Requirements implemented in the best possible way

The two existing 10 MW plants, including the boiler house and the electrostatic precipitator supplied by Urbas of Völkermarkt, have been running at full capacity for 17 years, ever since the plant was built in 2003, and had to be overhauled. “Production volumes have been growing continuously and last year, they reached nearly 1.5 million m³ in the sawmill and 100,000 tons in the pelleting plant at our Czech site. Despite the retrofitting with a flue gas condensation system in 2011, the heat generation capacity of the double boiler system was simply no longer sufficient,” explains Richard Metnitzer, Head of Investment Management at the Mayr-Melnhof Holz group.

“The increased heat demand and upcoming repairs prompted us to build a new 12 MW plant in 2020 before overhauling the existing plants one after the other,” tells us Metnitzer. From the point of view of those responsible for the project, this strategy ensured that production could continue without major interruptions during the construction and repair phases.

Turnkey project

The turnkey plant built by the Carinthian specialists includes fuel supply, ash disposal, controlled ventilation, air preheating, electrostatic precipitators, a 5.8 MW flue gas condensation system and the steel structure of the boiler building. The new plant was integrated into the existing hot water network. For this purpose, Urbas had to install a 50-meter-long pipe bridge, among other things.

For the bridge, high-quality units were pre-assembled at Urbas’s site and only the necessary connecting pipes were then built by qualified specialists on the construction site, as Urbas underlines. Due to the increase in production, it was necessary to expand the hot water network. To achieve this goal, Urbas adapted the district heating pipes and installed a 100 m³ buffer tank to better respond to peaks in heat production and demand.

Joint development of the plant concept

Already in 2019, Mayr-Melnhof Holz built a 10 MW biomass heating plant together with Urbas at the Russian production site Efimovskij. “In Paskov, we successfully drew on the experience we gained in that previous project. Together with Urbas, we defined and implemented detailed project requirements,” emphasizes Metnitzer.

In addition to boiler geometry, the choice of material and instrumentation, Mayr-Melnhof Holz’s requirements included the usability of extremely wet bark and wood chips and compliance with the strict emission standards. This requirement has to do with the fuel that comes from the wet storage facilities, which the group operates at its sites in the Czech Republic and in Russia. In 2020, Mayr-Melnhof Holz not only invested in a biomass power plant in Paskov, but also in a 1.4 hectare-big wet storage facility for up to 70,000 m³ of logs, four new drying chambers and in the expansion of the annual pelleting capacity to 130,000 tons. “This way, the entire production volume can be dried at the Paskov site and all sawmill byproducts can be recycled on site in a profitable way,” adds Metnitzer.

The Urbas plant is designed for the combustion of fuels with a water content of up to 70%. Thanks to the flue gas condensation plant, up to 5.8 MW can be generated additionally for the low-temperature network using the exhaust gas, with appropriately moist fuel and a low network return temperature. Ash removal is done with a solid, robust trough chain conveyor and screw conveyors to ensure a high fill level inside the containers.

Full performance with “reserves”

The planning phase started in spring 2019 and at the end of the year, Urbas received the order. In May 2020, after five months of construction work, Urbas started assembling the boilers and in November, the plant was started up as planned. At that time, the two existing plants were alternately repaired and their controls exchanged. “Shortly before Christmas, all three boiler plants were back to full performance,” underlines Metnitzer.

The agreed key performance indicators were achieved “with sufficient reserve”. “We opted for Urbas because the company took the individual requirements of each plant into account in the best possible way and because we had the opportunity to help develop the plant concept,” explains Metnitzer.

A short while ago, Mayr Melnhof Holz ordered another 11 MW biomass boiler plant with even stricter emission limits for its production site in Leoben, which is to be built by the end of 2021. Then, all three sawmills will be equipped with Urbas biomass boiler plants.