Combustion kinetics and ash particles structure analysis of biomass in-situ and cooling char

Biomass represents a viable alternative to fossil fuels. However, the reaction kinetics of biomass are not well-defined in boiler design, the conclusions derived from traditional kinetic measurement methods vary significantly. Cooling process following the preparation of biomass char is one of the factors influencing the kinetic measurements. A two-step reaction analyzer was employed to assess the combustion characteristics and kinetic parameters of in-situ and cooling birch branches char from 50 to 150 μm. This approach aimed to evaluate the impact of the cooling process on biomass char. The results indicate the cooling process leads to a decrease in reactivity and an increase in activation energy. However, the overall reaction rate of in-situ char was the lowest, particularly in the late stages of combustion compared to cooling char. Observations revealed the stable structure of cooling char, with higher porosity and a less dense ash film, facilitated more efficient oxygen penetration than the easily fragmented in-situ char, which formed particles with few pores and a dense surface ash film, impeding combustion. The results indicate that the cooling process significantly affects the reaction kinetics of biomass char, as evidenced by variations in reactivity, pore structure, and state of the surface ash film.