Effect of die temperature variation on biomass pelletizing and optimization of built-in heat source

Ring die densification is a key technology for agricultural and forestry waste utilization. The precise die temperature control is critical for efficient pellet formation. This paper establishes a frictional heat analysis model for die and conducts numerical simulation of the frictional heat during the forming process. The influences of the friction coefficient, ambient temperature, and built-in heat sources on the temperature distribution were analyzed. Results show that temperature variation is governed by frictional heat generation and dissipation, correlating closely with straw material properties. Cotton and peanut stalks enable rapid achievement of effective lignin activation temperatures with improved pelletizing quality and efficiency. Conversely, corn stalks cause fuel scorching and carbonization due to excessive temperature, while rice straw exhibits slow heating, resulting in insufficient lignin softening and compromised pelletizing quality. Under low-temperature conditions (-30 °C), die temperature cannot reach sufficient lignin softening conditions, severely affecting pelletizing quality and increasing equipment failure risk. To enhance performance under low-temperature environments, built-in heat sources were optimized by investigating the effects of number, shape, and distribution position on die temperature. Two circular heat sources positioned at 32 mm and 64 mm away from the outlet reduces overall temperature difference by approximately 70 %. Under the combined effect of the built-in heat source and frictional heat, the die can quickly heat up during the preheating stage and maintain a suitable temperature range during the working stage, promoting lignin activation and material bonding. This research provides a solution for biomass briquetting equipment optimization and efficient operation. • A frictional heat analysis model was established to simulate the ring die forming process. • The optimized embedded heat source strategy reduces internal model temperature gradients by about 70 %. • This ensures optimal lignin softening and material bonding in extreme low-temperature conditions.