Comprehensive study on morphology, composition, and structure evolutions of different biomass particles with torrefaction and low-temperature carbonization

Biomass torrefaction and carbonization pretreatments are common and essential to the subsequent utilization in the industry, such as gasification and combustion. The current work conducted a comprehensive investigation on the morphology, composition, and structure evolutions of five biomass particles during the torrefaction and low-temperature carbonization processes, with in situ experimental methods and multiple analytical technique. The color and morphological changes of biomass particles during the heating process were obtained by in-situ experiments. The results showed that a micron biomass particle performed a high shrinkage ratio, ranging from 20 to 45 vol% during the torrefaction and low-temperature carbonization processes, which the ratio was found to be lower than 5 % in the heating stage. With the increase of the pretreatment temperature, the surface fragments of particles increased and the structural damage was intensified. The mass loss, heating value, and energy yield was also compared with each biomass and related to the pretreatment temperatures. The changes of the hemicellulose, cellulose, and lignin contents with effects of temperature and biomass type displayed similar reducing tendency, with the analysis of functional group variation. In addition, an exponential relationship between the shrinkage ratio of the biomass particle and the total mass content change of extractives, hemicellulose, and lignin was found. Finally, the comprehensive mechanism diagram of the morphology, composition, and structure evolutions of different biomass particles were proposed.