Coating formation

I operate a 1000mtpd wet kiln, diameter 4600mm; length 145m, burning natural gas. I am experiencing a strange coating profile when I enter the kiln.

Typically when I enter the kiln, the coating starts at the 7m mark and then the dense burning zone coating thickness increases gradually to approx 17" thick and then ends abruptly at the 20m mark. Beyond the 20m mark there is usually no coating. But of late, I had some changes to the main burner (I changed the primary air fan (bearing failure) and the burner alignment was shifted slightly during insertion of the main burner.

Now the coating profile is as before, however, approximately 6m uphill of the end of the dense burning zone coating there is a very unstable ring of coating. So, the coating profile is from the 7m-20m and then there is no more coting except for a ring at the say 26m mark approximately 1-2m wide and 15" thick. I analyzed the coating in the lab and I am not seeing any higher levels of alkalis or sulphates. The analysis is looking exactly like clinker.

Does anyone have a theory/reasoning for this phenomenon.

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