The co-firing of biomass with coal presents an appealing approach for reducing CO2 emissions and leveraging renewable energy sources. Oxy-fuel combustion, employing pure oxygen instead of air, stands out as a noteworthy technology for efficient CO2 capture. This study focuses on the numerical investigation of the flame resulting from the co-combustion of pulverized coal and biomass. Utilizing the Fluent commercial CFD code, 2D numerical co-combustion calculations are conducted in a 100 kW vertical down-fired boiler equipped with a swirl burner. The accuracy of the pulverized coal combustion model is verified against experimental data before extending the model to incorporate biomass co-combustion. RANS turbulence models are employed to simulate the swirl burner, determining the most suitable model for co-combustion. The study explores three different blending ratios, such as 25%Biomass-75%Coal, 50%Biomass-50%Coal and 75%Biomass-25%Coal under an oxy-fuel atmosphere. Additionally, the investigation delves into the impact of turbulent particle dispersion on co-combustion flame.