Family company on its way to the future

Already in 2019, Pieper Holz in Olsberg/DE was thinking about investing in a pellet production facility. “We spent a long time honing the perfect concept for us before we decided to have a new building erected,” Isabell Pieper explains, who runs the company together with her father, Hans-Georg Pieper. “Our focus is on the production of high-quality pellets. Our output is tailored to the amount of wood waste that accumulates in the sawmill. At the same time, we have reached a level of flexibility that allows us to react to the market or raw material situation at any time,” the managing director explains during the tour of the new pellet mill.

A reliable partner

The company has been working with Rudnick & Enners of Alpenrod/DE for many years. When Pieper Holz’s new sawmill was built in 2006 and 2007, the machine manufacturer from Westerwald delivered the entire wood waste disposal system. “Following these many years of experience, we entrusted Rudnick & Enners with the construction of the pellet mill, the processing plant for industrial wood, as well as the shredding machine for bark and offcuts and the fuel infeed,” Pieper tells us (see article Optimal fuel processing). “Rudnick & Enners always provided us with great support during the implementation phase and was always available when we had questions,” Kristian Kriegesmann, Pellet Production Manager at Pieper Holz, adds.

Construction of the underground structure started in the summer of 2021, and the first pellets were produced on October 4, 2022.

Complex changes

The Rudnick & Enners tubular belt conveyor, which was built in 2007, transports the wood chips and sawdust from the sawmill into the three existing wood waste boxes. There, the residual wood, i.e. wood chips and sawdust or mixtures of different types of wood, can be stored separately. Three push floor boxes were integrated into the existing residual wood storage area. “The performance-controlled push floors can be filled up to a height of 13 meters and can also be driven on with a wheel loader. The materials used for pelleting are mixed with the help of the three push floors,” Rudnick & Enners Managing Director Sven Rudnick explains. Behind the push floors, two near-resonance vibrating conveyors with an integrated separator for overlengths make the mixture of sawdust and wood chips more homogenous, before a bucket elevator feeds it to the wet chip hammer mill.

Energy-conscious pelleting

Rudnick estimates the output of the RE-HM 500x1300 wet chip hammer mill at around 12 tons per hour. Thanks to a special grinding chamber, the hammer mill does not require an energy-intensive extraction system. It can grind both wood chips and a mixture of moist wood chips and sawdust. In addition, Rudnick & Enners designed the plant in such a way that it can also handle hardwood from industrial wood processing, and set up a bypass around the plant. Once the residual wood has been shredded, it enters the Stela & Laxhuber belt dryer and is then stored in the dry chip silo, which has a diameter of 12 meters and a height of 30 meters.

Next, the wood chips and sawdust are processed again in a Rudnick & Enners dry chip hammer mill before they enter the conditioner, where starch and water are added. The R+E conditioner is equipped with an automatic moisture measuring device. A trough chain conveyor transports the mixture into the spacious mixing container, which feeds the two pellet presses. Each press has an output of 6 tons per hour. “When it comes to pelleting, we rely on a horizontal design. Including the pressure boosting system, the device for dosing the starch, dry chip grinding and maintenance access points, we accommodated the pelleting plant with its output of 12 tons per hour in an area of around 11 by 14 meters with a low building height,” Rudnick tells us.

After they leave the pellet press, the pellets enter the R+E horizontal cooler, which is located directly under the press and gently cools the pellets. “Compared to a conventional counterflow cooler, our horizontal cooler offers a number of special features in terms of process technology and is able to influence the quality of the pellets as well as energy efficiency thanks to intelligent control technology. For us, it is important to cool the pellets down gently and to avoid ‘overdrying’ them. We offer our horizontal coolers with an output ranging from 3 to 8 tons per hour”, Rudnick explains. Via a discharge system, the first pellets, which are produced right after the plant has been started up, can be separated automatically via the cooler into a spacious container, which does not obstruct the maintenance access point of the pellet press, especially during the start-up or shutdown phase. In addition, a spark detection and extinguishing system was installed directly between the press and the cooler inlet. After the subsequent screening process, the pellets are transported into two concrete silos via tubular belt conveyors. “We operate the pellet plant from Sunday night to Saturday morning. A simple start-up and shutdown process is important to us, as is high pellet quality,” Kriegesmann comments.

Pieper Holz can also choose whether to load the pellets onto trucks or fill them into bags. The truck loading station has a capacity of around 100 tons per hour and more. The discharge below the pellet silos is done with the help of a tubular belt conveyor. “Thanks to the special, high-performance Rudnick & Enners vibrating screen, which sits directly above the movable loading belt, the amount of fines is very small. Our drivers can confirm that. Also, we are able to load a semi-trailer truck in less than 20 minutes, including the drive to the loading station and away from it,” Kriegesmann confirms. “To achieve the highest possible screening accuracy, we have further developed our vibrating screens. With the new configuration and in connection with the integrated material flow control, we can react more flexibly to the input material and actively influence screening quality,” Rudnick emphasizes. The screened out fine material is reintroduced into the pelleting process.

For the bagging, a tubular belt conveyor transports the pellets to the bagging machine, which was also supplied by Rudnick & Enners. In front of it, a second vibrating screen with a winnowing mechanism was installed, which further reduces dust and the number of broken pellets in the bags. The bagging machine has a capacity of up to 1,400 bags per hour and is suitable for 12 and 15 kg bags as well as for special formats.

In addition to the above-mentioned machines and the project planning, Rudnick & Enners is responsible for all electrical installations, the steel construction, the switching and control systems and the plant visualization including R+E Quick-Data, an Industry 4.0 tool. Daily production reports and analyses complete Rudnick & Enners’s scope of delivery.

Further expansion

At the end of May, Rudnick & Enners launched another project at Pieper Holz: This summer, an industrial wood plant will go into operation in Olsberg, to be precise a debarking and chipping line for industrial-quality softwood and hardwood logs with diameters of 10 to 60 cm. The Rudnick & Enners debarker is fed automatically by a cross conveyor and then sends the debarked logs via a power-controlled apron conveyor in the direction of the R+E chipping machine. The bark will be used in the heating plant. “This line will bring a maximum in flexibility,” Isabell Pieper explains and adds: “We are very satisfied with the way the project is handled. We can tell that we are working with a family company.”