Plant cells contain not only cellulose and hemicellulose, but also lignin (wood glue). Lignin is a structural monomer with aromatic characteristics, composed of phenylpropane units forming a three-dimensional condensed polymer. In broadleaf and coniferous wood, lignin content is 27%-32% (dry basis), while in grasses it is 14%-25%. Although lignin is present in all plants, its structure is extremely complex and varies among different plant species. Even within the same plant, lignin structure can differ significantly depending on its location. Lignin is amorphous and has no melting point but has a softening point. At appropriate temperatures (130-200°C), lignin softens, and when certain pressure is applied, the remaining cellulose bonds tightly together and adheres to adjacent particles. Upon cooling, it solidifies into pellets. Therefore, using the heating and extrusion method to produce crop straw fuel pellets requires no additives or binders, greatly reducing processing costs while meeting environmental requirements. Moreover, by leveraging the heat-softening characteristics of lignin, appropriately improving the temperature during hot press pelletizing helps reduce extrusion power consumption. Biomass pellet fuel is produced using this principle through extrusion.