“In recent years, purchasing structures for sawdust have changed. Selling sawmill byproducts has become difficult in our region, and we wanted to make sure that they don’t go to waste. That was one of the reasons why we decided to invest in a pellet mill,” Christian Keller, managing director of the Hermann Keller sawmill, tells us. In addition to the pellet mill, the project also involved the construction of a new combined heat and power plant, including an ORC turbine and hot water treatment. Thus, Keller built an entire energy center, which enables the company to generate part of the necessary electricity and also the heat required for production. The continuation of the company with a secure succession plan also played a role.
One general supplier
“Due to our lean structures, it was important to us to be able to award the contract for the pellet mill to one general supplier. We wanted a coherent overall plant layout. Since we have worked with Rudnick & Enners successfully for decades when it comes to our sawmill’s wood waste disposal, we once again opted for their technology,” Axel Baumann, operations manager at Hermann Keller, explains. He oversaw the construction of the new energy center, including the pellet mill. Keller adds: “Rudnick & Enners was a given from our side, so we were able to get started on the actual planning very quickly.”
Speaking of planning: The Hermann Keller sawmill placed great importance on getting the local council and the public on board early on. “At an event, we explained our project to politicians and citizens and informed them about noise and dust protection,” Keller tells us. Another positive aspect of the pellet mill is that round 3,000 truck journeys a year are now eliminated because all residual wood is processed on site. Sawdust and wood chips go to the pellet mill, and the bark is used in the adjacent new heating plant. “With this investment, we can significantly improve our carbon footprint,” Keller says, mentioning another advantage.
Capacity designed for self-sufficiency
In Achern, Hermann Keller cuts around 320,000 m³ of log wood a year. “However, we do expect log supply to become more difficult in the future, which is why we designed the pellet mill for an annual cutting capacity of 250,000 m³,” Baumann explains. Christian Gebele, Rudnick & Enners’s project manager, estimates the pellet mill’s production capacity at 40,000 t a year – assuming a five-day week with two-shift operation. “With this output, we can con cover 100% of our in-house demand,” Baumann tells us. Construction of the pellet mill began in March 2024, and the first pellets were already produced around Easter 2025. On the 14-hectare sawmill site, enough space was available for the new energy center – yet the machines were designed to be as compact as possible. The pellet mill and heating plant are located in adjacent, but separate, halls, which are monitored from a shared control center.
Since the new pellet mill is located some distance from the sawmill, the residual wood is transported there by tractor and trailer. “Installing a tubular belt conveyor of this length would have been disproportionate. Furthermore, we would have had to cross a public road,” Keller comments. The tractor driver loads the trailer with byproducts from the silos in the sawmill. The trailers are very large, so that nearly 50 m³ can be unloaded in under a minute. The tractor pushes the residual wood – a mixture of wood chips and sawdust – into an underground storage container where large dosing screws rapidly discharge the residuals and transport them towards the wet chip silo. In between, a separating mechanism sorts out metal and chips which are too long.
Leaving the wet chip silo, the residual wood is mixed and transported to a screener for processing. “The wood chips and coarse material are separated and transported to the wet chip hammer mill. The sawdust we transport past the mill and later, we combine both materials,” Gebele explains. Specifically, Rudnick & Enners supplied the RE-HM 500x1300 wet chip hammer mill, which operates without an additional extraction system and produces dryable chips. The chips then enter the KBT 5.0-26 belt dryer with its drying area of 130 m². This belt dryer, which was developed by Rudnick & Enners in collaboration with Swiss Combi, has a belt width of around 5 m. Rudnick & Enners also equipped it with a heat recovery system with condensate treatment. “Thanks to our heat recovery system, the belt dryer’s heat consumption is much more constant throughout the year. We can also achieve a higher throughput per MWh of heat. Our system is designed in such a way that we don’t need to increase the number of fans or their connected load compared to our conventional belt dryer,” Sven Rudnick, managing director of Rudnick & Enners, explains. The belt dryer was also equipped with silencers and tall exhaust air pipes to meet structural requirements.
Once they have left the belt dryer, the chips are transported to a dry chip silo. Next, the dried chips are milled. The dry chip hammer mill was further developed by Rudnick & Enners and equipped with a new shredding system. The latter optimizes energy consumption during crushing. “This way, we could reduce energy consumption during the shredding process. Furthermore, fine grinding, for example, of biomass pellets, is also possible with this shredding system,” Rudnick tells us. After shredding, the material is conditioned and enters the mixing container, where the starch is added.
Pressing and gentle cooling
Keller operates two Rudnick & Enners RE PM 7 pellet presses. “Each press has a capacity of 6.5 t/h,” Gebele says and adds: “In our pellet press, we rely on fully automatic roller adjustment. This makes starting up the press and shutting it down easier, and it also reduces the operator’s workload. We now have several pellet presses of this series in operation.” The pellets then enter the two horizontal coolers – which were also developed by Rudnick & Enners. “Our horizontal cooler offers several advantages over a conventional air counterflow cooler. For us, it is important to gently cool the pellets without over-drying them. We offer our horizontal coolers with output capacities of 3 to 10 t/h,” the project manager tells us. Each machine also determines the actual, specific energy consumption per tonne of pellets, which allows Keller to further optimize its energy management.
After the pellets have left the horizontal cooler, a screener separates fine dust from them. To ensure gentle transport, a tubular belt conveyor then transports the pellets to one of the two pellet silos, which have a total net capacity of 3,200 t.
The truck loading station is adjacent to the pellet production. The truck is positioned on the scales. Two loading spouts and a movable conveyor are located above it. The loading area is surrounded by a housing to reduce noise and dust emissions. Recently, a bagging machine, which was also supplied by Rudnick & Enners, was put into operation in the adjacent hall. Its capacity is 1,500 bags per hour. “The machine’s special feature is the so-called Varioformat: A fluctuating bulk density affects the volume of the bags. To ensure that they remain firm when handled, the back seams can be adjusted, if necessary,” Gebele explains. Finally, the bags are automatically stacked on pallets and wrapped in plastic foil.
In the pellet mill’s control booth, Rudnick & Enners installed the Quick Data software, which automatically sends all production data to Keller’s ERP system. The entire switchgear and control system, including the plant visualization, was also supplied by Rudnick & Enners.
Collaboration on an equal footing
“We started looking for staff early on. Most of them were involved already during the planning stage or when assembly started. So, the employees identified with the project and practically know every single screw,” Baumann says and adds: “Everything worked really well.” Rudnick & Enners and the Hermann Keller sawmill are very satisfied with the collaboration. “Whenever coordination was required during construction, there were no lengthy discussions. Instead, we worked together to find a good solution – and we always succeeded at that,” Keller and Gebele agree. “We made the right decision in choosing Rudnick & Enners,” Keller emphasizes.
