Recycled Heat

Energy-Saving Measures in Leoben

Some say, large-scale enterprises with aged facilities waste enormous amounts of energy. Others argue that precisely these plants also have the greatest energy-saving potential. Mühlböck, Eberschwang is one of these "others".

The company is currently installing eight new drying kilns at Mayr-Melnhof Holz in Leoben.

The headquarters of Mayr-Melnhof Holz in Leoben is one of the largest sawmills in the country with an annual sawing capacity of approximately 1 million cubic metres. Time and again, the company reached its performance limits over the last winters due to growing demand for dry, sawn lumber. It seemed the heating capacity of the 24-MW biomass power plant would soon no longer suffice in light of the company's power requirements. In addition to 36 classic fresh-air ventilation kilns and a belt dryer for processing shavings, the company also supplies the neighbouring brewery Göss with heat.

Savings with heat recovery
The company solved this problem by exchanging eleven existing drying kilns for eight new Mühlböck drying kilns, type 1003, each with 218 m3 net volume or 177,000 m3 annual capacity. "These can utilise the introduced thermal energy much more efficiently and dry the lumber much quicker," explains Mühlböck employee Heinz Reisenbichler. A drying facility must evaporate considerable amounts of water especially from the beginning of drying to fibre saturation. This in turn leads to peak utilisation of the boiler plant. Kilns of the type 1003 do not obtain the required heat from the heating system, but from energy recovered from other kilns that dry in the lower wood-moisture range.

Additional quality improvement
Water extraction via fibre saturation is performed with comparatively low temperatures, i.e. an annual average of 35°C. Air only passes through the lumber once, is saturated completely and almost cools to outside temperature. Using lower temperatures to dry moist boards is preferable as this results in a consistent final moisture content. "This quality improvement was another important criterion for us in the decision-making process," explains Richard Metnitzer, operating manager at Mayr-Melnhof.

It pays off
A sample calculation by Mühlböck especially elucidates the achieved energy savings. For conventional technology, the company estimates a thermal energy requirement of 250 to 290 kWh/m3 in all assortments or 450 to 490 kWh/m3 for sideboards. These values, according to Mühlböck, are cut in half with the usage of a type 1003 kiln. For Mayr-Melnhof, this results in thermal-energy savings of 22 to 43 GWh/year calculated for the utilised annual capacity of 177,000 m3. "Shorter drying times also provide significant power savings," adds Metnitzer.

Important investment
Ultimately, Mayr-Melnhof has increased its drying capacities in Leoben by 25 to 35% on account of this investment – a measure that was urgently required according to Metnitzer. The company still sells some of its goods fresh, but the Styrian saw millers are also aware of the rising demand for dry lumber. Mühlböck has also retrofitted four existing classic drying kilns in Paskov/CZ, another Mayr-Melnhof site, to the 1003 system.

Solid foundation of trust
Metnitzer explains why Mayr-Melnhof once again decided to go with Mühlböck: "Of course, one looks at different providers when making an investment of this magnitude. However, we quickly returned to our Upper Austrian partner as Mühlböck combines many years of good cooperation with compelling technology." The kilns were installed in the summer months and are about to be commissioned for service. A short conversion phase was also a crucial factor for Mayr-Melnhof. Metnitzer identifies the solid foundation of trust as another important criterion. "We knew that the deadlines we agreed on with Mühlböck would be observed."

Holzkurier 35/2016, Günther Jauk