Method for operating system comprising centrifugal separator

Abstract

The invention provides a method (100) for operating a system (1) comprising a centrifugal separator (2) for separating at least one liquid phase and a sludge phase from a liquid feed mixture. The method (100) includes alternating between a first mode of operation and a second mode of operation. The first mode of operation comprises the steps of: a) supplying (101) the liquid feed mixture to be cleaned to the centrifugal separator (2), the liquid feed mixture having a first temperature; and b) discharging (102) the at least one separated liquid phase from the centrifugal separator (2). The second mode of operation comprises the steps of: c) stopping (103) the supply of the liquid feed mixture to the centrifugal separator (2); and d) reducing (104) the temperature of the liquid feed mixture to a second temperature and / or reducing (105) the flow rate of the liquid feed mixture. The invention also provides a system (1) for separating at least one liquid phase and a sludge phase from a liquid feed mixture.

Description

Technical Field

[0001] The present invention relates to the field of centrifugal separators, such as those used for cleaning fuel oil on board ships, and more particularly to reducing the power consumption of a system comprising a centrifugal separator. Background Art

[0002] Centrifugal separators are generally used to separate liquids and / or solids from liquid or gas mixtures. During operation, the fluid mixture to be separated is introduced into a rotating drum. Due to centrifugal force, heavy particles or denser liquids such as water accumulate at the periphery of the drum, while less dense liquids accumulate closer to the central axis of rotation. This allows the separated fractions to be collected, for example, using different outlets arranged at the periphery and close to the axis of rotation, respectively.

[0003] Fuel supplied to ships is typically treated on board before use in the engines to remove solid contaminants known as catalyst fines, such as particles of silicon and aluminum compounds (e.g., microporous aluminum silicates or aluminosilicates known as zeolites), and liquid contaminants such as water. Marine diesel engines typically accept several types of commercially available fuel oil, provided they are adequately treated on board. Furthermore, the lubricating oil used in the engines may also contain a portion of solid and liquid impurities, such as water, which need to be separated before use.

[0004] Separating fuel oil from lubricating oil is a very energy-intensive application. As an example, when separating HFO (heavy fuel oil) to be used as fuel on ships, the oil is typically heated from 50°C to 98°C. To operate a common separator size with a capacity of ~5m3 / h, the energy required to heat the feed is ~130kW.

[0005] Therefore, there is a need in the art for improved separation procedures in order to reduce the overall energy consumption of the separation system. Summary of the Invention

[0006] A primary object of the present invention is to provide a system and method for reducing the overall energy consumption of a separation process, such as the separation of fuel oil or lubricating oil on board a ship.

[0007] As a first aspect of the present invention, there is provided a method for operating a system comprising a centrifugal separator for separating at least a liquid phase and a sludge phase from a liquid feed mixture, the method comprising alternating between a first operating mode and a second operating mode, wherein the first operating mode comprises the following steps a) supplying the liquid feed mixture to be cleaned to the centrifugal separator, the liquid feed mixture having a first temperature; b) discharging at least one separated liquid phase from the centrifugal separator; And the second operation mode includes the following steps c) stopping said supply of liquid feed mixture to the centrifugal separator; and d) reducing the temperature of the liquid feed mixture to a second temperature and / or reducing the flow rate of the liquid feed mixture.

[0008] The system may include a centrifugal separator and associated equipment for influencing process parameters of the liquid feed mixture to be separated, such as the flow rate and temperature of the liquid feed mixture.

[0009] The method comprises two different operating modes, namely a first operating mode in which at least steps a) and b) are performed, and a second operating mode during which at least steps c) and d) are performed.

[0010] The method includes alternating between a first mode and a second mode in a cyclic manner, i.e., executing the first mode, then executing the second mode, and then executing the first mode again, etc. Thus, in a further cycle of executing all steps a)-d), steps a) and c) may be executed after steps c) and d). Thus, the second mode may be executed immediately after the first mode, and vice versa.

[0011] However, the two modes may be performed during different time periods. As an example, a first mode in which a liquid feed mixture is supplied to and separated in a centrifugal separator may be performed during most of the time, while a second mode may be performed during intermittent time periods, such as during short pauses during operation in the first mode.

[0012] A centrifugal separator is used to separate at least one liquid phase and a sludge phase from a liquid feed mixture. Thus, the centrifugal separator can be configured to separate the liquid feed mixture into a single liquid phase and a sludge phase, or into two liquid phases and a sludge phase. The centrifugal separator can include a fixed frame and a drive member configured to rotate a centrifuge barrel within the frame. The centrifuge barrel encloses a separation space. The separation space can include a stack of separation discs centrally arranged around an axis of rotation. Such separation discs form surface-enlarging inserts in the separation space. The separation discs can have a frustoconical form, i.e., the stack can be a stack of frustoconical separation discs.

[0013] Thus, step a) of supplying the liquid feed mixture to be cleaned to the centrifugal separator may comprise supplying the liquid feed mixture from, for example, a tank for storing the liquid feed mixture (such as via an inlet pipe leading to the separation space) to the separation space of the centrifugal separator. The liquid feed mixture has a first temperature during step a). The first temperature may be above room temperature, such as above 50° C., such as above 90° C.

[0014] Step b) of discharging at least one separated liquid phase may be the continuous discharge of at least one separated liquid phase, such as the continuous discharge of only the first separated liquid phase or the continuous discharge of the first and the second separated liquid phase.

[0015] During the second operating mode, step c) is performed, i.e., the supply of the liquid feed mixture to the centrifugal separator is stopped. However, the liquid feed mixture to be separated can still flow to other parts of the system, such as being recycled to a storage tank from which it is supplied to the centrifugal separator. Thus, during step c), the liquid feed mixture can still have a flow rate greater than zero.

[0016] Furthermore, during the second mode, during step d), the temperature of the liquid feed mixture is reduced to a second temperature below the first temperature or the flow rate of the liquid feed mixture is reduced, or alternatively, both measures are performed, i.e., the temperature of the liquid feed mixture is reduced to a second temperature below the first temperature and the flow rate of the liquid feed mixture is reduced.

[0017] Step d) is performed during step c), ie during the time when the liquid feed mixture is not supplied to and therefore does not enter the centrifugal separator.

[0018] Thus, step d) may comprise reducing the temperature of the liquid feed mixture to a second temperature and / or reducing the flow rate of the liquid feed mixture when the liquid feed mixture is not supplied to the centrifugal separator.

[0019] A first aspect of the present invention is based on the insight that during the second operating mode, i.e., during the time of the entire process when no actual separation is performed in the separator, power-saving measures can be implemented on the liquid feed mixture to be separated. This can be done, for example, during a stoppage of the centrifugal separator or during the discharge of the sludge phase. It has been found that such power-saving measures still allow a good process and separation when the first operating mode is continued after the second operating mode. This has been found to be an advantage during the separation of bunker fuel, where the feed of oil to be separated is cut off or directed away from the separator during the discharge of the separated sludge. Such a discharge sequence can take approximately 60-200 seconds, such as between 90-150 seconds, during which the feed of oil to be separated has previously been run in recirculation and is still heated to 98°C. The inventors have found that reducing heating, for example during such a discharge sequence (second operating mode), still allows good separation performance when the feed is also directed back to the separator (first operating mode).

[0020] Therefore, in an embodiment of the first aspect of the present invention, the second operation mode further comprises the following steps: e) Discharge the separated sludge phase from the centrifugal separator.

[0021] Thus, the second operating mode may comprise an actual discharge sequence.Such a discharge sequence, ie the second operating mode, may be less than 3 minutes and may be performed less than 5 times, such as less than 3 times per hour during normal separation of, for example, bunker fuel.

[0022] Step e) may also include supplying a displacement liquid to the centrifugal separator. As is known in the art, so-called displacement liquid (such as water) is usually supplied to the centrifuge drum just before each discharge of the sludge. The purpose of supplying the displacement liquid is to reduce the amount of separated liquid phase in the separation space so that no such separated liquid phase leaves the separation space through any sludge outlet during the discharge. As an example, if the heavier liquid to be separated from the liquid feed mixture is water, water is usually used as the displacement liquid.

[0023] However, the centrifuge can also remain in standby mode during the second operating mode. This standby mode can include, for example, reducing the centrifuge's rotational speed before stopping the centrifuge. As an example, the centrifuge can be in standby mode for up to 10 minutes before stopping. Thus, lowering the feed temperature to the second temperature or reducing the flow rate of the liquid feed mixture (i.e., step d)) can also be performed during the centrifuge's standby mode to save energy.

[0024] In an embodiment of the first aspect, the method is a method for onboard treatment of fuel oil, ie a method for use on board a ship.

[0025] In an embodiment of the first aspect, step a) comprises supplying the liquid feed mixture from a tank, and step c) further comprises recycling the liquid feed mixture to the tank.Thus, the second operating mode may comprise recycling of the liquid feed mixture.

[0026] However, the second operating mode may also include actually stopping the flow of the liquid feed mixture.

[0027] In an embodiment of the first aspect, step a) comprises heating the liquid feed mixture to the first temperature using a heating device.

[0028] The heating device may be an electric heater. However, the heating device may also be a steam / hot water / hot oil heat exchanger. The first temperature may be above room temperature, such as above 50°C, such as above 90°C.

[0029] Step d) may comprise lowering the temperature by at least 10°C, such as at least 20°C, such as at least 30°C, such as at least 40°C.

[0030] Step d) of reducing the temperature of the liquid feed mixture to a second temperature may involve lowering the setpoint temperature of the heating device to the second temperature. Thus, the actual measured temperature of the liquid feed mixture during step d) may be higher than the second temperature. Thus, setting a lower setpoint temperature for the heating device saves energy.

[0031] As an example, step d) may comprise switching off the heating means.

[0032] In an embodiment of the first aspect, step a) comprises supplying the liquid feed mixture using a liquid feed pump.

[0033] In order to reduce the flow rate of the liquid feed mixture during step d), the set point flow rate of such feed pump may be reduced.

[0034] As an example, step d) may comprise shutting down the liquid feed pump.

[0035] In an embodiment of the first aspect, the liquid feed mixture is oil, and the first temperature in step a) is at least 50°C.

[0036] The separation temperature is usually determined by the viscosity of the oil. When processed in a separator, the lower the viscosity of the oil, the higher the separation efficiency.

[0037] The oil may be a lubricating oil or a fuel oil, such as fuel oil for a diesel engine.

[0038] The term "fuel oil for diesel engines" herein refers to an oil intended for use in an engine for generating power, such as an engine on board a ship or in a power plant. The term "fuel oil" may be as defined in ISO 8217, Petroleum Products - Fuels (Class F) - Marine Fuel Specification, 2005 and 2012 editions, or an oil component / phase derived from the pretreatment of such oil prior to use in an engine on board a ship or in a power plant. Diesel oil is considered herein to be fuel oil. Thus, fuel oil may be marine (residual) fuel oil (MFO) or Bunker C oil.

[0039] "Fuel oil for diesel engines" may consist of different types of fuel oil with different viscosities, generally stored in tanks, which means that the type of fuel oil sent to the separator for cleaning may differ over time.

[0040] As an example, fuel oils for diesel engines include heavy fuel oils (HFOs).HFOs are residual oils from distillation or from cracking in the processing of mineral oils.

[0041] Thus, step a) can comprise cleaning a fuel oil in a centrifugal separator to provide a cleaned oil phase and optionally a sludge phase and a water phase. The sludge phase can comprise solid impurities such as cat fines. Cat fines are a residue from a crude oil refining process called catalytic cracking, in which long hydrocarbon molecules are cracked into shorter molecules.

[0042] As an example, the liquid feed mixture can be a fuel oil, and the first temperature in step a) can be at least 50 °C, such as at least 70 °C, such as at least 95 °C, such as about 98 °C.

[0043] Further, when the liquid feed mixture is an oil and the first temperature in step a) is at least 50 °C, step d) can comprise reducing the temperature of the oil to a second temperature that is at least 10 °C lower than the first temperature.

[0044] As an example, the liquid feed mixture can be a fuel oil for a diesel engine, and the first temperature is at least 97 °C, and wherein step d) comprises reducing the oil to a temperature below 80 °C, such as below 70 °C.

[0045] Thus, in embodiments of the first aspect, there is provided a method for operating a system comprising a centrifugal separator for separating a cleaned oil phase and a sludge phase from a fuel oil, the method comprising alternating between a first operating mode and a second operating mode, wherein the first operating mode comprises the steps of a) supplying the fuel oil to be cleaned to the centrifugal separator, the fuel oil having a first temperature of at least 95 °C; b) discharging at least a cleaned oil phase from the centrifugal separator; and the second operating mode comprises the steps of c) stopping the supply of fuel oil to the centrifugal separator; and d) reducing the temperature of the fuel oil to a second temperature below 70 °C and / or reducing the flow rate of the fuel oil.

[0046] Also as mentioned above, the liquid feed mixture can be a lubricating oil. The lubricating oil can be a lubricating oil for an engine, such as a diesel engine. In embodiments of the first aspect, the method is a method for on-board treatment of a lubricating oil, i.e. a method used on board a ship.

[0047] The separation temperature of the lubricating oil is typically above 70°C, such as at least 95°C. The separated lubricating oil is then directed to an oil storage tank, such as an oil tank or oil sump located below the engine, from which it is supplied to the engine. However, when the lubricating oil is supplied to the engine, it is typically cooled to approximately 55°C. Therefore, if the method of the present invention is applied (in which the lubricating oil does not need to be fully heated during the second operating mode and is instead circulated back to the oil storage tank), the oil in the oil storage tank will have a lower temperature, and therefore, less energy will be required to cool it to the temperature required during supply to the engine.

[0048] Thus, in an embodiment of the first aspect, there is provided a method for operating a system comprising a centrifugal separator for separating a clean oil phase and a sludge phase from a lubricating oil, the method comprising alternating between a first operating mode and a second operating mode, wherein the first operating mode comprises the following steps a) supplying the lubricating oil to be cleaned to the centrifugal separator, the lubricating oil having a first temperature of at least 95° C.; b) discharging at least the clean oil phase from the centrifugal separator; And the second operation mode includes the following steps c) stopping said supply of lubricating oil to the centrifugal separator; and d) reducing the temperature of the lubricating oil to a second temperature below 70° C. and / or reducing the flow rate of the lubricating oil.

[0049] As a second aspect of the present invention, there is provided a system for separating at least one liquid phase and a sludge phase from a liquid feed mixture, the system comprising - a centrifugal separator arranged for separating at least one liquid phase and a sludge phase from the liquid feed mixture and further arranged for continuously discharging the at least one separated liquid phase and intermittently discharging the sludge phase, - a liquid feed pump for supplying the liquid feed mixture to the centrifugal separator, - a heating device for heating the liquid feed mixture, and - a control device configured for regulating the supply of liquid feed mixture to the centrifugal separator via the liquid feed pump and / or for regulating the temperature of the liquid feed mixture using the heating device, and further configured for initiating the discharge of the sludge phase from the centrifugal separator; and in addition Therein, the control means is configured for alternating between the first and second modes of operation in accordance with the first aspect of the invention discussed herein above.

[0050] The terms and definitions used in relation to the second aspect are the same as those discussed in relation to the first aspect above.

[0051] Thus, the centrifugal separator may be as described above with respect to the first aspect. The centrifugal separator may be arranged to separate two liquid phases and a sludge phase from the liquid feed mixture. The two liquid phases may be discharged continuously, or one may be discharged continuously and one may be discharged intermittently, for example, by means of a valve arranged downstream of the liquid outlet of the centrifugal separator.

[0052] The liquid feed pump may be arranged upstream of the heating device and thus upstream of the centrifugal separator.

[0053] The heating device can be an electric heater. However, the heating device can also be a steam / hot water / hot oil heat exchanger.

[0054] The control device is configured to regulate the supply of the liquid feed mixture and / or the temperature of the liquid feed mixture to be cleaned. Thus, the control device may include a processor and an input / output interface for communicating with the liquid feed pump and / or the heating device. Thus, the control device may include any suitable type of programmable logic circuit, processor circuit or microcomputer, such as 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), an FPGA (field programmable gate array), a microprocessor or other processing logic that can interpret and execute instructions.

[0055] The control device can be the same control device used to regulate and control the parameters of the centrifugal separator, such as the rotation speed of the centrifugal separator. Thus, the same software used to control the centrifugal separator can be used to control the liquid feed pump and / or the heating device.

[0056] In an embodiment of the second aspect, the control device is configured to perform steps a), c) and d) of the method according to the above first aspect.

[0057] Furthermore, the control device may be further configured to initiate step e) of discharging the separated sludge phase from the centrifugal separator.

[0058] Therefore, the control device may be arranged for initiating an intermittent discharge sequence of the centrifugal separator. To this end, the control device may be configured for sending instructions to an operating water module (OWM) which is used in the art to supply a certain amount of water to the intermittent discharge system of the centrifugal separator to intermittently open the sludge outlet of the centrifugal separator.

[0059] In an embodiment of the second aspect, the system further comprises a tank for storing the liquid feed mixture to be separated.A liquid feed pump may then be arranged for supplying the liquid feed mixture from the tank to the centrifugal separator.

[0060] Therefore, the system may further comprise a fuel tank or the like for storing the liquid feed mixture to be cleaned before it is supplied to the centrifugal separator.

[0061] Furthermore, the system may comprise valve means arranged upstream of the centrifugal separator and arranged for directing a supply of the liquid feed mixture towards the centrifugal separator during the first operating mode and directing a supply of the liquid feed mixture back to the tank during the second operating mode.

[0062] Thus, a valve member such as a three-way valve may be used to alternate between directing the liquid feed mixture to the centrifugal separator and returning it to the tank during recirculation. The control device may be configured to control such a valve member, i.e., to send instructions to the valve member to switch between sending the liquid feed mixture to the centrifugal separator and returning it to the tank.

[0063] As a third aspect of the present invention, a computer program is provided, comprising instructions for causing a control device to perform steps a), c), and d) of the method of the first aspect. For example, the computer program may comprise instructions for causing a control device to perform steps a), c), d), and e) of the method of the first aspect.

[0064] Furthermore, the computer program may comprise instructions for causing the control device to also perform step b) of the method of the first aspect described above. Thus, the instructions may, for example, be instructions for opening a valve arranged downstream of the outlet for the separated liquid phase so that the separated liquid phase can be discharged from the centrifugal separator.

[0065] As a fourth aspect of the present invention, there is provided a computer readable medium having stored thereon the computer program of the third aspect of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] Figure 1 A schematic diagram showing an embodiment of the system of the present invention during a first mode of operation is shown.

[0067] Figure 2 A schematic diagram showing an embodiment of the system of the present invention during a second mode of operation.

[0068] Figure 3 Schematic diagram showing the centrifugal separator of the system.

[0069] Figure 4 A method of operating a system according to the present invention is schematically illustrated. DETAILED DESCRIPTION

[0070] The method and system according to the present disclosure will be further illustrated by the following description with reference to the drawings. The example describes a system for cleaning fuel oil for a diesel engine and a method for operating such a system, but the teachings can of course be used in other applications, i.e. when using other types of liquid feed mixtures.

[0071] Figure 1 A schematic drawing of an embodiment of a system 1 for cleaning fuel oil for a diesel engine is shown. The system 1 comprises a centrifugal separator 2 arranged for separating at least a clean oil phase and a sludge phase from fuel oil stored in a fuel tank (or settling tank) 20. The fuel oil to be cleaned is supplied to the centrifugal separator 2 via a pipe 26 using a liquid feed pump 21 of the system 1. The system further comprises a heating device 22 for heating the fuel oil to be cleaned. In this embodiment, the fuel oil is initially heated by the heating device 22 to about 98°C.

[0072] The system further comprises a three-way valve 23 arranged upstream of the centrifugal separator 2 and arranged for directing the fuel oil to be cleaned either to the centrifugal separator 1 or back to the supply of the fuel tank (or settling tank) 20, i.e. during a circulation.

[0073] During a first operating mode of the method of the present disclosure as shown in Figure 1 The centrifugal separator is arranged for continuously discharging the clean oil phase via a liquid light phase outlet 13 and for continuously discharging a separated water phase via a liquid heavy phase outlet 14. During cleaning of the oil, a sludge phase accumulates inside the centrifugal separator. After some time of separation, such sludge needs to be discharged from the centrifugal separator 1. Therefore, the centrifugal separator is further arranged for intermittently discharging the sludge phase.

[0074] During a second operating mode, as shown in Figure 2 The supply of fuel oil to be cleaned to the centrifugal separator 1 is stopped. This is performed by using the three-way valve to direct the fuel oil back to the fuel tank 20, i.e. the fuel oil is recirculated to the tank 22.

[0075] The intermittent discharge sequence comprises supplying a displacement liquid, such as water, to the centrifugal separator via the inlet 8. The displacement water originates from a tank 30 from which it can be supplied to the inlet pipe 8 via a pipe 31. Then, using an operating water module (OWM) 41, operating water is supplied to the centrifugal separator to open the sludge outlet. Such outlet is opened within fractions of a second to displace the sludge accumulated inside the centrifuge bowl of the separator 1. During the intermittent discharge sequence, no clean oil phase or water phase is discharged from the outlets 13 or 14.

[0076] During this second operating mode, when the fuel oil to be cleaned is recirculated back to the tank 20, the temperature of the fuel oil is reduced to, for example, 60° C. or below, such as to 50° C. This is performed by lowering the set point temperature of the heating device 22 or simply by switching off the heating device 22. Alternatively or additionally, the flow rate of the fuel oil recirculated back to the tank 20 is reduced by lowering the set point flow rate of the liquid feed pump 21 or by switching off the liquid feed pump.

[0077] Therefore, and as Figure 4 As shown in the method steps in FIG. 1 , the method of the present disclosure comprises a first operating mode during which continuous cleaning of the fuel oil occurs when no fuel oil to be cleaned is supplied to the centrifugal separator 1 and a second operating mode during which energy is saved by reducing the temperature and / or flow rate of the recirculating fuel oil. Thus, in this example, the first operating mode comprises the following steps: a) supplying 101 the fuel oil to be cleaned from the tank to the centrifugal separator 2 and heating the fuel oil to be cleaned to a first temperature of about 98° C., and b) Discharge 102 the clean oil phase and water phase from the centrifugal separator 2.

[0078] The second operating mode includes c) stopping 103 the supply of fuel oil to the centrifugal separator 2 and recycling the fuel oil to be cleaned back to the tank; d) reducing 104 the temperature of the recycled fuel oil to a second temperature below 70° and / or reducing 105 the flow rate of the liquid feed mixture; and e) Discharge 106 the separated sludge phase from the centrifugal separator 2.

[0079] Furthermore, after step e) has been performed, the system 1 may then be operated again in the first operating mode until further sludge discharge needs to be performed.

[0080] like Figure 1 and Figure 2 As shown in FIG, the system further includes a control device 50 configured to regulate the supply of fuel oil (such as the flow rate of the fuel oil) to the centrifugal separator 2 via the liquid feed pump 21, as indicated by the dashed arrow "A". In addition, the control device 21 is further configured to regulate the temperature of the fuel-oil mixture using the heating device 22 (as indicated by the dashed line "B") and to regulate whether the fuel oil is supplied to the separator 1 or recirculated back to the tank 22 (as indicated by the arrow "E") using the three-way valve 23. Thus, the control device 50 is configured to alternate between a first operating mode and a second operating mode according to the method of the present disclosure.

[0081] For the purpose of regulation, the control device 50 may include a processing unit, such as a central processing unit, which is configured to execute computer code instructions, which may be stored on a memory, for example. Thus, the memory may form a (non-transitory) computer-readable medium for storing such computer code instructions. Alternatively, the processing unit may be in the form of a hardware component, such as an application-specific integrated circuit, a field programmable gate array, etc. Thus, the control device 50 may include a communication interface, such as a transmitter / receiver, via which the control device 50 may receive data from the liquid feed pump 21 and the heating device 22 and further transmit data including operation requests to the liquid feed pump 21 and the heating device 22.

[0082] Therefore, the present invention also provides a computer program comprising instructions for causing a control device to perform steps a), c) and d) of the method of the present disclosure.

[0083] The control unit 50 may be the same control unit used to regulate the centrifugal separator 2 itself. Thus, the control device may be configured to control the speed of the centrifugal separator, as indicated by arrow "C." The control device may also be configured to trigger the discharge of the sludge phase from the centrifugal separator 2. To this end, the control device 50 may be configured to regulate the operating water module (OWM) 41, as indicated by arrow "D."

[0084] Therefore, the present invention also provides a computer program comprising instructions for causing a control device to perform steps a), c), d) and e) of the method of the present disclosure.

[0085] The method and system 1 of the present invention are advantageous because they reduce the overall power consumption of the system 1. As an example, during the cleaning of fuel oil on a ship, the supply of fuel oil is typically heated from 50°C to 98°C. To operate a common separator size with a capacity of ~5m3 / h, the energy required to heat the feed is ~130kW. When it is time to discharge the sludge, the supply of fuel oil to the separator is almost always cut off. In total, the sludge discharge sequence, including the supply of operating water, may take 150 seconds. During these 150 seconds, the fuel oil is continuously running in the recirculation. Therefore, the present invention implements intelligent control of heating. When entering the recirculation, the temperature set point is changed to no heating at all, or only slightly heated, such as to 60°C. Assuming discharge once an hour (which is a common discharge interval), the total time spent in the second operating mode every 24 hours is about 1 hour. This means that the system can save up to 130 kWh per day, which is a significant saving.

[0086] Figure 3 Show and give the Figure 1 and Figure 2 Some additional details of the centrifugal separator 2 used in the system 1 are shown.

[0087] The centrifugal separator 2 comprises a rotatable centrifuge drum 9 which forms within itself a separation chamber 10 in which centrifugal separation of the fuel oil takes place during operation.

[0088] Separation chamber 10 is equipped with a stack of frustoconical separation discs 11 to achieve efficient separation of fuel oil. The stack of frustoconical separation discs 11 is an example of a surface-enlarging insert. These discs 11 fit centrally and coaxially with the centrifuge barrel and may include holes that, when the separation discs 11 are fitted in centrifugal separator 2, form channels 12 for the axial flow of liquid. An inlet pipe 8 forms the central conduit and is therefore arranged for introducing fuel oil for centrifugal separation in separation chamber 10. In this embodiment, the fuel oil is supplied from the top, but bottom-fed separators can also be used in system 1.

[0089] Centrifugal separator 2 has a liquid light phase outlet 13 extending therefrom for the lower density components separated from the fuel oil, and a liquid heavy phase outlet 14 for the higher density components or heavy phase separated from the fuel oil. Thus, liquid light phase outlet 13 can be used to discharge the cleaned oil phase, and liquid heavy phase outlet 14 can be used to discharge the separated water phase. Outlets 13 and 14 extend through a frame 15.

[0090] The centrifuge drum 9 is also provided at its outer periphery with a set of radial sludge outlets 16 in the form of intermittently openable outlets for discharging higher density components, such as sludge or other solids in the oil. Thus, this material is discharged from the radially outer portion of the separation chamber 10 into the space surrounding the centrifuge drum 9. For example, a phase comprising catalyst fines can be discharged via the outlets 16.

[0091] The centrifugal separator 2 is further provided with a drive motor 7 for rotating the main shaft 4 and the centrifuge barrel 9 attached thereto at a desired speed. The main shaft 4 and the centrifuge barrel 9 are suspended in a fixed frame 15 by means of upper and lower bearings 5 ​​and 6 .

[0092] exist Figure 3During operation of the separator in question, the centrifuge bowl 9 is rotated by the drive motor 7. Via the inlet pipe 8, the fuel oil to be separated is brought into the separation space 10. Depending on the density, different phases in the fuel oil separate between the separation discs 11. The heavier components, such as the water phase and the sludge phase, move radially outwards between the separation discs, while the least dense phase, such as the clean oil phase, moves radially inwards between the separation discs and is forced through the outlet 13 arranged in the radially innermost level in the separator. The higher density liquid is instead forced through the outlet 14, which is at a greater radial distance than the radial level of the outlet 13. Thus, during separation, an intermediate phase between the lower density liquid and the higher density liquid is formed in the separation space 10. Solids or sludge accumulate at the periphery of the separation chamber 10 and are intermittently evacuated from the separation space by opening the sludge outlet 16, whereupon sludge and a certain amount of fluid are expelled from the separation space by means of the centrifugal force.

[0093] In certain applications, the separator 1 only comprises a single liquid outlet, such as only the liquid outlet 13, and the sludge outlet 16. This depends on the fuel oil to be treated.

[0094] The present invention is not limited to the disclosed embodiments, but can be varied and modified within the scope of the claims stated below. The present invention is not limited to the type of separator as shown in the figures. The term "centrifugal separator" also includes centrifugal separators with a substantially horizontally oriented rotation axis and separators with a single liquid outlet.

Claims

1. A method (100) for operating a system (1) comprising a centrifugal separator (2) for separating at least a liquid phase and a sludge phase from a liquid feed mixture, the method (100) comprising alternating between a first operating mode and a second operating mode, wherein: The first operation mode includes the following steps a) supplying (101) the liquid feed mixture to be cleaned to the centrifugal separator (2), the liquid feed mixture having a first temperature; b) discharging (102) at least one separated liquid phase from the centrifugal separator (2); And the second operation mode includes the following steps c) stopping (103) said supply of liquid feed mixture to said centrifugal separator (2); as well as d) reducing (104) the temperature of the liquid feed mixture to a second temperature and / or reducing (105) the flow rate of the liquid feed mixture.

2. The method (100) according to claim 1, wherein: The second operation mode further comprises the following steps e) Discharging (106) the separated sludge phase from the centrifugal separator (2).

3. The method (100) according to claim 1, wherein: Step a) comprises supplying (101) the liquid feed mixture from a storage tank (20), and step c) further comprises recycling the liquid feed mixture to the storage tank (20).

4. The method (100) according to any preceding claim, wherein: Step a) further comprises heating the liquid feed mixture to the first temperature using a heating device (22).

5. The method (100) according to claim 4, wherein: Step d) comprises switching off said heating means (22).

6. The method (100) according to any preceding claim, wherein: Step a) comprises supplying (101) the liquid feed mixture using a liquid feed pump (21).

7. The method (100) according to claim 6, wherein: Step d) comprises shutting off the liquid feed pump (21).

8. The method (100) according to any preceding claim, wherein: The liquid feed mixture is oil and the first temperature in step a) is at least 50°C.

9. The method (100) according to claim 8, wherein: Step d) comprises lowering the temperature of the oil to a second temperature at least 10°C lower than said first temperature.

10. The method (100) according to claim 9, wherein The liquid feed mixture is fuel oil for a diesel engine and wherein the first temperature is at least 97°C and wherein step d) comprises reducing the oil to a temperature below 80°C, such as below 70°C.

11. A system (1) for separating at least a liquid phase and a sludge phase from a liquid feed mixture, the system (1) comprising - a centrifugal separator (2) arranged for separating at least one liquid phase and a sludge phase from the liquid feed mixture and further arranged for continuously discharging the at least one separated liquid phase and intermittently discharging the sludge phase, - a liquid feed pump (21) for supplying the liquid feed mixture to the centrifugal separator (2), - a heating device (22) for heating the liquid feed mixture, and - a control device (50) configured for regulating the supply of a liquid feed mixture to the centrifugal separator (2) via the liquid feed pump (21) and / or for regulating the temperature of the liquid feed mixture using the heating device (22), and also configured for initiating the discharge of the sludge phase from the centrifugal separator (2); and in addition in, The control device (50) is configured for alternating between the first operating mode and the second operating mode according to the method (100) of any one of claims 1-10.

12. The system (1) according to claim 11, wherein The control device (50) is configured to perform steps a), c) and d) of the method (100) according to any one of claims 1 to 10.

13. The system (1) according to claim 12, wherein The control device (50) is further configured to initiate step e) of discharging the separated sludge phase from the centrifugal separator (2).

14. The system (1) according to any one of claims 11 to 13, further comprising a tank (20) for storing the liquid feed mixture to be separated, and wherein, The liquid feed pump (21) is arranged for supplying the liquid feed mixture from the tank (20) to the centrifugal separator (2).

15. The system (1) according to claim 14, further comprising a valve member (23) arranged upstream of the centrifugal separator (2) and arranged for directing the supply of the liquid feed mixture to the centrifugal separator (1) during the first operating mode and directing the supply of the liquid feed mixture back to the tank (20) during the second operating mode.

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