Hi Tam,
We had this same problem at my plant several years ago. In the end, we installed a PGNA cross-belt analyser on the feed to the raw mill and doubled the capacity of our high-grade limestone corrective weigh-feeder from 50t/h to 100t/h. This (combined with efficient blending in our homogenising silo) effectively solved the kiln feed LSF variability problem.
However, in the period before we installed the cross-belt analyser, we compensated for the end-cone effect by measuring the chemistry effects of the segregation in the end cones during stockpile change-over and then developing a proactive procedure to compensate for these changes.
We took samples of rawmeal at 15min intervals over the entire course of the stockpile change-over and plotted the LSF vs time. We found that the peak of the end cone was high in fine clays and the LSF would drop dramatically when the reclaimer moved through this part of the end cone. The base of the cone was high in larger limestone pieces which made the LSF increase dramatically. The same thing occurred in the "start" cone of the next stockpile.
The attached graph shows our typical end cone behavior. I have noted on the graph the process events which correlate with the deviations shown on the curve.
To counteract this behavior we developed the following procedure to reduce LSF variations;-
1. Approximately half an hour before the predicted end of the current stockpile, the high-grade limestone corrective was reduced to zero and the sand corrective decreased slightly. (to counteract the low LSF from the peak of the end-cone)
2. As soon as the reclaimer started to move between stockpiles the process operator increased the high-grade corrective rate to maximum (approx .12-15% of mill feed ).
3. From this point the high-grade corrective usage rate was sequentially reduced based on a rolling 4hour average of rawmeal LSF. (hourly XRF analyses)
This procedure worked well for many years before we installed the raw mill cross-belt analyser and QCX control software.
I hope this helps you overcome your problem,
Regards,
Ted.
Test
Dear Ted
Thank you very much for your sharing. This is very useful for us to improve the quality of RM.
If anyone has more ideas related to this topic, we are highly appreciated to recieved your sharing.
Best regards,
Tam Nguyen
Dear all,
In my personal opinion the problem lies in the fact that during stockpiling of the limestone, the angle of repose of the limestone do not remain same as sopposed to be due to continuous motion of LS stacker.
The LS reclaimer which is designed on that basis get that inherent falacy of angle. The angle of repose due to the LS stacker motion should high than what it be in the state of free fall.
Due to this the inner cone is always of low grade. Why? Becausing the harrows slanted on an low angle reclaim more material from upper side and since this portion mainly consists of clay portion, the material is low grade.
At outer cone, low angle slanted harrows reclaim material from ground side more which is consist mainly of limestone boulders and therefore high grade material is
obtained here.
Therefore try by adjusting angle of harrows a little bit.
regards,
Gulam Dastgir