FI121787B - Method and apparatus for continuous pulping - Google Patents

Description

METHOD AND EQUIPMENT FOR THE CONTINUOUS MANUFACTURE OF PULP

According to conventional knowledge, the level of dissolved organic material (DOM) in cellulose kraft cooking is known to have a deleterious effect in the later stages of the cooking process because it complicates the delignification process due to wear of the active cooking chemical in solution before reacting with wood residual lignin. The dissolved organic material, DOM, consists mainly of dissolved hemicellulose and lignin but also of dissolved cellulose, extractives and other material extracted from wood in the cooking process. The effect of DOM concentration in earlier stages of cooking is considered to be insignificant according to traditional knowledge. The adverse effects of DOM in the subsequent stages of cooking can be minimized by some prior art leaching methods, in particular by using the 15 Andritz lnc.NCCC EMCC® from Glens Falls, New York, since the countercurrent flow of the solution (also containing white liquor) decreases DOM and at the end of the "bulk delignification" during "residual delignification".

In accordance with the present invention, it has been found not only that DOM has an unfavorable effect on the soup at the end of the cooking step, but also that the presence of DOM adversely affects the strength of the pulp produced at any stage of the cooking process - i.e., beginning, middle or end of bulk delignification. The mechanism by which DOM affects pulp fibers and thus adversely affects the strength of pulp produced at any stage of the cooking process is not fully understood, but is believed to be due to the reduced mass transfer rate of alkali-extracted organic: Y: 25 through fiber walls. due to: ***: that the DOM surrounds the fibers, and the crystalline and amorphous regions of the fibers (i.e.

· · Nodules). In any case, according to the invention, it has been shown that if the DOM level (concentration) is minimized throughout the cooking process, the strength of the pulp increases significantly. According to the invention, it has been found that if the DOM level is close to zero throughout the ... 30 kraft soups, the tear strength of the pulp is greatly increased, i.e. up to about 25% (e.g. 27%) • · · **! / 11 km: n tensile strength compared to conventionally made kraft pulp. Even lowering the DOM • · * ··· level to half or a quarter of the normal level significantly increases the mass: * ·. · Strength.

In prior art kraft soups, it is common for some * · · stages of cooking to have 130 grams per liter (g / l) or more and 100 g / l or more for several stages of kraft cooking * ... · (for example, Andritz Inc. MCC® Skimmer Bottom, Adjust, Up and Main Removals, and MC) even though DOM levels are maintained at 30-90 g / l 2 wash cycles (conventionally known in subsequent cooking stages). In such traditional situations, it is also common for the DOM-level lignin moiety to be greater than 60 g / l or even more than 100 g / l, and for the DOM-level hemicellulose moiety to be well above 20 g / l. It is not known whether the dissolved hemicellulose moiety has a more pronounced adverse effect on pulp strength -5 e.g. because it adversely affects the transport of organic matter from fibers - than lignin or vice versa, or whether the effect is synergistic but the dissolved hemicellulose is suspected to have a significant effect.

According to the invention, for the first time it has been found that the DOM content should be minimized throughout the kraft cooking so as to have a positive effect on the bleaching of the pulp, reduce chemical consumption and perhaps most significantly increase the strength of the pulp. By minimizing DOM levels, it is possible to design smaller passageways that still achieve similar throughput. This can also provide some of the benefits of renters with batch cooking systems. Many of these useful results can be anticipated by maintaining a DOM level of 100g / L or less for substantially all of the kraft cooking (i.e., at the beginning, middle and end of bulk delignification), and preferably at or below 50g / L (closer to zero DOM level). the better the results are). It is particularly desirable to maintain a lignin content of 50 g / l or less (preferably about 25 g / l or less) and a hemicellulose content of about 15 g / l or less (preferably about 10 g / l or less).

20

According to the invention, it has also been found that it is possible to at least largely passivate the adverse effects of the DOM content on pulp strength. According to this embodiment of the invention, it has been found that if the black liquor is removed and subjected to a pressure heat treatment according to U.S. Patent No. 4,929,307, e.g., at about 170 to 350 ° C for 25 (preferably at 240 ° C) for about 5 to 90 minutes. (preferably for about 30 to 60 minutes): * · * and then fed back, tear strength up to 15% can be increased. The mechanism by which DOM passivation by heat treatment occurs is also not fully understood, but it is consistent with the above hypothesis and has a noticeable and powerful effect on mass strength.

According to the invention, various methods for increasing the strength of kraft pulp, both for flow and batch cooking, are provided, taking into account the above adverse effects of DOM on strength. The invention also provides kraft pulp with increased strength ·: ··· and a device for achieving the desired results according to the invention.

Furthermore, according to the invention, the H-factor can be significantly reduced. It is possible to · · · '* [** reduce the H-factor by at least 5% to achieve a certain kappa number. Also, the amount of effective · · * ··· * effective alkali consumed can be significantly reduced, e.g., by about 0.5% calculated from wood (e.g., about 4%) to achieve a certain kappa number. In addition, 3 bleaches can be added which, for example, increases the ISO brightness by at least one unit of a given full sequence kappa factor.

According to one embodiment of the invention, there is provided a process for making kraft pulp 5 by cooking comminuted cellulosic and fibrous material. The method comprises the following events occurring during the various stages of material kraft cooking: (a) separating a solution having a DOM level significant enough to adversely affect the pulp strength, and (b) replacing part or all of the solution with an effective DOM to increase pulp strength. is substantially lower than the DOM level of the separated solution. Step (b) is typically accomplished by replacing the removed solution with a solution selected from the group consisting essentially of water, essentially DOM-free white liquor, pressure heat treated black liquor, washing filtrate, cold gauze filtrate, and combinations thereof. For example, during at least one cooking step, the black liquor may be removed and treated under pressure and heat (e.g., at a pressure of about 170 to 350 ° C for about 5 to 90 minutes and at least 20 ° C above the cooking temperature) to significantly inactivate the adverse effects of DOM. The term "effective DOM" as used in the specification and claims refers to that portion of the DOM that affects pulp strength, H-factor, effective alkali consumption and / or bleach. A low effective DOM can be achieved by 2 0 passivation (except for bleaching) or by initially having a low DOM content.

The method according to the invention may be implemented in a vertical spout, where, in the case of · · ·: V, steps (a) and (b) may be carried out on at least two different levels of the digester.

Typically, a further step (c) is also carried out in which the replacement solution from step (b): V: 25 is heated to substantially the same temperature as the removed solution before contacting the replacement solution with the material to be cooked. Steps (a) and (b) can be performed during impregnation, around the beginning of the cooking, during the middle of the cooking, and around the end of the cooking, i.e. substantially throughout the bulk delignification.

According to another embodiment of the invention, the kraft cooking process includes the following steps at the beginning of cooking: (a) separating a solution having a sufficient DOM level to adversely affect the strength of the pulp, and () (b) in order to increase the strength of the pulp, replace part or all of the solution with a solution of: · · ·: ·· | the effective DOM level is substantially lower than the DOM level of the separated solution.

According to another embodiment of the invention, the kraft cooking process comprises impregnating a cellulosic fibrous material with the following steps: (a) separating a solution having a DOM level sufficient to adversely affect the strength of the pulp 4; and (b) replacing some or all of the separated solution with a solution having an effective DOM level substantially lower than the DOM level of the separated solution to increase pulp strength.

According to yet another embodiment of the invention, the kraft pulping process comprises the steps of: (a) separating the black liquor from the pulp at a particular cooking stage; (b) pressurizing the black liquor to a temperature sufficient to substantially passivate the adverse effects of the DOM contained in the black liquor on the pulp strength; and (c) feeding the DOM-inactivated black liquor to the pulp 10 at a certain point.

The invention also includes kraft pulp, which is prepared by the above methods. This kraft pulp is different from previously made pulps in that its tear strength is up to 25% higher at a given tensile strength of the fully ground pulp (e.g. 9 km at 15 tensile strength or 11 km at tensile strength) (and at least about 15% higher) has been prepared under identical conditions without the DOM storage or removal steps of the invention, or at least 15% higher (e.g. at least about 10% higher) when passive black liquor is used.

The invention can also be applied to a kraft batch cooking of cellulosic fibrous material using a black liquor container and a batch digester containing the material. Such a kraft batch cooking method according to the invention comprises the following steps: (a): * Pressurizing the black liquor in a vessel to a temperature sufficient to passivate the · · DOM adverse effects on the pulp strength, and (b) feeding the black liquor into the digester; with cellulosic fibrous material therein.

: * · *: Step (a) is carried out by heating the black liquor under high pressure at a temperature of about 170 to 350 ° C for about 5 to 90 minutes (typically at least about 190 for 30 to 60 minutes and at least 20 ° C above the boiling point) temperature), and step (b) • · · can be performed by simultaneously feeding black liquor and white liquor to the digester ... 30 to effect cooking of cellulosic fibrous material.

According to another embodiment of the invention, an apparatus for kraft cooking of cellulosic pulp is provided. The unit consists of the following parts: vertical spout; at least two • · ·; ··· removal / separation strainers located at different levels of the digester and at different cooking stages; a recycling line 35 and a separation line communicating with each target; and a means for introducing a replacement solution into the recycling line to supplement the solution removed from the discharge line. Each • · * ··· * recycling line typically includes a heater, and the kettle may be associated with a separate impregnation vessel, which also removes and replaces the DOM-rich solution with 5 less DOM-containing solutions (the feed line also communicates with the impregnation vessel top and high pressure shutter) .

The invention also relates to a commercial method for carrying out a kraft cooking of comminuted cellulosic fibrous material in step (a), wherein a substantially non-DOM-containing solution is continuously contacted and removed to the end of the kraft cooking of the material, thereby producing pulp of at least 100 tons per day. This process is preferably carried out using a batch digester with a capacity of at least 8 tons per day (e.g., 8-20) and performing step (b) preceding step (a) 10, wherein the digester is filled with cellulosic material, and step (c) following step (a), where kraft pulp is removed from the digester. The invention also relates to a batch cooking system for implementing this embodiment, wherein each digester has a production capacity of at least 8 tons per day (meaning commercially achievable, not laboratory).

15

The invention also relates to a modification of several different types of cookers, conventional MCC® Andritz Inc. cookers, or EMCC® Andritz Inc. cookers which can significantly dilute the effective DOM of a cooking solution during at least one early or intermediate stage of cooking. By following the separation and recycling screens in a certain way, the conventional results of the invention can be achieved with all conventional types of dispensers, which include a single-vessel hydraulic kettle, a two-vessel hydraulic kettle, etc., by simply controlling different fluid streams and feeding a low DOM. diluent solution and / or white liquor at certain stages.

The object of the invention is primarily to produce an increased strength kraft pulp: 1 2 3: and / or also typically to reduce H-factor and alkali consumption and to increase bleaching.

This and other objects of the invention will be apparent from the detailed description of the invention and the appended claims.

Fig. 1 is a schematic representation of an exemplary embodiment of a kraft cooking apparatus according to the invention for implementing the exemplary methods of the invention; Figures 2 and 3 are graphical representations of the strength of the pulp according to the invention. 35 compared to the strength of the pulp manufactured under identical conditions but without application of the invention; • · • · ♦ ♦♦ 6

Figure 4 is a schematic view of an exemplary apparatus for the improved kraft batch cooking method of the invention; Figure 5 is a schematic side view of another exemplary batch digester embodiment of the invention;

Figure 6 is a graphical representation of the H-factor of the pulping according to the invention compared to the H-10 of the kraft pulp prepared under the same conditions without applying the invention;

Fig. 7 is a graphical representation of the effective alkali consumption of the pulping according to the invention compared to the effective alkali consumption of the kraft pulp prepared under identical conditions; 15

Fig. 8 is a graph of effective alkali consumption at different percentages of factory liquor in a DOM-free solution;

Fig. 9 is a graph comparing the brightness of the pulps 20 prepared according to the invention under identical conditions to the brightness of the pulp produced without applying the invention;

Figures 10 - 14B are still graphical representations of various strength aspects of the pulp: V according to the invention, which are compared in Figures 12A-B to kraft pulp made without the invention under identical conditions. lujuusaspekteihin; • · ♦ · • · · ···

Figure 15 is a graph of DOM concentrations based on the actual lye analysis of laboratory soups using three different sources of solution at different stages of cooking; Fig. 16 is a schematic representation of an exemplary digester of a two-stage hydraulic • · * ··· 1 cooking system applying the invention; Figure 17 is a graphical representation of a theoretical study comparing DOM content in 35 conventional MCC © diggers to DOM content in Figure 16 digester; • · · • · · · · · · · · · · · · · · · · · · · · · · · · · · · 7

Figures 18-20 are schematic representations of other exemplary digesters of the invention; and Figures 21 to 25 are graphical representations of theoretical studies of variable dilution and resolution parameters using the digester of Figure 19.

Figure 1 shows a two-pot hydraulic kraft cooker system, such as that sold by Andritz Inc. of Glens Falls, New York, 10 adapted to apply the exemplary methods of the invention. Of course, any other existing cooker systems, including single-pan hydraulic cookers and single- and double-cooker steam cookers, can be modified to suit the invention.

In the exemplary embodiment shown in Figure 1, the conventional impregnation vessel (IV) 10 is connected to a traditional vertical spout 11. The water-chopped cellulosic fibrous material is transported from the conventional high pressure barrier feeder through line 12 to the top 10 of the According to the invention, in order to reduce the DOM content (in this specification and claims, the dissolved organic material is defined as consisting mainly of dissolved hemicellulose and lignin but also dissolved ···: V cellulose, extracts and other material extracted from wood * · in the kraft cooking process) (or from the top of vessel 10): V: 25 and processed in step 16 to remove the DOM or certain of its components, or: * · *: to inactivate. Step 16 may comprise a precipitation step (e.g., lowering the pH to below 9), an absorption step (e.g., a cellulose fiber column or activated carbon) or means for filtration (e.g., ultrafiltration, microfiltration, nanofiltration, etc.), extraction with solvents, eg radiation bombardment), supercritical extraction, ... 30 gravity separation or evaporation (followed by condensation).

The replacement solution may or may not be added (eg after step 16) to line 13: * ·. · Pump 14 in line 17 depending on whether the impregnation is performed in a downstream or an upstream direction. .

• ·

In place of the treated separated solution in step 16, a replacement solution may be added in line 17. 35 dilution solutions, e.g., fresh (i.e. essentially DOM-free) white liquor, · · · '! ** water, wash filtrate (e.g., brown mass wash filtrate), cold trap filter, or combinations thereof. If it is desired to increase the sulfidicity of the solution 8 to be recycled in lines 12 and 13, black liquor may be added in line 17, but the black liquor must be treated to effect the passivation of the DOM therein, as will be described below.

In any case, the DOM content of the solution removed in line 15 is relatively high, while the effective DOM level of the solution added in line 17 is much lower so that the pulp strength can be positively affected.

Also, in the impregnation vessel 10 itself, the DOM is preferably controlled using conventional 10 strainer 18, pump 19, and feed back assembly 20. In each of the 20 recyclable solutions, a dilution solution as indicated by arrow 21 is added to dilute the DOM concentration. The diluent also contains at least some white liquor. In other words, the effective DOM level of the solution to be fed back to one through 20 is substantially lower than the DOM level of the solution to be discharged through screen 18, and has at least some white liquor. The processing step 16 '- as well as the step 16 - can also be carried out in the assembly 20, as indicated by the dotted line in Fig. 1.

The slurry of the finely divided cellulosic fibrous material is conveyed from the lower part of the impregnation vessel 10 through line 22 to the upper part of the digester 11, and as is known, a portion of the slurry solution 20 is removed in line 23 and white liquor is added at 24. The solution passes through heater 25 n 10 through line 26 and / or fed near one of the starting ends 22, such as · · ·: V is indicated by line 27 in Figure 1.

In existing dishwashers, the solution is usually removed at different levels of the digester, • it is heated and then fed back to the level at which it was removed.

However, under normal circumstances, the solution will not be separated from the system or replaced [·; ·. fresh solution with a reduced DOM level. In existing digesters, black liquor is separated in the middle of the digester, but the black liquor is not fed back but ... 30 is transported to the expansion tanks and from there to the recovery boiler or the like. Unlike the existing · · · · ** * in the present dispenser, the solution of the present invention has 11 solutions • · * * ·. ·: Separated at various levels and heights and replaced by a solution containing less DOM: · · · ·. This is done at the beginning of the soup, in the middle of the soup and at the end of the soup. Using the digester 11 shown in Fig. 1 and applying the invention. 35, the strength of the finished pulp to be removed in line 28 is higher than the conventional kraft pulp treated in an existing stern when otherwise treated in identical conditions.

9

The digester 11 includes a first set of outflow strainers 30 located at the top of the digester, a second screening set 31 for middle stages of cooking, and a third and fourth screening set 32, 33 for final stages of cooking, the screens 30-33 are connected to pumps 34-37 located in recycling lines 38-41. , which may include 5 also heaters 42 - 45. Recycling lines per se are traditional. However, according to the invention, part of the solution is separated in lines 46 to 49, for example by passing line 46 to the location of the expansion vessels 50 as shown in Figure 1 in connection with the first screening set 30.

In order to supplement the relatively high DOM-containing separated solution and to lower the DOM level, a replacement solution (diluent) is added as indicated at lines 51-54. The effective DOM concentration of the added solution at these points is significantly lower than the DOM content of the solution separated at lines 46-49, in order to increase the strength of the pulp. The solution to be added on lines 51 to 54 may be the same as the dilution solutions 15 shown above on line 17. The heaters 42-45 heat the replacement solution, as well as any recycle solution, to substantially the temperature of the removal solution (typically slightly above).

The digester 11 may include any number of screens 30-33.

20

Prior to transporting the separated solution to a remote location and replacing it with a replacement solution, it may be subjected to a heat exchange relationship with the replacement solution, as schematically indicated by reference numeral 56 in Fig. 1. The separated solution can be further processed to remove or • inactivate the DOM contained in it, and then immediately fed back: V: 25 as a replacement solution (with the option of adding another dilution solution). This · * · '; is schematically represented by reference numeral 57 in Figure 1, which shows that the solution separated in line 48 · · is treated to remove DOM at position 57 (similar to line /; ·, 16) and then fed back to step 53. White liquor such as · · is added. · Is shown in Figure 1. In fact, in each step ... 30 associated with the screens 30-33 in Figure 1, white liquor (for lines 51-54) can be added.

• · · • · · · ·

Another alternative in the treatment step 57 - which is schematically illustrated in Figure 1 - is:. The solution, which can be considered as "black liquor", is removed from the strainer 32, and part of this is separated at line 48.

The pressure heating in step 57 may occur according to U.S. Patent No. 4,929,307. Typically, in step · · · * ... · 57, the black liquor would be heated to a temperature of about 170-350 ° C (preferably above 190 ° C, e.g. about 240 ° C) under excess pressure for about 5 to 90 minutes (preferably about 10 30 to 60 minutes), at least 20 ° C above the boiling point. The result is a significant DOM passivation, after which the black liquor can be returned to line 53. The treatment step 58, associated with the final removal / separation screen 33, functions 5 as step 16. The treatment 58 may be included or omitted at any level of the digester 11 use a separating solution instead of adding a dilution solution. The white liquor can also be added in step 58, after which the DOM-passivated solution is returned to line 54.

Regardless of whether the treated separated solution or the diluent is used, it is desirable according to the invention to maintain the total DOM concentration of the cooking solution at or below 100 g / L for substantially all of the kraft cooking (bulk delignification), preferably below about 50 g / L. It is also desirable to maintain the lignin content at or below 50 g / l (preferably about 25 g / l or less) and the hemicellulose content at 15 g / l or less (preferably about 10 g / l or 15). The commercially optimal concentration is not yet known and may vary according to the wood species being cooked.

Figures 2 and 3 show the results of the actual laboratory tests performed according to the invention. Figure 2 shows the tear and tensile strength curves of three different laboratory kraft soups with the same wood raw material. The tear factor is a measure of the inherent fiber and pulp strength.

Curve A in Figure 2 indicates that the pulp has been prepared using conventional pulp • · ·: factory liquor samples (from a commercial pulp MCC © · · · pulping process) as a cooking medium. Curve B is obtained from a cooking solution in which the cooking solution sV: 25 is the same as curve A, except that the solution samples were heated at about 190 ° C · * · *: overpressure for one hour before being used in cooking. Curve C represents a soup using a synthetic white liquor substantially free of DOM (i.e. less than 50 g / L DOM) as the cooking solution. The soups of curves A and B were performed so that the alkali, • · · temperature (about 160 ° C) and DOM profiles were identical to those of the factory-scale ... 30 mass production process, from which the factory-scale • · ·

samples were obtained from the process. The alkali and temperature profiles of curve C were identical to those of curve A

• · * ··· * and B profiles, but there was no DOM in the broth.

Figure 2 clearly shows that when a low DOM solution is in contact. With 35 chips throughout the kraft soup, the tear strength increases by approximately 27% with a tensile strength of 11 km · · ·. DOM passivation, which according to the invention employed black liquor • · * ··· * pressure heating as in curve B, also resulted in a substantial increase in strength compared to the 11 standard curves A. In this case, the tear strength increased by about 15% at 11 km tensile strength.

Figure 3 further shows laboratory tests comparing traditional kraft soups with the soups of the invention. The soups represented by curves D to G were performed using identical alkali and temperature profiles and the same wood raw material but different DOM concentrations throughout the kraft cooking. The DOM content of curve D obtained from a standard (factory-scale lye) MCC® kraft soup was the highest and the DOM content of curve G was the lowest 10 (essentially free of DOM). The DOM content of curve E was about 25% lower than the DOM content of curve D, and the DOM content of curve F was about 50% lower than the DOM content of curve D. As can be seen, a substantial increase in tear strength was obtained, inversely proportional to the DOM present throughout the cooking.

The cooking according to the invention is preferably carried out so that the pulp strength (e.g., tear strength at a given tensile strength of the completely ground pulp, e.g. 9 or 10 km) is increased by at least about 10% and preferably at least about 15% compared to otherwise identical conditions; deal with.

Although the invention has been described in connection with Figure 1 mainly in connection with kraft cooking, the principles of the invention can also be applied to batch cooking.

Figure 4 schematically shows conventional equipment that can be used in the Beloit RDH ™ batch cooking process or the Sunds Super Batch ™ process. Fig. 4 schematically shows: 25 the ice system shown includes a batch cooker 60 having an outlet screen 61, a chip source 62, a first, second and third battery 63, 64, 65, a white liquor source 66, a filtrate tank 67, a · · f * · .. valve mechanisms, the most important of which is designated 69 in the figure. In a typical traditional Beloit RDH ™ process cycle * · ·, the machine 60 is filled with chips from source 62 and steamed as required. After this ... 30, the warm black liquor is fed to the digester 60. The warm black liquor typically has a high sulfide content and a low alkali content and has a temperature of about 110 to 125 ° C. Black liquor comes from a single battery (eg 63). The excess warm black liquor can be transported to the lye tank and finally to the evaporators, after which it can be subjected to chemical recovery. After impregnation, the warm black liquor in the digester 60 is returned to the battery 63, after which the digester 60 • · · '*!; * Is filled with hot black and white liquor. Hot black liquor can be derived from battery 65 and • · * ··· * hot white liquor from battery 63, originally from source 66. Typically, hot white liquor will have a temperature of about 155 ° C and black liquor will have a temperature of about 150-165 ° C. The chips in the digester 60 12 are cooked at a certain temperature for as long as predetermined to achieve the desired factor H. The hot liquor is then introduced directly into the battery 65 and replaced with filtrate from the tank 67. The chips are cold-blown with compressed air or pumped from the vessel 60 to the butt tank 68.

5

During a typical RDH ™ process, white liquor is continuously preheated with a solution from hot black liquor battery and then stored in hot white liquor battery 64. Black liquor is transported to warm lean black liquor battery 63. Warm black liquor is transported to a heat exchanger to provide hot water and before it is pumped into evaporators.

Referring further to Figure 4, the only significant difference between the invention and the process described above is the heating of the black liquor, which can take place directly in the battery 65 so that the DOM contained in the liquor can be significantly inactivated. This can be accomplished, for example, by heating the black liquor to a temperature above the boiling temperature of at least 20 ° C, e.g. at a pressure of at least 170 ° C for about 5 to 90 minutes, preferably at 190 ° C or higher (e.g. 240 ° C). ) for about 5-90 minutes.

Figure 4 schematically illustrates how this additional heat is introduced in step 71. The heat may be from any desired source. During the black liquor pressure heating 20, a large amount of organic sulfur-containing waste gases are produced and removed.

72. Typically, as is known per se, the DMS generated at 72

(dimethylsulfide) is converted into methane and hydrogen sulphide. Methane may be used as: V as a fuel supplement (for example, to provide heat at position 71). Hydrogen sulphide, in turn, can be used to pre-impregnate the chips at source 62 prior to pulping, or it can be converted to elemental sulfur and removed. It can also be used to form polysulphide, or it can be absorbed into white liquor to produce • · · * · "high-sulphide liquor, etc. If the heat treatment in the battery is carried out at about 20-40 ° C above the boiling temperature, black liquor can be used to facilitate early impregnation.

30 • · ·

Alternatively, according to the invention, in the embodiment of Fig. 4, the valve mechanism 69 may be associated with a processing step, e.g., step 16 of Fig. 1, to remove DOM from the broth which is removed from sieve 61 during batch cooking and recycled to the digester. 60.

35 • · ·

Figure 5 schematically illustrates an exemplary commercial (i.e.

· · · ··· * at least 8 (e.g., 8-20 tons pulp / day) batch digester system 74. Curve C in Figure 2 was obtained using a solid line depicted in Figure 5 for a system 74 13 laboratory test version that has been in use for several years. System 74 includes a batch cooker 75 having an upper portion 76 and a lower portion 77. The upper portion has a chips inlet 78 and a lower outlet 79. During cooking, a chips statue 80 is formed during cooking. One level (e.g., lower portion 77) has a strainer 81 82 and pump 83 through which the heater 84. is connected. The heated solution is circulated from heater 84 through line 85 back to digester 75 at a level other than screen 81 (e.g. near top 76).

Prior to transporting the solution to heater 84, a significant portion of the lignin removed in line 82 is separated in line 86 (e.g., to allow three cycles of solution per day). This relatively high DOM-containing solution is replaced at 87 with a substantially DOM-free solution (at least a solution with a significantly lower DOM concentration than the line 86 solution). The alkali content of the substantially DOM-free solution to be added at step 87 may be varied as desired to provide a suitable kraft soup. Variable alkaline content may be used to simulate kraft soup in batch 75. Valves 88, 89 may be used to prevent or generate solution streams and / or to replace or supplement the desired treatment using a dashed system.

According to the invention, the desired level of DOM and its constituents (e.g., <50 g / l DOM, <25 g / l lignin and <10 g / l hemicellulose) can be achieved in place of or in addition to the removal and dilution lines 86, 87 treating the separated solution, for example by passing in line 90 ·· ·: V a DOM-rich solution to treatment step 91 - such as step 16 in Figure 1.

• · In the treatment step, DOM and certain of its components are removed to significantly reduce their concentration: Y: 25 in solution. Supplemental white liquor can also be added (not shown in ***). The liquor can be reheated in the heater 92 and then returned to the digester 75 via line 93. Instead of lines 90 and 93, lines 86 and 87 may communicate with the processing unit 91, as shown schematically in Fig. 5 by dotted lines 95, 96.

30 i i ·

Other laboratory test results demonstrating the advantages of the invention are illustrated in Figures 6-15. In these test results, methods were used to simulate: * · · · · · · · · · · · · · · · · · · · · · · · · · · · · Cooking the pulping solution in successive cycles. The different stages of the soup. 35 were simulated by varying cycle time, temperature and chemical concentrations.

• · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · ·

14

The effect of minimizing DOM in pulping solutions on required pulping conditions (i.e., time and temperature) is shown in Figure 6. The figure compares the ratio of kappa to H-factor in laboratory cookware using factory-scale lye and essentially DOM-free white liquor. The wood raw material used for the soups shown in Figure 5 was a typical northwestern US softwood consisting of a mixture of cedar, spruce, pine, and spruce. The H-factor is a standard parameter that describes cooking time and temperature as a single variable and is described, for example, in Rydholm: Pulping Processes, 1965, p. 618.

The graph of Figure 6 98 illustrates the ratio of kappa to factor H in a laboratory scale using factory scale liquor (collected at the factory and then used in a laboratory batch digester). The lower curve 99 depicts the ratio of kappa to factor H in a laboratory cookware using essentially DOM-free laboratory-prepared white liquor. Curves 98 and 99 show that for a given kappa number, the H-factor is substantially lower when the DOM content is lower. For example, in Figure 6, the kappa number 30 has a difference in factor H of about 100 units. This means that if less DOM-containing cooking solution is used, a softer soup (i.e. less time and lower temperature) is needed for the same raw material and the same amount of chemical than in conventional cooking. For example, to obtain a significant reduction in factor H, a solution having a DOM level substantially sufficient to adversely affect factor H can be isolated and replaced with all or part of the separated solution with a solution having substantially less effective DOM than in the separated solution. Preferably, these ««: V steps aim to reduce the H-factor by at least 5% to reach a certain kappa number. During kraft cooking, the aim is to maintain effective DOM levels of about 25 to 50 g / l or less most of the time.

• · • · «♦ ♦ ♦ ♦ · • ·

Figure 7 shows that when using a solution having a reduced DOM content of · · · [·; * 'according to the invention, effective alkali (EA) consumption is reduced. EA indicates the amount of cooking chemicals, particularly NaOH and Na2S, used in cooking. The results shown in Figures 7, 100, ... 30 101 were obtained when experiments were carried out under the same conditions and using the same raw materials as in Fig. 6. Curve 100 shows the results when the cooking liquor was conventional • · · · .. * factory scale liquor. , while curve 101 shows results when the broth was: *. At number 30, DOM-free soup consumed about 30% less alkali (ie 5% less EA from wood) 35 than traditional factory-scale soup. Thus, when separating a solution having sufficient · · · * · * · * DOM to adversely affect the effective amount of alkaline • · · * ... · obtained to obtain a given kappa number, and replacing all or part of the separated solution with a solution having substantially less effective DOM, the amount of 15 effective alkali consumed to obtain a given kappa number can be substantially reduced. For example, the amount of alkali consumed to reach a certain kappa number can be reduced by at least 0.5% on a wood basis (e.g., about 4% on a wood basis).

Both the favorable Factor H results and the EA consumption results shown in Figures 6 and 7 can be achieved by replacing the separated relatively high DOM-containing solution with water, essentially DOM-free white liquor, pressure-heated black liquor, filtrate, and combinations thereof.

Figure 8 further schematically shows the consumption of effective alkali as compared to a percentage indicating the ratio of factory-scale lye to essentially DOM-free white liquor. Curve 101 shows that with the same relative kappa, the effective alkali consumption decreases with the percentage of factory-scale lye (i.e., with a 15% increase in essentially no DOM-free white liquor). The following Table 1 shows the actual laboratory results upon which the curve 101 of Figure 8 is based.

table 1

Effective Alkaline Consumption 20 Cooking No A3208 A3219 A3216 A3239 A3217

Description Tmk.l._75% tmk. 50% TKM. 25% tmk. Lab.l._ Total EA Consumption,% 15.8 16.5 14.9_15.7 14.0_

Number of tracks, *. *. 25 screened 30.7 30.6 28.0 29.8 30.8 ··· 9 9 9 9 9 · · · · · · · ·

Tmk.l. = factory-scale lye • · · · '· * Lab.l. = laboratory scale lye Reducing or removing the DOM in the pulping solution also facilitates the bleaching of the resulting pulp. Figure 9 shows actual laboratory test results showing how the brightness of the bleached cedar-spruce-pine-noble spruce increases with the amount of bleaching chemical. In the graph of Fig. 9, the parameter marked "X-axis kappa factor" is the ratio of the corresponding chlorine dose to the mass obtained by mass · · · ** * j. In other words, it describes a somewhat standardized relationship between the chlorine used and the original lignin content of the brown pulp. Figure 9 thus shows how the brightness of the pulp corresponds to the amount of bleaching chemical used.

• · • · «• · • · ··· 16

The graphs 102, 103, 104 and 105 of Figure 9 depict essentially DOM-free white liquor (102), traditional factory-scale liquor (103), factory-scale cooked pulp (not laboratory-scale liquor) 5 (104), and factory-scale heat-treated black liquor 105). These schematic representations clearly show that the best bleaching is achieved when a substantially free DOM-free solution is used as the cooking solution. Thus, by separating a solution containing sufficient DOM to degrade pulp bleaching, and replacing all or a portion of the separated solution with a substantially less effective DOM-containing solution, the pulp bleachability of the 10 pulp produced can be significantly improved, e.g., by at least one ISO brightness unit. sequence kappa factor. Alternatively, these results indicate that a certain ISO brightness can be achieved even if less bleaching chemical is used. However, curve 105 shows that although heat-treated black liquor can improve delignification (see Figure 2), residual lignin may not be as easily removed. Thus, the use of treated black liquor as a diluent solution is not necessarily desirable when it comes to improving bleaching, but more suitable diluent solutions would be water, essentially DOM-free white liquor, and filtrate (and combinations thereof). However, heat-treated liquor can be used for non-bleached pulp, i.e., for unbleached species.

20

As noted above, reducing the DOM content of pulp solutions appears to have the strongest effect on pulp strength. This is also supported by the results shown schematically in Figures 10 - • · ·: V 14b. All these results have been obtained using the same raw material already mentioned in Figures 6-9: Cedarwood, Spruce, Pine and Noble: Y: 25. According to the results, the tear strength under the same cooking conditions: * · *: increases significantly as the amount of DOM decreases. For example, Figure 10 shows that • · the tear strength at 11 km increases (see curve 106) with the amount of factory-scale lye. decreases (and thus substantially increases the amount of white liquor that does not contain DOM) in the laboratory cookings described. The same basic ratio is shown in curve 107 of Figure 11, which ... 30 illustrates the ratio of factory scale percentage to tear strength ** at 600 CSF.

• · · • »• ·

Table 2 illustrates tear strength at two tensile strengths in laboratory cookware using different ♦ solutions and compares one of the factory scale. 35 tear strength. The results for soups 2 and 3 in the table show that • · * * ·] · * tear strength increased by 20% at 10 km tensile strength in a laboratory cooker using essentially DOM free white liquor compared to a laboratory cooker using factory scale liquor. With a tensile strength of 11 km, the tear strength increased by 12 to 17 percent. The laboratory soups 4, 5 and 6 in Table 2 show the result of replacing the DOM-free solution in certain parts of the soup with the corresponding factory-scale liquor. For example, in laboratory cooking, a solution of 4 bottom circuits, BC, was replaced by a laboratory solution in the BC phase of laboratory cooking. Likewise, 5 BC and modified 5 MC, MC, used factory-scale alkaline BC and MC phases for laboratory cooking, while the other steps used essentially DOM-free solution. The results in Table 2 show that minimizing DOM is important throughout the cooking process, not just in the final stages. The results fully support the analysis presented in Figures 2 and 3.

Table 2

Effect of dissolved organic matter on tear strength of pulp when using hemlock raw material

Cooking conditions @ 10 km Ripping. @ 11 km_ 15 1) Factory scale soup_123_N / A__ 2) Laboratory soup (A) 174 156 + factory scale. lye (B) 173.150

Average_173.5_153_ 20 3) Laboratory soup (A) 207 174 + laboratory liquor (B) 206 170

Mean_206.5_172_ 4) Laboratory soup + factory-scale BC-25 liquor 183,159 ·· · • · *. \ 5) Laboratory soup :: + factory scale BC and MC liquor 181 157 · 30__: ***: 6) Laboratory soup). / + factory scale

: ** Washing Circulation Liquid 187 N / A

e · · • · · 3 · 5 (N / A = “not analyzed”)

: ***: Figures 12A-14B illustrate the effect of DOM on bleached pulp strength. 12A

···. *. tear and tensile strengths for unbleached pulp are seen. The mass of curve 108 is · · · '· made using essentially DOM-free laboratory liquor, the mass of curve 109 is 40 using press-heated black liquor, and the mass of curve 110 is conventional factory-scale liquor. Figure 12B illustrates the relationship between tear and tensile strength after the bleaching of the pulps depicted in Figure 12A using the laboratory bleaching sequence DEoD (nD). Curve 111 depicts a bleached pulp 18 prepared using essentially DOM-free white liquor. Curve 112 represents pulp made using pressure-heated factory-scale liquor, and curve 113 represents bleached pulp made using conventional factory-scale lye. For comparison, curve 114 depicts the strength of the factory scale pulp taken from the thickener after bleaching. Figure 12B shows that the pulp made with the substantially DOM-free solution is not only stronger than the pulp made with the factory-grade solution, but that this relative strength is retained even after bleaching. Also, the pulp cooked with the heat-treated solution retains 10 higher strength after bleaching than the pulp cooked with the factory-grade solution, but the difference in strength after bleaching is minimal.

Figures 13A and 13B depict test results for the same soups / bleaches as Figures 12A and 12B, with the difference that the tear strength factor is shown as a function of Canadian Standard Freeness 15 (CSF). Curve 115 is pulp made from essentially DOM-free solution, curve 116 is pulp with pressurized mill-scale solution, curve 117 is pulp with mill-scale solution, curve 118 is pulp made with substantially DOM-free solution, curve is 119, 20 bleached pulp made with factory scale solution and curve with pulp taken from 121 scale scale thickener.

Figures 14A and 14B illustrate the same soups / bleaches as Figures 12A and 12B, except that they show the relationship between tensile strength and freeness. Curve 122: V: 25 pulp, curve 123 pressure heated · '· *: pulp, 124 essentially DOM • · pulp 125 bleach, 126 pulp made with essentially no DOM • * · solution, curve 127 from pulp ... 30 pulp, and curve 128 bleached pulp with factory-heated solution • · ♦. Figures 14A and 14B show that the tensile strength of both the pulp prepared with the pressurized • · * ··· 'solution and the essentially free DOM-free solution is reduced; however, Fig. 14B also shows that the bleaching • · obtains the relative tensile strength of the pulp prepared with the pressure heated solution. 35 to lessen the tensile strength of the pulp prepared with the DOM-free solution.

As noted above, a heat-treated solution may be suitable for processes in which pulp is not bleached.

19

All of the above laboratory soups simulate the mass production sequence of the Andritz Inc. MCC® Steamer. Each lab cooker has a corresponding impregnation step, a parallel current cooking step, a counter current MCC® cooking step, and a counter current washing step. Figure 15 shows typical DOM contents of laboratory soups using three different sources of solution, based on the actual lye analysis. Curve 130 utilizes a factory-scale solution, curve 131 utilizes 50% factory-scale solution and 50% essentially DOM-free laboratory white liquor, and X 132 describes a soup using 100% essentially DOM-free laboratory white liquor. It should be noted from Figure 15 that when time = 0 at the start of impregnation, all laboratory solutions used were free of DOM because at this point in the cooking process there was no reliable method for sampling the solutions. Thus, according to these results, the DOM levels at the end of the impregnation of the plant-based soup and 50/50 solution soup are lower than expected; the more representative concentrations are extrapolated and shown in brackets in Figure 15. Figure 15 shows that each concentration shows a certain trend throughout the cooking process: the concentrations gradually increase up to the removal stage and then gradually decrease during the upstream MCOB> and the washing phase. Of course, even in the case of a substantially non-DOM-containing solution source, DOM will reach the solution as the cooking proceeds.

Figure 16 illustrates an exemplary tray dispenser system 133 which is intended to produce a stronger mass in accordance with the invention. Refrigerator 133 includes the traditional two-pan Andritz Inc. hydraulic spout with MCC® cooking system.

: *. * The impregnation vessel belonging to the steaming machine is not shown in the figure, but shows the · ·:. * ·· Steamer 134. The traditional MCC® digester 134 of Figure 16 has been modified to: V: 25 perform low DOM levels according to the invention cooking methods.

• · · • · · · ·

The digester 134 includes an inlet 135 at the top and an outlet 136 at the bottom for the finished mass. The slurry of the fine cellulosic fibrous material • · · (wood chips) is fed from the impregnation vessel in line 137 to the inlet 135.

... 30 The screening group 138 at the top removes some lye from the feed slurry • · · *;] / in line 139 which is fed back to the bottom circulation heaters and the impregnation vessel.

Below the upper screening group 138 is a separation screen 140, which includes line 141. Line 141 leads to a first expansion tank 142, which typically belongs to the • · · ··· expansion vessel group. Below the separation screen 140 there is a cooking screen 143, of which. 35 departs two lines. One line 144 takes care of the separation (and joins line 141), and the other • · · *; [; 'Line 145 leads to pump 145'. A valve * .. · * 146 may be provided at the junction of the lines 144,145 to vary the amount of solution passing through each line. The solution passes in line 145 through heater 147 and line 148 and returns to the interior of digester 134 through a conduit 151 having a mouth approximately at the level of cooking strainer 143. Also, the side line 149 may become a recycled solution into a tube 150 having a mouth approximately at the level of the separation strainers 140. Below the cooking screen set 143 is a washing screen set 152 from which outlet line 153 leaves. Outlet line 153 leads to a pump 154 which directs solution 5 through heater 155 to line 156. From line 156, the solution returns to the inside of digester 134 through line 157.

Production of the System 133 digester has recently been increased at the factory beyond its planned capacity and is currently limited by the amount of solution that can be separated. To reduce this 10 limitation, the techniques of the invention described in detail in Figure 16 can be used. Because the amount of solution to be separated in line 141 is limited, it can also be increased according to the invention by also separating from line 144. Typically. In practice, one of my solutions per ton of pulp is separated in line 144 and replaced by 15 dilution solution (wash solution) from source 158. This is accomplished in Figure 16 by passing wash solution from source 158 (e.g. filtrate water) through pump 159 and valve 160, 1.5 tons of solution per ton of pulp) is routed in line 161 to the bottom of the digester, while the remainder (e.g. one ton of solution per ton of pulp) is routed through line 162 to line 145 20 as a diluent. From source 163, white liquor substantially free of DOM can also be added in line 164 to line 145 prior to heater 147, and recirculation to the digester takes place through conduits 150 and / or 151. Of course, white liquor can also be added to the · · * wash cycle in line 153 (see line 165) to provide EMCC® cooking. Power • · *. * ·: The arrows 166 indicate the parallel current range of the digester 134. As a result of the variations shown in Fig. 16 • · v .: 25, the countercurrent in the MCC® Cooking Area 167 is: ***: a cleaner, less DOM-containing solution which provides a * * · .. stronger mass and, in this case, also capacity.

• • · · · · · · · ·

The effect of the variants depicted in Figure 16 on the DOM content has been investigated using a dynamic computer model of 30 Andritz lnc. The preliminary results of this theoretical study are shown schematically in Fig. 17. Fig. 16 compares the DOM concentration variation in a conventional MCC® digester with the DOM concentration variation in the Fig. 16 digester. The results obtained with a conventional MCC® digester are plotted against ·: ··· 168 and the results of Fig. 16 digester 169 are shown. As shown in Figure 17, the concentration of DOM-35 is greatly reduced at target group 143 with the addition of less M DOM-containing dilution solution. The DOM is also upstream, which • · * ··· * is directed back up to the Separation Screen Set 140. Also, the downstream wash solution contains less DOM because 21 less DOM is carried with the pulp. Curves 170,171, as well as part of curves 168, 169, show that in the countercurrent cooking zone, DOM always increases in the direction of the solution flow. In other words, the countercurrent boils and collects the DOM as it passes through the downward filing head.

Figures 16 and 17 thus illustrate the strong effect of only one difference-dilution step on the DOM profile in the scheduler. The reduction in DOM can also have a strong effect on the strength of the pulp produced.

Fig. 18 shows another plant variant using the methods of the invention. Also disclosed herein is a digester 134 which is part of a two-pot hydraulic digester. Since many components are the same in Figures 16 and 18, they are referred to with the same reference numerals. Only the variants for which these rigid systems differ are described in detail.

In the embodiment of Figure 18, the DOM decreases even more strongly. In this embodiment, the screens 140, 143 are in contrast to the embodiment of Figure 16, and another screen group is sequenced between the screen groups 138, 143. The screening group 173 is a control screening group; according to the invention, through the outlet port 174 therefrom, discharge to the expansion vessel 142 is provided.

20

In one practical example of the embodiment of Fig. 18, two tonnes of solution per tonne of pulp in line 174 and four tonnes of solution per tonne of pulp in line V141 are added. In line 162, dilution solution is added and line 164 is substantially free of DOM. As a result, the currents shown in Fig. 18 are generated: V: 25 176, 177, whereby the digester 134 acts on a parallel, countercurrent, * * · *: parallel, countercurrent (what can be called alternate circular flow).

• · ·· · · · · ·

In Fig. 19, there is shown one cooker system 179 according to the invention. This two-vessel system shows an impregnation vessel 180 having an ... 30 inlet 181 and a lower outlet 182. The solution removed from 183 is recycled to a conventional high pressure barrier feeder, and white liquor is added at • · * ♦ · ♦ * 184. The solution removed at 185 may be transported to the space between the first expansion vessel 186 and the second expansion vessel 187. The slurry from line 182 is directed from position 188 to the top of digester 189, which has a "distillation vessel system" 190, from which the solution is removed. 35 at 191 and recycled to the bottom of the impregnation vessel 180. The solution is heated • · · * · * · * during circulation in the heater 192.

· «· • · • • • ♦ · 22

Also, the digester 189 has a control sieve array 194 from which an outlet line 195 exits. In this case, the solution to be discharged is in line with the solution circulating in line 191. The cooking strainer group 196 is located below the control strainer group 194 and the solution exiting therein is directed through valve 198 to line 199. Part of the solution may also be conveyed from valve 198 in line 200 to the expansion vessel 186. The solution is diluted in line 199 with less DOM containing solution. white liquor 201 and filtrate 202 before being passed through heater 203 and fed back into digester 189 by means of 204 at about the level of screening group 196. The outlet screen group 206 leaves the outlet line 207 which leads to the expansion vessel 186. The screen screen group 208 includes a recycling line 209 to which white liquor can be added at 210 before the solution is passed through heater 211 and fed back 212 at about the level of wash screen group 208. The filtrate from which the washing solution is obtained is added at 213 and the mass produced is removed at line 193.

From ice system 179, it is worth noting that removal from line 197 through valve 198 to port 200. Also, dilution solution in filtrate form is preferably added at 214 to line 182, and substantially free DOM-containing white liquor is added at 214 '.

Figure 20 shows a one-pot hydraulic digester modified according to the invention. This variation also includes two cooking strainers, as is traditional. This allows separation / dilution in the other two locations.

· ♦ • · • • «« ««

The single-vessel hydraulic digester assembly 215 includes conventional chips container 216: V: 25 parts, a steaming vessel 217, a high pressure transfer device (high pressure barrier feeder) 218, line 219: * · *: Part of the solution is removed in line 223 and recycled to the high pressure barrier feeder 218.

• · ·

The strainers, for example, the first strainer set 224 and the second strainer set 225, ... 30 are located below line 223.

The first digester 224 includes a first apparatus for circulating a first portion of solution removed from the digester 224 back into the interior of digester 121. The equipment includes line 226, pump 227, and heater 228, outgoing. 35 feed line 229 to about the level of the screening group 224. The apparatus may also include a valve · · · *; [· * 230 solution separation before heater 228 to line 231 when adding dilution solution, e.g. · white liquor (e.g., 10% of total white liquor used), through 232 just prior to heater 228.

23

A second apparatus for circulating one of the removed solutions and separating the second removed solution is provided in connection with the second cooking screen group 225. This second system includes a unit 235, a pump 236, a heater 237, a valve 238, and a 5 return line 239. One dose of solution increases with the dilution solution at 242 when the dilution liquor is added in the form of white liquor on line 241 and a portion of the solution is separated in line 240. 224,225 in the adjacent cooking zone.

Below the second cooking strainer array 225 is located a separation strainer assembly 245, from which one extends 246 to valve 247. Line 248 exits line 248 to the first expansion vessel 249 of the recovery system.

15

The digester 221 further includes a third screening group 253 located below screening group 245, and a screening valve 254 associated with a screening outlet 255 and a discharge connection 256. That is, depending on the location of valves 247, 254, the solution can flow from line 246 to line 255.

20

Line 255 communicates with pump 257 to heater 260 and return connection 261 at the level of about a third screen group 253. Add dilution solution to line 255 before • · ·: *. * 'Heater 260; white liquor (e.g., about 15% of the white liquor used for cooking) is added through line 258, and a dilution solution, such as a wash filtrate from source 243, is added through line 259.

• · · • • I *. The digester 221 also includes a wash screen set 263 having a discharge line 264.

White liquor from source 233 (eg 15% of the total white liquor used in the process · · ·) can be added to the outlet via line 265. The digester also includes a pump 266, a ... heater 267, and a return connection 268 for returning the removed solution at about • · · screening group 263. The washing filtrate is also added below the screening group 263 through the interconnected 269 connected to the washing filtration source 243.

• • • • • • • • • •

In one embodiment of the invention, 55% for pulp treatment • ·. *. 35 of the white liquor used are added in line 271 to impregnate the chips when processed in high pressure transfer device 218 and lowered to line 219. 5% of white liquor * · .. * is added to high pressure barrier feeder 218 through line 272, 10% total added to lines 232,241 (e.g. 5% for both), and 15% is added to both line 258 and line 265.

By using the single-pan hydraulic hopper assembly 215 of Figure 20, a low DOM level can be maintained, and multiple operating models can be applied. For example, at least one of the following three modes of operation may be used: 5 (A) Continued Modified Cooking with Separation / Dilution from Lower Cooking Ratios: In this model, the solution is separated from digester 221 conventionally in line 246, and extended modified cooking. White liquor is added in lines 232,258,265. The solution is also removed in line 240, and the corresponding dilution solution is added in line 242 from the wash filtrate 10,243. This results in either a one-way or an upstream DOM-level solution flow between the separation screen group 245 and the lower cooking screen group 225. Whether the flow is parallel or upstream depends on the values of the lines 240,246 differences.

(B) Continued Modified Flow with Separation / Dilution in Modified 15 Flow Rounds: This model uses all the flows described in (A), in addition to separating the solution in line 256. Valves 247, 254 are adjusted to allow part of the solution to pass from the third screen group 253 ( modified dilution screening group) to line 248. The dilution solution replacing this separated solution is added at line 259 to provide another one with a lower DOM level upstream fluid flow between screening groups 245,253.

(C) Influence impregnation and differential dilution of upper cooking ratios: This model • · · •. * Can be used as such or in conjunction with the traditional modified bed process • · or in addition to the above models (A) and (B). This model includes • · V: 25 difference from upper screening group 224 to line 231 with valve 230 controlling: ***: flow of solution and white liquor dilution at line 232.

· * · .. Additional dilution can be performed from line 259 (not shown in Figure 20). This results in displacement impregnation, which is obtained when the counter current at the inlet of the digester accelerates. The acceleration is not caused by the difference but by the lye concentration of the incoming 30 chips. Due to the low lye content of the chips, the hydraulic digester 221 forces the dilution stream back to the inlet 220, · · · · · *, which results in a backflow of the lye with less DOM.

• · • · ·

• M

The system 215 shown in Figure 20 is not limited to the models A-C described above, but the models 35 are just examples of the many modified shapes that flow can take to produce a more robust mass of the low DOM of the invention. • · * ··· * by concentration.

25

It should be noted that the systems of all embodiments of Figures 16 and 18-20 may be installed in existing factories, and the detailed operating instructions will depend on the factory conditions under which the technique is applied. All embodiments result in the benefits of reduced DOM-5 content as described above, such as increased strength, increased bleaching, reduced effective alkali consumption, and / or lower H-factor. This is best illustrated by the apparatus of Figure 19 and the associated curves of Figures 21-25.

In Figure 19, reference numeral 185 denotes a first resolution, 200 a second resolution, 207 10 a third resolution, 214 a first dilution, 202 a second dilution, and 213 a third dilution.

Figure 21 compares, through computer simulation, the DOM profiles of a standard EMCC® soup and a similar invention soup, with the latter using the system of Figure 19 where extended parallel cooking is performed. In the standard EMCC® soup, the solution is removed from the conventional extractors and white liquor is added to the conventional cooking and washing circuits, whereby the solution flow from the top of the digester to the conventional extractors is parallel, while the solution flow is upstream. According to the extended parallel model of Figure 19, the third difference 207 is the principal difference so that parallel cooking takes place all the way to the target group 206. Figure 21 illustrates traditional EMCC® soup with curve 275 and extended parallel current soup with curve 276. V ADMT / D and white liquor in 60% impregnation, 184.5% BC in line 214 ', 15% in MCCXgMderro 201, and 20% in wash cycle 210. In line 213, 1.5 tonnes of solution: V: 25 per mass scrubbing filtrate were added to the countercurrent.

Figure 21 shows that, although the DOM content is initially reduced in the cooking zone, it is higher in the upstream stage. Thus, such an extended · · · parallel current cooking (276) provides only a slight improvement in the DOM-30 content. Although the computer model has its limitations, Figure 21 shows that the DOM content can be varied throughout cooking.

Figure 22 shows how the addition of white liquor in line 201 of Figure 19 and the addition of a little dilution solution in line 202 of DOM has a theoretical effect. In Figure 22, 1.0 tons of solution per ton of pulp filtrate in line 202 is added, as well as 0.6 t / t white liquor. The corresponding 1.6 t / tp solution stream is removed in line 200. Comparing curve 277 with curve 276 of Figure 21, it is noted that the DOM concentration drops sharply between the screens 196, 206.

26

Figure 23 illustrates the effect of alternating dilution of the wash filtrate on lines 202 and 213. In this case, the total amount of wash filtrate 1.5 + 1.0 = 2.5 t / tp is added on lines 213 and 202. In simulation of curve 278, 1/3 of the dilution solution is added in line 202; curve 279 in simulation 1/2 on line 202; and curve 280 in simulation 2/3 in line 202 (the rest is added in each case at line 213). Thus, it is clear that the DOM profile varies significantly with the different dilution flow rate: the more dilution solution is added to the cooking zone, the more strongly the DOM in it is reduced (although it increases in the washing area).

10

Figure 24 illustrates the theoretical effect of difference variation on line 200. Curve 281 depicts a DOM profile with a line difference of 1.35 t / tp; curve 282 DOM profiles with a line difference of 1.85 t / tp; and curve 283 when the difference at 200 is 2.6 t / tp. In each case, the total amount of 2.5 t / tp of the dilution solution is evenly distributed between the lines 202 and 15 213, and an additional 0.6 t / t of white liquor is added in line 201. Figure 24 clearly shows that the theoretical DOM concentration in the cooking zone decreases, as the amount of difference increases in line 200 and remains substantially constant throughout the upstream region. Therefore, this difference can be varied and adapted to the pressure loss of the separation strainer without affecting the DOM profile very much.

20

Figure 25 illustrates the effect of separation from line 185 (top of impregnation vessel 180) to create counter current impregnation using extended parallel cooking and: 1.1 dilution. In this case, the results obtained using the reference parallel current impregnation vessel are similar to those shown in Figure 22.

: V: 25 The difference current 185 is 1.1 t / tp; the separated solution is not replaced by the washing filtrate but by white liquor · 1 · 1: in line 184. In the patterns of Figures 21 to 24, 60% of white liquor was added in line 184 and 5% • · ". in line 214 '. % in line 214 '. Curve 284 shows the flow of the parallel current impregnation vessel, while · · · line 285 indicates the counterflow (60% white liquor in line 214') .This ... 30 indicates that the theoretical DOM content decreases in both vessel 180 and cooking zone. , and • · φ are comparable to the countercurrent cooking range, thus lower DOM contents • · * ··· 1 are possible due to the separation in vessel 180 and in the digester 189 due to separation and dilution.

Thus, it will be appreciated that the invention provides a method and apparatus for increasing the strength of kraft pulp by removing, minimizing (e.g., by dilution), or · · * · ..1 by passivating the DOM at any stage of kraft cooking and adding more mass! process parameters. While the invention is described and described herein with reference to the 27 most practical and preferred embodiments of the present state of the art, it will be appreciated that many modifications may be made within its scope, the claims of which must be interpreted as broadly as possible to cover all related structures, methods, and products.

• i ^ i ^ i ^ i ^ i ^ i «i i i i i i i i i i i i i i i t i n g i n g i n g i n g i n g. · · • • · • ♦ ♦ ♦ 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 3 · · • · 2 • · 3

Claims (20)

28 A process for the continuous production of kraft pulp using at least one screening group (143, 196, 225, 253) in a digester, characterized in that the process comprises at least 5 of the following steps: (a) delivering a liquid slurry of chopped cellulosic fibrous material a first level of dissolved organic material; (b) removing a portion of the liquid having the first level of dissolved organic material from the slurry at the screening group; (c) recycling at least a portion of the liquid removed in sub-step (b) in a return cycle (145, 199, 235, 255) to the digester at approximately the location of the screening group; (d) introducing the cooking solution (164, 201, 241, 258) into the reflux circuit; (e) introducing into the reflux a diluent (162, 202, 242, 259) having a second level of dissolved organic material which is significantly lower than the first level having a positive effect on pulp strength, effective alkali, factor H or bleaching; and (f) returning the liquid in the return cycle to the digester so that the liquid introduced from the return cycle has a third level of dissolved organic material which is significantly lower than the first level to have a positive effect on pulp strength, effective alkali, factor H or bleaching . • · · · · · · · Method according to Claim 1, characterized in that it comprises at least an additional sub-step (g) located between the sub-stages (b) and (c), in which (144, 200, 240, 25 256) the first liquid part removed in sub-stage (b) is introduced. recovery or other external treatment of the digester and recycling (145,199, 239, 255) the second portion in sub-step (c). • • ·· * * · • · · A process according to claim 2, characterized in that sub-steps (b) to (g) are carried out ... so that substantially all of the liquid removed in sub-step (b) is recycled or otherwise disposed of in the digester and substantially replaced by a dilution solution and With cooking liquor in sub-steps (d) and (e). A method according to claims 1-3, using a second screening group (140, 173, 224, 245) disposed in a first direction from said screening group, characterized by 35, that the process comprises the additional sub-steps (h) and (i) performed prior to sub-step • (') · · · · (a), wherein 29 (h) passes the liquid slurry of the chopped cellulosic fibrous material against the first direction to the second screening group and fourth level of organic material; and (i) removing the liquid having the fourth level of dissolved organic material from the slurry 5 at the second screening group and passing (141, 174, 231, 246/248) the removed liquid for recovery or other external digestion. Method according to claims 1-4, characterized in that the sub-step (e) is carried out to introduce a washing filtrate (162, 202, 242, 259) or water or combinations thereof. 10 Process according to claims 1 to 5, characterized in that sub-steps (a) to (i) are carried out before or at the beginning of the cooking. Process according to claims 1-6, characterized in that sub-steps (a) to (i) 15 are carried out to keep the dissolved organic material below 100 g / l substantially throughout the cooking process. Process according to claims 1-7, characterized in that sub-steps (a) to (i) are carried out to maintain the dissolved organic matter below 50 g / l for substantially all of the cooking. The process according to claims 1 to 8, characterized in that sub-steps (a) to (i) are carried out in order to maintain the dissolved hemicellulose at or below 15 g / l. • ·: substantially throughout the cooking process. t · ·: ·: 25 • · Method according to one of Claims 1 to 9, characterized in that it comprises an additional sub-step (j) located between the sub-steps (e) and (f), in which the liquid of the return cycle is heated before being returned to the digester. • · · • · · · · 11. A steaming machine having an upper part and a lower part, characterized in that it comprises at least • · * ·; * 'an inlet for cookable cellulosic material at the top of the digester and an outlet for cooked pulp at the bottom; a first screening group (143, 196, 225, 253) having ·; ··· a first discharge line (145, 197, 235, 256); means (162, 202, 242, 259) for adding a liquid "liquid" and a cooking solution containing only a small amount of "." * to said first outlet; and means (145, 204, 239, 261) for circulating a liquid · · 1 with the dissolved organic material fluid and the cooking solution added in said first outlet to the digester at about the first target group level. 12. A spout according to claim 11, characterized in that it comprises a second screening group (140, 173, 224, 245) at least above said first screening group having a second discharge line. 13. A dispenser according to claims 11 and 12, characterized in that it comprises a third screening group (140, 206, 245) located at least below said first screening group and having a third discharge line (141, 207, 246) operatively connected to a recovery system. system or other processing system outside the digester. 14. A dispenser according to claims 11 to 13, characterized in that it comprises at least means for recovering the first portion of solution removed by means of a first screening group or other external treatment of the digester. A spout according to claims 11-14, characterized in that it comprises at least a countercurrent spout (167, 176) located above said first screening group. 20 ... 16. A spout according to claims 11 to 14, characterized in that it comprises at least a downstream spout above said first screening group. 17. Spout according to one of Claims 11 to 16, characterized in that it is a hydraulic • V 25 spout. ·· • · • ♦ ·: 1 · 1; 18. A cooker according to any one of claims 11 to 16, characterized in that it is a vapor-phase cooker. ··· ♦ ♦ ♦ • «· 19. A spout according to one of claims 11 to 18, characterized in that it is a single-pan **: · 1 spout (215). • · ♦ · ♦ • ·· • · *: 2: 20. A spout according to any one of claims 11 to 18, characterized in that it is.]] ·. multi-pan crib. • · · • · 2 · · 31