Around 500 flat die pellet mills are in operation on the international market for the production of feedstuff, food, chemical and pharmaceutical products and alternative fuels from various raw materials. From the beginning of 2021, four more flat die pellet mills will be used by the industry for the production of alternative fuels from waste fractions - and all of them will be located in Germany.
Before the waste fractions, consisting of mixed plastic and cardboard fractions in a defined ratio, can be pelleted, they have to undergo conditioning through shredding to a particle size of < 20 mm with downstream screening, metal and impurity separation. Subsequently, the screened material is thermally dried to a residual moisture of < 10 %. The required heat is supplied by a combined heat and power plant that also supplies the entire plant with electrical energy.
After drying, the prepared input material is fed into the pelleting plant. By means of belt conveyors and a central trough chain conveyor, the dried material is transported to the pellet mills "in overflow". This ensures a sufficient product supply for all four pellet mills at any time. Excess input material is taken up by a proportioning bunker and returned into the feeding system in a controlled manner.
The four KAHL flat die pellet mills type 45-1250 are fed by means of individual proportioning units, each consisting of a frequency-controlled proportioning wheel and a horizontal proportioning screw. The material is fed into the press in free fall and without deflectors or forced feeding, thus trouble-free product supply is ensured, especially in case of voluminous, inhomogeneous products.
The flat die pellet mills have a die diameter of 1250 mm with a die perforation of 16 mm. The large pelleting chamber of the flat die pellet mills ensures an optimum feeding of the material to the rotating pan grinder rollers. Each pellet mill is equipped with an individual proportioning system so that the optimum quantity of material is fed into the machine. Due to the low speed of the flat die pellet mill and the resulting low circumferential speed of the pan grinder rollers, the product can be optimally deaerated during the pelleting process and pressed into the holes of the die. This also significantly increases the service life of the bearings; and the smooth, low-vibration press operation significantly reduces the noise emission of the press. The hydraulic system of the press with automatic roller gap monitoring and adjustment ensures optimum process control and product quality by automatically adjusting the process pressure and the thickness of the material layer on the die to possible product fluctuations during operation. The automatic central lubricating system of the roller bearings adds to the reduced maintenance requirements of the machines and thus increases their availability. Thanks to their robust design, the pellet mills are insensitive to the effects of impurities, which often occur in inhomogeneous waste fractions. The design of the machine and the easy access to the pelleting elements ensure a quick replacement of rollers and dies, which also improves the availability of the plant.
After pelleting, the hot pellets are cooled and stabilized in a counter-current cooler using ambient air. Possible fines are separated via a downstream screening system before the pellets are conveyed to the storage facility for finished products.
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