FI3580388T3 - System and method for silica removal in a pulping process - Google Patents

Claims (8)

Patent Claims 1. A system (1) for — removing — silica in the prehydrolysis process of sulfate pulp production, which system (1) comprises at least: a container (2) with an upper part (3) and a lower part (4); a chip feed hole (5) arranged in the upper part (3) for bringing wood chips into the container (2); the steam supply opening (6) arranged in the upper part (3) for bringing steam to the tank (2; the first liquid supply opening (7) arranged in the tank (2) for bringing liquids into the tank (2), to produce chip slurry at the temperature of the chip slurry to the soaking area (8) placed under the upper part (3), the soaking area (8) being the area where the wood chips are immersed in the liquid for a specified soaking time; the chip slurry outlet (9) arranged in the bottom part (4) and connected to the chip slurry transport pipe (10) for transporting the chip slurry; the second liquid supply opening (11) arranged in the bottom part (4) and/or the chip slurry transport pipe (10) to dilute the chip slurry in the chip slurry transport pipe (10) to a liquid-to-wood ratio of at least 10:1 when the temperature of the dilution liquid is higher than the temperature of the chip slurry; to remove the water of the chip slurry from the dewatering device (12) connected to the chip slurry transport pipe (10) and the first flow (13), containing chip slurry with a liquid-to-wood ratio of less than 3:1, and a silica-containing liquid to create a second stream (14); and a return pipe (15) connected to a dewatering device (12) for conveying a second flow of silica-containing liquid, and connected to the first liquid inlet (7) and/or the second liquid inlet (11), where at least one silica separator (16) is arranged in the return pipe (15), and that the soaking time is between 30 minutes and 120 minutes, that the temperature of the chip slurry is 95-105 °C, and that the temperature of the dilution liquid is 110-130 °C. 2. System (1) according to claim 1, characterized in that the process for the production of pulp is a process for the production of soluble cellulose. 3. The system (1) according to claim 1 or claim 2, characterized in that the mixer (20) is arranged in the chip slurry transport pipe (10). 4. The system (1) according to one of the previous claims, characterized in that the return pipe (15) is arranged before the silica separator (16) with a feed opening for the addition of agglomerating agent. 5. A method for removing silicon dioxide in the prehydrolysis process of sulfate pulp production, which method comprises at least the following steps: introducing wood chips into the container (2) through the chip feed opening (5) arranged in the upper part (3) of the container (2), said container comprising said upper part (3) and bottom part (4) ; introducing steam into the container (2) through the steam supply opening (6) arranged in the upper part (3); liquid is introduced into the tank (2) through the first liquid supply opening (7) arranged in the tank (2) to provide the chip slurry at chip temperature to the soaking area (8) located under the upper part (3), the chip soaking area (8) being the area where the wood chips are immersed in the liquid for a specified soaking time; the chip slurry is transported out of the tank (2) through the chip slurry outlet (9) arranged in the bottom part (4) and connected to the chip slurry transport pipe (10); the chip slurry is diluted in the chip slurry transport pipe (10) to at least a 10:1 liquid-to-wood ratio with a dilution liquid whose temperature is higher than the temperature of the chip slurry, via the second liquid supply opening (11) arranged in the bottom part (4) and/or the chip slurry transport pipe (10); the water in the chip slurry is removed with the dewatering device (12) connected to the chip slurry transport pipe (10) and the first flow (13) of the chip slurry is created with a ratio of less than 3:1 liquid to wood and the second flow (14) of liquid containing silicon dioxide; and conveying the second flow (14) of the silica-containing liquid through the return pipe (15) connected to the liquid removal device (12) and connected to the first liquid supply (7) and/or the second liquid supply (11) where the silica is removed from the silica-containing liquid with at least one silica separator (16) arranged in the return pipe (15), and that the soaking time is between 30 minutes and 120 minutes, that the temperature of the chip slurry is 95-105 °C, and that the temperature of the dilution liquid is 110-130 °C. 6. The method according to claim 5 characterized in that the process for the production of pulp is a process for the production of soluble cellulose. 7. The method according to claim 5 or claim 6, characterized in that the mixer (20) is arranged in the chip slurry transport pipe (10). 8. The method according to one of the previous claims 5-7, characterized in that the return pipe (15) is arranged before the silica separator (16) with a feed opening for the addition of agglomerating agent.