The 105-metre-high stack was the first structure completed at the Kemi bioproduct mill.
“Our goal is to build a path at the bioproduct mill that will enable us to eliminate wastewater emissions altogether.”
This also reduces the load on the wastewater treatment plant. Flue gases are purified by converting odorous pro- cess gases into sulphuric acid, which is needed when cooking tall oil. “Closed chemical cycles are prime examples of the circu- lar economy. We recover chemicals in the process and use them to produce chemicals needed in another process,” Pehu-Lehtonen says. Closed cycles also improve cost-effectiveness. For ex- ample, less energy is required for pumping water if the volume of fresh water used in the processes has been minimised. The portion that cannot be used for materials or chem- icals is consumed as energy by the mill itself and the surrounding integrated mill area. Production at the bio- product mill is energy self-sufficient and uses renewable sources, with no fossil fuels. “Secondary heat from the bioproduct mill process is used as efficiently as possible in the integrated mill area. For example, at Kemi, we must make sure that the thermal load on waterways does not increase in the winter.” Heat is also recovered from flue gases. For example, secondary heat is used in bark drying, when the bark is gasified and used as fuel. The Kemi bioproduct mill will have an energy self-suffi- ciency rate of 250 per cent. The surplus power, produced from renewable resources, will be sold to the Finnish na- tional power grid.
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