METHOD FOR DETERMINING OR MONITORING THE CONDITION OF AN ECCENTRIC SCREW PUMP

Description

[0001] The invention relates to a method for determining or monitoring the condition (e.g., operating condition, wear condition, or malfunction condition) of a progressive cavity pump, which has a stator made of an elastic material and a rotor rotating within the stator at a pump frequency. In such a progressive cavity pump, the rotor is connected to a drive, for example, via at least one connecting rod, also referred to as a drive shaft. The pump has a pump housing, e.g., a suction housing, connected to the stator on the suction side, which typically has a housing opening, e.g., an inlet opening, for the medium to be pumped. Furthermore, the pump has a pump housing connected to the stator on the discharge side, e.g., via a discharge port and / or a discharge line.An eccentric screw pump is a type of rotary positive displacement pump used to convey a wide variety of media, particularly highly viscous liquids, in various industrial sectors. These media can also contain solids.

[0002] The stator consists, for example, of an elastic, preferably elastomeric, material and is generally surrounded by a one-piece or multi-piece stator casing or housing. The pump housing connected to the stator on the suction side is generally referred to as the suction housing, and the housing connected to the stator on the pressure side as the pressure port. However, it is also possible, in principle, to operate such a pump in the opposite direction of flow. The rotating connection, which simultaneously ensures eccentricity, between the drive or connecting shaft on the one hand and the rotor on the other is achieved via the coupling rod located in the pump housing. The coupling rod can be connected, for example, to the rotor via a joint on the rotor side and to the drive shaft or connecting shaft via a joint on the drive side. However, embodiments with a flexible coupling rod without joints are also covered by the scope of protection.

[0003] Such eccentric screw pumps are known, for example, from DE 10 2014 112 552 A1, DE 10 2010 037 440 A1 and WO 2009 / 024279 A1.

[0004] In practice, progressive cavity pumps and their components are subject to wear during operation, necessitating regular maintenance or repairs. Typical wear parts include the elastic stator and the rotor rotating within it. Therefore, it is known to monitor the wear of these components during operation by determining suitable parameters. For example, the flow rate can be recorded and compared with the respective rotor speeds. Similarly, the pump's back pressure can be determined in relation to its rotational speed. These known methods thus provide an indirect determination of the wear condition.

[0005] Alternatively, an eccentric screw pump is known from DE 20 2005 008 989 U1 in which a sensor is assigned to the stator, measuring compressions and / or movements of the stator or the elastic material during rotation of the rotor. The sensor can be, for example, a pressure sensor or a force sensor integrated into the stator, which registers stator compressions. This registers a measurement signal as a function of time, and to determine the wear condition, the measured time-dependent signal is compared with stored reference signals. This method utilizes the fact that with increasing material wear in the stator area, the pressure or compression transmitted by the rotor to the elastomeric stator during rotation also decreases.If a pressure signal is detected and recorded at a specific time, and it is found that this pressure signal is significantly lower than the previously stored reference signals, this is a reliable indication of corresponding stator wear. Due to the periodic operation of the rotor, the measurement signal recorded over time is a periodic signal. While the period or frequency of this signal generally does not change with increasing wear at a given rotor frequency, the amplitude of the periodic signal decreases with increasing wear, as the pressure acting on the pressure sensor or the displacement registered by the displacement sensor decreases accordingly. This well-known principle is based directly on the periodic compression of the stator during the rotation of the rotor.

[0006] The invention is based on the technical problem of creating a method with which the condition of an eccentric screw pump, e.g. a wear condition, operating condition or malfunction condition, can be reliably determined in a simple way.

[0007] To solve this problem, the invention teaches a method for determining or monitoring the condition of an eccentric screw pump, which has a stator and a rotor rotating in the stator at a pump frequency, The system provides the temporal profile of an operating parameter of the pump, which pulsates periodically with the pump frequency or a multiple thereof, and whose pulsation amplitude depends on the state of the progressive cavity pump. The pulsation amplitude is determined from the temporal profile of the operating parameter, and the state of the progressive cavity pump is determined by comparing the pulsation amplitude with one or more reference values. Reference values ​​can, for example, be determined in advance and stored in memory. However, it is also possible to determine the reference values ​​during operation and store them in memory. Thus, reference values ​​can be dynamically determined based on a large number of values ​​recorded during (normal) operation, for example, using statistical or neural methods in the sense of machine learning. Therefore, learned reference values ​​are also suitable.A (parameterized) algorithm used to determine a reference value. Such reference values ​​or algorithms can be learned, for example, during pump operation. They are stored, for example, in volatile memory (registers, RAM).

[0008] According to the invention, the operating pressure of the progressive cavity pump is provided as an operating parameter, and the pulsation amplitude of the pressure pulsation is determined. In an ideal system, the operating pressure of the progressive cavity pump does not vary with the rotation or rotational frequency of the pump; that is, an ideal progressive cavity pump is free of pressure pulsations with respect to the operating pressure. In practice, while progressive cavity pumps are indeed comparatively low in pulsation, they nevertheless exhibit certain pressure pulsations, which are attributable to the changing sealing lines during a revolution and minimal geometric differences between the rotor and stator. The invention recognizes that the pulsation amplitude of the pressure pulsation depends very significantly on the wear of the relevant components of a progressive cavity pump, in particular the stator and / or rotor.This is due to the fact that with increasing wear of the rotor and / or stator, the sealing line and the pumping chamber change, and this is clearly visible in the pressure curve over time and can be used for wear determination or monitoring. In practice, the pressure of a progressive cavity pump, which is constant, decreasing, or increasing on a timescale of seconds or minutes, is superimposed on a periodically varying pressure pulsation, and the pulsation amplitude of this pressure pulsation increases with increasing wear of the stator and / or rotor. By determining the pulsation amplitude at a specific time or monitoring it over a specific period and comparing it with previously stored reference values, the wear condition of the progressive cavity pump, e.g., of the stator and / or rotor, can be easily determined / monitored.Alternatively, the determination or monitoring of the condition of a pump can also refer to a malfunction of the pump, e.g., dry running or overpressure of the pump.

[0009] From the temporal profile of the operating parameter, i.e., the pump's operating pressure, the pulsation amplitude and consequently the pressure pulsation amplitude can be directly determined, allowing conclusions to be drawn about the condition, e.g., the state of wear. In a preferred embodiment, however, the pulsation amplitude is not directly determined from the pressure profile over time. Instead, the temporal profile of the periodically pulsating operating parameter, e.g., the pressure profile, is first transformed into a frequency profile, e.g., by a Fourier transform. From this frequency profile, the amplitude at the pump frequency (i.e., the first harmonic) or at a harmonic within this frequency profile, e.g., the first harmonic (second harmonic) or the second harmonic (third harmonic), can be determined as a measure of pump wear.Surprisingly, experiments have shown that the amplitude development of the pressure pulsation in the first harmonic of the pump frequency is even greater than in the pump frequency itself. Therefore, for evaluation purposes, it is preferable to use the amplitude development of a harmonic of the pump frequency, e.g., the first or second harmonic, from the frequency spectrum. For further details, please refer to the figure description.

[0010] The invention consists of determining the pump's operating pressure or pressure pulsations directly by means of a pressure measurement, e.g., with a pressure gauge. The operating pressure is determined on the pressure side of the stator, e.g., in or on a pressure port connected to the stator on the pressure side, or in or on a line connected to the stator on the pressure side.

[0011] As an alternative to the operating pressure, but excluded from the scope of the attached claims, 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 motor current pulsation is determined. For example, wear on the stator and / or rotor of an eccentric shaft pump typically leads not only to pressure pulsations but also to pulsation-like changes in the pump's torque, which is why the torque pulsation can be used as an operating parameter. Furthermore, the pulsation-like changes in torque lead to a pulsating power consumption or current consumption, so that the power consumption or current consumption can also be used as an operating parameter. Likewise, wear-related changes in the rotor-stator geometry of the pump lead to periodic orPulsating changes in structure-borne sound, so that structure-borne sound can also be used as an operating parameter.

[0012] On the one hand, the invention focuses on determining and monitoring the wear condition of the pump, e.g., of the rotor and / or stator. On the other hand, a specific operating condition or malfunction can also be determined or monitored, e.g., dry running, overpressure, insufficient or excessive clamping of a clampable stator, changes in the rotor / stator geometry, e.g., the sealing line, or swelling of the stator due to media incompatibility.

[0013] As an alternative, which is not within the scope of the claims, the invention also includes the analysis of the temporal profile of other operating parameters of a pump that pulsate periodically with the pump frequency and whose pulsation amplitude depends on the state of the progressive cavity pump. Such an operating parameter can be provided, i.e., measured, in the manner described. Alternatively, it is also possible not to measure the respective operating parameter directly, but to calculate it from directly measured values. Preferably, the temporal profile is transformed into a frequency spectrum in the manner already described.

[0014] The method according to the invention also has the advantage that the occurrence of the frequencies of interest for wear as multiples of the pump frequency, which is known or can be easily determined, enables a simple and effective filtering of the data from influences from the process or the plant.

[0015] The invention also relates to a monitoring device for a progressive cavity pump or a progressive cavity pump with such a monitoring device for carrying out the described method. Such a monitoring device therefore comprises means, e.g., an electronic evaluation unit, a computer, or the like, which are suitable (and programmed accordingly) for carrying out the described method for determining and monitoring the condition of the progressive cavity pump. Such a monitoring device can, for example, have a sensor for measuring the operating parameter or be connected to such a sensor. The sensor can, for example, be a pressure sensor for determining and continuously recording the operating pressure of the progressive cavity pump.Furthermore, the monitoring device can have a visual and / or acoustic display that indicates the determined state of the progressive cavity pump. The monitoring device with visual or acoustic display can, in principle, be integrated directly into the progressive cavity pump, so that the wear condition or an operating or malfunction state of the progressive cavity pump can be displayed directly. However, a separate monitoring device is preferred, which only needs to access the operating parameters of the progressive cavity pump. In this respect, the monitoring device can also be a computer configured to carry out the described method and consequently to determine or monitor the state of the progressive cavity pump. The method according to the invention can, for example, be implemented as a computer program or...A computer program product is provided which includes commands that execute the described procedure on such a monitoring device, e.g., a computer or the like. Such a computer program can be installed, for example, on a standard computer, tablet, or smartphone, and the operating parameters required for carrying out the procedure, or the time course of the operating parameters, can be transmitted to the device via wired or wireless connection. The wear condition can then be determined from the transmitted operating parameters or data using the computer program.

[0016] Furthermore, the invention encompasses not only the determination of the wear condition of the progressive cavity pump, but also, alternatively, the determination and monitoring of an operating or fault condition, e.g., dry running of the progressive cavity pump. This is because the pulsation amplitude of the operating parameter, e.g., the pressure pulsations, also changes during dry running of the pump compared to normal operation, so that dry-running protection for a progressive cavity pump can also be implemented according to the invention. Moreover, the determination and monitoring of other operating conditions, e.g., fault conditions, is also possible, in particular the monitoring of geometric changes of the rotor and / or stator.

[0017] The monitoring device according to the invention preferably has a memory in which the comparative values ​​for the pulsation amplitudes required for evaluation are stored, so that the determined pulsation amplitudes can be compared with the stored pulsation amplitudes to determine a wear condition or operating condition of the pump. Furthermore, the monitoring device can also perform the aforementioned dynamic determination and storage of comparative values, so that corresponding algorithms for such dynamic determination, e.g., in the sense of machine learning, can also be included in the monitoring device. The monitoring device also preferably has an electronic evaluation unit that is configured to acquire and process the provided signals, e.g., signals from a measuring device, with the required frequency resolution.The sensor must also be able to capture the operating parameter along with the pump frequency in terms of time resolution.

[0018] Furthermore, the information obtained with the inventive method regarding the condition (wear condition or malfunction condition) can be used in various ways. Firstly, it can be used simply as a visualization, allowing maintenance measures to be carried out as needed. Alternatively, the progressive cavity pump can also be operated based on the determined condition, e.g., wear condition, and the pump's operation can be adapted to the information obtained.

[0019] This makes it possible, for example, to implement the invention in an eccentric screw pump with automated delivery, which is described, for example, in DE 10 2014 112 552 A1.

[0020] Furthermore, it is possible that the point in time at which wear begins, as determined by the system, serves as the starting point for a wear progression prediction based on other measured variables.

[0021] The invention will now be explained with reference to drawings illustrating only exemplary embodiments. These show Fig. 1 an eccentric screw pump with a monitoring device for monitoring the condition, e.g. wear condition, Figs. 2a to 2c the temporal course of pressure pulsations of the progressive cavity pump, Figs. 3a to 3c the pressure pulsation after Figs. 2a to 2c in a frequency spectrum Fig. 4 the temporal evolution of the pulsation amplitudes.

[0022] In Fig. 1Figure 1 shows a typical progressive cavity pump, comprising a stator 1 made of an elastic material and a rotor 2 rotating within the stator 1, the stator 1 being surrounded by a stator shell 3. The pump also includes a suction housing 4 and a connection port 5, which is also referred to as the discharge port 5. Furthermore, the pump has a pump drive 6, which acts on the rotor 2 via a connecting rod 7. The connecting rod 7 is connected to the drive 6 or a drive shaft via a drive-side coupling joint 8 and to the rotor 2 via a rotor-side coupling joint 9.

[0023] In the illustrated embodiment, a pressure sensor 11 is provided in the area of ​​the pressure port 5, with which the operating pressure of the progressive cavity pump is measured. The progressive cavity pump, or rather the sensor 11, is connected to a monitoring device 10, which allows the wear condition of the progressive cavity pump to be determined or monitored. This monitoring device 10 operates on the basis of the analysis of pressure pulsations. Even though a progressive cavity pump is relatively low in pulsations, pressure pulsations do occur in practice; that is, the temporal profile of the progressive cavity pump's operating pressure pulsates periodically with the pump frequency.The operating pressure, which is typically constant on a timescale of seconds or minutes during operation, is consequently superimposed with a periodic pulsation when analyzed in a higher frequency range. The pulsation amplitude depends on the wear state of the stator and / or rotor, increasing with the wear state. This results from a comparative analysis of the... Figures 2a to 2c These figures show the time course of the pressure pulsation Δp at a first time point T1 in Fig. 2a with low wear and at a second time point T2 with medium wear in Fig. 2b as well as a third time point T3 with high wear in Fig. 2c It is evident that the pulsation amplitude Δp increases significantly with increasing operating time of the pump and consequently increasing wear.

[0024] This effect becomes even more apparent in the Figures 3a to 3c The frequency spectra shown. Figures 3a to 3cshow the amplitude development A of the pressure pulsations in a frequency range, where the functions are according to Figures 3a to 3c each by Fourier transformation from the functions to Figs. 2a to 2c This resulted in the following: In the exemplary embodiment, the pump was operated at a pump frequency of 100 revolutions per minute and consequently a pump frequency of 1.7 Hz. In the Figures 3a to 3c The pulsation amplitudes for the pump frequency are discernible at approximately 1.7 Hz and the first harmonic at approximately 3.3 Hz, as well as the second harmonic at approximately 5 Hz and the third harmonic at approximately 6.7 Hz. It becomes clear that the pressure pulsations can be analyzed particularly significantly based on the first harmonic of the frequency spectrum.

[0025] The amplitude development of the pressure pulsations that occur in the Figures 3a to 3c The representation, which shows only three values, is in Fig. 4The pulsation amplitude was plotted as a function of operating time, with one experiment using a suitable medium to induce particularly high wear over a specific operating period. It is evident that the pulsation amplitude increases with increasing operating time for both the pump frequency and the first three harmonics, thus enabling the determination and monitoring of the wear of the progressive cavity pump, particularly by comparing the measured values ​​with previously recorded reference values.

[0026] This is the purpose of the in Fig. 1A monitoring device, merely suggested, captures sensor data and evaluates it with electronics capable of reading sensor signals at a high frequency, i.e., in the kHz range. Frequency spectra are then generated from the acquired data, and the wear or malfunction is determined by comparison with previously stored / acquired data.

Claims

1. A method for determining or monitoring the state of a progressive cavity pump which has a stator and a rotor which is rotating in the stator with a pump frequency, wherein the time curve of an operating parameter of the pump is provided, which operating parameter pulses periodically with the pump frequency or a multiple of the pump frequency and the pulsation amplitude of the operating parameter depends on the state of the progressive cavity pump, wherein the pulsation amplitude is ascertained and the state of the progressive cavity pump is determined by comparing the pulsation amplitude with one or more comparison values, wherein the state that is determined or monitored is a state of wear of the progressive cavity pump, wherein the operating pressure is provided as operating parameter by a measurement on the pressure side of the stator and the pulsation amplitude of the pressure pulsation is ascertained, wherein the pulsation amplitude of the pressure pulsation depends on the state of wear of the stator and / or the rotor.

2. The method according to Claim 1, wherein the pulsation amplitude increases with the state of wear of the stator and / or the rotor.

3. Method according to either of Claims 1 and 2, wherein the operating pressure or the pressure pulsation is ascertained directly by a pressure measurement using a pressure measuring device.

4. The method according to one of Claims 1 to 3, wherein the operating pressure is measured in or at a pressure connection that is connected to the stator on the pressure side or in or at a line that is connected to the stator on the pressure side.

5. The method according to one of Claims 1 to 4, wherein the time curve of the periodically pulsating operating parameter, namely the pressure curve over time, is transformed into a frequency curve, e.g. by Fourier transformation, wherein the amplitude in the pump frequency or a harmonic of the frequency curve, e.g. the first harmonic, is ascertained from the frequency curve as pulsation amplitude.

6. A monitoring device for a progressive cavity pump, comprising means which are suitable for carrying out the method according to one of Claims 1 to 5.

7. The monitoring device according to Claim 6, comprising at least one sensor for measuring the operating parameter and / or comprising an optical and / or acoustic indicator, using which the ascertained state of the progressive cavity pump is indicated.

8. The monitoring device according to Claim 6 or 7, comprising a memory in which comparison values are stored, with which comparison values the ascertained pulsation amplitudes are compared.

9. A computer program, comprising commands which cause the monitoring device according to one of Claims 6 to 8 to carry out the method according to one of Claims 1 to 5.

10. A progressive cavity pump having a monitoring device according to one of Claims 6 to 8.