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Biomass power benefits both mill and town

A new biopower plant at the Metsä Board Kyro mill in Finland is a joint venture between the boardmaker and two Finnish energy companies. The switch to a biomass boiler will improve the carbon footprint of three Metsä Board products – Carta Elega and Avanta Prima folding boxboards, and the Cresta wallpaper base family.
“We have been working on improving energy efficiency and sustainability of our mills. The new biopower plant will help us in these efforts, as well as meeting our target of cutting CO2 emissions by 30% across operations by 2020 compared to 2009 levels,” says Mikko Helander, CEO of Metsä Board.
The Kyro mill is now able to replace the use of natural gas with CO2-neutral woody biomass or wood-based fuel. This is predominantly bark and other biomass from industrial side streams, as well as logging residuals and chips from thinnings.
The EUR 50 million biopower facility (operating as Hämeenkyrö Voima Oy) will produce electricity and heat for Metsä Board Kyro, and also provide heat for the neighboring district of Hämeenkyrö. The use of biomass-based power is expected to reduce CO2 emissions from the plant by approximately 100,000 t/y, to about one quarter of previous levels.
Fuel delivery was the
biggest challenge
Hämeenkyrö Voima is owned jointly by Pohjolan Voima Oy, Leppäkosken Sähkö Oy and Metsä Board. It provides 12 MW electricity, 55 MW of district heat, and steam to the paper mill. The boiler strated-up in the fall of 2012, using a combination of woody biomass and peat.
The design and installation of the power plant were particularly challenging because the boiler will be in close proximity to a residential area.
The biomass is delivered by truck, already chipped or crushed. To avoid having trucks running during the night, deliveries are organized so that 20 trucks per day deliver during a 15-hour window. This is a just-in-time operation; the silos hold enough biomass to get through the night, but not enough to carry the mill for 24 hours.
Because this new biomass boiler replaced an older unit, the project required no new tie-ins to the mill, explains Juha Kouki, a specialist in bioenergy with co-owner Pohjolan Voima. The existing turbine and cooling water system were retained. The biggest challenge was the fuel receiving system, which was constrained by the congested space and the nearby residences.
The fuel handling system was supplied by Raumaster. To minimize dust, the trucks are unloaded in a closed room equipped with a dust collection system. Belt conveyors were chosen because of their lower noise and other operational benefits.
The biomass is dried by the supplier prior to delivery. Seppo Hulkkonen, Andritz’s technology director, bioenergy systems, notes that the biomass generally measures 50% moisture when fed into the boiler. Peat going to the boiler has 40% moisture.
The boiler is an EcoFluid bubbling fluidized bed boiler, supplied by Andritz. It can provide steam flow up to 105/115 t/h, at a pressure of 84 bar(g) and temperature of 510 °C. Andritz delivered the boiler island and auxiliaries, flue gas cleaning with bag filter, field instrumentation and electrification.
According to Andritz, the advantage of a bubbling fluidized bed (BFB) boiler is its fuel flexibility. They are commonly used for wood waste and sludge, for example, or agricultural waste plus wood waste.
BFBs allow fuel moisture content variation, have high combustion efficiency and low emissions. They also typically have high availability and long operating times, which are important for industrial applications because processes can depend on the steam generated by the boiler.
At the Hämeenkyrö Voima site, the steam produced by the boiler goes first to a back-pressure turbine for electricity production, then to the mill for process uses, and to the town for district heating.
Andritz’s Hulkkonen comments that for biomass boilers in this size range, there are not many competing suppliers because the combustion technology requires dedicated knowledge. Also, “this is industrial scale, so environmental regulations are much more stringent.”
For this project, the “driving force was to eliminate natural gas” says Kouki. Natural gas prices are rising and taxation is high on natural gas, he explains. Overall, says Kouki, the trend in Finland is for wood-based fuels to replace natural gas. Biomass prices are considered more stable and predictable.
Pohjolan Voima has been involved with 15 biomass power plants in last 20 years; the field is the subject of a huge investment program for the company. In the majority of cases, says Kouki, forest industry companies are part-owners.
“Fibre is no longer the only source of income for mills. They generate a lot of money selling power to the grid,” states Henrik Eneberg, director sales and marketing, recovery and power division, Andritz.
In this case, for Metsä Board, the benefits are numerous. The biomass power plant provides a more stable cost structure, and it furthers the company’s sustainability goals, as well as providing a “green” marketing edge for its products.