Numerical analysis of co-firing pulverized coal and biomass in vertical cylindrical laboratory furnace is explored. Ratio of coal and biomass in the fuel was 80:20 by mass.for all cases. Mathematical model of combustion in the furnace was established describing physical phenomena such as turbulent flow, heat and mass transfer, devolatilization and combustion. 3D-model of combustion in laboratory furnace was created using CFD software FLUENT. The shape of biomass particles was estimated as cylinder and was accounted in the calculation of particle trajectories via custom developed model. Newly developed model shows better agreement with experimental data than the existing model which estimates particles as spheres. Experimental measurements were conducted on 20 kW laboratory furnace with controllable wall temperature. Temparature varied in the range from 960°C to 1550°C depending on the case. Also, excess air for combustion was set at 10% or 20% depending on the case. The size of biomass particles was less than 500 μm. Analysis of the results shows that the influence of the particle size increases with the size of the particle. Also, the geometry of the cylindrical particlesstrongly influences the beginning and the intensity of devolatilization and subsequently the combustion.