Power Plant Engineering

Fig. 7.6
The classifier referred to above is located at the pulverizer exit. It is usually a cyclone with
adjustable inlet vanes. The classifier separates oversized coal and returns it to the grinders to maintain
the proper fineness for the particular application and coal used. Adjustment is obtained by varying the
gas-suspension velocity in the classifier by adjusting the inlet vanes.
The Pulverized-Coal System. A total pulverized-coal system comprises pulverizing, delivery,
and burning equipment. It must be capable of both continuous operation and rapid change as required by
load demands. There are two main systems: the bin or storage system and the direct-firing system.

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POWER PLANT ENGINEERING
The bin system is essentially a batch system by which the pulverized coal is prepared away from
the furnace and the resulting pulverized-coal-primary-air mixture goes to a cyclone separator and fabric
bag filter that separate and exhaust the moisture laden air to the atmosphere and discharge the pulverized
coal to storage bins (Fig. 7.7). From there, the coal is pneumatically conveyed through pipelines to
utilization bins near the furnace for use as required. The bin system was widely used before pulverizing
equipment became reliable enough for continuous steady operation. Because of the many stages of
drying, storing, transporting, etc., the bin system is subject to fire hazards. Nevertheless, it is still in use
in many older plants. It has, however, given way to the direct-firing system, which is used exclusively in
modern plants.
Pulverized
Coal Bin
To feed
Hopper
Pulverizer
Cyclone
Separator
Bag Filter
Exhaust
Coal Tripper
and Conveyor
Pulverizer
Fan
Air Heater
Coal Feeder
Raw Coal
Bunker