Biomass pellets prepared via low-temperature precarbonization: Biomass properties with flue gas treatment

In this paper, low-temperature precarbonization (LTPC) was proposed to remove oxygen-containing functional groups within biomass for subsequent pelletization. Influences of atmospheres (N₂, dry flue gas, and wet flue gas) and temperatures (210–350 °C) on LTPC product properties were thoroughly explored in a self-made rotary kiln with corn stalk (CS) as the typical feedstock. Results showed that conducted LTPC all caused the mass loss in CS, and increased temperatures reinforced this process. Characterizations revealed that these losses were mainly attributed to the degradation of cellulose and hemicellulose components, which simultaneously resulted in the enhancement of carbon content, fixed carbon proportion, and heating value of LTPC CSs. In addition, radicals in LTPC CSs were also monitored and together with the above characterizations confirmed the role of atmosphere on CS LTPC, with the order of dry flue gas ＞ N₂ ＞ wet flue gas. Optimal evaluation criteria were then introduced to select the preferred LTPC condition based on the overall consideration of mass yield, energy yield, and higher heating values of LTPC CSs, which was 270 °C in wet flue gas. This work matched well with the wet flue gas scenario in industry and provided a reference for biomass upgrading for subsequent pelletization.