TEMPERATURE, VELOCITY AND SPECIES PROFILE MEASUREMENTS FOR REBURNING IN A PULVERIZED, ENTRAINED FLOW, COAL COMBUSTOR

Abstract

An experimental program has been completed to make detailed measurements of a pulverized coal flame with reburning and advanced reburning. Maps of species (CO, CO{sub 2}, O{sub 2} , NO, HCN, and NH{sub 3}), temperature and velocity have been obtained which consist of approximately 60 measurements across a cross sectional plane of the reactor. A total of six of these maps have been obtained. Three operating conditions for the baseline flame have been mapped, two operating conditions with reburning, and one operating condition of advanced reburning. In addition to the mapping data, effluent measurements of gaseous products were obtained for various operating conditions. This report focuses on the advanced reburning data. Advanced reburning was achieved in the reactor by injecting natural gas downstream of the primary combustion zone to form a reburning zone followed by a second injection of ammonia downstream of reburning to form an advanced reburning zone. Finally, downstream of the ammonia injection, air was injected to form a burnout or tertiary air zone. The amount of natural gas injected was characterized by the reburning zone stoichiometric ratio. The amount of ammonia injected was characterized by the ammonia to nitrogen stoichiometric ratio or NSR and by the amount of carrier gas used to transport and mix the ammonia. A matrix of operating conditions where injector position, reburning zone stoichiometric ratio, NSR, and carrier gas flow rate were varied and NO reduction was measured was completed in addition to a map of data at one operating condition. The data showed advanced reburning was more effective than either reburning or NH{sub 3} injection alone. At one advanced reburning condition over 95% NO reduction was obtained. Ammonia injection was most beneficial when following a reburning zone which was slightly lean, S.R. = 1.05, but was not very effective when following a slightly rich reburning zone, S.R. of 0.95. In the cases where advanced reburning was most effective (reburning S.R. = 1.05), higher NSR values improved NO reduction but NSR was secondary to NH{sub 3} injector location. The optimal location for injection was found to coincide with changes in the temperature field. The mapped temperature, species and velocity data for advanced reburning showed that the largest drops in NO occurred in a region where the O{sub 2} concentration was between 0.7 and 3.0%, NH{sub 3} was between 0 and 2961 ppm, and temperatures were between 1274 and 1343 K. These are similar to optimal conditions known for SNCR. Significant NO reductions were seen when NSR values were near one, suggesting NH{sub 3} was very effective at NO reduction when surrounding temperature and species conditions were favorable. Because this was only one detailed set of data, it is difficult to conclude that these conditions are optimal or need to exist for optimal NO reduction. More detailed mapping data at other operating conditions would be useful in identifying optimal advanced reburning conditions.