Influence of nozzle height to width ratio on ignition and NOx emission characteristics of semicoke/bituminous coal blends in a 300 kW pulverized coal-fired furnace

Abstract

To improve the ignition behavior and to reduce the high NO x emissions of blended pulverized fuels (PF) of semicoke (SC), large-scale experiments were conducted in a 300 kW fired furnace at various nozzle settings, i.e., ratios (denoted by h f /b) of the height of the rectangular burner nozzle to its width of 1.65, 2.32, and 3.22. The combustion tests indicate that the flame stability, ignition performance, and fuel burnout ratio were significantly improved at a nozzle setting of h f /b = 2.32. The smaller h f /b delayed ignition and caused the flame to concentrate excessively on the axis of the furnace, while the larger h f /b easily caused the deflection of the pulverized coal flame, and a high-temperature flame zone emerged close to the furnace wall. NO x emissions at the outlet of the primary zone decreased from 447 to 354 mg/m 3 (O 2 = 6%), and the ignition distance decreased from 420 to 246 mm when the h f /b varied from 1.65 to 3.22. Furthermore, the ratio (denoted by S R /S C) of the strong reduction zone area to the combustion reaction zone area was defined experimentally by the CO concentration to evaluate the reduction zone. The S R /S C rose monotonously, but its restraining effects on NO x formation decreased as h f /b increased. The results suggested that in a test furnace, regulating the nozzle h f /b conditions sharply reduces NO x emissions and improves the combustion efficiency of SC blends possessing an appropriate jet rigidity. Keywords rectangular jet burner, nozzle height to width ratio, ignition characteristics, pyrolyzed semicoke (SC) and bituminous blend, NO x formation