Adjustment Procedures
6-18
750-211 (revised 2009)
Promethean Boilers, Model 4WI Manual
6.17 — Gas Fuel Combustion Adjustment
After operating for a sufficient period of time to assure a warm boiler, adjustments should be made to obtain effi-
cient 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 is a term used to describe a condition when there is the exact amount,
molecule for molecule, of air for the fuel burned. This can be accomplished under laboratory conditions, however,
it’s not practical to attempt to meet this condition in a boiler. 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 account for changes in boiler room temperature and
atmospheric conditions, and to ensure the combustion is on the proper side of the combustion curve, to avoid
occurances.
FIGURE 6-14. Flue Gas Analysis Chart for Natural Gas
Proper setting of the air/fuel ratios at all rates of firing must be established by the use of a combustion or flue gas
analyzer. The appearance or color of the gas flame is not an indication of its efficiency, because an efficient gas
flame will vary from transparent blue to translucent yellow.
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