Study on the mesoscopic characteristics of densified forming of shiitake mushroom residue biomass considering particle breakage

The development of biomass pellet fuels represents an important pathway for achieving a low-carbon energy transition. Based on the particle breakage behavior of the feedstock, this study investigated the mesoscopic characteristics of the densification process of shiitake mushroom residue (SMR) biomass using piston compression experiments and the discrete element method (DEM). The results indicate that the increase in the relative breakage rate exhibits a negative quadratic relationship with time. After breakage, the particle size distribution is mainly concentrated between the minimum and intermediate values of the original particle size, showing a bimodal tendency with enrichment at both ends and a relatively sparse distribution in the intermediate range. Similarly, the reduction in the voidage of the formed pellets also exhibits a negative quadratic relationship with time. SEM/EDS analyses reveal the presence of hard siliceous nodules and abundant pore structures within the pellets. Due to the combined effects of arching and die-wall friction, the compactness and hardness of the formed pellets gradually decrease along the pressure transmission direction, accompanied by an increase in voidage, and the hardness at the pellet center is significantly lower than that at the edge. After introducing sinusoidal vibration at the bottom of the mold, under the conditions of an amplitude of 1.5 mm and a frequency of 5-7.5 Hz, the axial and circumferential hardness of the pellet became significantly more uniform, indicating a marked improvement in pellet quality. The results of this study can provide valuable references for the theoretical understanding and engineering applications of biomass Pelletizing.