WO2022042918A1

WO2022042918A1 - Method and arrangement for throughflow measurement

Info

Publication number: WO2022042918A1
Application number: PCT/EP2021/068802
Authority: WO
Inventors: Ralf Huck
Original assignee: Siemens Aktiengesellschaft
Priority date: 2020-08-28
Filing date: 2021-07-07
Publication date: 2022-03-03
Also published as: DE102020210922A1

Abstract

The throughflow (V') of a fluid (2) conveyed through a technical system (1) by means of a pump (3) is ascertained from the pressures (P1, P1) measured upstream and downstream of a valve (6) and from the valve setting (h). In order to allow simple and inexpensive throughflow measurement and system monitoring even under different system conditions, in the system (1) with the installed valve (6), before the operation thereof, the dependency relationship of the throughflow (V'), the inlet pressure (P1), the outlet pressure (P2) and the valve setting (h) is ascertained using a throughflow meter (16) and is stored in a characteristic map (15). During the operation of the system (1), the throughflow (V') is ascertained directly from the characteristic map (15) on the basis of the inlet pressure (P1), the outlet pressure (P2) and the valve setting (h).

Description

description

Process and arrangement for flow measurement

Invention relates to an arrangement for measuring the flow of a fluid conveyed by a pump through a technical system and for monitoring the system during its operation, with a valve installed in a fluid line of the system for throttling the flow, with a valve actuating and the Actuator that detects the valve position, with a first pressure sensor that measures the inlet pressure of the fluid upstream of the valve and a second pressure sensor that measures the outlet pressure downstream of the valve, and with an evaluation device that is designed to calculate the flow from the pressures measured upstream and downstream of the valve and the valve position to determine .

Valves are used in process engineering systems to measure physical variables such as e.g. B. To regulate temperature, level, process pressure, with or in dependence on fluid flows. The control is carried out by a higher-level controller, which records the corresponding measured variable via a separate sensor and specifies a target value for the valve position according to the control task. The valve position is in turn controlled by a pneumatic or electric actuator with a positioner.

Pumps are also used in process engineering systems to convey media (fluids). Pumps, pipelines and valves form a hydraulic/pneumatic system. The sum of the pressure drops in the line network and across the valves is compensated for by the pump pressure. In the simplest case, the pumps are not controlled. The pressure provided is therefore not constant and decreases with increasing flow (e.g. centrifugal pump).

The most common control task is to regulate the process temperature, whereby a heating/cooling medium is replaced by a heat exchanger is passed, which affects the temperature of a process medium. The heating/cooling medium is brought to a specific flow temperature in a separate unit. The regulation takes place by changing the volume flow of the heating/cooling medium supplied to the heat exchanger.

In the simplest embodiment, only the process temperature is recorded and regulated by influencing the valve position of a valve in the heating/cooling circuit. However, it would often be interesting to also know the volume flow in the circuit, for example to determine the power supplied to the heat exchanger.

Another control task is to keep the process pressure or fill level constant using a valve. Again, it would be helpful to determine the amount of process fluid being added to the system through the valve .

If the flow through a valve is already known, it would also be interesting to recognize changes in the pipe network, at the valve or in the pump output supplied.

The desired information can be obtained by using additional sensors such as flow meters to measure and monitor fluid flows, temperature sensors to measure the flow and return temperature of heat exchangers, sensors to measure corrosion in pipes, pressure and speed sensors to measure pump pressure and speed, etc. be won . Since such additional sensors are expensive and space-consuming, they are often not used in real systems.

From JP 2010-107419 A, JP 2015-166720 A and

US 2017/0090485 A1 it is known to record the difference AP between the inlet pressure PI of a fluid in front of a valve and the outlet pressure P2 behind the valve and the valve position, using the recorded values from a table of flow coefficients a flow coefficient (Kv value , flow factor ) Cv to read and the flow Q of the fluid according to the formula

Q = A • Cv • (AP ) ^1/2 where A is a constant. In order to increase the accuracy of the flow measurement, different flow coefficient tables for normal, low and high value ranges of the pressure difference AP can be provided, and correction values can be determined using other tables to take into account the viscosity of the fluid or torsion of the valve drive.

It is also known from US 2013/0240045 A1 to detect the difference AP between the inlet pressure PI of a fluid in front of a valve and the outlet pressure P2 behind the valve, as well as the valve position and the flow rate Q of the fluid according to the formula

Q = Fi • Cv • (AP) ^1/2 to be calculated. F± is an instantaneous valve characteristic, which is calculated from the instantaneous valve position (valve opening) using a flow characteristic curve equation of the valve and a rangeability. The flow coefficient Cv, the flow characteristic equation and the turndown ratio are design dependent parameters provided by the manufacturer of the valve, where the flow characteristic equation gives the flow relative to the nominal flow as a function of the valve opening relative to the maximum valve opening and the turndown ratio corresponds to the quotient of the maximum and minimum flow rate for which the valve characteristic is valid.

The known methods and arrangements are based on the assumption that the flow can be calculated using simple formulas or tables via the flow coefficient (Kv value), but this only applies under very specific conditions. The Kv value used in each case is very imprecise because it only serves to roughly characterize the valve under specified conditions; under real conditions the Kv value itself is inversely proportional to (AP ) ^1/2 . Standard conditions are sufficient in real hydraulic systems, e.g. B. , a sequence of pump, pipe, valve, pipe and heat exchanger, since the pressure drop across the valve affects the flow. The flow in turn affects the pump pressure of an uncontrolled pump as well as the pressure drop in the piping before and after the valve. In contrast, with the known methods and arrangements, the hydraulic conditions in the system in which the valve is installed are not taken into account, so that the smallest deviations in the hydraulic system can no longer be measured precisely. Finally, the known methods for measuring pressure are largely based on information (tables, Kv value, valve characteristic curve equation, etc.) from the valve manufacturer and are therefore valve-specific and not universally applicable to different valves.

The invention is based on the object of enabling simple and cost-effective flow measurement and system monitoring for systems in which fluids are conveyed by means of pumps, even in the case of different system states.

According to the invention, the object is achieved by the method specified in claim 1 or the arrangement defined in claim 6, advantageous developments of which are specified in the dependent claims.

The subject matter of the invention is therefore a method for measuring the flow of a fluid conveyed by a pump through a technical system and for monitoring the system during its operation, with the valve position of a valve installed in a fluid line of the system being recorded and the inlet pressure of the fluid upstream of the valve and the outlet pressure behind the valve can be measured and the flow rate is determined from the pressures measured in front of and behind the valve and the valve position, characterized in that in the system with the built-in valve before its operation using a flow meter, the dependency relationship of the flow, the inlet pressure, the outlet pressure and the valve position is determined and in a Map is stored, and that during operation of the system, the flow rate is determined directly from the map using the inlet pressure, the outlet pressure and the valve position.

The invention also relates to an arrangement for measuring the flow of a fluid conveyed through a technical system by means of a pump and for monitoring the system during its operation, with a valve installed in a fluid line of the system for throttling the flow, with a valve that actuates and actuator that detects the valve position, with a first pressure sensor that measures the inlet pressure of the fluid upstream of the valve and a second pressure sensor that measures the outlet pressure downstream of the valve, and with an evaluation device that is designed to calculate the flow from the pressures measured upstream and downstream of the valve and the To determine the valve position, characterized in that the evaluation device contains a memory map in which a dependency relationship of the flow, the inlet pressure, the outlet determined in the system with the built-in valve before its operation using a flow meter ufdrucks and the valve position is stored, and that the evaluation device is designed to determine the flow rate using the inlet pressure, the outlet pressure and the valve position directly from the map during operation of the system.

In the initial state of the system, the valve is moved in a learning phase with the pump running by means of the actuator, for example as part of partial or full stroke tests, over a partial stroke or its entire stroke, with the inlet pressure and outlet pressure before or after . behind the valve and the valve position can be measured. At the same time, using a flow meter measured the flow (volume flow) . The measured values obtained represent a dependency relationship of the flow, the inlet pressure, the outlet pressure and the valve position, which is stored in a memory as a multidimensional characteristic map. If a flow meter is already installed in the fluid line before or after the valve and is therefore part of the hydraulic/pneumatic system, it can be used to measure the flow during the training phase. Otherwise a clamp-on flow meter is preferably used so as not to affect the pneumatic/hydraulic system.

If the pump can provide different pressures with the same flow rate, e.g. B. is the case with regulated pumps, the map is recorded at each of these pressures.

If a significant reduction in cross-section due to corrosion or deposits (fouling) is to be expected during later regular operation of the system, this can be simulated during the learning phase by means of a throttle that can be switched on upstream and/or downstream of the valve, so that the resulting values can also be entered into the Map can be taken on.

The map obtained contains the following mapping rule:

V = V(h, Pl, P2), where V is the flow rate, h is the valve position, PI is the inlet pressure, and P2 is the outlet pressure.

If different media densities are to be expected in the system, this information can also be trained, whereby in this case the temperature can also be measured. The latter applies in particular when the fluid being pumped is a gas or gas mixture is . The dependency stored in the map ness relationship is then increased by the density p or Temperature T extended :

V = V (h, Pl , P2 , p, T ) .

The map can also consist of sub-maps z. B. be taken on with differently throttled fluid lines or pumps. In normal operation of the system, the flow can then be determined by interpolation between those sub-characteristics whose measured values from the learning phase correspond to the current measured values of the inlet pressure PI, the outlet pressure P2, the valve position h and, if necessary. closest to the density p of the fluid and the temperature T. The characteristic field can advantageously also be described by a neural network.

New operating states can be learned when the system is commissioned or over the course of its life cycle.

After the training phase, the clamp-on flow meter used for this purpose can be removed so that during regular operation of the system, the flow can be determined directly from the map using the measured inlet pressure, the measured outlet pressure and the measured valve position and without further calculation. Without further calculation, this means that no equations are used in connection with design-dependent parameters which, as already explained above, are inaccurate on the one hand and for which valve-specific information from the manufacturer is required on the other. However, it is not excluded and may even be necessary for the flow rate to be calculated by interpolation from the stored supporting values of the map learned.

In order to be able to assess the reliability of the flow rate determined from the map, the values measured during the learning phase for the flow rate, the inlet pressure, the outlet pressure, the valve position and, if necessary, the density and / or temperature of the fluid are stored. In addition to the pure determination of the volume flow, error states occurring in the system can be recognized by changes in the learned state of the system, e.g. B. Reduced pump performance, changed pipe cross-sections (fouling, corrosion), defective valve bodies. If the focus is not on replacing a flow meter, but rather on more detailed monitoring of the system (pump performance, fouling, corrosion), permanent, direct measurement of the flow can be provided by a permanently installed flow meter or a clamp-on flow meter. With this additional measured variable, changed pressure conditions in the system, which can have the same cause if the flow rate is unknown, can now be easily distinguished from one another.

The invention is explained below using exemplary embodiments and with reference to the figures of the drawing; show in detail

Fig. 1 shows an example of an arrangement for flow measurement in a system based on a dependency relationship of the flow, the inlet pressure and the outlet pressure before or behind a valve and the valve position and

Fig. 2 an example of the characteristics map in the form of a neural network.

The same reference symbols have the same meaning in the different figures. The illustrations are purely schematic and do not represent any proportions.

Fig. 1 shows part of a technical installation 1 in which a fluid 2 is conveyed through a heat exchanger 4 by means of a pump 3 . A valve 6 is installed in a fluid line 5 between the pump 3 and the heat exchanger 4, with which the flow (volume flow) of the fluid 2 is throttled can . For this purpose, the valve 6 is actuated by an actuator 7 which, by means of a position sensor 8, detects the valve position (valve stroke) h and thus the valve opening. In the example shown, the actuator 7 comprises a pneumatic membrane drive 9 with an electropneumatic position controller 10, the detected valve position h with one of, e.g. B. , a higher-level controller of the system automation, not shown here, compares the target value h* generated and controls the pneumatic membrane drive 9 in terms of regulating the control difference.

A first pressure sensor 11 measures the inlet pressure PI of the fluid 2 in front of the valve 6 and a second pressure sensor 12 measures the outlet pressure P2 behind the valve 6 . Both pressure sensors 11 , 12 are preferably connected to pressure measuring sockets integrated in the valve housing, so that, apart from two pressure sensors, no expensive flow measuring devices are required that would have to be built into or attached to the fluid line 5 .

The measured values of the inlet pressure PI, the outlet pressure P2 and the valve position h are supplied to an evaluation device 13, which contains a characteristic diagram 15 in a memory 14, in which a dependency relationship V=V(h, Pl, P2) of the flow V of the fluid 2, of the inlet pressure PI, the outlet pressure P2 and the valve position h is stored and which, during operation of the system 1, determines an estimated value V for the flow rate using the measured values of the inlet pressure PI, the outlet pressure P2 and the valve position h directly from the characteristics map 15.

In order to create the map 15, the valve 6 is actuated by the actuator 7 in the initial state of the system 1 in a learning phase with the pump 3 running, the inlet pressure PI and outlet pressure P2 and the valve position h being measured. This happens with different pump capacities and/or different throttling of the sections of the fluid line 5 located in front of and behind the valve 6. The latter can be achieved by temporarily inserting chokes or Actuation of already existing throttles in the fluid line 5 happen. The flow rate V of the fluid 2 is measured by means of a flow meter 16 together with the inlet pressure PI, the outlet pressure P2 and the valve position h. If a flow meter is already installed in the fluid line 5 and is therefore part of the part of the technical system 1 under consideration, it can be used for the flow measurement in the training phase. Otherwise, a clamp-on flow meter can be used for the learning phase so as not to affect the pneumatic/hydraulic system. The measured values obtained represent the dependency relationship of the flow rate V, the inlet pressure PI, the outlet pressure P2 and the valve position h, which is learned for different simulated system states and stored in the memory 14 in the form of the multidimensional characteristic map 15 . The dependency relationship contained in the characteristics map 15 can, if necessary. to be extended by the density p of the fluid 2 and/or the temperature T:

V=V(h, P1, P2, T, p), the temperature T preferably being detected directly at the valve 6 by means of a temperature sensor 17.

As Fig . 1 is indicated, the map 15 can consist of several sub-maps, the z. B. are recorded at different throttling stages of the fluid line 5 or pump 3, in which case the estimated value V is then determined during normal operation of the system 1. the density p of the fluid 2 and the temperature T come closest.

The evaluation device 13 or their function or part functions can z. B. can also be implemented in the position controller 10 , in a cloud 18 or in some other remote location. In the training phase the measured values of the flow rate V, the inlet pressure PI , the outlet pressure P2 and if necessary . the density p of the fluid 2 and the temperature T by means of a radio interface 19 wirelessly via a mobile communication device (e.g. smartphone) 20 to the cloud 18 or by means of a gateway directly to the cloud 18 in order to create the characteristic map 15 there. In operation of the system 1 z. B. the current measured values of the inlet pressure PI, the outlet pressure P2 and the valve position h are queried using the communication terminal 20 and the estimated value V of the flow rate is determined using the characteristics map 15 in the cloud 18 and displayed to the user.

Fig. 2 shows an example of the characteristics map 15 in the form of a neural network 21 that contains the measured inlet pressure PI, outlet pressure P2 and the valve position h and, if applicable. the density p of the fluid 2 and/or the temperature T (not shown here) as input variables and generates an estimated value V of the flow as an output variable.

The neural network 21 shown is a feed-forward regression network that has an input layer with one input element 22 for each of the input variables P1, P2, h (and possibly p and/or T). The input layer has two hidden layers, each consisting of a plurality of neurons 23 and 24 subordinate. The input variables P1, P2, h are provided with individual weighting factors w±j in each neuron 23 of the first hidden layer and summed up to form a response from the relevant neuron 23. The responses of the neurons 23 of the first hidden layer are provided with individual weighting factors Wjk in each neuron 24 of the second hidden layer and summed up to form a response of the relevant neuron 24 . An output element 25 is arranged downstream of the second hidden layer, which adds up the responses of the neurons 24 in each case with an individual weighting factor Wk to form the estimated value V for the flow. In order to train the neural network 21 in the learning phase and to reproduce the To learn the relationship between the inlet pressure PI , outlet pressure P2 , the valve position h and the flow rate V, the weighting factors w = w±j , Wjk, Wk of the neural network 21 are used with the help of adaptation algorithms 26 in the sense of reducing the error AV = V - V between the estimated values V supplied by the neural network 21 and the measured values V of the flow rate V obtained from the flowmeter 16 . For the sake of simplicity, the individual amounts of change for the weighting factors w are denoted here as Aw.

Claims

patent claims

1. A method for measuring the flow rate (V) of a fluid (2) conveyed by a pump (3) through a technical system (1) and for monitoring the system (1) during its operation, the valve position (h) being one in one Fluid line (5) of the system (1) built-in valve (6) is recorded and the inlet pressure (PI) of the fluid upstream of the valve (6) and the outlet pressure (P2) downstream of the valve (6) are measured and the flow (V ) out the pressures (PI, PI) measured upstream and downstream of the valve (6) and the valve position (h), characterized in that in the system (1) with the built-in valve (6) before its operation using a flow meter ( 16) the dependency relationship of the flow (V), the inlet pressure (PI), the outlet pressure (P2) and the valve position (h) is determined and stored in a map (15), and that during operation of the system (1) the flow (V ) based on the inlet pressure (PI) , the outlet pressure (P2) and the Ve Position (h) is determined directly from the map (15).

2. The method according to claim 1, characterized in that the characteristic map (15) is determined at different pump capacities and/or differently throttled fluid line (5).

3. The method according to claim 1 or 2, characterized in that the temperature (T) of the fluid (2) is additionally measured and the dependency relationship determined and stored in the characteristic map (15) is expanded by the temperature (T).

4. The method according to any one of the preceding claims, characterized in that the determined and in the characteristic map (15) stored dependency relationship is expanded by the density (p) of the fluid (2).

5. The method according to any one of the preceding claims, characterized in that the characteristic map (15) is described by a neural network (21).

6. Arrangement for measuring the flow (V) of a means of a pump (3) through a technical system (1) funded fluid (2) and for monitoring the system (1) during its operation, with a in a fluid line (5) of System (1) built-in valve (6) for throttling the flow (V), with an actuator (7) actuating the valve (6) and detecting the valve position (h), with an inlet pressure (PI) of the fluid (2). the valve (6) measuring the first pressure sensor (11) and the outlet pressure (P2) downstream of the valve (6) measuring the second pressure sensor (12) and with an evaluation device (13) which is designed to calculate the flow (V ) from the to determine the pressures (Pl, P2) measured in front of and behind the valve (6) and the valve position (h), characterized in that the evaluation device (13) contains a characteristic map (15) in a memory (14) in which an in the plant (1) with the built-in valve (6) before its operation using a flow The dependency relationship of the flow rate (V), the inlet pressure (PI), the outlet pressure (P2) and the valve position (h) determined by the ss meter (16) is stored, and that the evaluation device (13) is designed to, during operation of the system (1 ) the flow rate (V ) based on the inlet pressure (PI) , des

Outlet pressure (P2) and the valve position (h) can be determined directly from the map (15).