Abstract: The present synergies for at least two parallel cooking plants, e.g., one producing dissolving pulp in a prehydrolysis kraft process, and the other producing kraft pulp by kraft pulping process, which may facilitate increased cooking yield in the kraft cooking plant producing kraft pulp by recovering the hemicelluloses solubilized in the acidic hydrolysate of the prehydrolysis kraft process. In some implementations, there may be no cold caustic extraction step on the dissolving pulp line as the target pulp purity can be achieved by performing just a prehydrolysis step, with reutilization of an acidic hydrolysate stream in a kraft pulp line.

Abstract: In general, the present disclosure is directed to compositions and processes to increase pulp yield, reduce extractives, and reduce scaling in a chemical pulping process. In one particular embodiment, for instance, the present disclosure is directed to a composition comprising a surface active agent, an alkaline mixture, at least one polymer, the polymer having a linear backbone segment having two ends, at least one phosphorus component, the phosphorus component chemically linked along the linear backbone segment of the polymer, and at least one end component, the end component chemically linked to one or both ends of the linear backbone segment of the polymer.

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 A final cooking fluid is present during the cook for the major part of the cock and is withdrawn through a withdrawal strainer only during the final 15 minutes of the cook.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 The withdrawn final cooking fluid during the final 15 minutes of the cook consists of spent black liquor that maintains a residual alkali level that lies under 15 g/l.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: 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: A method for the continuous cooking of chemical pulp with the aim of achieving improved heat economy in a digester system having a vessel (1) for impregnation and a vessel (2) for cooking the impregnated cellulose chips. A part of the black liquor (14) withdrawn from the digester (2) is added at the beginning of a transfer system (4) to increase the temperature of the chips mixture in the transfer system (4). A fraction of the transport fluid (10) from the transfer system (4) that is continuously withdrawn from the impregnated chips fed into the top of the digester is returned to the impregnation vessel (1) at essentially the maintained transfer temperature.

Abstract: A lignocellulose material is cooked by means of an alkaline cooking liquor containing polysulfides in the presence of a quinone-hydroquinone compound, of which the oxidation-reduction potential in the form present during the cooking, which potential is a value calculated as a standard oxidation-reduction potential (Ea) with a hydrogen ion activity of 1, is within a range of from 0.12 to 0.25V to the standard hydrogen electrode potential. It is thereby possible to cook the lignocellulose material with a low Kappa number and in good yield and at the same time, to reduce the amount of the chemical solution used and to reduce the load on a recovery boiler.

Abstract: The process is for continuously cooking chemical pulp in a digester system consisting of at least one vessel for impregnating and cooking comprising an inlet into which a mixture of chips and process liquid is fed. The chips are impregnated at a predetermined impregnation temperature, Timp, and cooked at a predetermined cooking temperature, Tcook, after which dissolved pulp is fed out at the outlet of the digester system. The process liquid which is continually extracted is retained outside the digester system during a dwell time, t, of at least 30 min, without any heating above 140°, and thereafter returned to the digester system to a position which is substantially at the same level as the extraction, or downstream thereof, and thereby constitute part of the process liquid in the subsequent treatment zone. The process results in improved tear strength, beatability, bleachability and reduced color reversion, and increased yield across the digester.

Abstract: A continuous, alkaline process for the production of pulp from wood chips, wherein the preheated chips are subjected to an extended impregnation step for at least 60 min, preferably longer, at a temperature not exceeding the impregnation liquor boiling point at atmospheric conditions, and a rapid heating and cooking period of less than 65 min, preferably shorter, followed by cooling to below reaction temperature. Fresh alkali is added both during impregnation and the heating/cooking period.

Abstract: An apparatus and process for solvent pulping of cellulose-containing biomass utilizes at least one steaming vessel, a plug screw feeder or compression screw device, at least one super-atmospheric impregnation vessel, a solvent delignification reactor capable of operating at a pressure of 350 psig or more, and a solvent containing line for introducing solvent-containing liquor at the plug screw feeder outlet or compression screw device outlet. The process and system can also include at least one series connected pressure diffuser and optionally a retention tube downstream of each pressure diffuser to provide sufficient retention time to substantially preclude re-deposition of lignin on the cellulose fibers of the biomass, a blow tank connected to the last of the pressure diffusers and retention tubes, and vessels for multistage alcohol washing.

Abstract: A system and method for improved filtrate addition in a continuous digester is disclosed. The system comprises a blow dilution header/nozzle assembly located in the blow dilution zone of the digester. The header/nozzle assembly comprises (i) a plurality of nozzles for introducing and distributing filtrate into the blow dilution zone, and (ii) a plurality of measurement and control devices for monitoring and controlling filtrate flow through the plurality of nozzles. The method comprises (a) introducing and distributing filtrate through a plurality of nozzles of a blow dilution header/nozzle assembly in the blow dilution zone of the continuous digester; and (b) measuring and controlling the filtrate flow through each nozzle of the plurality of nozzles.

Abstract: A set of spaced apart screen assemblies are provided within a continuous kraft digester. Liquor is extracted from a first screen assembly of the set without recirculation of at least a portion of the extracted liquor into the digester above the first screen. In such a manner, the need for circulation flow below the first screen assembly of the set to the second screen assembly of the set is minimized, thereby also minimizing (if not eliminating entirely) the packing problems such flow may cause. The liquor extracted from the first screen assembly in the set could be reintroduced, however, into the digester at some other location in the cooking system (e.g., at a location just above the bottom screen). By employing the present invention, the distance between the first and second screen assemblies is greater than one digester diameter (D).

Abstract: In the feeding of a slurry of comminuted cellulosic fibrous material to a digester (continuous or batch) in the production of chemical pulp, one of the tanks used in the feed system (which preferably includes a high pressure feeder) may be eliminated without consequent loss of its function by providing a single tank with the combined functions of controlling the level of liquid in a slurrying conduit which supplies slurry to a slurry pump, and storing and substantially continuously supplying liquid to a make-up liquid pump connected to the digester. The single tank preferably surrounds the slurrying conduit and is substantially concentric, and in liquid communication, with it. A gap of 3-48 inches may be provided between the bottom of the conduit and a connection to the slurry pump. A screen or strainer may be provided in the gap, which is substantially surrounded by the tank.

Abstract: The strength properties of chemical cellulose pulp (particularly kraft pulp) are improved by substituting a cold impregnation soak for conventional impregnation procedures. After steaming, wood chips are soaked in an alkaline liquid at a temperature of about 80-110° C. (preferably 80-100° C., or 90-105° C.) for between one-half-72 hours (typically about 2-4 hours) at a pressure of about 0-15 bar (preferably about 1-5 bar), to dissolve at least about 8% of the wood (preferably about 10-20%) and at least about 15% of the lignin. The alkaline liquid used preferably contains sulfide (e.g. black liquor, green liquor, white liquor, or mixtures thereof), but almost any alkaline liquid having an alkali concentration of about 1.0 mole of NaOH/liter or less (typically about 0.75 m/l or less) is suitable. The wood chips are then raised to a cooking temperature of about 145-180° C. and cooked to produce the cellulose chemical pulp.

Abstract: The production of chemical (e.g., kraft) cellulose pulp much more suited to totally chlorine free or elemental chlorine free bleaching is produced by reducing the bleaching chemical consumability of the produced pulp. The effective alkalinity of the pulp during at least the majority of the cooking stage is maintained at about 15 g/l or above (e.g., about 18-25 g/l), expressed as sodium hydroxide, so as to reduce the charged acid groups (including hexeneuronic acids) by at least 30% (e.g., at least about 50%) compared with pulp cooked at conventional alkalinity. Instead—or in addition to—the cellulosic material which produces the pulp may be heated to a temperature (at least about 100° C., preferably at least about 130° C.

Abstract: The method described herein will produce depolymerized lignins substantially free from sodium compounds. Black liquor supplied from a pulping process is utilized for providing a mixture of depolymerized lignins dispersed and dissolved in a solution containing sodium hydroxide. The mixture is then separated to form depolymerized lignins and a solution containing sodium hydroxide. Following separation, the depolymerized lignins are then extracted with water to produce an extractate containing sodium compounds. The extracted depolymerized lignins, containing sodium compounds, are then reacted with an acid to form sodium salts to form a slurry. The slurry containing sodium salts is, by means of a salt splitting method, separated from the extracted depolymerized lignins to produce substantially sodium free depolymerized lignins.

Abstract: A continuous pulp digester having an elongate horizontally aligned pressure vessel through which the wood chips and digesting fluid flow in a forward direction. In a first and second embodiments within the pressure vessel there is an inner container defining an elongate chamber or passageway having a square cross sectional configuration. In a third embodiment the digesting chamber is cylindrical. At locations along the digester, there are several pair of liquid flow inlets and liquid flow outlets which enable filtrate from a pulp washer and a digesting agent to be moved into and across the digesting chamber to flow out the flow outlets. These are recirculated in a net upstream flow pattern toward the outlet end of the digester, and discharged as black liquor at different locations in the digester.

Abstract: A method of cooking pulp in an alkaline batch process (using one or more batch digesters) improves pulp bleachability. The wood material is supplied to the digester; the cellulosic material is pre-treated in the digester with a first liquor, the first liquor is displaced by a second liquor, the displaced first liquor is led to a further treatment, the cellulose material is treated with the second liquor, and the cooked pulp is removed from the digester. The second liquor is displaced as two consecutive parts, i.e. as strong black liquor and weak black liquor, and after cooling in a heat exchanger the strong black liquor thus obtained is fed into the digester as the first liquor in a subsequent batch (in the same, or a different, batch digester).

Abstract: A screen used in the production of cellulose pulp may be mounted in a digester to minimize traditional screen problems (including clogging) without introducing new problems. The screen comprises a screen plate having a plurality of slots formed in it with an inclination angle, which is 30-60° with respect to the bottom edge of the screen plate. The screen plate may comprise a plurality of parallel screen bars side-by-side, or an integral metal plate with slots formed in it. The slots have a width between 1-5 (e.g. 2-4) millimeters and a spacing between them of 3-9 millimeters.

Abstract: A method for conditioning an ozone gas recycle stream in an ozone pulp bleaching process. The method includes the steps of providing an oxygen containing feed gas to an ozone generator; generating ozone from said feed gas to produce an ozone rich oxygen gas; bleaching pulp with said ozone rich gas, thereby producing an exhaust gas containing contaminants including carbon dioxide and entrained pulp fibers; removing at least some of said contaminants by at least removing entrained pulp fibers from the exhaust gas to produce a recycle gas; directing said recycle gas into the ozone generator to provide at least a portion of said oxygen containing feed gas; and removing carbon dioxide during said contaminant removal step in an amount sufficient to a level of about 6 wt. wt. % to thus allow operation of the ozone generator at or approaching full capacity.

Abstract: Yield, particularly when treating hardwood chips, can be improved by at least 1-2% in a kraft cellulose pulping process by keeping the temperature and effective alkali (EA) low during impregnation, and by keeping the EA low in at least a first cook stage. After cooking, the pulp is subjected to cooling low EA liquor, e.g. to reduce its temperature to below 120° C. (preferably below 100° C.) with an EA below about 5 g/L (expressed as NaOH). Continuous treatment in a continuous digester system is preferred, with the EA below about 20 g/L during impregnation and the first cook.

Abstract: This invention relates to a new and improved way of continuously cooking fiber material, wherein temperatures and alkaline levels are controlled to be maintained within specific levels in different zones of the digesting process in order to optimize chemical consumption and heat-economy, and, at the same time, achieving very good pulp properties.

Abstract: This invention relates to a new and improved way of continuously cooking fiber material in an over loaded digester, wherein temperatures and alkaline levels are controlled to be maintained within specific levels in different zones of the digesting process in order to optimize chemical consumption and heat economy and, at the same time, to achieve very good pulp properties.

Abstract: A method for cooking chips which are impregnated, in a vessel (3), with liquid in first and second concurrent impregnation zones (A, B), impregnation liquid being supplied, in a mixture with steamed chips, through a feeding system to the first impregnation zone, and liquid for recovery being extracted at a first point (41) at the end of the first impregnation zone, and further liquid being supplied to the second impregnation zone (B). According to the invention, liquid is extracted at a second point (43) at the start of the second impregnation zone (B) and is circulated in an impregnation circulation (44, 45) which empties out at the center of the vessel at a point between the first and second points (41, 43) for extraction of liquid so that a flow of liquid is established from the center of the vessel in a radial direction. The further liquid is supplied to the impregnation circulation for continued impregnation of the chips in the second impregnation zone.

Abstract: A screen used in the production of cellulose pulp mounted in a digester minimizes traditional screen problems (including clogging) without introducing new problems. The screen comprises a screen plate secured to an internal surface of the digester. The screen plate has a plurality of slots formed in it with an inclination angle, and the screen plate is positioned in the digester so that the inclination angle of the slots relative to the horizontal X axis of the X-Y plane defined by the internal surface of the digester is between 30-60.degree.. The screen plate may comprise a plurality of parallel screen bars side-by-side, or an integral metal plate with slots formed in it. The slots typically have a width between 1-5 millimeters and a spacing between them of 3-9 millimeters.

Abstract: In a vertical digester for producing chemical pulp, or other vessel for treating a slurry of comminuted fibrous cellulosic material, the cost of manufacturing the shell is significantly reduced by eliminating the external step increases in the digester shell. The digester shell has a substantially constant internal diameter from just below the inlet to just above the outlet, screen assemblies being provided by an internal transition (e.g. conical) having an angle of convergence of less than 40.degree. (e.g. about 10-25.degree.) above each screen assembly so that the slurry flows through the transition without bridging or hang-up, and a step increase, or other increase, in diameter back to the first diameter after the screen assembly.

Abstract: A method of treating wood chips allows chemical pulp (e. g. kraft pulp) to be produced having enhanced fiber strength properties. In a first zone or stage the chips are cool impregnated (e. g. a temperature of about 60-120.degree. C.) with a first alkali-containing liquid (25-35 g/l expressed as NaOH). In the top of a continuous digester in a second zone or stage the chips are then treated with a second alkali-containing liquid having an alkali concentration at least 5 g/l less than the first liquid (e. g. 10-20 g/l) and a temperature of between about 120-160.degree. C. (e. g. 130-150.degree. C.). An extraction typically takes place to effect the change in treatment zones. After the second zone the chips are cooked at about 140-180.degree. C. (e. g. 150-170.degree. C.), and higher than in the second zone.

Abstract: The present invention provides a method for continuously cooking kraft pulp in a digester having the steps of:feeding chips into an inlet of a digester;supplying black liquor to an impregnation zone of the digester in an amount such that the black liquor makes up greater than 40% by volume of the total volume of liquid present in the impregnation zone;extracting liquor from a screen girdle downstream of where the black liquor is added to the digester, in the direction the wood chips flow through the digester, in an amount greater than 50% by volume of the total volume of liquor present at the location of the screen girdle;maintaining a liquor:wood ratio in the impregnation zone of greater than 3:1; anddischarging cooked pulp from the digester.

Abstract: A method and device for cooking pulp by increasing the effective alkali concentration in the residual phase of the cooking process to substantially improve the residual delignification rate and thus improving the pulp properties such as the pulp strength and pulp yield at a given lignin content.

Abstract: This invention provides for the recovery of lignin and other by-products from the pulping of fibrous plant material. In accordance with this invention, solvents and filtrates are recovered and recycled for reuse. This results in significant solvent and energy savings. Filtrates from the bleaching and delignification of the pulp are recycled for reuse in pulping, separation, and recovery of lignin and other by-products which results in significant energy savings and mitigation if not the elimination of pollution typically associated with bleaching. This invention also relates to products derived from the process and apparatus for carrying out the process. Lignins of various molecular weights and by-products of the pulping process are also recovered. The lignins are precipitated in high yields and at a high rate from a black liquor produced by pulping wood at high temperature and pressures. As a by-product of this process a purified furfural product is recovered.

Abstract: Chemical (typically kraft) pulp having enhanced intrinsic fiber strength and bleachability compared to pulp produced using conventional or modified kraft cooking is produced by using high alkali and/or pH cooking. After being impregnated with a first cooking liquor (e.g. white liquor) having low effective alkali, the first liquor is extracted from the pulp, and it is impregnated with a second cooking liquor having an effective alkali concentration of at least 25 g/l and cooked at cooking temperature (e.g. 140.degree.-190.degree. C.) to produce a spent second cooking liquor having a residual effective alkali concentration of at least about 15 g/l, which is then extracted from the pulp. The spent second liquor may be used to preheat incoming white liquor, and then flashed and used as the first liquor. The pH of the first liquor is typically less than about 13.0, and the residual pH of the spent second liquor is about 13.0 or more.

Abstract: A method of recycling sodium-based salts used for digesting wood in a digester during the manufacture of pulp and paper. The method comprises collecting a black liquor from the digester, concentrating the black liquor, and adding a salt to the black liquor in an amount sufficient to reduce the viscosity thereof. Preferred salts are thiocyanate salts. The black liquor is then oxidized to produce a green liquor and a causticizer added to the green liquor to produce a white liquor containing the sodium-based salts to be recycled. The white liquor is then returned to the digester.

Abstract: The sulfide ion concentration and sulfidity of kraft cooking liquor during kraft cooking of cellulose pulp is selectively increased. After treatment in a first treatment zone in which impregnation or kraft cooking takes place using a kraft cooking liquor having a first sulfide ion concentration and sulfidity, black liquor is extracted from the material, liquid is withdrawn from the material and dilution liquid is added to the withdrawn liquid and the withdrawn liquid with dilution liquid is reintroduced. In a second treatment zone after the first zone a second kraft cooking liquor is introduced having a second sulfide ion concentration and sulfidity greater than the first sulfide ion concentration and sulfidity (typically by about 20-50%), including by manipulating controlling the flow rate of extraction and the flow rates of withdrawal of liquid and addition of dilution liquid.

Abstract: A method for the production of kraft pulps in a digester, by modifying the cooking chemical concentration, and lignin concentration profiles during the cook, has provided extended delignification and improved selectivity in a simpler way than has previously been possible. The cooking is performed at an elevated temperature in two stages. The first stage liquor is a mixture of 1) the spent liquor of the second stage and 2) a portion of the conventional charge of fresh cooking chemicals needed for the complete cook. The second stage liquor is made up by adding an aqueous diluent, for example, fresh water or washing filtrate to the remaining portion of the fresh cooking chemicals.

Abstract: Chemical pulp is produced from hardwood chips in a simplified manner utilizing a continuous digester. An inverted top separator is provided in the circulatory loop between the high pressure feeder and the top of the continuous digester for thermally isolating circulations on either side of the inverted top separator. Relatively cool liquor circulates between the inverted top separator and high pressure feeder, at a temperature such that it will not flash into steam in a high pressure feeder, while in the circulatory loop from the high pressure feeder to the digester the chips are in cooking liquor at cooking temperature. Since hardwood chips require less cooking than softwood chips, a single heating source for heating the liquor to cooking temperature is provided, external of the digester, and a conventional cooking circulation loop within the digester is not required.

Abstract: A conventional continuous digester is modified so as to provide a countercurrent cook throughout the entire height of the digester. Instead of connecting an upper mid-point extraction screen to a flash tank, that screen is closed off and extraction is provided at the top of the digester, utilizing an in-line drainer to remove some of the liquor and feed it to a flash tank. The liquor not removed recirculates through a pressure screen to an impregnation vessel, and then back to the digester. A cooling circulation is provided just below the top extraction. Valves are provided in the liquor discharged from the drainer and a conduit from the upper mid-point extraction which may be manipulated to return the digester to conventional operation, including the addition of white liquor to the bottom recirculation.

Abstract: An apparatus provide for the production of low kappa number (e.g. below 20) kraft paper pulp, and a low viscosity black liquor which is easily transported to a recovery or disposal stage. Comminuted cellulosic fibrous material is steamed, passed to a treatment vessel, land then introduced into the top of a continuous digester. Black liquor is withdrawn from the digester and heated about 20-40 degrees C above cooking temperature (e.g. about 170 degrees C), and then introduced into contact with the material in the treatment vessel. After the material is treated with the black liquor, it is withdrawn from the treatment vessel, and passed to the recovery or disposal stage. White liquor may be introduced into the treatment vessel after black liquor withdrawal, after passing in heat exchange relationship with liquid recirculated from an impregnation vessel to a high pressure feeder.

Abstract: A process for conditioning an ozone gas recycle stream in an ozone pulp bleaching process, wherein the level of carbon dioxide in the recycle stream is controlled to allow full capacity operation of the ozone generator. Carbon dioxide concentration is identified over the relevant operational ranges and maximum concentration is identified for full capacity/optimum efficiency operation. Specific methods are described for controlling carbon dioxide concentration including purging a portion of the recycle stream, counter-current scrubbing of the recycle stream with an alkaline solution and passing the recycle stream through an adsorbent material. Contaminants entering the system also may be reduced by directing the purged recycle stream, which is relatively oxygen rich, into the dewatering press where pulp consistency is increased. In this manner nitrogen surrounding the pulp is displaced by oxygen and thus, does not enter the bleaching/ozone system with the pulp.

Abstract: An apparatus and method for treating cellulosic wood chips in a digestion process for the liberation of pulp in a caustic hydroxide solution at high pressures and temperatures by delivering preconditioned wood chips to a first chamber and circulating a low temperature black liquor through the chamber to preheat the chips, while continuously feeding the chips through the chamber to a second chamber at high temperature and pressure, circulating high temperature black liquor to the chips in the second chamber to advance them to cooking temperature, feeding white liquor and the chips to a digester for the digestion process over a predetermined period of time, and removing digested pulp and delivering the pulp to a washer with the black liquor for washing being utilized for the first chamber, and heating the white liquor through a heat exchange process with the high temperature black liquor.

Abstract: In the continuous cooking of comminuted cellulosic fibrous material (e.g. wood chips) to produce paper pulp, the material passes upwardly in an impregnation vessel which is within and concentric with a continuous digester and open at the top to digester pressure. At the top of the impregnation vessel, a solids/liquid separator (a screw within a screen cylinder) is provided. Separated liquid is returned in a conduit adjacent the exterior of the impregnation vessel, and open at the top to digester pressure, and passes out the bottom of the digester. The impregnation vessel is welded to the bottom of the digester, and the bottom of the digester is generally hemi-spherical, and substantially devoid of packings.

Abstract: A method and apparatus provide for the production of low kappa number (e.g. below 20) kraft paper pulp, and a low viscosity black liquor which is easily transported to a recovery or disposal stage. Comminuted cellulosic fibrous material is steamed, passed to a treatment vessel, and then introduced into the top of a continuous digester. Black liquor is withdrawn from the digester and heated about 20-40 degrees C. above cooking temperature (e.g. about 170 degrees C.), and then introduced into contact with the material in the treatment vessel. After the material is treated with the black liquor, it is withdrawn from the treatment vessel, and passed to the recovery or disposal stage. White liquor may be introduced into the treatment vessel after black liquor withdrawal, after passing in heat exchange relationship with liquid recirculated from an impregnation vessel to a high pressure feeder.

Abstract: A process for the continuous digestion of cellulosic fiber material is described wherein the material is impregnated with liquid in a closed system comprising a concurrent flow zone and a countercurrent flow zone, the liquid in the concurrent flow zone including black liquor and possibly white liquor and the liquid in the countercurrent flow zone including white liquor. Liquid is withdrawn from the impregnation system at a point located between the concurrent flow zone and the countercurrent flow zone. Besides white liquor a predetermined amount of black liquor is added to the countercurrent flow zone in order to obtain a high liquid to wood ratio in the inlet of the digester.

Abstract: A process for the continuous digestion of cellulosic fiber material is described wherein the material is impregnated with liquid in a closed system comprising a concurrent flow zone and a countercurrent flow zone, the liquid in the concurrent flow zone including black liquor and possibly white liquor and the liquid in the countercurrent flow zone including white liquor. Liquid is withdrawn from the impregnation system at a point located between the concurrent flow zone and the countercurrent flow zone. Besides white liquor a predetermined amount of black liquor is added to the countercurrent flow zone in order to obtain a high liquid to wood ratio in the inlet of the digester.

Abstract: In a continuous digester for paper pulp (comminuted cellulosic material), abrupt variations in high pressure steam flow are minimized. First and second vertically spaced annular screens are provided in a vertical vessel. Each has an annular header associated with it and first and second circumferentially spaced liquid outlets associated with each header. The first outlet for the first screen is generally vertically in line with the first outlet for the second screen, and the second outlet of the first screen is generally vertically in line with the second outlet of the second screen. Simultaneous withdrawal of liquid from the first outlet of the first screen and the second outlet of the second screen takes place, and then is terminated, and then simultaneous withdrawal of liquid from the second outlet of the first screen and the first outlet of the second screen takes place, and then is terminated. This withdrawal sequence is repeated continously.

Abstract: A method and apparatus provide for the continuous digestion of comminuted cellulosic fibrous material (e.g. wood chips) to produce paper pulp, with increased sulfidity. When black liquor is withdrawn from the continuous digester, instead of merely passing it to a pair of flash tanks and then to recovery, the concentrated liquor from a first flash tank is fed to a vessel in which the comminuted material is slurried with a liquid. Since the black liquor remains in intimate contact with the chips for a significant period of time, the lignin in the chips is partly sulfonized. Ultimately the black liquor is replaced with white liquor or the like, and the separated out black liquor is circulated to recovery or disposal. A high pressure feeder and a solids/liquid separator are utilized.

Abstract: A method of removing dissolved and colloidal macro-molecular organic substances from effluents from processes used in the manufacture of pulp and paper, wherein an acid sludge containing cellulose fibres and being acidified to a pH value of 1.6-2.5, is added to an effluent containing said organic substances, and the pH value is adjusted to 4.5-6.0 before the mixture is subjected to sedimentation to achieve precipitation of the fibres with said organic substances adhered thereto. According to the invention the fibres used as precipitant are subjected to mechanical treatment prior to said acidification, so that the fibres are broken and split open, increasing their specific fibre surface and thereby their ability to catch the organic substances in the effluent.

Abstract: A process is provided for the activation and delignification of cellulose pulp, which comprises:(1) subjecting chemical cellulose pulp to activation by reaction with nitrogen dioxide in the presence of water at a temperature within the range from about 20.degree. to 120.degree. C., while(a) separating gas containing at least 1.2 mml nitrogen oxides, including NO, per liter of gas determined at 25.degree. C. and calculated as nitrogen, reacting nitrogen oxides in said withdrawn gas with oxygen gas in an amount within the range from about 10 to about 200 mole percent, calculated on the amount of NO present, and recycling the reacted gas to the activation; and(b) separating gas containing less than 0.4 mml nitrogen oxides, including NO, per liter of gas determined at 25.degree. C. and calculated as nitrogen from the cellulose pulp and removing said gas from the process; and(2) delignifying the activated cellulose pulp.

Abstract: A multi-stage wood chip cooking process performed in a single digester in a batch type operation. The wood chips to be cooked are introduced into the digester and soaked with a warm black liquor to remove most of the air from the digester and the chips. This warm black liquor is thereafter displaced from the digester with a mixture of a first stage hot black liquor and hot white liquor, the proportionate amount of hot white liquor being relatively high. The temperature of the digester contents is then raised to a cooking temperature for a predetermined amount of time. The original cooking liquor is then displaced with a mixture of a second hot black liquor and hot white liquor, the proportiionate amount of hot white liquor in this second cooking liquor being less than in the first. Again, the temperature of the digester is raised to a cooking temperature and the cooking is carried out for a shorter period of time than in the first cooking stage.

Abstract: A method of removing macromolecular organic dissolved and colloidal compounds from the effluents of a paper and cellulose mill by using waste sludge containing fibers and chemicals. The sludge is acidified to a pH of approx. 2 by a mineral acid prior to adding into the effluent. Organic material is precipitated with fibers in a sedimentation vessel at a pH of 4.5-6.

Abstract: A method of removing lignin from bleach plant effluents by using cellulose fibres. The method comprises an acidous phase during which sludge containing cellulose fibres is added to the acidous effluent, and an alkaline phase during which alkaline waste water is added to the effluent-sludge solution. A portion of the produced fraction containing fibres is recirculated to the acidous phase for reuse of the fibres.

Abstract: A process is disclosed for the pretreatment of lignocellulosic fibrous materials prior to delingification. The process in one of its embodiments is comprised of the following steps:1. Contacting the pulp material with treated filtrate and alkali for a short reaction period of about 1 to 2 minutes at 40.degree. C.,2. Withdrawing part of the liquid phase by filtration,3. Displacing substantially all of the remaining liquid phase with treated filtrate, and4. Allowing the pulp to react under conditions normally used for alkaline extraction or oxygen delignification.The treated filtrate is obtained by subjecting the liquor removed from the pulp at steps 2 and 3 to temperature of 5.degree. to 60.degree. C. for periods of about 5 to 10 minutes. Alternatively, step 3 can be eleminated.