| abstract |
A fuel pellet comprises from about 97 to about 99 percent by weight naturally occurring combustible material of which at least 50 percent is natural cellulosic material and from about 1 to about 3 percent by weight synthetic polymeric thermoplastic material. Any balance of the naturally occurring combustible material is filler and is preferably selected from bark, stillage, byproducts of distillation processes, and coal. If old bark, stillage, or byproducts, such as tar and pitch, or coal are used, the amount of the material is limited to 30 percent. The free moisture content of the naturally occurring combustible material is from about 5 percent to about 15 percent by weight, with 10 to 13 being preferred and 10.5 to 11.5 percent being ideal. Substantially all the thermoplastic material is finer than 30 mesh and coarser than 80 mesh. The cellulosic material is no greater than an order of magnitude coarser than the plastic particles and its minimum size is related to bonding requirements between it and the plastic; it is finer than 10 mesh and coarser than 40 mesh. The filler is finer than 10 mesh. The synthetic thermoplastic material is distributed throughout the fuel pellet as discrete particles. A sheath of plastic is on the outside of the pellet. The thermoplastic material is solid at room temperature and has an injection molding temperature of about 95 DEG C. or more. The fuel pellet is made in an extruder where the temperature of the pellet is controlled to assure softening of the plastic within the forming pellet without agglomeration. |