Fuel characterization and co-pyrolysis kinetics of biomass and fossil fuels

► The char yields of biomass and fossil fuels were almost independent of char ultimate temperature. ► Alkali and alkaline earth metals of biomass ash began to evaporate as the temperature rose. ► Biomass and fossil fuel pyrolyzed almost independently in blended mixtures. ► Pyrolysis of biomass and fossil fuels occurred in three stages. ► The reaction mechanism of each pyrolysis stage was inferred from the Coats–Redfern method. It is not well understood how co-feeding of coal and biomass influences the reaction kinetics of gasification and pyrolysis. Co-pyrolysis of biomass and fossil fuels is investigated in this paper. After fuel characterization, the influences of temperature on the physical and chemical properties of char produced from biomass and non-biomass fuels were investigated, and the kinetics of atmospheric-pressure pyrolysis in a nitrogen environment were determined. The results show that product physical properties, such as surface area, depend on the pyrolysis temperature. For individual fuels, pine sawdust char prepared at 750°C had the highest CO2 and N2 uptake, while switchgrass had very low N2 uptake, but high CO2 uptake. The surface area of the fluid coke decreased with increasing temperature, but was almost constant for coal. Co-pyrolysis in a thermogravimetric analyzer exhibited three stages. Devolatilization of the biomass and coal portions of blended samples occurred independently, i.e. without significant synergy. The Coats–Redfern method was used to analyze the kinetics of solid fuel pyrolysis, indicating that it can be described by multi-step reactions. The model was able to identify likely reaction mechanisms and activation energies of each pyrolysis stage, giving predictions consistent with the experimental results.