WO2019074416A1

WO2019074416A1 - Green liquor clarifier with tangential inlet

Info

Publication number: WO2019074416A1
Application number: PCT/SE2018/050776
Authority: WO
Inventors: Roger JANSSON; Jerk SÖDERMAN
Original assignee: Valmet Ab
Priority date: 2017-10-13
Filing date: 2018-07-25
Publication date: 2019-04-18

Abstract

The invention relates to a feedwell (11; 31) for a clarifier, comprising a tubular portion (12; 32), a tangential inlet (19; 39) arranged in an upper part (13; 33) of the tubular portion (12; 32), and a conical portion (15; 35) having an upper end (16; 36), which adjoins to a lower end (14; 34) of the tubular portion (12; 32), and a lower end (17; 37), which is wider than the upper end (16; 36), wherein a bottom plate (18; 38) is arranged at the lower end (17; 37) of the conical portion (15; 35) and that at least one horizontal outlet opening (22; 42) is provided in the conical portion (15; 35).

Description

GREEN LIQUOR CLARIFIER WITH TANGENTIAL INLET

TECHNICAL FIELD

The present invention relates generally to a clarifier, for example a green liquor clarifier to be used in the pulping industry, and in particular to a feedwell for a clarifier, which feedwell has an upper tangential inlet and lower, horizontally directed outlet openings.

BACKGROUND

Clarifiers are used in many industries to separate an influent flow, which contains solid, typically particulate, materials into an underflow sludge and a clarified liquid phase. In the pulping industry, green liquor clarifiers are commonly used to obtain a clean green liquor by separating and remove dregs from a raw green liquor. A conventional clarifier comprises typically a clarification tank, in which the clarification occurs by means of settlement and sedimentation, and the liquor to be clarified is introduced into the clarification tank via a feedwell disposed in an upper portion of the clarification tank.

To not disturb and impede with the separation process, it is generally desired that the feedwell is designed such that the liquor to be clarified is introduced into the clarification tank in a uniform and non-turbulent flow, to not agitate the solid materials that are about to settle or already have settled. An exemplifying clarifier feedwell is disclosed in the U.S. Patent No. 7,794,609 to Egan, III, in which the feedwell comprises a tangential inlet, which is arranged to create a fluid flow that is spread over the inside of the feedwell roof, wherefrom the fluid then drops essentially vertically into a clarification tank disposed below the feedwell.

In the patent GB 2025780 A, a sedimentation apparatus with a feedwell is described. In one embodiment, the feedwell has a cylindrical upper part and a conical lower part and a bottom. The angle of the conical part is selected to be small enough not to cause any turbulence within the diffuser. The bottom is closed and the outgoing flow is directed sideways between vertical side walls. To improve the clarification efficiency of a clarifier used in, for example, the pulping industry is a continuously ongoing project, and one object of the present invention is to provide an improved feedwell which, when installed in a clarifier, enables a higher clarification efficiency, such that the clarifier can manage a higher throughput flow - without deteriorating the quality (i.e. the clarity) of the effluent liquor - than a clarifier comprising a feedwell of a conventional design. Another object of the invention is to provide an improved feedwell for a green liquor clarifier, which - without reducing the flow volume through a clarifier - provides a cleaner effluent flow of clean green liquor from the clarifier.

SUMMARY OF THE INVENTION

The above-mentioned objects are achieved with a feedwell for a clarifier according to the independent claim. Preferred embodiments are set forth in the dependent claims. According to the present invention, a feedwell for a clarifier is provided, wherein the feedwell comprises an upper tubular portion, which has a tangential inlet arranged in an upper part thereof, and a lower conical portion having an upper end, which adjoins to a lower end of the tubular portion, and a lower end, which is wider than the upper end. The feedwell comprises further a bottom plate, which is attached to the lower end of the conical portion, and there is at least one outlet opening arranged in the conical portion, which at least one outlet opening is preferably arranged near the lower end of the conical portion. When installed in clarifier, i.e. in a clarification tank, the feedwell has a generally vertical disposition, and the tubular portion and the conical portion, which is positioned below the tubular portion, extend around an imaginary vertical central axis. By providing an inlet, which is arranged tangential and rather peripheral with respect to this vertical central axis, in an upper portion of the tubular portion, the incoming fluid flow is guided into contact with an inner wall of the tubular portion, wherefrom the centrifugal force forces the incoming fluid flow to follow a helical path downwards to an inner wall of the conical portion. By imposing this helical movement on the fluid flow, the fluid travels relatively slowly in the downward direction (and much slower than if the fluid flow would have been directed into the centre of the feedwell), and when the fluid flow then continues its helical motion downwards along the widening inner wall of the conical portion, its angular velocity decreases, in accordance with the well-known law of conservation of angular momentum. Thus, when the fluid flow ultimately is stopped by the bottom plate and reaches said at least one outlet opening, which preferably is located close to the bottom plate, the circumferential component of its velocity is reduced, and the fluid flow leaves the feedwell in a horizontal direction (with respect to the vertical central axis) via the at least one outlet opening, to thereby not, or at least not unnecessarily, interfere with the already ongoing settling and sedimentation process, which mainly takes place at a deeper level in the clarification tank. In accordance with the invention, the feedwell can be a feedwell for a green liquor clarifier.

To further reduce or essentially eliminate the circumferential component of the fluid flow velocity, baffles can be provided in a lower part of the conical portion; and preferably one baffle is arranged adjacent to each horizontal opening. Further, in one embodiment of the invention, horizontal outlet openings and baffles are created by arranging spacer elements between the bottom plate and the lower end of the conical portion, and by arranging the spacer elements in the shape of upright standing plate elements, which extend towards the centre of the bottom plate, both baffles and horizontal openings are created in a way that is easy and cost-effective to produce. To improve and enhance the tendency of the fluid flow to travel in a helical, downwardly directed path along the inner wall of the tubular portion and subsequently along the inner wall of the conical portion, the inner wall of the tubular portion can be provided with a flow guiding member, which in one embodiment is a helical member, i.e. a helix, which is extends downwardly along the inner wall of the tubular portion. Furthermore, the tangential inlet can be arranged with an inclination angle with respect to the vertical central axis of the feedwell, and this inclination angle can match and correspond to the pitch of the helical member, or the inclination angle can match and correspond to at least to the pitch of an upper portion of the helical member. By this configuration, the helical member, which extends in a downwardly directed, helical shape along the inner wall of the tubular portion, becomes a continuing portion of the tangential inlet, which provides for an efficient guiding of the incoming fluid flow. The invention is also directed to a clarifier comprising a feedwell as described above. BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be further explained hereinafter by means of non-limiting examples and with reference to the appended drawings, wherein:

5 Fig. 1 is a schematic cross-sectional view of a feedwell according to a first embodiment of the present invention; and

Fig. 2 is a schematic cross-sectional view of a feedwell according to a second embodiment of the present invention.

10 DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Fig. 1 illustrates schematically a longitudinal cross-section of a feedwell 11 according to a first embodiment of the invention. The feedwell 11 is designed for implementation in a clarification tank of a clarifier, e.g. a green liquor clarifier used in the pulping industry. The feedwell 11 is therefore configured for a vertical arrangement; and in Fig. 1, an

15 imaginary vertical central axis has been drawn and indicated by the reference character A.

The feedwell 11 comprises a tubular portion 12 having an upper part 13 and a lower end 14, a conical portion 15, which is disposed below the tubular portion 12 and has an upper end 16, which adjoins to the lower end 14 of the tubular portion 12, and a lower end 17, and a bottom plate 18, which is arranged at the lower end 17 of the conical portion 15 and

20 is in this particular embodiment attached to the lower end 17. The conical portion 15 is configured such that it widens downwards, i.e. the diameter of the lower end 17 is larger than the diameter of the upper end 16.

The feedwell 11 comprises further a tangential inlet 19, which is disposed in the upper part 25 13 of the tubular portion 12 and is arranged such that it is positioned rather peripheral and directed tangentially with respect to the central axis A. Thus, the tangential inlet 19 is configured to direct an incoming fluid flow towards and into contact with an inner wall 20 of the tubular portion 12, and imposes thereby a circumferential or centrifugal motion on the incoming fluid flow. By this arrangement of the tangential inlet 19 and the inner wall 30 20, the fluid flow travels relatively slowly downwards and along, and basically in contact with, the inner wall 20 of the tubular portion 12 in a helical path downwards. When the fluid flow then leaves the tubular portion 12 and enters the conical portion 15, the flow will be in contact with an inner wall 21 of the conical portion 15. Further, as the conical portion 15 widens downwardly, with the upper end 16 being smaller than the lower end 17, the circumferential component of the angular velocity of the fluid flow decreases, according to the principle of conservation of angular momentum. Thus, when the fluid flow encounters the bottom plate 18, which stops the relatively slow vertical movement of the fluid flow, there is nothing, or at least only a small fraction, left of its circumferential velocity, and the fluid leaves the feedwell 11 via at least one horizontal outlet opening 22, i.e. the outlet opening(s) 22 is(are) horizontally or orthogonally directed with respect to the vertical axis A. In other words, a portion connecting the lower end 17 of the conical portion with the bottom plate 18 has at least one horizontal outlet opening 22. By this arrangement, the effluent flow will have a minimum impact on the fluid which already is settling and in the clarification tank, and will not unnecessarily and negatively affect the sedimentation process. To further eliminate any remaining circumferential motion of the flow fluid, baffles can be arranged (preferably) in the vicinity of the outlet openings 22. Such baffles are, however, not disclosed in the embodiment illustrated in Fig. 1, but are instead disclosed in the embodiment shown in Fig. 2 and discussed below.

Fig. 2 illustrates schematically a longitudinal cross-section of a feedwell 31 according to a second embodiment of the present invention. The feedwell 31 is designed for implementation in a clarification tank of a clarifier, e.g. a green liquor clarifier used in the pulping industry. The feedwell 31 is therefore configured for a vertical arrangement; and in Fig. 2, an imaginary vertical central axis has been drawn and indicated by the reference character A. The feedwell 31 comprises a tubular portion 32 having an upper part 33 and a lower end 34, a conical portion 35, which is disposed below the tubular portion 32 and has an upper end 36, which adjoins to the lower end 34 of the tubular portion 32, and a lower end 37, and a bottom plate 38, which arranged at but not directly attached to the lower end 37 of the conical portion 35, as will be explained below. The conical portion 35 is configured such that it widens downwards, i.e. the diameter of the lower end 37 is larger than the diameter of the upper end 36. The feedwell 31 comprises further a tangential inlet 39, which is disposed in the upper part 33 of the tubular portion 32 and is arranged such that it is positioned rather peripheral and directed tangentially with respect to the central axis A. Thus, the tangential inlet 39 is configured to direct an incoming fluid flow towards and into contact with an inner wall 40 of the tubular portion 32, and imposes thereby a circumferential or centrifugal motion on the incoming fluid flow. By this arrangement of the tangential inlet 39 and the inner wall 40, the fluid flow travels relatively slowly downwards and along, and basically in contact with, the inner wall 40 of the tubular portion 32 in a helical path downwards. When the fluid flow then leaves the tubular portion 32 and enters the conical portion 35, the flow will be in contact with an inner wall 41 of the conical portion 35. Further, as the conical portion 35 widens downwardly, with the upper end 36 being smaller than the lower end 37, the circumferential component of the angular velocity of the fluid flow decreases, according to the principle of conservation of angular momentum. Thus, when the fluid flow encounters the bottom plate 38, which stops the relatively slow vertical movement of the fluid flow, there is nothing, or at least only a small fraction, left of its circumferential velocity, and the fluid leaves the feedwell 31 via at least one horizontal outlet opening 42, i.e. the outlet opening(s) 42 is(are) horizontally or orthogonally directed with respect to the vertical axis A. In other words, a portion connecting the lower end 37 of the conical portion with the bottom plate 38 has at least one horizontal outlet opening 42. By this arrangement, the effluent flow will have a minimum impact on the fluid which already is settling and in the clarification tank, and will not unnecessarily and negatively affect the sedimentation process.

To further eliminate any remaining circumferential motion of the flow fluid, baffles 43 are provided at the lower end 37 of the conical portion 35, and in the embodiment shown in Fig. 2, these baffles 43 are arranged as spacer elements disposed between and attached to the lower end 37 and the bottom plate 38, and are provided in the form of plates that are standing upright and extend towards the central axis A, such that the openings 42 are created between the baffles 43. In Fig. 2, it is seen that the baffles 43 are provided in the volume defined by the lower end 37 of the conical portion 35 and the bottom plate 38. This volume is thus comprised within a continuation or extrapolation of the conical portion 35. At least a major part of the baffles 43 are according to Fig. 2 provided within sight of the entire inner wall 41 of the conical portion 35 in order to perform the final elimination of the circumferential motion of the flow fluid. As was already mentioned, similar baffles can be provided for the embodiment discussed above in conjunction with Fig. 1. The feedwell 31 comprises further a flow guiding member disposed at the inner wall 40 of the tubular portion 32, and is in this embodiment arranged as a helical member 44, which is attached to the inner wall 40 and extends downwardly in a helical path. By the provision of the helical member 44, the fluid that enters the tubular portion via the tangential inlet 39 and is directed towards the inner wall 40 will effectively be forced to travel in a helical path down through the feedwell 31. The pitch of the helical member 44, or at least the pitch of an upper portion of the helical member 44, is preferably equal to, or at least substantially equal to, the inclination of the tangential inlet 39 with respect to the vertical central axis A, to give the incoming flow a smooth transition from the tangential inlet 39 to the helical member 44; and in Fig. 2, this inclination angle has been indicated with the reference character a. A guiding member, and in particular a guiding member in the form of a helical member, can be arranged also in the first embodiment of the invention, i.e. a helical member, such as helical member 44, can be provided at the inner wall 20 of the tubular portion 12 of the feedwell 11. When the feedwell 11 or the feedwell 31 is implemented in a green liquor clarifier, the feedwell is a relatively large object and can, for example, have a total height of about 4 to 10 meters, with the diameter of the tubular portion being about 1 to 3 meters, the diameter of the conical portion being about 2 to 6 meters, and the inlet having a diameter of about 0.1 to 0.5 meters.

Although the present invention has been described with reference to specific embodiments, also shown in the appended drawings, it will be apparent to those skilled in the art that many variations and modifications can be done within the scope of the invention as described in the specification and defined with reference to the claims below.

Claims

1. A feedwell (11; 31) for a clarifier, comprising:

a tubular portion (12; 32);

a conical portion (15; 35) having an upper end (16; 36), which adjoins to a lower end (14; 34) of the tubular portion (12; 32), and a lower end (17; 37), which is wider than the upper end (16; 36); and,

a bottom plate (18; 38) arranged to the lower end (17; 37) of the conical portion (15; 35) by a portion having at least one horizontal outlet opening (22; 42), characterized by a tangential inlet (19; 39) arranged in an upper part (13; 33) of the tubular portion (12; 32.

2. The feedwell (11; 31) according to claim 1, wherein the clarifier is a green liquor clarifier.

3. The feedwell (31) according to claim 1 or claim 2, wherein the feedwell (31) further comprises baffles (43), which are arranged in contact with the conical portion (15; 35) and preferably at the lower end (17; 37) of the conical portion (15; 35).

4. The feedwell (31) according to claim 3, wherein the baffles (43) are comprised in a volume within sight of the entire inner wall (41) of the conical portion (35).

5. The feedwell (31) according to claim 3 or 4, wherein the baffles (43) are configured as spacer elements, which are arranged between the lower end (37) of the conical portion (35), such that the outlet openings (42) are provided between the baffles (43).

6. The feedwell (31) according to anyone of claims 1 to 5, wherein an inner wall (40) of the tubular portion (32) is provided with a flow guiding member in the form of a helical member (44).

7. The feedwell (31) according to claim 6, wherein the tangential inlet (39) is arranged with an inclination angle (a) with respect to a vertical axis (A), which inclination angle (a) corresponds to the pitch of an upper portion of the helical member (44).