WO2025190636A1

WO2025190636A1 - Method for operating a centrifugal separator

Info

Publication number: WO2025190636A1
Application number: PCT/EP2025/054798
Authority: WO
Inventors: Per-Gustaf Larsson
Original assignee: Alfa Laval Corporate AB
Current assignee: Alfa Laval Corporate AB
Priority date: 2024-03-11
Filing date: 2025-02-21
Publication date: 2025-09-18
Anticipated expiration: 2026-09-11
Also published as: EP4616953A1

Abstract

The present invention provides a method (100) for operating a centrifugal separator (1) for separating at least one liquid phase and a solid phase from a liquid feed mixture The centrifugal separator (1) comprises a centrifuge bowl (5) arranged to rotate about an axis of rotation and comprising a separation space (9a), in which surface enlarging inserts (10) are arranged, and a sludge space (9b) arranged radially outside the separation space (9a). The centrifuge bowl (5) further comprises an inlet (14) for supply of the liquid feed mixture, at least one liquid outlet (6, 7) for discharge of a separated liquid phase, a sludge outlet (15) arranged for intermittently discharging a separated solid phase from said centrifuge bowl (5), and a first sensor (61) arranged at a first radial position in the centrifuge bowl (5). The first sensor (61) is a pressure or temperature sensor and said first radial position is within the inner half of the radial extension (ΔR) of the sludge space (9b). The method 100) is comprising the steps of a) rotating (101) the centrifuge bowl (5); b) supplying (102) the liquid feed mixture to the centrifuge bowl (5); c) separating (103) said liquid feed mixture in the centrifuge bowl (5) into at least one liquid phase and a solid phase; d) measuring (104) a pressure or temperature at said first radial position with said first pressure or temperature sensor (61); and e) determining (105) from the measurements in step d) if the solid phase has reached a critical position that is within the inner half of the radial extension (ΔR) of the sludge space (9b); and if so f) discharging (106) a solid phase from said sludge outlet (15).

Description

METHOD FOR OPERATING A CENTRIFUGAL SEPARATOR

Field of the Invention

The present invention relates to the field of high-speed centrifugal separators, and more specifically to methods for operating a high-speed centrifugal separator.

Background of the Invention

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, usually water, accumulates 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 the periphery and close to the rotational axis, respectively. Separation members, such as a stack of frustoconical separation discs, are usually used within the rotating bowl in order to enhance the separation performance. An example of a high-speed centrifugal separator is described in patent application EP 3315205.

During use of a centrifugal separator, a parameter of a liquid feed mixture or its separated light and heavy phase constituents may be measured. The measured parameter may be utilised for monitoring and/or controlling the separation of the liquid feed mixture into the light and heavy phases.

US 7485084 discloses a centrifugal separator and a method of separating a product to a heavy phase and light phase. The separator comprises a sensor for measuring a parameter related to the gas pressure in a central space of the separator.

WO202132353 discloses a centrifugal separation system having a first and second pressure sensor arranged at different radii and positioned to be submerged in the process liquid during operation of the centrifugal separator. The separator further comprises a control unit configured to determine a parameter of the process liquid within the separation space during operation of the centrifugal separator based on measurements from the first and second pressure sensors.

However, there is a need in the art for improved systems and methods for measuring parameters of the separation process and to further utilize such information for enhancing the separation process. Summary of the Invention

A main object of the present invention is to provide a method and a centrifugal separator for measuring parameters within the centrifuge bowl and utilize them for an effective discharge of separated solids.

As a first aspect of the invention, there is provided a method for operating a centrifugal separator for separating at least one liquid phase and a solid phase from a liquid feed mixture. The centrifugal separator comprises a centrifuge bowl arranged to rotate about an axis of rotation and comprising a separation space, in which surface enlarging inserts are arranged, and a sludge space arranged radially outside the separation space.

The centrifuge bowl further comprises an inlet for supply of the liquid feed mixture, at least one liquid outlet for discharge of a separated liquid phase, a sludge outlet arranged for intermittently discharging a separated solid phase from said centrifuge bowl, and a first sensor arranged at a first radial position in the centrifuge bowl. The first sensor is a pressure or temperature sensor, and the first radial position is within the inner half of the radial extension of the sludge space.

The method of the first aspect is comprising the steps of a) rotating the centrifuge bowl; b) supplying the liquid feed mixture to the centrifuge bowl; c) separating the liquid feed mixture in the centrifuge bowl into at least one liquid phase and a solid phase; d) measuring a pressure or temperature at said first radial position with said first pressure or temperature sensor; and e) determining from the measurements in step d) if the solid phase has reached a critical position that is within the inner half of the radial extension of the sludge space; and if so f) discharging a solid phase from said sludge outlet.

The first aspect of the invention is based on the insight that if a pressure sensor or temperature sensor is arranged within the inner half of the radial extension of the sludge space, i.e. at the “first radial position”, it provides a good position to use for initiating a sludge discharge. During the separation process, solids or sludge within the liquid feed mixture that is separated will accumulate at the radial outer position of the sludge space. The solid phase will thus accumulate and build radially inwards towards the outer radius of the separation space and thus the outer radius of the surface enlarging inserts. With measurements from the first sensor at the first position, it may e.g. be determined if a change of pressure or temperature occurs, which may thus indicate that the sludge level has reached the inner radial extension of the sludge space. This is thus a convenient trigger signal to use for initiating a sludge discharge, thereby decreasing the risk of the accumulated solid phase reaching and clogging the surface enlarging inserts, such as a disc stack. Furthermore, the method of the first aspect allows for discharging solids when it is actually needed and not at regular time intervals.

The first sensor is either a pressure sensor or a temperature sensor.

The “solid phase” may comprise some liquid, such as water, and be in the form of sludge, or a sludge phase.

The ’’critical position” is thus a position within the inner half of the sludge space, and indications that the solid phase has reached such a position is used for initiating sludge discharge. The inner half is closer to the axis of rotation as compared to the outer half. The axis of rotation may be vertical.

As an example, the “critical position” may be the first radial position of the first pressure or temperature sensor, or a position that is close to the first radial position of the first pressure or temperature sensor. The critical position may be within the inner 25 %, such as at within the inner 10 % of the radial extension of the sludge space.

Accordingly, the first radial position of the first sensor may be within the inner 25 %, such as at within the inner 10 % of the radial extension of the sludge space. Thus, the first sensor may be positioned just radially outside of the outer radial position of the disc stack.

Step a) of rotating the centrifuge bowl is performed using a drive unit of the centrifugal separator. This may for example be an electrical motor. The centrifuge bowl may be rotated at a speed that is above 3000 rpm, such as above 5000 rpm.

Step b) of supplying liquid feed mixture to the centrifuge bowl may be performed using a pump, as known in the art. Liquid feed mixture may be supplied continuously.

Step c) of separating the liquid feed mixture into a solid phase and at least one liquid phase takes place continuously during the separation process. The liquid feed mixture may be separated into a solid phase and one or two liquid phases, depending on the constituents of the liquid feed mixture and the type of centrifugal separator used.

Step d) of measuring the temperature and/or pressure at the first radial position may be performed continuously or at discrete time points with a certain measuring frequency. Step e) of determining from the measurements if the solid phase has reached the critical position may comprise comparing the measured temperature or pressure with reference values. Step e) may also comprise determining a change, such as an increase, in temperature or pressure, and thereby determining that the solid phase has reached, or is about to reach, a critical position within the sludge space.

Step f) of discharging the separated solid phase based on determining that the solid phase has reached the critical position may be performed by any known intermittent discharge method. As an example, the centrifuge bowl may comprise a set of intermittently openable sludge outlets in the outer wall of the centrifuge bowl. Such outlets may be opened and closed by means of axially moving a sliding bowl bottom within the centrifuge bowl, as known in the art. Thus, step f) may comprise axially moving a sliding bowl bottom to an open position, in which the set of sludge outlets are open to intermittently discharge the solid phase. Step f) may further comprise closing the sludge outlets after discharging the solid phase.

Thus, in embodiments of the first aspect, step f) further comprises continuing the separation of the liquid feed mixture within the centrifuge bowl.

In embodiments of the first aspect, the first sensor is a pressure sensor and wherein the centrifuge bowl further comprises a second pressure sensor arranged at a second radial position in the centrifuge bowl, and wherein step d) comprises d1) measuring a pressure at said first radial position with said first pressure sensor; d2) measuring a pressure at said second radial position with said second pressure sensor, and d3) determining the pressure difference between the first and second radial position.

As an example, the second radial position may also be within the inner half of the radial extension of the sludge space. Accordingly, the second radial position of the second sensor may be within the inner 25 %, such as at within the inner 10 % of the radial extension of the sludge space. The second radial position may be a different radial position than the first radial position but still within the inner half of the radial extension of the sludge space.

As a further example, the second radial position may be within the outer half of the radial extension of the sludge space.

The second radial position may be arranged within the outer 25 %, such as at within the outer 10 % of the radial extension of the sludge space. Step d3) thus comprises measuring the differential pressure between the first and second pressure sensors. This may be an advantage since parameters such as flow through the separator, pressure losses, the radial levels of the inlet and liquid outlets, the counter pressure at the liquid outlet or outlets, may be neglected since they affect the first and second pressure sensors within the sludge space to the same degree.

Based on the determined differential pressure in step d3), one may determine from if the solid phase has reached the critical position that is within the inner half of the radial extension of the sludge space; and if so, discharging a solid phase from the sludge outlet (steps e) and f)).

With two pressure sensors, also the density of the phase between the two pressure sensors may be determined. Thus, step d3) may also comprise determining a density of the phase between the two sensors. When such density has reached a certain level, a sludge discharge may be performed.

As a further example, the centrifuge bowl may further comprise a third pressure sensor arranged at a third radial position in the centrifuge bowl that is within the outer half of the radial extension of the sludge space, and wherein step d) comprises d1) measuring a pressure at said first radial position with said first pressure sensor; d2a) measuring a pressure at said second radial position with said second pressure sensor; d2b) measuring a pressure at said third radial position with said third pressure sensor; d3) determining the pressure difference between the first and second radial position; d4) determining the pressure difference between the first and third radial position; d5) determining the pressure difference between the second and third radial position; d6) determining the density of a solid phase between the second and third radial positions; d7) determining the radial position of the interface between the solid phase and a separated liquid phase based on the determined density in step d6) and the density of the separated liquid phase.

With three pressure sensors and the first radial position of the first pressure sensor being within the inner half of the radial extension of the sludge space, both the second radial position of the second pressure sensor and the third radial position of the third pressure sensor are advantageously within the outer half of the radial extension of the sludge space, such as within the outer 25 %, such as at within the outer 10 % of the radial extension of the sludge space. However, the second and third radial positions may be at different radial levels. As an example, the second radial position may be radially outside of the third radial position.

In step d6), the density is measured on a solid phase that is present between the second and third radial positions, e.g. when both second and third sensors are arranged within the outer half of the radial extension of the sludge space.

With three pressure sensors, step d) may thus comprise measuring the individual pressure differences between all sensors. This is used to determine the actual density of the phase, usually the solid phase, which is between the outer sensors, i.e. between the second and third sensors. The second and third sensors may thus be arranged radially close to each other, so both sensors are submerged in the same phase. The density of the solid phase may be calculated based on the measured pressure difference between the second and third sensors, the radial positions of the second and third sensors and the rotational speed of the centrifuge bowl.

For instance, the density may be calculated utilising the formula:

0.5 wherein p2 and p3 are the pressures measured by the respective second and third pressure sensors in bar, w is the rotational speed in rad/s, and rp2 and rp3 are the respective radial positions of the second and third pressure sensors in mm.

When the density of the phase, such as a solid phase, between the second and third radial positions is determined (step d6), the radial position the interface between the solid phase and a separated liquid phase may be determined with knowledge of the density of the separated liquid phase. This may be known e.g. from a look-up table. The separated liquid phase may for example be water. As an example, one may determine how much pressure increase it theoretically should be if the entire space between the pressure is filled with solid phase compared with separated liquid phase. Comparing this with the actual measured differential pressures, a level determination in percentage, such as. a radial position as a percentage of the distance between the second and first sensor, may be determined.

Consequently, in this example, step e) then comprises determining if the radial position of the interface between the solid phase and a separated liquid phase has reached the critical position. If so, solid phase may be discharged (step f)). Moreover, when using two or more pressure sensors, the measured absolute pressure values from the two pressure sensors could be used as an alternative to measuring the pressure differences between the sensors. However, this may be a less accurate but still functioning way to determine when the sludge should be discharged.

In embodiments of the first aspect, the first sensor is a temperature sensor and wherein step d) further comprises measuring a temperature in the liquid feed mixture. Then, step e) may comprise determining the temperature difference between the first sensor and the liquid feed mixture to determine if the solid phase has reached a critical position that is within the inner half of the radial extension (AR) of the sludge space.

For example, if the temperature sensor within the bowl is covered in sludge or solids, there will be a difference in measured temperature compared to the temperature of the liquid feed mixture. If this temperature difference is above a certain threshold, it may be determined that the solid phase has reached a critical position that is within the inner half of the radial extension of the sludge space in step e).

In embodiments of the first aspect, at least one sensor is positioned to be submerged in the process liquid during operation of the centrifugal separator. As an example, all sensors, such as a first and second sensor, or a first, a second and a third sensor, may be positioned to be submerged in the process liquid during operation of the centrifugal separator. The sensor or sensors may thus be positioned to be submerged in process liquid, i.e. liquid mixture that is separated or a separated phase, during the separation process.

As a second aspect of the invention, there is provided a centrifugal separator for separating at least one liquid phase and a solid phase from a liquid feed mixture. The centrifugal separator comprises a centrifuge bowl arranged to rotate about an axis of rotation and comprising a separation space, in which surface enlarging inserts are arranged, and a sludge space arranged radially outside the separation space. The centrifuge bowl further comprises an inlet for supply of the liquid feed mixture, at least one liquid outlet leading from the centrifuge bowl for discharge of a separated liquid phase, a sludge outlet arranged for intermittently discharging a separated solid phase from said centrifuge bowl, and a first sensor arranged at a first radial position in the centrifuge bowl, wherein the first sensor is a pressure or temperature sensor and said radial position is within the inner half of the radial extension of the sludge space; wherein the centrifugal separator further comprises a control unit that is configured to determine if the solid phase has reached a critical position that is within the inner half of the radial extension of the sludge space based on measurements from the first sensor; and if so, initiating a discharge of a separated solid phase from said centrifuge bowl via said sludge outlet.

This aspect may generally present the same or corresponding advantages as the former aspect. Effects and features of this second aspect are largely analogous to those described above in connection with the first aspect. Embodiments mentioned in relation to the first aspect are largely compatible with the second aspect.

The centrifugal separator of the second aspect may thus be used for performing the method of the first aspect as discussed above.

The centrifugal separator is for separation of a liquid feed mixture. The liquid feed mixture may be an aqueous liquid or an oily liquid. As an example, the centrifugal separator may be for separating solids and one or two liquids from the liquid feed mixture.

The centrifuge bowl encloses by it walls a separation space and a sludge space. The separation space, in which the separation of the fluid mixture takes place, comprises surface enlarging inserts, i.e. separation members that may be in the form of a stack of separation discs. The separation discs may e.g. be of metal. Further, the separation discs may be frustoconical separation discs, i.e. having separation surfaces forming frustoconical portions of the separation discs. The separation discs may be arranged coaxially around the axis of rotation at a distance from each other such that to form passages between each two adjacent separation discs.

The centrifuge bowl of the separator may be arranged to be rotated around vertical axis of rotation, i.e. the axis of rotation may extend vertically. The centrifuge bowl is usually supported by a spindle, i.e. a rotating shaft, and may thus be mounted to rotate with the spindle. Consequently, the centrifugal separator may comprise a spindle that is rotatable around the axis of rotation (X). The centrifugal separator may be arranged such that the centrifuge bowl is supported by the spindle at one of its ends, such at the bottom end or the top end of the spindle.

The centrifugal separator may further comprise a stationary frame in which the centrifuge bowl is mounted. The frame may comprise an upper hood section that covers the centrifuge bowl.

The centrifugal separator may further comprise a drive member that is arranged to rotate the centrifuge bowl around the axis of rotation. The drive member may comprise an electrical motor arranged to drive e.g. a spindle directly or may for example be provided beside the spindle and rotate the rotating parts of the centrifugal separator by a suitable transmission, such as a belt or a gear transmission.

The centrifugal separator also comprises an inlet for supply liquid mixture to be separated (the liquid feed mixture). This inlet may be arranged for receiving the liquid feed mixture and be arranged centrally in the centrifuge bowl, thus at the rotational axis. The centrifuge bowl may be arranged to be fed from the bottom, such as through a rotating spindle onto which the centrifuge bowl is mounted. However, the centrifuge bowl may also be arranged to be fed from the top, such as through a stationary inlet pipe extending into the bowl to the inlet.

Further, the at least one liquid outlet for a separated liquid phase may be in the form of one or two liquid outlets. Such liquid outlets for separated liquid phase or phases may be arranged at the top or the bottom of the centrifugal separator.

The centrifugal separator is also arranged for discharging a solid phase, i.e. a separated solid phase - that may also contain some liquid - to the surrounding space around the centrifuge bowl. This is performed by the sludge outlet, which may be in the form of a set of ports arranged to be opened intermittently during operation. The sludge outlets may thus be a number of ports arranged at or near the periphery of the centrifuge bowl. Hence, the centrifugal separator may further comprise an intermittent discharge system arranged for intermittently opening and closing the sludge outlet during operation, as known in the art. The centrifugal separator may be arranged for emptying a partial content of the bowl during such an intermittent discharge (partial discharge) or arranged for emptying the whole content of the centrifuge bowl during intermittent discharge (full discharge).

The intermittent discharge system thus controls the opening of the sludge outlets. For this purpose, the intermittent discharge system may comprise an operating slide in, e.g. in the form of a sliding bowl bottom, which is axially movable between a closed position, in which the sludge outlets are closed, and an open position, in which the sludge outlets are open. Keeping the operating slide in a closed position may be effected by supplying water via a channel to a closing chamber in order to hold the operating slide in the closed position. Opening the ports may be affected by supplying opening water to an opening chamber and/or draining water through valve members arranged in the centrifuge bowl.

A pressure sensor of the present disclosure is thus operable to generate a sensor output indicative of a pressure at the position at which it is mounted. Further, a pressure sensor of the present disclosure is configured to communicate with the control unit. The pressure sensor is further arranged to rotate with the centrifuge bowl. As mentioned above, the first sensor is a pressure sensor or a temperature sensor. The first sensor may thus as an alternative be operable to generate a sensor output indicative of a temperature at the position at which it is mounted.

The control unit is configured to communicate with the pressure sensor (or sensors) and/or the temperature sensor in of the bowl, and with help of such input from the sensor (or sensors) determine if the solid phase has reached a critical position that is within the inner half of the radial extension of the sludge space. If this is the case, the control unit is configured to initiate a sludge discharge via the sludge outlet, e.g. by the use of the intermittent discharge system. The control unit may thus be configured to receive measurement data from one or several sensors, such as pressure or temperature sensors.

The control unit may be arranged in a stationary part of the centrifugal separator and be configured to communicate with the sensors via a wireless connection. As an alternative, the control unit may be and arranged to rotate with the rotor.

The control unit 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 may comprise a processor and an input/output interface for communicating with the sensor or sensors for receiving information about a measured pressure or temperature.

Thus, the control unit may be operable to perform the steps d) and/or e) as discussed in relation to the first aspect above.

In embodiments of the second aspect, the first sensor is a pressure sensor and the centrifuge bowl further comprises a second pressure sensor arranged at a second radial position, and wherein the control unit is configured for determining the pressure difference between the first and second radial position to determine if the solid phase has reached a critical position that is within the inner half of the radial extension of the sludge space.

As an example, the second radial position is also within the inner half of the radial extension of the sludge space.

As an alternative, the second radial position is within the outer half of the radial extension of the sludge space. In a further example, the centrifuge bowl comprises a third pressure sensor arranged at a third radial position that is within the outer half of the radial extension of the sludge space, and wherein the control unit is configured for determining the pressure difference between the first and second radial position; determining the pressure difference between the first and third radial position; determining the pressure difference between the second and third radial position determining the density of a solid phase between the second and third radial positions, determining the radial position of the interface between the solid phase and a separated liquid phase based on the determined density of the solid phase and the density of the separated liquid phase, and based on the determined the radial position of the interface between a solid phase and a separated liquid phase, determine if the solid phase has reached a critical position that is within the inner half of the radial extension of the sludge space.

In embodiments of the second aspect, the first sensor is a temperature sensor and the centrifugal sensor further comprises a second temperature sensor operable to measure the temperature of the liquid feed mixture. Then, the control unit may be configured to determine the temperature difference between the temperature sensor in the bowl and such a second temperature sensor.

In embodiments of the second aspect, least one sensor is positioned to be submerged in the process liquid during operation of the centrifugal separator.

Submerging a sensor means that at least the pressure or temperature sensitive portions of the sensors are submerged in process liquid. That is, the sensor is mounted in the centrifuge bowl such that at least the pressure or temperature sensitive portions of the sensor will be covered by process liquid during operation of the centrifugal separator. Process liquid may be liquid mixture to be separated, a separated solid phase, or a separated liquid phase.

Brief description of the Drawings

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 a centrifugal separator. Figure 2 shows a schematic section drawing of a centrifuge bowl with inlet and outlets.

Figure 3 shows a schematic section drawing of the sludge space of a centrifuge bowl according to an embodiment.

Figure 4 shows a schematic section drawing of the sludge space of a centrifuge bowl according to another embodiment.

Figure 5 shows a schematic section drawing of the sludge space of a centrifuge bowl according to another embodiment.

Figure 6 shows a schematic section drawing of the sludge space of a centrifuge bowl according to another embodiment.

Figure 7 schematically shows the process steps of the general method of the present disclosure.

Figure 8 schematically shows some process steps in an embodiment of the method.

Figure 9 schematically shows some process steps in an embodiment of the method.

Detailed Description

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.

Figs.1 and 2 schematically show a centrifugal separator 1 and the centrifuge bowl 5 of the centrifugal separator according to an embodiment of the present disclosure.

The centrifugal separator 1 is configured to separate two liquid phases - a liquid heavy phase and a liquid light phase - as well as a solid phase from a liquid feed mixture. The centrifugal separator 1 has a rotatable part 4, comprising the centrifuge bowl 5 and drive spindle 4a.

The centrifugal separator 1 is further provided with a drive motor 3. This motor 3 may for example comprise a stationary element and a rotatable element, which rotatable element surrounds and is connected to the spindle 4a such that it transmits driving torque to the spindle 4a and hence to the centrifuge bowl 5 during operation. The drive motor 3 may hence be an electric motor. Alternatively, the drive motor 3 may be connected to the spindle 4a by transmission means such as a drive belt or the like, and the drive motor may alternatively be connected directly to the spindle 4a. The centrifuge bowl 5, shown in more detail in Fig. 2, is supported by the spindle 4a, which is rotatably arranged under an upper hood of the stationary frame 2. The bowl 5 is rotatably mounted around the vertical axis of rotation (X) in a bottom bearing 22 and a top bearing 21. The upper hood of the stationary frame 2 surrounds the centrifuge bowl 5.

In the centrifugal separator as shown in Fig. 1 , liquid feed mixture to be separated is fed to the bottom to the centrifuge bowl 5 via the drive spindle 4a. The drive spindle 4a is thus in this embodiment a hollow spindle, through which the feed is supplied to the centrifuge bowl 5. However, in other embodiments, the liquid feed mixture to be separated is supplied from the top, such as through a stationary inlet pipe extending into the centrifuge bowl 5.

After separation has taken place within the centrifuge bowl 5, separated liquid heavy phase is discharged through stationary outlet pipe 6a, whereas separated liquid light phase is discharged through stationary outlet pipe 7a. The separated solid phase is intermittently ejected to the space surrounding the centrifuge bowl 5.

Fig. 2. shows a more detailed view of the centrifuge bowl 5 of the centrifugal separator 1.

The centrifuge bowl 5 forms within itself a separation space 9a and a sludge space 9b that is located radially outside the separation space 9a. In the separation space 9a, a stack 10 of separation discs is arranged coaxially around the axis of rotation (X). The stack 10 is arranged to rotate together with the centrifuge bowl 5 and provides for an efficient separation of the liquid feed mixture into at least a liquid light phase and a liquid heavy phase. Thus, in the separation space 9a, the centrifugal separation of the liquid feed mixture takes place during operation. The sludge space 9b is in this embodiment confined between an inner surface of the outer wall 13 of the centrifuge bowl 5 and an axially movable operating slide 16.

The disc stack 10 is arranged under top disc 23 and is further supported at its axially lowermost portion by distributor 11. The distributor 11 comprises an annular conical base portion arranged to conduct liquid mixture from the central inlet 14 of the centrifuge bowl 5 to a predetermined radial level in the separation space 9a.

The centrifuge bowl 5 further comprises an inlet 14 in the form of a central inlet chamber formed within or under the distributor 11. The inlet 14 is arranged for receiving the liquid feed mixture and is thus in fluid communication with the hollow interior 4b of the spindle 4a, through which the liquid feed is supplied to the centrifuge bowl 5. The inlet 14 communicates with the separation space 9a via passages 17 formed in the base portion of the distributor 11. The passages 17 may be arranged so that liquid mixture is transported to a radial level that corresponds to the radial level of the cut-outs 25 provided in the separation discs of the stack 10. The cut-outs 25 form axial channels within the disc stack and distributes the liquid feed mixture throughout the disc stack 10.

The radially outer portion of the disc stack 10 communicates via a first liquid outlet 6 via channels 24 for discharge of a liquid heavy phase axially over the top disc 23. The radially inner portion of the disc stack 10 communicates with a liquid outlet 7 for a separated light phase of the liquid feed mixture. Separated liquid phases may then be discharged to stationary outlet pipes 6a, 7a that are connected to the centrifuge bowl via mechanical seals 50, 30. As this is an airtight design, they are also often called hermetic seals. The inlet channel 4b is also sealed at lower end of the hollow spindle 4a, thus preventing communication between the inlet channel 4b and the surroundings. The mechanical seal at the inlet is not shown in Fig. 2.

The centrifuge bowl 5 is further provided with sludge outlets 15 at the radially outer periphery of the sludge space 9b. These outlets 15 are evenly distributed around the rotor axis (X) and are arranged for intermittent discharge of a solid phase that is separated from the liquid feed mixture. The solid phase thus comprises solids. The opening of the outlets 15 is controlled by means of an operating slide 16 actuated by operating water channels below the operating slide 16, as known in the art. In its position shown in the drawing, the operating slide 16 abuts sealingly at its periphery against the upper part of the centrifuge bowl 5, thereby closing the sludge space 9b from connection with outlets 15, which are extending through the centrifuge bowl 5. The centrifuge bowl 5 is defined by a surrounding outer wall 13.

During operation of the separator as shown in Fig. 1 and 2, the centrifuge bowl 5 is brought into rotation by the drive motor 3. Via the spindle 4a, liquid feed mixture to be separated is brought into the separation space 9a, as indicated by arrow “A”. Depending on the density, different phases in the liquid feed mixture is separated between the separation discs of the stack 10. Heavier component, such as a liquid heavy phase and a solid phase, move radially outwards between the separation discs of the stack 10 to the sludge space 9b, whereas the phase of lowest density, such as a liquid light phase, moves radially inwards between the separation discs of the stack 10 and is forced through the outlet pipe 7a via liquid outlet 7, as indicated by arrow “C”. The liquid of higher density is instead discharged over the top disc 23 via discharge channels 24 to another liquid outlet 6 and further out via stationary outlet pipe 6a, as indicated by arrow “B”. Thus, during separation, an interphase between the liquid of lower density and the liquid of higher density is formed in the centrifuge bowl 5, such as radially within the stack of separation discs. Solids, or sludge, accumulate at the periphery of the sludge space 9b and is emptied intermittently from within the centrifuge bowl by the sludge outlets 15 being opened, whereupon sludge and a certain amount of fluid is discharged from the separation chamber by means of centrifugal force, as indicated by arrow “D”.

In this example, operating water for controlling the position of the operating slide is supplied via operating water module (OWM) 45, that is configured to supply operating water with a certain pressure to the centrifuge bowl 5, as known in the art. This is indicated by arrow “Y3” in Fig. 1. Further, the centrifugal separator comprises a control unit 40. This control unit may be the unit that controls operation, such as rotational speed, of the centrifugal separator 1. The control unit 40 may thus control drive unit 3. According to the present disclosure, the control unit further communicates with one or several sensors that are positioned within the centrifuge bowl 5, as indicated by arrow “Y1” in Fig. 1 and based on such input may initiate a sludge discharge via the OWM 45, as indicated by arrow “Y3” in Fig. 1. The sensor setup will further be discussed in relation to Figs. 3-6 below.

Fig. 3 shows a cross-section of the centrifuge bowl 5, more specifically the sludge space 9b that is arranged radially outside of the stack 10 of separation discs (that is arranged in the separation space 9a). The centrifuge bowl 5 comprises a first sensor 61 that is arranged at a first radial position R1. The sludge space 9b extends a radial distance of AR, and the first radial position R1 is within the inner half of the radial extension AR of the sludge space 9b. The first sensor 61 is arranged on or in the upper inner wall of the centrifuge bowl wall 13 and is in this case arranged just radially outside of the disc stack 10. Thus, the first radial position is within the inner 10% of the radial extension AR of the sludge space 9b.

The first sensor 61 may be a temperature or pressure sensor. During operation of the centrifugal separator, i.e. during a separation process, separated sludge builds up in the outer portion of the sludge space 9b and forms an interface with a liquid phase at position Ri. As long as the interphase is in the sludge space 9b, there is a minor influence on separation quality. As more and more sludge is separated, the interphase will grow radially inwards. The inventors have realised that a sludge discharge should be initiated before the solid phase reaches the disc stack - otherwise the discs could be clogged with solids that severely decrease separation quality - and that a position of a temperature or pressure sensor at the inner half of the radial extension AR of the sludge space 9b is advantageous since it may provide for alerting the control unit 45 to initiate a discharge. As discussed above, the control unit (not shown in Fig 3) communicates with the first sensor. As the solid phase grows radially inwards, a rise in measured temperature and/or pressure with the first pressure sensor may indicate that the solid phase has reached a critical position that is within the inner half of the radial extension AR of the sludge space 9b. This critical position may be at or near the first radial position R1.

In the embodiment shown in Fig. 3, the control unit 40 is configured to determine if the solid phase has reached a critical position that is within the inner half of the radial extension AR of the sludge space 9b based on measurements from the first sensor 61 , and if so, communicate to the intermittent discharge system - in this case the OWM 45 - to initiate a discharge of the separated solid phase from the centrifuge bowl 5 via the sludge outlet 15, i.e. by axially moving the operating slide. However, the intermittent discharge system does not have to comprise an OWM module 45, but may instead be based on other operating methods.

With the position of the first sensor 61 within the inner half of the radial extension AR of the sludge space 9b, sludge discharge may be performed when needed and not at regular time intervals. This optimizes the process with less loss of separated liquid phase during sludge discharge. Further, sludge is not allowed to reach the disc stack 10 before it is discharged.

Consequently, in the setup as shown in Fig 3, the method 100 as illustrated in Fig 7 may be performed, i.e. the process steps of a) rotating 101 the centrifuge bowl 5; b) supplying 102 the liquid feed mixture to the centrifuge bowl 5; c) separating 103 the liquid feed mixture in the centrifuge bowl 5 into a first and a second liquid phase and a solid phase. The method 100 further comprises steps d) of measuring 104 a pressure or temperature at said first radial position with the first pressure or temperature sensor 61 and a step e) of determining 105 from the measurements in step d) if the solid phase has reached a critical position that is within the inner half of the radial extension (AR) of the sludge space 9b.

Step e) may for example comprise determining a change, such as an increase, in temperature or pressure, and thereby determining that the solid phase has reached, or is about to reach, the critical position within the sludge space 9b. If it is determined that the solid phase has reached the critical position, step f) of discharging 106 a solid phase from the sludge outlet 15 is performed. If it has not reached the critical position, the step of continuing 107 with the separation process may be performed.

The temperature or pressure from the first sensor 61 may be measured continuously or at a specific frequency, depending e.g. on the expected rate of sludge build up in the sludge space 9b.

As an example, the first sensor 61 may be a temperature sensor. Then, the centrifugal separator 1 may comprise a second temperature sensor operable to measure the temperature of the liquid feed mixture that is supplied to the bowl via spindle 4a. Such second temperature sensor may be operable to measure the temperature of the liquid feed mixture in an inlet pipe that is connected to the spindle 4a, i.e. connected to the hollow interior 4b of the spindle (see Fig .2). Then, the measured temperature difference between the first sensor 61 and such a second sensor may be used as a trigger signal to initiate discharge of the solid phase. If the first sensor 61 is covered in solids, there may be a higher difference in temperature compared to the liquid feed mixture, and this may indicate that the solid phase has reached the first sensor 61 and that a solids discharge should be initiated.

Fig. 4 shows another embodiment of the centrifuge bowl 5. This functions as discussed in relation to Fig. 3 above, with the differences discussed below. In this example, the first sensor 61 is a pressure sensor, and the centrifuge bowl 5 further comprises a second pressure sensor 62 that is arranged at a second radial position R2. This second radial position R2 is also within the inner half AR of the radial extension AR of the sludge space 9b, but at a slightly larger radius than the first position of R1.

Using two sensors at R1 and R2 may be advantageous in that the pressure difference between the two sensors may be calculated, which makes the method less sensitive to measured absolute pressure levels. The pressure difference between the two sensors could thus be used to determine if the solid phase has reached a critical position that is within the inner half of the radial extension AR of the sludge space 9b.

The embodiment as illustrated in Fig. 5 is almost identical to the embodiment shown in Fig. 4, but in this example the second pressure sensor 62 is arranged within the outer half of the radial extension AR of the sludge space 9b.

The first 61 and second 62 sensors are thus positioned within the sludge space 9b but at different radius from the axis of rotation. As an example, the second pressure sensor 62 may be arranged as far out as possible and the first pressure sensor 61 as close to the disc stack 10 as possible. When the solid phase is starting to accumulate between the two sensors, the pressure will increase on the second sensor 62 but not on the first sensor 61. This means that the differential pressure between the two sensors will be a measure of the sludge accumulation within the sludge space, and from that, the control unit 40 may determine when the sludge space 9b needs to be discharged, thereby decreasing the need for timer-based discharges.

Having two sensors may also be advantageous in that the amount or level of separated liquid phase may affect the two sensors 61, 62 equally.

In the embodiments of Fig. 4 and 5, the control unit 40 is thus configured for determining the pressure difference between the first and second radial position to determine if the solid phase has reached the critical position that is within the inner half of the radial extension AR of the sludge space 9b.

Consequently, in the setup as shown in Figs. 4 and 5, step d) of measuring 104 a pressure at the first radial position with the first pressure sensor 61 may comprise the sub steps as illustrated in Fig. 8, i.e. the sub step of d1) measuring 20 the pressure at the first radial position with said first pressure sensor 61 ; d2) measuring 202 the pressure at the second radial position with the second pressure sensor 62; and a sub step d3) of determining 203 the pressure difference between the first and second radial position.

Fig. 6 shows yet another embodiment of the centrifuge bowl 5. This functions as discussed in relation to Figs. 3-5 above, with the differences discussed below.

The centrifuge bowl 5 comprises a first pressure sensor 61 that is arranged at a first radial position R1 in the centrifuge bowl 5 that is within the inner half of the radial extension AR of the sludge space 9b. The centrifuge bowl 5 also comprises a second pressure sensor 62 that is arranged at a second radial position R2 in the centrifuge bowl 5 that is within the outer half of the radial extension AR of the sludge space 9b as well as a third pressure sensor 63 that is arranged at a third radial position R3 in the centrifuge bowl 5 that is within the outer half of the radial extension AR of the sludge space 9b. The second pressure sensor 62 is arranged radially outside the third pressure sensor, but both are arranged within the outer 25 % of the radial extension AR of the sludge space 9b. All three pressure sensors 61 , 62, 63 communicate with the control unit 40. With the setup as disclosed in Fig. 3, the second 62 and third 63 pressure sensors may be used for determining the density of the solid phase that builds up and covers both second 62 and third 63 sensors. With these two sensors close to each other at the outer region of the sludge space 9b, it is possible to calculate the density of the solid phase based on the pressure readings from these sensors, the rotational speed of the centrifuge bowl and the second and third radial positions For instance, the density of the solid phase may be calculated utilising the formula:

Moreover, with knowledge of the density of the liquid phase, i.e. the phase that forms the radial interphase Ri with the solid phase, the radial level of the interphase may be calculated. As an example, one may determine how much pressure increase it theoretically should be if the entire space between the pressure is filled with solid phase compared with separated liquid phase. Comparing this with the actual measured differential pressures, a level determination in percentage, such as. a radial position as a percentage of the distance between the second and first sensor, may be determined.

With knowledge of the radial position of the interphase Ri, one may compare this level with a critical position within the inner half of the radial extension AR of the sludge space 9b, and thus determine if the interphase has reached this position. As discussed above, this critical position may for example be at, or slightly radially outwards from, the first position R1 of the first pressure sensor.

With three pressure sensors, step d) may thus comprise measuring the individual pressure differences between all sensors.

Consequently, in the setup as shown in Fig. 6, step d) of measuring 104 a pressure at the first radial position with the first pressure sensor 61 may comprise the sub steps as illustrated in Fig. 9, i.e. the sub steps of d1) measuring 301 a pressure at the first radial position with the first pressure sensor 61 ; d2a) measuring 302 a pressure at the second radial position with the second pressure sensor 62; d2b) measuring 303 a pressure at the third radial position with the third pressure sensor 63; d3) determining 304 the pressure difference between the first and second radial position; d4) determining 305 the pressure difference between the first and third radial position; d5) determining 306 the pressure difference between the second and third radial position; d6) determining 307 the density of a solid phase between the second and third radial positions; d7) determining 308 the radial position Ri of the interface between the solid phase and a separated liquid phase based on the determined density in step d6) and the density of the separated liquid phase.

In the embodiments above, at least one or all of the sensors shown may be positioned so that they are submerged in the process liquid during operation of the centrifugal separator, i.e. during separation of the liquid feed mixture into a solid phase and at least one liquid phase.

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 operating a centrifugal separator (1) for separating at least one liquid phase and a solid phase from a liquid feed mixture; wherein the centrifugal separator (1) comprises a centrifuge bowl (5) arranged to rotate about an axis of rotation and comprising a separation space (9a), in which surface enlarging inserts (10) are arranged, and a sludge space (9b) arranged radially outside the separation space (9a); wherein the centrifuge bowl (5) further comprises an inlet (14) for supply of the liquid feed mixture, at least one liquid outlet (6, 7) for discharge of a separated liquid phase, a sludge outlet (15) arranged for intermittently discharging a separated solid phase from said centrifuge bowl (5), and a first sensor (61) arranged at a first radial position in the centrifuge bowl (5); wherein the first sensor (61) is a pressure or temperature sensor and said first radial position is within the inner half of the radial extension (AR) of the sludge space (9b); the method (100) comprising the steps of a) rotating (101) the centrifuge bowl (5); b) supplying (102) the liquid feed mixture to the centrifuge bowl (5); c) separating (103) said liquid feed mixture in the centrifuge bowl (5) into at least one liquid phase and a solid phase; d) measuring (104) a pressure or temperature at said first radial position with said first pressure or temperature sensor (61); and e) determining (105) from the measurements in step d) if the solid phase has reached a critical position that is within the inner half of the radial extension (AR) of the sludge space (9b); and if so f) discharging (106) a solid phase from said sludge outlet (15).

2. A method (100) according to claim 1, wherein the first sensor (61) is a pressure sensor and wherein the centrifuge bowl (5) further comprises a second pressure sensor (62) arranged at a second radial position in the centrifuge bowl (5), and wherein step d) comprises d1) measuring (201) a pressure at said first radial position with said first pressure sensor (61); d2) measuring (202) a pressure at said second radial position with said second pressure sensor (62); and d3) determining (203) the pressure difference between the first and second radial position.

3. A method (100) according to claim 2, wherein the second radial position is also within the inner half (AR) of the radial extension of the sludge space (9b).

4. A method (100) according to claim 2, wherein the second radial position is within the outer half (AR) of the radial extension of the sludge space (9b).

5. A method (100) according to any one of claims 2-4, wherein the centrifuge bowl (5) further comprises a third pressure sensor (63) arranged at a third radial position in the centrifuge bowl (5) that is within the outer half of the radial extension (AR) of the sludge space (9b), and wherein step d) comprises d1) measuring (301) a pressure at said first radial position with said first pressure sensor (61); d2a) measuring (302) a pressure at said second radial position with said second pressure sensor (62); d2b) measuring (303) a pressure at said third radial position with said third pressure sensor (63); d3) determining (304) the pressure difference between the first and second radial position; d4) determining (305) the pressure difference between the first and third radial position; d5) determining (306) the pressure difference between the second and third radial position; d6) determining (307) the density of a solid phase between the second and third radial positions; d7) determining (308) the radial position (Ri) of the interface between said solid phase and a separated liquid phase based on the determined density in step d6) and the density of the separated liquid phase.

6. A method (100) according to claim 1, wherein the first sensor (61) is a temperature sensor and wherein step d) further comprises measuring a temperature in the liquid feed mixture, and further wherein step e) comprises determining the temperature difference between the first sensor (61) and the liquid feed mixture to determine if the solid phase has reached a critical position that is within the inner half of the radial extension (AR) of the sludge space (9b).

7. A method (100) according to any previous claim, wherein at least one sensor (61, 62, 63) is positioned to be submerged in the process liquid during operation of the centrifugal separator (1).

8. A centrifugal separator (1) for separating at least one liquid phase and a solid phase from a liquid feed mixture, wherein the centrifugal separator (1) comprises a centrifuge bowl (5) arranged to rotate about an axis of rotation and comprising a separation space (9a), in which surface enlarging inserts (10) are arranged, and a sludge space (9b) arranged radially outside the separation space (9a); wherein the centrifuge bowl (5) further comprises an inlet (14) for supply of the liquid feed mixture, at least one liquid outlet (6,7) leading from the centrifuge bowl (5) for discharge of a separated liquid phase, a sludge outlet (15) arranged for intermittently discharging a separated solid phase from said centrifuge bowl (5), and a first sensor (61) arranged at a first radial position in the centrifuge bowl (5), wherein the first sensor (61) is a pressure or temperature sensor and said radial position is within the inner half of the radial extension (AR) of the sludge space (9b); wherein the centrifugal separator (1) further comprises a control unit (40) that is configured to determine if the solid phase has reached a critical position that is within the inner half of the radial extension (AR) of the sludge space (9b) based on measurements from the first sensor (61); and if so initiating a discharge of a separated solid phase from said centrifuge bowl (5) via said sludge outlet (15).

9. A centrifugal separator (1) according to claim 8, wherein the first sensor (61) is a pressure sensor and wherein the centrifuge bowl (5) further comprises a second pressure sensor (62) arranged at a second radial position, and wherein the control unit (40) is configured for determining the pressure difference between the first and second radial position to determine if the solid phase has reached a critical position that is within the inner half of the radial extension (AR) of the sludge space (9b).

10. A centrifugal separator (1) according to claim 9, wherein the second radial position is also within the inner half of the radial extension (AR) of the sludge space (9b).

11. A centrifugal separator (1) according to claim 9, wherein the second radial position is within the outer half of the radial extension (AR) of the sludge space (9b).

12. A centrifugal separator (1) according to any one of claims 9-10, wherein the centrifuge bowl (5) further comprises a third pressure sensor (63) arranged at a third radial position that is within the outer half of the radial extension (AR) of the sludge space (9b), and wherein the control unit (40) is configured for determining (304) the pressure difference between the first and second radial position; determining (305) the pressure difference between the first and third radial position; determining (306) the pressure difference between the second and third radial position determining (307) the density of a solid phase between the second and third radial positions, determining (308) the radial position of the interface (Ri) between the solid phase and a separated liquid phase based on the determined density of the solid phase and the density of the separated liquid phase, and based on the determined the radial position (Ri) of the interface between a solid phase and a separated liquid phase, determine if the solid phase has reached a critical position that is within the inner half of the radial extension (AR) of the sludge space (9b).

13. A centrifugal separator (1) according to any one of claims 8-12, wherein at least one sensor (61, 62, 63) is positioned to be submerged in the process liquid during operation of the centrifugal separator (1).