Daniel Rotblatt on thu 28 jan 10
I'm designing a small kiln and have a question about burners. I have a s=
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mall bronze=3D20
casting foundry I have built in my studio (I'm primarily a sculptor), and=
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have built all my=3D20
furnaces and burners. I want to use the burners I use on my furnaces - t=
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hey are high=3D20
pressure naturally aspirated burners (what are often called venturi burne=
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rs). I have built=3D20
several models, the basic one is a 3/4" burner using plans from Ron Reils=
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website - what=3D20
he calls an easy burner (or maybe it's an EZ Burner), and I have made som=
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e from=3D20
Michael Porters book "Gas burners for forges, furnaces and Kilns."=3D20=3D2=
0
To give an idea of how powerful they are, I have a wax burnout kiln I mad=
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e, basically a=3D20
Raku kiln 20" inside diameter and about 2' or more high and I have troubl=
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e keeping the=3D20
temperature below 1500 degrees F (the temp I burnout my molds). One of t=
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hese burners=3D20
will also run my small furnace and melt 30 lbs of bronze in 35-40 minutes=
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- but the=3D20
furnace is small, maybe 12" diam x 15" tall. These burners run on propan=
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e and can run=3D20
all day on a small 20# tank (although I have a 100# tank). They put out =
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about 135,000=3D20
BTU's at medium pressure but can be candled to almost nothing or turned u=
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p to about=3D20
200,000 BTU at 20 lbs pressure (which is what I use them at for my furnac=
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es).
The question is, is anyone familiar with these burners for use in kilns? =
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Since they are=3D20
naturally aspirated, will the negative pressure within the kiln sucking a=
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ir through the=3D20
ports cause the mixture to become too lean? In my furnaces I run a stain=
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less nozzle into=3D20
the furnace and surround it with ceramic blanket - this is not what is do=
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ne with kilns=3D20
where there is an open port and the burner is set back a half inch or so.=
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This seems=3D20
inefficient to me since it lets in a lot of secondary air (this burners a=
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re tuned so they=3D20
need no secondary air).
Lastly the kiln I plan to make will be a downdraft of about 8-10 cu ft lo=
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ading space, IFB=3D20
walls 4.5" thick with additional 2" of ceramic blanket around the outside=
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. I'll be following=3D20
the design concepts in Nil Lou's book - flat top, double venturi flue/chi=
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mney, etc. There=3D20
will be two burners placed horizontally on either side of the chimney.
Thanks for your thoughts
Oh, one other comment - I have read many posts on this site about burners=
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and nozzles -=3D20
the nozzles I use are stainless pipe that has been flared on the end. Te=
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chnically, this=3D20
flare should be a 1:12 flare over about 1.5". The result is that the gas=
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slows down=3D20
(venturi effect) and is held in the end of the flare. This works really =
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well. In my larger=3D20
furnace (which uses a forced air burner) the flare is made with a 3200 de=
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gree F rated=3D20
castable refractory that was cast around the burner tube - works great. =
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I never get=3D20
flashbacks in my venturis unless I bring down the pressure to a fraction =
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of 1 lb (which is=3D20
a 10th of what the operating pressure should be).
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