Abstract: A method is disclosed for extracting liquor from a cellulose slurry for a continuous digester comprising the steps of: providing the cellulose slurry of liquor and chips of cellulose fiber material to a separator; extracting a first stream of liquor from the separator; extracting a second stream of liquor from the separator, where the second stream has an effective alkali (EA) concentration greater than the EA concentration of the first steam; outputting the first stream from the separator and outputting the second stream from the separator separately from the second stream, and outputting a condensed slurry from the separator to a digester vessel.

Abstract: A method is disclosed for extracting liquor from a cellulose slurry for a continuous digester comprising the steps of: providing the cellulose slurry of liquor and chips of cellulose fiber material to a separator; extracting a first stream of liquor from the separator; extracting a second stream of liquor from the separator, where the second stream has an effective alkali (EA) concentration greater than the EA concentration of the first steam; outputting the first stream from the separator and outputting the second stream from the separator separately from the second stream, and outputting a condensed slurry from the separator to a digester vessel.

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 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: Processes and systems for the treatment of wood chips prior to cooking remove substantially (e.g., at least about 30%) water-soluble compounds therein, especially those compounds which disassociate in water to form potassium and/or chloride ions and/or water-soluble metal compounds such as manganese, calcium and potassium. In preferred embodiments, wood chips entering the cooking system containing water-soluble compounds, such as those compounds which disassociate in water to form potassium and/or chloride ions and/or water-soluble metal compounds such as manganese, calcium and potassium, may be treated prior to cooking by being brought into contact with an aqueous treatment stream (e.g., water or steam condensate) at a temperature (e.g., between about 20° C. to about 120° C.) and for a time (e.g., between about 2 to 200 minutes) so as to reduce substantially (e.g., at least about 30%) such water-soluble compounds.

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 amount of metals that can be removed from comminuted cellulosic fibrous material (such as wood chips) in the production of chemical pulp, prior to bleaching, is enhanced by extracting metals during an early stage of digestion, and prior to the addition of a chelating agent. After the material is steamed and slurried it is impregnated with cooking liquor at a temperature of 90° C. or more, and during or after impregnation metals are removed by an extraction (e.g. in a continuous digester), which typically removes about 30% or more of the Mn. Prior to this extraction it is not necessary to introduce chelating agents, and undesirable to do so since they may compete or interfere with the natural removal of metals. After the extraction, such as during the first part of cooking, about 0.05-10 kg/dry ton of material of chelant (such as EDTA) is added, and the chelant combines with released metal ions in the slurry to produce metal complexes. The metal complexes are substantially removed before bleaching.

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: 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: In the treatment of cellulose pulp in connection with bleaching, the pulp is first cooked and, if necessary, oxygen delignified in order to reduce the Kappa number below 24, preferably below 14, and after that the pulp is treated in an acid stage at a pH of 2-5 and at a temperature range of 75-130° C. in order to reduce the Kappa number by 2-9 units. To prevent essential weakening of the strength properties of the pulp in the acid stage treatment tower, the retention time, t min, is 30 to 300 minutes and the treatment temperature, T° C. is Tmin<T<Tmax, in which T min = 10517 24 + ln ⁡ ( 2 ⁢ t ) - 273 and Tmax=Tmin+23° C.

Abstract: In the treatment of cellulose pulp in connection with bleaching, the pulp is first cooked and, if necessary, oxygen delignified in order to reduce the Kappa number below 24, preferably below 14, and after that the pulp is treated in an acid stage at a pH of 2-5 and at a temperature range of 75-130° C. in order to reduce the Kappa number by 2-9 units. To prevent essential weakening of the strength properties of the pulp in the acid stage treatment tower, the retention time, t min, is 30 to 300 minutes and the treatment temperature, T° C.

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: In the treatment of cellulose pulp in connection with bleaching, the pulp is first cooked and, if necessary, oxygen delignified in order to reduce the Kappa number below 24, preferably below 14, and after that the pulp is treated in an acid stage at a pH of 2-5 and at a temperature range of 75-130° C. in order to reduce the Kappa number by 2-9 units. To prevent essential weakening of the strength properties of the pulp in the acid stage treatment tower, the retention time, t min, is 30 to 300 minutes and the treatment temperature, T 0° C. is Tmin<T<Tmax, in which 1 T min = 10517 24 + ln ⁢   ⁢ ( 2 ⁢   ⁢ t ) - 273 and T max = T min + 23 ⁢ ° ⁢   ⁢ C .

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 alternatively 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: A cellulose pulp continuous digester (e.g. for producing kraft pulp) is operated so that it has an inverted top separator and is hydraulically filled to above the level of the inverted top separator, and may be substantially completely hydraulically full. A plurality of different liquor flows may be extracted from the inverted top separator, and an in-line drainer may be provided in a conduit through which liquid is extracted.

Abstract: A method of treating pulp and an apparatus for practicing the method are particularly suitable for the bleaching of medium consistency pulp when bleaching stages of varying temperature are used. Chemical pulp is treated in such a way that the pulp is allowed to flow prior to a bleaching reactor, in the reactor itself, and/or after the reactor, at a velocity of less than 5 m/s through an indirect heat exchanger in order to change the pulp temperature more than 5.degree. C., preferably more than 10.degree. C.

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 pretreatment of cellulosic fibrous material is adjusted to improve pulp strength. The cellulosic material is initially pretreated with a low temperature alkaline liquid (e.g. 80.degree.-110.degree. C.), and then with a higher temperature (but still below cooking temperature), higher alkali concentration liquor. Only then is the material--which has alkali which has completely penetrated the cellulose fiber walls--subjected to cooking with white liquor at a temperature of about 150.degree.-180.degree. C. Green, white, or black liquor can be used in the first impregnation zone, while white liquor (with polysulfide addition) is preferably used in the second zone.

Abstract: A method and continuous digester system provide for a high Na.sub.2 S concentration in the beginning of the cook of comminuted cellulosic fibrous material to produce cellulose pulp, providing a more selective cook and potential to lower cooking kappa. Two different streams of spent (e.g. "sulphurous" and "black") liquor are removed from different screens associated with continuous digesters. The spent liquor removed from the uppermost screen has a relatively high effective alkali and Na.sub.2 S concentration. The second spent liquor, removed from the second screen, has effective alkali and Na.sub.2 S concentrations which are at least 25% less than for the first spent liquor. The first spent liquor is circulated to an impregnation vessel, or other part of a chip feed system, to enhance the amount of sulphur present at the beginning of the cooking stage in the digester.

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.