WO2008028746A1

WO2008028746A1 - Method of and system for monitoring flow velocity

Info

Publication number: WO2008028746A1
Application number: PCT/EP2007/058290
Authority: WO
Inventors: Toni HEIKKILÄ; Lasse Panttila
Original assignee: Sulzer Pumpen Ag
Priority date: 2006-09-04
Filing date: 2007-08-09
Publication date: 2008-03-13

Abstract

A method of and apparatus for monitoring flow velocity in a fluid flow system, the method comprising the steps of injecting multiple RFID-tags at an injecting location, measuring final presence data of the RFID-tags at a final measuring location downstream of said injecting location by a RFID-transceiver, and calculating a flow velocity by using the measured final presence data. The flow system may be a pipeline system and it may comprise a tank, whereby measuring locations may be on the enclosure of, or within, the tank, to enable calculation of the flow velocity profile in the tank. The method and apparatus are especially suitable for monitoring flow velocity of medium consistency process fluid of chemical or mechanical wood processing industry.

Description

METHOD OF AND SYSTEM FOR MONITORING FLOW VELOCITY

BACKGROUND OF THE INVENTION

The present invention relates to a method of and a system for monitoring flow velocity in a fluid flow system. The method and system according to the invention are especially suitable for monitoring flow velocity in pipelines or flow velocity profile in tanks of process fluids, such as medium consistency process fluids of chemical and mechanical wood processing industry, but the invention is, of course, also suitable for use in other corresponding applications.

Different methods are used for monitoring flow velocities in fluid flow systems. Elec- tromagnetic, ultrasonic and optical methods are commonly used for measuring local flow velocities. Their usability, however, depends on the physical properties of the flowing matter, and their results may be distorted by changes in these properties, which may occur, e.g., in process fluids of chemical and mechanical wood processing industry. Moreover, the quality of the velocity indicating signal, obtained by these methods, depends on the fluid velocity, and thus these methods are usable only above a minimum flow velocity. NMR-imaging and, e.g., γ-radiation based Computerized Tomography are methods to observe a flow velocity profile in a measuring region. These methods are, however, complicated and expensive, and they are thus not generally suitable for routine measurements or for rapidly mount- able checking arrangements.

Introducing a dose of radioactive tracers into a fluid and subsequently monitoring the presence of the tracers at two regions along a flow path of the fluid gives the distribution of the transit times of the tracers between these regions. This method thus renders possible to measure the average velocity or distribution of velocities in the fluid by a relatively simple means. The use of radioactive tracers, however, requires the observation of necessary security issues and the acquiring of appropriate authorizations. Another disadvantage of this method is that due to dispersion of the tracer particles in the fluid, the method is not suitable for complicated or rapidly repeated velocity measurements.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a simple and reliable method of and a system for monitoring the flow velocity of a fluid.

Especially, an object of the present invention is to provide a simple and reliable method of and a system for monitoring the flow velocity or flow velocity profile of a process fluid, such as a medium consistency process fluid, in pipelines and tanks of chemical and mechanical wood processing industry.

To fulfill these objects, a method and a system are provided as disclosed in the ad- jacent independent claims.

Thus, a method of monitoring flow velocity in a fluid flow system is provided, the method comprising the steps of injecting multiple RFID-tags at an injecting location, measuring final presence data of the multiple RFID-tags at multiple instants at a fi- nal measuring location downstream of said injecting location by a final RFID- transceiver, and calculating a flow velocity by using the measured final presence data.

Also, a system for monitoring flow velocity in a fluid flow system is provided, the system comprising means for injecting RFID-tags at an injecting location, a final RFID-transceiver for measuring final presence data of the RFID-tags at a final measuring location downstream of the injecting location, and means for calculating a flow velocity by using the measured final presence data.

RFID-tags (radio frequency identification tags) are small pieces of suitable material containing a silicon chip and an antenna to enable them to receive and respond to radio-frequency queries from an RFID-transceiver. Such RFID-tags are often attached to or incorporated into a product, animal, or person, to enable data to be transmitted and read by an RFID-transceiver and processed according to the needs of a particular application. The data transmitted by the tag may provide identification of the tag or specifics about the product tagged, such as price, color, date of purchase, etc.

Smallest passive RFID-tags currently available are thinner than paper and have an area of 0,15 mm x 0,15 mm. Passive RFID-tags do not require batteries, and can have an unlimited life span. The minute electrical current induced in the antenna by the incoming radio frequency signal provides just enough power for a low-power integrated circuit in the tag to power up and transmit a response. Most passive tags signal by backscattehng the carrier signal from the transceiver. The aerial (antenna) of the tag is designed to both collect power from the incoming signal and also to transmit the outbound backscatter signal, which includes an ID-number of the tag. Passive tags have practical read distances ranging from about 2 mm up to a few meters depending on the radio frequency chosen and the design and size of the antenna.

As indicated above, conventional applications of RFID-tags are based on attaching RFID-tags on individual products or other individual objects to later identify the ob- ject at a reader station. The inventors of the present invention have noticed that RFID-tags can also be used by letting them freely flow with a fluid, such as a process fluid, in order to observe the flow velocity of the fluid. As such, the RFID-tags can replace radioactive tracers used earlier for the same purpose. A clear advantage of the RFID-tags is that because the tags are individually identifiable, the fluid velocity measurements can be made in complicated flow systems and they can be rapidly repeated or even continuous.

According to the present invention, the RFID-tags are advantageously low-cost, passive RFID-tags. Depending on the size of the tags chosen and on the require- ments of the process, the tags may be removed from the fluid downstream of the final measuring location by a suitable method, such as magnetically, by a screen or by a cyclone, or they may be left to the fluid and disposed. In some applications using a circulating fluid, it may even be possible to use the same RFID-tags repeat- edly without removing them from the fluid.

By injecting multiple RFID-tags at a first instant into the fluid and observing their appearance at multiple instants, preferably continuously, at a downstream location, so-called final measuring location, by an RFID-transceiver, gives a possibility to calculate the average flow velocity of each of the tags between the injecting location and the final measuring location simply by dividing the length of the travel path by the transit time of the corresponding tag.

However, in order to avoid separate identification of each of the tags when injecting them to the fluid, the method advantageously comprises a further step of measuring initial presence data of the multiple RFID-tags at multiple instants, preferably continuously, at a first measuring location downstream of the injecting location. The first measuring location is preferably within the immediate vicinity of the injecting loca- tion, but it may also be further away from the injecting location. The first measuring location is preferably equipped with a similar RFID-transceiver than the final measuring location.

The use of a separate RFID-transceiver immediately downstream of the injecting location, enables the tags to be identified in the same way at both of the measuring locations and the transit time of a tag can be measured on the basis of its appearances at the two measuring locations. The measuring of the transit times between two similar measuring locations is generally more accurate than the measuring of the transit times between the injecting of the tags and their appearance at the final measuring location.

The injecting locations and the first and final measuring locations are advantageously along a pipeline of a pipeline system, for example in chemical and mechanical wood processing industry. Thereby, the fluid is preferably a process fluid, even more preferably a medium consistency process fluid of chemical or mechanical wood processing industry, but it may also be other fluid, such as sludge or waste liquor. The flow of a medium consistency process fluid is often near to a plug flow, whereby the transit times of individual tags are typically nearly uniform. How- ever, by using multiple RFID-tags, any deviations from the ideal flow are easily identified by the distribution of the transit times.

According to an advantageous embodiment of the invention, the weight, size and shape of the RFID-tag pieces are varied in order to make more detailed conclusions about the characteristics of the flow on the basis of possible differences between their respective velocity distributions. Especially, in cases where the fluid comprises different phases, preferably at least two types of RFID-tag pieces are designed so as to make them flow along with the different phases. As an example, very light tags can be used to monitor the flow of the phase with lowest density in the fluid, typically gas or liquid, as the case may be, and somewhat heavier tags to monitor the higher density phase.

The present invention is also applicable to more complicated pipeline systems. For example, the measuring step may simultaneously be performed at multiple final measuring locations along different pipeline branches of a pipeline system, to simultaneously monitor different flows in the pipeline system. Because the individual RFID-tags are identifiable, the injecting step may also be performed simultaneously at multiple injecting locations along different pipeline branches of the pipeline sys- tern, so as to observe the velocities of different flows to one or more final measuring locations.

According to another preferred embodiment of the present invention, RFID-tags are used for monitoring flow velocity profiles in vessels, containers or other larger vol- umes, which are hereinafter denoted as tanks, in a fluid flow system. Thereby, the injecting location or a first measuring location is preferably arranged at or close to the fluid inlet of the tank, and the final measuring is performed at multiple measuring locations arranged at different regions of the tank. Preferably such multiple final measuring locations are arranged on the enclosure of the tank, but in some applica- tions final measuring locations can also be arranged within the tank.

In a simple application, RFID-tags are observed by transceivers, with relatively short read ranges, arranged in different locations on the enclosure of the tank. If the numbers of the tags observed at different final measuring locations are about the same and the observed transit times of the tags to the different locations are distributed according to an appropriate smooth pattern, the fluid flow may appear to be evenly distributed throughout the tank. On the other hand, if some of the measuring locations only show a small number of tags and/or relatively long transit times, the tank obviously has a non-uniform velocity profile, or even dead regions, where the fluid stays more or less stagnant.

When there is a need to observe the velocity profile throughout the tank, RFID- transceivers with relatively short read ranges can also be arranged within a tank. When the tank comprises suitable internal structures, it may be possible to arrange the transceivers in such structures. Otherwise, suitable mounting arms or other suitable structures have to be made for mounting the transceivers within the tank. Such special mounting structures can naturally be used only when they do not ex- cessively distort the actual function of the tank.

According to a preferred embodiment of the present invention, the multiple RFID- transceivers arranged on the enclosure of, or within, a tank have mainly mutually exclusive read ranges, which cover a large portion, preferably at least 30 %, even more preferably at least 50 %, of the volume of the tank. Thereby, the RFID-tags can be observed most of the time when they are within the tank, and their flow paths in the tank can be monitored. The actual fluid flow profile in the tank can then be obtained on the basis of a sufficient number of observed flow paths of the RFID- tags.

According to another preferred embodiment of the present invention, the multiple RF ID-transceivers arranged at different regions of a tank have directional and mutually partially overlapping read ranges, which cover at least 50 % of the total volume of the tank. By comparing the simultaneously observed presence data of mul- tiple readers, it is possible to infer, at different instants, the actual locations of the tags, and to infer the fluid flow velocity profile within the tank. Even more information of the evolution of instantaneous locations of the RFID-tags, and of the flow velocity profile of the fluid in the tank, can be obtained by varying the read ranges of the transceivers, e.g., by varying the amplitudes of the rf-signals from the transceivers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic view of a system for monitoring flow velocity of a fluid in a pipeline; FIG. 2 shows a schematic view of a system for monitoring flow velocity of a fluid in a pipeline system; FIG. 3 shows a schematic plan view of a tank with a system for monitoring fluid flow velocity profile; FIG. 4 shows a schematic horizontal cross sectional view of a tank with another system for monitoring fluid flow velocity profile; and

FIG. 5 shows a schematic horizontal cross sectional view of a tank with still another system for monitoring fluid flow velocity profile.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Fig. 1 shows schematically a system 10 for monitoring the velocity of a fluid 12 in a pipeline 14. The system comprises a feeder 16 for injecting RFID-tags 18 into the fluid arranged at an upstream section, so-called injecting location 20, of the pipeline 14 and a transceiver 22 arranged at a downstream section, so-called final measuring location 24 of the pipeline 14. The transceiver 22 sends at short intervals, or preferably practically continuously, rf-signals into the fluid, and each RFID-tag flow- ing at that moment within the read range of the transceiver 22 responds by back- scattering a signal comprising its individual ID-code. The reader part of the transceiver 22 receives the backscattered signal, and thus observes the moment of presence of each individual RFID-tag at the final measuring location 24. Thereby, the transceiver 22 is said to measure the final presence data of the RFID-tags.

The system further comprises a calculation unit 26, which calculates the velocity of the tags on the basis of the final presence data, which is sent to the calculation unit 26 via a first transmission line 28, and an initial data indicating an initial moment of presence of the same tag at an upstream portion 30 of the pipeline 14. The initial data may comprise the actual injecting moments of each of the RFID-tags, which may be transmitted to the calculation unit automatically by a second transmission line 32. However, according to a preferred embodiment of the present invention, the system comprises another transceiver 34 at the upstream portion 30, downstream, preferably immediately downstream, of the feeder 16, for measuring initial presence data of the RFID-tags and for sending them to the calculation unit 26 through a third transmission line 36.

Fig. 2 shows an example of a more complicated pipeline system, comprising three feeding pipelines 38, 38', 38", a fluid process unit 40 and two discharge pipelines 42, 42'. Each of the feeding pipelines 38, 38', 38" comprises an RFID-feeder 44, 44', 44" and a transceiver 46, 46', 46" for gathering initial presence data of the RFID-tags fed by the corresponding feeders, and for sending the initial presence data to a calculation unit 48. The system comprises also a final transceiver 50, 50' arranged at a downstream location at both of the discharge pipelines 42, 42', to gather final presence data of the RFID-tags, and to send it to the calculation unit 48. The system thus shows the transit times of the RFID-tags in each branch of the pipeline system, and correspondingly enables the calculation of flow velocities in each branch.

Naturally, fluid flow velocities could correspondingly be monitored in pipeline systems which comprise multiple initial pipeline branches which all connect to a single final pipeline, or in systems with one initial pipeline and multiple final pipelines. Cor- respondingly, it is also possible to include multiple "initial" measuring locations or multiple "final" measuring locations along a single pipeline, to monitor the fluid transit times in different portions of the pipeline.

Fig. 3 shows another preferred embodiment of the present invention, which is di- rected to monitoring a flow velocity profile in a tank 52 arranged in a fluid flow system. Preferably the tank includes an inlet duct 54, and an outlet duct 56. As an alternative, the tank may comprise multiple inlet ducts and/or multiple outlet ducts. The inlet duct 54 comprises an RFID-feeder 58 and an initial RF ID-transceiver 60 for monitoring the ID-codes and the inlet moments of the RFID-tags fed by the feeder 58. The feeder 58 may be located further away upstream of the tank 52, but the initial transceiver 60 is preferably close to the inlet of the tank 52, so as to obtain accurate inlet moments of the RFID-tags. Instead of using an initial RFID- transceiver 60, the initial moments of the RFID-tags could alternatively be observed in the RFID-feeder 58. The use of a separate initial transceiver 60 usually provides more accurate initial moments than what could be obtained directly in the feeder, especially if the feeder is located at a distance from the tank 52.

Advantageously the system comprises also a final transceiver 62 arranged in the outlet duct 56 of the tank 52, in order to obtain the total transit times of the RFID- tags through the tank 52. However, the main measuring devices of the system shown in Fig. 3 are a set of RFID-transceivers 64, 64', arranged on the enclosure 66 of the tank 52. The transceivers 64 have preferably relatively short read ranges for the RFID-tags used in the measurement, so that each transceiver can observe the moments of presence of the RFID-tags in its close vicinity. The inlet and outlet moments of individual RFID-tags, and their ID-codes, are transmitted to a calculation unit, as well as any other presence data observed by the transceivers 64, 64' arranged on the enclosure 66 of the tank 52.

The transceivers 64 are advantageously arranged in multiple height levels on the periphery of the tank 52, so as to observe the presence of at least some RFID-tags subsequently by different transceivers 64, 64'. On the basis of such presence data, it is possible to infer the paths 68 of individual RFID-tags and, thereby, an indication of the velocity profile in the tank 52. The arrangement shown in Fig. 3 includes multiple transceivers in four height levels, and can thus give a relatively good picture of the velocity profile in the tank 52. Usually it is preferable to have at least three transceivers arranged in at least two levels in the tank, but the number of transceivers may vary in large limits depending on the needs of the application in question.

The arrangement shown in FIG. 3 may in some applications be too inaccurate, because the flow velocity is monitored only close to the walls of the tank 52. Fig. 4 shows another embodiment of the present invention, which has transceivers 70 ar- ranged within the tank 52' by means of arms 72. The read ranges of the transceivers are in Fig. 4 depicted symbolically by circles 74. Advantageously, the read volumes of the transceivers are mutually excluding, but cover most of the volume of the tank 52'. Thus, an RFID-tag flowing through the tank 52' can be most of the time detected by one of the transceivers 70, and its approximate flow path can be detected. Thereby, the velocity profile of the fluid flowing through the tank 52' can be obtained on the basis of the presence information of multiple RFID-tags.

Fig. 5 shows a still further embodiment of the present invention, which comprises a set of RFID transceivers 76, 76' with highly directional read ranges 78, 78', which include pairwise overlapping regions 80. The overlapping regions 80 cover most of the volume of the tank 52", and therefore an RFID-tag flowing through the tank 52" can be most of the time detected by a pair of the transceivers 76, 76', whereby its presence in the overlapping region of their read ranges is observed. Thus, the flow path of individual RFID-tags can be monitored, and the velocity profile of the fluid flowing through the tank 52" can be obtained on the basis of the flow paths of multiple RFID-tags.

It should be noted from the above description that the invention has only been de- scribed with reference to a few exemplary solutions. These solutions are not intended as limiting the invention to the above-mentioned details only, but the invention is limited only by the accompanying claims and the definitions therein.

Claims

WE CLAIM:

1. A method of monitoring flow velocity in a fluid flow system, comprising the steps of: - injecting multiple RFID-tags at an injecting location,

- measuring final presence data of the multiple RFID-tags at multiple instants at a final measuring location downstream of said injecting location by a final RF ID-transceiver, and

- calculating a flow velocity by using the measured final presence data.

2. A method according to claim 1 , wherein the method comprises a further step of measuring initial presence data of the multiple RFID-tags at a first measuring location downstream of said injecting location by an initial RF ID-transceiver and calculating the flow velocity by using the measured initial presence data .

3. A method according to claim 1 or 2, wherein said injecting location and said final measuring location are along a pipeline of a pipeline system.

4. A method according to claim 3, wherein the measuring step is performed at multiple final measuring locations along different pipeline branches of the pipeline system.

5. A method according to claim 3 or 4, wherein the injecting step is performed at multiple injecting locations along different pipeline branches of the pipeline sys- tern.

6. A method according to claim 1 or 2, wherein the measuring step is performed at multiple final measuring locations at different regions of a tank.

7. A method according to claim 6, wherein the measuring step is performed by measuring the presence of the multiple RFID-tags within a predetermined read range of multiple final RFID-transceivers.

8. A method according to claim 7, wherein the multiple final measuring locations are on the enclosure of the tank.

9. A method according to claim 7, wherein at least one measuring location is within the tank.

10. A method according to claim 8 or 9, wherein the multiple final RF ID-transceivers have mainly mutually exclusive read ranges.

11. A method according to claim 10, wherein the read ranges of the multiple final RF ID-transceivers cover most of the volume of the tank.

12. A method according to claim 7, wherein the multiple final RF ID-transceivers have pairwise partially overlapping read ranges.

13. A method according to claim 7, wherein the presence data of the multiple RFID- tags is measured by varying the read ranges of the multiple final RFID- transceivers.

14. A method according to any of claims 6 - 13, wherein the calculating step includes calculating a flow velocity profile.

15. A method according to any of claims 1 - 14, wherein the multiple RFID-tags comprise tags of different sizes, shapes or weights for separately monitoring velocities of different phases in the fluid.

16. A method according to any of claims 1 -15, wherein the fluid is medium consistency process fluid of chemical or mechanical wood processing industry

17. A system for monitoring flow velocity in a fluid flow system, comprising:

- means for injecting RFID-tags at an injecting location,

- a final RFID-transceiver for measuring final presence data of the RFID-tags at a final measuring location downstream of the injecting location, and - means for calculating a flow velocity by using the measured final presence data.

18. A system according to claim 17, wherein the system comprises an initial RFID- transceiver for measuring initial presence data of the multiple RFID-tags at a first measuring location downstream of the injecting location and means for calculating the velocity by using the measured initial presence data .

19. A system according to claim 17 or 18, wherein the injecting location and the fi- nal measuring location are along a pipeline of a pipeline system.

20. A system according to claim 19, wherein the system comprises multiple final RF ID-transceivers arranged in multiple final measuring locations along different pipeline branches of the pipeline system.

21. A system according to claim 19 or 20, wherein the system comprises multiple means for injecting RFID-tags arranged in multiple injecting locations along different pipeline branches of the pipeline system.

22. A system according to claim 17 or 18, wherein the system comprises multiple final RF ID-transceivers arranged in multiple final measuring locations in different regions of a tank.

23. A system according to claim 22, wherein the multiple final RFID-transceivers are arranged on the enclosure of the tank.

24. A system according to claim 22, wherein at least one final RF ID-transceiver is arranged within the tank.

25. A system according to claim 23 or 24, wherein the multiple final RFID- transceivers have mainly mutually exclusive read ranges.

26. A system according to claim 25, wherein the read ranges of the multiple final RF ID-transceivers cover most of the volume of the tank.

27. A system according to claim 23 or 24, wherein the multiple final RFID- transceivers have pairwise overlapping read ranges.

28. A system according to claim 22, wherein the final RFID-transceivers have alterable read ranges.

29. A system according to any of claims 23 - 28, wherein the means for calculating comprises means for calculating a fluid flow velocity profile.

30. A system according to any of claims 17 - 29, wherein the multiple RFID-tags comprise tags of different sizes, shapes or weights for separately monitoring velocities of different phases in the fluid.