FI59828C - REFERENCE TO A CONTAINER CONTAINING BEHANDLING AV FIBERMASSA - Google Patents

Description

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National Board of Patents and Registration ...., „, _ * (44) Nthtivikilptnon and kuL | välalsun p» m.—

Patent and registration authorities Anxökan utlagd och utl.ikriftan publk.rad 30.06.81 (32) (33) (31) Pyydetty • Tuoikeu * —Begird prlorltet 30.06.75

Sweden-Sweden (SE) 7507 ^ 9_2 (71) Aktiebolaget Karlstads Mekaniska Werkstad, 20, Verkstadsgatan, S-652 21 Karlstad, Sweden-Sweden (SE) (72) Lars Erik Karl Axel Tell, Karlstad, Per Hjalmar Malmström, Skived,

The present invention relates to a method and apparatus for pulp pulp. This invention relates to a method and apparatus for pulp pulp (7M Leitzinger Oy (5M) to a method and apparatus for the continuous processing of fibrous pulp. More specifically, the method is as set forth in the species definition of claim 1 and as set forth in the species definition of claim 5.

Cellulose production processes require a variety of treatments, such as washing and bleaching the cellulosic pulp. Bleaching of pulp, for example, requires treatment in several steps, and a treatment medium, for example a reagent, is introduced into each step. Swedish Announcement 357 799 describes in detail the treatment at different stages with both highly gaseous reagents and water-soluble reagents and presents comparisons between the results obtained in strong and low concentration bleaching.

The results unequivocally show that treatment of the pulp at high concentrations (15-60%) with the reagents used in the bleaching process, preferably with gaseous reaction components, causes the reaction to proceed more rapidly than at low concentrations. For example, Table 1 shows the results for bleaching the pulp at a concentration of 20-30% (strong concentration) compared to similar bleaching processes of 59828 at a concentration of 3-12% (low concentration). The comparison shows that the total reaction time at low concentration was 600 minutes, while at high concentration it was 63 minutes. The calculated consumption of chemicals at high concentrations is only about 56% of consumption at low concentrations. Reducing the reaction time in high concentration bleaching to more than one tenth of the time required in low concentration bleaching means that the volume of pulp that must fit the bleaching device during the process is greatly reduced. The volume of equipment and treatment vessels required for the bleaching process can thus be significantly reduced.

In multi-bleaching with gaseous reagents, the pulp undergoes one treatment operation at each stage. Thus, for example, the strong-concentrated pulp is made porous by grinding or grinding, treated with a gaseous reagent, diluted with water after reaching the desired degree of reaction, dried and washed in a washing press or the like, further concentrated if necessary by re-compression, etc. Especially when the washing liquid is squeezed out, the main part of the liquid in the fibrous web, mainly the liquid in the cavities between the fibers, becomes air-replaced when using known methods and devices.

It is further known from Swedish patent publication 145 636 to fit a vacuum filter with a pressurized filter drum rotating about a horizontal axis, a discharge space sealed on the outside, outwardly against the outside air, which communicates with the inside of the drum via the drum strainer so that the vacuum inside the drum The pulp layer which, as the drum rotates, descends on its strainer surface is detached from it by a rolling roller from which it descends to the bottom of the discharge space where the dilution water can be passed through the line to the mass before it is discharged by means of an impeller or the like. An end seal fitted in front of the discharge roller is reported to seal the circumference of the strainer drum against the outside air. In order to ensure that the same vacuum prevails in the discharge space and in the suction space of the drum, as is known from Swedish patents 194 958 and 194 959, a special line can be adapted to connect the discharge space to at least one so-called suction head connected to the other end of the drum. with drum 3 59828 suction mode. A greater vacuum in the discharge space than a vacuum in the suction space would result in unwanted rewetting of the pulp web. With these three known vacuum filters, air will inevitably be absorbed into the pulp web while it is on top of the drum and with a vacuum that is practically possible to keep in the exhaust space, the air can only be partially removed from the pulp web.

Swedish Patent Publication 89,292 proposes a procedure for bleaching a fibrous cellulosic material. According to one embodiment of this procedure, the substance, in the form of a relatively thin (3 mm) pulp web with a concentration so high that it is self-supporting, can be fed through a closed bleaching chamber divided into three compartments. The entry and exit, as well as the supply from one compartment to the next compartment, take place via four pairs of rollers of backing material, which are hermetically fitted in the openings in the outer and partition walls of the chamber. In the first compartment, the thin pulp web is subjected to a vacuum of at least 380 mm of Hg, as a result of which at least most of the air in the pulp web is removed. In the next section, the pulp is subjected to a gaseous bleach, such as chlorine, at an atmospheric pressure or, preferably, a higher pressure of about 1.3 kp / cm, while being fed around a series of guide rollers for ten minutes. In the last compartment, the pulp web is re-vacuumed to remove free chlorine, which is returned to the second compartment. When the pulp web is thus fed out of the chamber for washing on the drum filter via the last pair of rollers, it will absorb air, which makes washing considerably more difficult. This proposed approach is costly for the equipment and operation required and has not been implemented.

Swedish patent application 7306613-6 proposes a pressure filter, i.e. a washing press, with two rotating filter drums in an overpressure bath with a pressing point between them. The drums are provided with separate, substantially vertical, scraper blades arranged above the nip, which remove the compressed solid from the drum casings. A drain line located vertically above the compression point opens toward the overpressure bath along its entire length to receive the compressed solid therefrom.

The drain line includes a standard drain screw that transports the solids away. Further disclosed is a washing press (i.e., an overpressure 59828 tub, filter drums, scraper blades, and a drain line) that covers a head that appears to prevent water and water vapor from the spray equipment cleaning them above both filter drums from entering the place where the washing press is installed. . In addition, a small reduction in the penetration of air into the system and the solid can possibly be considered, but nothing like this is disclosed in said patent application.

It is previously known that the air in the fiber suspension causes several disadvantages, see for example Pin 58 (1975): 2, p. 90 - 94 (May O W and Buckman S J, Practical effect of air in Papermaking). Disadvantages include foam formation and the tendency to flocculate, change the compressibility of the fiber suspension and change the apparent fiber density, and the negative effect of web formation, drying and tightness on the paper machine. Similar effects also occur before a paper machine, for example in a bleaching machine.

However, it has been found that the serious effect of the air in the pulp before the paper machine is caused by air retardation, i.e. the air becomes considerably or even more difficult. prevents the treatment agent from coming into contact with individual fibers. Thus, the presence of air in the pulp, for example in bleaching, causes not only difficulties in bringing the reaction component into contact with the individual fibers, but also an extended reaction time and the risk of an uneven degree of reaction at different points in the pulp.

It is an object of the present invention to provide a method and apparatus for continuous processing of fibrous pulp which avoids air retardation of the pulp.

This object is achieved by performing the tasks set forth in the characterizing part of claim 1 in a method of the quality mentioned in the preamble, wherein the device of the quality mentioned in the preamble has the features set forth in the characterizing part of claim 5.

Due to the fact that the fibrous web expands after the pressing point and is transported to the next processing step in a closed housing and that the cavities in the fibrous web are refilled with a gaseous medium which is passed under pressure and protects the fibrous web against air absorption. not only protection against absorption is achieved, but also the gaseous medium is rapidly and uniformly absorbed into the reconstituted cavities so that it rapidly comes into contact with the individual fibers. For example, if the pulp is now heated to a temperature between 70 ° C and 100 ° C, which is required in most bleaching steps of the bleaching process, the gaseous medium may be water vapor. Due to the fact that water vapor penetrates quickly and evenly into the pulp web, which is strongly concentrated, the heating reaction becomes fast and energy consumption and space requirements are reduced to a minimum. Of course, similar advantages are also obtained when the gaseous medium is other than water vapor, but in particular water vapor provides an increase in reaction rate compared to what can be achieved in conventional bleaching of a concentrated pulp with a gaseous medium, further reducing the bleaching equipment

Keeping the gaseous medium under pressure in the housing prevents air from leaking into the housing and mixing with the gaseous medium.

In conventional bleaching of an air-retarded pulp with a gaseous substance, it is otherwise necessary first to grind the pulp and then to finely grind the pulp to expose the individual fibers to a gaseous reagent which, after grinding, is fed in a relatively dilute form. In this case, the diluent is air and / or water vapor. Since, according to the present invention, air retardation is avoided and the gaseous medium is brought into contact with the individual fibers of the fibrous web immediately after the compression point, grinding in a special grinding device can be omitted and possible coarse grinding performed after the fibrous web re-formed cavities are filled with gaseous medium. This also results in cost savings in terms of the device used and the space required by this device.

Furthermore, due to the need for a movable, liquid-permeable strainer member in the endless web, which forms the second part forming the compression point and which acts as a strainer member for forming the web by drying the fiber suspension, further simplification and compact construction of the device is achieved.

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The invention can also be applied to heating or cooling the fibrous pulp, for example in strong concentration milling. Heating can be performed simply at a high concentration, which means a reduction in energy consumption.

The device according to the invention will be explained in more detail below with reference to the figures of the accompanying drawing.

Figure 1 shows a schematic cross-section of a preferred embodiment of a device according to the invention.

Figure 2 shows schematically the course of the displacement of the washing liquid and the subsequent course of impregnation.

According to Figure 1, the device comprises a rotating roller, i.e. a drum 11, with a jacket 13 made of a liquid-permeable strainer member. The drum 11 is mounted on shaft body 15 (not shown) and provided with drive and speed control devices 17. A housing 19 is arranged outside the drum 11. the closed space 21 between it and the jacket 13 of the drum 11 in such a way that the radial distance from the jacket 13 to the housing 19 decreases from the beginning of the space 21 towards the part at its end in the direction of rotation of the drum 11. At the beginning of the space 21, the housing 19 has adjustable fiber suspension inlet devices 23 adapted to distribute the suspension flow evenly over the entire width of the jacket 13. The first part of the space 21 as seen in the direction of rotation of the drum 11 acts as a web forming zone 25, followed in the space 21 by a first processing zone 27, a sealing zone 29, a second processing zone 31 and a compression zone 33. the housing is equipped with perforations. Outside the housing 19, along the first treatment or washing zone 27, a treatment or washing liquid chamber 35 is arranged for supplying the treatment or washing liquid through the perforations to the housing 19. The second chamber 37 is located outside the housing 19 along the second treatment zone 31 for supplying a treatment medium other than treatment or washing liquid. through the perforations in the treatment zone 31 to the housing 19. The treatment or washing liquid chamber 35 is provided with inlet devices 39 comprising at least one servo-controlled control valve 41. The chamber 37 is provided with one or more inlet pipes 43 provided with servo-controlled control valves 45. First treatment - i.e. between the washing zone 27 and the second treatment zone 31 there is a pressing member 7 59828 formed by a rotating pressing roller 47 with a liquid-impermeable jacket and which together with the jacket 11 of the drum 11 forms a sealing zone 29. In the longitudinal section of the sealing zone 29 7 is a surface which deflects inwardly from the circumferential direction of the housing 19 at the end of the first treatment or washing zone 27 and extends inwards towards the jacket 13. After the second processing zone 31, the compression zone 33 has a compression roll 49 with a liquid-impermeable jacket. The compression rollers 47 and 49 are mounted on shaft pins 51, respectively. 53 to the same machine body as the drum 11 and together with the casing 13 of the drum 11 form a nip 55. 57, which have substantially unchanged gap widths during operation. The shaft pins 53 of the compression roller 49 are provided with a pressure measuring device 59, for example a strain gauge 11a, which is adapted to transmit signals corresponding to the line pressure at the compression point 57.

After the nip 57, an outlet and outlet device 61 is provided, which is formed by a jacket 63 surrounding the combined tear and out feed screw 65. The jacket 63 is provided with a scraper 67 inclined relative to the jacket 11 of the drum 11 and a sealing device 69 one or more steam supply lines 71 with their valves 73 are connected. The outlet device 61 is provided with a connecting flange (not shown in the drawing) fitted to the outlet end of the device for a sealing connection against the downstream treatment device.

To control the web forming operation and the washing and handling operations, there is a control system comprising a control device 75 connected via lines 77, 79, 81, 83 to a pressure measuring device 59, a drum speed control device 17, a treatment valve 35 of the treatment liquid washing chamber 35 and a treatment tank 45. The components of the control system may be electrical, hydraulic, pneumatic or mechanical devices known per se. A drain pipe 85 is provided for discharging the liquid introduced into the drum 11.

The device according to Figure 1 operates as follows:

In a unit of time, a constant volume of the fiber suspension 87 is fed under pressure to the web forming zone 25 of the space 21 through the inlet devices 23, while the drum 11 is made to rotate at a substantially constant speed. Due to the pressure difference between the space 21 and the interior of the drum 11, the suspension liquid 89 flows through the jacket 13 of the drum 11 and a fibrous web 91 is formed on the surface of the jacket 13. As the sheath 13 passes through the web forming zone 25, the thickness of the fibrous web therefore increases until it completely fills the space between the sheath 13 and the housing 19. Thereafter, due to the narrowing of the space, the fibrous web 91 in the direction of rotation of the drum gradually becomes subjected to compression as it passes towards the sealing zone 29, whereby the suspension liquid 89 is compressed through the jacket 13. As the fibrous web passes through the first treatment or washing liquid zone 27, a constant volume of treatment or washing liquid is compressed per unit time into the fibrous web 91 under pressure in the housing 19. The treatment or washing liquid 93 displaces the remaining suspension liquid 89 in the fiber web 91 along line AA '(see Fig. 2). The displaced suspension liquid 89 flows out through the jacket 13. Therefore, as it passes between the wash zone 27 and the sealing zone 29, only the layer closest to the jacket 13 of the fibrous web 91, i.e. below the line AA ', contains the suspension liquid 89, while the fibrous web otherwise contains only the treatment liquid 93. When moving to the first treatment zone 27 from the end to the sealing zone 29, the surface of the fibrous web 91 away from the sheath 13 is subjected to a jump-like change of direction with respect to the sheath 13.

The compression point 55 formed in the sealing zone 29 further compresses the fibrous web 91 in one step, preferably to a tightness of 30 to 70%, i.e. to a thickness less than that of the portion of the fibrous web 91 containing only the treatment or washing liquid 93 at the beginning of the sealing zone 29. tight, drying at the pressing point 55 can only take place through the jacket 13 of the drum 11, whereby first all the suspension liquid 39 remaining in the fibrous web 91 and then a part of the treatment or washing liquid 93 are pressed out through the jacket 13 of the drum 11. Thus, only at the nip 55 itself is a certain amount of treatment or washing liquid 93 squeezed out through the jacket 13 and mixed with the suspension liquid 89 inside the drum 11.

Once the fibrous web has passed the compression point 55 of the sealing zone 29, it is allowed to expand in the second processing zone 31, while a constant volume of impregnating fluid 95 is pressed per pressure unit 95 penetration into the fiber web very quickly and efficiently. In the portion at the end of the impregnation zone 31 with respect to the direction of rotation of the drum 11, the impregnating liquid 95 causes the fibrous web to displace the remaining treatment or washing liquid, which is largely formed by the treatment or washing liquid which has wetted the fibrous web after the pressing point 55. The boundary layer between the impregnating liquid 95 and the treatment liquid 93 is formed in the fibrous web 91 along the line B-B '(see Fig. 2). The displaced treatment or washing liquid 93 flows out through the jacket 13. Displacement, which occurs in the same manner as the described washing liquid / suspension liquid displacement, peaks at the pressing point 57, where the treatment and washing liquid 93 is squeezed out and a portion of the impregnating liquid 95 penetrates through the fibrous web into the drum 11. Due to the strong compression at the compression point 55 of the fibrous web, the fibrous web 91 acts as a seal in the sealing zone between the first treatment zone 27 and the second treatment zone 31 and prevents the flow of treatment liquid from the second treatment zone 31 to the first treatment zone 31.

In order for the displacement events to be appropriate, i.e. displacement of the treatment or washing liquid 93 on line AA 'and displacement of the impregnating liquid 95 on line B-B', the following variables are assimilated to the control system, namely pressure line 57, drum 11 speed and wash liquid flow 95 volumes. The gap width of the compression point 57 and the flow of the fiber suspension to the compression point are kept essentially unchanged by devices known per se, not shown in the drawing. During operation, the pressure measuring device 59 transmits continuous signals indicating the actual value of the line pressure to the control device 75, where they are compared with the set target value. In the event of a difference between these values, the control device 75 simultaneously sends signals, depending on the actual drum speed, to the servo-controlled control valves 41 and 45 to correct the flow of the treatment or washing liquid 93 to the liquid chamber 35 and the saturation liquid 95 to the chamber 37.

After passing through the compression point 57 of the compression zone 33 of the fibrous web 91, it is separated by a scraper 67 from the casing of the drum 11 and discharged to the discharge device 61. Here the fibrous web is allowed to expand and tends to fill any cavities. The gaseous medium, preferably water vapor, is introduced under pressure to the outlet and outlet device 61 via a supply pipe 71. The above-mentioned cavities are filled with a gaseous medium which protects the fibrous web against air absorption. The fibrous web is torn and transported from the device under pressure to the next stage of manufacture by means of a friction and feed screw 65.

The treatment liquid may have bleaching properties and thus consists of a treatment liquid used for bleaching cellulosic fibrous pulp. In this case, in addition to the usual bleaching agents, such as chlorine, chlorine dioxide, hydrogen peroxide, oxygen gas, the reaction agents and catalysts used are also used, such as sodium hydroxide, ammonia, magnesium carbonate, alkali metal borates and combinations of the above-mentioned substances.

Claims (10)

A method for continuous processing of fibrous pulp, wherein a fibrous web (91) consisting of cellulosic material and in the cavities between the fibers contains liquid (89 or 93 or 95), is compressed in a press nip (57) between a non-removable web , liquid-permeable screen element (13) and a rotatable roll (49) for extruding the liquid, and the fiber web (91) being allowed to expand immediately after pressing the cut (57), characterized in that the fiber web (91) during its expansion and during a further transport to a subsequent processing step in a manner known per se in a closed housing (63), and filling the cavities in the fiber web (91) with a gaseous fluid which is supplied under pressure and blocks the fiber web (91) from air absorption as the fiber web is removed from the screen element (13). Process according to claim 1, characterized in that the gaseous fluid is constituted by water vapor. Method according to claim 1 or 2, characterized in that the fiber web (91) is torn after the filling. Method according to one of Claims 1 to 3, characterized in that the fiber web (91) is transported under pressure out of the housing (63) to the subsequent processing step. Apparatus for the continuous processing of fiber pulp for carrying out the method according to claim 1, which comprises a press nip (57) arranged between a non-removable, liquid-permeable screen element (13) and a rotatable roller (49) in which fiber web (91), which consists of cellulosic material and in cavities between the fibers containing liquid (89 or 93 or 95), can be compressed to extrude the liquid, the fiber web (91) expanding immediately after the press nip (57) during re-formation of the hollow spaces , characterized in that a closure housing (63) known per se known as a sealing connection at both ends is arranged to. surrounding the fiber web (91) during the expansion of the fiber web for a further