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kraythe

How to Push Gas Kiln through Stall?

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I am currently firing some high fire stuff and my gas kiln is seriously stalled and wont move. I have tried adjusting the propane, opening valves, adjusting airflow and it just stubbornly hangs at the same temp. Any suggestions? I need to get it to about 1290 to get just over cone 10. The kiln is a 2 burner olympic torchbearer.

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Digital pyrometer, top draft, only very slightly covered for light reduction. Stalled or moving extremely slowly, burners all the way open. I can try backing off on the propane, its almost full bore right now. and not doing much.

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1 minute ago, liambesaw said:

My gas kiln usually stalls when I'm feeding too much gas.  But it could be anything!  Mine is propane so I really have to ride a thin line on pressure otherwise the tank will freeze up.

I will back off on the propane. I use tanks 4 x the size of your barbequeue tank and they dont freeze.

 

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Just now, kraythe said:

I will back off on the propane. I use tanks 4 x the size of your barbequeue tank and they dont freeze.

 

Twice the size of my tank, I use 40lb with a high pressure regulator.  My tanks only freeze up when they are opened up too much and the tank is getting empty.

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(maybe you are pumping in to much gas?) THIS A COMMON MISTAKE . Its easy to think more gas should raise temp but often less is more. The sweet spot is a correct air to gas ratio. After you find that spot only use the damper to control reduction.

Glad it worked out

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@kraythe The thing to remember with a gas kiln is that you're not just trying pump heat into the kiln. Rather, you're moving heat through the kiln. The heat comes in, is transferred to the ware, and moves out, to be replaced by new heat. It's a flow, and your kiln can only manage a certain volume of flow. Pump too much gas or air into it, and the flow bogs down.

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A way to think of this is at some point you will have the exact air / fuel ratio through your burners to provide the most heat possible at a given pressure setting. So too much air through the burner primary air port for a given amount of gas results in a lean mixture with less output. Too much gas and not enough air through the primary air port results in an overly rich mixture with unburned fuel and again peak burner output is reduced.

you have atmospheric burners so they rely on an air shutter position (on the burner) as well as gas pressure and injection through the nozzle to influence the amount of air sucked in by Venturi effect through the primary air port. So without complicating things it is 1) too much air, 2) too much gas or 3) just right with respect to speed, efficiency and gas pressure.

so if I had to simplify I would try and set the primary air shutter  on my burner at its best setting (heat output) for top pressure operation. Then I would close my top damper slowly until I begin reduction or my temperature rise starts to decrease. Just prior to this point is where I can get the maximum heat from my burners while wasting the least amount of heat from my kiln.

Establishing a known good top end helps simplify getting the most from your burners and kiln when you need it. This is an over simplification but usually a decent compromise for many potters and is something they can do easily while simply moving their top damper a bit in and out at the end of the firing. As they desire.

just one way we approach this until folks can become more familiar and comfortable with how burners work etc....

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Yes, gas kilns are all about the fire triangle, oxygen/fuel/heat. If you keep that in mind when firing you're going to get a better idea of what's going on during a firing.

But we also have one more thing to consider, and that's draw, how the fuel and heat is being pulled through the kiln from burners to flue.

Until one gets it all dialed in (kiln schedule), it's a process that takes attention. I assume commercial gas kilns with automated devices help mitigate the guess work.

But I rememeber over-firing our college kiln first time I tried ;) 

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