JPH05125680A - Method for digesting wood chip by alternately changing chips having different kappa numbers in the same digester - Google Patents

Abstract

(57) [Summary] [Purpose] In the same vertical continuous digester, when pulps with different kappa number levels are alternately switched and produced, the generation of mixed pulp is reduced by rapidly switching the kappa number. .. [Composition] When switching from production of high kappa number pulp to low kappa number pulp, 60 minutes before the chips reach the top of the infiltration vessel 6, the cooking liquor supplied to the top of the vessel 6 is 76 m ³ / hour to 84 m ³ / Hour, and at the same time, the circulating fluid through the transfer circulation line 37 is 151 ° C.
To 163 ° C and maintained for 120 minutes, then the temperature was changed to 160 ° C and cooking was continued. At the same time, the cooking liquor supplied from the conduit 20 was changed from 6 m ³ / hour to 11
6 m ³ after increasing for m ³ / h and maintaining for 60 minutes
/ Hour was changed and cooking was continued. When the chips with changed alkali addition rate reached the lower cooking layer C, the temperature of the circulating liquid was raised from 161 ° C to 169 ° C and the amount of cooking liquid was increased from 20m ³ / hour to 22m ³ / hour to perform cooking. Continued.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cooking method for producing pulps having different kappa numbers by alternately switching wood chips in the same digester. More specifically, the present invention, when alternately producing pulps having different Kappa numbers by using one digester, the active alkali addition rate per absolute dry wood chip weight and the vertical digester at the time of switching are produced. The present invention relates to a cooking method in which the temperature of a cooking zone is appropriately increased or decreased according to the introduction of a wood chip into a digester and the passage of the cooking zone to change the quality, and the Kappa number can be changed quickly.

[0002]

2. Description of the Related Art Conventionally, the mainstream of the industrial method for producing chemical pulp from lignocellulosic materials such as wood is an alkaline cooking method using an alkaline cooking liquor, and particularly sodium sulfide-containing alkaline cooking liquor. The kraft method (sulfate method) using is used on a large scale because of its advantages such as pulp strength, pulp yield, and ease of chemical recovery in pulp production.

In the alkaline digestion method, a permeation zone is provided in another column and a digestion zone is provided in the other column, and a two-vessel vertical continuous digester or a vertical column has a digestion zone or a permeation zone and a digestion zone. With zone 1
It is preferably implemented in a vessel vertical continuous digester.

Generally, as a typical pulp obtained by the alkaline cooking method, unbleached pulp is obtained from softwood wood chips by the kraft method, and the pulp is delignified in the bleaching step to obtain a pulp having a high whiteness. A pulp having a low Kappa number in the range of 21 to 33 (hereinafter referred to as a low Kappa number pulp) for obtaining and a pulp having a high Kappa number in the unbleached range of the Kappa number in the range of 40 to 55 (hereinafter referred to as “pulp”) High-kappa number pulp) and unbleached pulp having a kappa number of 12-23 for bleaching from hardwood wood chips.

It is most preferable that these pulps are digested and produced in their respective dedicated digesters, but due to constraints such as the production scale of the factory, site conditions, and the type of production variety, softwood is used in one digester. A low kappa number pulp and a high kappa number pulp, a softwood low kappa number pulp and a hardwood unbleached pulp, etc. are combined and cooked by alternately switching these pulps at regular intervals.

In this case, what is important is that the cooking conditions such as the active alkali addition rate, the cooking temperature and the cooking time, and the liquid circulation amount are adjusted to the wood material, the water content of the chips, and the desired pulp copper level. It has to be changed accordingly. Inside the digester, a large amount of used liquor (generally called cooking liquor or black liquor) generated during cooking is circulated in various zones.
These circulating liquids have temperatures and residual alkalis corresponding to their respective zones.

However, when changing the final Kappa number level of unbleached pulp or the type of wood, as the wood chips descend in the digester and pass through the permeation, digestion and washing zones, they are correspondingly changed. Circulating liquor with temperature and residual alkali needs to be supplied in each zone, and if the level of these circulating liquors deviates from the desired one, the Kappa number level will be significantly increased due to insufficient cooking or overcooking. Go crazy. As a result, in addition to the operational problem that the operation of the equipment in the digestion and the subsequent steps becomes unstable, the strength of the finally obtained pulp is insufficient, or foreign matters such as undigested bundled fibers. This may cause troubles in the quality of paper products due to the inclusion of such substances.

Therefore, when two kinds of pulps having different wood types (hereinafter referred to as grades) or different kappa numbers are alternately produced in the same digester, it is appropriate to change each grade. Although devising has been done to change the setting of cooking conditions so that a pulp of Kappa number can be obtained, even if the setting of the temperature and the active alkali addition rate is changed, the temperature and residual alkali in each zone in the digester are Since it changes only slowly, the Kappa number of the pulp is also affected by the change, and as a result, the pulp having an unfavorable Kappa number level is produced.

Further, the biggest drawback of the method for producing pulps having different Kappa number levels by using the same digester is that the pulp is discharged from the digester at the time when the pulp is discharged.
Pulp with an intermediate level of two different Kappa number levels is generated, and the mixing of these different levels of pulp is promoted during the washing process, resulting in a pulp significantly deviated from the desired pulp Kappa number (hereinafter referred to as mixed pulp). ) Occurs in large quantities. If a small amount of this mixed pulp is generated, it can be distributed to each line of the process little by little and digested so as not to have a serious effect, but if it is a large amount, products that require unbleached pulp will have different colors and strength. However, even if multi-stage bleaching is performed in the subsequent bleaching process, it will greatly affect the bleaching cost and increase in pollution load, which will cause obstacles to change production activities. It will be.

For this reason, it is considered that the period or cycle of cooking using one kind of wood is set as long as possible to reduce the generation of mixed pulp and stabilize the Kappa number level. The large number of very large pulp storage tanks or towers necessitates a large capital investment, and in some cases even such capital investment may not be acceptable due to site conditions.

However, as long as the pulp Kappa number can be quickly changed to a desired level in accordance with the grade change, the process and tanks can be quickly changed in accordance with the discharge of pulps having different Kappa numbers. Although it is possible to minimize the generation of pulp, at the present time, no cooking technique for rapidly changing the Kappa number is provided.

[0012]

DISCLOSURE OF THE INVENTION In view of the present situation, the present inventors have earnestly studied, and as a result, at the time of switching production of pulps having different Kappa numbers, the amount of cooking chemical liquid supplied to a digester together with chips and a permeation zone ( It has been found that rapid Kappa number switching and stabilization of Kappa number levels can be achieved by optimizing the temperature in the digestion zone (if any) and at a particular time corresponding to the current production rate and complete the invention. Came to.

Therefore, an object of the present invention is to alternately mix different types of pulp from softwood and hardwood wood chips in combination with low kappa and high kappa pulps, or softwood and hardwood unbleached pulp in the same digester. In the cooking method to switch and produce, quickly obtain the desired Kappa number level according to the switch of the material type, and there is little variation in the level of the Kappa number, and the occurrence of mixed pulp is small due to the switching in a quick process, As a result, stabilization in the bleaching process used for bleaching pulp can be achieved, and the quality of the pulp such as whiteness and strength is excellent. In addition, there are no contaminants and the quality of unbleached pulp with a high kappa number is also good. The object of the present invention is to provide a cooking method capable of obtaining stable pulp.

[0014]

The first object of the present invention is to introduce a wood chip and an alkaline cooking liquor into a vertical digester having a cooking zone, and to dry the active alkali contained in the alkaline cooking liquor into an absolutely dry wood. 15 to 20 per chip weight
% (As Na ₂ O) and the temperature of the cooking zone having one zone or multiple zones is 14
In the method of altering within the range of 0 to 175 ° C. and alternately cooking different kinds of wood in the same digester,
In the case of switching from a low alkali addition rate to a high alkali addition rate, the cooking liquor is increased to a desired level amount 30 to 90 minutes before the chips reach the cooking system inlet, and at the same time the digestion zone inlet temperature is increased. 60 to 1 to 5 ℃ from the desired temperature
In the case of switching from a high alkali addition rate to a low alkali addition rate by keeping it high for a range of 180 minutes, the cooking liquor reduces to the desired level at the same time as the wood chips reach the cooking system inlet, and at the same time the cooking zone Identical pulps with different Kappa numbers in the Kappa number range of 12-55 as described in TAPPI Test Method T-236hm-85 which keeps the inlet temperature below the desired temperature by 1-4C for a range of 30-90 minutes. The method for cooking wood chips is characterized in that the wood chips are alternately produced in the digester.

A second aspect of the present invention is that a vertical infiltration vessel is installed in front of the vertical digester, and the digester has an upper digestion trim zone, an upper digestion zone, and a lower digestion zone from the top to the bottom. And a washing zone are provided. Two vessel vertical continuous type in which co-current cooking is carried out in the upper cooking trim zone and upper cooking zone, countercurrent cooking is carried out in the lower cooking zone, and high heat countercurrent washing is carried out in the cleaning zone. Introducing 50-90% of the alkaline cooking liquor into which the wood chips and the alkaline cooking liquor are introduced into the digester and the active alkali is added in the range of 15-20% (as Na ₂ O) based on the weight of the absolutely dried wood chips 0-45% in the upper digestion trim zone,
45% is fed to the lower digestion zone, and appropriately changed within the range of 140 to 175 ° C. of the temperature of each digestion zone, and in the same digester, different types of wood are switched to each other in the digestion method, In the case of switching from a low alkali addition to a high alkali addition, the alkaline cooking liquor supplied to the infiltration vessel is increased to the desired level 30-90 minutes before the chips reach the inlet of the infiltration vessel. , As soon as the chips reach the inlet of the infiltration vessel, the upper digestion trim zone inlet temperature is maintained above the desired temperature by 1-5 ° C for a range of 60-180 minutes and is simultaneously fed to the upper digestion trim zone. The cooking liquor is 30 to 9 in the range of ³ to 8 m ³ / H from the desired amount.
0 minutes, and 120 to 200 minutes after the chips reach the infiltration vessel, the lower cooking zone inlet temperature and the amount of cooking liquor are increased to desired levels to switch from a high alkali addition rate to a low alkali addition rate. In this case, the cooking liquor supplied to the osmotic vessel reduces the chips to a desired level at the same time when the chips reach the osmotic vessel inlet, and at the same time, the upper cooking trim zone inlet temperature is 1 to 4 ° C. lower than the desired temperature by 20 to 20 ° C. Keeping low for the 90 minute range, the cooking liquor fed to the upper digestion trim zone is stopped for 15-45 minutes to allow the chips to reach the infiltration vessel and reach 120-200
Pulps with different Kappa numbers in the range of 12 to 55 described in TAPPI Test Method T-236hm-85, which reduce the inlet temperature and the cooking liquor amount to the desired levels after a minute, in the same digester. It is a method of cooking wood chips that are produced alternately by switching.

The method of the present invention can be used for digesting chips in a 1-vessel gas-phase liquid-phase digester and a liquid-phase digester, but a 2-vessel liquid-phase digester is also preferably used. FIG. 1 is a schematic flow chart showing the flow of wood chips, cooking liquor, circulating liquid, etc. in the cooking of wood chips by a 2-vessel vertical liquid-phase digester.

In FIG. 1, a wood chip (hereinafter referred to as a chip) a is supplied to an atmosphere open heating type chip bin 1,
The rotary volume meter 2 conveys a certain amount of chips to the steaming vessel 3, where the chips are heated and degassed, and then mixed with the extraction liquid supplied from the conduit 7 by the high-pressure feeder 4 and then permeated into the vessel. Conduit 5 to the top of 6
Will be introduced. On the other hand, the main stream of kraft cooking liquor (hereinafter referred to as cooking liquor) is supplied to the top of the permeation vessel 6 via conduits 17 and 18, and most of the liquor is separated by a strainer provided at the top, and is extracted as an extract. It is circulated via conduit 7.

At the top of the permeation vessel 6, the chips descend in the permeation vessel 6 together with the remaining deliquored cooking liquor, during which the cooking liquor is sufficiently permeated into the chips. A strainer 39 is provided in the middle part of the permeation vessel 6, and the extract is circulated through conduits 40 and 41 so that the chips can easily descend and the cooking liquor permeates the chips uniformly.

The mixture of chips and cooking liquor from the bottom of the permeation vessel 6 is then piped 37 with a thermometer 45.
Is introduced to the top of the digester 8 and is drained by a strainer provided at the top to descend in the digester. The extracted liquid by deliquoring is circulated back to the bottom of the permeation vessel 6 via the conduit 36 provided with the sensor 43 for measuring the alkali concentration and the heater 16 to which the medium pressure vapor 35 is supplied (this line is Transfer circulation). On the other hand, the sensor 43 provided in the return line of the transfer circulation measures the alkali concentration in the circulating return liquid, and the necessary amount of alkali is determined by a part of the cooking liquid introduced from the conduit 17 passing through the conduits 19 and 20. It is replenished to the transfer circulation return liquid.

From the top to the bottom, the digester 8 is provided with an upper cooking trim zone A, an upper cooking zone B, a lower cooking zone C and a washing zone D, each of which is a strainer 9, 10, 11 and 12. It is roughly divided through. While the mixture of chips and cooking liquor descends in the digester 8, a part of the cooking liquor is first extracted by the pump 38 from the strainer 9 provided in the lower portion of the upper cooking trim zone A. , And is circulated together with the circulating return liquid in the transfer circulation line 36. The chips, which are partially cooking, are considerably cooked while passing through the upper cooking zone B in parallel with the cooking liquor while descending and passing through this zone (cocurrent cooking). From the strainer 10 provided, a digested liquid having a high concentration (referred to as black liquor) is extracted and sent to a recovery process via a conduit 30 (not shown).

The considerably cooked chips are supplemented with cooking liquor flowing from the bottom to the top while passing further through the lower cooking zone C and brought into contact with the liquor whose alkali concentration and temperature are adjusted in countercurrent. And the delignification degree of the chips is finally adjusted (countercurrent cooking). The liquid extracted from the strainer 11 provided in the lower part of the lower cooking zone is returned to the digester again by the circulation line constituted by the conduits 24 and 27. This circulation line is provided with a sensor 44 for measuring alkali concentration and a thermometer 46, which is branched from the conduit 19 in order to maintain the necessary alkali concentration as described above while constantly monitoring the alkali concentration and temperature. The cooking liquor is replenished to the conduit 24 via the conduit 21, and the temperature of the circulating liquid is adjusted by the medium pressure steam 33 in the heater 14. The freshly replenished cooking liquor and other excess liquor come into contact with the chips and countercurrent together,
The liquid flowing from the bottom to the top is recovered from the strainer 10 as black liquor via the conduit 30 to the outside of the system.

After the cooking is completed, the chips come into contact with the liquid flowing upward from below while moving further in the washing zone D, and the high heat countercurrent washing is carried out. In the lower part of the washing zone D, a strainer 12 and a conduit 2 are provided.
A circulation line composed of Nos. 5 and 28, a thermometer 47, and a heater 15 is provided, and the temperature of the circulating liquid is adjusted by the medium-pressure steam 34. The cleaning liquid is introduced into the digester 8 from the conduit 29, taken into the circulation line from the strainer 12 as the extraction liquid, adjusted in temperature as described above, and then introduced into the cleaning zone D through the circulation line,
After being subjected to the washing, the digested chips which have been further washed from the strainer 10 together with other surplus liquid through the conduit 30 through the lower cooking zone and the washing are completed.
After being sent to the next washing step via 1, the pressure is released, and the pulp is fibrillated by a mechanical action. The above-mentioned cooking method is called a modified cooking method (MCC method), and the cooking system inlet used in the method of the present invention means the top inlet of the vertical digester.

For the digestion of chips in the above-mentioned 2 vessel digester, the pressure of the steaming vessel 3 is in the range of 0.5 to 2.0 kg / cm ² (gauge pressure), the temperature is in the range of 110 to 130 ° C., the infiltration vessel. The pressure at the top of 6 is in the range of 12.0 to 15.0 kg / cm ² , and the temperature is 1.
The temperature of the upper digestion trim zone A of the digester 8 is in the range of 140 to 170 ° C, and the temperatures of the upper digestion zone B and the lower digestion zone C are in the range of 145 to 175 ° C. Wash zone D temperature is 1
The heater outlet temperature of each circulation line is adjusted so that it can be operated in the range of 20 to 150 ° C. Furthermore, the kraft cooking liquor with an alkali concentration of 105-115 g / l (as active alkali, Na ₂ O) introduced via conduit 17 is in the range 50-90% from conduit 18 to the top of the permeation vessel, conduits 19 and 20. From the transfer circulation line to the upper cooking trim zone A in the range of 0-45%, from conduits 19 and 21 to the lower cooking zone C via the circulation line to the lower cooking zone C 5-4.
It is appropriately distributed in the range of 5% as needed.

In the present invention, in the digestion system using the digester as described above, the chips are introduced into the infiltration vessel at the time of switching when producing pulps having different Kappa numbers, and then the respective digestion zones A, B and C are introduced. And the time to reach D are calculated using the following equation 1, and the amount of alkali addition, temperature and circulating fluid amount in the zone are changed according to the time to reach.

[0025]

[Equation 1] Time required for chips to reach a certain zone and pass therethrough, min = [packing factor of chips, ton (absolute dry chips) / m ³ ] × [volume of a certain zone, m ³ ] / [Tip supply, tons (extra dry chips) /
Min] The backing factor of the chip varies greatly depending on the material type, but as shown in Table 1, it is empirically determined within a certain range, so in actual operation, the most suitable value for the continuous digester should be selected. Will be adopted.

[0026]

[Table 1]

The volume of each zone is determined at the stage of designing the digester, and the chip supply amount is also obtained from the rotary volume meter 2. Therefore, the time required to pass through a certain zone is obtained. The time during which the chips are introduced from the infiltration vessel and discharged as pulp and the time at any passing point therebetween can be obtained by accumulating the times.

In the present invention, when switching from a low alkali addition rate to a softwood chip to a high addition rate,
In order to maintain the same production rate, the yield is generally lower when the alkali addition rate is high. Therefore, the rotation speed of the rotary volume meter 2 in FIG. 1 is increased to increase the chip supply amount. 30 to 90 minutes, preferably 45 to 75 minutes before the switched chips a reach the permeation vessel, the cooking liquor supplied from the conduit 18 is changed to a corresponding liquid quantity with a high alkali addition rate. In this way, increasing the alkali concentration in the infiltration vessel in advance is an important point in this case, and the time varies depending on the pulp's Kappa value level, chip moisture, type of material, etc. The effect is insufficient less than 30 minutes before reaching the vessel, and when it exceeds 90 minutes, the pulp with a high Kappa number is overcooked, and the effect of changing the alkali concentration in advance has an adverse effect. Is.

In the present invention, at the same time when the chips reach the digestion system (or permeation vessel) inlet, the inlet temperature of the digestion zone is 1 to 5 ° C., preferably 2 to above the desired temperature.
4 ° C only, 60-180 minutes, preferably 100-140
Maintained high for the minute range. In FIG. 1, at the same time when the chips reach the infiltration vessel inlet, the temperature of the transfer circulating liquid measured by the thermometer 45 is maintained higher than the desired temperature in the upper digestion trim zone A for the above-mentioned temperature and time range. This temperature and time may be used in combination of low temperature and long time, high temperature and short time, or intermediate temperature and time, but a combination of temperature and time outside the above-mentioned range will produce a satisfactory effect. I can't. The chips reach the permeation vessel and raise the temperature and at the same time additionally increase the cooking liquor volume from the conduit 20 by 3-8 m ³ / h for 30-90 min.

Further, the circulating liquid whose temperature is measured by the thermometer 46 after the chips reach the intermediate position of the lower cooking zone C while undergoing the cooking action is the medium pressure steam 33 up to the desired temperature.
And correspondingly the cooking liquor fed into the circulating liquor from the conduit 21 to the lower cooking zone C is also increased to a liquor level corresponding to the desired high alkali addition rate.

On the other hand, in the case of switching from a high alkali addition rate to a low alkali addition rate, in order to keep the production rate the same, the supply amount of chips is reduced and the supply level of the cooking liquor is the same as the cooking system (or Upon reaching the inlet of the permeation vessel, the amount of cooking liquor corresponding to the desired alkali addition rate is reduced.

In the case of the method shown in FIG. 1, the rotary volume meter 2
The feed rate of the chips is reduced by lowering the rotation speed of No. 1, and at the same time when the switched chips a reach the permeation vessel, the cooking liquor supplied from the conduit 18 is changed to a liquid amount corresponding to a low alkali addition rate.

Further in tandem with the above changes, the digestion zone inlet temperature is maintained below the desired temperature by 1 to 4 ° C., preferably 2 to 3 ° C. for a range of 20 to 90 minutes, preferably 40 to 70 minutes. ..

In the two-vessel digester shown in FIG. 1, the temperature of the transfer circulating liquid, as measured by thermometer 45, is maintained below the desired upper digestion trim zone temperature for the temperature and time ranges described above, and the conduit The supply of the amount of cooking liquor introduced from 20 is set to zero for 15 to 45 minutes and then returned to the desired amount of cooking liquor. Outside the combination range of these temperature, time and liquid amount, pulp with a high alkali addition rate becomes insufficient at the time of switching, and the Kappa number of the pulp becomes high, or conversely pulp with a low alkali addition rate becomes overcooked. However, since the Kappa number becomes low and a large amount of pulps having different Kappa numbers, that is, mixed pulp, is likely to be generated at the time of switching, it is not suitable for the present invention outside the range of the above conditions.

Further, in the divided feeding system of the cooking liquor in the 2-vessel digester shown in FIG. 1, the circulating fluid whose temperature is measured by the thermometer 46 120 to 200 minutes after the chip reaches the infiltration vessel, The temperature is lowered to the desired temperature and, correspondingly, the cooking liquor fed to the circulating liquid from the conduit 21 is also reduced to a liquid level corresponding to the desired low alkali addition rate.

Other than the above-mentioned cooking conditions, after applying known conditions, it depends on the production rate from the supply of chips to the extraction from the discharge pipe 31 as pulp. Since it takes time, in the actual operation of the digester, the work of setting complicated cooking conditions from the time of switching the material type and putting into practice is managed by making full use of the computer. Thus, according to the method of the present invention, it is possible to switch to a desired pulp having a different level very quickly,
Since there is little variation in Kappa number, the reduction of mixed pulp can be achieved very easily.

[0037]

The present invention will be described in more detail with reference to the following examples, but of course the present invention is not limited thereto. In the following,% means% by weight.

Example 1 In a 2-vessel vertical digester (production capacity: NUKP800T / day) manufactured by Kamiya Co., Ltd. shown in FIG. 1, a Kappa number of 26 to 28 was obtained by a modified kraft cooking method using coniferous wood chips and kraft cooking liquor. No. 1 pulp (low Kappa number pulp) and Kappa number 45-50 pulp (high Kappa number pulp) were produced. Pulp production rate 800T /
Table 2 shows the main conditions for the day.

[0039]

[Table 2]

Low alkali addition rate (high Kappa number pulp)
In order to change from high to high alkali addition rate (low Kappa number pulp), first rotate the volume meter from 10.4 rpm to 1 rpm.
Change to 1.1 rpm and increase the chip supply to achieve a production rate of 800 T / day. 60 minutes before the tip reaches the top of the infiltration vessel, 76m ³ / H of the cooking liquor to be supplied to the permeate vessel top from the conduit 18 in FIG. 1
Changed to 84 m ³ / H. At the same time, the temperature of the circulating liquid measured by the thermometer 45 provided in the conduit 37 of the transfer circulation line is changed from 151 ° C. to 163 ° C. (+ 3 ° C. above the target temperature), and the medium pressure steam 35 is supplied in the heater 16. The temperature was increased and the temperature was increased, and the temperature was maintained as it was for 120 minutes. Then, the temperature was changed to 160 ° C. and the cooking was continued. At the same time, the amount of cooking liquor supplied from the conduit 20 is reduced to 6
m ³ / H to 11 m ³ / H (+5 m from the target liquid volume)
³ / H) and maintained as it was for 60 minutes, and then the liquid volume was changed to 6 m ³ / H and cooking was continued.

When the chips with the changed alkali addition rate reach the intermediate position of the lower digestion zone C, the temperature of the circulating liquid measured by the thermometer 46 provided in the conduit 27 of the lower digestion circulation line is changed from 161 ° C. In the heater 14, the supply of the medium pressure steam 33 is increased to 169 ° C. to raise the temperature, and the amount of cooking liquor supplied from the conduit 21 is changed from 20 m ³ / H to 22
It was increased to m ³ / H and cooking was continued.

When the chip with the changed alkali addition rate reaches the intermediate position of the cleaning zone D, the temperature of the circulating liquid measured by the thermometer 47 provided in the conduit 28 of the cleaning circulation line is set to 133 ° C. to 142 ° C. In the heater 15, the supply of the medium pressure steam 34 is increased to raise the temperature, and the amount of the cleaning liquid supplied from the conduit 29 has a dilution factor (DF) of 1.8 to 2.3.
And the cooking was continued.

The pulp cooked in this way is fed into the conduit 3
When it was discharged from No. 1, the Kappa number was measured with the collection over time. FIG. 2 shows how the Kappa number of the obtained pulp changes.

Example 2 While continuing the cooking described in Example 1, in order to change from a high alkali addition rate (low Kappa number pulp) to a low alkali addition rate (high Kappa number pulp), the number of revolutions of the volume meter was measured. Was changed from 11.1 rpm to 10.4 rpm, while reducing the chip supply and continuing the production rate at 800 T / day, while the chips reached the top of the permeation vessel,
The cooking liquor supplied from the conduit 18 in FIG. 1 to the top of the infiltration vessel was changed from 84 m ³ / H to 76 m ³ / H.
Further, the temperature of the circulating liquid measured by a thermometer 45 provided in the conduit 37 of the transfer circulation line is set to 160 ° C.
From 149 ° C. to −149 ° C. (-2 ° C. below the target temperature) in the heater 16 by reducing the supply of the medium pressure steam 35 to reduce the temperature,
After maintaining it for 0 minutes, the temperature was changed to 151 ° C. At the same time, the cooking liquor supplied from the conduit 20 was reduced from 6 m ³ / H to 0 m ³ / H, maintained for 30 minutes as it was, and then the cooking liquid was changed to 6 m ³ / H to continue cooking.

160 minutes after the chips whose alkali addition rate was changed to the one with a high Kappa number reached the infiltration vessel (when the chips reached the intermediate position of the lower cooking zone C)
In addition, the temperature of the circulating liquid measured by the thermometer 46 provided in the conduit 27 of the lower digestion circulation line is changed from 169 ° C to 16 ° C.
In the heater 14, the supply of the medium pressure steam 33 was reduced to 1 ° C. to reduce the temperature, and the amount of cooking liquor supplied from the conduit 21 was further reduced from 22 m ³ / H to 20 m ³ / H to continue the cooking.

350 minutes after the tip with the alkali addition rate changed reaches the permeation vessel (the tip is washed in the cleaning zone D
The intermediate position of 2), the conduit 2 of the washing circulation line
The temperature of the circulating fluid measured by the thermometer 47 provided at 8 is reduced from 142 ° C. to 133 ° C. by reducing the supply of the medium pressure steam 34 in the heater 15 to reduce the amount of the cleaning fluid supplied from the conduit 29. The dilution factor (DF) was changed from 2.3 to 1.8 and cooking was continued. The pulp cooked in this way was sampled over time when discharged from the conduit 31, and its Kappa number was measured. FIG. 3 shows how the Kappa number of the obtained pulp changes.

Comparative Example 1 While the production of high kappa number pulp is continued under the cooking conditions described in Example 2, the low alkali addition rate (high kappa number pulp) is changed to the high alkali addition rate (low kappa number pulp). Therefore, the rotation speed of the volume meter was changed from 10.4 rpm to 11.1 rpm, and the pulp production rate was changed to 800T.
/ Day maintained. Example 1 except for the conditions described below
Cooking was carried out using the same conditions as.

(1) The cooking liquor supplied from the conduit 18 in FIG. 1 was increased when the chips reached the inlet of the permeation vessel. (2) The temperature measured by the thermometer 45 of the transfer circulation line 37 ranges from 151 ° C. to 160 ° C. 45 minutes after the tip reaches the inlet of the permeation vessel (that is, when the tip reaches the outlet of the permeation vessel). Increased to ° C. (3) The amount of cooking liquor supplied to the transfer circulation line from the conduit 20 was not increased before the chips reached the outlet of the permeation vessel. (4) The temperature measured by the thermometer 46 in the lower digestion circulation line 27 was increased from 161 ° C to 169 ° C when the chips reached the outlet of the permeation vessel. (5) The cooking liquor supplied from the conduit 21 to the lower cooking circulation line is 2 when the chips reach the outlet of the permeation vessel.
It was increased from 0 m ³ / H to 22 m ³ / H.

The pulp cooked in this way is fed into the conduit 3
When discharged from No. 1, the Kappa number was measured by sampling over time. FIG. 4 shows how the Kappa number of the obtained pulp changes.

Comparative Example 2 While continuing to produce a low Kappa number pulp under the cooking conditions described in Example 1, the high alkali addition rate (low Kappa number pulp) is changed to a low alkali addition rate (high Kappa number pulp). Therefore, the rotation speed of the volume meter was changed from 11.1 rpm to 10.4 rpm, and the pulp production rate was changed to 800T.
/ Day maintained. Cooking was carried out using the same conditions as in Example 2 except for the conditions described below.

(1) The cooking liquor supplied from the conduit 18 in FIG. 1 was reduced when the chips reached the inlet of the permeation vessel. (2) The temperature measured by the thermometer 45 of the transfer circulation line 37 is set to a desired value 45 minutes after the tip reaches the inlet of the permeation vessel (that is, when the tip reaches the outlet of the permeation vessel). The temperature was reduced from 160 ° C. directly to 151 ° C. without being kept below the temperature by 2 ° C. for 60 minutes. (3) The cooking liquor supplied from the conduit 20 to the transfer circulation line 37 was not reduced to 0 m ³ / H for 30 minutes in advance when the chips reached the outlet of the permeation vessel. (4) The temperature measured by the thermometer 46 in the lower digestion circulation line 27 was reduced from 169 ° C to 161 ° C when the chips reached the outlet of the permeation vessel. (5) cooking liquid supplied through conduit 21 to the lower cooking circulation line 27, the chip is reduced from 22m ³ / H when it reaches the outlet of the permeation vessel to 20 m ³ / H.

The pulp cooked in this way is fed into conduit 3
When it was discharged from No. 1, the Kappa number was measured over time and collected. FIG. 5 shows how the Kappa number of the obtained pulp changes.

As is clear from FIGS. 2 and 3, the amount of pulp produced in the kappa number range of 30 to 44, which is difficult to use in the bleaching process and the unbleached product even if the kappa number is changed in the cooking according to the present invention. Is 6-10 AD by switching once
Ton (8 AD ton on average), which is extremely small (see Examples 1 and 2). On the other hand, in the conventional cooking method, every time the Kappa number is changed, 50-60 AD tons (average 55 A)
The generation of pulp deviating from the desired Kappa number level of D ton) is observed (see Comparative Examples 1 and 2).

The pulp deviating from the desired Kappa number level tends to be further increased during the subsequent washing and refining steps when switching the Kappa number, but the pulp cooked by the method of the present invention. The Kappa number changes sharply so that the change point can be easily found, and thus it is easy to minimize the generation of mixed pulp.

[0055]

According to the method of the present invention, when pulps having different Kappa numbers are alternately produced by the same digester, the desired Kappa number level is set by optimizing the amount of cooking liquor supplied to the digesters and the cooking temperature. Since the generation of deviating pulp can be extremely reduced, it is possible to produce pulp without increasing the bleaching cost and wastewater pollution load, and without impairing the pulp quality.

[0056]

[Brief description of drawings]

FIG. 1 is a schematic flow diagram showing the flow of wood chips, cooking liquor, circulating liquid, and pulp in the cooking of wood chips by a 2-vessel vertical liquid-phase digester.

FIG. 2 is a diagram showing changes in the Kappa number of pulp obtained by the method of the present invention when switching from a low alkali addition rate (high Kappa number pulp) to a high alkali addition rate (low Kappa number pulp).

FIG. 3 is a diagram showing changes in the Kappa number of pulp obtained by the method of the present invention when switching from a high alkali addition rate (low Kappa number pulp) to a low alkali addition rate (high Kappa number pulp).

FIG. 4 is a diagram showing changes in the Kappa number of pulp obtained by a conventional method when switching from a low alkali addition rate (high Kappa number pulp) to a high alkali addition rate (low Kappa number pulp).

FIG. 5 is a diagram showing changes in the Kappa number of pulp obtained by a conventional method when switching from a high alkali addition rate (low Kappa number pulp) to a low alkali addition rate (high Kappa number pulp).

[Explanation of symbols]

a ... Wood chips, 1 ... Heating type chip bin, 2 ... Rotary volume meter, 4 ... High pressure feeder, 6 ... Infiltration vessel, 8
... Digester, 9, 10, 11, 12, 39 ... Strainer, A ... Upper cooking trim zone, B ... Upper cooking zone, C ... Lower cooking zone, D ... Washing zone, 17 ... Alkaline liquid supply pipe, 30 ... Black Liquid discharge pipe, 31 ... Pulp discharge pipe

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[Procedure amendment]

[Submission date] October 30, 1992

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be amended] Claims

[Correction method] Change

[Correction content]

[Claims]

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0021

[Correction method] Change

[Correction content]

The considerably cooked chips flow downward and upward while passing through the lower cooking zone C, and supplement the cooking liquor to contact the liquor whose alkali concentration and temperature are adjusted and countercurrently. And the delignification degree of the chips is finally adjusted (countercurrent cooking). The liquid extracted from the strainer 11 provided in the lower part of the lower cooking zone is returned to the digester again by the circulation line constituted by the conduits 24 and 27. This circulation line is provided with a sensor 44 for measuring alkali concentration and a thermometer 46, which is branched from the conduit 19 in order to maintain the necessary alkali concentration as described above while constantly monitoring the alkali concentration and temperature. The cooking liquor is replenished to the conduit 24 via the conduit 21, and the temperature of the circulating liquid is adjusted by the medium pressure steam 33 in the heater 14. The freshly replenished cooking liquor and other excess liquor come into contact with the chips and countercurrent together,
The liquid flowing from the bottom to the top is recovered from the strainer 10 as black liquor via the conduit 30 to the outside of the system.

Claims (2)

[Claims] 1. A wood digester and an alkaline cooking liquor are introduced into a vertical digester having a cooking zone, and the active alkali contained in the alkaline cooking liquor is contained in an amount of 15 to 20% (Na ₂ O) based on the weight of the absolutely dried wood chips. The temperature of the cooking zone having one zone or a plurality of zones is changed within the range of 140 to 175 ° C.,
In the method for producing pulps having different Kappa numbers by switching from each other, in the case of switching from a low alkali addition rate to a high alkali addition rate, the alkali liquid is 30 to 90 minutes before the chips reach the cooking system inlet. To the desired level and at the same time maintain the digestion zone inlet temperature higher than the desired temperature by 1-5 ° C. for a range of 60-180 minutes,
In the case of switching from a high alkali addition rate to a low alkali addition rate, the alkali liquid reduces the wood chips to a desired level amount at the same time when the wood chips reach the digestion system inlet, and at the same time, makes the digestion zone inlet temperature 1 to 4 from the desired temperature. TAPPI Test Method T-236, kept low for 30 to 90 minutes only
A method for cooking wood chips, wherein pulps having different kappa numbers in the range of 12 to 55 described in hm-85 are alternately switched and produced in the same digester. 2. A vertical infiltration vessel is installed in front of the digester, and an upper digestion trim zone, an upper digestion zone, a lower digestion zone and a washing zone are provided from the top to the bottom inside the vertical digester. Wood chips in a 2-vessel vertical continuous digester in which parallel cooking is carried out in the upper cooking trim zone and upper cooking zone, countercurrent cooking is carried out in the lower cooking zone, and high heat countercurrent washing is carried out in the washing zone. And alkaline cooking liquor were introduced, the active alkali was 1 per 1
From 50 to 90% of the alkaline cooking liquor added in the range of 5 to 20% (as Na ₂ O),
About 45% is fed to the upper cooking trim zone and 5 to 45% is fed to the lower cooking zone, and pulps with different Kappa numbers are mutually changed by appropriately changing the temperature in each cooking zone within the range of 140 to 175 ° C. In the method of manufacturing by switching to No. 3, in the case of switching from a low alkali addition rate to a high alkali addition rate, the chips of the alkaline cooking liquor supplied to the infiltration vessel reach the inlet of the infiltration vessel 30.
~ 90 minutes before increasing to the desired level amount, as soon as the chips reach the inlet of the infiltration vessel, the upper digestion trim zone inlet temperature is 1-5 ° C below the desired temperature 60-18
Keep it high for the range of 0 minutes, and at the same time, the alkaline liquid supplied to the upper digestion trim zone is 3 to 8 m from the desired liquid amount.
^In the range of ³ / H for 30 to 90 minutes, and 120 to 200 minutes after the chips reach the infiltration vessel, the lower cooking zone inlet temperature and the cooking liquor volume are increased to desired levels.
In the case of switching from a high alkali addition rate to a low alkali addition rate, the alkaline cooking liquor supplied to the infiltration vessel is reduced to a desired level amount at the same time when the chips reach the infiltration vessel inlet, and at the same time, the upper digestion trim zone. The inlet temperature is kept below the desired temperature by 1 to 4 ° C. for a range of 20 to 90 minutes, the cooking liquor fed to the upper cooking trim zone is stopped for 15 to 45 minutes and the chips reach the permeation vessel. After 120 to 200 minutes, TA for lowering the temperature at the lower cooking zone and the amount of cooking liquor to desired levels
A method for cooking wood chips, wherein pulp having different Kappa numbers in the range of 12 to 55 described in PPI test method T-236hm-85 is alternately produced in the same digester.