Separation of oil-water mixtures

Abstract

The present disclosure relates to a method for continuously separating an oil-containing aqueous liquid mixture having an oil content of 5% or less into a heavy aqueous phase and a light aqueous phase in a separation system (32), the method comprising: - conducting the liquid mixture from the tank (34) through an inlet conduit (36) into the inlet passage (22) of the centrifuge (2); - separating the liquid mixture in a centrifuge (2) into a heavy aqueous phase and a light phase; - determining an oil concentration parameter of the light phase; in response to the oil concentration parameter exceeding a threshold value; - directing the light phase through the light phase outlet passage (24) into a container (38) for the light phase; in response to the oil concentration parameter falling below a threshold value; - recycling the light phase from the light phase outlet passage (24) to the inlet passage (22); Includes.

Description

[Technical field]

[0001] The present invention relates to a method for separating an oil-containing aqueous liquid mixture and a separation system configured for separating an oil-containing aqueous liquid mixture. [Background technology]

[0002] The separation of the oil-containing aqueous liquid mixture into a heavy aqueous phase and a light oil-containing phase can be carried out in a high speed centrifuge. Separation of the light and heavy phases can be particularly problematic when the oil content of the oil-containing aqueous liquid mixture is low and when the oil content changes over time.

[0003] This may be the case, for example, in the case of the separation of so-called bilgewater on board a ship: Disposal of the separated heavy aqueous phase overboard requires a very low residual oil content, whereas large amounts of water separated in the light phase should be avoided in order to minimize the generation of slop liquids and their disposal costs.

[0004] US 2016 / 0339452 A1 discloses an example of separating an oil-containing aqueous liquid mixture, where the light phase is metered to automatically adjust the flow through the separator. US 7635328 A1 discloses an example of separating an oil-containing aqueous liquid mixture, but the example does not show a return conduit for recirculation of the light phase. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] US Patent Application Publication No. 2016 / 0339452 [Patent Document 2] U.S. Patent No. 7,635,328 Summary of the Invention

[0006] It would be advantageous to be able to separate a low oil water liquid mixture into a heavy phase and a light phase to accommodate changes in the oil content of an oil-water liquid mixture.

[0007] In particular, it is desirable to address operating conditions where the separated light phase also comprises a significant portion of the heavy aqueous phase portion of the liquid mixture. In order to better address one or more of these problems, a method and / or a separation system is provided having the features defined in the independent claims.

[0008] According to one aspect of the present invention, there is provided a method for continuously separating an oil-containing aqueous liquid mixture having an oil content of 5% or less into an aqueous heavy phase and a light phase in a separation system comprising a tank for the oil-containing aqueous liquid mixture, a centrifuge, an inlet conduit leading to the centrifuge, and a container for the light phase. The centrifuge comprises a bowl rotatable about an axis of rotation, a plurality of separating members arranged in a separation space defined by a body of the bowl, an inlet passage for the oil-containing aqueous liquid mixture connected to the inlet conduit, a light phase outlet passage, and a heavy phase outlet passage. The method comprises: - feeding the oil-water mixture from a tank through an inlet conduit into an inlet passage of the centrifuge; - separating the oil-containing aqueous liquid mixture in a centrifuge into a heavy aqueous phase and a light aqueous phase; - determining an oil concentration parameter of the light phase; in response to the oil concentration parameter exceeding a threshold value; - directing the light phase through a light phase outlet passage into a container for the light phase; in response to the oil concentration parameter falling below a threshold value; - recirculating the light phase from the light phase outlet passage to the inlet passage of the centrifuge; Includes.

[0009] The steps of providing the oil-water-containing liquid mixture, separating the oil-water-containing liquid mixture, and directing the light phase from the light phase outlet passage to the light phase vessel may be performed continuously.

[0010] According to a further aspect of the invention, there is provided a separation system configured for continuously separating an oil-water-containing liquid mixture having an oil content of 5% or less into a heavy aqueous phase and a light phase. The separation system comprises a tank for the oil-water-containing liquid mixture, a centrifuge, an inlet conduit leading to the centrifuge, a container for the light phase, and a control arrangement. The centrifuge comprises a bowl rotatable about an axis of rotation, a separating member disposed in a separation space defined by a body of the bowl, an inlet passage leading to the separation space for the oil-water-containing liquid mixture, a light phase outlet passage from the separation space, and a heavy phase outlet passage from the separation space. The control arrangement comprises a sensor and a controllable light phase valve arrangement. The light phase valve arrangement is fluidly connected to the light phase outlet passage, a light phase conduit connected to the container for the light phase, and a return conduit connected to the inlet passage of the centrifuge. The control arrangement is adapted to control, during use of the separation system, - determining the oil concentration parameters of the light phase; in response to the oil concentration parameter exceeding a threshold value; - controlling the light phase valve arrangement to direct the light phase from the light phase outlet passage to the light phase conduit; in response to the oil concentration parameter falling below a threshold value; - configured to control the light phase valve arrangement to recirculate the light phase from the light phase outlet passage to the return conduit.

[0011] Depending on the determined oil concentration parameter, the light phase is either led to a container for the light phase or recycled to the inlet passage of the centrifuge, so that the operating conditions determine the destination of the separated light phase, whereby the method and / or separation system avoids filling the container for the light phase with water if the light phase mainly comprises water. This is particularly advantageous when the oil content of the oil-water liquid mixture varies within the range of 0-5% and when there is a high risk of a high aqueous portion in the light phase.

[0012] In the separator, the radial level of the oil-water interface can vary, so that the heavy phase outlet passage can contain an excessive amount of oil. This is because the oil-water liquid mixture is composed of a high density oil, e.g., one with a density of 980 kg / m at 15°C. 3This can be particularly problematic when the light phase exceeds 100%. The present invention can reduce that risk by providing a separator with a sufficient light phase flow that always contains water. If the light phase contains mostly water, it can be returned to the inlet or feed tank. If it contains a large amount of oil, it can be directed to a slop tank.

[0013] In the broadest sense, the method and / or separation system is configured to continuously separate any oil-water-containing liquid mixture having a low concentration of oil. In particular, the concentration of oil in the oil-water-containing liquid mixture may vary over time. One example of an application of the method and / or separation system is the treatment of bilge water on ships, where the oil content may vary over time between 0-5%, 0-2%, or 0-0.5%. Another application of the method and / or separation system is, for example, the treatment of deck drains on ships or offshore platforms, and the deoiling of produced water in the field of crude oil production.

[0014] When this method is applied, i.e. during operation of the separation system, the oil content of the liquid mixture can vary within the range of 0-5%.

[0015] It should be noted that in practical operation the oil content of the liquid mixture can vary and even exceed 5% and even reach significantly higher levels. Under such high oil content conditions there is no risk that the separated light phase will contain mainly water. The invention applies again when the oil content of the liquid mixture falls below 5%.

[0016] The percentages may be % by volume. The term "oil content" relates to the amount of oil, e.g., the ratio or concentration of oil, contained in a liquid mixture, light phase, heavy phase, etc. The same applies to the term "water content" which relates to the amount of water.

[0017] The centrifuge is configured to separate the oil-water-containing liquid mixture into a heavy aqueous phase and a light aqueous phase. The oil-water-containing liquid mixture is the feed to the centrifuge and may be referred to herein simply as the liquid mixture. The liquid mixture may also include solid and / or liquid particles.

[0018] The separated aqueous heavy phase contains primarily water. Only small amounts of oil may remain in the heavy phase, such as less than 0.1%, less than 50 ppm, or less than 15 ppm. For bilge water treatment, if the separated heavy phase, i.e. water, is to be discharged overboard of the relevant vessel, the heavy phase must contain less than 15 ppm. In some regions, more stringent requirements may apply, such as 5 ppm or less.

[0019] The light phase may contain oil and / or water. Depending on the oil content of the liquid mixture, the oil content of the light phase may vary.

[0020] The threshold of the oil concentration parameter determines the level at which the amount of water in the light layer is considered low enough to be directed to the light layer vessel. The threshold of the oil concentration parameter may depend on the liquid mixture being separated. In some applications, such as bilge water cleaning, the threshold may be 25% or 50% oil content. In other applications, the threshold may be higher, for example 75% oil content or 90% oil content.

[0021] The oil concentration parameter may be directly related to the oil content of the light phase, or alternatively, the oil concentration parameter may be indirectly related to the oil content of the light phase.

[0022] The oil concentration parameter may be determined, for example, by measuring the amount of oil in the light phase, or by measuring the amount of water in the light phase, or by measuring any suitable indirect parameter, such as, for example, the water content, conductivity or transparency or density of the light phase. Determining the oil concentration parameter may involve calculations relating to the measurement data.

[0023] A sludge phase may also be separated in the centrifuge. Such a sludge phase may comprise water in which solid and / or liquid particles heavier than water are suspended. The sludge phase is separated at the periphery of the separation space and may be discharged from the separation space in a known manner, for example via an outlet that can be intermittently opened or closed.

[0024] The separation takes place in a separation space of the centrifuge, which comprises a separation member, which may be a disc arranged radially or axially around the axis of rotation, which may comprise, for example, a stack of frusto-conical separation discs.

[0025] The mixed liquor is introduced into the separation space along the axis of rotation. The separated light phase is discharged from the separation space along the axis of rotation or radially adjacent to the axis of rotation. The separated heavy phase may be discharged from the separation space along the axis of rotation or radially adjacent to the axis of rotation. According to some embodiments, a sludge phase may be separated from the liquid mixture and discharged from the radial periphery of the bowl.

[0026] When the centrifuge is in use, the bowl may rotate at several thousand revolutions per minute, such as 3,000 to 12,000 rpm. Thus, the centrifuge may be a high speed centrifuge.

[0027] The bowl may be disposed within a stationary housing of the centrifuge and may be driven to rotate about a vertical axis of rotation by a drive including, for example, an electric motor.

[0028] Here, the axial, radial, circumferential and rotational directions are defined with reference to the axis of rotation. The axial direction extends parallel to the axis of rotation of the bowl, the radial direction extends perpendicular to the axis of rotation, and the circumferential and rotational directions extend around the axis of rotation.

[0029] The flow of the light phase from the centrifuge through the light phase outlet passage may be different between the step of directing the light phase from the light phase outlet passage to the light phase container and the step of recycling the light phase from the light phase outlet passage to the inlet passage of the centrifuge, for example, during the step of directing the light phase to the light phase container, the flow of the light phase may be greater than during the step of recycling to the inlet passage.

[0030] The flow of the light phase during the recirculation step may be large enough to perform a step of measuring the oil content of the light phase. That is, the flow rate may be of a sufficient volume that the sensor of the control arrangement may reliably sense a parameter related to the oil content of the light phase. The appropriate flow rate will depend on the particular sensor used. In general, however, a flow rate that is too low may result in unreliable measurements, and a flow rate that is too high may reduce the capacity of the separation system.

[0031] According to an embodiment of the method, the step of recirculating the light phase may include directing the light phase to a tank. In this manner, the light phase having an oil concentration below the threshold may be directed to the tank and the liquid mixture therein for re-feeding from the tank to the inlet passage of the centrifuge. The recycled light phase may be mixed with the liquid mixture in the tank and / or held in the tank for a period of time before being fed to the inlet passage.

[0032] Similarly, according to an embodiment of the separation system, the return conduit may be connected to a tank for the oil-water liquid mixture.

[0033] According to an embodiment of the method, the step of recirculating the light phase may include a step of directly conducting the light phase to the inlet conduit. In this way, the light phase having an oil concentration below the threshold value may be mixed in the inlet conduit with the liquid mixture provided directly from the tank without being held in the tank.

[0034] Similarly, according to an embodiment of the separation system, the return conduit may be connected directly to the inlet conduit.

[0035] The control arrangement may include a heavy phase valve arrangement connected to the heavy phase outlet passage. According to an embodiment of the method, the step of recirculating the aqueous heavy phase from the heavy phase outlet passage to a tank via the heavy phase valve arrangement may be included. In this way, if the oil content of the aqueous heavy phase exceeds a desired or required level, the aqueous heavy phase may be returned to a tank upstream of the inlet passage of the centrifuge. Thus, it is ensured that the separation system does not produce an aqueous heavy phase with too high an oil content.

[0036] The control configuration of the separation system may include an oil content meter (OCM) upstream of the heavy phase valve configuration, so that the oil content of the heavy aqueous phase may be measured in order to control the heavy phase valve configuration.

[0037] According to an embodiment, the separating member may comprise a stack of separating discs, the separating discs being provided with distribution holes, the distribution holes being arranged in the radially inner half of the separating discs. In this way, the centrifuge may be configured as a thickener and thus in particular for the separation of low oil content aqueous liquid mixtures.

[0038] Further features and advantages of the present invention will become apparent from a review of the appended claims and the following detailed description. [Brief description of the drawings]

[0039] Various aspects and / or embodiments of the present invention, including particular features and advantages thereof, will be readily understood from the illustrative embodiments discussed in the following detailed description and the accompanying drawings.

[0040] [Figure 1] 1 shows a schematic cross-section of a centrifuge according to an embodiment. [Figure 2a] 1 illustrates a schematic diagram of an exemplary embodiment of a separation system; [Figure 2b] 1 illustrates a schematic diagram of an exemplary embodiment of a separation system; [Diagram 3] 1 shows a control configuration according to an embodiment. [Figure 4] 1 illustrates a method according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0041] Aspects and / or embodiments of the present invention are now described in more detail. Like numbers refer to like elements throughout. Well-known functions or constructions are not always described in detail for conciseness and / or clarity.

[0042] 1 shows a schematic cross-section of a centrifuge 2 according to an embodiment. The centrifuge 2 may form part of a separation system according to aspects and / or embodiments discussed herein. The centrifuge 2 may be utilized in aspects and / or embodiments of a method for separating an oil-containing aqueous liquid mixture discussed herein.

[0043] The centrifuge 2 comprises a bowl 4. The bowl 4 is rotatable about an axis of rotation 6. The bowl 4 is suspended on a spindle 8. The spindle 8 forms part of a drive for rotating the bowl 4 about the axis of rotation 6. The spindle 8 is supported in a housing 10 of the centrifuge 2, for example via two or more bearings. The housing 10 comprises a number of individual parts and can therefore be assembled from several parts.

[0044] In these embodiments, the drive electric motor 12 comprises part of the spindle 8, i.e., the spindle 8 and bowl 4 are directly driven by the electric motor 12. In alternative embodiments, the drive may instead comprise an electric motor connected to the spindle via a transmission including, for example, a gear or belt drive.

[0045] The body 14 of the bowl 4 defines a separation space 16 therein, within which continuous centrifugation of the liquid mixture takes place during operation of the centrifuge 2. Disposed within the separation space 16 is a separating member 18. In the illustrated embodiment, the separating member comprises a stack of frusto-conical separating discs 20. The stack of frusto-conical separating discs 20 is centrally mounted coaxially with the axis of rotation 6 and rotates together with the bowl 4.

[0046] The separating member 18 is capable of efficiently separating a liquid mixture, in this case an oil-water containing liquid mixture, into a light phase and a heavy aqueous phase.

[0047] The centrifuge 2 comprises an inlet passage 22 for the liquid mixture, a light phase outlet passage 24 for the light phase, and a heavy phase outlet passage 26 for the heavy aqueous phase. The inlet passage 22 leads into the separation space 16. The light phase outlet passage 24 leads from the separation space 16, and the heavy phase outlet passage 26 also leads from the separation space 16.

[0048] In the illustrated embodiment, during operation of the centrifuge 2, the liquid mixture to be separated is fed into the bowl 4 from the top center via inlet passage 22 and distributed from there into the separation space 16. The separated light phase is conducted upwardly from the radially innermost portion of the separation space 16 via light phase outlet passage 24. The separated heavy aqueous phase is conducted upwardly from a portion of the separation space 16 radially outward from the innermost portion of the separation space 16, for example, at or near the periphery of the separation space 16, via heavy phase outlet passage 26.

[0049] Centrifuges of this kind are known and come in many different types and sizes. The invention is generally applicable to centrifuges of this kind of different types and sizes. The invention is not limited to the type and arrangement of the inlet passage, the light phase outlet passage and the heavy phase outlet passage. The inlet passage and the outlet passage may, for example, be open and / or mechanically hermetically sealed and / or may be provided with a paring disk. They may be provided at the upper end of the bowl as shown in FIG. 1. Alternatively, one or more of them may be provided at the lower end of the bowl, for example via a spindle.

[0050] Some examples are: the inlet passage 22 may be hermetically sealed between the bowl 4 and the stationary part of the centrifuge 2; the light phase outlet passage 24 may be mechanically sealed between the bowl 4 and the stationary part of the centrifuge 2; the heavy phase outlet passage 26 may be mechanically hermetically sealed between the bowl 4 and the stationary part of the centrifuge 2; the mechanical hermetically sealed comprises two sealing members, one connected for rotation with the rotating bowl 4 and the other fixedly arranged on the associated stationary part. The two sealing members are arranged in sealing abutment with each other to provide a seal between the rotating bowl 4 and the stationary part during operation of the centrifuge. Instead of the heavy phase outlet passage 26 being mechanically hermetically sealed, the heavy phase outlet passage 26 may include a pairing disk connected to the stationary part and arranged within the heavy phase pairing chamber of the bowl 4; instead of the light phase outlet passage 24 being mechanically hermetically sealed, the light phase outlet passage 24 may include a pairing disk connected to the stationary part and arranged within the light phase pairing chamber of the bowl 4. As an alternative to a mechanically hermetically sealed inlet passage 22, the inlet passage 22 may be open and, optionally, the inlet passage 22 may be provided with a so-called hydrohermetic inlet formed by horizontally arranged weir / weirs and / or flange / flanges.

[0051] As mentioned above, the separating member 18 may comprise a stack of separating discs 20. The separating discs 20 may be provided with distribution holes 28 forming distribution channels extending substantially vertically through the stack of separating discs 20. Through the distribution channels, at least a part of the liquid mixture fed to the separation space 16 is distributed within the stack of separating discs 20. The distribution holes 20 may be arranged in the radially inner half of the separating discs 20. Thus, the centrifuge 2 may be configured as a thickener and may be particularly devised for separating a light phase containing oil from a low-oil aqueous liquid mixture, such as a mixture with an oil content of 5% or less.

[0052] The distribution holes 28 can be circular or elliptical. The number of distribution channels is in the range of 4-12.

[0053] According to some embodiments, the distribution holes may be elongated in the radial direction. Thus, the stack of separation disks and the distribution channels may be devised to achieve good separation of liquid mixtures with different oil contents even at high levels above 5%. In such embodiments, the elongated distribution holes may also extend to the radially outer half of the separation disk.

[0054] The liquid mixture contains solid and / or liquid particles that are heavier than water and these particles may be separated from the liquid mixture as part of the sludge phase.

[0055] According to some embodiments, the centrifuge 2 may comprise a sludge outlet passage 30 arranged at the radial periphery of the bowl 4. A control arrangement, as described below with reference to Figures 2a, 2b and the description of the separation system, may be configured to intermittently open the sludge outlet passage 30 to discharge the separated sludge phase.

[0056] 1, only one sludge outlet passage 30 is shown. The bowl 4 may be provided with further sludge outlet passages 30.

[0057] 2a and 2b show diagrammatically an exemplary embodiment of a separation system 32. The direction of flow in the passages and conduits is indicated by arrows.

[0058] 2a and 2b, separation system 32 is configured to separate an oil-water-containing liquid mixture having an oil content of 5% or less into a heavy aqueous phase and a light phase. Separation system 32 comprises a tank 34 for the oil-water-containing liquid mixture, centrifuge 2, an inlet conduit 36 ​​leading to centrifuge 2, a container 38 for the light phase, and a control arrangement 40. Inlet conduit 36 ​​is located downstream of tank 34.

[0059] The centrifuge 2 may be as described above with reference to Figure 1 and may comprise a bowl rotatable about a rotation axis, a separating member disposed in a separation space defined by the body of the bowl, an inlet passage 22 for the oil-containing water-containing liquid mixture leading to the separation space, a light phase outlet passage 24 from the separation space, and a heavy phase outlet passage 26 from the separation space.

[0060] The control arrangement 40 comprises a sensor 42 and a controllable light phase valve arrangement 44. Thus, the separation system 32 comprises a controllable light phase valve arrangement 44.

[0061] The light phase valve arrangement 44 is fluidly connected to the light phase outlet passage 24, to a light phase conduit 46 connected to the light phase container 38 and to a return conduit 48 connected to the inlet passage 22 of the centrifuge 2. Thus, via the light phase valve arrangement 44, the separated light phase from the light phase outlet passage 24 can be directed to the light phase container 38 or to the inlet passage 22.

[0062] The control arrangement 40 is configured, during use of the separation system 32, to: - determining an oil concentration parameter of the light phase. The determination of the oil concentration parameter may be performed at least in part by the sensor 42. A calculation unit 50 of the control arrangement may contribute to the determination of the oil concentration parameter. - in response to an oil concentration parameter exceeding a threshold value, controlling the light phase valve arrangement 44 to direct the light phase from the light phase outlet passage 24 to the light phase conduit 46. Thus, if the light phase has an oil concentration exceeding the threshold value, the light phase is directed via the light phase conduit 46 to the light phase vessel 38. The calculation unit 50 may adjust the light phase valve arrangement 44. In response to the oil concentration parameter falling below a threshold value, the light phase valve arrangement 44 is controlled to recirculate the light phase from the light phase outlet passage 24 to the return conduit 48. Thus, when the oil concentration of the light phase is below the threshold value, the light phase is directed via the return conduit 48 to the inlet passage 22 of the centrifuge 2. Again, the calculation unit 50 may adjust the light phase valve arrangement 44.

[0063] That is, it is ensured that the light phase has a constant oil concentration to be sent to the vessel for the light phase, thus avoiding unnecessary directing of the aqueous portion of the liquid mixture to the vessel for the light phase 38. A threshold level can be set in the control system to control the amount of the aqueous portion sent to the vessel for the light phase 38.

[0064] The sensor 42 may include one or more of a conductivity sensor, a capacitance (dielectric) sensor, an acoustic sensor, or any other suitable sensor capable of contributing to the determination of the oil content in the separated light phase.

[0065] The return conduit 48 may be provided with a flow restriction, for example a specific flow restriction element 49, or at least a part of the return conduit 48 has a small diameter in order to maintain a flow rate suitable for the sensor 42 and the calculation unit 50 to establish the oil concentration parameter and perform a comparison of the oil concentration parameter with a threshold value. A flow of light phase greater than necessary for this purpose may cause unnecessarily large amounts of light phase to be recirculated to the inlet passage 22.

[0066] Thus, the flow of the light phase from the centrifuge 2 through the light phase outlet passage 24 may differ depending on whether the separated light phase is directed to the light phase vessel 38 or recycled to the inlet passage 22. A greater flow of the light phase through the light phase conduit 46 to the light phase vessel 38 than through the return conduit 48 may be beneficial to ensure that separated light phase having an oil content above a threshold is easily directed to the light phase vessel 38.

[0067] In the illustrated embodiment, the light phase valve arrangement 44 comprises a controllable three-way valve. Alternatively, the light phase valve arrangement 44 may comprise, for example, two controllable two-way valves, one each disposed in the light phase conduit 46 and the return conduit 48.

[0068] According to an embodiment, the oil-containing water liquid mixture may be bilge water.

[0069] According to such an embodiment, the tank 34 for oil may be a bilge water tank on board the ship, in which the ship's bilge water is collected and from which it is supplied to the centrifuge 2 for removal of oil and, optionally, for removal of sludge. The vessel 38 for the light phase may be a slop oil tank.

[0070] In the embodiment of Fig. 2a, the return conduit 48 is directly connected to the inlet conduit 36. That is, during operation of the separation system 32, when the oil concentration parameter falls below a threshold value, the light phase is recirculated directly to the inlet conduit 36 ​​and the inlet passage 22 via the return conduit 48. In the inlet conduit 36, the recirculated light phase is added to the liquid mixture provided from the tank 34.

[0071] In the embodiment of Fig. 2b, the return conduit 48 is connected to a tank 34 for the oil-water liquid mixture, i.e. during operation of the separation system 32, when the oil concentration parameter falls below a threshold value, the light phase is recycled to the tank 34. In the tank, the light phase is mixed with the liquid mixture, and such mixture is fed to the inlet passage 22 via the inlet conduit 36.

[0072] The following features are described with reference to FIG. 2b, although one or more of them may also be implemented in the embodiment of FIG. 2a.

[0073] The separation system 32 may include a pump 52 for pumping the oil-water liquid mixture from the tank 34 to the inlet passage 22 of the centrifuge 2 .

[0074] Downstream of one or both of the light phase passage 24 and the heavy phase passage 26, the control arrangement 40 may comprise constant pressure valves 43, 45 in order to provide a suitable back pressure for the operation of the centrifuge 2, for example constant pressure valves 43, 45 are required in the case of a centrifuge with mechanically hermetically sealed outlet passages 24, 26. The constant pressure valves 43, 45 may be controlled by a computing unit 50.

[0075] The control arrangement 40, and therefore the separation system 32, may include a heavy phase valve arrangement 54 connected to the heavy phase outlet passage 26. The heavy phase valve arrangement 54 is configured to direct the heavy phase separated in the centrifuge 2 back to the tank 34 or to a heavy phase conduit 56 away from the separation system 32.

[0076] The control arrangement 40 upstream of the heavy phase valve arrangement 54 may include an OCM or other suitable sensor 58. The OCM / sensor 58 determines the oil content of the heavy aqueous phase separated in the centrifuge 2, and the calculation unit 50 is also utilized in this determination. The determined oil content is utilized to control the heavy phase valve arrangement 54.

[0077] Thus, if the oil content of the aqueous heavy phase is too high to be conducted out of the system 32, the aqueous heavy phase may be recirculated from the heavy phase outlet passage 26 to the tank 34 via the heavy phase valve arrangement 54. The aqueous heavy phase is mixed with the liquid mixture in the tank 34 and is ultimately fed to the inlet passage 22 of the centrifuge 2.

[0078] In the illustrated embodiment, the heavy phase valve arrangement 54 comprises a controllable three-way valve. Alternatively, the heavy phase valve arrangement 54 may comprise, for example, two controllable two-way valves, one each disposed in the heavy phase conduit 46 and the return conduit 48.

[0079] In the illustrated embodiment, the heavy phase valve arrangement 54 is connected to the light phase return conduit 48. In such an embodiment, a check valve 47 may be provided in the return conduit 48 to prevent the heavy phase from mixing with the separated light phase. Alternatively, the heavy phase valve arrangement 54 may be connected to a separate conduit leading to the tank 34.

[0080] In embodiments in which the centrifuge 2 comprises a sludge outlet passage 30, as shown in FIG. 1, the control arrangement 40 may be configured to control the discharge of the separated sludge phase via the sludge outlet passage.

[0081] The separation system 32 may comprise an oil filter 51 and a further valve arrangement 53 configured to direct the separated heavy phase through the oil filter 51 or to bypass the oil filter 51. The oil filter 51 may be a membrane filter or any other suitable filter for reducing / removing small amounts of residual oil from the aqueous heavy phase. For example, the oil filter 51 may be utilized to reduce the oil content of the heavy phase, for example from 15 ppm to 5 ppm or less, when required to dump water overboard in certain areas.

[0082] The further valve arrangement 53 may be controlled by the computing unit 50 and / or the OCM 58. In the illustrated embodiment, the further valve arrangement 53 comprises two two-way valves. Alternatively, the further valve arrangement 53 may include a three-way valve.

[0083] Figure 3 shows a control arrangement 40 according to an embodiment. The control arrangement 40 is adapted to be utilised in connection with different aspects and / or embodiments of the invention. The control arrangement 40 is also shown in Figures 1 to 2b.

[0084] The control arrangement 40 comprises a computation unit 50, which may take the form of substantially any suitable type of processor circuit or microcomputer, such as, for example, a circuit for digital signal processing (digital signal processor, DSP), a central processing unit (CPU), a processing unit, a processing circuit, a processor, an application specific integrated circuit (ASIC), a microprocessor, or other processing logic that may interpret and execute instructions. The expression computation unit used herein may represent a processing circuit comprising a plurality of processing circuits, such as, for example, any, some, or all of those mentioned above. The control arrangement 40 may comprise a memory unit 60. The computation unit 50 is connected to the memory unit 60, which provides the computation unit 50 with, for example, stored program code and / or stored data necessary to enable the computation unit 50 to perform the computation. The computation unit 50 may also be configured to store partial or final results of the computation in the memory unit 60. The memory unit 60 may comprise a physical device utilized to temporarily or permanently store data or programs, i.e., instruction sequences.

[0085] The control arrangement 40 further comprises one or more sensors and / or meters 42, 58 and one or more controllable valves 43, 44, 45, 53, 54. The control arrangement 40 communicates with the one or more sensors and / or meters and the one or more controllable valves via one or more of a cable, a data bus, e.g., a CAN (Controller Area Network) bus, a MOST (Media Oriented System Transport) bus, or other bus configuration, or a wireless connection. Although in the illustrated embodiment only one computing unit 50 and memory 60 are shown, the control arrangement 40 may comprise two or more computing units and / or memories.

[0086] The sensor may be a sensor 42 that provides data for determining an oil concentration parameter and / or an oil content of the light phase, and the meter may be an oil content meter 58. The controllable valves may form part of the controllable light phase valve arrangement 44 and the controllable heavy phase valve arrangement 54.

[0087] The calculation unit 50 may be configured to determine an oil concentration parameter and / or an oil content of the separated light phase based on data from the sensor 42. The calculation unit 50 may be configured to determine the oil content of the heavy phase or to receive an oil content value based on data from the oil content meter 58. The calculation unit 50 may be configured to compare the oil concentration parameter and / or the oil content value to a threshold value.

[0088] The control arrangement 40 may be configured to carry out the method 100 according to any one of the aspects and / or embodiments described herein, as described below with reference to FIG.

[0089] Figure 4 shows an embodiment of a method 100 for separating an oil-containing aqueous liquid mixture. The execution of the method 100 may be controlled by a control arrangement 40 as described above with reference to Figure 3. In the following, reference is also made to Figures 1 to 3.

[0090] The method 100 is applied for separating an oil-water-containing liquid mixture having an oil content of 5% or less into an aqueous heavy phase and a light phase in a separation system. The separation system may be a separation system 32 as described above with reference to figures 2a, 2b. The separation system 32 thus comprises a tank 34 for the oil-water-containing liquid mixture, a centrifuge 2, an inlet conduit 36 ​​leading to the centrifuge 2 and a container 38 for the light phase. The centrifuge may be a centrifuge 2 as described above with reference to figures 1 to 2b. The centrifuge 2 thus comprises an inlet passage 22 for the oil-water-containing liquid mixture connected to the inlet conduit 36, a light phase outlet passage 24 and a heavy phase outlet passage 26.

[0091] Method 100 is - a step 102 of feeding the oil-water liquid mixture from a tank via an inlet conduit 36 ​​into the inlet passage 22 of the centrifuge 2; - a step 104 of separating the oil-containing aqueous liquid mixture in a centrifuge 2 into an aqueous heavy phase and a light phase; - a step 106 of determining an oil concentration parameter of the light phase; In response to the oil concentration parameter exceeding a threshold value, - a step 108 of directing the light phase through the light phase outlet passage 24 into the light phase container 38; in response to the oil concentration parameter falling below a threshold value; - a step 110 of recirculating the light phase from the light phase outlet passage 24 to the inlet passage 22 of the centrifuge 2; The operating conditions thus determine the destination of the separated light phase, avoiding filling the light phase container 38 with water if the light phase mainly comprises water.

[0092] The light phase oil concentration parameter is the flow rate value of the oil content of the light phase.

[0093] The step 110 of recycling the light phase may include a step 112 of directing the light phase to the tank 34 (see also FIG. 2b). In this way, if the separated light phase has a high water content, it can be directed to the tank 34, from where it can be fed again to the inlet passage 22.

[0094] Alternatively, the step 110 of recirculating the light phase may include a step 114 of directing the light phase directly to the inlet conduit 36 ​​(see also FIG. 2a). In this way, if the separated light phase has a high water content, it may be mixed in the inlet conduit 36 ​​with the liquid mixture provided from the tank 34.

[0095] According to an embodiment, the oil-containing water liquid mixture may be bilge water.

[0096] According to an embodiment, in step 104 of separating the oil-containing aqueous liquid mixture into a heavy aqueous phase and a light phase, the heavy aqueous phase may have an oil content of less than 15 ppm. In this manner, the method 100 may be adapted to separate a heavy aqueous phase from bilge water, the heavy aqueous phase being suitable for disposal overboard.

[0097] According to an embodiment, the directing step 102 may include a step 116 of pumping the oil-water liquid mixture from the tank 34 to the inlet passage 22 of the centrifuge 2. In this manner, the liquid mixture may be transferred from the tank 34 to the centrifuge 2.

[0098] As mentioned above, the separation system 32 may include a light phase valve arrangement 44 connected to the light phase outlet passage 24. According to an embodiment of the method 100, the step 108 of directing the light phase may include a step 118 of directing the light phase via the light phase valve arrangement 44 to the light phase container 38, and the step 110 of recirculating the light phase may include a step 120 of directing the light phase via the light phase valve arrangement 44 to the inlet passage 22 of the centrifuge 2. In this manner, the flow of the separated light phase may be conveniently directed.

[0099] The separation system 32 may include a heavy phase valve arrangement 54 connected to the heavy phase outlet passage 26. According to an embodiment, the method 100 may include a step 122 of recirculating the aqueous heavy phase from the heavy phase outlet passage 26 to the tank 34 via the heavy phase valve arrangement 54. In this manner, the aqueous heavy phase may be returned to the tank 34 if the oil content of the aqueous heavy phase exceeds a desired or required level.

[0100] Prior to the step 122 of recirculating the heavy aqueous phase, a step of measuring the oil content of the separated heavy aqueous phase may be carried out, for example in the manner described above with reference to FIG. 2b.

[0101] As mentioned above, the centrifuge 2 may include a sludge outlet passage 30 disposed around the separation space 16 of the bowl 4 of the centrifuge 2. The method 100 includes: - a step 124 of separating the sludge phase from the oil-containing aqueous liquid mixture; - a step 126 of intermittently discharging the sludge phase via the sludge outlet passage 30; In this way, the particulate containing sludge phase can be removed from the oil-water liquid mixture.

[0102] According to a further aspect, a computer program is provided comprising instructions that, when the program is executed by a computer, cause the computer to perform the method 100 according to any one of the aspects and / or embodiments discussed herein.

[0103] Those skilled in the art will appreciate that the method 100 for separating an oil-containing aqueous liquid mixture having an oil content of 5% or less into an aqueous heavy phase and a light phase in a separation system 32 may be implemented by programmed instructions in the control arrangement 40 of the separation system 32. These programmed instructions are typically configured by a computer program, which, when executed in a computer or computing unit 50, ensures that the computer or computing unit 50 performs the desired control, such as the method steps 102-126 according to the invention. The computer program is typically part of a computer readable storage medium, including any suitable digital storage medium on which the computer program is stored.

[0104] The above describes various exemplary embodiments, and it should be understood that the present invention is defined solely by the appended claims. Those skilled in the art will appreciate that the exemplary embodiments may be modified and different features of the exemplary embodiments may be combined to create embodiments other than those described herein, without departing from the scope of the present invention as defined by the appended claims. [Explanation of symbols]

[0105] 2. Centrifuge 4 Rotating Bowl 6 Rotation Axis 8 Spindle 10. Housing 12 Electric motor 14 Main unit 16 Separation space 18 Separation member 20 Separation Disc 20 distribution holes 22 Entrance Passage 24 Light phase passage, light phase exit passage 25 Oil content 26 Heavy phase passage, heavy phase outlet passage 28 Separation Disc 30 Sludge outlet passage 32 Separation System 34 Tank 36 Inlet conduit 38 Light phase vessels 40 Control Configuration 42 Meters, sensors 43 Constant pressure valve 44 Light Phase Valve Configuration 45 Constant Pressure Valve 46 Heavy phase conduit 46 Light phase conduit 47 Check valve 48 Conduit 49 Limiting Factors 50 Computational Units 51 Oil filter 52 Pump 53 Valve configuration 54 Heavy-phase valve configuration 56 Heavy phase conduit 58 Oil content meter, sensor 60 Memory Unit ASIC Integrated Circuit CPU Central Processing Unit OCM oil meter

Claims

1. A method (100) for continuously separating an oil-water-containing liquid mixture having an oil content of 5% or less into a heavy aqueous phase and a light phase in a separation system (32) comprising a tank (34) for the oil-water-containing liquid mixture, a centrifuge (2), an inlet conduit (36) leading to the centrifuge (2), and a container (38) for the light phase, comprising: The centrifuge (2) comprises a bowl (4) rotatable about a rotation axis (6), a plurality of separating members (18) arranged in a separation space (16) defined by a body (14) of the bowl (4), an inlet passage (22) for an oil-water-containing liquid mixture connected to the inlet conduit (36), a light phase outlet passage (24), and a heavy phase outlet passage (26), The method comprises: - conducting (102) an oil-water liquid mixture from said tank (34) through said inlet conduit (36) into the inlet passage (22) of said centrifuge (2); - separating (104) the oil-containing aqueous liquid mixture in said centrifuge (2) into a heavy aqueous phase and a light aqueous phase; - determining (106) a light phase oil concentration parameter; In response to the oil concentration parameter exceeding a threshold value, - conducting (108) the light phase through said light phase outlet passage (24) into said container (38) for the light phase; in response to the oil concentration parameter falling below a threshold value, - a step (110) of recycling the light phase from said light phase outlet passage (24) to the inlet passage (22) of said centrifuge (2); The method of separating (100) comprising:

2. The method (100) of claim 1, wherein the step (110) of recirculating a light phase comprises the step (112) of directing a light phase to the tank (34).

3. The method (100) of claim 1, wherein the step (110) of recycling the light phase comprises the step (114) of conducting the light phase directly to the inlet conduit (36).

4. The method (100) according to any one of claims 1 to 3, wherein in the step (104) of separating the oil-containing aqueous liquid mixture into a heavy aqueous phase and a light phase, the heavy aqueous phase has an oil content of 15 ppm or less.

5. The method (100) for separating oil and water according to any one of claims 1 to 3, wherein the oil-containing liquid mixture is bilge water.

6. The method (100) of any one of claims 1 to 3, wherein the step (102) of directing comprises the step of pumping (116) the oil-water liquid mixture from the tank (34) to an inlet passage (22) of the centrifuge (2).

7. the separation system (32) comprising a light phase valve arrangement (44) connected to the light phase outlet passage (24); Directing (108) the light phase includes directing (118) the light phase through the light phase valve arrangement (44) to the container (38) for light phase; The method (100) for separating according to any one of claims 1 to 3, wherein the step (110) of recirculating a light phase comprises the step (120) of directing a light phase through the light phase valve arrangement (44) to an inlet passage (22) of the centrifuge (2).

8. the separation system (32) comprising a heavy phase valve arrangement (54) connected to the heavy phase outlet passage (26); 4. The method (100) of any one of claims 1 to 3, comprising the step (122) of recirculating the aqueous heavy phase from the heavy phase outlet passage (26) to the tank (34) via the heavy phase valve arrangement (54).

9. the centrifuge (2) comprises a sludge outlet passage (30) arranged around the separation space (16) of the bowl (4) of the centrifuge (2); The method (100) of any one of claims 1 to 3, comprising the steps of separating (124) a sludge phase from the oil-aqueous liquid mixture and intermittently discharging (126) the sludge phase via a sludge outlet passage (30).

10. A separation system (32) configured for continuously separating an oil-containing aqueous liquid mixture having an oil content of 5% or less into a heavy aqueous phase and a light phase, comprising a tank (34) for the oil-containing aqueous liquid mixture, a centrifuge (2), an inlet conduit (36) leading to the centrifuge (2), a container (38) for the light phase, and a control arrangement (40), The centrifuge (2) comprises a bowl (4) rotatable about a rotation axis (6), a separating member (18) arranged in a separation space (16) defined by a body (14) of the bowl (4), an inlet passage (22) leading to the separation space (16), a light phase outlet passage (24) from the separation space (16), and a heavy phase outlet passage (26) from the separation space (16), The control arrangement (40) comprises a sensor (42) and a controllable light phase valve arrangement (44); the light phase valve arrangement (44) is fluidly connected to the light phase outlet passage (24), to a light phase conduit (46) connected to a container (38) for the light phase, and to a return conduit (48) connected to the inlet passage (22) of the centrifuge (2); The control arrangement (40) during use of the separation system (32) comprises: - configured to determine an oil concentration parameter of the light phase; In response to the oil concentration parameter exceeding a threshold value, - configured to control said light phase valve arrangement (44) to direct the light phase from said light phase outlet passage (24) to said light phase conduit (46); in response to the oil concentration parameter falling below a threshold value, a separation system (32) configured to control said light phase valve arrangement (44) to recirculate the light phase from said light phase outlet passage (24) to said return conduit (48).

11. The separation system (32) of claim 10, wherein the return conduit (48) is connected to the tank (34) for the oil-water liquid mixture.

12. The separation system (32) of claim 10, wherein the return conduit (48) is directly connected to the inlet conduit (36).

13. A separation system (32) according to any one of claims 10 to 12, wherein the oil-containing liquid mixture is bilge water.

14. The separation system (32) according to any one of claims 10 to 12, wherein the centrifuge (2) comprises a sludge outlet passage (30) arranged on the radial periphery of the bowl (4), and the control arrangement (40) is configured to intermittently open the sludge outlet passage (30) to discharge a separated sludge phase.

15. A separation system (32) according to any one of claims 10 to 12, wherein the separation member (18) comprises a stack of separation disks (20), the separation disks (20) being provided with distribution holes (28), the distribution holes (28) being arranged in a radially inner half of the separation disks (28).

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