Centrifugal separator and method of operating a centrifugal separator

Abstract

The invention provides a centrifugal separator (1) for separating a liquid heavy phase and a liquid light 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) relative to the frame (2) about a rotation axis (X), and wherein the rotating part (4) comprises a centrifugal rotor (5) enclosing a separation space (9a) and a sludge space (9b). The separation space (9) comprises a stack (10) of separation discs (10a) arranged coaxially about the rotation axis (X), and wherein said sludge space (9b) is arranged radially outside said stack (10) of separation discs (10a). The centrifugal separator (1) further comprises an inlet (14) for receiving the liquid feed mixture into the centrifugal rotor (5), a first outlet (6) for the liquid heavy phase and a second outlet (7) for the liquid light phase. Furthermore, the centrifugal separator (1) further comprises a conduit system (30) for recirculating the separated liquid heavy phase discharged from the first outlet into the sludge space (9b) within the centrifugal rotor (5) of the centrifugal separator without mixing the recirculated separated liquid heavy phase with the liquid feed mixture. The centrifugal separator further comprises a sludge outlet in addition to the first and second outlets for discharging sludge separated from said liquid feed mixture. The invention also provides a method for separating a liquid heavy phase and a liquid light phase from a liquid feed mixture.

Description

Technical Field

[0001] This invention relates to the field of centrifugal separators, and more particularly to a method of operating a centrifugal separator (such as a centrifugal separator for cleaning marine fuel oil). Background Technology

[0002] Centrifuges are generally used for the separation of liquids and / or for the separation of solids and liquids. During operation, the liquid mixture to be separated is introduced into a rotating drum, and heavier particles or denser liquids (typically water) accumulate at the periphery of the drum, while less dense liquids accumulate closer to the central axis of rotation. This allows the separated portions to be collected, for example, by means of separate outlets located at the periphery and near the axis of rotation.

[0003] Fuel supplied to ships is typically treated on board before being used in engines to remove solid contaminants, such as particles of silicon and aluminum compounds called catalyst powder (e.g., microporous aluminum silicate or aluminosilicates called zeolites), and liquid contaminants such as water. Marine diesel engines can generally accept several types of commercially available fuel oils, provided they are adequately treated on board. Additionally, lubricating oils used in engines may also contain some solid and liquid impurities, such as water, that need to be separated before use.

[0004] Heavy phase recirculation is a well-known technique in oil separation, where the heavy phase, such as that used for water separation, is fed back to the inlet. This is to reduce the amount of light liquid (i.e., oil) separated from the heavy phase (i.e., water).

[0005] Therefore, water can be recycled to the inlet of the centrifuge, and this process will take place during a predetermined time period or until a certain amount of separated water has been collected in the separation chamber. When the predetermined time has elapsed, the so-called sludge outlet can be opened, allowing the separated solids, along with the water accumulated in the centrifuge rotor, to be ejected from the separation chamber.

[0006] However, there is still a need in the field to improve oil separation, such as separating water from fuel oil or lubricating oil. Summary of the Invention

[0007] The object of the present invention is to overcome, at least in part, one or more limitations of the prior art. In particular, one object is to provide a method and centrifugal separator having an enhanced ability to separate oil from, for example, water and dirt.

[0008] As a first aspect of the invention, a centrifugal separator is provided for separating a heavy liquid phase and a light liquid phase from a liquid feed mixture, comprising:

[0009] Frame, drive components, and rotating parts,

[0010] The drive component is configured to rotate the rotating part about the rotation axis (X) relative to the frame, and

[0011] The rotating part includes a centrifugal rotor that surrounds the separation space and the sludge space;

[0012] The separation space includes a stack of separation discs arranged coaxially around a rotation axis (X), and the sludge space is arranged radially outside the stack of separation discs.

[0013] The centrifuge further includes an inlet for receiving the liquid feed mixture into the centrifugal rotor, a first outlet for the heavy phase of the liquid, and a second outlet for the light phase of the liquid.

[0014] The centrifuge further includes a conduit system for recirculating the separated liquid heavy phase discharged from the first outlet to the sludge space within the centrifugal rotor of the centrifuge, without mixing the recirculated separated liquid heavy phase with the liquid feed mixture. The centrifuge further includes a sludge outlet in addition to the first and second outlets for discharging sludge separated from the liquid feed mixture.

[0015] Centrifuges are used for separating liquid feed mixtures. The liquid feed mixture can be an aqueous or oily liquid. As an example, a centrifuge can be used to separate impurities (such as water and / or particles) from oil (such as fuel oil or lubricating oil). The liquid feed mixture is thus separated into at least two phases: a light liquid phase and a heavy liquid phase. The heavy liquid phase has a higher density than the light phase. Centrifuges can be arranged to separate the liquid feed mixture into a light liquid phase, a heavy liquid phase, and a solid phase, i.e., a sludge phase.

[0016] The separated liquid heavy phase may include more than 50% by weight of liquid, such as more than 75% by weight of liquid, such as more than 90% by weight of liquid. Similarly, the sludge phase may include a small amount of liquid, but such as at least 50% by weight of solids, such as more than 75% by weight of solids.

[0017] The frame of the centrifuge is the non-rotating part, and the rotating part is supported by the frame by at least one bearing arrangement, which may include ball bearings. The rotating part of the separator may be arranged to rotate about a vertical axis of rotation, i.e., the axis of rotation (X) may extend vertically. The rotating part includes a centrifugal rotor. The centrifugal rotor is typically supported by a main shaft (i.e., the axis of rotation) and is therefore mounted to rotate with the main shaft. Thus, the rotating part may include a main shaft that is rotatable about the axis of rotation (X). The centrifuge may be arranged such that the centrifugal rotor is supported by the main shaft at one of its ends (such as at the bottom or top end of the main shaft).

[0018] The drive component for rotating the rotating part of the separator may include an electric motor having a rotor and a stator. The rotor may be fixedly connected to the rotating part, such as to a main shaft. Advantageously, the rotor of the electric motor may be provided on or fixed to the main shaft of the rotating part. Alternatively, the drive component may be provided alongside the main shaft and rotate the rotating part via a suitable transmission mechanism such as a belt or gear drive.

[0019] The centrifugal rotor is surrounded by rotor walls, which enclose a separation space and a sludge space. The separation space, where the fluid mixture is separated, comprises a stack of separation discs. For example, the separation discs may be metallic. Furthermore, the separation discs may be truncated conical separation discs, i.e., separation surfaces having a truncated conical portion forming the separation disc. The inclination angle of the separation surface relative to the radial direction can be in the range of 30-50 degrees, preferably about 40 degrees. The radially outer side of the stack of separation discs is the sludge space, in which the sludge and heavy phase separated during operation are collected. Therefore, the sludge space extends radially from the outer portion of the stack of separation discs to the inner periphery of the centrifugal rotor.

[0020] The separating discs are arranged coaxially around the axis of rotation (X) at a certain distance from each other, so that a passage is formed between every two adjacent separating discs. The separating discs in the disc group can be arranged such that the liquid mixture to be separated flows radially inward in the passage between every two adjacent separating discs in the stack.

[0021] As used herein, the term "axial" refers to a direction parallel to the axis of rotation (X). Therefore, relative terms such as "above," "upper," "top," "lower," "below," and "bottom" refer to relative positions along the axis of rotation (X). Correspondingly, the term "radial" refers to a direction extending radially from the axis of rotation (X). Therefore, "radially inner position" refers to a position closer to the axis of rotation (X) than "radially outer position."

[0022] The centrifuge can be arranged such that the separated heavy liquid phase moves toward the periphery of the separator space and is then guided to the first outlet above the stack of discs.

[0023] The centrifuge also includes an inlet for the liquid mixture to be separated (liquid feed mixture). This inlet is arranged to receive the liquid feed mixture and is centrally located in the centrifugal rotor, thus at the axis of rotation (X).

[0024] The first and second outlets are liquid outlets. The second liquid outlet, used for the light liquid phase, can be located at a smaller radius than the first liquid outlet.

[0025] The centrifuge further includes sludge outlets in addition to the first and second outlets for discharging sludge separated from the liquid feed mixture. Therefore, the separator may further include a third set of outlets for discharging sludge and heavy liquid phase accumulated in the sludge space. For this purpose, the centrifuge rotor may, for example, include a set of radial sludge outlets in the form of intermittently openable outlets at its outer periphery. Alternatively, the centrifuge rotor may include open nozzles at its outer periphery through which a certain flow rate of sludge and / or heavy phase is continuously discharged.

[0026] Therefore, a centrifugal separator may include a first liquid outlet for the heavy phase, a second liquid outlet for the light phase, and a sludge outlet for the separated sludge.

[0027] In one embodiment, the sludge outlet is arranged for intermittent discharge of sludge separated from the liquid feed mixture. Therefore, in such embodiments, the centrifuge drum may not have any outlet for continuous discharge of the separated sludge phase.

[0028] The first outlet and / or the second outlet may be arranged on the upper portion of the centrifugal rotor, such as axially above the stack of separation discs.

[0029] The first liquid outlet and the second liquid outlet may be arranged in a first outlet chamber and a second outlet chamber, respectively. These chambers may include a fixed water distribution device for discharging the separated liquid phase. Therefore, the first liquid outlet may be in the form of a first fixed water distribution device arranged in the first outlet chamber, and the second liquid outlet may be in the form of a second fixed water distribution device arranged in the second outlet chamber.

[0030] Therefore, during operation, the separated liquid phase can form a liquid rotating with the rotating part in the outlet chamber, and a fixed water distribution device arranged in the outlet chamber can be configured to distribute the liquid phase out of the centrifuge. The fixed water distribution device can be a water distribution plate such as an annular water distribution plate.

[0031] The centrifuge further includes a conduit system for recirculating the separated liquid heavy phase into the sludge space within the centrifugal rotor of the centrifuge, without mixing the recirculated separated liquid heavy phase with the liquid feed mixture. The conduit system may include pipes or channels both inside and outside the centrifugal rotor.

[0032] Therefore, the phrase "without mixing the recirculated separated heavy liquid phase with the liquid feed mixture" refers to the recirculating separated heavy liquid phase without mixing it with the liquid feed before it is supplied to the radially inner portion of the sludge space or at a location within the radially inner portion. Thus, the recirculated heavy phase is not mixed with the liquid feed mixture upstream of the sludge space (such as at the inlet of a centrifuge). However, once the recirculated heavy liquid phase is supplied to the sludge space, it can be mixed with the liquid feed mixture within the volume of the sludge space.

[0033] The first aspect of the invention is based on the understanding that the recirculated heavy phase can form a difficult-to-separate phase when mixed with the feed mixture. For example, during the separation of water from oil (such as lubricating oil and fuel oil), an emulsion between water and oil may form in the separator drum during conventional recirculation of the heavy phase (water) to the inlet feed. Such emulsions are even more difficult to separate in centrifugal separators. However, with the centrifugal separator according to the first aspect of the invention, the liquid heavy phase can be recirculated without mixing with the inlet feed before reaching the sludge space of the centrifugal rotor. Furthermore, the separation of the liquid heavy phase becomes more efficient through the construction of the conduit system, because the recirculated water does not need to be separated several times compared to prior art recirculation solutions.

[0034] In one embodiment, the conduit system is arranged to recirculate the separated liquid heavy phase to a radially inner location within the sludge space. This "radially inner location" can be within the radially inner half of the sludge space. This contrasts with pipes used for cleaning open nozzles arranged around the periphery of the rotating drum. Therefore, the conduit system can be arranged to recirculate the separated liquid heavy phase to the sludge space at a radial location located at the radially outer edge of the distributor. The distributor serves to hold the separation disc and guide the liquid feed mixture from the inlet into the separation space.

[0035] The centrifuge may include an inlet pipe extending into the centrifugal rotor for conveying a liquid feed mixture to the inlet. Furthermore, the inlet pipe may be arranged coaxially with the axis of rotation (X). In an embodiment of a first aspect of the invention, the centrifuge further includes an inlet pipe arranged to introduce the liquid feed mixture into the inlet, and a conduit system includes a recirculation inlet pipe disposed within the inlet pipe.

[0036] Therefore, a recirculation inlet pipe with a smaller outer diameter can be used to perform the recirculation of the separated heavy phase compared to the inner diameter of the inlet pipe used for the feed mixture. The inlet pipe can be a stationary inlet pipe. Alternatively, the recirculation inlet pipe can be a stationary pipe. The inlet pipe and the recirculation inlet pipe can be concentric pipes about the axis of rotation (X).

[0037] As an example, the inlet pipe can extend axially from the top into the centrifugal rotor. Therefore, the recirculation inlet pipe can also extend axially from the top into the centrifugal rotor.

[0038] In an embodiment of a first aspect of the invention, the stack of the separation disc is axially arranged on top of the distributor, and the conduit system includes at least one channel arranged axially below the distributor for guiding the recirculated liquid heavy phase radially outward into the sludge space.

[0039] Therefore, the stack of separation discs can be supported by the distributor. The inlet pipe can extend axially from the top through the distributor to the inlet.

[0040] The distributor is arranged to guide the liquid feed mixture from the inlet to the separation space. Therefore, the distributor may include or form a set of channels for guiding the liquid feed mixture. These channels may be arranged to guide the liquid feed radially outward.

[0041] The channel axially downward of the distributor may include different parts, such as grooves, recesses, channels, or guides on the centrifugal rotor.

[0042] At least one channel arranged axially below the distributor for guiding the recirculated liquid heavy phase into the sludge space may be arranged to guide the recirculated liquid heavy phase radially outward. Thus, at least one channel may have a radially external outlet arranged such that the recirculated heavy phase is conveyed below the distributor into the sludge space and then released into the sludge space at a radial location at the outer edge of the distributor.

[0043] Therefore, the recirculated heavy phase can be introduced into the sludge space at a radial position greater than that of the liquid feed introduced into the stack of the separation disc.

[0044] The disk stack can be further axially compressed between the top disk and the distributor. The top disk may have an outer radius larger than the separating disk of the disk stack, so as to guide the separated heavy phase out of the separator space axially upward from the top disk. The top disk may further have a greater thickness than the separating disk of the disk stack. In an embodiment, the top disk is integrally integrated with the wall of the centrifugal rotor. Therefore, the top disk may be formed from, for example, the inner wall of the upper portion of the centrifugal rotor.

[0045] Furthermore, the recirculation inlet pipe may extend to at least one channel arranged axially below the distributor. Thus, the recirculation inlet pipe may extend through the entire distributor and therefore may have an end portion near the channel below the distributor for conveying the recirculated liquid heavy phase to these channels.

[0046] In an embodiment of a first aspect of the invention, the centrifugal separator further includes a throttling valve arranged for throttling and separating the heavy phase of the liquid, wherein the throttling valve is arranged upstream of a first outlet for the heavy phase.

[0047] A throttle valve can be used to restrict the flow of the separated heavy phase liquid to a first liquid outlet and can have an opening sized for the intended liquid mixture to be separated. The throttle valve can be positioned at a radius greater than the radial position of the first liquid outlet (i.e., the heavy phase liquid outlet).

[0048] The separated liquid heavy phase can be axially guided above the top plate into a channel defined by the upper inner wall of the centrifugal rotor. A throttle valve can be arranged in this channel.

[0049] In an embodiment of a first aspect of the invention, the conduit system further includes a recirculation inlet and a conduit connecting a first outlet for the liquid heavy phase to the recirculation inlet.

[0050] The recirculation inlet can be arranged within the frame of the centrifuge. For example, the recirculation inlet can be connected to a recirculation inlet pipe as described above to introduce the recirculated liquid heavy phase into the recirculation inlet pipe.

[0051] As an example, the conduit connecting the first outlet for the liquid heavy phase to the recirculation inlet includes a valve device arranged to determine the amount of separated liquid heavy phase recirculated to the recirculation inlet.

[0052] The valve device can be a check valve used to completely shut off recirculation in the conduit system. Therefore, during operation, the heavy liquid phase may accumulate in the centrifugal rotor until the check valve opens. Thus, the valve device allows control over when the recirculation of the heavy liquid phase should occur.

[0053] As a first aspect of the construction, a centrifugal separator is provided for separating a heavy liquid phase and a light liquid phase from a liquid feed mixture, comprising:

[0054] Frame, drive components, and rotating parts,

[0055] The drive component is configured to rotate the rotating part about the rotation axis (X) relative to the frame, and

[0056] The rotating part includes a centrifugal rotor that surrounds the separation space and the sludge space;

[0057] The separation space includes a stack of separation discs arranged coaxially around a rotation axis (X), and the sludge space is arranged radially outside the stack of separation discs.

[0058] The centrifuge further includes an inlet for receiving the liquid feed mixture into the centrifugal rotor, a first outlet for the heavy phase of the liquid, and a second outlet for the light phase of the liquid.

[0059] The centrifuge further includes a conduit system for recirculating the separated heavy liquid phase discharged from the first outlet into the sludge space within the centrifugal rotor of the centrifuge, without mixing the recirculated separated heavy liquid phase with the liquid feed mixture.

[0060] The embodiments described above regarding the first aspect are compatible with the construction of the first aspect.

[0061] As a second aspect of the invention, a centrifugal separator is provided for separating a heavy liquid phase and a light liquid phase from a liquid feed mixture, comprising:

[0062] Frame, drive components, and rotating parts,

[0063] The drive component is configured to rotate the rotating part about the rotation axis (X) relative to the frame, and

[0064] The rotating part includes a centrifugal rotor that surrounds the separation space and the sludge space;

[0065] The separation space includes a stack of separation discs arranged coaxially around a rotation axis (X), and the sludge space is arranged radially outside the stack of separation discs.

[0066] The centrifuge further includes an inlet for receiving the liquid feed mixture into the centrifugal rotor, a first outlet for the heavy liquid phase, and a second outlet for the light liquid phase.

[0067] The centrifuge further includes a fixed inlet pipe arranged to introduce the liquid feed mixture into the inlet, and a conduit system at a radially internal location for introducing liquid into the sludge space of the centrifuge, wherein the conduit system includes a fixed recirculation inlet pipe arranged within the inlet pipe.

[0068] The radially inner location of the sludge space can be at the radially inner half of the sludge space, such as at the radially outer edge of the distributor. Furthermore, the centrifuge may include a sludge outlet in addition to the first and second outlets for discharging sludge separated from the liquid feed mixture. The sludge outlet can be used for intermittent sludge discharge.

[0069] This aspect generally offers the same or corresponding advantages as the first aspect. The effects and features of this second aspect are largely similar to those described above in combination with the first and second aspects. The embodiments mentioned with respect to the first aspect are largely compatible with the second aspect.

[0070] As a third aspect of the present invention, a method for separating a liquid heavy phase and a liquid light phase from a liquid feed mixture is provided, comprising the following steps:

[0071] a) Introducing the liquid feed mixture into a centrifugal separator according to a first aspect of the invention;

[0072] b) The separated light liquid phase is discharged from the centrifuge.

[0073] c) Discharge the separated heavy liquid phase from the centrifuge.

[0074] d) Recycle at least a portion of the discharged separated liquid heavy phase into the sludge space without mixing the recycled separated liquid heavy phase with the liquid feed mixture, and

[0075] e) The separated solid phase is discharged through a set of radial outlets arranged at the outer periphery of the centrifugal rotor.

[0076] This aspect generally offers the same or corresponding advantages as the preceding aspects. The effects and features of this third aspect are largely similar to those described above in conjunction with the first and second aspects. The embodiments mentioned with respect to the first and second aspects are largely compatible with the third aspect.

[0077] Step d) may include recirculating the separated liquid heavy phase to a radially inward location within the sludge space. Therefore, the radially inward location may be the radially inner half of the sludge space.

[0078] In a third aspect embodiment, the centrifugal separator includes an inlet pipe arranged to introduce a liquid feed mixture into an inlet, and wherein recirculation is performed via a recirculation inlet pipe arranged within the inlet pipe.

[0079] As discussed above, when a recirculated liquid heavy phase is introduced, the inlet pipe for the liquid feed mixture provides a suitable location for the recirculation inlet pipe.

[0080] As an example, the inlet pipe can extend axially from the top into the centrifugal rotor.

[0081] In an embodiment of a third aspect of the invention, the stack of the separation discs is arranged axially on top of the distributor, and wherein recirculation includes guiding the recirculated liquid heavy phase radially outward below the distributor.

[0082] Therefore, recirculation can be performed via a pipe extending downward from the top of the centrifuge to below the distributor in the inlet pipe, with the recirculated liquid heavy phase being guided radially outward from below the distributor.

[0083] As an example, step d) may include guiding the separated liquid heavy phase into the sludge space at a radial location located at the radial outer edge of the distributor.

[0084] Therefore, the method may include introducing the recirculated liquid heavy phase into the radially innermost position of the sludge space located radially outside the disk stack.

[0085] In an embodiment of the third aspect, step e) includes intermittently discharging the separated solid phase through a set of radial outlets arranged at the outer periphery of the centrifugal rotor.

[0086] As is known in the art, during intermittent discharge, the sludge, i.e., the solid phase, that accumulates around the centrifugal rotor can be discharged into the space beneath the frame outside the centrifugal rotor. The sludge may also include some liquid. In addition, some liquid heavy phase present in the centrifugal rotor may also be discharged during intermittent discharge.

[0087] The method may further include the step of stopping the recirculation flow during the separation of the liquid feed mixture introduced into the centrifugal separator.

[0088] As an example, step e) may further include introducing a displacement liquid into the centrifugal rotor via a conduit system for recirculating the separated liquid heavy phase before discharging the separated solid phase.

[0089] Therefore, the conduit system for recirculating the heavy phase of the liquid can also be used to introduce a displacement liquid before the solids are discharged. As is known in the art, the so-called displacement liquid (such as water) is generally supplied to the centrifuge rotor just before each opening of the sludge outlet. The purpose of supplying the displacement liquid is to reduce the amount of light liquid separated in the separation space so that this light liquid does not leave the separation space through the sludge outlet when the sludge outlet is opened. If the heavier component of the liquid to be separated is water, then water is generally used as the displacement liquid.

[0090] Introducing the replacement fluid via a conduit system such as a recirculation inlet pipe is also advantageous because it prevents the formation of emulsions within the centrifugal rotor.

[0091] Furthermore, the recirculation flow can be stopped during step e) of the intermittent solids discharge.

[0092] In an embodiment of the third aspect, the method includes performing only steps a) and b) during a first time interval, and performing all steps a) to d) during a second time interval.

[0093] Furthermore, step c) of discharging the separated heavy liquid phase can be performed at different outlet flow rates of the separated heavy liquid phase. Therefore, step c) can be performed by first allowing only no discharge or discharge of the separated heavy liquid phase at a first flow rate during a first time period, and then allowing discharge of the separated heavy liquid phase at a second flow rate greater than the first flow rate during a second time period.

[0094] Therefore, during operation, the liquid feed mixture can be separated into a heavy liquid phase and a light liquid phase. The light liquid phase can be continuously discharged from the second outlet of the separator, while the discharge of the separated heavy liquid phase via the first liquid outlet can be performed when enough heavy liquid phase has been separated from the liquid feed mixture in the centrifugal rotor, i.e., during a discontinuous time period.

[0095] In an embodiment of the third aspect, the liquid feed mixture is an oily mixture, and the liquid heavy phase is an aqueous phase such as water.

[0096] The oily mixture can be fuel oil or lubricating oil. The third method can be carried out on board. Attached Figure Description

[0097] The above and other objects, features, and advantages of the present invention will be better understood from the following exemplary and non-limiting detailed description with reference to the accompanying drawings. In the drawings, similar reference numerals will be used for similar elements unless otherwise stated.

[0098] Figure 1 A schematic diagram of a centrifugal separator according to an embodiment of the present invention is shown.

[0099] Figure 2 A schematic diagram of the cross-section of the centrifugal rotor is shown.

[0100] Figure 3 A flowchart of the method according to this disclosure is shown. Detailed Implementation

[0101] The centrifuge and method according to this disclosure will be further illustrated by the following description with reference to the accompanying drawings.

[0102] Figure 1 A cross-section of an embodiment of a centrifugal separator 1 configured to separate the heavy phase and the light phase from a liquid feed mixture is shown. The centrifugal separator 1 has a rotating portion 4 including a centrifugal rotor 5 and a drive shaft 4a.

[0103] The centrifuge 1 is further provided with a drive motor 3. This motor 3 may, for example, include a stationary element and a rotatable element surrounding and connected to the main shaft 4a, such that it transmits drive torque to the main shaft 4a and thus to the centrifugal rotor 5 during operation. 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 device. The transmission device may be in the form of a worm gear, which includes a pinion and an element connected to the main shaft 4a to receive the drive torque. The transmission device may alternatively take the form of a propeller shaft, a drive belt, etc., and the drive motor may alternatively be directly connected to the main shaft 4a.

[0104] exist Figure 2The centrifugal rotor 5, shown in more detail, is supported by a main shaft 4a, which is rotatably arranged in a frame 2 about a vertical axis of rotation (X) in a bottom bearing 22 and a top bearing 21. The fixed frame 2 surrounds the centrifugal rotor 5.

[0105] Figure 1 The diagram also shows an inlet pipe 14a extending axially from the top into the centrifugal rotor 5. After separation occurs within the centrifugal rotor 5, the separated heavy liquid phase is discharged through a fixed outlet pipe 6a, while the separated light liquid phase is discharged through a fixed outlet pipe 7a.

[0106] Figure 2 A more detailed view of the centrifugal rotor 5 of the centrifugal separator 1 is shown.

[0107] The centrifugal rotor 5 forms a separation space 9a within itself and a sludge space 9b located radially outside the separation space 9a. In the separation space 9a, the stack 10 of the separation discs 10a is arranged coaxially about the axis of rotation (X) and axially below the top disc 11, and is thus arranged to rotate together with the centrifugal rotor 5. The separation discs 10a provide efficient separation of the liquid mixture into at least a light liquid phase and a heavy liquid phase. Therefore, centrifugal separation, for example, of the liquid feed mixture occurs during operation in the separation space 9a.

[0108] The stack 10 is supported at its lowest axial portion by a distributor 13. The distributor 13 includes an annular conical base portion 13a arranged to guide liquid from the center of the centrifugal rotor 5 into a predetermined radial level in the separation space 9, and a central neck portion 13b extending upward from the base portion 13a.

[0109] In this embodiment, the sludge space 9b is confined between the upper portion 28 of the centrifugal rotor 5 and the axially movable operating slider 18.

[0110] The centrifuge 1 further includes an inlet 14 in the form of a central inlet chamber formed within or below the distributor 13, with a fixed inlet pipe 14a extending into the inlet 14 for supplying the liquid feed mixture to be separated. The inlet 14 communicates with the separation space 9 via a passage 20 formed in the base portion 13a of the distributor 13. The passage may be arranged such that the liquid mixture is conveyed to a radial level R1, which may correspond to the radial level of the outer portion of the stack of separation discs. For example, the radial level R1 may be at a radial level provided with a plurality of slits in the separation disc 10a. The slits may, for example, be in the form of slots provided at the radially outer portion of the separation disc 10a, opening toward the outer radius of the separation disc 10a. When the liquid feed mixture is oil, for example, this slot may be provided in the separation disc.

[0111] The upper inner wall portion 28 of the top plate 11 and the centrifugal rotor 5 defines at least one channel 25 extending from the radially inner portion of the sludge space 9b toward the central portion of the centrifugal rotor 5. A 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 heavy liquid phase. The first liquid outlet 6 is in the form of a fixed water distribution plate, which is arranged in the outlet chamber 15 for discharging the heavy phase into the outlet pipe 6a.

[0112] The radially inner portion of the stack 10 communicates with a second outlet 7 for separating the light phase of the liquid feed mixture. The second outlet 7 is arranged in a second outlet chamber 8. The second outlet 7 is in the form of a fixed distribution tray for discharging the light phase into an outlet pipe 7a. The distribution tray 12 is supported in the second outlet chamber 8 by a fixed inlet pipe 14a.

[0113] The centrifugal rotor 5 is also provided with outlets 17 at the radially outer periphery of the sludge space 9b. These outlets 17 are uniformly distributed around the rotor axis (X) and arranged for intermittent discharge of the sludge component of the liquid feed mixture. The sludge component comprises relatively dense particles that form the sludge phase. As is known in the art, the opening of the outlets 17 is controlled by means of an operating slider 18, which is actuated by operating water in the channel 19. In the position shown in the figure, the operating slider 18 is sealed against the upper portion 28 of the centrifugal rotor 5 at its periphery, thereby closing the sludge space 9b from connection with the outlets 17 extending through the centrifugal rotor 5.

[0114] However, centrifuge 1 can also be a solid-wall rotary centrifuge, that is, a centrifuge without an outlet around the centrifugal rotor 5.

[0115] like Figure 2 As seen, the centrifuge 1 also includes a conduit system 30 for recirculating the separated liquid heavy phase into the sludge space 9b within the centrifuge rotor 5 without mixing the recirculated separated liquid heavy phase with the liquid feed mixture. This is achieved by a fixed recirculation inlet pipe 31 arranged within a fixed inlet pipe 14a for the liquid feed mixture. The recirculation inlet pipe 31 connects to the recirculation inlet 31a at the top of the separator and then extends concentrically downward from the top through the inlet pipe 14a and inlet 14 to a position axially below the distributor 13. The size of the recirculation inlet pipe can be selected based on the required recirculation flow rate. As an example, the conduit system 30 can be arranged to recirculate the liquid heavy phase in the recirculation inlet pipe 14a at a flow rate of less than 20 m / s.

[0116] The recirculation inlet 31a is connected via conduit 34 to a fixed outlet pipe 6a for the liquid heavy phase. This conduit also includes a regulating valve 35 for determining whether the liquid heavy phase released from the separator should be recirculated via conduit 34 to the recirculation inlet 31a or released via conduit 44 to the discharge port. The regulating valve 35 can also be used to completely stop the discharge of the separated liquid heavy phase.

[0117] Furthermore, the recirculation inlet 31a is also connected to a liquid source 42. This liquid may be a displacement liquid, which may be introduced into the centrifugal rotor 5 via the recirculation inlet before the sludge is discharged via the sludge outlet 17. Valve 41 may be used to control whether the displacement liquid should be introduced into the centrifugal rotor. The liquid source 42 may, for example, be part of a ship's water system.

[0118] Furthermore, a throttling valve 33 is arranged upstream of the first outlet 6 for the heavy liquid phase. This throttling valve 33 is configured to throttle the heavy liquid phase discharged through the first outlet 6. The size of the throttling valve 33 can be selected based on the expected amount of heavy phase present in the liquid feed mixture to be separated.

[0119] The conduit system 30 further includes at least one channel 32 arranged axially below the distributor 13 for guiding the recirculated liquid heavy phase into the sludge space 9b. In this embodiment, these channels 32 below the distributor 13 include a radially inner portion 32b formed as a channel in a cone 40 that secures the centrifugal rotor 5 to the main shaft 4a. The channels below the distributor 13 further include a radially outer portion 32a arranged to guide the recirculated heavy phase into the sludge space just below or partially below the radially outer edge of the distributor (in this case, just below the radial edge of the base portion 13a of the distributor). Thus, as discussed above, at least one channel 32 below the distributor 13 is arranged to guide or release the recirculated liquid heavy phase into the sludge space at a radial position R2 greater than the radial position R1.

[0120] In such Figure 1 and Figure 2During operation of the separator shown, the centrifugal rotor 5 is rotated by the drive motor 3. The liquid feed mixture to be separated is brought into the separation space 9a via the inlet pipe 14a. Depending on density, different phases in the liquid feed mixture are separated between the separation discs 10a of the stack 10. Heavier components, such as the aqueous and sludge phases, move radially outward between the separation discs 10a to the sludge space 9b, while the least dense phases, such as the oil phase, move radially inward between the separation discs 10a and are forced through the second outlet 7 arranged in the second liquid outlet chamber 8. The higher density liquid is instead forced outward above the top disc through passage 25 to the liquid outlet 6 for the heavy phase, which is arranged at a radial distance greater than the radial horizontal distance of the outlet 7 for the light phase. A throttle valve 33 is used to determine the flow rate of the separated heavy liquid phase to the first outlet 6. However, a valve 35 downstream of the first liquid outlet 6 can be closed until sufficient heavy liquid phase is separated from the liquid feed mixture. Thus, opening the valve 35 allows the heavy liquid phase to be discharged via the first liquid outlet 6.

[0121] Therefore, during separation, an interface is formed between the lower-density liquid and the higher-density liquid in the centrifugal rotor 5, such as radially within the stack of the separation discs. In the sludge space, solids or sludge accumulate at the periphery of the sludge space 9b and are intermittently emptied from the centrifugal rotor through the open sludge outlet 17, thus discharging sludge and a certain amount of fluid from the separation chamber 17 by means of centrifugal force. However, sludge discharge can also occur continuously, in which case the sludge outlet 17 is in 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.

[0122] The discharged heavy liquid phase is recirculated back to the sludge space via a recirculation inlet pipe 31a and a passage 32 arranged axially below the distributor. In this way, the recirculated heavy phase, such as water, is prevented from mixing with the liquid feed mixture, such as oil, at the inlet.

[0123] Figure 3 A method 100 is shown for separating a heavy liquid phase and a light liquid phase from a liquid feed mixture. Method 100 includes the following steps:

[0124] a) Introduce the liquid feed mixture into centrifugal separator 101.

[0125] b) Discharge the light liquid phase separated by centrifuge 1 from centrifuge 1.

[0126] c) The heavy liquid phase separated by centrifuge 103 is discharged from centrifuge 1, and

[0127] d) Recycle at least a portion of the discharged separated liquid heavy phase 104 to sludge space 9b without mixing the recycled separated liquid heavy phase with the liquid feed mixture.

[0128] Centrifuges can be as described above. Figure 1 and Figure 2 As discussed.

[0129] This method is preferably used when the centrifugal separator 1 includes an inlet pipe 14a arranged for introducing a liquid feed mixture into an inlet 14 and wherein recirculation is performed via a recirculation inlet pipe 31 arranged within the inlet pipe 14a. As discussed above, the stack 10 of the separation discs 10a may be arranged axially on top of the distributor 13, and the recirculation in step d) may include guiding the recirculated liquid heavy phase radially outward below the distributor 13.

[0130] Furthermore, step d) may include guiding the separated liquid heavy phase into the sludge space 9b at a radial position located at the radial outer edge of the distributor 13. Therefore, step d) may include releasing the recirculated liquid heavy phase into the sludge space at a radial inner portion of the sludge space.

[0131] The method may further include step e): intermittently discharging the separated solid phase 105b through a set of radial outlets 17 arranged at the outer periphery of the centrifugal rotor 5. Step e) may further include introducing a displacement fluid 105a into the centrifugal rotor before discharging the separated solid phase. The displacement fluid may be supplied, for example, via a conduit system 3 for recirculating the separated liquid heavy phase.

[0132] The liquid feed mixture can be an oily mixture, and the liquid heavy phase can be an aqueous phase such as water. Therefore, this method can be used, for example, to clean fuel oil or lubricating oil on a ship. Figure 1 and Figure 2 During this oil cleaning period in the separator shown, the oil feed is continuously supplied through inlet pipe 14. After a certain period of separation operation, the cleaned oil continuously exits the centrifugal rotor 5 through the second liquid outlet 7. During this period, a certain amount of solids and a certain amount of water are separated from the oil flowing through the stack 10 of the separation disc 10a, and an interface layer between the oil and water may form at a certain radial level within the stack. Any water discharged via the first liquid outlet 6 is recycled back to the sludge space 9b. Recirculation is stopped, for example, by guiding the discharged water to the discharge port via conduit 44 before the sludge phase (i.e., the separated solids) is discharged, and replacement water is instead introduced via conduit system 30 to force the oil out of the centrifugal rotor to prevent oil loss during subsequent intermittent discharges. The sludge outlet 17 is opened for a duration long enough for all separated solids and replacement water to be ejected from the centrifugal rotor, but short enough to prevent oil loss. After the intermittent discharge, a new separation cycle begins, and the oil feed is supplied to the separator 1 again.

[0133] This invention is not limited to the disclosed embodiments, but can be varied and modified within the scope of the following claims. The invention is not limited to the orientation of the rotation axis (X) disclosed in the drawings. The term "centrifuge" also includes centrifuges having a substantially horizontally oriented rotation axis. In the foregoing, the inventive concept has been described primarily with reference to a limited number of examples. However, as will be readily understood by those skilled in the art, other examples besides those disclosed above are equally possible within the scope of the inventive concept as defined by the appended claims.

Claims

1. A centrifugal separator (1) for separating a heavy liquid phase and a light liquid phase from a liquid feed mixture, comprising: Frame (2), drive component (3) and rotating part (4). The drive component (3) is configured to cause the rotating part (4) to rotate about the axis of rotation (X) relative to the frame (2), and The rotating part (4) includes a centrifugal rotor (5) surrounding the separation space (9a) and the sludge space (9b); The separation space (9) includes a pile (10) of separation discs (10a) arranged coaxially around the axis of rotation (X), and the sludge space (9b) is arranged radially outside the pile (10) of the separation discs (10a). The centrifuge (1) further includes an inlet (14) for receiving the liquid feed mixture into the centrifugal rotor (5), a first outlet (6) for separating the heavy phase of the liquid, and a second outlet (7) for separating the light phase of the liquid. The centrifuge (1) further includes a conduit system (30) for recirculating the separated liquid heavy phase discharged from the first outlet into the sludge space (9b) within the centrifugal rotor (5) of the centrifuge, without mixing the recirculated separated liquid heavy phase with the liquid feed mixture. Furthermore, the centrifugal separator (1) further includes a third set of outlets (17) in addition to the first outlet (6) and the second outlet (7) for discharging sludge and heavy liquid phase accumulated in the sludge space (9b).

2. The centrifuge (1) according to claim 1, wherein, The conduit system (30) is arranged to recycle the separated liquid heavy phase to a radially inward location within the sludge space (9b).

3. The centrifuge (1) according to claim 1, further comprising an inlet pipe (14a) arranged for introducing the liquid feed mixture into the inlet (14), wherein the conduit system (30) includes a recirculation inlet pipe (31) arranged within the inlet pipe (14a).

4. The centrifugal separator (1) according to any one of claims 1-3, wherein, The third set of outlets (17) is arranged for intermittent discharge of sludge separated from the liquid feed mixture.

5. The centrifugal separator (1) according to any one of claims 1-3, wherein, The stack (10) of the separation disc (10a) is axially arranged on top of the distributor (13), and the conduit system (30) therein includes at least one channel (32) arranged axially below the distributor (13) for guiding the recirculated liquid heavy phase radially outward into the sludge space (9b).

6. The centrifuge according to claim 3, wherein, The stack (10) of the separation disc (10a) is axially arranged on top of the distributor (13), and the conduit system (30) therein includes at least one channel (32) arranged axially below the distributor (13) for guiding the recirculated liquid heavy phase radially outward to the sludge space (9b), and the recirculation inlet pipe (31) extends to the at least one channel (32) arranged axially below the distributor (13).

7. The centrifugal separator (1) according to any one of claims 1-3, wherein, The centrifugal separator (1) further includes a throttling valve (33) arranged for throttling the separated heavy liquid phase, wherein the throttling valve (33) is arranged upstream of the first outlet (6) for the heavy liquid phase.

8. The centrifugal separator (1) according to any one of claims 1-3, wherein, The conduit system (30) further includes a recirculation inlet and a conduit connecting the first outlet (6) for the heavy phase of the liquid to the recirculation inlet.

9. The centrifuge (1) according to claim 8, wherein, The conduit connecting the first outlet (6) for the liquid heavy phase to the recirculation inlet includes a valve device arranged to determine the amount of separated liquid heavy phase recirculated to the recirculation inlet.

10. A method for separating a heavy liquid phase and a light liquid phase from a liquid feed mixture, comprising the following steps: a) Introducing the liquid feed mixture into a centrifugal separator (1) according to any one of claims 1 to 9; b) Discharge the separated light liquid phase from the centrifuge (1), c) Discharge the separated heavy liquid phase from the centrifugal separator (1), d) Recycle at least a portion of the discharged separated liquid heavy phase into the sludge space (9b) without mixing the recycled separated liquid heavy phase with the liquid feed mixture, and e) The liquid heavy phase and the separated solid phase accumulated in the sludge space (9b) are discharged through a set of radial outlets arranged at the outer periphery of the centrifugal rotor (5).

11. The method according to claim 10, wherein, The centrifuge (1) includes an inlet pipe (14a) arranged to introduce the liquid feed mixture into the inlet (14), and wherein the recirculation is performed via a recirculation inlet pipe (31) arranged within the inlet pipe (14a).

12. The method according to claim 10, wherein, The stack (10) of the separation disc (10a) is axially arranged on top of the distributor (13), and the recirculation includes guiding the recirculated liquid heavy phase radially outward below the distributor (13).

13. The method of claim 12, wherein step d) comprises guiding the separated liquid heavy phase into the sludge space (9b) at a radial position located at the radial outer edge of the distributor (13).

14. The method according to any one of claims 10 to 13, wherein, Step e) includes The separated solid phase is intermittently discharged through a set of radial outlets arranged at the outer periphery of the centrifugal rotor (5).

15. The method according to claim 14, wherein, Step e) further includes introducing a displacement liquid into the centrifugal rotor via the conduit system (30) for recirculating the separated liquid heavy phase before discharging the separated solid phase.

16. The method according to any one of claims 10 to 13, wherein, The liquid feed mixture is an oily mixture, and the liquid heavy phase is an aqueous phase.

17. The method according to claim 16, wherein, The heavy phase of the liquid is water.

18. The method according to any one of claims 10 to 13, wherein, Step d) includes recirculating the separated liquid heavy phase to a radially inward location within the sludge space (9b).

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