Pulverized coal and biomass co-firing in the 150MWe unit of Tuncbilek power plant is computationally investigated, within the scope of a preliminary feasibility study. The considered furnace, burning Turkish lignite, has totally eighteen burners, positioned at three different levels. First, the pulverized coal combustion in the furnace is calculated and the predicted temperatures in the boiler first pass are compared with the previous measurements. Subsequently, a co-firing scenario is computationally analyzed, where the burners of the lowest level that supply 43% of the total fuel mass are fed by biomass, instead of coal. Turkish red pine is assumed to be the source of the biomass. In replacing the coal by biomass, the mass flow rates of the biomass and the corresponding air are adjusted in such a way that the thermal load and the equivalence ratio remain unaltered. Due to the lack of more accurate data for the biomass, the rate constants for the pyrolysis and chemical conversion of biomass are assumed to be the same as those of coal, along with the assumption of the same particle size distribution for both fuels. It is observed that the resulting flame structure for the case of co-firing is very similar to that of coal combustion. This result is encouraging for the application of biomass co-firing in the considered furnace.