steam.
Larger units are usually the vertical type.
The type of pulverizer will be determined from the
coal analysis and the boiler manufacturer's
requirements. The pulverizer selected also affects
the control system requirements. The furnace ash
disposal system components will depend on the ash
characteristics and EPA requirements. Volumetric
heat release should be 745.2 Megajoules/cubic meter
(20,000 Btu/per cubic foot) of furnace volume. Coal
is crushed in a central plant and stored in bunkers.
Each boiler has two pulverizers, fed by a drag type
coal feeder, and in turn feed the burners. This
system requires room within the plant to accommodate
the coal pulverizers. Fineness of pulverized coal
may vary with different designs, and fine pulverized
coal will significantly affect the selection of ash
handling and pollution control equipment and will
require special consideration for erosion control on
induced-draft fan. Where pulverized coal boilers
are specified, reference to stoker fired boilers
will be deleted.
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Where indicated, pulverized coal boilers shall be provided. Boiler and
boiler accessories shall be specifically designed to operate on the fuel
specified. Boilers shall be complete with coal feeders, crushers, dryers,
burners, ignition system, air preheater, economizer, soot blowers,
controls, and complete furnace ash handling facilities. Fly ash collection
and pollution control equipment is specified in Section 11500 AIR POLLUTION
CONTROL. Boilers shall be [horizontal] [vertical] type and shall be [top]
[bottom] supported. Ash hoppers shall be dry, refractory-lined type
divided into compartments, each of which shall have a
hydraulically-operated clean-out door. The hopper shall be supported from
the boiler and a dry seal shall provide gastight connection. Forced draft
and induced draft fans shall be furnished with the boiler.
2.4.1
Coal Pulverizers
Each boiler shall be provided with a minimum of two pulverizers arranged to
allow operation of boiler at reduced capacity when one pulverizer is taken
out of service either for maintenance or for operation of low loads. Coal
pulverizer shall be provided complete with all required accessories such as
rotary drum feeder unit, air preheater, fans for drying coal by either the
primary air or suction system, coal classifier distributor unit, and shut
off coal valves to allow isolation of individual burners. Drum feeder unit
shall have a tramp metal rejection device incorporated in the unit.
2.4.2
Burners
Pulverized coal burners shall be specifically designed for the boiler
provided. Burner shall include an ignition system designed for ignition of
pulverized coal.
2.4.3
Furnace Ash System
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NOTE: Detail of piping supported in trenches will
appear on the drawings.
SECTION 15559A
Page 37
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