FI121788B - Method and apparatus for power boiling of pulp - Google Patents

Description

METHOD AND EQUIPMENT FOR CRAFTING MASS

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 EMCC® digester of Andritz Inc. of Glens Falls, New York, since the countercurrent flow of the solution (also containing white liquor) reduces DOM concentration and at the end of the 'external delignification' and throughout the so-called 'residual delignification'.

According to the present invention, it has been found that DOM has an unfavorable effect. 20 at the end of the cooking step, also that the presence of DOM adversely affects the strength of the pulp produced at any stage of the cooking process - i.e., at the beginning, middle or end of bulk delignification. The mechanism by which DOM affects pulp fibers and thus adversely affects pulp produced at any stage of the cooking process. ·: ·. strength, is not fully known, but is thought to be due to the reduced mass transfer rate of alkali-extractable organic materials through the fiber walls due to the presence of DOM around the fibers, and the crystalline and amorphous regions of the fibers (ie.

: * · *: Different extractability of nodules). In any event, according to the invention, it has been shown that if the DOM level (concentration) is minimized throughout the cooking process, the mass strength will increase significantly. According to the invention, it has been found that if the DOM level is close to zero throughout the kraft soup, the tear strength of the pulp is greatly increased, i.e. up to about 25% (e.g. 27%) Λ 11 km. 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 strength of the pulp.

• · 2

It is common in prior art kraft soups to have a DOM content of 130 grams per liter (g / l) or more at some cooking stages and 100 g / l or more in several stages of kraft cooking (e.g., Andritz Inc. MCC® Steamers, 5 Adjustments) , top and bottom exhausts, and MC cycles), even though DOM levels are maintained at 30-90 g / l wash cycle (according to traditional knowledge, 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 stronger deleterious effect on pulp strength - e.g. because it adversely affects the transport of organic matter from the 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, it has been found for the first time 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. . 20 for the duration of the kraft cooking (i.e., the beginning, middle, and end of bulk delignification), and preferably at about 50 g / l or less (as close as zero The DOM level goes, 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 25 of about 10 g / l or under).

: '· *: According to the invention, it has also been found that it is possible to at least largely passivate: ***: Adverse effects of 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 in accordance with U.S. Patent 4,929,307, e.g., at about 170 to 350 ° C (preferably at 240 ° C) For 90 minutes (preferably about 30-60 minutes • · ·) and then fed back, the tear strength can be increased by up to 15%. The mechanism by which DOM passivation occurs by heat treatment is also not fully understood, but it 3 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 for both 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 provides 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 10 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, bleaching can be increased, 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 by cooking comminuted cellulosic and fibrous material. The method comprises the following events occurring during the various stages of the kraft cooking of the material: (a) separating a solution having a DOM level significant enough to adversely affect the pulp strength; and (b) replacing part, ·, · 20 or with an effective DOM level • · · • · substantially lower than the DOM level of the separated solution. Step (b) is typically carried out 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 soda filtrate, and combinations thereof. For example, at least •: * · * · 25 for one cooking step, black liquor can be removed and treated under pressure and heat (e.g., overpressure at about 170 to 350 ° C for about 5-90 minutes and at least 20: T: ° C above cooking temperature). ) To significantly inactivate the IJ of the adverse effects of DOM. The term "effective. ·.: DOM" as used in the specification and claims refers to that part of the DOM that affects pulp strength, H-factor, effective · · ....: 30 alkali consumption and / or bleach. A low effective DOM can be achieved by Λ passivation (except for bleaching) or by an initially low DOM content.

♦ · ··· 4

The method of the invention may be implemented in a vertical spout, in which case steps (a) and (b) may be carried out at least on two different levels of the digester. Typically, an additional step (c) is also carried out in which the replacement solution from step (b) 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 carried out 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 method comprises, at the beginning of cooking 10, the following steps: (a) separating a solution having a DOM level sufficient to adversely affect the pulp strength, and (b) replacing part or all of the solution with the effective DOM level is substantially lower than the DOM level of the extracted solution.

According to another embodiment of the invention, the impregnation of a cellulosic fibrous material comprises the steps of: (a) separating a solution having a DOM level sufficient to adversely affect the pulp strength, and (b) replacing part or all of the solution with with a significantly lower effective DOM level. : 20 as the DOM level of the separated solution.

• · · · · · · · · · · · ·

In 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; . * J '; (b) heating the black liquor under pressure to a temperature sufficient to passivate • the adverse effects of the DOM contained in the black liquor on the strength of the pulp; and (c) feeding the DOM-passivated black liquor back into the pulp at some point.

• · · • • • • •; #: The invention also includes kraft pulp prepared by the above methods. This • · 30 kraft pulp is different from previously made pulp, with a tear strength of up to 25% higher at a given tensile strength of fully ground pulp (e.g., 9 km tensile strength or 11 km tensile strength) (and at least about 15% higher) compared to a · · · · 9 mass produced under identical conditions without the 5 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 in which a black liquor container and a material batch digester are used. 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 adverse effects of DOM on the pulp strength, and (b) feeding the black liquor to the digester where it contacts the cellulosic fibrous material. Step (a) is carried out by heating the black liquor under high pressure at a temperature of about 170 to 350 ° C for about 5-90 minutes (typically at least about 190 ° C for 30-60 minutes and at least 20 ° C above the boiling point), and step (a). b) can be accomplished by simultaneously feeding black liquor and white liquor to the digester to effect cooking of cellulosic fibrous material.

15

According to another embodiment of the invention, there is provided a device for kraft cooking pulp. 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 and a separation line which are associated with each target; and instrument. : 20 to bring the replacement solution into the recycling line to replenish 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 the DOM-rich solution and replaces it with a lower DOM-containing solution (in the feed line: ':': there is also a connection and high pressure barrier).

• · ·::: 25

The invention also relates to a commercial method for carrying out a kraft cooking of a pulp-containing cellulosic fibrous material by step (a) of continuously contacting a · · · essentially DOM-free solution with the material and again: · · · out to the very end of the kraft cooking of the material. mass of at least 100 • · ·; ··· 30 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 carrying out step (a). · · ·. the preceding step (b) of filling the digester with cellulosic material and the step (c) of step (a) of removing the kraft pulp from the digester. The invention also relates to a batch cooking system for carrying out these 6 embodiments, wherein each digester has a production capacity of at least 8 tons per day (meaning commercially achievable, not laboratory).

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 tracking the separation and recycling screens in some way, the advantageous results of the invention can be achieved with all conventional types of 10-hopper, including single-vessel hydraulic digester, double-vessel hydraulic digester, etc. by simply reintroducing different fluid streams and feeding low DOM dilution solution and / or white liquor. .

The object of the invention is primarily to produce increased strength kraft pulp and / or also typically to reduce H-factor and alkali consumption and to increase bleachability. 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 bed apparatus according to the invention. implementing the methods; Figures 2 and 3 are graphical representations of the strength of the pulp produced according to the invention under identical conditions but not to the strength of the pulp produced without applying the invention; Figure 4 is a schematic view of an exemplary apparatus for the improved batch cooking method of the invention; Figure 5 is a schematic side view of another exemplary, ·. ·. a batch digester embodiment; • · · • · · · · · · · · · · · · · 7

Fig. 6 is a graph showing the H-factor of the pulp according to the invention compared to the H-factor of kraft pulp prepared under the same conditions; Fig. 7 is a graph showing the effective alkali consumption of a pulping according to the invention as compared to the effective alkali consumption of kraft pulp prepared under identical conditions;

Fig. 8 is a graph showing effective alkali consumption at various 10% percentages of factory liquor in a DOM-free solution;

Fig. 9 is a graph showing the brightness of the pulps prepared according to the invention under identical conditions to the luminance of the pulps produced without applying the invention; Figures 10 to 14B are still graphical representations of various strength aspects of the pulp according to the invention

Figures 12A-B compare the strength aspects of kraft pulp prepared without the invention under identical conditions; .:: 20 • · · • ·

Figure 15 is a graph of DOM concentrations based on three different solution sources j * · *. actual lye analysis of utilizing laboratory soups at various stages of cooking; • · • ·

Fig. 16 is a schematic representation of an exemplary two-stage hydraulic: T: 25 digester apparatus of the invention; • · · V! Figure 17 is a graphical representation of a theoretical study comparing DOM concentration in a traditional MCC® digester to DOM concentration in Fig. 16 digester; Figures 18 to 20 are schematic representations of other exemplary digesters of the invention; and • · · • · ··· • · · · · · 8

Figures 21 to 25 are graphical representations of theoretical studies of variable dilution and resolution parameters using the digester of Figure 19.

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

10

In the exemplary embodiment shown in Figure 1, the conventional impregnation vessel (IV) 10 is connected to a traditional vertical spout 11. The water-pulverized cellulosic fibrous material is transported from the conventional high pressure barrier feeder 12 through line 12 to the upper

According to the invention, in order to reduce the DOM content (in this specification and requirements, the dissolved organic material is defined as consisting mainly of dissolved hemicellulose and lignin but also dissolved cellulose, extracts and other material extracted from wood in the kraft cooking process). ) and is processed in step 16 to remove or inactivate the DOM or certain of its components. Step 16 may comprise · * · *; a precipitation step (e.g., lowering the pH below 9), an adsorption step (e.g.

• · ·; ··· cellulosic fiber column or activated carbon) or means for filtering (e.g.

ultrafiltration, microfiltration, nanofiltration, etc.), solvent extraction, decomposition: T: 25 (e.g., radiation bombardment), supercritical extraction, gravity separation or evaporation (followed by condensation).

· ♦ · • · · · · · · · ·

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

· · Jassa: alle 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 water, washing filtrate (eg brown mass washing filtrate), cold shot filtration or their ··· combinations. If the sulfide of the solution to be recycled in lines 12 and 13 is to be increased, black liquor 9 in line 17 may be added, but the black liquor must be treated so that the DOM in it is passivated, 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 a conventional sieve 18, a pump 19, and a backfeed assembly 20. The dilution solution - as indicated by arrow 21 - is added to the recycle solution 10 together 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 step 16 - can also be carried out in the joint 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 is removed in line 23 and white liquor is added at 24. The solution passes through 20 heaters 25 back • ·: * · *: to the lower part of the IV 10 via line 26 and / or fed near one of the starting ends 22 as indicated by line 27 of Figure 1.

· · · · ···:: In existing dishwashers, the solution is usually removed at different levels of the digester, ··· V: 25 is heated and then returned to the same level as the one being removed.

Under normal circumstances, however, the solution is not separated from the ice system and is not replaced by ··· V: fresh solution with a reduced DOM level. In existing digesters ··· black liquor is separated in the center of the digester, but the black liquor is not fed back but transported to the expansion tanks and from there to a recovery boiler or the like. In contrast to existing dispensers 11, the dispenser 11 of the invention separates the solution at various levels and heights, and replaces the separated solution with a solution containing less ♦ · DOM. This is done around the beginning of the soup, in the middle of the ··· and around the end of the soup. Using the digester 11 shown in Figure 1 and applying the process of the invention 10, the strength of the finished pulp to be removed in line 28 is greater than the conventional kraft pulp treated under an otherwise identical condition in an existing digester.

The digester 11 comprises a first saga of first 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 41, which may also include heaters 42 to 45. Recycling lines are traditional in themselves. However, according to the invention, a portion of the solution is separated in lines 46 to 49, for example by passing line 46 into a series of expansion vessels 50 as shown in Figure 1 in connection with the first screening set 30.

A replacement solution (dilution solution), as indicated by lines 51-54, is added to supplement the separated DOM-containing separated solution and to lower the DOM level 15. At these points, the effective DOM concentration of the solution added is significantly lower than the DOM content of the solution separated at lines 46-49 to increase the pulp strength. The solution to be added on lines 51-54 may be the same as the dilution solutions described above for line 17. The heaters 42-45 heat the replacement solution, as well as any recirculating solution, to substantially the temperature of the removal solution (typically • · · * · * · slightly above).

The stove 11 can include any number of strainers 30-33.

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

Another alternative in processing step 57 - which is schematically illustrated in Figure 1 - is pressure heating of black liquor 5. The solution, which can be considered "black liquor", is removed from the strainers 32, and part of it is separated in line 48. The pressure heating in step 57 can take place according to U.S. Patent 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 5-90 minutes (preferably about 30-60 minutes), at least 20 ° C. C io at a temperature higher than the cooking temperature. 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 as step 16. The treatment 58 may be included or omitted at any level of the digester 11 using solution instead of adding dilution solution. The white liquor may also be added in step 58, after which the DOM-passivated solution is returned to line 54.

Whether used as the treated separated solution or the diluent, it is desirable according to the invention to maintain the total DOM concentration of the cooking solution at 100 g / l or below substantially throughout the kraft cooking (bulk delignification), preferably below about 50: 20 g / l. It is also desirable to maintain a lignin content of 50 g / l or less (preferably about 25 g / l or less) and a hemicellulose content of 15 g / l or: ** (preferably about 10 g / l or less). The commercially optimal concentration is not yet known and may vary according to the wood species being cooked.

Figs. 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, when the wood raw material is the same. The tear factor is a measure of the inherent fiber and pulp strength • · · • · * · .. *.

Curve A in Figure 2 shows that the pulp has been prepared using traditional pulp mill liquor samples (from a commercial scale-scale MCC®-: ***: pulping process) as a cooking solution. Curve B is obtained from a soup in which the cooking solution is · · · identical to curve A except that the solution samples were heated at about 190 ° C at 12 ° C for one hour before being used in cooking. Curve C depicts 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 the corresponding profiles of the factory-scale pulping process, from which the factory-scale samples were obtained. The alkali and temperature profiles of curve C were identical to those of curves A and B but no DOM in the broth.

Figure 2 clearly shows that when a low DOM solution is in contact with 10 chips throughout the kraft cooking, the tear strength increases by about 27% at a tensile strength of 11 km. DOM passivation using black liquor pressure heating according to the invention as in curve B also resulted in a substantial increase in strength compared to standard curve A. In this case, the tear strength increased by about 15% at 11 km tensile strength.

15

Figure 3 further shows laboratory experiments 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 concentration of the curve D obtained from the standard

· * ·, · 20 (factory-scale lye-based) MCC® kraft soup was the highest and the curve G

• · DOM content was lowest (essentially no DOM). The DOM content of curve E was about 25% lower than the DOM content of curve D, and the content of curve F DOM *: ** was about 50% lower than the DOM content of curve D. As can be seen, a substantial increase in tear strength was achieved, which is inversely proportional to the size of the · · ·: 25 DOM present during cooking.

The soup according to the invention is preferably carried out so that the strength of the pulp (e.g.

··· the tear strength at a given tensile strength of the completely ground pulp (e.g. 9 or 10 km) would increase: at least about 10% and preferably at least about 15% compared to otherwise identical conditions, however, the DOM is not specifically treated.

• · • · · · · ·

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.

13

Figure 4 schematically illustrates conventional equipment that can be used in a Beloit RDH ™ batch cooking process or a Sunds Super Batch ™ process. The system schematically illustrated in Figure 4 includes a batch cooker 60 having an outlet screen 61, a chip source 62, a first, second and third accumulators 63, 64, 65, a white liquor source 66, a filtrate tank 67, a butt tank 68 and a plurality of valve mechanisms. In a typical conventional Beloit RDH ™ process actuator, the machine 60 is filled with chips from source 62 and steamed as required. The warm black liquor 10 is then fed to the digester 60. The warm black liquor 10 typically has a high sulfide content and a low alkali content and typically has a temperature of about 110-125 ° 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 led to chemical recovery. After impregnation, the warm black liquor in the digester 60 is returned to the battery 63, after which the digester 60 15 is filled with hot black and white liquor. Hot black liquor can be from battery 65 and hot white liquor from battery 63, originally from source 66. Typically, the hot white liquor will have a temperature of about 155 ° C and the black liquor will have a temperature of about 150-165 ° C. The chips in digester 60 are cooked at a certain temperature for as long as predetermined to achieve the desired factor H. The hot liquor is then led 20 directly to the battery 65 and replaced with filtrate from the tank 67. The chips • · are blown cold by compressed air or by pumping from vessel 60 to the buttress tank 68.

· · · · · · · · ·

During a typical RDH ™ process, the white liquor is continuously preheated with a solution from a hot ··· V * black liquor battery and then stored in a hot ··· · · 25 white liquor battery 64. The black liquor is transported to the warm lean black liquor battery 63.

Warm black liquor is transported to a heat exchanger to provide hot water, and ··· '· * stored in a pressurized container before being pumped into evaporators.

Referring 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 it can be significantly inactivated. the DOM contained in the lye. This • ·

: ***: can be achieved, for example, by heating the black liquor to at least 20 ° C

··· cooking temperature to a higher temperature, e.g., at a pressure of at least 170 ° C for about 5 to 90 minutes for 14 minutes, preferably 190 ° C or higher (e.g. 240 ° C) for about 5 to 90 minutes. Figure 4 schematically illustrates how this additional heat is introduced in step 71. The heat may be from any desired source. During black liquor pressure heating, a large amount of organic sulfur-containing exhaust gases are produced and removed at step 72 of the figure. Typically - as is known per se - the DMS (dimethyl sulfide) formed at step 72 is converted to methane and hydrogen sulfide. Methane can be used as a fuel supplement (for example, to provide heat at 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 10 elemental sulfur and removed. It can also be used to form polysulfide, or it can be absorbed into white liquor to produce a high sulfide alkali, etc. If the heat treatment in the battery is carried out at a temperature above about 20-40 ° C, black liquor can be used to facilitate impregnation during kraft cooking.

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

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

• ·: * · *; at least 8, e.g. 8 to 20 tons of pulp per day) batch digester system 74. The curve C in Figure · '· *: 2 was obtained using a laboratory test version of the system marked with a solid line in Figure 5; 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 • · ·:: 25 an outlet 79 at the lower portion.

At one level of the digester (e.g., lower portion 77) is a screen 81 communicating with a discharge line • · *: 82 and a pump 83 through which the heater 84. is connected. The heated solution • · · is circulated from heater 84 through line 85 back to digester 75 81 levels (eg near top 76).

• ♦ ·: · ♦: 30

Before transporting the solution to heater 84, a significant portion of · ·. *** is separated in line 86. line 82 of the lignin removed (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 contents may be used to simulate kraft soup in batch 75. Valves 88, 89 may be used to prevent or generate solution streams and / or replace or supplement the desired treatment with a dashed ice system.

According to the invention, the desired level of DOM and its constituents (e.g., <50 g / l DOM, <25 g / l10 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 with, for example, directing a high DOM solution in line 90 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 concentrations in the solution. Supplemental white liquor can also be added (not shown in Figure 15). The liquor may be reheated in heater 92 and then returned to 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 dashed lines 95, 96 in FIG.

Other laboratory test results demonstrating the benefits of the invention, • ·; *; *; 6-15. In these test results, methods were used to simulate · * · *; recycle the heated pulp solution in successive cycles • · *: ··· through a container with a constant amount of wood chips. The various stages of the cooking soup were simulated by varying the time, temperature and chemical concentrations used in the cycles. : T: 25 The actual factory-scale solution was used in the simulations when the corresponding step of the transponder was reached in the laboratory cooking.

··· • ♦ ♦ • ♦ ·

The effect of minimizing DOM in mass production solutions on the required: * · · mass production conditions (i.e., time and temperature) is shown in Figure 6. Figure • · *: * ·: 30 compares kappa to H factor in laboratory-scale lye and substantially DOM-free white liquor. In the figure ♦ · · • ♦. ···. The wood raw material used for the soups presented was typical of Northwestern United States ♦ ♦ · Coniferous, consisting of a mixture of cedar, fir, pine and fir. The H-factor is 16 standard parameters that describe cooking time and temperature as a single variable and are described, for example, in Rydholm: Pulping Processes, 1965, p. 618.

The graph of Figure 6 98 illustrates the ratio of kappa number to factor H in a laboratory cooker using 5 factory scale liquor (collected at the factory and then used in a throughput 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, with a 10 kappa number 30, the difference in factor H is about one hundred 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 with substantially less effective DOM than in the separated solution. Preferably, these steps aim to reduce the H-factor by at least 5% in order to reach a certain kappa number. During kraft cooking, the aim is to keep the effective DOM level at about 50 g / l or ring less than most of the time.

: * · *: Figure 7 shows that when using a solution with a reduced DOM content: * · *: according to the invention, the consumption of effective alkali (EA) is reduced. EA indicates the amount of cooking chemicals, particularly NaOH and Na2S, used in cooking · · *: **. The results shown in Fig. 7: T: 100, 101 were obtained when experiments were carried out under the same conditions and using ··· Y: 25 using the same raw materials as in Fig. 6. Curve 100 shows results when the cooking solution was conventional factory scale lye, shows results when the broth • · ·: was essentially DOM-free white liquor. With a unit count of 30 DOMs, · · ·, the soup not used consumed about 30% less alkali (ie 5% less EA from wood) than traditional factory-scale soup. Thus, when separating a solution containing *: **: 30 sufficient DOM to adversely affect the effective amount of alkali consumed to obtain a given kappa number, and replacing all or part of the separated solution with a solution, • ·. * * *. with substantially less effective DOM, the effective alkali consumed to obtain a specific kappa number can be substantially reduced. For example, the amount of alkali consumed to reach a certain kappa number 17 can be reduced by at least 0.5% calculated on wood (e.g. about 4% calculated on wood).

Both the favorable H-factor results and the EA consumption results shown in Figures 6 and 7, 5 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 S further schematically depicts the effective alkali consumption versus 10%, which indicates 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., substantially increased with the percentage of DOM-free white liquor). The following Table 1 shows the actual laboratory results on which the graph 101 of Figure 8 is based.

table 1

Effective Alkaline Consumption

Keittonro A3208 A3219 A3216 A3239 A3217. . 20 Description Tmk.l. 75% thousand. 50% thousand. 25% thousand. Läb.l.

• · · ——........ I.!. - - —...... - '· EA Total: T: Consumption,% _15,8 16.5_H9_15J_I4en_

Number of pieces,: \ screened_30,7 30.6_283_293_303_ 25 • · · • · * * * Tmk.l. = factory-scale lye • · · • · · · · Lab.l. = laboratory scale lye Reducing or removing the DOM in the pulp solution also facilitates the whitening of the resulting pulp. Figure 9 shows the actual laboratory test results, showing · · *. *: How does the brightness of the bleached cedar-fir-pine-noble-spruce increase as the amount of '* bleaching chemical increases. The ί, ί, ί parameter, "full sequence kappa factor", plotted on the X-axis of the graph of Figure 9, is the ratio of the corresponding chlorine dose to the mass kappa number obtained by · · *. In other words, it describes a somewhat standardized relationship between the chlorine used and the original lignin content of the 18 brown pulp. Figure 9 thus shows how the brightness of the pulp corresponds to the amount of bleaching chemical used.

The graphs 102, 103, 104, and 105 of Figure 9 depict essentially DOM-free 5 white liquor (102), traditional factory scale liquor (103), factory scale cooked pulp (not laboratory scale using alkaline scale) (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 part of the sputtered solution with a substantially less effective DOM-containing solution, the bleaching of the pulp produced can be greatly improved, for example by at least one ISO brightness unit with a given full sequence kappa factor. . Alternatively, these results indicate that a certain ISO brightness can be achieved even if less bleaching chemicals are 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 water, substantially free of DOM, would be a more suitable dilution solution. *. #: 20 white liquor and filtrate (and combinations thereof). However, heat-treated lye may be · * · *; used for non-bleached pulp, ie for unbleached species.

As noted above, reducing the DOM content of pulp solutions seems to have the strongest effect on pulp strength. This is also supported by the results shown schematically in Figures 10 -::: 25b. All these results have been obtained using the same raw material already mentioned in Figures 6-9, consisting of cedar, spruce, pine, and spruce • · ·: 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) as the factory-scale lye content decreases (and thus substantially increases the amount of DOM-free white liquor) in the described laboratory cookers. The same basic relationship is apparent from curve 107 of Fig. 11, which. * · *. describes the ratio of factory scale percentage to tear strength · «# at 600 CSF.

19

Table 2 illustrates tear strength at two tensile strengths in laboratory cookware using different solutions, and for comparison, shows the tear strength of pulp produced on a factory scale. The results for soups 2 and 3 in the table show that the tear strength of 5 increased by 20% at a tensile strength of 10 km 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% The laboratory soups 4, 5 and 6 in Table 2 show the result of replacing the DOM-free solution with the corresponding 10 mill scale liquor in certain parts of the soup. 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 cooking, MC, used factory scale liquor in the BC and MC stages of 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 and not just in the final 15 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 using hemlock raw material. 'J 20 Cooking conditions_Refraction. @ 10 km Ripping. @ 11 km_ 1) Factory scale-

* ·· * formula soup 123 N / A

·· · - - - · · · · · 2) Laboratory Soup (A) 174,156 I./25 + factory measuring. lye (B) 173 150 V *: Average_173 ^ 5_153_ • · · · · · · · 3) Laboratory Soup (A) 207 174 + Laboratory Liquid (B) 206 170: T: 30 Mean_206.5_172_. · · ·, 4) Laboratory soup **; · * + factory scale BC-: \ · liquor_183_159_t] Mj 5) Laboratory soup '35 + factory scale BC and MC liquor 181,157 • · · "- 6) Laboratory soup * ... · + factory scale washing detergent_187_N / A_ 20

Figures 12A-14B illustrate the effect of DOM on bleached pulp strength. Figure 12A shows tear and tensile strengths for unbleached pulp. The mass of curve 108 is prepared using essentially DOM-free laboratory liquor, the mass of curve 109 using pressure heated black liquor, and the mass of curve 110 using conventional factory-scale liquor. Fig. 12B illustrates the relationship between tear and tensile strength after the bleaching of the pulps depicted in Fig. 12A using the laboratory bleaching sequence DEoD (nD). Curve 111 depicts a bleached pulp prepared using essentially DOM-free white liquor. Curve 112 depicts pulp made using pressure-heated factory-scale liquor, and curve 113 represents bleached pulp made using conventional factory-scale liquor. For comparison, curve 114 depicts the strength of the factory scale pulp taken from the thickener after bleaching. Figure 12B shows that the pulp prepared with essentially no DOM-containing solution 15 is not only stronger than the pulp made with the factory-level solution, but that relative strength is retained even after bleaching. Even when using a heat-treated solution, the boiled pulp retains a higher strength after bleaching than the pulp boiled with the factory-grade solution, but the difference in post-bleaching strength is minimal.

: 20 • ·· • ·

: * j * j Figures 13A and 13B illustrate test results for the same soups / bleaches as Figures 12A

: * · *: And 12B with the difference that the tear strength factor is represented as a function of Canadian standard • · *: · *: freeness (CSF). Curve 115 is pulp made from essentially DOM-free solution; solution bleached 9 · m mass, curve 120 bleached, factory - scale solution mass and curve:. · 121 pulps from a factory scale thickener.

• · ·: ··: 30

Figures 14A and 14B illustrate the same soups / bleaches as Figures 12A and 12B with it. except that they show the relationship between tensile strength and freeness. Curve 122 depicts ··· pulp made with solution, curve 123 pulp with pressure heated 21 factory scale, curve 124 pulp with essentially no DOM solution, curve 125 pulp with whitened solution, curve 126 with whitened solution, pulp, 127 pulp from thickener, 5 and 128 bleached pulp, made by pressure heated factory scale solution. Figures 14A and 14B show that the tensile strength of both the pulp prepared with the pressure heated solution and the pulp made with the substantially DOM-free solution is reduced; Fig. 14B, however, also shows that bleaching causes the relative tensile strength of the pulp prepared with the pressurized solution to decrease below the tensile strength of the pulp with the DOM-free solution. As noted above, the heat-treated solution may be suitable for processes in which pulp is not bleached.

All of the above laboratory soups simulate the mass production sequences 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 uses a factory-scale solution, curve 131 uses 50%: 20 factory-scale solutions and 50% essentially DOM-free • ·; 1 · 1; 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 was impregnated initially, all laboratory solutions used were free of DOM because at this stage of the cooking process there was no reliable · · ·:: 25 sampling method for 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 · · · shows that each concentration shows a particular trend throughout the cooking time: 1 · · · gradually increases to the removal stage and then gradually decreases • · *; · ·: 30 during MCC® and wash phase. Of course, even when it comes to substance. 1. ·. A source of non-DOM solution, gets into solution as the cooking progresses.

• · · x • · · · • • • • 22

Figure 16 illustrates an exemplary dispenser system 133 which aims 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 stove is not shown in the figure, but it shows the 5 strainer 134. The traditional MCC® stove 134 of Figure 16 has been modified to carry out the cooking methods using the low DOM levels of the invention.

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 io (wood chips) is fed from the impregnation vessel in line 137 to the inlet 135. The screening group 138 at the top removes some of the lye from the fed slurry, which is fed back to the bottom circulation heater and 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 15 expansion tank group. Below the separation screen 140 there is a cooking screen 143 from which two lines leave. One line 144 takes care of the separation (and joins line 141), and the other line 145 leads to the pump 145 '. At the junction of lines 144, 145, a valve 146 may be followed 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 via a tube 151 20 having a tube mouth approximately at the level of the cooking strainer group 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 screens 140. Below the cooking strainer group 143 is a washing strainer group 152, from which • · ·; · *: the outlet line 153 leaves. The outlet line 153 leads to the pump 154 which controls the solution: V: through the heater 155 to the line 156. From line 156 ·: 25 through a tube 157 having a tube mouth approximately at the level of screen 152.

• · · V; System 133 digester production 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 limitation, the techniques of · · *: **: 30 according to the invention, which are described in detail in Figure 16, can be used. \. the solution is limited, it can be increased according to the invention by performing the separation also • ·. ***. 144. The application rate of the invention is typically about two tonnes of solution per tonne of pulp. In practice, one of my solutions per ton of pulp is separated in 23 lines 144 and replaced by a diluent (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 remaining 5 (e.g., one ton of solution per ton of pulp) is routed through line 162 to line 145 as a diluent. From source 163, white liquor substantially free of DOM in line 164 may also be added to line 145 prior to heater 147, and recirculation back to the digester via conduits 150 and / or 151. Of course, white liquor can also be added to the washing cycle in line 153 (see line 165) to provide EMCC® cooking. Arrows 166 indicating current 10 illustrate the parallel current range of digester 134. As a result of the modifications shown in Figure 16, the MCC® Cooking Area 167 has a cleaner, less DOM-containing solution upstream, which provides a stronger mass and, in this case, also increases the capacity of the digester 134.

The effect of the variants depicted in Figure 16 on the DOM content has been investigated using a dynamic computer model of Andritz Inc. The preliminary results of this theoretical study are shown schematically in Figure 17. Figure 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 • * .J 20 are plotted against curve 168 and the digester results shown in Fig. 16 by curve 169. As shown in Fig. 17 • ·: *: * j, the DOM concentration decreases sharply at 143 when adding · * · ' : less DOM-containing dilution solution, which also reduces DOM in the • · ·: * ·· countercurrent, which is directed back up to the separation target 140. Also down: T: the upstream wash solution contains less DOM because with the mass: 25 less DOM is transported. The curves 170,171 and part of the curves 168,169 show that in the countercurrent cooking zone the 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 flowing log.

• · · · · · ··· ·

Figures 16 and 17 thus illustrate the strong effect of only one difference-dilution step on the · · *: **: 30 DOM profile in the simulator. A decrease in DOM can also have a strong impact. the strength of the prepared pulp.

• · »·· • · • · ··· 24

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 systems differ 5 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 10; according to the invention, through the outlet port 174 therefrom, discharge to the expansion vessel 142 is provided.

In one practical example of the embodiment of Figure 18, two tonnes of solution per tonne of pulp in line 174 and four tonnes of solution per tonne of pulp in line 15141 are added in line 162 to the dilution solution and in line 164 essentially DOM-free white liquor. As a result, the currents 176, 177 shown in FIG. 18 are generated, wherein the digester 134 is powered by a parallel current, a counter current, a parallel current, a counter current (what can be called alternate flow cooking).

Fig. 19 shows another digestion system 179 according to the invention. This two-vessel system shows an impregnation vessel 180 having at its top: * · *: an inlet 181 and at the bottom an outlet 182. Solution removed from 183 • * *: ·· : is recycled to a conventional high pressure barrier feeder and white liquor is added at * · · y ': 184. The solution removed from 185 can be transported to the space between the first expansion vessel 186 and the · · · V * 25 second expansion vessel 187. The slurry from line 182 is directed from position 188 to the top of digester 189 having a "distillation vessel system" 190 from which the solution is removed. * * * V; at 191 and recycled to the bottom of the impregnation vessel 180. The solution is heated • · · * ...: circulating in heater 192.

The digester 189 also has a control sieve array 194 from which the discharge line 195 departs. 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 197 ··· is directed through valve 198 to line 199. Part of the solution can also be transported from valve 198 in line 200 to expansion vessel 186. The solution is diluted in line 199 less DOM: solution, such as substantially DOM-free white liquor 201 and filtrate 202, before being passed through heater 203 and fed back to digester 189 by means of one of 204 at the level of about 5 screening groups 196. The outlet screen group 206 leaves the outlet line 207, which leads to the expansion vessel 186. The wash screen group 208 includes a recycle 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 system 179, it is worth noting that removal from line 197 through valve 198 to outlet 200. Also, dilution solution in filtrate form is preferably added at 214 to line 182, and substantially DOM-free white liquor is added at 214 '.

15

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.

: * ·. · 20 Single Container Hydraulic Boiler Array 215 includes conventional chips container 216 • parts, evaporation vessel 217, pressure transfer device (high pressure barrier feeder) 218, line 219: '* *: for feeding cellulosic fibrous material slurry * and slurry tank 22: a bottom mass outlet port 222. A portion of the solution ··· Y: removed in line 223 and recycled to the high pressure barrier feeder 218.

· · · A: 25 Cooking strainers, for example, the first cooking strainer group 224 and the second cooking strainer group 225 are located below line 223.

··· • · · · · · · · ·

The first cooking screen set 224 comprises a first apparatus for circulating a first portion of solution removed from the cooking screen set 224 to the interior of the digester 121 30. The apparatus includes line 226, pump 227, and heater 228 from which it departs; ; ; feed line 229 to about the level of screen group 224. The apparatus may also include a valve · ·: ***: 230 for separating 230 solutions prior to heater 228 to line 231 when diluting a dilution solution, e.g. · white liquor (e.g., 10% of the total amount of white liquor used) is added to one 232 immediately prior to heater 228.

A second apparatus for circulating one of the removed solutions and separating the second removed solution 5 is provided in connection with the second cooking screen group 225. This second system includes a compound 235, a pump 236, a heater 237, a valve 238, and a 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 diluted in line 240. 10,224,225 in the adjacent cooking area.

Below the second cooker screen set 225 is located a separator screen set 245, from which one 246 to valve 247. From valve 247, line 248 leaves to first expansion vessel 249 of the recovery system.

The digester 221 further comprises a third screening group 253 located below the screening group 245, and a screening valve 254 associated with a screening group, from which outlet 255 and: * · · 20 separator connection 256. That is, depending on the location of valves 247, 254, solution may flow. *: From line 246 to line 255 or line 256 to line 248.

**: Line 255 is connected via pump 257 to heater 260 and return connection • · · * 261 at approximately the level of third filter 253. Dilution solution is added to line 255 before • · ·: 25 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.

• · · · · · · · · ·

The digester 221 also includes a washing screen array 263 having an outlet 264. The white liquor from source 233 (e.g., 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 feeding back the removed solution at about · · · 27 at the level of the screening group 263. The wash filtrate is also added below the screening group 263 via the interconnect 269 connected to the wash filtration source 243.

In one embodiment of the invention, 55% of the white liquor used for pulping 5 is added in line 271 to impregnate the chips when processed in the high pressure transfer device 218 and lowered to line 219. 5% of white liquor is added to the high pressure barrier 218 through line 272, 5% for both), and 15% is added to both line 258 and line 265.

By using the single-pan hydraulic tray 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: (A) Continued Modified Cooking with separation / dilution from 15 lower cooking ratios: In this model, the solution is separated from digester 221 conventionally in line 246 and extended modified cooking is used.

White liquor is added at lines 232, 258, 265. The solution is also removed at line 240, and the corresponding dilution solution is added at line 242 from the wash filtrate 243. This results in either one-way or: * ·. · 20 counter-current lower DOM flow • ·: * · *: between the separation screen 245 and the lower cooking screen 225. Whether the flow is parallel or upstream depends on the values of the lines 240, 246 *: · *:.

• · ·: (B) Continued modified bed cooking with separation / dilution • · · v ': 25 modified bed cooking cycles: This model uses all the flows described in (A), plus the solution is separated in line 256.

• ·· · Valves 247, 254 are adjusted to allow a portion of the solution to pass from the third • ·· screening group 253 (modified leach screen group) to line 248.

The dilution solution to replace this separated solution is added in line 259, *: **: 30 to provide another lower DOM level. *. *. upstream fluid flow between screen groups 245,253.

• · (C) Cause Improvement and Differential Dilution from Upper Cooking Ratios: This model can be used as such or in conjunction with the traditional modified • · · 28 cooking process or in addition to the models (A) and (B) above. This model includes the difference from the upper screening group 224 to the line 231, with valve 230 controlling the flow of solution and white liquor dilution occurring at line 232. Further dilution can be made 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. Acceleration is not caused by decay but by the lye content of incoming chips. Due to the low lye content of the chips, the hydraulic digester 221 forces the dilution stream back to the inlet 220, resulting in a backflow of liquor containing less than 10 DOM.

The system 215 shown in Figure 20 is not limited to the models A-C described above, but the models are merely examples of the many modified shapes that flow can take to produce a more robust mass according to the low DOM-15 content of the invention.

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. For all; '. the embodiments result in a reduction in DOM- · · * · 'as above; Concentration benefits such as increased strength, increased bleaching, · * · *: reduced effective alkali consumption and / or lower H-factor. This is illustrated by: · · •: · ·: The apparatus of Fig. 19 and the associated curves of Figs.

V *: 25 In Figure 19, reference numeral 185 denotes the first difference, 200 the second difference, 207 the third difference, 214 the first dilution, 202 the second dilution, and 213 the third dilution.

• · · · · · · · · ·

Figure 21 compares, through computer simulation, the DOM profiles of a standard EMCC® soup and a · · *: ··: 30 similar invention soup using the system of Figure 19 where extended parallel cooking is performed. • · · EMCC® steaming removes the solution from the traditional strainers and adds white liquor to the traditional cooking and washing circuits, so that the solution flow from the top of the stove is parallel, while the solution flow at the end of the stove is upstream. According to the extended parallel model of Figure 19, the third difference 207 is the main difference so that the parallel cooking takes place all the way to the sieve group 206. Figure 21 illustrates conventional EMCC® soup with curve 275 and extended 5 parallel current soup with curve 276. proportion 60% in impregnation, 184.5% in BC line 214 ', 15% in MCC® cycle 201 and 20% in wash cycle 210. In line 213, 1.5 tonnes of solution per mass scrubbing filtrate were added to the countercurrent.

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

15

Figure 22 shows how the addition of white liquor in line 201 of Figure 19 and the addition of low-DOM dilution solution in line 202 has a theoretical effect.

In Figure 22, 1.0 tons of solution per ton of pulp filtration line 202 is added, as well as 0.6 t / t white liquor. The corresponding 1.6 t / tp solution stream is removed at line 200. When comparing; * ·.! 20 curves 277 to curve 276 of Fig. 21, it is noted that the DOM concentration drops dramatically • ·: * · *; between the sieves 196,206.

**: **: Figure 23 illustrates the effect of varying addition of wash filtrate: dilution at lines 202 and 213. In this case, the total amount of wash filtrate is 1.5 V · 25 + 1.0 = 2, 5 t / tp is added at lines 213 and 202. In simulation of curve 278, 1/3 of the dilution solution at line 202 is added; curve 279 in simulation 1/2 on line 202; and curve 280 ···: in simulation 2/3 on line 202 (the rest is added in each case on line 213). Thus, it is clear that the DOM profile varies significantly with the different dilution flow rates: 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).

• · • · · · ***; Figure 24 illustrates the theoretical effect of difference variation on line 200. Curve 281 ··· illustrates a DOM profile with a line difference of 1.35 t / tp; a curve of 282 DOM profiles with a 30 difference of 200 at 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 lines 202 and 213, and additional 0.6 t / t of white liquor in line 201 is added. Figure 24 clearly shows that the theoretical DOM concentration in the cooking zone decreases as the amount of difference 5 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 separating strainer without greatly affecting the DOM profile.

Fig. 25 illustrates the effect of separation from line 185 (top of impregnation vessel 180) when it is desired to create countercurrent impregnation using extended parallel cooking and dilution. In this case, the results obtained from the use of a reference parallel current impregnation vessel are similar to those shown in Figure 22. The differential current 185 is 1.1 t / tp; the separated solution is not replaced by washing filtrate but by white liquor in line 184.

In the models of Figures 21 to 24, 60% of the white liquor was added in line 184 and 5% in line 214 '.

In Fig. 25, the reverse is true: 5% was added at line 184 and 60% at line 214 '.

Curve 284 shows the flow of a parallel current impregnation vessel, while line 285 indicates a counter current (60% white liquor in line 214 '). Thus, this demonstrates that the theoretical DOM content decreases in both the vessel 180 and the cooking zone and is comparable to the countercurrent cooking zone. Thus, lower DOM contents: 1 · · 20 are possible due to separation in vessel 180 and separation and dilution in digester 189.

♦ ♦ · ·: 2 2: 2: 2 2 2: 2 2: 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2: 2 ! 25 by passivating DOM at any stage of kraft cooking and adding more mass! process parameters. Although the invention is set forth and described herein by reference! ··· *. · According to current knowledge, in the most practical and preferred embodiment, it is clear that · · · · · · · · · · · · · · · · · · · · · · · the invention can be varied within its scope, which claims must be interpreted as broadly as possible. Products.

• • • • • • • • • • • • 2 • · 3

Claims (23)

A process for power boiling cellulose pulp with a batch boiler capable of producing at least one tonne of cellulose pulp per day, which boiler is provided with a strainer and an ether circulation line for removing the solution from the strainer and for conducting the solution to the batch boiler at different levels. in relation to the strainer, characterized in that the process comprises the following steps: (a) at least eight tonnes of mass of pulp are boiled in the batch digester per day; and (b) the solution is treated in the ether circulation line to substantially reduce effectively the halo of the organic matter (DOM) dissolved in the solution, including the content of lignin, hemicellulose and cellulose, by at least one of the following methods: dilution, separation and dilution, absorption, precipitation, filtration, degradation, gravity separation, supercritical extraction and evaporation. 15 A method for power boiling cellulose pulp in a batch boiler capable of producing at least one tonne of cellulose pulp per day, which boiler is provided with a strainer and an ether circulation line for removing the solution from the strainer and for conducting the solution to the batch boiler at various levels. relative to the strainer, characterized in that the process comprises the following steps: (a) at least one tonne of mass of pulp is boiled in the batch boiler per day; and (b) the solution is treated in the etheric circulation line to substantially reduce the effective content of the organic matter (DOM) dissolved in the solution, ... including the content of lignin, hemicellulose and cellulose, by adding a • · · • · · ". .. dilution solution, whose DOM content is lower than the DOM content of the solution removed from the strainer to the ether circulation line. • · · • · · • · ·. ···. Process according to claim 2, characterized in that step (b) is carried out by using water, filtrate or a combination thereof as a diluent. • · 30 ··· • · • · ··· 1 • · · • · · · · · · 36 Method according to claim 2 or 3, characterized in that the step (b) is carried out by using washing filters, washing filters from brown pulp, cold blowing filters or a combination of these as a diluent. Method according to any of the preceding claims, characterized in that step (b) is performed before step (a) or at the beginning of step (a). Method according to any one of the preceding claims, characterized in that a bulk delignification phase is included in step (a) and that step (b) is performed before the bulk delignification phase in step (a) or at the beginning thereof. Process according to any of the preceding claims, characterized in that an impregnation phase is included in step (a) and that step (b) is carried out before the impregnation phase in step (a) or during it. 15 Method according to claim 1, characterized in that a further step (c), in which the solution is transferred from the step (b) to the batch digester via the ether circulation line, is included in the process for improving the strength and bleachability of the produced pulp or for achieving it. a more favorable alkali consumption or 9. A method according to claim 2, characterized in that a further step, in which. The solution is transferred from step (b) to the batch digester via the ether circulation line, is included in the process to improve the strength and bleachability of the produced pulp, or to achieve a more favorable alkali consumption or H-factor. in the increase • · S (a). • · · • · · • · ·. ·· 1. Method according to claim 9, characterized in that the step (b) is performed by: · · · · · *. use the water, filtrate or a combination thereof as a diluent. • ·… 30 • · • • • · · • · · · · · · · · · · 37 11. A process according to claim 9 or 10, characterized in that step (b) is carried out by using washing filters, washing filters from brown pulp, cold blowing filters or a combination of these as a dilution solution. 5 Method according to any of claims 8-11, characterized in that the step (c) is performed before the step (a) or in the book thereof. Method according to any of claims 8 to 11, characterized in that a bulk delignification phase is included in step (a) and step (c) is performed before the bulk delignification phase or in the book thereof. Process according to any one of claims 8-13, characterized in that a cooking chemical is added in the process to a second solution before step (e). Apparatus for boiling cellulose pulp power, characterized in that the apparatus comprises - a batch kettle capable of treating at least a light ton of pulp per day; - a strainer connected to the batch digester; means for removing a first solution containing dissolved organic matter up to a first level, from said screen; • · · • ·· * .. 1 - means for treating the first solution to produce a second. solution containing dissolved organic matter up to a second level which is substantially lower than the first level, which agents are selected from the group consisting essentially of diluents, separators and diluents. absorbents, precipitants, decomposers; • gravity separation agents, supercritical extraction agents and evaporation agents; and; ***; means for transferring the second solution to the batch digester. • · · • ·. ···. 30 Apparatus according to claim 15, characterized in that said means for conduction of the second solution to the batch digester comprises an ether circulation line for transferring the second solution to the batch digester different levels in relation to said strainer. 17. Apparatus according to claim 16, characterized in that said treatment means comprise diluents and said diluents comprise means for adding a diluent solution containing little dissolved organic material in said ether circulation line. 18. Apparatus according to claim 17, characterized in that said diluent comprises means for adding a diluent solution containing little dissolved organic material and a boiling liquid in said ether circulation line. 19. Apparatus according to claim 16, characterized in that said means for treating the second solution processes the second solution before the power boiling or at the beginning of boiling in said electric cooker. 20. An apparatus for power boiling cellulose pulp, characterized in that the apparatus comprises 20. a batch kettle capable of treating at least eight tonnes of pulp per day; • · · ** * · - a tile connected to the batch cooker; ··· '• · · • · · .1. - means for removing a first solution containing dissolved organic matter up to a first level, from said screen; Means for treating the first solution to produce a second solution containing dissolved organic matter up to a second level which is substantially lower than the first level, which means includes means for mixing the first solution with a third solution containing .1 2. dissolved organic matter up to a third level lower than the first level. And means for transferring the second solution to the batch digester. • · ··· • · · • · · • · 2 • · 39 20 H factor in step (a). • · · • · · · · ··· • Il Apparatus according to claim 20, characterized in that the aqueous, filtrate or a combination thereof is used as a third solution in said mixing agent. Apparatus according to claim 15, 20 or 21, characterized in that it comprises additional means for adding a cooking liquid to the second liquid before the second solution is fed to the batch cooker. Apparatus according to any one of claims 15, 20 - 22, characterized in that said means for conducting the second solution leads the second solution to the batch electric kettle before boiling or at the beginning of boiling. · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · ··· · · · ··· ·· · · · · · · ··· · · · ··· · · · · · · · · · · · · · · · · · · · · · ·