2nd stage showing dead cold on infrared image

The bottom section of our 2nd stage is blue (cold) all the way on an infrared thermal image. This is a 4 stages preheat/precalciner system. Curious thing is that our thermocouple is showing a normal temperature. We do have dip tubes out on the third stage, but I wouldnt expect this to be causing a complete bypass/shortcircuit around the 2nd stage, material flow into tipping vavle to 3rd stage is somewhat restricted by what appears to be buildup (but no completely).

Any ideas/suggestions besides hard buildup?

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Re: 2nd stage showing dead cold on infrared image

Are you numbering from the top or bottom of the preheater?

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Re: 2nd stage showing dead cold on infrared image

Firstly could you please inform what temperature is indicated by "blue" on the thermal image.

Secondly it would be interesting to get the cyclone gas temperature (at outlet or inlet) for each stage.

Material clogging or build ups in the cone area could be caused by several conditions. The most likely one is sticking of volatiles (in combination with or without to shallow cone angle)

Volatiles can be originating from preheater gas from the lower stage cooling down. It can be expected that by high chloride/sulafate internal circulation and insufficient bypass (or no bypass) volatiles will clogg onto walls (especially with limited gas velocities).

For chloride those build ups can be expected in the temperature range between 650°C to 800°C and for Sulfate from 800°C to 1100°C. This is to be taken as a rough guide only it depends on the actual chemical composition of the volatiles.

Another reason may be open (not properly closing) pendelum flaps whereby hot fine meal is being transported through the meal pipe and diptube to the next stage upwards where it will cool down and cause clogging.

Of course there is still the possibility of wrong calibrated or malfunction of instruments.

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Re: 2nd stage showing dead cold on infrared image

Thank you for your reply. Blue temperature was about 60C when all the other stages are around 130C. Almost 2/3 of this stage is blue where the other 1/3 seems "normal". Yes we have had problems recently with rings and balls coming in the kiln. Our sulfur/alkali inputs and outputs are slightly unbalanced (only by 2 or 3%). We have seen more unbalances before without any kiln and ring formations. We have also raised the silica ratio, played with different oxygen levels at the inlet, changed the burner pipe, etc. Why is it translating to the 2nd stage though? Nothing seems to help this coating and ball formations.  

Dr. Clark,

From the top of the preheater.

Thanks

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