Pressing For Success
Machine design and manufacturing history books are littered with stories of machines that were initially designed for a particular task in a particular industry, but were modified to perform a similar task in an altogether different industry. The story of wood pelleting presses is one of them. The idea of compressing materials into a pellet originated in the feed industry as a way to conglomerate a variety of feed ingredients. Livestock farmers were discovering that their animals were picking out and eating only certain ingredients from feed bunkers and leaving behind other ingredients, including important nutrients. Pelletizing presses emerged as a means of solving this problem, as these varied components were pelletized forcing livestock to consume every component of the ration.
“In the late ‘80s, those presses underwent some modification so that they could handle the stress of pelletizing wood. Pellets made from feed products pelletize much easier than wood,” says Mike Curci, capital sales manager of biomass for Andritz. Scott Anderson, general sales manager for CPM, echoes that sentiment. “Pelleting wood is not a single thing. It is one of the most difficult things that you can attempt to pelletize,” he says. “The customers have very tight quality specifications. It is a real challenge taking a natural product with the variations that you are going to get in nature and spitting out a consistent, tightly controlled final product.”
The fundamentals of making a wood pellet are common throughout the industry. Essentially, making a pellet is an exercise in extrusion. Woody material is driven through a die under extreme pressure and cut to length. Material is forced completely through the die by new material entering the other end of the die.
It is here that the commonalities end and the differences between pellet presses begin to become evident. While subtle variations abound from manufacturer to manufacturer, generally pellet presses can be distinguished from one another in two ways. The first is the means by which power from the motors is delivered to the pellet press. The second is the shape of the die itself.
Gear Driven vs Belt Driven
All pellet presses rely on horsepower generated by large electric motors. The manner in which this power is delivered to the press itself is where the differences can be found. The power from these motors is transferred either by gears or a belt. Both gear-and belt-driven pellet presses can be found throughout the industry, and the manufacturers of each stand ready to articulate the value of their approach.
“We are a gear-driven pellet mill,” says Anderson. “Some customers, many users, have a feeling that a gear drive is a less desirable design than a belt drive design. That’s a situation that we frequently have to overcome. We talk about the robustness, the lower overall maintenance cost of a single reduction gear drive, versus the cost of replacing belts, even if it’s just the preventative maintenance aspect and the energy efficiency of a gear drive versus a belt drive, which can be substantial.”
Manufacturers of belt-driven pellet presses are quick to remind their prospects and customers of the risk of using gear-driven presses: the shock that results when wet material or tramp metals show up in the pelleting chamber and that sudden energy is transferred directly back to a gear box. “The v-belt drive protects the pellet mill from severe shock loads and pelleting surges, thus reducing potential damage to the motor and machine,” says Curci about Andritz’s belt-driven approach.
Gear-driven manufacturers note that belts cannot completely transfer the energy from the motor without some loss, while belt-driven manufacturers assert that the power loss with belts is modest. Jase Locke, the biofuels application manager at Ponca City, Okla.-based Bliss Industries says of Bliss’s belt-driven presses, “We feel that with our machine the way it is set up and driven, our belt is 95 percent efficient transferring that horsepower from the motor down to the front end.”
Ring Die vs Flat Die
A difference that is easier to visually discern is the shape and position of the pellet die itself. The names of the dies aptly describe their differences in shape, but there are also differences between the two approaches that are not immediately evident. In ring die pellet presses, the die itself moves around a series of rollers, whereas in flat die pellet presses, the die is stationary and the rollers move around a vertically oriented shaft and deliver power downward onto the die.
Patrick Clark, Amandus Kahl vice president of sales and marketing, points to the advantages of this die orientation, saying, “feedstock that is light and fluffy and has difficulty flowing can create problems for pellet producers. With a flat die press the material comes straight into the pelleting chamber via gravity. We also have an excellent transfer of energy for hard materials; the woods, and the hulls off of cereal grains.”
Normal Wear and Tear
For pellet producers, the name of the pellet-press game, regardless of style, is to keep them up, on line and making pellets. Any downtime a producer experiences, whether planned or unplanned, means lost revenue. Pellet press original equipment manufacturers (OEMs) know and keep this top of mind as they design and build their machines. “I think the biggest key to a pellet producer’s success is efficiency and reliability,” says Curci. “We all know that margins are very slim and if we can help protect those margins for the producer, that is key.”
Pellet press OEMs deploy a number of design strategies to extend the lifetime of the wearable parts while also trying to synch up component life cycles so that items are ready to be serviced or replaced at or around the same time.
Amandus Kahl extended the life of bearings by slowing down the main shaft. “Our main shaft speed is approximately four times slower than others, so we’ve got increased bearing life,” says Clark.
For Bliss Industries, distributing roller wear evenly in its three-roller presses synchronizes roller wear for the 33 plants that operate their presses. “If you look at a two-roll press, the leading roll gets about 70 percent of the material, and the back roll gets 30 percent,” says Locke, “so that leading roll wears out faster than the back roll. With the Bliss three-roll press and the way we feed it, each roll gets about 33 percent of the material. In pellet facilities, down time means lost money, so we want everything to wear out those rolls evenly.”
In an increasingly competitive environment, press OEMs are acutely aware of the ongoing costs of operating their and their competitor’s presses. “If our capital expense is higher,” says Anderson, “we’ve got to demonstrate our value through a lower overall operating expense.”
Robust Demand Across Entire Industry
Articulating their competitive advantages is top of mind for OEMs as the pellet market continues to experience a robust period of growth. For CPM, the robust activity in planning and building of export-scale facilities drove a decision late last summer to put together a sales and marketing team with an exclusive focus on this market. “That demand is certainly one of the things that showed us that we need to carve out a group dedicated solely to the wood pellet industry,” says Anderson. “That was a decision that was made due to two main factors. One is the predominance of European companies that are either partially or wholly owners of new industrial wood pellet plants that are being built in the Americas, as well as that group’s broader experience with modern pellet plants.”
Curci, too, sees increased activity with producers and developers eyeing the growing export market. “What we’re seeing is a trend where we’re moving away from the infancy of the industry and we are starting to mature,” he says. “With that maturity we’re seeing a lot of activity with large-scale producers.”
While all OEMs are aggressively calling on and targeting the up-and-coming fleet of export-scale facilities, no one is overlooking the continued opportunities amongst existing, operating pellet mills that service the residential market, particularly after last winter’s heating season. “Some of these smaller facilities, especially with last year’s heating season being as strong as it was, now have the opportunity and the ability, both financially and marketwise, to add a little extra capacity,” Curci says.
Clark agrees. “That 50,000 to 100,000 ton a year market is still there with last winter’s extreme cold and extreme fuel prices, the wood pellet market is still there to offset that,” he adds.
Locke notes that existing Bliss customers are thinking similarly. “We’ve seen our existing customers adding capacity going into this year’s heating season and we’re very hopeful that they do so.”
Still, the market inertia delivered by the rapidly growing demand for wood pellets overseas is moving press OEMs to react, with both organizational changes and design changes. Dieffenbacher has introduced a pellet press that is capable of producing up to 20 tons of pellets per hour from a single unit. CPM continues to support four manufacturing centers globally and has just opened a parts and service facility in Jackson, Miss., to support customers in the Southeast U.S. Bliss Industries, while admittedly a much smaller organization, is feeling the market pull created by this export market after having won the business for pellet presses at the recently built and commissioned, Go Green International pellet facility, a 200,000-ton facility near Paige, Texas.
Growing industries generate profits and drive reinvestment within their supplier base. As the pellet industry grows, innovation will undoubtedly continue to emerge from the industry’s enviable stable of pellet press OEMs.
Author: Tim Portz
Executive Editor, Biomass Magazine