The hopper is a container designed to receive feedstock and serve as a reservoir that maintains enough raw material for a sustainable flow throughout the pellet mill’s operation. The hopper should be designed to store at least enough material to run two times the capacity of the mixer. It is usually placed above other components in order to take advantage of the force of gravity.
As the condensed feedstock is extruded from the die in pellet form, it must be cut to the correct length. Cutting blades are installed outside of the die area. These components prevent excessive fines by limiting the size of a pellet before it becomes too long and brakes against the side of the pellet press door.
A pellet mill can be equipped with an electric motor or diesel engine. The capacity of the power source should be adequate for the processing needs of the mill, loosely measured by the pressing area of the die. A general rule of thumb is that 1 kilowatt of power is needed for every 10 cubic centimeters of die area, or around 2/3 of a unit of horsepower.
Pellet production is an energy intensive process; however the ends justify the means.
The hammer mill and pellet mill demand high-energy inputs, which usually mean they require a three-phase supply of electricity. A three-phase supply is only normally found in farming and industrial locations. However many locations do not have three phase supply and installation can be expensive. Before purchasing pellet production equipment, check that the available power supply is suitable. If the installation of three-phase power is not possible for logistic or cost reasons there are other solutions. Diesel generators are one possibility, as is powering the equipment directly with a diesel engine.
Gears relay the power generated by the motor or engine to the die and rollers, imparting rotational force. Different pellet mills are geared for different materials. Different gearing confers different speeds of rotation to the die and rollers. A low gear ratio means more torque but a lower speed, which is better for processing dense materials like woods and particularly hard woods. A low-geared pellet mill requires less binder and lubrication. A high gearing means less torque but a higher speed, which is beneficial for low-density materials such as grasses, straws, and animal feed products. Clearly the higher the speed, the higher the productivity; however this can be detrimental to pellet quality. For example some woods processed in a high-speed pellet mill will not form dense, shiny pellets as the necessary pressure and heat was not generated, as the material passes through the die too quickly. There is also a possibility when wood is processed in a high-speed pellet mill because of the increased density of the wood the pellet mill motor may not have the power required. This will result in the pellet mill motor laboring and may even stall. Adding an additional binder can sometimes compromise these issues, this can help lubricate the pellet mill and reduce resistance, while still producing hard shiny pellets. Some pellet mills are geared in the middle; they can therefore have a good productivity and still retain pellet quality, even for wood pellets.