Abstract: A pulp-digester screen cleaner having a pneumatic actuator with a cylinder and a rod coaxially disposed within the cylinder. An actuator mounting plate is used to mount the actuator outside of a pulp-digester screen housing pipe. A rod seal has a body disposed on the pipe that prevents any loss of fluid or pressure, yet allows the rod to pass into the pipe. The cylinder contains all of the mechanics of the pneumatic actuator and can be easily serviced without draining the digester. The rod is disposed through a first aperture of each of a pair of scrapers. A treated edge of each of the pair of scrapers varies to match different digester screen types and patterns. The present pulp-digester screen cleaner eliminates the need for chemical cleaning or other mechanical cleaning solutions. It will also improve pulp quality, increase pulp production, and promote overall digester efficiency.

Abstract: A discharge assembly including: a chamber having an sidewall extending around a perimeter of the chamber, an open upper region, an flange coupling at an upper region of the sidewall and extending around the upper region and a bottom, wherein the chamber receives a rotating impeller; a plurality of discharge openings in at least one of the sidewall and bottom of the chamber; a plurality of valves each coupled to one of the discharge openings, and a plurality of nozzles each coupled to one of the discharge openings and downstream in the opening to the valve for the opening.

Abstract: The invention relates to an improved design of the bottom of a continuous digester reducing the torque load on conventional bottom scrapers with scraper arms arranged at an angle ? in relation to the horizontal plane in the range between 5°-30°. A simple digester shell extension VE is installed below the lowermost wash screen WS, ending at a small distance D above the end of the outer end of the scraper arm. The shell extension prevents the descending pulp column from expanding below the wash screen and enables easier shaving action from the scraper, using a dilution and expansion volume established at the outer ends of the scraper arms.

Abstract: Systems and processes may be used for continuously processing a solid material at a non-atmospheric pressure. In some examples, the material is delivered to a process vessel at substantially the same non-atmospheric pressure condition as the process vessel so as to avoid shearing the material. In some examples, the solid material is continuously fed into a process vessel, continuously processed in the process vessel, and continuously discharged from the process vessel.

Abstract: A prehydrolysis of wood chips or other lignocellulosic material in a vessel having a gaseous portion and a liquid portion. The vessel includes at least one stress relieving piece that inhibits overcompression of the lignocellulosic material. The vessel operates in a continuous process. A slurry of lignocellulosic material and liquid is removed from the bottom of the vessel.

Abstract: The feed system is for a continuous digester where at least two pumps are arranged in parallel at the bottom of a pre-treatment vessel and a stirrer is provided in direct connection to inlets to pumps. The system makes it possible to provide a feed system with an improved accessibility and operational reliability, and to operate the main part of the pumps at optimal efficiency even if the production capacity is reduced.

Abstract: The method and arrangement are for adding treatment liquid to comminuted cellulose material, preferably wood chips, during the manufacture of chemical pulp in a continuous process. The process is using a down-flow vessel wherein chips are descending down the vessel in a plug flow and wherein treated chips are continuously fed out at the bottom of the vessel. By arranging at least one telescopic pipe inside the vessel that extends down into the plug flow makes it possible to adjust the position for the addition of treatment liquid depending on current operational parameters.

Abstract: The method and arrangement is for adding treatment liquor to comminuted cellulose material, preferably wood chips, during the manufacture of chemical pulp in a continuous process. The process uses a down-flow vessel where chips are descending down the vessel in a plug-flow and where treated chips are continuously fed out at the bottom of the vessel. By arranging more than two parallel pipes offset from the center of the vessel a better distribution of treatment liquor is obtained. Any disturbance of the chip plug flow descending down the vessel is reduced to a minimum.

Abstract: An apparatus to pulp thin wood chips including: a chip screen receiving chips of comminuted cellulosic material, the screen assembly including a screening assembly which outputs thin chips; a chip bin and conveyor assembly receiving the thin chips output from the chip screen, the lower portion of the chip bin is flooded with white liquor; a continuous digester vessel having an chip inlet at an upper region of the vessel coupled to the chip bin and conveyor assembly, a cooking zone extending vertically from the upper region of the vessel to a wash zone which extends from the cooking zone to a bottom region of the vessel, and a pulp discharge outlet in the bottom region; a steam inlet at the upper region of the inlet, an upper region of the digester vessel at an elevated cooking temperature, and a screen assembly near the wash liquid inlet for the wash zone.

Abstract: A method to pulp cellulosic fibrous material including: alkaline cooking cellulosic fibrous material in a continuous digester vessel to produce a pulp having a kappa number in a range of 50 to 120; washing the pulp discharged from the digester vessel; treating the washed pulp in the presence of oxygen and alkali to remove lignin; washing the oxygen-treated pulp such that the kappa number is recued by at least at least 30; separating lignin from wash filtrate generated by the washing of the oxygen-treated pulp, and using the separated wash filtrate as a washing liquid in the washing of the pulp from the digester vessel.

Abstract: The method and arrangement are for adding treatment liquid to comminuted cellulose material, preferably wood chips, during the manufacture of chemical pulp in a continuous process. The process is using a down-flow vessel wherein chips are descending down the vessel in a plug flow and wherein treated chips are continuously fed out at the bottom of the vessel. By arranging at least one telescopic pipe inside the vessel that extends down into the plug flow makes it possible to adjust the position for the addition of treatment liquid depending on current operational parameters.

Abstract: The method, system and a withdrawal screen section are for the impregnation of chips during the manufacture of chemical pulp. Chips are both steamed and impregnated in a low pressure impregnation vessel, using pressurized hot spent cooking liquor BL as the main part of the impregnation liquid. The hot spent cooking liquor produces most of the steam BLST necessary for steaming the chips. At least two independent first and second screen rows, SC1 and SC1b respectively, are installed in order to improve the process in the impregnation vessel. The first screen row withdraws acidified treatment liquor for disposal which otherwise would be a parasitic acidified waste fluid in the system. The second screen row recirculates treatment fluid back to center of treatment vessel in order to even out the pH profile over the cross section of the vessel.

Abstract: The continuous digester is for producing pulp from comminuted cellulosic material. The digester has a cone diverter on a bottom scraper arranged in the bottom of the digester for assisting in out feed of pulp produced. The cone diverter of the bottom scraper has an upper inclined surface of the cone diverter with an inclination angle in the range 30±10 degrees in relation to the vertical. In order to improve washing performance in the bottom of the digester, especially for overloaded digesters, the upper inclined surface is equipped with draining apertures in fluid communication with a liquid receiving chamber inside the cone diverter. The liquid receiving chamber is connected via a drainage channel to the exterior of the vessel.

Abstract: The continuous digester is for producing pulp from comminuted cellulosic material. The digester has a cone diverter on a bottom scraper arranged in the bottom of the digester for assisting in out feed of pulp produced. The cone diverter of the bottom scraper has an upper inclined surface of the cone diverter with an inclination angle in the range 30±10 degrees in relation to the vertical. In order to improve washing performance in the bottom of the digester, especially for overloaded digesters, the upper inclined surface is equipped with draining apertures in fluid communication with a liquid receiving chamber inside the cone diverter. The liquid receiving chamber is connected via a drainage channel to the exterior of the vessel.

Abstract: The method, system and a withdrawal screen section are for the impregnation of chips during the manufacture of chemical pulp. Chips are both steamed and impregnated in a low pressure impregnation vessel, using pressurized hot spent cooking liquor BL as the main part of the impregnation liquid. The hot spent cooking liquor produces most of the steam BLST necessary for steaming the chips. At least two independent first and second screen rows, SC1 and SC1b respectively, are installed in order to improve the process in the impregnation vessel. The first screen row withdraws acidified treatment liquor for disposal which otherwise would be a parasitic acidified waste fluid in the system. The second screen row recirculates treatment fluid back to center of treatment vessel in order to even out the pH profile over the cross section of the vessel.

Abstract: A method including: pretreating biomass feed stock in a first pressurized reactor, wherein the feed stock undergoes hydrolysis in the first pressurized reactor; discharging the feed stock from the first pressurized reactor to a pressurized sealing device having a first pressurized coupling to a feedstock discharge port of the first pressurized reactor; maintaining a vapor phase in the first pressurized reactor by injecting steam; washing the feed stock; draining dissolved hemi-cellulosic material extracted from the feed stock; discharging the feed stock from the pressurized sealing device through a second pressurized coupling to a second pressurized reactor; in the second pressurized reactor, infusing cells of the feed stock with steam or water vapor, and rapidly releasing the pressure applied to the feed stock to cause steam expansion in the cells of the feed stock and refine the feed stock.

Abstract: A method and system for pulp manufacturing used in connection with a kraft process includes a vertical pressure vessel operated in batch mode, a single-vessel or multi-vessel continuous digester, and other equipment for further processing brown stock, such as for washing, oxygen delignification, bleaching, and drying. A feeder and conveyance system may include a high pressure feeder or direct pump system, and selectively provides fiber-containing material to the continuous digester when making lower grade pulp product and to the vertical pressure vessel when making higher grade pulp such as dissolving pulp. The vertical pressure vessel is used for pre-hydrolysis and neutralization, after which the resulting pulp is fed to the continuous digester for cooking. White liquor and black liquor from the same mill may be used for the neutralization fluids. The same continuous digester is selectively used for cooking in connection with making pulp products of different grades or quality.

Abstract: The high pressure sluice feeder has a conical rotor mounted in a housing having a complementary conical interior. The rotor has a plurality of trough-going pockets arranged offset to each other in the rotor. The housing has ports distributed evenly around a circumference of the housing and exposed to the pockets during rotation of the rotor. A conical exterior surface of the rotor or the conical interior surface of the housing is equipped with a flush-out groove. The groove catches any abrasive particles caught between the complementary conical surfaces of the rotor and housing. The abrasive particles are flushed out towards the trough-going pockets of the rotor when one end of the groove is pressurized by either one neighboring trough-going pocket or a sealing liquid supply to a gable end of the rotor/housing.

Abstract: Digested softened non-defibrated chips are fed out from a bottom of a digester. The chips are fed out under an influence of a bottom scraper at the bottom of the digester and through an outlet tap at the bottom of the digester and onwards to an outlet line connected to the outlet tap. This takes place before the softened chips pass through a blow-valve arranged in the outlet line, across which blow-valve a pressure drop of at least 0.5 bar and at most 3-5 bar has been established. The chips are exposed to a displacement wash after the chips have passed the outlet tap. The displacement wash has been established in the flow of chips through the outlet line before the chips are defibrated by the pressure drop across the blow-valve.

Abstract: The method and an arrangement are for the improvement of a wash after completed digestion in a continuous digester for the production of cellulose pulp. The softened chips are exposed to a radially directed displacement wash after they have passed the rotating bottom scraper. The displacement wash has been established in the flow of digested softened chips through the outlet tap before the softened chips are defibrated by the fall in pressure across the blow-valve that is arranged after the digester.

Abstract: Systems are provided for continuously producing chemical cellulose pulp from a slurry of comminuted hardwood material by subjecting the slurry of comminuted hardwood material to a first cooking stage under conditions sufficient to reduce syringyl lignin (s-lignin) content in the hardwood material as compared to guaiacyl lignin (g-lignin) content therein, and thereafter subjecting the slurry of comminuted hardwood material to a second cooking stage under conditions sufficient to reduce the g-lignin content remaining therein after the first cooking stage.

Abstract: The system and method is for the pumping of finely divided cellulose material to a continuous digester. The system has a concentric arrangement of pipes. A fluid (Liq) is added to a chamber formed between the pipes to establish a cylindrical film of fluid around a rod-shaped flow of cellulose material before the inlet to the pump. It is possible in this way to reduce the pressure drop in the lines, reduce wear in the pump, and ensure a maximal pressure build up in the pump.

Abstract: The method and an arrangement are for the improvement of a wash after completed digestion in a continuous digester for the production of cellulose pulp. The softened chips are exposed to a radially directed displacement wash after they have passed the rotating bottom scraper. The displacement wash has been established in the flow of digested softened chips through the outlet tap before the softened chips are defibrated by the fall in pressure across the blow-valve that is arranged after the digester.

Abstract: A prehydrolysis of wood chips or other lignocellulosic material in a vessel having a gaseous portion and a liquid portion. The vessel includes at least one stress relieving piece that inhibits overcompression of the lignocellulosic material. The vessel operates in a continuous process. A slurry of lignocellulosic material and liquid is removed from the bottom of the vessel.

Abstract: The method and arrangement is for adding treatment liquor to comminuted cellulose material, preferably wood chips, during the manufacture of chemical pulp in a continuous process. The process uses a down-flow vessel where chips are descending down the vessel in a plug-flow and where treated chips are continuously fed out at the bottom of the vessel. By arranging more than two parallel pipes offset from the center of the vessel a better distribution of treatment liquor is obtained. Any disturbance of the chip plug flow descending down the vessel is reduced to a minimum.

Abstract: The system and method reduce the liquid/wood ratio at the top of a vapor phase digester in a continuous digester plant. Chips that are to be cooked in the vapor phase digester are fed as a mixture of chips and liquid at a liquid/wood ratio that exceeds 8:1 in a transfer line to an inverted top separator arranged at the top of the vapor phase digester. The top separator feeds the chips upwardly. More than 50% of the liquid content of the mixture of chips and liquid is withdrawn in the top separator and the remaining liquid is fed out from the top separator to the top of the vapor phase digester. A pile of chips and a liquid volume are established at the top, wherein the pile of chips is disposed above the liquid surface of the liquid volume.

Abstract: The arrangement and method for the steam pre-treatment of chips during the production of cellulose pulp avoids the blow-through of gases in the steam pre-treatment vessel. This prevents foul-smelling gases from being released into the atmosphere. The inlet of the vessel has an inclined feeder device in a feeder-housing. In the event of the initiation of the risk for blow-through of steam, the feeder housing is sprayed with cooling liquid in order to increase condensation capacity of the chips being fed into the vessel. Ultimately the feeder housing is filled with liquid that establishes a liquid lock, and preferably at the same time as the feeder drive (M) is shut off. This avoids the emission of gases from the chip bin when interruptions in the process occur so that the release of odors into the surroundings is minimized.

Abstract: The invention proposes an installation (10) in which the impregnation and fractionation of the raw material (MP) are conducted at atmospheric pressure, characterized in that it comprises means (18, 20) for transferring the raw material (MP) successively to a first treatment station (PT1) and a second treatment station (PT2), each comprising means (G1, G2) for temporarily combining, at the first station (PT1), the raw material (MP) with a quantity of a first mixture of organic acids and, at the second station (PT2), for temporarily combining the raw material (MP) with a quantity of a second mixture; and means, after impregnation, for at least partially recovering the quantity of second mixture after impregnation and for recycling at least a portion of the second recovered mixture to form at least partially said first impregnation mixture used at the first station (PT1).

Abstract: The digester screen is for a continuous digester in which cooked cellulose pulp is produced. The digester screen has a number of screen bars arranged vertically in the continuous digester that have withdrawal slots (S) between the fixed screen bars through which withdrawal slots cooking fluid can be withdrawn from the column of pulp (P) of the digester. By having every second screen bar fixedly arranged and recessed a distance (D) relative to the neighboring screen bar an increased withdrawal capacity for the screen is obtained.

Abstract: The feed system is for a continuous digester where at least two pumps are arranged in parallel at the bottom of a pre-treatment vessel. The outlets of the pumps are combined at a merging point before a common transfer line extends to the top of the digester. The system makes it possible to provide a feed system with an improved accessibility and operational reliability, and to operate the main part of the pumps at optimal efficiency even if the production capacity is reduced.

Abstract: A system and method for digesting cellulosic material to extract fermentable sugars, lignin, and pulp is disclosed. One embodiment comprises a continuous digester comprising a cellulosic material feed section including a pre-steam and impregnation zone, a sugar extraction zone, a lignin extraction zone and a cooking zone, the continuous digester to impregnate the cellulosic material with a mild acid solution and continuously digest the cellulosic material to extract fermentable sugars, lignin, and pulp.

Abstract: Improvements in a process for rapid acid hydrolysis of lignocellulosic material and in a hydrolysis reactor, said lignocellulosic material being fed in different levels of a reactor and contacted with flows of lignin organic solvent, water and an extremely dilute solution of a strong inorganic acid, for obtaining a liquid phase of hydrolysis extract and a solid phase of non-reacted and non-dissolved material. A controlled steam flow is injected into the different levels of the reactor, so as to provide adequate temperatures of organic solvent and strong inorganic acid and forming the desired products (sugars). A flow of the liquid phase is recirculated in different levels of the reactor, the remainder thereof being withdrawn from the reactor, abruptly cooled with the solvent submitted to evaporation to obtain a concentrate. The lignin is transferred by decantation and the concentrate is transferred to subsequent process steps.

Abstract: In a continuous digester system the digester system is greatly simplified by using a single vertical atmospheric vessel, replacing the conventional chip bin, steaming vessel, chip chute, high pressure pumping or sluice feeders, impregnation vessels and top separator. Chips are simply fed to the top of the atmospheric vessel, and a chip level is established in the vessel. Treatment liquids are added to the vessel such that a total liquid volume (Z1+Z2) with a liquid level (LIQ LEV) is established under the chip level (CH LEV). Impregnation stage and subsequent cooking stages are implemented in the atmospheric vessel at successively increasing temperature and depths into the total liquid volume, thus preventing boiling in the stages and preferably reducing steam blow trough of the chip surface in the top of the vessel.

Abstract: A pulping apparatus includes a hollow mixing cylinder selected to retain a volume of pulping fluid and cellulose fibres therein. The mixing cylinder is journaled for rotation about a central axis oriented at approximately +20° from horizontal. In a preferred construction, the mixing cylinder is divided internally into at least two discrete mixing chambers configured to facilitate outward flow of defibred pulp from an infeed end of the cylinder to and outwardly from the outlet end. The mixing chamber adjacent the inlet end is delineated by an end cover which closes the inlet end, and by a first divider positioned across the cylinder interior. The next adjacent mixing chamber is delineated longitudinally by the distal-most divider of the end mixing chamber, and by a second further downstream divider spaced longitudinally therefrom. The dividers include at least one through-opening therethrough.

Abstract: The feed system is for a continuous digester where at least two pumps are arranged in parallel at the bottom of a pre-treatment vessel. The transfer to the top of the digester takes place without a conventional top separator. The system makes it possible to provide a feed system with an improved accessibility and operational reliability, and to operate the main part of the pumps at optimal efficiency even if the production capacity is reduced.

Abstract: The invention relates to an apparatus for continuous digestion of wood chip comprising an upright generally cylindrical vessel having a top end and a bottom end. The top end of the cylindrical vessel is adapted to receive wood chips mixed with a cooking liquor to be treated therein. A first conduit is integrally attached at a first location positioned between the top and bottom ends of the vessel for selectively extracting a first quantity of cooking liquor from the vessel. The first location is positioned upstream of a second location within the vessel where the cooking liquor being at substantially full cooking temperature. A second conduit is integrally attached at a third location positioned downstream from the first and second locations of the vessel.

Abstract: The feed system is for a continuous digester where at least two pumps are arranged in parallel in the bottom of a pre-treatment vessel and a liquid level of at least 10 meters is established. The system makes it possible to provide a feed system with an improved accessibility and more reliable operation, and to operate the main part of the pumps at optimal efficiency even if the production capacity is reduced.

Abstract: The feed system is for a continuous digester where at least two pumps are arranged in parallel at the bottom of a pre-treatment vessel. Each pump has its own independent transfer line extending to the top of the digester. The system makes it possible to provide a feed system with an improved accessibility and operational reliability, and to operate the main part of the pumps at optimal efficiency even if the production capacity is reduced.

Abstract: The feed system is for a continuous digester where at least two pumps are arranged in parallel at the bottom of a pre-treatment vessel and a stirrer is provided in direct connection to inlets to pumps. The system makes it possible to provide a feed system with an improved accessibility and operational reliability, and to operate the main part of the pumps at optimal efficiency even if the production capacity is reduced.

Abstract: The continuous digester system has an inlet defined therein for the feed of a chips suspension and an outlet for the output of a cooked suspension of pulp. The suspension of chips is fed in to the inlet through a line at the beginning of the cook, where the chips suspension has a volume of starting cooking fluid that establishes a fluid/wood ratio that is greater than 3.5. A final cooking fluid is present during the cook for the major part of the cock and is withdrawn through a withdrawal strainer only during the final 15 minutes of the cook. The final cooking fluid ensures a fluid/wood ratio that is greater than 3.5 in association with the withdrawal. The withdrawn final cooking fluid during the final 15 minutes of the cook consists of spent black liquor that maintains a residual alkali level that lies under 15 g/l.

Abstract: In a continuous digester system the digester system is greatly simplified by using a single vertical atmospheric vessel, replacing the conventional chip bin, steaming vessel, chip chute, high pressure pumping or sluice feeders, impregnation vessels and top separator. Chips are simply fed to the top of the atmospheric vessel, and a chip level is established in the vessel. Treatment liquids are added to the vessel such that a total liquid volume (Z1+Z2) with a liquid level (LIQ LEV) is established under the chip level (CH LEV). Impregnation stage and subsequent cooking stages are implemented in the atmospheric vessel at successively increasing temperature and depths into the total liquid volume, thus preventing boiling in the stages and preferably reducing steam blow trough of the chip surface in the top of the vessel.

Abstract: A continuous biomass pretreatment system and method is provided. The system comprises a pipe reactor having an input end, an output end, an interior and an exterior. The pipe reactor does not have a mixing component that passes from the interior to the exterior and rotates with respect to the pipe. The system further comprises a pump in communication with the input end of the pipe reactor, a valve in communication with the output end of the pipe reactor, and a flash vessel having an input opening in communication with the output of the valve.

Abstract: The system and method reduce the liquid/wood ratio at the top of a vapor phase digester in a continuous digester plant. Chips that are to be cooked in the vapor phase digester are fed as a mixture of chips and liquid at a liquid/wood ratio that exceeds 8:1 in a transfer line to an inverted top separator arranged at the top of the vapor phase digester. The top separator feeds the chips upwardly. More than 50% of the liquid content of the mixture of chips and liquid is withdrawn in the top separator and the remaining liquid is fed out from the top separator to the top of the vapor phase digester. A pile of chips and a liquid volume are established at the top, wherein the pile of chips is disposed above the liquid surface of the liquid volume.

Abstract: The continuous digester system has an inlet defined therein for the feed of a chips suspension and an outlet for the output of a cooked suspension of pulp. The suspension of chips is fed in to the inlet through a line at the beginning of the cook, where the chips suspension has a volume of starting cooking fluid that establishes a fluid/wood ratio that is greater than 3.5. A final cooking fluid is present during the cook for the major part of the cook and is withdrawn through a withdrawal strainer only during the final 15 minutes of the cook. The final cooking fluid ensures a fluid/wood ratio that is greater than 3.5 in association with the withdrawal. The withdrawn final cooking fluid during the final 15 minutes of the cook consists of spent black liquor that maintains a residual alkali level that lies under 15 g/l.

Abstract: The digester screen is for a continuous digester in which cooked cellulose pulp is produced. The digester screen has a number of screen bars arranged vertically in the continuous digester that have withdrawal slots (S) between the fixed screen bars through which withdrawal slots cooking fluid can be withdrawn from the column of pulp (P) of the digester. By having every second screen bar fixedly arranged and recessed a distance (D) relative to the neighboring screen bar an increased withdrawal capacity for the screen is obtained.

Abstract: A method for generating steam in a digester plant of a chemical pulp mill including: producing black liquor in the digester plant, extracting a first stream of black liquor from the digester; generating vapor by evaporating the first stream of black liquor by heating the first stream with fresh steam; heating fibrous material in the digester with the generated vapor from the evaporated first stream of black liquor; extracting a second stream of black liquor from the digester; flashing the second stream of black liquor to generate flashed black liquor and flashed black liquor vapor; introducing the flashed black liquor vapor to at least one heat exchanger to indirectly heat a clean evaporable liquid to produce clean steam from the clean evaporable liquid; and steaming, with the clean steam produced in the at least one heat ex-changer, cellulosic feed material before feeding the cellulosic feed material to the digester plant.

Abstract: A pulp digester includes a vessel having an inlet, an outlet and a wall extending between the inlet and the outlet, the wall of the vessel having a curved interior surface. The digester includes a screen assembly positioned inside the vessel adjacent to the curved interior surface of the wall for removing liquid from pulp material. The screen assembly is movable relative to the curved interior surface of the vessel wall. The digester includes at least one support element permanently attached to the vessel wall for limiting movement of the screen assembly relative to the curved interior surface of the vessel wall. In certain embodiments, the at least one support, such as a ledge permanently attached to the vessel wall, supports a portion of the screen assembly. The screen assembly may have an inner face that is concave in a horizontal direction and convex in a vertical direction.

Abstract: The method and arrangement is for the feed of a chips suspension from one vessel to a subsequent digester in a continuous cooking process for the production of chemical cellulose pulp. The vessel has an inlet defined therein for the input of chips and an outlet defined therein for the output of a chips suspension. The chips suspension in the vessel has a first fluid/wood ratio established above a second fluid/wood ratio that is established at the bottom of the vessel. The second fluid/wood ratio is at least as great as, preferably greater than, the first fluid/wood ratio. After the output of the chips suspension from the vessel and before the chips suspension is placed under pressure for onwards transport to a subsequent digester, a fraction of fluid is withdrawn from the chips suspension, whereby a third fluid/wood ratio is established in the chips suspension.

Abstract: The continuous digester system has an inlet defined therein for the feed of a chips suspension and an outlet for the output of a cooked suspension of pulp. The suspension or chips is fed in to the inlet through a line at the beginning of the cook, where the chips suspension has a volume of starting cooking fluid that establishes a fluid/wood ratio that is greater than 3.5. A final cooking fluid is present during the cook for the major part of the cook and is withdrawn through a withdrawal strainer only during the final 15 minutes of the cook. The final cooking fluid ensures a fluid/wood ratio that is greater than 3.5 in association with the withdrawal. The withdrawn final cooking fluid during the final 15 minutes of the cook consists of spent black liquor that maintains a residual alkali level that lies under 15 g/l.

Abstract: In a continuous digester system the digester system is greatly simplified by using a single vertical atmospheric vessel, replacing the conventional chip bin, steaming vessel, chip chute, high pressure pumping or sluice feeders, impregnation vessels and top separator. Chips are simply fed to the top of the atmospheric vessel, and a chip level is established in the vessel. Treatment liquids are added to the vessel such that a total liquid volume (Z1+Z2) with a liquid level (LIQ LEV) is established under the chip level (CH LEV). Impregnation stage and subsequent cooking stages are implemented in the atmospheric vessel at successively increasing temperature and depths into the total liquid volume, thus preventing boiling in the stages and preferably reducing steam blow trough of the chip surface in the top of the vessel.