JP2005336668A - Method for digesting lignocellulose material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for digesting lignocellulose material, capable of improving a digestion yield of the material, when the lignocellulose material is digested by using a one-vessel digestion apparatus having a penetration zone and digestion zones. <P>SOLUTION: This method for digesting the lignocellulose material comprises supplying the material to the one-vessel digestion apparatus having the penetration zone A and the digestion zones B and equipped with a plurality of strainers 5, 6, 7, and continuously digesting the material, while adding black liquor extracted from the strainers to the penetration zone A, wherein an amount of the black liquor extracted from the strainer 5 positioned between the penetration zone and a following digestion zone is at least 60 and an amount thereof extracted from the strainers 6, 7 of the digestion zones corresponds to an amount other than the above, when an amount of the black liquor added to the penetration zone is assumed to be 100, and white liquor and polysulfide in an additive ratio of 0.3 to 1.5 mass% (based on a bone dry weight of the lignocellulose material) are added to a top part of the penetration zone, and further the white liquor is added to at least one of the plurality of the strainers. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for cooking lignocellulosic material. More specifically, it relates to a method for improving the cooking yield of lignocellulosic material using a continuous digester.

  In order to use a lignocellulosic material as a papermaking raw material in many applications, it is necessary to digest it into chemical pulp or mechanically treat it with a refiner or the like to obtain mechanical pulp. These pulps are bleached as necessary, adjusted to a desired whiteness, and then used as a papermaking raw material. At present, the chemical pulping method is mainly used because it is easy to adjust to the desired whiteness and pulp characteristics. Especially, the cooking method called kraft method can regenerate chemicals and there are few restrictions on raw materials used. From the mainstream of chemical pulping. The kraft pulp method has also been developed in terms of equipment, and a large-scale production type called a continuous digester has become mainstream. Various improvement methods have been proposed for the kraft pulp method. For continuous digesters, MCC method, EMCC method, ITC method, Lo-Solids method and the like have been proposed. All of these improvement methods are methods for improving pulp quality.

  Among these, the MCC method divides the addition of cooking liquor into a continuous digester into three parts, and adds a counter-current flow with chips from the middle or lower part of the kettle to make the degree of pulp strength uniform. Compared to the conventional batch addition method of cooking liquor, it is said that the alkali concentration in each stage of the cooking process becomes uniform, and the disintegration of cellulose in the wood due to excessive alkali is suppressed. ing. However, this method does not contribute much to the improvement of the pulp yield, and there is a problem that it involves a major modification of equipment when applied to an existing continuous digester. In addition, the Lo-Solids method can maintain a state of less dissolved organic matter throughout the entire cooking process by combining a step of extracting black liquor and a step of replenishing with a solution having less dissolved organic matter than the extracted black liquor. It is disclosed in Patent Document 1 and Patent Document 2 that a uniform cooking reaction is performed by the above method, and a high strength pulp can be obtained. According to this method, a high strength pulp can be obtained, but the cooking yield is not clear. Not.

On the other hand, improvements in cooking liquor and delignification aids aimed at improving pulp yield have also been developed. The former includes polysulfide cooking, and the latter includes addition of quinone compounds.
Among these, the polysulfide cooking method converts white sulfide to polysulfide sulfur by oxidizing white liquor, or directly adding sulfur to the cooking liquor to protect the end groups of hemicellulose by oxidation, and by alkali during cooking. It is said that the pulp yield is improved to suppress the elution of cellulose. As this polysulfide cooking method, there is a method of adding 1.4% polysulfide sulfur (to wood chips) (Non-Patent Document 1), but when the cooking method by the conventional cooking method is 100, this method is used. The cooking yield due to is only 102-104.

  Moreover, although the method of producing | generating polysulfide sulfur by the electrolytic oxidation method is described in patent document 3-patent document 5, the electrode film indispensable to this method is easy to be clogged, and it has not yet reached practical use. Further, Patent Document 6 discloses a method of gasifying a part of the black liquor to generate hydrogen sulfide and forming polysulfide sulfur using an acid gas containing the hydrogen sulfide and carbon dioxide. It has not yet been put into practical use because of the equipment load of installing a Claus plant and the safety aspect of using a toxic gas called hydrogen sulfide, and there is no description of the cooking yield.

As a method for improving the cooking yield, the so-called COMPACT COOKING ^TM method, KOBUDO ^MARI method (Patent Document 7 to Patent Document 9), in which black liquor is returned to the permeation zone, the alkali profile of cooking is made uniform, and cooking is performed at low temperature for a long time. However, according to Non-Patent Document 2, when the yield of the conventional cooking method is 100, the cooking yield by the method is only 102 to 103.
Japanese translation of Japanese translation of PCT publication No. 8-51583 Japanese National Patent Publication No. 10-504614 JP-A-10-166374 Japanese Patent Laid-Open No. 11-5016 JP 11-51033 A Special table 2003-526740 gazette US Pat. No. 6,086,717 US Pat. No. 6,123,807 US Pat. No. 6,159,336 Akira Yamaguchi, “Polysulfide Cooking of Factory Chips”, Paper-Paper Technology Association, Vol. 33, No. 8, p1-9 Gunobu, “Yield Evaluation Method for COMPACT COOKINGTM and KOBUDOMARI Methods”, Proceedings of Annual Meeting of Paper and Pulp Technology Association, 2003, p49-59

  An object of the present invention is to provide a method for improving the cooking yield of a lignocellulosic material in a method of digesting a lignocellulosic material with a one-vessel cooking apparatus having an infiltration zone and a cooking zone in this order.

  The inventors of the present invention have conducted various studies on a method capable of improving the cooking yield in a method of cooking a lignocellulosic material using a one-vessel cooking device having an infiltration zone and a cooking zone in this order. It was found that the cooking yield can be improved by selecting the ratio of adding polysulfide to the mixture and adding the extracted black liquor to the infiltration zone. More specifically, the decomposition of polysulfide in the chemical solution is suppressed by cooking at a low temperature that could not be achieved by conventional cooking methods, and the black liquor containing a large amount of polysulfide is introduced into the infiltration zone and the like. By returning, it brought about an effect more than the amount of newly added polysulfide, and found that the cooking yield was greatly improved, and the present invention was completed. The present invention includes the following inventions.

(1) Supply lignocellulosic material to a one-vessel cooking device that has an infiltration zone, a cooking zone, and a washing zone in order, and is provided with a plurality of strainers, and add black liquor extracted from the strainer to the infiltration zone However, when the amount of black liquor added to the permeation zone is 100, extraction from the strainer between the permeation zone located at the top of the 1 vessel digester and the next digestion zone The amount of black liquor is at least 60 and the balance is a black liquor extracted from the strainer in the middle of the cooking zone of the 1 vessel digester and / or the strainer between the cooking zone and the washing zone, and / or the top of the infiltration zone and / or Prior to that, white liquor was added to the lignocellulosic material, and the addition rate was 0.3% to 1.5% by mass (against dry lignocellulose material). Polysulfide is added, digestion method lignocellulosic material, characterized by further addition of white liquor to at least one of the plurality of strainer).

(2) Item (1), wherein the remaining black extract from the strainer in the cooking zone and / or the strainer between the cooking zone and the washing zone is sent to an evaporator via a flash tank for processing. Cooking method of lignocellulosic material.

(3) An anthraquinone derivative is added to the lignocellulosic material at the top of the infiltration zone and / or before it, and the method for digesting a lignocellulosic material according to (1) or (2) .

(4) The lignocellulose material according to any one of (1) to (3), wherein the polysulfide is prepared by oxidizing sulfide using an oxidation catalyst. Cooking method.

(5) When the amount of black liquor added to the permeation zone is 100, the black liquor extracted from the strainer between the permeation zone and the digestion zone of the digester is 70 or more. The method for cooking lignocellulosic material according to any one of items (4) to (4).

(6) The method of digesting a lignocellulosic material according to any one of (1) to (5), wherein the temperature of the extracted black liquor added to the infiltration zone is 100 to 130 ° C.

(7) A part of the extracted black liquor from the plurality of strainers is added together with white liquor at the beginning of the cooking zone, (1) to (6) Cooking method of lignocellulosic material.

  According to the method of the present invention, at least two strainers are provided in a one-vessel cooking apparatus having a lignocellulosic material in the order of an infiltration zone and a cooking zone, and the extracted black liquor from the strainer is circulated at the beginning of the infiltration zone. In the continuous cooking method used, the amount of black liquor added to the permeation zone is used to circulate most of the amount of black liquor extracted from the strainer between the permeation zone located at the top of the digester and the next cooking zone. By using it, it becomes possible to effectively use the polysulfide added to the cooking apparatus by suppressing the decomposition and loss, and a cooking method of lignocellulosic material in which the cooking yield is greatly improved is provided.

The raw lignocellulosic material used in the cooking method of the present invention is preferably hardwood and softwood, but may be called non-wood and is not particularly limited.
Further, as the cooking method of the present invention, known cooking methods such as kraft cooking (polysulfide method), soda cooking, alkali sulfite cooking, etc. can be used, but considering pulp quality, energy efficiency, etc., the kraft cooking method Are preferably used.

  In the cooking method of the present invention, for example, as shown in FIG. 1, a continuous cooking apparatus having an infiltration zone (A), a cooking zone (B1, B2), and a washing zone (C) in this order from the top to the bottom is used. The The cooking zone in the continuous cooking apparatus is preferably a continuous cooking apparatus having a first cooking zone (B1) on the upper side and a second cooking zone (B2) on the lower side. A strainer is arranged between the infiltration zone (A) and the first cooking zone (B1), between the cooking zones (B1) and (B2), and between the cooking zone (B2) and the washing zone (C). Yes. In the case of FIG. 1, the zone (A) from the top of the 1 vessel digester to the strainer 5 is the infiltration zone, the zone (B1) from the strainer 5 to the strainer 6 is the first cooking zone, and the strainer 6 to the strainer 7. The zone until the second cooking zone (B2) and the zone from the strainer 7 until the pulp exits the cooking device is the washing zone (C).

  In the cooking method of the present invention, the cooking liquid is supplied from one or more places for each of the zones excluding the washing zone. For example, in the case of FIG. 1, the white liquor from the cooking liquor introduction tube 2 is supplied to the infiltration zone (A) in a state of being mixed with the lignocellulosic material and taken out from the strainer 5 through the black liquor extraction tube 16. The extracted black liquor is supplied from the black liquor introduction tube 4. Moreover, the white liquor from the white liquor introduction pipe 1 is supplied to the first cooking zone (B1) in addition to the cooking liquor accompanying the chips from the infiltration zone.

  As a supply ratio of the white liquor, the supply rate to the cooking zone is 20% by mass or more, preferably 25% by mass or more of the total white liquor. When the white liquor supply rate to the cooking zone is less than these, the elution of hemicellulose increases and the cooking yield decreases. As shown in FIG. 1, the white liquor to be dividedly supplied may be supplied by adding polysulfide to the white liquor to the permeation zone and further adding anthraquinone. Polysulfide and anthraquinone may be added and supplied to the white liquor to the cooking zone, but it is preferable to supply only the white liquor because the penetration of these cooking aids into the chips in the cooking zone is poor. As the white liquor, those having different degrees of sulfidation may be used. For example, when kraft cooking wood, the degree of sulfidation of white liquor is 5 to 75%, preferably 15 to 45%, and the effective alkali addition rate is The total amount is 5 to 30% by mass, preferably 10 to 25% by mass, based on the mass of the absolutely dry wood.

  Examples of the method for producing polysulfide sulfur used in the cooking method of the present invention include an oxidation catalyst method and an electrolysis method as practical methods. The oxidation catalyst method is a method in which an alkaline solution containing sodium sulfide is oxidized with molecular oxygen such as air in the presence of a catalyst such as activated carbon. In addition, the electrolytic method is a method of electrochemically oxidizing sulfide ions in a solution containing sulfide ions such as alkaline cooking liquid mainly composed of sodium hydroxide and sodium sulfide or sodium carbonate and sodium sulfide (Patent Document 2). ). The oxidation catalyst method has a problem that sodium thiosulfate, which is a by-product, is generated. Therefore, it can be added only up to 1.5% by mass with respect to the absolutely dry chip. Has been used in the past. The electrolysis method suppresses the reaction of by-products and can obtain polysulfide sulfur at a high concentration, but in Japan, it is not adopted in the factory because of the high electric cost, and the electrolysis method has an anode and cathode diaphragm. It is easy to clog and it is difficult to produce polysulfide sulfur stably. Therefore, in the present invention, polysulfide produced by the oxidation catalyst method was used. However, this is not limited if the situation in Japan is changed in the future, the electric cost is reduced, and the performance of the diaphragm is improved.

  The addition rate of polysulfide sulfur in this invention is 0.3-1.5 mass% with respect to an absolutely dry chip | tip. If the content is lower than 0.3% by mass, the yield is not sufficiently improved. If the content is higher than 1.5% by mass, as shown above, a large amount of by-products are generated, which is not suitable.

In addition, known cyclic keto compounds as cooking aids, for example, benzoquinone, naphthoquinone, anthraquinone, anthrone, phenanthroquinone, and quinone-based compounds such as alkyl and amino substitutions, or reduced forms of the quinone-based compounds. One or more selected from a hydroquinone compound such as anthrahydroquinone, and a 9,10-diketohydroanthracene compound which is a stable compound obtained as an intermediate of an anthraquinone synthesis method by Diels Alder method May be added, and the addition rate is a normal addition rate, for example, 0.001 to 1.0% by weight per the dry weight of the wood chips.
Other usable cooking aids include chelating agents such as ethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaacetic acid (DTPA), various surfactants, etc., and green liquor can also be used. It is not something. These cooking aids can be added in the same manner as the cooking liquor, and the place of addition is not limited.

  The cooking method of the present invention is characterized in that the following treatment is performed in the infiltration zone. The first is to increase the liquid ratio sufficiently, the second is to add sufficient alkali, and the third is not to raise the temperature too much. If the temperature is set too high, the reaction takes place before the chemical sufficiently penetrates the lignocellulosic material, leading to uneven cooking and polysulfide decomposition. In the present invention, the above condition is satisfied by adding a black liquor sufficiently containing polysulfide and containing a large amount of residual alkali together with the cooking liquor to the top of the infiltration zone.

  The cooking method of the present invention is a continuous cooking method in which at least two strainers are provided in one vessel cooking device, and the extracted black liquor from the strainer is added to the top of the cooking device, that is, at the beginning of the infiltration zone. For example, in the case of the method using the apparatus of FIG. 1, black liquor is extracted from the black liquor extraction tubes 16, 17, 18, and 19. Part or all of the black liquor extracted from the black liquor extraction tubes 16 and 19 is supplied to the infiltration zone through the black liquor introduction tubes 3 and 4, and the black liquor extracted from the black liquor extraction tubes 17 and 18 is entirely flushed. It is sent to the tank 15. Assuming that the total amount of black liquor supplied to the permeation zone is 100, the amount of black liquor extracted from the strainer 5 located at the top of the digester is at least 60, preferably 70 or more. When the black liquor extraction amount is less than 60, unreacted polysulfide is sent to the cooking zone having a high temperature and is ineffectively decomposed.

  As the extracted black liquor, the extracted black liquor from the black liquor extraction pipe 19 may be supplied to the permeation zone through the black liquor introduction pipe 3, but polysulfide has already been decomposed in the high temperature cooking zone (B1). Since it is hardly present in the extracted black liquor, this extracted black liquor portion cannot contribute to the chip processing in the permeation zone. In the cooking method of the present invention, the advantage of circulating the extracted black liquor from the strainer in the permeation zone is that polysulfide remaining without reacting with carbohydrates in the permeation zone is sent to the high temperature cooking zone. The polysulfide contained in the black liquor is circulated and supplied to the permeation zone before being effectively decomposed.

In the cooking method of the present invention, the liquid ratio in the permeation zone is 4-7. If the liquid ratio is less than 4, the chemical solution may not sufficiently permeate into the raw material. In addition, if a raw material with a small bulk weight is used, the raw material will not easily settle in the kettle, and the raw material will move inside the device. Becomes non-uniform, resulting in non-uniform cooking, which is not suitable. In particular, JAPAN TAPPI paper pulp test method no. When a raw material having a bulk weight measured in accordance with 3 is 450 kg / m ³ or less, this tendency becomes strong, which is effective. Raw materials with a bulk weight of 450 kg / m ³ or less include conifers such as Radiata pine, Kara pine, Todo pine, Ezo pine, etc., and some eucalyptus such as E.deglupta and E.grandis (for example, paper pa 48, No. 2, p294, Table 5) and Acacia. In addition, in the type of digester called a liquid kettle, the raw material is less likely to settle compared to the type of cooker called a gas phase kettle, so the liquid ratio is preferably set higher. On the other hand, if the liquid ratio is greater than 7, it is not suitable because the black liquor recovery load becomes too large.

  In the cooking method of the present invention, the temperature of the infiltration zone is 100 to 130 ° C., and the residence time of the lignocellulosic material is 0.5 to 2 hours. When the temperature is lower than 100 ° C. or the residence time is less than 0.5 hours, the chemical solution permeates and reacts insufficiently in the permeation zone, rapidly warms in the subsequent digestion zone, and digests at a high temperature. It is not suitable because of the high possibility of uneven cooking. On the other hand, when the temperature is higher than 130 ° C. or when the residence time is longer than 2 hours, the polysulfide is ineffectively decomposed, and the cooking reaction starts before the chemical solution sufficiently penetrates into the raw material. It is not suitable because it may not be possible or uniform cooking may not be possible due to side reactions caused by organic substances in the black liquor. In the infiltration zone of the present invention, a cocurrent flow treatment is always performed from the viewpoint of avoiding channeling.

The processing conditions of the cooking zone in the cooking method of the present invention include supplying white liquor from at least one place, extracting black liquor from the middle of the cooking zone, and at least 4 m ³ or more per 1 ton of undried unbleached pulp. There is no particular limitation except that black liquor is returned to the beginning of the infiltration zone, the remaining black liquor is extracted, and black liquor is extracted at the end of the cooking zone, but the amount of black liquor returned should be less than 4 m ^3. In this case, the improvement in yield is not remarkable, so it is not suitable. For example, in the case of the cooking method using the apparatus of FIG. 1, white liquor is supplied to the first cooking zone (B1) via the white liquor introduction pipe 1, and between the infiltration zone (A) and the first cooking zone (B1). Most of the black liquor extracted from the strainer 5 installed in the tank is supplied to the infiltration zone through the cooler 12, and if necessary, part of the black liquor passes through the heater 14 to the first cooking zone (B1). Supplied.

  The black liquor extracted from the strainer 6 by the black liquor extraction tube 19 is also supplied to the infiltration zone through the cooler 13 in the same manner as the extracted black liquor from the strainer 5. Of the black liquor extracted from the strainers 6 and 7, the black liquor extracted from the black liquor extraction tubes 17 and 18 is sent to the evaporator via the flash tank 15.

  The treatment in the cooking zone in the cooking method of the present invention is not limited to both countercurrent cooking and cocurrent cooking, and countercurrent cooking and cocurrent cooking are appropriately selected according to the situation. For example, as shown in FIG. 1, when the cooking zone is divided into an upper first cooking zone (B1) and a lower second cooking zone (B2), countercurrent cooking + countercurrent cooking, countercurrent cooking Four combinations of + cocurrent cooking, cocurrent cooking + cocurrent cooking, cocurrent cooking + countercurrent cooking are possible. These selections are appropriately made in consideration of the properties of the lignocellulosic material used as a raw material, operability, economy, pulp quality, and the like.

The liquid ratio in the cooking zone of the cooking method of this invention is 4-10. If the liquid ratio is less than 4, uncooked dust is generated due to insufficient penetration of the cooking liquid. On the other hand, if the liquid ratio exceeds 10, the recovery load of black liquor becomes too large, which is not suitable.
The maximum temperature in the cooking zone is, for example, 130 to 150 ° C when hardwood is used as a raw material, and 140 to 160 ° C when softwood is used as a raw material. The residence time of the lignocellulosic material in the cooking zone is 2 to 10 hours. If the residence time is shorter than 2 hours, cooking is insufficient and the chips are not pulped. On the other hand, if the residence time is longer than 10 hours, the pulp fibers are damaged by excessive cooking, which is not desirable. The amount of residual alkali in the black liquor extracted at the end of the cooking zone is 5 to 20 g / l, preferably 8 to 12 g / l. When the residual alkali concentration is lower than 5 g / l, the delignification reaction in the cooking zone does not proceed sufficiently. On the other hand, when the residual alkali concentration is higher than 20 g / l, damage to the cellulose increases and the digested pulp yield decreases. Therefore it is not suitable.

  The conditions in the cleaning zone of the cooking method of the present invention are not particularly limited except that the processing time is 1 hour or less. This is because, in the present invention, in order to digest the entire cooking apparatus at as low a temperature as possible, the cleaning time is inevitably shortened. In the washing zone, either counter-current cooking or co-current cooking may be used, and it is not particularly limited. However, considering the efficiency of washing in the apparatus, the counter-current cooking is a preferred embodiment. .

  In the cooking method of the present invention, a part of the black liquor extracted from a plurality of locations is sent to the flash tank 15, and after the flash vapor is collected, it is sent to the evaporator. After being concentrated by the evaporator, the organic material is recovered as thermal energy by combustion, and the inorganic material is finally regenerated into a cooking liquor.

  The cooking method of the present invention is a method in which a lignocellulosic material is cooked by a one-vessel cooking device having an infiltration zone and a cooking zone in this order, and at least two strainers are provided in the cooking device, and in particular an extraction black containing polysulfide. The liquid is circulated and supplied to the permeation zone for effective use. In the case of the cooking method of the present invention, the reason why the cooking yield is improved by cooking under relatively mild conditions is presumed as follows. That is, it becomes possible to perform cooking at a low temperature that could not be achieved by the conventional cooking method, so that polysulfide in the chemical solution becomes difficult to be decomposed, and black liquor containing a large amount of polysulfide is returned to the infiltration zone. Therefore, it is presumed that the cooking yield is greatly improved because the effect of the amount of polysulfide actually added is brought about and the decomposition of the carbohydrate in lignocellulose is hardly caused by polysulfide.

  Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. The digestion was evaluated using a laboratory digester that can reproduce the factory continuous digester. Numerical values such as blending ratio,%, and parts in each example are based on mass.

In Example 1 and Comparative Examples 1 and 2, the methods for measuring the kappa number and cooking yield of unbleached pulp are as follows.
<Measurement of copper number>
The kappa number was measured according to JIS P 8211.

<Measurement of cooking yield>
The measurement of the cooking yield was calculated from the following formula.
Cooking yield (%) = [Absolute dried chips (g) ÷ Absolutely dried pulp after cooking (g)] × 100

Example 1
As shown in FIG. 1, between the infiltration zone and the cooking zone, in the middle of the cooking zone (between B1 on the upper side of the cooking zone and B2 on the lower side) and the lower cooking zone (B2) of the cooking zone Using a 1 vessel digester with strainers (5, 6, 7) installed at three locations between the washing zone and Acacia mangum: Eucalyptus grandis: domestic hardwood = 30:40:30 (mass ratio) Hardwood chips were digested according to the following procedure. First, in the permeation zone (A), a digestion liquid corresponding to 12.6% effective alkali, 1.0% polysulfide sulfur, 0.03% anthraquinone, and 28% sulfidity is shown in FIG. The black liquor was introduced into the permeation zone (A) by adding 0.58 liters from the cooking liquor introduction tube 2 and 0.58 liters of black liquor from the black liquor introduction tubes 3 and 4 respectively. In the permeation zone (A), co-current cooking was performed, the chip residence time in the permeation zone (A) was 37 minutes, and the temperature was 125 ° C.

  Next, in the first cooking zone (B1) on the upper side of the cooking zone, 0.25 liter of cooking liquid (cooking liquid introducing pipe 1) corresponding to an effective alkali of 5.4% and a sulfidity of 28% with respect to 500 g of chip dry air Was used to circulate the liquid. Thereafter, 2.5 liters of black liquor was extracted from the strainers 6 and 7 through the black liquor extraction tubes 17 and 18 to 500 g of the absolutely dry chip, and sent to the flash tank 15. Both the upper side first cooking zone (B1) and the lower side second cooking zone (B2) were co-current cooking. The total residence time of the chips in the cooking zone (B1, B2) was 257 minutes, and the cooking temperature was 139 ° C. and 146 ° C. as the average values of the upper cooking zone (B1) and the lower cooking zone.

  Thereafter, in the cleaning zone (C), the residence time of the chips was 0.5 hour. Through the washing filtrate introduction tubes 20 and 21, 2.6 liters of unbleached pulp washing filtrate was added as diluted washing water from the bottom of the washing zone. The unbleached pulp has a copper number of 19.8 and 15.1 respectively for cooking temperatures of 139 ° C. and 146 ° C., and the undried pulp has an absolute dry yield of 289.5 g and 284.0 g. Were 57.9% and 56.8%.

Comparative Example 1
In the infiltration zone, the same as in Example 1 except that 0.75 liters of the extracted black liquor was added from the black liquor extraction tubes 3 and 4 respectively and the average temperature of the cooking zone was 138 ° C and 140 ° C. The operation was performed. The unbleached pulp has a copper number of 20.6 and 16.5 for cooking temperatures of 138 ° C. and 140 ° C., respectively, and the absolute dry yields of unbleached pulp are 276.0 g and 271.0 g, respectively. Were 55.2% and 54.2%.

Comparative Example 2
The same operation as in Example 1 was performed except that 0.1% of polysulfide sulfur was added in the infiltration zone and the average temperature of the cooking zone was 138 ° C, 139 ° C, and 146 ° C. The unbleached pulp has a copper number of 21.0, 17.9 and 14.8 for cooking temperatures of 138 ° C., 139 ° C. and 146 ° C., respectively, and the absolute dry yield of unbleached pulp is 271.5 g, 266. The cooking yield was 54.3%, 53.3%, and 52.8%.

  As apparent from the graphs of Table 1 and FIG. 2, when the lignocellulosic material is digested by a one-vessel digester having an infiltration zone and a digestion zone in order, at least two strainers are provided in the digester, In the continuous cooking method in which the extracted black liquor is added to the infiltration zone, when the amount of black liquor added to the infiltration zone is 100, the amount of extracted black liquor from the strainer located at the top of the digester is 60 or more. In addition, when the extracted black liquor, white liquor and polysulfide are added to the top of the infiltration zone, and the addition of the polysulfide is in a desired amount, it can be seen that the cooking yield is improved. That is, by carrying out the cooking method of the present invention, polysulfide in the chemical solution is difficult to decompose, and a large amount of black liquor containing polysulfide is extracted from the top strainer of the digester, and the spilled black liquor is extracted. By adding to the top of the permeation zone, an effect that exceeds the amount of polysulfide actually added was brought about, and the cooking yield could be greatly improved.

  The method of the present invention can further improve the cooking yield and further improve the relationship between the kappa number and the cooking yield. That is, the present invention can improve the cooking yield at the same kappa number at the same effective alkali addition rate.

It is a schematic diagram which shows an example of the cooking flow for implementing the cooking of this invention. It is a figure which shows the relationship between the copper number of unbleached pulp, and a cooking yield.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... White liquor introduction tube 2 ... Polysulfide and anthraquinone containing white liquor introduction tube 3, 4 ... Black liquor introduction tube 5, 6, 7 ... Strainer 8, 9, 10, 11 ... Pump 12, 13 ... Cooler 14 ... Heater 15 ... Flash tanks 16, 17, 18, 19 ... black liquor extraction tubes 20, 21 ... washing filtrate introduction tubes

Claims (7)

  A lignocellulosic material is supplied to a one-vessel cooking apparatus having an osmosis zone, a cooking zone, and a washing zone in order, and a plurality of strainers are provided, and the extracted black liquor from the strainer is continuously added to the osmosis zone. A method of cooking, where the amount of black liquor added to the permeation zone is 100, and the amount of black liquor extracted from the strainer between the permeation zone located at the top of one vessel cooking device and the next cooking zone Is at least 60 and the balance is the strainer in the middle of the cooking zone of the digester and / or the extracted black liquor from the strainer between the cooking zone and the washing zone, and at the top of the infiltration zone and / or earlier In the above lignocellulosic material, white liquor and polysulfate having an addition rate of 0.3% by mass to 1.5% by mass (against dry lignocellulosic material) A lignocellulosic material cooking method, wherein a white liquor is added to at least one of the plurality of strainers.   2. A part of the extracted black liquor from a strainer in the middle of the cooking zone and / or a strainer between the cooking zone and the washing zone is sent to an evaporator via a flash tank for processing. Cooking method of lignocellulosic material.   The method for cooking a lignocellulosic material according to claim 1 or 2, wherein an anthraquinone derivative is added to the lignocellulosic material at the top of the infiltration zone and / or at a location before that.   The method for cooking a lignocellulosic material according to any one of claims 1 to 3, wherein the polysulfide is prepared by oxidizing sulfide using an oxidation catalyst.   When the amount of black liquor added to the permeation zone is 100, the black liquor extracted from the strainer between the permeation zone of the digester and the next digestion zone is 70 or more. Item 5. The method for digesting a lignocellulosic material according to any one of Items 4 to 5.   The method for cooking a lignocellulosic material according to any one of claims 1 to 5, wherein the temperature of the extracted black liquor added to the infiltration zone is 100 to 130 ° C.   7. The lignocellulosic material cooking according to claim 1, wherein a part of the extracted black liquor from the plurality of strainers is added together with white liquor at the beginning of the cooking zone. 8. Method.

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