Process for purifying a gas

Abstract

Method for purifying a gas Method for purifying a gas by radiolysis of the impurities contained in the gas, the method comprising irradiating the gas with at least one electromagnetic and / or particulate radiation, the energy carried by at least one, preferably each, particle of the radiation being less than or equal to 300 keV. Figure for abstract: Fig. 1

Description

Title of the invention: Method for purifying a gas Technical field

[0001] The present invention relates to a method for purifying gases and gaseous effluents, in particular by electron beam. Prior art

[0002] The injection of biomethane (mixture of CH4 and various impurities) into existing transport and storage networks for use in industry or for private purposes requires controlling its impurity content down to levels of the order of ppm (i.e. parts per million). Such control is necessary to meet the requirements of current regulations and the additional requirements of the industrial user. To meet this need, the gas is treated during its circulation in a gas purification system which generally comprises several filtration stages.

[0003] Several existing biogas purification technologies allow the production of biomethane compatible with network specifications. Examples include water washing, amine washing and pressure reversal adsorption, which are technologies suitable for medium and large installations, as well as membrane purification, which is more suitable for small installations. The emergence of new biogas purification technologies is also observed, such as cryogenics, cold plasma-assisted catalysis or radiolysis.

[0004] Amine washing and cryogenics are, for example, technologies whose implementation is specific to high biogas flow rates, or highly polluted biogas and are poorly suited to the context of agricultural or territorial methanization. Water washing generally results in an enrichment of the gas in oxygen and nitrogen, and therefore in impurities. Membrane purification generally does not allow the separation of methane and nitrogen. Furthermore, membranes tend to foul, which limits the effectiveness of purification. Finally, adsorption by pressure inversion results in losses of methane, which is generally not desired during purification.

[0005] There are catalytic filtration systems in the literature, for example as described in Y. Lu et al., “Catalytic Removal of Oxygen and Pollutants in Exhaust Gases from Pressurized Oxy-Combustors” (2019), doi: 10.2172 / 1716839, but which have problems of stability over time. Such filtration systems are also generally sized for the most penalizing conditions. In addition, the catalysts equipping these filtration systems have limited lifespans due to the highly mixed nature of biogas. This purification process presents prohibitive costs for the methanization sector.

[0006] Currently, another known technology for depolluting gases uses one or more electron beams produced by accelerators. However, the energy of these electron beams, generally several MeV, is too high to interact effectively with dilute media such as gases. In addition, the use of this technology requires compliance with numerous constraints related to radiation protection.

[0007] Among the radiation sources that can activate gases (Gamma, X-rays, UV, electrons), accelerators are the least expensive. To date, decontamination by electron beams is only implemented in the world in a few rare large prototype plants, where the investment is justifiable.

[0008] The power in Watt (W) of the electron beam is related to the impurity concentration by the following formula: P > F*D*C / G*1.24*108, where: - D is the gas flow rate expressed in Nm' / h, - G is the radiolytic efficiency of the conversion expressed in Mol / J which depends on the pressure and temperature of the gas and the energy of the beam particles, - It is the concentration of impurities in the gas, expressed in ppm, - F, greater than 0 and less than 1, is the fraction of the beam energy of electrons absorbed in the gas.

[0009] This formula implies that a more energetic beam makes it possible to treat a greater thickness of gas. However, radiation protection requirements evolve almost exponentially depending on the beam energy, which makes it difficult to construct a facility capable of generating high-energy radiation.

[0010] There is therefore a need for a gas decontamination process which is simpler to implement than current processes, preferably without adding reagents, without injecting undesirable molecules, limiting gas losses through leaks, and which in particular can be operated in small-scale infrastructures. Statement of the invention

[0011] The subject of the invention is a method for purifying a gas by radiolysis of the impurities contained in the gas, the method comprising irradiation of the gas by at least one electromagnetic and / or particulate radiation, the energy carried by at least one, preferably each, particle of the radiation being less than or equal to 300 keV.

[0012] The invention thus provides a technical solution allowing general treatment of impurities in a gas, simple to implement by generating electromagnetic radiation and / or low-energy particulate radiation.

[0013] The invention makes it possible, by irradiating the gas with electromagnetic and / or particulate radiation, to trigger chemical reactions consuming the impurities contained in the gas. When the gas is a biomethane, the compounds thus produced by irradiation of the impurities, for example methanol and formic acid, are heavier than the biomethane before treatment by the process. They can therefore be isolated easily, for example by condensation or absorption.

[0014] The method according to the invention can be operated by means of a compact device, simple to use and maintain, unlike existing devices. For example, the device can be transferred from one installation to another, for example without disassembly and by simple conveyance with a handling machine.

[0015] The generation of low-energy electromagnetic and / or particulate radiation can make it possible to dispense with specific means of radiation protection. It also has the advantage that the particles thus exhibit a strong interaction with dilute media.

[0016] The gas to be purified may be stored and / or may flow in a container, for example a tank or a pipe. Radiation

[0017] The energy carried by said radiation particle is preferably between 1 eV and 300 keV, better between 1 eV and 100 keV, even better between 1 eV and 20 keV.

[0018] Said particle can be an electron or a photon.

[0019] The radiation may be emitted from at least one emission source selected from a continuous electron source, a pulsed electron source, an X-ray source, a gamma-ray source, a beta-ray source, an alpha-ray source, a UV-ray source, a VUV-ray source and a heavy ion source. Arrangement of the sources

[0020] The emission source may have a small size, being adapted to emit low-energy radiation. Advantageously, the method may comprise the emission of the radiation with several emission sources, for example arranged in a network, in particular in order to cover large treatment areas.

[0021] The radiation can be emitted by a network of emission sources, in particular a network comprising at least four emission sources, better still ten emission sources. The network of emission sources makes it possible to offer flexibility of use and energy efficiency better than existing solutions, which are often disproportionate.

[0022] Alternatively, the radiation may be emitted by a single emission source.

[0023] The radiation may be emitted from at least one emission source housed inside the container.

[0024] The radiation may be emitted from at least one emission source located outside the container. For example, in the variant where the radiation is emitted from several sources, said sources are arranged regularly around the pipe. Container

[0025] The wall of the container may be metallic and / or plastic. It may optionally be covered with a catalyst material.

[0026] The gas to be purified can flow in the pipe at a mass flow rate of between 1 Nm3 / h and 10000 Nm3 / h.

[0027] A cubic normometre Nm3 of the gas to be purified is equal to the volume that said gas to be purified would occupy at a temperature of 0°C and under a pressure of 101,325 Pa.

[0028] The container may have a circular cross-section. Alternatively, the container has a polygonal cross-section.

[0029] The container may have an internal diameter of between 0.01 m and 10 m. By internal diameter is meant the diameter of the smallest circle inscribed in the cross-section of the container. Gases and impurities

[0030] The impurities may belong to the group comprising dioxygen O2, siloxanes, hydrogen sulfide H2S, carbon dioxide CO2, VOCs (Volatile Organic Compounds), ammonia NH3, nitrogen N2, sulfur oxides SOX and nitrogen oxides NOX.

[0031] The gas may be chosen from a hydrocarbon, in particular methane, dihydrogen, a biogas, in particular from biomethanization, a gas from pyrogasification, and mixtures thereof.

[0032] The method according to the invention can make it possible to depollute gases in industrial or agricultural sites, at the chimney outlet for example, and / or to recover gases.

[0033] The method according to the invention may comprise the measurement of an impurity content in the gas, in particular by detection of X-rays emitted by the impurities under the action of the radiation and / or by analysis of a gas sample, for example by gas chromatography and / or by ion mobility spectrometry.

[0034] The method according to the invention may comprise the modulation of the power of the radiation as a function of the measurement of the impurity content in the gas.

[0035] The method according to the invention may include modulation of the power of the radiation as a function of the operating mode of the installation (continuous, intermittent, by cycle) and the gas flow rate.

[0036] The method according to the invention may include the purification of the gas by an additional device, in particular by a membrane.

[0037] The process can be coupled with existing purification processes based on other technologies (filtration, cold plasmas, etc.) Installation

[0038] The invention also relates to an installation, in particular for implementing the method, the installation comprising: - a container designed for the storage or flow of a gas, - at least one emission source, in particular one, arranged to emit electromagnetic and / or particulate radiation formed by at least one particle with an energy less than or equal to 300 keV and to irradiate the gas with said radiation, and - preferably a condensation device for collecting by condensation the compounds produced by the irradiation of the impurities contained in the gas by the radiation emitted by the source.

[0039] The emission source may be housed inside the container. Alternatively, the emission source is located outside the container.

[0040] The installation may comprise a plurality of radiation emission sources arranged to each emit at least one particle with an energy of less than or equal to 300 keV towards the gas.

[0041] The plurality of emission sources may be inside the container. Alternatively, the emission sources may be regularly arranged over an annular portion of the container.

[0042] The installation may include a first additional gas purification device, in particular a membrane.

[0043] The installation may include a second additional device for detecting the level of impurities in the gas. This second additional device makes it possible in particular to modulate the power of the radiation as a function of the level of impurities.

[0044] The second additional device may comprise a detector of X-rays emitted by the impurities, the emission being triggered by the irradiation of the impurities by electromagnetic and / or particulate radiation. Alternatively, the second additional device may be arranged to directly analyze the gas, in particular by ion mobility or gas chromatography. Brief description of the drawings

[0045] The invention may be better understood by reading the detailed description which follows, presented for illustrative and non-limiting purposes, and the attached drawing in which:

[0046] [Fig-1] illustrates a schematic and partial longitudinal section of an example installation according to the invention,

[0047] [Fig.2] illustrates a schematic and partial cross-section of four exemplary embodiments of the installation according to the invention,

[0048] [Fig.3] illustrates a longitudinal, schematic and partial section of an alternative embodiment of the installation illustrated in [Fig.l], and

[0049] [Fig.4] illustrates a schematic and partial cross-section of another example of installation according to the invention. Detailed description

[0050] [Fig.l] illustrates an installation 1 comprising a pipe 2 of gas G and a source 3 of electrons, configured to emit electromagnetic and / or particulate radiation in the direction of the gas G flowing in the pipe.

[0051] The wall 20 of the pipe 2 may be metallic and / or made of plastic. It may optionally be covered with a catalyst material.

[0052] The pipe has an internal diameter d preferably between 0.01 m and 10 m.

[0053] Source 3 emits electrons with an energy between 1 eV and 20 keV.

[0054] The source 3 may be a continuous or pulsed emission source. The source 3 is in particular photo-triggered, for example by laser or by LED, or by a VUV lamp.

[0055] The largest dimension L of the source 3 is for example between 5 mm and 100 mm, better between 20 mm and 50 mm.

[0056] By “largest dimension” is meant the diameter of the circle circumscribing the largest section of the source 3.

[0057] Gas G is for example a hydrocarbon, in particular methane, or dihydrogen. Alternatively, gas G is a biogas, in particular from biomethanization, or a gas from pyrogasification.

[0058] Impurities may be present in gas G. These include oxygen, siloxanes, hydrogen sulfide, ammonia, or volatile organic compounds, nitrogen, and sulfur and nitrogen oxides.

[0059] When the gas G passes in front of the source, the gas is irradiated by electromagnetic and / or particulate radiation, which induces one or more chemical reactions whose impurities are reactants and which produce compounds I.

[0060] The compounds I produced by the irradiation of the impurities are for example methanol, formic acid, acetic acid, water, or any oxidation product of methane. These compounds I are preferably heavier than the gas G and can therefore be insulated by condensation for example, in particular by means of a condensation device 7.

[0061] [Fig.2] illustrates four examples A, B, C and D of the installation 1 according to the invention, differing in their number of radiation sources 3 and their arrangement.

[0062] The electrons can be emitted from at least one network 33 of sources 3 housed inside the conduit 2, as illustrated in FIGS. 2B and 2D.

[0063] Alternatively, the electrons are emitted from at least one source 3 located outside the pipe 2, as illustrated in FIGS. 2A and 2C. The source 3 is, in these examples, preferably directly in contact with the pipe 2, in particular opposite it. The pipe comprises in particular a window for extracting the radiation towards the gas, not shown in the figures, said window providing an interface between the source 3 and the gas.

[0064] Figure 2A illustrates an exemplary embodiment of the installation 1 comprising a single source 3 located outside the pipe 2 and arranged to emit electrons directly towards the gas.

[0065] Figure 2B illustrates an exemplary embodiment of the installation 1 comprising two networks 33 of sources 3 housed inside the pipe 2, at the level of the same cross-section of the pipe 2. Each network 33 comprises for example two lines of eight sources 3, each source being oriented in the direction of the gas G, in the direction of the wall or a central zone of the pipe. The two lines of sources of each network 33 are preferably oriented in opposite directions. The alignments of the sources 3 in the two networks 33 are for example in the same direction.

[0066] Figure 2C illustrates an exemplary embodiment of the installation 1 comprising a plurality of sources 3, located outside the pipe 2, at the level of the same cross-section of the pipe 2. The sources 3 are preferably arranged in the form of a circle, on the periphery of the pipe 2. The sources 3 are oriented so as to emit electrons into the gas G. The sources 3 are preferably equally distributed around the pipe 2. The zones subjected to the radiation of at least two of said sources 3 are preferably at least partially superimposed. Preferably, at the level of the same cross-section of the pipe 2, the entire surface of the section is subjected to the radiation.

[0067] Figure 2D illustrates an exemplary embodiment of the installation 1 comprising a network 33 of sources 3 housed inside the pipe 2. The sources 3 of the network 33 are for example organized along a circle centered on the axis of extension of the pipe 2 and transverse to said axis, each source 3 being oriented to direct the beam that it emits according to a vector comprising a radial component and a orthoradial component, in the direction of the pipe wall, in the direction of gas G. Space A in the center of the circle is preferably empty of gas G, being used in particular for the electrical services of the sources.

[0068] In an alternative embodiment, the installation may include a measurement of the impurity content in the gas G. The installation may in particular include a detector 4 arranged to detect the X-rays emitted by the impurities irradiated by the electromagnetic and / or particulate radiation. The detector 4 is for example located outside the pipe 2, at the same cross-section as the source(s) 3. This detection makes it possible to modulate the power of the electromagnetic radiation as a function of the measurement of the impurity content in the gas G. Preferably, the detector 4 is in contact with the pipe and opposite it.

[0069] In another alternative embodiment, the installation comprises an additional gas purification device. [Fig. 4] thus illustrates an installation 1 according to the invention comprising a membrane 5 contributing to the purification of the gas G.

[0070] The membrane 5 extends for example over the entire length of the pipe 2 in one direction, and over the diameter of the pipe 2 in another direction. The membrane 5 is for example a material permeable to methane but not to CO2.

[0071] Numerous modifications can be made to the installation which has just been described, without departing from the scope of the present invention.

Claims

Claims

1. A method of purifying a gas by radiolysis of the impurities contained in the gas, the method comprising irradiating the gas with at least one electromagnetic and / or particulate radiation, the energy carried by at least one, preferably each, particle of the radiation being less than or equal to 300 keV.

2. A method according to claim 1, the electromagnetic and / or particulate radiation being emitted from at least one emission source selected from a continuous electron source, a pulsed electron source, an X-ray source, a gamma-ray source, a beta-ray source, an alpha-ray source, a UV-ray source, a VUV-ray source and a heavy ion source.

3. Method according to one of claims 1 and 2, the energy carried by said particle of the radiation being between 1 eV and 300 keV, better between 1 eV and 100 keV, even better between 1 eV and 20 keV.

4. Method according to any one of the preceding claims, comprising the emission of electromagnetic radiation with several emission sources, for example arranged in an array, the array comprising for example at least four emission sources, better still ten emission sources.

5. A method according to any one of claims 1 to 3, the electromagnetic radiation being emitted by a single emission source.

6. A method according to any one of the preceding claims, the gas to be purified being stored and / or flowing in a container, for example a tank or a pipe.

7. Method according to claim 6, the gas to be purified flowing in the pipe at a mass flow rate of between 1 Nm3 / h and 10000 Nm3 / h.

8. A method according to any one of the preceding claims, the impurities belonging to the group comprising dioxygen O2, siloxanes, hydrogen sulfide H2S, carbon dioxide CO2, volatile organic compounds, ammonia NH3, nitrogen N2, sulfur oxides SOX and nitrogen oxides NOX.

9. Method according to any one of the preceding claims, the gas being chosen from a hydrocarbon, in particular methane, dihydrogen, a biogas, in particular resulting from biomethanization, a gas resulting from pyrogasification, and their mixtures.

10. A method according to any one of the preceding claims, comprising measuring an impurity content in the gas, in particular by detecting X-rays emitted by the impurities and / or by analyzing a gas sample, for example by gas chromatography and / or by ion mobility spectrometry.

11. Installation for implementing the method according to any one of the preceding claims, the installation comprising: - a container shaped for the storage or flow of a gas, - at least one emission source arranged to emit electromagnetic and / or particulate radiation formed by at least one particle of energy less than or equal to 300 keV and to irradiate the gas with said radiation, and. - preferably, a condensation device (7) for collecting by condensation the compounds produced by the irradiation of the impurities contained in the gas by the radiation emitted by the source.

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