Rettenmeier’s Ingrid Benčová and stela Laxhuber’s Yves-Marc Schade in front of the new system © Ulrike Knaus
Slovakia’s biggest sawmill is located in Liptovský Hrádok. It has been part of the German Rettenmeier group for more than 20 years and has been managed by Ingrid Bencová for ten years. Each year, 670,000 to 700,000 m³ of spruce logs from the nearby area are used for the production of sawn timber, glued solid timber products, planed timber, wood briquettes, slats and packaging wood.
80% of the products are exported to Austria, Italy, Germany and Greece. Since May, pellets are also produced at the production site.
The new pelletizing plant was supplied by Rudnick & Enners of Alpenrod/DE. In order to be able to produce high-quality pellets, Rettenmeier opted for a belt dryer by stela Laxhuber of Massing/DE.
Efficient – modular – low-emission
The RecuDry has a frost protection housing in order to ensure the efficient operation of the plant in winter © Ulrike Knaus
Four years ago, Stela Laxhuber specially developed the new RecuDry-system for belt dryers. The system separates the technology into two sections, the condensation module and the RecuDry module. Thanks to this modular structure, several elements can be connected in series according to the respective requirements. At Rettenmeier’s sawmill in Slovakia, two are in use with a plant length of 30 meters.
“What distinguishes the stela belt dryer is the circulation and reheating of the air inside the RecuDry module which gives the air an optimal saturation before it is then fed into the condensation module. The mostly latent energy preheats the fresh air for the condensation module. Thanks to the use of an air-air heat exchanger most of the energy used is recovered which guarantees highly efficient drying. During this process, the circulating air is reheated again,” explains Yves-Marc Schade, product manager at stela Laxhuber. With the RecuDry system, exhaust air flows can be reduced by 50% which leads to a considerable minimization of emissions. Heat loss is also kept low which means that 35 to 55% of energy can be saved compared to conventional fresh air-exhaust air drying.
Accessibility and cleanability
The system’s software is available in several languages © Ulrike Knaus
After nine months of planning and construction, the belt dryer was started up at Rettenmeier Tatra Timber. Every hour, 14.4 tons of sawdust with a moisture of 50% are dried to 8 tons with a moisture of 8% before they are conveyed on to the pelletizing plant.
Currently, 60,000 tons of pellets are produced each year. However, the plant’s capacity is designed for a possible increase at a later time. The main export market for the pellets is Eastern and Southern Europe.
Since winters can be quite cold in this part of Slovakia, with temperatures of around -25° C, the entire belt dryer has a frost protection housing which is designed for temperatures of up to -40° C. Additionally, the housing reduces the belt dryer’s acoustic emission which made it easier to install it in a built-up area. The operation software is available in several languages and can be integrated in the existing system if desired.
For stela’s engineers, it was also important to make sure that all components are easy to reach and maintain. All modules can be opened, maintained and cleaned through hatches. The RecuDry belt dryer’s air-air heat exchangers are continuously washed with the accumulating condensate which means that for deep cleaning, the entire system needs to be shut down only once a year.
“The drying belt is constantly cleaned with compressed air and is kept clean sequentially with high-pressure cleaners,” explains Schade.
As with this plant in particular, the condensate is treated by stela. The pH value is set to 7 and the condensate is desilted which is why it can be released into the public sewage system without problems.
