To solve the problem of loose and friable biomass pellets, measures should be taken from multiple aspects including raw material selection, process optimization, equipment adjustment and post-treatment. Below is a systematic solution:
1. Raw Material Optimization
Adjust raw material proportioning Mix high-lignin raw materials (such as wood and bamboo) with low-binder raw materials (such as straw and rice husk). The natural adhesiveness of lignin can improve pellet strength. Add binders (e.g. starch, lignosulfonate, bentonite, etc.) at a ratio of 1%~5% to enhance the bonding force of pellets.
Control raw material particle size Grind raw materials to 3~5 mm to fully expose the fiber structure and improve interweaving performance during compression.
Moisture regulation Maintain the moisture content of raw materials at 12%~18% (12%~15% for woody materials, 15%~18% for straw materials). Precisely adjust moisture with drying or humidifying equipment.
2. Pelletizing Process Optimization
Adjust die parameters Increase the die compression ratio (6:1~8:1 recommended) to extend the compression duration of materials inside the die. Inspect die wear regularly and replace dies in a timely manner (repair or replace when the wear depth exceeds 0.3 mm).
Control temperature and pressure Set the pressing temperature at 70~90 ℃ to soften lignin and improve its adhesion. Boost the ring die pressure to 100~150 MPa (adjust according to raw material hardness) to ensure dense pellets.
Steam pre-treatment Soften raw materials by steam (105~120 ℃, 3~5 minutes) to increase plasticity.
3. Post-treatment Process
Cooling and drying Use a counter-flow cooling system for slow cooling (cooling time: 15~20 minutes) to prevent cracking caused by excessive temperature difference. Control the moisture content of dried pellets at 8%~12% to avoid loose pellets due to moisture reabsorption.
4. Equipment Maintenance and Upgrade
Regular maintenance of dies and rollers Check die holes after producing every 500~800 tons of pellets to ensure no blockage or deformation. Adjust the roller gap to 0.1~0.3 mm to avoid insufficient pressure.
Equipment upgrade Adopt double-layer ring die pellet mills to extend the compression path; or use a hydraulic drive system for dynamic pressure regulation.