Pellet mill capacity and feed distribution
Pellet mill capacity is one of the most discussed topics in compound feed production. Provided that conditioning with saturated steam is optimized, the following points are decisive for the press capacity (throughput):
- active die surface (open area)
- installed power drive
- requested pellet quality: for example, a pellet mill running at 30 t/h with broiler feed in the US or South America produces 15-20% fines, but in Western Europe only 3% fines (PDI 97%) are accepted, resulting in a throughput of only 25 t/h
Press capacity depends substantially on pellet quality (stability according to the PDI, Pellet Durability Index). The durability of pellets shall be determined by tumbling the test sample for 10 seconds at 500 rpm, in a dust-tight enclosure. PDI is a number that describes the percentage of remaining pellets that are not reduced to fines after being agitated under controlled time and conditions by various mechanical means.
Feed distribution is the most overlooked factor in a pellet mill operation.
The distribution must be uniform on the working track of the die. Otherwise, the rolls work badly and, in addition to the loss of productivity, there is the risk of clogging the die with the consequent lockup of the machine.
The rotary feed cone and the correct positioning of the deflectors are fundamental for the correct distribution of the product.
When feed distribution is controlled properly, spreading material across the entire working track, the production capacity of the pellet mill is increased.
An uneven distribution causes irregular wear of the die and consequently productivity lower than expected and premature wear.
The image on the side shows a pellet mill that does not work across the entire working track of the die.