COAL COMPOSITION EFFECTS ON NOX FORMATION DURING INITIAL-STAGE OF PULVERIZED COAL COMBUSTION

Eighteen coals covering wide ranks from semianthracite through subbitumious coal were burned in a turbulent-flow furnace under two-stage combustion to investigate the influence of coal composition on nitric oxide formation. These experimental results showed that the conventional model could not reflect the influence of coal properties on NO formation during the initial stage. Fuel nitrogen mainly decompsed into gas phase as HCN, NH3 and N2. Both the behavior of devolatilization and yields of volatile nitrogen species differed among coal ranks. It seemed that these species affected NO formation during the initial stage, because they differ froin one another in rate of NO formation and destruction. On the basis of the data of both the pyrolysis and the laminar flow combustion, devolatilization rates of HCN, NH3 and N2 were determined. A model combined with the devolatilization paths of volatile nitrogen species was proposed to explain the influence of coal composition on NO(x) formation during the initial stage of combustion. One-dimensional analysis based on the proposed model was performed by using the overall reaction rates. Calculation results were compared with experimental data from the turbulent flow furnace. The proposed model gave a better fit of the data than did the conventional model.