Method for filtering dairy products

Abstract

A method for filtering a dairy product is used in a filter system, the filter system comprising at least one pump circuit having a pump and a filter, the pump being arranged to feed a feed product to the filter to filter the feed product and output a permeate product and a retentate product. The method comprises: supplying the feed product to the pump at a feed pressure; during a first operating mode in which the feed pressure is below a first predetermined threshold, controlling the pump to operate at a first power within a first percentage range of a maximum rated power of the pump; and during a second operating mode in which the feed pressure is above the first predetermined threshold, controlling the pump to operate within a second percentage range of the maximum rated power, the second percentage range being higher than the first percentage range.

Description

Technical Field

[0001] The present invention relates to a method of filtering a dairy product using a filter system that filters a feed product and outputs a permeate product and a retentate product. Background Art

[0002] Membrane filtration is used in the production of milk, for example in reverse osmosis or nanofiltration processes. In membrane filtration, the use of the pressure difference across the membrane is the driving force for separating the feed product fed to the filter. Membrane separation technology can be used for different purposes. In reverse osmosis, membrane separation can be used for the dehydration of milk, whey, ultrafiltration permeate and condensate. In nanofiltration, membrane separation can be used for partial desalination of milk, whey, ultrafiltration permeate or retentate.

[0003] A membrane filter system typically comprises two filter modules arranged in series to form a filter circuit together with one retentate circulation pump and one permeate circulation pump. The feed product is pumped into the module at a high flow rate, and the operation of the membrane filter system depends on the pressure generated by the pumps used. The system comprises a feed pump and a circulation pump to pass the feed product through the system. The capacity of the pump is selected to match the flow rate and module characteristics required for a particular application. The speed of the circulation pump, or in some applications, the speed of the multi-circulation pump is usually controlled or adjusted based on the pressure difference (Δp) across the filter circuit. The pressure difference can be about four bars.

[0004] A disadvantage of conventional control methods is that the pump may be operated at a higher power than is required to output the desired amount of filtered feed product. Often, the pumps used in filter systems are oversized and have a higher capacity than is required for adequate operation of the system. As a result, running the pump at a high speed results in wasted energy during operation of the filter system. Another disadvantage of conventional systems is that regulating the temperature in the system may further increase energy use because more cooling is required to maintain process temperatures when the pump is regularly running at a high speed. Summary of the invention

[0005] An object of the present invention is to at least partially overcome one or more limitations of the prior art. In particular, an object is to provide a method for filtering a dairy product, the method comprising controlling the operation of a circulation pump based on determining whether a feed pressure in a filter system is above or below a predetermined threshold.

[0006] According to one aspect of the invention, a method for filtering a dairy product is used in a filter system, the filter system comprising at least one pump circuit having a pump and a filter, wherein the pump is arranged to supply a feed product to the filter to filter the feed product and output a permeate product and a retentate product. The method comprises supplying the feed product to the pump at a feed pressure during a first operating mode in which the feed pressure is below a first predetermined threshold, controlling the pump to operate at a first power within a first percentage range of a maximum rated power of the pump, and during a second operating mode in which the feed pressure is above the first predetermined threshold, controlling the pump to operate within a second percentage range of the maximum rated power of the pump, the second percentage range being at least 10% higher than the first percentage range.

[0007] Here, "power" is the ratio of the work done by the pump relative to time (i.e., the time derivative of work: P = dW / Dt, where P is power, W is work, and t is time). That is, controlling the pump to run at 100% power means that it is pumping at maximum performance. Power may also be referred to as "efficiency" in this article. Efficiency is also defined as the ratio of the work done by the pump relative to time.

[0008] The feed pressure is of course a pressure value that is large enough to complete the product feeding. Obviously, the feed pressure is greater than zero in both operating modes. Typically, in the first operating mode, the feed pressure is at least 3 bar.

[0009] In the second operating mode, the feed pressure is higher than in the first operating mode, which is evident because the pump then operates at a power within a second percentage range that is at least 10% higher than the first percentage range. In the second operating mode, the feed pressure may be at least 5% higher than in the first operating mode.

[0010] The first operating mode may represent normal operation, i.e. filtration of dairy products. The second operating mode may represent a start-up phase of filtration, which usually lasts for a much shorter time than the first operating mode. The second operating mode may also represent cleaning of the filter. During cleaning, cleaning liquid may be supplied to the pump.

[0011] The method described herein is conducive to controlling the operation of the filter pump to reduce the amount of energy used by the pump in the filter system. At least one predetermined feed pressure threshold can be set for the pump used in a specific application, such as a circulating pump used in a membrane separation filter for a reverse osmosis process or a nanofiltration process. When the feed pressure in the system is within one of the ranges defined by a predetermined pressure threshold or below, the pump can be operated at a specific power within a percentage range of the maximum rated power of the pump. The power of the pump can be about 25% when the feed pressure is below the predetermined pressure threshold, and the power of the pump can be within a percentage range between 25% and 85% when the feed pressure is above the predetermined pressure threshold. An upper limit threshold can also be predefined to represent the production set point of the pump, such as 85%, which is the maximum power at which the pump can operate. In contrast, the pump in the conventional system is adjusted according to the pressure difference on the filter loop, which causes the pump to operate at a much higher efficiency than the efficiency required for the filter system to operate. The speed of the pump increases regularly, causing the energy sucked by the pump to exceed the energy required to produce the desired output. Compared to conventional filter pump systems, the pump in the filter system described herein is controlled based on the amount of feed pressure and operates at a lower speed to reduce circulation in the filter loop while still producing the desired amount of filtered product and maintaining a constant output capacity. The speed of the pump can be increased until the feed pressure exceeds a predetermined threshold, and after exceeding the predetermined threshold, the operation of the pump will be limited when the pump reaches the production set point. Testing conducted in an operating dairy filter system has shown that this method can be used successfully while maintaining total filtration output during most of the time when production is ongoing.

[0012] Thus, the methods and systems described herein can waste less energy than conventional filter systems and pump controls. Yet another advantage of the energy-efficient systems described herein is that, due to the reduced pump energy during operation, less cooling fluid is used to regulate the system temperature than conventional systems. Thus, using less cooling fluid can further reduce the overall energy used by the filter system. In reverse osmosis applications, another advantage of the methods described herein is that the chemical oxygen demand (COD) level in the output permeate product can be significantly reduced compared to conventional systems.

[0013] Although various aspects of the invention are set out in the accompanying independent claims, further aspects of the invention may comprise any combination of features from the described and / or features of the accompanying dependent claims with features of the independent claims and not just the combinations explicitly set out in the accompanying claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Features of the present invention will now be described by way of example with reference to the accompanying schematic drawings.

[0015] Figure 1is a schematic diagram of a membrane filter system used in milk production.

[0016] Figure 2 yes Figure 1 Schematic diagram of the control system of the membrane filter system.

[0017] Figure 3 Is displayed for adjustment Figure 1 Schematic representation of the parameter data of the circulation pump speed in the membrane filter system.

[0018] Figure 4 is the use of membrane filter systems (e.g. Figure 1 Flow chart of a method for filtering dairy products using a membrane filter system (using a membrane filter system). DETAILED DESCRIPTION

[0019] The method and system according to the invention have particular application in membrane filter systems for producing dairy or milk products. More specifically, the method can be used in membrane filter systems or devices for reverse osmosis, such as during dehydration of milk, whey, ultrafiltration permeate and condensate, or for nanofiltration, such as during partial desalination of milk, whey, ultrafiltration permeate or retentate.

[0020] The invention relates to a method for filtering a dairy product using a filter system, the filter system comprising at least one pump circuit having a pump and a filter, the pump being arranged to supply a feed product to the filter to filter the feed product and output a permeate product and a retentate product. The method comprises supplying the feed product to the pump at a feed pressure during a first operating mode in which the feed pressure is below a first predetermined threshold, controlling the pump to operate at a first power within a first percentage range of a maximum rated power of the pump, and during a second operating mode in which the feed pressure is above the first predetermined threshold, controlling the pump to operate within a second percentage range of the maximum rated power of the pump, the second percentage being greater than the first percentage.

[0021] Advantageously, the filter system is configured to output a desired amount of filtered feed product while providing more energy-efficient control of a circulating pump based on feed pressure compared to conventional systems that adjust pump speed based on pressure differentials in the filter loop. The speed of the circulating pump is controlled based on the detected feed pressure in the system and at least one predetermined threshold pressure level so that the circulating pump does not operate at an efficiency higher than that required to achieve the desired output. The filter loop will have fewer cycles and the pump will operate at an efficiency lower than the maximum rated power of the particular pump while still producing the desired output for the filter system. Controlling the circulating pump based on feed pressure and predefined threshold pressure levels reduces the overall speed of the pump by 70% to 80% during the operating cycle compared to the higher speeds of the pump in conventional systems. In reverse osmosis applications, another advantage of the method described herein is that the chemical oxygen demand (COD) level in the permeate product can be significantly reduced compared to conventional systems.

[0022] First reference Figure 1 , a filter system 1 for dairy or milk products is shown. The filter system 1 comprises a source of a feed product 2, which is to be filtered by the filter system 1, which outputs a permeate product 3, or filtrate or liquid that passes through the membrane, and a retentate product 4, or concentrate or retentate. The feed product 2 may comprise whey, such as cheese whey, or milk or any other dairy-based product. The filter system 1 comprises at least one pump circuit or filter circuit 5 with a circulation pump 6 (also referred to as a booster pump), and a filter membrane 7 for separating the feed into a permeate product 3 and a retentate product 4. The filter circuit 5 is arranged within the filter system 1 and is fluidly connected between the source of the feed product 2 and the lines for the retentate product 4 and the permeate product 3.

[0023] The filter circuit 5 including the filter membrane 7 can be applicable to different systems or membrane filtration equipment used in dairy processing. Membrane separation can be used for reverse osmosis to dehydrate milk, whey ultrafiltration permeate and condensate, and for partial desalination of milk, whey, ultrafiltration permeate or retentate in nanofiltration. The filter system 1 described herein can also be applied to use with other filtering processes in other applications. The pump in the filter system 1 can be a feed pump or a circulation pump, and the pump can include different pump types, such as a centrifugal pump or a volumetric pump. The pump can have different configurations, and the configuration of the pump will depend on the application. Multiple pumps can be arranged in series for specific applications.

[0024] The filter system 1 comprises at least one tank 8 connected to a source fluid of a feed product 2 for receiving the feed product. The at least one tank 8 has a compartment for the feed product and another compartment for the permeate product, which are separated by a wall 81 in the tank 8. The compartment for the feed product is connected to a feed pump 9 and the compartment for the permeate product is connected to a permeate pump 10, which is arranged to extract the permeate from the tank 8. The permeate pump 10 is configured to pump the permeate product 3 in the permeate line 11 out of the filter system 1. The feed pump 9 pumps the feed product 2 to be filtered along the feed line 13 to the filter circuit 5. The feed line 13 comprises a high pressure pump 14 and a frequency controller 15 to control the amount of electricity supplied to the high pressure pump 14. The circulation pump 6 for the filter circuit 5 may also comprise a frequency controller 16. The feed line 13 has a flow bypass loop 133 that allows the high pressure pump 14 to be bypassed, so that only the feed pump 9 pumps the feed product 2. The filter system 1 may be supplemented with a cooling system integrated into the internal circulation loop to maintain the process temperature between 10 and 50 degrees Celsius.

[0025] The filter loop 5 is a closed system and uses membrane separation to filter the feed product 2. The filter membrane 7 of the filter loop 5 can be selected to have a desired separation characteristic, such as one or more of thickness, surface porosity and pore size. The filter membrane 7 can be formed of any suitable material according to the needs of a specific application. In a reverse osmosis or nanofiltration process, the filter membrane 7 can be a polymer membrane. The higher flow rate of the feed product 2 through the filter system 1 leads to higher shear and lower polarization effects at the membrane surface. A pressure drop occurs between the retentate and permeate sides of the filter membrane 7, and the pressure drop corresponds to the force that pushes the permeate through the filter membrane 7. The feed product 2 can extend parallel to the membrane surface, and the permeate product 3 can be perpendicular to the surface of the filter membrane 7 and flow upward to the permeate line 11. The permeate line 11 flows out of the filter system 1 and returns to the tank 8. At least one cooler 18 or multiple coolers can be arranged on the filter loop 5 to maintain the process temperature during operation.

[0026] More than one filter circuit 5, 19 may be provided in the filter system 1, and the filter circuits 5, 19 may be arranged in parallel so that each filter circuit 5, 19 is fluidly connected between the feed line 13 and the permeate line 11 and the retentate line 24. The retentate line 24 may flow out of the filter system 1 or return to the tank 8. The valve 131 regulates how much retentate leaves the system 1 as the retentate product 4 and how much returns to the compartment in the tank 8 for the feed product. The retentate returned to the tank 8 then becomes the feed product pumped to the filter circuits 5, 19. During operation of the system 1, most or all of the retentate returns to the tank 8. The second filter circuit 19 may be identical to the first filter circuit 5 and also include a circulation pump 20, a frequency controller 21 for the circulation pump 20, a filter membrane 22, and a cooler 23. The circulation or capacity in the filter circuits 5, 19 may be controlled identically because the operation of the circulation pumps 6, 20 may be synchronized or nearly synchronized. Various sensors, such as pressure sensors, temperature sensors and flow meters, may also be arranged in the filter system 1. Advantageously, the feed pressure 25 may be detected in the feed line 13 of the filter system 1 by a feed pressure sensor for controlling the circulation pumps 6, 20 in response to the detected feed pressure. The feed pressure 25 generated in the filter system 1 is a combination of the pressure generated by the feed pump 9 and the pressure generated by the high-pressure pump 14 that pumps the feed product to the circulation pumps 6, 20.

[0027] Additional references Figure 2 , the filter system 1 includes a control system 26 to control the operation of the circulation pump 6, 20 based on the feed pressure 25 in the filter system 1. In contrast to conventional systems in which the speed of the circulation pump 6, 20 is adjusted according to the pressure difference across the filter circuit 5, 19, the control system 26 can control the circulation pump 6, 20 based on determining whether the feed pressure 25 is within a range defined by at least one predetermined pressure threshold. The circulation pump 6, 20 can be operated at a specific speed, which corresponds to the efficiency of the circulation pump 6, 20 based on the feed pressure 25 in the filter system 1.

[0028] The control system 26 may include a feed pressure sensor 27 for detecting the feed pressure 25, a computer or processor 28, and a memory 29 storing predetermined pressure threshold data. The memory 29 for the feed pressure 25 and the feed pressure sensor 27 are communicatively coupled to the processor 28 for communication therewith. The processor 28 may include any suitable electronic control mechanism, such as a central processing unit (CPU), a microprocessor, a control circuit, etc. Based on the detected feed pressure, the processor 28 controls at least one circulation pump 6, 20, and the high pressure pump 14 may also be controlled by the control system 26. If more than one filter circuit and circulation pump are provided, such as Figure 1, the circulation pumps 6, 20 operate together, and the high pressure pump 14 operates separately from the circulation pumps 6, 20. A control system 26 is used to control the operation of at least one of the circulation pumps 6, 20 based on the feed pressure so that the circulation pumps 6, 20 operate at a lower efficiency than a conventional system that operates the pumps at a higher speed that is not necessary to achieve the same output as produced by the filter system 1 described herein.

[0029] Additional references Figure 3 The control system 26 is configured to use data 30 representing parameters of a specific application to execute a method of adjusting the speed of the circulation pumps 6, 20. The data 30 may be stored in the memory 29 and the processor 28 is configured to execute commands based on the stored data 30. The data 30 includes parameters related to the feed line 13 (e.g. Figure 1 31, and the output or pump power of the circulation pumps 6, 20, as represented by line 32. The total feed pressure in the feed line 13 is increased by the high-pressure pump 14 or the feed pressure regulator, so that the output of the circulation pumps 6, 20 can be higher than the initial feed pressure in the filter system 1, for example 4 bar higher. Figure 3 As shown, the pressure output from the feed pressure regulator may be higher than the maximum feed pressure along line 31 representing the feed pressure. The output of the feed pressure regulator is represented by line 33.

[0030] The data 30 includes parameters for defining when the at least one circulation pump 6, 20 is in a first operating mode 34. The at least one circulation pump 6, 20 may be in the first operating mode 34 when the feed pressure 25 in the feed line 13 is below a first predetermined threshold 35, and may be in a second operating mode 36 when the feed pressure in the feed line 13 is above the first predetermined threshold 35. When in the first operating mode 34, the at least one circulation pump 6, 20 may be operated or rotated at a first power 37, which is a percentage of the maximum rated power (i.e., 100%) of the circulation pump 6, 20. The first operating mode 34 defines a first percentage range of the maximum rated power of the circulation pump 6, 20. The first power 37 may be within a first percentage range between 20% and 60%. The first power 37 may be 25%. When the feed pressure 25 is below the first predetermined threshold 35, the circulation pump 6, 20 may be operated at the same first power 37 for any feed pressure. When a feed pressure of any value between 5 and 20 bar is detected in the filter system 1, the circulation pumps 6, 20 may be operated in a first operating mode 34 at a first power 37. The pressure values ​​and pump efficiencies described herein are merely exemplary and the system may have different ranges and parameters suitable for different applications.

[0031] When the system or equipment requires more pressure and the feed pressure 25 reaches the first predetermined threshold 35, the control system 26 can be configured to increase the speed of the circulation pump 6, 20 so that the circulation pump 6, 20 can operate in a second operating mode 36, which is defined as a second percentage range between the first power 37 and a second power 38 that is higher than the first power 37. The circulation pump 6, 20 can operate at any power within the second percentage range between the first power 37 and the second power 38. The flow rate of the feed product 2 can increase by at least 70% during the second operating mode 36. The second power 38 can be between 80% and 90% of the maximum rated power of the circulation pump 6, 20. The second power 38 can be 85% and the second power 38 can be the maximum operating power of the circulation pump 6, 20. Therefore, the circulation pump 6, 20 will never operate at a power higher than the second power 38, and the maximum operating power will always be less than 100%. When the feed pressure 25 is between 20 and 34 bar, the operating range of the circulation pump 6 , 20 when in the second operating mode 36 may be any power between 25% and 85%.

[0032] For any feed pressure 25 above the feed pressure at a second predetermined threshold 39, the circulation pump 6, 20 can remain running at a second power 38, which can be set as a production set point for the circulation pump 6, 20. The production set point can be set to 85% power. If the feed pressure 25 is greater than the second predetermined threshold 39, the circulation pump 6, 20 can remain operable at 85% power. The second predetermined threshold 39 can correspond to a pressure of 34 bar or between 34 and 36 bar. When the feed pressure is 34 bar or higher, the circulation pump 6, 20 can be operated at a minimum power of 80%. Therefore, the circulation pump 6, 20 effectively has only two operating modes 34, 36 that depend on the feed pressure, relative to the pressure difference in the filter circuit 5 (about four bars in a conventional system). Since the circulation pump 6, 20 will maintain a lower efficiency during a certain pressure increase and will never reach 100% power, the filter system 1 will use less energy. Use of the control system 26 also enables the chiller 18 and other cooling components in the filter system 1 to operate at lower energy levels or supply less cooling fluid during operation of the filter system 1 because the average process temperature during operation is lower due to the controlled operation of the circulation pumps 6 , 20 .

[0033] Before reaching the first operating mode 34, the filter system 1 may additionally have a startup mode during which the circulation pump 6, 20 may be operated at an initial power higher than during the first operating mode 34, for example between 70% and 80%. During the startup mode, the speed of the circulation pump 6, 20 may be increased until the feed pressure 25 reaches a value within the range of the first operating mode 34, so that the speed of the circulation pump 6, 20 may stop increasing and the circulation pump 6, 20 may be operated in the first operating mode 34 at the first power 37. When the circulation pump 6, 20 may be operated in the first operating mode 34 at the first power 37 (which may be 25%) after the initial startup, the feed pressure 25 may be 5 bar.

[0034] In an exemplary application, the feed capacity of the filter system 1 in the feed line 13 for a given period of time may be approximately 10,000 liters, and the filter system 1 or apparatus may remove 2000 liters of permeate product 3 such that 2000 liters flow out of the filter loop 5 (and loop 19 if used) and up to the permeate line 11, with 8000 liters of the remaining product flowing to the second filter loop 19. When a greater feed pressure is required in the filter system 1, the flow rate provided by the circulation pumps 6, 20 is varied by the control system 26. The flow rate in the filter loops 5, 19 may be lower than in conventional systems where the flow rate increases with increasing pressure. The filtering effect and output in the filter system 1 are not affected by the lower flow rate. The first filter loop 5 may include a feed line portion 13a that may operate at 90% and a feed line portion 13b that is fluidly connected from the first filter loop 5 to the second filter loop 19 to output 10% to the pump 20. The feed line portion 13c of the second filter circuit 19 can also be operated at 90%, and the feed line portion 13d can be operated at 10% and be fluidly connected to the retentate line 24. Thus, the circulation in each filter circuit 5, 19 is identical and the desired output capacity is maintained. The circulation in each circuit 5, 19, and therefore in the portions 13a, 13c, can be 4 to 10 times higher than the circulation in the feed line 13, or even higher.

[0035] Additional references Figure 4 , showing the use of Figure 1 The filter system 1 and Figure 2 Flow chart of a method 40 of filtering a dairy product using a control system. The control system 26 may include a non-transitory computer readable medium having a program stored thereon for performing the filtering of the dairy product by a computer or processor 28 (e.g., Figure 2 The method 40 is performed when the feed product 2 is supplied 41 to at least one circulating pump 6, 20 (as shown in FIG. 25 ) at a feed pressure 25. Figure 1 ), and determining 42 whether the feed pressure 25 is below a first predetermined threshold 35 (eg Figure 3The method 40 may include supplying the feed product 2 to at least two filter circuits 5, 19 fluidly connected between a feed line 13, a permeate line 11, and a retentate line 24 (e.g., Figure 1 shown).

[0036] If the control system 26 determines that the feed pressure 25 is below the first predetermined threshold 35, the method 40 includes controlling 43 the circulation pump 6, 20 to operate at a first power 37 within a first percentage range of the maximum rated power of the circulation pump 6, 20 during the first operating mode 34 (e.g., Figure 3 If the control system 26 determines that the feed pressure 25 is above the first predetermined threshold 35, the method 40 includes increasing 44 the speed of the circulation pump 6, 20 and controlling 45 the circulation pump 6, 20 to operate within a second percentage (higher than the first percentage) of the maximum rated power of the circulation pump 6, 20 during the second operating mode 36 (e.g. Figure 3 The second percentage range is defined between the first power 37 and the second power 38 (as shown in FIG. Figure 3 The method 40 may further include defining the first predetermined threshold 35 to be between 15 and 25 bar, and defining a second predetermined threshold 39 (as shown) representing a production set point of the circulation pumps 6, 20. Figure 3 ), so that the circulation pumps 6 , 20 will not be operated at a power higher than the second power 38 .

[0037] The method 40 may include operating the circulation pump 6, 20 at 60% of the maximum power during the first operating mode 34 when the feed pressure 25 is in the range between 5 and 30 bar. The method 40 may include increasing the flow rate of the feed product 2 by at least 70% during the second operating mode 36, and operating the circulation pump 6, 20 in a second percentage range between 25% and 85% power during the second operating mode 36 when the feed pressure is between 20 and 34 bar. When the feed pressure is 34 bar or higher, the circulation pump 6, 20 may be operated at a minimum power of 80%. Using the control system 26, the method 40 also includes outputting 46 a constant volume of filtered feed product from the filter system 1, and operating the circulation pumps 6, 20 of at least two filter circuits 5, 19 to have a common flow rate in the filter circuits 5, 19. The pressure values ​​and pump efficiencies described here are merely exemplary and different ranges suitable for different applications may be used.

[0038] A method for filtering a dairy product is used in a filter system, the filter system comprising at least one pump circuit having a pump and a filter, the pump being arranged to supply a feed product to the filter to filter the feed product and output a permeate product and a retentate product. The method comprises supplying the feed product to the pump at a feed pressure during a first operating mode in which the feed pressure is below a first predetermined threshold, controlling the pump to operate at a first power within a first percentage range of a maximum rated power of the pump, and during a second operating mode in which the feed pressure is above the first predetermined threshold, controlling the pump to operate within a second percentage (higher than the first percentage) of the maximum rated power of the pump.

[0039] The method may include defining a second predetermined threshold for the feed pressure, wherein the second predetermined threshold is higher than the first predetermined threshold.

[0040] The method may include outputting a constant volume of filtered feed product from the filter system. In other words, the method may include outputting a constant flow of product that has passed through the filter from the filter system.

[0041] The method may further include, during the second operating mode, controlling the pump to operate at a pump power that increases the flow rate of the feed product during the second operating mode by at least 70% compared to the flow rate during the first operating mode.

[0042] The method may comprise defining the first predetermined threshold value as being between 15 and 25 bar.

[0043] The method may comprise operating the pump at a maximum of 35% power during the first operating mode. Alternatively, the method may comprise operating the pump at a maximum of 60% power during the first operating mode.

[0044] The method may comprise operating the pump at a maximum of 35% power when the feed pressure is in the range between 5 and 30 bar. Alternatively, the method may comprise operating the pump at a maximum of 60% power when the feed pressure is in the range between 5 and 30 bar.

[0045] The method may include operating the pump within a second percentage range between 25% and 85% power during the second operating mode.

[0046] During the first operating mode, the first percentage range may be from 40% to 60%, i.e. the pump then operates at a power between 40% and 60% of its maximum power. During the second operating mode, the second percentage range may be at least 70%, i.e. the pump then operates at a power between at least 70% and 60%. The method may include operating the pump within the second percentage range when the feed pressure is between 20 and 34 bar.

[0047] The method may comprise operating the pump at a minimum of 80% power when the feed pressure is 34 bar or higher.

[0048] The method may include supplying a feed product to a filter assembly including at least two pump circuits fluidly connected between a feed line, a permeate line, and a retentate line.

[0049] The method may include operating the pumps of the at least two pump circuits to have a common flow rate in the at least two pump circuits.

[0050] The non-transitory computer-readable medium may store thereon a program that, when executed by a computer, performs the filtering method described herein.

[0051] Although the present invention has been described with reference to one or more preferred features, which have been set forth in considerable detail to achieve a complete disclosure of the present invention, these features are merely exemplary and are not intended to limit or represent an exhaustive enumeration of all aspects of the present invention. Therefore, the scope of the present invention shall be limited only by the appended claims. In addition, it will be apparent to those skilled in the art that many changes may be made to these details without departing from the spirit and principles of the present invention.

Claims

1. A method of filtering a dairy product using a filter system, the filter system comprising at least one pump circuit having a pump and a filter, the pump being arranged to feed a feed product to the filter, to filter the feed product and to output a permeate product and a retentate product, the method comprising: supplying the feed product to the pump at a feed pressure; During a first operating mode in which the feed pressure is below a first predetermined threshold, controlling the pump to operate at a first power within a first percentage of a maximum rated power of the pump; and During a second operating mode in which the feed pressure is above the first predetermined threshold, controlling the pump to operate within a second percentage range of the maximum rated power of the pump, the second percentage range being at least 10% higher than the first percentage range, Also included is defining a second predetermined threshold for the feed pressure, the second predetermined threshold being higher than the first predetermined threshold.

2. The method according to claim 1, further comprising outputting from the filter system a constant flow of product that has passed through the filter.

3. The method according to claim 1 or 2 further includes controlling the pump during the second operating mode to operate at a power of the pump such that the flow rate of the feed product during the second operating mode is increased by at least 70% compared to the flow rate of the feed product during the first operating mode.

4. The method according to the preceding claim 1 or 2, further comprising defining the first predetermined threshold value as between 15 and 25 bar.

5. The method of claim 1 or 2, further comprising operating the pump at a maximum of 60% power during the first operating mode.

6. The method of claim 5, further comprising operating the pump at a maximum of 35% power when the feed pressure is in the range between 5 and 30 bar.

7. The method of claim 1 or 2, further comprising operating the pump within the second percentage range between 25% and 85% power during the second operating mode.

8. The method of claim 7, further comprising operating the pump within the second percentage range when the feed pressure is between 20 and 34 bar.

9. The method according to claim 1 or 2, further comprising operating the pump at a minimum of 80% power when the feed pressure is 34 bar or higher.

10. The method according to claim 1 or 2, wherein the pump circuit is a first pump circuit, and the filter system comprises a second pump circuit having a second pump and a second filter, the second pump being arranged to feed the feed product to the second filter to filter the feed product and output a permeate product and a retentate product, the method further comprising supplying the feed product to the filter assembly, the filter assembly comprising the first pump circuit and the second pump circuit fluidly connected between a feed line, a permeate line and a retentate line.

11. The method of claim 10, further comprising operating pumps of at least the first pump circuit and the second pump circuit to have a common flow rate in the at least the first pump circuit and the second pump circuit.

12. A non-transitory computer-readable medium storing a program which, when executed by a computer, performs the method according to any one of the preceding claims.

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