FIELD OF THE INVENTION

[001] The present invention relates generally to operating an electromagnetic flowmeter and more particularly to a method for operating an electromagnetic flowmeter for detecting flow of multiphase fluids and the electromagnetic flowmeter thereof.

BACKGROUND OF THE INVENTION

[002] Flow of multiphase fluids is a simultaneous flow of materials with different states or phases (i.e. gas, liquid or solid), or materials with different chemical/physical properties but in the same state or phase (i.e. liquid-liquid systems where the fluids are having stratified flow). Measurement of flow of fluids through a conduit or pipe can be done by numerous ways like using electromagnetic flowmeters. Electromagnetic flow meters are popular flow measurement devices owing to their non-invasiveness and accuracy.

[003] A typical electromagnetic flow meter works on Faraday's law of electromagnetic induction. An electromagnetic field is imposed within a fluid with a certain level of conductivity flowing through a conduit or pipe. Electromotive force (EMF) induced as a result of the interaction of the electromagnetic field with the ions in the fluid, is measured using electrodes provided at the pipe side walls. The measured EMF is proportional to the flowrate and can be used to measure flowrate. While electromagnetic flow meters can be used to measure flowrate with high accuracy, their capability of measuring multiphase flow is limited.

[004] Conventionally, for detecting multiphase flow using electromagnetic flow meters one of the methods used is to provide electrodes spanning a substantial portion of the pipe inner circumference, so that the flow meter operates even when the fluid level is low. Another method used is to provide a third electrode at the top of the pipe to detect partial filling of the pipe. In this technique, an alarm can be raised when liquid level drops. In yet another method electromagnetic flow meter measurement technique is used in combination with other techniques (Electrical impedance tomography, electrical resistance tomography) to measure multiphase flows. In one method, a level indicator is used to determine pipe level. However, provision of a level indicator requires providing openings on the pipe surface, leading to chances of leakage, increasing product footprint and affecting the electromagnetic induction measurement process.

[005] Using existing methods, the detection of multiphase flow requires additional component and/or modifications to be made to the existing flow meter which could entail costs and increase complexity of the device. Additionally, although current flow meters can be used to detect partial filling of pipes (a kind of multiphase flow condition), determination of the extent of partial filling (or quantification of water level in pipe) is still a challenge in the art. Hence there is a need for an electromagnetic flowmeter that is able to detect multiphase flow of fluid as well as determine the extent of partial filling of the pipe or conduit in a reliable, simplistic and cost-effective manner.

SUMMARY

[006] The above-mentioned shortcomings, disadvantages and problems are addressed herein which will be understood by reading and understanding the following specification.

[007] In one aspect, the present invention provides a method for operating an electromagnetic flowmeter for detecting a flow of multiphase fluids passing through a conduit, the electromagnetic flowmeter comprising a pair of coils for generating electromagnetic fields that interact with the fluid passing through the conduit, a pair of potential sensing electrodes for measuring potential difference from electromotive forces generated by the interaction of electromagnetic fields in the fluid, wherein the pair of coils are placed opposite to each other on the conduit along a first axis perpendicular to the flow of the fluid passing through the conduit and the pair of potential sensing electrodes are placed opposite to each other on the conduit along a second axis that is perpendicular to the first axis and to the flow of the fluid, the method comprising the steps of: generating an electromagnetic field by an electrical excitation of a first coil from the pair of coils; obtaining a first electric potential difference between the pair of the potential sensing electrodes for the electrical excitation of the first coil; generating an electromagnetic field by an electrical excitation of a second coil from the pair of coils; obtaining a second electric potential difference between the pair of the potential sensing electrodes for the electrical excitation of the second coil; detecting a flow of multiphase flow of fluids based on a difference between the first electric potential difference and the second electric potential difference.

[008] In an embodiment, obtaining the first electric potential difference and second electric potential difference includes obtaining sets of values for the first electric potential difference and the second electric potential difference.

[009] In an embodiment, multiphase flow of fluids include partial flow of fluids in the conduit.

[0010] In an embodiment, the difference between the first electric potential difference and the second electric potential difference corresponds to an extent of filling of the conduit.

[0011] In an embodiment, the extent of filling of the conduit is depicted in terms of percentage of filling.

[0012] In an embodiment, the electrical excitation of the first coil and the electrical excitation of the second coil done alternately is implemented in a fraction of a period of time during detection of the flow of multiphase fluids.

[0013] In another embodiment, the present invention discloses an electromagnetic flowmeter for detecting a flow of multiphase fluids passing through a conduit that performs the steps of claim 1 , wherein the electromagnetic flowmeter comprises an excitation unit to excite a pair of coils for generating an electromagnetic field that interact with the fluid passing through the conduit, wherein the excitation unit is controlled by a processing device wherein the processing device is used for taking measurements from potential sensing electrodes. [0014] In an embodiment of the electromagnetic flowmeter mentioned herein above there are even number of coils for generating an electromagnetic field in the electromagnetic flowmeter.

[0015] In an embodiment, the electromagnetic flowmeter comprises a display for indicating the detected multiphase flow.

[0016] In an embodiment, the detected multiphase flow of fluids is transmitted to a remote control centre of the electromagnetic flowmeter for further analysis.

BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 illustrates an electromagnetic flowmeter,

[0018] Figure 2 illustrates multiple views of an electromagnetic flowmeter showing a partially filled conduit,

[0019] Figure 3 is a block diagram representation of the functional elements in the electromagnetic flowmeter,

[0020] Figure 4 illustrates views of an electromagnetic flowmeter powered on alternately, and

[0021] Figure 5 is a flowchart of the method performed by the electromagnetic flowmeter.

DETAILED DESCRIPTION

[0022] The present invention is related to a method of operating an electromagnetic flowmeter for detecting flow of multiphase fluids and the electromagnetic flowmeter thereof. In the present invention a method of operating an electromagnetic flowmeter is disclosed for detecting multiphase flow of fluid as well as determine the extent of partial filling of the pipe/conduit in a non-invasive and cost-effective manner. The present invention provides an electromagnetic flow meter, which consists of two coils placed at top and bottom of the conduit. In the method disclosed herein, the electromagnetic flow meter coils are powered alternately (when top coil is powered the bottom coil is powered off and vice versa). For each coil powered, the EMF is measured and recorded. The difference between the corresponding EMFs measured when the top and bottom coils are individually powered is calculated. Under 100% filled condition the EMFs measured when the top and bottom coils are individually powered is the same due to horizontal symmetry of the conduit. However, under partial flow conditions (air gap above fluid surface), there is no symmetry with respect to horizontal plane. In such case, EMF's generated will be different for both top and bottom powered coils (the bottom coil when powered yields a higher EMF than the top coil). This difference is useful in detecting occurrence of partial flow. Thus no additional device is required for partial flow or multiphase (stratified) flow measurement.

[0023] In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific embodiments, which may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the embodiments, and it is to be understood that other embodiments may be utilized. The following detailed description is, therefore, not to be taken in a limiting sense.

[0024] Figure 1 illustrates an electromagnetic flowmeter 100. Figure 1 shows an electromagnetic flow meter, which comprises a conduit/pipe 110 through which fluid flows, a pair of coils (a top coil 120 and a bottom coil 130) for generating electromagnetic fields that interact with the fluid passing through the conduit, wherein the pair of coils are placed opposite to each other on the conduit along a first axis perpendicular to the flow of the fluid passing through the conduit and a pair of potential sensing electrodes (140 and 150) for measuring electromotive forces by means of measuring potential difference between the electrodes generated by the interaction of electromagnetic fields in the fluid, the pair of potential sensing electrodes are placed opposite to each other on the conduit along a second axis that is perpendicular to the first axis and to the flow of the fluid, The pair of coils (120 and 130) are placed horizontally parallel to the direction of fluid flow along the conduit 110. The pair of potential sensing electrodes (140 and 150) which are placed across the diameter provide the induced EMF as a result of the difference in potential across the conduit diameter. The induced EMF is proportional to the flowrate and hence is used in measuring flowrate. The electromagnetic field generated by the pair of coils interact with the fluids passing through the conduit wherein the interaction because of different phases and/or fluids depending on fluid electrical/magnetic properties for e.g. conductivity (electric property), permeability (magnetic property) and permittivity (electric property).

[0025] Figure 2 illustrates multiple views of an electromagnetic flowmeter showing a partially filled conduit i.e. the conduit has two fluid phases that are stratified. Figure 2 shows views 100 and 200 wherein view 100 is the electromagnetic flowmeter of figure 1 with partially filled conduit 210, and view 200 is a cross-sectional view of the electromagnetic flowmeter 100. The views 100 and 200 are placed parallel to each other to indicate the placement of the various functional elements of the electromagnetic flowmeter like the top and bottom coils (120,130), potential sensing electrodes (140,150) and the conduit (110). It may be noted by the person skilled in the art that the placement of the various functional elements of the electromagnetic flowmeter are described in an exemplary manner and any other mode of placing the functional elements may be adopted to attain the objects of this invention.

[0026] Figure 3 is a block diagram representation of the functional elements in the electromagnetic flowmeter. Figure 3 depicts an electromagnetic flowmeter 300 for detecting and quantifying the flow of multiphase fluids comprising the functional blocks of a processing device 310, an excitation unit 320, potential sensing electrodes 330, top coil 340, bottom coil 359 and a conduit 360 through which multiphase fluids flow. The excitation unit 320 is controlled by the processing device 310 wherein the processing device 310 is used for taking measurements from potential sensing electrodes 330. The top coil 340 and the bottom coil 350 are excited by the excitation unit 320 wherein the power of excitation is controlled by the processing device 310. The excitation unit 320 powers on the top coil 340 and bottom coil 350 in an alternate manner which is controlled by the processing device 310. The potential sensing electrodes 330 measure the induced EMF across the diameter of the conduit 360 alternately and provide the processing device 310 with values of induced EMF measured on each excitation. The difference in induced EMF is determined by the processing device 310 for each excitation of the top coil 340 and the bottom coil 350. If no difference in values of induced EMF is determined by the processing device 310, it is established that the conduit is fully filled. Under a partially filled condition of the conduit 360, the processing device detects an unsymmetrical result or a difference in values of measured induced EMF of the two coils is detected. It may be known to the person skilled in the art that the processing device can internally calibrate the rate of flow of the fluid corresponding to the induced EMF and results can be displayed or transmitted to a remote control centre for further analysis. The processing device can also provide the extent of filling of the conduit by internally calibrating the relation between the difference in induced EMF corresponding to the extent of filling of the conduit as the difference in induced EMF is proportional to the extent of partial filling (e.g. 90% full or 70% full), and hence is useful in quantification of partial flow.

[0027] An aspect of the invention provides placing thermal conductivity probes along the conduit circumference. Air has a much lower conductivity than water. Hence, in the event of partial flow, the conductivities registered by the upper probes will be lower than that registered by the lower probes. Hence using thermal conductivity measurements as well partial flow can be detected.

[0028] Figure 4 illustrates views 400 of an electromagnetic flowmeter powered on alternately. As shown in the Figure 4, 400a shows a cross-sectional view of the electromagnetic flowmeter with a powered on top coil 410a and powered off bottom coil 420a. And, 400b shows a cross-sectional view of the electromagnetic flowmeter with a powered off top coil 410b and powered on bottom coil 420b. When the top coil is powered on the bottom coil is off and when the bottom coil is powered on the top coil is off. In each case the EMF across the conduit is measured by the potential sensing electrodes and recorded. The difference between the EMFs for each coil powered is calculated. Under fully filled conditions the EMF is the same no matter which coil is powered, due to symmetry of the system. Under partially filled condition, symmetry of the process is affected and EMFs are different for each coil powered.

[0029] Figure 5 is a flowchart of the method 500 performed by the electromagnetic flowmeter. As depicted at step 510, an electromagnetic field is generated by an electrical excitation of a first coil. Following the generation of electromagnetic field in the first coil, as shown in step 520, a first electric potential difference for the electrical excitation of the first coil is obtained. As depicted at step 530 an electromagnetic field is generated by an electrical excitation of a second coil. Following the generation of electromagnetic field in the second coil, as shown in step 540, a second potential difference value for the electrical excitation of the second coil is obtained. It may be noted that the first coil and the second coil are excited in an alternate manner, and hence the electromagnetic fields generated are occurring one after the other and the values of potential difference are obtained for alternate electromagnetic fields generated for each coil. As shown in step 550, a flow of multiphase fluids is detected based on a difference between the first potential difference and the second potential difference. As mentioned before, a fully filled conduit with one fluid (single phase) will give a symmetrical result with no difference between the first value of potential difference measured between the electrodes and the second value of potential difference measured between the electrodes, whereas a partially filled conduit (two phase- one phase of the flowing fluid and another air or filler material) will give an unsymmetrical value or a difference in value between the first value of potential difference and the second value of potential difference when alternatively energizing the coils. Also, the conduit fully filled with two phases of flowing fluids will result in unsymmetrical values of potential difference between the electrodes hence detecting a multiphase flow of fluid in the conduit. Similarly, for a partially filled conduit with two or more phases, will also result in unsymmetrical values of potential difference. The level of asymmetry in potential difference measured at the electrodes will vary depending on the property of individual fluids flowing in the conduit as well as the extent of filling of the fluid in the conduit (fully filled or partially filled).

[0030] A relation is observed between the extent of filling of the conduit and the difference in induced EMF, and hence the processing device can internally calibrate to give an indication of the extent of the filling of the conduit corresponding to the difference in induced EMF. This is further illustrated with the table given below.

Table 1 below shows the powering scheme for different filling conditions of the conduit.

Table 1 : Powering scheme for different filling conditions of the conduit. [0031] The table shows induced EMF in the flowmeter for the 100% full pipe case and

75% full pipe case, wherein the coils are alternately powered. For the 100% full pipe case, the induced EMF is the same irrespective of which coil is powered. However in case of the 75% full pipe, powering the top coil on (0.4 amperes) and the bottom coil off (0 amperes), yields a lower EMF compared to the case of the top coil being off and the bottom coil being on. This is due to flow asymmetry arising due to partial filling. The difference indicates a partial flow situation and is a measure of the extent of partial filling. In other words the greater the difference, more is the extent of partial filling.

[0032] In an embodiment, sets of values for potential differences may be obtained for each excitation of the top coil and the bottom coil and then further analysis may be done to detect the multiphase flow of fluids.

[0033] In an embodiment, the potential sensing electrodes can be in the shape of arcs hence spanning a substantial portion of the conduit circumference.

[0034] In another embodiment, a general powering scheme can be adopted, where the top coil is at X amperes and the bottom coil is at X' amperes (ensuring X and X' are not equal). The induced EMF (E) is measured. Next, the top coil is powered at X' amperes and the bottom coil at X amperes. The induced EMF (Ε') is measured. E and E' should be same under 100% full pipe conditions. However under partially filled conditions E and E' will not be the same and will indicate presence of partial filling. Also the difference will enable quantification of the extent of partial filling.

[0035] In another embodiment, the powering scheme of alternately powering the top and bottom coils can be implemented in a fraction of some period of time during which diagnosis is to be done. For example the customer can be given an option to run the diagnosis for 5 seconds in every 30 seconds of flowmeter operation. During the 5 seconds the alternate coil powering scheme will be activated. During the remaining 25 seconds the electromagnetic flowmeter can run like a general flowmeter as known in the art. [0036] In another embodiment, in addition to powering the top and bottom coils in terms of Amperes unit the top and bottom coils can also be powered using different values in frequencies of the electrical excitation. For example, on a first instance the electrical excitation of the top coil is done with waveforms having frequency f 1 and the bottom coil with frequency f2. Now, on a second instance the frequencies for powering the top and bottom coils is reversed that is, the top coil is powered with frequency f2 and bottom coil is powered with frequency fl. In case of a 100% filled pipe there should be no difference in induced EMF between both the instances, due to symmetry. However there will be a difference in induced EMF in case of partial filling of the conduit.

[0037] It may be known to the person skilled in the art that the present invention has disclosed a method for operating an electromagnetic flowmeter for a single coil arrangement of the electromagnetic flowmeter. However, the present invention can be extended to a two coil arrangement as well. In an embodiment, the electromagnetic flowmeter can use a two coil arrangement for improving accuracy wherein each set of the two coils are powered on alternately. The two coils in the set are connected in series to each other. The coils are usually hundreds of turns of copper wire and thus offer significant inductance load by its driver circuit. The electromagnetic field alternates its direction within each cycle when the driver circuit changes the direction of the excitation current, which is done by turning on and off different pair of switches on an H-bridge. The alternating frequency is generally an integer fraction multiple of the power- line frequency for noise cancelation. The driver circuit consists of a constant current source and an H-bridge under the control of the processing device. Hence for a two coil arrangement, even number of coils are required to meet the objects of the present invention.

[0038] This written description uses examples to describe the subject matter herein, including the best mode, and also to enable any person skilled in the art to make and use the subject matter. The patentable scope of the subject matter is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.