Jon Bares-Anderson on mon 11 aug 97
Mel I worked with Mike Mickkelson at Grain Bin Pottery for two years. The
first year I was there we built a salt kiln and our first firing we were
unable to get to temperature, we got up to maybe a good bisque and that took
a long time. We decided that we needed around 40% more propane to get the
desired results so since I was the mathematition on this project I decided
that to get our 40% increase in BTU's we would increase the diameter of the
orifice by 40%. When we were able to finally turn up the gas to high after
the warm up we were convinced that we had something with our fine tuning
,those four squirrel cage burners were just humming. The kiln just shot up
to cone 6 but there it stayed to our dismay, couldn't seem to get another
degree out of it. I started checking everything, the pipes seemed a little
frosty. I went outside to check the tank and holy cow the 500 lb tank must
of had 2000 lbs of ice over the top of it on a 80 deg day.
We decided that we didn't have enough surface area on the tanks so we
ordered another 500 lb. tank, that gave us another cone and only 1000 lbs
of ice so we thought we were going in the right direction. Then we decided
that the line from the tank to the kiln was to long or maybe to small a
diameter so Mike found out about a preheater that you connect the propane
line to warm the gas up high enough to
to stop the cold temperature restriction. We got another cone out of that
but what a cone.
Even though our frosty little operation would'nt go to cone 10 the flame
temperature was awesome , melted the bagwall and all the interior bricks
inside the burner ports and the bricks above the burner ports were bowed in
6 inches before the propane flow temperature slowed the heat rate down.
For the good people that are in the mathematical handicapped zone with
me, when you increase the diameter of a orifice by 40% and you square things
up and throw pie at it.The orifice ends up producing twice the BTU as
before.
Expensive lesson but boy did that kiln sing.
Jon Anderson
WardBurner@aol.com on tue 12 aug 97
Jon,
In a message dated 8/11/97 12:16:16 PM, you wrote:
<me, when you increase the diameter of a orifice by 40% and you square things
up and throw pie at it.The orifice ends up producing twice the BTU as
before.>>
You ain't kidding....The critical size of the orifice as related to BTU
output is the area of the hole not the diameter. If you double the area, you
double the output. Everyone remember your Junior High math; Pie-R-Squared
(3.14 x radius x radius = area. This is easily figured out with fractional
drill bits, but if you use numbered or lettered drill bits, you'll need to
give the burner manufacturer or a pointy headed math geek like me a call to
determine the area.
The part of the equation dealing with orfice size/gas type is a linear
equation. That's a big word meaning straight multiplication and division. The
other side of the equation that deals with pressure/specific gas gravity is
quadratic. This means is involves a square root. With a square root, doubling
the root (pressure) will NOT double the output.
From a practical point this means that messing around with your orifice can
produce big results, some of them unpleasant. Screwing around with your
pressure will not make big changes in output unless you increase/decrease by
many factors. It takes a four fold increase in pressure to double the output.
Hope this helps. For a more detailed explaination, folks can refer to my
article,"The Mysterious Hole" in the May '95 Ceramics Monthly. Hey, it's even
got drawings!
If you have specific questions about orifices, feel free to give me a call...
Marc Ward
Ward Burner Systems
PO Box 333
Dandridge, TN 37725
USA
423.397.2914 voice
423.397.1253 fax
wardburner@aol.com
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