WO2012062960A1

WO2012062960A1 - Bottom diluter structure in a vortex cleaner, and method in a bottom diluter structure in a vortex cleaner

Info

Publication number: WO2012062960A1
Application number: PCT/FI2011/050970
Authority: WO
Inventors: Timo Vuorinen; Tuomo Aho
Original assignee: Metso Paper, Inc.
Priority date: 2010-11-11
Filing date: 2011-11-04
Publication date: 2012-05-18
Also published as: FI20106186A; EP2637798A4; EP2637798A1; FI123014B; FI20106186L; EP2637798B1; CN103201042B; CN103201042A; FI20106186A0

Abstract

The present invention relates to a bottom diluter duct (6) of a vortex cleaner, the bottom diluter duct (6) comprising at least a flow channel (7), a dilution water inlet (8) for supplying dilution water to the flow channel (7), and an outlet (9) for discharging dilution water from the bottom diluter duct (6) into the vortex cleaner (1). The bottom diluter duct (6) also comprises a means (10) for controlling the flow of dilution water, arranged movable between a first and a second position. In the first position, the outlet (9) is closed, and in the second position, the outlet (9) is open, wherein the outlet (9) is arranged to open as a function of the ratio between the inlet pressure (P2) of dilution water and the pressure (P1) effective on said means (10) for controlling the flow of dilution water in the vortex cleaner. The invention further relates to a vortex cleaner and a method for supplying dilution water to a vortex cleaner through a bottom diluter duct (6).

Description

BOTTOM DILUTER STRUCTURE IN A VORTEX CLEANER, AND METHOD IN A BOTTOM DILUTER STRUCTURE IN A VORTEX CLEANER

Field of the invention

The present invention relates to a bottom diluter structure in a vortex cleaner, comprising at least a flow channel, a dilution water inlet for supplying dilution water to the flow channel, and an outlet for discharging dilution water from the bottom diluter structure into the vortex cleaner. The invention also relates to a vortex cleaner with a pulp inlet for supplying pulp into the vortex cleaner, a separation cone for separating impurities from the pulp, an outlet for impurities, and an outlet for pulp. Furthermore, the invention relates to a method in a bottom diluter of a vortex cleaner, in which method dilution water is supplied to a bottom diluter duct, and dilution water supplied to the bottom diluter duct is discharged via an outlet in the bottom diluter duct to the vortex cleaner.

Background of the invention Vortex cleaners are used, for example, in the process of treating recycled pulp used for papermaking, for the purpose of removing detrimental impurities (reject) from the recycled pulp. Recycled pulp, from which larger impurities may have been removed in a previous process step, such as coarse screening, is introduced in the vortex cleaner. In the vortex cleaner, the aim is to generate a vortical flow in the pulp, wherein by the effect of the centrifugal force and gravity, the heavier elements in the pulp sink to the bottom of the vortex cleaner, from where they can be removed. The principle of operation of the vortex cleaner is shown in Fig. 1 , in which pulp to be processed is supplied from the side of the vortex cleaner 1 via a pulp inlet 2 in such a way that the pulp supplied at a high flow rate is entrained in a movement of circulation within the walls 1 a of the vortex cleaner. At least part of the wall of the vortex cleaner constitutes a separating cone 5 whose diameter decreases in such a way that the diameter is smaller close to the outlet 3 for impurities than at the end of the cone on the side of the pulp inlet 2. Thus, the heavier elements in the pulp are brought to the outer periphery of the vortex and sink down until they can be removed from the process via the inlet 3 for impurities. Particles with a lighter weight are, however, carried by the vortex to the top of the vortex cleaner, comprising a pulp outlet 4 for removing cleaned pulp from the vortex cleaner 1 and for leading it to other steps of the process.

Dilution water is led to the vortex cleaner 1 via a bottom diluter duct 6, to provide better separation of impurities in the vortex cleaner 1. Such vortex cleaners involve, among other things, the problem that the bottom diluter duct 6 may be blocked, for example when some pulp to be cleaned ends up inside it.

In many cases, slushed recycled fibre pulp is first processed in a high consistency vortex cleaner to separate sand and/or other heavy particles from the recycled fibre pulp, to avoid the entry of such abrasive material in other processing steps. After this, the recycled fibre pulp can be processed, for example, in a coarse screen, whose accepted fraction, or accept, can be led further, for example, to low consistency vortex cleaning, and the reject returned to the high consistency vortex cleaning. The vortex cleaning steps downstream of the coarse screen supplement the separation of heavy parti- cles of high density from the recycled fibre pulp. Vortex cleaners can also be used conversely, wherein they are used for separating light material, such as expanded polystyrene, wherein the heavier fraction of a higher density is the accepted fraction, or the accepted pulp, or the accept. In high consistency vortex cleaners, the consistency of the pulp to be processed is often in the order of 1 to 4%. In low consistency vortex cleaners, the consistency or the dry matter content of the pulp to be processed is, in turn, normally 0.5 to 1.5%.

Brief summary of the invention

It is an aim of the present invention to provide an improved bottom diluter structure for a vortex cleaner, and a method for implementing bottom dilution. The invention is based on the idea that the bottom diluter duct inside the vortex cleaner is provided with a valve structure which is opened by the pres- sure of dilution water and is closed in a situation in which the pulp to be cleaned would have a chance to enter the dilution water duct. To put it more precisely, the bottom diluter structure of the vortex cleaner according to the invention is primarily characterized in that the bottom diluter duct also comprises a means for controlling the flow of dilution water, arranged to be movable between a first and a second position, in which first position the outlet is closed and in which second position the outlet is open, wherein the opening of the outlet is arranged to take place as a function of the ratio between the inlet pressure of dilution water and the pressure effective on said means for controlling the flow of dilution water in the vortex cleaner. The vortex cleaner according to the present invention is primarily characterized in that the bot- torn diluter duct also comprises a means for controlling the flow of dilution water, arranged to be movable between a first and a second position, in which first position the outlet is closed and in which second position the outlet is open, wherein the opening of the outlet is arranged to take place as a function of the ratio between the inlet pressure of dilution water and the pres- sure effective on said means for controlling the flow of dilution water in the vortex cleaner. The method according to the present invention is primarily characterized in that the flow of dilution water led via the outlet is controlled by a control means with at least a first position and a second position, in which first position the outlet is closed and in which second position the outlet is open, wherein the opening of the outlet is arranged to take place as a function of the ratio between the inlet pressure of dilution water and the pressure effective on said means for controlling the flow of dilution water in the vortex cleaner. In an advantageous embodiment of the invention, the bottom diluter duct comprises a spring for making the operation more efficient.

The inner structure of the bottom diluter duct can be designed to determine the optimal direction of the dilution water discharging from the bottom diluter duct.

The means for closing the bottom diluter duct may comprise a structure which enables the rotation of the part to be closed and a more even distribution of dilution water discharging from the bottom diluter duct in the vortex cleaner. The self-closing technique of supplying dilution water prevents or at least reduces the likelihood of blocking the dilution water ducts and lines. The construction according to the invention makes it possible to effectively wash out and dilute impurities (reject) in the vortex cleaner locally in a given area. This enables a high supply consistency into the vortex cleaner and a high separation efficiency.

The solution according to the present invention is suitable for use not only in vortex cleaners used in context with processes of recycled pulp but also in vortex cleaners used in processes of mechanical pulp and chemical pulp. Advantageously, the vortex cleaner according to the invention can be placed in a process for producing or processing pulp used for manufacturing paper or cardboard. Furthermore, the location of the vortex cleaner may be in a process belonging to the short circulation of a paper or cardboard machine. Herein, some applications for the vortex cleaner of the invention are presented without limiting the application of the invention solely to them.

Description of the drawings In the following, the present invention will be described in more detail with reference to the appended drawings, in which

Fig. 1 shows a principle view of the operation of a vortex cleaner; Figs. 2a and 2b

show the operating principle of bottom dilution in a vortex cleaner according to an advantageous embodiment of the invention;

Fig. 3 shows the control of the direction of dilution water by means of a radius and an angle in connection with bottom dilution in a vortex cleaner according to an advantageous embodiment of the invention;

Figs 4a to 4c show the operation of a spring assisted valve to be used in connection with bottom dilution in a vortex cleaner according to another advantageous embodiment of the invention; Figs. 5a to 5c

show further advantageous embodiments of the invention; and

Fig. 5d shows a detail of a bottom diluter duct according to the embodiment of Fig. 5c in a reduced view.

Detailed description of the invention

In the following, we will describe the operating principle of bottom dilution in a vortex cleaner according to a first advantageous embodiment of the invention with reference to Figs. 2a and 2b. Figures 2a and 2b show a bottom diluter duct 6 which comprises a flow channel 7, whose first end 7a is provided with an inlet 8 for dilution water, for supplying dilution water to the bottom diluter duct 6, and the second end 7b of the flow channel 7 of the bottom diluter duct is provided with an outlet 9 for discharging dilution water from the bottom diluter duct 6 to the separation cone 5 of the vortex cleaner. The diameter of the flow channel 7 is not necessarily constant, but it may comprise, for example, a conical part shown in Figs. 2a and 2b so that the diameter of the flow channel 7 is greater at the second end 7b than at the first end 7a of the flow channel. The outlet 9 may also be an opening.

Further, the bottom diluter duct 6 comprises e.g. a cover part 10 which is used as a means for controlling the flow of dilution water, that is, as a kind of a valve. The cover part 10 is connected to the flow channel 7 of the bottom diluter duct in such a way that the cover part 10 can move to some extent, advantageously in the flow direction of dilution water flowing via the inlet 8 to the flow channel 7. In the example of Fig. 2, this direction of movement is the direction up and down. The movement of the cover part 10 is limited in one direction by the second end 7b of the flow channel 7 and in another direction by limiter means 1 1 fastened to the cover part 10. Thus, the cover part can move between a first position and a second position. These limiter means 1 1 comprise, for example, one or more nuts which have been threaded around a threaded rod 12 or the like possibly provided in the cover part 10. Such a solution makes it possible, for example, that the movement of the cover part 10 (the play G) in the flow direction of the dilution water (in Fig. 2 upwards) can be adjusted, if necessary. This movement makes it possible to adjust the rate of the flow coming in through the bottom diluter duct 6, if necessary.

The cover part 10 can further be provided with a sealing, if necessary, for improving the tightness of the bottom diluter duct 6 further. The cross section of the cover part 10 in the flow direction is, for example, circular, but it may also have a different shape, such as oval or rectangular. Letter D in the appended drawings indicates the diameter of that point of the cover part 10 which abuts the second end 7b of the flow channel in the closed position.

Next, we shall describe the operation of the bottom diluter duct 6 according to the first advantageous embodiment of the invention for controlling the supply of dilution water. In a situation in which the vortex cleaner 1 is operating, pulp to be cleaned is supplied via the pulp inlet 2 to the separation cone 5. Thus, the pulp is brought to a movement of circulation inside the separation cone, and by the centrifugal force and the gravity, the heavier particles are moved close to the wall of the separation cone and towards the outlet 3 for impurities at the second end of the separation cone. Thus, a pressure P1 is generated in the separation cone 5, effective on the cover part 10 of the inlet valve 6, tending to press it towards the second end 7b of the flow channel of the bottom diluter duct. Consequently, the pressure P1 produces a force F1 effective on the cover part 10. Thus, if dilution water is not led to the bottom diluter duct 6, the pressure P2 inside the flow channel 7 of the bottom diluter duct is lower than the pressure P1 effective on the cover part 10. As a result, the cover part 10 is pressed towards the second end 7b of the flow channel 7 of the bottom diluter duct, closing the outlet 9. This prevents or at least reduces the entry of solid matter present in the separator 5 into the bottom diluter duct 6. In the present application, this position of the cover part 10 is called the first position or the cover part closed position, shown by Fig. 2b. Correspondingly, in a situation in which dilution water is supplied via the inlet 8 for dilution water to the bottom diluter duct 6, the pressure inside the flow channel 7 of the inlet valve increases. At the stage when the pressure P2 produced by the dilution water is higher than the pressure P1 effective on the cover part 10, or the force effect F2 produced by the pressure P2 is greater than the force effect F1 caused by the pressure P1 effective on the cover part 10, the cover part 10 moves farther away from the flow channel 7, opening a flow path via the outlet 9 of the bottom diluter duct to the separation chamber 5; in other words, dilution water can flow to the separation chamber 5. In the present application, this position of the cover part 10 is called the second position or the cover part open position, shown by Fig. 2a. The flow of dilution water prevents or at least reduces the entry of particles possibly present in the separation chamber to the bottom diluter duct 6. In this way, the blocking of the outlet 9 of the bottom diluter duct can be prevented in an effective way.

Gravity can also have some effect on the cover part 10, wherein the force effect F2 generated by the pressure P2 is greater than the force effect F1 generated by the pressure P1 effective on the cover part 10 and the force effect generated by gravity. In practice, the effect of gravity is often relatively small compared with the pressure P1 , wherein the gravity does not necessarily need to be taken into account separately.

In an embodiment, the condition for the opening of the outlet 9 can also be presented by the following formula: the outlet 9 is opened, when P2^*A2 > P1 ^*A1 , that is, P2/P1 > A1 /A2, when the gravity effective on the cover part 10 is of low significance.

Figure 3 shows a bottom diluter duct 6 according to another advantageous embodiment of the invention. The difference to the embodiment shown in Figs. 2a and 2b is primarily in the design of the cover part 10. In this embodiment, the cover part is, also with respect to its inner surface 10a, a curved spherical piece whose function is to direct the liquid flow from the bottom diluter duct 6 obliquely downwards, that is, towards the bottom of the separation cone 5 where the outlet 3 for impurities is located. In the situation of Fig. 2a, the liquid flow from the bottom diluter duct 6 is directed substantially transversely away from the bottom diluter duct 6. The outlet direction of the liquid flow can be controlled by selecting the radius 4 and the angle a of the inner surface 10a of the cover part 10 in a suitable way.

Figures 4a to 4c illustrate the structure and operation of the bottom diluter duct 6 used in connection with bottom dilution in a vortex cleaner according to a third advantageous embodiment of the invention in a reduced manner. The bottom diluter duct 6 comprises a spring 13 or the like to generate a force effective on the cover part 10. The direction of this force effect is selected such that it tends to move the cover part 10 towards the second end 7b of the flow channel 7 or to press it towards the second end 7b of the flow channel. In this case, the pressure P2 produced by the liquid flow in the flow channel 7 has to be higher than in the bottom diluter duct 6 operating without a spring, to move the cover part 10 and to open the outlet 9. However, the tightness of such a solution may be even better than the tightness of the bottom diluter duct 6 operating without a spring in a situation in which no dilution liquid flows via the bottom diluter duct 6 to the separation cone 5.

In the situation of Figs. 4a and 4b, the outlet is open, and in the situation of Fig. 4c, the outlet is closed.

Further, Figs. 5a to 5c illustrate the structure and operation of the bottom diluter duct 6 used in connection with bottom dilution in a vortex cleaner according to a fourth advantageous embodiment of the invention in a reduced manner. Figure 5a shows a bottom diluter duct 6 whose cover part is spherical, but its lower surface is substantially straight, wherein the liquid flow from the bottom diluter duct 6 is directed substantially transversely from the bottom diluter duct 6.

Figure 5b shows a bottom diluter duct 6 whose cover part is spherical, but its lower surface is oblique, wherein the liquid flow from the bottom diluter duct 6 is directed obliquely from the bottom diluter duct 6. The direction of this liquid flow can be influenced, among other things, by selecting the angle of the oblique part of the lower surface suitably, for example by simulating or by testing different angles. Figure 5c shows a bottom diluter duct 6 which is partly similar to that of Fig. 5b but in which the cover part 10 is provided with wings 14 or the like for making the even distribution of the liquid flow discharging from the bottom diluter duct 6 more efficient and for securing that the outlet 9 of the bottom diluter duct 6 remains clean. Thanks to these wings, the liquid flow generates a rotating motion of the cover part 10 around its axis, which may further intensify the even distribution of the liquid flow discharging from the bottom diluter duct 6. In a situation of normal use, liquid typically comes out of the bottom diluter duct 6, that is, a gap is provided between the cover part 10 and the second end 7b of the flow channel. In a fault situation, the bottom diluter duct 6 is closed; that is, the gap between the cover part 10 and the second end 7b of the flow channel is closed. This protects the bottom diluter duct 6 from being blocked.

The rate of dilution water flowing via the bottom diluter duct 6 to the separation cone can be adjusted by utilizing the solution of the invention in a variety of ways. One way to control the volume flow of dilution water is to change the pressure P2 of the flow channel 7 of the bottom diluter duct. The adjustment of the pressure P2 can be implemented, for example, by changing the throttle of the valve arranged in the inlet pipe for dilution water. The volume flow via the outlet 9 or opening of the bottom diluter duct increases when the pressure P2 is increased, and correspondingly decreases when the pressure P2 is decreased. The volume flow of the outlet 9 of the bottom diluter duct changes when the pressure P2 is changed, even though the cross-sectional area of the outlet 9 of the bottom diluter duct remains constant. Correspondingly, the opening of the outlet 9 is also resisted by the pressure P1 effective on the separation cone 10, wherein the opening of the outlet 9 of the bottom diluter duct may be dependent, on one hand, on the pressure ratio P2/P1 , if the pressure P1 effective on the separation cone 10 changes during the operation of the vortex cleaner.

On the other hand, the cross-sectional area of the outlet 9 of the bottom diluter duct can be arranged to be steplessly changed by the pressure P2. This arrangement is possible, for example, when the bottom diluter duct is provided with a spring 13 as shown in Figs. 4a to 4c, wherein the spring 13 resists the movement of the cover part 10 of the bottom diluter duct, that is, the opening of the cross-sectional area of the outlet 9 by the effect of the pressure P2. The cross-sectional area of the outlet will open the more, the higher the pressure P2 is arranged. Naturally, the opening of the outlet 9 is also resisted by the pressure P1 effective on the separation cone 10, wherein the opening of the outlet 9 of the bottom diluter duct may be dependent, on one hand, on the pressure ratio P2/P1 , if the pressure P1 effective on the separation cone 10 can also change.

One way to control the cross-sectional area of the outlet 9 of the bottom diluter duct during the operation is to provide the bottom diluter duct 6 with an arm introduced in a sealing manner through the wall of the bottom diluter duct, for changing the position of the limiter means 11. The position of the limiter means 11 can be changed by the arm, for example by rotating, when the limiter means 11 comprises a threaded rod and a nut for adjusting the position of the outlet of the bottom diluter duct.

By increasing the flow of dilution water to the separation cone, it is possible to intensify the washing out of the reject matter in such a way that the entry of accepted pulp in the reject is largely avoided. The acceptable material is thus washed out from the rejected material and is discharged with the accept flow from the vortex cleaner 1 via the pulp outlet 4. In a corresponding manner, it may be necessary to increase the proportion of the material to be rejected from the supplied pulp, for example if a flow of rejectable material into the accept, that is, to the pulp outlet 4, is detected. Thus, the flow of rejectable material to the pulp outlet 4 can be avoided by reducing the quantity of dilution water, wherein a larger proportion of material processed by the vortex cleaner is removed from the vortex cleaner 1 via the reject outlet, that is, the outlet 3 for impurities, wherein a larger part of the rejected material can be separated from the pulp to be processed.

The control of the quantity of dilution water can also be arranged to be changed on the basis of the volume flow of the reject flow. As the volume flow of the reject flow decreases, it is possible to arrange the volume flow of dilution water to increase, wherein the volume flow from the reject outlet 3 increases. In a corresponding manner, as the volume flow of the reject flow increases, it is possible to arrange the volume flow of dilution water to decrease, wherein the volume flow from the reject outlet 3 decreases. A reduction in the volume flow of the reject flow may be an early sign of block- ing of the vortex cleaner 1 , which can be prevented by increasing the volume flow of dilution water.

It may be advantageous to arrange the bottom diluter duct 6 to operate in such a way that its outlet 9 is closed during the start-up of the vortex cleaner or upon turning off the vortex cleaner 1. In this way, it is possible to prevent the entry of pulp to the outlet 9 of the bottom diluter duct of the vortex cleaner 1 , which may block the outlet 9 and prevent its operation, so that the bottom diluter duct 6 is clean and functional when the vortex cleaner 1 is used again. Advantageously, the outlet 9 of the bottom diluter duct is normally open during the use of the vortex cleaner 1. Thanks to the invention, it is possible, however, to close the outlet 9 of the bottom diluter duct, if necessary, or to adjust the cross-sectional area of the outlet 9 of the bottom diluter duct, which enables the control of the flow of dilution water via the outlet 9 in many ways.

The flow via the outlet 9 of the bottom diluter duct can also be arranged to be directed towards the inlet 2 of the vortex cleaner, that is, in the direction opposite to the direction shown in the figures, or obliquely upwards, or even towards the pulp outlet 2, that is, in the directly upwards direction of the figures. The direction of the flow of dilution water via the outlet 9 of the bottom diluter duct can be arranged in said way obliquely upwards or upwards by designing the flow channel of the outlet 9 of the bottom diluter duct to open obliquely upwards.

In the illustrations in the drawings, the outlet 9 of the bottom diluter duct is on the circumferential surface directed towards the side of the bottom diluter duct. However, the outlet 9 of the bottom diluter duct can also be arranged with a smaller diameter in the cover part 10 of the bottom diluter, wherein the flow of dilution water via the outlet 9 of the bottom diluter can be easily directed more towards the pulp inlet 2 and the pulp outlet 4 of the vortex cleaner. Yet another solution applying the present invention is one in which the cover part 10 of the bottom diluter is provided with at least two outlets 9 of the kind shown in the figures, wherein outlets 9 open in at least two radii or in two different points in the cover part 10 of the bottom diluter. Such an arrangement can be implemented, for example, by arranging the support of the cover parts 10 belonging to the arrangement by means of sleeve parts supported on the same supporting axle and supporting arms supporting the cover parts 10. The outlet 9 or outlets of the bottom diluter are opened and closed by suitably changing the pressure ratio P2/P1 , or the outlet 9 or outlets 9 of the bottom diluter are arranged to open when the pressure ratio P2/P1 is suitably changed. In an advantageous embodiment of the invention, the bottom diluter duct 6 comprises means for controlling the volume flow of dilution water in the flow channel 7. These means can be arranged to control, for example, the supply pressure of dilution water, the cross-sectional area of the outlet 9, the maximum opening of the outlet 9, and/or the spring force of a spring 13 possibly provided in connection with the cover part 10.

The present invention is not limited to the above-presented embodiments, but it can be modified within the scope of the appended claims.

Claims

Claims:

1. Bottom diluter duct (6) in a vortex cleaner, comprising at least

- a flow channel (7),

- a dilution water inlet (8) for supplying dilution water to the flow channel (7), and

- an outlet (9) for discharging dilution water from the bottom diluter duct (6) into the vortex cleaner (1),

characterized in that the bottom diluter duct (6) also comprises a means (10) for controlling the flow of dilution water, arranged to be movable between a first and a second position, in which first position the outlet (9) is closed and in which second position the outlet (9) is open, wherein the opening of the outlet (9) is arranged to take place as a function of the ratio between the inlet pressure (P2) of dilution water and the pressure (P1 ) effective on said means (10) for controlling the flow of dilution water in the vortex cleaner.

2. Bottom diluter duct (6) according to claim 1 , characterized in that the opening of the outlet (9) is arranged to take place when the inlet pressure (P2) of dilution water exceeds a predetermined first limit value.

3. The bottom diluter duct (6) according to claim 1 or 2, characterized in that the bottom diluter duct (6) comprises means for controlling the volume flow of dilution water in the flow channel (7).

4. The bottom diluter duct (6) according to claim 3, characterized in that said means for controlling the volume flow of dilution water in the flow channel (7) are arranged to control the inlet pressure of dilution water.

5. The bottom diluter duct (6) according to claim 3, characterized in that said means for controlling the volume flow of dilution water in the flow channel (7) are arranged to control the cross-sectional area of the outlet (9).

6. The bottom diluter duct (6) according to claim 3, characterized in that said means for controlling the volume flow of dilution water in the flow channel (7) are arranged to control the maximum opening of the outlet (9).

7. The bottom diluter duct (6) according to any of the claims 1 to 6, characterized in that the bottom diluter duct (6) also comprises a spring (13) arranged in connection with the cover part (10), for providing a force effective on the cover part (10).

8. The bottom diluter duct (6) according to claim 7, characterized in that the bottom diluter duct (6) comprises means for controlling the spring force of the spring (13).

9. The bottom diluter duct (6) according to any of the claims 1 to 8, characterized in that the bottom surface of said cover part (10) is substantially flat, wherein the liquid flow from the outlet (9) is arranged to be directed substantially perpendicularly away from the bottom diluter duct (6).

10. The bottom diluter duct (6) according to any of the claims 1 to 8, characterized in that the bottom surface of said cover part (10) is oblique, wherein the liquid flow from the outlet (9) is arranged to be directed substantially obliquely away from the bottom diluter duct (6).

11. The bottom diluter duct (6) according to any of the claims 1 to 10, characterized in that the bottom surface of said cover part (10) is provided with wings, wherein the liquid flow in the flow channel (7) is arranged to generate a rotating motion of the cover part (10) to intensify the even distribution of the liquid flow discharging from the bottom diluter duct (6).

12. A vortex cleaner, comprising:

- a pulp inlet (2) for supplying pulp into the vortex cleaner (1 ),

- a separation cone (5) for separating impurities from the pulp,

- an outlet (3) for impurities;

- an outlet (4) for pulp, and

- a bottom diluter duct (6) comprising at least

- a flow channel (7),

- an outlet (9) for discharging dilution water from the bottom diluter duct (6) into the vortex cleaner (1 ), characterized in that the bottom diluter duct (6) also comprises a means (10) for controlling the flow of dilution water, arranged to be movable between a first and a second position, in which first position the outlet (9) is closed and in which second position the outlet (9) is open, wherein the opening of the outlet (9) is arranged to take place as a function of the ratio between the inlet pressure (P2) of dilution water and the pressure (P1 ) effective on said means (10) for controlling the flow of dilution water in the vortex cleaner.

13. A method for supplying dilution water to a vortex cleaner (1 ) via a bottom diluter duct (6), in which method

- dilution water is supplied to the bottom diluter duct (6), and

- dilution water supplied to the bottom diluter duct (6) is led via an outlet (9) of the bottom diluter duct (6) to the vortex cleaner (1),

characterized in that the flow of dilution water led via the outlet (9) is con- trolled by a control means (10) with at least a first position and a second position, in which first position the outlet (9) is closed and in which second position the outlet (9) is open, wherein the opening of the outlet (9) is arranged to take place as a function of the ratio between the inlet pressure of dilution water and the pressure effective on said means for controlling the flow of dilution water in the vortex cleaner.

14. The method according to claim 13, characterized in that the volume flow of dilution water in the flow channel (7) is controlled by controlling the inlet pressure of dilution water.

15. The method according to claim 13, characterized in that the volume flow of dilution water in the flow channel (7) is controlled by controlling the cross- sectional area of the outlet (9).

16. The method according to claim 13, characterized in that the volume flow of dilution water in the flow channel (7) is controlled by controlling the maximum opening of the outlet (9).

17. The method according to any of the claims 13 to 16, characterized in that said pressure required for opening the outlet (9) is controlled by means of a spring (13) connected to the cover part (10).

18. The method according to any of the claims 13 to 17, characterized in that the liquid flow from the outlet (9) is directed substantially perpendicularly away from the bottom diluter duct (6).

19. The method according to any of the claims 13 to 16, characterized in that the liquid flow from the outlet (9) is directed obliquely away from the bottom diluter duct (6).

20. The method according to any of the claims 13 to 19, characterized in that dilution water supplied to the bottom diluter duct (6) is used to generate a rotating motion of the cover part (10) to intensify the even distribution of the liquid flow discharging from the bottom diluter duct (6).