EP3037668A1 - Operating method for a pump, in particular a multi phase pump as well as a pump - Google Patents

Abstract

Operating method for a pump, in particular a multi-phase pump, wherein a return line (8) for returning the fluid from the high pressure side to the low pressure side is provided, in which method by means of a surge limit control unit (4) to avoid an unstable operating condition, a control valve (9) in the return line (8) is controlled, which controls the flow through the return line (8), wherein a limit curve (60, 60 ') for a control parameter in the surge limit control unit (4) is maintained, a current value of the control parameter during operation of the pump with the Limit curve (60, 60 ') is compared and where, as soon as the current value of the control parameter reaches the limit curve (60, 60'), the control valve (9) is controlled such that the current value of the control parameter of the limit curve (60, 60 '), and wherein an operating parameter of the pump (1) is used as a control parameter. Furthermore, a corresponding pump, in particular a multiphase pump (1), is proposed.

Description

The invention relates to an operating method for a pump, in particular a multi-phase pump and a pump, in particular a multi-phase pump for conveying a fluid according to the preamble of the independent claim of the respective category.

Multiphase pumps are pumps that can be used to deliver fluids containing a mixture of several phases, such as a liquid phase and a gaseous phase. Such pumps have long been well known and are manufactured in numerous embodiments, often as centrifugal pumps, for example as single or double-flow pumps and as single-stage or multi-stage pumps. The range of application of these pumps is very wide, for example, they are used in the oil and gas industry for the transportation of petroleum-natural gas mixtures and especially as booster pumps, also referred to as booster pumps.

It is a known technology to increase or prolong the utilization or the skimming of oil fields with such booster pumps. In particular, as the naturally occurring pressure in an oil field decreases with increasing oil production, a booster pump lowers the pressure on the well by pumping the fluid so that the oil can continue to exit the well.

Very often, these booster pumps need to generate high pressures because the wells are very deep or inaccessible, requiring very long pipelines or pipelines between the wellbore and the processing or storage facilities. This is especially true in subsea applications where, for example, the well bore is on the ocean floor and the processing or storage facilities on land, on a drilling platform or on a ship are designated as FPSOs (Floating Production Storage and Offloading Units). Especially in such cases, a booster pump must promote over large geodetic heights and generate a correspondingly high pressure.

The efficiency and performance of a multiphase pump depends very much on the actual phase composition or phase distribution of the multiphase fluid to be pumped. The relative volume fractions of the liquid and the gaseous phase - for example in the oil extraction - are subject to very large fluctuations, which is due to the natural source, on the other hand, but also caused by the connecting lines. Here there are several effects that allow the liquid phase to accumulate in certain areas until the line cross section is completely filled with the liquid phase, so that upstream there is an increase in pressure in the gaseous phase until the pressure becomes so high that the liquid phase is suddenly ejected. Other interactions between the gaseous and liquid phases can also lead to pressure pulsations in the conduit. The fluctuations in the phase distribution of the multiphase fluid are thus also caused by the architecture and dynamics of the conduit system.

Such effects may cause the multiphase pump to go into an unstable operating condition, also called a surge, due to a too low flow rate. Such unstable operating states are characterized by extremely fluctuating flow rates, pressure surges, large power and pressure fluctuations as well as strong vibrations of the pump. Such unstable operating conditions place an extremely heavy burden on the pump itself and the adjacent installations. Operating a multiphase pump in such an unstable operating condition too long may lead to prematurely Material fatigue, a significantly higher wear, lead to defects or failure of the entire pump, resulting in adverse effects on the downstream of the pump installations provided. It can even happen by the failure of the multi-phase pump that the entire production process is interrupted, which is of course very disadvantageous in economic terms.

To intercept or at least mitigate the problems resulting from variations in the phase distribution, it is known to provide upstream of the multiphase pump a buffer tank whose volume and internal configuration are adapted to the particular application. This buffer tank acts like a filter or as an integrator and can absorb or dampen sudden changes in the phase distribution of the fluid, so that they can not penetrate or only greatly attenuated to the inlet of the multiphase pump.

Since such buffer tanks but can not be designed arbitrarily large and also can not attenuate all variations of the phase distribution out, a underflow fuse or a surge limit control is often provided in a multi-phase pump, which is commonly referred to as Surge Control or Surge Protection and it To prevent the multiphase pump gets into such an unstable operating condition. For the surge limit control, it is a known measure to provide a return passage through which the fluid delivered by the multi-phase pump can be returned from the pressure side of the pump to the suction side. In this return line one or more, for example two, control valves are provided which can be controlled by the surge limit control and accordingly allow a smaller or larger flow through the return line. For example, if two control valves are provided, one is often intended to compensate for fluctuations in the phase distribution, while the other in the case of extremely large fluctuations very quickly opens the entire flow cross-section of the return line. The logic of the surge limit control is usually integrated in the control device of the pump, which is nowadays designed regularly as a digital control system.

In particular, in the case of very high proportions of gas in the multiphase fluid to be delivered, a cooling system can also be provided in the return line in order to avoid an excessive heat load or heat accumulation.

Further, a flow meter is provided between the confluence of the return line on the suction side and the inlet of the multi-phase pump.

For the surge limit control, a limit curve is usually stored in the corresponding control unit, at which point countermeasures are to be taken. The limit curve is determined based on a lower surge limit line, which indicates at which parameter constellations the transition to an unstable operating state occurs. This surge limit line is determined on the basis of empirical values and / or experimentally determined data. The limit curve is then set with a certain "safety margin" from the surge line to avoid unstable operating conditions during operation of the pump. When the pump reaches the limit during operation, the surge limit control activates the check valve or control valves to increase the return flow in the return line so that the pump moves away from the limit curve.

Known pump limit regulations or underflow fuses require knowledge of the actual flow rate, the current phase distribution of the delivered multiphase fluid, and the current rotational speed of the pump. However, a direct measurement of the flow rate and the actual phase distribution with a single instrument or sensor is not possible because such measuring instruments do not exist. Therefore, the flow meter must be designed as a multi-phase flow meter. The multi-phase flow meter determines the flow rate based on a simultaneous metrological acquisition of directly accessible process variables such. Absolute pressure, differential pressure, density, temperature, which are then processed in a semi-empirical model to determine or estimate the actual flow rate and phase distribution of the fluid in the multi-phase flowmeter.

Such multiphase flowmeters are very complicated, expensive and expensive devices that have some other disadvantages. The various sensors in a multi-phase flowmeter for measuring the various process variables have very large variations in the update rate of each determined process variable. Of course, then the sensor with the lowest update rate will determine the maximum possible update rate of the multi-phase flowmeter. This maximum refresh rate is sometimes insufficient to ensure reliable pump limit control or reliable underflow protection. Particularly in subsea installations and the associated maritime environment, the corresponding devices have even lower update rates, which further reduces the dynamic performance of the surge limit control. Since greater safety distances from the limit curve are thus necessary to avoid unstable operating states, the operating range of the multiphase pump is further restricted.

In addition, these complex multiphase flowmeters require considerable space for their installation, which is often unavailable, for example, on platforms, FPSOs or on a subsea formation on the seabed.

Furthermore, the flow of a multi-phase fluid has dynamic effects that alter the actual phase distribution along the conduit. Therefore, for a robust and reliable surge limit control, it would be desirable to measure the flow rates immediately upstream of the inlet of the pump to truly determine the phase distribution present in the multi-phase pump. However, the installation of a multi-phase flow meter immediately upstream of the inlet of the pump is often not possible at all, for example for reasons of space.

Similar problems can also occur in single-phase pumps, ie in pumps which serve to convey a single-phase fluid, for example a liquid. Again, it is often necessary or desirable to provide surge limit controls or underflow fuses for the pump. Use today known surge limit regulations Usually, signals from flowmeters, which in the same way as described above on the basis of the multiphase flowmeters, measure the flow of the fluid. Even with these flow meters similar problems arise as described above, namely in particular that they often can not be placed at the desired location or only with great effort and that their update rates are often too low or the delays in the signal transmission are too large, so that the surge limit control must be designed with very large safety distances. This limits the operating range in which the pump can be safely operated.

Based on this prior art, it is therefore an object of the invention to provide an operating method for a pump, in particular for a multi-phase pump and a corresponding pump, in particular a multi-phase pump, in which realized in a simple manner a reliable surge limit control or a reliable underflow fuse in particular, which does not rely on complicated multiphase flowmeters or flowmeters.

The object of the invention solving this object are characterized by the features of the independent claim of each category.

According to the invention, therefore, an operating method for a pump, in particular for a multiphase pump, for conveying a fluid from a low-pressure side to a high-pressure side is proposed, wherein a return line for returning the fluid from the high-pressure side to the low-pressure side is provided, in which method by means of a surge limit control unit for avoiding an unstable operating state, a control valve in the return line is controlled, which controls the flow through the return line, wherein a limit curve for a control parameter in the surge control unit is maintained, a current value of the control parameter during operation of the pump is compared with the limit curve and wherein, as soon as the current value of the control parameter reaches the limit curve, the control valve in the return line is controlled in such a way that the current value of the Control parameter from the limit curve, and being used as a control parameter, an operating parameter of the pump.

By the term "operating parameters" are meant those parameters which determine the operation of the pump and which can be adjusted by the control or control device of the pump, for example the speed of the pump, its power consumption, the torque with which the pump is driven, etc .. In particular, such quantities are not operating parameters in the sense of this application, which are predetermined by the fluid itself, so for example the phase distribution of the fluid (in the case of a multi-phase fluid) or its viscosity, because these sizes can not be entered on the pump itself or be set.

Because the surge limit control unit uses an operating parameter to avoid an unstable operating state of the pump, it is no longer necessary to estimate or determine metrologically - if at all - variables that are very difficult to detect, such as the current phase distribution in the fluid to be delivered , In particular, can be dispensed with so complicated and very expensive devices such as a multi-phase flow meter or on a flow meter and still a reliable and stable border control or underflow protection of the pump, in particular the multi-phase pump can be ensured.

According to a preferred embodiment of the invention, the limit curve indicates a clear relationship between the operating parameter and the pressure difference generated by the pump, in particular the multi-phase pump, because this pressure difference is very easily determinable or metrologically detectable.

Preferably, to compare the current value of the operating parameter with the limit curve, the pressure difference between the pressure at an inlet and the pressure at an outlet of the pump is detected by measurement. This makes it possible to ensure in a simple manner that in each case the current value is exactly the pressure difference is detected, which is currently generated by the pump.

In practice, it has proved to be advantageous if the operating parameters used by the surge limit control unit are clearly related to the torque with which the pump is driven.

Particularly preferably, the operating torque used is the torque with which the pump is driven. What is surprising here is the realization that the dependence of the instantaneous torque on the pressure difference generated by the pump makes it possible to establish a limit curve with which it is possible reliably to prevent the pump from entering an unstable operating state.

A preferred measure is that the limit curve indicates the dependency of the torque on the pressure difference at which the pump is still safely operated in a stable operating state. This means that the limit curve is preferably set so that it does not run exactly where the pump is in an unstable operating state, but that a safety margin is provided.

For this purpose, it is advantageous if the limit curve is set at a distance from a lower surge limit line, wherein the lower surge limit line indicates the respective value of the operating parameter at which the pump changes to an unstable operating state.

This lower surge boundary line is preferably determined with the aid of experimental test data, for the determination of which the pump is guided into an unstable operating state. This can be done, for example, before starting the pump in a test stand, where the pump is then deliberately brought into the unstable operating state (surging), so as to determine at which values of the operating parameter, this transition occurs.

Of course, it may also be advantageous if empirical values are used to determine the lower surge limit line. This can save time by reducing the experimental effort to determine the lower surge limit line for the particular pump.

From an apparatus point of view, it is preferred if the surge limit control unit is integrated in a control device for controlling the pump.

In order to minimize the effort and thus to make the operating method particularly simple, it is an advantageous measure if the current value of the operating parameter is provided by a variable frequency drive for the pump.

A preferred application of the operating method is when the pump is used as a booster pump in oil and gas production, particularly in undersea oil and gas production.

The invention further proposes a pump, in particular a multiphase pump, for conveying a fluid from a low-pressure side to a high-pressure side, with an inlet and an outlet for the fluid, and with a surge limit control unit for avoiding an unstable operating state, which is a control signal for a control valve in a return line for returning the fluid from the high-pressure side to the low-pressure side, wherein a limit curve for a control parameter is present in the surge limit control unit, the surge limit control unit comparing a current value of the control parameter with the limit curve during operation of the pump, and wherein the surge limit control unit, as soon as the current value of the control parameter reaches the limit curve, provides the control signal which can control the control valve in the return line such that the current value of the control parameter from the limit curve, where the control parameter is an operating parameter of the pump.

The advantages and the preferred embodiments of the pump in this case correspond to those which are explained above in connection with the operating method according to the invention.

In particular, it is also particularly preferred with respect to the pump when the operating parameter is the torque for driving the pump, and the limit curve indicates the dependency of the torque on the pressure difference between the pressure at the inlet and the pressure at the outlet.

Preferably, the pump is designed as a centrifugal pump and as a booster pump for oil and gas production, in particular for the undersea oil and gas production.

By means of the operating method according to the invention or the pump according to the invention, an extremely reliable surge limit control to avoid unstable operating states is possible. Since the operating parameters required for the control are very simple and available at a very high refresh rate, even very rapid changes in the process conditions can be detected and governed. Especially in subsea applications, the use of the operating parameter of the pump ensures that there are no signal delays caused, for example, by the subsea components or their connection to the subsea components. Furthermore, the advantage results that the safety distance from the unstable operating states can be reduced or minimized so that the pump can be operated in a significantly larger operating range.

A further advantage of the operating method according to the invention or of the pump according to the invention is that it can be easily retrofitted even in already existing pumps or existing pumps can be modified in a simple way to pumps according to the invention. Frequently, no major changes in the equipment are needed.

Further advantageous measures and embodiments of the invention will become apparent from the dependent claims.

Fig. 1:

ein schematische Darstellung zur Veranschaulichung eines Ausführungsbeispiels der Erfindung,

Fig.2:

eine Darstellung des Zusammenhangs der von dem Ausführungsbeispiel der Multiphasenpumpe generierten Druckdifferenz mit der Flussrate, und

Fig. 3:

eine Darstellung einer Grenzkurve und einer unteren Pumpgrenzlinie in einem Auftrag des Drehmoments gegen die Druckdifferenz.

In the following, the invention will be explained in more detail both in terms of apparatus and process technology with reference to embodiments and with reference to the drawing. In the drawing show:

Fig. 1:

1 is a schematic illustration for illustrating an embodiment of the invention,

Figure 2:

a representation of the relationship between the generated by the embodiment of the multi-phase pump pressure difference with the flow rate, and

3:

a representation of a limit curve and a lower surge boundary line in an order of the torque against the pressure difference.

Fig. 1 illustrates in a schematic representation of an embodiment of the invention both in terms of apparatus and in terms of process engineering. Based on Fig. 1 In the following, an exemplary embodiment of the operating method according to the invention and an exemplary embodiment of a pump according to the invention, which is embodied here as a multi-phase pump, will be explained, which is designated overall by the reference numeral 1. Reference is made by way of example to the case of application, which is important in practice, in that the multiphase pump 1 is designed as a centrifugal pump and as a booster pump, which is usually also referred to as a booster pump. In this application, the multiphase pump is used for oil and gas production, and in particular for undersea oil and gas production, where the output of a well 100 is located on the seabed, from where the oil and gas to a above the sea arranged storage and processing device 200 is conveyed. The borehole 100 extends into an oil field, which in Fig. 1 not shown. The storage and processing device 200 may be installed on the mainland or in the offshore area, for example on a platform that is anchored on the seabed. Of course, the storage and processing device 200 may also be floating on the sea, for example in the form of an FPSO.

In this embodiment, therefore, the fluid to be delivered by the multi-phase pump 1 is a multi-phase fluid which comprises at least one gaseous and one liquid phase. The task of used as a booster pump Multiphase pump 1 is designed to lower the pressure at the exit of borehole 100, for example to a value in the range of 10 bar to 40 bar, so that the fluid can escape from borehole 100, or increases the flow rate of the fluid delivered from wellbore 100 becomes. This measure known per se is particularly advantageous with increasing skimming of the oil field, because then the natural pressure, under which the oil field stands, decreases. The multiphase pump 1 can generate, for example, pressure differences of up to 150 bar, the generated pressure difference, of course, strongly depends on the current density of the fluid and thus its current phase distribution. Depending on the application, the multi-phase pump 1 can be located on the seabed near or at a distance from the borehole 100, or in the offshore area, for example on a (drilling) platform or an FPSO, or even on land.

Of course, the invention is not limited to this specific application, but is also suitable for all other applications in which multi-phase pumps can be used or used. In particular, the invention is suitable for multi-phase pumps, which are centrifugal pumps. Also, the invention is not limited to multi-phase pumps, but is generally suitable for pumps, including for single-phase pumps, in which the fluid to be delivered contains only one phase, that is, for example, is a liquid.

In Fig. 1 are lines through which the fluid can flow, shown in solid lines, while signal connections are shown in dashed lines.

The multiphase pump 1 comprises an inlet 10, through which the fluid passes into the multiphase pump 1 and an outlet 20, through which the delivered fluid leaves the multiphase pump 1. Hereinafter, the area located upstream of the multi-phase pump 1 will be referred to as the low-pressure side and the downstream area as the high-pressure side.

At the inlet 10 of the multi-phase pump 1, a first pressure sensor 11 is provided, with which the pressure is measurable, with which the fluid flows into the multi-phase pump 1. At the outlet 20 of the multiphase pump, a second pressure sensor 12 is provided, with which the pressure is measurable, with which the fluid leaves the multi-phase pump 1. The current value of the pressure difference generated by the multi-phase pump 1 can thus be determined from the difference signal of the two pressure sensors 11, 12. As pressure sensors 11,12 all known pressure sensors are suitable. Preferably, the pressure sensors 11, 12 are respectively arranged directly at the inlet 10 and at the outlet 20 of the multi-phase pump 1.

The multi-phase pump 1 is driven by a variable frequency drive 2 (variable frequency drive VFD or variable speed drive VSD), which rotates the shaft of the multi-phase pump 1 with the angeordenten impeller or the impellers arranged thereon (not shown). The variable frequency drive 2 is signal-connected to a control device 3 for the control of the multi-phase pump, as the double arrow A in Fig. 1 indicates and can exchange data bidirectionally with the control device 3. The control device 3 is preferably designed as a digital control device 3.

The two pressure sensors 11 and 12 are each signal-connected to the control device 3, as the two arrows B and C in Fig. 1 suggest.

Furthermore, a surge limit control unit 4 is provided for avoiding unstable operating states of the multi-phase pump 1, which is preferably integrated into the control device 3. For the surge limit control unit 4, the terms "underflow fuse" or "surge control" are also commonly used.

The inlet 10 of the multi-phase pump 1 is connected to the low-pressure side via a supply line 5 with the borehole 100, through which the fluid from the borehole 100 to the inlet 10 can flow. The outlet 20 of the multi-phase pump 1 is connected on the high pressure side via an outlet line 6 to the storage and processing device 200, through which the Fluid from the multi-phase pump 1 to the storage and processing device 200 can flow. Depending on where the multi-phase pump 1 is arranged in the respective case, the supply line 5 and the outlet line 6 can each be from less than one meter to many kilometers long.

In the supply line 5, a buffer tank 7 is preferably provided, which serves in a conventional manner to compensate for variations in the phase distribution of the fluid. These variations can be caused by naturally induced variations in the gas-to-liquid ratio of the fluid exiting the borehole, or by the architecture and ducting dynamics of the supply line 5. The buffer tank 7 acts as a filter or integrator and can thus accommodate sudden changes in the flow Absorb or damp phase distribution of the fluid.

Further, a return line 8 for the fluid is provided which connects the high-pressure side to the low-pressure side. The return line 8 branches off the outlet line 6 downstream of the outlet 20 of the multiphase pump 1 and flows into the supply line 5 upstream of the buffer tank 7, so that the fluid can be returned through the return line 8 from the high pressure side to the low pressure side. In the return line 8 at least one control valve 9 is provided which is signal-connected to the surge limit control unit 4, as indicated by the arrow D in FIG Fig. 1 suggests. The control valve 9 is designed as a control valve, with which the flow cross-section of the return line 8 from the completely closed state (no return of fluid) can be changed to the fully open state (maximum flow area open). The return line 8 is used for the surge limit control and thus the avoidance of unstable operating states of the multi-phase pump 1, which are also referred to as surging.

If the flow through the multi-phase pump 1 is large enough, the control valve 9 is completely closed, so that no fluid can flow back through the return line 8 to the low pressure side. If, as will be described further on, the surge limit control unit 4 detects the exceeding of a limit curve for a control parameter, For example, caused by too little fluid getting to the inlet 10 (underflow region), the surge limit control unit 4 controls the check valve 9 to partially or fully open the return passage 8, thus part of the conveyed fluid from the high pressure side can flow back to the low pressure side. The control valve 9 is opened so far until the current value of the control parameter is again below the limit curve.

Preferably, the control valve 9 is designed so that it can change the open flow cross-section of the return line 8 steplessly from the fully closed state to the fully open state. Of course, it is also possible to provide more than one, for example two, control valves in the return line 8, which are then arranged in parallel in the return line 8. Alternatively, in the return line 8 and two valves one behind the other, ie in series, be arranged, in which case preferably one of the two valves is a fast open / close valve and the other valve is a control valve which is designed as a control valve.

Furthermore, a cooling 13, for example a heat exchanger, may be provided in the return line 8 in order to remove heat from the recirculated fluid. This measure is particularly advantageous if the fluid has a high gas content. By cooling 13 can then prevent accumulation of heat.

As already mentioned, the surge limit control unit 4 uses the current value of a control parameter to avoid unstable operating states of the multi-phase pump 1 or the pump 1. According to the invention, this control parameter is an operating parameter. As already explained, the term "operating parameters" means those parameters which determine the operation of the pump 1 and which can be adjusted by the control device 4 of the pump 1, that is, for example, the speed of the multiphase pump 1, its power consumption, the torque with the Multiphase pump 1 is driven, etc. Operating parameters are therefore such variables that the operation of the pump 1 and the multi-phase pump. 1 regulate and directly -oder indirectly via another Betriebsparameter- on the pump 1 and the multi-phase pump 1 are adjustable.

The use of an operating parameter as a control parameter has the particular advantage that those process variables that are not or only very expensive or only very inaccurate determinable, such as the current phase distribution of the fluid, no longer need to be known for the surge limit control. In the case of an embodiment of the pump as a single-phase pump, for example, it is no longer necessary to know the current flow, so that it is possible to dispense with flow meters.

In the embodiment described here, the relationship between the operating parameter and the pressure difference generated by the multi-phase pump 1 is used for the surge limit control. During operation of the multi-phase pump 1, this pressure difference is metrologically very easy and very accurately determined by means of the two pressure sensors 11 and 12.

For a better understanding shows Fig. 2 a typical operating diagram of the multi-phase pump 1, in which the relationship of the generated by the multi-phase pump 1 pressure difference with the flow rate of the funded by the multi-phase pump 1 fluid is shown. The flow rate Q is plotted on the horizontal axis and the pressure difference DP on the vertical axis. In a multiphase fluid of course, this relationship is very much dependent on the phase distribution of the pumped fluid. This phase distribution of a fluid with a liquid and a gaseous phase is usually characterized by the GVF value (GVF: gas volume fraction), which indicates the ratio of the volume flow of the gas phase and the volume flow of the fluid. The GVF value is therefore between 0 and 1 or between 0 and 100%, where the value 0 means that there is only one liquid phase and the value 1 or 100% that only one gaseous phase is present.

Fig. 2 shows the pressure difference DP as a function of the flow rate Q for five different GVF values. The GVF value is constant on the iso-GVF curves denoted by 101 and shown in solid lines. there the lowest or most left Iso-GVF curve 101 corresponds to the highest GVF value. The higher, or as shown, the further to the right is the iso-GVF curve 101, the smaller the associated GVF value becomes. Additionally are in Fig. 2 Iso power curves 102 are also shown in dot-dashed lines, on each of which the power consumed by the multi-phase pump 1 is constant.

Furthermore, in Fig. 2 a lower surge boundary line 50 (shown with a solid line), which is commonly referred to as a surge line. If this lower surge boundary line 50 is exceeded, so that the multiphase pump 1 reaches above the lower surge boundary line 50 in the region designated by 40, then the multiphase pump 1 is in an unstable operating state. Based on Fig. 2 It is easy to see how changes in the current phase distribution of the fluid can very suddenly lead to the exceeding of the lower pump limit line 50 and thus to unstable operating states. For example, a change in the current phase distribution corresponds to a jump from one Iso-GVF curve 101 to another.

In order to reliably avoid such unstable operating states in the region 40 during the operation of the multiphase pump 1, a limit curve 60 is defined for the operating parameter used as the control parameter, which boundary curve extends at a distance from the lower surge boundary line 50, as shown in FIG Fig. 2 below the lower surge boundary line 50. The limit curve 60 is in Fig. 2 shown in dashed lines.

Now, during operation of the multi-phase pump 1, when the operating parameter used as the control parameter reaches the limit curve 60, the surge limit control unit 4 controls the control valve 9 to increase the flow through the return line 8 until the current value of the control parameter is used Operating parameters of the limit curve 60 and 40 of the unstable operating conditions away.

For this it is of course necessary that one for the operating parameters used concretely in the surge limit control unit Limit curve or a lower surge boundary line knows and their course depending on a variable that can be easily and reliably measured or determined during operation of the multi-phase pump 1.

It has proven to be particularly advantageous if the dependence of the operating parameter on the pressure difference, which is currently generated by the multi-phase pump 1, is determined. The limit curve or the lower surge limit line then indicates a clear relationship between the operating parameter and the pressure difference.

In principle, all operating parameters are suitable for the surge limit control. However, it has proven to be advantageous if the operating parameter is in a clear relationship with the torque with which the multi-phase pump 1 is driven. Particularly preferably, the operating torque used is the torque with which the multi-phase pump 1 is driven.

The torque is an operating parameter that is constantly available during operation, thus enabling a very high refresh rate. The current value of the torque absorbed by the multi-phase pump 1 can be made available by the variable frequency drive 2 at any time.

The pressure difference DP can be measured in a very simple and reliable manner by means of the two pressure sensors 11, 12, which transmit the pressure values measured by them via the signal connections B and C to the surge limit control unit 4, which determines therefrom the current value of the pressure difference DP.

To determine a limit curve 60 '(see Fig. 3 ) or a lower surge boundary line 50 'for the torque absorbed by the multi-phase pump 1, preferably experimental data are used which are determined, for example, before the multi-phase pump 1 is put into operation on a test stand.

Fig. 3 shows a representation of the limit curve 60 'and the lower surge boundary line 50' in an order of the torque against the pressure difference. The horizontal axis represents the pressure difference DP and the vertical axis the torque T picked up by the multiphase pump. The diamonds labeled 105 represent experimentally determined test data in which the multiphase pump operates in an unstable operating state. In order to determine this test data 105, the multiphase pump 1 is deliberately brought to an unstable operating state on a test stand, for example by varying the flow and / or by varying the phase distribution of the fluid. The latter is of course possible in a test stand. In each case, it is determined at which values of the torque T and at which values of the pressure difference DP the multiphase pump 1 enters an unstable operating state. These unstable operating conditions can be detected very easily, for example by the occurrence of strong vibrations, by a sudden drop in the delivery pressure at the outlet 20 of the multi-phase pump 1 or by other changes. In this way, the test data 105 can be determined.

Subsequently, the lower surge boundary line 50 'is then set so that - as shown in FIG Fig. 3 - All test data 105 just below the lower surge boundary line 50 'lie. In the Fig. 3 Dashed line shown limit curve 60 'is then set with a safety distance above and preferably parallel to the lower surge boundary line 50'. A suitable distance for the application between the lower surge boundary line 50 'and the limit curve 60' is not a problem for the expert. For the operation of the multi-phase pump 1, it is now certain that the multi-phase pump 1 is not in an unstable operating state, as long as they are presented ( Fig. 3 ) is operated above the limit curve 60 '.

Alternatively or additionally, it is also possible to use empirical values for determining the limit curve 60 'which have already been determined, for example by means of other pumps, or are known in another way. Also, calculated operating data or by simulations obtained data alternatively or in addition to the determination of the lower surge boundary line 50 'and the limit curve 60' are used.

For normal operation, the limit curve 60 'is now kept in the surge limit control unit 4. This can be realized, for example, by storing the limit curve 60 'as a look-up table or as an analytically parameterized function in the surge limit control unit 4. If the determined relationship between the operating parameter, in this case the torque T, and the pressure difference DP is particularly simple, for example linear, then a corresponding function, for example a straight line equation, can be stored in the surge limit control unit 4. During operation of the multiphase pump 1, the surge limit control unit 4 uses the signals from the pressure sensors 11, 12 to determine the respectively current value of the pressure difference DP, which is currently being generated by the multiphase pump 1. With the current value for the torque T provided by the variable frequency drive 2, the surge limit control unit 4 can now determine, by comparison with the limit curve 60 ', whether the current value of the torque T is still removed from the limit curve 60'. As soon as the current value of the torque T for the current pressure difference DP reaches the limit curve 60 ', the surge limit control unit 4 activates the check valve 9 in the return line 8, thereby opening or further opening the return line 8. The return line 8 is opened further until the torque T is again removed from the limit curve 60 'and the lower surge boundary line 50'.

This ensures that the multiphase pump 1 does not get into an unstable operating state during normal operation. Particularly advantageous here are the very high update rates with which the pressure difference DP and the current value of the operating parameter, here the torque T, can be determined.

It has been found that the determination of the limit curve based on a correlation of the torque T received by the multiphase pump 1 with the pressure difference DP generated by the multiphase pump 1 leads to a unique relationship for the respective hydraulic configuration, which is otherwise independent of the current Operating conditions of this multi-phase pump 1, such as the current phase distribution in the multi-phase fluid is.

Although the invention is described with reference to the embodiment of a multi-phase pump 1, it is understood that the invention is not limited to multiphase pumps, but in a similar manner also includes single-phase pumps and pumps in general. In this case, the pump can be configured in each case as a single-stage or multi-stage pump. Preferably, the pump is configured as a centrifugal pump or as a helicoaxial pump.

Claims (15)

Operating method for a pump, in particular for a multiphase pump, for conveying a fluid from a low pressure side to a high pressure side, wherein a return line (8) for returning the fluid from the high pressure side to the low pressure side is provided, in which method by means of a surge limit control unit (4) Avoiding an unstable operating state, a control valve (9) is controlled in the return line (8), which controls the flow through the return line (8), wherein a limit curve (60, 60 ') is provided for a control parameter in the surge limit control unit (4), a current value of the control parameter during operation of the pump is compared with the limit curve (60, 60 ') and, as soon as the current value of the control parameter reaches the limit curve (60, 60'), the control valve (9) in the return line (8 ) is controlled such that the current value of the control parameter of the Gren Zkurve (60, 60 ') away, characterized in that an operating parameter of the pump (1) is used as a control parameter. Method according to Claim 1, in which the limit curve (60, 60 ') indicates a clear relationship between the operating parameter and the pressure difference (DP) generated by the pump, in particular the multiphase pump (1). Method according to one of the preceding claims, in which the pressure difference between the pressure at an inlet (10) and the pressure at an outlet (20) of the pump (1) for comparing the current value of the operating parameter with the limit curve (60, 60 ') metrologically recorded. A method according to any one of the preceding claims, wherein the operating parameter is uniquely related to the torque with which the pump is driven. Method according to one of the preceding claims, wherein the operating parameter used is the torque (T) with which the pump is driven. The method of claim 5, wherein the limit curve (60 ') indicates the dependence of the torque (T) on the pressure difference (DT) at which the pump is still safely operated in a stable operating condition. Method according to one of the preceding claims, in which the limit curve (60, 60 ') is set at a distance from a lower surge boundary line (50, 50'), the lower surge boundary line (50, 50 ') indicating the respective value of the operating parameter, in which the pump (1) goes into an unstable operating state. Method according to Claim 7, in which the lower pumping limit line (50, 50 ') is determined with the aid of experimental test data (105), for the determination of which the pump (1) is guided into an unstable operating state. Method according to Claim 7 or 8, in which empirical values are used to determine the lower surge boundary line (50, 50 '). Method according to one of the preceding claims, in which the surge limit control unit (4) is integrated in a control device (3) for controlling the pump (1). Method according to one of the preceding claims, in which the current value of the operating parameter is provided by a variable frequency drive (2) for the pump (1). Method according to one of the preceding claims, wherein the pump (1) is used as a booster pump in the oil and gas production, in particular in the undersea oil and gas production. A pump, in particular a multi-phase pump, for conveying a fluid from a low-pressure side to a high-pressure side, with an inlet (10) and an outlet (20) for the fluid, and with a surge limit control unit (4) for preventing an unstable operating state, which a drive signal for a Control valve (9) in a return line (8) for returning the fluid from the high pressure side to the low pressure side, wherein in the surge limit control unit (4) a limit curve (60, 60 ') for a control parameter is present, the surge limit control unit (4) comparing the current value of the control parameter with the limit curve (60, 60 ') during operation of the pump, and with the surge limit control unit (4) providing the drive signal as soon as the current value of the control parameter reaches the limit curve (60, 60'); which the control valve (9) in the return line (8) can control such that the current value of the Kon trollparameters from the limit curve (60, 60 '), characterized in that the control parameter is an operating parameter of the pump. A pump according to claim 13, wherein the operating parameter is the torque (T) for driving the pump (1) and the limit curve (60 ') is the dependence of the torque (T) on the pressure difference (DP) between the pressure at the inlet (10). and the pressure at the outlet (20). Pump according to one of claims 13 or 14, configured as a centrifugal pump and as a booster pump for the oil and gas production, in particular for the undersea oil and gas production.

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