Graduate Thesis Or Dissertation
 

Formation of NO during pyrolysis combustion of Kraft black liquor / by Rungsun Pianpucktr

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/3r074x33d

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  • Nitrogen evolution during black liquor pyrolysis and black liquor combustion were studied using a laminar entrained-flow reactor. The experimental conditions were 700-1100°C and 0.3-2.2 seconds residence time. The pyrolysis experiments were performed in a pure nitrogen atmosphere. The oxygen concentrations during the combustion of black liquor experiments were 4 and 21% oxygen in a nitrogen atmosphere, and 3 and 15% oxygen in a helium atmosphere. The black liquor used was a southern pine liquor with 0.09 wt.% nitrogen on dry basis. During black liquor pyrolysis, volatile species release and nitrogen release increased as residence time increased. Part of the released nitrogen formed NO. The NO formation depended on residence time and temperature. A maximum in the amount of NO formed was observed in the residence time range studied at 700 and 900°C. At 1100 °C, there was a maximum in the NO formation at a residence time below the shortest residence time studied, 0.3 seconds. NO destruction mechanisms dominated NO formation at long residence times and high temperatures. The NO formation data seemed to fit fairly well with a simple pyrolysis model developed by Iisa et al. The model included three stages: instantaneous release of N, oxidation of volatilized N to NO and reduction of NO to N₂. It was suggested that the model could be improved by using a more complicated reduction model. During black liquor combustion, total mass loss and nitrogen release increased as residence time and temperature increased as well. The total mass loss and the nitrogen release were higher during combustion than during pyrolysis. Volatile and char combustion began earlier at higher temperatures. At 700°C and 4% oxygen, there was no combustion, at 1100°C and 21%, combustion was complete at the shortest residence time. The amount of NO formed was higher during combustion than during pyrolysis. NO formation increased with increasing residence time except at long residences times when NO reduction was evident. During complete combustion, 90% of mass, 98% of nitrogen were released and the maximum NO formed was 49% of fuel nitrogen. Thermal and prompt NO formation occurred during black liquor combustion when pyrolysis occurred along with volatile and char combustion. During char combustion alone, there was no thermal NO formed.
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