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ceramic tip burner help

updated mon 26 jul 04


Ben on sun 25 jul 04

Hi All,
Just finished converting a skutt 1227-3 to fire on low pressure propane. =
Much thanks to Peter Addessi at Summit Kilns for his help on flue =
sizing etc. Being new to firing gas kilns I'm still not confident that =
my burners are performing satisfactorily and would like to resolve it =
before I fire. I am using some older ceramic tip venturi burners that =
do not have an adjustable primary air, just an open cup with a bar =
welded across to thread down on the spud. Otherwise the ceramic venturi =
is identical to Laguna's. I am using #40 orfices and substantially =
oversized everything on the gas supply but... When I light up, the only =
flame I can get, at any pressure from 2" wc to 12"wc, is about 6" of =
lazy blue followed by about 12" of yellow. Is this normal for this type =
of burner? Will it clean up at red heat? Or do I have a structural =
problem somewhere?
I had burner problems on my last conversion too. I finally got a clean =
blue flame out of the MR-750 by going to high pressure a #45 orifice and =
a wad of old kiln elements in the end. I never could get it to work =
right on low pressure.
Any help would be greatly appreciated,

Steven D. Lee on sun 25 jul 04

Make sure that you experiment with how much secondary air is getting
to the burner by placing it 2" from the burner port and then slowly
modifying that distance and see if that would help you get a good
flame. Also, start at one pressure and try to see what it takes to
get a good flame and then make a rough estimate of the square inches
you are allowing for the primary and secondary air and the calculated
btu that you are getting out of the burner. Take this and figure out
the total air the burner is taking in per minute and then hour.

Remember that a propane burner with a # 40 orifice you will get
something like the following:

WC" 3 3.5 4 4.5 7 11
0.098 22576 24384 26068 27649 34485 67087
Gallon hr .246 .266 .30 .302 .377 .73
CU.FT.air /hr 534 582 657 661 826 1599

Fuel/Air Ratio of 20 to 1
For every cu ft of propane you will need 23.86 cu. ft of air

Note that for every one molecule of propane you need five oxygen
molecules. In regular air that means almost 20 to 1 ratio for propane
to air.

remember that the typical properties of propane are as follows:

Formula C3H8
BTU/gal 91,500
BTU/cu. ft. of gas at 60F,
atmospheric pressure 2,520
BTU/lb. of gas 21,560
Range of inflammability: percent
of gas in gas-air mixture 2.15% to 9.60%
Vapor pressure, psig at 60F 92
Vapor pressure, psig at 100F 172
Lbs. per gal. of liquid at 60F,
storage tank pressure 4.23
Specific gravity of liquid at 60F
(water = 1) 0.51
Boiling point of liquid at
atmospheric pressure -44F
Cu. ft. of gas per pound of liquid
(at 60F, atmospheric pressure) 8.59
Cu. ft. of gas per gallon of liquid
(at 60F, atmospheric pressure) 36.5
Specific gravity of gas (air = 1) 1.53

--- In, Ben wrote:
> Hi All,
> Just finished converting a skutt 1227-3 to fire on low pressure

Steven D. Lee on sun 25 jul 04

You can also use the following link to download the excel spreadsheet
to help you figure out the combustion of propane based on orifice size
and air requirements.

Steven D. Lee
SDPottery - The Little Texas Potter
14341 FM 112
Thrall, TX 76578

--- In, Ben wrote:
> Hi All,
> Just finished converting a skutt 1227-3 to fire on low pressure