A kind of receiving canister stirring arrangement

Abstract

The invention is a receiving tank arrangement for mixing pulp fibre suspensions without causing sedimentation or build-up at the bottom of the tank. The receiving tank has side walls (3, 4) in the form of two opposite arched end portions (2) and an elongated portion (1) between the arched end portions (2). The receiving tank has at least two mixers (10) and at least one of these mixers (10) is located in an arched end portion (2). The mixers (10) have propellers (12) at the end of their shafts (11). For optimal performance, at least two of the shafts (11) of the mixers (10) are arranged horizontally in relation to the direction of the elongated portion (1) and the centre line of at least one of the shafts (11) of the mixers (10) is aimed at a point at the side wall (3) of the elongated portion (1) and at a distance of at least 25% of the length of the elongated portion (1) from the beginning of the elongated portion (1). Preferably, the propellers (12) are positioned and / or arranged symmetrically in relation to the centre point of the receiving tank. Inside the centre of the elongated portion is an elongated centre part (6) with a rounded end. The receiving tank has a substantially flat bottom at least at the elongated portion (1) of the receiving tank.

Description

TECHNICAL FIELD

[0001] The present invention is an arrangement for agitating a suspension in a receiving tank in the form of two opposite arched ends and an elongated section between these arched ends. In particular, the invention aims at agitating a pulp fibre suspension of cellulose fibres from recycled material. BACKGROUND

[0002] Receiving tanks are used in the paper industry for agitating screened fibres and small particles supplied from a drum pulper. The receiving tank is placed below the last screen section of the drum pulper. The purpose of the tank can or can not be to separate the heaviest particles, such as sand or glass, to the bottom of the tank.

[0003] The publication CN108330719 discloses an arrangement where the propulsion of the agitator is arranged so that it is aligned with the side walls of the arched ends of the tank. SUMMARY

[0004] By a sufficiently stable and coherent circulation flow in the receiving tank, the minimum energy consumption is best achieved. Separation of particles is generally not desired to take place in the receiving tank, as this can be better performed in a later stage with minimal loss of fibres. The agitating conditions should then keep the particles in flow with the liquid agitation and prevent sedimentation. A strong coherent and stable flow is desired. Local backflow, eddies and water accumulation will result in accumulation of particles at the bottom of the tank. The accumulation can grow and make the flow unstable, which will make the accumulation grow further. The process should then be stopped occasionally to remove the accumulation. Simulations and practice have shown that the position and arrangement of the propeller of the agitator in the prior art in the receiving tank will create excessive turbulence, areas of different flow and even counterflow in the tank.

[0005] It is the object of the present invention to achieve the best mixing result with the least energy consumption and the least sedimentation of particles in the headbox. These and other objects become apparent from the following summary and description, by means of a headbox arrangement for mixing a pulp fibre suspension in a headbox, said headbox having the form of two opposite arch-shaped end portions with side walls and an elongated portion between said arch-shaped end portions with side walls, and said headbox having at least two mixers, and at least one of said mixers being located in said arch-shaped end portions, and said mixers having a propeller at the end of their shafts, and said shafts of said mixers pointing to the same side of said headbox when viewed from said arch-shaped end portion to which said mixers are attached, and said headbox having a stock outlet, wherein at least two of said shafts of said mixers are arranged horizontally in relation to the direction of said elongated portion, and the centre line of at least one of the shafts of the mixers is aimed at a point on the side wall of said elongated portion and at least 25% of the length of said elongated portion from the beginning of said elongated portion.

[0006] In particular, the headbox for mixing a pulp fibre suspension has the form of two opposite arch-shaped end portions with curved side walls and an elongated portion between these arch-shaped end portions with opposite side walls. The tank has a stock outlet and it can have a reject outlet. The headbox has at least two mixers, and at least one of these mixers is located in the arch-shaped end portion. The mixer has a propeller at the end of its shaft. At least two of the mixers should have a shaft pointing horizontally in the direction of the elongated portion. When viewed from the arch-shaped end portion to which the mixer is attached, the shaft should point to the same side of the tank. The centre line of at least one of the shafts of the mixers is aimed at a point on the side wall of the elongated portion and at least 25% of the length of the elongated portion from the beginning of the elongated portion. Advantageously, in order to achieve the best flow conditions, the length of the tank is 1.5 to 2 times longer than the width of the tank. The diameter of the propeller of the mixer should be 10% to 20% of the width of the tank to create a flow of suitable size width.

[0007] Preferably, the number of stirrers is two, as the number of stirrers also increases the manufacturing and operating costs. One stirrer is not enough to achieve this. Preferably, the propellers are positioned and / or arranged symmetrically with respect to the center point of the receiving tank. In simulations, the feature that the shafts are angled with respect to the center line to point to the side wall of the elongated section creates the most uniform distribution of flow velocity within the tank. At least the shaft of the stirrer pointing to the side wall of the elongated section should point to the other side of the tank, not the side where the acceptant outlet is located. To achieve the best flow characteristics, the propeller at the end of the at least one shaft should be located within the arched end. The orientation and location of the acceptant outlet can affect the flow such that the optimal position and arrangement of the propeller on one side of the receiving tank can be different from the optimal arrangement of the other propeller on the other side of the receiving tank.

[0008] Advantageously, within the center of the elongated section is an elongated center section having a length of at least 50% of the length of the elongated center section. There will then be no pooling and turbulence between the different flow directions at the center line of the tank. Preferably, the elongated center section has rounded ends and a width of less than 30% of the width of the elongated center section. At least within the elongated section of the tank, the tank should have a substantially flat bottom. So, even if it has a sloped or concave bottom, the amount of variation in depth should be less than 5% of the length of the elongated section. A fairly flat bottom prevents the accumulation of particles within this area.

[0009] Advantageously, at least a portion of the acceptant outlet is positioned at least partially in the end half of the elongated section and / or within the arched end opposite the side of the stirrer in the direction of flow. The rejectant outlet is preferably located at the bottom of at least one of the arched ends of the tank. The rejectant outlet is preferably positioned after the acceptant outlet within the same elongated section, or at the next arched end, in the direction of flow. BRIEF DESCRIPTION OF DRAWINGS

[0010] The application will be described in more detail with reference to the drawings, in which:

[0011] Figure 1 Fig. 1 shows a top view of an embodiment of a receiving tank arrangement, and

[0012] Figure 2 Fig. 1 shows a top view of an embodiment of a receiving tank arrangement, and DETAILED DESCRIPTION

[0013] Figure 1 Fig. 1 shows a top view of an embodiment of a receiving tank arrangement, and Figure 2A side view of a receiving tank arrangement is illustrated. The receiving tank is usually placed underneath the screened end portion of a drum pulper that processes waste paper or other fibrous material. A suspension of pulp fibers and small particles falls directly into the receiving tank through the screen or flows down along a funnel portion 5 around the tank. The receiving tank preferably has a substantially flat bottom at least at the central elongated portion 1. The elongated portion 1 has side walls 3 that are usually vertical and straight. The side walls 3 can also be curved along the longitudinal direction, preferably outwardly, so as to form an oval tank. At both ends of the tank are arched end portions 2 with vertical arched side walls 4. A straight portion can exist between the two arched side wall 4 portions. The arched corner portions ensure that the flow will circulate smoothly in and out of the arched end portions 2. The bottom of the receiving tank preferably has a bevel 7 at all edges to avoid standing water and sedimentation of the heaviest particles at the edges. In Figure 1 The direction of the circulating flow is indicated with arrows in the middle.

[0014] Preferably, an elongated central member 6 is positioned in the middle of the elongated portion 1 for preventing interaction between the left and right direction flows. To obtain the best flow characteristics, both ends of the elongated central member 6 are rounded. The elongated central member should have a width sufficient to minimize the turbulence at its ends where the circulating flow will turn to the other side of the tank. The preferred width of the elongated central member 6 is between 10% and 30% of the width of the tank.

[0015] The agitator 10 usually comprises an electric motor, a gear box and a shaft 11 with a propeller 12 at the end of the shaft 11. The propeller 12 usually creates a propulsion flow in a direction away from the center line of the shaft 11. Any other combination illustrated can be used to implement the invention, as the main effect is based on the initial position and direction of the propulsion flow. For example, a short propeller shaft 11 and a 90 degree gear box as in an outboard motor can be used instead. The propeller 12 can have a fan tube around it for optimal propulsion performance, but any stable cross flow obstacles should be avoided to avoid accumulation of fibers around it.

[0016] The horizontal arrangement a of the at least one shaft 11 of the agitator 10 is such that the centre line of the shaft, i.e. the thrust vector of the agitator, is aimed at a point P at the side wall of the elongated portion 1 and at a distance of at least 25% of the length of the elongated portion 1 from the start of the elongated portion 1. More advantageously, the point P is located within 30% to 60% of the length of the elongated portion 1 from the start of the elongated portion 1. To achieve optimal flow characteristics, the propeller 12 at the end of the at least one shaft 11 is located within the arched end portion 2. In principle, optimal flow characteristics can be achieved if the position and arrangement are symmetrical with respect to the centre point of the tank. The horizontal arrangement a of the at least one shaft of the agitator is between 15 and 35 degrees, more preferably between 20 and 30 degrees, with the longitudinal centre line of the receiving tank. Because the acceptant outlet 8 has some influence on the flow, the propeller 12 at that side of the tank can be positioned and / or arranged differently depending on the position, size and form of the acceptant outlet 8.

[0017] The acceptant outlet 8 is preferably positioned away from the propeller 12 in the direction of flow. The acceptant outlet 8 can be for example a downwardly curved pipe. The pipe of the acceptant outlet 8 can be shaped with an optimised streamline shape to minimise the resistance influence on the circulating flow. If the tank has a reject outlet 9, it should be placed after the acceptant outlet 8 where the flow is slowest and most turbulent. Preferably, the reject outlet 9 is at least partly located within the curved end portion 2. Any known design of reject outlet 9 with conveying means can be used. Some examples of suitable reject outlets are disclosed in publication CN108330719.

Claims

1. A receiver arrangement for agitating a pulp fibre suspension in a receiver tank, which receiver tank has the form of two opposite arched end portions (2) and an elongated portion (1) between the arched end portions (2), wherein the arched end portions (2) have side walls (4), the elongated portion (1) has side walls (3), and the receiver tank has at least two agitators (10), and at least one of the agitators (10) is located in the arched end portions (2), and the agitators (10) have propellers (12) at the end of their shafts (11), and the shafts (11) of the agitators (10) point towards the same side of the receiver tank when viewed from the arched end portion (2) to which the agitator (10) is attached, and the receiver tank has a recipient outlet (8), characterised in that At least two of the shafts (11) of the stirrers (10) are arranged horizontally with respect to the direction of the elongated portion (1), and the center line of at least one shaft (11) of the stirrers (10) is aimed at a point (P) which is located at the side wall (3) of the elongated portion (1) and which is at least 25% of the length of the elongated portion (1) away from the beginning of the elongated portion (1).

2. The receiving tank arrangement according to claim 1, wherein, The at least one shaft (11) of the stirrers (10) is located at the other side of the longitudinal center line of the receiving tank compared to the receiving outlet (8), and the propeller (12) at the end of the shaft (11) is located within the arched end (2).

3. The receiving can arrangement according to claim 1 or 2, wherein The number of the stirrers (10) is two.

4. The receiving can arrangement according to claim 1 or 2, wherein The propellers (12) are positioned and / or arranged symmetrically with respect to the center point of the receiving tank.

5. The receiving can arrangement according to claim 1 or 2, wherein Within the center of the elongated portion is an elongated central part (6) which has a length of at least 50% of the length of the elongated portion (1).

6. The receiving can arrangement of claim 5, wherein, The elongated central part (6) has rounded ends, and the width of the elongated central part (6) is less than 30% of the width of the elongated portion (1).

7. The receiving can arrangement according to claim 1 or 2, wherein The receiving tank has a flat bottom at least at the elongated portion (1) of the receiving tank, and / or the amount of change in depth at the elongated portion (1) is less than 5% of the length of the elongated portion.

8. The receiving can arrangement according to claim 1 or 2, wherein, The waste outlet (9) is located at least partially at the bottom of at least one of the arched ends (2) of the receiving tank.

9. The receiving can arrangement according to claim 1 or 2, wherein, At least a part of the receiving outlet (8) is located at the end half of the elongated portion (1) pointed by the stirrers (10) and / or within the arched end (2) opposite to the side of the stirrers (10).

10. The receiving tank arrangement of claim 8, wherein, The waste outlet (9) is located after the receiving outlet (8) in the direction of flow within the same elongated portion (1) and / or at the next arched end (2).

11. The receiving can arrangement according to claim 1 or 2, wherein The horizontal arrangement of the at least one shaft (11) of the stirrers is at an angle of 15 to 35 degrees with respect to the longitudinal center line of the receiving tank.

12. The receiving can arrangement according to claim 1 or 2, wherein The horizontal arrangement of the at least one shaft (11) of the stirrers (10) is at an angle of 20 to 30 degrees with respect to the longitudinal center line of the receiving tank.

13. The receiving can arrangement according to claim 1 or 2, wherein, The length of the receiving tank is 1.5 to 2 times longer than the width of the receiving tank.

14. The receiving can arrangement of claim 1 or 2, wherein, The diameter of the propeller (12) of the stirrers (10) is 10% to 20% of the width of the receiving tank.

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