NOx controlling in a municipal solid waste incinerator by selective non-catalytic reduction (SNCR) using urea-water solution is studied by means of computational fluid dynamics (CFD) simulation, which is validated with on-site experiments A three-dimensional turbulent reacting flow CFD model including the reduced chemical kinetics and the reagent droplet phase is developed to predict the performance of the SNCR process installed in the incinerator. At normalized stoichrometric ratio (NSR) = 18, 70% NO (nitrogen oxide) reduction is obtained from on-site experiments, while 66% NO reduction is from the CFD simulation with the nonuniform droplet size NH3 slip obtained from the CFD simulation is in reasonable agreement with the in-situ experiment. The effect of the droplet size distribution on the nitrogen oxide reduction efficiency is examined on CFD simulation results. Since the NO concentration at the SNCR exit is more dispersed in the nonuniform droplet size than in the uniform one, the nonuniform droplet size enhances mixing with the flue gas and increases the NO reduction efficiency. (C) 2009 Elsevier B.V. All rights reserved.