Method for measuring pump flow

Abstract

A method for estimating an output flow provided by a pump (1) in a system comprising said pump, an upstream conduit (2) and a downstream conduit (3), said output flow being calculated by using pressure information from a first downstream pressure sensor (12) and a second downstream pressure sensor (14), a first downstream pressure sensor (12) is placed on the downstream conduit (3) at a first distance (d1) from the pump (1) and a second downstream pressure sensor (14) is placed on the downstream conduit (3) at a second distance (d1 + d2) from the pump (1).

Description

Technical Field

[0001] The invention relates to the field of pump systems, in which a pump, in particular a centrifugal pump, pumps a fluid from an upstream conduit to a downstream conduit. Background Art

[0002] Pump systems are used in a variety of hydraulic applications. Such systems convey different kinds of fluids with different properties and densities, for example from clean water to wastewater applications. During operation, the different mechanical parts that make up the pump (such as impellers, blades, wear rings, diffusers) are subject to wear, which varies depending on the cause of wear (such as cavitation, corrosion, abrasion, abnormal use, etc.). The degradation of these components generates internal losses and reduces the performance of the centrifugal pump. The losses can be quantified in terms of flow loss and the total dynamic head loss of the pump.

[0003] In some cases, there is a pressure sensor located at the pump output and a flow meter is not used because flow meters are much more expensive than pressure sensors. Without a flow sensor, it is difficult to monitor system operation and drift in pump characteristics without flow information.

[0004] However, estimation of the flow rate downstream of the pump can be done by using a pump curve provided by the pump manufacturer and measured or estimated power, i.e. a power versus flow curve, which allows the flow rate to be inferred by extrapolating from the configured pump curve at the corresponding pump speed. However, this method is not very accurate.

[0005] Document EP2726827B1 proposes a method for calculating the fluid wave velocity by using a generator to generate a transient fluid wave and two pressures at two positions on a pipeline. This method, which requires the injection of a transient fluid wave and a generator, is not a passive method and cannot be used for any working condition of the pump, transient or steady state, without additional equipment and conditions. Summary of the invention

[0006] The present invention improves this situation and proposes a new passive method of obtaining flow measurement of a pump.

[0007] More specifically, the present invention proposes a method for estimating an output flow rate provided by a pump, the method being performed in a system comprising the pump, an upstream pipeline and a downstream pipeline under any operating condition, transient or steady state, of the pump, by using pressure information from a first downstream pressure sensor and a second downstream pressure sensor, the first downstream pressure sensor being placed on the downstream pipeline at a first distance from the pump, the second downstream pressure sensor being placed on the downstream pipeline at a second distance from the pump, such that a known distance L separates the first and second pressure sensors, the method comprising estimating the output flow rate by an iterative process using the downstream pipeline characteristics, the distance between the first and second sensors, the pressure sensed by the pressure sensors and a flow estimator model E1 defined by the following equation

[0008]

[0009] And the equation:

[0010]

[0011] and

[0012]

[0013] in is the estimated flow rate (m 3 / h), is the estimated pressure difference (bar), ΔP measured is the measured pressure difference (bar), is the estimated friction loss coefficient, L is the length of the pipeline between the first pressure sensor and the second pressure sensor, D is the pipeline diameter, v is the fluid flow rate (m / s), A is the cross-section of the pipeline (m 2 ), ρ is the fluid density (kg / m 3 ), K p is the proportional gain of the flow estimator, Where T iq is the integrator time constant in the flow estimator.

[0014] In the present disclosure, due to the additional downstream pressure sensor at a defined distance from the first downstream pressure sensor, which itself is located away from the pump, by knowing two downstream pressure information and pipeline characteristics for identifying the flow in the defined pipeline section, an estimator model or observer can be used to estimate the flow in the system.

[0015] In the first embodiment, the friction loss coefficient Can be a fixed constant.

[0016] In an improved implementation, the friction loss coefficient It can be calculated based on the friction loss coefficient estimator model E2, which is defined by the following equation:

[0017]

[0018] in is a dimensionless coefficient, K1 is a dimensionless proportional gain, and K2 is in s -1 , where the Reynolds coefficient R of the flow in the downstream pipe is e Greater than or equal to 2300;

[0019]

[0020] The method may also include the friction loss coefficient Calculate, where the Reynolds coefficient R of the flow in the downstream pipe is e When it is less than 2300,

[0021]

[0022] The method may comprise measuring pump speed and power information from a command unit of the pump to compare an estimated output flow rate with a flow rate calculated using a pump curve of the pump to detect wear of the pump.

[0023] The pump may be a centrifugal pump.

[0024] The present disclosure also proposes a computer program comprising instructions for implementing the method according to any of the preceding claims when a processor executes the software.

[0025] The present disclosure also proposes a computer-readable non-transitory recording medium on which a computer program is registered to implement the method when a processor executes such computer program. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Additional features, details and advantages will be seen in the following detailed description and accompanying drawings, in which:

[0027] Figure 1 is a schematic diagram of the pump and piping with a pressure sensor and flow meter;

[0028] Figure 2A and 2B They are the head-flow curve and the power-flow curve from the pump data sheet;

[0029] Figure 3 is a schematic diagram of the pump and piping with an attached downstream pressure sensor;

[0030] Figure 4 is a schematic diagram of the flow estimation process;

[0031] Figure 5 It is a schematic diagram of the friction loss estimation process. DETAILED DESCRIPTION

[0032] In this disclosure, the following symbols are used in the following equations:

[0033]

[0034]

[0035] The unit is kg·2·m -1 ·s -2 .

[0036] The unit is m 3 ·s -1

[0037] K p The unit is m 4 ·s·kg -1

[0038] In this system, A is the cross-section of the pipe and Q is the flow rate through the interior of the pipe.

[0039] Pumping stations usually do not have flow meters giving information on the flow rates coming out of the pumps of the pumping station, since flow meters are generally complex to install, depending on the pumping station, and more expensive than less complex pressure sensors installed on the pipes of such pumping stations. Apart from using a power supply and manufacturer data sheets, there are no known methods in the literature that can provide an accurate value of the flow rate outside the pump without using an external flow sensor. Furthermore, using a power supply and manufacturer data sheets only gives the flow rate inside the pump, which is usually higher due to internal recirculation in the pump.

[0040] Traditionally, flow can be derived from the manufacturer's pump curve at the corresponding pump speed when using an upstream pressure sensor, a downstream pressure sensor to calculate pump head, the pump head-flow characteristics from the pump data sheet, and measured inlet and outlet pressures. This can be expressed mathematically as follows:

[0041] The pump characteristics are determined by the following equation:

[0042] H pump =x 2 ·F(Q pump ,x)

[0043] P pump =x 3 ·G(Q pump ,x)

[0044] Where: H pump is the pump head, Q pump is the pump flow rate, in

[0045] ω is the mechanical speed of the pump (rpm), ω n is the nominal mechanical speed of the pump from the list above (rpm), and F and G are interpolated functions.

[0046] To determine the flow rate of the pump, the functions "F" and "G" need to be inverted.

[0047] When using the pump characteristic "Pump head and flow", such as Figure 2A As shown, the equation is:

[0048] Q pump = x·F -1 (H pump ,x 2 )

[0049] When using Figure 2B When the pump characteristic "Power vs. Flow" is shown, the equation is:

[0050] Q pump = x·G -1 (Pw pump ,x 2 )

[0051] In reality, the pump flow inside the pump is higher than the system flow measured outside the pump due to internal recirculation in the pump:

[0052]

[0053] As the pump ages, the pump characteristics change and no longer provide correct information on the flow rate downstream of the pump.

[0054] The present disclosure proposes a solution to identify the flow rate coming out of a pump which is different from the flow rate inside the pump due to internal recirculation. The present invention includes identifying the pump output flow rate without using a flow sensor, but by using additional pressure sensor information and known pipe characteristics.

[0055] Figure 3 A schematic diagram of an example of the present disclosure is provided that uses two pressure sensors 12, 14 that are placed at well-known distances d2 and d1+d2 on a downstream pipeline and measure a first pressure P1 at a distance d2 from the pump and a second pressure P2 at a distance d1+d2 from the pump to estimate the flow through the pipeline by estimating the pressure loss and comparing it to the pressure difference measured on the pipeline.

[0056] The principle is to use the following E1 estimator model to estimate the flow through the pipe segment between two pressure sensors:

[0057] E1:

[0058]

[0059] And the equation:

[0060]

[0061] and

[0062]

[0063] in is the estimated flow rate (m 3 / h), is the estimated pressure difference (bar), ΔP measured is the measured pressure difference (bar), is the estimated friction loss coefficient, L is the length of the pipeline between the first pressure sensor and the second pressure sensor, D is the pipeline diameter, v is the fluid flow rate (m / s), A is the cross-section of the pipeline (m 2 ), ρ is the fluid density (kg / m 3 ), K p is the proportional gain of the flow estimator, Where T iq is the integrator time constant in the flow estimator, ΔP and The unit is kg.m -1 .s -2 , The unit is m 3 ·s -1 , K p The unit is m 4 ·s·kg -1 , K i The unit is m 4 .kg -1 .

[0064] K p and Based on the identification of system characteristics, the estimator model E1 is configured and programmed in a computerized system having a programmable logic circuit that is programmed to perform iterative calculations based on the estimator to determine the estimated flow rate. processor.

[0065] The principle of the present disclosure is to use the pressure and pipe characteristics at two separate points downstream of the pump to build an observer and estimator model that allows estimating the fluid flow without taking any action or means on the pump, such as transient changes in fluid flow or pressure. The estimated fluid flow is introduced into the ΔP calculation in order to obtain convergence towards the fluid flow, e.g.

[0066] like Figure 4 As shown, to implement the estimator, the first step 100 consists in calculating ΔP as P2-P1 measured , calculate with initial value ΔP estimated Equations (1) and (2) are then calculated with the known pipe characteristic 200 and equation (4) to obtain the new ΔP estimated The calculation is then repeated to obtain the estimated flow of convergence.

[0067] In this model, can be a fixed value, but to provide a more precise estimate, Depends on the Reynolds coefficient R of the flow in the downstream pipe e , and is calculated in another algorithm, such as Figure 5 In this case, the input pipeline characteristic 200 and the R e After the test 210, The calculated value becomes:

[0068] In step 230, if The following second estimator model E2 is used Calculation:

[0069] E2:

[0070]

[0071] in is a dimensionless coefficient, K1 is a dimensionless proportional gain, and K2 is in s -1 ,in:

[0072]

[0073] Otherwise, in step 220, if R e <2300,

[0074]

[0075] In this second estimator, the integrator time constant T iq is chosen to have a larger dynamic range than the physical pump system time constant, and the integration time constant T of the second estimator i is chosen to be less than Tiq , for example T iq / 2.

[0076] Then, the estimated friction loss coefficient is calculated Input to the first estimator E1.

[0077] The following quantities are stored in the memory of the computerized system: T iq : integrator time constant of the flow estimator, Kp: proportional gain of the flow estimator, and the required pipeline characteristics and fluid characteristics; L: pipeline length (m); D: pipe diameter (m); v: fluid flow rate (m / s); ρ: fluid density (kg / m 3 );R e : Reynolds coefficient; μ: dynamic viscosity kg / (ms); nu: pipeline roughness (m).

[0078] The computerized system may be an electronic control unit having a microcontroller with analog-to-digital conversion means and receiving the pressures P1 and P2 as input and comprising a program provided with a data memory of the estimator algorithm and the required constants, or may be such as Figure 3 A part of a command unit 4 is shown, for example a variable speed drive for a pump, such command unit comprising a power controller 41 for the pump motor and a processor system 42 for implementing the drive command software and the above-mentioned process software.

[0079] In this regard, the process may include obtaining pump speed N and power P information from a variable speed drive of the pump to compare the estimated output flow rate to the flow rate calculated using a pump curve of the pump to detect wear of the pump.

[0080] This method is particularly applicable if the pump is a centrifugal pump.

[0081] Industrial Applicability

[0082] The present disclosure avoids the use of flow meters that are more expensive than pressure sensors and more complicated to install on existing stations. The solution will provide information on the flow rate given by the centrifugal pump in the system by using only the information of a dual pressure sensor installed on the upstream and downstream pipelines. The benefits of this solution are huge, as it simplifies the installation and provides pump flow information for different applications, including: control, protection, monitoring, pump wear monitoring and predictive maintenance.

[0083] The invention is not limited to the above description, and the inventive subject matter of the appended claims can be used in a remote survey system or in a local fault detection program.

Claims

1. A method for estimating an output flow rate provided by a pump, the method being performed in any operating condition, transient or steady state, of the pump (1) in a system comprising the pump, an upstream pipeline (2) and a downstream pipeline (3), by using pressure information from a first downstream pressure sensor (12) and a second downstream pressure sensor (14), the first downstream pressure sensor (12) being placed on the downstream pipeline (3) at a first distance (d1) from the pump (1), the second downstream pressure sensor (14) being placed on the downstream pipeline (3) at a second distance (d1+L) from the pump (1), such that a known distance L separates the first pressure sensor (12) and the second pressure sensor (14), the method comprising estimating the output flow rate by an iterative process using downstream pipeline characteristics, the distance between the first sensor and the second sensor, the pressure sensed by the pressure sensors and a flow estimator model E1 defined by the following equation And the equation: and in is the estimated flow rate (m 3 / h), is the estimated pressure difference (bar), ΔP measured is the measured pressure difference (bar), is the estimated friction loss coefficient, L is the length of the pipeline between the first pressure sensor and the second pressure sensor, D is the pipeline diameter, v is the fluid flow rate (m / s), A is the cross-section of the pipeline (m 2 ), ρ is the fluid density (kg / m 3 ), K p is the proportional gain of the flow estimator, Where T iq is the integrator time constant in the flow estimator.

2. The method according to claim 1, wherein the friction loss coefficient is a fixed constant.

3. The method according to claim 1, comprising: Calculation, the friction loss coefficient estimator model E2 is defined by the following equation: in is a dimensionless coefficient, K1 is a dimensionless proportional gain, and K2 is in s -1 ,in, When the Reynolds coefficient R of the flow in the downstream pipe e Greater than or equal to 2300; 4. The method according to claim 1, comprising the friction loss coefficient Calculate the Reynolds coefficient R of the flow in the downstream pipe e When it is less than 2300, 5. A method according to any one of the preceding claims, comprising measuring pump speed (N) and power information (P) from a command unit (4) of the pump to compare an estimated output flow with a flow calculated using a pump curve of the pump, in order to detect wear of the pump.

6. A method according to any one of the preceding claims, wherein the pump is a centrifugal pump.

7. A computer program comprising instructions which, when a processor executes the software, implement the method according to any one of the preceding claims.

8. A computer-readable non-transitory recording medium on which the computer program according to claim 7 is registered, so as to implement the method according to any one of claims 1 to 6 when such computer program is executed by a processor.

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