[Venturi burners backburning]

5 hours ago, neilestrick said:

Do you know for sure that the burners were the problem? More often than not what we see here on the forum is that there's a design problem with the kiln itself, or just user error in firing it.

Hi Neil, yes both those are possibilities. It will take me a couple of weeks to install an inline valve and re-test, and then come back to the forum with success or failure. Thanks for all the suggestions.

[Venturi burners backburning]

Thanks Babs. Fired once to cone 6 previously but struggled, so new burners and regulator. I start with  a small burner. 

[Venturi burners backburning]

5 hours ago, Bill Kielb said:

Hmmm, pretty small actually I would  feel better if it was stamped. .5mm is .0280” which is a number 70 orifice which gets you  [5.9 kw] @ 34 Kpa so seems to be a high pressure burner. When burners burn backwards the combustion velocity is greater than the physical velocity so the flame travels back towards the orifice which is counter intuitive to having too much pressure. I assume it backfires in free air, so maybe an easy test I would suggest is to put a hand operating valve upstream of the burner and see if you can stabilize the flame slowly closing the valve ( in free air) - maybe to near zero flow.  The primary air needs to be fairly open, don’t close it. Again counter intuitive but nothing makes sense here really. If that works then I think we can safely assume it is low pressure or medium pressure burner and work from there rather than buying a bunch of stuff guessing.

Propane and natural gas have relatively slow combustion velocities which make this issue fairly rare for Venturi burners, stove burners, you name it. I think worth the test and observing the result.

Thanks Bill - I will  put a hand operating valve upstream of the burner as you suggest, and take into account all the other information supplied by you and others. Thanks again!

[Venturi burners backburning]

Hi Babs,

 

You can see in the image posted with the arrow to where the flame is at the inspirator. 

 

And yes Neil it backburns when not at the kiln.

[Venturi burners backburning]

 

There is one like this in the burner, not drilled as I have had since it was new. It is 0.75mm by my calipers, (and sliding a .5mm wire through). The gasfitter and I checked the orifices for critters etc and they are clear. I can't get the regulator to reduce the pressure to single digits though. Maybe I need another inline valve that I can use to reduce the pressure? Thanks for your help!

[Venturi burners backburning]

Thanks Babs - it back-burns even when right away from the kiln with flaps open.

[Venturi burners backburning]

On 11/15/2023 at 5:54 PM, Bill Kielb said:

Atmospheric burners contain orifices sized for a particular range of pressure and the fuel used to produce a certain amount of heat. No new news there, but for all that to work the velocity of the gas has be be greater than the combustion velocity of a fuel air mixture expected to enter let’s say at a 5:1 air fuel ratio or about 50%% of the required air. The remaining 50% of the required air must enter around the side of the burner through a sufficient overcut all the way around.

So:

• Wrong pressure
• wrong orifice
• Too much back pressure from the kiln
• Any chance you are feeding liquid to this?
• Not enough overcut around burner
• Adding a metering valve upstream of the burner and downstream of the main gas valve allows variability, how are you controlling the gas to the burners?

What size orifice, what is the burner rating (kilowatts, btuh - thermal output) , what pressure is this operating at (typically in the 2-3 kilo paschal range) not the maximum pressure ratings on the valves, what size regulator is installed on the tank, pictures of the installed burner, picture of it burning back ….. and never close the primary air 100%, it should likely sit at least 1/2 open or better and not really need adjustment.

Propane boils about -41c so at 21c there will be about 850 Kpa of pressure in the tank. Definitely way higher than your burner rating. So in the end sounds like these might be high pressure burners and need a first stage regulator to operate correctly.

This is fairly easy to solve but often folks, even licensed fitters confuse the pressures and installation requirements for kiln operation. Tell us a bit more

 

Here is a bit more thank you Bill:

The burner size is 50mm (2 inch) with capacity 400MJ (380,000 BTU) per hour @ 100kPa propane.

The images show the burners being tried at 100kPa, controlled by winding the knob on the 500kPa regulator attached to the changeover valve on the 45kg 3.3Mpa capacity propane cylinder.

Also shown is the burner installed, and burning back, plus the burner port as seen during building.  I have put them all in one image, plus a larger one of the burning back. If I should include larger pictures please let me know.   I also tested the burner in the open, off the kiln, on a small bbq propane tank with a regulator and also had back-burning. Thanks again for your help!

 

 

 

[Venturi burners backburning]

Thanks so much Bill! I will compile answers to all those excellent questions, and take some more pictures.

[Venturi burners backburning]

Hello folks,

 

I have been trying for some time to fix a problem with a venturi burner that is burning gas back at the inspirator, and would appreciate any suggestions. The burners and regulator are capable of 250kpi and higher, but the two gas cocks are  each1060 kpi.

So far I have:

1. Replaced one entire burner from the same company
2. Had a licenced gas fitter check the nozzles and install the two burners.
3. Tried with air fully open to closed.
4. Tried at high pressure and low pressure.
5. The burners and regulator are capable of 250kpi and higher, but the two gas cocks are 1060 kpi.

It's got me stumped so any ideas welcome

Thanks for pondering,

 

Brett