SPECIAL STORY 54 FEED & ADDITIVE MAGAZINE July 2022 vital to the operation. It is also difficult to inspect. Erratic pellet mill blockages very often originate from condensate separation problems. As steam penetrates meal particles from the outside, a high retention time, a minimum of 40 seconds or more, is required to improve the effect of steam conditioning. To maintain uptime, adhere to a predefined maintenance plan for your steam components. 6. Correct pellet mill operation. When the pellet mill blocks it is very seldom where the root cause lies but it is the area where operators tend to look to solve the problem. They will do that by pushing a roller into the die, thereby damaging the die surface inside. Clean your feed for impurities, look for stable amps trends and stick to your maintenance plan. A vibration monitoring system will give you immediate operational feedback but also supply long term wear and tear profiling, allowing you to plan and schedule maintenance stops rather than recover from costly downtime and repairs. 7. Cooling. Excessive cooling causes costly shrinkage (loss of product), inefficiencies, and introduces mold formation and mycotoxins in finished feed. Condensation in the cooler exhaust during line startup causes back-flow of water from the exhaust, which is one root cause of mold formation in pellets. Be sure that your discharge grid doesn’t have any leaks when closed. When discharge is needed, assure that an adequate opening is provided, dropping the product level significantly and thereby preventing the accumulation of fines in the cooler. Don’t forget your regular cleaning routines. 8. Screening. Removing fines from pellets seems like an easy job, but please remember how to handle the last fines during order changes and the closing of intermediate gate in the cooler. Oversized pellet accumulations are not intended for the finished product and should be removed using a coarse top mesh and a return route for oversize. Product accumulations may originate from corners in the cooler and build-up in the pellet chamber (door). 9. Coating. Operating the continuous flow coater is easy when the product flow is constant because the liquid flow is constant. However, as the cooler discharges in large surges, it is important to optimize nozzles and control software to handle this. Batch coaters do not have this problem, but they are harder on the pellets. Both coater types require regular cleaning, especially in areas where dry material comes into contact with liquids. An ever-present huge improvement point is as also previously mentioned: stability. It cannot be repeated too often. The pellet mill is very sensitive to instabilities in the composition of the mash. If the rollers slip, it could be caused by a number of things. It could be that the filters are discharging large amounts of dust, sticky condensate has accumulated between the conditioner and the pellet mill dripped into the pelleting chamber, causing roll slip, or large steam consumers causing a sudden drop in boiler pressure which hampers the quality of steam conditioning. Regardless of where the supposed erratic pellet mill blockages originate, the consequences are still the same. The pellet mill capacity will drop to a level that can overcome the variations without blocking. That could be as much as a 50% reduction compared to the design capacity – for example, 6-7tph of broiler feed on a Ø700mm pellet mill, which should easily do 20tph.
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