TECHNOLOGY FOCUS - BIOLOGY - Preferred Components: The wood-based feed comprises wood-based by-products of forestry and felling (e.g. trees removed in thinning, stubs, rootstocks, branches, brushwood and bark).    TECHNOLOGY FOCUS - ENVIRONMENT - Preferred Components: The organic matter comprises biomass (e.g. wood-based feed, agricultural waste, by-products of forest industry, waste water slurry of forest industry or municipal waste).    TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Method: The carbon dioxide stream is formed as a by-product of the production of synthetic hydrocarbon chains. The purity of the carbon dioxide stream is more than 90 (preferably more than 95, more preferably more than 97, most preferably more than 99) wt.%. The pressure of the carbon dioxide stream is more than 5 bar (preferably more than 10, especially more than 20, particularly more than 30) bar. The pressure of the continuous reactor is more than 5 (preferably more than 10, especially more than 20, particularly 20-30) bar. The calcium is carbonated in a continuous reactor; batch reactor or semi-continuous reactor; or in-situ in a papermaking process. The gasification of organic matter is integrated into the carbonation of calcium to enable the utilization of the generated carbon dioxide stream. The gasification of organic matter and the carbonation of calcium take place in the same factory area to enable the utilization of pressure of the carbon dioxide. In the process (M1), the carbonation of calcium is adjusted according to the needs of the papermaking process and the use of the carbon dioxide stream is adjusted according to the calcium carbonate need. In the method (M1), the continuous reactor is integrated into a papermaking process. Preferred Components: The sulfur content of the carbon dioxide stream is less than 1 ppm. The carbon dioxide stream comprises nitrogen (less than 10, preferably less than 5, especially less than 3, particularly less than 1 wt.%).    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - The production of synthetic hydrocarbon chains involving biofuels; physical purification that requires pressurized synthesis gas mixture and/or the use of a Fischer-Tropsch synthesis. In the method (M1), the carbon dioxide stream is generated as a by-product in the production of synthetic hydrocarbon chains; the synthesis gas mixture obtained by the oxygen gasification is purified by physical purification that requires pressurization of the synthesis gas mixture and/or that the synthetic hydrocarbon chains are formed by Fischer-Tropsch synthesis. EXAMPLE - Biomass was gasified as follows: Wood-based by-products formed during felling, such as trees removed in thinning, stubs, rootstocks, branches, brushwood and bark were crushed and dried. The biomass was gasified by using oxygen and steam, where the biomass was treated in an entrained flow gasifier at high pressure and high temperature, thus a synthesis gas mixture comprising carbon monoxide, nitrogen and carbon dioxide was obtained as the product. The product was cooled down before purification. Then the synthesis gas was purified by using the necessary chemical and physical treatments, of which the Rectisol (RTM: physical treatment) requires that the synthesis gas mixture was pressurized to 30 bar. The purified gas was led into a Fischer-Tropsch (FT) reactor to form FT fuels. The conditions of the Fischer-Tropsch synthesis were selected so that the desired hydrocarbon chain length was obtained. The carbon dioxide stream formed as a by-product in the purification of the synthesis gas mixture was used for carbonating calcium. The nitrogen content of the carbon dioxide was less than 1 wt.%, and it had pressure of 30 bar. Precipitated calcium carbonate was prepared by continuous method as follows: A calcium hydroxide-containing water suspension and the carbon dioxide (99 wt.%, pressure 20 bar) were led into a reactor in an integrated production process of biofuel and calcium carbonate. The pressure of the continuous reactor was 20 bar and the calcium carbonate obtained as a product was used as a filler and coating agent in a paper and board manufacturing process in the same factory area. For use as a filler, the carbonated calcium was added to the short circuit of a paper machine, where it was mixed with water and fibers to obtain the desired paper pulp. Calcium carbonate was also added onto finished paper as a coating.