Numerical investigation into the effect of burner swirl direction on furnace and superheater heat absorption for a 620 MWe opposing wall-fired pulverized coal boiler

摘要

The paper investigates the effects of pulverized coal swirl burners' secondary air swirl directions on furnace water-wall, platen superheater and high temperature superheater heat absorption by using numerical simulations. The resultant effect on the carbon-monoxide and unburnt carbon levels was also investigated to establish the furnace performance. The conventional RANS approach was used along with a two-equation turbulence closure model to simulate the multispecies gas phase flow. Fuel particles were modeled as a discrete phase. The gas phase combustion was simulated using the eddy dissipation finite rate kinetics model and the surface reactions using a diffusion-kinetics limited model. To establish the validity of the modelling approach an actual 620 MWe boiler furnace and its superheaters were modelled, and the results compared to processed plant data. Once the model showed that it can predict the plant performance with reasonable accuracy it was used to investigate the performance changes for various burner swirl arrangements. Six swirl arrangement cases were simulated to determine the effect on the furnace performance indicators. It was found that by swirling all the burners per wall in the same direction that the furnace heat absorption could be increased by up to 6.67% and the unburned carbon fraction reduced from 0.029% to 0.022% when compared to the current boiler swirl configuration results, which has a staggered swirl direction arrangement. Furthermore, it was shown that the enhanced mixing in the volume adjacent to the burners also reduced the carbon-monoxide levels. The simulations demonstrated, for the given modelling methodology, that there is indeed interaction between adjacent burners which influences the combustion rate and in turn heat absorption in the water-cooled furnace walls and platen superheater for the modelled boiler. (C) 2019 Elsevier Ltd. All rights reserved.