Features of Primary Fragmentation of Wood Biomass during Fast Heating and Devolatilization

Results are presented from experimental studies into primary fragmentation of wood particles during their fast heating and devolatilization. The experimental equipment and the study procedure are described. It has been demonstrated that the probability and intensity of primary fragmentation of wood particles increases with an increase in their initial size, process temperature, and the ratio of their longitudinal and transverse dimensions. The results of experimental studies suggest that the stresses arising from the pressure of volatiles and wood shrinkage control the primary fragmentation of wood particles. Based on the study into the microstructure of char fragments formed during primary fragmentation, assumptions were made about the mechanism of cracking and its dependence on the structure and shape of wood particles. As applied to wood biomass, it is proposed to use the ratio of the volatile yield to the specific volume of wood as a criterion of devolatilization resistance. Processing of experimental data has revealed that smaller specific volumes and, accordingly, higher devolatilization resistances facilitate primary fragmentation. An analysis of the obtained data enabled the authors to determine the main lines of further studies into the primary fragmentation of wood particles during combustion and gasification in fluidized and dense beds.