Bowl mills are used for pulverizing coal in pulverized coal fired boilers. The coal to the mill is fed by a coal feeder from the coal bunker. There are many type of feeders used for coal feeding like the belt feeder which can be in volumetric or gravimetric mode, the chain link feeder, the drag feeder, etc. Row coal from the yard is sized in crushers and stored in coal bunkers. It is sometimes experienced, depending upon coal quality, that the smooth flow to the coal mill can get disrupted. The mill will trip on no coal flow protection, and such a mill trip can upset boiler parameters and require corrective action.
For taking corrective action during a coal hang-up in bowl mills, the operator will have to know the reason for such a hang up, how the plant will respond, what he has to respond to, and what the local operator will have to do. This will reduce the chance of mill trip and bring the boiler back to normal condition as early as possible.
The reasons for coal hang-up to mills can be many, like large raw coal size, jamming of the feeder, jamming of the coal chute from the bunker due to high moisture in the coal, foreign material at raw coal inlet to feeder, etc.