DEVICE FOR COLLECTING A SAMPLE OF ELEMENTS OF INTEREST PRESENT AS TRACES IN A COMPRESSED GAS

Description

Technical field

[0001] The present invention relates to a device for sampling elements of interest present in trace amounts in a gas such as natural gas or biogas circulating in a conduit. The device of the present invention is particularly suitable when the gas is packaged under high pressure. Prior art

[0002] Natural gas is one of the main commercial energy sources. The chemical composition of commercial natural gas mainly includes methane (70-90%), some hydrocarbons (7-11%), impurities (< 3-15%) and trace elements of interest. These trace elements can be metals such as mercury and / or organic compounds such as BTEX (benzene, toluene, ethylene and xylenes). Natural gas can circulate in a supply line. It can also be stored in reservoirs, generally underground.

[0003] Other forms of non-fossil fuel gas are also known, such as biogas, which can be processed to a chemical composition similar to that of natural gas. This treated biogas, also known as biomethane, can be injected into the supply network used for natural gas. As with natural gas, trace compounds, including metals, can also be found in biogas.

[0004] The chemical composition of natural gas and biogas must meet precise specifications to ensure gas quality. The presence of certain elements, even in trace amounts, can alter gas quality.

[0005] Trace elements such as mercury or one of the compounds listed above present in natural gas can also cause damage to industrial infrastructure. For example, mercury can be responsible for the corrosion of aluminum pipes. In addition, when these elements are present in particulate form, they can cause abrasion in pipes and pumps.

[0006] Finally, in addition to these industrial and infrastructure impacts, these metallic elements present even in trace amounts in natural gas or biogas can also have an impact on health if their concentration exceeds a certain threshold.

[0007] Given these industrial, environmental, and health constraints, it is important to be able to regularly determine the chemical composition of the gas and, in particular, to monitor the presence of trace elements in the gas in dissolved or particulate form. This not only provides information on the quality of the gas, but also allows us to predict a possible impact on the environment and therefore indirectly prevent health risks. In particular, it is important to determine the concentration of these elements before injecting the gas into the storage tank or distribution networks.

[0008] To regularly monitor the chemical composition of the gas, a sampling technique is used which involves taking a volume of gas from a production line or tank for subsequent chemical analysis by a suitable analyzer. An example of a gas sampling device is described in GB2538080A.

[0009] Sampling must meet certain criteria so that the samples are representative of the matrix from which they are taken. In addition, the samples must be free from any contamination or loss of elements studied. Thus, the sampling conditions must be adapted to the field conditions of the installations (distribution networks, storage tank) to avoid any loss of information. In the case of a pre-concentrated sampling or sampling device, the device must also be designed in a material that prevents pollution of the sample and respects the site conditions, for example ATEX conditions. In particular, the materials in contact with the fluid to be sampled must be adapted to avoid adsorption (retention of molecules) and desorption (release of molecules) phenomena that could alter the integrity of the sample taken.

[0010] In addition, the sampling device must be designed to ensure operator safety and environmental protection.

[0011] A well-known sampling system is used to collect gas under pressure using a sealed metal cylinder. The gas flows continuously through the cylinder, usually made of stainless steel. When sampling is complete, the gas flow is stopped by valves and the cylinder containing the sample is removed from the system to be transported to another site for analysis. The pressurized cylinder must be transported by an approved company. The main disadvantage of this technique is the impossibility of pre-concentrating the elements of interest, limiting the feasibility of measurements when they are present at very low concentrations (from the order of nanograms to hundreds of micrograms per cubic normo-meter). In addition, this technique requires a depressurization step during the transfer phase of the sampled gas to the analyzer, leading to a risk of loss of information.

[0012] Cachia et al. (Development of a high-pressure bubbling sampler for trace element quantification in natural gas, Energy Fuel 2017, 31, 4294-4300 ) describe a system designed to pre-concentrate at pressures ranging from 1 to 100 bar with a flow rate of up to 40 L / min metallic compounds present in trace amounts in a natural gas. As illustrated in figure 1, system 1 comprises a gas inlet A and a gas outlet B connected to the gas pipes and three bubblers 2, 3, 4 connected in series. The gas arrives at the inlet A of the system and first passes through a condenser 5 and a filter 6 in order to remove water and solid particles possibly present in the gas. Then, the gas circulates through three bubblers 2, 3, 4. A bubbler is a stainless steel cylinder inside which is placed a Teflon cylinder containing 50 mL of a trapping solution specific to the targeted metallic elements. For example, the solution for mercury can be a solution of 1%w permanganate and 5%w sulfuric acid. At the outlet of the bubblers, a pressure regulator 7 triggers the depressurization of the sampled gas to atmospheric pressure and a rotameter 8 counts the volume of the sampled gas. Technical problem

[0013] The prior art ogive sampling device allows for the collection of pressurized gas samples. However, this technique does not allow for pre-concentration of the elements, thus limiting the feasibility when these are present at concentrations in the order of nanograms to hundreds of micrograms per cubic meter. Such devices require a specific, complex and expensive installation. In addition, these sampling devices require that the analysis bench operates at the same pressure or involve the use of a regulator in order to supply the analyzer with a gas having an appropriate pressure. Transporting a pressurized sample requires the use of an approved carrier from the sampling site to the analysis site.

[0014] The bubble sampling system ( Figure 1) under high pressure allows this necessary pre-concentration of the sample, at the pressure of a network such as that in natural gas distribution pipes. However, such a system is difficult to clean due to an often unsuitable configuration (inaccessible dead volumes), which is not compatible with the search for traces. Furthermore, the implementation of such a system in the field is relatively complex due to the use of three bubblers. It has a significant footprint which does not facilitate its transport from one site to another or its installation in the field. Finally, the very principle of sampling by bubbling with a permanganate / sulfuric acid solution for mercury or nitric acid for other metallic compounds remains relatively complex to implement. The trapping solution also presents a risk for the cleanliness of the sampling system.

[0015] The present invention aims to propose a device and a method for taking a sample of elements of interest present in trace amounts in a gas under network conditions, in particular at network pressure, in order to avoid any loss of information. The device and the method must be simple to implement and reliable so that the sample collected is representative of the matrix from which it is taken. Furthermore, given the low element concentrations in natural gas, for example, the proposed device must allow pre-concentrated sampling of the elements of interest. In addition, the sample thus taken must require the least preparation before analysis in order to limit possible contamination and to preserve the integrity of the sample. Finally, the associated analysis technique must be easy to implement. Statement of the invention

[0016] A device is proposed for taking a sample of elements of interest present in trace amounts in a gaseous fluid, such as natural gas or biogas circulating under pressure in a conduit, said device comprises: a support comprising an inner wall delimiting a sealed housing, each of the ends of the support comprising a gaseous fluid passage orifice allowing the passage of the gaseous fluid; a tube arranged in the sealed housing and two ends, a medium for trapping elements of interest being arranged in the tube; holding means; the two ends of the tube being held in position in said housing by said holding means, the dimension of said housing being configured so that the outer wall of said tube and the inner wall of the support delimit an annular free space; said holding means and the arrangement of said tube in the sealed housing being configured to allow the passage of a portion of the gas into the free annular space when the gas enters the device in order to put the annular space at the same pressure as the interior of the tube.

[0017] The features set out in the following paragraphs may optionally be implemented. They may be implemented independently of each other or in combination with each other: the support comprises a first hollow body and a second hollow body, the two bodies being configured to be assembled together to form the sealed housing, the first hollow body comprises a first cavity extending between one end comprising a first gas passage orifice and a first opening, and the second hollow body comprises a second cavity extending between one end comprising a second gas passage orifice and a second opening, the first body comprises at the end of the first opening an external thread and the second body at the end of the second opening a complementary internal thread, at least one annular seal is arranged in a groove formed near one of the threads so that the screwed assembly of the two bodies forms a sealed housing,the holding means comprise at least one substantially tubular holding piece sized to be mounted on an open end of the tube and received in one end of the housing, a substantially tubular stop piece forming a bearing surface for the opposite open end of the tube and received in the opposite end of the housing, said stop piece having a passage putting the open end of the tube into communication with a gas passage orifice, the holding pieces are made of an inert and non-porous material, for example from the family of poly(aryletherketones).

[0018] According to an advantageous embodiment of the invention, when the tube is positioned in the housing, an open end of the tube bears against one end of the housing and faces a gas passage orifice and the other open end bears against a stop piece placed in the other end of the housing and faces the other gas passage orifice.

[0019] According to another advantageous embodiment of the invention, the first body comprises a first guide channel putting the gas passage orifice in communication with the open end of the tube and the second body comprises a second guide channel putting the other open end of the tube in communication with the second gas passage orifice (35).

[0020] According to one embodiment of the invention, the trapping medium is an adsorption trapping medium.

[0021] Preferably, the trapping medium is configured to trap elements of interest which are metallic elements selected from the group comprising mercury, arsenic, tin, aluminum, lead and titanium or volatile organic elements such as BTEX (benzene, toluene, ethylbenzene, xylene), polycyclic aromatic hydrocarbons (PAHs) and / or halogenated.

[0022] Advantageously, the device further comprises a valve connected to each of the ends of the support.

[0023] Advantageously, one of the gas passage orifices forms the gas inlet and the other gas passage orifice forms the gas outlet.

[0024] Another aspect of the invention relates to an installation for taking a sample of elements of interest present in trace amounts in a gas circulating under high pressure in a circuit, said installation comprising: a sampling device as defined above; a gas inlet valve; a gas supply circuit connecting the inlet valve to one end of the device; an outlet valve; a second gas discharge circuit connecting the outlet valve to the other end of the device; a gas discharge tank connected to the outlet valve; at least one pressure gauge for measuring the gas pressure circulating in the installation.

[0025] Another aspect of the invention relates to a method for taking a sample of elements of interest present in trace amounts in a gas circulating under high pressure in a circuit comprising the following steps: connecting the sampling device as defined above to the gas circulation circuit; circulating the gas through the adsorption medium for a determined period; interrupting the gas circulation; evacuating the gas to an evacuation tank; removing the tube from its support to carry out the analysis of the sample taken.

[0026] According to one embodiment of the invention, the gas circulates under a pressure of between 1 and 1000 bars, preferably between 3 and 300 bars. Brief description of the drawings

[0027] Other characteristics, details and advantages of the invention will appear on reading the detailed description below, and on analyzing the attached drawings, in which: Fig. 1 [ Fig. 1 ] shows a schematic view of a device for sampling elements of interest present in trace amounts in a pressurized gas according to the state of the art; Fig. 2 [ Fig. 2 ] shows an exterior view of a device for taking a sample of elements of interest present in trace amounts in a pressurized gas according to the invention; Fig. 3 [ Fig. 3 ] shows a sectional view along a section plane AA of the figure 2 ; Fig. 4 [ Fig. 4 ] shows a schematic view of an installation comprising a device for taking a sample of elements of interest from the figure 3 . Description of the embodiments

[0028] The drawings and the description below contain, for the most part, elements of a certain character. They may therefore not only serve to better understand the present invention, but also contribute to its definition, if necessary.

[0029] In this application, the term “gas” will be used to designate “natural gas” or biogas or any other gaseous matrix.

[0030] In the case of natural gas, the gas undergoes several stages from its geological reservoir to the place of consumption. These stages are production, processing, transportation, storage if necessary, and finally distribution. In the case of biogas, the stages are production, processing, transportation, and distribution. During these different stages, it is essential to determine the chemical composition of the gas such as natural gas or biogas, in particular to determine the content of the elements of interest present in trace amounts in the gas.

[0031] There figure 2 and the figure 3 illustrate a device for taking a sample of elements of interest 10 according to one embodiment of the invention.

[0032] Elements of interest can be metallic elements such as mercury, tin, arsenic, lead, or aluminum. They can also be organic compounds such as BTEX (benzene, toluene, ethylbenzene, xylene). They can also be polycyclic aromatic hydrocarbons (PAHs) and halogenated hydrocarbons. These elements are, for example, dissolved in the gas or present as particles in the gas.

[0033] The device 10 comprises a support 11, the internal wall of the support delimiting a sealed housing, and a tube 40 comprising a trapping medium 41 for the elements of interest held in position in the sealed housing.

[0034] Preferably, the trapping medium is an adsorption trapping medium for adsorbing the elements of interest.

[0035] For the sake of simplicity, the adsorption trapping medium will be referred to in the remainder of the description as “the adsorption medium”.

[0036] The support 11 has a substantially cylindrical shape oriented along a main axis xx. Each of the ends of the support comprises a passage orifice 25, 35 to allow the circulation of gas through the trapping medium contained in the tube.

[0037] According to a preferred embodiment as illustrated in the figure 4 , each of the ends of the device 10 is connected directly to a stop valve 103, 104. Thus, during the operation of taking a sample, the mounting of the device on a gas circulation circuit consists of connecting the two valves to the connectors present on the circuit. At the end of the sample taking operation, the two valves are closed to be able to remove the device from the gas circulation circuit.

[0038] According to one embodiment, the support 11 comprises a first substantially cylindrical hollow body 20 and a second substantially cylindrical hollow 30. The first hollow body 20 comprises one end comprising a first gas passage orifice 25 and a first cavity. The second hollow body 30 comprises one end comprising a second gas passage orifice 35 and a second cavity. When the two bodies are assembled and the two ends of the support are closed, the two cavities form a sealed housing.

[0039] The first cavity has a substantially cylindrical shape which extends along the axis xx between an opening and a gas passage orifice 25. The bottom of the first cavity comprises a hole 26 which communicates with the gas passage orifice 25 via a guide channel 24.

[0040] Preferably, the section of the gas passage orifice 25 is greater than the section of the hole 26. The section of the hole 26 may be greater than or equal to the section of the guide channel 24. In the embodiment illustrated in the figure 3 , the guide channel 24 is in the form of a funnel comprising a straight part and a cone, the straight part being oriented towards the hole 26 and the cone towards the gas passage orifice 25.

[0041] The first cylindrical hollow body 20 comprises at the end of the opening a neck 27. A portion of the external wall of the neck is provided with an external thread 22.

[0042] The second cavity of the second hollow body 30 has a substantially cylindrical shape which extends along the axis xx between an opening and a gas passage orifice 35. The bottom of the second cavity comprises a hole 36 which communicates with the gas passage orifice 35 via a guide channel 34.

[0043] Preferably, the section of the gas passage orifice 35 is greater than the section of the hole 36. The section of the hole 36 may be greater than or equal to the section of the guide channel 34. In the embodiment illustrated in the figure 3 , the guide channel 34 is in the form of a funnel comprising a straight part and a cone, the straight part being oriented towards the hole 36 and the cone towards the gas passage orifice 35.

[0044] As illustrated by the figure 3, the second cavity comprises a first chamber having a first internal diameter D1 and a second chamber having a second internal diameter D2. The diameter D1 is adjusted relative to the external diameter of the neck 27 of the first cylindrical body to receive the neck in the first chamber, the internal wall of this first chamber being provided with an internal thread 32 which cooperates with the external thread 22 of the neck 27 to assemble the first body with the second body by screwing. When the two bodies are assembled together, the first cavity and the second cavity together define the housing intended to receive the tube 40.

[0045] According to the example illustrated on the figure 3, the length of the neck 27 of the first body is defined so that when the neck is introduced into the second cavity of the second body, the end 28 of the first body does not bear against the bottom 38 of the first chamber of the second body, thus defining a free annular space 31. According to another embodiment of the invention, the end 28 of the first body bears against the bottom 38 of the first chamber of the second body.

[0046] According to the invention, the housing formed by the two cavities is a sealed housing in order to be able to take the sample under the conditions of circulation of the gas in the circuit, and in particular under high pressure, generally between 1 and 1000 bars, and preferably between 3 bars and 300 bars.

[0047] According to the example illustrated on the figure 3, the neck 27 is provided with an annular groove in which a first sealing ring 60 is received. The internal diameter D1 of the first chamber of the second body is adjusted relative to the external diameter of the neck so that when the neck is engaged in the first chamber and held by thread in the first chamber, the sealing ring 60 is compressed radially between the internal wall of the first chamber and the bottom of the groove to achieve sealing.

[0048] According to a variant not illustrated, the internal wall of the first chamber is provided with an annular groove in which a first sealing ring 60 is received. The internal diameter D1 of the first chamber of the second body is adjusted relative to the external diameter of the neck so that when the neck is engaged in the first chamber and held by thread in the first chamber, the sealing ring 60 is compressed radially between the internal wall of the first chamber and the bottom of the groove to seal the housing.

[0049] According to a form illustrated on the figure 3 , the device comprises a second sealing ring 61 mounted on the neck 27, close to the thread to reinforce the sealing of the housing.

[0050] According to the invention, the tube 40 comprises an adsorption medium 41. The tube comprises a first open end forming a gas supply orifice and a second open end forming a gas discharge orifice.

[0051] According to the example illustrated on the figure 3 , when the tube is positioned in the sealed housing, the first open end 43 of the tube is opposite the gas passage orifice 25 of the support and the second open end 44 is opposite the gas passage orifice 35 of the support.

[0052] The tube is made of glass, for example. The adsorption medium has a surface covered with an adsorbent phase adapted to the elements of interest to be adsorbed. Preferably, the medium has a large surface area to volume ratio in order to effectively adsorb unwanted elements.

[0053] For example, in the case of mercury sampling, the adsorption tube consists of a quartz tube inside which is placed a mixture of sand and gold particles to trap the mercury. The latter has the property of amalgamating on the gold at room temperature and being released at high temperature. After the sampling phase, the device is disconnected from the gas supply circuit and the tube is removed from its support to be analyzed by a known technique. More precisely, the tube is first heated to 500 °C to release the mercury adsorbed during trapping. The quantification of the mercury was then carried out by atomic fluorescence spectrometry.

[0054] According to an essential technical characteristic of the invention, the tube has an external diameter smaller than the internal diameter of the housing so that when the tube is arranged in the housing, the external wall of the tube and the internal wall of the support delimiting the sealed housing delimit an annular free space 21.

[0055] To be able to delimit this annular space 21, the device further comprises holding means 50, 51, 52 for holding the tube in position in the housing.

[0056] According to the example illustrated on the figure 3, the holding means comprise a first holding part 50 and a second holding part 51. The two parts have a substantially tubular shape. Their internal diameter is adjusted relative to the external diameter of the tube so that the two parts can be mounted on one end 44 of the tube. The external diameter of the two parts 50, 51 is adjusted relative to the internal diameter D2 of the second chamber of the second hollow body 30 so that it can be received in the second chamber by insertion. The end 44 is held in position in the housing. Thus the tube is locked in position by means of these two parts in the housing formed by the two cavities.

[0057] Advantageously, the holding parts further comprise a substantially tubular stop part 52 forming a bearing surface for the opposite end 43 of the tube. The external diameter of the stop part is adjusted relative to the internal diameter of the cavity of the first hollow body 20 so that the part is received in the bottom of the cavity of the first cylindrical body 20. The stop part 52 comprises a passage 53 putting the open end 43 of the tube into fluid communication with the gas passage orifice 25. The end of the tube 43 abuts against the stop part 52 which thus forms a safety interface for the glass tube so that the end of the tube 43 cannot come into direct contact against the bottom of the first cylindrical body which is made of stainless steel, to thus limit the risk of rupture of the tube under the effect of the gas pressure.

[0058] Ensuring that the tube is held in position in the housing by the two ends 43, 44 makes it possible to limit the risks of breaking the tube when handling the device, for example when installing or removing it from a fluid line. These holding parts make it possible to position the tube in the housing simply and easily. Finally, holding the two ends of the tube makes it possible to avoid the risk of ejection of the adsorbent tube when the gaseous fluid circulation valve is opened too abruptly.

[0059] Preferably, the holding parts 50, 51 and the stop part 52 are made of an inert and non-porous material, from the family of poly(aryletherketones) (PAEK), such as PEEK (poly(phenylene ether-ether-ketone)).

[0060] According to one embodiment of the invention as illustrated in the figure 3, the device comprises a third sealing ring 62 sized to be mounted on the tube, interposed between the two holding pieces 50, 51. The internal diameter of the sealing ring 62 is adjusted relative to the external diameter of the tube so that the ring 62 can be mounted on one end 44 of the tube. The external diameter of the sealing ring is adjusted relative to the internal diameter of the housing of the support so that it can be received in the housing by insertion. The sealing ring therefore has the function on the one hand of participating with the two holding pieces 50, 51 in holding one end of the tube in position and on the other hand of forcing the circulation of the gas in the tube to prevent it from circulating in the annular space around the tube when the gas enters the device.In this way, when for example, the gas passage orifice 35 forms the gas inlet and the gas passage orifice 25 forms the gas outlet, the presence of the sealing ring 62 forces the gas when it enters the device to first circulate in the tube through the adsorption medium 41 before a part of the gas passes into the free annular space 21 to achieve pressure balancing between the annular space 21 and the interior 42 of the tube.

[0061] According to a particularly advantageous form of the invention, the dimension of the housing is adapted so that when the tube is positioned in the housing, the first end of the tube 43 bears against the stop piece 52 placed in the bottom of the first cavity of the first cylindrical body 20 and the other end 44 bears against the bottom of the second cavity. The housings are dimensioned so as to be able to use tubes existing on the market and having standard dimensions.

[0062] The annular space 21 defined between the outer wall of the tube 40 and the inner wall of the support 11 advantageously has a very small volume, of a few milliliters, thus allowing simple and risk-free degassing during extraction of the adsorbent tube for analysis at ambient conditions.

[0063] According to a particularly advantageous embodiment, when the tube 21 is placed in the housing, the two open ends 43, 44 of the tube are positioned respectively opposite the first guide channel 24 and the second guide channel 34. Thus, the open end of the tube 43 is in direct fluid communication with the gas passage orifice 25 via the first guide channel 43 and the other open end of the tube 44 is in direct fluid communication with the passage orifice 35 via the second guide channel 34. This specific configuration makes it possible to ensure a more directional circulation of the gaseous fluid in the tube.

[0064] So when the tube is positioned in the housing and according to the example illustrated on the figure 3, the gas enters through the gas passage orifice 35, then successively passes through the guide channel 34, the interior of the tube passing through the adsorption medium 41, the passage 53 of the stop piece, the guide channel 24 and exits through the gas passage orifice 25. The gas which enters the device first passes into the tube then a part of this gas enters the annular space to balance the pressure on either side of the wall of the tube.

[0065] According to another form of operation, the gas enters through the gas passage orifice 25, then successively passes through the guide channel 24, the passage 53 of the stop piece, the interior of the tube passing through the adsorption medium 41, the guide channel 34 and exits through the gas passage orifice 35. When the gas enters the device, part of the gas enters the interior of the tube and another part of the gas passes immediately into the annular space to balance the pressure on either side of the wall of the tube.

[0066] Preferably, the section of the open ends 43, 44 of the tube is greater than or equal to the section of the passage 53 and the hole 36 respectively.

[0067] There figure 4 illustrates an example of an installation 100 comprising a device 10 for taking a sample of elements of interest present in trace amounts in a gas according to the invention.

[0068] The installation comprises a gas supply valve 101 and a gas discharge valve 102, a first gas supply circuit 105 connecting the inlet valve 101 to one end forming the gas inlet of the sampling device 10 via a connector 108 and a second gas discharge circuit 106 connecting the outlet valve 102 to the other end forming the gas outlet of the device 10 via a second connector 109. During operation of the installation, the inlet valve is connected to the gas circulation circuit and the outlet valve is connected to a discharge tank. The gas therefore circulates from the inlet valve 101 to the outlet valve 102 via the adsorption medium 41 of the device 10. On the figure 4, the direction of gas flow is indicated by the arrows. The gas, after passing through the adsorption medium, is discharged into the tank. During operation, the elements are extracted from the gas by adsorption and are concentrated in the adsorption medium.

[0069] The duration of this adsorption phase is for example between 1 minute and several days, depending on the element of interest, the type of gas, the pressure and the absorbance. When a sufficient quantity of gas has been treated, the inlet valve 101 is then closed to initiate the purge phase. Once the purge phase is complete, the valves 103 and 104 are closed so that the device can be removed from the installation.

[0070] Preferably, the installation comprises at least one pressure gauge 107 for measuring the gas pressure flowing in the installation. The pressure gauge is arranged at the gas inlet. The installation further comprises a flow meter 110, between the gas inlet valve of the installation and the gas inlet of the device.

[0071] In the illustrated example of the figure 4 , the ends of the device are equipped with a stop valve 103, 104 which close the gas passage orifices of the device. Thus the device can be a separate module which can be ready to be used by the installation and portable. In addition, by having a portable module, it is possible to have several modules, each being equipped with an adsorption medium specific to an undesirable element to be quantified.

[0072] The operation of installation 100 is described below.

[0073] In the sample collection position, the four valves are in the open position so that the gas circulates under pressure in the installation circuit from the inlet valve 101 to the outlet valve 105 through the device 10.

[0074] When sampling is complete, valve 101 of device 10 is closed, which isolates the device from the supply line. Valves 103, 104 and 102 remain open to purge the gas. Once the purging phase is complete, valves 103, 104, and 102 are closed and the device can be removed from the installation.

[0075] The support is then opened by unscrewing the two cylindrical bodies to extract the adsorption tube for analysis of the sample taken. Industrial application

[0076] The invention applies to all gases and more particularly to natural gas or biogas circulating under pressure in a circuit thanks to a pressure balancing support which makes it possible to subject an adsorption tube which conventionally operates at atmospheric pressure to a high pressure.

[0077] Such an adsorption tube is particularly suitable for extracting elements of interest such as metallic elements or volatile organic compounds present in trace amounts in a gas such as natural gas or biogas.

Claims

1. A device (10) for collecting a sample of elements of interest present as traces in a gaseous fluid circulating under pressure in a pipe, said device comprises: - a support (11) comprising an internal wall delimiting a sealed compartment, each of the ends of the support including a gaseous fluid passage orifice (25, 35) enabling the passage of the gaseous fluid; - a tube (40) arranged in the sealed compartment, a medium (41) for trapping elements of interest being arranged in the tube; - holding means (50, 51, 52); characterised in that: - the two ends (43, 44) of said tube (40) being held in position in said compartment by said holding means (50, 51, 52), the dimension of said compartment being configured so that the external wall of said tube and the internal wall of the support delimit an annular free space (21); - said holding means (50, 51, 52) and the arrangement of said tube in the sealed compartment being configured to enable the passage of a portion of the gas in the free annular space (21) when the gas enters the device in order to set the annular space (21) at the same pressure as the inside (42) of the tube.

2. The device according to claim 1, wherein the support (11) comprises a first hollow body (20) and a second hollow body (30), the two bodies being configured to be assembled together to form the sealed compartment.

3. The device according to claim 2, wherein the first hollow body (20) comprises a first cavity extending between an end including a first gas passage port (25) and a first opening, and the second hollow body (30) comprises a second cavity extending between an end including a second gas passage orifice (35) and a second opening.

4. The device according to claim 2 or 3, wherein the first body comprises at the end of the first opening an external thread (22) and the second body at the end of the second opening a complementary internal thread (32), at least one annular sealing gasket (60, 61) is arranged in a groove formed proximate to one of the threads so that the screwed assembly of the two bodies forms a sealed compartment.

5. The device according to one of claims 1 to 4, wherein the holding means comprise at least one substantially tubular holding part (50, 51) sized so as to be mounted on an open end (44) of the tube (40) and received in one end of the compartment, a substantially tubular stop part (52) forming a bearing surface for the opposite open end (43) of the tube and received in the opposite end of the compartment, said stop part (52) having a passage (53) setting the open end (43) of the tube in communication with a gas passage orifice (25).

6. The device according to claim 5, wherein the holding parts (50, 51, 52) are made of an inert and non-porous material of the polyaryletherketone (PAEK) family.

7. The device according to one of claims 1 to 6, wherein when the tube is positioned in the compartment, an open end (44) of the tube bears against one end of the compartment and opposite a gas passage orifice (35) and the other open end (43) bears against an stop part (52) placed in the other end of the compartment and opposite the other gas passage orifice (25).

8. The device according to claim 2 and one of claims 3 to 7, wherein the first body (20) comprises a first guide channel (24) setting the gas passage orifice (25) in communication with an open end (43) of the tube and the second body (30) comprises a second guide channel (34) setting the other open end (44) of the tube in communication with the second gas passage orifice (35).

9. The device according to one of claims 1 to 8, wherein the trapping medium (41) is an adsorption trapping medium.

10. The device according to one of claims 1 to 9, wherein the trapping medium (41) is configured to trap elements of interest which are metal elements selected from the group comprising mercury, arsenic, tin, aluminium, lead and titanium or volatile organic elements such as BTEX (benzene, toluene, ethylbenzene, xylene), polycyclic aromatic hydrocarbons (PAHs) and / or halogenated hydrocarbons.

11. The device according to one of claims 1 to 10 further comprising a valve (103, 104) connected at each of the ends (27, 37) of the support (11).

12. The device according to one of claims 1 to 11, wherein one of the gas passage orifices forms the gas inlet and the other gas passage orifice forms the gas outlet.

13. A facility (100) for collecting a sample of elements of interest present as traces in a gas circulating under high pressure in a circuit including: - a collection device (10) according to one of the claims 1 to 12; - a gas inlet valve (101); - a gas supply circuit (105) connecting the inlet valve to an end of the device; - an outlet valve (102); - a second gas evacuation circuit (106) connecting the outlet valve to the other end of the device; - a gas evacuation tank connected to the outlet valve; - at least one pressure gauge (107) for measuring the pressure of the gas circulating in the facility.

14. A method for carrying out a collection of a sample of elements of interest present as traces in a gas circulating under high pressure in a circuit comprising the following steps: - connecting the collection device according to one of claims 1 to 12 to the gas circulation circuit; - circulating the gas through the adsorption medium (41) for a determined duration; - interrupting the gas circulation; - evacuating the gas towards an evacuation tank; - removing the tube from its support to carry out the analysis of the collected sample.

15. The method according to claim 14, wherein the gas circulates under a pressure comprised between 1 and 1,000 bar, preferably between 3 and 300 bar.