Managing propane kiln temperature

[Jimmymmm]

Hi All!

I am building my second small propane fired kiln, and looking for advice on managing the temperature.

I built a ribbon burner for my first kiln, and found that it produced too much heat too quickly. In fact, it ended up melting my first round of pottery when I wasn't watching it closely enough.

Anyway, how are you controlling the amount of heat in your gas fired kiln, and running it at a specific temperature? I'm hoping someone with experience can help save me from further stupidity.

Thanks!

[Bill Kielb]

This is a tough one as we have equipment that spits out how many degrees per hour we are going. Anyone can figure that out with their phone and timing the temperature rise for a minute or two and doing some math but most folks don’t like to do this.  In the process of developing some software for kiln  firing we found it useful to provide a predictor for students. So they learned 400-600 degrees per hour is not usually an issue for their glaze firing of ordinary wares.  Then how much to turn up the gas as time goes by?

best I can stress is the relationship between energy and pressure is fairly exponential, so a 10% change in pressure actually increases heating more like 30%. Small increments are usually the order of the day until you have sufficient experience to know your settings. It becomes more difficult as time goes by and the kiln losses grow exponentially a 10% increase in pressure now only has a 20% net effect. Yikes!

So experience counts, go slow, learn your kiln, every once in a while check your rate per hour so you have a better sense of how fast you are going.

[Jimmymmm]

Great feedback! 

I realize that my current setup doesn't have the small increments you mentioned. Each small change actually has a much larger impact than expected. I need to rethink this as I require both granular inputs and a very high max temperature. 

I think a ribbon burner may be too much for this application. I love the heat and efficiency, but it seems to produce too much heat for the level of control I need. I'll do some research around the formulas you mentioned and see what I can figure out. 

Thanks again!

[Bill Kielb]

Give me a day or so and I will post some data from one of the 16 cuft  gas kilns. They are 800,000 btu and the data is recorded every fifteen minutes. It will give you an idea of the gas increments, and corresponding rate per hour increments. This may help you with sizing.  You mentioned your burner but I have no idea how many BTU and what size your kiln is.

[neilestrick]

At the very least you need to have a pressure gauge on the gas line and a digital thermocouple reading the kiln temp. Inexpensive digital thermocouple setups work fine, because you're just using it to see changes in rate of climb. Use type K thermocouples. Use cones for actual heat work.

Controlling temperature at the start of the firing can be difficult. You may need to just use a pilot burner for the first few hundred degrees.

I'm curious about how you melted your clay. What cone is your clay rated to?