SO3 obtained in clinker by raw maetrails like fuel (petcoke) & SO3 from gypsum are different in what ways? which SO3 is useful & which is helpful for quality as well as production basis? & why? what is the total SO3 limit in clinker for kiln operation without build ups? pl. expalin raj
Dastgir
Dear XXX,
Excess Alkalis after being consumed by chloride, combine with SO3. Alkalis , as chloride or sulpahte, are volatiles and form a cycle. Such cycle causes chocking at upstream stage of cyclones.
Alkali Sulphates in burning zone, acts as mineraliser and facilitate conversion of C2S to C3S and thus reflect this in increased earlier strength on the demise of later strength.
SO3 in excess of alkalis, combined with CaO to form CaSO4. This sulphate is hard burnt as compared with sulphate of Gypsum and thus hardly changes setting behavior of cement, though such consumption of CaO will certainly down later strength of cement.
Regards,
Gulam Dastgir
Ted Krapkat
Dastgir:
SO3 in excess of alkalis, combined with CaO to form CaSO4. This sulphate is hard burnt as compared with sulphate of Gypsum and thus hardly changes setting behavior of cement, though such consumption of CaO will certainly down later strength of cement.
Gulam,
In addition to this, it has been experimentally verified that in clinkers which have a large excess of SO3 over alkalis, there exists a significant quantity of SO3 in solid-solution with the silicate phases, particularly belite (C2S).
Concentrations of SO3 in belite were found to range up to about 2% in fast-cooled laboratory clinker and up to 1.5% in industrial clinker.
So it is even less likely that the non-water soluble SO3 in such clinkers is present as anhydrite (CaSO4). In any case, CaSO4 decomposes at 1250oC into CaO and SO3, so there should be very little anhydrite present in properly-burned clinker anyway... even clinker with a very high SO3/K2O ratio.
I would guess that the evaporation of excessive amounts of SO3 in the burning zone in such a situation would cause catastrophic process problems in the kiln inlet before much CaSO4 could escape with the clinker.
Regards,
Ted.
REFERENCES:
Hertfort, Duncan. "Distribution of Sulphates on Portland Cement Clinker", International RILEM TC 186-ISA Workshop on Internal Sulfate Attack and Delayed Ettringite Formation, 4-6 September 2002, Villars Switzerland.
Dastgir
Dear Ted,
Thanks. This is new thing for me to learn. But a query is trickling in my mind.
C2S being hudrophilic, should have liberated any form of SO3 in water and may have modified setting behaviour of cement . But in case of pet coke use, no such modification is observed in cement setting behaviour.
Please comment.
Regards,
Gulam Dastgir