FI57454C - FRAMSTAELLNING AV FOERBAETTRAD HOEGUTBYTESMASSA - Google Patents

Description

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Patent- oc regiaterstyreleen Antöktn utitgd oeh uti. »Krifwn pubifcand 30.04.00 (32) (33) (31) Requested Muol access — B« gird prloritat 23.09-7 ^

Sweden-Sweden (SE) 7 ^ H950-U

(71) Mo och Domsjö Aktiebolag, Fack, 891 01 Örnsköldsvik 1, Sweden-Sweden (SE) (72) Jonas Arne Ingvar Lindahl, Domsjöverken, Lars Gustaf Rudström,

Domsjöverken, Sweden-Sverige (SE) (7 ^) Berggren Oy Ab (5 ^) Method for the production of improved high-yield pulp - Framställning av för-bättrad högutbytesmassa

The present invention relates to the production of even better high-yield pulps by a semi-chemical, chemimechanical, thermomechanical or mechanical route, and to an apparatus for the production of such pulps. With the prior art, strong chemimechanical pulp can be made from Nordic softwood in about 85% yield. However, the pulp thus obtained has proved to be quite difficult to bleach. In addition, its fibers are very resistant to grinding, which makes it difficult to improve the strength by grinding them from paper. In addition, the produced paper has a rough surface, so that it is not properly suitable for use as writing and printing paper.

If the yield is increased to more than 90% according to the prior art, a pulp is obtained which is in many respects more suitable for papermaking and which is also relatively easy to bleach. However, due to the increase in yield, the strength deteriorates to such an extent that the pulp becomes unsuitable for the production of writing and printing paper without mixing according to the stronger materials. As for high-yield pulps made from hardwoods, they are, with a yield of more than 90%, easily silenced but inherently poor in strength. In less than 85% yield, hardwood 2 57454 gives a strong pulp which, moreover, is less difficult to grind. In addition, such a pulp is readily present in silent lignin-preserving bleaches such as hydrogen peroxide. It is also known to mix pulps of the above-mentioned type, in which the starting materials are thus hardwood and softwood, respectively. However, the downside here is that the two pulps have to be made by different methods and then mixed before the paper is made, which makes the method relatively poor economically. In order to improve the product, high-yield pulps have also been made from mixtures of hardwood and softwood. In this case, however, it has proved difficult to achieve satisfactory strength and flatness properties. The following Experiments 1-3 illustrate the above problems.

Experiment 1: Soup in different yields from the same (long-fiber) wood species

The spruce chips, with pieces about 30 mm long, about 15 mm wide and about 3 mm thick, were washed and steamed with steam at atmospheric pressure for 10 minutes. The chips were then compressed in a laboratory press and then allowed to swell in cooking liquor containing 50 g / l NaOH (calculated as Na 2 O) and 65 g / l SO 2. The pH of the liquid was 6.0. The chips absorb it thus by impregnating 1000 ml of a solution with 100 g of abs. per dry wood chips. The saturated chips were charged to a digester and heated with saturated steam at 443 K (170 ° C). The overpressure in the digester was 825 kPa. One batch (A) was boiled for 5 min in 443 Cats and the other batch (B) was boiled for 25 min in 443 Cats. These cooking times can be considered as long as the total cooking time, as the heating to cooking temperature took less than 1 minute. Batches A and B were each fiberized separately in a plate mill at cooker pressure while adding dilution water. The defibered pulp was pushed into a hydrocyclone to separate the steam from the fibrous slurry. The resulting pulp slurry contained about 30% dry pulp and had a temperature of 360 K (87 ° 0 · The fibrous pulp was ground in another plate mill. In this case, dilute water was added so that the grinding was performed at a consistency of 23%. The ground pulp was sieved and raised to 35> 8. by removing water, then bleached with 58 μl of hydrogen peroxide and 0.8 μl of sodium dithionite, ground in 1000 revolutions in a laboratory mill and made into laboratory sheets, which were tested to give the following results: 1 '3 57454

Lot A Lot B

Mass yield,% 91.2 84

Grinding degree, ° Schopper-Riegler 56.5 15

Brightness after bleaching, SCAN,% 77, ^ 70.7

Breaking length, meters 4200 6800

Tear coefficient 72 84

Light scattering coefficient, m2 / kg 36.7 21.4

Porosity, Bendtsen, ml / min 980 2300

Comparing batch A with a yield of 91.2% and batch B with a yield of 84%, it is found that the degree of grinding and brightness of batch A are higher than those of batch B, i. The pulp made according to A is easily ground and silenced. Moreover, lot A has given a better opacity, which is determined by measuring the light scattering coefficient and is directly proportional to this. Instead, method B gave a mass that was stronger than that of batch A.

Test 2; Soup in different yields from the same (short-fiber) wood species Experiment 1 was repeated with the difference that birch chips were used instead of spruce chips. The following results were obtained:

Lot A Lot B

Mass yield,% 93.0 84.2

Grinding degree, ° Schopper-Riegler 12.5 18

Brightness after bleaching, SCAN,% 81.5 80.7

Breaking length, meters 270 4900

Tear coefficient 13 63

Light scattering coefficient, m ^ / kg 37.5 31.3

Porosity, Bendtsen, ml / min> 3000 1173

The table shows that hardwood treated according to method A gives a mass which is easily silent but inherently poor in strength. If the yield of the pulp is reduced to 84.2%, batch B, the strength will improve considerably, and the pulp will still be easily silenced and less difficult to grind than the pulp according to batch A.

Experiment 3: Soup in high yield from mixtures of different wood species (long-fiber and short-fiber)

A chip mixture of 50% birch and 50% spruce with the same piece dimensions as in Experiment 1, except that the piece thickness was 2 mm, was steam roasted and impregnated in cooking liquid as in Experiment 1. The chip mixture was then boiled at 433 K (160 ° C). 20 minutes.

This partially delignified chip was defibered, ground and bleached as in Experiment 1. The mass obtained is then denoted by the symbol batch 3 · Α. This pulp was ground in 500 revolutions in a laboratory mill, after which laboratory sheets were prepared and tested for paper properties. The experiment was repeated with the difference that the spruce chips were changed to pine chips, in which case the obtained mass was marked with the symbol batch J>: B. The following results were obtained.

Lot 3 · A Lot 3: B

Mass yield,% 89.0 89.5

Grinding degree, ° Schopper-Riegler 40.5 14.5

Brightness after bleaching, SCAN,% 78.4 77.5

Breaking length, meters 3900 3100

Tear coefficient 68 63

Light scattering coefficient, m ^ / kg 36.1 33.4

Porosity, Bendtsen, ml / min 1560> 3000 As shown in the table, these masses are both easily silent and relatively turbid. However, the strength of the pulps is inferior to that of pulp made from softwood alone in corresponding yields. In factory papermaking, the smoothness of the paper surface also becomes unacceptably poor (reflected in, for example, high porosity). These pulps also yield hard and brittle paper that bends poorly.

The object of the present invention is to eliminate the above-mentioned drawbacks and to provide an even better high-yield mass more economically than has hitherto been possible. Accordingly, the present invention is directed to a process for producing a pulp of lignocellulosic material in a yield range of 70-93% with improved quality properties according to which at least a portion of the lignocellulosic material is washed, vaporized, impregnated with dissolving chemicals and dissolved, and then fiberized. the fact that the lignocellulosic material is divided into at least two different material streams, the first of which, after washing and steam roasting, is dissolved in 65-92, preferably 78-88% yield and the second material stream is at least washed, then immediately without intermediate washing, mixed and heated to 363- 473 K, preferably 373-458 K, in a common pressure vessel in such a way as to further partially delignify and soften the lignin, after which the product thus obtained is mechanically defibered.

According to a preferred embodiment, the second material stream is also steam-evaporated after washing at a temperature of 363-383 K for at least 5 minutes. In certain cases, it is also appropriate, after washing and steam roasting, to impregnate the second stream of material with dissolving chemicals to effect its slight delignification during subsequent processing in a pressure vessel.

The partial delignification in the common pressure vessel must be carried out so that the final yield of the first stream of material becomes 60-80%, preferably 73-85% »and the yield of the second stream of material becomes 100-85%» preferably 96-90%. For this, a heating time of 1-20, preferably 2-10 minutes is required in most cases. It is particularly suitable, before dissolving the first stream of material, to impregnate it with dissolving chemicals and to remove the excess thereof, after subsequent dissolution in a common pressure vessel. The product obtained after the treatment of the pressure vessel is mechanically defibered and possibly further ground and possibly also bleached, preferably with lignin-preserving bleaching agents.

According to the present invention, a reduced lignocellulosic material such as wood chips, straw chips, sawdust, etc. is used as a starting material in the production of the pulp. According to the invention, it is essential that the raw material is in smaller pieces in order to carry out the process. The reduction of the lignocellulosic material, which may be in the form of logs, for example, can be carried out in a chipper which gives a chip having a particle size of 15-30 x 20- ^ 0 mm and a thickness of 0.5-10 mm. It is particularly suitable to use a thin chip, i.e. chips with a thickness of 0.5-5 mm, as this facilitates the penetration of chemicals into the lignocellulosic material.

According to the invention, all the chips are washed in one or two chip washers to remove foreign objects such as metal parts, etc. The excess heat of the pulp process and the frictional heat of the refiners can also be used to wash the chips. By washing the chips at an elevated temperature, the washing is made more efficient and the residence time according to the invention in the subsequent steam treatment can be shortened. According to the invention, the desired equalization of the normal moisture fluctuations of the fed chip material is also achieved, which increases the uniformity of the quality of the produced pulp. According to the invention 6 57454, the washed and preheated chips are transferred by belt conveyors or helical feeders to one or two containers for treating the chips with steam at atmospheric pressure (roasting). In the method according to the invention, the chips are thus divided either before washing the chips, after washing, or after roasting, into two streams, after which pulp is produced from each chip stream so that the yield of the pulp is different in them. The second chip stream is always impregnated with chemicals after washing and roasting, and boiled, after which it is taken to a common pressure vessel. The second chip stream can be taken to a common pressure vessel immediately after washing the chips, or after washing and roasting. Alternatively, this chip stream may be impregnated with chemicals after washing and roasting the chips before being introduced into a common pressure vessel. This chip stream is therefore not boiled separately. Further delignification of the feed material may occur in the common pressure vessel. In a pressure vessel, the material is treated with steam at a temperature of 0-981 kPa, preferably 49-785 kPa overpressure and 363-473 K (90-200 ° C), preferably 373-458 K (100-185 ° C). With steam, heating can also be carried out indirectly to a corresponding or lower temperature if it is desired to apply such a pressure to the pulp that the buffer can be carried out at a pressure exceeding the steam saturation pressure. The chips used in the above-mentioned chip streams can be chips of the same or different wood species or a chip mixture comprising two or more wood species. The method according to the invention is shown schematically in Figure 1, to which the following application example illustrating the invention relates.

Example 1

Manufacture of chemimechanical pulp from two different types of wood, one of which is partially delignified

Technical birch chips with a piece size of approx. 30 x 15 mm and a thickness of approx. 5 mm - wood chip batch A - washed in wood chip washer 1 and steam roasted in roasting vessel 2 at atmospheric pressure 373 K (100 ° C) for 10 minutes · Roasted wood chips were fed by spiral feeder 3 to the impregnation chamber 4. The spiral feeder was designed to compress the chips during transport and thus remove water from about 35% of the dry content to about 50% of the dry content. After passing the chips through the spiral feeder, it was allowed to swell in the impregnation chamber 4, which contained cooking liquid, the surface height of which was kept constant and supplemented from the chemical production section 5. When swelling in the impregnation chamber, the chips absorbed about 1 liter of cooking liquid per kg of dry chips. The cooking liquor was prepared from sulfur dioxide mixed with sodium hydroxide, the amount of sodium hydroxide (calculated as Na 2 O) being 50 g / l and the amount of sulfur dioxide 65 g / l. The pH of the cooking liquid was 6.0. The impregnated chips were then transferred to a digester 6, where they were cooked in the steam phase by feeding direct steam at 735 kPa to line 7, bringing the cooking temperature to 443 K (170 ° C). The residence time in the cooker 6 was 20 min. After dissolving the chip batch A in the digester 6, the chips were transferred to a common pressure vessel 9 by a helical feeder 8 having the same structure as the helical feeder 3 and squeezing out too much cooking liquid and condensate. The spent cooking liquid can be used to impregnate the second chip stream B in the impregnation vessel 23 or to make a new cooking liquid in the chemical production section 5, or it can be fed directly to the cooking chemical recovery plant 10. The pulp yield after delignification of chip batch A in digester 6 was 83. was the same as the chip batch A, and was passed, after passing the chip wash 11, directly to the common pressure vessel 9, where.he equal amount of chips from the chip stream A was mixed. Excess steam was introduced into pressure vessel 9 down line 12 from helical feeder 8 at an overpressure of 245 kPa, after which the mixture of chips A and B was further delignified in the vapor phase at 398 K (125 ° C) for 3 minutes. Under these conditions, the pulp yield from the chip batch B was about 95%. The steam-heated mixture of the partially delignified chips A and the slightly delignified chips B thus obtained was transferred by means of a helical conveyor 13 at the bottom of the pressure vessel to a defiberizer, disc refiner 14 At K (120 ° C), the pulp thus defibered was passed to a steam separation cyclone 15, to which cooling water was added down line 16. From the cyclone, the pulp was passed to a second plate mill 17 where it was further milled at atmospheric pressure, at a temperature of about 358 K (85 ° C) and a pulp consistency of 25%. The resulting pulp was then sieved, diluting with water, in a pressure screen 18 to a consistency of about 1% of the pulp. The screened pulp was then treated in a vortex separator 19. The scrap from the pressure screen 18 and the vortex separator 19 was thickened to 20% consistency and ground in a grinder 20. The ground scrap was returned to a pressure screen 18. The valid pulp was thickened to 20% consistency and bleached with hydrogen peroxide. The total yield of the obtained mass became 87% and the brightness 78% SCAN. The strength and optical properties of the pulp were such that it could be used for the production of writing and printing paper.

8 57454

Example 2

Manufacture of chemimechanical pulp from wood chips of several different species

The procedure of Example 1 was repeated with the difference that chip chip A consisted of a mixture of birch, aspen and beech chips in a ratio of 40:40:20 with the same piece dimensions as in Example 1, and chip chip B consisted of pine and spruce chips. in a ratio of 60:40, with the same piece dimensions as in Example 1. The total yield of the pulp became 87% and the brightness 77%. The pulp was well suited for the production of writing and printing paper and cardboard.

Example 3

Preparation of chemomechanical pulp from a single wood species The procedure of Example 1 was repeated with the difference that the chip batch A and the chip batch B were both six chips with the same piece dimensions as in Example 1. The total pulp yield was 89% and the brightness after bleaching was 76% SCAN. The pulp had very good strength and good optical properties, and was well suited for the production of writing and printing paper, paperboard and tissue paper.

Example 4

Manufacture of chemomechanical pulp from a batch of wood chips of the same species, divided into two streams, both of which are partially delignified

Technical birch chips with the same length and width dimensions as in Example 1 but a thickness of 3 mm were treated as chip stream A in Example 1. The chip stream B consisted of birch chips with the same piece dimensions as chip stream A. The chip stream B was washed in a chip washer 11 and roasted in a roasting paste and passed through a helical feeder 22 to an impregnation chamber 23 where it was impregnated with the same type of cooking liquid as in the impregnation chamber 4. From the impregnation chamber 23 the chip stream B was led directly to the pressure vessel 9 where it was mixed with the chip stream A in a ratio of 30:70. The pressure vessel 9 was then supplied with 638 kPa of pressurized direct steam down line 24, corresponding to a temperature of 433 K (160 ° C). The mixture was steam cooked for 15 min. In this case, the whole mixture was partially delignified, whereby the yield of the chip stream A became about 79% and the yield of the chip stream B was about 90%. Further work-up was then carried out as in Example 1. The overall yield of the pulp was 85% and the brightness was 81JS SCAN. The pulp obtained had very good strength and optical properties and was well suited for the production of writing and printing paper and paperboard.

Example 5

Manufacture of chemimechanical pulp from two chips streams of different wood species, both partially delignified

The procedure of Example 4 was repeated with the difference that fiber stream A consisted of a mixture of birch and aspen chips in a ratio of 50:50, with piece dimensions of 50 x 15 mm and 1 mm. Chip stream B was six chips with the same piece dimensions as chip stream A. The total mass yield was 84% and the brightness was 79% SCAN. The obtained pulp was well suited for the production of writing and printing paper, cardboard and tissue paper.

Other embodiments of the processing steps described in Examples 1-5 may be used in the process of the invention. Thus, as the basic chemical in the cooking liquid, sodium carbonate, ammonia or magnesium hydroxide, etc. can be used instead of sodium hydroxide, etc. The cooking liquid can also contain only basic chemicals without sulfur dioxide, which can also be replaced by oxygen gas. A suitable pH of the cooking liquid used is 2-13 and preferably 5-9. The chemical content of the cooking liquid can, of course, be varied as desired.

Instead of the cooking in the digester 6 being carried out in the steam phase, it can be carried out in the liquid phase, in which case considerably less concentrated cooking liquid is used than in the steam phase cooking. In liquid phase cooking, the chips are fed directly from the roasting vessel 2 to the digester 6 up to line 26 and the dissolution chemicals are fed to digester 6 from the chemical manufacturing department 5 down line 27. A suitable temperature range for cooking is 373-453 K (100-180 ° C) and a suitable overpressure range 49-127 kPa. A suitable cooking time is 2-240 min. According to the invention, the yield of pulp during delignification of fiber batch A in digester 6 is maintained between 65-92% and preferably between 78-88%. As can be seen from the examples, the chip batch B can be fed directly to the common pressure vessel 9 to be mixed with the chip stream A after washing the chips, but it is also possible to add a small amount of cooking chemicals to the chip batch B after feeding before feeding it to the pressure vessel. The residence time in the pressure vessel is suitably kept at a maximum of 20 minutes. A residence time of 2-10 minutes is preferred. An overpressure of 49-883 kPa is suitably maintained in the pressure vessel 9. The chips treated in the pressure vessel and fed to the fiberizing device 14 can also be defibered at atmospheric pressure, and the defibering device can also be a cone mill or a helical fiberizing device (so-called FROTAPULPEF®).

10 57454

When two defibering devices are used, part of the batch of chips coming from the pressure vessel 9 can be defibered under pressure, while the rest of the chips are defibered under pressure. In the case where the fiberization is carried out under pressure, the chips coming from the pressure vessel must first pass through a steam separation cyclone 25. The separated steam can be passed to the chip washer 1 and / or 11 or its heat content can be utilized in a chemical recovery plant, e.g. for evaporation. When the chips are defibered under pressure, after defibering, they can be passed to a steam separation cyclone 15. If desired, diluent and cooling liquids can be added to the cyclone along line 16, as well as bleach-containing liquids, for example bleaching effluents. After defibering, it is advantageous to further modify the pulp in a defibering or milling step, for example in a plate mill, cone mill or helical conveyor 17, but mills other than those mentioned above can then be used. It is also possible to defiber the said two fiber streams separately, in which case the latter grinding can also be performed for different streams, i. the chips that have been defibered at an overpressure can be post-ground separately and the chips that have been defibered at atmospheric pressure can be post-ground separately. According to another embodiment of the invention, the two masses are mixed after defibering and post-treated in a common refining device. One advantage of grinding each batch of pulp separately after defibering is that the pulps can be ground with different high forces. When using two refiner members after the pressure vessel, different amounts of defibering energy can also be used. The ground pulp may contain incompletely fibrous small chips, so-called sticks. To separate the sticks from the pulp, it is suitable to sieve the pulp. This gives a fraction consisting of coarse mass and sticks. This fraction is called wreck pulp and is usually thickened to a relatively high consistency, preferably between 15-30%, and processed in suitable grinding means, whereby the sticks become fibrous into private fibers. The waste fibers are then usually fed to a pulp stream to the screen compartment. The pre-screened pulp is usually thickened, primarily with filters, and can then either be bleached or immediately dried. In integrated pulp mills, bleached or unbleached pulp is fed from the screening department directly or after intermediate thickening to a paper mill. Suitable bleaching agents for bleaching the obtained pulp are so-called lignin-preserving bleaching agents such as peroxide and dithionite. Other bleaching agents such as borohydride, peracetic acid, thioglycolic acid and hydroxylamine may be used.

11 57454

To compare the method of the present invention and the prior art, a series of comparative laboratory experiments were performed. The results of these experiments are shown in the following Examples 6-8.

Example 6

Method according to the invention compared to experiment 3 Spruce chips with a piece size of about 30 mm x about 15 mm x about 2 mm - chip flow B were washed, followed by steam firing at atmospheric pressure for 10 minutes. The chips were pressed in a laboratory press and then swelled in a cooking liquor of pH 6.0 consisting of NaOH (calculated as 50 g / l Na 2 O) and SC 2 (65 g / l). At this impregnation, the chips absorb 1000 ml of cooking liquid per 1000 g of abs. dry wood chips. In parallel, exactly the same procedure was followed for birch chips of similar particle size - chip stream A. According to the invention, the birch chips were then boiled separately for 10 minutes, after which they were mixed well in a pressure vessel with a 1: 1 impregnated spruce chip. The chip mixture was boiled in the vapor phase at 433 K (160 ° C), corresponding to an overpressure of 638 kPa, for 10 minutes. The total cooking time for the birch portion was thus 10 minutes of separate cooking plus 10 minutes of combined cooking, equal to 20 minutes. The dissolved chip mixture was defibered in a plate mill at digester pressure while adding dilution water. The defibered pulp was buffered into a hydrocyclone to separate steam from the pulp slurry. The pulp slurry had a dry matter content of about 30% and a temperature of 36Ο K (87 ° C). The defibered pulp was ground in another plate mill. In this case, dilution water was added so that grinding took place at about 23% of the consistency of the pulp. The ground mass was sieved and thickened to about 35! to consistency and then bleached with 3 # hydrogen peroxide and 0.8% sodium dithionite. The pulp was then ground 500 rpm in a laboratory mill and formed into laboratory sheets for paper testing. The following is a comparison of this example, i. between the pulp paper test of the invention and the pulp lot 3: A of the paper test results of the previously described Experiment 3. The pulp according to the invention is distinguished from the pulp 3 · Ά by the fact that according to the invention the birch section is cooked both separately for 10 minutes at 433 K (160 ° C) and together with the spruce section for 10 minutes at 433 K (16 ° C), while the 3: A birch and six portions have been boiled together for 20 minutes at 433 K (160 ° C).

The results were as follows: 12 57454

Lot 3: A According to the invention.

Mass yield,% 89.0 88.7

Grinding degree, ° Schopper-Riegler 40.5 42.0

Brightness after bleaching, SCAN,% 80.4 80.2

Breaking length, meters 5900 4800

Tear coefficient 68 76 p

Light scattering coefficient, m / kg 36.1 34.8

Porosity, Bendtsen, ml / min 1560 1110

Elongation,% 3.4 4.0

Double fold number 6 18

As can be seen from the table, the method according to the invention has obtained a stronger paper than the conventional method, while retaining other advantageous properties. Thus, the surface uniformity, elongation and toughness of the paper obtained according to the invention are good.

Example 7

Method of the invention compared to Experiment 3 This experiment was performed as in Example 6, except that pine was used instead of spruce. In addition, the experiment was carried out according to Example 3 previously described, but instead of spruce, with pine wood, to obtain a mass denoted by the symbol lot 3: B. What distinguishes the batch 3-B from the pulp according to the invention is that in batch 3: B pine chips and birch chips have already been initially mixed together and have therefore been cooked together for 20 minutes at 433 K (160 ° C), while birch and the pine chips according to the invention have been treated as separate streams so that the birch section is cooked both separately for 10 minutes and together with the pine section for 10 minutes (which is the only cooking with pine chips) at 433 K (160 ° C). The results were as follows:

Lot 3: B According to the invention.

Mass yield,% 89.5 89.0

Grinding degree, ° Schopper-Riegler 14.5 26.0

Brightness after bleaching, SCAN,% 77.5 77.8

Breaking length, meters 3100 3900

Tear coefficient 63 70

Light scattering coefficient, m2 / kg 33.4 33.6

Porosity, Bendtsen, ml / min> 3000 1820

Elongation,% 2.7 3.3

Double fold number 0 7 13 5 74 5 4

It is clear from the present that, by producing the pulp according to the present invention, surprisingly, a stronger paper has been obtained which has good surface uniformity, extensibility and toughness while maintaining good optical properties. Furthermore, it is surprising that by using, for example, a mixture of pine chips and birch chips, a considerably higher degree of grinding is obtained with the new method than with the method according to Example 3.

Example 8

The method according to the invention compared to the mixing of mechanical and chemical pulp

In papermaking, mechanical pulp is often mixed with chemical pulp to make woody paper, whereby the chemical pulp gives the paper its strength, while mechanical pulp mainly contributes to good formation (i.e., even distribution of fibers in the paper) and good opacity. In the experiment, a mixture of 35% peroxide bleached mechanical pulp with a brightness of 80% SCAN and 65% chemical pulp with a brightness of 91% SCAN was prepared, the mixture was ground 500 rpm in a laboratory mill, after which laboratory sheets were formed. These sheets were paper tested and the results were compared with those obtained with the paper according to the invention prepared according to Example 6. The results were as follows:

Mechanical pulp / Chemical pulp according to the invention

Mass yield,% 65 88.7

Grinding degree, oschopper-Riegler 31 42

Brightness, SCAN,% 83 80.2

Breaking length, meters 3200 4800

Tear coefficient 76 76

Light scattering coefficient, m2 / kg 41.2 34.8

Porosity, Bendtsen, ml / min 1150 1110

The results show that paper made from pulp according to the invention has better tensile strength than conventional wood-containing paper. The only properties that are slightly worse are opacity and, to some extent, brightness. Thus, the process of the invention can produce high quality paper having properties equivalent to those obtained by mixing mechanical and chemical pulp, and this in a total pulp yield of about 24% higher.

** 57454

The reason why the method according to the invention gives a pulp which, in addition to being easy to silence, easy to grind and have good optical properties, is also so strong that it can be used, for example, for writing and printing paper without adding any reinforcing pulp (very strong). not known. One explanation could be that grinding in the method according to the invention becomes more efficient. The reason that grinding would become more efficient when two types of chips with different degrees of delignification are defibered and ground together may be that less delignified chips, which are at the same time harder, help to soften the softer, stronger delignified chips. It is also probable that harder chips will help to degrade private fibers. It is also conceivable that the deterioration takes place at an earlier stage in the defibering and grinding process than when the relatively soft chips are ground separately. Another or concomitant factor that contributes to the favorable result may be that the softer chip fills the disc pattern of the disc refiner faster than the relatively hard chip. As the plates fill faster, the supplied energy is better utilized on the one hand, and on the other hand a larger shaping zone and a longer residence time as the pulp material passes through the grinding member. Another possible factor, or a factor acting together, may be that the fibers concerned come into close contact with each other during defibering, in which case it is possible to develop bonding potentials between the fibers which cannot be achieved by defibering and grinding the fibers separately.

The method according to the present invention has the important advantage that it gives a high pulp yield, which is essential when there is a shortage of wood fibers and every step to obtain a higher amount of pulp from wood becomes very important. Thanks to the invention, it has become possible to produce pulp in the highest yields, from which paper with good strength properties, good surface evenness, good elongation, low brittleness and good optical properties is obtained. In addition, the pulp is easily ground and easily silenced. In addition, the method according to the invention in certain cases consumes less energy. Since different tree species can be advantageously used in the method according to the invention, the invention also offers great possibilities for efficient use of the available raw material from wood harvesting areas where several tree species grow and at the same time only a small number of each tree species. Another advantage is that the dry matter content of the cooking liquor recovered in the process 57454 according to the invention is higher than in the previously known processes, which improves the thermal economy. The extract content of the cooking liquor also becomes higher than in co-cooking, resulting in a lower extract content in the finished pulp.

In addition, in the application of the invention, the same equipment can be used to a very large extent, in contrast to the case where different types of pulps from different factories are mixed. Examples of this are the chemical manufacturing department, a common pressure vessel and plate grinders. In addition, according to the invention, a common screen compartment, a thickening equipment, a bleaching plant and a pulp drying system as well as the same chemical recovery system are used.

The present invention also relates to a suitable device for carrying out the method according to the invention. The device shown schematically in Figures 2 and 3 * comprises a vertical pressure vessel with an impregnation chamber with vertical conveyors inside the upper part thereof, which communicates via a dewatering spiral feeder with a roasting vessel fitted with and is characterized in that the pressure vessel communicates via a dewatering spiral feeder with a vertical digester, the top of which is fitted with an impregnation chamber with vertical transport coils, the bottom of which communicates with a dewatering spiral feeder which in turn communicates with a roasting vessel.

The device according to the invention operates as follows.

After the wood has been chipped and washed, it is fed to the device according to the invention, as shown in Figure 2, in two streams A and B. The chip stream A is first fed to a roasting vessel 28 where the chips are treated with steam fed to line 29, then further, removing the water, with a helical feeder 30. The water squeezed from the chips is removed down the line 31. The chips are fed by means of a helical feeder 30 to the impregnation chamber 32 to which impregnation chemicals are added along the line 33. The chips are conveyed through the impregnating or cooking liquid with two vertical conveyor coils 3 ^ · After the chips have been conveyed through the impregnating liquid and saturated with it, it crosses the upper edge 35 of the impregnating vessel and falls into the digester J> 6. The placement of the impregnation vessel 32 and said two conveyors in the digester 36 is shown in more detail in Figure 3, which is a cross-sectional view of the digester 36 at 3-3 · Steam is introduced into the digester 36 along the line 37. After the wood chips have been dissolved, i.e. cooked to the desired extent, it is conveyed from the digester 36 to the common pressure vessel 38 by a helical feeder 39 · As the chips pass through the helical feeder 39, a large part of the cooking liquor is squeezed out. The extruded cooking waste is removed up to line 40. In the common pressure vessel 38, the chip stream B is mixed with the chip stream A prior to mixing. . The impregnation chamber 44 may contain either impregnation chemicals or water alone. The required fluid is fed up to line 46. The chips are conveyed through the impregnation chamber 44 by two vertical conveyor coils 47 similar to those shown in Figure 3. The chips then pass over the upper edge 48 of the impregnation chamber 44 and fall, and mix with the chip stream A in a common pressure vessel 38. Steam is introduced into the pressure vessel 38 down line 49.

After the application flows. The mixture of A and B is treated with pressure and heat, conveyed by a helical conveyor 50 to a defibering device 51. The pulp obtained can then be fed to a cyclone to separate the steam, after which the pulp is optionally ground in a second stage and then sieved and bleached. The ends of the helical feeders 30 and 43 which are connected to the digester 36 and the pressure vessel 38, respectively, have seals which prevent steam from penetrating through it. This is not shown in Figure 2.

Claims (10)

A process for producing pulp of lignocellulosic material in the exchange range 70-93% with improved quality properties, wherein at least a portion of the lignocellulosic material is washed, meadow-based, impregnated with digestive chemicals and digested, and then defibrated, differentiated into lignocellulosic material, characterized in that of which a first material stream after washing and meadow basing is dissolved in a mass yield of 65-92%, preferably 78-88%, and a second material stream is at least washed, after which the two material streams are directly mixed without intervening washing and subjected to heating. a temperature of 363-473 K, preferably 373-458 K, in a common pressure vessel in such a manner that further partial delineation and softening of the lignin is effected, after which the obtained product is mechanically defibrated. 19 57454 Process according to claim 1, characterized in that the second material stream after washing also is meadow-based at a temperature of 363-383 K for a period of at least 5 minutes. 3- Process according to claim 1, characterized in that the second material stream after washing and meadow base is also impregnated with digestive chemicals. il. Process according to claims 1-3, characterized in that the partial delignification in the common pressure vessel is carried out such that a final mass yield of 60-88%, preferably 73-85%> is obtained in the first material stream and a mass exchange of 100%. -85%, preferably 96-90%, is obtained in the second material stream. Process according to claims 1-4, characterized in that the heating time in the common pressure vessel is poured at 1-20 minutes, preferably 2-10 minutes. 6. A process according to claims 1-5, characterized in that the digestion chemicals are sodium hydroxide and / or sulfur dioxide. Process according to claims 1-6, characterized in that the first material stream prior to digestion is impregnated with digestive chemicals and that excess digestion liquid is removed after digestion. 8. A method according to claims 1-7, characterized in that the digestion of the first material stream is carried out as meadow phase cooking. 9. A process according to claims 1-8, characterized in that the defibrated product is also refined and bleached. Apparatus for carrying out the method according to claims 1-9, comprising a vertical pressure vessel (38), the upper part of which is