2.4.3
Positioning Type Combustion Control Equipment
Positioning controls shall be a type wherein separate parallel controllers
are provided for fuel feed and air flow, and both are modulated by the
boiler load. Manual means shall be provided for readily adjusting the
fuel-to-air ratio for the most efficient combustion. An adjustable
compensating device shall maintain the proper ratio of fuel and air over
the entire range of operation to provide combustion efficiency within the
range specified. When a furnace draft controller is required, it shall be
supplied. All controllers shall be flush-mounted on the control and
instrument panel; all adjustments and calibrations of fuel feed, air flow
and furnace draft, shall be made at the front of the panel.
2.4.4
Semimetering Type Combustion Control Equipment
Two controllers per boiler shall be provided, one for fuel feed and one for
air flow. The first of these shall be positioned in proportion to the
boiler load to deliver a proportionate impulse to the second controller
which shall function in direct relation to that impulse; the second
controller then shall measure the fuel feed or air flow provided and
automatically make necessary adjustments to maintain the fuel-to-air ratio
for which it is set over the entire range of operation. Furnace draft or
pressure controllers shall be provided where required. All controllers
shall be flush-mounted on the control and instrument panel; all adjustments
and calibrations of fuel feed, air flow, and furnace draft or pressure,
shall be made at the front of the panel, and indicators shall be provided
to show the amount of adjustment and the results obtained.
2.4.5
Metering Type Combustion Control Equipment
Metering controls shall provide adequate means for automatically adjusting
both fuel feed and air flow in strict relation to the load requirements.
In addition, they shall measure the rates of fuel feed and air flow and
maintain the required ratios over the full range of boiler operation. In
addition to the master controller, there shall be separate controllers for
fuel feed and air flow. These controllers shall respond either in parallel
or series. Air flow-fuel flow cross limiting shall be included. [If
required by a particular system, a separate fuel-to-air ratio controller
may be provided.] Actual rate of fuel flow shall be metered accurately in
the fuel line to the burner. Actual air flow may be measured by a
differential orifice in the forced draft duct. Operation of either
controller for both functions will not be acceptable. In addition, a
separate controller shall be provided to control the draft or pressure in
the boiler furnace. Controllers shall be flush-mounted on the control and
instrument panel; all adjustments and calibrations of fuel feed, air flow,
fuel-to-air ratio, and furnace draft or pressure, shall be made at the
front of the panel and indicators shall be provided to show the degree of
adjustment.
2.4.6
Combustion Control with Oxygen Trim
Flue gas oxygen trim may be provided as an adjunct to the metering system
of control. The oxygen content in combustion gases shall be determined;
from this, an impulse shall be sent to the oxygen controller, which shall
readjust the air flow to maintain the required oxygen content. The oxygen
set point shall be a function of generator load with operator biasing
capability. The amount of oxygen controller trim shall be limited to
prevent potentially hazardous conditions created by equipment failure or
misoperation.
SECTION 15555A
Page 36
Previous Page
