Release of nitrogen species from the recovery processes of three kraft pulp mills

The study centers on gaseous nitrogenous emissions (NOx and NH3) found in the recovery boiler and the causticizing area at three kraft mills. It covers the NOx emission tendencies of the black liquors, the cyanate (OCN-) formation during black liquor combustion, and the formation of ammonia (NH3) from cyanate in the mill liquors. Mass balances were carried out to calculate the nitrogen flow with the smelt, and these data were compared to the nitrogen flow with the black liquor based on black liquor analysis and mill process data. In all cases, about 30% of the black liquor nitrogen formed NO, of which approximately 60% was from the pyrolysis combustion step and the remaining 40% was formed during char combustion and smelt oxidation.