experiment with it.
>
>
> the idea is to create an imbert type hour glass hearth out of varying 
> sized
> tubes, welded in concentrically above and below a flat restrictor plate.
> somewhat like the sweedish inverted V hearth, but with better insulation
> both above and below the constricition point, and without the tricky cone 
> or
> hourglass fabrication problems.
>
> here's an ascii drawing of the idea.
>
>
>                     |   |
>                     |   |
>                     |   |
>       ________|   |_______
>      |              |   |             |
>      |              |   |             |
>      |              |   |             |
>      |              |   |             |
>      |  |                          |  |
>      |  |  |                     |  |  |
>      |  |  |  |               |  |  |  |
>      |  |  |  |  |          |  |  |  |  |
>      |  |  |  |  |          |  |  |  |  |
>      |--|--|--|--|          |--|--|--|--|
>      |  |  |  |                |  |  |  |
>      |  |  |                     |  |  |
>      |  |                           |  |
>      |  |                           |  |
>      |  |                           |  |
>      |_|_______________| _|
>
>
> when filled and run, the tubes above the restrictor plate will fill with
> char, and thus insulate excellently.  the ones below will not fill with
> char, but will be end plugged with char from the piled reduction zone.
> either way, the "tube within tube" will greatly reduce convective and
> conductive heat flow, thus greatly improving insulation, thus do much to
> keep temps up and correct in the combustion and reduction zones.
>
> this is essentially an elaboration of the hearth zone in the same manner
> that we elaborated the multi wall "tube within tube" gasifier building
> process on the woodgas truck unit.  see
> http://whatiamupto.com/gasification/woodgastruck.html.  i've learned that
> there are many tanks and pipes in the world.  cutting and welding them is
> much easier than more exotic shapes and configuration.
>
> and "tanks within tanks" or "tubes within tubes" produce excellent
> insulation.  i'm finding that insulation is as important as sizing. 
> single
> wall designs with red hot steel exposed to air or relatively cool gases 
> are
> not good.
>
> ==============================
>
> how to build.
>
> to build a "tube within tube" hearth, take a plate, cut the desired hole
> size in the center.  pass the smallest tube through it and weld in place.
> i think the center tube should be between 1 and 3 inches long to insure a
> hotter combustion zone for tar cracking.  but it could also just be a
> "point" restriction like done traditionally, though this will eliminate 
> the
> insulation around the immediate restriction point.  if a short tube is 
> used
> for the center restriction, it should be stainless steel, which you can 
> weld
> to mild steel i recently learned.  one more problem solved.
>
> all the rest of the tubes are welded above and below the constrictor 
> plate.
> weld from the smallest to the largest.  you'll never see the welds again 
> on
> the inside ones, so finish as you go outward.
>
> vary lengths and number of tubes to get the taper you desire.  argue with
> yourself about the relative virtues of taper, insulation and mechanical 
> fuel
> handling above and below the restriction point, and adjust accordingly.
> note that the best insulation will be above the restrictor plate, where 
> the
> char is held between the tubes.  below the restrictor plate char will not
> similarly collect.
>
> i've never seen a hearth done like this, but i think it will work well, 
> and
> it is very buildable.  just tubes welded within tubes.
>
> i'm going to build the first of the above "tube within tube" elaboration 
> for
> a hearth next weekend for our workshop.  if anyone wants to come out and
> join us, good sleeping quarters are arrangeable.
>
> jim
>
>
>
>
> --------------------------------------------------------------------------------
> jim mason
> website: www.whatiamupto.com
> email: jimmason at whatiamupto.com
> current project: mechabolic (http://whatiamupto.com/mechabolic/index.html)
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