3.1.7 Pellet mill operation

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.