1. Principle of Operation
Bowl Mill is driven by AC motor, coupled with flexible coupling to the worm shaft.
The worm shaft drives worm gear, mounted on the Main Vertical Shaft. A bowl
mounted on the top of the shaft rotates at a speed of 40 to 65 rpm. For a particular
mill the speed is constant .Integral coolers are provided in the mill base with
circulating water for removing heat from the oil. External lube oil systems are also
used for cooling the oil in the gear box, which consists of a motor driven pump,
cooler and filter. To prevent coal entering in to the Gear case, an air sealing system
is provided.
Hot primary air for drying and carrying pulverized coal, enters through insulated Mill
side and Liner Assembly. Tramp Iron, pyrites and stones coming in the mill with raw
coal move out of the bowl and being heavy, fall into the mill side and linear
assembly. These are scraped and dumped in the pyrite hopper assembly through
the Tramp Iron and Spout valve.
The journal assembly consisting of Grinding Rolls is mounted on Separator Body.
Grinding force is applied by pressure spring adjustment. The roller assembly can be
moved up and down depending upon the roll condition and coal bed. Separator Body
consisting of linear assemblies deflects the air stream to the center of bowl.
Mill is equipped with the stationery classification with adjustable vanes for
adjustment of coal fineness. The coarser particles in the in the pulverised coal are
separated in the classifier and returned back to the bowl for further grinding.
Mill Discharge Valves mounted on the Separator top consist of Flap type closure
plates operated by pneumatic Cylinders, which can be tilted out of the path of coal
stream. This is used to isolate the mill from Boiler during maintenance.