MXPA00008561A - Gas meter dust filter - Google Patents

Abstract

The invention concerns a gas meter comprising, an ultrasonic metering conduit with longitudinal axis including an inner part wherein the gas flows, at least two ultrasonic transducers spaced along the longitudinal axis. The invention is characterised in that said meter comprises between each transducer and the metering conduit inner part a portion of greater width relative to said transducer active surface dimensions, said meter further comprising at least an element located at least in one of said at least wider portions and extending over the whole internal part thereof so as to form a filtering screen with respect to the dust particles transported by the gas, said element being traversed by ultrasonic waves emitted by the transducers over at least part of its width which is greater than said transducer active surface dimensions.

Description

GAS METER WITH ANTI-DUST FILTERS DESCRIPTION OF THE INVENTION The present invention relates to a gas meter comprising an ultric measuring conduit of the longitudinal axis that includes an internal part in which the gas flows, and at least two ultric transducers separated along the longitudinal axis. It is well known that the gases that seek to measure expenditure transport quantities of diverse powders that are far from negligible. In the course of time, the powders end up being deposited in different parts of the gas meter that are not always intended to receive them. It is thus frequently verified that the powders are deposited on the ultric transducers, which has the effect of disturbing their operation and therefore affecting the linearity of the ultric measurements carried out. To reduce the volume of powders transported by the gas flow, it is known to provide powder traps in this type of meter, upstream of the ultric measuring conduit.

However, these dust traps are not always effective since they allow the less heavy powders that can eventually be deposited on one and / or the other of the transducers to pass through nevertheless. It is also known from EP-0,606,536, a fluid meter comprising two ultric transducers disposed on a common axis with a measuring conduit. Transparent ultrnd membranes protect the active surfaces of the transducers from deterioration due to the fluid flowing in the meter. The membranes close the box or container where the measuring conduit is, hermetically and insulate the transducers of the fluid. However, the powders are deposited on these membranes which has the effect of disturbing the operation of the ultric transducers by strongly attenuating the acoustic signal coming from said transducers. It would therefore be interesting to find an effective solution to the problem of dust. The invention also aims at a gas meter that includes an ultrnd measuring conduit, of the longitudinal axis, which includes an internal part in which the gas flows, at least two ultric transducers spaced along the longitudinal axis, the meter comprises between each transducer and the internal part of the measuring conduit a widened portion in relation to the dimensions of the active surface of said transducer, characterized in that the meter further comprises an element placed in at least one of the flared portions and extending over the entire internal width of these, so as to form a filter mesh against the powders transported by the gas, the element being traversed by the ultric waves emitted by the transducers over at least a part of its width, which is greater than the dimensions of the active surface of said transducer. Having in front of one and / or another of the transducers an element that forms a mesh that filters the powders, and that has a surface in contact with the gas flow, offers the ultric waves and therefore the width is greater than the dimensions of the active surface of the transducers, the volume of the powders is distributed over a larger surface than if the filter element had the same dimensions as the active surface of the transducers. Such a filtering element is therefore not susceptible to being obstructed in the course of time. According to one embodiment of the invention, said at least one element forms a filtering screen located against the transducer. According to another embodiment of the invention, said at least one element forms a filtering screen located at a distance from the transducer. Said at least one element that forms a filtering screen can be located in front of the transducer upstream or adjacent to it depending on the configuration of the meter, and more particularly, of the measuring conduit, the enlarged portions and the transducers. Advantageously, the meter may comprise at least one obstacle positioned longitudinally within the internal part of the measuring conduit so as to form at least one annular passage for the passage or flow of the gas. Preferably, the measuring conduit comprises an inlet and an outlet for the gas flow, which are respectively arranged between one of the flared portions and said measuring conduit.

The gas inlet and outlet each have a place where the gas flow, respectively penetrates and leaves the measuring conduit, a passage section subjected to gas where the normal is inclined with respect to the longitudinal axis following an angle other than 90 ° and can also be equal to 90 °. Said orientation of the gas inlet and outlet allows to better channel the flow of the gas with respect to the prior art and for the same reason the powders transported by said gas flow. In this way, the powders are better directed towards the transducers than in the prior art. Since the intended meter of said oriented inlet and outlet also comprises an obstacle such as the one defined above, the gas flow is still advantageously channeled and the powders that are also channeled are the gas flow, are kept away from the transducers , reducing by this same fact the contamination risks of said transducers. The element that forms the filtering screen is made of a material composed of metallic or synthetic fibers.

The material may be of the type in which the fibers form a sieve, or of the type in which the fibers are interlaced and distributed within a volume. The measuring conduit can, for example, take the form of an ellipsoid of revolution, of a tube, or have a rectangular cross-section. Other features and advantages will appear in the course of the description given below and consigned only by way of example and made with reference to the accompanying drawings, in which: Figure 1 is a longitudinal schematic view of an ultrasonic gas meter, according to the present invention; Figure 2 is an enlarged view of the measurement conduit and of the ultrasonic transducers shown in Figure 1 according to a first embodiment; Figure 3 is an enlarged longitudinal view of the measurement conduit and of the ultrasonic transducers shown in Figure 1 according to a second embodiment. Figure 4 is an enlarged longitudinal view of the measurement conduit and of the ultrasonic transducers shown in FIG. Figure 1 according to a third embodiment; Figure 5 is a partially enlarged view of the enlarged portion (50) shown in Figure 4; Figure 6 represents a variant embodiment of the enlarged portion (50) of Figure 4; Figure 7 is a longitudinal view of a variant embodiment of the measurement conduit shown in Figures 1 to 4; Figure '8 is an enlarged view of the enlarged portion in which the component forming the screen according to a variant embodiment shown in Figure 7 is located; Figure 9 is a longitudinal view of a second variant embodiment of the measurement conduit shown in Figures 1 to 7; Figure 10 is a longitudinal view of a second variant embodiment of the measurement conduit shown in Figures 1 to 9; Figure 11 is a cross-sectional view of the measurement conduit shown in Figure 10; Figure 12 is a longitudinal view of a fourth variant embodiment of the measurement conduit shown in Figures 1 to 9. As shown in Figure 1, a gas meter is indicated with the general reference (10). ultrasound comprising a box or envelope (12) in which an entry opening is practiced (14) for the gas flow as well as an exit opening (16). An ultrasonic measurement block (18) is housed inside the casing (12) and comprises a measuring conduit (20) with longitudinal axis XX ', for example made in the form of a tube, at the ends of which they are positioned two ultrasound transducers (22, 24) along said longitudinal axis. The gas flow (represented by the arrows on the figures), penetrates through the opening (14) into the interior of the casing or box (12), is fractioned on the wall of the ultrasonic measurement block (18) located facing said opening and is distributed within the inner volume comprised between said casing and said ultrasonic measurement block. The gas flow is directed towards the lower part of the casing and penetrates an opening (26) 'made inside the measuring block inside the latter. The downward movement plus the bend made by the gas flow when going back to the opening (26), allows said gas flow to get rid of an important part of the heavy powders it transports. The gas flow then penetrates the inner portion of the measuring conduit (20), within which the ultrasonic measurements of the gas flow or expenditure are made, through an inlet. (27) made in the form of an annular opening, and escapes from said conduit through an evacuation opening (28) also made in the form of an annular opening. The annular inlet and outlet openings have a passage section offered to the gas in which the normal is inclined with respect to the longitudinal axis following an angle that is substantially equal to zero in the example shown in Figures 1 and 2. The flow of Outgoing gas from the measuring block (18) penetrates through a chimney (29) which is perpendicular to said measuring block and which communicates with the outlet (16) of the meter. As shown in Figure 1 and in more detail on Figures 2 to 4, the meter comprises, between each ultrasonic transducer (22, 24) and the inner portion of the measuring conduit within which the gas flow flows, a portion (30, 32) defining a housing and a support for said corresponding transducer. In this way, each of the annular inlet (27) and outlet (28) openings is made between one of said enlarged portions and the measuring conduit (20). Each of the portions (30, 32) has a widened transversal dimension with respect to the transverse dimensions of the active surface of the transducers. Each portion (30, 32) has, for example, a cylindrical external general shape which evidently implies an equally cylindrical inner shape (34, 36) and within which the corresponding transducer is mounted. Each of these portions comprises a peripheral collar (38, 40) that extends the general cylindrical shape and determines against. each transducer a cylindrical free space (42, 44) having a transverse dimension enlarged with respect to the transverse dimensions of the active surface of the transducers. Taking into account the configuration of the measuring conduit and the direction of flow within the inner portion of the measuring conduit that directs the powders directly on the active surface of the transducer (24) it is preferable to locate an element (46) at least within of the free space (44) located in front of the transducer (24) that is downstream (Figure 2). The element (46) is arranged against the transducer and extends transversely over the entire interior transverse dimension along said free space so as to form in front of said transducer a screen that fulfills the mission of a filter that obstructs the powders transported by the gas that arrives at the transducer. The filter element is for example fixed by adhesion on the annular portion (32a) of the portion (32) located at the bottom of the free space and around the transducer (24).

The filter element is made of a material that is formed by metallic or synthetic fibers. Each fiber constitutes an obstacle for dust particles where the flow path crosses said fibers. In order to ensure proper filtering, it is advisable to provide a sufficient number of fibers. The filter can be of the sieve type, that is to say that the powder particles are distributed on the almost flat surface of said filter. The material can be for example a stainless steel fabric where the diameter of the metal fibers is 25 μm and the dimension of the interstices is 16 μm. However, if it is desired to further increase the efficiency of the present invention, it is preferable to provide a material that allows having a filter in which the powder particles are distributed within a volume. Consequently, with a material within which the fibers are interlaced, the filter is able to accumulate a greater amount of dust than in the sieve filter before it is covered.

Such a material is for example a cotton. More precisely, the material is, for example, produced by the company 3M under the trademark "" FÍLTRETE 50 g'A The density of the fibers within the material is, for example, between 10 and 500 g / m2 and is, for example, of the order of 50 g / m2 and with a thickness equal to 2 mm. If the density of the fibers within the material is less than 10 g / m 2, then the need for a greater thickness of the fiber layer is observed to obtain a sufficient filtering action. Conversely, if the density of the fibers inside the material is higher than 500 g / m2, then it is verified that the acoustic signal emitted by the transducers is strongly attenuated, which is not acceptable. The title of the fibers is also an important parameter and it is preferable to have thin fibers for the same interstitial value between the fibers since the porosity of the fibers will be higher. The like within which the ultrasonic waves emitted by the transducer (24) are contained is indicated in interrupted lines in Figure 2 and is designated by the reference (47).

The transverse dimension of the surface of the filter element (46) is higher than the active surface of the transducer and the filter element - is, on the one hand, made of a material transparent to the ultrasonic waves. and on the other hand, it is located within an area where the ultrasound waves emitted by the transducer (24) pass through a part of its transverse dimension that is greater than the transverse dimension of the transducer active surface. Consequently, when a certain volume of dust particles is deposited on the filter element and obstructs it in part, the free portion thereof offered to the ultrasonic waves is sufficient to allow its passage without suffering too much attenuation. In any case, when the filter element is placed against the transducer (Figure 2) and the filter material is of the type in which the powders are distributed within a volume, it is possible to increase the thickness or the longitudinal dimension of the material and reduce its density in order that the ultrasonic waves are not too attenuated in the case that the amount of dust is very high.

In effect, for the same amount of powders, the volume of material within which the ultrasonic waves propagate and within which the powders are deposited is prolonged and the fibers are equally more spaced than in the above, which comes to cause a "dilution" effect of the powders and allows the ultrasonic waves to propagate more freely inside the material than if we had a reduced thickness.The efficiency of the filtration remains substantially the same.It should be noted that if the thickness of the material is increased and the same density is retained, the efficiency of the filtering action will be increased but the ultrasonic waves will be more attenuated, in the case in which the configuration of the measuring conduit and / or the enlarged portion and / or of the filter element it is such that in the absence of dust the filter element is not crossed by ultrasonic waves that on a part of its transversal dimension equal to the dim cross-sectional area of the active surface of the transducer, then, for a minimum volume of powders that the above-mentioned, the filter element will be strongly obstructed in its part crossed by the ultrasonic waves, which will considerably affect the transmission of the same and consequently of the measurement of the gas flow rate. Advantageously, the filter element (46) located in front of the transducer (24) allows to eliminate the turbulences present in the transit of the gas, which, if produced in front of said transducer, would affect the linearity of the measurement. As shown in Figure 3, in a new embodiment, a filter element (48) analogous to the filter element (46) is disposed in the free space (42) of the elongated portion (30, 32) in order to also protect the transducer (22) against dust. This precaution can be verified useful when the meter must be subjected to use under severe dust conditions, or when it is planned to use it for the measurement of reputed gases particularly loaded with powders. According to a third particularly advantageous embodiment shown in Figure 4, each of the elongated portions (50, 52) of a generally cylindrical shape comprises a peripheral collar (54, 56) _ which extends said general cylindrical shape and which defines in front of each transducer a cylindrical free space (58, 60). The longitudinal dimensions of the peripheral collars (54, 56) and of the free spaces (58, 60) are respectively superior to that of the collars (38, 40) and of the free spaces (42, 44) of Figure 2. Consequently, the greater dimension of the internal free spaces in the enlarged portions (50, 52) allows positioning each filtering element (62, 64) at a distance from the corresponding transducer (22)., 24) leaving between the filter element and its respective transducer a zone of free space where the gas has been at rest. It will be possible to dispose within the free space (58) and / or (60) of several filter elements of the sieve type, displaced along the longitudinal axis and where the fibers and the interstices will be displaced transversely between two consecutive filtering elements for the purpose of catch more dust than with a single filter of the same type. Within this configuration, it will be highly advantageous to combine the two types of filter elements by placing a volume filter * (of the type in which the powder particles are distributed within a volume), away from the transducer, and a filter of the type sieve between these in order to improve the reliability of the filtering action, in fact, in the hypothesis in which a dust particle would not be stopped by the volume filter, it will be definitively stopped by the sieve filter. It may also be considered to combine the free space in front of the transducer with a single thick filter element. Figure 5 is an enlarged partial view of the portion (50) shown in Figure 4 showing a portion of said portion, the other part being obtained by symmetry with respect to the longitudinal axis XX '. On said figure, the filter element (62) has been pinched or locked between one end of the collar (54) forming a back of back (55) and a washer (57) that is integral with said end of the collar, for example, by ultrasonic welding. Figure 6 shows a variant embodiment of the enlarged portion (50) of Figure 4, in which the collar (6) extends the cylindrical part of the enlarged portion (68) so as to confer to the interior free space (70) to said enlarged portion a cuvette shape progressively flared in the direction opposite to that of the transducer. The filter element (62) is positioned remotely from the transducer in said flared space. Figure 7 illustrates a variant execution of the measurement conduit shown in Figures 1 to 4, which takes here in the form of a revolution ellipsoid (72) such as that described in French Patent 2,683,046. The ellipsoid of Figure 7 shows a structure difference with that of French Patent 2,683,046: the gas flow is obtained through two openings made in the conduit wall (72) and not around the transducers. Said enlarged portions (74, 76) serve as a housing for the ultrasonic transducers (78, 80) each having an internal free space (82, "84) of progressively flared shape within which the filter element (86) is located. 88) analogous to those described with reference to Figures 4 and 6. Said annular openings (90, 92) respectively serve to enter and exit the gas flow inside the internal part of the measuring conduit (72) and are performed between each enlarged portion (74, 76) and said measuring conduit, said openings each having in the discharge or in the evacuation of the gas, respectively, the inlet and outlet of the measuring conduit (72), a passage section offered to the gas where the normal N is inclined with respect to the longitudinal axis XX 'according to an angle a other than 90 ° For example, the angle of inclination a is 45 ° On the other hand, an elongated obstacle (94) having a general ogival shape it's position on the longitudinal axis XX '. This obstacle defines an annular passage with the internal surface of the measuring conduit. Thanks to the annular form of the passage. { 96 J and the orientation of the normal N in the passage sections offered to the gas at the gas inlet and outlet, respectively, penetrates and is evacuated from the measurement conduit (72), and said gas flow rate is channeled which allows to keep the powders it transports on a trajectory aligned with the transducers (78, 80). With such a configuration the filtering element located in front of the upstream transducer (78) can receive the powders when a powder distribution (98) is seen from the filtering element (88) located in front of the water transducer. the periphery of said filter element, as indicated in Figure 7. Figure 8 indicates another possible variant of the enlarged portion (100) usable with the measurement conduit (72) of Figure 7 in which the clearance ( 102) takes the form of a cylindrical space in the bottom of which the filter element (86) is located against the transducer (78). Figure 9 illustrates another configuration of the ultrasonic meter (110) in which on the measurement block (112) (housed inside an external shell) has been represented and described in the European patent application EP-0682, 773. The measurement block comprises a tubular measuring conduit (114) provided with inlet (116) and evacuation (118) openings in which the normal ones are to the passage section offered to the gas at the gas inlet and outlet, respectively, at the entrance and exit of the measuring conduit (114), it forms an angle of 90 ° with the longitudinal axis XX '. An improvement over said configuration may consist in practicing the openings (116, 118) along a slope forming with the longitudinal axis XX 'an angle less than 90 ° in order to align the flow rate and thereby the dust particles in the area where the transducers are located. An aligned obstacle (120) is positioned along the longitudinal axis in the interior of the measurement conduit (114) to form an annular passage (122) into which the gas flow flows. Two enlarged portions (124, 126) form with the longitudinal axis XX 'an angle of 90 ° and thus allow the ultrasonic transducers (128, 130) housed within said portions to be fixed. The ultrasonic waves emitted by said transducers are reflected by the walls (132, 134) in the annular passage (122). Two filter elements (136, 138) according to the description that has been made with reference to the preceding figures are mounted on the two ends of the obstacle (120). It will also be possible to arrange the filtering elements within the part of the enlarged portions (124, 126) where the transducers will be located, in a position located at 90 ° to that shown in Figure 9.

The gas meter (140) partially represented in a longitudinal view in Figure 10 comprises a measuring conduit (142) of longitudinal axis XX 'where the cross section shown in Figure 11 is rectangular in shape.

Two portions (144, 146) enlarged with respect to the dimensions of the ultrasonic transducers (148, 150) are practiced on one of the walls (142a) of the measurement conduit along a slope inclined with respect to the longitudinal axis XX '. The transducers (148, 150) are mounted on the bottom of the enlarged portions (144, 146) which act as a housing for the filter elements (152, 154) according to what is described with reference to Figure 4, and are remotely positioned of said transducers within the corresponding cylindrical clearances (156, 158). The ultrasonic waves emitted by one of said transducers propagate along a path in the form of V or W. The operation of such a meter where the path of the ultrasonic waves has a form in is for example explained in the EP patent -0,521,855.

It should be noted that the two transducers can also be arranged on the opposite wall (142b) of the measuring conduit or one of the transducers can remain on the wall (142a) and the other one is mounted facing the opposite wall (142b) so that the transducers are aligned according to a dummy line YY 'perpendicular to their active surfaces and that intersects the longitudinal axis XX' at an angle less than 90 ° (see Figure 12). It is also possible to use said configuration of the rectangular cross section duct with the enlarged portions containing the ultrasonic transducers disposed at the opposite ends of said duct.

Claims (6)

1 . A gas meter comprising an ultrasound measuring conduit of the longitudinal axis including an internal part in which the gas flows, at least two ultrasonic transducers spaced along the longitudinal axis, the meter comprises between each transducer and the internal part of the conduit measuring an enlarged portion relative to the dimensions of the active surface of the transducer, characterized in that the meter further comprises at least one element placed in at least one of the flared portions and extending over the entire internal width thereof, in a manner to form a filter mesh against the powders transported by the gas, the element is traversed by the ultrasonic waves emitted by the transducers over at least a part of its width that is greater than the dimensions of the active surface of the transducer.

2. The gas meter according to claim 1, wherein at least one element forming the filter mesh is placed against the transducer.

3. The gas meter according to claim 1, wherein at least one element forming the filter mesh is placed at a distance from the transducer.

4. The gas meter according to any of claims 1 to 3, wherein at least one element forming the filter mesh is placed in front of the upstream transducer.

5. The gas meter according to any one of claims 1 to 3, wherein at least one element forming the filter mesh is placed in front of the downstream transducer.

6. The gas meter according to any of claims 1 to 5, comprising at least one obstacle placed longitudinally in the internal part of the measuring conduit, so as to form at least one annular passage for the gas flow and for channeling the gas. flow of the powders at a distance from the ultrasonic transducers.