Re: Stoves at the Summit

[Harmon Seaver <hseaver@cybershamanix.com>]

Crispin;
  There seems to be something wrong with your website. After getting to the
opening page, the graphics are all missing, and if I click on the boxes where
they should be, it takes me to an error page. They all do the same thing.



On Sun, Sep 08, 2002 at 11:29:05PM +0200, Crispin wrote:
> Dear All and Sundry
> 
> Well, I have been back for a few minutes from the Summit and am wading
> through the junk-filled inbox to sort out the wheat which definitely
> includes the messages below.
> 
> Tom asked:
> 
> >I'd love to see Crispin's stove.
> 
> Well, go the website www.newdawn-engineering.com to the Products section.
> Look under stoves for "Stove burning, boiling and efficiency tests" and then
> click on "Basintuthu Stove Tests" to arrive at
> <stove\Tests\basitests\basitest1.htm>  (that is not the whole URL).
> 
> The one in the top picture is exactly what Dr Agnes Klingshurn from GTZ has
> taken back to Zimbabwe today for pretty comprehensive testing.  It is not
> perfect (which David Hancock was quite insistent it should be) but it will
> give an indication of what a hand-crafted one will do.  Don't be put off by
> the fact it has a small 10 litre can under it.  There are two versions that
> work the same way and one has an ash can under it.  The stove has partial
> primary air pre-heating.  It is a 4 litre pot.  The bakelite handles have
> been removed and a wire loop put on so it can be lifted easily.
> 
> Dr Agnes and Marliss (head of the RSA wood stove program who brought Peter
> Scott in) were justifiably sceptical of the stove when they saw and heard
> about it.  It breaks a lot of 'rules' being taught hither and yon.  An hour
> of cooking was pretty convincing I guess.  At a very low power it is very
> efficient though I will wait for them to say what they think it is.  The
> pre-heating of the air can keep a tiny fire going.  I am formulating a plan
> to do some comprehensive improvement testing of some hardware
> changes/versions to get the primary air firmly under control.  That plan
> should be ready for scrutiny in 90 days.
> 
> Tom adds:
> >1)  I don't think air preheat is necessary or even desirable as
> >it doesn't mix as well with hot gases as dense cold air and
> 
> It allows us to burn pretty crummy fuel, and to pyrolize wood to charcoal
> with a very small fire.  It also obviates the need for insulation or ceramic
> pipes and so on.  Most 'leaking' heat is re-directed into the fire.  At low
> power the bottom half of the stove doesn't reach 60 on the outside inspite
> of being over 600C in the centre.
> 
> >2)  The good thick steel for combustion zone soaks up heat before
> >it can deliver it.  I have been amazed that tin cans (tincanium)seem
> >to last forever, are widely available and easy to machine.
> 
> Ron's report is slightly misleading.  The grate is indeed strong and very
> stiff but it is only 1.2mm thick.  The material is a titanium stabilized
> low-chrome stainless steel called 3CR12 which is made in Middleburg, a town
> between Swaziland and Johannesburg.  It is very strong but not very
> malleable - almost brittle.  It is a little less than 1/2 the price of
> stainless (304L etc).  It is shiny (reflective) with an 'as rolled' finish
> called 2B.  It discolours with high heat and eventually discolours over time
> anyway.  It is welded with a rod called 309L which we use in 1.2mm wire form
> on a MIG welder using an Argon-CO2 blend with a tiny amount of Oxygen in it.
> It will spot-weld.
> 
> Ron commented:
> >It is the best I have seen for sale ($26 now - likely to go lower).
> 
> This is indeed the present price and we will try hard to get it down to $20.
> 
> Dan noted:
> >This looks like a good application for thin rolled iron someday in the
> future.
> 
> The temperatures involved will not allow thin unprotected steel to last
> long.  It will rust through and especially at the welded points where the
> chemistry is a little wonky.  The parts of the stove that do not get touched
> by fire are made from epoxy-coated tin-plated steel.  The 25 litre container
> (285mm dia at the top) with a rolled top lip, seam welded with a water tight
> rolled-seal bottom costs only $2 and I am not going to treat the material at
> all.  It is impossible to make a can of that size and quality for that price
> by any normal means.  We will have to live with what is available unless we
> want to invest literally millions in tooling.
> 
> The "... upper outer baffle for getting higher efficiency for the convective
> transfer to the pot. [Ron]" can be made from something better than the 0,6mm
> galv sheet I used but that was just because I had some around the shop. It
> is very malleable which means making a square lip on a ring is a cinch.  One
> problem we have seen is that at high power the galvanizing melts and runs
> down like wet paint.
> 
> Ron sez: > 4.  Controllable primary air (and power out)...
> 
> The variability of power out is about 1:7 or 1:5 depending on fuel load and
> conditions.  When turning the power down there is a delay during which the
> combustion lower down decreases but gassification continues and the flames
> move up and/or it smokes a little.  After a time (1-3 minutes) the internal
> temps drop and it stabilizes at a lower output.  Separately controllable
> primary and secondary air would probably fix that.  Opening the air vent
> increases the power immediately.
> 
> Dan sez:  > I am concerned that this pail might be galvanized.
> 
> I hope to get it galvanized but that is a difficult option.  Zinc, when and
> if it burns off, I understand, is positively beneficial to people with lung
> infections. The olden day treatment for TB was to get a job in a galvanizing
> plant.  Breathing the zinc fumes would eventually cure or ameliorate the
> condition.  We have terrible TB problems in this region of the world.  The
> problem with zinc protection is that it is sacrificial, not real protection.
> Cadmium plating is a terrible danger in a stove and must be avoided
> completely.
> 
> My conclusion : Thin, uncoated steel will not last in this device.
> 
> Ron sez: >    6.  Looked very clean burning after short time in startup.
> 
> In the test he saw it took about 30 seconds to 'go secondary' which is
> better than average.  The reason was the tiny amount of fuel in it.  A
> couple of hardwood sticks and two square briquettes (90gms total) boiled 1.5
> litres of water and kept it simmering (bubbling) for about 50 minutes.  I
> found the fuel to be a bit smokey initially though it was certainly hard.
> The firebox was a little over filled height-wise (contributing to smoke) but
> no one had a saw and it was too strong to break.  The second demo on
> Saturday(?) used damp newspaper and rained-on wood but apart from taking
> longer to get going it was just fine.
> 
> >The stove went, after a high output pyrolyzing period, into
> >a charcoal burning mode.
> 
> When the gassification is finished the air vents are opened up to allow for
> a faster charcoal burn to maintain the heat output.
> 
> >I haven't yet convinced him that this is worth saving
> 
> That's true!
> 
> >Can Paul Anderson's, or another version of the removable charcoal
> >holding cartridge be used to remove the char and replace with
> >additional wood?
> 
> The present configuration is such that the grate can be lifted out, the
> charcoal removed and some coals swept back inside, more fuel loaded and the
> grate replaced. This is done with a long wire hook (5mm nail wire).  The
> Basintuthu Baking Stove comes with a hook for this purpose.  The grate in
> the baking stove has a loop over the top for lifting it out.  If it is
> important I can put one on the single pot stove grate as well.  The baking
> stove is run for longer at higher power so there is a real chance of the
> grate getting plugged up.  It is occasionally necessary to remove the grate,
> tip it over and remove the unwanted material.  It takes about 1 minutes to
> do this.  Also, it allows one to see that it is well lit before returning it
> to the stove.  It is removed through the larger pot hole directly over the
> grate.
> 
> I apologize for the website not being up to date with the pictures.  There
> are actually pictures of the Tsotso stove on most of the pages.
> 
> Regards to all
> Crispin back home in the Ezulwini Valley
> 
> 
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-- 
Harmon Seaver	
CyberShamanix
http://www.cybershamanix.com

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>
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Other Biomass Stoves Events and Information:
http://www.bioenergy2002.org
http://www.crest.org/articles/static/1/1010424940_7.html Bioenergy
http://www.crest.org/articles/static/1/1011975339_7.html Gasification
http://www.crest.org/articles/static/1/1011975672_7.html Carbon
>
For information about CHAMBERS STOVES
>http://www.repp.org/discussiongroups/resources/stoves/Chambers/Chambers.htm