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Hello Stovers,<br>
<br>
Spent some time working on the stove last week and things are
beginning to take shape.<br>
<br>
You can see a basic diagram of what I'm working towards on the
attachment to my mail to this group on 30th January.<br>
<br>
Some photos of things as they stand. -<br>
<br>
<a class="moz-txt-link-freetext" href="http://www.b-e-t.org.uk/uploads/images/firebox.jpg">http://www.b-e-t.org.uk/uploads/images/firebox.jpg</a> <br>
<br>
shows the ceramic lined combustion area. The gases will exit
through the heat exchanger behind this and the fuel hopper will be
to the left. You can just about make out the secondary air inlet
here in the middle of the back wall, just above the ceramic block -
the air will be flowing in through the box section you can see
running across from the left through the fuel hopper. This runs
across and then down to where the air will exit into the firebox.
This box is 20mm x 20mm ID.<br>
<br>
***** Do people think this should this provide sufficient secondary
air or should I put another similar secondary inlet in the front of
the burner??? *****<br>
<br>
The ceramic blocks are not fitted correctly in this picture.
Currently aiming for a 'throat' area of 10cm x 10cm<br>
<br>
<a class="moz-txt-link-freetext" href="http://www.b-e-t.org.uk/uploads/images/choke.jpg">http://www.b-e-t.org.uk/uploads/images/choke.jpg</a><br>
<br>
this shows the choke / bleed hole in the heat exchanger section. We
decided to make a sliding 'door' in channels that can be moved
(between burns, by reaching down into the burner after lifting away
the flue) and then wedged or welded into place when set right. With
this 'door' wide open the bleed hole is 5cm x 10cm<br>
<br>
<a class="moz-txt-link-freetext" href="http://www.b-e-t.org.uk/uploads/images/top.jpg">http://www.b-e-t.org.uk/uploads/images/top.jpg</a><br>
<br>
Finally a poorly focussed top view that shows a bit more of the
layout.<br>
<br>
We decided to make the hopper smaller than on the diagram - if I
remember correctly 20cm x 25cm.<br>
<br>
My friend had a grate from an old coal stove that appeared to be a
suitable size and we intend to use - from memory this grate is
approx 15cm x 20cm. Thinking of having the 15cm side in front of
the 10cm throat through into the combustion area.<br>
<br>
If anyone has got any comments/ideas I'm hoping to get some more
work done on the stove tomorrow (if I can correctly diagnose a
spluttering Mitsubishi diesel engine today)<br>
<br>
Also I had some questions below, to which some answers would help
guide the construction process.<br>
<br>
Best<br>
<br>
Darren<br>
<br>
On 30/01/2011 00:31, Darren Hill wrote:
<blockquote cite="mid:4D44B15C.6040506@vegburner.co.uk" type="cite">
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Hello Crispin,<br>
<br>
Thanks very much, once again for the detailed response...
responses and a few more questions in your text.... Also latest
design attached.<br>
<br>
On 29/01/2011 04:10, Crispin Pemberton-Pigott wrote:
<blockquote cite="mid:009501cbbf6a$768afd50$63a0f7f0$@gmail.com"
type="cite">
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<div class="WordSection1">
<p class="MsoNormal"><span style="font-size: 11pt;
font-family: "Calibri","sans-serif";
color: rgb(31, 73, 125);">Dear Darren<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 11pt;
font-family: "Calibri","sans-serif";
color: rgb(31, 73, 125);"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size: 11pt;
font-family: "Calibri","sans-serif";
color: rgb(31, 73, 125);">Based on the hopper size, and
presuming you have about 4 metres of chimney, </span></p>
</div>
</blockquote>
<br>
If the chimney was shorter what would be the effect? I know less
draft but how would that effect the fire in practical operation?
difficulty lighting? <br>
<br>
<blockquote cite="mid:009501cbbf6a$768afd50$63a0f7f0$@gmail.com"
type="cite">
<div class="WordSection1">
<p class="MsoNormal"><span style="font-size: 11pt;
font-family: "Calibri","sans-serif";
color: rgb(31, 73, 125);">that size is probably going to
be enough air to heat a home. Do you have a kW rating in
mind? I think you should be able to get 40 kW from it. Do
you want that much?</span></p>
</div>
</blockquote>
<br>
No - 4kw would be enough most of the time!! I picked the stove
dimensions in a fairly arbitrary way - what felt right (based upon
?) + the space I have available. I'm happy to modify to suit. <br>
<br>
<blockquote cite="mid:009501cbbf6a$768afd50$63a0f7f0$@gmail.com"
type="cite">
<div class="WordSection1">
<p class="MsoNormal"><span style="font-size: 11pt;
font-family: "Calibri","sans-serif";
color: rgb(31, 73, 125);"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 11pt;
font-family: "Calibri","sans-serif";
color: rgb(31, 73, 125);"><o:p> </o:p></span></p>
<p class="MsoNormal"><b><span style="font-size: 10pt;
font-family: "Tahoma","sans-serif";
color: windowtext;" lang="EN-US">>></span></b><span
style="font-size: 11pt; font-family:
"Calibri","sans-serif";">The area of
the hole should be about 30 x 120mm.</span><o:p></o:p></p>
<p class="MsoNormal"><br>
The primary air hole should be 30x120mm? With a valve so
its adjustable?<br>
<br>
<span style="font-size: 11pt; font-family:
"Calibri","sans-serif"; color: rgb(31,
73, 125);"> The hopper should have no air leaks into it at
all. I hope you saw the stove from Eastern Canada that
Kevin passed around. That top was good – it had a woven
seal.</span></p>
</div>
</blockquote>
My friends has been constructing fire-in-a-metal-box stoves for
some years and most of her customers have wanted air tight stoves
that they can fuel-up and then shut-down so that they are still
alight in the morning. Shes got plenty experience making air
tight doors<br>
<blockquote cite="mid:009501cbbf6a$768afd50$63a0f7f0$@gmail.com"
type="cite">
<div class="WordSection1">
<p class="MsoNormal"><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size: 11pt;
font-family: "Calibri","sans-serif";
color: rgb(31, 73, 125);"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size: 11pt;
font-family: "Calibri","sans-serif";
color: rgb(31, 73, 125);">>></span><span
style="font-size: 11pt; font-family:
"Calibri","sans-serif";">Lastly,
constrain the entrance into the combustion area (where the
secondary air enters) to about 1/3 of the area of the
hopper. Keep it square-ish, definitely not long and thin
as is often seen in furnaces. </span><o:p></o:p></p>
<p class="MsoNormal"><br>
<span style="color: rgb(31, 73, 125);">></span>You mean
the 'throat' from hopper (A) to combustion area (B). Third
of the hopper width <span style="color: rgb(31, 73, 125);">></span>would
be about 7cm. 7x7 then?<br>
<br>
<span style="font-size: 11pt; font-family:
"Calibri","sans-serif"; color: rgb(31,
73, 125);">No, a third of the area, not a third of the
dimension. If you have 20 x 30 cm = 600 cm^2 then 1/3 =
200 cm^2 = about 140 x 140. My little model says 14.5 x
14.5 but that is a bit big, just looking at it (subjective
opinion). If you only want 20 kW, meaning a max of 20 and
sometimes 4, make the constriction smaller, say 100 x
100mm. That constriction is perhaps 100 to 125mm above the
lower end of the grate, just as you drew it.<br>
</span></p>
</div>
</blockquote>
<br>
I dont need anything like the KW ratings you are suggesting here.
The 20x30 hopper was as big as I thought I could get away with in
the space I have available. I was thinking of the amount of fuel
I could fit in the hopper and the time it could burn between
refuelling. I think 4 kw output would be fine for me, possibly a
bit more occasionally. <br>
<br>
Am I better reducing dimensions more than we are talking here?<br>
Throat?<br>
Hopper area? -which I guess is also the grate area? - or do I not
want the entire floor of the hopper to also be a grate?<br>
<br>
<blockquote cite="mid:009501cbbf6a$768afd50$63a0f7f0$@gmail.com"
type="cite">
<div class="WordSection1"><span style="font-size: 11pt;
font-family: "Calibri","sans-serif";
color: rgb(31, 73, 125);"><o:p></o:p></span>
<p class="MsoNormal"><span style="font-size: 11pt;
font-family: "Calibri","sans-serif";
color: rgb(31, 73, 125);"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size: 11pt;
font-family: "Calibri","sans-serif";
color: rgb(31, 73, 125);">About the bricks, you can use
any bricks. Go for the hardest, strongest bricks you can
find, if you can’t get genuine low thermal expansion
materials. Put them in a way so that when they crack they
don’t fall out of place.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 11pt;
font-family: "Calibri","sans-serif";
color: rgb(31, 73, 125);"><o:p> <br>
</o:p></span></p>
</div>
</blockquote>
My friend has a few spare bricks bricks she 'rescued' from a
disused cement kiln - shes got some in the bottom of her coke
fired blacksmiths forge and they've not cracked yet.<br>
<br>
<div class="moz-text-plain" wrap="true" style="font-family:
-moz-fixed; font-size: 24px;" lang="x-western">
<pre wrap="">Actually I should have mentioned something before about the termination of
the grate on the left (lower) end.
It really should extend farther under the combustion area. The grate will
never really get covered by ash and char, so it lets air enter the gas
stream at the bottom end (part of the secondary air not coming through the
secondary air port I mentioned before).
>>>Changed on image. Far enough??
I like the angle shown. We made it movable perhaps 15-20 mm left-right by an
external ring (which can be hooked and moved by a lot of convenient tools).
>>> Is this to loosed up the coal? Is this necessary/advantageous for a wood stove?
The divider between the combustion chamber and the hopper will get really
hot.
>>> I'm going to try to use Ceramic blocks.
There is a stove called the Kitchen King made in Pretoria that uses a
similar secondary air entry method but places it as the hopper/fire divider,
passing the air into the gas stream as it goes under the divider. The
advantage is that the part gets really hot but remains an 'air cooled' part
= longer life.
>>> If for some reason I cant make the blocks work I'll try something like this, although I guess from your previous descriptions it would be best if the secondary air did not join the combustion here. I could have it ducted through this part though.
Oh, yeah, what is your chimney height?
>>> As short as I can get away with.... Will insulated stack pipe help? Thinner?
Thanks again
Darren
</pre>
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<pre wrap="">
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