Page 57 - Boiler plant and distribution system optimization manual

42 Boiler Plant and Distribution System Optimization Manual

TUNE-UP
Sources of Air Fuel Ratio Errors
Figure 4.13 shows the first step in dealing
with boiler losses. The Tune-Up is almost always 1. Fuel: gravity, temperature, Btu content
found to be necessary. Problems in the burner
2. Fuel System: pressure variations & wear
system, control system and other components are
often “corrected” by plant personnel by increas- 3. Combustion air: pressure, temperature, hu-
midity fan performance, dampers & duct-
ing excess air.
ing
When a boiler is having problems it usual-
ly begins to smoke. Problems have often been 4. Exhaust system: back pressure variations,
“fixed” by increasing excess air. If no one is mon- boiler fouling, stack effect & wind effect
itoring and correcting the excess air level, this sit- 5. Control System: fuel & air positioning ac-
uation can cost a lot of wasted fuel. Be advised curacy, alignment, synchronization, repeat-
that problems that have been “fixed” by increas- ability & linearity
ing excess air will reappear when a tune-up is at-
tempted. Figure 4.14—A troubleshooting table
By reducing excess air from 35.5% to 9.3% in for reducing excess air.
the example boiler, fuel losses have been reduced
by 1.8%. This is a typical fuel savings for many
boilers.

Figure 4.15—Reducing outlet temperature produces
higher efficiency.
Figure 4.13—The first step in improving efficiency is
to reduce excess air losses by tuning up a boiler. Stack Temperature Check List
—————————————————————
1. Check for over firing
REDUCING STACK TEMPERATURE 2. Firesides deposits of soot and slag
3. Waterside deposits of scale and baked on sludge
Figure 4.15 shows that a fuel savings of 2.7% 4. Gas pass short circuits
5. Install economizer
can be produced by reducing net stack tempera-
6. Install air preheater
ture from 400F [205C] to 250F [121C]. This high
7. Reduce Excess Air
as-found temperature may be caused by soot or
8. Install turbulators
scale deposits in the boiler or by hot gas short cir-
9. Install condensing heat recovery
cuits through defective baffles. Figure 4.16 is a list
—————————————————————
of things to check when boiler exit temperatures Figure 4.16
are too high. Check list for reducing stack temperature.