INSUFFICIENT LITRE WEIGHT OF CLINKER
IN OUR KILN WE ARE GETTING LOW LITRE WEIGHT WEIGHTS [ 1080 TO 1130 G/LT] WITH FREE LIME 1.8 TO 2.1%.
FOR A REMIDIAL ACTION I HAVE REDUCED KILN FILLING, COAL MIX RESIDUE & RAW MEAL RESIDUE. BUT IT HAS REDUCED MY FEED.
MY COAL MIX IS 80% PETCOKE + 20% SOUTH AFRICAN COAL , RETENTION ON 90 MIC. OF THE MIX IS 3 TO 4% [PREVIOUSLY 5 TO 6%].
LSF IN RAW MEAL 94.5 TO 95% , SILICA MODULUS 2.27-2.28 .
RAW MEAL RETENTION ON 90 MIC IS 17% & 2% ON 212 MIC.
IS THERE ANYTHING WHICH CAN BE DONE WITH THE RAW MIX.
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re INSUFFICIENT LITRE WEIGHT OF CLINKER
There are two areas to look at with this type of sudden free lime problem;- changes in the kiln system and changes in raw mix burnability.
- Burning zone temperature may be low or fluctuating due to faulty burner pipe, inadequate fuel rate or drop in fuel quality. Do you have any way of measuring the BZ temperature?
- The degree of calcination of the kiln feed may be too low.(should be ~90-95%) Much lower values would cause uncalcined hot meal to enter the kiln, reducing the burning zone temperature and causing high free limes. Do you test the calcination degree of the final stage cyclone(s) i.e by Loss On Ignition?
- Have fuel usage rates changed recently? Do you frequently measure the GCV and ash content of the petcoke and coal?
- How do you blend your petcoke and coal? Since these two fuels have such large differences in ash (and energy) content, fluctuations in blending of the fuels could increase the LSF or the clinker, resulting in high free limes.
- What about the kiln inlet temperature... do you measure it? If so, has it changed significantly or become very variable?
- Petcoke contains a lot of sulphur which normally results in strongly increased SO3 recirculation. If this recirculation becomes high enough, quite a lot of CaSO4 can form as the SO3 reacts with CaO in the incoming hot meal. This CaSO4 breaks down in the burning zone releasing SO3 which returns to the preheater and CaO which remains in the clinker, thus increasing the clinker LSF in the burning zone, resulting in increased free limes.
- High sulphur recirculation also increases the chances of rings and build-ups in the system. Do you have frequent meal "flushes" through the kiln or slabs of unburnt preheater build-up falling into the kiln inlet?
Chemically, your kiln feed already appears easy to burn, so the problem may lie with oversize quartz (>32um) or calcite (>90um).
- Have any of your raw materials changed recently? e.g. sourced from a different location in the mine or purchased from a different supplier?
- Are you using more of a quartz-rich corrective or limestone containing a lot of quartz seams, or a harder limestone component ?
- Variations in kiln feed quality such as widely varying LSF or SM could cause clinker free lime to increase intermittently. How often do you measure your kiln feed chemistry and what is the s.d. of your kiln feed LSF and SM on a hourly and on a daily basis?
- At 17%, your raw meal 90um residue is still a little bit high. Depending on the capability of your raw mill, I would recommend 12% on 90um and 1% on 212um.
And finally, what is your clinker free lime target? Normally, 1.0 - 2.0% is considered quite acceptable.