Chapter 5 Adjustment Procedures
5-12 750-177
T. FUEL OIL COMBUSTION ADJUSTMENT
After operating for a sufficient period of time to assure a warm boiler, adjustments should be made to obtain
efficient combustion.
Burner efficiency is measured by the amount or percentage of O
2
present in the flue gas. O
2
readings
determine the total amount or excess air in the combustion process, above the point of stoichiometric
combustion or perfect combustion. Stoichiometric combustion however, is the reference point used when
setting fuel/air ratios in a boiler.
There must always be excess air in the combustion process to ac
count for changes in boiler room conditions
and to ensure the combustion is on the proper side of the combustion curve .
Proper setting of the air/fuel ratios at all rates of firing must be
established by the use of a combustion gas
analyzer. Efficient combustion cannot be solely judged by flame condition or color, although they may be used
in making approximate settings. Combustion settings should be done so that there is a bright sharp flame with
no visible haze.
Most flue gas analyzers in use today measure the content, by percentage, of oxygen (O
2
) and in some cases,
smoke. Carbon dioxide (CO
2
) is not normally measured with modern gas analyzers, but may be displayed as
a calculation.
The O
2
levels through the entire firing range of the burner, low fire to high fire should be tested. Cleaver-Brooks
recommendations on turndown should also be followed and the turndown range of the burner should not be
exceeded.
It is required to set the burner to operate with a rea
sonable amount of excess air to compensate for minor
variations in the pressure, temperature, or burning properties of oil. Fifteen to 20% excess air is considered
reasonable. This would result in an O
2
reading of 3% to 4%, at high fire.
Final adjustment to fuel input must be made to produce a minimum
of smoke. A maximum smoke spot density
of a No. 2 for light oil, as measured in conformance to ASTMD 2156-63T.
Through the use of the manual flame control, slowly bring the unit to high fire by stages
while monitoring
combustion for overly rich or lean conditions. At the high fire position, the air damper should be fully opened.
U. LOW OIL PRESSURE SWITCH
The L.O.P.S. prevents burner ignition, or stops its operation, when the oil pressure is below the setpoint. Adjust
the control by turning the screw on top of control case to an indicated pressure 10 psi below the established
primary oil pressure setting indicated on the oil supply pressure gauge. The switch will remain in a closed
position as long as the oil pressure exceeds this setting. The control normally used automatically resets when
pressure is restored after a drop.
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