Centrifugal separator

Abstract

A centrifugal separator (1) for separating at least one liquid phase from a liquid feed mixture is provided. A centrifugal separator (1) comprises a frame (2), a drive member (3) and a rotating portion (4), where the drive member (3) is configured to rotate the rotating portion (4) relative to the frame (2) about an axis of rotation (X), and where the rotating portion (4) comprises a centrifuge drum (5) surrounding a separation space (9). The centrifuge drum (5) further comprises an inlet (14) for receiving the liquid feed mixture and at least one liquid outlet (6, 7) for the separated liquid phase; wherein the separation space (9) comprises a surface enlarging insert (10) for improving separation performance. The centrifuge drum (5) comprises a drum wall (30) in which a first channel (31) and a second channel (32) extend, where the first channel (31) and the second channel (32) extend in different directions (D1, D2) but intersect at an intersection point (Y) where there is a fluid contact between said first channel (31) and said second channel (32). The first channel (31) is arranged such that during rotation of the centrifuge drum (5), as seen in a cross-section in a plane (A) perpendicular to the direction (D1) of the first channel (31), stress concentration zones (40) are generated in the drum wall (30) on two opposite sides (31a, 31b) of the first channel (31) and lower stress zones (41) are generated in the drum wall (30) on the other two opposite sides (31c, 31d) of the first channel (31). The second channel (32) is arranged such that, as seen in a cross-section in a plane (A) perpendicular to the direction (D1) of the first channel (31), the second channel intersects the first channel (31), transitioning with its centerline (Z2) towards the lower stress zone (31c, d).

Description

Field of the Invention

[0001] The present invention relates to the field of centrifugal separators and, more particularly, to the formation of channels within the wall of a centrifuge bowl. Background Art

[0002] Centrifugal separators are generally used for the separation of liquids and / or for separating solids from liquids. During operation, a liquid mixture to be separated is introduced into a rotating bowl, and the heavy particles or the denser liquid (usually water) accumulates at the periphery of the rotating bowl, while the less dense liquid accumulates closer to the central axis of rotation. This allows for the collection of the separated fractions, for example, by means of different outlets arranged at the periphery and close to the axis of rotation, respectively. Separation elements, such as a stack of frustoconical separation discs, are typically used within the rotating bowl to enhance the separation performance. An example of a centrifugal separator is described in patent application EP 3315205.

[0003] The centrifuge bowl of a centrifugal separator is subjected to high stresses. As an example, when two drilled holes in the wall of the centrifuge bowl intersect, high stresses may occur at some of the intersection points, which may ultimately lead to fatigue cracks.

[0004] Accordingly, there is a need in the art for an improved centrifugal separator in which the risk of fatigue cracks in the centrifuge bowl during operation is reduced. Summary of the Invention

[0005] It is an object of the present invention to overcome at least one or more limitations of the prior art. In particular, it is an object of the present invention to provide a centrifugal separator having a reduced risk of fatigue cracks occurring at the location where two channels in the wall of the centrifuge bowl intersect.

[0006] As a first aspect of the present invention, there is provided a centrifugal separator for separating at least one liquid phase from a liquid feed mixture, comprising:

[0007] a frame, a drive member, and a rotating part,

[0008] wherein the drive member is configured to rotate the rotating part relative to the frame about a rotation axis (X), and

[0009] wherein the rotating part includes a centrifuge bowl surrounding a separation space;

[0010] wherein the centrifuge bowl further includes an inlet for receiving the liquid feed mixture and at least one liquid outlet for the separated liquid phase;

[0011] wherein the separation space includes a surface-expanding insert for enhancing the separation performance; and

[0012] wherein the centrifuge drum comprises a drum wall, and a first channel and a second channel extend in the drum wall,

[0013] wherein the first channel and the second channel extend in different directions (D1, D2), but intersect at an intersection point (Y), at which there is fluid contact between the first channel and the second channel; and wherein

[0014] the first channel is arranged such that during rotation of the centrifuge drum, as seen in a cross-section in a plane (A) perpendicular to the direction (D1) of the first channel, stress concentration zones are generated in the drum wall on two opposite sides of the first channel, and lower stress zones are generated in the drum wall on the other two opposite sides of the first channel,

[0015] and wherein the second channel is arranged such that as seen in a cross-section in a plane perpendicular to the direction (D1) of the first channel, the second channel intersects the first channel with its center line shifted towards the lower stress zone.

[0016] As used herein, the term "axial" denotes a direction parallel to the axis of rotation (X). Accordingly, relative terms such as "above", "upper", "top", "below", "lower" and "bottom" refer to relative positions along the axis of rotation (X). Correspondingly, the term "radial" denotes a direction extending radially from the axis of rotation (X). Thus, a "radially inner position" refers to a position closer to the axis of rotation (X) compared to a "radially outer position".

[0017] Thus, the first channel and the second channel are located within the drum wall of the centrifuge drum, i.e., within the wall surrounding the separation space. The first channel and the second channel extend in different directions but intersect such that there is fluid contact between the channels. Thus, liquid or gas in the first channel can be directed to the second channel and vice versa. Due to the intersection, the first channel and the second channel form a continuous channel extending in different directions.

[0018] The first channel and the second channel can extend in any direction, i.e., any angle can exist between the first direction D1 and the second direction D2. The first channel can, for example, have a larger extension in the radial direction, while the second channel can have a larger extension in the axial direction, or vice versa.

[0019] As seen in a cross-section in a plane perpendicular to the direction D1 of the first channel, the second channel can be arranged such that its direction D2 forms an angle with the direction of the force lines generated during rotation of the centrifuge drum.

[0020] During the rotation of the centrifuge drum, stress concentration regions or stress concentration bands are formed in the drum wall near the channels. Thus, a stress concentration region is a region in the drum wall where the stress is significantly higher compared to other nearby regions. Such stress concentration is attributed to the irregularities in the drum wall material due to the formed channels, which cause an interruption in the stress flow. As seen in a cross-section in a plane perpendicular to the direction of the channels, stress concentration regions are formed on two opposite sides, and lower stress regions are formed on the other two opposite sides. Therefore, the "stress concentration regions" in the drum wall have a higher stress concentration factor than the "lower stress regions" in the drum wall.

[0021] A first aspect of the present invention is based on the recognition that, in order to reduce stress and minimize the fatigue risk, the first and second channels should be formed in such a way that the channels intersect each other on at least one of their sides with compressive stress (i.e., in the "lower stress region"). Thus, the inventors have realized that during the operation of the centrifuge separator (due to, for example, changes in liquid pressure, changes in rotational speed) and during the discharge of the separated phases (such as the sludge phase), the stress in the centrifuge drum wall can change. This can lead to fatigue cracks, but if the channels intersect another channel on one of their compressive stress sides (i.e., in the "stress concentration region"), the maximum stress at the intersection will be significantly lower compared to the case where the channels intersect on the tensile stress side (i.e., in the "lower stress region"). Therefore, the risk of cracks in the centrifuge drum wall is reduced.

[0022] The centrifuge drum wall can be made of or include a metallic material. The centrifuge drum wall can be made of stainless steel or at least include stainless steel.

[0023] In an embodiment of the first aspect, the stress concentration regions and the lower stress regions are generated in the drum wall due to the circumferential stress formed during the rotation of the centrifuge drum.

[0024] The circumferential stress is a force applied to each particle in the centrifuge drum wall in two directions along the circumferential direction (perpendicular to both the rotation axis and the radius of the centrifuge drum).

[0025] The centrifuge separator is used to separate a liquid feed mixture. The liquid feed mixture can be an aqueous liquid or an oily liquid. As an example, the centrifuge separator can be used to separate at least one liquid phase (such as one or two liquid phases) and a solid phase from the liquid feed mixture. The solid phase can be a sludge phase.

[0026] The frame of the centrifugal separator is a non-rotating part, and the rotating part can be supported by the frame through at least one bearing device, which may include ball bearings. The rotating part of the separator can be arranged to rotate around a vertical rotation axis, that is, the rotation axis (X) can extend vertically. The rotating part includes a centrifuge drum. The centrifuge drum is usually supported by a main shaft (i.e., the rotating shaft) and can thus be mounted to rotate together with the main shaft. As a result, the rotating part can include a main shaft that can rotate around the rotation axis (X). The centrifugal separator can be arranged such that the centrifuge drum is supported by the main shaft at one of the ends of the main shaft, such as at the bottom end or the top end of the main shaft.

[0027] The drive component for rotating the rotating part of the separator may include an electric motor having a rotor and a stator. The rotor can be fixedly connected to the rotating part such as the main shaft. Advantageously, the rotor of the electric motor can be provided on or fixed to the main shaft of the rotating part. Alternatively, the drive component can be provided beside the main shaft and rotate the rotating part through a suitable transmission mechanism, such as a belt transmission mechanism or a gear transmission mechanism.

[0028] The centrifuge drum surrounds the separation space through the rotor wall. The separation of the fluid mixture occurs in the separation space, which includes surface-expanding inserts for improving the separation performance. Such inserts can be a stack of separation discs arranged coaxially around the rotation axis (X). The separation discs are arranged at a certain distance from each other to form a gap between every two adjacent separation discs. For example, the separation discs can be made of metal. In addition, the separation discs can be frustoconical separation discs, that is, having a separation surface forming a frustoconical part of the separation disc. As an example, the stack of separation discs can include more than 100 separation discs, such as more than 200 separation discs. The thickness of the separation discs can be less than 1 mm, such as less than 0.6 mm.

[0029] The centrifugal separator further includes an inlet for receiving the liquid mixture to be separated (liquid feed mixture). The inlet can be centrally arranged in the centrifuge drum and thus arranged on the rotation axis (X). The centrifugal separator can be arranged to feed from the bottom, such as through the main shaft, so that the liquid feed mixture is delivered from the bottom of the separator to the inlet. Alternatively, the centrifugal separator can be arranged to feed from the top, such as through a fixed inlet pipe extending into the centrifuge drum.

[0030] At least one liquid outlet can be arranged on the upper part of the centrifuge drum, such as above the axial direction of the stack of separation discs. The at least one liquid outlet can be a single outlet for the separated liquid phase or include a first liquid outlet for the liquid light phase and a second liquid outlet for the liquid heavy phase. The liquid heavy phase has a higher density than the liquid light phase.

[0031] In an embodiment of the first aspect, the centrifuge separator further comprises a sludge outlet arranged at the periphery of the centrifuge bowl. As an example, the sludge outlet may be in the form of a set of intermittently open outlets or a set of permanently open nozzles.

[0032] Thus, the centrifuge separator can be arranged to separate a liquid feed mixture into a liquid light phase, a liquid heavy phase and a solid phase, i.e., a sludge phase, and thus, the centrifuge separator can comprise a first liquid outlet for the heavy phase, a second liquid outlet for the light phase and a sludge outlet for the separated sludge.

[0033] The radius of the first channel and / or the second channel can be at least 2 mm, such as at least 5 mm, such as at least 10 mm.

[0034] In an embodiment of the first aspect, as seen in a cross-section in a plane (A) perpendicular to the direction of the first channel, the second channel is displaced by at least half of the radius of the first channel with its center line (Z2) towards a lower stress zone. Thus, the center line Z2 is along the direction D2 of the second channel.

[0035] As an example, as seen in a cross-section in a plane (A) perpendicular to the direction of the first channel, the second channel can be displaced by at least the radius of the first channel with its center line (Z2) towards a lower stress zone. Thus, the center line Z2 can be displaced such that it does not overlap with the cross-section of the first section.

[0036] In an embodiment of the first aspect, the second channel is displaced with its center line (Z2) towards a lower stress zone such that the imaginary extension of the second channel does not overlap with the center line (Z1) of the first channel.

[0037] Thus, the imaginary extension is an extension along the direction D2 of the second channel. The second channel can be arranged such that the imaginary extension does not overlap with the center line of the first channel, i.e., the center line of the first channel is located outside the imaginary extension of the second channel.

[0038] In an embodiment of the first aspect, the centrifuge bowl has a radius R, and the intersection point (Y) is arranged at a radius greater than 0.3R, such as greater than 0.5R.

[0039] At a larger radius of the centrifuge bowl, the risk of fatigue cracks is greater, i.e., for the first and second channels located at a larger radius, the teachings of the present invention can be more useful.

[0040] The radius R of the centrifuge bowl can be at least 120 mm, such as at least 150 mm, such as at least 200 mm.

[0041] In an embodiment of the first aspect, the second channel is arranged such that the intersection point (Y) between the first channel and the second channel is also shifted towards the lower stress region of the second channel.

[0042] The first channel and the second channel may be arranged such that the channels intersect each other on the side where both channels have their compressive stress (i.e., in the "lower stress region" of both channels).

[0043] As a result, the second channel may also be arranged such that during rotation of the centrifuge bowl, as seen in a cross-section in a plane perpendicular to the direction (D2) of the second channel, stress concentration regions are generated in the bowl wall on two opposite sides of the second channel, and lower stress regions are generated in the bowl wall on the other two opposite sides of the second channel. Then, the second channel may be arranged such that as seen in a cross-section in a plane perpendicular to the direction (D1) of the first channel, the second channel intersects the first channel with its centerline shifted towards the lower stress region of the first channel, and also such that as seen in a cross-section in a plane perpendicular to the direction (D2) of the second channel, the centerline of the first channel is shifted towards the lower stress region of the second channel.

[0044] In an embodiment of the first aspect, the first channel and the second channel are connected to a liquid outlet for the separated liquid phase.

[0045] Thus, the first channel and the second channel may form part of an outlet channel through which the separated phase (such as the liquid heavy phase) is conveyed after separation in the separation space.

[0046] In an embodiment of the first aspect, the centrifuge further includes a sludge outlet arranged at the periphery of the centrifuge bowl. Thus, the first channel and the second channel may be part of a liquid system for intermittently discharging sludge from such a sludge outlet.

[0047] In certain types of centrifuges, the separated sludge is discharged through a number of ports in the periphery of the separator bowl. Between discharges, these ports are covered by, for example, an operating slide that forms an internal bottom in the separation space of the bowl. This operating slide may be pressed upwards against the upper part of the bowl by the force of a hydraulic fluid (such as water) below. To initiate sludge discharge, the hydraulic fluid is discharged from below the operating slide such that the lifting force acting to press the operating slide upwards is reduced, which in turn starts the movement of the operating slide such that the ports open. To close the ports again, the hydraulic fluid is supplied again to the space below the operating slide. This hydraulic operating system only allows the ports to be opened and closed for a fraction of a second and can cause the contents of the separation bowl to be partially or completely emptied.

[0048] The first and second channels can be part of a system for conveying hydraulic fluid to move an operating slider up or down. As an example, the first and second channels can be connected to an operating water module (OWM) arranged to supply water to an intermittent discharge system.

[0049] The first and second channels can also be part of different types of intermittent discharge systems, such as a system that uses at least one actuator to close and open a sludge outlet. Thus, the first and second channels can be channels that include electrical wires.

[0050] In an embodiment of the first aspect, the centrifuge drum includes at least one sensor for measuring a physical property of the centrifuge drum itself or a physical property within the centrifuge drum, and wherein the first channel and the second channel include wires connected to the at least one sensor.

[0051] The wire can be, for example, an electrical wire or an optical fiber cable. The at least one sensor can be arranged within the separation space or in the drum wall. As an example, the at least one sensor can be arranged on the inner surface of the drum wall, i.e., on the surface facing the separation space.

[0052] The at least one sensor can be configured to sense, for example, the temperature or pressure within the drum.

[0053] In an embodiment of the first aspect, the first channel and / or the second channel are formed by a method selected from drilling and electrical discharge machining (EDM).

[0054] In EDM, an electrical discharge (spark) is used to create the channel.

[0055] As a second aspect of the present invention, there is provided a method of forming a first channel and a second channel in a drum wall of a centrifuge drum for a centrifuge separator. The method comprises the steps of:

[0056] a) providing the centrifuge drum;

[0057] b) forming the first channel extending in a first direction D1 in the drum wall, wherein the first channel is formed such that during rotation of the centrifuge drum, as seen in a cross-section in a plane (A) perpendicular to the direction (D1) of the first channel, stress concentration zones are generated in the drum wall on two opposite sides of the first channel, and lower stress zones are generated in the drum wall on the other two opposite sides of the first channel,

[0058] c) A second channel extending in a second direction is formed in the drum wall such that the first channel intersects the second channel at an intersection point (Y), at which there is fluid contact between the first channel and the second channel, and wherein the second direction D2 is different from the first direction D1, and wherein the second channel is formed such that, as seen in a cross-section in a plane (A) perpendicular to the first channel direction (D1), the second channel intersects the first channel with its centerline (Z2) shifted towards the lower stress zone.

[0059] This aspect may generally exhibit the same or corresponding advantages as the previous aspect. The effects and features of this second aspect are largely similar to those described above in connection with the first aspect. The embodiments mentioned in connection with the first aspect are largely compatible with the second aspect.

[0060] Step b) and / or c) may be performed using a method selected from drilling and electrical discharge machining (EDM).

[0061] The method of the second aspect can be used to produce a centrifuge drum for a centrifuge separator according to the first aspect above.

[0062] In an embodiment of the second aspect, the second channel is formed in step c) such that, as seen in a cross-section in a plane (A) perpendicular to the first channel direction (D1), the centerline (Z2) of the second channel is shifted towards the lower stress zone by a distance of at least half the radius of the first channel.

[0063] In an embodiment of the second aspect, the second channel is formed in step c) such that the centerline (Z2) of the second channel is shifted towards the lower stress zone such that the imaginary extension (32a) of the second channel does not overlap with the centerline (Z1) of the first channel.

[0064] In an embodiment of the second aspect, the centrifuge drum has a radius R, and steps b) and c) are performed such that the intersection point (Y) is arranged at a radius greater than 0.3R, such as greater than 0.5R.

[0065] As discussed with respect to the first aspect above, the first channel and the second channel may be formed such that the channels intersect each other on the side where both channels have their compressive stress (i.e., in the "lower stress zone" of both channels). As a result, in an embodiment of the second aspect, step c) includes forming the second channel such that, during rotation of the centrifuge drum, as seen in a cross-section in a plane (A) perpendicular to the second channel direction (D2), stress concentration zones are generated in the drum wall on two opposite sides of the second channel, and lower stress zones are generated in the drum wall on the other two opposite sides of the second channel.

[0066] Then, step c) may further include forming a second channel such that, as seen in a cross-section in a plane perpendicular to the direction (D1) of the first channel, the second channel intersects the first channel with its centerline shifted towards the lower stress region of the first channel, and further such that, as seen in a cross-section in a plane perpendicular to the direction (D2) of the second channel, the centerline of the first channel is shifted towards the lower stress region of the second channel. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] The above and other objects, features and advantages of the inventive concept will be better understood from the following exemplary and non-limiting detailed description with reference to the accompanying drawings. In the figures, like reference numerals will be used for like elements unless otherwise noted.

[0068] Figure 1 A schematic view of a centrifugal separator according to an embodiment of the present invention is shown.

[0069] Figure 2 A schematic view of a cross-section of a centrifuge drum is shown.

[0070] Figure 3 A schematic perspective view of intersecting first and second channels is shown.

[0071] Figure 4 A schematic view of internal force lines surrounding the first channel as seen in a plane perpendicular to the direction of the first channel is shown.

[0072] FIG. 5 shows a schematic view of intersecting first and second channels according to a prior art method as seen in a plane perpendicular to the direction of the first channel.

[0073] Figure 6 A schematic view of intersecting first and second channels as seen in a plane perpendicular to the direction of the first channel is shown.

[0074] Figure 7 A schematic view of intersecting first and second channels as seen in a plane perpendicular to the direction of the first channel is shown.

[0075] Figure 8 Exemplary positions of first and second channels within the drum wall of a centrifuge drum are shown.

[0076] Figure 9 A flowchart of a method for forming first and second channels in the drum wall of a centrifuge drum for a centrifugal separator is shown. DETAILED DESCRIPTION

[0077] The centrifugal separator and method according to the present disclosure will be further illustrated by the following description with reference to the drawings.

[0078] Figure 1 A cross-section of an embodiment of a centrifugal separator 1 is shown, which is configured to separate at least one liquid phase from a liquid feed mixture, in this case a liquid heavy phase and a liquid light phase. The centrifugal separator 1 has a rotating part 4, which includes a centrifuge drum 5 and a drive main shaft 4a.

[0079] The centrifugal separator 1 is further provided with a drive motor 3. The motor 3 may for example include a fixed element and a rotatable element, which rotatable element surrounds the main shaft 4a and is connected to the main shaft 4a such that it transfers a driving torque to the main shaft 4a during operation and thus to the centrifuge drum 5. The drive motor 3 may be an electric motor. Alternatively, the drive motor 3 may be connected to the main shaft 4a by a transmission mechanism device. The transmission mechanism device may be in the form of a worm gear, which includes an element connected to the main shaft 4a for receiving the driving torque. Alternatively, the transmission mechanism device may be in the form of a drive belt or the like.

[0080] In Figure 2 The centrifuge drum 5, shown in more detail in

[0081] In Figure 1 is supported by the main shaft 4a, which in turn is rotatably arranged about a vertical axis of rotation (X) in a bottom bearing 22 and a top bearing 21 in a fixed frame 2. The fixed frame 2 surrounds the centrifuge drum 5. Thus, the drive motor 3 is configured to rotate the rotating part 4 relative to the frame about the vertical axis of rotation (X).

[0082] In the centrifugal separator as shown in

[0083] Figure 2 a more detailed view of the centrifuge drum 5 of the centrifugal separator 1 is shown.

[0084] The centrifuge drum 5 forms (i.e., encloses) a separation space 9 within itself. In the separation space 9, a stack 10 of separation discs 10a is arranged coaxially about the axis of rotation (X) and axially below a top disc 11. Thus, the stack 10 is arranged to rotate with the centrifuge drum 5 and serves as a surface-expanding insert in the centrifuge drum 5, thereby providing for the efficient separation of a liquid mixture into at least a liquid light phase and a liquid heavy phase. Thus, in the separation space 9, centrifugal separation of, for example, a liquid feed mixture takes place during operation.

[0085] The separating discs 10a in stack 10 are separated from the distance piece. Such a piece is arranged on the conical part of the separating disc and is arranged such that a gap 35 is formed between adjacent separating discs 10a in the disc stack 10.

[0086] Stack 10 is supported at its axially lowest part by distributor 13. Distributor 13 includes a base part 13a and a central neck part extending upward from base part 13a. Distributor 13 is arranged to direct the liquid mixture from the central inlet 14 of centrifuge bowl 5 to a radial level in separation space 9.

[0087] Inlet 14 is in the form of a central inlet chamber formed inside or below distributor 13. Inlet 14 is for receiving the liquid feed mixture and is thus in fluid communication with the hollow interior 4b of main shaft 4a, through which the liquid feed is supplied to centrifuge bowl 5.

[0088] Inlet 14 communicates with separation space 9 via a passage 20 formed in or below the base part 13a of distributor 13.

[0089] Passage 20 can be arranged such that the liquid mixture is conveyed to a radial level corresponding to the radial level of cutouts 10c provided in separating discs 10a. Cutouts 10c form axial channels within the disc stack and distribute the liquid feed mixture over the entire disc stack 10.

[0090] The top disc 11 and the upper inner wall of centrifuge bowl 5 define at least one channel 25, which extends from the radially outer part of separation space 9 towards the central part of centrifuge bowl 5. The first liquid outlet 6 is arranged in a first outlet chamber 15, which is in fluid communication with at least one channel 25 for discharging the separated liquid heavy phase.

[0091] The radially inner part of disc stack 10 communicates with a second outlet 7 for the separated liquid light phase of the liquid feed mixture. Second outlet 7 is arranged in a second outlet chamber 8.

[0092] Centrifuge bowl 5 is further provided with outlets 17 at the radially outer periphery of separation space 9. These outlets 17 are evenly distributed around the axis of rotation (X) and are arranged for intermittently discharging the sludge component of the liquid feed mixture. The sludge component includes denser particles forming a sludge phase. As is known in the art, the opening of outlets 17 is controlled by an operating slide 18 actuated by operating water in channel 19. In its position shown in the figure, operating slide 18 seals against the upper part of centrifuge bowl 5 at its periphery, thus closing the connection between separation space 9 and the outlets 17 extending through centrifuge bowl 5.

[0093] In as Figure 1 andFigure 2 During the operation of the separator shown in, the centrifuge bowl 5 is rotated by the drive motor 3. Via the main shaft 4a, the liquid feed mixture to be separated is brought into the separation space 9. Depending on the density, the different phases in the liquid feed mixture separate between the separation disks 10a of the stack 10. The heavier components (such as the liquid heavy phase and the sludge phase) move radially outwards between the separation disks 10a to the radially outer part of the separation space 9, while the phase with the lowest density (such as the liquid light phase) moves radially inwards between the separation disks 10a and is forced through the second outlet 7 arranged in the second liquid outlet chamber 8. The higher density liquid is instead forced outwards through the passage 25 above the top disk 11 to the liquid outlet 6 for the liquid heavy phase. Thus, during separation, an interface between the lower density liquid and the higher density liquid forms in the centrifuge bowl 5, such as radially within the stack of separation disks. Solids or sludge accumulate at the periphery of the separation space and are intermittently emptied from within the centrifuge bowl by opening the sludge outlet 17, so that the sludge and a certain amount of fluid are discharged from the separation chamber 17 by means of centrifugal force. However, the discharge of the sludge can also be continuous, in which case the sludge outlet 17 takes the form of an open nozzle and a certain flow rate of sludge and / or heavy phase is continuously discharged by means of centrifugal force.

[0094] Figure 3 Shown are a first channel 31 and a second channel 32 extending in the bowl wall 30 of the centrifuge bowl 5. In this example, the first channel 31 and the second channel 32 have been formed by drilling, but they could also have been formed by another method, such as electrical discharge machining (EDM). The first channel 31 extends in a first direction D1 and the second channel 32 extends in a second direction D2 different from the first direction D1. D1 and D2 can be any direction relative to the axis of rotation X of the centrifuge bowl 5. The two channels 31, 32 intersect at an intersection point Y, where there is fluid contact between the first channel 31 and the second channel 32. Figure 3 Also shown in is a plane A, which will be referred to in connection with the discussion below regarding Figures 4 - 7 Thus, the plane A is a plane perpendicular to the direction or extension D1 of the first channel 31.

[0095] Figure 4 Shown is the cross-section of the first channel 31 as seen in the plane A as discussed above regarding Figure 3 Thus, the plane A is a plane perpendicular to the direction or extension D1 of the first channel 31. Figure 4Also schematically shown therein are internal force lines 5 of the material of the drum wall 30. These force lines 5 of the drum wall 30 represent the force flow around the first channel 31 generated when the centrifuge drum 5 is subjected to a stress σ, so that the stress σ can be the circumferential stress formed during the rotation of the centrifuge drum 5. The spacing between the force lines 50 reflects the stress concentration. As is known theoretically, as seen in plane A, stress concentration regions 40 are formed in the material near two opposite sides 31a, 31b of the first channel 31, and lower stress regions 41 are formed in the material near the other two opposite sides 31c, 31d of the first channel 31. If calculated around a hole in an infinite plate, the stress concentration in the stress concentration region 40 is three times that of the lower stress region 41 regardless of the size of the hole or (in this case) the diameter of the cross-section of the first channel 31. Therefore, the lower stress region 41 can be the region with the lowest stress in the drum wall 30 near the first channel.

[0096] Figure 5 represents a prior art situation in which a second channel 32 is formed to intersect the first channel 31. As shown in Figure 5, the second channel 32 is arranged such that its center lies on the first channel, i.e., such that the center line Z2 of the second channel is aligned with the center line Z1 of the first channel 31. Therefore, the center line Z2 of the second channel 32 is aligned with the direction D2 of the second channel 32. Additionally, in this prior art situation, the imaginary extension 32a of the second channel 32 entering the first channel 31 will surround the center line Z1 of the first channel 31.

[0097] The inventors have realized that if stress variations (which typically occur within a centrifuge drum, e.g., due to differences in rotational speed) occur, then such prior art solutions will result in a higher risk of fatigue cracks. Therefore, according to the present invention, the second channel 32 is arranged such that as seen in a cross-section in a plane A perpendicular to the direction D1 of the first channel 31, the second channel intersects the first channel 31 with its center line Z2 shifted towards the lower stress regions 31c, d. As Figure 6 indicated therein, where as seen in plane A, the second channel 32 is shifted towards the low stress region 41. This will reduce the risk of fatigue cracks in the centrifuge drum wall 30. As an example, as seen in a cross-section in a plane A perpendicular to the direction D1 of the first channel 31, the second channel 32 can be shifted with its center line Z2 towards the lower stress region 41 by a distance of at least half the radius of the first channel 31.

[0098] Figure 7 The embodiments therein show examples in which as seen in a cross-section in a plane A perpendicular to the direction D1 of the first channel 31, the second channel 2 is shifted with its center line Z2 towards the lower stress region 41 such that the imaginary extension 32a of the second channel 32 does not overlap with the center line Z1 of the first channel 31.

[0099] During rotation of the centrifuge bowl 5, as seen in a cross-section in a plane perpendicular to the direction (D2) of the second channel 32, stress concentration zones can also be generated in the bowl wall 30 on two opposite sides of the second channel 32, and lower stress zones can be generated in the bowl wall on the other two opposite sides of the second channel 32. The intersection point Y can then be shifted such that it lies both in the lower stress zone of the first channel 31 and in the lower stress zone of the second channel 32.

[0100] The first channel 31 and the second channel 32 can be arranged within the centrifuge bowl 5 such that the intersection point Y lies at a larger radius, i.e., at a location where the centrifugal force is large. As an example, and as Figure 8 shown, the centrifuge bowl 5 can have a radius R, and the intersection point Y can be arranged at a radius greater than 0.3R, such as greater than 0.5R.

[0101] As discussed above, the first channel 31 and the second channel 32 can be arranged at any position within the centrifuge bowl and for any purpose. This is schematically shown in Figure 8 which shows the centrifuge bowl 5 and its bowl wall 30. The first channel 31 and the second channel 32 can be arranged, for example, such that they are connected to a liquid outlet 6 for a separated liquid phase (such as a separated liquid heavy phase) for separation. Thus, the separated phase can flow within the first channel 31 and the second channel 32 towards the liquid outlet 5. Figure 8 Moreover, the first channel 31 and the second channel 32 form part of a liquid system 50 for intermittently discharging sludge from a sludge outlet. Thus, the first channel 31 and the second channel 32 can be arranged for transporting operating water to or from an operating water module (OWM) arranged outside the centrifuge bowl 5. As an example, the first channel 31 and the second channel 32 can be arranged for transporting the water required to press the operating slider 18 towards its upward position, thereby closing the sludge outlet 17 (see

[0102] ). Figure 1 )

[0103] The first channel 31 and the second channel 32 can also be used to provide lines for different sensors or actuators within the centrifuge bowl. As an example, and as Figure 8 shown, the centrifuge bowl 5 can include a sensor 51 for measuring physical properties of the centrifuge bowl 5 itself or physical properties within the centrifuge bowl 5. Such sensors can be, for example, temperature or pressure sensors for measuring the temperature and / or pressure of a liquid mixture separated in the separation space. Thus, the sensor 51 can be arranged for measuring the physical properties of the liquid mixture in the separation space. The first channel 31 and the second channel 32 can include at least one line for an electrical or optical connection from outside the bowl wall 30 to this sensor 51.

[0104] Figure 9 shows the basic steps of a method 100 for forming a first channel 31 and a second channel 32 in a drum wall 30 of a centrifuge drum 5 for a centrifuge separator 1. As discussed above with respect to Figures 1 - 8 As discussed above, this method can thus be used to form channels in a centrifuge drum. Method 100 includes a first step a): providing 01 a centrifuge drum 5, and a step b): forming 102 in the drum wall 30 a first channel 31 extending in a first direction D1, wherein the first channel 31 is formed such that during rotation of the centrifuge drum, as seen in a cross-section in a plane A perpendicular to the direction D1 of the first channel (31), stress concentration zones 40 are generated in the drum wall 30 on two opposite sides 31a, 31b of the first channel 31, and lower stress zones 41 are generated in the drum wall 3 on two other opposite sides 31c, 31d of the first channel 31.

[0105] Method 100 further includes a step c): forming 103 in the drum wall 30 a second channel 32 extending in a second direction D2 such that the first channel 31 and the second channel 32 intersect at an intersection point Y, at which there is fluid contact between the first channel 31 and the second channel 32, and wherein the second direction D2 is different from the first direction D1, and wherein the second channel 32 is formed such that as seen in a cross-section in a plane A perpendicular to the direction D1 of the first channel 31, the second channel intersects the first channel 31 with its centerline Z2 shifted towards the lower stress zones 31c, 31d.

[0106] Steps b) and c) can be carried out, for example, by drilling the first channel 31 and / or the second channel 32 or by using electrical discharge machining (EDM) to form the first channel 31 and / or the second channel 32.

[0107] As discussed above with respect to Figure 6 and Figure 7 As discussed above, the second channel 32 can be formed in step c) such that as seen in a cross-section in a plane A perpendicular to the direction D1 of the first channel 31, the second channel 32 is shifted with its centerline Z2 towards the lower stress zone 41 by a distance of at least half the radius of the first channel 31.

[0108] Moreover, as discussed above with respect to Figure 6 and Figure 7 As discussed above, the second channel 32 can be formed in step c) such that the second channel 32 is shifted with its centerline Z2 towards the lower stress zone 41 such that the imaginary extension 32a of the second channel 32 does not overlap with the centerline Z1 of the first channel 31.

[0109] In addition, the first channel 31 and the second channel 32 may intersect at a large radius. As an example, the centrifuge bowl 5 may have a radius R, and steps b) and c) may be performed such that the intersection point Y between the first channel 31 and the second channel 32 may be arranged at a radius greater than 0.3R, such as greater than 0.5R.

[0110] The invention is not limited to the disclosed embodiments, but may vary and change within the scope of the claims set forth below. The invention is not limited to the orientation of the axis of rotation (X) disclosed in the figures. The term "centrifugal separator" also includes centrifugal separators having an axis of rotation with a substantially horizontal orientation. Above, the inventive concept has mainly been described with reference to a limited number of examples. However, as will be readily understood by a person skilled in the art, within the scope of the inventive concept as defined by the appended claims, other examples in addition to the examples disclosed above are equally possible.

Claims

1. A centrifuge (1) for separating at least one liquid phase from a liquid feed mixture, comprising a frame (2), a drive member (3) and a rotating part (4), wherein the drive member (3) is configured to rotate the rotating part (4) about a rotation axis (X) relative to the frame (2), and wherein the rotating member (4) includes a centrifuge bowl (5) surrounding a separation space (9); wherein the centrifuge bowl (5) further includes an inlet (14) for receiving the liquid feed mixture and at least one liquid outlet (6, 7) for the separated liquid phases; wherein the separation space (9) includes a surface-expanding insert (10) for improving separation performance; and wherein the centrifuge bowl (5) includes a bowl wall (30), and a first channel (31) and a second channel (32) extend in the bowl wall, wherein the first channel (31) and the second channel (32) extend in different directions (D1, D2) but intersect at an intersection point (Y), at which there is fluid contact between the first channel (31) and the second channel (32); and wherein the first channel (31) is arranged such that during rotation of the centrifuge bowl (5), as seen in a cross-section in a plane (A) perpendicular to the direction (D1) of the first channel (31), stress concentration zones (40) are generated in the bowl wall (30) on two opposite sides (31a, 31b) of the first channel (31), and lower stress zones (41) are generated in the bowl wall (30) on the other two opposite sides (31c, 31d) of the first channel (31), and wherein the second channel (32) is arranged such that as seen in the cross-section in the plane (A) perpendicular to the direction (D1) of the first channel (31), the second channel intersects the first channel (31) with its center line (Z2) shifted towards the lower stress zones (31c, d).

2. The centrifugal separator (1) according to claim 1, wherein, The stress concentration zones (40) and the lower stress zones (41) are generated in the bowl wall due to circumferential stresses formed during rotation of the centrifuge bowl (5).

3. The centrifugal separator (1) according to claim 1 or claim 2, wherein, As seen in the cross-section in the plane (A) perpendicular to the direction (D1) of the first channel (31), the second channel (32) is shifted with its center line (Z2) towards the lower stress zone (41) by a distance of at least half the radius of the first channel (31).

4. The centrifuge separator (1) according to any one of the preceding claims, wherein, The second channel (32) is shifted with its center line (Z2) towards the lower stress zone (41) such that the imaginary extension (32a) of the second channel (32) does not overlap with the center line (Z1) of the first channel (31).

5. The centrifugal separator (1) according to any one of the preceding claims, wherein, The centrifuge bowl (5) has a radius R, and the intersection point (Y) is arranged at a radius greater than 0.3R, such as greater than 0.5R.

6. The centrifugal separator (1) according to any one of the preceding claims, wherein, The second channel (32) is arranged such that the intersection point (Y) between the first channel (31) and the second channel (32) is also shifted towards the lower stress zone of the second channel (32).

7. The centrifugal separator (1) according to any one of the preceding claims, wherein, The first channel (31) and the second channel (32) are connected to liquid outlets (6, 7) for the separated liquid phase.

8. The centrifuge separator (1) according to any one of the preceding claims, wherein, The centrifuge further includes a sludge outlet (17) arranged at the periphery of the centrifuge bowl (5).

9. The centrifugal separator (1) according to claim 8, wherein, The first channel (31) and the second channel (32) are part of a liquid system for intermittently discharging sludge from the sludge outlet.

10. The centrifuge separator (1) according to any one of the preceding claims, wherein, The centrifuge bowl (5) includes at least one sensor (51) for measuring physical properties of the centrifuge bowl (5) itself or physical properties within the centrifuge bowl (5), and wherein the first channel (31) and the second channel (32) include wires connected to the at least one sensor.

11. The centrifugal separator (1) according to any one of the preceding claims, wherein, The first channel (31) and / or the second channel (32) have been formed by a method selected from drilling and electrical discharge machining (EDM).

12. A method (100) for forming a first channel (31) and a second channel (32) in a bowl wall (30) of a centrifuge bowl (5) for a centrifuge separator (1), comprising the steps of: a) providing (101) the centrifuge bowl (5); b) forming (102) in the bowl wall (30) the first channel (31) extending in a first direction D1, wherein the first channel (31) is formed such that during rotation of the centrifuge bowl (5), as seen in a cross-section in a plane (A) perpendicular to the direction (D1) of the first channel (31), stress concentration zones (40) are generated in the bowl wall (30) on two opposite sides (31a, 31b) of the first channel (31), and lower stress zones (41) are generated in the bowl wall (30) on two other opposite sides (31c, 31d) of the first channel (31); c) forming (103) in the bowl wall (30) the second channel (32) extending in a second direction D2 such that the first channel (31) and the second channel (32) intersect at an intersection point (Y) where there is fluid contact between the first channel (31) and the second channel (32), and wherein the second direction D2 is different from the first direction D1, and wherein the second channel (32) is formed such that as seen in a cross-section in the plane (A) perpendicular to the direction (D1) of the first channel (31), the second channel intersects the first channel (31) with its centerline (Z2) shifted towards the lower stress zones (31c, d).

13. The method (100) according to claim 12, wherein, In step c), the second channel (32) is formed such that as seen in a cross-section in the plane (A) perpendicular to the direction (D1) of the first channel (31), the centerline (Z2) of the second channel (32) is shifted towards the lower stress zone (41) by a distance of at least half the radius of the first channel (31).

14. The method (100) according to claim 12 or claim 13, wherein, In step c), the second channel (32) is formed such that the second channel (32) is shifted with its center line (Z2) towards the lower stress region (41) such that the imaginary extension (32a) of the second channel (32) does not overlap with the center line (Z1) of the first channel (31).

15. The method (100) according to any one of claims 12 to 14, wherein The centrifuge drum (5) has a radius R, and steps b) and c) are carried out such that the intersection point (Y) is arranged at a radius greater than 0.3R, such as greater than 0.5R.

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