There are three main types of abnormal combustion phenomena: flameout, flashback, and yellow flame (light flame).
1) Defire: The gas should have a certain speed when leaving the burner fire hole to ensure normal combustion of the gas. When the air flow speed increases to a certain limit value and the flame burns at a certain distance away from the nozzle, it is called flame separation. If the air flow speed continues to increase, the flame will be blown out, which is called defire.
2) Backfire: When the air flow velocity reaches a certain limit, that is, less than the flame propagation speed, the flame will retract into the nozzle, which is called backfire.
3) Yellow flame (glow flame): When the primary air supply is insufficient, combustion is incomplete due to insufficient oxygen, and the hydrocarbons are decomposed by heat to form carbon particles and soot. The flame is yellow and glows, which is called yellow flame (glow flame).
Most of the NO generated by the combustion of gaseous fuel is temperature (thermal) type NO. The main factors affecting its generation are combustion temperature, oxygen concentration and the time the flue gas stays in the high temperature zone.
Staged combustion: Combustion is completed in two stages, the temperature and oxygen concentration are reduced, and the generation of NOₓ is reduced;
Flue gas recirculation: Resupply part of the burned flue gas for combustion to reduce the combustion temperature and inhibit the generation of NOₓ;
Rich and light combustion: The gas is premixed and burned at a non-stoichiometric ratio, the combustion temperature is reduced, and the generation of NOₓ is suppressed;
Combined combustion: combine 2 to 3 of the aforementioned combustion methods