To improve thermal efficiency of a boiler, by a method wherein oxygen contained in at least one level of air in the level of secondary air or a level higher than the secondary air is enriched, in a black liquor recovery boiler equipped with at least two levels of air injection.
Primary air 2 is introduced into a boiler 1 in a level A, secondary air 3 is introduced in a level B and tertiary air 4 is introduced in a level C, respectively, while a liquid gun for injecting black liquor is arranged in a level D. Further, a superheating unit 5, a boiler bank 6 and an economizing device unit 7 are provided continuously above the boiler 1. Upon operating such a boiler 1, combustion oxidizing agent is injected under secondary air or the same level to increase the concentration of oxygen from 21% into the degree of 30% in order to effect the complete combustion of the black liquor. According to this method, necessary air is reduced and the thermal efficiency of the boiler 1 is improved. The third level is preferably arranged at the same level as or near that of the injection port of the black liquor.
PHILIPPE LOUIS C
DUCHATEAU ERIC L
VERLOOP ARIE
DYE EDWARD C
AIR LIQUIDE
JANSEN COMBUSTION & BOILER TEC
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