The relationship between different types of materials and compression ratio selection
Different biomass materials have different compositions, with varying lignin and cellulose levels. Denser materials (visually heavier) usually have more lignin, as lignin is denser. Higher lignin content means better binding properties, allowing pellets to form with a lower compression ratio during production. Conversely, lower lignin content requires a higher compression ratio.
The way to choose the compression ratio is: with the same fineness, the higher a material's bulk density, the smaller the compression ratio should be.
For example: Poplar wood - 1:5 Pine wood - 1:4.5-1.5.5
Oak wood - 1:4 Redwood - 1:3.5 Jujube wood - 1:3.5
The above method for choosing compression ratio assumes materials have very little or no moisture or oil. But if a material contains moisture or oil, this affects how to select the compression ratio. That's because both moisture and oil have sticky properties—they're naturally sticky, no need for outside conditions. So whenever a material has moisture or oil, the compression ratio for pellet production will change.
Specifically, the higher the sugar content, the smaller the needed compression ratio (e.g., corn stover). Theoretically, the higher the oil content, the smaller the required compression ratio too. However, because oil expands at 80-110°C in the pelletizing chamber, this makes choosing the compression ratio uncertain when making pellets (e.g., small fruit palm shells).