Modelling NOx Formation in Commercial Swirl and Low NOx Burners

A wall-fired 350 MW(e) boiler firing pulverised coal was operated with low NOx burners in one portion of the furnace and standard swirl burners in the other portion. Axial in-flame measurements of temperature, oxygen and nitric oxide were obtained for the two types of 35 MW (thermal) burner at the same relative locations. Computational modeling of the burners was carried out using simplified nitrogen chemistry, with HCN and NH3 considered to be the NOx precursors. Coal moisture with associated in-flame drying of particles and subsequent ignition delay is considered. The particle trajectories, flow patterns and volatile release patterns for the two types burners were compared. In particular the influence on NOx reduction of particle penetration into the internal recirculation zone was explored. The hydrocarbon reburying effect of volatiles was investigated and found to have particular relevance to the low NOx burner. Overall the predictions of NO concentrations are in good agreement with the measurements, and it is concluded that simplified NOx chemistry has been successfully applied to both high and low NOx pf coal flames.