From Plant to Plant: Lessons Learned

Pelletizing is conceptually simple: dried and ground-up sawdust is compressed under high pressure and temperature to ensure sufficient density, but efficient, reliable operation of the pellet mill requires considerable skills and experience.
By Holger Streetz | July 23, 2018

With nearly a decade of experience in renewable energies, I work with a Swiss supplier for the pellet industry, Bathan AG. My position requires knowledge of all aspects of a pellet plant, so I joined our service and maintenance team on several jobs to enhance my knowledge of the inside of mills—in particular, what to observe, and how to keep plants running smoothly. In this column and future editions, I plan to share with you lessons I have learned while on the job.

I have two very talented and experienced engineers on my team, go-to guys with a combined 30-plus years of experience, who brought me up to speed on technical aspects of pellet mills and other equipment in pellet plants.

As you know, the process of pelletizing is conceptually simple: dried and ground-up sawdust is compressed under high pressure and temperature to ensure sufficient density. However, efficient and reliable operation of the pellet mill requires considerable skills, experience and, sometimes, a lot of improvisation. Therefore, the learning curve in the pellet-making business is long and steep, especially when you see different companies with individual setups and feedstock mixtures.

North America and Europe contribute 67 percent of global pellet production, so it is worth knowing much about both markets. From several visits of pellet plants in Europe and North America, I perceived several differences. In Europe, almost all pellet plants use starch as binder, and the majority of pellets is produced under the EN Plus standard for residential heating. In the U.S. and Canada, industrial pellets for export, make up the bulk of the market, and the biggest share is for industrial heating, such as Drax power plants in the U.K. Hardwood and mixtures of softwood and hardwood are processed quite often, and debarking does not always take place, thus wear on equipment is much higher. As a result, North America cup and cone bearings are very popular, because in comparison to cartridge bearings, they are serviceable. Also, the absence of a race from a cup and cone system frees up space, placing more surface area in contact with the cup, thus spreading the load more effectively. Besides the setup, another major difference lies with operation—temperature monitoring is often nonexistent, which leaves the operators blind regarding the condition of the rollers, increasing the risk of fires. This led us to develop a retrofit temperature monitoring upgrade to track individual roller temperatures.

On both continents, the trend is in-house roller refurbishment, to keep track of quality and reduce maintenance costs. The best way to refurbish rollers is warm-fitting to prevent assembly damages. The shell may be heated up through a gradual temperature increase using an inductive heater or an oven. The ideal temperature is around 260 degrees Fahrenheit for the shell, and 155 degrees F for the bearing, which should slide into the shell easily. With cup and cone rollers, it is easy to just change the shell, and not dismantle a well-running bearings-shaft package. Pictured right is a roller after 1,000 operating hours—the bearings are reusable. Dirty grease distribution of a refurbished roller is shown in the left image—initial damages are obvious.

I am looking forward to sharing more recommendations, best practices and observations. Please do not hesitate to reach out and ask questions that I can address privately, or in future columns.

Author: Holger Streetz
International Operations Manager, Bathan AG