Patent ID: 8641865

Claim:
A method to cook thin chips in a continuous digester vessel comprising: introducing a flow of thin chips in which at least 85% of the chips have a thickness of no greater than 6 mm and no thinner than 2 mm; adding white liquor to the chip bin or to a chip transport passage extending from the chip bin to an upper inlet of the continuous digester vessel; injecting steam or other heated fluid to an upper region of the digester vessel to elevate a cooking temperature of the chips in the vessel to at least 130 degrees Celsius; cooking the chips in the vessel as the chips flow downward through the vessel without substantial extraction or introduction of liquor in the cooking section of the vessel; injecting wash liquid at or adjacent a discharge outlet at the bottom of the vessel; extracting from the chips at least a portion of the wash liquid and a portion of black liquor from the vessel through a wash liquid extraction screen in or surrounding the vessel, wherein the wash liquid extraction screen is above the injection of the wash liquid, and discharging the cooked thin chips as pulp from the discharge outlet, wherein the pulp discharged from the vessel has a Kappa number of at least 50 for pulp formed from softwood thin chips and at least 25 for pulp formed form hardwood thin chips, wherein the introduction of the flow of thin chips, the cooking of the chips and the discharge of the cooked thin chips are performed simultaneously in the continuous digester vessel.