JP2003301392A - Method for digesting lignocellulose material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for homogeneously digesting a lignocellulose material by using a continuous digester. <P>SOLUTION: The method for digesting the lignocellulose material by using the continuous digester comprising an impregnation zone, a digestion zone and a cleaning zone in order comprises adding a digesting liquor at least to one position per each zone, and extracting a black liquor at the finishing of the impregnation zone and the digestion zone. The recovered black liquor after recovering flushed steam is cooled to ≤99°C, and the cooled recovered black liquor in an amount regulated so that the liquid ratio at the impregnation zone may be 3-7 is added to the lignocellulose material simultaneously with the digesting liquor at the starting of the impregnation zone. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for cooking lignocellulosic material. More specifically, the present invention relates to a method for uniformly cooking lignocellulosic material using a continuous digester.

[0002]

In order to use a lignocellulosic material as a raw material for papermaking in many applications, it is necessary to cook it into a chemical pulp or mechanically process it with a refiner or the like into a mechanical pulp. is there. If necessary, these pulps are bleached, adjusted to a desired whiteness, and then used as a raw material for papermaking. Currently, the chemical pulping method is mainly used because it is easy to adjust the desired whiteness and pulp characteristics. Especially, the cooking method called Kraft method is capable of regenerating chemicals and has few restrictions on raw materials used. Has become the mainstream of chemical pulping method. Further, the kraft pulp method has also been developed in terms of equipment, and a mass-produced type called a continuous digester and a large one have become mainstream. However, as the size of the apparatus increases, it becomes difficult to uniformly advance the digestion reaction in the cross-sectional direction and the vertical direction inside the kettle.

Japanese Patent No. 3126763 (Japanese Unexamined Patent Publication No.
(-132882), it is disclosed that a uniform cooking reaction can be carried out by impregnating with the extraction black liquor prior to the addition of the cooking liquor during cooking. However, when the alkali concentration in the black liquor is insufficient, there is a problem that the organic component in the black liquor is adsorbed to the lignocellulosic material such as wood chips, which rather causes a heterogeneous reaction.

Japanese Patent Publication No. 8-504483 discloses that a countercurrent digestion in the kettle can achieve a uniform cooking reaction at a lower temperature. However, when a raw material that has a small volume weight and is hard to settle is used, there is a problem that non-uniform settling occurs in the kettle, resulting in a non-uniform reaction.

Japanese Patent No. 2971947 (Patent Document 8)
No. 511583) and Japanese Patent Publication No. 10-504614.
In the craft publication, by combining the step of extracting black liquor and the step of replenishing the solution with a solution containing less dissolved organic matter than the extracted black liquor, it is possible to maintain a state of low dissolved organic matter throughout cooking. It is disclosed that a uniform cooking reaction is thereby carried out and a pulp having high strength is obtained. This cooking method is based on Lo-sol.
It is widely known as the ids method. However, depending on the amount of liquid to be replenished, the actual concentration of the cooking liquor may be reduced, and there is a problem that cooking deficiency may occur in some cases.

US Pat. No. 6,086,717,
No. 6,123,807, No. 6,159,3
No. 36, in the infiltration zone of a continuous digester,
Add black liquor of 100 to 160 ° C, preferably 130 ° C or higher, more preferably 130 to 160 ° C to pulp so that the liquid ratio becomes 2 to 10, preferably 3 to 8, and more preferably 4 to 6. Discloses that a uniform cooking reaction can be achieved, and the cooking method is COMPACT.
It is widely known as a cooking method. However, in the permeation zone, in order to add such a high temperature black liquor, the peripheral equipment must be special, not only costly, but if the temperature is raised too high in the permeation zone, There is also a problem that the digestion reaction proceeds before the chemical solution sufficiently penetrates, which rather leads to non-uniform digestion.

[0007] In Japanese Patent Publication No. 2001-512795, the black liquor is extracted after the permeation zone of the continuous digester is finished, the extracted black liquor is once cooled, and then the black liquor is added to the permeation zone again, whereby the chemical liquid permeation in the permeation zone It has been disclosed that the cooking is enriched and uniform cooking can be achieved. However, there was a problem that a cooling machine had to be newly installed to cool the black liquor.

On the other hand, JP-A-53-58003 discloses a method for improving pulp yield by adding black liquor produced by cooking hardwood when cooking softwood. . However, there is no mention of the effect of adding black liquor derived from hardwood to start digestion of softwood and extracting black liquor immediately after the end of the permeation zone.

[0009]

In view of the above situation, the present inventors have made various studies on a method for uniformly digesting a lignocellulosic substance using a continuous digester having an infiltration zone, a digestion zone, and a washing zone in this order. As a result of stacking, if the lignocellulosic substance is sufficiently permeated with the chemical liquid in the permeation zone, and if the dirt generated in the permeation zone is removed,
It has been found that the cooking can be performed under relatively mild conditions in the cooking zone and the washing zone, and as a result, uniform cooking can be performed. Furthermore, as a result of continuing the study, after cooling the extracted black liquor to 99 ° C. or lower, the above-mentioned matter can be carried out by adding it to the lignocellulosic substance at the same time as the cooking liquor at the start of the permeation zone. The inventors have found that the black liquor before being sent, that is, using the existing black liquor cooled to 99 ° C. or lower after recovering the vapor in the flash tank, can be easily implemented, and have completed the present invention.

It is an object of the present invention to provide a method for uniformly cooking lignocellulosic material using a continuous digester.

[0011]

The present invention is a method for cooking a lignocellulosic substance using a continuous digester having an infiltration zone (A), a digestion zone (B) and a washing zone (C) in this order. At least one cooking liquor for each zone
In a cooking method in which black liquor is extracted at the end of at least one of the permeation zone (A) and the cooking zone (B), after the flash vapor is recovered from the extracted black liquor,
A method for cooking a lignocellulosic material, characterized in that the recovered black liquor cooled to 9 ° C. or lower is added to the lignocellulosic material at the same time as the cooking liquor at the start of the infiltration zone, and the liquid ratio in the infiltration zone is set to 3 to 7. Is.

The present invention is the method for cooking lignocellulosic material, wherein the cooking zone (B) comprises two zones, an upper cooking zone (B1) and a lower cooking zone (B2).

The present invention is a method for cooking lignocellulosic material, characterized in that the extracted black liquor from the lower cooking zone (B2) is added to the upper cooking zone (B1) together with the cooking liquor without cooling. is there.

According to the present invention, a black liquor extraction step is provided at the end of the washing zone (C), and the black liquor extracted from the black liquor extraction step is not cooled, but together with the white liquor, the upper cooking zone (B1) and And / or a method for cooking lignocellulosic material, which comprises adding to the lower cooking zone (B2).

The present invention is based on Japan TAPPI Paper Pulp Test Method No. The volume weight measured according to 3 is 450
A method for cooking a lignocellulosic material, which comprises using a lignocellulosic material having a weight of not more than kg / m ³ .

According to the present invention, the recovered black liquor is a recovered black liquor obtained by digesting the same type or different types of lignocellulosic substances in the same continuous digester or another continuous digester. It is a characteristic method for cooking lignocellulosic material.

The present invention relates to a method for cooking lignocellulosic material derived from softwood using a continuous digester having an infiltration zone (A), a digestion zone (B) and a washing zone (C) in this order. As a recovered black liquor cooled to ℃ or less, there is a recovered black liquor obtained by cooking lignocellulosic material derived from hardwood in the same continuous digester or in different continuous digesters Is.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION The lignocellulosic material used in the present invention is preferably hardwood and softwood,
It may be called non-wood and is not particularly limited. As the cooking method used in the present invention, kraft cooking (including polysulfide method), soda cooking, known cooking methods such as alkaline sulphite cooking can be used, but considering pulp quality, energy efficiency, etc.,
The kraft cooking method is preferably used.

In the present invention, for example, as shown in FIG. 1, a continuous digester having a permeation zone (A), a digestion zone (B) and a washing zone (C) in order from the top to the bottom, preferably further A continuous digester in which the cooking zone (B) is divided into an upper cooking zone (B1) and a lower cooking zone (B2) is used. Each zone is separated by a strainer. For example, in the case of FIG. 1, after the cooking liquor from the white liquor introduction pipe 1 and the recovered black liquor from the recovered black liquor introduction pipe 27 are added to the lignocellulosic material, the steps up to the strainer 5 include the permeation zone (A), The process from strainer 5 to strainer 6 is the upper cooking zone (B1), the process from strainer 6 to strainer 7 is the lower cooking zone (B2), and the process from strainer 7 to strainer 8 is the cleaning zone (C).

FIG. 1 shows an example of a one-column type continuous digester, but in the present invention, either one-column type or two-column type continuous digester may be used and is not particularly limited. is not. However, in the present invention, since the reaction shortage in the permeation zone, which is a major drawback of the one-column type continuous digester, can be compensated, the one-column type, which has a small installation space and can be simplified in equipment, is more preferably used. .

In the present invention, the cooking liquor is always added at one or more places in each zone. For example, in the case of FIG.
The cooking liquor is dividedly added to the permeation zone (A) by the white liquor introduction pipe 1, the cooking zone (B1) by the white liquor introduction pipe 2, and the washing zone (C) by the white liquor introduction pipe 4. Also,
In the case of FIG. 1, the upper cooking zone (B
1), the cooking liquor can be further dividedly added to the lower cooking zone (B2) by the white liquor introducing pipe 3. The addition ratio of the cooking liquor is not particularly limited, but it is preferable to make the addition ratio to the permeation zone and the cooking zone higher than that to the washing zone.

The cooking liquor added in portions is as shown in FIG.
The same thing may be used, and different cooking liquors having different properties such as different sulfurization degrees and different polysulfide contents may be used. For example, when kraft cooking wood, the sulfidity of the cooking liquor is 5 to 75%, preferably 15 to 4
5%, and the total effective alkali addition rate is 5 to 30% by weight, preferably 10 to 25% by weight, based on the weight of the absolutely dried wood.
Is.

Further, known cyclic keto compounds as cooking aids, for example, benzoquinone, naphthoquinone, anthraquinone, anthrone, phenanthroquinone, and alkyl or amino substitutions of the above quinone compounds, or reduction of the above quinone compounds. A hydroquinone compound such as anthrahydroquinone which is a type, and a stable compound obtained as an intermediate of an anthraquinone synthesis method by the Diels-Alder method, or a compound selected from the group consisting of 9,10-diketohydroanthracene compounds and the like, or Two or more kinds may be added, and the addition rate is a normal addition rate, for example, 0.001 to 100% by dry weight of wood chips.
It is 1.0% by weight. Other cooking aids that can be used include ethylenediaminetetraacetic acid (EDTA),
Examples include chelating agents such as diethylenetriaminepentaacetic acid (DTPA), various surfactants, and the like. Green liquor can also be used and is not particularly limited. These cooking aids, like the cooking liquor, can be added in portions,
The place of addition is also not limited.

In the cooking method of the present invention, black liquor is extracted from at least two places at the end of the permeation zone and the digestion zone. For example, in the case of FIG. 1, at least the black liquor extraction tube 2
3 and the black liquor extraction pipe 25, black liquor is extracted and sent to the flash tank 21. However, as shown in FIG. 1, it is also possible to extract the black liquor from the black liquor extraction pipe 24 or the black liquor extraction pipe 26 and send it to the flash tank 21, and there is no particular limitation. The residual alkali concentration in each extracted black liquor is systematically set and operated according to the type of lignocellulosic material used as a raw material, the target Kappa number and whiteness of the pulp to be produced, and the subsequent usage of the black liquor. .

In the present invention, the condition setting of the permeation zone is particularly important. The permeation zone of the present invention is characterized by the following implementation. The first is to raise the liquid ratio sufficiently, the second is to add sufficient alkali, and the third is to not raise the temperature too much. This is because if the temperature is set too high, a reaction will occur before the drug solution has sufficiently penetrated into the lignocellulosic material, leading to uneven cooking. In the present invention, the above matter is achieved by adding black liquor having a large amount of residual alkali cooled to 99 ° C or lower together with the cooking liquor at the start of the permeation zone.

In the method of the present invention, the black liquor added to the permeation zone is the black liquor immediately before being normally sent to the evaporator, that is, 99% after the vapor is recovered in the flash tank.
Use the existing recovered black liquor cooled below ℃. For example, in FIG. 1, it corresponds to the recovered black liquor in the recovered black liquor introduction pipe 27. In the present invention, the advantage of using the recovered black liquor is that it is cooled to 99 ° C. or less and meets the temperature setting of the permeation zone, has sufficient alkalinity and sulfidity, and is quantitative. It is abundant and it is possible to make a sufficient liquid ratio, and harmful gases such as methyl mercaptan and hydrogen sulfide have been removed, and it is relatively safe even if a trouble should occur. These are also major features.

The recovered black liquor used in the present invention is preferably generated from the same continuous digester and is made from the same lignocellulosic material, but is not particularly limited. Absent. Using the same continuous digester,
When alternately cooking multiple raw materials, or when individually cooking multiple raw materials using multiple dedicated continuous digesters, recovered black liquors of different raw materials may be mixed and used.
The individually recovered black liquor may be intentionally used for cooking different raw materials. For example, recovered black liquor derived from hardwood has a smaller amount of foaming components than that derived from softwood and is easy to handle. Therefore, it is rather positively used for cooking softwood. Further, in the present invention, since black liquor cooled to 99 ° C. or lower is used, peripheral equipment such as a raw material supply equipment can be simplified, or existing equipment can be used.

In the present invention, the liquid ratio in the permeation zone is 3-7. If the liquid ratio is less than 3, the chemical liquid may not sufficiently permeate the raw material, and when a raw material having a small volume weight is used, it becomes difficult for the raw material to settle in the pot, and the raw material moves in the pot. Is not suitable because it results in uneven cooking, resulting in uneven cooking. In particular, JAPAN TAPPI Paper Pulp Test Method No. The volume weight measured according to 3 is 450
This tendency is effective when a raw material of kg / m ³ or less is used, which is effective. Examples of raw materials having a volume weight of 450 kg / m ³ or less include coniferous trees such as radiata pine, kara pine, sea lion pine, and pine pine, and E. deglupta and E.I. gra
Some eucalyptus such as ndis (for example, Paper and Paper Cooperative Magazine, 48, No. 2, P294, Table 5) and acacia can be mentioned. Further, in a digester of the type called a liquid phase cooker, it is more difficult for the raw materials to settle than in a digester of the type called a gas phase cooker, so it is preferable to set the liquid ratio higher. On the other hand, if the liquid ratio is larger than 7, the strainer load becomes too large, which is not suitable.

In the permeation zone in the method of the present invention, the amount of residual alkali in the black liquor extracted after the end of the permeation zone is 2
-20 g / l, preferably 6-12 g / l. When the residual alkali concentration is lower than 2 g / l, even if the liquid ratio is increased, the alkali content may not sufficiently penetrate into the raw material, which is not suitable. On the other hand, 20 g /
When it is higher than 1, the black liquor recovery load becomes high thereafter, which is not suitable.

The temperature in the permeation zone of the present invention is 70 to 140 ° C., preferably 90 to 120 ° C., and the residence time of the lignocellulosic material is 10 to 90 minutes,
It is preferably 20 to 60 minutes. When the temperature is lower than 70 ° C or when the residence time is less than 10 minutes, the permeation and reaction of the chemical liquid in the permeation zone become insufficient, and the material must be rapidly heated in the subsequent digestion zone and digested at a high temperature. It is not suitable because it is likely to result in uneven cooking.
On the other hand, when the temperature is higher than 140 ° C or the residence time is 90
If it is longer than a minute, the cooking reaction may start before the chemical solution has sufficiently penetrated into the raw material, and thus uniform cooking may not be possible, or the side reaction due to the organic matter in the black liquor may prevent uniform cooking. Not suitable because it exists.

In the infiltration zone of the present invention, cocurrent cooking is always carried out from the viewpoint of avoiding channeling. Also,
In the permeation zone, a circulation pump and a heater are installed as needed, like the circulation pump 9 and the heater 10 in FIG. 1, so that liquid circulation and heating in the zone can be performed.

The conditions in the cooking zone of the method of the present invention are not particularly limited except that the cooking liquor is added at at least one point and the black liquor is extracted at the end of the cooking zone. However, it is preferable to divide the cooking zone into an upper cooking zone and a lower cooking zone, and further perform divided addition of cooking liquor and liquid circulation. For example, as shown in FIG. 1, black liquor extracted from the strainer 6 (black liquor extraction tube 2
While adding the cooking liquor (white liquor introduction pipe 2) to 4), liquid circulation and heating are performed using the circulation pump 11 and the heater 12.
Black liquor simultaneously extracted from the strainer 7 (black liquor extraction tube 2
Part of 5) is sent to the flash tank (21), and while the cooking liquor (white liquor introduction pipe 3) is added to the remaining black liquor, the circulation pump 13 and the heater 14 are used to circulate and heat the liquor. This is a preferred embodiment.

Further, as a preferred embodiment, a method of sending a part of the black liquor in the black liquor extraction pipe 24 to the flash tank (21) can be mentioned. In addition, during the liquid circulation in the upper digestion zone (B1) and the lower digestion zone (B2) of FIG. 1, a washing filtrate (washing filtrate introducing pipes 17 and 18), which is a washing filtrate of unbleached pulp after digestion, is used as a replenishing liquid. It is also possible to add. Black liquor (black liquor extraction tubes 25 and 26) can also be used as a similar replenisher. When a washing filtrate is added as a replenisher, there is an advantage that the organic solid content concentration in the reaction solution is decreased and the reactivity is increased, while when the extraction black liquor is added, a heat source and an added white matter are added. There is an advantage that the amount of liquid can be saved, and it can be used properly according to the situation and purpose.

In the cooking zone of the method of the present invention, the countercurrent digestion and the cocurrent digestion are not particularly limited, and the countercurrent digestion and the cocurrent digestion are appropriately selected depending on the situation. For example, when the cooking zone is divided into an upper cooking zone and a lower cooking, countercurrent cooking + countercurrent cooking, countercurrent cooking + cocurrent cooking, cocurrent cooking + cocurrent cooking, cocurrent cooking + countercurrent cooking Four combinations are possible. These selections are made in consideration of the properties of the lignocellulosic material as a raw material, operability, economic efficiency, pulp quality, and the like.

The maximum temperature in the digestion zone of the method of the present invention is, for example, 120 to 15 when hardwood is used as the raw material.
It is 0 ° C., preferably 130 to 140 ° C., and when softwood is used as a raw material, it is 145 to 170 ° C., preferably 150 to 160 ° C. The retention time of the lignocellulosic material in the digestion zone is not particularly limited, but it is preferably as long as possible in order to keep the maximum temperature as low as possible. The amount of residual alkali in the black liquor extracted at the end of the cooking zone is 5 to 20 g.
/ L, preferably 8-12 g / l. When the residual alkali concentration is lower than 5 g / l, the delignification reaction in the cooking zone does not proceed sufficiently, and when it is higher than 20 g / l, damage to cellulose becomes large and cooking pulp yield becomes low, which is suitable. Absent.

The conditions in the washing zone of the method of the present invention are not particularly limited except that the cooking liquor is added at at least one place. However, it is a preferred embodiment that the liquid is circulated in the washing zone and the black liquor is extracted at the end of the washing zone. For example, in the case of FIG. 1, part of the black liquor (black liquor extraction pipe 26) from the strainer 8 which is the end point of the washing zone is sent to the flash tank, the remaining black liquor is replenished with cooking liquor, and the circulation pump 15
It is a preferred embodiment that the liquid circulation and the heating are performed using the heater 16 and the heater 16. Further, in some cases, a part of the black liquor (black liquor extraction pipe 26) can be used as a replenisher for liquid circulation in the upper cooking zone (B1) and the lower cooking zone (B2).

In the washing zone of the method of the present invention, either countercurrent digestion or parallel stream digestion may be used and is not particularly limited, but considering the efficiency of washing in the kettle, it is considered as countercurrent digestion. Is the preferred embodiment.

In the present invention, the black liquor extracted from a plurality of locations is sent to the flash tank (21), and after collecting the flash vapor, it is cooled to 99 ° C. or lower in the cooler (22). A part of the cooled black liquor is added to the permeation zone (A), and the rest is sent to an evaporator. After being concentrated by an evaporator, the organic substance is recovered as heat energy by combustion, and the inorganic substance is finally regenerated into a cooking liquor.

In the present invention, at least one cooking liquor is added to each zone using a continuous digester having a permeation zone, a digestion zone and a washing zone in that order, and at least at the end of the permeation zone and the digestion zone, a black liquid is added. After extracting the liquid and further recovering the flash vapor, the recovered black liquor cooled to 99 ° C. or lower is added to the lignocellulosic substance at the same time as the cooking liquor at the start of the infiltration zone, and the liquid ratio in the infiltration zone is 3 to The reason why the lignocellulosic material can be uniformly cooked according to No. 7 is not clear until further study, but it is speculated as follows.

First, by adding black liquor simultaneously with the cooking liquor at the start of the infiltration zone, the initial infiltration and cooking reactions can be promoted with a sufficient amount of alkalinity, sulfidity and liquid amount, while the infiltration zone is terminated. After that, by extracting the black liquor, it is possible to avoid the demerit due to the addition of the black liquor, that is, the cooking interference reaction by the organic matter in the black liquor. Further, by extracting the black liquor after the end of the permeation zone, it is possible to efficiently remove the pollutants generated in the early stages of cooking, and as a result, the delignification reaction that stalls in the latter stages of cooking can also be performed. It is speculated that a uniform cooking can be achieved because it proceeds relatively smoothly.

[0041]

The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples. In Examples 1 to 4 and Comparative Examples 1 to 3 shown below, the following methods were used to measure the Kappa number, whiteness and viscosity of unbleached pulp.

1. Measurement of Kappa number The Kappa number was measured according to JIS P 8211.

2. Whiteness Measurement After disintegrating pulp, Tappi test method T205os-
71 (JIS P 8209), basis weight 60 g / m
The sheet of No. ² was prepared, and the whiteness of the pulp was measured according to JIS P8123.

3. Viscosity Measurement Pulp viscosity measurement is described in J. It carried out according to TAPPI 44.

Example 1 Using the one-tower continuous digester of Fig. 1, 100% radiata pine
Softwood chips consisting of (capacity weight 410 kg / m³)
Cooked according to the procedure below. First, in the penetration zone (A)
In addition, for every ton of coniferous wood chips dried, effective alkali
Fig. 1 shows a cooking liquor corresponding to 8.3% and a sulfidity of 28%.
0.8m from the white liquor introduction tube³And recovered black liquor (90 ° C)
From the black liquor introduction pipe 27 to 3.0 m³Add and cook
It was made to start (liquid ratio was 4.7). Then the circulation pump 9
90m using ³Black liquor while circulating the liquid at a flow rate of / H
Through extraction tube 23, 4.4m per ton of chips
³Drain the black liquor and send it to the flash tank 21.
It was In the permeation zone (A), parallel flow cooking is carried out and
The residence time of the chips in the transparent zone A) is 40 minutes.
The temperature of the discharged black liquor was 115 ° C.

Next, in the upper cooking zone (B1), the black liquor (black liquor extraction tube 24) from the strainer 6 was digested to an amount of 9.5% as an effective alkali and 28% of sulfidity for 1 ton of dried chips. Liquid (white liquor introduction tube 2) 0.9 m
³ and washing filtrate of unbleached pulp (washing filtrate introducing pipe 17)
1.0 m ³ was added, and the liquid was circulated at a flow rate of 150 m ³ / H using the circulation pump 11 while heating with the heater 12. After that, from the strainer 7, the black liquor extraction pipe 25
3.0 m ³ of black liquor was extracted per 1 ton of chips completely dried via the, and sent to the flash tank 21. The upper cooking zone (B1) was countercurrent cooking and the lower cooking zone (B2) was cocurrent cooking. Residence time of chips in the cooking zone is 2
The time was 20 minutes, and the temperature of the black liquor sent to the flash tank 21 was 155 ° C.

Thereafter, in the cleaning zone (C), black liquor (black liquor extraction pipe 26) from the strainer 8 was treated with 2.0% of an effective alkali and a sulfidation degree of 28 per 1 ton of chips completely dried.
% Was added cooking liquor (white liquor inlet tube 4) 0.2 m ³ equivalent to, liquid was circulated at a flow rate of 95 m ³ / H using a heated while circulating pump 15 in heater 16. Countercurrent digestion was carried out in the washing zone (C), and the total residence time of the chips in the kettle was 5 hours. After the completion of cooking, 4.0 m ³ of the washing filtrate of unbleached pulp was added from the bottom of the kettle as washing water for dilution through the washing filtrate introducing pipes 19 and 20. The unbleached pulp obtained had a whiteness of 29.0%, a Kappa number of 27.0, and a viscosity of 40.2 mPa · s.

Example 2 The same operation as in Example 1 except that the recovered black liquor added to the softwood chips together with the cooking liquor in the infiltration zone was replaced with the recovered black liquor derived from hardwood (generated in another digester). Was done. The unbleached pulp obtained had a whiteness of 29.5%, a Kappa number of 26.8, and a viscosity of 41.3 mPa · s.

Example 3 The amount of black liquor sent to the flash tank 21 through the black liquor extraction pipe 23 was changed to 5.2 m ³ per ton of chip dry matter, and black sent to the flash tank 21 through the black liquor extraction pipe 25. The liquid volume and temperature were changed to 1.0 m ³ and 154 ° C., and 1.4 m ³ of black liquor was newly added to the flash tank 2 through the black liquor extraction pipe 24.
1, the amount of cooking liquor added in the upper cooking zone (B1) was changed to 0.4 m ³ (corresponding to 3.8% as an effective alkali and 28% of sulfidity), and the washing filtrate (washing filtrate introducing pipe 1
Black liquor (black liquor extraction tube 25) 0.4 m ³ was added in place of 7), and cooking liquor 0.6 m ³ (as an effective alkali was newly added through the white liquor introduction tube 3 in the lower cooking zone (B2). (Corresponding to 5.7%, sulfidity 28%) and washing filtrate introducing pipe 18
Example 1 except that 0.6 m ³ of the unbleached pulp washing filtrate was added via the reactor and the liquid was circulated at a flow rate of 90 m ³ / H using the circulation pump 13 while heating with the heater 14. The same operation was performed. However, the lower cooking zone (B
2) was countercurrent cooking. The unbleached pulp obtained has a whiteness of 29.1%, a Kappa number of 26.8, and a viscosity of 43.6 m.
It was Pa · s.

Example 4 In the lower cooking zone (B2), black liquor (black liquor extraction pipe 26) was added in place of the washing filtrate (washing filtrate introducing pipe 18), and the black liquor (black liquor extraction) was sent to the flash tank 21. Tube 2
The same operation as in Example 3 was performed except that the temperature in 5) was changed to 153 ° C. The whiteness of the obtained unbleached pulp is 29.
5%, kappa number 27.0, viscosity 44.3 mPa.
It was s.

Comparative Example 1 In the permeation zone (A), the recovered black liquor to be added to the softwood chips together with the white liquor was replaced with the washing filtrate (80 ° C.) of unbleached pulp, and the flash tank 21 was passed through the black liquor extraction pipe 25. The same operation as in Example 1 was carried out, except that the cooking temperature in the cooking zone was changed so that the temperature of the black liquor sent to No. 1 was 162 ° C. The whiteness of the obtained unbleached pulp is 27.1%,
The Kappa number was 27.0 and the viscosity was 32.4 mPa · s.

Comparative Example 2 In the permeation zone (A), the amount of the recovered black liquor added to the softwood chips together with the cooking liquor was 0.5 m ³ (liquid ratio: 2.
2), the amount of black liquor sent to the flash tank 21 via the black liquor extraction pipe 23 is changed to 1.9 m ^3, and the temperature of the black liquor sent to the flash tank 21 via the black liquor extraction pipe 25 is 165 ° C. The same operation as in Example 1 was performed except that the cooking temperature in the cooking zone was changed so that The unbleached pulp obtained has a whiteness of 26.6% and a Kappa number of 2.
The viscosity was 7.0 and the viscosity was 30.4 mPa · s.

Comparative Example 3 In the permeation zone (A), the recovered black liquor to be added to the softwood chips together with the cooking liquor was changed to that immediately before the flash tank 21 (142 ° C.), and the black liquor was transferred to the flash tank 21 via the black liquor extraction pipe 25. Example 1 except that the cooking temperature in the cooking zone was changed so that the temperature of the black liquor sent was 157 ° C.
The same operation was performed. The whiteness of the obtained unbleached pulp is 28.1%, the Kappa number is 27.0, and the viscosity is 35.4 m.
It was Pa · s.

[0054]

[Table 1]

[0055]

[Table 2]

[0056]

As is apparent from Tables 1 and 2, when a lignocellulosic substance is digested using a continuous digester having an infiltration zone (A), a digestion zone (B) and a washing zone (C) in that order. , At least one cooking liquor is added to each zone, and at least the permeation zone (A)
And in the cooking method of extracting black liquor at the end of the digestion zone (B), after recovering the flash vapor from the extracted black liquor, the recovered black liquor cooled to 99 ° C. or lower is passed through the permeation zone (A).
It can be seen that the whiteness and the viscosity of the unbleached pulp are improved by adding to the lignocellulosic material at the same time as the cooking liquor at the start of, and adjusting the liquid ratio in the permeation zone (A) to 3 to 7.

Further, the recovered black liquor obtained when other lignocellulosic materials are digested is used, or the digestion zone (B) is divided into an upper digestion zone (B1) and a lower digestion zone (B2), and a lower digestion zone is prepared. By using the hot black liquor extracted after the end of (B2) and the hot black liquor extracted at the end of the washing zone (C) as a replenisher for the upper cooking zone (B1) and the lower cooking zone (B2), It can be seen that the effect increases. That is, by carrying out the above-described cooking method, the lignocellulosic material could be uniformly cooked, and as a result, the pulp quality after cooking could be improved.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an example of a cooking flow for carrying out the cooking of the present invention.

[Explanation of symbols]

1, 2, 3, 4 ... White liquor introduction tube 5, 6, 7, 8 ... Strainer 9, 11, 13, 15 ... Circulation pump 10, 12, 14, 16 ... Heater 17, 18, 19, 20 ... Washing filtrate introducing pipe 21 ... Flash tank, 22 ... Cooler 23, 24, 25, 26 ... Black liquor extraction tube 27 ... Recovery black liquor introduction tube 28 ... 1 tower type continuous digester

Continued front page    (72) Inventor Tomofumi Izuka             373 Yoshioka, Yonago, Tottori Prefecture Oji Paper Co., Ltd.             Inside Yonago Factory F-term (reference) 4L055 AB20 BA24 BA27 BA40 FA03                       FA30

Claims (6)

[Claims] 1. A method of digesting a lignocellulosic substance using a continuous digester having an infiltration zone (A), a digestion zone (B) and a washing zone (C) in this order. In a cooking method in which at least one point is added, and black liquor is extracted at the end of at least the permeation zone (A) and the digestion zone (B), flash vapor is recovered from the extracted black liquor and then cooled to 99 ° C or lower. Black liquor was added to the lignocellulosic material at the same time as the cooking liquor at the start of the infiltration zone, and the liquor ratio in the infiltration zone was 3 to
7. A method for cooking lignocellulosic material, characterized in that 2. The method for cooking a lignocellulosic material according to claim 1, wherein the cooking zone (B) comprises two zones, an upper cooking zone (B1) and a lower cooking zone (B2). 3. Lignocellulosic material according to claim 2, characterized in that the extracted black liquor from the lower cooking zone (B2) is added to the upper cooking zone (B1) together with the cooking liquor without cooling. Cooking method. 4. A black liquor extraction step is provided at the end of the washing zone (C), and the black liquor extracted from the black liquor extraction step is not cooled, but together with the cooking liquor, the upper cooking zone (B
The lignocellulosic material cooking method according to claim 2 or 3, wherein the lignocellulosic material is added to 1) and / or the lower cooking zone (B2). 5. Japan TAPPI Paper Pulp Test Method No. The volume weight measured according to 3 is 450 kg / m
A lignocellulosic material cooking method according to any one of claims 1 to 4, characterized in that a lignocellulosic material of ³ or less is used. 6. The recovered black liquor is a recovered black liquor obtained by cooking lignocellulosic material of the same type or different types in the same continuous digester or another continuous digester. The cooking method of the lignocellulosic material according to any one of claims 1 to 5.