How and Why Rotary Debarkers Came to North American Paper Mills

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Before roller debarkers (rotary debarkers) were introduced to the North American paper industry in the late ’90s, the industry lacked good solutions to debark logs in northern climates, where temperatures averaged well below freezing during winter. Dennis Widdifield, a consultant in Canada, worked for Boise Cascade in Ontario at that time, and he was tasked with solving this problem. That he did—and what started as a project for his plant turned into the wide-scale introduction of these machines to North America.

The Need for Better Debarking

In the early ’90s, a Boise Cascade mill used a wet debarking process to debark their wood logs in their groundwood pulping wood room. During this process, millworkers treated the wood logs with water in the two debarking drums to soften and peel the bark when the hardwood and softwood Logs were low moisture and/or frozen. They would then press and drain the bark and burn it as a low-grade fuel.

The problem was that the result was rather toxic. When bark gets wet, it releases oils and resins. So, the plant had to treat water used in this process.

To rid themselves of the need to treat this wastewater and to make room for their craft mill, they needed to change their debarking process.

Looking at Debarking Options

Dennis was already familiar with drum debarkers in a wet process or a dry debarking process at other paper mills he had worked at. The Boise Cascade Mill had several dry bebarking drums in the kraft pulping wood room area for softwood Logs. But in the winter, it was very difficult to remove bark with these machines, and the process suffered high wood fiber loss. Trials were conducted on the ground wood pulping hardwood and softwood logs in the dry debarking drums. The frozen hardwood and softwood logs in the drums for up to two hours at a time, and the drums would do nothing more than polish the bark. The friction, which drum debarkers rely on to debark logs, simply wasn’t enough to peel these logs. Groundwood pulping requires a very low remaining bark surface content. Typically, less than 0.5 percent bark by weight remaining content on a log.

So Dennis and his coworkers looked at other options. Mechanical options of the era included flail debarkers. But flails were hard on wood. They removed too much usable fiber with the bark. They also required constant maintenance. The chains on these machines would wear down fast and break off. Broken chains were bad news if they reached the chippers.

And, of course, most flails were diesel powered, which didn’t help companies sell them in the frigid North. (Diesel gelatinates in cold unless treated.)

Dennis also considered ring debarkers. A Boise Cascade plant across the U.S. border was using four in parallel. But this debarker, too, had its issues. The U.S. Boise Cascade plant could only run a single log through the debarker at the time, and they had to singulate the logs using a step feeder or operator controls ahead of each ring debarker. This required a lot of space for the setup (the company was trying to open up space), and it would severely bottleneck the system at the Ontario plant. While running a single log through the debarker at a time may work for sawmills debarking 60’ softwoods, it’s too slow when running short wood lengths.

To keep up with their production needs in Ontario, they would have to install four ring debarkers. That would lead to another drawback for these machines. Because each of these debarkers required an operator, the company would have to increase manpower from two operators in the ground wood wood room to six operators plus maintenance personnel with ring debarkers.

Going with Rotary Debarkers

After considering these options, Dennis then saw an advertisement for the first rotary debarker. It caught his attention. In February of 1994, he arranged for trial of the debarker in Northern Alberta. It was the middle of winter, and the machine was debarking frozen hardwood aspen logs. As soon as he saw it running, he was sold.

He wouldn’t have to singulate the wood—roller debarkers are mass-feed systems. He could easily adjust it (unlike drum debarkers). And he could easily discharge the logs over a gate.

He contacted the debarker’s manufacturer, and the company designed a machine with 36” rotors—big enough to meet the production demands at Boise Cascade. Dennis and this team bought three, 50’ identical machines. They were able to put them in one building, feed them off of one existing drum debarker feed conveyor system with a plow, and discharge them again to the existing drum debarker discharger / collecting chain conveyor.

They installed the debarkers in 1996. The debarkers were the first installation at a paper/pulp mill in North America.

After installing the machines, word spread, and companies stopped by the Boise Cascade plant on a regular basis to view the machines. Dennis soon became an expert on them and eventually moved onto a sales position with a manufacturer that produced its Canadian version of these debarkers.

Why Roller Debarkers Work

Roller debarkers work in cold climates because, unlike drum debarkers, they debark through mechanical means followed by friction log to log rolling action. While drum debarkers rely on log impact from other logs and the drum internal shell staves friction / impacts to debark the wood, roller debarkers cut the bark with abraders (mechanical component of debarking), and these cuts work with the friction caused as the log to log tumble action against each other to peel them of their loosen bark with minimal log fibre loss.

Roller debarkers are excellent machines for debarking virtually any wood. They handle frozen wood, softwood, and hardwoods. They even handle tropical harwood species or North American basswood with stringy bark.

Biomass Engineering & Equipment offers roller debarkers for the global market. Built to your specifications, our roller debarkers are the right debarkers for high-volume pulpwood processing.

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