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Technical Cement Forum / Correlating Kilnfeed & Clinker LSF

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Mike M 30/09/2014 12:53:01

Correlating Kilnfeed & Clinker LSF

All,

I need some help on this one. We have a 5 stage preheater/calciner
kiln. As long as I have been here, we have had to set our Rawmill and Kilnfeed
LSF targets higher than our desired Clinker LSF because of inefficient stage 1 cyclones
and dust loss. We recently replaced 60ft of brick around the 120ft mark. Since
the kiln has come back up, kilnfeed LSF and Clinker LSF have been almost
matching. We ran like this for about 6 days and then developed a ring. I
analyzed the ring material (thoughts were it was an ash ring) but Xray results
suggest dust ring. It was 32% freelime. Looked at it under microscopy and
looked to be mostly freelime with some matrix and partially developed Alite and
Belite.

Let me know if I can provide any more data to help solve
this mystery.

Thanks,

Mike

Ted Krapkat 02/10/2014 02:58:58

Hello Mike,

Firstly, if you are using coal as a fuel, your rawmeal and kiln feed LSF should always be higher than your clinker LSF... the higher the coal ash the bigger the difference. What's the %ash of your coal?

Secondly, you mentioned dust loss... do you actually remove a certain proportion of dust from the kiln system or are both raw meal bag-filter and conditioning tower dust all returned to the kiln feed. If the dust is returned to the kiln feed, is it added to the top of the blending silo or to the kiln feed after the silo? And what sort of t/h dust figures are we talking here?

Thirdly, where exactly was the ring? From what you describe it sounds like a meal ring and I would guess that it would probably be located towards the kiln inlet.(maybe 2-8m inside the kiln). These types of rings are normally composed of fairly soft material. Was there much SO3, K2O and Cl- in the ring sample you tested? Also, did you notice much alkali sulphates in the microscopy?

I'm guessing that the ring formation was caused by excessive sulphur and/or alkali chloride recirculation. Do you have a kiln inlet gas analyser installed? If so, was there frequently a lot of CO present in the kiln inlet during the 6 days after start-up? Also, do you analyse your bottom stage cyclone hot-meal?

It would also help if I knew your full raw meal, kiln feed and clinker chemical analyses, kiln feed rate, total coal usage rate (main burner and calciner burners) and coal %ash content & ash chemistry, as well as the hot-meal chemistry.

Regards,

Ted.

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