Page 124 - Boiler plant and distribution system optimization manual

Boiler Tuneup 109

————————————————————————
Tuning Boiler Controls
Large, Interactive, Non-linear Control Loops

Important Impacts
• Efficiency
• Ramp Rate
• Turndown
• Low load operations
• Unit availability
• Ability to survive upsets and equipment fail-
ures
————————————————————————
Figure 9.36—Tuning boiler controls, important im-
Figure 9.34—This figure shows that differences exist pact
between the performance of individual burners, the
reasons should be established and corrected if pos-
sible. ————————————————————————

———————————————————————— Tuning Boiler Controls
The Reasons for Deviations Between Burners Basics
• Start from the bottom up
1. Gas. Gas port dimension differences & Piping
— Control drives
differences
— Valve operators
2. Oil. Atomizer port tolerances, surface finish & — Final control elements
erosion. Piping differences.
All measurements must be accurate beyond any doubt
3. Air. Variations in air flow to burners. and backed up by duplicate Instruments

4. Variation in pressure drops across burners. ————————————————————————
Figure 9.37—Tuning boiler controls, basics
[Air doors, swirl vanes, flow splitters, surface
finish & refractory damage.

5. Wind box symmetry & cross flow. ————————————————————————

6. Windbox air temperatures and buoyancy forc- Tuning Boiler Controls
es. Deadband and Repeatability
———————————————————————— Controlling Process Variables
Figure 9.35—Reasons for deviations between perfor-
mance of otherwise identical burners as illustrated • No amount of upper loop tuning will fix 5%
in Figure 9.34 deadband

• Over 3% to 5% deadband is unacceptable
TUNING BOILER CONTROLS
Process variables: feedwater flow, gas flow, air
The following section is composed of figures flow, fuel flow, spray valve, etc.
which cover the subject of tuning boiler controls.
They are designed for a classroom presentation ————————————————————————
Figure 9.38—Tuning boiler controls, deadband and
and make up a simple presentation of a complex
repeatability
subject.