A method of separating a liquid feed mixture in a centrifugal separator and a centrifugal separator

Abstract

The present invention provides a method (100) for separating a liquid feed mixture into at least one separated phase in a centrifugal separator (1) comprising a centrifuge bowl (10). The method (100) is comprising the steps of a) rotating (101) the centrifuge bowl (3); b) supplying (102) said liquid feed mixture to the centrifuge bowl (3); c) separating (103) said liquid feed mixture in the centrifuge bowl (3) into at least one separated phase; d) discharging (104) said at least one separated phase from the centrifuge bowl (10); e) deaerating (105) a portion of the liquid feed mixture and / or a portion of a discharged separated phase to provide a deaerated portion; and f) measuring (106) the density, turbidity or a physical property related to the solids concentration, or any combination thereof, of the deaerated portion.

Description

Field of the Invention

[0001] The present invention relates to the field of high-speed centrifugal separators, and more specifically to a method for separating a liquid feed mixture in a centrifugal separator.Background of the Invention

[0002] High-speed centrifugal separators are generally used for separation of liquids and / or for separation of solids from a liquid. During operation, liquid mixture to be separated is introduced into a rotating centrifuge bowl and heavy particles or denser liquid accumulate at the periphery of the rotating bowl whereas less dense liquid accumulates closer to the central axis of rotation. This allows for collection of the separated fractions, e.g. by means of different outlets arranged at different radial distance from the axis of rotation. Separation members, such as a stack of frustoconical separation discs, are usually used within the rotating bowl to enhance the separation performance. An example of a high-speed centrifugal separator is described in patent application EP 3315205.

[0003] In several separation processes, there is an advantage in being capable of measuring the density of the liquid feed mixture that is to be separated or the density of one of the separated phases. This may be for making sure that a separated phase has a density within a certain target range, or the density measurements may be used for controlling the separation process in any way. As an example, in separation processes in the refinement of starch, it is an advantage to measure the density of the separated starch fraction for several reasons. WO 94 / 08722 discloses a centrifugal separator of the disk-nozzle type having an overflow effluent and an underflow concentrated solids flow stream containing starch, and in which part of the underflow (heavy phase) is recirculated to the centrifuge bowl.

[0004] However, density may a property that is difficult to measure due to the complexity of the media that is to be separated. A liquid feed mixture may comprise solids of varying amount and the process conditions may lead to uptake of air within the separated phases. Thus, there is a need in the art for improved methods for measuring the density in a separation process.Summary of the Invention

[0005] A main object of the present invention is to provide a method and a centrifugal separator that allows for improved density measurements of the liquid feed mixture and / or any of the separated phases. A further object is to provide for improved inline measurements of the density during a separation process.

[0006] As a first aspect of the invention, there is provided a method for separating a liquid feed mixture into at least one separated phase in a centrifugal separator comprising a centrifuge bowl. The method comprises the steps of a) rotating the centrifuge bowl; b) supplying said liquid feed mixture to the centrifuge bowl; c) separating said liquid feed mixture in the centrifuge bowl into at least one separated phase; d) discharging said at least one separated phase from the centrifuge bowl; e) deaerating a portion of the liquid feed mixture and / or a portion of a discharged separated phase to provide a deaerated portion; and f) measuring the density, turbidity or a physical property related to the solids concentration, or any combination thereof, of the deaerated portion.

[0007] The method may be for separating the liquid feed mixture into a single liquid phase and a solids phase, into two liquid phases and a solids phase or into two liquid phases.

[0008] Step a) of rotating the centrifuge bowl may be rotating the bowl at a speed of at least 200 rpm, such as at least 4000 rpm, such as between 2000 and 10 000 rpm.

[0009] Step b) of supplying the liquid feed mixture may comprise pumping the liquid feed mixture to an inlet of the bowl. Supply may be from the top, such as through a stationary inlet pipe that extends to or into the bowl, or through the bottom, such as through a hollow spindle onto which the centrifuge bowl is mounted.

[0010] Step c) of separating the liquid feed mixture may comprise separating the liquid feed mixture in a separation chamber of the centrifuge bowl. The separation chamber may comprise surface enlarging inserts, such as separation discs.

[0011] Step d) of discharging at least one separated phase may comprise discharging at least one heavy phase and a light phase. The heavy phase may be a solid phase, and the light phase may be a liquid phase. Alternatively, two liquid phases - a liquid light phase and a liquid heavy phase - may be discharged from the centrifuge bowl. Then, also a solids phase may be discharged from the centrifuge bowl. This depends on the components of the liquid feed mixture that is separated.

[0012] Step e) of deaerating a portion of the liquid feed mixture and / or a portion of discharged separated phase refers to decreasing the amount of air bubbles, or the size of air bubbles, in the liquid feed mixture and / or a discharged separated phase. Step e) may thus be a step of degassing a portion of the liquid feed mixture and / or a discharged separated phase.

[0013] In embodiments of the invention, step e) comprises diluting the portion before deaerating the portion.

[0014] Step f) then comprises measuring the density, turbidity or a physical property related to the solids concentration, or any combination thereof, of the deaerated portion obtained in step e). Thus, in examples, only one of the density, turbidity and the physical property related to the solids concentration is measured. In other examples, two of these are measured. In other examples, all of the density, turbidity and the physical property related to the solids concentration are measured. A physical property related to the solids concentration may be a property that is related to the amount of particles within the portion that is measured.

[0015] In embodiments of the invention, step f) comprises diluting the deaerated portion before measuring the density, turbidity or a physical property related to the solids concentration, or any combination thereof, of the deaerated portion obtained in step e). This may be if e.g. the density is too high to be practically measured in the deaerated portion.

[0016] Steps e) and f) may be performed repeatedly or continuously during the method for separating a liquid feed mixture.

[0017] The first aspect of the invention is based on the insight that gas bubbles present within the mixture or portion that is measured may severely reduce the accuracy of the measurements, especially measurements of the density, turbidity or a physical property that relates to the particle concentration. Thus, in certain process, there is gas present in the feed that is separated, or air may picked-up by any of the separated phases during e.g. discharge from the centrifuge bowl. The inventors have found that the measurements are improved if such air is removed or at least decreased before measuring the density, turbidity or a physical property related to the solids concentration. Consequently, reducing the amount of or the size of any air bubbles present may severely enhance accuracy of the measurements.

[0018] This has been demonstrated when measuring the Baume concentration of a separated starch fraction during the separation of a feed of gluten and starch into starch phase and a gluten phase. Quick and reliable measurements of the density of a separated starch fraction have previously been a problem due to the large pick-up of air but has now been possible due to the features of the disclosed method.

[0019] Further, the method of the first aspect allows for inline measurements of the liquid feed mixture and / or a discharged separated phase. Thus, in embodiments of the first aspect, steps e) and f) are performed as inline process steps in the method for separating a liquid feed mixture.

[0020] "Inline process steps" refer to procedures and techniques that are applied during the ongoing separation process, as opposed to "offline process steps" that are carried out separately from the main process. Thus, steps e) and f) may comprise deaerating a portion directly from the running product stream without the need to stop or interrupt the separation process. Steps e) and f) may thus be integrated into the separation path or transportation path. Performing steps e) and f) as inline process steps allow for continuous or nearly continuous monitoring of the density, turbidity or a physical property related to the solids concentration. Further, steps e) and f) as inline process steps may provide for little to no interruptions or disruptions of the separation process and / or be automated or semi-automated.

[0021] In embodiments of the first aspect, step e) of deaerating comprises pressurizing said portion of the liquid feed mixture or a separated phase to decrease the amount of absorbed air in said portion.

[0022] Pressurizing the portion thus refers to increasing the pressure, such as increasing the pressure 4-6 bars. Pressurizing may lead to decreasing the size of absorbed air bubbles. Thus, the pressure on the gas bubbles will influence their size and stability. If the pressure on the bubbles increases, they may become smaller and potentially burst, thus not disturbing the measurements in a negative way.

[0023] In embodiments of the first aspect, step e) comprises vacuumizing said portion of the liquid feed mixture or a separated phase to decrease the amount of absorbed air in said portion.

[0024] Vacuumizing the portion refers to decreasing the pressure or creating a vacuum in the portion, e.g. by passing the portion to a vacuum chamber connected to a vacuum pump. Applying vacuum may decrease the dissolved gas in the portion and thereby decrease bubble formation.

[0025] In embodiments of the first aspect, step f) comprises measuring the density or solids concentration of the deaerated portion based on a particle detection method. As an example, the size and concentration of particles suspended in a fluid may be measured by detecting changes in electrical resistance. Further examples of particle detection methods involve methods that utilizes radio waves, or acoustic wave absorption. Also, method utilizing any wavelength of light or a wavelength close to or at IR may be used. Air bubbles in the portion that is measured may lead to false interpretations, which is why there is an advantage in reducing the amount of air bubbles by deaerating the portion that is measured.

[0026] In embodiments of the first aspect, the method is further comprising step g) of controlling the centrifugal separator and / or the separation process based on the measuring in step f). As an example, the measurements in step f) may be used to control that the measured density, turbidity or a physical property related to the solids concentration is within a certain target range. As an example, step g) of controlling may comprise controlling the flow rate of the liquid feed mixture to the centrifuge bowl, controlling the recirculation of a discharged phase to the centrifuge bowl, controlling a backpressure on an outlet for a separated phase of the centrifuge bowl, controlling the interval for a solid discharge and / or controlling the rotational speed of the centrifuge bowl.

[0027] In embodiments of the first aspect, the liquid feed mixture comprises starch and wherein step d) comprises discharging a light phase and a heavy phase, wherein the heavy phase comprises starch, and step e) comprises deaerating a portion of the heavy phase comprising starch, and step f) comprises measuring the Baumé concentration of the deaerated heavy phase portion comprising starch.

[0028] There is a well-known challenge in measuring the Baumé concentration in starch applications due absorbed air influence. Air may be absorbed at an outlet of the centrifugal separator, making it extremely useful to deaerate a portion of the heavy phase comprising starch before measuring the density of that portion.

[0029] The Baumé concentration refers to a measurement of the density of a liquid solution using the Baumé scale, which is used to measure the specific gravity of liquids. As an example, when the method comprises a step g) of controlling the centrifugal separator and / or the separation process based on the measured density or densities in step f), step g) may comprise controlling the amount of discharged heavy phase comprising starch that is recirculated to the centrifuge bowl.

[0030] The method of the first aspect may be used for a variety of applications. As a further example, the liquid feed mixture may comprise citrus fruit juice, wine or a protein mixture. Furthermore, the liquid feed mixture may be an oil.

[0031] As a second aspect of the invention, there is provided centrifugal separator for separating liquid feed mixture at least into at least one separated phase. The centrifugal separator is comprising a centrifuge bowl that is rotatable around an axis of rotation (X) and in which the separation takes place; a drive motor for rotation of the centrifuge bowl around the axis of rotation (X) an inlet for supply of the liquid feed mixture to the centrifuge bowl, at least one outlet for discharging a separated phase,

[0032] The centrifugal separator further comprises at least one measurement system arranged upstream the inlet and / or downstream any outlet for discharging a separated phase and arranged for measuring the density, turbidity or a physical property related to the solids concentration of a portion of said liquid feed mixture and / or a portion of a separated phase. The measurement system comprises a deaeration unit for deaerating said portion, and a meter for measuring the density, turbidity or a physical property related to the solids concentration of the deaerated portion.

[0033] The centrifugal separator of the second aspect may thus be used when performing the method of the first aspect discussed above. The centrifugal separator may be arranged for separating at least one liquid phase and a solids phase from the liquid feed mixture. The centrifugal separator may be arranged for separating the liquid feed mixture into a single liquid phase and a solids phase, into two liquid phases and a solids phase or into two liquid phases

[0034] The centrifugal separator may further comprise a stationary frame and a hood covering the centrifuge bowl.

[0035] The drive motor may be configured to rotate a centrifuge bowl within the hood. The axis of rotation for the centrifuge bowl may be a vertical axis of rotation. The centrifuge bowl may be enclosing a separation space in which the separation takes place. The separation space may comprise a stack of separation discs arranged centrally around the axis of rotation. Such separation discs form surface enlarging inserts in the separation space. The separation discs may have the form of a truncated cone, i.e. the stack may be a stack of frustoconical separation discs.

[0036] The drive motor may be an electrical motor comprising a stator and a rotor. As an example, the rotor may be directly connected to a shaft used for rotating the centrifuge bowl. The drive motor may also be connected by other means, such as via a gear or belt drive.

[0037] The inlet may be arranged centrally in the centrifuge bowl. Further, the at least one outlet may comprise one or several open outlets, e.g. allowing contact with air, or one or several sealed outlets, such as mechanically sealed or sealed with a liquid seal.

[0038] The measurement system may be integrated in the stationary part of the centrifugal separator or as a stand-alone unit connected to one of the outlets or the inlet. "Arranged upstream the inlet and / or downstream or any outlet for discharging a separated phase" may thus mean that the measurement system is connected, e.g. as an inline system, to an inlet pipe for feeding the liquid feed mixture to the inlet or to an outlet pipe arranged for transporting discharged heavy phase, such as a discharged liquid heavy phase from the separator. The measurement system may also be arranged in connection to a unit for collecting discharged solids, such as a cyclone, for measuring the density of a discharged heavy phase comprising solids.

[0039] The measurement system is comprising a deaeration unit for deaerating said portion, and a meter for measuring the density, turbidity or a physical property related to the solids concentration of the deaerated portion. The meter may thus be a density meter or a turbidity meter or a meter for measuring a physical property related to the solids or particle concentration of a liquid sample. The density meter may be a Coriolis flow meter.

[0040] As an example, the deaeration unit may comprise a pressurizing unit for pressurizing the portion of which the density, turbidity or a physical property related to the solids concentration, or any combination thereof, is measured. The pressurizing unit may comprise a valve.

[0041] As another example, the deaeration unit may comprise a vacuum unit for decreasing the pressure of the portion of which the density, turbidity or a physical property related to the solids concentration, or any combination thereof, is measured. The vacuum unit may comprise a vacuum chamber and a vacuum pump.

[0042] In embodiments of the second aspect, the meter is arranged for measuring the density or solids concentration based on a particle detection method. Such a particle detection method may involve acoustic wave absorption or radio waves. Further examples include detecting particles based on light absorption, scattered light devices, IR (or close to IR) light measurements.

[0043] In embodiments of the second aspect, the measurement system is arranged in a sampling connection that is connected to the inlet or an outlet for a separated phase. The sampling connection may thus be a branched connection connected to an inlet pipe or outlet pipe of the centrifugal separator. The sampling connection may be arranged for allowing inline measurements of the density.

[0044] In embodiments of the second aspect, the centrifugal separator further comprises a control unit configured for controlling the centrifugal separator and / or the separation process based on the measured density by the measurement system. The control unit may be a stand-alone component arranged remotely from - but in communicative connection with - the centrifugal separator but may alternatively be embedded in the separator for separator control. The control unit may be a central processing unit (CPU) and may be embodied in the form of one or more microprocessors.

[0045] As an example, the control unit may be operable to control the flow rate of the liquid feed mixture to the centrifuge bowl, control the recirculation of a discharged phase to the centrifuge bowl, control a backpressure on an outlet for a separated phase of the centrifuge bowl, control the interval of solid discharges and / or control the drive unit to adjust the rotational speed of the centrifuge bowl.Brief description of the Drawings

[0046] The above, as well as additional objects, features and advantages of the present inventive concept, will be better understood through the following illustrative and nonlimiting detailed description, with reference to the appended drawings. In the drawings like reference numerals will be used for like elements unless stated otherwise. Figure 1 shows a schematic drawing of an embodiment of a centrifugal separator of the present disclosure. Figure 2 shows a schematic drawing of a further embodiment of a centrifugal separator of the present disclosure. Figure 3 shows a schematic drawing of centrifuge bowl of a centrifugal separator. Figure 4 shows a schematic drawing of an embodiment of a measurement system. Figure 5 shows a schematic drawing of a further embodiment of a measurement system. Figure 6 shows a schematic drawing of an embodiment of a centrifugal separator for separating a liquid mixture comprising starch. Figure 7 schematically shows the process steps of the general method of the present disclosure. Detailed Description

[0047] The method and the centrifugal separator according to the present disclosure will be further illustrated by the following description with reference to the accompanying drawings.

[0048] Fig. 1 shows an embodiment of a centrifugal separator 1 that is arranged for separating two liquid phases from a liquid feed mixture. The separator 1 comprises a rotatable centrifuge bowl 10, in which the separation takes place, as well as a drive motor 4 for rotating the centrifuge bowl 10 around the axis of rotation (X).The drive motor 4 is in this case an electrical motor comprising a stator and rotor directly attached to the rotatable shaft 5 upon which the centrifuge bowl 10 is mounted. The centrifuge bowl 10is arranged to rotate relative a stationary frame comprising a hood 3 within which the centrifuge bowl 10 is mounted.

[0049] The liquid feed mixture is in this example introduced to the centrifuge bowl 3 via inlet 6 from the top of the separator 1. The two separated phase - a liquid heavy phase and a liquid light phase - are discharge via outlets at the top of the bowl 10. The liquid light phase is discharged via outlet 7 that is closer to the rotational axis as compared to the outlet 8 for discharging the liquid heavy phase. A sludge phase that may be constantly or intermittently ejected to a sludge tank 15, as known in the art, see for example US11027290.

[0050] The centrifugal separator 1 further comprises one or several measurement systems 20. In Fig. 1, such a system 20 has been illustrated with a dotted box, meaning that they optionally may be arranged upstream the inlet 6, downstream the liquid outlet 7 for the liquid light phase, downstream the liquid outlet 8 for the liquid heavy phase or connected to the sludge tank 15, or alternatively arranged between the sludge tank 15 and the centrifuge bowl 10. The measurement system 20 is arranged for measuring the density, turbidity or a physical property related to the solids concentration of a portion of the liquid feed mixture or any of the separated phases and will be further discussed in relation to Figs. 4 and 5 below.

[0051] Fig. 2 shows a further embodiment of a centrifugal separator 1 arranged for separating two liquid phases and a sludge phase from a liquid feed mixture. This separator function in most ways as the separator of Fig. 1, but in this embodiment, the liquid feed mixture is supplied to the centrifuge bowl 10 from the bottom, such as through a hollow spindle 5 onto which the bowl 10 is mounted. The rotor portion of the drive motor 4 is directly connected to the spindle 5. The liquid feed mixture is supplied to the inlet 6 - here illustrated as the bottom portion of the hollow spindle - using a liquid feed pump 31. The inlet is mechanically hermetically sealed using a mechanical seal (not shown). Moreover, the tow liquid outlets 7, 8 are mechanically hermetically sealed with mechanical seals and there is a first valve 32 arranged downstream of the liquid outlet 7 for the separated liquid light phase and for regulating the backpressure of this outlet as well as a second valve 33 arranged downstream of the liquid outlet 8 for the separated heavy phase and for regulating the backpressure of this outlet. In this embodiment, there is a single measurement system 20 arranged downstream of the liquid outlet 8 for the separated liquid heavy phase, more specifically downstream of the second valve 33. The system 20 is arranged for measuring the density, turbidity or a physical property related to the solids concentration of a portion of the separated and discharged heavy phase.

[0052] The centrifugal separator 1 also comprises a separator control unit 50 that is configured for receiving information about the measured density, turbidity or a physical property related to the solids concentration from the measurement system 20, as illustrated by arrow M1. The control unit 50 may comprise any suitable type of programmable logical circuit, processor circuit, or microcomputer, e.g. 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. Thus, the control unit 50 may comprise a processor and an input / output interface for communicating with the measurement system 20 and other parts of the centrifugal separator 1. In this example, the control unit 50 is configured to communicate, by wire or wirelessly, to the liquid feed pump 31, illustrated by arrow C3, and to the first 32 and second valves 33, as illustrated by arrows C1 and C2, respectively. Thus, based on the received input from the measurement system 20, the control unit may control the separation process, e.g. by controlling the amount of backpressure on the liquid outlets by controlling the first 32 and second 33 valves and / or the liquid feed flow by controlling the liquid feed pump 31. As an example, a measured density of the discharged liquid heavy phase as measured by the measurement system 20 may reflect the purity of the separated and discharged liquid heavy phase, and such information may be used by the control unit 50 to control the separator e.g. when the concentration of heavy phase in the liquid feed mixture varies over time. Controlling the feed flow and the backpressures may regulate the radial level of the separation interface within the centrifuge bowl and may thus affect the density of the separated liquid heavy phase.

[0053] Alternatively, the information received by the measurement system 20 may be used by the control unit 50 to check that the density - or purity- of the discharged and separated liquid heavy phase is within a specific target range, and the control unit 50 may further be configured to raise an alarm signal if the measured density is outside such a range.

[0054] As a further example, the information received by the measurement system 20 may be used by the control unit 50 to control the rotational speed of the centrifuge bowl 10 and / or the interval of intermittent solid discharges (explained more in relation to Fig. 3 below

[0055] Fig. 3 shows some more details of the interior of a centrifuge bowl 10 that may be used in a separator 1 of the present invention, such as the separator 1 of Fig. 2. The centrifuge bowl 1 encloses a separation space 13 that is provided with a stack 14 of frustoconical separation discs to achieve effective separation of the liquid feed mixture. The stack 14 is arranged on distributor 12, which also which guides the liquid feed mixture from a central inlet chamber 11 to the separation space 13. The separated liquid light phase moves radially inwards between the separation discs of the stack 14 and is discharged via the liquid light phase outlet chamber 16, whereas separated liquid heavy phase is guided over the top disc 14b to the liquid heavy phase outlet chamber 15. These chamber thus form part of the liquid outlets of the centrifugal separator 1. Both the liquid light phase outlet 16 and the liquid heavy phase outlet 15 are sealed using a single or a double mechanical seal 17. Heavier components in the liquid mixture, e.g. sludge particles and / or heavy phase, move radially outwards between the separation discs and accumulate at the periphery of the separation space 21 at the sludge outlets 14.

[0056] The centrifuge bowl 10 further comprises a set of openable outlets 18 at the periphery of the centrifuge bowl 10. The outlets 18 are for discharging any solids or sludge that have accumulated as a solids phase in the periphery of the bowl 10. The opening and closing of the outlets 18 are controlled by means of an operating slide 19 - also referred to as a sliding bowl bottom. The operating slide 19 forms the lower part of the inner wall of the centrifuge bowl 10 and is movable between a closed position, shown in Fig 3, in which the outlets 18 are closed, and an open position, in which sludge outlets 18 are open. A closing chamber (not shown) is provided below the operating slide 19. During operation, the closing chamber contains that is acting on the operating slide 19 to close the outlets 18. In order to initiate a sludge discharge, the water pressure from underneath the operating slide 19 is reduced so that the lifting force acting to press the operating slide 19 upwards is decreased, which in turn initiates a motion of the operating slide 19 so that the sludge outlets 18 are opened. To reduce the pressure from underneath the operating slide 19, water may for example be introduced from the water source 40 to an opening chamber (not shown) via a line 41, as well-known in the art. When the water has been drained from such an opening chamber, the operating slide 19 is again moved to an upper position to close the sludge outlets 18. In other type of separators, the sludge outlets 18 may take the form of a set of permanently open nozzles.

[0057] Fig. 4 further shows an embodiment of a measurement system 20 that may be used together with a centrifugal separator 1. The measurement system 20 - below just referred to as the system 20 - is arranged as a sampling connection L2 that may be added to an existing pipe L1. This pipe L1 may for example be a stationary inlet pipe for a liquid feed mixture that is arranged upstream of the inlet 1 of the separator 1, or L1 may be a stationary outlet pipe arranged downstream any of the outlets for a discharged phase. The system 20 comprises a regulating valve 25 for directing a portion of the liquid within pipe L1 to sampling connection L2. The portion having been analysed by the system 20 is the directed back to the pipe L1. Alternatively, the portion directed to sampling line L2 may be discarded or directed to anywhere else in the separation process. The system 20 used as a sampling connection L1 may thus be used as an inline measurement system, that allows for measuring the density, turbidity or a physical property related to the solids concentration without interrupting the flow of the liquid within pipe L1. The sampling pipe L2 further comprises a feed pump 21 arranged for pumping the portion to be analysed to density meter 22. Also arranged within the sampling connection L1 is a valve member 24 used as a pressurizing unit - i.e. for increasing the pressure within - the portion within sampling connection L2. The pressure is measured by pressure meter 23, which is also arranged in the sampling connection L2. In this example, the meter 22 for measuring the density, turbidity or a physical property related to the solids concentration is a density meter, such as a Coriolis flow meter. The increased pressure reduces the amount of, or decreases the size of, air bubbles within the portion of which the density is measured, thereby leading to improved and mor accurate density measurements as compared to the prior art.

[0058] Fig. 5 shows an alternative version of a measurement system 20. The system 20 is arranged as a sampling connection L2 as discussed in relation to Fig. 4 above, but the means for deaerating the portion of the sampling connection L2 is different. Instead of increasing the pressure within sampling connection L2, the system 20 comprises a vacuum unit 26 arranged for decreasing the pressure within sampling connection L2 before the density, turbidity or a physical property related to the solids concentration is measured by meter 22. The vacuum unit 26 is used for vacuumizing or reducing the pressure in the portion in L2 and comprises in this example a vacuum chamber 26a through which the portion in sampling connection L2 is directed, as well as a vacuum pump 26b that is connected to vacuum chamber 26a to decrease the pressure within the vacuum chamber 26a. As in the system 20 of Fig. 4, the system 20 with its sampling connection L2 may be used as an inline measurement system in the centrifugal separator 1, and the portion that has been analysed may be directed back to the main pipe L2 onto which the sampling connection L2 is connected or optionally be discarded or directed to another position of the separation process.

[0059] Fig. 6 shows a further embodiment of a centrifugal separator 1 of the present invention. This centrifugal separator 1 is especially adapted for separating a liquid feed mixture containing starch and discharging the separated starch phase as the liquid heavy phase.

[0060] The liquid feed, consisting of both liquid and solids, is led into the rotating centrifuge bowl 10 from the top via a stationary inlet 6, as illustrated by arrow "A. It is then accelerated in a distributor 12, before being led to the separation chamber and the disc stack 14. The actual separation process takes place between the separation discs of the disc stack 14, with the liquid phase moving through the disc stack 14 towards the centre of the bowl 10 and further discharged over a power ring 67 to a liquid light phase outlet 7, as illustrated by arrow "C".

[0061] The heavy phase containing starch is collected at the periphery of the bowl 10 and then continuously discharged through the permanently open nozzles 18 to a heavy phase outlet 8, as illustrated by arrow "B". Part of the heavy phase that is discharged through the nozzles 18 and comprising concentrated solids can be recirculated into the periphery of the centrifuge bowl 10 through a set of recirculation tubes 62 that are connected to a recirculation line 61. Regulating valve 60, such as a three-way valve, arranged downstream of the heavy phase outlet 8 may be used to direct a portion of the discharged solid phase to the recirculation line 61 and thus to the recirculation tubes 62. This is illustrated by arrow "D" in Fig. 6. Further, wash water used to free solubles and other impurities from the solids can also be recirculated to the periphery of the bowl 10 the same way. Therefore, the recirculation line 61 is connected to wash water line 63 and wash water may be introduced to the recirculation line 61 using valve 64 arranged on the wash water line 63, as illustrated by arrow "E". In this embodiment, the centrifuge bowl 10 is mounted on a vertical spindle 5 that is driven via belts by a vertically mounted motor 4. The discharged heavy phase containing starch that is not recirculated is directed through pipe 65. Thus, regulating valve 60 regulates how much of the discharged heavy phase that is to be recirculated via recirculation line 61 and discharged further via discharge pipe 65. Connected to this pipe 65 is a measurement system as a sampling connection for inline density measurements as discussed in relation to Fig. 4 above. Thus, three-way valve 25 is used to direct apportion of the discharged heavy phase to sampling connection L2, in which the portion is degassed or deaerated using the valve 24 arranged within the sampling connection L2 and for pressurizing the portion within sampling connection L2. The density of the pressurized portion is measured as the Baumé concentration by density meter 22. These measurements are received by separator control unit 50 - as illustrated by arrow M1- and is in this example used for regulating the regulating valve 61 that is used for regulating the amount of discharged heavy phase that is to be recirculated to the bowl 10. The measurement system 20 may thus be used for controlling that the discharged starch phase being transported downstream from the separator, i.e. the phase being transported in line 65, arrow "F", has the correct concentration of starch. Furthermore, in this example, the method and separator of the present invention is used for allowing even working conditions of the nozzles 18 within the centrifuge bowl 10, thereby avoiding or decreasing the risk of imbalances. Further, unnecessary recirculation of the starch phase via recirculation line 61 may be avoided. As an alternative or complement, the control unit may be further configured to regulate the amount of wash water based on the measured density from the measurement system 20, e.g. by regulating the valve 64 in wash water line 63.

[0062] Fig. 7. illustrates the general process steps of the method 100 separating a liquid feed mixture into at least one separated phase in a centrifugal separator 1. The method comprises a step a) of rotating 101 the centrifuge bowl 3, a step b) of supplying 102 the liquid feed mixture to the centrifuge bowl 3, a step c) of separating 103 the liquid feed mixture in the centrifuge bowl 3 into at least one separated phase. The method further comprises a step d) of discharging 104 the at least one separated phase from the centrifuge bowl 10 as well as a step e) of deaerating 105 a portion of the liquid feed mixture and / or a discharged separated phase to provide a deaerated portion. Further, the method 100 comprises a step f) of measuring 106 the density, turbidity or a physical property related to the solids concentration, or any combination thereof of the deaerated portion.

[0063] Steps e) and f) may be performed repeatedly during the method 100. Further, steps e) and f) may be performed as inline process steps in the method 100.

[0064] The deaeration of step e) may be comprise pressurizing or vacuumizing the portion of the liquid feed mixture or a portion of a separated phase to decrease the amount of absorbed air in the portion.

[0065] In certain embodiments, the method 100 may further comprise a step g) of controlling 107 the centrifugal separator 1 and / or the separation process based on the measurements in step f). The controlling may comprise controlling the flow rate of the liquid feed mixture to the centrifuge bowl 10, controlling the recirculation of a discharged phase to the centrifuge bowl 10, and / or controlling a backpressure on an outlet for a separated phase of the centrifuge bowl 10.

[0066] If the centrifugal separator comprises a control unit 50, such control unit may be operable to perform the steps of receiving information about the measured density from step f) and operable to perform step g) of controlling the centrifugal separator 1.

[0067] The invention is not limited to the embodiments disclosed but may be varied and modified within the scope of the claims set out below. The invention is not limited to the type of separator as shown in the Figures. The term "centrifugal separator" also comprises centrifugal separators with a substantially horizontally oriented axis of rotation.

Claims

1. A method (100) for separating a liquid feed mixture into at least one separated phase in a centrifugal separator (1) comprising a centrifuge bowl (10), the method (100) comprising the steps of a) rotating (101) the centrifuge bowl (3); b) supplying (102) said liquid feed mixture to the centrifuge bowl (3); c) separating (103) said liquid feed mixture in the centrifuge bowl (3) into at least one separated phase; d) discharging (104) said at least one separated phase from the centrifuge bowl (10); e) deaerating (105) a portion of the liquid feed mixture and / or a portion of a discharged separated phase to provide a deaerated portion; and f) measuring (106) the density, turbidity or a physical property related to the solids concentration, or any combination thereof, of the deaerated portion.

2. A method (100) according to claim 1, wherein steps e) and f) are performed as inline process steps in the method (100) for separating a liquid feed mixture.

3. A method (100) according to claim 1 or 2, wherein step e) of deaerating (105) comprises pressurizing said portion of the liquid feed mixture or a separated phase to decrease the amount of absorbed air in said portion.

4. A method (100) according to claim 1 or 2, wherein step e) of deaerating (105) comprises vacuumizing said portion of the liquid feed mixture or a separated phase to decrease the amount of absorbed air in said portion.

5. A method (100) according to any previous claim, wherein step f) comprises measuring (106) the density or the solids concentration of the deaerated portion based on a particle detection method.

6. A method (100) according to any previous claim, further comprising the step g) of controlling (107) the centrifugal separator (1) and / or the separation process based on the measuring in step f).

7. A method (100) according to claim 6, wherein step g) of controlling (107) comprises controlling the flow rate of the liquid feed mixture to the centrifuge bowl (10), controlling the recirculation of a discharged phase to the centrifuge bowl (10), controlling a backpressure on an outlet for a separated phase of the centrifuge bowl (10), controlling the interval for a solid discharge and / or controlling the rotational speed of the centrifuge bowl (10).

8. A method (100) according to any previous claim, wherein the liquid feed mixture comprises starch and wherein step d) comprises discharging (104) a light phase and a heavy phase, wherein the heavy phase comprises starch, and step e) comprises deaerating (105) a portion of the heavy phase comprising starch, and step f) comprises measuring (106) the Baumé concentration of the deaerated heavy phase portion comprising starch.

9. A method (100) according to claim 6 and 8, wherein step g) comprises controlling (107) the amount of discharged heavy phase that is recirculated to the centrifuge bowl (10).

10. A method (100) according to any one of claims 1-7, wherein the liquid feed mixture comprises citrus fruit juice, wine or a protein mixture.

11. A centrifugal separator (1) for separating liquid feed mixture at least into at least one separated phase, comprising - a centrifuge bowl (10) that is rotatable around an axis of rotation (X) and in which the separation takes place; - a drive motor (4) for rotation of the centrifuge bowl around the axis of rotation (X) - an inlet (6) for supply of the liquid feed mixture to the centrifuge bowl (10), - at least one outlet (6,7) for discharging a separated phase; and wherein the centrifugal separator (1) further comprises at least one measurement system (20) arranged upstream the inlet (6) and / or downstream any outlet (6, 7, 18) for discharging a separated phase and arranged for measuring the density, turbidity or a physical property related to the solids concentration of a portion of said liquid feed mixture and / or a portion of a separated phase, said measurement system (20) comprising - a deaeration unit (24, 26) for deaerating said portion, and - a meter (22) for measuring the density, turbidity or a physical property related to the solids concentration of the deaerated portion.

12. A centrifugal separator (1) according to claim 11, wherein the deaeration unit (24) comprises a pressurizing unit for pressurizing said portion.

13. A centrifugal separator (1) according to claim 11, wherein the deaeration unit comprises a vacuum unit (26) for decreasing the pressure of said portion.

14. A centrifugal separator (1) according to any one of claims 11-13, wherein the meter (22) is arranged for measuring the density or solids concentration based on a particle detection method.

15. A centrifugal separator (1) according to any one of claims 11-14, wherein said measurement system (20) is arranged in a sampling connection that is connected to the inlet (6) or an outlet (6, 7, 18) for a separated phase.

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