FI120362B - Method and apparatus for cooking cellulose - Google Patents

Description

METHOD AND APPARATUS FOR BOILING CELLULOSE

The two most important active cooking chemicals for treating the pulverized cellulosic fiber during sulfate-5 or "kraft" cooking are sodium sulfide Na2S and sodium hydroxide NaOH. The amount of cooking chemical involved in the cooking of cellulose is expressed in mass production by the term "effective alkali". The effective alkali concentration value describes the hydroxide ion, or OH, concentration of the cooking liquor. Since sodium sulphide is hydrolyzed in aqueous medium to form sodium hydroxide or "alkali" and sodium hydrosulphide, the definition of effective alkali in fresh white liquor is as follows: sodium hydroxide content plus half the sodium sulph l / 2 (Na 2 S).

Various methods for treating cellulosic material with alkali have been disclosed. For example, in conventional 20 kraft cooking, all cooking chemicals, i.e. effective alkali, are introduced into the process at the beginning of the cooking, before the impregnation step. In this process, alkali is gradually consumed as the · · · I treatment progresses. In conventional kraft cooking, the effective amount of alkali in the cooking liquor is typically high at the beginning of the cooking and lowest at the end of the cooking.

According to research conducted by the Swedish Forest Products Research Institute (STFI) in the early 1980s

... modified soup was introduced in the first half of the 1980s. As described by Sjöblom et al. (Paper and Wood, 1983, No. 4, p. 227), one of the aims of this type of cooking is to provide a "low and effective concentration of effective alkali" and viscosity. that the yield • • ·.;. as a means of healing. Johansson et al., Svensk Papperstid- · 35 Ning, 1984, No. 10, have described the concentration profile of the effective alkali, i.e., the change in concentration value throughout the modified continuous kraft cooking, and compared it with conventional kraft soup. Johansson et al described how such a more alkaline modified soup e.g. improves the viscosity and bleaching of the pulp and reduces the burden on the environment. This study and subsequent experiments by others confirmed that low concentration and uniform distribution of effective alkali in both continuous and batch cooking (kraft) are preferred. This pulp treatment became the cornerstone of MCC® and EMCC® machines and cooking processes marketed by Andritz Inc. (formerly Ahlström Kamyr), Glens Falls 10 NY. Such equipment became very popular in mass production in the late 1980s and 1990s.

15 While the benefits of low and steady concentration of effective alkali for the viscosity and yield of the pulp have been accepted in the art, it has surprisingly been found that the pulp produced by these profiles is not the strongest in its intrinsic fiber strength.

20

The term "pulp viscosity" is directly conceived of in the fiber. The viscosity of the pulp is sometimes interpreted as an indirect measure of the relative fiber damage or depolymerization of the pulp. According to this thinking: the lower the viscosity, the greater the fiber damage. Often there is a · · · ·; it is assumed that the damaged fiber produces a weaker mass and that the lower viscosity is interpreted as a reduced specific fiber strength. However, in accordance with the present invention, it has been found that high concentrations and / or high pH of the effective alkali in bulk and residual delignification, although they may possibly reduce the viscosity of the pulp. , produce pulp with a higher specific fiber strength. For example, in laboratory soups that used high time lipid concentrations during cooking, such as 32 g / L of effective alkali, only about 40% of the usual H was needed. factor to obtain a kappa number of 21 for softwood pulp and a stronger mass. The high concentration of effective alkali as well as the high pH during cooking also results in a higher pulp bleaching mass, as has been reported in the literature. In addition, the high effective alkali content gives a 5 high residual alkali content to the waste cooking liquor, which can be effectively used to pre-treat the chips prior to the bulk bulk delignification step. According to the present invention, it is possible to use lower cooking temperatures and / or shorter cooking times compared to conventional soups. In other words, by using the present invention, cookware can be designed to be smaller and less expensive. This also means that existing cookware, whose operation is limited by current processes, can be made to produce 15 more mass per unit of time without having to increase their temperature or the amount of effective alkali therein.

The terms "bulk" and "residue" applied to delignification are standard concepts in the pulp and paper industry and are defined in Pulp and Paper Manufacturing, Part 5, Alkaline Pulping, Grace et al., Technical Section, ··· · {* # C Canadian Pulp & Paper Association, 1989, ss. 60-62. Briefly, "bulk delignification" is the stage of delignification whereby most of the lignin is removed with a high degree of selectivity compared to the preceding initial step. "Residual delignification", in turn, is a step after bulk crystallization, characterized by ... much slower lignin depletion, higher yield loss and also higher alkali consumption per unit of lignin removed.

• · • · · · · ·

The exact mechanism that produces the above desired results is not fully understood. High pH - not identical to 35 · high alkaline content (and which may be a more accurate indicator of active cooking chemicals), although high alkaline content is usually a prerequisite for high pH - may be more important than high the alkali content itself, and the combination of the two may be most meaningful.

According to a broadest aspect of the present invention, the invention comprises a process for cooking comminuted cellulosic fibrous material using high concentrations of effective alkali in at least one treatment step. This high alkali content is advantageously used in the bulk deliquescence step of the soup. Preferably, the effective alkali concentration exceeds 15 g / L (more preferably 20 g / L) in both bulk and residual delignification. The process may be carried out as a flow or batch cooking, in one or more vessels, in a hydraulic or in a steam / liquid phase cooker. However, according to a preferred embodiment, the method of the invention is carried out continuously using different types of conventional transceivers.

According to the invention there is also provided a process for treating comminuted cellulosic fibrous material in the manufacture of a chemical pulp having a higher chemical fiber specificity than conventional pulp or modified pulp. The process consists of the following continuous and sequential steps: a) · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · loose fiber material in a first cooking liquor having a · · · first effective alkali content of more than 10 · · · g / l; b. the cellulosic fibrous material (e.g., now impregnated) with the first cooking liquor 30 such that alkali is consumed in the first cooking liquor, so that the effective alkali content of the first waste liquor is reduced to about 10 g / l; c) removing the first waste cooking liquor from the cellulosic fibrous material; d) ·· ♦ treated (eg by impregnation) with cellulosic fibrous material ***. 35 second cooking liquors with a second effective time concentration of more than 25 g / l and higher than the first concentration and a pH of at least 13, each of the other 5 cooking liquors contains at least 50% cellulose fiber total alkali consumed in chemical pulp production; e) boiling the cellulosic fibrous material in a second cooking liquor at cooking temperature to produce a chemical pulping liquor to form a second waste cooking liquor having an effective alkali content of greater than 15 g / L (e.g., greater than about 20 g / L); (f) removing the second waste cooking liquor from the pulp.

Step b) is preferably carried out using the second waste cooking liquor from step f) as the first cooking liquor; some cooking liquor, typically white liquor, can still be added. In conventional mass production processes, whether conventional or modified, the cellulosic material must be treated with cooking chemicals of the type known in the art. for pretreatment or impro- gation of the material prior to actual cooking or bulk crystallization. Typically, more than 25%, sometimes more than 50%, of the total alkali consumption in pulp production occurs during this pretreatment, step b). However, among other advantages, the present invention also has the advantage of not having to feed the fresh cooking chemical to this pretreatment step, since this is used as a source of the cooking chemical in a high alkaline cooking ··· · ··· 25 residual aliquots contained in the black liquor produced in the process. Kalia.

According to a preferred embodiment of the present invention, to achieve a high concentration of effective alkali, at least 30% of the other waste is consumed at the end of the cooking, without increasing the consumption of fresh white liquor. Σ /: of the cooking liquor alkaline preferably in step a) before transferring the waste liquor to the recovery. Therefore, the first element to be removed in step c) ··· y .. and used in step a). The EA content (i.e., the effective alkali • · · * · * · content) of its waste cooking liquor is 15-50 g / l (as NaOH), typically 18-40 g / l, and preferably 20-35 g / l. The 6 liquors used in step a) contain at least some of the lye removed in step c), or preferably due to alkaline consumption in step b), the amount of total alkali added to step a) in the waste liquor 5 removed during step c) should be at least 5 %, typically at least 7%, and preferably at least 9%, or even 11% effective alkali (EA) based on NaOH. This alkali from the waste liquor fed to the steps prior to step c) should be at least 50%, typically at least 70%, and preferably at least 90% of the amount of alkali fed to these steps. Therefore, the total effective alkali content of one or more waste liquors removed in step c) is at least 5%, typically at least 7%, preferably at least 9%, or even 15 at least 11% NaOH from wood, and these waste liquors are reused and consumed prior to step c). stages of the cooking process. Some fresh cooking liquor, for example kraft white liquor or green liquor, may be added to the waste liquor stream to achieve the desired EA value. This ensures that effective alkali is consumed to a limited extent in steps d) and e) so that relatively high pH and EA are achieved in the stiffest part of step e).

The second cooking liquor of step 25 d) is preferably in the washing liquor; white liquor, or black liquor, and it is desirable that more than about 80% of the total white liquor consumed in the pulp (total alkali consumed) is added in step d) as a second cooking liquor.

• · · 30 Wash liquors used to dilute white liquor into another • · · · · cooking liquor to obtain the desired effective alkali content and · liquid-wood ratio. The passage of the d) stage may naturally cause the material to heat up to the boiling temperature. Heating can also be performed separately • · 35. The cooking temperature is usually 140-180 ° C, typically 150-170 ° C. Preferably, the concentration of the effective alkali in the second cooking liquor in the digester is greater than about 25 g / l, e.g. about 25-60 g / l, typically about 30-50 g / l. These effective alkali concentration ranges are typically obtained by chemically diluting fresh cooking liquor, starting at a concentration of about 90 g / l 5 or more effective alkali, using an available dilution source. Dilution can be done eg. black liquor, washing filtration, including bleach washing filtration, or cold-shot filtration. The invention also encompasses the steps below for cooling and washing the pulp, and prior to step a), the material is preferably steamed to heat it and remove air therefrom. Steps (a), (b), (d) and (e) can also be carried out either in a downstream or in a counter current (material flow relative to the cooking liquor flow). The waste liquors removed from steps 15 c) and f) should be kept separate and used for different purposes, the liquor from step f) is usually used to preheat the second cooking liquor and then expand, and the residual liquor is used as the first cooking liquor. The steam, in turn, is fed into a chips silo or pre-steam tank to pre-treat the material. Heat can also be recovered from the liquor of step · ···,. Ϊ c), for example by swelling or heat exchanger, followed by the lye to the normal heat recovery of the kraft plant;

• · · · 25 • · · ·. . ·. A process has also been developed for the production of a chemical pulp of high specific fiber strength from a chopped cellulosic fibrous material comprising ... the following continuous and sequential steps: a) · · · 30 Treating (e.g. by impregnating) chopped cellulose * · * · ·· * succulent in a first cooking liquor having: \ i a first pH greater than about 13.0 (e.g.

higher than about 13.2); b. pulp ··· .1. of loose fiber material (impregnated) still in the first • · • · ***. 35 cooking liquor such that the first cooking liquor • · · * · * · consumes alkali so that the residual pH of the first cooking liquor is about 13.0 or less (or about 13.2 or less); c) removing the first waste cooking liquor from the cellulosic fibrous material; d) treating (e.g. impregnating) the cellulosic fibrous material with a second cooking liquor having a second pH of about 13.5 or more, e.g., 13.7 or more than 5 and higher than the first pH, wherein the second cooking liquor contains at least 50% of the total alkali consumed in the chemical pulp production of the cellulosic fibrous material; e) boiling the cellulosic fibrous material in a second cooking liquor at cooking temperature to produce a chemical pulp, thereby producing a second waste cooking liquor having a residual pH of at least about 13.0, e.g., about 13.4 or above or about.

13.6 or more; and f) removing the second waste cooking liquor from the pulp.

Also provided is a kraft pulp having high specific fiber strength and bleachability as compared to conventional kraft pulp and modified cooking. Kraft pulp is prepared using one or both of the above methods.

20

According to the invention, there is provided a process for preparing a chemical pulp from a comminuted cellulosic fiber material using a feeder with an inlet port. The method comprises the steps of: a) continuously supplying ··· 25 milled cellulosic fibrous material to a liquid · · · ·; . * · In the suspension inlet of the stern; (b) cooking

IM

here. cellulosic fibrous material in the digester for more than 30 minutes, e.g., over an hour at a temperature of about 140 ° C to 190 ° C before cooking is complete; for which the method is known ···. 30, step (b) is carried out such that, for at least the last minute before the end of the cooking process, the effective alkali concentration, expressed as NaOH or equivalent, is at least 15 g / l in the digester.

• · · • · • · · ·. ·. : 35 When and where the "soup ends" in the pulp maker

• M

a somewhat vague concept and largely dependent on the cooking equipment used, the process and the species of wood being treated. Pulp cooking is generally considered to be substantially complete when the temperature of the material drops to about 130-140 ° C. However, some delignification, albeit very slow, occurs at temperatures as low as about 100 ° C. Where and when this temperature is reached will vary depending on the case. For example, in cooker hoods with poor detergent distribution or with no washing liquid added, the cooking reaction may continue even if the mass has already come out of the 10 actual cookware. The other extreme is continuous cooking processes, in which no cooking chemical is added to the final stages of the cooking process and a Hi-Heat ™ wash zone with counter current. In these, the cooking reaction may end well before the 15 lowest strainers. Although the end and time of the cooking process cannot be well defined, it is desirable according to the present invention that at the end of the actual cooking process, the alkaline content of the chopped cellulosic fibrous material is relatively high and / or high.

20 ... Step b) is preferably carried out such that at least • · · · · · * during the last 15 minutes, and more preferably at least · · · · * - · · · · * during the last 30 minutes before the end of cooking · ·: the alkali content is about 15-50 g / l, e.g.

18-50 g / l, more preferably about 18-40 g / l, and most preferably: # 20 more than 35-35 g / l). Step (b) is typically carried out by: T: removing the liquid from the suspension at least at the first and second points, the first of which is closest to the inlet of the digester, adding time. 30 l, and more than 50% of the total time to be added to the suspension during steps a) and b) is added during the first time. *! after the dot. Preferably, more than 70%, more preferably more than 80%, and most preferably more than 90% of the total time added to the suspension throughout the pulp production is added after the first point. However, the alkali is added after the first point preferably at more than one point, and preferably at more than two different points, and the alkali is added so that the highest effective alkali content during step b) is less than 50 g / l, preferably less than 40 g / l, and most preferably less than 35 g / l. Prior to the first point 5, the cellulosic material has already consumed at least 5%, preferably at least 7%, even more preferably at least 9%, and most preferably at least 11%, expressed as effective alkali calculated from wood and expressed as NaOH.

According to the present invention there is also provided a process for the production of pulp from comminuted cellulosic fibrous material having a high specific fiber strength, comprising the following continuous and sequential steps: a) treating the comminuted pulp with a first cooking liquor having a first effective alkali content greater than 10 g / l; b) further treating the cellulosic fibrous material with a first cooking liquor such that alkali is consumed in the first cooking liquor so that the effective alkali content of the first waste liquor 20 is reduced to about 10 g / l or less; (c) removing the first waste cooking liquor ··· · ... · from cellulosic fibrous material; (d) treating the cellulosic fiber material with a second cooking liquor having a second potable alkali content greater than 25 g / l and higher ··· 25 than the first concentration of the second cooking liquor.

• IM

• contains at least 50% of the total alkali consumed by the pulp in the pulp production; e) boiling • · «cellulosic fibrous material in a second cooking liquor at a cooking temperature to produce a chemical pulp to produce a second cooking liquor with an effective alkali content of more than 15 g / l; (f) removing the other waste cooker • · ί # *. «from the pulp; characterized by: ***: that step (e) lasts more than 30 minutes and that at least ·· ♦ y .. 'during the last 15 minutes, the effective alkali content • · ***. 35 mouth expressed as NaOH is 18-40 g / l. According to the present invention, the details of step e) may be carried out in step c) of the previous embodiment. Preferably, about 80 to 11% or more of the total amount of white liquor and alkali needed to make the pulp is added to step d) as a second cooking liquor. Other details of this method follow the above.

5

Another way to achieve a cooking process with a high effective alkali content at the end of cooking is to modify an existing countercurrent cooking process, e.g. MCC® or EMCC® soups marketed by Andritz 10 Inc. (Glens Falls, New York), such that the amount of alkali added to the end of the last upstream zone is significantly increased. Usually, the amount of alkali added to the end of the last upstream cooking zone ranges from about 15 to 20 percent of the total amount of alkali fed. The total amount of alkali supplied is typically about 18-22% EA based on wood. In other words, in conventional methods, the amount of alkali fed at the end of the last countercurrent cooking zone is typically only about 1-4% EA on the wood, expressed as NaOH. A typical concentration of EA at the end of the last upstream: cooking zone is about 10-15 g / l. The present · * · *: according to the invention, this concentration should be the quality of the pulp. to be greater than 15 g / l, preferably more than 20 g / l and most preferably more than 25 g / l. These high concentrations can be • · · ·. . ·. reaches when more than 5%, preferably more than 7%, and preferably more than 9% of effective alkali, calculated from wood, is fed to the end of the last countercurrent cooking zone.

In accordance with the present invention, there is also provided a continuous hydraulic or vapor phase digester comprising: a vertical vessel having a suspension. . * ··. inlet, pulp outlet, first cooking zone, • · · ^ ke, second cooking zone, and lye removal filter, and a spiral system that • separates the zones. It hand- • · · *. * also provides means for introducing alkali into the circulatory system so that the effective amount of alkali 12 removed by the strainer, expressed as NaOH, is about 18-40 g / L. Preferably, the digester also comprises means for heating the circulation system and for adding alkali to adjust the final kappa number of the pulp discharged from the pulp outlet. The digester also comprises means for screening closer to the suspension inlet than the pulp outlet for reusing the discharged liquid in the digester.

The first cooking zone may be upstream or downstream. Likewise, the second cooking zone may be downstream or upstream, but preferably upstream, e.g., MCC® or EMCC® cooking zone, or upstream washing and cooking zone, e.g., Hi-Heat ™ wash zone. The liquor circuit typically includes a pump, an indirect steam heater, and possibly means for adding a dilution broth. A system known as a "shut-off cycle" can be used as a screening and circulation system.

The main object of the present invention is to provide a pulp of high specific fiber strength and bleachability by cooking at high alkalinity and / or high pH. This and other objects of the invention: *: The objects will be apparent from the detailed description of the invention and from the appended claims.

• · · · 25 • · · ·. . ·. Figure 1 is a diagram of the first embodiment, i.e., · · · ···. a new two-vessel digester for implementing a process for the production of pulp of high specific fiber strength; Figure 2 is a schematic view of another embodiment and illustrates a prior art two-pot brewing apparatus for implementing a high specific gravity method. »··.;. for the production of high-strength pulp; Fig. 3 is a diagrammatic view of a third embodiment and illustrates a prior art single-vessel digester apparatus 13 for implementing a process for making pulp of high specific fiber strength;

Fig. 4 is a diagrammatic view of an embodiment of a method for producing a pulp of high intrinsic fiber strength;

Figure 5 is a graph comparing the alkali content to the cooking time in conventional cooking; 10

Fig. 6 is a graph comparing alkali content to cooking time in modified cooking;

Fig. 7 is a graph comparing the alkali concentration to the boiling time in the exemplary method of this invention;

Figure 8 graphically shows the strength of pulp as a function of residual alkali at two different tensile strengths.

20

Figure 9 graphically illustrates the strength of the pulp as a function of the residual pH at two different tensile strengths. Fig. 10 is a schematic diagram of an exemplary digester apparatus of the present invention. . . ·. for carrying out the process of the invention; • · · · · · · · · · · · · ·

Figures 11 to 13 graphically illustrate the effect of effective residual alkali content on pulp properties • · · * · * * in the practice of the invention; • · · · · · · · · ·

Fig. 14 is a view similar to Fig. 10, showing a second system according to the invention; and FIGS. 15-17 graphically illustrate the effect of high concentration of alkaline effective · · · * · on the test runs performed using the system of FIG. 14.

14

The present invention may be implemented in conjunction with other preferred cooking methods to provide a cooking system that produces the highest possible strength, while utilizing the energy, material, and chemicals available in the most efficient manner. Typical cooking systems are illustrated in the drawings.

Figure 1 shows a typical system having the advantages of the present invention. It describes a typical two-bowl hydraulic spout system 10 for carrying out the process of the invention. Wood chips 11 or other comminuted cellulosic fiber material is fed to ha-15 digester 12 for pre-steaming and / or pretreatment. Typically, silo 12 is a vessel having a one-dimensional tapered portion and a lower flow resistance range, as described in U.S. Patent Application 08 / 189,546, filed February 2, 1994, and U.S. Patent Application No. 20 08 / 354,005, filed December 5, 1994, by Andritz Inc., Glens.

Falls, New York under the trademark DIAMONDBACK®. Steaming • · · can be performed either under atmospheric pressure or under pressure. The chips can be fed into the chip silo via channels such as • · •; *; In U.S. Patent 4,927,312 or through Synchronized Channels • · · ·.:. 25, as in U.S. Patent Application Nov. 11, 1994. 08/350, 129 are disclosed.

The steamed chips are discharged from the chips silo to the joint or to the school 13 where the chips are submerged in cooking liquor 14 and the impregnation process of the cooking medium begins. To dismantle the chips • · * ··· * from the silo can be used a rotary air lock type feeder (not shown) as marketed by Andritz Inc. • ·. ***. application meter (Chip Meter). The surface of the liquor at the joint 13 is held at a certain level by a conventional surface adjuster * ··· '35 (not shown). If desired, the surface of the lye can be held in the chips silo 12 together or above the trough 13.

15

Unit 13 leads to a conventional high pressure feeder 15, also a device marketed by Andritz Inc. The rotary pocket type feeder 15, which is connected to a high pressure inlet pump (not shown), pressurizes and 5 conveys the chips suspension from low pressure to high pressure of the cooking vessel (e.g. 19). The pressure of the chips suspension can be increased, for example, from 0 to 2 bar (0 to 30 psi) to 3 to 14 bar (45 to 200 psi) for the delignification reaction. This feed system 10 typically includes a chute pump, an in-line fluid drainage device, an equalization tank, etc. (not shown), which are known to be connected to a circulating system 16. This pressurization and transport can also be performed by a slurry pump, such as / 267,171 or U.S. Patent Application 08 / 428,302, filed April 25, 1995. During this pressurization and transport, the lingering suspension is typically contacted with hot cooking liquor at a temperature of 80 to 120 ° C, typically 90 to 110 ° C in a circulating system 17.

The heated pressurized system conveys the suspension of the chips and the lye through one 18 to the top of the cooking vessel 19. Ko. the cooking vessel may be, for example, an impe .. 25 'recovery or pretreatment vessel or a kettle. Figure 1 ·, · .ί illustrates a typical impregnation vessel 19 that may be used to practice the present invention. Excess liquor is removed from the suspension by means of strainers 20 and returned together through 17 for use in feeder 15. ·· *. 30 slurry. In container 19, the chips suspension is subjected to a relatively long, cold, downstream • · · *. * Impregnation treatment in the I zone. This impregnation treatment is described in U.S. Patent Application Serial No. **, filed June 2, 1995. 08 / 460,723. For long, cold impregnation steps ·· ·. ·. In 35 I, which begins when the liquor is fed to the high pressure feeder 15, the chips suspension is typically maintained at a temperature of 80 to 1610 ° C, preferably 90 to 105 ° C. Although this treatment is shown in Fig. 1 as a downstream treatment, it can also be countercurrent.

The impregnation zone I may include a screen 21 and a circulating system 22 which facilitates downward movement of the wood chips and distributes heat and chemicals more evenly to the wood chips. This circulation system may have a conventional lye pump and an indirect steam heater (not shown). The circulatory system may further include the supply of black liquor, white liquor, or bulking agents such as polysulfides and anthraquinones and their derivatives. In Figure 1, the black liquor removed from the next treatment step is fed into the circuit through 23.

15

After the suspension has been treated with impregnation zone I, it typically passes to zone II, which is a counter current heating zone. Zones I and II are separated by one or more lye removal screens 20 and 24 which, by pressure or pumping of the vessel, remove the lye from the impregnation zone and provide a driving force to transfer the lye to the upstream zone II. Removed lye can be used elsewhere in the · · j cooking process, or it can be routed to a lye and heat ··· 25 recovery system. As shown, for example, in Fig. 1 · · · ·; j *; ie, the cooler diluted black liquor removed from the ··· upper strain 24 can be fed to the recovery through 26. The hotter liquor removed through sieve 25, which may contain useful times • · · 30 l and sulfide, may be led through one cycle of 23 to increase the alkali and sulfide and temperature distribution · · · / ·· at the top of zone I. Even if only one screening apparatus is used, the lye, albeit mixed # * ··>, can be distributed and used as required.

V \ 35 • · · • · · · 17

The hot liquor from the joint 26 may also be introduced into an indirect heat exchanger as disclosed in U.S. Patent Application 08 / 420,730, filed April 10, 1995.

Removal of the liquor through the screen 24 completes the impregnation step and also removes moisture and vapor condensate from the wood which tend to dilute the concentration values of the cooking chemicals in the cooking zones. The entire impregnation step from the time the chips are in contact with the lye at temperatures above 80 ° C up to the colder lye removal through the strainers may take from thirty minutes to three days. Typically, however, it will last from one to six hours, preferably from one to three hours. During countercurrent heating and downstream impregnation chips in impregnation zone II, the impregnated chips are heated with hotter cooking liquor which is passed upwardly through screens 24 and 25. This lye is typically heated to 28 120-160 ° C, typically 130-20-150 ° C, and preferably 135-145 ° C by a circulating system. This. ···. countercurrent heating can last from five minutes to • ·. '•' 1 'hours, but typically lasts from half an hour to three hours. A countercurrent step is preferred, · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · V: cross), external heating of the vessel, or flow from the vessel, etc. Like cycle 22, cycle 28 also comprises: T: typically one or more strainers 27, a pump, and an indirect steam heater (not shown). In this tour • · *. *. heated liquor may be added to the liquor, which has been removed from the following cooking steps. Here, a cleaner filtrate, with or without cooking liquor, can also be added to the Rossa liquor so that: * · · · 35 wood is removed from the cooking system. It also utilizes the LO-SOLIDS® Steamer and • 18 processes sold by Andritz Inc., as disclosed in U.S. Patent Application 08 / 056,211, filed May 4, 1993, and International Application WO 94/25668. In the preferred embodiment shown in Fig. 1, both hot black liquor from the two-vessel rotation together through 29 and cold butt wash filtration to the one through 30 are added to the circulation.

After heating at the bottom of the impregnation vessel 19, the impregnated suspension is removed from the impregnation vessel 10, heated to a cooking temperature and transported to a second cooking vessel, i.e. a digester 33. While a conventional rotary outlet instead of a mechanical device. This type of outlet is described in U.S. Patent Application 08 / 401,503, filed March 10, 1995 and marketed by Andritz Inc., Glens Falls, under the trademark DIAMOND-BACK®.

20

During the emptying of the impregnation vessel, the suspension formed by the chips and lye • · · ϊ.,. Ϊ is in contact with the cooking liquor: * · [: substantially at full cooking temperature, i.e. 140-180 ° C, typically 150-170 ° C. Hot liquor fed through one of 35 into the outlet of 25 vessels 19 pushes: the suspension into the upper part of the digester 33. Extra lye • · ·; * · *; is then typically removed from the suspension by means of a strainer 34 and returned to one of the 35 through the outlet 31. This reflux liquor circuit 35 is typically heated by steam · · · 30 in a conventional indirect heat exchanger 36.

Before feeding into heat exchanger 36, some of this • · ·. * ·· circulation liquor may be removed and fed to the liquor circulation 28 together 29.

35 Cooking liquors, typically kraft white liquor, are fed · · · preferably into the set of material 35 of the circulation 35 by means of the heater 36. As is characteristic of the invention, much of this cooking liquor to be added to the system is added via the 37 35. Typically, at least 50%, preferably at least 80% (e.g., about 90%) is added to the cycle 35. This results in 5 very high effective alkali contents in the digester; i.e., more than 25 g / l, preferably more than 35 g / l. Residual liquor can be added to cycle 16 together through 38 or to cycles 22 or 28 to ensure a minimum alkali concentration in these cycles to prevent lignin condensation, acid hydrolysis, etc. The cooking liquor added through one of the 37 can be indirectly heated by heat exchanger 39 by means of steam or hot waste cooking liquor removed from the boiler, e.g. from strainer 40.

In order to achieve the desired high alkali content and high pH in accordance with the present invention, a cooking liquor such as kraft white liquor added together in one 37 may have the following properties: total alkali from about 15% to about 25% (typically approx.

20 to 22%), effective alkali content of about 90 to about 130 g / l (typically about 100 to about 120 g / l) as NaOH, diluted to the desired dilution of 25-60 g / l, preferably 30-50 g / l, prior to the invention; and a flow of about 2.0 - 5.0 m3 / BDMT (m3 / absolute ··· 25 dry metric tons) mass, typically about 3.0 - ····. 4.0 m3 / BDMT pulp.

♦ · · '··· • · · · · · · «

The heated suspension as well as the cooking liquor, which are essentially at cooking temperature, are transferred under pressure from · · · · · · · · · · · · · from the outlet 31 31 to one 32 through the top of the vessel, i.e. the cooker 33. Excess lye is removed through the screening apparatus 34 provided in the inlet of the digester and returned to the outlet of the impregnation vessel 31 together 35 ··· .1. through wood chips. This restored lye • • ”*. Typically, 35 is vapor discharged in an indirect heat exchanger 36 before being fed to outlet 31. The heated liquor may be fed to a plurality of outlet nozzles to uniformly drain the suspension.

The chips, which are now fully impregnated, pass downstream in zone III of the digester 33 in the cooking heat 5 state as the cooking reaction proceeds. Although this treatment is described as downstream, it can also be countercurrent. This cooking reaction with a high alkali content can last from half an hour to six hours. Typically, however, it lasts one to three hours. At the bottom of the digester, the hot waste cooking liquor is now removed from the fully cooked chip by means of one or more screening devices 40 and 41. The colder wash filtrate of the mass scrubbers below (not shown) may be fed to the bottom of the kitchen 15 by one or more of the two 42 to terminate the cooking reaction and reduce the temperature of the cooked chips suspension.

The wash liquor passing through 42 may also be added 20 to the required locations, e.g., circuits 155, 135, or 17, to dilute the dissolved material. Hereby, the · · ·: ... ί cooled cooked chips are then removed from the kitchen via the outlet 43 to the 44. Cooked mass •: 1; is then passed to the warehouse or to the following process steps, such as washing and bleaching the brown pulp (not shown). If a single strainer 40 is used, the removed liquor may be dispensed and then used as required.

30 Although the chips suspension is commonly used to remove t 21

As shown in Figure 1, the hot waste cooking liquor is preferably removed from the digester by means of the upper screen apparatus 40 and one 45. Since most of the effective alkali is fed to the inlet of the digester, the content of this hot lye 5 unused alkali, i.e. residual alkali, is relatively high. The alkali content of each of the 45 lyes is typically at least 15 g / l, e.g. at least 20 g / l, preferably at least about 25 g / l. Typically, the residual alkali content of conventional kraft soup and modified kraft soup is maintained at about 6-12 g / l. This lower residual alkali content is usually sought to ensure that there is sufficient alkali at the lye removal site for proper cooking, while minimizing unnecessary alkali consumption in the tal-15 recovery system. The relatively high residual alkali content according to the present invention results from the fact that the amount of alkali fed into the digester is preferably high.

20 However, this waste liquor, although not entirely waste liquor, because it has a relatively high alkali content, ··· can be advantageously recycled for wood chips pre-treatment. Further, it should be noted that, through one of the 45:: *: the lye removed also contains a considerable amount of sulfide ··· 25 slides, typically 10-30 g / l, which is also advantageous. . *. during chip pre-treatment or impregnation. The ratio of sulphide • »· to effective alkali is higher ♦ ·« than in white liquor. Therefore, the sulphide ... content and / or sulphide content of the waste cooking liquor is higher, so that at the beginning of the delignification process, with the aid of the caustic soda, the sulphide content is higher than in conventional and modified cooking. .

• · • · • · ···.!. Preferably, the flowing liquor 45, which contains both the alkali · · · ·, 35 and the sulfide, is fed to the circulation system • · · * · *: for use in pretreatment or impregnation of the wood chips to be fed. Since one of the 45 liquors is 22 typically at a cooking temperature of 140-180 ° C, it can be used as a heating medium 39 for heating the white liquor supplied in combination 49. This hot liquor can also be expanded in the expansion vessel 46 to generate steam and to further cool the liquor. The steam can be used together through 47 for the pre-steaming of the chips in the chips silo 12. The cooled liquor can be led to the circulation 16 together through 48. Instead of swelling, hot liquor can also be used to indirectly heat water in the heat exchanger to produce "pure" steam.

Also, the second lower screening apparatus 41 may be used at the bottom of the digester 33 to remove the cooled wash liquor 15 to be removed upstream. The lower portion of vessel 33 may include a countercurrent heated washing zone (Hi-Heat ™ wash in conventional Kamyr cookers) or a countercurrent cooking zone, such as Andritz Inc.'s EMCC® cooking zone, wherein some cooking chemical 20 is added to the washing liquor 50, . The sulphide content of the 50 flowing effluent filtrates is lower because it is diluted by the washing filtrate. The filtrate from one of the 50 can be used to • · · pretreat the chips entering the digester by recycling • j * 25 in the lye return cycle 35 to 52. Recirculation: through 52 allows the adjustment of effective alkali content and liquid-wood ratio during cooking.

The 52 flowing relatively pure filtrate to which the washing filtrate can be added can also be used to displace dissolved solids and thus

and LO-SOLIDS® soup by Andritz Inc. (see, e.g., WO

• · 94/25668). Since one of the 50 liquids may contain fiber, a fiber filter or screen 51 s ·· 'can be used to remove it and return it to the pulp stream 53 together.

*: **! 35 · · · * * One of 50 lean black liquors and one of 45 strong black liquors may also be used in the two-step lye impregnation process disclosed in U.S. Patent Application Serial No. 08 / 299,103 filed September 2, 1994, U.S. Patent Application Serial No. 08 / 345,822 filed November 21, 1994; 1995, U.S. Patent Application Serial No. 08 / 403,932. For example, lean-5 black liquor from joint 50 may be fed into cycle 16 or 22 for pretreatment of chips and strength black liquor from joint 45 may be introduced into circulation 22 or 28 as second processing of chips. This sequence may also be reversed so that the treatment with the strong black liquor 10 precedes the treatment with the weak black liquor.

In the system of Figure 1, the long countercurrent cooking zones are limited to the pretreatment zones 15 and not to the end of the cooking. Because wood pulp (or other pulp containing comminuted cellulosic fibrous material) is softer at the end of the cooking process, it is more difficult to pass lye upstream. By limiting the size of the countercurrent zone at the end of cooking, the kettle is easier to operate. In turn, 20, the stronger the applied pretreatment step allows the countercurrent moving liquor to pass through easier, and thus the kettle is easier to operate. This aspect of the invention is very important when applying the invention to older overloaded cookers with either limited or no backflow ♦ ···. . ·. countercurrent at the end of cooking.

♦ · · «« · ·· ♦ • · · • · ♦

Figure 2 illustrates the implementation of the processes of Figure 1 ... in an existing dual cooker system. The parts ♦ ♦ · * · [/ 30 which in Figure 2 are identical or similar in function to those of Figure 1 are denoted by the same reference numerals. Uniforms, albeit in Figure 1 • ♦: ***; in front of reference numbers of parts similar to parts • · ».1. is "1" added in Figure 2.

: 35 • · • · · · · · · · 24

Figure 2 shows a pulping system 110 having an identical feed system to the feed system shown in Figure 1. (Note that the feeding system shown includes a new DIAMONDBACK® steaming bowl.

5 This system may also include a conventional feed system comprising a conventional chips silo and a steaming vessel. After pre-steaming in vessel 12, the cellulosic material is treated with cooking liquor in a long, cold impregnation or pre-treatment step 10. This treatment in step I is typically carried out at a temperature of 80 to 110 ° C, preferably 95 to 105 ° C, and lasts from half an hour to six hours, preferably from one to three hours. This treatment is carried out in a first cooking vessel or impregnation vessel 119 as a co-current treatment. An existing vessel typically does not contain any lye circulation or strainers, although it may have circulation systems and strainers. For example, vessel 119 may have one or more outlet screens forming belt-zones for upstream and downstream treatments.

• · ·

After pretreatment, the impregnated material is transferred at about 100 ° C from a conventional container 119 • ·: through opening 131 to one 132 through a second cooking pan or .. * · * 25 top of the digester 133. Excess liquor is recovered from the suspension by sieves 134 and returned via 135: * · *: to the outlet of the vessel for suspension liquid. The liquor present in the joint 135 may be supplemented with the liquor removed from the other parts of the soup, e.g. Because of this, · · · · · · · · · · · · 30, the suspension entering the top of the digester 133 is of the type. 110-120 ° C, more typically approx.

• · · *: ./ 115 ° C.

The pretreatment step continues in downstream zone 35 of digester 133 until the suspension reaches one or more of the strainers 152 and 154. The pretreatment broth, i.e., lean black liquor, can be removed by the strainers. 152 through and leads to a total of 153 through recovery. Stronger black liquor removed from countercurrent cooking zone II may be removed through a strainer 151 and added to a circulator 135 5 through 151.

The high alkali treatment characteristic of this invention is carried out in countercurrent cooking zone II of digester 133. Most of the white liquor, typically at least 50%, preferably at least 80% (e.g., about 90%) is added to the suspension via circuit 155. This produces a very high effective alkali content in the digester of more than 25 g / l, preferably greater than 35 g / l. Circulation 155 includes one or more strainers 156 and 15 indirect steam heater 157. Cooking liquor, typically kraft white liquor, is added to circulation 155 through 137 together, and said cooking liquor can be preheated by heat exchanger 39 with hot liquor removed from the rest of the stove 119. 20, typically a suspension with cooking liquors to a cooking temperature of typically 140-180 ° C, preferably 150-180 ° C, prior to the flow of said suspension to a flow of up to 1 ° C. cooking zone III (which may also include ·:: countercurrent cooking zone). Circulation 155 may also include the removal and feeding of a liquid having: less organic matter in the liquid, and: 1 · 1: this is the LO-SOLIDS® soup of Andritz Inc.

The cooking process in step III always goes to one or. ···. 30 for multiple screens up to 40 and 41. As with the processes described in connection with Fig. 1, these screens also have 1 ·. 1: the cooking process is terminated and waste liquors containing various chemical compositions are used for pre-treatment, .2 ·. chemicals and heat recovery.

• · * · · · 35 2 • ··

Although one of the liquors 42 is not shown in the figure, it can also be led anywhere in the digester, where it can be used to dilute the decomposed material during cooking, for example in cycles 17, 135 or 155.

Figure 3 illustrates the implementation of the processes using the apparatus of Figure 5 1 in an existing single digester system. In parts of Figure 3 which are identical or functionally identical to parts of Figures 1 and 2, the same reference numerals are used. In Fig. 3, "2" is added in front of the reference numerals of the unique parts 10, albeit similar to those shown in Figs. 1 and 2.

Figure 3 shows a single-vessel pulping system 210 having an identical feed system to those shown in Figures 1 and 2. Again, it should be noted that the feeding system shown includes a new DIAMONDBACK® steamer. This system may also include a conventional feed system having a conventional chips silo and a steaming vessel. After pre-steaming in vessel 12, the cooking liquors fed to the cellulosic material 20 as well as the cellulose material itself are subjected to a long, cold impregnation or pre-treatment stage. This step, or zone I, begins at the gutter 13 and continues at the transfer port 18 and the upper part * of the digester 219 at 233. The treatment is typically carried out at 80 to 110 ° C, preferably 95 to 105 ° C: n, and lasts from about five minutes to six hours, preferably from about half an hour to three hours. The treatment is typically carried out downstream, but it can also be upstream. Excess lye is removed by suspending • · ♦, * ♦ ·. 30 through the screen 234 and is recycled • · yhteen * together 17 through the high pressure feeder 15 where it · · acts as a transfer medium.

· «· • · • · · ·. · * ·. The pretreatment step I may include a liquor cycle 260.

• · '' S '. Circulation 260 may include one or more screens 261 and • · · * * heat exchanger (not shown). Liquid 260 may be added to liquor 260 removed from other areas of the digester, e.g. As a result, the temperature of the suspension during the pre-treatment step below strainer 261 may rise to 110-120 ° C, usually to about 115 ° C.

The pretreatment ends with one or more of the strainers 263 and 264 located below the strainer 261. The upper screen 263 may be used to remove the pretreated lye from the suspension. This lye, at 265, does not usually contain many useful treatment chemicals, such as alkali and sulfide, and is usually fed into a recovery system. As before, the liquor flowing in tube 265 may also be used to generate steam either by expansion or through an indirect heat exchanger. The lye removed from the lower strainer 264 typically contains a substantial amount of alkali and sulfide and can be recycled to the recirculation system 260 for pre-treatment of the incoming material.

The upstream cooking zone II is located below strainer 264 20. This zone can also be downstream. The invention is characterized in that this cooking zone II is fed together with 237 effective alkali, which has a high concentration value. As before, most of the white liquor, typically at least 50%, preferably at least about 80% (e.g. about 90%), is added to the suspension: via circuit 266. This gives rise to the cooking zone • · ·; * · *. a very high effective alkali content of more than 25 g / l, preferably greater than 35 g / l. Circulation 266 includes one or more strainers 267 and an indirect steam heater • · · 30 268. Cooking liquor, typically kraft white liquor, is • · * 1 * added to circulation 266 through 237 and can be preheated in the heat exchanger. 39 hot liquors ···! ... · removed from the rest of the cooker 219. Heated circulation ···. The 266 usually heats the suspension with cooking liquors to a cooking temperature of typically 140-180 ° C, preferably 150-170 ° C before flowing into the downstream cooking zone III. Cooking can take from five minutes to six hours, but typically takes about half an hour to three hours. Circulation 266 can also be accompanied by LO-SOLIDS removal and dilution.

As before, the cooking process proceeds to stage 40 and 41 in step III. As in the processes described with reference to Figures 1 and 2, the cooking process ends with sieves 40 and 41, and waste liquors of different chemical compositions are used for pretreatment, chemical recovery and heat recovery. The washing liquor may be introduced into the process in the same manner as described in connection with the embodiment of Figure 2.

15

Figure 4 is a schematic view of another exemplary system that may be used in accordance with the present invention. Figure 4 shows the typical bound and free-flow liquor flows (m3 / BDMT) and the free-flow flow direction-20 nan. It also illustrates a hydraulic digester system 310 comprising a single digester, similar to the system 210 shown in Fig. 4 (parts of Fig. 4 which are · · «| identical to those shown in the other Figures) are denoted by the same reference numerals with "3".) • · · · ··· 25 This machine performs the cooking according to the invention, • ·· ·. where the effective alkali concentration and pH are high. In Fig. 4, the numbers indicate the total liquor flow • · · m3 / BDMT. What part of each stream is "bound" and ... what is "free" can be defined as "Bound" • · · *]. * 30 lyes are the liquids carried with the cellulosic material while • · '·; · * "free" lye is lye that is not bound but which can flow in and around the cellulosic material; ***.

··· • · · · · ***. The container 12 and supply system 15 shown in Figure 4 are the same as in the other figures. However, the system shown in Fig. 4 employs a white liquor condenser 29 70 which is not used in other embodiments. The cooler 70 lowers the temperature of the white liquor (which may be present even though it is 0 in Fig. 4) and other liquids, such as mus-5 alkaline liquor entering the feed system e.g. via pipe 16. In the example of Figure 4, about 9.4 m 3 / BDMT of lye flows into the feed system through one of 16, while 2.2 m 3 / BDMT comes with the chips, giving a total flow of about 11.6 m 3 / BDMT. Of this 11.6 m3 / BDMT fed to the top of the digester 319, approximately 4.4 m3 / BDMT 10 is bound and approximately 7.2 m3 / BDMT free. The impregnation continues until the lye is removed through the screen 365. Of the 9.2 m 3 / BDMT removed through the screen 365, about 7.2 m 3 / BDMT is impregnation liquor, while about 2.0 m 3 / BDMT is lye conducted upstream of the 15 upstream portions of the screen 365 of the digester 319. The 4.4 m3 / BDMT that is bound when it enters the top of the digester 319 is still bound the entire distance through the digester 319.

After the screen 365, the cellulose suspension is heated, 20 white liquors are added, and the solids are displaced by the passage 71 in connection with the screen 72. With the addition of 2.5 m3 / BDMT of white liquor and 2.5 m3 / BDMT of washing liquor into circulation 71, about 2.0 m / BDMT flows upstream and is removed •: * and about 3.0 m3 / BDMT flows with cellulosic material 25 down in the stove 319.

···· • · ♦ • · ·

The cellulosic material in the suspension is · · · cooked at high alkali content and low solids solids up to 75 · · · l [* 30] for a sieve 74 attached. Black liquor with high ice-alkaline and sulphide content is removed through tube 76 from circuit 75, about 4.0 m3 / BDMT, and fed to the feed system. Some removed lye ··· .1. is replaced by white liquor and washing filtrate by adding • · * · ** [35 about 1.0 m3 / BDMT each. The material is further cooked underneath the strainer 74 under the strainer 74, although there is less free liquor than before.

The cooking ends with a strainer 77, where about 5.4 m3 / BDMT of waste-5 liquor is removed and combined with the liquor removed through tube 76 and fed to the feed system. The lye (black liquor) is cooled in the heat exchanger 70. Cold wash liquor, about 7.0 m3 / BDMT, is added to the bottom of the digester 319 and from there it is led upstream to the pulp, where it stops cooking, cools the pulp before washing. Of the added 7.0 m3 / BDMT, about 4.4 m3 / BDMT is led upwards and discharged through a strainer 77, while about 2.6 m3 / BDMT is removed from the digester with ca. 4.4 m3 / BDMT of brine. and forms 7.0 with 15 m3 / BDMT of pulp removed as shown in Figure 4.

Figures 5-7 show typical alkali concentration variations or profiles for each step of kraft cooking in different cooking methods as a function of cooking time. Figure 5 shows the alkaline profile of a conventional kraft soup.

• · ·

In it, alkali is added to the feed system before impregnation. Curve 301 shows how the alkali is at its maximum: initially and continuously decreasing as the cooking progresses, and a minimum concentration of • · · · ··· is reached at the end of the cooking.

···· · · · · · ···

Figure 6 shows a typical alkaline profile of modified soup. In it, about half of the alkali is added at the beginning of the soup and about half is added at the end of the impregnation. As shown in the curve 401 of the · · · · 30, the alkali concentration peaks are at the · · * ··· * alkali addition sites, but the peak is at a lower level than the peak in Figure 5.

• · · • • • • • •.;. Figure 7 shows a typical alkaline profile of the kraft soup according to the present invention. After impregnation, the total amount of alkali or substantially all of the alkali is added at step 502, and after cooking, the residual alkali in the lye is recycled to the beginning of the cooking at step 503. As shown by curve 501, recycling a residual alkali causes a moderate alkali peak at the higher peak is at the point 5 where all the alkali is added, i.e. at 502. According to the present invention, it has been found that the alkali profile of Figure 7 produces a chemical pulp having higher specific fiber strength and better bleaching than the modified or conventional 10 cooking methods shown in Figures 5 and 6. mass obtained.

Figures 8 and 9 graphically show test results showing the effect of residual alkali and high pH (preferably about 13.4 or above, typically about 13.6 or above) at the end of laboratory cookings. Figure 8 shows how the tear index (indicating the specific fiber strength) increases as the residual alkali content increases at the end of cooking. Alkali is expressed in grams of NaOH per liter in Figure 8. Tear indices at tensile strengths of 70 (curve 801) and 90 (curve 20 802). Figure 9 shows a similar trend between the tear index value and the residual pH at the same lye as in Figure 8; curve 901 for 70 and ·· · • V curve for tensile strength 902 90. Figures 8 and 9 thus clearly show that the specific fiber strength of the pulp increases by ··· 25 as the residual alkali and / or residual pH increases.

• • o • · · · · · · · ·

It should be noted that the pH and alkali values shown in Figures 8 and 9 are from laboratory batches. Under actual factory conditions, the pH and residual alkali values of soluble salts, · · · 30, and other substances are usually · · · · *; * lower than those indicated herein.

Figure 10 schematically illustrates an exemplary digester system for carrying out the invention. Like • · Γ *. 35 and FIG. 10 also show a single-cooker system 410 in which the present invention is implemented. The digester may be either a new device designed for the present invention 32 or an existing device modified for the present invention. Although the one-pot hydraulic cooker is described herein, it is clear that the multiple-pot system or the two-pot steam-liquor phase cooker is also suitable for use. One difference between the digesters shown in Fig. 10 and Figs. 3 and 4 is that the digester shown in Fig. 10 has an upstream cooking zone, for example a Hi-Heat ™ or EMCC® cooking zone, near the bottom of the digester. System 410 10 uses the same feed system 12, 15, 16, 17 and 18 as previously described. Again, in this system, the "bound" and "free" liquor stream, previously described in connection with Figure 4, can be referred to. These liquor flows as well as those described below are approximate. 15 Actual discharges vary, e.g. depending on the equipment used, the type of wood and the speed of production. The chips entering the feed system typically contain 2.2 cubic meters of bound fluid / BDMT pulp produced from cellulosic material, typically from hardwood or softwood chips. Structures similar to or similar to those shown in the previous figures are otherwise denoted by the same reference numerals, ·· · I but preceded by a "4".

· · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · . *. boil and lye suspension digester 419 • · ». *: ·. feed slot. The digester 419 has four screening devices • · · 80, 81, 85 and 95. These do not include the upper screening device, ... from which return flow 17 is fed to the high pressure feeder.

30 · Cooking liquor, ie kraft white liquor need only be added • · * ··· * little or no at all 38 times in cycle 17. Almost all or all of the cooking liquor: ***; ie 3.5 m3 / BDMT according to one example, added by ··· .1. 49 and 437 for the cooking zones below.

** · *! According to a preferred embodiment of the present invention, the cooking chemical, or effective alkali (EA, always expressed as NaOH or the like), is typically added to 33 vessels 419 by the addition of a spent cooking chemical containing residual EA from a subsequent cooking process. This waste liquor, e.g., kraft black liquor, is fed, for example, into port 17 through 93, top 5 of digester 419 through 94, or at any convenient point in the feed system, e.g., through loop 16 or chute 13 or chute silo 12, cf. Figure 3.

The suspension flows into the digester 419 and the excess liquor 10 is removed through the sieve and one 17 and returned to the high pressure feeder 15. The precipitated suspension is then conducted downwardly in the first "pretreatment zone". This suspension usually contains ca. 4.4 m3 / BDMT of free cellulose and 3.8 m3 / BDMT of free lye. In the pretreatment zone, the free lye flows in the same direction as the chips, i.e., the treatment occurs downstream. The effective alkali, expressed as NaOH, of the suspension entering this zone is about 20 to 25 g / L. The temperature of the suspension in this zone is about 80-130 ° C and the treatment time varies from 6 minutes to 4 hours; for example 0.5-2 hours.

The pretreatment step is virtually complete when the suspension is applied to one or more of the strainers 80. The suspension flows over: 25 passes the strainer 80 past the other zone. , which is the so-called. impregnation zone. In this zone, the lye is led in a direction opposite to the chipping stream, i.e.

• · · 'processing is done upstream. The liquor is removed as well. • from the upper pretreatment zone to the lower impregnation zone • ♦ · 1 .. ^ 30 through the sieve 80 to the 98. The combined stunning effective • ·:. * ·· alkali content removed from the sieve 80 is approximately 2 to 10 g / l. Relatively lean waste liquor from connection 98 is typically conducted to a pulp mill. ···. • · · 35, but it can first be expanded, for example, in an expansion vessel 99 to produce steam, or lead to a heat exchanger to heat the other fluid stream of the mill. This leach liquor stream 34 can also be used to pre-treat incoming chips, for example in chips 13 or chips 12, cf. Figure 3.

The impregnation zone has a heated circulation system 82 which removes lye from the end of the zone through one or more sieves 81 by means of a pump (not shown). Cooking liquor and waste cooking liquor are usually added to this cycle. For example, kraft white liquor diluted with wash-10 liquor is added together over 83 times at about 4.0 m3 / BDMT, with EA at about 50-100 g / L. Waste cooking liquor, preferably liquor removed from the subsequent cooking process, having an EA of about 20 to 40 g / L, is added together through 84 at about 3.0 m3 / BDMT. Addition of fresh cooking liquor to waste cooking liquor results in an EA value close to sieve 81 of about 20-30 g / l. Approximately 4.9 m 3 / BDMT of lye added through cycle 82 is led upstream through the impregnation zone and removed through screen 80 at a combined flow of about 8.7 m 3 / BDMT. The temperature of the suspension in this impregnation zone is about 100-170 ° C and the treatment time varies from 6 minutes to · · 2 hours. However, the impregnated chips of the suspension still contain approximately 4,4 m / BDMT of normally bound alkali.

Preferably, the suspension is heated to a boiling point of 140-180 ° C (280-360 ° F) by means of a heated cycle 82, after which the suspension enters the cooking zone.

In the cooking zone, about 2.1 m3 / BDMT of free lye is led: * Γ downstream with the chips. The chips, on the other hand, typically contain bound brine of 4.4 m3 / BDMT. This. in the zone, the chips are boiled downstream in the presence of fresh cooking liquor and · 82 spent cooking liquor added. The treatment time in the cooking zone ranges from 6 minutes to 4 hours, and is preferably more than 30 ···: * ·. · 35 minutes. The co-current cooking step ends when the suspension • comes to one or more of the strainers 85. Below the strainer 85, the suspension enters the upstream cooking zone. The waste cooking liquor from both the downstream and upstream cooking zones is removed through screen 85. At least some of the liquor removed through the screen 85 is pumped by a pump (not shown), heated and circulated through the circulation system 86 near the screen 85.

One important feature of the invention is that some of the waste liquor removed through the screen 85 is removed from the unit 86 through the 87 and used for pre-treatment 10 in the earlier cooking step. Preferably, the waste liquor having an EA of about 25 to 35 g / L (although it may be 10 to 60 g / L) is recycled through the ports 87, 90, 92 and 94 (or 93) to the beginning of the pre-treatment step. This hot liquor can also be used to heat other liquids or to generate steam. The hot waste liquor from the conduit 87 may, for example, be passed through a heat exchanger 89 and heated together with the cooking liquor fed through 437 or any other liquor stream that requires heating. Steam can also be generated from this hot liquor 20 by passing it through a single 90 to an expansion vessel 91.

• * · * ... · In the countercurrent cooking zone, chips containing ·· · - • *, ί about 4.4 m / BDMT-bound liquor are led to free ϊ #: *: upstream of the liquor, which is approximately ·· · 25 2.9 m3 / BDMT. The upstream cooking zone extends to one

• • M

• or more strainers 95. Free liquor is fed through a · · circulation system 96 connected to strainer 95 and through a wash liquor port 42 to the bottom of digester 419. The temperature of the upstream cooking zone suspension is from about 140 ° C to about 180 ° C and the treatment time ranges from 6 minutes to · 1 * 6 hours, and is preferably greater than 30 minutes. As • · loops 82 and 86, cycle 96 also removes waste cooking liquor ···: ... J through strainer 95 with a pump (not shown) and always supplies. ···. also some lye near re-strainer 95, after heating 35. As previously described, one feature of the invention is that some of the waste cooking liquor removed through strainer 95 is recycled 36 to 84 through the previous cooking step, in this case cooking circuit 82. The liquor removed through strainer 95 typically has an EA value of about 20- 30 g / l. Also, some cooking liquor, typically 0.5 m3 / BDMT, 5 is added to this circuit through 97.

Below the screen 95, the cooking process is virtually completed by adding the wash filter, i.e. the cold shot filter, to one of the 42 and two or more nozzles. The nozzles 10 are located at the bottom end of the digester 419. Typically, about 9.0 m3 / BDMT of filtrate is added to the bottom of the digester to stop cooking and cool the pulp before removing it. This filtrate is also typically added to a 2.0 m3 / BDMT white liquor feed line to dilute 437 white liquor 15 to effect Andritz

Inc. marketed and described in U.S. Patents 5,489,363 and 5,547,012, LO-SOLIDS® soup. The cooled pulp is removed from the digester 419 to a container containing 8.0 m3 / BDMT of free and bound liquor at about 10-12% sa-20 lb. absolute dry.

Thus, using a steaming machine 419, which may be a continuous · · · hydraulic or steam-phase digester, • ·; . ·. the suspension of cellulosic fiber and liquid • · · ** V 25 is continuously fed at the top of digester 419! but into the inlet, and the material is cooked in a digester typically 41 hours at about 140-190 ° C before the cooking is completed as described above.

... Cooking is carried out such that at least the last 30 minutes (and preferably at least the last 15 minutes, and most preferably at least the last 30 minutes), before the cooking is completed, The concentration of alkali (expressed as NaOH or equivalent) in the digester is at least 15 g / l, typically 15-50 g / l / preferably 18-40 g / l, and most preferably 20-35 g / 1. Also, at least at the first point or sieve 80 and at the second point or sieve 85, and preferably also at the third point or sieve 95 or more points, the first of which is closest to the inlet of the digester, the suspension is dehydrated and alkali can be added. During the treatment of the wood chips required for chemical pulping, more than 50%, preferably more than 70%, more preferably more than 80% and most preferably more than 90% of the total alkali added to the suspension is added after the first point 80. As shown in Figure 10, the alkali is preferably added from more than 10 from one and preferably more than two points, such as through tubes 83, 88, 97, Figure 10. The alkali is added from a number of different points and in such a manner that alkali profile. The alkali is preferably added such that the highest effective alkali content during cooking is less than 50 g / l, preferably less than 40 g / l, and most preferably less than 35 g / l. Prior to the addition of alkali, after the first point, i.e. the sieve 80, at least 5%, preferably more than 7%, more preferably more than 9%, and most preferably more than 11% of the effective 20 alkali calculated from NaOH on wood has already been used.

In the digester 419, the turns 86 and 96 and the connections 88 and 97 and: other conventional devices provide means for adding alkaline ··· · ··· 25 to the circuits 86 and 96 so that the effective · · · · ·. . ·. the concentration of alkali, expressed as NaOH, in the cooking zone • · · just before the end of cooking (which is by lowering the temperature by supplying the cold trickle filtrate with one ... 42, etc.) is 15-50 g / l, preferably about 18-40 · · · **] / 30 g / l, and most preferably 20-35 g / l. The devices may also include means for increasing the heat of the circuits 86 and 96, such as a conventional indirect heat exchanger 96 'and 88' • »: ***: or any suitable conventional liquid heating means. . *. men that can be used in the circulatory system. Heat Enhancement • · * ··· [35 for 88 'or 96' and Alkaline for 88 * · * * '' or 97 together control the final kappa number of pulp outlet 44 with a much shorter 38 feedback time than if the kappa number were conventionally adjusted 82 temperature. The screen 95 is connected to the circuit 96, and the device comprises means, such as one 84, and any conventional parts for reusing the liquid removed from the screen of the digester 5. The strainer is located closer to the suspension inlet at the top of the digester 419 than to the mass outlet port 44. This allows the bottom temperature of the digester to be more accurately controlled; for example, by using a high counter current, i.e., a higher "dilution factor", in the zone above the screen 95, the pulp temperature can be sharply reduced to stop cooking. If the kettle is unable to maintain a positive dilution factor between screens 85 and 95, the pulp temperature and boiling end can be better controlled by using 15 or 86 cycles 86 and 96. The dilution factor is a measure of the amount of lye displaced by the wash water. A positive dilution factor indicates that the washing liquid is used more than is required for total pulp fluid displacement. A negative dilution factor indicates no total displacement of the pulp fluid.

• · ·

The system illustrated in Fig. 10 illustrates an equally advantageous method required to implement the present invention; quantity and device. In particular, by feeding most or all of the · · · · · · · · · · · · · · · · · · · · · · · · · · · · to a later stage of the process and selectively circulating at least some alkaline waste digester • ♦ ♦ toluene to an earlier treatment or cooking stage, ... providing an advantageous high time lipid profile in the cooking process. As shown in Figures 11-13 and 15-17, the results of laboratory and factory measurements ensure that this high alkali content: ***: produces cellulosic pulp with high strength and brightness values ··· impaired.

Figures 11 to 13 illustrate the results of laboratory tests on the pulp produced in accordance with the present invention. In these 39 laboratory tests, the treated wood chips were Scandinavian coniferous and were treated under the following conditions: the pretreatment step took about two hours at about 100 ° C and the EA content decreased from about 20 g / L to about 8 g / L. The impregnation step lasted about one hour at about 125 ° C and the EA content was about 20 g / L. The pretreatment and impregnation steps were the same in all soups. The cooking step took about two hours at various temperatures and EA concentrations to obtain the target number of 25. At the end of the impregnation step, different amounts of alkali (0-27% EA based on wood) were fed to provide different concentrations of EA in the cooking step. All laboratory tests were downstream.

Figure 11 is a tear index curve at a tensile strength of 100 to 70 Nm / g for the residual alkali of the waste cooking liquor at the end of cooking. As the results show, the amount of residual alkali raised in accordance with the invention increases the tear index, which is a measure of the specific fiber strength.

Fig. 12 is a brown mass lightness (ISO) curve 101 for the residual alkali retrieved in Fig. 11. Fig. 12 • · · j · * indicates that the addition of residual alkaline increases the brightness, · · · · · ·! which also demonstrates the merits of the present invention.

• 2 S

Fig. 13 is a reject content curve 102 with respect to the residual alkali of the pulp shown in Figs. 11 and 12. "Reject" is the amount of uncooked wood which is manifested in the pulp obtained as fines or small wood slats. The less re- ···. The result is 30 milliliters, the more complete the cellulose soup and the less wood is wasted. As you can see • · * *. 'Kyy, as the amount of residual alkali remaining in the cooking process increases, the percentage of reject decreases.

• · · • · • · · ·. ·. Figure 14 illustrates another preferred embodiment of the present invention and compares it to a conventional system. The difference between the systems is that in one system, white liquor was added to the two system cycles in addition to the feed system and bottom circuit. This feeding of white liquor later in the process increased the EA of the liquor in the first cycle from 20 g / l (expressed as NaOH) to 35 g / l and the EA of the liquor removed from the digester from 10 g / l to 25 g / l . Throughout this specification, the total chemical concentration is expressed as the corresponding concentrations of NaOH, unless otherwise stated.

The spout system 510 depicted in Figure 14 comprises a conventional feed system 511, a conventional impregnation vessel IV 512, and a continuous steam phase cooker 513 having two heated liquor cycles 520 and 530. During the test runs of this invention, 15 piston chips were fed, slurried with cooking liquor 515, pressurized and fed 516 to the top of the impregnation vessel IV 512 at a temperature of about 116-119 ° C. The hot suspension of chips and liquor 20 was passed downstream of the impregnation vessel IV 512 and discharged therefrom via the liquor fed through 517. More white liquor was fed to the 517 through 518 • · ·:. * So that the effective alkali in · · · · · · · · · · · · and the effective alkali fed into the digester into one of the chips #> * j ′ 25 through 519 was about 30 g / l. and the reference method.

• · · · · · · · · ·

A heated suspension containing cooking liquor was fed. *! *. at the top of digester 513 at a temperature of about 127 ° C to about 129 ° C.

. ** ·. 30 Excess lye was removed from the suspension through the first · · · / # # decalcifying strainer (not shown) and passed • · · * · ** through 517 back to the bottom of impregnation vessel IV 512 ··· to form lye which carries chips to digester 513 This circulating system also had a compound 517 'through which some lye compound 517 could be fed to the top of the impregnation vessel IV 512 to facilitate chip movement and improve the fluidity ratio at the top of the impregnation vessel IV as needed. The suspension fed to the digester 513 was then led downstream to the first cycle 520, or "control loop", which included the first slipper-5 filter 521, the drain and recycle connection 522, and the heater 523. In the reference method, no fresh cooking liquor was added about 20 g / l. In the tests performed in accordance with the present invention, white liquor was added to connector 522 through 524 10 so that the amount of effective alkali in the 520 test run was about 35 g / L, or about 75% higher than conventional methods.

After strainer 521, in each system, the suspension, now heated to a cooking temperature of about 160-170 ° C, continued to flow and heated in the first cooking zone of the digester. The first cooking step ended with the suspension entering the second and third liquor removal strainers 525 and 526. The cooking liquor was removed from the suspension with strainers 525 and 526 and led through 527 to the conventional expansion tanks 528 and • · * ··· * 529 to develop steam · :. * leading to chemicals and heat recovery.

The second firing liquor rotor was connected to the screen 526]: Thu 530 or "extinguishing cycle" comprising the recirculation nozzle 531 and the heating device 532. According to the tested method of the invention and, unlike the reference method, more white liquor was fed through 533 to 531.

• · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · ϊ included to continue cooking in the counter current zone.

··· • · • ·. · [; 35 The system shown in Figure 14 is a schematic view of an existing cooking system. Because the piping needed to carry out the invention was not available 42, i.e., piping that could recycle the alkaline waste liquor from the common 527 to the impregnation vessel 512, the invention was simulated by adding alkali to cycles 520 and 530. This resulted in an alkaline content of about 25 g / l. According to the invention, this relatively high alkali vapor in the conduit 527 is preferably fed, for example, into the impregnation vessel 512 to replace the effective alkali from the fresh white liquor in the conduits 515 and 518. However, this could not be done in the experiments. However, the potency of the high alkali content at the end of the cooking was evaluated by feeding additional alkali through the terminals 524 and 533, which resulted in a higher alkali content in the waste-liquor medium 527.

15

The actual alkali additions used in these experiments, calculated as the effective alkali from the wood, were about 13% for feed to pipeline 515, about 7% for bottom cycle through pipeline 518, about 5% for cycle 522 or 20 "control cycles" through 524 and n. 5% to Circuit 531 or "Shutdown Circuit" through one 533. The total increase ··· · ... · calculated from the tree was thus about 30% in this experiment. This ·· · • \ i is more than the typical total increase of 20%: for example 13% and 7% in the basic tests of this experiment. True ··· · ··· 25 actually added alkali throughout the process are displayed ····. . *. in the implementation of the present invention, about 20%, i.e. 18-22%, which is conventional. Alkali is preferably added in subsequent steps of cooking. However, by using a relatively high alkaline content and thus a high pH of · · · 30 at the end of the cooking process, a waste liquor with a relatively high alkaline content and pH is obtained. This high alkali waste liquor is preferably used as a source of alkali in the lower cooking stages.

Thus, according to the present invention, when using high-waste liquor with high lipid content, cellulose is exposed to an effective alkali (calculated from wood) with a content higher than 20%. , typically more than 25%, or even more than 30%, even though fresh cooking liquor is not fed at the usual rate of 20% (based on wood). Alternatively, by using some of the 5 effective alkali supplied to the post-cooking stages, some fresh cooking liquor can be fed to the system while still maintaining the same cooking degree. In other words, by utilizing this invention, a pulp mill can save on the use and cost of chemicals.

10

After strainer 526, the suspension was fed to the countercurrent cooking / washing zone, i.e., the Hi-Heat ™ wash zone of Andritz Inc. (Glens Falls, New York), at the bottom of the stove 513. Although the actual treatment of this zone was the countercurrent displacement of 15 cooking liquors with washing liquor, the supply of boiling liquor to circulation 530, i.e. the EMCC® wash marketed by Andritz Inc., resulted in additional boiling in this zone. The Hi-Heat phase ended when the cooked slurry came on strainer 534. The filtrate 526 used in countercurrent wash zone 20 was fed through nozzles 535 to the bottom end of the digester. The brown pulp was unloaded into a · · ·; ... · 527. The pulp was then bleached using the val-: **: sequencing 0-0-D0-E-D1-D2.

• • • • • • • • • · · · · · · · · · · · · · · · · · · · · · · · · ·. Although it is advantageous to supply at least some alkaline ····. . ·. to the final countercurrent cooking / washing zone • · · to maintain the desired alkalinity and pH, the lack of processing • * · power can sometimes render the addition of alkali unnecessary. Ideally, any alkali coming into the countercurrent • · · *] / 30 zone should be separated from the chips to the liquor and removed through strainer 526. However, when the displacement or alkali separation from the chips is uneven, some alkali and excess heat may · · · remain in the downstream application. This alkaline and thermal; **. 35a may be sufficient to provide the desired alkalinity and pH according to the present invention. This was the case in the digester where these test runs were performed. Although 44 no alkali was added in the vicinity of strainer 534, sufficient alkali and heat (about 130 ° C) were retained to maintain the alkalinity and pH of the countercurrent cooking / washing zone.

5

When testing the system of Figure 14, the washing cycle (not shown) with the screen 534 was on, but the flow rate was very low.

A comparison of the results obtained with coniferous wood using the prior art method and the method according to the invention (Figure 14) is shown in Figures 15, 16 and 17.

The production rate during the test was about 600 ADMT / D (or metric tons of dry air per day). The number of pieces during the experiment 15 was relatively well controlled, 24-30. To obtain this Kap return, the cooking temperature was reduced by 5 ° C compared to the prior art by the new method of delivery of the cooking chemical.

Figure 15 shows the variation in the consumption of bleaching chemicals and ... the brightness of the final bleached pulp during the trial. (Birch chips were treated outside this section; hardwoods usually require less potency •, ·::: · rusting chemicals, i.e. have a higher bleaching ...: 25 than softwoods.) The abscissa indicates the service life; left-side ·. ·. · side ordinate for chlorine dioxide (D) relative • · · ί.ί: total consumption; the right ordinate in ISO units for the final bleached pulp. Conventional cooking took place on either side of 103 experiments (high concentration of effective. ** · .30 alkaline). The consumption of chlorine dioxide is indicated by the vertical bars 105. The final brightness is indicated by a solid line 106. As can be seen, the consumption of chlorine dioxide clearly decreases after the experiment is started. hour 7. There is also a clear increase in the final brightness of the · · · ·! 35 because the adjustment of the bleaching chemical · · reacts belatedly to the reduced bleaching chemical requirement of the pulp used in the experiment, but when lightness is stabilized, chlorine dioxide consumption decreases by about 9%: This occurs even if the kappa numbers (not shown) are higher than the reference soup during the trial period.

Fig. 16 illustrates an increase in bleached pulp strength 110 according to the present invention, compared to a reference cooking 111. The abscissa of Figure 16 shows the tensile strength of the paper in Nm / g. The ordinate has a tear strength of Nm 2 / kg. This curve clearly shows that the tear strength 110 of the paper produced by the process of the present invention is greater than the tear strength of the reference pulp. For example, at a tensile strength of 90 Nm / g, the tear strength of the pulp of this invention is about 20% higher than the reference pulp.

Figure 17 compares the bleached "sweat" or dry specific volume of paper as a function of tensile strength. This paper is made from pulp made with these two methods. The bulk of a sheet of paper is the ratio of the thickness of the sheet to its weight per unit area, and is expressed in units of · · · · ... · volume per weight; in this case, • cubic meters per tonne (mVt). Bulk indicates sheet density; a low bulk corresponds to a high density. Figure 17 ··· 25 shows that ····. the bulk paper 112 produced is about 5% higher than the reference paper bulk 113 at a given tensile strength. This * * · means that the fine paper of the present invention ... can in some situations be lightened (grams of mass · · · 30 per square meter of paper) while still maintaining the same quality.

Thus, it is clear that the high alkaline cooking cellulose cooking method disclosed in this application. can be well combined with several existing systems; **. 35 · · · ** * · to produce a stronger chemical pulp than that produced by known techniques. Although the invention has been described and described herein in the light of what is currently considered to be the most practical and preferred embodiment, it will be apparent to one skilled in the art that many modifications are possible within the scope of the invention. covers all related processes, products and systems.

··· • · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · ·–back Li pieces - · ♦ · • 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 · · · · · · · · · · · · · · ·

Claims (27)

47 A method for the continuous production of a chemical pulp by an alkaline cooking process from pulverized cellulosic fibrous material comprising the following sequential steps: a) feeding the pulverized cellulosic fibrous material to a processing vessel (19, 119, 219, 319, 419) from an upper portion thereof; B) feeding the first cooking liquor to a processing vessel (19, 119, 219, 319, 419) having a first effective alkali content of greater than 10 g / l; c) treating the comminuted cellulosic fibrous material with a first alkaline cooking liquor at a temperature below the subsequent cooking steps such that the first cooking liquor consumes alkali and the first alkaline waste cooking liquor is formed; : ***: 20 (d) removing the first alkaline waste cooking liquor from cellulosic fibrous material; · ·: (E) feeding a second cooking liquor to the cellulosic fiber material to process said cellulosic fiber; (F) cooking the cellulosic fibrous material with another cooking liquor at a cooking temperature of about 140 ° C to about 180 ° C to produce a pulp which produces: another alkaline waste cooking liquor; • · ·. * ·· (g) removal of the second alkaline waste cooking liquor • · · from the pulp; j *** j h) adding washing liquor to the pulp to cool and / or wash it before removing the pulp from the cooking process; 48 i) feeding at least a portion of the second waste cooking liquor to the first cooking liquor in the processing vessel (19, 119, 219, 319, 419) in step b); characterized in that the second cooking liquor contains 5 at least 50% of the total alkali consumed in the chemical pulping of the cellulosic fibrous material and that the effective alkaline content of the second alkaline waste cooking liquor removed in step g) and used in step i) is 18-50 g / l; and the effective alkali content of the first waste cooking liquor removed in step d) is about 10 g / l or less. A method according to claim 1, characterized in that the impregnation treatment of step c) is carried out at least partially in one downstream treatment step. Method according to claim 1 or 2, characterized in that the second waste cooking liquor from step g). 20 is cooled before using as the first cooking liquor ·· «in step c). The method according to claim 1 or 2, characterized by the fact that other possible liquids, such as, for example: * · *: 25 coli or green liquor are added to the fiber for processing in step c). ··· • · · · · »··· Σ J The method of claim 1 or 2, ··· '. : characterized by the fact that another cooker used in step e) • ·. · * ·. 30 pe contains at least 80% and more preferably at least 90% · · · · of fresh alkali used in the chemical pulping of cellulosic fiber material. • ·· • · 49 Method according to Claim 1 or 2, characterized in that softwood pulp to be bleached is produced. Process according to claim 1 or 2, characterized in that the second waste cooking liquor produced in step f) has an alkali content higher than 20 g / l, more preferably higher than 25 g / l. Process according to claim 1 or 2, characterized in that in step c) more than 25%, more preferably more than 50% of the total alkali consumed by the cellulosic fiber material is consumed by the alkali. Method according to Claim 1, characterized in that step c) is carried out in addition to one downstream step in at least one upstream step. The method of claim 1 or 2,. 20 characterized in that step f) is performed in more than • · · · · jV. in one upstream and / or downstream phase. The process according to claim 1 or 2, characterized in that the effective cooking alkali content of the second cooking liquor is greater than 25. g / 1. : Method according to claim 1 or 2, • · · ί! characterized in that all steps a) - h) are carried out in a ··· '' 'continuous cooker (119, 219, 319, 419) and / or • ·. **. 30 in impregnation vessels (19, 119). • · · • · · · · A process according to any one of claims 1 to 12, characterized in that the process is carried out in a single-stage hydraulic or vapor-liquid-phase digester (219, 319, 419). A method according to claims 1-12, characterized in that the method is carried out in a two- or multi-vessel hydraulic or vapor-liquid phase digester (119). Method according to claim 1, characterized in that step c) is carried out in a first processing vessel, so-called. in the impregnation vessel (19, 119) at least partially downstream that between the steps c) and d) the cellulosic fibrous material is removed from said impregnation vessel (19, 119), that step d) is carried out after said impregnation vessel 15 (19, 119); c) and e) in a second treatment vessel so-called. the digester. Method according to claim 1 or 2, characterized in that the method is carried out in a two-vessel * · '• · · • V. in a vapor-liquid phase digester (119), wherein steps a) - c) are performed mainly in the impregnation vessel (19, 119) and steps (d) - h) after the impregnation vessel (19, 119). • · · · · · · · · · mi: 25 Method according to Claim 1 or 2, characterized in that it is carried out in a two-pot steam / phase or hydraulic cooker (119) having an impregnation vessel (19, 119). ) and a digester (119) for removing liquor at two points, 30 of which are removed from the first point for the recovery of the liquor and for the latter • M. · * ·. the lye removed from this point is recycled to the first • · ·. ·, the point of removal to the earlier addition point in the process, with a concentration of effective alkali greater than 18 g / l removed from the latter point and the first lye removal point is and that the impregnation vessel (19, 119) has a counter current processing zone. 5 Method according to Claim 1 or 2, characterized in that it is carried out continuously in a double-pot steam-phase or hydraulic digester (119) having an impregnation vessel (19, 119) and a digester (119), wherein the liquor is removed at two points, the lye removed from the point is removed to recover the lye and the lye removed from the latter point is recycled to the first addition point in the process, and that the effective alkali content of the latter is higher than 18 g / l and the impregnation vessel (19, 119) the lye removal is performed after the impregnation vessel (19, 119). Method according to claim 17 or 18, characterized in that the liquor removed from the latter outlet is cooled during recycling. The method according to claim 17 or 18, characterized in that the first exit point to the earlier addition points is fed from the latter to the exit point. *: other possible liquids, such as white liquor or green liquor, in addition to the liquor removed from the tea. • · • · · «♦ · • · The method of claim 17 or 18,. characterized by the fact that the first lye removal point was · · ···. ·. 50%, more preferably at least 80%, and most preferably 52 at least 90% of the fresh alkali used to make the chemical pulp of the cellulosic fiber are fed to the cellulosic fiber material. Process according to claim 17 or 18, characterized in that the alkali content of the liquor removed from the latter liquor removal point is higher than 20 g / l, more preferably higher than 25 g / l. A method according to claim 17 or 18, characterized in that more than 25%, more preferably more than 50% of the total amount of alkali consumed by the cellulosic fiber material is consumed before the first lye removal point. Method according to claim 17 or 18, characterized in that after the first lye removal point the temperature is raised to a cooking temperature of 140-180 ° C. A method according to claim 17 or 18, characterized by: ***: 20 characterized in that the latter liquor depletion point ϊ is preceded and / or followed by more than one counter-and / or! ϊ: low current phase. • · · · ··· · · · 26. A digester system for the continuous production of chemical pulp by an alkaline digestion process from pulverized cellulosic fibrous material, comprising a system (12, 15) for supplying a finely divided cellulosic fibrous material to a processing vessel (19, 119). 219, 319, 419) • · 30 to the top,. ···. means (38, 16, 18; 38, 16, 18) for supplying a first alkaline cooking liquor to said processing vessel (19, 119, 219, 319, 419), 53 means (26, 53, 265) means (45) for removing the first alkaline waste cooking liquor from the cellulosic fibrous material, means (28) for supplying the second alkaline cooking liquor 5 to the cellulosic fibrous material, , 18) for recycling said second alkaline waste cooking liquor as the first alkaline cooking liquor back to the upper end of the treatment vessel (19, 119, 219, 319, 419), said treatment vessel being a downstream impreg-15 treatment vessel (19, 119) connected to said second waste cooking liquor recycling equipment such as lye and cellulose fiber es flow downstream that the digester system includes a second processing vessel 20 so-called. a steaming machine (119), the impregnation vessel (19, 119) being provided with means for transferring the cellulosic fiber material to a second processing vessel (119), and The digester system is provided with means (26, · · · v: 25,153) for removing the first waste liquor from the cellulosic fibrous material at a point located outside the impulse vessel (19, 119). • · · • · • »• · · A digester system according to claim 26, characterized by the fact that the digester (119) is provided with means ···. ···. (26, 153), the removal of said first waste cooking liquor. : sex among cellulosic fibers. • ·· «· 54