Refractories Question 7
We have faced the serious coating formation at 12 to 26 meter of Kiln and plant have to be forced stopped for coating removal. I am attaching the three files for your observations:
1. photograph of the Kiln coating.
2. Observation about the breakdown.
3. Analysis data for coating, Rawmix and coal.
I may request you to please look into the coating formation details and furnish us your valuable comments.
I have studied the data you have submitted. We receive regular reports of heavy coating and ball formation associated with petcoke firing. I note that on the 12th & 13th, prior to the kiln stoppage the petcoke firing in the kiln had been increased to 70 per cent. However, the clinker sulphate levels are not excessive and neither is the sulphate in the coating sample. One othet item of note is that the MgO content of the clinker has risen to above 1.5 per cent on the 11th, 12th and 13th. In my experience only minor changes in the MgO content can lead to significant changes in the coating tendency of the kiln and also the formation of clinker balls. Do you know the reason for the increase in MgO content?
Refractories Question 8
We need to know the distribution temperature on preheater kiln - in-line calciner - double string - four-stages cyclones cross bar cooler , kiln diameter 4.8 metre, kiln length 67 metre, kiln KHD design, and the collar from FLS, kiln feed 320 ton /h, dry kiln, by pass 20 per cent, preheater fan capacity 380,000 m3/ h. Also the type of bricks is Almag 85 per cent , perlix 80 per cent , kronex 85 per cent ...etc.
The shell temperature profile varies with the kiln process (precalciner, preheater, long dry, wet etc.), type of refractories installed (due to different conductivities), the residual thickness of the refractories (which reduces with wear during service), and the thickness of coating on the refractories (which changes dependent on process conditions). For an in-line calciner kiln I would expect shell temperatures of around 200 degrees C for the first 30 per cent of the kiln length where you will have the more insulating refractories installed. The girth gear will be in the region and the shell at this approximate temperature. I would then expect the shell temperature to rise to around 300 degrees C in the upper transition zone from 30 to 60 per cent of the kiln length. The refractories are likely to have little coating in this area. In the burning zone from 60 to 90 per cent of kiln length the shell temperature will be very variable due to coating formation. It could be as low as 150 degrees, but if the coating breaks away and the residual lining thickness is low then it could rise to over 400 degrees.