Feeder Speed for Coal mills.

[tsfly]

I need some information on minimum feeder speed requirements for coal mills. Right now the minimum feeder speed on the mills is 20%. I would like to drop that to 15%. Could this create any problems when starting, or stopping a mill under normal operation? I could not find anything specific in NFPA 85.

 

[wde3477]

I don't know of any issues with mill operation. Relating to our feeders, the thing I would be concerned about is sufficient cooling for the motors if they are running off a Variable Frequency Drive. Lower RPM = lower cooling fan speeds.

 

[JGG]

The minimum feeder speed is usually fixed by the following
1 To maintain a stable coal bed.
2 Maintain a max PA to fuel ratio in the PF lines for flame stability.
3 The PF piping system turndown depending of mill to fuel ratio control

These areas must be investigated to decide to reduce the feeder speed

 

[Flyash]

We have had a few mill puffs when the feeder speed is low.

We run 25% for minimum and move up quickly from there. Our burner flames are not stable (from the operator's point of view) without oil at that level.

 

[JGG]

We have had a few mill puffs when the feeder speed is low.

What about your coal, Is your Volatile/coal ratio higher than 1.5 ?