3.1.7 Pellet mill operation
The main purpose of this operation is to convert mash feed into pellet form by mixing with steam. Pelleting improves digestibility of feed and hence better the pellet, better the performance (Fig. 3.10 & 3.11). Pellet mill section consists of the feeder, conditioner, pellet mill, pellet cooler, elevator, pellet sieve, pellet cooler cyclone & its blower and air lock etc. The molassed feed is fed from the storage bin to the feeder and thereafter to the conditioner, where dry saturated steam is mixed with the feed and is fed to the pellet mill at a controlled rate.
Fig. 3.10 Better the pellets, better the performance
Fig. 3.11 Pelleting improves digestibility of feed
The feeder is driven by Variable Frequency Drive & conditioner is driven by mechanically controlled PIV gear. Both feeder and conditioner shall be of stainless steel AISI 304 to avoid rusting. Conditioner shall have machined steel rotor with adjustable and removable paddles and arrangement for electric heat shield of body for sanitary feed production along with all necessary insulation, earthing and thermostat. Apart from having arrangement of injecting and mixing dry saturated steam normally for 30 seconds, the conditioner shall have provision for injecting and mixing two different liquids uniformly. The rate of feeding into pellet mill (Fig. 3.12) depends upon the condition of the pelleting die (if the die is new, it will not start immediate pelleting). Pelleting will start when all the holes of the die get polished and filled with the feed, condition of the feed (i.e. the feed should be neither too moist nor too dry). Pelleting takes place due to the process of extrusion. The press rolls provided inside the die, force the material to pass through the holes of the die and when the feed comes out of the die, it is in pellet form.
Fig. 3.12 Pellet mill
The length of pellets can be adjusted by the knives provided in the machine. To review the operation of the pellet mill, the animal nutrition officer should check the moisture per cent in feed before conditioning. He should collect sample after the ingredients are thoroughly mixed in the steam injection chamber and note the moisture content and temperature at which the material is being fed to the pellet mill matrix. This may also serve as an index of molasses content in the material. After pelleting, he should collect some hot pellets to have an idea about the quality of pellets (the broken portions, fines, size, pellets etc.). For efficient conditioning, the steam should be dry, temperature of feed in the conditioner should be in between 80-85ºC and moisture before and after conditioning should be 12-13 per cent and 14 per cent, respectively.
