Re: Truncated cone basket grates

["Paul S. Anderson" <psanders@ilstu.edu>]

Stovers,

Good description by Crispin.

Only difference I have is that when I close off almost all of the air in 
the lower 2 thirds of the basket grate, I do NOT bottom-light as Crispin 
does.  Instead, I top-light (ala Reed-Larson IDD gasifier) and thereby I do 
not get the smoke that Crispin mentions, nor the pre-heated primary air 
because it comes in from the air-pipe into the bottom of the basket-grate.

Paul

At 07:58 PM 1/5/02 +0200, Crispin wrote:
>Dear Stovers
>
>The nomenclature problem for the grate is recognized.  I have no real
>opinion on it.  What is clear to you?
>
>If you want to make a basket grate and try it out, make a truncated cone
>with a large diameter (the top) of about 135-140mm and a bottom of about
>115mm. The height should be about 250-275mm.  Space the holes in it so that
>the are approximately evenly distributed. Make 60-80 holes with a diameter
>of 7.5mm (a-la-Hancock) or 10.5 (a-la-New Dawn).  The bottom is completely
>open with just enough wire or grate or expanded steel sheet to hold the fuel
>while it is burning.
>
>It has to sit inside a secondary air tube that is very loose, about 145mm in
>diameter and similar height.  Hold it as you will, fill with about 150-250
>grams of small wood and bottom light!  Once it is heated up, it should boil
>a litre of water in under 3 minutes depending on the pot's mass
>size/colour/finish.
>
>You can create a charcoaling grate by placing a large washer cut from sheet
>metal so the bottom hole is reduced to 25-40 in diameter and then drop in a
>sleeve made from a rolled up sheet so that it blocks half or more of the
>holes.
>
>Paul, you might try this so you can block secondary air in portions of the
>grate in an experimental fashion.  The fuel at the bottom, though
>bottom-burning not top-burning, is starved of air and smokes excessively.
>This smoke is burned in the upper section of the grate when mixed with
>pre-heated secondary air.  Substantial charcoal is produced because of a
>lack of primary air.  I do not find this useful.
>
>You can continue to add fuel from the top as long as you only add it up to
>the top of the inner sleeve.  More charcoal can be made in this way.
>Removing the sleeve and washer turns it into a regular stove again.  The
>washer will block the ash from falling out so it will not clear itself like
>a Tsotso or Basintuthu.
>
>One problem I have had with the choked stoves is that if the primary air is
>preheated it is difficult to turn the power down without continuing to
>generate so much wood gas that it lights up when it has left the stove/pot
>area and flames off like an oil rig.  It is impressive but it is not very
>efficient when doing that.  The immediate cause appears to be that heat
>stored in the steel work drives the gassing and as the temperature of the
>incoming air rises significantly due to its decreased velocity, the process
>may even accelerate!  Not what I have in mind.  My cure is to limit the fuel
>content as the main power control mechanism on that layout.
>
>Regards
>Crispin
>
>
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Paul S. Anderson, Ph.D.,  Fulbright Prof. to Mozambique 8/99 - 7/00
Dept of Geography - Geology (Box 4400), Illinois State University
Normal, IL  61790-4400   Voice:  309-438-7360;  FAX:  309-438-5310
E-mail: psanders@ilstu.edu - Internet items: www.ilstu.edu/~psanders


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