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Burner Basics - Industrial Burners (Nozzle and Premix)

Nearly all industrial gas burners are one of two types – premix or nozzle mix. The difference lies in the way the gas and air are brought together before combustion.

Premix Burners
Premix burner systems have two major components – a gas-air mixer and a burner nozzle.

Nozzle Mix Burners
Nozzle mix burners serve as their own mixers with gas and air mixing prior to ignition.

Industrial Gas Burners
The left branch is the major types of premix burners – flame retention nozzles, line and ribbon burners, tunnel burners and infrared heaters. In the nozzle mix branch, the major types are low and high velocity forward flame burners, line-type, tube-firing and flat & short flame burners. Within each family, the main distinguishing feature is the flame shape or configuration. These different flame characteristics are required to suit the needs of a variety of industrial heating processes.

In a premix system, regardless of the flame configuration, proportioned flows of gas and air are brought to the mixer (#1), where they are blended into a combustible mixture (#2). This mixture, which is under pressure, is then carried through piping to the burner nozzle or head (#3), where it's ignited and burned (#4).

Burners operating lean (not enough gas) have purplish flames that get smaller as the amount of gas decreases. When they become extremely lean, they take on a ragged, broken appearance and may have a harsh, hissing sound. A burner operating at correct ratio has a sharp, bright blue, well-defined flame. Burners operating rich (too much gas) tend to have yellow and orange flames, which get longer and softer as more gas is added. If the amount of gas is really excessive, the flame will develop yellow tips and begin to smoke. It also burns so slowly that it will begin to lift off the burner nozzle.

An issue with premix burners is their susceptibility to flashback if they are turned down to firing rates that are too low. This happens when the speed of the combustible mixture leaving the nozzle is so low that the flame can work its way back upstream through the nozzle. Sometimes the flame will stop somewhere in the supply piping, burning and creating a hot spot. Other times, it will make it all the way back to the mixer, creating a loud bang.

Liftoff can also happen on a properly-adjusted burner if the mixture flow is set higher than the nozzle can handle. The mixture speed is so high that it literally pushes the flame out of the nozzle into open space, where it extinguishes.