A reduced NOx reaction model for pulverized coal combustion under fuel-rich conditions

A reduced NOx reaction model was developed for analysis of industrial pulverized coal firing boilers. The model was developed from experiments of laminar premixed combustion under a variety of stoichiometric ratios, burning temperatures, coal ranks (from sub-bituminous coal to anthracite) and particle diameters. Calculations agreed with experimental results for NOx and nitrogen species (NH3 and HCN), if the model assumed that the hydrocarbon radicals were formed not only from pyrolysis of volatile matter, but also from char oxidation and gasification. The presence of hydrogen in char at the final burnout stage supported this assumption. NOx reduction by hydrocarbon radicals was the most important reaction in high temperature (>1500 K), fuel-rich, char combustion regions. NOx reduction from nitrogen species was sensitive to peak NOx concentration in volatile combustion regions, but NOx emission downstream had little influence from the peak NOx concentration. The heterogeneous reaction between char and NOx was important for fuel-lean or low-temperature conditions.