TM 5-810-15
the primary air to fuel ratio above a minimum level
system to properly modulate fuel flow in response
for all pulverizer loads.
to the system demand.
g. Gas/oil system controls.
(2) Combustion air control. The combustion
(1) Fuel flow control. Fuel flow in gas/oil fired
air is normally controlled at the FD fan. Air flow
boilers is controlled by operation of gas or oil
for package boilers is normally controlled by outlet
control valves in the supply lines to the burners.
dampers at the FD fan. Other methods that are
The gas or oil control valves are modulated to
used include control of the FD fan inlet vanes or
control fuel flow based on the demand signal
control of the FD fan inlet damper. The relationship
generated by the combustion control system. Gas
between inlet vane or damper position and air flow
flow to the burner is measured by taking the
will be determined for characterizing the final
differential pressure across an orifice. Oil flow to
control element. When a metering type control
the burners will be measured by a rotating disk type
system is used air flow is measured downstream of
meter. Metering type control systems utilize the
the FD fan or a piezometer may be installed at the
fuel flow and unit load in the combustion control
FD fan inlet.
9-6
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