BURNER STABILITY:

Stable burner operation is critical to good incinerator operation.  A few incinerators can operate with zero fuel, but most benefit from at least a small burner.  Where the waste contains almost all of the heating value needed for operation, the entire waste entry area should be considered part of the "burner"!   At best, an unstable burner will cause variations in waste destruction efficiency or irritating combustion noise. At worst, burner instability can be responsible for repeated nuisance shutdowns of the incinerator system and damage to expansion joints and other components.

Air Availability: Most often the total air supply is OK, but air and fuel / waste positioning within the burner or furnace is the problem. Errors in mixing the air and fuel components create localized instability although the stack gas may contain precisely the amount of excess O2 desired. Combustion noise (pulsation) is generated as the flame enters and then leaves zones where the air / fuel mixture is in the combustible range. 

Too much air: Quench combustion reactions => flame unstable or generates products of incomplete combustion (PIC) like carbon monoxide and even soot.  Excessive fuel usage - if you heat a little air that you don't have to, you are wasting fuel.

Too little air: Combustion reactions cannot go to completion => flame unstable or generates PIC.  Stack smokes. Combustion noise may be present as the flame pulsates.

Source of problem: Air flow control (control logic problem), air blower too small, or bad air placement relative to fuel placement (burner layout problem)

A well designed burner injects high BTU (high air demand) fluids well inside the main air flow path. Inerts (nitrogen, aqueous wastes) are added away from the main flame area in order to avoid quenching the flame before it fully develops. Switching the locations of the fuel and inert streams here would make the burner unworkable.

Waste Flow / Composition Variations:  Waste is an undesired byproduct plant production. The flow and composition might swing as the plant’s control loops focus on keeping the main product on spec.

Waste flow varies too rapidly: air flow cannot track and air availability is a problem or auxiliary fuel / quench medium cannot track and furnace temperature varies out of range (possible system shutdown).

Waste composition varies too rapidly:  can cause the same problems as rapid waste flow changes.

Source of problem:  the control system can't anticipate the shifting combustion requirements so adjustments are often out of phase.

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