What are the possible causes of sinter ring formation at beginning of burning zone and subsequent large ball formation in marginal grade limestone deposit having low sulphur and high potash?
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Re: Sinter ring
Coincidentially we had the same experience in our 5000tpd, dual string preheater, precalciner kiln last week, but we think the cause was not chemical but process related.
Our kiln is prone to ring formation every so often, probably due to fluctuating flame length and variable coal ash (we blend two types of coal, one with 20% ash and the other with 10% ash)
Once a ring forms it constricts gas flow and induces increased CO in the back end of the kiln, invariably causing large buildups in the "smoke" box and/or preheater due to high SO3 cycle.
These buildups often fall and slide into the kiln as large slabs, coming to rest behind a ring (if it is large enough). If this happens, the slab can roll around behind the ring forming a ball, or boulder which can then grow larger due to accretion.
In our case we had to stop the kiln and cool the kiln rapidly to break up the ring and boulder. Luckily this worked and we were able to restart the kiln within 36hrs. (the last time it happened, the kiln was off for several days)
For us it is important to keep the O2 content at the back end of the kiln to at least 4% to prevent CO and associated high SO3 in hotmeal, otherwise we have continual slabs forming in the preheater/smoke box and sliding into the kiln.
We also try to CARDOX the areas prone to buildups, but some areas are difficult or impossible to get at, so it is not possible to remove/prevent all buildups
Not sure if this helps you at all though.