volume and static pressure rating sufficient for pressure losses, excess
air requirements at the burner or grate, leakages, temperature and
elevation corrections for a dirty boiler with worst ambient conditions, all
at full combustion to meet net rated output at normal firing condition. In
addition, fan sizing shall include margins of 10 percent volume and 21
percent static pressure, plus margins of 5 degrees C 10 degrees F for
forced draft fans and 22 degrees C 40 degrees F for induced draft fans.
Induced-draft fans shall be designed for handling hot flue gas at the
maximum boiler outlet temperature adjusted for boiler surface fouling.
[Induced draft fans shall be provided with outlet dampers.] Noise levels
for fans shall not exceed 85 decibels at 914.4 mm 3 foot station. Fan
bearings shall be [air-cooled] [or] [water-cooled], and backward curved fan
blade type with bearings not requiring water cooling may be of the
self-aligning antifriction type. [Scroll sheets and rotor blades shall
have liners.]
2.10.1
Draft Fan Control
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NOTE: Variable speed control, inlet vane control,
and inlet damper control are, in descending order of
efficiency, capable of control draft fan conditions.
The choice is based on economics. However, in
erosive services, inlet vane control is not
desirable.
**************************************************************************
Forced-draft centrifugal fans shall have [inlet vane controls] [variable
speed control] where indicated. Induced-draft centrifugal fans shall have
[inlet vane control] [inlet damper control] [variable speed control].
[Axial propeller fans shall have variable propeller pitch control.] Inlet
vanes or dampers shall be suitable for use with combustion control
equipment.
2.10.2
Draft Fan Drives
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NOTE: Where motor starters for mechanical equipment
are provided in motor control centers, delete the
reference to motor starters.
Steam driven boiler auxiliaries will not be used
unless the exhaust steam can be utilized completely.
Reference to steam drives will be deleted if
inapplicable for the equipment specified.
**************************************************************************
Fan shall be driven by [an electric motor] [or] [a steam turbine].
[Electric motor shall be [drip-proof] [totally enclosed nonventilated]
[totally enclosed fan-cooled] [totally enclosed fan-cooled, suitable for
installation in a Class II, Division 1, Group F, hazardous location
conforming to NFPA 70].] [Motor starter shall be magnetic
[across-the-line] [reduced voltage start] type with [general-purpose]
[weather-resistant] [watertight] [dust-tight] [explosion-proof] enclosure
and shall be furnished with four auxiliary interlock contacts.] [Steam
turbines shall operate properly in a steam pressure range of [_____] Pa psig
with steam back pressure of [_____] Pa psig. Turbines shall have
horizontally-split, centerline supported casings, water-cooled bearing
housings with ring-oiled, babbitt-lined, bronze packed sleeve bearings.
SECTION 15559A
Page 58
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