Mathematical modelling and simulation can be used to assess the effect of modifications of the combustion process and pollutant formation. In this paper two pulverized coal combustion plants are considered. The first plant is a bituminous coal-fired furnace with eight swirl burners and a thermal power of 490 M W. In order to reduce NOx-formation, the furnace system was modified using a different burner design and a modified burnout air arrangement for realizing the staging of combustion air. Both cases were investigated. The second plant is a brown coal-fired furnace with an electric power of 150 MW. The goal was to reduce CO-emissions and to improve the burnout of the coal. For a more flexible discretization of the domain a method was developed which allows that each burner can be discretized by an independent grid system. Using this method, details of the burner geometry can be considered and the governing processes of pollutant formation in the near-burner zone may be described in more detail.