537 posts
re Raw mix.Design
Hello Mohan,
The external dust cycle starts at the top of the preheater. Since the top cyclone(s) are only about 95% efficient at removing solid particles, a portion of the dust is returned with the hot gases. Normally this dust-laden gas is cooled via a conditioning tower and most of the dust is removed and returned to the kiln feed.
If the dust is returned to the inlet of the homogenising/blending silo with the fresh raw meal, then this can cause layering in the silo and consequently large variations in the LSF of the kiln feed coming out of the silo, especially when the raw mill is turned off and only the dust from the preheater / waste heat recovery system is being added to the silo. Therefore, it is preferable to add all dust streams to the kiln feed after the blending silo.
However, from your data, the clinker LSF seems to be fairly constant (93 to 94) even though the observed kiln feed sample varies from 97 to 101. It seems to me that even though the amount of dust in your 'kiln feed' sample is varying, most of this dust is removed from the incoming meal at the top of the preheater, leaving a real kiln feed (which has a fairly constant LSF) to enter the kiln.
Is this correct, Mohan? When using coal with the same ash content, is your clinker LSF normally fairly constant, despite the large LSF variations in the kiln feed sample?
Regards,
Ted.
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85 posts
re Raw mix.Design
Dear Mr Ted, We have no separate blending/ Homogenizing Silo.We have the present day Tangential Silo where all the mixing blending takes place in that silo.before it emerges as Kiln feed. So if some of the dust escapes from the preheater , and reenters the silo again then why there is no uniformity between the Lsf of Kiln feed and that of the Clinker
537 posts
re Raw mix.Design
Hello Mohan,
The reason for the discrepancy between 'kiln 'feed' and clinker LSF is that the kiln feed sample always contains a certain amount of dust mixed in with it. Most of this dust does not actually enter the kiln since it is part of a dust cycle, external to the preheater. So the LSF of the hot meal exiting the bottom of the top preheater cyclone(s) is actually lower than that of the measured kiln feed sample. eg;-
In the silo;- Raw meal + dust (from the preheater) ---> kiln Feed
In the preheater;- Kiln feed -----> Hot meal + dust (sent back to the silo)
In the kiln;- Hot meal + coal ash ----> Clinker
Put simply, the LSF problem arises because the analysed 'kiln feed' sample, is contaminated with high LSF dust which is removed before the meal enters the kiln.
I hope this makes it clear...
Regards,
Ted.
85 posts
re Raw mix.Design
Thanks MR TED for the clarification