I am operating a wet kiln that is experiencing frequent refractory failures. Burner alignment is very important to an extensive refractory campaingn.
I position the burner pipe centrally, not leaned into any quadrant, and the insertion depth is just in line with the nose ring (approx 200mm)
Is this the industry standard for geometric alignment of the main burner for kiln operation?
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Re: Burner Positions
Dear Dr. Zoey
When inclining the axis of burner nozzle to that of the kiln it must be noted that a steep angle towards the material bed will permit radiation from the material to break out the fuel and increase the rate of combustion . it will also hinder the flow of uncommitted secondary air at combustion acroos the bed of material to extract heat & slow down the sintering process .the reaction between fuel and secondary air when the flame is very near to material bed will be confined to the remaining areas of conical sleeve and will somewhat slow down the combustion .
the burner is usualy set at smal angle to the kiln axis and slightly directed on to material . thereby it must be remembered that the material is bieng cooled by the stream of secondary air flowing over it . provided no overheating effects take place in the material it is thermodynamically desirable to let the flame sweep over it . To prevent the material is getting too hot in to the cooler the final area of the kiln out let is used AS cooling zone . the point of burner is therfore normally pushed forward into the kiln for a distance ( 0.5 - 1.25 m ) in practice its found that a very short flame is most suitable for kiln operation in the other hand a very short flame should be used only if a sufficiently thick material crust has been formed .
Good result are also obtained with withdrawn kiln and a correspondingly longer flame . Trail should being on principle with too long flame during which the temp. of the kiln shell must be carfully watched for over heating
Re: Burner Positions
The optimum position depends on many factors.
In the past, it was common practice to point the burner a little bit down compared to kiln axis, in direction of the charge.This was primarily done to compensate the tendency of the flame to go upward due to convection and entrainement by the secondary air.
Today, with modern high momentum burners, this is no longer recommended. The jet momentum being stronger, if you point the burner toward the charge, the risk is that the flame will touch the charge. The local reducing conditions would increase sulphur circulation and increase the risk of coating and blockages in the preheater. Concensus is that high momentum burners should be placed parallel to kiln axis.
Basic positions would be on kiln axis, but the burner can also be shifted sideways (still parallel to kiln axis). Some recommend to shift the burner horizontally away from the charge when using coarse waste fuel to limit the risk that coarse particles would fall into the charge. Similarly, if you use only fine, easy to burn fuel, the burner can be shifted toward the charge to improve heat exchange. As radiation is the primary heat exchange mechanism, the effect is however limited.
Concerning insertion depth, in theory, the further inside the better. This is to get away from the perturbation of the change of direction of the secondary air and to improve the precooling zone to avoid snowmen in the cooler. There is however a limit due to the length and related weight of the burner and the risk of damage by big pieces of coating falling on the burner. Usual insertion depth would be 50cm-1m inside the kiln. But many kilns operate with the burner just at the limit of the kiln (0cm). Having the burner outside the kiln is generally not recommended.
O. Van Cantfort