In-furnace measurement of sulfur and nitrogen species in a recovery boiler

There is a lack of experimental data on the gas composition in recovery boiler furnaces, particularly in the lower furnace and at the black liquor spraying level. Experimental determination of the gas composition in full-scale furnaces is important for the understanding of the kinetics of the gas phase reactions and the formation of different intermediates in the combustion process. The gas composition was measured in the furnace of a large recovery boiler, using a new gas sampling probe concept. The measurements were carried out from the primary air level to the upper tertiary air level. The measurements were a part of an extensive campaign planned and carried out to support validation of models based on Computational Fluid Dynamics (CFD). This paper will focus on the sulfur and nitrogen species measured in the furnace and on the developed gas sampling probe. A number of reactive sulfur and nitrogen intermediates were identified and quantified in the measurements. Especially high concentrations of different intermediates could be measured at the black liquor spraying level. Measured nitrogen and sulfur species include: nitrogen monoxide (NO), nitrogen dioxide (NO₂), ammonia (NH₃), hydrogen cyanide (HCN), hydrogen sulfide (H₂S), sulfur dioxide (SO₂), methyl mercaptan (CH₃SH), ethyl mercaptan (C2H₅SH), dimethyl sulfide, (CH₃)2S dimethyl disulfide (CH₃)2S₂, carbonyl sulfide (COS) and carbon disulfide (CS₂). Some of these have not been reported before in full scale measurements.