Patent ID: 7686919
Filing Date: 2010-03-30
Classification: D21C

Abstract:
1. A method for the continuous cooking of wood chips for the production of paper pulp in a digester system, comprising: providing at least one continuous digester, continuously feeding input chips to a top of the digester, forming a suspension of chips at a beginning of a cook, the suspension of chips having a volume of a starting cooking fluid constituted by one or more fluids from condensate, fresh cooking fluid, chips moisture, washing filtrate and spent black liquor, the spent black liquor having been present during at least 75% of a retention time of the cook in the digester, the volume of the starting cooking fluid establishing a fluid/wood ratio that is greater than 3.5, a final cooking fluid, being a partial volume of the starting cooking fluid being present in the cook during a major part of the retention time of the cook, withdrawing the final cooking fluid only during a final 15 minutes of the retention time of the cook, the final cooking fluid ensuring a fluid/wood ratio that is greater than 3.5, the final cooking fluid withdrawn during the last 15 minutes of the retention time of the cook consisting of spent black liquor which maintains a residual alkali concentration of less than 15 g/l, a volume of final cooking fluid being less than the volume of the starting cooking fluid, affecting the volume of the starting cooking fluid to regulate an H factor for hemicellulose, that is present in the cooking fluid and that has been dissolved from the input chips while maintaining a pulp consistency of the cooked pulp, increasing the volume of starting cooking fluid to reduce the H factor for the hemicellulose that is present in the cooking fluid and that has been dissolved from the input chips, decreasing the volume of the starting cooking fluid to increase the H factor for the hemicellulose that is present in the cooking fluid and that has been dissolved from the input chips, affecting the volume of the starting cooking fluid principally through changing a volume of either the washing filtrate or the spent black liquor, and continuously feeding out cooked pulp from a bottom of the digester at the pulp consistency.