SIMULTANEOUS REDUCTION TECHNIQUES OF NITROUS AND NITROGEN-OXIDES FROM FLUIDIZED-BED COAL COMBUSTOR

Some techniques for simultaneous reduction of nitrous and nitrogen oxide emissions in bubbling fluidized-bed combustion were systematically Examined and evaluated with an experimental combustor having an inner diameter of 0.16 m. Several kinds of fine solid particles, such as red mud, calcium and magnesium oxides, were fed into the fluidized bed with coal and injected into the Rue gas duct. No satisfactory effect on nitrous oxide decomposition was found from the above experiments. Although propane gas injection with premixed air into the top of the freeboard decreased nitous oxide substantially, nitrogen oxides emission increased remarkably. Two-stage combustion was rather effective for simultaneous reduction of nitrous and nitrogen oxides. An Improved Three-Stage Combustion System (ITS) in which propane gas with substoichiometric air was injected from the secondary-air injection port was examined to reinforce the effectiveness of two-stage combustion. Excellent performance in the system, more than 85% of reduction ratio for nitrous oxide without any increase in nitrogen oxides, was confirmed at a maximum freeboard temperature of around 925 degrees C.