Comparative analysis of combustion behavior of raw and torrefied biomass pellets in a customized high-temperature flat flame furnace

Torrefied biomass pellets are emerging as a sustainable alternative to coal in energy-intensive industries, offering enhanced energy density, lower moisture content, and improved fuel properties that facilitate storage, transport, and co-firing compatibility in existing thermal power plants. However, conventional combustion systems lack real-time diagnostic capabilities to accurately monitor and analyze the thermochemical degradation dynamics of these biomass pellets, limiting optimization of combustion efficiency. This study investigates the combustion behavior of raw and torrefied biomass pellets at 1100,1200, and 1300 °C in a custom-built flat flame furnace. The experimental setup integrated two-color photometry and weight loss analysis for non-intrusive real-time measurement of flame temperature and mass loss, enabling comprehensive combustion assessment. The results indicated that torrefaction significantly improved energy density, fixed carbon content, and higher heating values by reducing volatile components. The ignition times of volatiles in torrefied pellets were affected by their moisture content, however, this influence lessened with rising temperatures due to the faster heating of the pellets. As the severity of torrefaction increases, the torrefied pellets become more energy dense, their carbon combustion rates are generally lower than those of raw pellets, and decrease with both combustion temperature and torrefaction severity. In the customized combustion system, Torrefied pellets exhibit higher peak flame temperatures (1000–1891 K) compared to raw pellets (1000–1788 K), primarily due to their increased energy density and lower moisture content. Although torrefied pellets demonstrated lower but more stable flame heights, this contrasted with the unstable combustion of raw pellets. The findings of this study indicate that torrefaction improves the combustion behavior of biomass, enhancing its suitability for energy applications.