Contamination can appear anywhere in the animal feed and premix production process at every premix plant. From intake to outloading, there are many possibilities for components to mix. Although contamination is receiving more attention at animal feed producers, it can be even more important for premix producers. Where should you look to avoid contamination? I’ve put together a simple overview to help you avoid it every step of the way.
By Tim Broeke - Project Sales Engineer, KSE Process Technology B.V.
Pneumatic conveying systems are most often used for raw materials intake. Here, it’s best to use dedicated pneumatic pressure piping, and dedicated filters for each silo (components can stick to filters in one batch and be released in a later batch).
Make sure the silos you store your raw materials in are cleanable and suitable for static-sensitive, sticky or similar materials. In extreme cases such materials can be dosed directly from the silo, although only when accuracy is not that important. Then, you don’t need a hopper between silos and for instance a mixer, which makes your production less contamination sensitive.
Dosing instruments should have a minimum amount of resting material after the silo is depleted. They should not compact or force the material against the silo wall, since this allows product to build up and causes poor product flow or inefficient silo use. The dosing instrument should also be easily cleanable, and should not increase any of these problems because of wear during normal use.
Contamination can be prevented in weighing hoppers by minimizing the adhesive properties of hopper walls by using knockers, vibrators and coatings. Another solution is to make the hopper using flexible rubberized materials. Make sure that you minimize the actual area of the hopper. When you have a large silo you normally need a large hopper underneath to cover the entire surface. The bigger the hopper, though, the easier it is for sticky or static-sensitive materials to remain in the hopper and thus allow contamination. By using a smaller hopper which rides underneath the silos, you can minimize this kind of contamination.
Everyone using weighing hoppers will be familiar with the problem of dust. You can solve it by using dedicated, separately discharging dust extraction systems. Then, there are two possibilities for getting rid of the extracted dust: put it back into the hopper on the next batch, or dispose of it. If the material is not contamination sensitive you can easily put it back in the hopper, otherwise it is better to dispose of it. Think carefully about the choice because disposing of (chemical) materials can be an expensive affair!
To exclude contamination from internal transport, it is best to minimize the use of conventional horizontal transportation like chain conveyors. Better is gravity transportation, for instance pipework that slopes with an angle of 65-70º to the horizontal , equipped with vibrator and or knocking systems to avoid poor flowing. In extreme cases the transport system can use flexible material to minimize possible contamination.
To maximize contamination-free batch collection and transportation, reserve specific movable hoppers for each contamination-sensitive material group.The internal transport can be fully automated, which also excludes the costs of personnel and other transport systems like forklifts. This becomes financially interesting if the cycle time of the batches is short and the production capacity dictates a large number of movements.
Even with hand tipping, contamination can be an issue. Perhaps it is a bit obvious, but use dedicated hand tipping stations for different contamination groups, and reject any extracted dust! Hand tipping station(s) should be placed at the last possible point in the production process so that any sensitive material doesn’t need to be handled and transported through the whole production line. This can be in the mixer, or just before packaging.
To avoid contamination in your mixing line you can use a different mixer for each contamination group, but it is easier to replace the filter installation on top of a mixer. That prevents dust from the previous batch from being discharged directly into the current batch. Special mixers can allow the entire mixer to be cleaned in place, and taken apart using special guidance and rails for the heavy parts.
If you have contamination problems in your packaging line, you might think of using multiple packaging lines. This is an effective way of creating process continuity and separating contamination groups. An additional advantage is that you don’t block further production, since cleaning the packaging line can be labor intensive.