Measurement and characterization of pressure and temperature of the biomass during pelletization process

The pressure field within a pelletizer die during biomass pelletization remains largely uncharacterized, limiting the development of mechanistic models for pelletizer design and optimization. To address this gap, pressure conditions within a stationary die biomass pelletizer were investigated using sensors installed at three depths (0.78, 1.98, and 2.31 cm from the die entry) in a 29.8 mm-thick die. A flat-die pelletizer was instrumented with miniature pressure sensors installed at three die depths and thermocouples at corresponding locations, enabling real-time, in situ measurement of pressure and temperature during pelletization for the first time. Real-time pressure and temperature were recorded during pelletization of switchgrass and willow. Both feedstocks exhibited distinct peak pressure spikes, caused by the roller forcing material into the die, and baseline pressure plateaus between spikes. Peak pressures for switchgrass reached 6.86, 3.10, and 0.59 MPa at the top, middle, and bottom sensor locations, respectively, while willow registered slightly higher values of 8.59, 3.25, and 1.10 MPa. Pressure fluctuations were most pronounced at the top sensor, reflecting the roller’s intermittent feeding action. The baseline pressure represents residual frictional resistance in compacted biomass, preventing material spring-back between roller passes. Temperature was highest at the top of the die, with the greater drop occurring between the middle and bottom sensors. These findings inform the development of viscoplastic compaction models and suggest that controlling pressure and temperature conditions can impact pellet quality. This study provides foundational data for designing more efficient pelletizers tailored to specific biomass feedstocks, advancing bioenergy production technologies.