UNIQUE BIOPRODUCT MILL CONCEPT BEING REFINED
TECHNOLOGY THAT EXCEEDS STANDARDS
MEASURING ENVIRONMENTAL AND ENERGY EFFICIENCY
FOSSIL FREE PRODUCTION The new bioproduct mill would be completely fossil free. 100% UTILISATION OF WOOD The mill would use all of the wood supplied as raw material. Nothing would go to waste. 100% CYSTRATE The processes would produce so much renewable bioenergy that the mill’s electricity self-sufficiency rate would be 250 per cent. 250%
The Metsä Fibre bioproduct mill in Äänekoski has been in operation since 2017. Its concept, which has already been tested in practice, would be developed a step further in Kemi. “The Äänekoski concept is functional, but technology and expertise are constantly evolving. For example, the con- struction of a sulphuric acid plant is now an obvious part of a working bioproduct mill concept,” Johansson points out. Sulphuric acid is used in the tall oil cooking plant, and if necessary, it would also be used for bleaching pulp in Kemi. The annual use of pulpwood at the new bioproduct mill would be approximately 7.6 million cubic metres, about 4.5 million more than in the current mill. The raw material would mainly be pulpwood from thinning and regenera- tion felling in northern Finland. Every single part of the trees brought to the mill would be used. “In the new mill area, advanced wood processing would be enabled by an electrical automatic wood yard cranes powered without the use of fossil fuels,” says Technical Director Pekka Kittilä . “The wastewater treatment process would also be de- veloped further. In Äänekoski, sludges go to the digestion plant and from there the end product is converted into pellets, but in the new Kemi mill the primary and tertiary sludge would be dried and pelleted. The biosludge would be incinerated in the recovery boiler.”
In accordance with the European Union’s Industrial Emis- sions Directive and the Finnish Environmental Protection Act, the mill must be built using the best available technol- ogy (BAT) in order to minimise the environmental impact. In the case of the new Kemi bioproduct mill, the tech- nology used would in many respects exceed these require- ments. An example of this is the sulphuric acid plant where sulphuric acid would be produced from odorous gases which would reduce the amount of sulphur emissions into waterways. “Crystallisation equipment for potassium and chloride reduces critical contaminant concentrations in the chem- ical cycle and thus further reduces the amount of concen- trated saline,” Kittilä explains. The wastewater treatment plant would also be designed to exceed the current BAT requirements. “The wastewater treatment plant would have a tertiary plant where COD (Chemical Oxygen Demand) emissions and inorganic compounds would be chemically precipitated before being dumped into the waterways. This would sig- nificantly reduce phosphorus and COD emissions.” The mill would also have high-performance electric fil- ters to reduce particulate emissions.
“Production emission limits would be very low in Kemi. In addition improving wastewater treatment, the mill’s heat load to the water system would not increase from the current level, even if production increased significantly,” Kittilä says. The heat load of the new mill would be controlled by a closed cooling water cycle. In that way, the volume of water intake from the Kemijoki river would not increase from the current level – it would even slightly decrease. “The heat generated would be transferred to the air with cooling towers, so heat release entering the waterways would not increase compared to the current situation.” Many of the planned solutions are related to the goals of fossil free production. For example, tall oil can be made into tar oil, which would be used in exceptional circum- stances as a fossil free support fuel in a recovery boiler and lime kiln. “The lime kiln would use fossil free product gas from gas- ified bark as its fuel. This is a fossil free and energy-efficient process. Around 50 per cent of the bark would be used in the bark gasification to produce heat for the lime kiln, and the rest of the bark would be sold outside the integrated mill area as fuel for the communities’ power plants.” In addition, secondary heat, such as the heat from the flue gases of the lime kiln, would be used as an energy source for bark drying. It would also be used, via the water circu- lation, at the debarking department for thawing the trees.
Thanks to the modern solutions, the amount of heat from the mill area entering the waterways would not increase from the current level.
The bioproduct mill completed in Äänekoski in 2017 serves as a model for the new mill to be built in Kemi.
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