O&M Tips for Efficient Pellet Production

A pellet mill is built to pelletize. Each hour that it is not in operation equals to lost money.
By Timo Müller | August 25, 2022

In the current market situation with fuel shortages and pellet prices going through the roof, it is more important than ever to reduce downtime to the absolute minimum. In addition, increasing energy costs and material scarcity requires pellet producers to optimize their processes. The following are some operations and maintenance guidelines that will help producers stay online maximize their bottom lines.

Roller and Die Lifetime
Rollers are one of the main wear parts in every pellet mill. Extending their lifespan means saved maintenance time and lower operating costs. The main reason a roller needs to be changed is a worn down surface. In fact, the inner components of a roller can often be reused up to three times. A major accelerator of the roller’s surface wear is a high mineral content (e.g., sand). Therefore, it is advisable to keep the material input as clean as possible. This can be achieved through cleaning processes and a monitoring system of the raw material.

It is also important to keep the rollers at the right temperature, roughly 194 to 212 degrees Fahrenheit (90 to 100 degrees Celsius) in order to ensure a smooth operation and protect the components. Many modern pellet mills have integrated sensors that constantly monitor the heat within the press chamber. Based on this data, the rollers can then, during operation, be automatically or manually cooled from the inside with grease or oil.

If the material input is too high, rollers can slow down, and the press chamber may eventually become clogged. To prevent this early on, the roller RPM, or revolutions per minute, should be monitored as well. Some machines have this feature integrated as well. When the roller speed slows down, the material input rate should be decreased.

However, even the best treatment will eventually require a roller change. After a couple thousand hours of operation, the roller surface loses friction and efficiency decreases. If that is the case, it is advisable to use a spare set of rollers and refurbish the used ones. When taken apart with care, the inner components can often be used again. This reduces the amount of metal waste and saves costs for new parts.

As well as roller lifetime, pellet die lifetime also heavily depends on the material input. If holes become clogged, chances of the die breaking increases, especially if there are clusters of clogged holes. If the machine operator notices this soon enough, the die can be changed in order to prevent breakage and possible damages to other press components. To do this, production should schedule routine inspections. Afterward, the affected holes can be cleared through a combination of high-pressure water cleaning and heat treating. If this does not work, it sometimes makes sense to drill the holes free.

A common cause of hole clogging is foreign objects falling into the press chamber. If the percentage gets too high, it not only risks the die, but also decreases overall pellet quality. Filtering systems are a solution for this. Magnets installed between the conditioner and the pellet mill can detect and sort out metal parts that would otherwise cause major damage in the press chamber. Those parts might be nails or saw parts that came from the raw material, or pieces of tools that got into the material flow during transportation or pretreatment (e.g., truck parts, screws, hammer mill components, etc.).

Key to a long die lifetime and a high material throughput is the correct die configuration. With high capacities of several tons per hour, the slightest change can have a big impact. Therefore, it is of great importance to find the best configuration regarding the die’s thickness, width and press length. The best parameters depend on the characteristics of the input material.

With longer delivery times, it makes more and more sense to keep the most essential wear parts in stock. It is advisable to keep one extra set of rollers (two or three individual rollers) and one die per pellet mill in stock. These components are custom-made and require several weeks of production and shipping during peak times.

Lubrication and Safety
Every pellet mill requires sufficient lubrication in order to run smoothly and protect its components. Many pellet mills come with a central lubrication system that can be automated to a high degree. There are also big differences between lubricants. Whereas traditional greases require high amounts, special lubricants such as ceramic-based greases can reduce the volume significantly, by up to 95%, while also extending the bearing lifetime.

Finally, safety should be the highest priority at every pellet operation. Ignoring important safety measures does not only bring the risk of sudden and long-lasting production stops, but also puts machine operators in danger. Therefore, protective devices and features installed by the machine manufacturer should not, under anycircumstances, be bypassed. There are no shortcuts when it comes to safety. This includes dust formation, too. The production facility should be kept clean with a powerful extraction system and regular cleanups. Too much dust can not only lead to dangerous explosions but have negative effects on workers’ health.

In conclusion, there are several aspects that need to be kept in mind when producing high-quality wood pellets in large quantities. Regular checkups are the key to prevent major damages and production stops, and to keep downtime as short as possible, critical wear and spare parts such as rollers and dies should be kept in stock.

Author: Timo Müller
Salmatec GmbH
[email protected]