Device, kit and method for purifying a gas predominantly comprising methane

Abstract

The invention relates to a device (100) for purifying a gas comprising methane, the device comprising: - a methanisation reactor (101) comprising: - a dioxygen inlet (104), - a means (105) for regulating the dioxygen flow rate, and - a gas outlet (107); - a purification reactor (111) comprising: - a bed (112) of iron hydroxide, - an inlet (110) for the gas connected to the outlet of the methanisation reactor, and - a purified gas outlet (115); - a sensor (108) for sensing a dioxygen concentration of the gas; - a programmable logic controller (118) that sends a command for regulating the dioxygen flow rate on the basis of the sensed dioxygen concentration.

Description

[0001] DESCRIPTION

[0002] TITLE OF THE INVENTION: DEVICE, KIT AND METHOD FOR PURIFYING A GAS COMPRISING MAJORITY IN METHANE

[0003] TECHNICAL FIELD OF THE INVENTION

[0004] The present invention relates to a device, a kit, and a method for purifying a gas consisting mainly of methane. It applies, in particular, to the purification of biomethane and its preparation for injection into a natural gas network, especially with regard to the concentration of hydrogen sulfide (H2S) and oxygen (O2) in the purified gas.

[0005] STATE OF THE ART

[0006] The most economical existing solutions for removing H2S rely on staged purification. Other solutions exist for large-volume methanization units using, for example, biological absorber-neutralizers ("scrubbers") or adsorption with modulated pressure, under vacuum or not.

[0007] A staged treatment process comprises primary and secondary treatment. Primary treatment, carried out by micro-aeration, consists of injecting oxygen-enriched air directly into the gas heads of the biogas reactors, also called digesters. At this point, a biochemical reaction occurs on desulfurization nets: a bacterial flora metabolizes H₂S in the presence of Û₂ to form elemental sulfur directly on these nets. The sulfur accumulates on these nets and then falls into the digesters where it is eliminated with the digestate. Primary treatment does not reduce the H₂S concentration in the gas exiting the biogas reactor to levels compatible with injection into a methane or natural gas network.

[0008] Secondary or complementary purification is mainly carried out by adsorption processes on activated carbon. The biogas stream to be purified from primary purification passes through a bed of adsorbent made up of activated carbon in the form of granules or powders; the H2S is captured by these activated carbons and the outgoing gas is therefore completely free of this harmful compound (this purification technology makes it possible to obtain ultra-purity levels if implemented correctly).

[0009] The most economical solution for removing H2S, micro-aeration, requires the addition of oxygen, which is undesirable in biogas. This oxygen addition raises quality issues, as the Û2 molecule is difficult to remove from a biogas stream without resorting to costly solutions.

[0010] Furthermore, micro-aeration does not reduce H2S to sufficiently low concentration levels to meet the technical specifications for injection into a natural gas network. Additional purification is necessary to achieve sufficient purity levels; this additional purification is currently carried out primarily through adsorption on activated carbon.

[0011] This additional purification is much more expensive than primary purification, which only requires the addition of enriched oxygen to the digester's air head. Here, the activated carbons are progressively saturated with residual H2S from the primary purification stream. Once the activated carbon is saturated and the H2S is transformed into elemental sulfur by a chemical reaction within the activated carbon bed, it must be replaced. This represents significant costs for raw materials, waste management, transportation, and process interruption when multiple activated carbon filters are not operating in parallel.

[0012] For economic reasons, digester operators therefore have an incentive to promote primary purification by injecting excess oxygen in order to limit the H2S concentration upstream of the secondary purification stage, thereby extending the lifespan of the activated carbon and increasing its performance. Indeed, activated carbon is more effective when excess oxygen is injected. However, these operating methods raise issues related to the increased oxygen content in the injected biomethane, sometimes reaching levels of several thousand ppm, which are incompatible with certain applications sensitive to the presence of this molecule.

[0013] Existing solutions for removing H2S are inexpensive and effective, but they require the addition of excess oxygen to the biogas, which ultimately ends up in the biomethane. Unfortunately, oxygen is a harmful compound for certain uses of biomethane, while also complicating methane extraction and storage, particularly in aquifers. Examples of uses where oxygen is a harmful compound include combined cycle power plants, certain furnaces, and some "raw material" applications, notably the production of ammonia by methane reforming.

[0014] Other FkS purification technologies exist, but they are currently used very little in the biomethane sector for economic reasons. For example, these processes include biological scrubbers, water scrubbing, scrubbing with alcohols, amines or solvents, biological processes, sacrificial chemical deoxygenation (scavenging), and catalytic reactions.

[0015] The gradual injection of biomethane into the networks could lead to disruption of certain processes due to the increasing concentration of dioxygen in the networks.

[0016] To anticipate these future limitations, it is necessary to have technological building blocks to remove this residual oxygen or to develop alternative H2S purification methods that limit or eliminate the need to resort to injecting O2 into digesters.

[0017] We know of Chinese patent application CN 107 899 384, US patent application US 2018 / 298 298 and US patent application US 20211221755 which disclose prior art.

[0018] SUMMARY OF THE INVENTION

[0019] The present invention aims to remedy all or part of these drawbacks.

[0020] To anticipate future limitations, it is necessary to have technological building blocks to remove residual oxygen or to develop alternative H2S purification methods that limit or eliminate the need to resort to injecting Û2 into digesters.

[0021] In particular, the present invention allows the use of an adsorbent bed that is continuously regenerated by the components to be purified in the gas. This therefore provides a less expensive purification solution, which is easier to manage, requires less frequent changes to the adsorbent bed, and limits the amount of oxygen injected into the network.

[0022] Furthermore, the solution can be adapted as a kit for existing installations currently using activated carbon. In particular, it is possible to modernize ("retrofit" in English) existing installations without changing the installed biogas and wastewater treatment reactors.

[0023] BENEFITS PROVIDED

[0024] The present invention aims to remedy all or part of the drawbacks of the prior art described above.

[0025] According to a first aspect, the present invention relates to a device for purifying a gas consisting mainly of methane, the device comprising:

[0026] - at least one methanization reactor comprising:

[0027] - an influx of dioxygen,

[0028] - a means of regulating the flow rate of dioxygen injected into the methanization reactor by the dioxygen inlet and

[0029] - a gas outlet consisting mainly of methane and at least some hydrogen sulfide,

[0030] - at least one purification reactor comprising: - an iron hydroxide bed,

[0031] - a gas inlet consisting mainly of methane and at least hydrogen sulfide connected to the outlet of the methanization reactor and

[0032] - a purified gas outlet consisting mainly of methane

[0033] - a first sensor for the concentration of dioxygen in the gas circulating between the outlet of the methanization reactor and the inlet of the gas in the purification reactor;

[0034] - a control system including a means of sending a command by means of regulating the flow of dioxygen injected into the methanization reactor according to the concentration of dioxygen captured.

[0035] Thanks to these arrangements, a feedback loop is implemented based on the composition of the gas exiting the methanation reactor. Such a feedback loop produces a synergistic effect and allows the purification reactor to operate within an optimal concentration range to minimize H2S and O2 exiting the purification reactor by varying the O2 injection rates during primary purification.

[0036] Furthermore, using iron hydroxide instead of activated carbon reduces the cost of the system while providing comparable or even superior H2S adsorption capacities to activated carbon. Iron hydroxide is also readily available commercially. The advantage of iron hydroxide compounds compared to activated carbon is their ability to remove some of the residual oxygen from the primary treatment stage, in addition to their excellent H2S capture capacity. H2S reacts with iron oxides to form iron sulfides. These iron sulfides then react with residual oxygen to regenerate the iron oxides. Elemental sulfur is trapped in the adsorbent bed.

[0037] Furthermore, residual oxygen, usually considered an "undesirable" compound at the outlet of primary treatment (i.e., the methanation reactor), plays a beneficial role here, as it allows for the continuous regeneration of the adsorbent bed. The lifespan of the iron hydroxide bed is thus greatly extended while consuming the residual oxygen for regeneration. Iron sulfides are formed into iron oxides, which are then available again to capture I-kS. The oxygen concentration in the biogas stream exiting the treatment reactor is therefore significantly reduced. Continuous regeneration of the bed is advantageous because it prevents the formation of hot spots that can occur with sequential regeneration. The present invention makes it possible to avoid significant temperature gradients in the iron hydroxide bed.

[0038] Field tests have shown that it is possible to use these iron oxides for H2S purification directly in place of activated carbon in reactors dedicated to activated carbon. These tests demonstrated, for the site in question, that iron salts are more competitive than activated carbon for the specific removal of H2S. Indeed, 400 kg of iron oxides were able to remove as much H2S as 1000 kg of activated carbon over an equivalent operating period, with an oxygen content injected into the reduced networks of approximately 40%. Furthermore, laboratory tests have shown that it is possible to achieve at least 95% oxygen removal with the device that is the subject of the present invention.

[0039] The performance achieved is sufficient to allow for effective sulfur removal without substantial modifications to existing installations, resulting in economic gains coupled with increased oxygen removal performance. This makes it possible to operate the production site with lower oxygen levels and reduced operating costs. This is the case in the present invention, where the oxygen level at the inlet of the methanation reactor is adjusted to modernize existing installations.

[0040] In some embodiments, the device of the present invention further comprises a first sensor for the hydrogen sulfide concentration of the gas circulating between the outlet of the methanization reactor and the gas inlet of the purification reactor, and wherein a control unit comprises: - a means for calculating a ratio between the concentration of oxygen captured and the concentration of hydrogen sulfide captured and

[0041] - a means of sending a command by means of regulating the flow of dioxygen injected into the methanization reactor according to the calculated ratio.

[0042] Thanks to these arrangements, the amount of oxygen is adjusted according to the amount of hydrogen sulfide which depends on the organic matter placed in the methanization reactor.

[0043] In some embodiments, the control system includes a means of comparing the calculated ratio to a first predetermined limit ratio called the "lower ratio", and when the calculated ratio is lower than the lower ratio, the control system includes an instruction to increase the flow rate of dioxygen injected into the methanization reactor.

[0044] In some embodiments, the control system includes a means of comparing the calculated ratio to a second predetermined limit ratio called the "upper ratio", and when the calculated ratio is greater than the upper ratio, the control system includes an instruction to reduce the flow rate of dioxygen injected into the methanization reactor.

[0045] Thanks to these provisions, it is possible to adapt the flow rate of dioxygen injected into the methanization reactor to maintain a ratio between the concentration of dioxygen and the concentration of hydrogen sulfide within a predetermined range of values ​​for which the purification in the purification reactor is most efficient and the iron hydroxide bed regenerates continuously, simultaneously with the adsorption of hydrogen sulfide, in the same bed.

[0046] In some embodiments, the purification device further comprises a second sensor for the concentration of dioxygen in the gas flowing out of the purification reactor and in which the command sent by the control means is further based on the concentration of dioxygen captured by the second sensor.

[0047] These measures allow for the detection of potential malfunctions in the automated system and / or the oxygen flow control system. Furthermore, before injection into a network, it is possible to recirculate a portion of the gas to obtain a purer gas and reduce oxygen consumption.

[0048] Indeed, an oxygen concentration sensor for the gas flowing out of the wastewater treatment reactor, in addition to the inlet sensor, allows for a comparison of the oxygen content upstream and downstream and the establishment of an oxygen mass balance. In steady state, that is, when the stable concentrations of H2S and O2 are stable in the gas entering the wastewater treatment reactor, the reactor captures a certain mass flux of H2S and O2, which are generally stable. If the mass flux captured by the wastewater treatment reactor changes, this provides information about what is happening within the reactor. The captured mass flux is obtained by subtracting the O2 concentration from the O2 concentration at the reactor outlet from the O2 concentration at the inlet.

[0049] For example, if the oxygen mass flow rate at the outlet of the purification reactor increases, and the H2S mass flow rate also increases, it likely means the bed is saturated, or, if the bed has just been changed, that the reactor is too small to handle these flows. Similarly, if the O2 flow rate increases and the H2S flow rate decreases at the outlet of the purification reactor, it probably means too much O2 is being injected, and conversely, if the H2S flow rate increases and the O2 flow rate decreases. This second level of control allows the controller to confirm or deny that the primary feedback is functioning correctly.

[0050] In some embodiments, the purification device further comprises a second sensor for the concentration of hydrogen sulfide in the gas flowing out of the purification reactor and in which the command sent by the control means is further based on the concentration of hydrogen sulfide captured by the second sensor.

[0051] Thanks to these provisions, it is possible to detect saturation of the iron hydroxide bed or a sizing defect in the purification reactor.

[0052] In some embodiments, the purification device also includes a means for measuring the saturation of the iron hydroxide bed.

[0053] These features make it possible to detect a situation where the iron hydroxide bed is saturated and to react before a breakthrough occurs in the scrubber reactor. In some embodiments, the control unit includes:

[0054] - a means of comparing the measured saturation to a first predetermined saturation limit called "alert saturation",

[0055] - a means of activating an alert when the measured saturation is greater than the alert saturation.

[0056] Thanks to these provisions, it is possible to alert the operator to an abnormal situation.

[0057] In some embodiments, the device of the present invention further comprises a means for diverting the gas at the outlet of the methanization reactor, the control unit comprising:

[0058] - a means of comparing the measured saturation to a second predetermined saturation limit called "critical saturation", which is higher than the warning saturation and

[0059] - a means of activating the means of diverting the gas at the outlet of the methanization reactor when the measured saturation is greater than the critical saturation.

[0060] Thanks to these arrangements, it is possible to convey the gas from the outlet of the methanization reactor to another purification reactor and / or to recirculate the gas at the inlet of the methanization reactor while the iron hydroxide bed is being replaced.

[0061] In embodiments, the device of the present invention further comprises a means for extracting a portion of the iron hydroxide bed and in which the control unit comprises a means for sending a command to extract a portion of the iron hydroxide bed as a function of the measured saturation.

[0062] Thanks to these arrangements, the iron hydroxide bed is replaced as it becomes saturated, allowing continuous operation with a single purification reactor.

[0063] In some embodiments, the control system includes a means for adapting the control of the means for regulating the flow rate of dioxygen injected into the methanization reactor according to the measured saturation.

[0064] Simultaneous adsorption and regeneration in the scrubbing reactor produce elemental sulfur that remains in the bed and progressively blocks the iron oxide adsorption sites. The breakthrough front advances inexorably over the long term. Thanks to these arrangements, the oxygen supply is matched to the iron hydroxide bed's adsorption capacity.

[0065] In embodiments, the device of the present invention comprises, downstream of the purification reactor, an elemental sulfur separator from the purified gas stream consisting mainly of methane configured to extract elemental sulfur from the purified gas stream.

[0066] These embodiments allow the inert S8 to be separated from the gas stream, for possible future treatment of said gas, particularly when the sulfur hydroxide bed in the purification reactor is a fluidized bed.

[0067] In some embodiments, the device of the present invention includes a means of conveying elemental sulfur extracted from the purified gas stream to the methanization reactor.

[0068] These embodiments allow the sulfur to be recycled for use in the methanization reactor.

[0069] In some embodiments, the iron hydroxide bed is a fixed bed.

[0070] In some embodiments, the iron hydroxide bed is a fluidized bed.

[0071] These embodiments make it possible to improve the humidity level within the purification reactor to have values ​​close to optimal values ​​in terms of humidity within the purification reactor and to improve purification capacities.

[0072] In some embodiments, the device of the present invention further comprises, downstream of each purification reactor, a means of separating water from purified methane.

[0073] Tests revealed that the activated carbon was used under degraded conditions with moisture levels of around 20 to 25%, compared to a recommended usage level of approximately 80%. Integrating the fixed-bed reactor upstream of the water-purified methane separation system allows purification to be carried out with a moisture content generally close to saturation, for example, above 90%. These implementations significantly increase purification performance. In particular, the higher H2S capture rate provides greater flexibility in operation and allows for a higher saturation level of the iron hydroxide bed without risking bed penetration. Consequently, the iron hydroxide bed requires less frequent replacement.Furthermore, a higher H2S capture rate provides more available sites for regeneration, resulting in improved residual oxygen capture performance. Specifically, capturing H2S with iron oxide forms iron sulfide, which can react with O2 to regenerate. A higher H2S capture rate leads to more localized iron sulfide formation, resulting in a gas flow entering a bed with a locally higher concentration of active sites containing iron sulfides. A higher concentration of either reactant further enhances the reaction.

[0074] In embodiments, the device of the present invention further comprises a means of conveying the separated water to the purification reactor, and a sensor of a water concentration of the gas circulating between the outlet of the methanization reactor and the gas inlet of the purification reactor, in which the control unit comprises a means of sending a command to the means of conveying the separated water according to the concentration of dioxygen captured.

[0075] Thanks to these measures, it is possible to ensure an optimal humidity level in the purification reactor.

[0076] In some embodiments, a heat exchanger is configured to provide a heat input upstream of the outlet of the purification reactor.

[0077] These embodiments make it possible to accelerate the chemical purification reaction, particularly in the case of a fluidized bed reactor.

[0078] In embodiments, the device of the present invention comprises, downstream of the purification reactor, a means for separating carbon dioxide from methane, a methane outlet and a carbon dioxide outlet containing residual methane.

[0079] International standards stipulate that a small amount of methane may remain in the carbon dioxide-containing gas exiting such a separation device. However, this must be less than 1% of the molar quantity of gas and sometimes 0.5%.

[0080] These embodiments make it possible to remove carbon dioxide from the purified methane stream.

[0081] In embodiments, the device of the present invention comprises, downstream of the carbon dioxide outlet, a catalytic oxidation reactor of residual methane.

[0082] Thanks to these measures, residual methane is transformed into water and carbon dioxide rather than being released into the atmosphere in an exothermic reaction.

[0083] In some embodiments, the thermal energy from the cracking of residual methane is supplied as a thermal input to the iron hydroxide bed by means of the heat exchanger.

[0084] Thanks to these measures, the thermal energy generated by methane cracking is reused to heat the purification reactor. Energy savings are therefore achieved.

[0085] According to a second aspect, the present invention relates to a kit for a device for purifying a gas consisting mainly of methane, the device comprising:

[0086] - at least one methanization reactor comprising:

[0087] - an influx of dioxygen,

[0088] - a means of regulating the flow rate of dioxygen injected into the methanization reactor by the dioxygen inlet and

[0089] - a gas outlet consisting mainly of methane and at least some hydrogen sulfide,

[0090] - at least one purification reactor comprising: - a gas inlet consisting mainly of methane and at least hydrogen sulfide connected to the outlet of the methanization reactor and

[0091] - a purified gas outlet consisting mainly of methane;

[0092] - the kit includes:

[0093] - a bed of iron hydroxide,

[0094] - a first sensor for the concentration of dioxygen in the gas circulating between the outlet of the methanization reactor and the inlet of the gas in the purification reactor;

[0095] - a control system including a means of sending a command by means of regulating the flow of dioxygen injected into the methanization reactor according to the concentration of dioxygen captured.

[0096] Since the aims, advantages, and specific characteristics of the kit that is the subject of the present invention are similar to those of the device that is the subject of the present invention, they are not repeated here. Furthermore, the kit allows for the modernization of existing installations.

[0097] According to a third aspect, the present invention relates to a process for purifying a gas consisting mainly of methane, the process comprising:

[0098] - a methanation stage in a methanation reactor comprising:

[0099] - an influx of dioxygen,

[0100] - a means of regulating the flow rate of dioxygen injected into the methanization reactor by the dioxygen inlet and

[0101] - a gas outlet consisting mainly of methane and at least some hydrogen sulfide,

[0102] - a purification stage in a purification reactor comprising:

[0103] - a bed of iron hydroxide,

[0104] - a gas inlet consisting mainly of methane and at least hydrogen sulfide connected to the outlet of the methanization reactor and

[0105] - a purified gas outlet consisting mainly of methane

[0106] - a step of measuring the oxygen concentration of the gas circulating between the outlet of the methanization reactor and the gas inlet of the purification reactor;

[0107] - a control step including a step for regulating the flow rate of dioxygen injected into the methanization reactor according to the concentration of dioxygen captured.

[0108] Since the aims, advantages and special characteristics of the process which is the subject of the present invention are similar to those of the device which is the subject of the present invention, they are not recalled here.

[0109] BRIEF DESCRIPTION OF THE FIGURES

[0110] Other advantages, purposes and particular features of the invention will become apparent from the following non-limiting description of at least one particular embodiment of the device, kit and method which are the subject of the present invention, with reference to the accompanying drawings, in which:

[0111] Figure 1 schematically represents a first particular embodiment of the device that is the subject of the present invention,

[0112] Figure 2 schematically represents a second particular embodiment of the device that is the subject of the present invention,

[0113] Figure 3 schematically represents different breakthrough front states in a purification reactor that is the subject of the present invention, and

[0114] Figure 4 represents, schematically and in the form of a flowchart, a particular sequence of steps of the process which is the subject of the present invention.

[0115] DESCRIPTION OF IMPLEMENTATION METHODS

[0116] This description is not exhaustive, as each feature of one embodiment can advantageously be combined with any other feature of any other embodiment. The term "and / or," as used in this document and in the claims, shall be understood as meaning "one or the other or both" of the elements thus combined, i.e., elements that are present conjunctively in some cases and disjunctively in others. Multiple elements listed with "and / or" shall be interpreted similarly, i.e., "one or more" of the elements thus combined. Other elements may optionally be present, other than those specifically identified by the "and / or" clause, whether or not they are related to those specifically identified elements.Thus, by way of non-limiting example, a reference to "A and / or B", when used in conjunction with an open language such as "including", may refer, in one embodiment, to A only (possibly including elements other than B); in another embodiment, to B only (possibly including elements other than A); in yet another embodiment, to A and B (possibly including other elements); etc.

[0117] As used here in the description, "or" should be understood to have the same meaning as "and / or" as defined above. For example, when separating elements in a list, "or" or "and / or" should be interpreted as inclusive, meaning the inclusion of at least one, but also more than one, of a number or list of elements, and optionally, additional unlisted elements. Only terms explicitly stating the contrary, such as "only one of" or "exactly one of," or, when used in claims, "consisting of," refer to the inclusion of only one element of a number or list of elements.

[0118] As used in this description and in the claims, the expression "at least one," with reference to a list of one or more elements, should be understood as meaning at least one element chosen from one or more elements in the list of elements, but not necessarily including at least one of each element specifically listed in the list of elements and not excluding any combination of elements in the list of elements. This definition also allows for the optional presence of elements other than those specifically identified in the list of elements to which the expression "at least one" refers, whether or not they are related to those specifically identified elements.Thus, by way of non-limiting example, "at least one of A and B" (or, equivalently, "at least one of A or B", or, equivalently, "at least one of A and / or B") may refer, in one embodiment, to at least one, possibly including more than one, A, without B present (and possibly including elements other than B); in another embodiment, to at least one, possibly including more than one, B, without A present (and possibly including elements other than A); in yet another embodiment, to at least one, possibly including more than one, A, and at least one, possibly including more than one, B (and possibly including other elements); etc.

[0119] In the claims, as well as in the description below, all transitive expressions such as "comprising", "including", "carrying", "having", "containing", "implying", "holding", "composed of", and others, shall be understood as open, that is, as meaning "including, but not limited to". Only the transitive expressions "consisting of" and "consisting essentially of" shall be understood as closed or semi-closed transitive expressions, respectively.

[0120] It should be noted from the outset that the figures are not to scale.

[0121] It is important to remember that "majority" means the most abundant component. In the context of gases, a gas predominantly composed of one component means that the concentration of that component in the gas is greater than the concentration of all the other components in the gas. For example, a gas with three components A, B, and C, whose respective concentrations represent 45%, 30%, and 25% of the gas, is a gas predominantly composed of component A.

[0122] In the present invention, a gas consisting mainly of methane means a gas in which the concentration of methane is greater than the concentration of each of the other components of said gas. Figure 1, which is not to scale, shows a schematic view of an embodiment of the device 100 that is the subject of the present invention.

[0123] Device 100 for purifying a gas consisting mainly of methane, the device comprising at least one methanization reactor 101 comprising:

[0124] - an oxygen inlet of 104,

[0125] - a means of regulating 105 the flow rate of dioxygen injected into the methanization reactor 101 by the dioxygen inlet 104 and

[0126] - an outlet 107 of gas consisting mainly of methane and at least hydrogen sulfide.

[0127] A methanation reactor 101 comprises a sealed reaction chamber equipped with agitation and mixing means to promote the anaerobic biodegradation of organic matter 102. The reaction chamber is designed to maintain optimal conditions to promote the growth of methanogenic microorganisms. The reaction chamber includes a bed of organic matter 102 and a gaseous headspace 103.

[0128] Preferably, and in a manner known to those skilled in the art, the methanation reactor 101 includes a means of feeding organic matter into the reaction chamber in a controlled manner. The organic matter can be agricultural residues, food waste, or sewage sludge, for example.

[0129] Preferably, and in a manner known to those skilled in the art, the 101 biogas reactor includes a means of temperature control in the reaction chamber to maintain a constant and optimal temperature inside the reaction chamber. This thermal control means includes heating and cooling systems, thus optimizing the biodegradation conditions, as known to those skilled in the art.

[0130] Furthermore, the methanation reactor 101 includes a means for collecting and conveying biogas from the gaseous duct 103, which recovers the biogas produced during the methanation stage and conveys it to the gas outlet 107, which consists mainly of methane. It should be noted that biogas is primarily composed of methane. Given the reactions carried out in the methanation stage, the biogas contains at least hydrogen sulfide. The biogas exiting the methanation reactor 101 may also contain carbon dioxide, water, and oxygen. The biogas may also contain other compounds present in trace amounts, such as nitrogen, siloxanes, and / or volatile aromatic compounds.

[0131] Preferably, the oxygen inlet 104 of the methanation reactor 101 is connected, by a pipe, to an oxygen generator 106. The oxygen generator 106 is of a type known to those skilled in the art, for example by pressure-modulated adsorption.

[0132] The means 105 for regulating the flow rate of dioxygen injected into the methanation reactor 101 is, for example, a solenoid valve, controlled by a programmable logic controller (PLC) 118. The solenoid valve is of the proportional type, meaning that the valve opens with a greater or lesser degree of amplitude. For example, the opening of the solenoid valve can be proportional to the electrical current of the power supply, or to the electrical voltage of the power supply.

[0133] The device that is the subject of the present invention also includes, downstream of the methanization reactor 101, at least one purification reactor 110 comprising:

[0134] - a bed 112 of iron hydroxide,

[0135] - a gas inlet 110 consisting mainly of methane and at least hydrogen sulfide connected to the outlet 107 of the methanization reactor 101 and

[0136] - a 115 outlet of purified gas consisting mainly of methane.

[0137] The purification reactor 111 has a sealed, airtight chamber with a means for retaining the iron hydroxide bed 112, such as a hopper. The purification reactor 111 has a gas inlet 110 and a gas outlet on either side of the iron hydroxide bed 112, such that the gas to be purified passes through the iron hydroxide bed 112. Embodiments of purification reactors 111 are known to those skilled in the art. Preferably, the purification reactor 111 is in the form of a truncated cylinder with a substantially vertical axis. The inlet 110 of the purification reactor 110 is located on one end of the cylinder, and the outlet 115 is located on the other end. The iron hydroxide bed 112 is positioned between the inlet 110 and the outlet 115. Preferably, the outlet 115 is positioned on the highest base.

[0138] In some embodiments, iron hydroxide is inserted into the purification reactor 111 in the form of granules.

[0139] In some embodiments, the iron hydroxide bed is a fixed bed.

[0140] In some embodiments, the iron hydroxide bed is a fluidized bed.

[0141] In some embodiments, the iron hydroxide is introduced into the purification reactor in powder form. These embodiments are particularly advantageous when the bed is a fluidized bed. These embodiments notably reduce costs since the powder form is less expensive than the granular form.

[0142] Preferably, and more particularly when the iron hydroxide is in powder form, the device 100 includes, downstream of the purification reactor 111, a separator 136 for elemental sulfur from the purified gas stream, which is predominantly methane, configured to extract the elemental sulfur from the purified gas stream. Such a separator is, for example, a cyclone separator or an overflow separator. Preferably, the device 100 includes a means 137 for conveying the elemental sulfur extracted from the purified gas stream to the methanation reactor 101. Such a means is known to those skilled in the art. When the iron hydroxide bed is in powder form, the powder separation means allows the elemental sulfur to be collected mixed with the iron oxides and sulfides.This mixture can be reinjected into the methanation reactor to return the reduced sulfur and iron to the liquid phase in the digestate, thus limiting the production of H2S in the gaseous headspace. This gives a second life to this powder composed of iron and sulfur while improving the efficiency of the device and process described in the present invention, since there is less sulfur to remove from the gaseous phase.

[0143] Although these embodiments are shown opposite Figure 1, they are compatible with the embodiments shown opposite Figure 2.

[0144] The iron hydroxide from bed 112 reacts with the hydrogen sulfide from the gas entering the purification reactor 111 to form iron sulfides according to formula 1 below:

[0145] [Formula 1]

[0146] 2 Fe(OH)3 + 3 H2S Fe2S3 + 6 H2O

[0147] Then, the iron sulfides react with the oxygen from the gas entering the purification reactor 111 to form elemental sulfur and iron hydroxide according to formula 2 below:

[0148] [Formula 2]

[0149] Fe2S3+ 1.5 O2+ 3H2O 2 Fe(OH)3+ 3 S

[0150] Since oxygen and hydrogen sulfide are present in the gas entering the purification reactor 111, the adsorption described by formula 1 and the regeneration described by formula 2 are simultaneous and continuous.

[0151] The device and method of the present invention make it possible to optimize these two chemical reactions.

[0152] A pipe connects the outlet 107 of the methanization reactor 101 to the inlet 110 of the purification reactor 111. Preferably, the pipe is equipped with a first sensor 108 of an oxygen concentration of the gas circulating between the outlet 107 of the methanization reactor 101 and the inlet 110 of the gas of the purification reactor 111.

[0153] In preferred embodiments, the pipeline is also equipped with a first sensor 109 for the hydrogen sulfide concentration of the gas flowing between the outlet 107 of the methanation reactor 101 and the inlet 110 of the gas from the purification reactor 111. The first sensor 108 for the oxygen concentration of the gas and the first sensor 109 for the hydrogen sulfide concentration of the gas may be two separate sensors known to those skilled in the art or a single sensor for analyzing the composition of a gas. For example, the first sensor 108 for the oxygen concentration of the gas and the first sensor 109 for the hydrogen sulfide concentration of the gas are at least one chromatograph.The first sensor 108 of a concentration of dioxygen of the gas and the first sensor 109 of a concentration of hydrogen sulfide of the gas can be positioned on the pipe which connects the outlet 107 of the methanization reactor 101 to the inlet 110 of the purification reactor or on a diversion pipe.

[0154] Preferably, the first sensor 108 of a dioxygen concentration of the gas and the first sensor 109 of a hydrogen sulfide concentration of the gas provide the measured concentration to a control automaton 118.

[0155] The control unit 118 includes a means 120 for sending a command to the regulation means 106 of the flow rate of dioxygen injected into the methanization reactor as a function of the concentration of dioxygen captured.

[0156] For example, the control unit 118 can execute instructions to compare the measured oxygen concentration value with at least one predetermined limit value. Based on the comparison result, the control unit 118 prepares and sends a command to increase or decrease the injected oxygen flow rate.

[0157] Preferably, the control unit 118 includes:

[0158] - a means of calculating 119 a ratio between the concentration of dioxygen captured and the concentration of hydrogen sulfide captured and

[0159] - a means of sending 120 a command to the means of regulation 106 of the flow of dioxygen injected into the methanization reactor according to the calculated ratio.

[0160] The control unit 118 is preferably a microcontroller configured to store and execute programmed instructions. Preferably, the control unit includes:

[0161] - a means of display, such as a screen and / or indicator lights,

[0162] - a user interface, such as a keyboard,

[0163] - a means of communication, wired or wireless, with each sensor of the device that is the subject of the present invention,

[0164] - a memory configured to store the instructions executed.

[0165] In preferred embodiments, the control unit 118 includes a means of communication with a management system. The management system can be an application hosted on a server configured to remotely monitor and control at least one control unit.

[0166] Preferably, the calculation means 119 for a ratio between the captured oxygen concentration and the captured hydrogen sulfide concentration is included in the microcontroller that executes instructions for calculating said ratio. The command sending means 120 is a communication means, wired or wireless, from the corresponding control unit to a corresponding communication means of the control unit 106.

[0167] Preferably, the control unit 118 includes a means 121 for comparing the calculated ratio to at least one predetermined limit ratio. The comparison means 121 is, for example, the microcontroller executing comparison instructions. Each predetermined limit ratio can be stored in a memory of the control unit 118. In some embodiments, the management system is configured to define each predetermined limit ratio and / or modify a predetermined limit ratio. In some embodiments, a user can, by means of a user interface, define each predetermined limit ratio and / or modify a predetermined limit ratio.

[0168] Preferably, the comparison method compares the calculated ratio to:

[0169] - a first predetermined limit ratio called the "lower ratio", and / or - a second predetermined limit ratio called the "upper ratio".

[0170] The lower ratio represents a ratio at which the amount of oxygen entering the methanation reactor 101 is too low to allow continuous regeneration of the iron hydroxide bed. Therefore, when the calculated ratio is lower than the lower ratio, the control includes an instruction to increase the flow rate of dioxygen injected into the methanation reactor 101. The flow control means 105 is controlled to increase the dioxygen flow rate at the inlet 104 of the methanation reactor 101. In other words, when the control means 105 is a solenoid valve, the solenoid valve is more open than before the comparison.

[0171] The upper ratio represents a ratio at which excess oxygen is injected into the methanation reactor 101 and therefore ends up in the gas stream to be injected into the network. Thus, when the calculated ratio is higher than the upper ratio, the control system includes an instruction to reduce the flow rate of dioxygen injected into the methanation reactor 101. The flow control device 105 is activated to reduce the incoming dioxygen flow rate.

[0172] 104 of the methanization reactor 101. In other words, when the control means 105 is a solenoid valve, the solenoid valve is more closed than before the comparison.

[0173] When the calculated ratio falls between the lower and upper ratios, the oxygen flow rate remains unchanged. In other words, when the control device 105 is a solenoid valve, the valve position remains the same.

[0174] Preferably, the lower and upper ratios are selected according to the operating conditions and dimensions of the methanization and / or purification reactor.

[0175] Furthermore, if the main constraint concerning the gas exiting device 100 is to have as little Û2 as possible, the upper and lower ratio values ​​can be less than or equal to 0.2, with the upper ratio value being strictly greater than the lower ratio value. This ensures the absence of Û2 at the reactor outlet, at the expense of degraded continuous regeneration. Indeed, more iron oxides would be consumed, implying more frequent bed changes.

[0176] Conversely, if the main constraint concerning the gas at the outlet of device 100 is to eliminate as much H2S as possible, the lower ratio is equal to 0.45 and even more preferably equal to 0.5, and the upper ratio is equal to 0.5 and even more preferably equal to 0.6.

[0177] When the upper ratio is greater than or equal to 1.7, it is possible to undersize a reactor 130 comprising a bed 131 of activated carbon described below. The reactor 130 can be retained and subjected to very low loads, thus minimizing operating costs related to the carbon. In some embodiments, the calculated ratio is a ratio between a molar concentration of oxygen and a molar concentration of sulfur hydroxide (O2 / H2S). In some embodiments, the lower limiting ratio is preferably greater than 0.3 and even more preferably equal to 0.33, while the upper limiting ratio is preferably less than 0.45 and even more preferably equal to 0.38.

[0178] The first sensors, 108 and 109, the control unit 118 and the regulation means

[0179] 105 define a virtuous feedback loop aimed at optimizing the amount of enriched dioxygen injected in primary purification, i.e., in the methanization reactor 101, according to different operating regimes. The operating regimes are detailed below.

[0180] A - When the Û2 flux exactly compensates for the H2S load of the catalytic bed, then the injection of Û2 into the methanization reactor 101 is maintained in the same proportions.

[0181] B - When the Û2 flow is insufficient to regenerate the adsorbent bed 112, then the H2S content is too high compared to the C>2, and the bed 112 gradually becomes loaded with iron sulfides. Increasing the Û2 injection rate in primary treatment increases the residual O2 content at the inlet of secondary treatment, i.e., in the treatment reactor 111, but also decreases the H2S content at this point, because primary treatment would be favored by a higher Û2 injection.

[0182] C - When the Û2 flux is too high to regenerate the adsorbent bed 112: the C>2 concentration is too high in the bed, which regenerates faster than it saturates. It is not necessary to inject as much Û2 to meet the injection specifications. Reducing the Û2 injection rate in primary treatment decreases the amount of Û2 available for primary treatment, thus degrading the performance of this treatment stage. The biogas exiting primary treatment then has a decreasing O2 concentration while the H2S concentration increases, gradually reaching operating regime A.

[0183] The feedback loop created by the device of the present invention is synergistic and allows the secondary treatment to operate within an optimal concentration range by varying the O2 injection rates during the primary treatment. The present invention makes it possible to balance the operation of the treatment reactor 111 to maintain a stable regime and thus optimize the regulation of both H2S and O2.

[0184] It is noted that the concentration of hydrogen sulfide at outlet 107 of the methanation reactor 101 depends on the organic matter inserted into the methanation reactor 101. It is therefore necessary to continuously monitor the concentration of hydrogen sulfide at outlet 107 of the methanization reactor 101.

[0185] In some embodiments, a first oxygen concentration sensor 108 and a first hydrogen sulfide concentration sensor 109 are configured to perform measurements simultaneously at regular intervals. For example, the measurements are taken at a frequency on the order of minutes or tens of minutes. Preferably, the measurement frequency corresponds to the sampling frequency required for the operation of at least one sensor 108 and / or 109. Furthermore, in these embodiments, the control unit 118 may include a means for synchronizing an internal clock of each sensor, 108 and 109, in order to perform the measurements synchronously.

[0186] In some embodiments, the control unit 118 can send a measurement instruction to each sensor, 108 and 109.

[0187] Preferably, the means of calculation and the means of sending a command are therefore implemented at each iteration of a measurement by each first sensor, 108 and 109.

[0188] In some embodiments, the device 100 further includes a second sensor 116 for the oxygen concentration of the gas flowing out of the outlet 115 of the purification reactor 111. In these embodiments, the command sent by the command sending means 120 is further dependent on the oxygen concentration captured by the second sensor 116.

[0189] The second sensor 116 can correspond to any type of dioxygen concentration sensor known to a person skilled in the art.

[0190] The second sensor 116 for a gas oxygen concentration can be positioned on the pipe coming from the outlet 115 of the purification reactor 111 or on a diversion pipe.

[0191] Preferably, the second oxygen concentration sensor 116 may include a means of communication, wired or wireless, with the programmable logic controller (PLC) 118. The communication means is configured to provide the PLC 118 with each measurement taken. In some embodiments, the communication means is configured to:

[0192] - receive a synchronization instruction to an internal clock of the programmable logic controller 118, and / or

[0193] - to receive an instruction to take measurements.

[0194] Preferably, the comparison means 121 is configured to compare the value measured by the second sensor 116 of an oxygen concentration of the gas at the outlet 115 of the purification reactor, to at least one predetermined limit value.

[0195] A first predetermined limit value corresponds to a value beyond which the composition of the gas exiting the purification reactor 111 indicates a failure in the regulation of the oxygen flow rate at the inlet of the methanation reactor 101, but remains compatible with injecting the gas into a natural gas network. For example, the first predetermined limit value is equal to 500 ppm, 2000 ppm, or 2500 ppm.

[0196] When the comparator means 121 detects that the value measured by the second sensor 116 of an oxygen concentration of the gas at the outlet 115 of the purification reactor is greater than the first predetermined limit value, a command is generated by the programmable logic controller 118 and sent by the sending means 120 to decrease the oxygen flow at the inlet 104 of the methanization reactor 101.

[0197] A second predetermined limit value corresponds to a value beyond which the composition of the gas exiting the purification reactor 111 is incompatible with injection of the gas into a natural gas network. For example, the second predetermined limit value is equal to 1000 ppm or 4000 ppm.

[0198] When the comparison means 121 detects that the value measured by the second sensor 116 of the oxygen concentration of the gas at the outlet 115 of the purification reactor is greater than the second predetermined limit value, a command is generated by the programmable logic controller 118 and sent by the sending means 120 to:

[0199] - switch the output flow 107 from the methanization reactor 101 to another purification reactor 111,

[0200] - close inlet 110 of the purification reactor 111,

[0201] - recirculate the flow from outlet 107 of the methanation reactor 101 back to the inlet of the methanization reactor and notify a user of the need to change the iron hydroxide bed, and / or

[0202] - reduce to zero the oxygen flow rate at the inlet 104 of the methanization reactor 101 to stop the gas production and purification process.

[0203] In some embodiments, the device 100 further includes a second sensor 117 for the hydrogen sulfide concentration of the gas flowing out of the outlet 115 of the purification reactor 111. In these embodiments, the command sent by the command sending means 120 is further dependent on the hydrogen sulfide concentration captured by the second sensor 117.

[0204] The second sensor 117 can correspond to any type of hydrogen sulfide concentration sensor known to a person skilled in the art.

[0205] The second sensor 117 for a hydrogen sulfide concentration of the gas can be positioned on the pipe coming from the outlet 115 of the purification reactor 111 or on a diversion pipe.

[0206] The second sensor 116 of a dioxygen concentration of the gas and the second sensor 117 of a hydrogen sulfide concentration of the gas can be two separate sensors known to a person skilled in the art or a single sensor for analyzing the composition of a gas.

[0207] Preferably, the second sensor 117 for measuring the hydrogen sulfide concentration of the gas may include a means of communication, wired or wireless, with the programmable logic controller (PLC) 118. The communication means is configured to provide the PLC 118 with each measurement taken. In some embodiments, the communication means is configured to:

[0208] - receive a synchronization instruction to an internal clock of the programmable logic controller 118, and / or

[0209] - to receive an instruction to take measurements.

[0210] Preferably, the comparison means 121 is configured to compare the value measured by the second sensor 117 of a hydrogen sulfide concentration of the gas at outlet 115 of the purification reactor 111, to at least one predetermined limit value.

[0211] A first predetermined limit value of hydrogen sulfide concentration corresponds to a value beyond which the composition of the gas at the outlet of the purification reactor 111 is representative of a saturation of the iron hydroxide bed, for example 2ppm.

[0212] When the comparison means 121 detects that the value measured by the second sensor 117 of a hydroxide sulfide concentration in the gas outlet 115 of the purification reactor 111 is greater than the first predetermined limit value, a command is generated by the programmable logic controller 118 and sent by the sending means 120 to:

[0213] - switch the flow from outlet 107 of the methanization reactor 101 to another purification reactor 111, - close the inlet 110 of the purification reactor 111,

[0214] - recirculate the flow from outlet 107 of the methanation reactor 101 back to the inlet of the methanization reactor and notify a user of the need to change the iron hydroxide bed, and / or

[0215] - reduce to zero the oxygen flow rate at the inlet 104 of the methanization reactor 101 to stop the gas production and purification process.

[0216] The embodiments in which the control relates to switching or recirculation are described below, opposite Figure 2.

[0217] A second predetermined limit value for hydrogen sulfide concentration corresponds to a value below which the gas exiting the purification reactor complies with the standards for injection into a network. For example, the second predetermined limit value is 3.6 ppm, and even more preferably 0 ppm.

[0218] When the comparison means 121 detects that the value measured by the second sensor 117 of hydroxide sulfide concentration at outlet 115 of the purification reactor 11 is less than or equal to the second predetermined limit value, and when the comparison means 121 detects that the value measured by the second sensor 116 of a dioxygen concentration of the gas at outlet 115 of the purification reactor is less than the first predetermined limit value of dioxygen concentration, no change in the dioxygen flow rate at inlet 104 of the methanization reactor 101 is commanded.

[0219] When the comparator means 121 detects that the value measured by the second sensor 117 of hydroxide sulfide concentration at outlet 115 of the purification reactor 111 is greater than the second predetermined limit value, and when the comparator means 121 detects that the value measured by the second sensor 116 of a dioxygen concentration of the gas at outlet 115 of the purification reactor is less than a third predetermined limit value of dioxygen concentration, a command is generated by the programmable logic controller 118 and sent by the sending means 120 to increase the dioxygen flow rate at the inlet 104 of the methanization reactor 101.

[0220] For example, the third predetermined limit value for dioxygen concentration is equal to 400 ppm.

[0221] Such a situation is representative of an oversizing of the purification reactor and / or a measurement defect by at least one of the first sensors, 108 and 109.

[0222] When the comparison means 121 detects that the value measured by the second hydrogen sulfide concentration sensor 117 at the outlet 115 of the purification reactor 111 is greater than the first predetermined limit value, and when the comparison means 121 detects that the value measured by the second oxygen concentration sensor 116 at the outlet 115 of the purification reactor is less than a third predetermined oxygen concentration limit value, a command is generated by the programmable logic controller 118 and sent by the sending means 120 to:

[0223] - switch the output flow 107 from the methanization reactor 101 to another purification reactor 111,

[0224] - close inlet 110 of the purification reactor 111,

[0225] - recirculate the flow from outlet 107 of the methanation reactor 101 back to the inlet of the methanization reactor and notify a user of the need to change the iron hydroxide bed, and / or

[0226] - reduce to zero the oxygen flow rate at the inlet 104 of the methanization reactor 101 to stop the gas production and purification process.

[0227] Such a situation is indicative of a malfunction in the purification reactor. For example, the third predetermined limit value is equal to 400 ppm.

[0228] The reaction in bed 112 of the purification reactor 111 can be described by a thermal front. The thermal front refers to the region of bed 112 in the purification reactor 111 where a temperature gradient occurs. The thermal front moves as the reactor operates and chemical or physical reactions take place, generating heat. As mentioned above, two reactions occur in bed 112: a H2S capture reaction and an adsorbent regeneration reaction.

[0229] Each of these two reactions has a reaction front, that is, a region in which the associated reaction takes place. These regions can overlap.

[0230] The breakthrough front zone designates the I-S breakthrough. When this zone approaches the top of reactor 111, it means that bed 112 is saturated. When this zone reaches the top of reactor 111, some of the I-kS does not react with bed 112; this is called a breakthrough.

[0231] The thermal front corresponds to the front of the regeneration reaction, which is exothermic. Generally, the thermal front is lower than the breakthrough front, because the regeneration reaction can only occur if the bed has already reacted with H2S.

[0232] If the gas contains a high concentration of H₂S and low concentration of C>2, the breakthrough front can be located at the very top of reactor 111 and the thermal front at the very bottom. However, if the ratio of captured oxygen concentration to captured hydrogen sulfide concentration is approximately 1.6, the thermal front follows the breakthrough front. There is then a slight excess of C>2 for the regeneration reaction, but this regeneration can only occur if the I-kS (in slight deficiency) has reacted with the bed. In this case, the breakthrough front and the thermal front are generally located in the same place.

[0233] The movement of the thermal front is illustrated in particular with regard to Figure 3. Figure 3 represents different states of thermal front in a purification reactor 111 which is the subject of the present invention.

[0234] The purification reactor 111 is represented as having a shape substantially in the form of a truncated cylinder with a circular base, the lower base having the gas inlet 110 and the upper base having the gas outlet 115.

[0235] The iron hydroxide bed 112 is represented as two stacked cylinder truncates inside the purification reactor 111.

[0236] In the different states, 301, 311 and 321:

[0237] - the lower cylinder trunk represents a zone in which the adsorption reaction (formula 1) is faster than the regeneration reaction (formula 2) or in which the regeneration reaction is impossible in the absence of oxygen; this part has a brown to black coloration; in other words, the lower cylinder trunk represents a part of the bed in which iron is present mainly in the form of sulfide.

[0238] - the upper cylinder trunk represents a zone in which the adsorption reaction (formula 1) is slower than the regeneration reaction (formula 2) or in which the adsorption reaction is impossible in the absence of hydrogen sulfide; this part has an ochre to yellow color; in other words, the upper cylinder trunk represents a part of the bed in which iron is present mainly in the form of hydroxide.

[0239] State 301, shown on the left of Figure 3, represents a so-called "normal" operating condition in which the ratio of oxygen concentration to hydrogen sulfide concentration at the inlet of the purification reactor 111 is, for example, on the order of 1.6. The chemisorption reactions of hydrogen sulfide (formula 1) and the regeneration of iron sulfide by oxygen (formula 2) are generally in equilibrium. The thermal front, or breakthrough front, is visually fixed.

[0240] State 311, shown in the middle of Figure 3, represents operation in which hydrogen sulfide is in excess. The ratio of oxygen concentration to hydrogen sulfide concentration at the inlet of the purification reactor 111 is, for example, less than 1.5. The chemisorption reactions of hydrogen sulfide are faster than the regeneration reactions of iron sulfide by oxygen. The breakthrough front therefore progresses towards the outlet 115. If the ratio is not increased, the bed will eventually break through, and the entire system will have to be shut down because the hydrogen sulfide concentration in the gas exiting the purification reactor will exceed the second predetermined limit value for hydrogen sulfide concentration; the gas will therefore be unsuitable for injection into a biogas network. State 321, shown on the right of Figure 3, represents operation in which oxygen is in excess.The ratio of oxygen concentration to hydrogen sulfide concentration at the inlet of the purification reactor 111 is, for example, greater than 1.7. The chemisorption reactions of hydrogen sulfide are slower than the regeneration reactions of iron sulfide by oxygen. The breakthrough front regresses. This means that more oxygen is injected into the methanation reactor 101 than necessary, which degrades the quality of the biomethane and increases the energy consumption of the device 100. The oxygen flow rate at the inlet 104 of the methanation reactor 101 must therefore be reduced.

[0241] Despite the simultaneous regeneration of bed 112 during the adsorption reaction, wear (also known as "saturation") of the iron hydroxide bed occurs. Thus, the breakthrough front progresses slowly towards outlet 115 with the bed becoming progressively saturated with elemental sulfur in the form of S8. The lifetime of the iron hydroxide bed is not infinite, even with continuous regeneration.

[0242] For these reasons, in some embodiments, the device 100 further includes a means 113 for measuring the saturation of the bed 112 of iron hydroxide.

[0243] The measuring means 113 can be at least one temperature sensor placed in the iron hydroxide bed. Such a sensor makes it possible to detect the position of the thermal front in the iron hydroxide bed 112.

[0244] A shift in the thermal front, particularly towards outlet 115 of the scrubber reactor 111, indicates that the iron hydroxide bed 112 is becoming saturated. When the iron hydroxide bed 112 is saturated, iron hydroxide regeneration is ineffective and the bed 112 must therefore be replaced.

[0245] In some embodiments, the purification reactor 111 is equipped with a transparent wall to visible light, facing the iron hydroxide bed 112. The measurement means may include a camera configured to capture at least one image of the iron hydroxide bed, and an image processing means configured to detect the position of the thermal front based on the captured image. In some embodiments, the measurement means may include a thermal camera and an image processing means configured to detect the position of the thermal front based on the image captured through a wall, opaque or not, of the purification reactor 111. Indeed, the thermal front represents the separation between the portion of the iron hydroxide bed 112 that reacts according to formula 1 and the portion that reacts according to formula 2.The portion of the iron hydroxide bed 112 that reacts according to formula 1 has an ochre or yellow color, while the portion of the iron hydroxide bed 112 that reacts according to formula 2 has a brown to black color.

[0246] Preferably, the control unit 118 includes:

[0247] - a means of comparing 122 the measured saturation to a first predetermined saturation limit called "alert saturation",

[0248] - a means of activating an alert 123 when the measured saturation is greater than the alert saturation.

[0249] The comparison means 122 is, for example, the microcontroller executing comparison instructions.

[0250] For example, an alert saturation corresponds to the position of a breakthrough front, at a position greater than 90% of the height of bed 112, at at least one point of bed 112.

[0251] The means of activating an alert 123 is, for example, the microcontroller sending an alert message to the management system or a command to emit an audible or visual alert.

[0252] In embodiments shown in Figure 2, the device 200 further includes means, 201 and 202, for diverting the gas at the outlet 107 of the methanation reactor 101. The elements shown in Figure 2, having identical reference numerals to the elements shown in Figure 1, exhibit embodiments similar to those described above. Figure 2 notably shows a second purification reactor 211, comprising an inlet 210 connected to the outlet 107 of the methanation reactor 101 and an outlet 115. The purification reactor 211 may include a means 213 for measuring the saturation of the bed 212 with iron hydroxide. The embodiments of the second purification reactor 211 are similar to those of the first purification reactor 111 described above.

[0253] In the embodiment shown in Figure 2, the conduit between the inlet 110 of the first purification reactor 111 and the outlet 107 of the methanization reactor 101 is equipped with a valve controlled by the automaton 118. Similarly, the conduit between the inlet 210 of the second purification reactor 211 and the outlet 107 of the methanization reactor 101 is equipped with a valve controlled by the automaton 118.

[0254] Preferably, the controller 118 includes a means 122 for comparing the measured saturation to a second predetermined saturation limit called the "critical saturation," which is higher than the alert saturation. The controller 118 also includes a means 124 for activating the diversion means 201 and 202 for the gas outlet 107 of the methanization reactor 101 when the measured saturation is higher than the critical saturation. For example, the activation means 124 is a means for controlling the closing of the valve, 201 or 202, connecting the outlet 107 of the methanization reactor 101 to the purification reactor, 110 or 210, supplied with gas and whose saturation is critical and the opening of the valve, 201 or 202, connecting the outlet 107 of the methanization reactor 101 to the purification reactor, 110 or 210, not supplied with gas and whose iron hydroxide bed has a lower saturation.

[0255] In embodiments, the device, 100 or 200, further includes a means for extracting, 114 or 214, a portion of the bed, 112 or 212 of iron hydroxide and in which the control unit 118 includes a means for sending 120 a command to extract a portion of the bed of iron hydroxide as a function of the measured saturation.

[0256] The extraction means, 114 or 214, is, for example, a conveyor belt configured to transport a portion of the saturated iron hydroxide bed to a storage tank for further processing. The extraction means, 114 or 214, may include a means for supplying the bed 112 with iron hydroxide. Preferably, the amount of iron hydroxide extracted is equal to the amount supplied. In this way, a portion of the iron hydroxide bed can be replenished before saturation becomes critical. Or, in the embodiment shown in Figure 2, when the saturation of a bed, 112 or 212, has reached critical saturation, and when the bed, 112 or 212, is no longer supplied with gas at the outlet 107 of the methanation reactor 101, the iron hydroxide 112 or 212 can be completely replaced.

[0257] In embodiments shown in Figure 2, the outlet 107 of the methanation reactor 101 can be routed to an inlet 204 of the methanation reactor 101. The pipe between the outlet 107 and the inlet 204 in the methanization reactor 101 can be equipped with a valve 203 controlled by the controller 118. Such recirculation makes it possible to avoid feeding each purification reactor, 114 and / or 214, in the event of saturation of both beds, 112 or 212, with iron hydroxide while at least one of the two beds is being replaced.

[0258] In some embodiments, the control unit 118 includes a means for adapting the control of the regulation means 105 of the flow rate of dioxygen injected into the methanization reactor 101 according to the measured saturation.

[0259] For example, the adaptation means is the microcontroller configured to execute adaptation instructions. Preferably, the adaptation means is configured to apply a coefficient to the flow rate command sent to the control means 105. The coefficient is preferably proportional to the saturation of the iron hydroxide bed 112. For example, when the bed 112 is new, the coefficient is less than 1, and when the bed is worn, the coefficient is greater than 1.

[0260] In preferred embodiments, the inlet, 110 or 210, of the purification reactor, 111 or 211, includes a means for regulating the flow rate of gas entering the purification reactor, 111 or 211. Such a regulating means may be a set of valves controlling the flow entering each purification reactor 111 and 211. These embodiments make it possible, in particular, to adjust the residence time of the gas in one of the purification reactors, 111 or 211. Preferably, the gas flow rate is adjusted so that the residence time is greater than 4 seconds, even more preferably greater than 10 seconds, and even more preferably between 20 and 30 seconds.

[0261] Figures 1 and 2 also show, connected to outlet 115 of the purification reactor, 112 or 212, a means 125 for separating carbon dioxide from methane. Such a means is known to those skilled in the art and comprises a methane outlet 127 and a carbon dioxide outlet 126 containing residual methane.

[0262] Preferably, the device 100 includes, downstream of the carbon dioxide outlet 126, a catalytic oxidation reactor 138 for residual methane. Catalytic oxidation reactors 138 for methane are known to those skilled in the art, with or without air injection. Such reactors allow the transformation of methane into water, on the one hand, and into carbon dioxide, on the other. The catalytic oxidation reaction of methane is an exothermic reaction.

[0263] In preferred embodiments, the thermal energy 140 from the cracking of residual methane is conveyed 140 to a heat exchanger 139.

[0264] As shown in Figure 1, the heat exchanger 139 is positioned on the methane outlet 107 of the methanization reactor 101.

[0265] In other embodiments, for example when the iron hydroxide bed is a fluidized bed, the heat exchanger 139 can be placed in the bed 112 of the purification reactor 111 and / or in a wall of the purification reactor.

[0266] Thus, the thermal energy 140 from the catalytic oxidation of residual methane is supplied as a thermal input by means of the heat exchanger 139.

[0267] In other embodiments, the heat exchanger 139 can be placed at any location in the device requiring a heat input to operate more efficiently, for example in the methanization reactor 101, which may require heat input, particularly in winter.

[0268] In general, the device 100 may include a heat exchanger 139 configured to provide heat input upstream of the outlet of the purification reactor 111. These embodiments may utilize the thermal energy 140 from the catalytic oxidation of residual methane or any other thermal energy source. These embodiments allow for preheating the gas entering the purification reactor 111 and / or the iron hydroxide bed 112 to increase the reaction temperature in the purification reactor 111.

[0269] Preferably, the temperature in the purification reactor 112 is adapted to be between 60°C and 70°C.

[0270] Although these embodiments are shown opposite Figure 1, they are compatible with the embodiments shown opposite Figure 2.

[0271] In some embodiments, the carbon dioxide separation means 125 is positioned upstream of a methane water separation means 128. The purified gas, separated from the carbon dioxide, can be conveyed to the methane water separation means 128, which is known to those skilled in the art. The separation means 128 includes a water storage element and an outlet 129 for the purified gas, separated from the water and carbon dioxide. The outlet 129 of the separator 128 can be conveyed to a purification reactor 130 comprising an activated carbon bed 131, which is known to those skilled in the art. The gas at the outlet 132 of such a purifier is suitable for injection into a methane network. These embodiments are shown in Figure 2, but can be adapted to the embodiments described opposite Figure 1.

[0272] In preferred embodiments, the carbon dioxide separation means 125 is positioned downstream of a water-methane separation means 128 and downstream of a purification reactor 130 comprising an activated carbon bed. The separation means 128 includes a water storage means and an outlet 129 for the purified gas, separated from the water and carbon dioxide, which is then conveyed to the purification reactor 130 comprising an activated carbon bed. The gas at the outlet 132 of such a purifier is conveyed to a carbon dioxide-methane separator 125, known to those skilled in the art. At the outlet 127, the gas is suitable for injection into a methane network. These embodiments are shown in Figure 1, but can be adapted to the embodiments described opposite Figure 2.These embodiments are particularly suitable when the carbon dioxide separation means 125 includes a membrane network sensitive to the presence of water in the treated gas.

[0273] The water separation means 128, the reactor comprising an activated carbon bed 131 and the carbon dioxide separation means 138 can be interchanged.

[0274] Preferably, the purification reactor, 111 or 211, is positioned upstream of the separation means 128.

[0275] In some embodiments, the pipe is equipped with a sensor 135 to capture the water concentration of the gas flowing between the outlet 107 of the methanation reactor 101 and the inlet

[0276] 110 of the gas from the purification reactor, 111 or 211.

[0277] The water concentration sensor 135 can be a separate sensor from the first oxygen concentration sensor 108 and the first hydrogen sulfide concentration sensor 109, or a single gas composition analysis sensor, or coupled to one of the sensors 108 and 109 and separate from the other sensor, 108 or 109.

[0278] Preferably, the water concentration sensor 135 provides the measured concentration to the control unit 118. In some embodiments, the water-methane separation means 128 includes a recirculation line 134 for the stored water to the purification reactor, 111 or 211, equipped with a pump and a solenoid valve.

[0279] The sending means 120 of a command from the control unit 118 can send a command to the pump and the solenoid valve to convey the stored water to the purification reactor,

[0280] 111 or 211.

[0281] Preferably, the control unit 118 can execute instructions to compare the concentration value of the captured water with at least one predetermined limit value. Based on the result of the comparison, the control unit 118 prepares and sends a command to transport the stored water.

[0282] The present invention also relates to a device for purifying a gas consisting mainly of methane, the device for example as described opposite Figures 1 and 2, comprising:

[0283] - at least one methanization reactor comprising:

[0284] - an influx of dioxygen,

[0285] - a means of regulating the flow rate of dioxygen injected into the methanization reactor by the dioxygen inlet and

[0286] - a gas outlet consisting mainly of methane and at least some hydrogen sulfide,

[0287] - at least one purification reactor comprising:

[0288] - a gas inlet consisting mainly of methane and at least hydrogen sulfide connected to the outlet of the methanization reactor and

[0289] - a purified gas outlet consisting mainly of methane.

[0290] The kit includes the elements shown in figures 1 and 2, and in particular:

[0291] - a bed 112 of iron hydroxide,

[0292] - a first sensor 108 of an oxygen concentration of the gas circulating between the outlet of the methanization reactor and the gas inlet of the purification reactor;

[0293] - a control automaton 118 comprising a means of sending 120 a command by means of regulating the flow of dioxygen injected into the methanization reactor according to the concentration of dioxygen captured.

[0294] Figure 4 shows a process 400 which is the subject of the present invention.

[0295] The purification process, 400 of a gas consisting mainly of methane, includes:

[0296] - a methanation stage 401 in a methanation reactor comprising: - an oxygen inlet,

[0297] - a means of regulating the flow rate of dioxygen injected into the methanization reactor by the dioxygen inlet and

[0298] - a gas outlet consisting mainly of methane and at least hydrogen sulfide, process 400 comprising:

[0299] - a purification step 402 in a purification reactor comprising:

[0300] - a bed of iron hydroxide,

[0301] - a gas inlet consisting mainly of methane and at least hydrogen sulfide connected to the outlet of the methanization reactor and

[0302] - a purified gas outlet consisting mainly of methane

[0303] - a measurement step 403 of the oxygen concentration of the gas circulating between the outlet of the methanization reactor and the gas inlet of the purification reactor;

[0304] - a control step 407 of a regulation of the flow of dioxygen injected into the methanization reactor according to the concentration of dioxygen captured.

[0305] In preferred embodiments, the process further comprises:

[0306] - a measurement step 404 of the hydrogen sulfide concentration of the gas circulating between the outlet of the methanization reactor and the gas inlet of the purification reactor,

[0307] - a command step 405 comprising:

[0308] - a calculation step 406 of a ratio between the concentration of captured dioxygen and the concentration of captured hydrogen sulfide and

[0309] - a control step 407 of a regulation of the flow of dioxygen injected into the methanization reactor according to the calculated ratio.

[0310] Preferably, the means of devices 100 and / or 200 are configured to implement the steps of process 400 and their modes of embodiment as set out above and process 400 as well as its various modes of embodiment can be implemented by the means of device 100 and / or 200, in the form of corresponding steps.

Claims

DEMANDS 1. A device for purifying (100, 200) a gas consisting mainly of methane, the device comprising: - at least one methanization reactor (101) comprising: - an inlet (104) of dioxygen, - a means of regulating (105) the flow rate of dioxygen injected into the methanization reactor by the dioxygen inlet and - an outlet (107) of gas consisting mainly of methane and at least hydrogen sulfide, - the device being characterized in that it comprises: - at least one purification reactor (111, 211) comprising: - a bed (112, 212) of iron hydroxide, - an inlet (110, 210) of gas consisting mainly of methane and at least hydrogen sulfide connected to the outlet of the methanization reactor and - an outlet (115) of purified gas consisting mainly of methane, - a first sensor (108) of an oxygen concentration of the gas circulating between the outlet of the methanization reactor and the gas inlet of the purification reactor; - a control automaton (118) comprising a means of sending (120) a command by means of regulating the flow of dioxygen injected into the methanization reactor according to the concentration of dioxygen captured.

2. Purification device (100, 200) according to claim 1, which further comprises a first sensor (109) for the hydrogen sulfide concentration of the gas circulating between the outlet of the methanization reactor and the gas inlet of the purification reactor, and in which a control unit (118) comprises: - a means of calculating (119) a ratio between the concentration of dioxygen captured and the concentration of hydrogen sulfide captured and - a means of sending (120) a command by means of regulating the flow of dioxygen injected into the methanization reactor according to the calculated ratio.

3. Purification device (100, 200) according to claim 2, wherein the control unit (118) includes a means for comparing (121) the calculated ratio to a first predetermined limit ratio called the "lower ratio", and when the calculated ratio is lower than the lower ratio, the control includes an instruction to increase the flow rate of dioxygen injected into the methanization reactor.

4. Purification device (100, 200) according to any one of claims 2 or 3, wherein the control unit (118) includes a means for comparing (121) the calculated ratio to a second predetermined limit ratio called the "upper ratio", and when the calculated ratio is greater than the upper ratio, the control unit includes an instruction to reduce the flow rate of dioxygen injected into the methanization reactor.

5. Purification device (100, 200) according to any one of claims 1 to 4, which further comprises a second sensor (116) of an oxygen concentration of the gas flowing out of the purification reactor and in which the command sent by the control unit (118) is further based on the oxygen concentration captured by the second sensor.

6. Purification device (100, 200) according to any one of claims 1 to 5, which further comprises a second sensor (117) of a hydrogen sulfide concentration of the gas flowing out of the purification reactor and in which the command sent by the control unit (118) is further based on the hydrogen sulfide concentration captured by the second sensor.

7. Purification device (100, 200) according to any one of claims 1 to 6, which further comprises a means for measuring (113, 213) the saturation of the iron hydroxide bed.

8. Purification device (100, 200) according to claim 7, wherein the control unit (118) comprises: - a means of comparison (122) of the measured saturation to a first predetermined limit saturation called "alert saturation", - a means of activating (123) an alert when the measured saturation is greater than the alert saturation.

9. Purification device (200) according to claim 8, further comprising a means for diverting (201, 202) the gas outlet (107) of the methanization reactor (101), the control unit (118) comprising: - a means of comparison (122) of the measured saturation to a second predetermined limit saturation called "critical saturation", higher than the warning saturation and - a means of activating (124) the means of diverting the gas at the outlet of the methanization reactor when the measured saturation is greater than the critical saturation.

10. Purification device (100, 200) according to any one of claims 7 to 9, further comprising an extraction means (114, 214) of a portion of the iron hydroxide bed and wherein the control unit (118) comprises a means for sending a command to extract a portion of the iron hydroxide bed as a function of the measured saturation.

11. Purification device (100, 200) according to any one of claims 7 to 10, the control unit (118) includes a means for adapting the control of the regulation means (105) of the flow of dioxygen injected into the methanization reactor according to the measured saturation.

12. Purification device (100) according to claim 11, which includes downstream of the purification reactor (111), a separator (136) of elemental sulfur from the purified gas stream consisting mainly of methane configured to extract elemental sulfur from the purified gas stream.

13. Purification device (100) according to claim 12, comprising a means for conveying (137) the elemental sulfur extracted from the purified gas stream to the methanization reactor (101).

14. Purification device (100) according to any one of claims 1 to 13, wherein the iron hydroxide bed (112) is a fixed bed.

15. Purification device (100) according to any one of claims 1 to 13, wherein the iron hydroxide bed (112) is a fluidized bed.

16. Purification device (100) according to any one of claims 1 to 15, which further comprises, downstream of each purification reactor (111), a means for separating water from purified methane.

17. Purification device (100) according to claim 16, which further comprises a means for conveying (134) the separated water to the purification reactor (111), and a sensor (135) of a water concentration of the gas circulating between the outlet of the methanization reactor and the gas inlet of the purification reactor, in which the control unit (118) comprises a means for sending (120) a command to the means for conveying the separated water according to the concentration of dioxygen captured.

18. Purification device (100) according to any one of claims 1 to 17, which further comprises a heat exchanger (139) configured to provide a heat input upstream of the outlet of the purification reactor (111).

19. Purification device (100) according to any one of claims 1 to 18, comprising, downstream of the purification reactor (111), a means for separating carbon dioxide from methane (125), a methane outlet (127) and a carbon dioxide outlet (126) comprising residual methane.

20. Purification device (100) according to claim 19, which comprises, downstream of the carbon dioxide outlet (126), a catalytic oxidation reactor (138) of residual methane.

21. Purification device (100) according to claim 20 when it depends on claims 19 and 18, wherein the thermal energy (140) from the catalytic oxidation of residual methane is supplied as a thermal input by means of the heat exchanger (139).

22. Kit for a purification device (100, 200) for a gas consisting mainly of methane, the device (100, 200) comprising: - at least one methanization reactor (101) comprising: - an inlet (104) of dioxygen, - a means of regulating (105) the flow rate of dioxygen injected into the methanization reactor by the dioxygen inlet and - an outlet (107) of gas consisting mainly of methane and at least hydrogen sulfide, - at least one purification reactor (111, 211) comprising: - an inlet (110, 210) of gas consisting mainly of methane and at least hydrogen sulfide connected to the outlet of the methanization reactor and - an outlet (115) of purified gas consisting mainly of methane; characterized in that the kit comprises: - a bed (112, 212) of iron hydroxide, - a first sensor (108) of an oxygen concentration of the gas circulating between the outlet of the methanization reactor and the gas inlet of the purification reactor; - a control automaton (118) comprising a means of sending (120) a command by means of regulating the flow of dioxygen injected into the methanization reactor according to the concentration of dioxygen captured.

23. A process for purifying (400) a gas consisting mainly of methane, the process comprising: - a methanation stage (401) in a methanation reactor (101) comprising: - an inlet (104) of dioxygen, - a means of regulating (105) the flow rate of dioxygen injected into the methanization reactor by the dioxygen inlet and - an outlet (107) of gas consisting mainly of methane and at least of hydrogen sulfide, the process being characterized in that it comprises: - a purification step (402) in a purification reactor (111, 211) comprising: - a bed (112, 212) of iron hydroxide, - an inlet (110, 210) of gas consisting mainly of methane and at least hydrogen sulfide connected to the outlet of the methanization reactor and - an outlet (115) of purified gas consisting mainly of methane, - a measurement step (403) of the oxygen concentration of the gas circulating between the outlet of the methanization reactor and the gas inlet of the purification reactor; - a control step (405) comprising a control step (407) of a regulation of the flow of dioxygen injected into the methanization reactor as a function of the concentration of dioxygen captured.

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