TL;DR
A drop in separator efficiency means fines are being sent back to the mill and the circuit is over-grinding. Check the rotor speed, separator feed air volume, and reject vanes before adjusting the circuit.
What you might see
- product Blaine fineness below target
- separator returns (rejects) mass flow high
- mill fresh feed rate reduced to compensate
- separator rotor bearing temperature elevated
Likely causes
Separator rotor speed below setpoint from a drive fault or belt slip
Separator reject vanes worn or mispositioned allowing coarse particles to pass
Air volume through the separator below design from a blocked filter or fan fault
Excessive mill feed rate overloading the separator with fines
Required tools
- Sample containers for Tromp curve sampling
- Tachometer to verify rotor speed
- LOTO kit
- Wrench set for vane adjustment
Safety first
- Lock out the separator rotor drive before opening any inspection access. Rotor inertia allows continued rotation after power off.
- Cement dust explosion risk. No hot work near the separator without a permit.
Procedure
- 1
Read the separator rotor speed from the control panel. Compare to the setpoint.[1]
- 2
If the rotor speed is below setpoint, check the VFD output frequency and the rotor drive belt or coupling.[1]
- 3
Check the separator inlet air volume or the filter bag differential pressure. Restricted airflow reduces separation efficiency.
- 4
Collect samples from the mill feed, separator reject, and separator product streams. Calculate the separator sharpness using the Tromp curve.
- 5
Stop the separator and lock out the drive. Inspect the reject vanes for wear or displacement from the design angle.
- 6
Replace worn vanes and reset any that have shifted from the design angle.
- 7
After repair, tune the rotor speed and air volume in small steps and resample to confirm efficiency improvement.
Sources
FLSmidth FLSmidth UMS / TMS Cement / Ball Mill general technical documentation, FLSmidth
FLSmidth ball mill separator operation and maintenance documentation (general)
More guides for FLSmidth FLSmidth UMS / TMS
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