The Behavior of NH3 and NOx in a Two-Stage Fluidized-Bed Coal Combustor

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Axial concentration profiles of NH3 and NOx were measured in a two-stage fluidized-bed combustor and effects of NH3 injection into the combustor at various positions were experimentally evaluated for Nox reduction. The values of NOx emission from the first-stage bed was shown to decrease with decreasing the primary air ratio, while NH3 emission increased up to 3 to 5 times that of NOx at the primary air ratio of 0.7.In the first-stage freeboard NH3 decomposed very rapidly and only apart of NH3 remained available for subsequent NOx reduction. NOx emission increased by NH3 injection at any position where the residual oxygen concentration is appreciable.Although a fair extent of NOx reduction was observed when conciderable amount of NH3 was injected into the second-stage freeboard, the contribution of NH3 to NOx reduction was generally small. In conclusion, it was indicated for reducing NOx emission that the first-stage freeboard should be long enough to decompose NH3 completely before it enters the second-stage and that the concentration of oxygen contacting NH3 should be minimized by means of partial feed of secondary air.
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