Method for determining or monitoring delivery flow of eccentric worm pump

Abstract

The invention relates to a method for determining or monitoring an effective delivery flow (Q) of an eccentric worm pump during operation, the eccentric worm pump having a stator (1) and a rotor (2) eccentrically rotating in the stator (1) at a pump frequency, the effective delivery flow (Q) being determined from the difference between an ideal delivery flow (Q0) and a return flow (QB) oriented opposite the ideal delivery flow (Q0), the flow rate is dependent on at least one gap in the sealing line between the rotor (2) and the stator (1), an operating parameter of the pump, which represents the gap and thus the flow rate (QB), is measured, the rotor (2) has an operating parameter which is periodically pulsated at a pump frequency and the pulsation amplitude of which depends on the wear state of the rotor and / or the stator and on the other hand is associated with a tilt of the rotor (2) in the stator (1), which tilt influences the gap (w) and thus the reflux quantity (QB), the return flow rate (QB) and the effective delivery flow rate (Q) are calculated from the measured value of the operating parameter and a predetermined characteristic value of the pump and / or of the medium to be delivered repeatedly by means of a mathematical model.

Description

Technical Field

[0001] The invention relates to a method for determining or monitoring the effective delivery flow, ie the flow rate, of an eccentric screw pump during operation, wherein the eccentric screw pump has a stator and a rotor rotating in the stator at a pump frequency (eccentricity). Background Art

[0002] In such an eccentric worm pump, the rotor is connected to the drive, for example, by at least one coupling rod or similar element, so that the rotor or its rotor end rotates eccentrically about the drive axis. The pump has, for example, a pump housing connected to the stator on the suction side, which is also called a suction housing and which usually has a housing opening, such as an inlet opening, for the medium to be conveyed. In addition, the pump can have, for example, a pump housing connected to the stator on the pressure side, which is also called a pressure connection in practice. An eccentric worm pump is a pump in a rotary positive displacement pump group, which is used to convey different media and in particular highly viscous liquids in different industrial fields. The medium to be conveyed may also contain solid components.

[0003] The stator is made, for example, of an elastic, preferably elastomeric material and is usually surrounded by a one-piece or multi-piece stator housing or stator housing. The rotational and eccentricity-guaranteed connection between the drive or drive shaft or connecting shaft on the one hand and the rotor on the other hand is realized, for example, by a coupling rod arranged in the pump housing. The coupling rod can be connected to the rotor, for example, via a joint on the rotor side and to the drive shaft or connecting shaft via a joint on the drive side. Alternatively, however, embodiments with a flexible coupling rod without joints are also included.

[0004] The rotor is configured to be spiral, more precisely, preferably with a relatively large pitch and thread depth and a relatively small core diameter. The rotor is eccentrically arranged in the stator or in the through hole of the stator and the stator or its spiral inner cavity has one more pitch than the rotor. In a pump with a clamping device, the rotor diameter is larger than the inner diameter of the stator or the diameter of the through hole. However, the present invention also includes pumps without a clamping device. In a pump with a clamping device, the rotor rests on the inner surface of the stator or on the inner surface of the through hole through one or more uninterrupted sealing lines in ideal movement. The sealing lines separate the conveying chambers from each other, which move from the suction side (continuously) to the pressure side or from the inlet side (continuously) to the discharge side during the rotation of the rotor. The one or more sealing lines separate and seal the conveying chambers from each other, so that the suction side of the stator is sealed relative to the pressure side.

[0005] Eccentric screw pumps of the type mentioned at the outset are known, for example, from DE 10 2014 112 552 A1, DE 10 2010 037440 A1 and WO 2009 / 024279 A1.

[0006] Furthermore, DE 10 2018 113 347 A1 discloses a method for determining or monitoring the state of an eccentric worm pump, wherein a time curve of an operating parameter of the pump, such as a pressure or a pressure difference, is provided, the operating parameter periodically pulsating at the pump frequency and the pulsation amplitude of the operating parameter depending on the state of the eccentric worm pump. In an ideal system, the operating pressure of the eccentric worm pump does not change with the rotation or rotation frequency of the pump, that is, the ideal eccentric worm pump has no pressure pulsations in terms of the operating pressure. In practice, although the eccentric worm pump actually pulsates relatively little, the eccentric worm pump has certain pressure pulsations, which are attributed to the sealing line that changes during the rotation and the minimum geometric difference between the rotor and the stator. DE 10 2018 113 347 A1 is based on the recognition that the pulsation amplitude of the pressure pulsation depends on the wear of the important components of the eccentric worm pump, so that the wear state of the pump can be explained by analyzing the pressure pulsation.

[0007] During the use of eccentric worm pumps, it is necessary in practice to monitor the operation of the pump and provide specific operating parameters. This, for example, involves monitoring the actual delivery flow, i.e. the flow rate, of the eccentric worm pump. For this purpose, special flow sensors are used in practice, with the help of which the delivery flow can be directly measured. The disadvantage is that such flow sensors have a high investment cost, so they cannot be used economically in many applications. For this reason, it has been proposed to roughly determine the delivery flow only based on the pump characteristic curve and knowing the current pump speed. Since this approximate determination of the delivery flow is based on the pump characteristic curve, which is usually given by the pump manufacturer and involves a new pump, the delivery flow estimation in this method becomes increasingly inaccurate as the wear of the pump components increases. The actual state of the pump components cannot be taken into account in this delivery flow estimation. Therefore, for example, a reduced delivery flow may be ignored and thus cause a process stagnation. The present invention addresses this. Summary of the invention

[0008] Starting from the known prior art and the above-mentioned disadvantages, the object of the present invention is to provide a method which makes it possible to better determine the actual delivery flow without using a dedicated flow sensor, more precisely, in particular taking into account the actual wear of the rotor and / or stator and the geometric changes associated therewith.

[0009] In order to achieve this object, the invention discloses a method for determining or monitoring the (wear-related) effective delivery flow of an eccentric worm pump during operation.

[0010] The eccentric worm pump has a stator and a rotor rotating in the stator at a pump frequency.

[0011] wherein the effective delivery flow is determined by the difference between an (ascertained) ideal delivery flow (e.g. of a new pump) and a return flow directed in the opposite direction to the ideal delivery flow, which is dependent on at least one gap in the sealing line between the rotor and the stator,

[0012] wherein an operating parameter of the pump representing the gap and thus the return flow is measured (or alternatively provided), the operating parameter pulsating periodically at the pump frequency and the pulsation amplitude of the operating parameter depending on the wear state of the rotor and / or stator on the one hand and being linked to the tilting of the rotor in the stator on the other hand, which influences the gap and thus the return flow,

[0013] In this case, the return flow and thus the effective delivery flow are calculated repeatedly with the aid of a mathematical model from measured values ​​of operating parameters and (fixed) predetermined, for example stored, characteristic values ​​of the pump and / or of the medium to be conveyed.

[0014] Preferably, at least one operating pressure of the eccentric screw pump is provided or measured as an operating parameter and the pulsation amplitude of the pressure pulsation is evaluated. The operating pressure is particularly preferably measured or determined as a differential pressure, more precisely preferably the difference between the pressure on the pressure side of the stator on the one hand and the pressure on the suction side of the stator on the other hand. Alternatively, other operating parameters can also be used, such as a torque that also indicates pulsations.

[0015] The ideal delivery flow rate can be determined in advance, for example, by calculation. Alternatively, the ideal delivery flow rate can be determined in advance by measurement, for example, by measuring in a test field.

[0016] The invention is firstly based on the recognition that the effective or actual delivery flow in a pump can be determined in practice by the difference between, for example, a calculated ideal delivery flow and a return flow directed in the opposite direction to the ideal delivery flow, which is caused by an imperfect seal or sealing line between the rotor and the stator and therefore depends on at least one gap in the sealing line between the rotor and the stator. The gap or return flow depends on the pressure difference, i.e. the difference between the pressure on the pressure side and the pressure on the suction side. The pressure difference leads to an (approximately) constant tilt of the rotor, for example about the Y axis, which influences the return flow. This is because the tilting of the rotor lifts the rotor from the stator and thus produces a sickle-shaped gap in the sealing line.

[0017] In addition to this constant or "static" tilt (e.g. about the Y-axis) caused by the static pressure difference, there is also a changing (periodic) tilt of the rotor, e.g. about the X-axis. This tilt changes the volume of the cavity open to the pressure side and thus produces pressure pulsations or pressure difference pulsations. The periodic tilting of the rotor (about the X-axis) directly leads to a periodic variation of the pressure difference, i.e. the pulsation amplitude (e.g. of the pressure pulsation) is associated with the tilt of the rotor and therefore with the size of the gap and the gap in turn is associated with the return flow. Therefore, by evaluating the pressure pulsation or the pulsation amplitude of the pressure pulsation, the return flow can be modeled accordingly and the actual delivery flow can therefore be determined with the help of a mathematical model taking into account the measured pressure difference and in particular the pulsation amplitude of the pressure pulsation determined thereby.

[0018] Of particular importance here is the fact that the pulsation amplitude, i.e. the "peak-to-peak value" of the pressure difference, depends significantly on the wear of the rotor and / or stator of the eccentric worm pump. According to the invention, therefore, in the analysis with the aid of the mathematical model, not (only) the pressure pulsations which could have occurred in the new state of the pump are included, but rather the actually occurring, wear-related pressure pulsations or wear-related pulsation amplitudes, so that the gap in the sealing line between rotor and stator which increases with increasing wear is actually taken into account with the aid of the mathematical model.

[0019] Thus, the actual delivery flow of the eccentric worm pump can be monitored overall with the aid of very simple sensor devices, since according to the invention the delivery flow is not measured with the aid of a flow sensor, but is determined by calculation with the aid of a mathematical model, in which however measured values ​​that can be easily provided are incorporated, for example in the form of pressure measured values ​​and in particular in the form of a pressure difference between the pressure side and the suction side of the pump. Alternatively, other measured values, such as torque measured values, can be used. Thus, the delivery flow can be determined in the form of a "virtual sensor" based on advantageous measured variables and taking into account the actual rotor / stator wear and the geometric changes that accompany it. Thus, the delivery flow or delivery flow estimate can also be reliably determined and monitored with the aid of simple, economical means, which can be used to increase process reliability and minimize downtimes.

[0020] Preferably, in addition to the operating parameters such as the differential pressure, the rotational speed of the pump or of the rotor is also measured or provided in some other way and taken into account in the calculation using the mathematical model.

[0021] As fixed predetermined characteristic values ​​of the pump, in particular geometrical parameters of the pump, i.e. geometrical parameters of the rotor and / or stator, are stored and taken into account in the calculation. Furthermore, characteristic values ​​of the medium to be conveyed can be taken into account. It goes without saying that the mathematical model is adapted for a specific pump type and, if necessary, also for a specific application, by determining the relevant characteristic values ​​experimentally and / or theoretically in advance and integrating them into the system in the sense of calibration.

[0022] The calculation carried out in the described manner is particularly preferably based on the measurement and evaluation of an operating pressure, such as a differential pressure, since the pulsation amplitude of the pressure pulsations depends significantly on the wear of critical components and the delivery flow can therefore be monitored in a wear-dependent manner.

[0023] In principle, the present invention also includes the detection and analysis of the time variation curve of other operating parameters of the pump, which periodically pulsate at the pump frequency and the pulsation amplitude of the other operating parameters depends on the state of the eccentric worm pump. Such operating parameters can be provided by measurement in the described manner, that is, measured. Alternatively, the corresponding operating parameters can also be calculated from the directly measured values ​​instead of being directly measured. Therefore, instead of the operating pressure, for example, the torque or motor current of the pump drive can also be provided or used as an operating parameter. In this case, the pulsation amplitude of the torque pulsation or the motor current pulsation is determined. Therefore, for example, the wear of the stator and / or rotor in the eccentric worm pump usually not only causes pressure pulsation, but also causes a pulsating change in the torque of the pump, so the torque pulsation can be used as an operating parameter. In addition, the pulsating change of the torque leads to a pulsating power consumption or current consumption, so the power consumption or current consumption can also be used as an operating parameter. Similarly, the wear-induced changes in the rotor-stator geometry of the pump lead to periodic or pulsating changes in the structure-borne sound, so the structure-borne sound can also be used as an operating parameter.

[0024] The present invention here makes use of the knowledge from DE 10 2018 113 347 A1. However, the present invention is also based on the surprising knowledge that the pulsation or pulsation amplitude to be well analyzed is directly related to the inclination of the rotor in the stator, which in turn is related to the gap in the sealing line between the rotor and the stator and therefore to the return flow, so that the return flow and therefore the delivery flow of the pump can be modeled by the pressure pulsation.

[0025] The present invention relates not only to the described method, but also to a monitoring device for an eccentric worm pump, which includes a device suitable for executing the method. The monitoring device therefore includes suitable hardware, which is configured to execute the method with the help of corresponding software. The hardware includes, for example, a computer. In addition, the monitoring device may include at least one sensor for measuring operating parameters. In a preferred extension, the monitoring device includes at least one pressure sensor for measuring the operating pressure. Multiple pressure sensors may also be provided, such as a pressure sensor for measuring the operating pressure on the pressure side of the stator and / or a pressure sensor for determining the operating pressure on the suction side of the stator. If necessary, a sensor on the pressure side may also be sufficient to determine the pressure difference, more precisely, for example when the pressure on the suction side corresponds substantially to the ambient pressure or is close to the ambient pressure.

[0026] The invention also relates to an eccentric screw pump equipped with such a monitoring device or connected to such a monitoring device.

[0027] Finally, the invention also relates to a computer program comprising instructions for causing a monitoring device to execute the method. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The invention is explained in more detail below with the aid of the accompanying drawings which show only one exemplary embodiment.

[0029] Figure 1 An eccentric worm pump having a device for determining or monitoring the effective delivery flow is shown;

[0030] Figure 2 Show according to Figure 1 The geometry of the rotor of the eccentric worm pump;

[0031] Figure 3 A schematic diagram showing a method according to the invention for determining or monitoring the effective delivery flow of an eccentric worm pump; and

[0032] Figure 4 A and 4B respectively show the Figure 2 Partial cross section of a rotor. DETAILED DESCRIPTION

[0033] Figure 1A conventional eccentric worm pump is shown, which comprises a stator 1 made of elastic material and a rotor 2 rotating in the stator 1, wherein the stator 1 can be surrounded by a stator housing 3. The pump also has a suction housing 4 and a connecting pipe 5, which is also called a pressure pipe 5. The pump also has a pump drive 6, which acts on the rotor 2 via a coupling rod 7. The coupling rod 7 is connected to the drive 6 or the drive shaft via a drive-side coupling joint 8 and to the rotor 2 via a rotor-side coupling joint 9.

[0034] In this embodiment, a pump with a clamping device is realized, that is, the rotor 2 rests on the inner surface of the through-hole of the stator 1 via a plurality of uninterrupted sealing lines in the ideal movement. Figure 2 The surface of the rotor 2 is shown in hatching.

[0035] In the exemplary embodiment shown, a pressure sensor 11a for determining the operating pressure on the pressure side D is provided in the region of the pressure connection 5, and a pressure sensor 11b for determining 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, by means of which the delivery flow Q of the eccentric screw pump can be determined or monitored during operation.

[0036] However, the delivery flow Q is not measured directly by a flow sensor, but a system with a "virtual" sensor is implemented, which is based on a delivery flow estimation or delivery flow determination by means of a mathematical model taking into account a simplified measured operating parameter, namely the operating pressure of the pump. In this case, the invention uses the relationship between the delivery flow Q of the pump and certain phenomena and correlations, which will be discussed in detail below.

[0037] In an eccentric worm pump, the actual effective delivery flow Q is calculated from the ideal delivery flow Q 0 and the ideal delivery flow Q 0 Reverse directional return flow Q B The difference between the ideal delivery flow Q and the ideal delivery flow Q is obtained, wherein the return flow depends on at least one gap in the sealing line between the rotor and the stator. 0 For example, the pump speed n and the delivery volume V can be calculated from the pump speed n and the delivery volume V 0 Sure:

[0038] Q=V 0 x B .

[0039] Reflux Q B The analysis of is of particular importance within the scope of the present invention.

[0040] For example, the differential pressure Δp to be monitored by measurement technology, ie the (operating) pressure p on the pressure side D 1 and the (operating) pressure p on the suction side S 2 The difference between the two causes the rotor to rotate around the Figure 2 The constant inclination of the Y axis shown in t y The constant tilt t y Causes a gap w, which in turn causes a backflow Q B , where the gap w and hence the return flow Q B Basically it depends on the average pressure difference averaged over a cycle

[0041] In addition, a periodic pressure difference is generated between the pressure side D and the suction side S, which is caused by the rotor surrounding the Figure 2 The periodic tilt of the X-axis shown in t x Produce. Tilt t x At the rotational frequency of the rotor 2 (or at double the rotational frequency, since two cavities are open per revolution) and at a sloped pulsation amplitude (which is also called the sloped “peak-to-peak” t x,pp ) pulsation. Periodic tilt t x Caused by the periodic change of the pressure difference Δp, the pulsation of the pressure difference Δp and especially the pulsation amplitude of the pressure difference Δp pp Direct and inclined x The pulsation amplitude t x,pp Associated.

[0042] According to the invention, the effective delivery flow Q can now be modeled mathematically, more precisely taking into account the measured values ​​of the pressure difference Δp and in particular the pressure pulsation of the pressure difference. Of particular importance here is the fact that the pulsation amplitude, i.e. the peak-to-peak value of the pressure difference Δp pp The wear state of the rotor and / or stator is sensitively dependent on the wear state of the rotor and / or stator, so that the wear that increases during operation of the rotor and / or stator can be directly taken into account in the modeling process. Figure 3 Flowchart of the process.

[0043] exist Figure 3 It can be seen from the box surrounded by dotted lines at the bottom that the reflux flow Q B And therefore the actual delivery flow Q is simply modeled based on the average pressure difference The average pressure difference is directly related to the size of the sickle-shaped gap w in the sealing line between the rotor 2 and the stator 1, more precisely, based on the inclination t of the rotor about the Y axis generated by the pressure difference Δp. y , which results in a gap w. Figure 3 (lower part) "calc.w" indicates the calculation of the sickle-shaped gap w, and "calc.Q B" indicates the reflux volume or reflux Q B Calculation, and "calc.Q 0 " represents the ideal delivery flow rate Q 0 The gap w is calculated. Figure 4 Shown in A.

[0044] exist Figure 3 The periodic tilting of the rotor about the X-axis is shown in the solid line box in the upper part of x The influence of the pressure pulsation Δp pp , the pressure pulsations depend significantly on the wear of the rotor and / or stator, which is therefore directly incorporated into the modeling shown in the upper part. Thus, the pulsation amplitude Δp of the pressure pulsations can be determined from the measurement of the pressure difference Δp pp , that is, the peak-to-peak value of the periodically changing pressure difference (calc.Δp pp ). However, since pressure pulsations already occur in the new state of the pump regardless of wear, the pressure pulsations are calculated via the inclined "peak-to-peak" (calc.t x,pp ) Determine the wear-independent pulsation amplitude by calculation and in a standardized sense from the measured pulsation amplitude Δp pp In any case, the wear-related clearance w can be modeled and taken into account by determining the pulsation amplitude w Contribution to the gap w in the sealing line (see Figure 4 B) Therefore, according to Figure 3 The graph in is obtained by the following relationship Figure 4 The wear-related component w of the clearance shown in b w :

[0045] w w =k 3 n(Δp pp -k 2 t x，pp )

[0046] Among them, t x,pp And therefore Determined by pure calculation. Gap w w Therefore, it is possible to repeatedly calculate based on the continuous measurement of the pressure pulsation.

[0047] A virtual sensor is thus provided, which is based on adaptive determination or monitoring of a representative operating parameter, in this case the pressure difference Δp. By repeatedly calculating the wear-related clearance component w wThe wear state is adapted as a function of the pressure pulsation. The invention is based on the important insight that the pressure pulsation to be measured is directly linked to the inclination of the rotor, which causes the clearance that influences the return flow. Since the pressure pulsation is in turn related to the wear, the wear can be taken into account directly in the modeling by analyzing the pressure pulsation.

[0048] The invention enables improved monitoring and also maintenance prediction, for example from a “predictive maintenance” perspective.

Claims

1. A method for determining or monitoring the effective delivery flow (Q) of an eccentric worm pump during operation, wherein: The eccentric worm pump comprises a stator (1) and a rotor (2) which rotates eccentrically in the stator (1) at a pump frequency. The effective delivery flow (Q) is the sum of the ideal delivery flow (Q0) and the return flow (Q B ), the reflux amount being determined by the difference between the rotor (2) and the stator (1), the reflux amount being determined by at least one gap (w) in the sealing line between the rotor (2) and the stator (1), The measurement of the pump represents the clearance and thus the reflux volume (Q B ), which pulsates periodically at the pump frequency and whose pulsation amplitude depends on the wear state of the rotor and / or stator on the one hand and is associated with the tilting of the rotor (2) in the stator (1) on the other hand, which influences the gap (w) and thus the return flow (Q B ), The return flow (Q) is calculated repeatedly with the aid of a mathematical model from measured values ​​of operating parameters and predetermined characteristic values ​​of the pump and / or of the medium to be conveyed. B ) and calculate the effective delivery flow (Q) from this.

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

3. The method according to claim 2, wherein: The operating parameter used is a parameter difference, such as a pressure difference, preferably the difference (Δp) between the pressure ( p1 ) on the pressure side (D) of the stator and the pressure ( p2 ) on the suction side (S) of the stator.

4. The method according to any one of claims 1 to 3, wherein: In addition, the rotational speed (n) of the pump or of the rotor (2) is measured or provided and included in the calculation performed with the aid of the mathematical model.

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

6. The method according to any one of claims 3 to 5, wherein: From the measured parameter difference, such as the pressure difference (Δp), on the one hand a mean value averaged over at least one cycle is determined as, for example, a static pressure difference and on the other hand determine the pulsation amplitude (Δp pp ) as, for example, a dynamic pressure difference.

7. The method according to any one of claims 1 to 6, wherein: Considering the nominal pulsation amplitude In the case of a calibrated wear-related pulsation amplitude (Δp pp ), the nominal pulsation amplitude being based, for example, on the pump in a new state.

8. Monitoring device for an eccentric worm pump, comprising means suitable for carrying out 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 an operating parameter.

10. A monitoring device according to claim 9, comprising at least one pressure sensor for measuring the operating pressure, for example at least one pressure sensor (11a) for measuring the pressure (p1) on the pressure side (D) of the stator and / or at least one pressure sensor (11b) for determining the pressure (p2) on the suction side (S) of the stator (1).

11. A computer program comprising instructions for causing a monitoring device according to any one of claims 8 or 10 to execute a method according to any one of claims 1 to 7. 12 . An eccentric screw pump having a monitoring device according to claim 8 .

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