Method for specifying or monitoring the conveying flow rate of an eccentric screw pump

Abstract

The present invention is a method for specifying or monitoring the effective delivery flow rate (Q) of an operating eccentric screw pump, wherein the eccentric screw pump has a stator (1) and a rotor (12) that rotates eccentrically at a predetermined pump frequency within the stator (1), and the effective delivery flow rate (Q) is determined from the difference between the ideal delivery flow rate (Q0) and a reverse flow rate (Q B ) that depends on at least one gap in the seal line between the rotor (2) and the stator (1), and that pulsates periodically at the pump frequency, the pulsation amplitude of which depends on the one hand on the wear state of the rotor and / or the stator and on the other hand on the inclination of the rotor (2) within the stator (1) that affects the gap (w) and thus the reverse flow rate (Q B ), measuring the operating parameters of the pump representing the gap and thus the reverse flow rate (Q B ), and repeatedly calculating the reverse flow rate (Q B ) and the effective delivery flow rate (Q) therefrom by means of a mathematical model as a function of the measured values of the operating parameters and also as a function of predetermined characteristic values of the pump and / or the medium to be conveyed.

Description

Technical Field

[0001] The present invention relates to a method for determining or monitoring the effective delivery flow rate (i.e., the flow rate) of an eccentric screw pump during operation, wherein the eccentric screw pump has a stator and a rotor that rotates (eccentrically) within the stator at a predetermined pump frequency.

Background Art

[0002] In such an eccentric screw pump, the rotor is connected to the drive unit, for example, via at least one connecting rod or equivalent element such that the rotor or its rotor end rotates eccentrically with respect to the drive shaft. The pump has, for example, on the suction side, a pump housing connected to the stator, which pump housing is also referred to as the suction housing and generally has a housing opening, for example an inlet opening, for the medium to be conveyed. Furthermore, the pump may have a pump housing connected to the stator, for example on the discharge side, which pump housing is actually also referred to as the pressure pipe piece. The eccentric screw pump is one of the group of rotary positive displacement pumps, which is used in various industrial fields for conveying a very wide variety of media, especially highly viscous liquids. The medium to be conveyed may also contain solid components.

[0003] The stator is made of, for example, an elastic material, preferably an elastomer material, and is generally surrounded by a single-piece or multi-piece stator jacket or stator housing. On the one hand, a connection that rotates and at the same time ensures eccentricity between the drive unit or drive shaft or connecting shaft and, on the other hand, the rotor, is effected, for example, via a connecting rod arranged within the pump housing. The connecting rod can be connected to the rotor, for example, via a rotor-side joint and can be connected to the drive shaft or connecting shaft via a drive-unit-side joint. Alternatively, embodiments with a flexible connecting rod without joints are also included.

[0004] The rotor is formed in a screw shape, specifically, preferably having a relatively large pitch and thread depth, and a relatively small valley diameter (shaft diameter). The rotor is eccentrically arranged in the stator or in the through-opening of the stator, and the stator or its screw-shaped interior has one more thread than the rotor. In a pump having a clamp (fastening), the rotor diameter is larger than the inner diameter of the stator or the diameter of the through-opening. However, the present invention also includes pumps without a clamp. In a pump having a clamp, when the rotor moves ideally, it abuts against the inner surface of the stator or the inner surface of the through-opening via one or more continuous seal lines. The seal lines separate the conveying spaces from each other, and these conveying spaces move (continuously) from the suction side to the discharge side or from the inlet side to the outlet side as the rotor rotates. Since one seal line or a plurality of seal lines separate and seal the conveying chambers from each other, sealing of the suction side of the stator against the discharge side occurs.

[0005] The eccentric screw pump of the type described at the beginning is known, for example, from German Patent Application Publication No. 102014112552, German Patent Application Publication No. 102010037440, and International Publication No. 2009 / 024279.

[0006] Furthermore, from German Patent Application Publication No. 102018113347, a method for identifying or monitoring the state of an eccentric screw pump is known, which provides the time evolution of an operating parameter of the pump, such as pressure or pressure difference, that pulsates periodically at a predetermined pump frequency and whose pulsation amplitude depends on the state of the eccentric screw pump. In an ideal system, the operating pressure of the eccentric screw pump does not vary with the rotation or rotational frequency of the pump, i.e., an ideal eccentric screw pump has no pressure pulsations with respect to the operating pressure. In practice, the eccentric screw pump does have relatively few pulsations, but still has a certain degree of pressure pulsations, which are caused by the change of the seal line during one rotation and the minimal shape difference between the rotor and the stator. Since German Patent Application Publication No. 102018113347 is based on the finding that the pulsation amplitude of the pressure pulsations depends on the wear of the relevant components of the eccentric screw pump, the wear state of the pump can be referred to by analyzing the pressure pulsations.

[0007] During the use of an eccentric screw pump, in practice, it is necessary to monitor the operation of the pump and provide specific operating parameters. This relates to, for example, the monitoring of the actual conveying flow rate, i.e., the flow rate, of the eccentric screw pump. In practice, for this purpose, special flow sensors are used, and the conveying flow rate can be directly measured by these flow sensors. The drawback is that the investment cost of such flow sensors is high, so they cannot be used economically in many applications. For this reason, it has already been proposed to determine the conveying flow rate simply approximately based on the pump characteristic curve and taking into account the actual pump speed. This approximate determination of the conveying flow rate is generally based on the pump characteristic curve for a pump corresponding to a new product described by the pump manufacturer. Therefore, the estimation of the conveying flow rate in this approach becomes increasingly inaccurate as the wear of the pump components increases. In this estimation of the conveying flow rate, the actual state of the pump components cannot be taken into account. Thus, for example, a decrease in the conveying flow rate may go unnoticed, and as a result, a process stop may be caused. This is where the present invention is used.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0009] Starting from the known prior art and the described drawbacks, the present invention is based on the object of describing a method that enables a specific improvement of the actual conveying flow rate without using a dedicated flow sensor, specifically, taking into account the actual wear of the rotor and / or stator and, consequently, the associated shape changes.

Means for Solving the Problems

[0010] To achieve this object, the present invention is a method for determining or monitoring the (wear-dependent) effective conveying flow rate of an eccentric screw pump during operation, wherein the eccentric screw pump has a stator and a rotor that rotates at a predetermined pump frequency within the stator, and the effective conveying flow rate is determined from the difference between the (specified) ideal conveying flow rate (e.g., of a pump corresponding to a new product) and the return flow rate in the direction opposite to the ideal conveying flow rate, which depends on at least one gap in the seal line between the rotor and the stator. Measure (or provide) the operating parameters of the pump representing the clearance and thus the return flow rate, where these operating parameters pulsate periodically at the pump frequency, and the pulsation amplitude depends on the wear state of the rotor and / or stator on the one hand and is related to the inclination of the rotor in the stator that affects the clearance and thus the return flow rate on the other hand. Repeatedly calculate the return flow rate and the effective conveyance flow rate therefrom according to the measured values of the operating parameters and, for example, according to the stored characteristic values of the pump and / or the medium to be conveyed, which are (fixedly) set, by means of a mathematical model. It teaches a method.

[0011] Preferably, as the operating parameter, at least one operating pressure of the eccentric screw pump is provided or measured, and the pulsation amplitude of the pressure pulsation is evaluated. As the operating pressure, in particular preferably, the measurement or determination of the pressure difference is considered, specifically preferably, the measurement or determination of the difference between the pressure on the discharge side of the stator and the pressure on the suction side of the stator on the one hand and the other hand is considered. Alternatively, another operating parameter, such as torque, can also be used, which also shows pulsation.

[0012] The ideal conveyance flow rate can, for example, be determined mathematically in advance. Alternatively, the ideal conveyance flow rate can be determined in advance by measurement, for example, by measurement in the test area.

[0013] The present invention starts from the finding that, first, the effective or actual conveyance flow rate in a pump can be determined from the difference between, for example, an ideally calculated conveyance flow rate and a return flow rate in a direction opposite to the ideally calculated conveyance flow rate, and this return flow rate results from an imperfect sealing or seal line between the rotor and the stator, and thus depends on at least one gap in the seal line between the rotor and the stator. Here, the gap or return flow rate depends on the pressure difference, i.e., the difference between the pressure on the discharge side and the pressure on the suction side. This pressure difference causes a (substantially) constant inclination of the rotor, for example centered on the Y-axis, which affects the return flow rate. This is because the inclination of the rotor causes the rotor to be separated from the stator, thereby creating a sickle-shaped gap in the seal line.

[0014] Not only such a constant or "static" inclination (e.g., centered on the Y-axis) resulting from the static pressure difference, but also a varying (periodic) inclination of the rotor, for example centered on the X-axis, occurs. These cause the volume of the cavity open towards the discharge side to change, and then pressure pulsations or pressure difference pulsations occur. The periodic inclination of the rotor (centered on the X-axis) is directly related to the periodic change in the pressure difference, i.e., the pulsation amplitude (e.g., the amplitude of the pressure pulsation) is related to the inclination of the rotor and thus the size of the gap, which is in turn related to the return flow rate. Therefore, by evaluating the pressure pulsation or the pulsation amplitude of the pressure pulsation, the return flow rate can be appropriately modeled, and thus the actual conveyance flow rate can be determined by a mathematical model taking into account the measured pressure difference, in particular the pulsation amplitude of the pressure pulsation determined therefrom.

[0015] Here, the fact that the pulsation amplitude (i.e., the "peak-to-peak value" of the pressure difference) strongly depends on the wear of the rotor and / or stator of the eccentric screw pump is particularly interesting. Thus, according to the present invention, in the analysis using the mathematical model, not only the pressure pulsations that may already have occurred in some cases in the new state of the pump, but also the wear-dependent pressure pulsations or wear-dependent pulsation amplitudes that actually occur are incorporated. Therefore, in fact, the gap that increases with the increase in wear in the seal line between the rotor and the stator is considered using the mathematical model.

[0016] Thus, according to the present invention, the calculation is performed using a mathematical model in which the measurement of the transport flow rate by the flow sensor is not performed, and instead, for example, measurement values that can be easily provided in the form of pressure measurement values, particularly the pressure difference between the discharge side and the suction side of the pump, are incorporated. As a result, overall, the actual transport flow rate of the eccentric screw pump can be monitored with a very simple sensor system. Alternatively, other measurement values, such as torque measurement, can be used. Therefore, the determination of the transport flow rate is performed without problems in the manner of a "virtual sensor" based on convenient measurement variables and taking into account the actual wear of the rotor / stator and the associated shape changes. Therefore, reliable determination and monitoring of the transport flow rate or estimation of the transport flow rate can be achieved by simple and economical means, thereby improving the reliability of the process and minimizing downtime.

[0017] Preferably, in addition to the described operating parameters, for example, the pressure difference and the rotational speed of the pump or the rotor are also measured or provided by another method and taken into account in the calculation using the mathematical model.

[0018] As fixed characteristic values of the pump, in particular, the geometric parameters of the pump, i.e., the shape parameters of the rotor and / or stator, are stored and taken into account during the calculation. Furthermore, the characteristic values of the medium to be conveyed can be considered. For a specific pump type and in some cases for a specific application, it is understood that the relevant characteristic values are determined in advance experimentally and / or theoretically and the mathematical model is adapted by integrating them into the system in the sense of calibration.

[0019] Particularly preferably, the calculation in the described method is based on the measurement and analysis of the operating pressure, for example the pressure difference, because the pulsation amplitude of the pressure pulsation depends strongly on the wear of the relevant components, whereby it is possible to monitor the conveying flow rate depending on the wear.

[0020] Basically, the present invention also includes the detection and analysis of the time course of other operating parameters of the pump, which pulsate periodically at the pump frequency and the pulsation amplitude of which depends on the state of the eccentric screw pump. Such operating parameters can be provided by measurement in the described manner, i.e., they can be measured. Alternatively, instead of directly measuring each operating parameter, it is also possible to calculate it directly from the measured values. Therefore, for example, the torque of the pump drive or the motor current can also be used or employed as an operating parameter instead of the operating pressure. In this case, the pulsation amplitude of the torque pulsation or the motor current pulsation is determined. Thus, for example, wear in the stator and / or rotor of an eccentric screw pump typically not only results in pressure pulsations but also in changes such as pulsations in the torque of the pump, and therefore the torque pulsation can be used as an operating parameter. Furthermore, due to changes such as pulsations in the torque, a pulsating power consumption or current consumption occurs, so that the power consumption or current consumption can also be used as an operating parameter. Similarly, changes due to wear in the geometry of the rotor-stator of the pump result in periodic or pulsating changes in the structure-borne sound, so that the structure-borne sound can also be used as an operating parameter.

[0021] Here, the present invention is based on the findings of German Patent Application Publication No. 102018113347. However, furthermore, the present invention is based on the surprising finding that a pulsation or pulsation amplitude that can be excellently analyzed is directly related to the inclination of the rotor within the stator, and this inclination is further related to the gap in the seal line between the rotor and the stator, and thus the return flow. Therefore, it can be modeled by the pressure pulsation, and thus by the return flow of the pump and the conveying flow rate.

[0022] The present invention relates not only to the described method, but also to a monitoring device for an eccentric screw pump comprising means suitable for carrying out the described method. Accordingly, the monitoring device comprises suitable hardware in which software corresponding to carrying out the described method is implemented. This hardware includes, for example, a computer. Additionally, the monitoring device may comprise at least one sensor for measuring operating parameters. In a preferred development, the monitoring device comprises at least one pressure sensor for measuring the operating pressure. A plurality of pressure sensors may also be provided, for example, a pressure sensor for measuring the operating pressure on the discharge side of the stator and / or a pressure sensor for identifying the operating pressure on the suction side of the stator. In some cases, for example, if the pressure on the suction side substantially corresponds to or is close to the ambient pressure, only the sensor on the discharge side may be sufficient to identify the pressure difference.

[0023] Furthermore, the present invention relates to an eccentric screw pump equipped with such a monitoring device or connected to such a monitoring device.

[0024] Finally, the present invention also relates to a computer program comprising commands for causing the monitoring device to execute the described method.

[0025] Hereinafter, the present invention will be described in more detail based on the drawings, which merely represent embodiments.

Brief Description of the Drawings

[0026]

Figure 1

Figure 2

Figure 3

Figure 4a

Figure 4b

[0027] Fig. 1 shows a general eccentric screw pump having a stator 1 made of an elastic material and a rotor 2 rotating within the stator 1, the stator 1 being able to be surrounded by a stator jacket 3. Further, the pump has a suction housing 4 and a connecting pipe piece 5, also referred to as a pressure pipe piece 5. Further, the pump has a pump drive 6 acting on the rotor 2 via a connecting rod 7. The connecting rod 7 is connected to the drive 6 or the drive shaft via a connecting joint 8 on the drive side and is connected to the rotor 2 via a connecting joint 9 on the rotor side.

[0028] In an embodiment, a pump having a clamp is realized, i.e., when the rotor 2 moves ideally, it abuts against the inner surface of the through-opening of the stator 1 via a plurality of continuous seal lines. In Fig. 2, these seal lines are suggested by hatching on the surface of the rotor 2.

[0029] In the illustrated embodiment, on the one hand, a pressure sensor 11a for specifying the operating pressure on the discharge side D is provided in the region of the pressure pipe piece 5, and on the other hand, a pressure sensor 11b for specifying the operating pressure on the suction side S is provided in the region of the suction housing 4. The eccentric screw pump or the sensors 11a, 11b are connected to a monitoring device 10 that can specify or monitor the delivery flow rate Q of the eccentric screw pump during operation.

[0030] However, here, the direct measurement of the transport flow rate Q through the flow sensor is not performed, and a system with a "virtual" sensor is implemented. This system is based on the estimation of the transport flow rate or the determination of the transport flow rate using a mathematical model that takes into account the operating parameters, i.e., the simplified measurement of the operating pressure of the pump. Here, the present invention utilizes the relationship between the transport flow rate Q of the pump and specific phenomena and relationships, which will be referred to in more detail below.

[0031] In an eccentric screw pump, the actual effective transport flow rate Q is obtained from the difference between the ideal transport flow rate Q0 and the return flow rate Q that is opposite to the ideal transport flow rate Q0. The return flow rate depends on at least one gap in the seal line between the rotor and the stator. The ideal transport flow rate Q0 can be determined, for example, by calculation from the pump rotational speed n and the transport volume V0: B Q = V0 × n - Q Q = V0×n - Q B

[0032] The analysis of the return flow rate Q B is particularly important within the scope of the present invention.

[0033] For example, in an eccentric screw pump, a constant inclination t of the rotor around the Y-axis shown in FIG. 2 is brought about by the pressure difference Δp to be monitored in terms of measurement technology, i.e., the difference between the (operating) pressure p1 on the discharge side D and the (operating) pressure p2 on the suction side S. y This constant inclination t y results in a gap w, and this gap w further results in the return flow rate Q B The gap w, and thus the return flow rate Q B substantially depends on the pressure difference Δp averaged over a certain period.

[0034] Furthermore, a periodic pressure difference occurs between the discharge side D and the suction side S, and this pressure difference results from the periodic inclination t of the rotor around the X-axis shown in FIG. 2. The inclination t x from which it results. The inclination t xis the pulsation amplitude t of the rotational frequency of the rotor 2 (or twice the rotational frequency since two chambers open per rotation), and the slope, also referred to as the "peak-to-peak value" of the slope x,pp which pulsates due to x,pp . The periodic slope t x results from the periodic change in the pressure difference Δp, so the pulsation of the pressure difference Δp, particularly the pulsation amplitude Δp of the pressure difference pp is also directly related to the pulsation amplitude t x of the slope t x,pp and is directly related to it

[0035] According to the present invention, the effective conveyance flow rate Q can be mathematically modeled specifically considering the measured value of the pressure difference Δp, particularly the pressure pulsation of the pressure difference. Here, this pulsation amplitude, that is, the peak-to-peak value Δp in the pressure difference pp is particularly interesting because it is highly dependent on the wear state of the rotor and / or stator, so it can be directly considered when modeling the wear of the rotor and / or stator that increases during operation. For this purpose, refer to the process diagram according to FIG. 3

[0036] In the box surrounded by the dotted line at the bottom of FIG. 3, a simple modeling of the return flow rate Q B and thus the actual conveyance flow rate Q is shown. This modeling is based on the measurement of the averaged pressure difference (Δ￣p) directly related to the size of the sickle-shaped gap w in the seal line between the rotor 2 and the stator 1, specifically, the slope t y of the rotor centered on the Y-axis that results in the gap w due to the pressure difference Δp. Here, in FIG. 3 (bottom), the calculation of the sickle-shaped gap w by "calc.w", the calculation of the return flow rate or return flow Q B by "calc Q B ", and the calculation of the ideal conveyance flow rate Q0 by "calc.Q0" are illustrated. This gap w is shown in FIG. 4a

[0037] In the box illustrated by the solid line in the upper part of FIG. 3, the influence of the periodic slope t x of the rotor centered on the X-axis and the related pressure pulsation Δp ppis illustrated, and this pressure pulsation Δp pp is highly dependent on the wear of the rotor and / or stator. Therefore, due to the modeling shown in the upper part, it is directly affected by the wear of the rotor and / or stator. Thus, from the measurement of the pressure difference Δp, the pulsation amplitude Δp pp of the pressure pulsation, that is, the peak-to-peak value of the periodically changing pressure difference can be obtained (calc.Δp pp ). However, since pressure pulsations already occur in a new pump state regardless of wear, the non-wear-dependent pulsation amplitude (Δp^ x,pp ) is determined by calculation based on the "peak-to-peak value" (calc.t pp ) of the slope and is subtracted from the measured pulsation amplitude Δp pp in the sense of normalization. In both cases, by specifying the pulsation amplitude, the influence of the wear-dependent gap w w on the gap w of the seal line can be modeled and taken into account (see Fig. 4b). Therefore, the wear-dependent part w w of the gap shown in Fig. 4b is obtained by the following relational expression corresponding to the diagram in Fig. 3: w w =k3n(Δp pp -k2t x,pp ) wherein t x,pp , and thus (Δp^ pp ) are determined purely by calculation. Therefore, the gap w w can be repeatedly calculated based on continuous measurement of the pressure pulsation.

[0038] Therefore, a virtual sensor is created based on the additional specification or monitoring of a representative operating value, in this case the pressure difference Δp. The wear-dependent gap ratio w wBy performing repeated calculations, additional adaptation to the wear state is achieved. Here, the present invention is based on the important finding that the pressure pulsation to be measured is directly related to the inclination of the rotor, and this inclination creates a gap that affects the return flow rate. Also, since the pressure pulsation depends on wear, wear can be directly considered during modeling by analyzing the pressure pulsation.

[0039] The present invention enables improved monitoring and, for example, also enables maintenance prediction from the aspect of "predictive maintenance".

Explanation of Signs

[0040] 1 Stator 2 Rotor 3 Stator jacket 4 Suction housing 5 Pressure pipe piece 6 Pump drive unit 7 Connecting rod 8 Connecting joint on the drive unit side 9 Connecting joint on the rotor side 10 Monitoring device 11a Pressure sensor 11b Pressure sensor D Discharge side n Pump rotational speed p1 Pressure p2 Pressure Q Delivery flow rate Q0 Ideal delivery flow rate Q B Return flow rate S Suction side t x Inclination t y Inclination t x,pp "Peak-to-peak value" of the inclination V0 Carrier volume w Gap w w Wear-dependent gap Δp Pressure difference Δp pp Pulsation amplitude

Claims

1. A method for specifying or monitoring the effective delivery flow rate (Q) of an eccentric screw pump during operation, wherein the eccentric screw pump has a stator (1) and a rotor (2) that rotates eccentrically at a predetermined pump frequency within the stator (1), The effective conveying flow rate (Q) is determined from the difference between the ideal conveying flow rate (Q ０ ), and a return flow rate (Q ０ ) in a direction opposite to the ideal conveying flow rate (Q Ｂ ) that depends on at least one gap (w) in the seal line between the rotor (2) and the stator (1). The gap, and thus the return flow rate (Q Ｂ ), of the operating parameters of the pump are measured, and the operating parameters pulsate periodically at the pump frequency, and the pulsation amplitude depends, on the one hand, on the wear state of the rotor and / or the stator, and on the other hand, on the gap (w), and thus the return flow rate (Q Ｂ ), is related to the inclination of the rotor (2) in the stator (1) that affects The return flow rate (Q Ｂ ) and the effective conveyance flow rate (Q) therefrom are repeatedly calculated by a mathematical model according to the measured values of the operation parameters and according to predetermined characteristic values of the pump and / or the medium to be conveyed. method.

2. The method according to claim 1, wherein the operating pressure of the pump or the operating pressure of the medium to be conveyed in or by the pump is used as an operating parameter.

3. As the operation parameter, a parameter difference, for example, a pressure difference, preferably the pressure (p １ ) on the discharge side (D) of the stator and the pressure (p ２ ) on the suction side (S) of the stator (1) is used, and the method according to claim 2.

4. Furthermore, the rotational speed (n) of the pump or the rotor (2) is measured or provided and incorporated into the calculation using the mathematical model. The method according to any one of claims 1 to 3.

5. The method according to any one of claims 1 to 4, wherein the geometric parameters of the pump are used as predetermined characteristic values of the pump.

6. From the measured parameter difference, for example the pressure difference (Δp), on the one hand, an average value averaged over at least one period is taken as, for example, the static pressure difference (Δ￣p), and on the other hand, the pulsation amplitude (Δp ｐｐ ), for example, is identified as the dynamic pressure difference, the method according to any one of claims 3 to 5.

7. A wear-dependent pulsation amplitude (Δp ｐｐ ), identified from the measurement of a parameter difference, e.g., a pressure difference, is corrected taking into account a nominal pulsation amplitude (Δp^ ｐｐ ) based on a pump in a new state, according to the method of any one of claims 1 to 6.

8. A monitoring device for an eccentric screw pump, comprising means suitable for implementing the method according to any one of claims 1 to 7.

9. The monitoring device according to claim 8, comprising at least one sensor (11a, 11b) for measuring the operating parameter.

10. At least one pressure sensor for measuring the operating pressure, for example, the pressure (p １ ) of at least one pressure sensor (11a) for measuring the pressure on the discharge side (D) of the stator and / or the pressure (p ２ ) of at least one pressure sensor (11b) for identifying the pressure on the suction side of the stator (1), the monitoring device according to claim 9.

11. A computer program comprising a command for causing the monitoring device according to claim 8 or 10 to execute the method according to any one of claims 1 to 7.

12. An eccentric screw pump having the monitoring device according to any one of claims 8 to 10.

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