Our 6 stage PH ILC upgraded kiln is suffering frequent shut downs due to the appearance of red spots evry 4-5 days. This phenomean was present a few months ago but subsidized on its own after the 3rd 5 day shutdown, it has started reouccuring again now. What may be the reason for this?

Kiln dimensions =

3.2 dia

48m long

designed capacity 1800tpd.

Note. Our other 4-stage Ph (no calciner) 800tpd kiln is running fine with the same raw mix and coal.