FI119998B - Feeding of fiber suspension flow to flotation cell and flotation cell injector - Google Patents

Abstract

The method involves supplying fiber suspension stream to an injector (2) and dividing the fiber suspension stream into sub flows/partial flows, where the flows suck air which is to be mixed with the fiber suspension stream in the injector and the air is mixed to the fiber suspension stream. Different amounts of air in the flows are sucked such that an atmospheric load of mixture of air and fiber mass is different at different points of a diffuser (5) of the injector, where the mixture leaks out/exhausts from the diffuser of the injector. An independent claim is also included for an injector comprising tubing sections.

Description

Input of the fiber suspension flow into the flotation cell and the injection cell of the floatation cell

Background of the Invention

The invention relates to a method for feeding a fiber suspension stream into a flotation cell by means of an injector, the method of injecting a fiber suspension stream into an injector, dividing the fiber suspension stream into the injector into partial flows, blowing air into the injector and mixing air into the fiber suspension stream.

The invention further relates to a flotation cell injector comprising a flow divider for dividing the fiber suspension stream fed into the injector into partial streams, at least one air supply point for sucking air to be mixed into the fiber suspension, a mixing apparatus for mixing air into the fiber suspension and a diluent.

The invention further relates to a flotation cell for removing ink or impurities from a fiber suspension.

Flotation cells, or flotation tanks, are used to remove ink and other impurities from a fiber suspension made from disintegrated and sorted recycled paper. The procedure also uses the designation-20 de-inking. The aim is to produce as white and pure recycled fiber as possible. Flotation cells are used for flotation defoaming, whereby flotation is performed in the cells by adding a soap or other foam-inducing surface tension reducing chemical as a foaming chemical to a dilute approximately 1% fiber suspension. In addition, air is mixed with the fiber suspension. Ink and other impurities adhere to the air bubbles that rise to the surface of the fiber suspension, whereby ink and other impurities can be removed from the surface of the fiber suspension by overflow or scraping.

U.S. Pat. No. 5,465,848 discloses a typical flotation cell 30, which includes an injector through which a fiber suspension to be cleaned is fed to the flotation cell through a feed tube. In addition to the feed tube, the injector includes a perforated plate, which acts as a flow splitter element, which divides the fiber suspension stream fed into the flotation cell into smaller partial streams. Below the perforated plate, at a distance from the perforated plate, are formed tubular portions of the mixing apparatus, in which partial streams of the fiber suspension flow through the holes of the perforated plate and the air supplied to the injector are premixed. The air 2 is supplied to the injector through said air intake point between said hole plate and the tubular sections, whereby the air supplied to the injector is transferred with said partial flows to a mixing apparatus forming a pre-mixing step. The partial flows of the mixing apparatus join at the bottom of the injector, from which the mixture is blown through a diffuser into a flotation cell pool. The diffuser is a radial diffuser and produces a homogeneous jet in all directions. When located at the edge of the pool, the mass jet caused by the injector causes foam surface instability at the edge of the pool.

EP 1 124000 discloses a flotation cell injector in which 10 fiber suspensions are aerated at at least two successive aeration points. Plates can be fitted to the diffuser of the injector to direct the flow of the fiber mass suspension and the air mixture out of the diffuser. However, such a solution does not sufficiently control the mass jet so that the foam surface instability can be completely avoided.

BRIEF DESCRIPTION OF THE INVENTION It is an object of the present invention to provide a novel and improved method of feeding a fiber suspension flow into a flotation cone and a flotation cell injector.

The process according to the invention is characterized in that different amounts of air are sucked in at different partial flows so that the air load of the mixture of air discharged from the diffuser of the injector and the pulp is different at different points of the diffuser.

Further, the injector according to the invention is characterized in that the injector includes means for sucking in different amounts of air into different partial streams so that the air loads of the fiber suspension and air mixtures discharged at different points in the diffuser are different.

The flotation cell according to the invention is further characterized in that the flotation cell comprises at least one injector according to claim 4.

In the solution shown, the fiber suspension flow is divided into sub-streams and different amounts of air are sucked in so that the air discharged from the diffuser of the injector and the pulp mixture has different air loads at different points in the diffuser. In this case, the mass jet and the amount of air contained therein can be adjusted and / or directed to best suit the type of pool used. Thus, the jet from the dif-35 injector is customizable to the shape of the basin. In this way, the flow field of the pool is very well controlled and thus the flotation process is also very well controlled. The foam surface is made stable by, for example, injecting a higher air-to-fiber mixture of air-pulp and a smaller air-to-pulp mixture to the nearest edge of the pool from an injector near the pool edge. Thus, the discharge jet can be tailored to the flow state, for example, with the injector positioned asymmetrically in the flotation chamber.

The injector includes a flow divider for dividing the fiber suspension stream fed into the injector into partial streams, means for supplying air to the fiber suspension, and mixing apparatus for mixing the air into the fiber suspension. According to one embodiment, at least the partial flows are not mixed together before the diffuser. In this case, the distribution of mixtures of different air loads from the diffuser in different directions can be ensured.

Another idea is that the holes for the flow and test element and the mixing tubes for the mixing apparatus are located at the edge of the injector. In this case, it is easy to form a separate vent hole or air channel for each hole and mixing tube, which can be individually adjusted if necessary to achieve the desired aeration.

The idea of a third embodiment is that the mixing apparatus 20 consists of mixing tubes separated by partitions into individual mixing tubes or groups of mixing tubes, and an air hole or air channel is arranged for each mixing tube or set of mixing tubes.

The air load describes how much air is present in the fiber suspension / air mixture. The air load represents the amount of air per unit volume mixed with the fiber suspension in the same volume unit. The air load shall be expressed as a percentage such that, if the mixture of fiber suspension and air contains an equal volume of air relative to the volume of the fiber suspension, the air load is 100%. Thus, if the mixture of fiber suspension and air contains 100 volumes of fiber suspension and 100 volumes of air, there is 100% vol. Similarly, for example, if the fiber suspension and air mixture has a fiber suspension of 100 volumes and air 60 volumes is an air load of 60% and again, for example, if the fiber suspension and air mixture contains 100 volumes of air suspension and 120 volumes of air.

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BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are explained in more detail in the accompanying drawings, in which Figure 1 schematically shows a side view of a flotation cell and sectional view, Figure 2 schematically shows a top view of a flotation cell injector Figure 4 is a schematic and sectional detail of a diffuser of the injector of Figure 2; Figure 5 is a schematic view of a portion of the diffuser of Figure 4; Figure 6 is a top plan view of the injector of Figure 2; Figure 7 is a plan view of the nozzle plate Fig. 9 is a plan view of the nozzle plate in position, Fig. 10 schematically shows a side view of a third injector Fig. 11 is a schematic sectional view of a fourth injector, Fig. 12 is a schematic cross-sectional view of the injector of Fig. 11 at BB, Fig. 13 is a schematic view of a fifth injector, Fig. Figure 15 schematically shows the upper part of a sixth injector as viewed from above and partially cut out, and Figure 17 schematically shows a top view of a seventh injector as shown in Fig. 13.

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In the figures, some embodiments of the invention are shown in simplified form for clarity. Like parts are denoted by like reference numerals in the figures.

DETAILED DESCRIPTION OF SOME EMBODIMENTS OF THE INVENTION Figure 1 is a schematic side elevational view of a flotation cell 1 for removing ink and other impurities from a fiber suspension. The flotation cell 1 includes an injector 2 through which the fiber suspension entering the feed tube 3 and an added foaming chemical, such as soap, are fed to the flotation cell 1. The injector 2 is positioned relative to the surface 4 of the fiber suspension in the flotation cell 1 below.

At the lower end of the injector 2 is a diffuser 5. The diffuser 5 can be used to direct the fiber suspension in the desired direction and position at the flotation cone 1. The diffuser 5 is a nozzle that reverses the flow direction of the fiber suspension 15 from vertical to horizontal. The flow can also be directed downwards, upwards, or in different directions from different angular positions. The diffuser 5 may be a radial diffuser and the fiber suspension may flow out of the diffuser 5 over or around the periphery of the diffuser. By adjusting the size of the radial diffuser between the lower and upper lip, it is possible to adjust how much of the fiber suspension is directed to which angle. Alternatively, by selecting the distance between the lower lip and the upper lip, the desired flow rate is obtained for the fiber suspension.

In the flotation cell 1, the ink and other impurities adhere to the bubbles of air and blowing agent which rise to the surface of the fiber suspension, from which the ink and other impurities can be removed, for example, by scraping or by overflow. In the solution shown in Fig. 1, the overflow is formed by a dam plate 6, whereby the foam formed on the surface of the fiber suspension and the ink and other impurities therein are transferred to the rejection space 7 from where they are further transferred to a reject outlet not shown in the figures. The flotation cell accept is removed through the accept channel 19 for the next step of the process. The basic structure and mode of operation of the flotation cell 1 will be obvious to one skilled in the art and will not be further discussed herein.

Fig. 2 shows an injector 2. The injector 2 includes a flow divider, which in the case of Fig. 2 is a nozzle plate 8. The flow divider 35 may also be formed, for example, from interconnected elongated nozzles or otherwise formed by Jolla to divide the fiber suspension flow into partial flows. The holes 9 in the nozzle plate 8 divide the fiber suspension flow through the feed pipe 3 into partial streams which, when viewed in the flow direction of the fiber suspension, are further fed to the mixing apparatus 10 following the nozzle plate 8. . While the partial streams of the fiber suspension flow flow from the holes 9 of the nozzle plate 8 to the mixing apparatus 10, these partial flows absorb air into the mixing apparatus 10 from the air supply 10 following the nozzle plate 8 downstream of the nozzle plate 8.

Figure 3 shows more precisely the air supply points 12. The tube portions 11 extend from the inner edges of the injector 2 to the mouth plate 8. Instead, openings 13 are formed in the outer peripheral portion of the injector to allow air to flow into the fiber suspension. Partitions 14 are formed between the upper parts of the pipe sections 11, whereby air is flowing into each pipe section 11 through its own opening 13. By controlling the size of the opening 13, it is possible to control how much air is mixed with each of the partial streams of the fiber suspension 20.

Figure 4 shows a detail of the diffuser 5. Figure 4 shows that the tube section 11 extends to the diffuser 5. Thus, the partial flows of the mixing device 10 are not at least significantly mixed with the diffuser 5 of the lower part of the injector. This allows the desired mass flow and the air load adjusted thereto from the diffuser 5 to be directed in the desired direction depending on the pool design of the flotation cell 1.

Figure 5 shows the diffuser 5 inverted with respect to Figure 4 and without the bottom plate 15 of the diffuser 5 for clarity. Thus, Figure 5 illustrates the diffuser partitions 16 separating the air-loaded fiber suspension from the various pipe sections 30 until the air is discharged pool space. In the embodiment of Figures 2-5, each pipe section 11 is separated into its own unit, whereby the air load of the mixture discharged at each pipe section 11 can be adjusted and maintained as desired. However, the partitions 14 at the top 35 of the injector 2 need not necessarily be fitted between the tops of all tubular sections 11, but may have fewer partitions 7 to form groups of sections through which a certain amount of air can be fitted. Also, the diffuser 5 may have fewer partitions 16 than between each tube section 11, whereby partial streams 5 discharged from tube sections 11 belonging to the same set of tubes may mix with each other before the mixture is discharged from the diffuser 5. However, two or more partitions 16 are provided. in the desired direction from the diffuser 5. The upper partition walls 14 and lower partition walls 16 of the injector 2 may be in the same position, whereby a certain amount of air is supplied to certain tube portions 11 and discharged at the same location from the diffuser 5. The upper partition walls 14 and lower partition walls 16 of the injector 2 may also be at different positions. For example, a solution may be provided in which air is supplied to certain tube portions 11 such that the mixture has an air load of 80%, and to other tube portions 11 on the other side of the partition 14 of the injector 2 %. If this is the case, the lower partition wall 16 of the injector 2 is not at the same position as the upper partition wall 14 mixing mixtures with different air loads before flowing out of the diffuser 5 into the pool space, for example, with 70% air loading.

Figure 6 illustrates a case where the partitions 14 are low and thus, as illustrated in Figure 7, the openings 13 are low. Fig. 8 illustrates again a solution in which the partitions 14 are slightly higher, and thus, as illustrated in Fig. 9, the openings 13 are mouth-larger. The amount of air flowing through the openings 13 can be choked, for example, by means of flaps. Hereby, the desired amount of air can be adjusted to each pipe section 11. Of course, such an embodiment is possible in which all the openings 13 and the holes 9 of the nozzle plate 8 are the same, so that a similar amount of air is supplied to each pipe section. similar in every direction.

In the injector 2 of Figure 10, the inlet duct 3a of the injector 2 extending from the feed tube 3 is located in the middle of the structure of the injector 2. The upper part of the supply channel 3a extends above the nozzle plate 8 with the injector 2 as shown in Fig. 10. The orifice plate 8, acting as a flow splitting element, and the mixing apparatus 10 below it, in turn, are disposed immediately around the feed duct 3a so that each of them for their part 8 surrounds the feed duct 3a. The supply channel 3a, the nozzle plate 8 and the mixing apparatus 10 thus have a common central axis. Due to the structure shown, the fiber suspension can be fed from the bottom through the first end, i.e. the lower part of the injector 2, through the supply channel 3a. The feed channel 3a located in the center 5 of the structure of the injector 2 leads to the upper part of the injector 2 as indicated by the arrows A of the fiber suspension, whereby the fiber suspension makes a 180 ° downward movement from the supply channel 3a through its upper end, the injector 2.

The upper part of the injector 2 is closed by a lid 17. When the lid 17 is attached to the injector 2, for example by bolt-nut fastening so that the lid 17 can be removed from the injector 2 by opening the bolt-nut fasteners, the lid 17 can be used as a cleaning hatch and thereby easily clean and flush the feed duct 3a, nozzle plate 8

Thus, in the injector 2 shown in Fig. 10, the fiber suspension can be fed along the feed duct 3a to the injector 2 from the bottom up, but through the nozzle plate 8 and the mixing apparatus 10, the fiber suspension moves from top to bottom. Thus, in the injector 2 as shown, the fiber suspension flows in the opposite direction to the flow direction of the fiber suspension 20 through the holes 9 of the nozzle plate 8 and the pipe sections 11 of the mixing apparatus 10 in the supply channel 3a.

Fig. 11 shows an injector in which the fiber suspension flow through the first end of the supply conduit 3a, i.e. below the injector 2, is injected into the injector 2 as shown by the arrows A. The flow direction of the fiber suspension at the upper end of the supply conduit 3a rotates 180 ° from the fiber conduit 8a. divides the fiber suspension flow into sub-streams, after which the sub-streams are passed through a slot 12 acting as an air supply point 12 to the mixing apparatus 10.

The injector 2 of Fig. 11 is, as illustrated in Fig. 12, rectangular in cross-sectional shape and its interior 30 is divided by a partition structure 18 such as viewed from the right side of the injector 2 with a 8 and the mixing apparatus 10. Thus, the nozzle plate 8 and the mixing apparatus 10 are immediately adjacent to the supply channel 3a. At the bottom of the mixing-35 apparatus 10 is a diffuser 5 which guides the fiber suspension to the left when viewed in Figures 11 and 12.

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A partition 14 is provided at the top of the tube sections 11, by means of which the tube sections 11 are divided into groups. Thereby, a desired amount of air can be supplied to each group, whereby a mixture of different air loads can be discharged from different locations of the diffuser 5. In the case illustrated in Figures 11 and 12, the holes 9 and the tube sections 11 of the nozzle plate 8 are arranged in two rows. The holes 9 and the pipe sections 11 can be arranged in even more rows. Most preferably, however, the holes 9 and tube portions 11 are arranged in a single row so that they can be fitted to the edge of the injector 2. Hereby, each nozzle tube 11 may be provided with its own air duct or provided with its own air opening, whereby each of the 10 ducts or orifices may be individually adjusted as necessary to achieve the desired fiber-bed aeration.

Figures 13, 14 and 15 illustrate that the air openings 13 are of different sizes. The size of the air outlet 13 determines how much air can be mixed with the partial flow of the fiber-15 pension flowing into each tube portion 11. In the embodiment illustrated in Figure 14, the holes 9 in the nozzle plate 8 are all of the same size, so that the air load for each partial flow depends on the size of the air outlet 13. In the case illustrated in Figure 15, the holes 9 of the nozzle plate 8 are of different sizes, each flow rate of partial flow being determined by the size of the hole 9. Further, the air vents 13 20 are of different sizes, whereby the size of the holes 9 of the nozzle plate 8 and the size of the air vents 13 determine the flow rate and air load of each partial flow. Further, such a solution may be provided in which the air openings 13 are of the same size but the holes 9 of the nozzle plate 8 are of different sizes. Here, the flow rates of the different partial streams are different, and thus the air loads 25 of each partial flow also become different.

Figures 16 and 17 illustrate an embodiment in which the air supply to the injector 2 is implemented such that the cross-sectional area of the top of the mixing apparatus 10 is greater than the cross-sectional area of the nozzle plate 8. In the circular cross-sectional structures shown in the figure, the upper part of the mixing device 30 has an outer diameter which is larger than the outer diameter of the nozzle plate 8. The upper ends of the tube portions 11 are fixed in the nozzle plate 8, but due to the larger cross-sectional area of the mixing apparatus 10, slot openings 13 remain in the outer periphery.

In Figure 16, the air vents 13 are formed by sloping air ducts formed by the upper end-35 of the pipe sections 11. The throttling of the air vents 13 may be controlled by changing either the radial dimension of the air passages or the circumferential dimension 10. The radial dimension of the air vents 13 may be varied by varying the distance between the outer surface of the nozzle plate 8 and the outer surface of the mixing apparatus 10. The circumferential dimensions of the air vents 13 are altered by changing the width of the air passages in the circumferential direction.

5 In the embodiment of Figure 17, the pipe sections 11 are at least unchanged at least at the upper end of the mixing apparatus 9. Also in this case, the amount of air flowing through the vents 13 is controlled by adjusting the distance between the outer edge of the nozzle plate 8 and the outer edge of the mixing apparatus 10. The circumferential dimension of the air vents 13 can be changed by changing the cross-sectional shape of the mixing tubes 10. In this way, the air opening 13 visible outside the nozzle plate 8 can be resized.

Thus, in the embodiment shown, a plurality of structural members can be individually dimensioned and shaped independently of the other parts of the injector. Thus, for example, the size and shape of the holes 9 in the nozzle plate 8 may vary as desired. Thus, the nozzle plate 15 8 may be, for example, a perforated plate in which the holes 9 in the annular assembly divide the fiber suspension flow fed into the injector 2 into partial streams. The nozzle plate 8 may also be, for example, a nozzle plate having, in the downstream direction of the fiber suspension, special nozzles fitted to its orifices 9 in the perforated plate to influence, for example, the shape and / or velocity of the jet cross section of the fiber suspension streams. By influencing the jet shape and / or velocity of the partial streams of fiber suspension streams, for example, how much air is transferred to the flotation cell 1 with the fiber suspension stream, for example, the cross sectional shape of the partial stream jet when the partial flow flows from the flow divider to the mixing apparatus.

The shape of the holes 9 may be round or oval or polygonal, for example.

By controlling the size of the air vents 13, the air load of each partial flow is naturally controlled.

The shape of the tube sections 11 may also vary as desired. Typically, the inside diameter of the round tube portion 11 is approximately twice the diameter of the round hole 9. By way of example, when the height of the injector is, for example, of the order of one meter, the diameter of the round hole may vary, for example, from 11 to 60 mm, the diameter of the round tube portion being, for example, 20-120 mm. Also, the cross-sectional shape of the mixing tubes 11 may be round or oval or polygonal, for example.

The diffuser 15 can also be formed in a number of ways. The partitions 16 of the dif-5 fuser 5 may be arranged at different angles, i.e. they are not necessarily radial. Further, the partitions 16 are not necessarily straight but may be curved, so that the flow is directed from the diffuser as desired. Further, by changing the dimension between the diffuser base 16 and the upper lip, the amount of fiber suspension to be directed in which direction is to be adjusted. One or more of the holes 9 in the nozzle plate 8 and the pipe sections 11, respectively, can also be fitted to the central portion of the injector. In this case, an air supply can be provided in the middle section pipe section 11 via its own duct. On the other hand, the upper end of the tube portion 11 in the central portion can also be connected to the upper end of the tube portion 11 on the edge of the injector, whereby they are supplied with air through the same opening 13. Most preferably, however, the holes 9 and the tube portions 11 of the nozzle plate 8 are fitted to the edge of the injector. Here, it is easy to fit the air duct or orifice to the pipe sections 11, and to adjust the amount of air to be supplied is also simple.

The injector 2 has a fiber suspension 20 fed into the pool space of the flotation cell 1 and the air load of the mixture can be, for example, between 30 and 120%. Typically, the air load varies between 70% and 100%.

In some cases, the features set forth in this application may be used as such, despite other features. On the other hand, the features disclosed in this application may be combined, if necessary, to form various combinations.

The drawings and the description related thereto are intended only to illustrate the idea of the invention. The details of the invention may vary within the scope of the claims.

In the solution shown in the figures, the tubular sections 11 and their partitions 30 form a single unit formed by an outer periphery formed by a portion of the mixing apparatus 10 of the injector 2. The pipe sections 11 of the mixing apparatus 10 may also be formed of separate pipes supported by a support structure in the shell structure formed by the periphery of the injector 2. Herein, the injector 2 can be implemented, for example, by connecting the tube sections 11 to the nozzle plate 35 and forming openings of the desired size in the tube sections 11, which allow the desired amount of air to flow into the tube sections 11. The upper ends of the tubular sections 11 how close the upper end of the tube is to the nozzle plate 8 is to strangle the air flow, i.e., by fitting the tubes at different distances from the nozzle plate 8, a different amount of air is released into each tube portion 11.

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Claims (8)

A method for feeding a fiber suspension stream into a flotation knife (1) by injector (2), the method of feeding a fiber suspension stream into the injector (2), dividing the fiber suspension stream supplied to the injector (2) into subflows 5, mixing the air with the fiber suspension flow, characterized in that different amounts of air are sucked in so that the air load of the mixture of air discharged from the diffuser (5) of the injector (2) is different at different points of the diffuser (5). Method according to Claim 1, characterized in that the partial flows are prevented from mixing before entering the diffuser (5). Method according to claim 1 or 2, characterized in that the flow rate of the jet discharged from the diffuser (5) is adjusted to different positions at the diffuser (5). An injector (2) for a flotation cell (1), comprising a flow splitting element for dividing the fiber suspension stream fed into the injector (2) into at least one air supply point (12) for sucking air mixed into the fiber suspension into the injector (2). and a diffuser (5) discharging the mixture of fiber suspension and air into the pool space of the flotation cell (1), characterized in that the injector (2) comprises means for sucking different amounts of air into different partial flows. different sorts of. Injector according to Claim 4, characterized in that the mixing apparatus (10) comprises tubular sections (11) and that the lower part of the injector (2) has partitions (16) arranged to prevent mixing of the fiber suspension and air mixture at least partially discharged from one of the tubular sections (11). with a fiber suspension and a mixture of air discharged from the second tube portion (11) before the diffuser (5). Injector according to claim 4 or 5, characterized in that the holes (9) of the flow divider and the mixing device (10) are arranged on the edge of the injector (2). Injector according to one of Claims 4 to 6, characterized in that the mixing apparatus (10) consists of tubular sections (11) which are separated at one end by partitions (14) into individual tubular sections (11) or groups of tubular sections (11). Flotation cell for removing ink or impurities from a fiber suspension, characterized in that the flotation cell comprises at least one injector according to claim 4.