JPS602790A - Digesting method and kettle - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved method and digester for producing high quality pulp, and more particularly to an improved thermal digester for producing high quality pulp. Concerning chemical and/or thermomechanical methods. The improved digester consists of two or more separate tubular chambers with means for blowdown provided between each chamber. and the second chamber and the subsequent chamber are the first
configured to provide a longer fiber residence time in the second and subsequent chambers than in the tubular chambers;
and/or manipulated.

Most of the world's newsprint is manufactured from wood fibers.

This includes the use of softwood and hardwood. The reason is that the fibers made from wood are long and as a result strong newsprint can be produced. Also, because the initial wood fibers are long compared to fibers made from plants such as sugarcane lees, straw, reeds, bamboo, etc., they can undergo fairly intense pulping and bleaching, resulting in high It has been shown that it is possible to make newsprint with a GE brightness of 55-60 and an opacity of 95-q6% while maintaining strength. Sugarcane lees and bamboo are the most commonly used non-wood fiber sources for papermaking, but these fiber sources cannot be pulped and bleached in exactly the same way as wood fibers. Unable to make good products. If these fibers were so processed, the relatively short fibers would produce a paper product of relatively poor strength.

This applies in particular to newsprint.

However, when using the digester of the present invention, pulp can be produced from sugarcane dregs, bamboo and other non-wood sources, which can be used to produce newsprint and other paper products. It is used to create.

The steamer of the present invention can also be used for wood fibers. The very same reasons that make these cookers useful for non-wood fiber sources also make them useful for wood sources. The end result is a relatively long fiber and relatively strong paper product.

The present invention primarily relates to a method and a steamer for processing non-wood fibers such as sugarcane dregs and bamboo, but it is also very applicable to processing fibers made from wood. effective. When the present invention is used to process fibers made from wood, relatively less pulping chemicals are required compared to conventional pulping methods. It also produces a higher quality pulp than conventional wood pulping methods and the case where the pulp is made using a boiler. However, as noted above, the present technique requires pulping conditions that are milder than those typically used to process wood fibers because the non-wood fibers are of relatively short length. , especially useful for processing non-wood fibers. Therefore, although the methods and apparatus of the present invention are described with respect to sugarcane dregs and bamboo, it should be understood that they are also applicable to fibers made from hardwoods and softwoods. .

Moreover, the method and digester of the present invention have the flexibility of being used to produce pulp for making either high strength paper products or low strength paper products. This is achieved by employing thermochemical and/or thermomechanical pulping. For pulping sugarcane dregs or bamboo, the pulping process of the invention consists of starting with well demyelinated and water-washed fibers. Preferably, it was prepared in a paper mill using one of the techniques described in US Pat. No. 4,2511!16 or US Pat. No. 4,237,582. As a result of applying these techniques, the fibers are substantially free of pith, dust and soluble substances, which in part allows subsequent processing to be carried out by mild processing methods.

The demyelinated and washed fibers are then subjected to thermochemically pulped or thermomechanically pulped conditions. Regardless of the method of pulping, at least a two-stage digester is used. The boiler is of a type in which the residence time of the fibers is different at each stage. It is generally preferred to have at least two stages of cooking and a longer residence time in the second stage. The reason why multiple stages are preferred is that the blowdown between each stage allows for better penetration of steam and/or chemicals, resulting in better pulping. The reason why it is preferred to have a long residence time in the second stage is that the fibers undergo blowdown and the water in the fibers is converted to steam, thereby blowing the fiber bundle apart. That is, in the second stage, the fibers become more spread out, resulting in greater liquid penetration and effective cooking. This means that
This is particularly the case in thermochemical pulping processes where the pulping agent is preferably added just before or after blowdown from the first stage of the digester. After being cooked, the fibers undergo other manufacturing steps such as heat refining, washing and screen cleaning operations. Thermomechanical pulps undergo disk refining before washing, whereas thermochemical pulps are usually bleached after washing and screening.

The method of the present invention will be described in detail with reference to the accompanying drawings.

The steamer in Figure 1 is shown as a thermomechanical steamer;
Also, although the steamer in FIG. 2 is shown as a thermochemical steamer, this need not be identified as such. Either one can be used as a thermomechanical or thermochemical steamer. That is, there is no need for either type of digester to have any specific length/diameter requirements. If desired, the steamer of Figure 1 can be designed as a thermochemical steamer, and the steamer of Figure 2 can be designed as a thermomechanical steamer. You can also do it.

FIG. 1 shows a steamer used for thermomechanical processing. The residence time of the fibers is longer in the second stage because it has a larger internal volume. this is,
This is accomplished in FIG. 1 by configuring the second stage to have a longer length than the first stage. In this method, the second stage can accommodate many fibers in time at any instant.

The fibers are metered into the first tubular chamber together with water vapor. The required residence time of the fibers at each stage of cooking depends on the processing conditions and the raw material. However, under normal circumstances, the fibers remain in the digester (both stages) for a total of about 5-45 minutes. The time in each stage is different, but the residence time in the second stage is greater.

The pressure in the steamer pit is approximately 3-20 K in the first stage.
- but in the second stage at least 0.5
Kf/crI, preferably about I Ky/crA (7J
) A pressure drop is performed. Due to the large volume of the second stage, at least a slight pressure drop occurs.

This pressure drop can be reduced by using a blowdown valve.
Alternatively, this can be achieved by using a refiner as shown in FIG. The refiner is a type of blowdown valve in the apparatus of the present invention.

To explain FIG. 1 in more detail, the conveyor 70
feeds the fiber source into a screw conveyor //. The screw conveyor weighs and conveys the fibers and feeds them into the screw feeder 73 through conduit /2. The screw feeder feeds the fibers into the conduit/da. There the fibers mix with water vapor and enter the first tubular stage/7 of a two stage thermomechanical cooker. The letter M in each case indicates an electric motor. These are usually 20-
It is a 40 horsepower electric motor.

The water vapor is sent to the tubular chamber /7 through line /S and the aforementioned conduit /4'. The fibers are passed through the tubular chamber /7 by a screw driven by a motor M.

The fibers pass through this tubular chamber in about 5-20 minutes. The fibers exit this tubular chamber at line/g and undergo blowdown at line/g.

After blowdown, the fibers are conveyed via line 20 into the tubular chamber λ/. The tubular chamber 2/ is shown to have the same diameter as the tubular chamber 2/, but is considerably longer in length. A screw driven by an attached motor M moves the fibers through this tubular chamber. In this X,
Since tubular chamber 7 has the same diameter as tubular chamber 7, the screws in each chamber rotate at the same speed. This creates a continuous mode in which the fibers have a longer residence time in the tubular chamber 2/ of the digester than in the tubular chamber /7. The fibers exit line, 22 and are sent for further processing.

This process often includes one or more stages of refining, 23. The fibers then pass through line 211 to 2. After being depressurized at point t, it passes through a line and is sent to blow tank 2g. Water vapor is recovered from the blow tank in line, 27, while product is recovered at point 290.

FIG. 2 shows the case where the second tubular boiler has the same length but a larger diameter. Also shown is a steamer used for thermochemical steaming. In order to provide the second stage with a large external volume, the diameter of the tubular chamber of the second stage is increased. In thermochemical methods of operation, cooking chemicals are added just before and/or after blowdown. The first tubular chamber serves to soften the fiber bundles, which are then broken apart in the blowdown.

After this breaking apart process, the chemicals more fully penetrate the fibers and remove lignin and other undesirable fiber components.

Since the steamer of FIG. 2 is similar in many respects and in operation to that of FIG. 1, only the differences will be described. The differences lie in the addition of chemicals to the fibers after the first stage of cooking and in the greater diameter to length ratio of the second tubular chamber. Drugs are on line 30. It is then sent to the cooking system via lines 3.2 and/or 33.

Addition through line 32 provides faster penetration because the drug is present during blowdown.

However, addition of drug through line 33 also provides good penetration. The fibers then enter the tubular chamber 3/
, carried by a screw from one end to the other. This screw operates at a slower speed compared to the tubular chamber /7 since the latter has a larger volume and can contain more fibers. As a result, the residence time in the second tubular chamber is approximately 1.2-5 times longer than the residence time in the first tubular chamber.

If sodium hydroxide is used alone for cooking, an 8-12% by weight solution is used. This is about 1
It has a pH of 2-14. The preferred sulfite cooking liquor (co
ok 1 equor) consists of sodium sulfite and sodium hydroxide in a molar ratio of about 5:1. This is about 1
This results in a drug solution with a ratio of 0.8-11. A typical raft fluid that can be used consists of sodium sulfite and sodium hydroxide in a molar ratio of about 2:1. This fluid has a sulfidity factor of approximately 2:1. Regardless of the cooking liquor used, the ratio of cooking liquor to fiber (on a dry basis) is within the range of 3-10:1.

If desired, the raw fibers can be pre-moistened or the water can be added together with the steam introduced into the digester. This may be fresh water or plant process water. In the case of plant process water, this is white water (from the paper machine) or black liquor. In the first tubular digester, the fibers have a moisture content of about 50-85% by weight on a parched dry basis.

Both thermomechanical and thermochemical digesters use conventional pumps, piping, motors, conveyors, refiners, etc. These need to be dimensioned according to the requirements of the particular equipment. The tubular chamber may be of any reasonable size. Usually, the length of these steamers is about 2-20yx, and the inner diameter is about 0.2-4
It is m. The volume of the second stage steamer is approximately 1-5 times larger than the volume of the first stage. The ratio of the total time in the second tubular chamber to the total time in the first tubular chamber will be the same as the ratio in volume above.

It is possible to make the residence time in the second stage of the steamer longer than in the first stage while keeping the volume of each steamer the same.

This can occur because some fiber components continue to dissolve in the first tubular chamber of the digester. This causes a loss in overall volume and results in the screw in the second tubular chamber being operated at a slower speed. This increases the residence time of the fibers. However, if each tubular chamber has the same volume, the residence time in the second tubular chamber will only be about 1.1-1.5 times greater than in the first tubular chamber.

FIG. 5 shows the use of two more stages of steaming in a thermochemical process, with the residence time of the pulp at a stage of steaming increasing with each stage of steaming. There is also a blowdown between each stage of cooking, which serves to break apart the fibers so that they receive better liquid penetration in the next stage of cooking.

More specifically, raw fiber sources such as sugar cane lees, bamboo, eucalyptus wood or wood chips are fed from the conveyor SO into the screw conveyor 5/. Preferably, the raw fiber has a moisture content of about 50-60% by weight. A screw conveyor and screw feeder 53 meter the fibers into the inlet field of the tubular digester. The screw feeder also functions as a valve mechanism to maintain high pressure in the tubular chamber. The screw conveyor and screw feeder each have a screw driven by a motor M. Each tubular chamber also has a conveyor screw driven by motor M. A screw conveyor in each tubular chamber moves the fibers from one end to the other. The speed of the screw determines the residence time of the fibers in the tubular chamber.

Each tubular chamber has an inner diameter of about 0.2-4771.0 and about 2
-It has a length of 20m. The tubular chambers need not have the same dimensions. Varying the size of the tubular chamber changes the residence time of the fibers within the tube, and in fact this is a convenient way to change the residence time in the tube. Each tubular chamber is constructed of steel and has a wall thickness sufficient to withstand internal pressures of up to approximately 30 h/ca.

Water vapor is injected into the tubular chamber llt in the inlet line, 1. This steam is injected together with the raw fibers. The pressure of water vapor is about 2-20 K? /ffl, preferably about 5
-15Kz/enemy. This water vapor serves to further moisten the fibers and heat them to a temperature of about 150-200°C. The exact temperature depends on the pressure of the water vapor. Water vapor with constant pressure has a corresponding temperature. While traversing the tubular chamber 6, the fibers are heated to the temperature of steam.

Although the cooking agent may be added alone to the raw fiber, it is preferred to add the agent before each cooking step. In a further preferred embodiment, the cooking chemicals should be added before blowdown to the next cooking stage.

In FIG. 5, the cooking chemicals are added through lines lI/, lλ, g3 and lllI. 215 (by volume) 1 of the cooking chemical is added to the raw fiber through line lI2. All or part of the residue cooking agent is
and added through the pufferfish. The liner adds a cooking agent to the partially cooked fibers exiting the tubular chamber 116. This is added just before the first blowdown. Line lI<z adds the remaining cooking chemical to the partially cooked fibers exiting tubular chamber 1I-7 before the second blowdown.

Preferably, most of the drug is added before blowdown into the second tubular chamber.

The screw in the tubular chamber moves the fibers through the steamer, but at the same time acts gently on the fibers, helping the chemicals penetrate into the fibers. The fibers exit the tubular chamber 'IA' in the line field and at && at least 1 Kq/', preferably at least 2 K9/+:J
receive a blowdown.

Blowdown is accomplished using a conventional blowdown valve or disc refiner. This is shown as B in FIG. The disc refiner functions as a blowdown means and at the same time acts to further break up the fibers and separate the fiber bundles. Blowdown itself also separates fibers by rapidly converting water in the fibers to water vapor. The water vapor contained in the fiber bundle causes the fiber bundle to explode separately thereby causing the fibers to separate. The fiber under reduced pressure is conduit S
It passes through Otsu and enters the tubular Murogua.

The motor M rotates the screw in the tubular chamber I1.7 at such a speed that a continuous flow of fibers passes through the chamber. The screw acts gently on the fibers, thereby separating them and aiding the penetration of the drug. Since the tubular chamber 7 has a larger volume than the tubular chamber 'it, the screw in each chamber is operated at such a slow speed that the residence time in the tubular chamber l17 is greater. As a result, the fibers have different residence times in each tubular chamber.

At the outlet S7 of the tubular chamber 17, the fiber passes through the line Sg and again undergoes another blowdown at i. The decrease in pressure is again about I Kti/cr! , preferably about 2Kr/ca. Also, as in the blowdown from chamber 116 to 4'7, the blowdown means is a conventional blowdown valve or disc refiner.

After blowdown, the fibers pass through line Otsu0 into a tubular chamber +! Enter g. This tubular chamber is the tubular chamber Gua υ
is also shown as having a large internal volume. However, the internal volumes of these tubular chambers may also be the same. Cooking chemicals are added through line 2+ if desired. Of course, in most methods, sufficient penetration occurs in the tubular chamber 17g and 117 without the addition of drug immediately before the tubular chamber 17g. The fibers leave the tubular chamber g in line 6/ and undergo refining at point 3.

The fibers then pass through conduit 6 and undergo blowdown at 4+. This blowdown again reduces the pressure by at least 1 Kq/ca, preferably 2 Kq/cJ. The blowdown means is a conventional blowdown valve or disc refiner. The fibers are then sent to blowdown tank 6A through line IJ,
There the pressure is reduced to atmospheric pressure. The fibers exit the blow tank at Otsu 7, where they are washed with water and subjected to other processing steps. An example of such a processing step is U.S. Pat.
No. 47101.

If the fiber source is wood, the steamer should have a larger volume in both tubular chambers than in the case of sugarcane slag or bamboo.

This is because a longer residence time is required for each stage. Moreover, the pressure in the first tubular chamber should be higher and the pressure difference between the tubular chambers should be larger. This is necessary to obtain good spreading and steaming of the fibers.

The operations described below show the preferred method when the present invention is applied to a two-stage steaming method.

The bamboo fiber source is chopped into small pieces, washed with water, and demyelinated. The resulting material is a wet bulk fiber source consisting of small fiber bundles. The preferred scale of the steaming operation is per day,! It is sufficient to process 175-200 mm (on a dry basis) of fiber.

A steaming pot has the following dimensions.

(a) First tubular chamber: diameter Q, 9 m, length 14.1
m(b) Second tubular chamber - diameter 1.65 m, length IO, 8771° The volume of the second digester is approximately 1.7 times the volume of the first chamber. Also in the second tubular chamber, the screw controls the amount of fiber entering the first tubular chamber such that the residence time in the second tubular chamber is twice the residence time in the first tubular chamber. The values calculated as necessary based on the values are also slowly manipulated.

The finely cut bamboo is fed into a screw conveyor at a rate of 1.7) and 4:00. Black liquor and steam are added to bring the moisture content to 75% by weight (based on parched fibers). The pressure in the first tubular chamber is 9 Kg/crl gauge and the residence time of the fibers in the first tubular chamber is about 14-45 minutes. To give a caustic solution content of 11% by weight to the fibers,
Immediately prior to blowdown, 11 parts by weight of caustic solution is added to the fibers. The pressure reduction during blowdown (refiner blowdown) is 1.5 K91 crl. The pressure in the second tubular chamber is 7.5 Kr/J;
Moreover, the fiber residence time is about 30 minutes. Upon exiting the second tubular digester, the fibers are first subjected to hot stock refining and then blowdown to atmospheric pressure. The fiber yield is approximately 50 inches based on the weight of fiber entering the first tubular chamber. This is calculated on a parched basis.

Various modifications can be made to the boiler method of the present invention and these modifications also fall within the scope of the present invention. The key features of blowdown between cooking stages and long residence time in the second stage are utilized. Also, in the case of thermochemical pulping, the pulping agent should be added immediately before or after blowdown. There is no pulping agent present in the first tubular chamber.

These are features that produce valves with improved properties.

[Brief explanation of the drawing]

FIG. 1 shows a two-stage thermomechanical cooking trench such that the second stage has a length υ greater than the first stage. Figure 2 shows a two-stage thermochemical steaming of the ox, where the second stage has a larger diameter than the first stage. FIG. 6 shows a thermochemical cooker with six stages of cooking, each stage having a larger volume than the previous stage, and with a blowdown between each stage. It is. 10.5θ... Conveyor, //, j/... Screw conveyor, /3. ! 3...Screw tweeter-117...First tubular chamber, /9...Blowdown, 2/, 3/...Second tubular chamber, 3...Refiner, 2g , At. ... Blowdown tank, M... Motor, B...
・Followdown, qoto-lIg... 1st to 5th tubular chambers. Patent Applicant Process Evaluation and

Claims (9)

[Claims] (1) contacting a source of cellulose fibers with high pressure steam in a first tubular chamber for a first period of time: removing the cellulose fibers from the first tubular chamber and removing the source of cellulose fibers from the first tubular chamber; rapidly reducing the pressure to a first lower pressure, thereby at least partially separating the cellulose fibers; and placing the at least partially separated cellulose fibers in a second tubular chamber. and the cellulose fibers are contacted with the first lower pressure water vapor for a period of time that is 1.1-5 times the time that the cellulose fibers are in the first tubular chamber; from the second tubular chamber and rapidly reducing the pressure on the cellulose fibers. (2) Upon removal from the second tubular chamber, the cellulose fibers are subjected to disc sofaning before being subjected to a reduction in pressure. Fiber pulping method. 3. A continuous fiber nollification method as claimed in claim 1, characterized in that a cooking agent is added to the cellulose fibers in the first tubular chamber. (4) The cooking agent is added to the cellulose fibers after they have been removed from the chamber of the first tube and before undergoing a sudden decrease in pressure. A continuous fiber pulping method according to scope 1. (5) A steaming agent is added to the cellulose fibers after receiving a sudden decrease in pressure and before contacting with water vapor in the second tubular chamber. A method for forming a continuous fiber layer according to item 1. (6) the cellulose fibers removed from the second tubular chamber are sent to a sixth tubular chamber under a second pressure; Continuous fiber pulping process according to claim 1, characterized in that the fibers are brought into contact with steam for a period of time corresponding to 1-5 times. (7) The cooking agent is added to the cellulose fibers after they have been removed from the first tubular chamber and before undergoing a sudden decrease in pressure. A continuous fiber pulping method according to scope 6. (8) at least two interconnected tubular chambers each having an inlet end with an inlet aperture and an outlet end with an outlet aperture; an outlet aperture at the outlet end of the first tubular chamber;
sump conduit means for joining an inlet aperture at the inlet end of the second tubular chamber, wherein the internal volume of the second tubular chamber is greater than the internal volume of the first tubular chamber. , a multi-stage tubular steamer. (9) A multi-stage system as claimed in claim 8, characterized in that the conduit means includes depressurization means employed to reduce the pressure in the second tubular chamber. Steam pot. α1 There is a conduit means for coupling the outlet of the second tubular chamber to the inlet of the fifth tubular chamber, and the internal volume of the sixth tubular chamber is larger than that of the second tubular chamber. 9. A multi-stage steamer according to claim 8, characterized in that the internal volume is equal to or larger than the internal volume. (1) Conduit means for connecting the outlet of the second tubular chamber with the inlet of the sixth tubular chamber are employed to reduce the pressure in the second tubular chamber. 11. The multi-stage steam boiler according to claim 10, characterized in that it includes a pressure reducing means. (b) The multi-stage steaming trench according to claim 10, characterized in that the internal volume of the fifth tubular chamber is larger than the internal volume of the second tubular chamber. 0. A multi-stage steamer according to claim 9, characterized in that each tubular chamber has one screw means for moving the fibers from one end to the other. (b) A multi-stage steamer according to claim 11, characterized in that each tubular chamber has one screw means for moving the fibers from one end to the other.