Page 127 - Boiler plant and distribution system optimization manual

112 Boiler Plant and Distribution System Optimization Manual

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Tuning Boiler Controls Tuning Boiler Controls

Drum Level Stability Runbacks

Drum level stability is needed for: • Runbacks must be tuned and demonstrated or
disconnected.
1. Good ramp rate
• A single equipment failure could cause a Domino
2. Minimum load operations Trip Effect.

3. Runback capability (Staying on the line after ————————————————————————
an upset] Figure 9.51—Tuning boiler controls, runbacks

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Figure 9.49—Tuning boiler controls, drum level sta- ————————————————————————
bility Tuning Boiler Controls
Why?

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• Improved ramp rate
Tuning Boiler Controls • Lower excess air

• Higher final steam temperatures
• Adaptive tuning
Every critical loop should be tuned at 6 dif- • Economic payback
ferent positions
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• Tuning requires Figure 9.52—Tuning boiler controls, why?
a. Time
b. Patience
c. Good engineering judgment
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• Tuning is the art of selecting acceptable compro-
Reducing Excess Air
mises

1. Oxygen Trimming
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a. Compensates for Many Variations of Buffer
Figure 9.50—Tuning boiler controls, requirements
zone Required
b. Does not Maintain “Optimum” A/F Ratio

2. CO Trimming
a. Establishes ‘Best’ A/F Ratio
b. No Buffer zone Required.

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Figure 9.53—Oxygen trim systems vs. carbon monox-
ide trim systems