JPH06510091A - Continuous cooking method for cellulose fiber materials - Google Patents

Abstract

A process for the continuous digestion of cellulosic fiber material, comprising impregnation with impregnating liquid consisting of at least one fresh digesting liquor, in a closed impregnating system and subsequent digestion with digesting liquid in a closed digester system, said impregnating liquid being supplied through a supply system, together with steamed fibre material, to an inlet end of the impregnating system, liquid being withdrawn from the impregnating system at a point (46) located at a predetermined distance from said inlet end. According to the invention such a first quantity of liquid (F) is withdrawn at said withdrawal point (46) and recirculated directly to the supply system that a predetermined minimum ratio between liquid and fibre material is continuously maintained in the impregnating system prior to said withdrawal point (46), the liquid in said liquid to fibre material ratio being derived from original moisture (A) in the fibre material, condensates (B, C) from an initial steaming of the fibre material, and added fresh digesting liquor(s) (D and/or E) besides said withdrawn and recirculated quantity of liquid (F).

Description

[Detailed description of the invention] Continuous cooking method for cellulose fiber materials The sedimentation rate of the cellulose fiber material extracted from the plant system is It will be disturbed. Typically the amount of liquid required is the supply system for soaking the chip. It is obtained by adding cooking liquor, such as white liquor, to the cooking liquor. If necessary, the temperature or number It must be met by step removal or addition by indirect cooling.

This necessitates subsequent steaming. Another drawback is that the cooking chemistry in the first stage the quality of the product or that it will be too low to achieve the desired effect of this method. Maybe. The addition of black liquor to the feed system is described in Swedish Patent No. 359.33. No. 1 and Swedish Patent Application No. 8804578-6. Said In literature methods, the liquid is placed at a predetermined distance from the inlet end. The liquid is removed from the steeping system at a point where the liquid is mixed with black liquor.

70-100% of the required supply equipment for immersion vessels via high-pressure pumps and more To increase the amount, black liquor can be added to the dipping vessel via the feed system.

The temperature of the black liquor should not exceed 100°C. Too little liquid in the immersion volume by the formation of water vapor in the downcomer pipe located before the high pressure valve. This would lead to disruptions within the supply system. The temperature of the liquid depends on the pressure placed upstream Do not exceed the temperature corresponding to the steam pressure in the steaming vessel. Chips in a dipping container Sedimentation is also prevented. Free liquid, i.e. the part of the liquid that is not absorbed by the chip. The amount becomes too low and the liquid flow rate is correspondingly reduced. free liquid The flow rate ratio of causes a driving force to act on the tip pillar. This driving force or the chip is still Larger at the top of the immersion container, which is not saturated with liquid but has a tendency to float That is important. This requirement is substantially saturated with chips or liquid by this stage. This is important at the bottom of the immersion vessel, as it tends to settle under its own weight. Or less. processing or carried out in several stages using different cooking liquors at various stages. and a sufficiently high wood-to-liquid ratio in the first stage, i.e. in the initial free-flow zone in the soaking vessel. The same requirements apply to maintaining body proportions. However, the method or operating economy is Requires that the first stage cooking liquor must be added in limited quantities and In some cases, it may be difficult to achieve a sufficiently high wood-to-liquid ratio. child At the same time, the liquid flow at the digester inlet is High pressure steam and direct steam consumption into the top of the digester results in very high consumption. And it must be controlled so that it does not become too large. In addition, cooking The recovery filter at the top of the countercurrent washing zone of the vessel becomes overloaded.

The object of the present invention is to eliminate the above-mentioned problems and to prevent the liquid flow in the digester from being too large. Maintain a sufficiently large liquid flow in at least the first part of the immersion vessel without , to provide an easy and reliable method. In other words, the present invention fully A high wood-to-liquid ratio can be maintained in the digester without such a ratio becoming too high. Solve the problems that exist when black liquor cannot be used to serve in a pickling container The purpose is to

The method according to the invention allows such a first amount of liquid (F) to be removed at said removal point. a predetermined minimum ratio between the liquid and the fibrous material or prior to said point. The fiber material to liquid ratio is circulated directly to the feed system which is continuously maintained within the dipping system. liquid at the rate or the initial moisture in the fiber material (A), due to the initial cooking of the fiber material Added to the condensate (B, C) and the amount of liquid removed and circulated (F) It is characterized in that it is obtained from fresh cooking liquor (D and/or E). here As used, the term “directly” refers to direct , meaning that it is circulated without being mixed with black liquor.

The present invention comprises a continuous cellulose fibrous material in the form of wood material ground into chips. Further details are provided below with reference to a drawing showing a flow diagram of a cooking plant. It will be described in detail.

The plant shown in the drawing consists of vertical steaming vessel 1, horizontal steaming vessel 2, vertical &a vessel 3 , and a vertical digester 4. The chip passes through tube 5, which heats the chip and the air Vertical steamer 1 supplied with low pressure steam through pipe 6 to reduce the content sent to. This pre-steaming step is carried out at atmospheric pressure. The heated chips are divided into two It is weighed by a tip meter placed at the connection 7 between the steaming vessels, said connection 7 also houses a low pressure valve 8 which is closed by a tip into the horizontal steaming vessel 2. low pressure Steam is added through tube 9. The pressure inside this second steaming container 2 is 1 to 1.5 Bar overpressure. From the pressure steaming vessel 2, there is a high pressure valve 11 located at the lower end. It falls into the downcomer pipe 1.0. The liquid level is maintained within the downcomer pipe 10. High pressure valve 11 Has a pocketed rotor. One pocket always has a pre-cooked capacity The other pocket is always in the low pressure position and open in communication with vessel 1. It is opened in communication with the dipping container 3 via a supply pipe 12 connected to the top of the container 3. simultaneously in a high pressure position. The liquid in the circulation loop 13 with the pump 20 is from the downcomer pipe 10 into the high pressure valve 11 to fill one of the rotor pockets.

The case of the high pressure valve 11 should be A net is installed inside the space. The liquid displaced by the chip in the high pressure valve 11 is circulated. The removed liquid is removed from the circulation loop by a screen 14 placed in the annular loop. The body is led to a level bath 15 via a tube 16. The level tank 15 contains the liquid taken out. By means of a pipe 17 with a high-pressure pump 18 for pumping the water into the dipping vessel 3, Connected to the top of the container 3.

The high pressure valve 11 and the dipping vessel 3 are connected to the supply pipe 1 connected to the top of the dipping vessel 3. 2, and for returning the liquid separated by the top separator placed in the immersion vessel 3. In order to Therefore, it is connected.

The liquid is circulated by a pump 22 located within the return pipe 21. Satisfaction rotor pockets in a high pressure position, i.e. in direct communication with the circulation loop 12.21. When the rotor pocket reaches the position where it passes, the return liquid in this circulation loop be cleaned thoroughly by The return liquid flow rate is determined by the tip or rotor pocket. It is so high that it is flushed all at once from the tank into the dipping container. The pressure inside the immersion container 3 is normally 8 ~15 bar overpressure. However, in certain methods, this pressure may exceed 15 It may be as high as an overpressure of ~45 bar.

Fresh cooked eD from the first storage tank is sent via pipe 23 to the top of dip vessel 3.

The pipe 23 is connected to the high pressure pump 18 or to the liquid drawn from the first circulation loop 13. to be used for pumping both cooking liquor and constituting the new soaking liquid. The tube 17 from the tank 15 is suitably connected to the tube 17 .

Fresh cooking liquor E is passed from the second storage tank to the digester via a pipe 24 equipped with a high-pressure pump 25. Sent. Some of the cooking liquor E is used as an immersion liquid and is connected to a branch pipe 26 equipped with a valve. and is sent to the top of the &i container 3.

This branch pipe 26 is suitably connected to the pipe 17 from the level tank 15.

The soaked chips are transferred from the bottom of the soaking vessel 3 to the top of the digester 4 via a pipe 27. be done. A filter or filter installed at the top of the digester 4 to separate a volume of liquid. , this liquid is then used to pump the chips into the digester 4 using the separated liquid. It is returned to the bottom of the immersion vessel 3 via a return pipe 28 with a pump 29. Return pipe 2 8 for heating the liquid passing therethrough by supplying high pressure steam via pipe 31. It passes through the air exchanger 30. The supply pipe 27 and the return pipe 28 are connected to the soaked chips and the boiling pipe. Forming a liquid suspension transfer circuit. A larger amount of cooking liquid E can be stored in the cooking liquid pipe 24. A point connected to the return line 28 before the pump 29 is added to the transfer circuit.

If desired, a smaller amount of cooking liquor can be passed through the digester circulation line 33 via the valved line 19. may be added to. The digester uses a pump 34 to circulate liquid through a tube 33. The liquid is heated in a heat exchanger 35. Tube 33 opens to the filter. It has a mouth and a central tube located in the center of the digester.

The cooked chips are fed through the pipe 36 and pumped into the digester by a high pressure pump 37. The digester is adjusted to ensure that it remains full of liquid, pumped to the bottom. The lower part of the digester is washed by countercurrent flow using the same amount of washing liquid. wash The cleaning liquid is supplied to a heat exchanger 38 disposed in a pipe 39 for circulation of cleaning liquid by a pump 40. It is indirectly heated by the supplied steam. The cleaning liquid passes through the filter 41 is removed and returned via a central tube extending from the bottom of the digester and having an opening in the filter 41. Ru. The cleaning solution heated in this way should be ticked so that it slowly moves downward. The water is allowed to flow in countercurrent through the columns of the filter, thereby removing it through the filter 42. A flash cyclone (not shown) and a recovery device (not shown) are connected via pipe 43. ) to move the contents of the cooking liquor. Cooked chips should be washed with a suitable scraper. It is discharged at the bottom of the digester using a pipe and is led to the next step via pipe 44.

In addition to the indirect heating of the cooking liquor and wood in the transfer circuit 27,28, indirect heating It is also carried out by steam supplied to the top of the digester via pipe 45. To the present invention According to A filter placed a predetermined distance from the top of the dipping vessel as A container 46 is provided. Furthermore, according to the invention, the return pipe 47 equipped with a valve is This filter 46 and the immersion filter are used to return a predetermined amount of liquid to the starting point of the immersion zone. It is connected between the top of the pickling container and the top of the container. The return pipe 47 has a high pressure pump 48 and After passing through the exchanger 49, the other fluid side of the heat exchanger is supplied with new fluid via a branch 50.51. It is connected to a pipe 24 for cooking liquid E. The flow to heat exchanger 49 is for fresh cooking liquor E. regulated by valve 52 in tube 24. The return pipe 47 connects the level tank 15 to the pipe 17. is connected to the high pressure pump 18 at a point located in front of the high pressure pump 18.

To avoid turbulence in the feeder, the chip tower is cooled to an appropriate temperature in the cooler 49. is sufficient to give a constant downward motion of . The amount of liquid F is the same as that of other liquids into the immersion container. Depending on the flow rate of the body and other operating conditions, all liquids, i.e. liquid volumes A, B, C, The sum of D and E is transferred to the digester. This concerns thermal economy and operational reliability. , provides a flow rate of liquid received by the digester 4.

If the process is repeated without removing or returning liquid F, However, such operation requires that a large amount of liquid be transferred to the high pressure steam in the heat exchanger 30 of the transfer system. steam consumption and direct steam consumption to the top of the digester will be too high. It's actually inappropriate.

The filter at the top of the countercurrent washing zone of the digester is also overloaded.

The temperature at the top of the dip vessel is generally about 110-120°C and at the bottom, i.e. the transfer circuit. On paths 27 and 28 it is about 130-160°C. is taken out through a filter 46 The liquid has a temperature of approximately 120-130 °C, while II! ! , through the filter 42 The black liquor removed from the digester has a temperature of about 150-170°C.

The method according to the invention of maintaining a sufficiently large liquid flow in the upper part of the immersion vessel is suitable for the cooking process. can be used in a variety of implementations. For example, new cooking liquor is expensive. Alkaline solution with sodium sulfide content or solution containing only thorium sulfide Can be configured. Sodium sulfide is consumed in relatively small amounts during the immersion condition and The immersion liquid F is then removed to a sufficiently high sodium sulfide content in the immersion vessel. Even if it is returned to the entrance, it can be maintained. The new cooking liquid E is ordinary white liquor. , i.e. a mixture of substantially sodium sulfide and sodium hydroxide, or substantially It may consist of a white liquor containing sodium hydroxide.

The chips are soaked with a portion of fresh cooking liquor E and another fresh cooking liquor is added. If not, a sufficient flow rate of liquid is required to remove a sufficient amount of liquid F from the immersion vessel 3. The initial amount obtained in the dipping vessel is Dew. The fresh cooking liquor E required for the remainder of the process is transferred to the transfer circuit 27, 28 and/or It is added to the digester 4 through the circulation pipe 33 mentioned above or other pipes that circulate the cooking liquor in the digester. It will be done.

The liquid F withdrawn from the first countercurrent immersion zone is large enough to accommodate the total free liquid. It can be a quantity. The liquid captured by the chip is placed at the bottom of the container where the liquid is immersed. The liquid then flows upwardly toward the filter 46.

In such operations, some of the cooking liquor E added to the transfer circuit flows countercurrently through the chips. , thereby resulting in improved immersion. Bottom countercurrent immersion via filter 46 Supplemental liquid removed from the soaking zone may be returned to the transfer circuit 27.28 or used for other purposes. Can be used on the go. Therefore, it is possible to circulate the amount of liquid that is withdrawn and returned to the supply device. It is not included when

Accounting for a large proportion of the immersion liquid returning to the supply system is important when it is used Increase the concentration of the new cooking liquor, especially if the new cooking liquor modified immersion when consisting of ruphide solutions or solutions containing anthraquinones. It is brought about to generate. As mentioned earlier, the temperature inside the immersion vessel 3 By cooling the discharged immersion liquid with a cooler 49, the height can be adjusted to an appropriate level. It is advantageous to do so.

The fresh cooking liquor stream may also contain the presence of a small amount of fresh cooking liquor E1, e.g. white liquor. An organic substance such as methanol or ethanol is used to soak the chips in the boiling water. It can also be composed of The remainder of the fresh cooking liquor E is then transferred to the transfer circuit 27.28. and/or added to one of the liquid circuits of the digester, e.g. 33.

The method according to the invention can also be applied in several stages to sulfite cooking, e.g. acidic sulfite cooking. can. Is it not limited to continuous digesters with separate immersion vessels? For use in continuous cooking digesters with an initial soak zone, such as single-vessel hydraulic digesters. Can be used.

The extracted immersion liquid F is fed to a point supply device in the pipe 17 located after the high-pressure pump 18. will be returned to. This reduces pump energy requirements.

If the withdrawn liquid F is enriched with gases that may cause operational disturbances. For example, it may be appropriate to rapidly reduce the pressure of the liquid to a low pressure for degassing before sending it to the supply system. May.

As will be understood from the above specification and the following claims, black liquor is an immersion system. is not added to the supply system.

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Claims (1)

[Claims] 1. a soaking liquor consisting of at least one fresh cooking liquor in a closed soaking system; and subsequent cooking with cooking liquor in a closed cooking system. The soaking liquid is delivered by the feed system to the inlet end of the soaking system along with the cooked fiber material. a point at which the liquid is supplied at a predetermined distance from said inlet end; (46) in a method for continuous cooking of cellulose fiber material removed from a soaking system. such first liquid quantity (F) is withdrawn at said withdrawal point (46) and the liquid A predetermined minimum ratio between the fiber material and the fiber material is The liquid against the fiber material is circulated directly into the supply system which is maintained continuously in the standing dipping system. The liquid in the proportion of the initial moisture in the fiber material (A), the initial steaming of the fiber material condensate (B, C), and the amount of liquid added in addition to the amount of liquid (F) taken out and circulated. A method characterized in that it is obtained from added fresh cooking liquor (D and/or E). 2. the ratio of fiber material to liquid is at least 2.5, calculated on dry fiber material: 1, preferably at least 3.0:1. Method described. 3. The new cooking liquor (F) added via the feed system is supplied to the cooking system. Claim 1, or The method described in Section 2. 4. A new cooking liquor (E) with a different chemical composition is added to the cooking system. Claim 1, characterized in that the cooking liquor (D) is added to the supply system; or The method described in Section 2. 5. A portion of the new cooking liquor (E) for the cooking system is also added to the feed system. A method according to claim 4, characterized in that: 6. The temperature in the immersion system causes a first volume (F) of liquid to be removed and circulated to the supply system. conditioned by passing it through a heat exchanger (49) before being introduced into the A method according to any one of claims 1 to 5, characterized in that: 7. The cooking liquor added to the cooking system or water for hot water production is used as a heat exchange medium. 7. A method according to claim 6, characterized in that: 8. Neutral or alkaline sodium sulfide solution, such as methanol or ethanol If the organic compound solution, polysulfide solution, or anthraquinone solution Claims characterized in that the cooking liquor (D) is used as the cooking liquor (D) having a chemical composition of The method described in paragraph 4 or paragraph 5. 9. The amount of liquid (F) withdrawn and circulated into the supply system is Claims 1 to 8, characterized in that it is equal to the amount of free liquid in the soaking system. The method according to any one of the above. 10. A countercurrent flow removes a second volume of liquid from the immersion system above said free liquid (F). is maintained downstream of the take-off point (46) with respect to the movement of the fibrous material. , the second liquid volume is a soaking liquid for transferring the soaked fibrous material to a cooking system. Claims forming part of the liquid introduced at the outlet end of the system The method described in paragraph 9.