Abstract: Methods of increasing the throughput of recovery boilers equipped with at least three levels of injection of air with oxygen enrichment of the air in at least one air level. In one method, a black liquor recovery boiler has three levels of air injection, and oxygen enrichment is applied to at least the secondary and the tertiary air injection levels. In another method, a black liquor recovery boiler has four levels of air injection, and oxygen enrichment is applied to one or more of the tertiary or quaternary air injection levels. In another method, a black liquor boiler has three levels of air injection, with oxygen enrichment applied to at least two air injection levels. After combustion, the oxygen concentration in the resultant flue gas is sensed. The oxygen injection is then adjusted in order to maintain the sensed oxygen concentration at the previously selected oxygen set point.

Abstract: Methods are presented to increase the throughput of a recovery boiler equipped with at least primary and secondary levels of injection of air. The methods comprise operating the recovery boiler with a third level of oxidant injection below or at the same level as the secondary level, and oxygen enrichment applied to at least the secondary level and said third level.

Abstract: Methods of increasing the throughput of recovery boilers equipped with at least two levels of injection of air, the methods improving the thermal efficiency of the boiler with oxygen enrichment of the air in at least one level of the combustion air system, at or above the secondary air level. In one method, a black liquor recover boiler having two levels of air injection is retrofitted with a third level of oxidant injection below or at the same level as the original secondary air, and oxygen enrichment is applied to at least the original secondary air stream and the third level air stream. A preferred method is for the third level to be placed at or close to the same level as the black liquor injector ports.