draft controller shall fix the position of the boiler outlet
damper through a power operator. An indicator shall be provided
to show the amount of any manual adjustment that might be made.
The draft regulator shall be equipped with a manual-automatic
switch.
2.7.3
Combustion Controls with Oxygen Trim
[Flue gas oxygen trim may be furnished with combustion controls specified.
An oxygen analyzer and oxygen controller shall be provided. The oxygen
controller shall be of the proportional band and reset type and shall feed
its signal in a biasing fashion into the fuel-to-air ratio system. The
oxygen setpoint shall be a function of boiler load with operator biasing
capability. The amount of oxygen controller trim shall be limited to
prevent potentially hazardous conditions caused by equipment failure or
misoperation.]
2.7.4
Boiler Limit Controls
a.
Two low-water cutoffs shall be provided to prevent startup and to
shutdown the fuel if the boiler water level is below the preset
safe level. The primary interlock may be automatic or manual
reset type. The secondary interlock shall be the manual reset
type.
b.
A high-pressure limit switch shall be provided to shutdown the
fuel when steam pressure exceeds the preset safe limit. This
equipment shall be additional to the operating controls.
c.
A draft loss interlock and air-flow switch or a suction switch
shall be provided to prevent startup and to shutdown fuel supply
when air is inadequate to safely support combustion. Limit and
operating controls shall be provided for operation on a two-wire
grounded branch circuit.
d.
Safety interlocks required by the applicable NFPA standard shall
be provided.
2.7.5
Burner Control/Fuel Safety System
2.7.5.1
a.
General: The control system shall be of the microprocessor-based
(distributed digital or programmable controller) or relay type. A
dedicated hardwired insert panel shall be furnished for monitoring
and operator interface with the burner control/fuel safety system.
This insert panel shall also provide the operator with direct
fuel tripping capability in emergency situations. The burner
control system shall be sufficiently subdivided to permit
inservice checkout and maintenance without impairing the
reliability of the overall control system. The logic cabinets
shall include status indicating lights for logic inputs and
outputs, and for monitoring availability of control power to
subsystems as required to facilitate troubleshooting. Indication
of equipment status and system permissives shall be provided at
the operator interfaces. Where common power supplies internal to
the system are furnished, a full-capacity on-line backup supply
shall be included. Failure of either power supply shall be
alarmed.
SECTION 15559A
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