DEVICE, KIT AND METHOD FOR PURIFYING A GAS COMPRISING MAJORITY IN METHANE

Abstract

TITLE OF THE INVENTION: DEVICE, KIT AND METHOD FOR PURIFYING A GAS COMPRISING MAJORITY IN METHANE. A device for purifying a gas containing methane comprising: - a methanation reactor (101) comprising: - an oxygen inlet (104), - a means for regulating the oxygen flow rate (105) and - a gas outlet (107), - a purification reactor (111) comprising: - an iron hydroxide bed (112), - a gas inlet (110) connected to the outlet of the methanation reactor and - a purified gas outlet (115), - a sensor (108) for the oxygen concentration of the gas; - a control unit (118) sending a command to regulate the oxygen flow rate according to the oxygen concentration detected. Figure for the abstract: Figure 1

Description

Title of the invention: DEVICE, KIT AND METHOD FOR PURIFYING A GAS COMPRISING MAJORITY IN METHANE Technical field of the invention

[0001] 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. State of the art

[0002] The most economical existing solutions for removing H2S are based 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 without vacuum.

[0003] A staged purification process comprises primary and secondary purification. Primary purification, carried out by micro-aeration, consists of injecting oxygen-enriched air directly into the gas heads of the methanation reactors, also called "digesters." At this point, a biochemical reaction occurs on desulfurization nets; a bacterioarchean flora metabolizes H2S in the presence of O2 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 purification does not reduce the H2S concentration in the gas exiting the methanation reactor to levels compatible with injection into a methane network.

[0004] Secondary or complementary purification is mainly carried out by adsorption processes on activated carbons. The biogas stream to be purified from the primary purification passes through a bed of adsorbent made up of activated carbons 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 it is implemented correctly).

[0005] The most economical solution for removing H2S, micro-aeration, requires the addition of oxygen, which is undesirable in biogas. This addition of oxygen raises quality issues, as the O2 molecule is difficult to remove from a biogas stream without resorting to costly solutions.

[0006] Furthermore, micro-aeration does not allow H2S to be reduced 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 predominantly by adsorption onto activated carbon.

[0007] This additional purification is much more expensive than primary purification, which only requires the addition of enriched oxygen within the digester's gaseous 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 chemical reaction within the activated carbon bed, it must be replaced. This represents significant costs in terms of raw materials, waste management, transportation, and process interruption when there are not several activated carbon filters in parallel.

[0008] For economic reasons, digester operators therefore have an interest in promoting 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 problems related to the increased oxygen content in the injected biomethane, sometimes reaching levels of several thousand ppm, which are incompatible with certain uses sensitive to the presence of this molecule.

[0009] Existing solutions for removing H2S are inexpensive and effective, but they require the addition of excess dioxygen to the biogas and ultimately end up in the biomethane. Unfortunately, dioxygen is a harmful compound for certain uses of biomethane, while also complicating methane extraction and storage, particularly in aquifers. Uses for which dioxygen is a harmful compound include, for example, combined cycle power plants, certain furnaces, and certain "raw material" uses, notably the production of ammonia by methane reforming.

[0010] Other H2S purification technologies exist, but they are currently used very little in the biomethane sector for economic reasons. For example, these processes are of the biological scrubber type, water scrubbing, scrubbing with alcohols, amines or solvents, biological process, sacrificial chemical deoxygenating process ("scavenger"), catalytic reaction.

[0011] 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.

[0012] 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 limiting or eliminating the need to resort to injecting O2 into digesters. Summary of the invention

[0013] The present invention aims to remedy all or part of these drawbacks.

[0014] To anticipate future limitations, it is necessary to have technological building blocks to remove residual oxygen or to develop alternative H2S purification methods limiting or eliminating the need to resort to O2 injection in digesters.

[0015] In particular, the present invention makes it possible to use 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.

[0016] Furthermore, the solution can be adapted as a kit for existing installations currently using activated carbon. In particular, it is possible to retrofit existing installations without changing the installed methanation and purification reactors. Benefits provided

[0017] According to a first aspect, the present invention relates to a device for purifying a gas consisting mainly of methane, the device comprising: - at least one methanization reactor comprising: - an oxygen inlet, - a means of regulating the flow rate of dioxygen injected into the methanization reactor by the dioxygen inlet and - a gas outlet consisting mainly of methane and at least some hydrogen sulfide, - at least one purification reactor comprising: - a bed of iron hydroxide, - a gas inlet consisting mainly of methane and at least hydrogen sulfide connected to the outlet of the methanization reactor and - a purified gas outlet consisting mainly of methane - 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; - 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.

[0018] 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.

[0019] Furthermore, using iron hydroxide instead of activated carbon reduces the cost of the device while providing comparable or even superior H2S adsorption capacities to activated carbon. Moreover, iron hydroxide is commercially available on a large scale. The advantage of iron hydroxide compounds compared to activated carbon is that they are also capable of removing some of the residual oxygen from the primary purification stage, in addition to their excellent H2S capture capacity. H2S reacts with iron oxides to form iron sulfides. The iron sulfides, in turn, react with residual oxygen to regenerate the iron oxides. Elemental sulfur is trapped in the adsorbent bed.

[0020] Finally, 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 H2S. The oxygen concentration in the biogas stream exiting the treatment reactor is therefore greatly 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.

[0021] In 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 in which an automated control system comprises: - a means of calculating a ratio between the concentration of oxygen captured and the concentration of hydrogen sulfide captured and - a means of sending a command by means of regulating the flow of dioxygen injected into the methanization reactor according to the calculated ratio.

[0022] Thanks to these provisions, the quantity of oxygen is adapted according to the quantity of hydrogen sulfide which depends on the organic matter placed in the methanization reactor.

[0023] In 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.

[0024] In 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.

[0025] 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 in a predetermined range of value 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.

[0026] In 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.

[0027] Thanks to these provisions, it is possible to detect a possible malfunction of the controller and / or the oxygen flow control system. Furthermore, it is possible to react, before injection into a network, by recirculating a portion of the gas to obtain a purer gas and limit oxygen consumption.

[0028] Indeed, an oxygen concentration sensor for the gas flowing out of the purification reactor, in addition to the inlet sensor, makes it possible to compare the oxygen content upstream and downstream and to establish an oxygen mass balance. In steady state, that is, when the stable H2S and O2 concentrations are stable in the gas inlet to the purification reactor, the purification reactor captures a certain overall stable mass flux of H2S and O2. If the mass flux captured by the reactor The change in purification process provides information about what is happening in the reactor. The captured mass flow is obtained by the difference between the O2 entering and exiting the reactor.

[0029] 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 is likely that the bed is saturated, or, if the bed has just been changed, that the reactor is too small to handle these flows. Alternatively, if the O2 flow rate increases and the H2S flow rate decreases at the outlet of the purification reactor, it is probably because 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.

[0030] In 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.

[0031] Thanks to these provisions, it is possible to detect a saturation of the iron hydroxide bed or a sizing defect in the purification reactor.

[0032] In embodiments, the purification device further comprises a means for measuring the saturation of the iron hydroxide bed.

[0033] Thanks to these provisions, it is possible to detect a situation in which the iron hydroxide bed is saturated and to react before a breakthrough in the purification reactor.

[0034] In some embodiments, the control system comprises: - a means of comparing the measured saturation to a first predetermined saturation limit called "alert saturation", - a means of activating an alert when the measured saturation is greater than the alert saturation.

[0035] Thanks to these provisions, it is possible to alert the operator to an abnormal situation.

[0036] 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: - a means of comparing the measured saturation to a second predetermined limit saturation called "critical saturation", higher than the alert saturation and - a means of activating the means of diverting the gas at the outlet of the methanization reactor when the measured saturation is higher than the critical saturation.

[0037] 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 into the inlet of the methanization reactor while the iron hydroxide bed is being replaced.

[0038] 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.

[0039] Thanks to these arrangements, the iron hydroxide bed is replaced as it becomes saturated, which allows continuous operation with a single purification reactor.

[0040] In embodiments, the control unit includes a means for adapting the control of the means for regulating the flow of dioxygen injected into the methanization reactor according to the measured saturation.

[0041] 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 progresses inexorably over the long term. Thanks to these arrangements, the oxygen supply is matched to the iron hydroxide adsorption capacity of the bed.

[0042] 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: - at least one methanization reactor comprising: - an influx of dioxygen, - a means of regulating the flow rate of dioxygen injected into the methanization reactor by the dioxygen inlet and - a gas outlet consisting mainly of methane and at least some hydrogen sulfide, - 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 - a purified gas outlet consisting mainly of methane; - the kit includes: - a bed of iron hydroxide, - 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; - 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.

[0043] Since the objectives, 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.

[0044] According to a third aspect, the present invention relates to a process for purifying a gas consisting mainly of methane, the process comprising: - a methanation stage in a methanation reactor comprising: - an influx of dioxygen, - a means of regulating the flow rate of dioxygen injected into the methanization reactor by the dioxygen inlet and - a gas outlet consisting mainly of methane and at least some hydrogen sulfide, - a purification stage in a purification reactor comprising: - a bed of iron hydroxide, - a gas inlet consisting mainly of methane and at least hydrogen sulfide connected to the outlet of the methanization reactor and - a purified gas outlet consisting mainly of methane - 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; - a control step comprising a means control step for regulating the flow rate of dioxygen injected into the methanization reactor according to the concentration of dioxygen captured.

[0045] The aims, advantages and special characteristics of the process which is the subject of the present invention being similar to those of the device which is the subject of the present invention, they are not recalled here. Brief description of the figures

[0046] 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: [Fig. 1] schematically represents a first particular embodiment of the device that is the subject of the present invention, [Fig.2] schematically represents a second particular embodiment of the device that is the subject of the present invention, [Fig.3] schematically represents different breakthrough front states in a purification reactor that is the subject of the present invention, [Fig.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. Description of the implementation methods

[0047] The present description is given by way of non-limiting grammatical reason, each feature of an embodiment being able to be advantageously combined with any other feature of any other embodiment.

[0048] The expression "and / or", as used in this document and in the claims, shall be understood as meaning "either or both" of the elements thus joined, that is, elements that are present conjunctively in some cases and disjunctively in others. The multiple elements listed with "and / or" shall be interpreted in the same way, that is, "one or more" of the elements thus joined. Other elements may be present, other than the elements 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.

[0049] As used herein in the description, "or" should be understood as having 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, that is, the inclusion of at least one, but also more than one, of a number or list of elements, and optionally, of additional unlisted elements. Only terms clearly indicating the contrary, such as "only one of" or "exactly one of", or, when used in the claims, "consisting of", refer to the inclusion of only one element of a number or list of elements.

[0050] As used in this description and in the claims, the expression "at least one," with reference to a list of one or more elements, is to 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 enumerated 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 the elements 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, with at least one, possibly including more than one, A, without B present (and possibly including elements other than B); in another embodiment, with at least one, possibly including more than one, B, without A present (and possibly including elements other than A); in yet another embodiment, with 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.

[0051] 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 to say, 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.

[0052] It should be noted from the outset that the figures are not to scale.

[0053] It is recalled here that "majority" means that which is in the greatest quantity. 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 of that gas. For example, a gas composed of 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.

[0054] 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.

[0055] Figure 1, which is not to scale, shows a schematic view of one embodiment of the device 100 which is the subject of the present invention.

[0056] The device 100 for purifying a gas consisting mainly of methane, the device comprising at least one methanization reactor 101 comprising: - an oxygen inlet 104, - a means of regulating 105 the flow rate of dioxygen injected into the methanization reactor 101 by the dioxygen inlet 104 and - an outlet 107 of gas consisting mainly of methane and at least hydrogen sulfide.

[0057] A methanation reactor 101 comprises a hermetically sealed reaction chamber equipped with stirring 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 micro methanogenic organisms. The reaction chamber comprises a bed of organic matter 102 and a gaseous headspace 103.

[0058] Preferably, 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 may be agricultural residues, food waste, or sewage sludge, for example.

[0059] Preferably, and in a manner known to those skilled in the art, the methanation reactor 101 includes a means for regulating the temperature in the reaction chamber to maintain a constant and optimal temperature inside the reaction chamber. The thermal regulation means includes heating and cooling systems, thus optimizing the biodegradation conditions, which are known to those skilled in the art.

[0060] Furthermore, the methanation reactor 101 includes a means for collecting and conveying biogas from the gaseous manifold 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 composed primarily 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.

[0061] 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.

[0062] 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 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.

[0063] The device of the present invention also includes, downstream of the methanization reactor 101, at least one purification reactor 110 comprising: - a bed 112 of iron hydroxide, - an inlet 110 of the gas comprising mainly methane and at least hydrogen sulfide connected to the outlet 107 of the methanization reactor 101 and - an outlet 115 of purified gas comprising mainly methane.

[0064] 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.

[0065] Preferably, the purification reactor 111 takes the form of a truncated cylinder, the axis of which is substantially vertical. The inlet 110 of the purification reactor 110 is located on one of the bases of the cylinder and the outlet 115 is located on the other base. The iron hydroxide bed 112 is positioned between the inlet 110 and the outlet 115. Preferably, the outlet 115 is positioned on the taller base.

[0066] Preferably, iron hydroxide is inserted into the purification reactor 111 in the form of granules.

[0067] 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:

[0068] [Math 1] 2 Fe(OH)3 + 3 H2S Fe2S3 + 6 H2O

[0069] 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:

[0070] [Math 2] Fe2S3+ 1.5 O2 + 3H2O 2 Fe(OH)3 + 3 S

[0071] 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.

[0072] The device and method of the present invention make it possible to optimize these two chemical reactions.

[0073] 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 for the 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.

[0074] In preferred embodiments, the pipe is also equipped with a first sensor 109 for a hydrogen sulfide 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.

[0075] The first sensor 108 of a dioxygen concentration of the gas and the first sensor 109 of a hydrogen sulfide concentration of the gas can 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 for the oxygen concentration of the gas and the first sensor 109 for the hydrogen sulfide concentration of the gas can be positioned on the pipe that connects the outlet 107 of the methanization reactor 101 to the inlet 110 of the purification reactor or on a bypass pipe.

[0076] 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.

[0077] The control unit 118 includes a means 120 for sending a command to the control means 106 of the flow rate of dioxygen injected into the methanization reactor as a function of the concentration of dioxygen captured.

[0078] 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 result of the comparison, the control unit 118 prepares and sends a command to increase or decrease the injected oxygen flow rate.

[0079] Preferably, the 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 to the means of regulation 106 of the flow of dioxygen injected into the methanization reactor according to the calculated ratio.

[0080] The control unit 118 is preferably a microcontroller configured to store and execute programmed instructions. Preferably, the control unit comprises: - a means of display, such as a screen and / or indicator lights, - a user interface, such as a keyboard, - a means of communication, wired or wireless, with each sensor of the device that is the subject of the present invention, - a memory configured to store the instructions executed.

[0081] In preferred embodiments, the control unit 118 includes a means of communication with a management system. The management system may be an application hosted on a server configured to remotely monitor and control at least one control unit.

[0082] Preferably, the calculation means 119 for a ratio between the concentration of captured dioxygen and the concentration of captured hydrogen sulfide is included in The microcontroller executes instructions to calculate said ratio. The means of sending a command 120 is a communication means, wired or wireless, from the corresponding control unit to a corresponding communication means of the regulation means 106.

[0083] 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.

[0084] Preferably, the means of comparison compares the calculated ratio to: - a first predetermined limit ratio called the "lower ratio", and / or - a second predetermined limit ratio called the "upper ratio".

[0085] 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. Thus, 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.

[0086] The upper ratio represents a ratio at which excess oxygen is injected into the methanation reactor 101 and is therefore present in the gas flow to be injected into the network. Thus, when the calculated ratio is greater than the upper ratio, the control includes an instruction to reduce the flow rate of dioxygen injected into the methanation reactor 101. The flow control means 105 is controlled to reduce 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 closed than before the comparison.

[0087] When the calculated ratio is between the lower and upper ratios, the oxygen flow rate remains unchanged. In other words, when the control means 105 is a solenoid valve, the valve position remains the same.

[0088] Preferably, the lower ratio and the upper ratio are selected according to the operating conditions and the dimensions of the methanization and / or purification reactor.

[0089] Furthermore, if the main constraint concerning the gas outlet of device 100 is to have as little O2 as possible, the upper and lower ratio values ​​can be less than or equal to 1, with the upper ratio value being strictly greater than the lower ratio value. This ensures the absence of O2 at the reactor outlet, at the expense of degraded continuous regeneration. Indeed, more iron oxides would be consumed, which implies a more frequent change of bed 112.

[0090] 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 1.4 and even more preferably equal to 1.5, and the upper ratio is equal to 1.8 and even more preferably equal to 1.6.

[0091] When the upper ratio is greater than or equal to 1.7, it is possible to dispense with reactor 130, which includes a bed 131 of activated carbon described below. Alternatively, reactor 130 can be retained and used at a very low capacity, thereby minimizing operating costs related to the carbon.

[0092] The first sensors, 108 and 109, the control unit 118, and the regulation means 105 define a virtuous feedback loop aimed at optimizing the quantity of enriched dioxygen injected in primary purification, i.e., into the methanization reactor 101, according to different operating regimes. The operating regimes are detailed below. A - When the O2 flux exactly compensates for the H2S load of the catalytic bed, then the O2 injection into the methanization reactor 101 is maintained in the same proportions. B- When the O2 flow is insufficient to regenerate the adsorbent bed 112, the H2S concentration is too high compared to the O2, and the bed 112 gradually becomes loaded with iron sulfides. Increasing the O2 injection rate in primary treatment increases the residual O2 content at the inlet of secondary treatment, i.e., in treatment reactor 111, but also decreases the H2S content at this point, because primary treatment would be favored by a higher O2 injection. C- When the O2 flow rate is too high to regenerate the adsorbent bed 112: the O2 concentration in the bed is too high, causing it to regenerate faster than it saturates. It is not necessary to inject as much O2 to meet the injection specifications. Reducing the O2 injection rate in primary treatment decreases the amount of O2 available for primary treatment, thus degrading the performance of this treatment stage and the biogas exiting the primary treatment process. then presents an O2 concentration which decreases while the H2S concentration increases to gradually reach operating regime A.

[0093] The feedback loop thus 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.

[0094] It is noted that the concentration of hydrogen sulfide at outlet 107 of the methanization reactor 101 depends on the organic matter inserted into the methanization reactor 101. It is therefore necessary to continuously monitor the concentration of hydrogen sulfide at outlet 107 of the methanization reactor 101.

[0095] In some embodiments, a first sensor 108 for measuring the oxygen concentration of the gas and a first sensor 109 for measuring the hydrogen sulfide concentration of the gas are configured to perform measurements simultaneously at regular intervals. For example, the measurements are performed 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 in a synchronized manner.

[0096] In some embodiments, the control unit 118 can send a measurement instruction to each sensor, 108 and 109.

[0097] 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.

[0098] In embodiments, the device 100 further comprises 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.

[0099] The second sensor 116 can correspond to any type of oxygen concentration sensor known to a person skilled in the art.

[0100] 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.

[0101] Preferably, the second sensor 116 for a gas oxygen concentration may include a means of communication, wired or wireless, with the automaton programmable logic controller 118. The communication means is configured to provide the programmable logic controller 118 with each measurement taken. In some embodiments, the communication means is configured to: - receive a synchronization instruction to an internal clock of the programmable logic controller 118, and / or - to receive an instruction to take measurements.

[0102] 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 a predetermined limit value.

[0103] A first predetermined limit value corresponds to a value beyond which the composition of the gas exiting the purification reactor 111 indicates a failure to regulate 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.

[0104] When the comparison 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.

[0105] 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.

[0106] When the comparison means 121 detects that the value measured by the second sensor 116 of an oxygen concentration in the gas 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: - switch the output flow 107 from the methanization reactor 101 to another purification reactor 111, - close inlet 110 of the purification reactor 111, - 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 - reduce to zero the oxygen flow rate at the inlet 104 of the methanization reactor 101 to stop the gas production and purification process.

[0107] In some embodiments, the device 100 further comprises a second sensor 117 for the concentration of hydrogen sulfide in 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 concentration of hydrogen sulfide captured by the second sensor 117.

[0108] The second sensor 117 can correspond to any type of hydrogen sulfide concentration sensor known to a person skilled in the art.

[0109] 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.

[0110] 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 the person skilled in the art or a single sensor for analyzing the composition of a gas.

[0111] 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: - receive a synchronization instruction to an internal clock of the programmable logic controller 118, and / or - to receive an instruction to take measurements.

[0112] 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 a predetermined limit value.

[0113] 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.

[0114] 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: - switch the output flow 107 from the methanization reactor 101 to another purification reactor 111, - close inlet 110 of the purification reactor 111, - 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 - reduce to zero the oxygen flow rate at the inlet 104 of the methanization reactor 101 to stop the gas production and purification process.

[0115] The embodiments in which the control relates to switching or recirculation are described below, opposite [Fig.2].

[0116] 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 equal to 3.6 ppm, and even more preferably 0 ppm.

[0117] 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 modification of the dioxygen flow rate at inlet 104 of the methanization reactor 101 is commanded.

[0118] 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 111 is greater than 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 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 inlet 104 of the methanization reactor 101.

[0119] For example, the third predetermined limit value for dioxygen concentration is equal to 400 ppm.

[0120] 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.

[0121] When the comparison means 121 detects that the value measured by the second sensor 117 of hydrogen sulfide concentration 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 sensor 116 of a dioxygen concentration of the gas at the outlet 115 of the purification reactor is below a third predetermined limit value for dioxygen concentration, a command is generated by the programmable logic controller 118 and sent by the sending means 120 for: - switch the output flow 107 from the methanization reactor 101 to another purification reactor 111, - close inlet 110 of the purification reactor 111, - 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 - reduce to zero the oxygen flow rate at the inlet 104 of the methanization reactor 101 to stop the gas production and purification process.

[0122] Such a situation is representative of a malfunction in the purification reactor. For example, the third predetermined limit value is equal to 400 ppm.

[0123] The reaction in bed 112 of the purification reactor 111 can be described by a thermal front. The thermal front designates the region of bed 112 in the purification reactor 111 in which a temperature gradient appears. The thermal front moves as the reactor operates and chemical or physical reactions occur, generating heat.

[0124] As indicated above, two reactions occur in bed 112: - a H2S capture reaction and - a regeneration reaction of the adsorbent.

[0125] Each of these two reactions has a reaction front, that is to say a zone in which the associated reaction takes place. These zones may overlap.

[0126] The breakthrough front zone designates the H2S 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 H2S does not react with bed 112; it is then said to have broken through.

[0127] The thermal front corresponds to the front of the regeneration reaction, which is exothermic. In general, the thermal front is lower than the breakthrough front, because the regeneration reaction can only occur if the bed has already reacted with H2S.

[0128] If the gas contains a lot of H2S and little O2, the breakthrough front can be at the very top of reactor 111 and the thermal front at the very bottom of reactor 111. However, if the ratio between the concentration of captured oxygen and the concentration of captured hydrogen sulfide is on the order of 1.6, the thermal front follows the breakthrough front. There is then a slight excess of O2 for the regeneration reaction, but this Regeneration can only occur if the H2S (in a slight deficiency) has reacted with the bed. In this case, the breakthrough front and the thermal front are located roughly in the same place.

[0129] The movement of the thermal front is illustrated in particular with regard to [Fig. 3]. [Fig. 3] represents different thermal front states in a purification reactor 111 which is the subject of the present invention.

[0130] 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.

[0131] The iron hydroxide bed 112 is represented as two stacked cylinder truncates inside the purification reactor 111.

[0132] In the various states, 301, 311 and 321: - 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. - 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.

[0133] State 301, shown on the left of [Fig. 3], represents so-called "normal" operation 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 globally balanced. The thermal front, or breakthrough front, is visually fixed.

[0134] State 311, shown in the middle of [Fig. 3], represents operation in which hydrogen sulfide is in excess. The ratio of the oxygen concentration to the 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 device will have to be shut down, because the hydrogen sulfide concentration in the gas exiting the purification reactor will exceed the second value Due to a predetermined limit on hydrogen sulfide concentration, the gas will therefore not be compatible with injection into a biogas network.

[0135] State 321, shown on the right of [Fig. 3], represents an operation in which oxygen is in excess. The ratio of the oxygen concentration to the 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.

[0136] Despite the regeneration of bed 112 occurring simultaneously with the adsorption reaction, wear (also known as "saturation") of the iron hydroxide bed occurs. Thus, the breakthrough front progresses slowly towards the outlet 115 with the progressive saturation of the bed with elemental sulfur in the form of S8. The lifetime of the iron hydroxide bed is not infinite even if it is continuously regenerated.

[0137] For these reasons, in embodiments, the device 100 further includes a means for measuring 113 of the saturation of the bed 112 of iron hydroxide.

[0138] 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.

[0139] A shift in the thermal front, particularly towards the outlet 115 of the scrubbing 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.

[0140] In some embodiments, the purification reactor 111 is equipped with a wall transparent to visible light, against the iron hydroxide bed 112. The measuring 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 measuring 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 part of the iron hydroxide bed 112 that reacts according to formula 1 and the part that reacts according to formula 2.The portion of the iron hydroxide bed 112 that reacts according to formula 1 is ochre or yellow in color, while the portion of the iron hydroxide bed 112 that reacts according to formula 2 is brown to black in color.

[0141] Preferably, the control unit 118 comprises: - a means of comparing 122 the measured saturation to a first predetermined saturation limit called "alert saturation", - a means of activating an alert 123 when the measured saturation is greater than the alert saturation.

[0142] The comparison means 122 is, for example, the microcontroller executing comparison instructions.

[0143] 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.

[0144] 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.

[0145] In embodiments, represented in [Fig.2], the device 200 further comprises a means for diverting, 201 and 202, the gas at the outlet 107 of the methanization reactor 101. The elements represented in [Fig.2] having identical references to the elements represented in [Fig.1] present embodiments similar to those described above.

[0146] Figure 2 represents, in particular, a second purification reactor 211, comprising An inlet 210 is connected to the outlet 107 of the methanation reactor 101, and an outlet 115 is also present. 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.

[0147] In the embodiment shown in [Fig.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.

[0148] 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 further 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 valve 201 or 202, connecting the outlet 107 of the methanization reactor 101 to the purification reactor 110 or 210, which is supplied with gas and whose saturation is critical, and for opening 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.

[0149] In embodiments, the device, 100 or 200, further comprises an extraction means, 114 or 214, of a portion of the bed, 112 or 212 of iron hydroxide and in which the control unit 118 comprises a means of sending 120 a command to extract a portion of the bed of iron hydroxide as a function of the measured saturation.

[0150] 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 [Fig.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 outlet 107 of the methanization reactor 101, the iron hydroxide 112 or 212, can be completely replaced.

[0151] In embodiments shown in [Fig.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 the two beds, 112 or 212, with iron hydroxide while at least one of the two beds is being replaced.

[0152] In 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.

[0153] 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.

[0154] Figures 1 and 2 also show, connected to outlet 115 of the purification reactor, 110 or 210, 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. The purified gas, separated from the carbon dioxide, can be conveyed to a water separation means 128. of methane, known to those skilled in the art. The separation means 128 includes a water storage means 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, 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.

[0155] 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: - at least one methanization reactor comprising: - an influx of dioxygen, - a means of regulating the flow rate of dioxygen injected into the methanization reactor by the dioxygen inlet and - a gas outlet consisting mainly of methane and at least some hydrogen sulfide, - 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 - a purified gas outlet consisting mainly of methane.

[0156] The kit comprises the elements shown in Figures 1 and 2, and in particular: - a bed 112 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.

[0157] Figure 4 shows a process 400 which is the subject of the present invention.

[0158] The purification process 400 for a gas consisting mainly of methane comprises: - a methanation stage 401 in a methanation reactor comprising: - an influx of dioxygen, - a means of regulating the flow rate of dioxygen injected into the methanization reactor by the dioxygen inlet and - a gas outlet consisting mainly of methane and at least some hydrogen sulfide, process 400 comprising: - a purification step 402 in a purification reactor comprising: - a bed of iron hydroxide, - a gas inlet consisting mainly of methane and at least hydrogen sulfide connected to the outlet of the methanization reactor and - a purified gas outlet 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 407 of a regulation of the flow of dioxygen injected into the methanization reactor according to the concentration of dioxygen captured.

[0159] In preferred embodiments, the process further comprises: - 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, - a control step 405 comprising: - a calculation step 406 of a ratio between the concentration of captured dioxygen and the concentration of captured hydrogen sulfide and - a control step 407 of a regulation of the flow of dioxygen injected into the methanization reactor according to the calculated ratio.

[0160] Preferably, the means of devices 100 and / or 200 are configured to implement the steps of process 400 and their embodiments as set out above and process 400 and its various embodiments 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 methanation reactor (101) having: - an oxygen inlet (104), - a means for regulating (105) the flow rate of oxygen injected into the methanation reactor by the oxygen 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) having: - a bed (112, 212) of iron hydroxide, - an inlet (110, 210) of the 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 a oxygen concentration of the gas circulating between the outlet of the methanization reactor and the gas inlet of the purification reactor;- a control unit (118) comprising a means of sending (120) a command by means of regulating the flow rate 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) of a 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 automaton (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 to regulate the flow rate 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) comprises a means (121) for comparing the calculated ratio to a first limiting ratio predetermined so-called "lower ratio", and when the calculated ratio is lower than the lower ratio, the command 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, further comprising 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, further comprising a second sensor (117) of a hydrogen sulfide concentration of the gas flowing out of the purification reactor and wherein 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, further comprising 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 comparing (122) 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 means for diverting (201, 202) the gas outlet (107) of the methanization reactor (101), the control unit (118) comprising: - a means of comparing (122) the measured saturation to a second predetermined limit saturation called "critical saturation", higher than the alert 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 higher 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. Kit for a device for purifying (100, 200) a gas consisting mainly of methane, the device (100, 200) comprising: - at least one methanization reactor (101) comprising: - an oxygen inlet (104), - a means for regulating (105) the flow rate of oxygen injected into the methanization reactor by the oxygen 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 a dioxygen concentration of the gas circulating between the outlet of the methanization reactor and the inlet of the gas of the purification reactor;- a control automaton (118) comprising a means (120) for sending a command by means of regulating the flow rate of; Oxygen is injected into the methanization reactor according to the concentration of oxygen captured.

13. A process for purifying (400) a gas consisting mainly of methane, the process comprising: - a methanation step (401) in a methanation reactor (101) comprising: - an oxygen inlet (104), - a means for regulating the flow rate of oxygen injected into the methanation reactor by the oxygen inlet, and - an outlet (107) of gas consisting mainly of methane and at least 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 the 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 methanation reactor and the gas inlet of the purification reactor; - a control step (405) comprising a control step (407) for regulating the flow rate of oxygen injected into the methanization reactor as a function of the captured oxygen concentration.

Images