Biofuel pellets made at low moisture content - Influence of water in the binding mechanism of densified biomass

For all raw materials, a maximum moisture content for pellet density and strength could be found. For birch at all compression pressures, maximum pellet density and maximum strength coincided at 6.1% moisture content. For reed canary grass, optimal pellet density occurred at 5.2% moisture content, the maximum pellet strength was at 8.5% moisture content for compression pressure of 300 MPa and 400 MPa. For spruce, maximum pellet density was found at 5.1% moisture content, and maximum pellet strength at 8.3% moisture content for compression pressure of 300 MPa and 400 MPa and at 10.7% for 200 MPa. When the process temperature was increased to 80 °C, the optimal moisture content for pellet strength shifted to a lower value. The moisture content for monolayer coverage was 6.2%, 7.7%, 7.5% for birch, RCG and spruce, respectively. Optimal moisture content coincided with monolayer coverage at room temperature when the compaction pressure was sufficient high, in the case of spruce and RCG, the pressure should be above 300 MPa.