Special Maintenance Considerations - Effective Building Maintenance: Protection of Capital Assets - page 92

to the burner can be made that will increase the overall firing ef-
iciency.
— Preheat Combustion Air: Preheating air entering the burner
to support combustion will reduce the cooling effect when it
enters the combustion chamber and improve boiler efficiency.
In most boiler rooms, air is heated incidentally by hot boiler and
pipe radiation losses and rises to collect below the ceiling or
roof. This air can be easily ducted down to the burner. Boiler
efficiency increases approximately 2% for every 100°F increase
in combustion air temperature, up to a maximum temperature
of approximately 300-350°F.
— Change Oil-Fired Boiler Burners from Steam Atomizing to Air
Atomizing: Compressed air can be used for atomizing fuel oil in
lieu of steam, eliminating a parasitic boiler load that be as much
as 3-5% of the boiler capacity.
— Add Boiler Trim Control: Boiler efficiency can be improved by
incorporating an excess air trim loop into the boiler controls. It
is easy to monitor excess air as oxygen not used for combustion
is heated and discharged with the exhaust gases. A stack gas
oxygen analyzer can be installed to continuously monitor
excess air and adjust the boiler fuel-to-air ratio for optimum
efficiency. A carbon monoxide trim loop, used in conjunction
with the oxygen analyzer, assures that incomplete combustion
cannot occur due to deficient air supply.

Table 4-2 illustrates the effect of excess air control on overall
combustion efficiency for natural gas firing:

Table 4-2. Excess Air (%) vs. Combustion Efficiency
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CombustionEficiency(%)atFlueGasTemperatureLess

CombustionAirTemperature(F)
————————————————————————————————

Excess(%)

600
————————————————————————————————
9.5 2.0 85.4 83.1 80.8 78.4 76.0
15.0 3.0 85.2 82.8 80.4 77.9 75.4
28.1 5.0 84.7 82.1 79.5 76.7 74.0
81.6 10.0 82.8 79.3 75.6 71.9 68.2
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Air Oxygen 200 300 400 500