AT504955B1 - DIFFUSER FOR AN INJECTOR IN A FLOTATION CELL AND METHOD FOR FEEDING A FIBER SUSPENSION INTO THE FLOTATION CELL - Google Patents

Description

2 AT 504 955 B1

Background of the invention

The invention relates to a diffuser for an injector in a flotation cell for feeding a fiber suspension flow into the flotation cell, the diffuser having a diffuser element having at least a first surface, at least a second surface and at least one gap between the first surface and the second surface in the flotation cell Transverse direction with respect to the flow direction of the fed into the diffuser fiber suspension flow, wherein the fiber suspension flow is intended to be discharged from the diffuser from the gap.

The invention also relates to an injector in a flotation cell, wherein the injector comprises an inlet tube for supplying a fiber suspension flow into the injector, at least one air supply point for supplying air to be mixed with the fiber suspension flow introduced into the injector, a mixing tube for mixing the fiber suspension flow and into the Injector introduced air and a diffuser for deriving the flow of the mixture of the fiber suspension and the air from the injector.

The invention further relates to a method of feeding a fiber suspension into a flotation cell, comprising an injector having an inlet tube for delivering a fiber suspension stream into the injector, at least one air supply point for supplying air to be mixed with the fiber suspension stream introduced into the injector, a mixing tube for mixing the fiber suspension stream and the air, and a diffuser for supplying the mixture of the fiber suspension and the air into a tank space of the flotation cell, the method comprising feeding the fiber suspension stream into the injector, supplying air to the injector, mixing air into the fiber suspension stream and supplying the stream of mixture of the fiber suspension and the air into the pool space of the flotation cell.

Flotation cells or flotation tanks are used to remove inks and possible contaminants from a fiber suspension made from rotted and sorted waste paper. This process is also referred to as decolorization or deinking. The goal of decolorization is to create as white and clean, recycled pulp as possible. Flotation decolorizing uses flotation cells wherein flotation is performed in the cells such that soap or other flotation promoting and surface tension reducing chemical is added to a dilute, about 1% fiber suspension as a flotation chemical. In addition, the fiber suspension is mixed with air. The ink and other contaminants stick to the air bubbles which rise to the surface of the fiber suspension in the pelvic space and the ink and contaminants can be removed as an overflow or scraper.

U.S. Patent 5,465,848 discloses a flotation cell having an injector for delivering a fiber suspension stream into the cell and for mixing air into the fiber suspension stream to be fed into the cell. Typically, with the injectors in the lower part of the injector in the flotation cell according to the publication, a slit nozzle or a radial diffuser having a circular cross section is used for feeding the air introduced into the injector into the fiber suspension volume already present in the cell.

Figure 1 shows schematically in cross section the slot nozzle or diffuser of the type shown in US-A-5 465 848 which is provided with a gap passing through two surfaces in the transverse direction with respect to the flow direction of the fiber suspension stream to be introduced into the diffuser is limited, wherein the gap is typically dimensioned so that the aerated Fasersuspensionsstrom C, which is discharged from the gap, with a sufficient flow rate and a corresponding turbulence level 3 AT 504 955 B1 is provided. A bottom plate forming the lower part of the slit nozzle causes a hydraulic impact on the adjoining fiber suspension flow, which further increases the turbulence level of the flow and prevents the air bubbles in the flow from adhering to each other. When properly dimensioned, the slot die causes a relatively low pressure drop and produces a homogeneous quality pulp stream, the rate of which is typically 2 to 3 m / s. Due to the considerable flow rate thereof, the jet discharged from the slot nozzle penetrates unrestrictedly into the surrounding pelvic space of the flotation cell. In a sufficiently large pelvic space, this does not create problems in controlling the flow field, but it may be difficult or even impossible to create a controlled flow field in a small pelvic space, resulting in poor quality of recycled pulp content attained by the flotation cell ,

Small pelvic volumes require a slow flow rate of the jet to achieve a controlled flow field. By increasing the height of the slit of the slit nozzle, as shown schematically in Figure 2, the flow rate can be reduced to a sufficiently low level in a simple manner.

However, enlarging the gap can easily cause the flow to detach from the top plate of the nozzle, thereby creating vortices designated by the reference character B, as shown diagrammatically in FIG. Such vortices interrupt the homogeneous flow and collect air to form large air bubbles. Large bubbles rapidly rise to the surface of the fiber suspension in the flotation cell pool and break the foam layer formed thereon.

Brief description of the invention

It is an object of the present invention to provide a novel diffuser.

A diffuser according to the invention is characterized in that the diffuser comprises at least two diffuser elements arranged one after the other in the flow direction of the fiber-suspension flow to be supplied to the diffuser and arranged to separate the fiber-suspension flow to be supplied into the diffuser into at least two separate sub-flows to separate the two sub-streams separated from each other from the columns in the diffuser elements.

An injector according to the invention is characterized in that the diffuser is the diffuser according to claim 1.

A method according to the invention is characterized by separating the flow of the mixture of the fiber suspension and the air in the diffuser into at least two separate sub-streams and diverting the sub-streams separately from the diffuser to a flotation cell pool space.

In accordance with the basic idea of the invention, the diffuser of the injector in the flotation cell has at least two diffuser elements successively arranged in the flow direction of the fiber suspension flow to be fed into the diffuser, each diffuser element having at least a first surface, at least a second surface and at least one gap between the at least first surface and the second surface in the transverse direction with respect to the flow direction of the fiber suspension flow to be supplied to the diffuser, the fiber suspension flow being adapted to be discharged from the gap from the diffuser. Furthermore, according to a basic idea, the diffuser elements are intended to divide the fiber suspension stream to be fed into the diffuser into at least two separate sub-streams for discharging the sub-streams separately from the gaps in the diffuser elements 4 AT 504 955 B1. According to one embodiment of the invention, the diffuser element comprises a pipe or a pipe section which is arranged to extend in the opposite direction with respect to the flow direction of the fiber suspension flow and is arranged so as to direct the fiber suspension flow to be fed into the diffuser shares at least two separate sub-streams. According to a second embodiment of the invention, the tube section of the diffuser element is arranged inside the tube section of a preceding diffuser element in the flow direction of the fiber suspension flow. According to a third embodiment of the invention, the diameters of the tube sections arranged inside one another are dimensioned such that the flow cross-sectional area of the flow channels bounded by the walls of the tube sections, which are arranged inside one another, have substantially the same size.

An advantage of the diffuser of the type shown above is that it allows the fiber suspension to be fed into the pelvic space at a low velocity so that the pulp jet remains homogeneous. The diffuser shown above is particularly well suited to flotation cells in which the pelvic volume is small and in which high output flow rates of the fiber suspension stream can not be used. When the pipe section of the diffuser element is disposed within a pipe section of a preceding diffuser element in the flow direction of the fiber suspension flow, the fiber suspension flow to be fed into the diffuser is effectively divided into sub-streams. When the diameters of the pipe sections disposed within the diffuser are dimensioned such that the flow cross-sectional area in the flow channels bounded by the walls of the pipe sections disposed within each other is substantially the same size, equal amounts of the fiber suspension can easily enter the gap be directed by each diffuser element.

Brief description of the drawings

Hereinafter, embodiments of the invention will be explained in more detail in the accompanying drawings, in which

FIG. 1 schematically shows a side view in cross section of a diffuser known from the prior art,

FIG. 2 schematically shows a side view in cross-section of another diffuser known from the prior art,

FIG. 3 shows schematically a side view in cross-section of a flotation cell,

Figure 4 shows schematically a side view of a diffuser,

Figure 5 and Figure 6 show schematically a side view in cross-section of the diffuser shown in Figure 4,

Figure 7 shows a second diffuser, and

Figure 8 shows schematically a side view in cross-section of a third diffuser.

For clarity, the figures show embodiments of the invention in a simplified form. Similar parts in the figures are designated by the same reference numerals.

Detailed description of embodiments of the invention

FIG. 3 schematically shows a side view in cross section of a flotation cell 1 for removing printing ink and possible impurities from a fiber suspension. The flotation cell 1 has an injector 2, wherein a fiber suspension stream and a flotation chemical added thereto, such as soap, are introduced into the flotation cell 1 through an inlet pipe thereof. The injector 2 according to FIG. 3 also has at least one air supply point 4 and at least one air supply duct 5 for supplying air which is to be mixed with the fiber suspension flow inside the injector. The injector 2 also has a mixing tube 6 and the mixing tube 6 may be provided with a mixing device 7, which is typically disposed within the tube for mixing the fiber suspension flow and the air. The injector 2 is arranged with respect to a surface 8 of the fiber suspension in the flotation cell 1 so that a diffuser 9, which is arranged in connection with the lower part of the injector 2 or in practice as an extension for the mixing tube 6, below the surface. 8 the fiber suspension remains. The diffuser 9 is a nozzle which allows rotation of the flow direction of the fiber suspension flow to be supplied into the flotation cell and supply of the fiber suspension flow to a pool space 10 of the flotation cell 1 at a desired speed.

In the flotation cell, the printing ink and other impurities adhere to the air-formed bubbles and to the flotation agent, which rise to the surface 8 of the fiber suspension, from where the ink and other impurities are scanned using a scraper, not shown in FIG. or can be removed by means of an overflow. The mentioned in Figure 3 overflow is formed using a baffle plate or a slag sheet 11, whereby the foam formed on the surface of the fiber suspension and the ink and other impurities are transferred therein via the baffle plate 11 in a Spuckstoffraum 12, from where they by a Spuckstoffausgabekanal 13 reach for further processing. The flotation cell according to FIG. 3 also has a schematically represented drainage channel 14 for feeding the cleaned fiber suspension into the pulp production process. The basic structure and mode of operation of the flotation cell 1 are known per se to those skilled in the art and therefore will not be described in more detail in this context.

FIG. 4 schematically shows a side view of a diffuser 9 arranged on a mixing tube 6 of the injector 2, and FIGS. 5 and 6 schematically show the diffuser 9 of FIG. 4 in cross-section. The diffuser 9 according to FIGS. 4 to 6 has four diffuser elements 15. Each diffuser element 15 has a first surface 16 and a second surface 17, between which a gap 18 is provided, which is arranged in the transverse direction with respect to the flow direction A of the fiber suspension flow to be supplied to the diffuser 9. What is meant by a transverse direction with respect to the flow direction A of the fiber suspension to be supplied into the diffuser 9 is a direction which is not parallel to the flow direction A of the fiber suspension flow to be supplied to the diffuser 9. The diffuser elements 15 are successively arranged with respect to each other in the flow direction A of the fiber suspension flow to be supplied to the diffuser 9. The diffuser element 15 according to Figures 4, 5 and 6 is formed of two plate elements 19 and 19 'which are spaced apart and provided with an opening 22 and a gap 18 between them. The plate members 19 and 19 'are abutted against each other using support members 20 disposed between the plate members 19. Each diffuser element 15 further comprises at least one pipe or pipe section 21 which is directed substantially in the opposite direction with respect to the flow direction A of the fiber suspension flow to be fed into the diffuser 9, i. H. in Figures 4 to 6 upwards. The pipe sections 21 are arranged one inside the other so that the pipe section 21 of the last diffuser element 15 or the lowermost diffuser element in the flow direction A of the fiber suspension flow to be supplied to the diffuser 9 is the innermost pipe section and the pipe section in the preceding diffuser element 15 is the second-innermost pipe section Pipe section is clearly shown in Figure 5. The pipe section 21, d. H. the walls of the tube section 21 divide the fiber suspension stream fed into the diffuser into separate sub-streams and direct such sub-streams to the gaps 18 of the diffuser elements 15, the sub-streams being discharged from the gaps 18 from the diffuser 9 as separate streams as indicated by arrows D. shown.

The pipe sections 21 thus divide the flow cross-sectional area of the diffuser 9 into a plurality of separate, rotationally symmetrical flow channels 23 arranged in the case shown in FIGS. 4 to 6, which are arranged inside one another and bordered by the peripheral surface Pipe sections 21 are limited. The outermost wall of the outermost flow channel is formed of the mixing tube 6 of the injector or an extension thereof. After the vertical section formed from the pipe sections 21, the flow channels 23 turn outward in the direction of the diffuser radius, into the gaps 18 bounded by the first surfaces 16 and the second surfaces 17 of the diffuser elements 15, wherein the cross-sectional area of the gaps increases constantly as they move toward the outside environment of the diffuser. Such a sharp bend creates a hydraulic impact on the fiber suspension flow and maintains a high level of turbulence, and the flow cross-sectional area, which increases smoothly in the flow direction, prevents the generation of adverse vortices. Subsequently, the fiber suspension flow is derived from the diffuser 9 from the overlapping flow channels 23 formed of columns 18 as indicated by arrows D.

The above-illustrated diffuser allows feeding the fiber suspension into a pelvic space at a low speed while still maintaining a uniform fiber flow. The diffuser is particularly well suited for such flotation cells where the pelvic space used is small and where high rates of fiber suspension flow rate can not be used.

The fiber suspension stream to be fed into the diffuser 9 may be a mixture of fiber suspension and air when the supply of the fiber suspension to the flotation cell takes place as shown in FIG. The fiber suspension stream to be fed into the diffuser 9 may also be exclusively a fiber suspension if another solution is used to aerate the fiber suspension.

Therefore, the diffuser 9 shown in Figs. 4 to 6 is used to have four diffuser elements 15, thereby starting to exhaust the fiber suspension from the diffuser 9 to four planes, but depending on the application, the diffuser may have two or more diffuser elements 15 be provided.

In the solution illustrated in FIGS. 4 to 6, the tube sections 21 are dimensioned in the longitudinal direction such that the upper ends 24 thereof, ie. H. the ends in the opposite direction with respect to the flow direction A of the fiber suspension stream to be fed into the diffuser 9 are substantially at the same level and extend partially to the vertical portion of the injector 2, where the flow rate of the fiber suspension downwards is between 1 and 5 m / s is. In FIGS. 4 to 6, the fiber suspension flow to the flow channels 23, which is directed to different diffuser elements 15 in the diffuser 9, is thus formed from a single level. The fiber suspension flow to the flow channels 23 directed to the different diffuser elements 15 in the diffuser 9 may also be formed from different levels, for example, such that the flow to the gap 18 of the uppermost diffuser element 15 in the flow direction of the or to be supplied to the second top layer from a second or second highest division point, or so that the flow to the gap 18 of the highest diffuser element 15 in the flow direction of the to be supplied to the diffuser fiber suspension of may be formed from the last or lowest division point and the second highest layer from the second last or second lowest division point.

In the diffuser illustrated in Figs. 4-6, the flow channels 23 delimited by the walls of the tube sections 21 in the diffuser all have the same flow cross-sectional area. However, in some embodiments, the diameters of the pipe sections 21 may be configured in such a manner that the different flow channels 23 are provided with different flow cross-sectional areas, whereby the flow rate in the sub-streams D flowing from the gaps 18 of the diffuser elements 15 AT 504 955 B1 are derived at different levels, differ from each other. This can be carried out, for example, in such a way that the underflow, which has either the largest volume flow or the smallest flow, is directed into the middle flow channel 23.

In the diffuser 9 shown in FIGS. 4 to 6, the gaps 18 of the diffuser elements 15 are arranged to widen toward the outside of the diffuser, so that some of the gaps 18 are directed upwards and some downwards towards the diffuser 9 Fiber suspension flow to be supplied. The gaps 18 may also be formed so that the height of the gaps 18, i. the first surface 16 and the second surface 17 of the diffuser element 15 remain uniformly at the same distance from each other. Furthermore, the gaps 18 may also be formed so that sub-streams D from the columns 18 of the diffuser 9 can be directed downwards from all the columns. The gaps 18 may also be formed so that all or some of the sub-streams D arrive from the diffuser in the horizontal direction, or the streams may also be directed in the horizontal direction or so that the sub-streams D from the diffuser 9 like a fan be derived with different elevation angles.

The cross section of the diffuser 9 according to FIGS. 4 to 6 is circular. Diffusers which are circular in cross-section are generally referred to as radial diffusers. Instead of a circular cross-section, the diffuser may, for example, have an elliptical, triangular, square or rectangular cross section or a cross section, which preferably has a different equilateral and polygonal shape. For example, Figure 7 shows schematically a diffuser 9 having a square cross section in which the gaps 18 of the diffuser elements 15 are formed on the two sides of the diffuser 9 and the two other sides of the diffuser are enclosed. Therefore, the fiber suspension flow from the diffuser may be arranged in a direction of the circumferential angle, in two directions of the circumferential angle, as shown in Fig. 7, in a plurality of directions of the circumferential angle or so as to be directed to the entire circumference.

In the diffusers illustrated in FIGS. 3 to 7, the diffuser elements 15 are shaped such that the gaps 18 of the diffuser elements 15 extend equidistant from an imaginary central axis of the diffuser, but the diffuser elements 15 can also be shaped such that the gaps 18 of FIGS Diffuser elements 15 extend at different distances from the imaginary central axis of the diffuser. Then the shape of the diffuser 9 can be like a ball. Further, by selecting the cross-sectional areas of the flow channels of the diffuser elements 15, a larger or smaller volume flow or, alternatively, a flow having a higher or lower discharge velocity through the flow channels may be directed in different ambient angle directions and at different heights according to need. Thus, the sub-streams D discharged from the diffuser 9 can be arranged so that the volume of the surrounding pool space is used as much as possible, as far as the success of the flotation is concerned.

In the diffuser according to FIGS. 4 to 6, the plate elements 19 are formed from a single annular plate element, the plate elements 19 being supported against one another by support elements 20 arranged between them, the support elements 20 extending only partially in the direction of the radius of the plate elements 20 , Regardless of whether the plate elements 19 are annular or of another shape, they may be made up of a plurality of individual parts joined together to form a single plate element, in which case the plate element is provided with one or more first and / or second surfaces is provided. In addition, the support members 20 may extend across the entire width of the plate member 19 in the direction of the plate member, which is the transverse direction with respect to the flow direction A of the fiber suspension flow to be fed into the diffuser, thereby providing in the single diffuser member 15 a plurality of gaps 19 between the support members 20 are formed.

Claims (14)

FIG. 8 schematically shows a side view in cross section of a third diffuser 9. In the diffuser shown in FIG. 8, the first surfaces 16 and the second surfaces 17 of the diffuser elements 15 are arcuate surfaces, which means that the Plate member 19 having the first surface 16 and the plate member 19 'having the second surface 17 are bent in such a manner that the plate members 19 and 19' bend in the feeding direction direction of the fiber suspension flow. The diffuser elements of the diffuser shown in FIG. 8 do not have special pipes or pipe sections for dividing the fiber suspension flow into sub-streams, but the bent ends facing the central axis of the diffuser 9 in the plate elements 19 and 19 ', in other words the plate elements 19 and 19 'themselves divide the fiber suspension flow into sub-streams without any aids. For clarity, Figure 8 does not show the support elements used to support the plate members. In the diffuser 9 according to FIG. 8, the underflows smoothly circulate, in which case the hydraulic impact remains small. Such a solution is particularly applicable when the turbulence level of the flow in the inlet pipe 6 preceding the diffuser 9 is so high that, in order to prevent the foam bubbles from bonding, there is no need to significantly increase the turbulence level in the diffuser 9 increase. The parts connected to the diffuser according to FIG. 8 can each be made from a single part by molding, whereby the number of parts in this solution as a whole remains very small. The diffusers 9 and the diffuser elements 15 therein shown in FIGS. 3 to 8 all have symmetrical structures with respect to the central axis of the diffuser 9. However, the diffuser 9 can also be designed in such a way that the diffuser elements 15 are asymmetrical with respect to each other remain on the central axis of the diffuser 9, so that the sub-streams of the fiber suspension flow are supplied asymmetrically with respect to the central axis of the diffuser 9 in the pelvic space 10 of the flotation cell 1. In some cases, the features illustrated in the present application may be used as such, independently of other features. On the other hand, the features illustrated in the present application may be combined if necessary to form different combinations. The accompanying drawings and description are merely intended to illustrate the idea of the invention. With regard to the details, the invention may vary within the scope of the claims. In the embodiments illustrated in FIGS. 3 to 8, the diffuser is a fixed part of the injector, in that the diffuser is formed to be a fixed part of the injector. However, it is obvious that the diffuser may be formed as a structure which is completely separate from the remainder of the injector structure, which is then connected to the vertical portion of the injector, i. H. for example with the mixing tube 6, either in a fixed manner, for example by welding, or releasably, for example by means of a flange connection. It will also be understood that although all figures of the examples show that the injector and associated diffuser are arranged in a vertical position, the injector and associated diffuser or diffuser separate from the injector are also horizontal or at different oblique angular positions can be arranged in the flotation cell. Claims 1. A diffuser (9) for an injector (2) in a flotation cell (1) for feeding a fiber suspension stream into the flotation cell (1), the diffuser (9) comprising a diffuser element (15) having at least a first surface (Fig. 16), at least one second surface (17) and at least one gap (18) between the first surface (16) and the second surface (17) in the transverse direction with respect to the flow direction (A) of the Having the diffuser (9) to be supplied fiber suspension flow, wherein the fiber suspension flow is intended to be discharged from the diffuser (9) from the gap (18), characterized in that the diffuser (9) at least two diffuser elements (15), which in the direction of flow (A) of the Fasersupsensionsstroms to be supplied to the diffuser (9) are arranged one after the other and which are provided, in the diffuser (9) to be supplied to the fiber suspension flow in we at least two separate sub-streams (D) to separate to separate the two sub-streams (D) separately from the columns (18) in the diffuser elements (15). 2. Diffuser according to claim 1, characterized in that the diffuser element comprises at least one pipe or a pipe section (21), which is arranged so that it extends in substantially the opposite direction to the flow direction (A) of the fiber suspension flow, and so is arranged so that it divides the fed into the diffuser fiber suspension flow into at least two separate sub-streams. 3. Diffuser according to claim 1, characterized in that the pipe section (21) of the diffuser element (15) within the tube section (21) of the preceding diffuser element (15) in the flow direction (A) of the fiber suspension flow is arranged. 4. A diffuser according to claim 3, characterized in that the ends (24) of the pipe sections (21), which are arranged in the opposite direction to the flow direction (A) of the in the diffuser (9) to be supplied fiber suspension flow, at least approximately the same Level. 5. Diffuser according to claim 3 or 4, characterized in that the diameters of the pipe sections (21) are dimensioned such that the flow cross-sectional area of the walls of the pipe sections (21) limited flow channels (23) have substantially the same size. 6. Diffuser according to one of the preceding claims, characterized in that the diffuser element (15) comprises two plate elements (19) which are arranged at a distance from each other, of which the first plate element (19) at least a first surface (16) and the second Plate element (19 ') has at least one second surface (17). 7. Diffuser according to one of the preceding claims, characterized in that the gap (18) between the first surface (16) and the second surface (17) in the diffuser element (15) is arranged so that it is in the direction of the outer circumference the diffuser (9) widened. 8. Diffuser according to one of the preceding claims, characterized in that at least a part of the gaps (18) in the diffuser (9) are arranged so that they 1 0 ΑΤ 504 955 Β1 undercurrent (D) of the columns (18 ) while the diffuser (9) remains in a substantially vertical position. 9. Diffuser according to one of the preceding claims, characterized in that at least a part of the gaps (18) in the diffuser (9) are arranged so that they direct the undercurrent (D) of the columns (18) discharged fiber suspension flow downwards while the diffuser (9) remains in a substantially vertical position. 10. Diffuser according to one of the preceding claims, characterized in that at least a part of the gaps (18) in the diffuser (9) are arranged so that they direct the downstream (D) of the outgoing from the columns (18) fiber suspension flow sideways, while the diffuser (9) remains in a substantially vertical position. 11. Injector (2) in a flotation cell (1), wherein the injector (2) has an inlet pipe (3) for feeding a fiber suspension flow into the injector (2), at least one air supply point (4) for feeding into the injector (2). 2), a mixing tube (6) for mixing the fiber suspension flow and the air introduced into the injector (2) and a diffuser (9) for discharging the flow of the mixture of the fiber suspension and the air from the injector (2) characterized in that the diffuser (9) is the diffuser (9) according to claim 1. 12. An injector according to claim 11, characterized in that the injector (2) further comprises a mixer disposed on the mixing device (7) for mixing the fiber suspension flow and the injector (2) supplied air. A method for feeding a fiber suspension into a flotation cell (1) comprising an injector (2) having an inlet pipe (3) for feeding a fiber suspension stream into the injector (2), at least one air supply point (4) for feeding with the one in the Injector (2) introduced fiber suspension stream to be mixed air, a mixing tube (6) for mixing the fiber suspension flow and the air and a diffuser (9) for supplying the mixture of the fiber suspension and the air in a pelvic space (10) of the flotation cell (1), the method comprising feeding the fiber suspension stream into the injector (2), supplying air into the injector (2), mixing air into the fiber suspension stream, and supplying the stream of mixture of the fiber suspension and the air into the pool space (10). the flotation cell (1), characterized by separating the flow of the mixture of the fiber suspension and the air in the diffuser (9) into at least two of one Separate sub-streams (D) and the discharge of the sub-streams (D) separated from each other from the diffuser (9) to a pelvic space (10) of the flotation cell (1). 14. The method according to claim 13, characterized in that the injector (2) further comprises a mixing device (7) which is arranged on the mixing tube, and that in the mixing device (7) air is mixed with the fiber suspension stream. Including 4 sheets of drawings