Kiln supply duct temp

[JustinC]

I have one kiln that won't get to the supply duct temp set point. I usually run my supply duct at 500 degrees farenheight. This kiln tops out around 400 regaardless of fuel and I can't figure it out.

[GeorgeCulp]

What kind of direct  fired kiln do you have? Shavings fired, vortex style burner, or a saw dust, slope grate burner?

I assume you have operated at 500 degrees before, am I correct? And now you can't get above 400? Correct?

Barring a massive leak of heat there are only two things can affect your supply duct temperature as you have described....1. you are not burning fuel at a rate you previously did (could also mean wet fuel if you have a vortex burner), 2. you are moving more air now than before with your recirculation blower.

Is your kiln taking longer to get to temperature? If so, then you most likely are not combusting the same amount of fuel. If your kiln is getting to temperature in the same amount of time at 400 as you were at 500 then you most likely are moving more air with your recir blower.

Knowing if you are  shavings fired or green sawdust would help a lot.

George Culp