Even more green energy thanks to twins

With the commissioning of the glued timber production facility in spring 2023, the development of the HS Timber Productions sawmill has progressed further. The company is particularly satisfied with the Urbas biomass boiler, which went into operation in June 2020. “The plant has been running continuously at full capacity without any problems,” Siegfried Lehfeld, power plant manager of HS Timber Productions at the Kodersdorf site, tells us.

“The two CHP plants replace our existing plant, i.e. the two 10-MW double hot water boiler plants from 2004 (also from Urbas). For us, the advantage is that we are able to generate both heat and electricity,” Lehfeld explains.

As with the first boiler plant, Urbas was the general contractor for the second one, too, while HS Timber built the concrete structure. The second CHP plant was planned and built directly next to the first boiler but positioned at a 180-degree angle to it. “Thanks to this plant layout, we could optimize the fuel storage and keep the hot water network as short as possible,” Lehfeld says.

Identical plant

The second biomass-powered cogeneration plant went into trial operation in April. Like the plant which was completed four years ago and has been running at full capacity since then, the steam boiler’s output is 21.3 MW, the combustion heat output is 24.8 MW and the turbine’s power output is 5.5 MWel (see CHP plant with bark combustion). The safety temperature of the steam boiler is 535°C at a maximum operating pressure of 81 bar. Both plants produce electricity and 31 MWth of heat for the sawmill’s in-house consumption. “With the new biomass cogeneration plant, we are taking a significant step towards sustainability and security of supply with base-load, carbon-neutral electricity. Our sawmill will produce significantly more green energy than we need for production at the site,” Thomas Kienz, managing director of HS Timber Productions in Kodersdorf, explains. The waste heat generated during electricity generation is used for drying the high-quality wood products in the sawmill.

The energy is fed into the power grid and helps supply private households with green electricity. With the two plants, 80,000 MWh of electricity are generated each year, which, according to HS Timber, is enough to supply all residents of Kodersdorf and the neighboring town of Niesky. One difference between the two boilers is that in the new boiler, a Multi Cyclone was installed for flue gas cleaning. This has the advantage that larger dust particles are separated from the flue gas already before it reaches the electrostatic precipitator.

Bark and wood chips as fuels

In the boiler plant in Kodersdorf, one of the fuels used is bark with a water content of up to 60%. The daily consumption of each CHP plant is 450 stere of untreated bark. “At the moment, we almost exclusively use spruce bark. A mixture of 50% spruce and 50% pine bark is possible, too. Pine bark burns very well. From a financial point of view, though, it is better to sell it and to use lower-quality spruce bark as main fuel for our site,” Kienz tells us. In addition to bark, wood chips are also used. They are purchased from external suppliers and consist of forest wood chips or biomass which accumulates during road maintenance. Another change made is the possibility to adapt the combustion temperature to the quality of the raw material. “In order to avoid clinker formation during the combustion process, the combustion temperature was lowered slightly,” Lehfeld explains. “Our boilers can be operated continuously at around 1000° C while complying with the emission limits, even when the fuel used is of inhomogeneous quality,” Urbas emphasizes. The selected boiler system enables continuous year-round operation, which is only interrupted by planned service and maintenance shutdowns. The “twin power plant” in Kodersdorf guarantees redundancy in energy supply and, as a result, security of supply during operation.

Heat for the sawmill, glulam plant and pellet mill

In four-shift operation, two employees are responsible for the system control, ash management, infeed management and the maintenance processes. The water-tube boiler with the vertical flue gas pipes has been the standard design at Urbas for decades. All boiler components are prefabricated as modules in the biggest possible size at Urbas’s production site, which significantly reduces assembly times. The turnkey plant with its step grate conveyor and generously dimensioned combustion chamber is equipped with a vertically positioned secondary combustion chamber. In each plant, 15.5 MWth are decoupled for heating the 28 Mahild drying chambers, the Valutec continuous kiln for glued timber production and the belt dryer for pellet production.

High quality of service

Lehfeld specifically emphasizes the high-quality service provided by Urbas. “Whenever we need spare parts, an Urbas technician arrives on site within a very short time or provides information so that we can replace worn parts ourselves together with regional partners.”