Operational Modifications – These involve changing
certain boiler operational parameters to create conditions
in the furnace that will lower NOx production. Examples
are burners-out-of-service (BOOS), low excess
air (LEA), and biased firing (BF). In BOOS, selected
burners are removed from service by stopping fuel flow,
but air flow is maintained to create staged combustion
in the furnace. LEA involves operating at the lowest
possible excess air level while maintaining good combustion,
and BF involves injecting more fuel to some
burners (typically the lower burners) while reducing fuel
to other burners (typically the upper burners) to create
staged combustion conditions in the furnace.