master demand only. Change in master demand shall be multiplied by the
derivative circuit to assist in overfiring on load increase and underfiring
on a load decrease. Provision shall be made for taking any one of the
pulverizers for each boiler out of service with firing continuing at
reduced rates for extended periods during maintenance or during low demand
intervals. Alarms and interlocks of the fuel master control shall be as
required by the boiler but shall include, as a minimum, a unit trip to run
the fuel master to zero and alarm contacts for "fuel master at maximum,"
"fuel master at minimum," "fuel greater than air," and "air demand limiting
fuel."
2.4.5.2
Primary Air
Primary air fan or suction air fan control for each system shall be
provided with all required damper operating and sensing control devices.
Primary air system fans shall exhaust into a duct common with individual
pulverizer primary air flow dampers in order to control the flow required
by each pulverizer. Common duct pressure shall be maintained at a given
set point by modulating fan inlet dampers. Gain compensation shall be
provided to maintain system response with a different number of fans in
operation. Biasing between fans shall be provided.
2.4.5.3
Air Temperature Control
Pulverizer coal air temperature control, for each pulverizer coal air exit,
shall assume the maximum safe mixture temperature required to increase the
firing efficiency at the furnace and to remove additional residual moisture
that may be present in the coal. Tempering air inlet with controls shall
be provided to prevent combustion in the pulverizer.
2.4.5.4
Flame Safety System
A burner control/flame safety system shall be provided with the boiler.
The system shall meet the requirements specified in NFPA 8501 as a minimum.
An interface shall be provided between the analog control system and the
flame safety system or burner control system. As a minimum, coal feeders
and pulverizer air dampers shall be positioned to respond to "unit tripped"
and "pulverizer tripped" signals. Burner controls shall incorporate a
pulverized coal ignition system. The burner control system shall
incorporate boiler shutdown as well as normal monitoring of startup
sequencing and normal operation. Each burner shall have a scanner for the
lighting system as well as a scanner for the main flame.
2.5
FLUIDIZED BED COMBUSTION BOILERS
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NOTE: The designer will perform an economic
analysis to compare the installation and operating
costs of a fluidized bed combustion boiler against
the use of a conventional boiler and its associated
air pollution control equipment.
**************************************************************************
Where indicated, fluidized bed combustion boilers shall be provided. The
Contractor may provide either bubbling bed (AFB) or circulating bed (CFB)
boilers. Fluidizing velocities shall range from 1.2 to 3.7 m/second 4 to
12 fps for AFB boilers and range from 4.3 to 9.1 m/second 14 to 30 fps for
CFB boilers. Each boiler shall be in compliance with sulfur dioxide,
nitrogen oxides, particulate, carbon monoxide, and all other emission
SECTION 15559A
Page 39
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