Page 126 - Boiler plant and distribution system optimization manual

Boiler Tuneup 111

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Tuning Boiler Controls
Tuning Boiler Controls
Feed Forward Signals
Fuel Flow
1. The necessary influence of feed forward sig-
nals should be calculated from steady state • Fuel should never lead air supply
tests.
• Fuel and air should move together
2. No more than 80% - 90% of actual influence
should be set • Adaptive tuning is most often required for
fuel and air to synchronize variations over
———————————————————————— turn-down range
Figure 9.44—Tuning boiler controls, feed forward
signals ( ————————————————————————
Figure 9.47—Tuning boiler controls, fuel flow re-
quirements
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Tuning Boiler Controls

Feed Forward Signals ————————————————————————

Example: superheat spray set point Is 15 F for 100 Tuning Boiler Controls
psi of first stage pressure
Drum Level Stability
— Use only 12 -13 F/100 psi feed-forward sig-
nal • Drum level instability can de-stabilize an en-
tire boiler
— Let feedback control handle last 2 degrees to
eliminate Instability • Smaller drums may need 3-element control

———————————————————————— • Extended range of feedwater and steam flow
Figure 9.45—Tuning boiler controls, feed forward measurement may also be needed to measure
signals low and high range temporary excursions In
boiler operations

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Figure 9.48—Tuning boiler controls, drum level sta-
bility
Tuning Boiler Controls

Fuel Flow

• During the first 30 to 90 seconds after a load
change the required energy comes from storage
[boiling water in the drum]

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Figure 9.46—Tuning boiler controls, fuel flow