Our paper investigates the problems of co-combustion of select grades of biomass, i.e. hay, straw, and wood waste, with natural gas. Research comprised both a laboratory experiment and numerical simulations with the use of a professional software application, Chemkin-Pro. The chemical mechanism of co-combustion of biomass with natural gas was described using 224 reactions and 56 chemical compounds. Based on the flow data determined on an experimental stand, the initial conditions were formulated and numerical simulations were performed. As a result of numerical simulations, the detailed chemical composition of combustion gas at the heating chamber outlet was obtained. The investigation has shown that the use of biomass for energy perposes significantly contributes to the reduction of pollutant emissions in flue gas.