METHOD FOR DETERMINING OR MONITORING THE DELIVERY FLOW OF AN ECCENTRIC SCREW PUMP

Abstract

A method for determining or monitoring the effective delivery flow of an eccentric screw pump that has a rotor rotating eccentrically in a stator at a pump frequency. The effective delivery flow is determined from the difference between an ideal delivery flow and a backflow, which backflow is dependent on at least one gap in the sealing line between rotor and stator. An operating parameter of the pump representing the gap is measured which pulses periodically with the pump frequency, the pulsation amplitude of which is dependent on the state of wear of the rotor and/or of the stator and is related to a tilting of the rotor in the stator. The backflow is calculated repeatedly using a mathematical model in dependence on the measured values for the operating parameter and on predetermined characteristic values of the pump and/or of the medium to be delivered.

Claims

1. A method for determining or monitoring an effective delivery flow (Q) of an eccentric screw pump during operation, wherein the eccentric screw pump has a stator (1) and a rotor (2) that rotates eccentrically in the stator (1) at a pump frequency, wherein the effective delivery flow (Q) is determined from a difference of an ideal delivery flow (Q.sub.0) and a backflow (Q.sub.B) that is directed counter to the ideal delivery flow (Q.sub.0), which backflow is dependent on at least one gap (w) in a sealing line between the rotor (2) and stator (1), the method comprising the steps of: measuring an operating parameter of the pump, which parameter represents the at least one gap and thereby the backflow (Q.sub.B), which parameter pulsates periodically with a pump frequency, wherein a pulsation amplitude of the operating parameter is dependent, on a wear state of the rotor and/or of the stator, and, is related to a tilt of the rotor (2) in the stator (1), which tilt influences the at least one gap (w) and thereby the backflow (Q.sub.B), and repeatedly calculating the backflow (Q.sub.B) and from it, the effective delivery flow (Q), using a mathematical model, as a function of the measured values for the operating parameter and of predetermined characteristic values of the pump and/or of a medium to be delivered.

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

3. The method according to claim 2, wherein a parameter difference in the form of a pressure difference measured as a difference (p) between a pressure (p1) on the a pressure side (D) of the stator and a pressure (p.sub.2) on a suction side (S) of the stator (1) is used as the operating parameter.

4. The method according to claim 1, wherein in addition, a speed of rotation (n) of the pump or of the rotor (2) is measured or made available, and flows into the calculation using the mathematical model.

5. The method according to claim 1, wherein geometry parameters of the pump are used as the predetermined characteristic values of the pump.

6. The method according to claim 3, wherein from the measured parameter difference, an average value averaged over at least one period is determined as a static pressure difference (.sup.p), and a pulsation amplitude (p.sub.pp) is determined as a dynamic pressure difference.

7. The method according to claim 1, wherein a wear-dependent pulsation amplitude (p.sub.pp) determined from the measurement of the parameter difference, for example pressure difference, is corrected, taking into consideration a nominal pulsation amplitude ({circumflex over (p)}.sub.pp), which is based on the pump in the a new state.

8. A monitoring device for an eccentric screw pump, comprising means that are suitable for carrying out the method according to claim 1.

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

10. The monitoring device according to claim 9, wherein the at least one sensor comprises at least one pressure sensor configured for measuring an operating pressure, the at least one pressure sensor comprising at least one first pressure sensor (11a) configured for measuring the pressure (p.sub.1) on the pressure side (D) of the stator and/or at least one second pressure sensor (11b) configured for determining the pressure (p.sub.2) on the suction side (S) of the stator (1).

11. A computer program comprising commands that when installed in a monitoring device carries out the method according to claim 1.

12. An eccentric screw pump having a monitoring device according to claim 8.

Description

[0028] In the following, the invention will be explained in greater detail using drawings that merely show an exemplary embodiment. The figures show:

[0029] FIG. 1 an eccentric screw pump having a device for determining or monitoring the effective delivery flow,

[0030] FIG. 2 the geometry of a rotor of an eccentric screw pump according to FIG. 1,

[0031] FIG. 3 a schematic representation of the method according to the invention for determining or monitoring the effective delivery flow of the eccentric screw pump,

[0032] FIG. 4a, b in each instance, a partial cross-section through the rotor according to FIG. 2.

[0033] In FIG. 1, a usual eccentric screw pump is shown, which has a stator 1 composed of an elastic material and a rotor 2 that rotates in the stator 1, wherein the stator 1 can be surrounded by a stator mantle 3. Furthermore, the pump has a suction housing 4 as well as a connecting piece 5, which is also referred to as a pressure joint 5. The pump furthermore has a pump drive 6, which acts on the rotor 2 by way of a coupling rod 7. The coupling rod 7 is connected to the drive 6, i.e., to a drive shaft by way of a drive-side coupling joint 8, and to the rotor 2 by way of a rotor-side coupling joint 9.

[0034] In the exemplary embodiment, a pump is implemented with clamping, i.e., the rotor 2 lies against the inner surface of the passage opening of the stator 1 by way of multiple uninterrupted sealing linesin the case of an ideal motion. These sealing lines are indicated with hatched lines on the surface of the rotor 2 in FIG. 2.

[0035] In the exemplary embodiment shown, a pressure sensor 11a for determining the operating pressure is provided on the pressure side D, in the region of the pressure joint 5, on the one hand, 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, on the other hand. The eccentric screw pump 10, i.e., the sensors 11a, 11b is/are connected to a monitoring device 10 with which the delivery flow Q of the eccentric screw pump can be determined or monitored during operation.

[0036] In this regard, however, no direct measurement of the delivery flow Q by way of a through-flow sensor takes place, but rather a system having a virtual sensor is implemented, which is based on a delivery flow estimate or delivery flow determination using a mathematical model, taking into consideration a simplified measurement of an operating parameter, namely the operating pressure of the pump. In this regard, the invention makes uses of the relationship between the delivery flow Q of the pump and certain phenomena and relationships that will be discussed in greater detail below.

[0037] In an eccentric screw pump, the actual, effective delivery flow Q results from the difference of an ideal delivery flow Q.sub.0 and a backflow Q.sub.B directed counter to the ideal delivery flow Q.sub.0, wherein the backflow depends on at least one gap in the sealing line between rotor and stator. The ideal delivery flow Qo can be determined by calculations, for example, from the pump speed of rotation n and the delivery volume V.sub.0:

[00001]$Q=V_{0}n-Q_B.$

[0038] The analysis of the backflow Q.sub.B is of particular importance within the scope of the invention.

[0039] In the case of an eccentric screw pump, the pressure difference p, i.e., the difference between the (operating) pressure p.sub.1 on the pressure side D and the (operating) pressure p.sub.2 on the suction side S, which difference is to be monitored by means of measurement technology, leads to a constant tilt t.sub.y of the rotor about the Y axis shown in FIG. 2. This constant tilt t.sub.y produces a gap w that in turn brings about a backflow Q.sub.B, wherein this gap w and thereby the backflow Q.sub.B are essentially dependent on the pressure difference .sup.p averaged over a period.

[0040] Furthermore, periodic pressure differences between the pressure side D and the suction side S occur, which result from a periodic tilt t.sub.x of the rotor about the X axis shown in FIG. 2. The tilt t.sub.x pulsates at the rotation frequency (i.e., at twice the rotation frequency, since two chambers open per revolution) of the rotor 2 and at a pulsation amplitude for the tilt, which is also referred to as a peak-to-peak value of the tilt t.sub.x,pp. The periodic tilt t.sub.x results from periodic changes in the pressure difference p, so that pulsations in the pressure difference p and, in particular, also the pulsation amplitude p.sub.pp of the pressure difference are directly related to the pulsation amplitude t.sub.x,pp of the tilt t.sub.x.

[0041] According to the invention, the effective delivery flow Q can now be modeled mathematically, specifically taking into consideration measured values for the pressure difference Ap and, in particular, the pressure pulsation of the pressure difference. In this regard, the fact that this pulsation amplitude, i.e., the peak-to-peak value p.sub.pp in the pressure difference is sensitively dependent on the wear state of rotor and/or stator, so that the wear of rotor and/or stator, which increases during the course of operation, can be taken into consideration directly during the course of modeling. In this regard, reference is made to the method schematic according to FIG. 3.

[0042] In the lower box in FIG. 3, outlined with a broken line, one can see the simple modeling of the backflow Q.sub.B and thereby of the actual delivery flow Q on the basis of a measurement of the averaged pressure difference .sup.p, which is directly related to the size of the sickle-shaped gap w in the sealing line between rotor 2 and stator 1, specifically on the basis of the tilt t.sub.y of the rotor about the Y axis, produced on the basis of the pressure difference Ap, which tilt leads to the gap w. In this regard, in FIG. 3 (bottom), calc. w represents the calculation of the sickle-shaped gap w, calc. Q.sub.B represents calculation of the backflow or back stream Q.sub.B, and calc. Q.sub.0 represents the calculation of the ideal delivery flow Q.sub.0. This gap w is shown in FIG. 4a.

[0043] In the upper part of FIG. 3, in the box shown with a solid line, the influence of the periodic tilt t.sub.x of the rotor about the X axis and thereby the pressure pulsation p.sub.pp is shown, which significantly depends on the wear of rotor and/or stator, so that the wear of rotor and/or stator flows in directly, by way of the modeling shown in the upper part. Thus, it is possible to determine the pulsation amplitude p.sub.pp of the pressure pulsation, i.e., the peak-to-peak value of the periodically changing pressure difference, from the measurement of the pressure difference p (calc. p.sub.pp). Since, however, pressure pulsations already occur in the new state of the pump, independently of wear, a wear-independent pulsation amplitude ({circumflex over (p)}.sub.pp) is determined by calculations, by way of the peak-to-peak value of the tilt (calc. t.sub.x,pp), and deducted from the measured pulsation amplitude p.sub.pp in the sense of standardization. In any case, the contribution of the wear-dependent gap w.sub.w to the gap w in the sealing line can be modeled and taken into consideration by way of the determination of the pulsation amplitude (cf. FIG. 4b). The wear-dependent component w.sub.w of the gap shown in FIG. 4b consequently results from the following equation, in accordance with the diagram in FIG. 3:

[00002]$w_w=k_{3}n\left(p_{\mathrm{pp}}-k_2{t}_{x,\mathrm{pp}}\right)$

wherein t.sub.x,pp and thereby {circumflex over (p)}.sub.pp are determined purely by calculations. The gap w.sub.w can consequently be calculated repeatedly on the basis of the continuing measurement of the pressure pulsations.

[0044] In this way, a virtual sensor is created, which is based on an adaptive determination or monitoring of a representative operational value, in this case the pressure difference p. By means of repeated calculation of the wear-dependent gap component w.sub.w as a function of the pressure pulsations, adaptive adaptation to the wear state takes place. The invention is based, in this regard, on the important recognition that the pressure pulsations to be measured are directly related to the tilt of the rotor, which pulsations bring about a gap that influences the backflow. Since the pressure pulsations in turn are wear-dependent, it is possible to take the wear into consideration directly in the modeling, by way of the analysis of the pressure pulsations.

[0045] The invention allows improved monitoring and, for example, also maintenance predictions, under the aspect of predictive maintenance.