TM 5-810-15
flow to the boiler is metered and the feedwater
valve is positioned by summing steam flow and
drum level error through a controller. This system
should be used when multiple boilers are connected
to a common feedwater supply system since
feedwater flow is a metered feedback signal and the
control system demands a feedwater flow.
(3) System selection. Table 9-3 summarizes
the types of feedwater control systems and the
parameters which should be used for selection of
the proper system.
c. Furnace pressure controls.
(1) Single element control. Furnace pressure
controls are primarily single element type. The final
control element is the ID fan inlet damper, ID fan
inlet vanes or adjustable speed drive for ID fan.
The control loop shown in figure 9-14 also uses a
feed-forward demand signal that is representative
Table 9-3. Feedwater Control System Selection Guide
Boiler Requirements
Steady-State
Swinging
Multiple
Control System
Load
Load
Boiler
Two-element
X
X
Three-element
X
X
9-15
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