MULTI-LAYER TEMPERATURE CONTROLLED CATALYTIC METHANATION DEVICE

Abstract

TITLE OF THE INVENTION: MULTI-LAYER TEMPERATURE CONTROLLED CATALYTIC METHANATION DEVICE The methanation device (115) comprises, within the same methanation reactor (120) through which a gas flow passes between an inlet (123) and an outlet (124) of this reactor, successively in the direction of movement of the gas flow, at least two reaction layers (121, 122) of catalyst, the first of which (121) forms a fluidized bed, and, between two successive reaction layers, a separation means (136) physically separating said two reaction layers.This device also includes cooling means (125 to 128, 130 to 133) for each of the reaction layers and, for each reaction layer, a temperature control means (127, 132) for said reaction layer, said control means being configured to maintain a decreasing temperature between successive reaction layers in the direction of gas flow. Figure 4 for the abbreviation.

Description

Title of the invention: MULTI-LAYER CATALYTIC METHANATION DEVICE TEMPERATURE-CONTROLLED REACTIONS Technical field of the invention

[0001] The present invention relates to a temperature-controlled, multi-layer catalytic methanation device. In particular, it is applicable to minimizing the residual hydrogen (H2) content in the syngas (synthesis gas or SNG) exiting a catalytic methanation reactor, thereby reducing subsequent adjustment steps before injection into a natural gas network. Prior art

[0002] The approaches described in this section are approaches that could be pursued, but not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated, it should not be assumed that any of the approaches described in this section constitutes prior art simply because of its inclusion in this section.

[0003] In the fight against climate change and the reduction of greenhouse gas emissions, the production of low-carbon energy carriers is an essential alternative. The present invention relates to the production of synthetic methane by methanation of carbon monoxide, CO, and / or carbon dioxide, CO2. The following are examples of methanation: - Syngas (or synthesis gas or SNG) from the "Pyrogasification" process of biomass or waste or hydrocarbon materials. - of a mixture of carbon dioxide and dihydrogen (CO2 / H2) in a "Power-to-Methane" process, which consists of converting electricity ("power") into methane or in a process with any other source of hydrogen, for example, waste hydrogen.

[0004] In the remainder of this document and for the sake of simplicity, the term "methane" shall refer to all types of synthetic methane produced by methanation of CO and / or CO2.

[0005] The first sector concerned by this invention is the pyrogasification sector. This family of processes makes it possible to produce numerous energy carriers (electricity, heat, liquid biofuels, chemicals, methane, hydrogen, etc.) while integrating into a circular economy approach. From low capacity (from a few kWth to two MWth) to high capacity (greater than 100 MWth), these processes can also provide decentralized solutions for waste recovery. Indeed, only 30% of global waste is currently recovered (through recycling, Incineration or composting is used to dispose of the remaining biomass, with the remainder being buried in dedicated facilities or dumped in the open countryside, creating significant health and environmental problems. The first step in this process involves the thermal conversion of biomass or waste, which undergoes successive drying and devolatilization of the organic matter to produce a carbonaceous residue (char), a synthesis gas (called syngas), and condensable or non-condensable compounds (tars). The carbonaceous residue can then be oxidized by the gasification agent (water vapor, air, oxygen, carbon dioxide) to produce a gas primarily composed of H2 and CO. Depending on its nature, this gasification agent may also react with the tars or the major gases.Thus, if it is water vapor (H2O), a WGS (Water Gas Shift) reaction occurs in the gasification reactor according to the following balanced reaction, called "WGS" (acronym for Water Gas Shift for water-gas conversion): . CO + H2O Û H2 + CO2 AG298K = - 41 kJ / mol (RI)

[0006] Char can also be extracted from the reactor for further use, while syngas is produced by secondary and tertiary reactions of the pyrolysis products. Reactor pressure has little effect on this reaction; however, the equilibrium is strongly linked to the reactor temperature and the initial concentrations of the reactants. The gas resulting from these reactions is called syngas. It consists of a mixture of major gases (H2, CO, CO2, CH4, CxHy), condensable or non-condensable compounds (tars), particles (char, coke, elutriated bed material), and inorganic compounds (alkali metals, heavy metals, H2S, HCl, NH3, etc.). As a reminder, the term "elutriated" derives from Stokes' law. The term "elutriation" refers to a particle floating in a fluid flow.In process terminology, by extension, a particle is said to be "elutried" when it is carried away by the flow of a fluid outside of its initial reactor.

[0007] After the removal of impurities, the major gases can be transformed into numerous energy carriers, including methane. For the production of this methane, the H2 / CO concentration ratio in the syngas is a determining factor. At the outlet of the gasification reactor, this ratio generally does not exceed two.

[0008] Syngas can be converted into methane by the catalytic methanation reaction of CO, also known as the "Sabatier reaction". This catalytic reaction, which has rapid kinetics at the temperatures used, is characterized by very high exothermicity: CO + 3 H2 Û CH4 + H2O AG298K = -206 kJ / mol (R2)

[0009] To maximize CH4 production, H2 and CO should be in a stoichiometric ratio close to 3:1. This ratio is obtained by carrying out a Complementary WGS reaction (RI). This can be carried out prior to methanation in a dedicated reactor, using specific catalysts. It can also be achieved directly in the same reactor as methanation with an adapted catalyst. In both cases, this reaction requires the presence of steam, obtained, for example, by co-injection, with the syngas produced by pyrogasification. Even when maintaining the stoichiometric H2 / CO ratio, the reaction remains incomplete due to chemical equilibria that are also dependent on operating conditions (temperature, pressure, etc.).

[0010] CO2 also present in the syngas or from an external source produces CH4 by methanation reaction of CO2: CO2 + 4 H2 → CH4 + 2 H2O AG298K = -164 kJ / mol (R3)

[0011] Like reaction (R2), this reaction is strongly exothermic. For To maximize CH4 production, H2 and CO2 should be in a stoichiometric ratio close to 4:1. As with CO methanation, even when respecting the H2 / CO stoichiometric ratio, the reaction remains incomplete due to chemical equilibria.

[0012] Reaction (R3) can be carried out in conjunction with reaction (R2) in a single methanation reactor within a pyrogasification process if the H2 / (CO+CO2) ratio is sufficiently high (>7): this is then referred to as co-methanation. To achieve these high ratios, a prior WGS (RI) reaction or an external H2 supply may be necessary.

[0013] The CO2 (R3) methanation reaction can also be carried out independently, for example in the so-called "Power-to-Methane" process. This process involves utilizing CO2 streams (of industrial origin) by reacting them with hydrogen in a methanation device to form methane.

[0014] In both cases (Pyrogasification and Power-to-Methane), a final specification step separates certain constituents of the produced gas to obtain methane that meets the specifications for injection into the natural gas or mobility methane network. For example, in France, the CO2 content must be less than 2.5% and the H2 content must be less than 6% for injection into a natural gas network and less than 2% for vehicle natural gas. Beyond the simple H2 limit for injection into the networks, a HHV (Higher Heating Value) criterion, for example in France it must be greater than or equal to 10.7 kWh / Nm3, implicitly leads to lowering the H2 content of the injected gas to values ​​often below 2%, due to the very low C2+ content in the SNG at the methanation outlet.

[0015] To meet the injection specifications for natural gas networks, and particularly to comply with the low hydrogen content requirements that may apply, several gas treatment processes downstream of methanation, and / or several methanation reactors are currently necessary. Consequently, the investment, operating, and maintenance costs of the production units are high, which significantly increases the overall cost of methane production.

[0016] At the outlet of existing catalytic methanation reactors, the purification chain required to achieve a quality meeting the standards set by transmission and distribution networks or end users is quite complex. Although the separation of H2O and CO2 is sufficient to achieve a compliant Wobbe index value, separation of residual hydrogen is required to meet the hydrogen concentration criterion and, above all, the criterion regarding the HHV (Higher Heating Value) range of methane.

[0017] Furthermore, the incomplete conversion of hydrogen during balanced methanation reactions in current reactors negatively impacts the unit's efficiency.

[0018] Under the conditions generally used to produce methane from syngas from gasification, the methanation reaction of CO (R2) is very largely favoured.

[0019] The methanation reaction is an exothermic reaction with a decrease in the number of moles; according to Le Chatelier's principle, the reaction is favored by pressure and disfavored by temperature.

[0020] Methane production is maximal for a gas with a composition close to the stoichiometric composition, i.e., with an H2 / CO ratio close to three. Syngas produced by steam gasification, particularly of biomass, is characterized by a lower H2 / CO ratio, on the order of 1.5 to 2.

[0021] The heat released during the conversion of CO is approximately 2.7 kWh during the production of 1 Nm³ of methane. Controlling the temperature within the reactor, and therefore removing the heat produced by the reaction, is a key factor in minimizing catalyst deactivation (sintering, carbon deposition, etc.) and maximizing methane conversion rates with a minimum number of reactors in series (ideally a single reactor). As explained previously, if the reactor temperature increases, the conversion of synthesis gas to methane decreases sharply.

[0022] The composition of the raw SNG at the reactor outlet is closely linked to the reactor operating conditions (pressure, temperature, adiabatic or isothermal, stoichiometry, etc.) which govern the chemical equilibria of reactions RI, R2, and R3. These reactions generally form water, and a separation of this species is Therefore, it is required. Regarding the other species (CO, CO2, and H2), their respective concentrations can be modified by adjusting the reactor's operating mode (adiabatic or isothermal) and by changing the temperature or pressure. High pressure and low temperature thus allow for a considerable reduction in the concentrations of these compounds. When the operation is carried out in an adiabatic reactor, a series of steps is also necessary to achieve a conversion quality equivalent to that of an isothermal reactor. In any case, the composition of the produced gas is generally not in accordance with the injection specifications, and adjustment steps are necessary to eliminate residual CO2 and / or H2. Thus, the operating mode represents a key obstacle to simplifying the process chain. Summary of the invention

[0023] The present invention aims to remedy all or part of these drawbacks.

[0024] To this end, the invention relates to a methanation device, which comprises, within a methanation reactor through which a gas flow passes between an inlet and an outlet of this reactor, successively in the direction of movement of the gas flow, at least two reaction layers of catalyst, the first of which forms a fluidized bed, and, between two successive reaction layers, a separation means physically separating said two reaction layers, the device further comprising means for cooling each of the reaction layers and, for each reaction layer, a means for controlling the temperature of said reaction layer, said control means being configured to maintain a decreasing temperature between successive reaction layers in the direction of movement of the gas flow.

[0025] Thanks to these arrangements, the final reaction layer, in the direction of gas flow, has a lower temperature, which reduces the hydrogen content and increases the gross calorific value (GCV) of the gas exiting the methanation reactor. At the outlet of the methanation devices of the present invention, a gas rich in methane and very poor in hydrogen is obtained. This simplifies the purification process required to achieve a quality that meets the specifications set by transmission and distribution networks or end users. Indeed, methane purification then consists of dehydration and separation of any residual excess CO2.

[0026] In optional embodiments, at least the first reaction layer, in the direction of gas flow movement, forms a dense or bubbling fluidized catalytic bed.

[0027] This prevents the particles from the fluidized bed from going downstream of this fluidized bed, for example onto a means of physical separation of the reaction layer forming this fluidized bed, which could damage or clog it or into the SNG produced by the reactor.

[0028] In optional embodiments, each reaction layer includes a catalyst for converting pyrogas syngas from hydrocarbon materials and water into methane.

[0029] In optional embodiments, each reaction layer includes a catalyst for converting a mixture of hydrogen and carbon dioxide into methane.

[0030] In optional embodiments, at least two reaction layers comprise catalysts with different physico-chemical properties.

[0031] In optional embodiments, at least two reaction layers comprise a catalyst identical in its physico-chemical properties.

[0032] In optional embodiments, the cooling means of each of the reaction layers are configured so that more than three-quarters of the cooling capacity of the cooling means are located in the first reaction layer through which the gas flow passes.

[0033] Each reaction layer downstream of the first reaction layer thus carries out only a small part of the methanation reaction.

[0034] In optional embodiments, said control means are configured to maintain a temperature difference, between the first reaction layer and the last reaction layer, greater than or equal to 5 °C.

[0035] In optional embodiments, said control means are configured to maintain a temperature of the first reaction layer greater than or equal to 300 °C and a temperature of the last reaction layer less than or equal to 295 °C.

[0036] In optional embodiments, each reaction layer forms an isothermal fluidized catalyst bed and at least one heat exchanger present in one of the reaction layers is absent from another reaction layer.

[0037] Thus, for at least one reaction layer, the temperature control means of this reaction layer is independent of the temperature control means of another reaction layer.

[0038] In optional embodiments, the methanation device of the invention comprises, for each reaction layer, a temperature sensor for said reaction layer, wherein the temperature control means for said reaction layer is configured to control the flow rate and / or temperature of the heat transfer fluid passing through at least one of said heat exchangers present in said reaction layer at the temperature measured by the temperature sensor in said reaction layer.

[0039] Thus, for each reaction layer, the operation of a heat exchanger present in this reaction layer is controlled by the temperature of this reaction layer.

[0040] In optional embodiments, the means for cooling at least the last reaction layer, in the direction of movement of the gas flow, comprise a heat exchanger configured to cool the gas flow exiting the methanation reactor to provide a cooled gas flow and an injection of this cooled gas flow into said reaction layer or between said reaction layer and the previous reaction layer.

[0041] The gas produced by the methanation reactor is thus recirculated after cooling, to cool the last reaction layer, which avoids introducing different fluids, which could disrupt the reaction and / or change the composition of this gas.

[0042] In optional embodiments, the methanation device of the invention further comprises a device for bringing the gaseous flow exiting the reactor to specifications, the cooled gaseous flow coming from this device for bringing to specifications.

[0043] In optional embodiments, the last reaction layer forms a fixed catalytic bed and the injection of the cooled gas stream is carried out between said last reaction layer and the previous reaction layer.

[0044] The cooled gas flow thus passes uniformly through this fixed bed.

[0045] In optional embodiments, said last reaction layer forms a fluidized bed in transported regime, the methanation device further comprising, at the outlet of the reactor, a gas and solids separator configured to extract the transported catalyst particles, and a recirculation pipeline for these particles by injection into said last reaction layer.

[0046] Thanks to these arrangements, the need to have a heat exchanger in this last reaction layer is reduced or eliminated.

[0047] In optional embodiments, the methanation device of the invention further comprises, on the recirculation pipeline, a cooler configured to cool said catalyst particles before their injection into said last reaction layer.

[0048] Thus, the particles of the fluidized bed of the last reaction layer ensure the removal of heat from this reaction layer.

[0049] In optional embodiments, the last reaction layer, in the direction of gas flow, forms a fluidized bed in the transported regime, the methanation device further comprising, at the outlet of the reactor, a gas and solids separator configured to extract the transported catalyst particles, and a heat exchanger configured to cool the flow of gas and catalyst particles at the outlet of the methanation reactor to provide at least cooled catalyst particles, and a recirculation pipeline for these cooled particles by injection into said last reaction layer.

[0050] In optional embodiments, in the direction of gas flow movement, the first reaction layer forms a dense isothermal fluidized bed and at least the last reaction layer forms a fixed adiabatic bed, the cooling means comprising a heat exchanger before said last reaction layer, in the sky of the previous reaction layer. Brief description of the figures

[0051] Other advantages, purposes and features of the present invention will become apparent from the following description, given for explanatory purposes and in no way limiting the effect of the accompanying drawings, in which: [Fig. 1] schematically represents, in cross-section, a prior art fluidized catalytic bed reactor and a reactor of the invention, and the temperature profiles inside the fluidized catalytic beds, [Fig.2] represents hydrogen concentrations within the catalytic bed in the prior art fluidized bed reactor illustrated in [Fig.1] and in an example of a reactor that is the subject of the invention, [Fig.3] represents methane concentrations within the catalytic bed in the prior art fluidized bed reactor illustrated in [Fig.1] and in the example reactor that is the subject of the invention in [Fig.2], [Fig.4] schematically represents a first embodiment of a catalytic methanation device, the subject of the invention, with several fluidized catalyst reaction layers, each thermally controlled by a dedicated temperature control means, [Fig.5] schematically represents a variant of the device illustrated in [Fig.4], [Fig.6] is a graph representing the evolution of the HHV (Higher Heating Value) at the outlet of the reactor of a methanation device according to the first embodiment, after the removal of water and carbon dioxide, [Fig.7] is a graph representing the evolution of the residual dihydrogen mole fraction at the outlet of the reactor of a methanation device according to the first embodiment, after the removal of water and carbon dioxide, [Fig.8] graphically represents, as a percentage, the thermal power to be extracted from each of the two reaction layers of catalyst, as a function of their temperatures. [Fig.9] schematically represents a first example of a heat exchanger structure in a methanation device according to the first embodiment, [Fig. 10] schematically represents a second example of a heat exchanger structure in a methanation device according to the first embodiment, [Fig. 11] schematically represents a third example of a heat exchanger structure in a methanation device according to the first embodiment, [Fig. 12] schematically represents a first variant of a second embodiment of a catalytic methanation device of the invention, with several fluidized catalyst reaction layers and fluid injection acting by cooling to control the temperature of one of these layers, [Fig. 13] schematically represents a second variant of the device illustrated in [Fig. 12], [Fig. 14] schematically represents a third variant of the device illustrated in [Fig. 12], [Fig. 15] is a graph representing the evolution of the PCS at the outlet of the reactor of a methanation device according to the second embodiment, after the removal of water and carbon dioxide, [Fig. 16] is a graph representing the evolution of the residual dihydrogen mole fraction at the outlet of the reactor of a methanation device according to the second embodiment, after removal of water and carbon dioxide, [Fig. 17] represents, schematically, a fourth variant of the device illustrated in [Fig. 12], [Fig. 18] schematically represents a fifth variant of the device illustrated in [Fig. 12], [Fig. 19] is a graph comparing the PCS, after the removal of water and carbon dioxide, for the first four variants of the device according to the second embodiment, on the one hand, and the fifth variant of this second embodiment, on the other hand, [Fig.20] is a graph comparing the residual dihydrogen mole fraction, after removal of water and carbon dioxide, for the first four variants of the device according to the second embodiment, on the one hand, and the fifth variant of this second embodiment, on the other hand, [Fig. 21] schematically represents a third embodiment of a catalytic methanation device of the invention, coupled between a [Fig. 22] schematically represents a variant of the device illustrated in [Fig. 21], [Fig. 23] schematically represents a fourth embodiment of a catalytic methanation device of the invention, coupling a dense fluidized bed catalyst reaction layer with a transported fluidized bed catalyst reaction layer, and [Fig. 24] schematically represents a variant of a cooling method for a reaction layer of a catalytic methanation device of the invention. Detailed description

[0052] The present description is given by way of non-limiting grammar, each feature of an embodiment being able to be advantageously combined with any other feature of any other embodiment.

[0053] It should be noted from the outset that the figures are not to scale.

[0054] As can be understood from reading the present description, various concepts The inventive features can be implemented by one or more of the methods or devices described below, several examples of which are provided herein. The actions or steps performed in carrying out the method or device can be ordered in any appropriate manner. Consequently, it is possible to construct embodiments in which the actions or steps are performed in a different order than that illustrated, which may include performing certain acts simultaneously, even if they are presented as sequential acts in the illustrated embodiments.

[0055] The expression "and / or", as used in this application, shall be understood as meaning "either or both" of the elements thus joined, that is to say, elements which 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 to say, "one or more" of the elements thus joined. Other elements may possibly 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.

[0056] As used in this patent application, 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 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.

[0057] In the present application, all transitional 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 transitional expressions "consisting of" and "consisting essentially of" shall be understood as closed or semi-closed transitional expressions, respectively.

[0058] In all the figures where a pump or compressor followed by a single controlled valve is shown (Figures 4, 12, 13, 14, 17, 18, 21, 22 and 23) for regulating the temperature of a catalytic layer, according to a temperature setpoint (TIC1 or TIC2), alternatively this pump or compressor and this valve are replaced by a pump or compressor whose flow rate is controlled for the same regulation according to the same temperature setpoint. These regulation means constitute control means configured to maintain a decreasing temperature between successive reaction layers in the direction of gas flow.

[0059] Preferably, these control means are configured to maintain a temperature difference, between the first reaction layer and the last reaction layer, preferably greater than or equal to 5°C and, even more preferably, greater than or equal to 10°C, and even more preferably, greater than or equal to 20°C and preferably greater than or equal to 30°C.

[0060] In embodiments, these control means are configured to maintain a temperature of the first reaction layer greater than or equal to 300 °C. Preferably, the control means are configured to maintain a temperature of the last reaction layer less than or equal to 295 °C and, preferably, less than or equal to 290 °C and, preferably, less than or equal to 280 °C and, preferably, less than or equal to 270 °C.

[0061] The different embodiments of the methanation device of the invention described below are equally applicable to the pyrogasification process of hydrocarbon materials for the production of methane, and to the power-to-methane process for the production of e-methane by the hydrogenation of CO2.

[0062] To increase the conversion of hydrogen to methane, the methanation device of the invention employs at least two reaction layers of catalyst physically separated by a distribution system (perforated plate, injection nozzle, distributor, etc.). The temperatures of successive reaction layers are preferably controlled separately to obtain a decreasing temperature profile in the direction of the gas flow to be converted: the temperature of the first reaction layer of catalyst is strictly higher than that of the next, and so on. This invention allows the use of relatively high temperatures on the first reaction layer(s). This ensures that the majority of the reaction takes place rapidly, without kinetic limitation of the catalyst within the temperature ranges used, regardless of the catalysts employed.Identical or different catalysts, differing in their physicochemical properties, particularly in their compositions, dimensions, densities, surface states, shapes and sphericities, can be used in each of the reaction layers.

[0063] Figure 1 [Fig. 1] shows a schematic cross-sectional view of a prior art fluidized catalytic bed reactor 100 101 and a reactor 102 of the invention, also with reaction layers of catalyst in a fluidized bed (the quantities of catalyst being identical in both reactors) and the temperature profiles, respectively 103 and 104, inside the fluidized catalytic beds.

[0064] In this representation and these examples, reactor 100 operates at a nominal temperature of 330°C. Reactor 102 comprises two fluidized bed catalyst reaction layers, lower 105 and upper 106, physically separated by a gas distributor 107, and regulated at two distinct temperatures: 330°C for the lower catalyst reaction layer 105, and 300°C for the upper catalyst reaction layer 106. The temperature profile 103, which represents temperatures on the x-axis and the height in the fluidized bed 101 on the y-axis, shows an almost linear shape, with a decrease on the order of 10 °C over the upper 80% of the height of the fluidized bed 101. In contrast, the temperature profile 104 shows a temperature drop of about 40 °C in the upper catalyst reaction layer 106, compared to the lower catalyst reaction layer 105.

[0065] As previously mentioned, if the reactor temperature decreases, the conversion of synthesis gas to methane increases. Furthermore, for the other species (CO, CO2, and H2), high pressure and low temperature significantly reduce the concentrations of these compounds.

[0066] [Fig-2] represents, at the top, the hydrogen contents 108 and 109, respectively within the catalytic bed 101 in the fluidized bed reactor 100 and in the catalyst reaction layers of reactor 105. [Fig.3] represents, at the top, the contents of methane 110 and 111, respectively within the catalytic bed 101 in reactor 100 and in the catalyst reaction layers of reactor 105. At the bottom of each of these figures is given an enlargement of the highest zone of the fluidized beds.

[0067] Figures 2 and 3 show that, under the effect of a lower temperature on the upper catalyst reaction layer 106, the methanation reactions are driven towards an equilibrium state leading to a greater conversion of hydrogen to methane, thus improving the quality of the gas produced and the reaction yield. These performance characteristics are reflected in: - a significant decrease in residual hydrogen content, in [Fig.2] from 3.41% to 2.64%, and - An increase in methane content, in [Fig.3], from 25.11% to 25.42%.

[0068] By considering even lower temperatures on the uppermost catalyst reaction layer 106, the residual hydrogen content in the SNG can be significantly reduced further. Thus, for an upper catalyst reaction layer 106 temperature of 280 °C, the residual hydrogen content is 1.67%. For an upper catalyst reaction layer 106 temperature of 260 °C, the residual hydrogen content is 1.18%. For an upper catalyst reaction layer 106 temperature of 240 °C, the residual hydrogen content is 0.80%. These significant gains result in a drastic simplification of the SNG specification stage prior to injection into natural gas networks.

[0069] To increase the efficiency of heat transfer in the reaction layers, solutions known to those skilled in the art can be used, such as: - increasing the heat transfer coefficient by optimizing the hydrodynamic conditions (increasing convection) and / or - increase the heat exchange surface area (number of tubes, wetted surface area of ​​the tubes by corrugation, fins ...).

[0070] These ways of improving heat transfer can obviously be applied to all variants of the embodiments of the methanation device that is the subject of the invention described in this description.

[0071] In summary of the description of the inventive concept, with reference to Figures 1 to 3, the present invention is based primarily on obtaining a decreasing temperature profile, in the direction of gas flow, of catalytic layers in series, the first reaction layer forming a fluidized bed. The following description describes various embodiments for improving the efficiency of CO or CO2 methanation in order to reduce the residual H2 content of the SNG produced and thus limit the effort required to meet the injection specifications for natural gas networks.

[0072] First embodiment

[0073] The first embodiment relates to a catalytic methanation device with reaction layers of catalyst in fluidized beds, the temperature of each being controlled independently.

[0074] The methanation device, 115 or 116, comprises, within a single reactor 120, a cascade of isothermal fluidized catalytic layers whose setpoint temperatures decrease with TICn+l <TICn, n étant le numéro de la couche réactionnelle, dans le sens de déplacement du flux gazeux. En [Fig.4] et en [Fig.5], seulement deux couches catalytiques 121 et 122 sont représentées, pour limiter la complexité de représentation du dispositif de méthanation. On note que, dans la description, le terme « isotherme » signifie que les gradients de température dans la couche concernée sont faibles en comparaison de ceux que l’on observe dans une couche adiabatique. La description qui suit concerne ainsi uniquement deux couches réactionnelles de catalyseur, ou couches 121 et 122.However, the invention is not limited to this number and can be extended to a number of layers greater than two, following the general rule of decreasing temperatures between these layers, in the direction of passage of the gas flow to be converted (from bottom to top in figures 4 and 5).

[0075] As can be seen in [Fig. 4], the reactor 120 also includes a heat exchanger 125 in the lower layer 121 and a heat exchanger 130 in the upper layer 122. The device 115 further includes an inlet 123 for syngas and steam or CO2 and hydrogen, an outlet 124 for SNG, and two cooling circuits, respectively connected to the heat exchangers 125 and 130. The first cooling circuit includes a heat exchanger 126 removing heat from the lower layer 121 to the outside of the device 115, a valve 127, and a pump or compressor 128. The second cooling circuit includes a heat exchanger 131 removing heat originating from the upper layer 122 towards the outside of the device 115, a valve 132 and a pump or compressor 133. The flow rates through the valves 127 and 132 are controlled by temperature measurements TIC1 and TIC2 taken by sensors 137 and 138, respectively, in layers 121 and 122.

[0076] In [Fig.5], the same elements are found in the methanation device 116 as in [Fig.4], except that the exchanger 131 and the pump or compressor 133 are absent and the second cooling circuit is in parallel with the first cooling circuit, downstream of the pump or compressor 128, via a heat transfer fluid pipe 134.

[0077] A stream containing a mixture of syngas and steam or CO2 and hydrogen feeds the reactor 120 from below through a distributor 135 (for example, a perforated plate, a nozzle, a metal sinter, etc.) in order to fluidize a first reaction layer of catalyst 121 with a particle size between 100 and 1500 µm, and preferably between 150 and 500 µm. Upon contact with the catalyst of the first reaction layer 121, at temperature TIC1, the CO or CO2 is hydrogenated to produce a methane-rich SNG according to the Sabatier methanation reactions. The heat released by the conversion is extracted from the gas / solid reaction medium by means of the heat exchanger 125 immersed in it. Thus, the catalytic particles transfer their energy by convection and conduction to a heat transfer fluid circulating in the heat exchanger 125. This exchanger 125 is, for example, made up of a bundle of horizontal or vertical tubes (smooth, corrugated, finned...), a coil, plates ..., as illustrated in Figures 9 to 11. The temperature TIC1 of the first reaction layer of catalyst 121 is controlled by regulating the flow rate and / or temperature of the heat transfer fluid passing through the exchanger 125. The intensity of the particle movements resulting from the fluidization and the associated heat exchanges allow for very efficient conversion of the syngas from this first reaction layer of catalyst 121. However, since Sabatier reactions are limited by chemical equilibria, the SNG1 gas exiting this first fluidized layer 121 contains, depending on its temperature TIC1, a residual hydrogen content often higher than that imposed by the specifications of natural gas networks.

[0078] To overcome this difficulty and reduce the downstream steps for bringing the product to specification, the SNG1 passes through a second distributor 136 located at the outlet of layer 121 to supply a second catalyst reaction layer 122 operating at a temperature TIC2 lower than the temperature TIC1. Similar to the catalyst reaction layer 121, the fluidized catalyst reaction layer 122 includes the immersed heat exchanger 130, which allows the heat of conversion to be extracted and maintains isothermal fluidized operation for layer 122. As for In heat exchanger 125, a heat transfer fluid, whose flow rate through valve 132 and / or temperature are controlled by a temperature measurement taken by sensor 138 in layer 122, circulates through heat exchanger 130 (of similar or different technology to that of heat exchanger 125) to extract the heat of reaction. As illustrated in Figures 4 and 5, the heat transfer fluids (thermal oil, water, CO2, N2, water vapor, etc.) used in heat exchangers 125 and 130 can be integrated into the same cooling loop ([Fig. 5]) or be of different types, in which case each has its own loop ([Fig. 4]).

[0079] The graphs shown in Figures 6 and 7 respectively represent the evolution of the PCS and the mole fraction of H2 at the outlet of a methanation reactor according to the first embodiment, with two reaction layers of catalyst 121 and 122 with TIC1 = 320°C and TIC2 = 270°C, after the removal of water and carbon dioxide. This involves the conversion of a syngas and water vapor mixture whose feed conditions (Pressure, Temperature, Composition) are summarized in the following table, with the molar concentrations of the different molecules abbreviated by the letter X preceding the formulation of that molecule. Pressure (bar) 4.98 Temperature (°C) 250 Flow rate (kg / h) 7265.83 XH2 0.404 XCO 0.214 XCO2 0.160 XCH4 0.0583 XC2H4 0.0144 XH20 0.15

[0080] In order to compare the gains obtained by the first embodiment, the graphs in figures 6 and 7 were drawn considering water separation by condensation (10°C / 5 bar) and CO2 separation with a reduction of 98.5%, a priori feasible with the available technical solutions.

[0081] To illustrate the advantages of the first embodiment of the device of the invention, the graphs in Figures 6 and 7 represent, by means of dashed lines, a reactor with two reaction layers of catalyst, 121 and 122, whose temperatures TIC1 and TIC2 are respectively 320°C and 270°C

[0082] The HHV (Higher Heating Value), illustrated in [Fig. 6] by curve 140, reached at the outlet of layer 121 is 10.55 kWh / Nm3, at point 141, which is a value lower than that of the injection specification in natural gas networks (by (example here, the value in force in France of 10.7 kWh / Nm3 is considered for illustration).

[0083] The presence of the second layer 122 allows the PCS to be brought to a value 142 in accordance with the injection specification. This result is a consequence of a reduction in the residual H2 content of the SNG, represented on the curve 150. This content is reduced from 4%, at point 151 corresponding to the outlet of the lower reaction layer 121, to approximately 1.8% at point 152 corresponding to the outlet of the upper reaction layer 122, i.e. a concentration respecting the injection specification which is 2% in France on the natural gas transmission network (Natran, ex-GRTgaz).

[0084] Preferably, the cooling means of each of the reaction layers are configured so that more than three-quarters of the cooling capacity of these cooling means are located in the first reaction layer through which the gas flow passes, more preferably more than 85% and even more preferably more than 90%.

[0085] For example, to achieve this conversion in several isothermal catalyst reaction layers, [Fig. 8] shows that, for the temperature conditions mentioned in this figure, more than 95% of the heat exchange effort must be carried out in layer 121 via exchanger 125, the remainder being provided by exchanger 130 in layer 122. The power capacity shares of exchangers 125 and 130 are a direct consequence of the control temperature choices made for these two reaction layers 121 and 122. To illustrate this, [Fig. 8] also shows an example of a conversion where TIC1 is set at 400°C and TIC2 remains at 270°C to maintain a similar conversion. These two examples show that the characteristics (PCS, compositions, ...) of the SNG produced are a function of the temperature of the last reaction layer of catalyst 122, while the proportion of power to be extracted is more particularly linked to the temperature of the first reaction layer of catalyst 121. .

[0086] Different geometric arrangements of the heat exchangers 125 and 130 of the methanation device, 115 or 116, described below, can be implemented by combining identical or different heat exchanger systems in the various reaction layers. Figures 9, 10, and 11 show three examples in which the reactor 120 has two types of heat exchangers: submerged heat exchanger tubes, 160 and 161, and "near-wall" tubular heat exchangers ("coils"), 165 and 166, are shown in different geometric configurations. This coupling simplifies the reactor design by limiting the number of heat exchanger tubes that must pass through the upper reactor wall.

[0087] In [Fig. 9], the catalyst reaction layers 121 and 122 are traversed by immersion heat exchanger tubes 160, of the immersion pin type. The upper reaction layer 122 is, moreover, traversed by a "near wall" tubular heat exchanger 165.

[0088] In [Fig. 10], the upper reaction layer 122 is traversed by immersion heat exchanger tubes 160, of the immersion pin type. The lower reaction layer 121 is traversed by a "near wall" tubular heat exchanger 166.

[0089] In [Fig. 11], the catalyst reaction layers 121 and 122 are traversed by immersion heat exchanger tubes 160, of the immersion pin type. Preferably, the upper reaction layer 122 is also traversed by immersion heat exchanger tubes 161, of the immersion pin type, which do not reach the lower reaction layer 121. In other embodiments, the device comprises a set of heat exchangers dedicated to each of the catalytic layers.

[0090] Second embodiment

[0091] The second embodiment relates to a catalytic methanation device with several reaction layers of catalyst in fluidized beds, which implements a fluid injection reducing the temperature of at least one upper reaction layer of catalyst.

[0092] The methanation device, 215 to 219 depending on the variant, comprises, within a single reactor 220, a cascade of isothermal fluidized catalytic layers whose setpoint temperatures decrease with TICn+l <TICn, n étant le numéro de la couche réactionnelle, dans le sens de déplacement du flux gazeux.

[0093] In this second embodiment, a first reaction layer of catalyst is used in an isothermal fluidized bed cooled by an immersed heat exchanger, and at least one other reaction layer of catalyst is used in a fluidized or fixed adiabatic bed without a specifically immersed heat exchanger. However, for each reaction layer of catalyst without an immersed heat exchanger, a cold fluid is injected upstream or directly into this reaction layer.

[0094] This cold fluid is preferably a cooled SNG from any stage (inlet, with SNG partially brought to specification or outlet) of the bringing to specification (also called "up-grading") located downstream of the methanation reactor 220. The advantage of using this fluid is to avoid any contamination of the SNG thus produced.

[0095] In Figures 12 to 14, 17 and 18, only two catalyst reaction layers, here catalytic reaction layers, 221 and 222, are shown, to limit the complexity of representing the methanation device. The following description therefore relates only to two reaction layers, 221, on the one hand, and 222, 252 or 262, on the other. However, the invention is not limited to this number and can be extended to a number of catalyst reaction layers greater than two, following the general rule of decreasing temperatures between these layers, in the direction of passage of the gas flow to be converted (from bottom to top in figures 12 to 14, 17 and 18).

[0096] Figure 12 shows a methanation device 215, in which the reactor 220 includes a heat exchanger 225 in the lower layer 221. The device 215 further includes an inlet 223 for syngas and steam or CO2 and hydrogen, an outlet 224 for SNG, and a cooling circuit connected to the heat exchanger 225. This cooling circuit includes a heat exchanger 226 that removes heat from the lower layer 221 to the outside of the device 215, a valve 227, and a pump or compressor 228. The flow rate through the valve 227 is controlled by a temperature measurement TIC1 taken by a sensor 237 in the lower layer 221. Alternatively (not shown) or in addition, the temperature of the heat transfer fluid passing through the heat exchanger 225 is controlled by this temperature measurement.

[0097] At least one heat exchanger 239 and a specification adjustment device 240 are connected successively to the SNG outlet 224. A pipe 246 is connected to an SNG outlet of the device 240 and includes a pump or compressor 241 and an SNG outlet 242 in the reactor 220, upstream (in the direction of gas flow) of the second catalytic layer 222. The flow rate through the injection pipe at point 242 is controlled by a measurement of TIC2 temperatures taken by a sensor 238 in the upper layer 222.

[0098] It is noted that the pump or compressor 241 can be integrated into the device for bringing into specification 240 and is only necessary if the recirculation is carried out from a point located downstream of the reactor 222 where the pressure is lower than the pressure prevailing at the injection point 242.

[0099] A stream containing a mixture of syngas and steam or CO2 and hydrogen feeds the reactor 220 from below through a distributor 235 (for example, a perforated plate, a nozzle, a metal sinter, etc.) in order to fluidize a first reaction layer of catalyst in a bed of catalytic particles 221 with a particle size between 100 and 1500 µm, and preferably between 150 and 500 µm. Upon contact with the catalyst of the first reaction layer 221, at temperature TIC1, the CO or CO2 is hydrogenated to produce a methane-rich SNG according to the Sabatier methanation reactions. The heat released by the conversion is extracted from the gas / solid reaction medium by means of the heat exchanger 225 immersed in it. Thus, the catalytic particles transfer their energy by convection and conduction to a heat transfer fluid circulating in the heat exchanger 225.

[0100] In the second embodiment, the SNG from the lower reaction layer 221 is cooled by direct injection of a cold fluid. This cold fluid lowers the temperature of the SNG / cold fluid mixture before it passes through a second distributor 236 to feed the upper reaction layer, which can be a fluidized bed 222 (first variant 215 [Fig. 12]) or a fixed bed 252 (third variant 217 [Fig. 14]). In the upper reaction layer 222, the catalyst operates under adiabatic conditions. Thus, no heat exchanger dedicated to this upper reaction layer 222 is immersed in the catalytic bed.

[0101] Alternatively, the cold fluid can be directly injected through an outlet 243 of the SNG into the upper reaction layer 222 or 262, as in the second variant 216 ([Fig. 13]), the fourth variant 218 ([Fig. 17]), and the fifth variant 219 ([[Fig. 18]), to cool this reaction medium. To avoid any contamination of the SNG exiting the upper reaction layer 222, the cooling fluid is preferably SNG recirculated from a tap in the compliance chain (after cooling by the heat exchanger 239, after H2O condensation, or after CO2 separation, or a mixture of these different streams). Depending on the recirculation tap point (pressure, temperature, H2O composition), the recirculation loop 246 may optionally have a blower 241, a condenser...or any other equipment which promotes its injection into the SNG exiting the lower reaction layer 221 or directly into the upper reaction layer 222. .

[0102] Alternatively, in variants (not shown), to avoid any contamination of the SNG exiting the upper reaction layer, the cooling fluid is, for example, CH4 or CO2.

[0103] The graphs in Figures 15 and 16 correspond respectively to the evolution of the PCS and the mole fraction of H2 through a methanation reactor according to the second embodiment of the device, after the removal of water and carbon dioxide, as a function of the temperature setpoint TIC2. The recycling rate (TR), i.e., the proportion of flow taken downstream to obtain cooling to TIC2, has also been shown in these Figures 15 and 16. The feed conditions (pressure, temperature, and compositions) used to illustrate such operation are the same as those reported in the table describing the first embodiment. Furthermore, and for comparison purposes, two different values ​​of temperature TIC1 of the reaction layer of catalyst 221, 320°C and 400°C respectively, were studied.Finally, for the cases presented in figures 15 and 16, the cold fluid recirculated in the pipe 246 corresponds to SNG diverted from . an output of the CO2 separation stage carried out by device 240, a stage whose abatement efficiency is considered to be 98.5% and the temperature 10°C.

[0104] As a result of the chemical equilibria of the Sabatier reactions, an increase in the TIC2 temperature of layer 222 leads to a decrease in conversion efficiency, which is reflected in a decrease in the PCS, the Wobbe index, the CH4 content, and a higher residual H2 level. A higher TIC1 temperature of layer 221 results in higher recycling rates (TR) being required to cool layer 222 to a TIC2 temperature corresponding to the specifications to be achieved.

[0105] However, this recycling rate allows layer 222 to operate at a higher temperature to meet the specifications in terms of GCV and residual H2 content, primarily through dilution. The significant recycling rates (approximately 60%) resulting from higher TIC1 temperatures have a less favorable impact on the sizing of the equipment extending from the methanation reactor 220 to the SNG sampling point in device 240 and its reinjection into layer 222. Consequently, the second embodiment of the device is preferably implemented with a TIC1 temperature below 400°C, more preferably below 350°C, and even more preferably less than or equal to 320°C. Such conditions reduce the recycling rate TR from approximately 60% to less than 40%.Thus, to achieve the SNG characteristics in terms of maximum permissible H2 content, a temperature regulation (TIC2) of approximately 287°C via the recycling rate (TR) would be necessary. However, even if this first criterion is met, a lower temperature of approximately 273°C is required to also comply with the minimum acceptable HHV specification for injection. This reduction in the TIC2 temperature allows the residual H2 content to be lowered to approximately 1.5%.

[0106] Figures 17 and 18 show two variants of the device according to the second embodiment, 218 and 219 respectively, also using the injection of a cold fluid, cooled in the calibration device 240, which then includes a heat exchanger (not shown), to control the temperature of at least one downstream reaction layer. To prevent contamination of the produced gas by compounds not present in the reactive system, these variants 218 and 219 use recirculation of cooled SNG during the downstream calibration steps. These variants exhibit behavior similar to that described in the graphs of Figures 15 and 16.

[0107] In its variant 218 illustrated in [Fig. 17], the injection of cold fluid not only cools the upper catalyst reaction layer 262, but also drives the catalyst into the outlet 224. This solid catalyst is separated from the SNG in a gas and solids separator 248, then injected into the upper reaction layer 262 via a pipe 250. In this case, the upper reaction layer 262 operates in a transported fluidized bed regime and forms, together with the gas and solids separator 248 and the return leg (also called "Standpipe") 250, a transported fluidized bed. The main advantage of this variant 218 lies in the intensification of energy and mass exchange between the solid and fluid phases. The key factor remains the control of the TIC2 temperature by injecting the cold fluid through a gas outlet pipe 251 from the separator 248, the temperature control device 240, a valve 249 controlled by the temperature measured in the upper reaction layer 262 by the sensor 238, and a cold fluid inlet 247 into the layer 222.

[0108] The particle size and / or diameter of the layer 222 is adapted to achieve speeds at least greater than Ut (Terminal free fall speed of catalyst particles) and preferably between one and three times Ut, or even more, but preferably between one and a half and two and a half times Ut.

[0109] In its variant 219 illustrated in [Fig. 18], and unlike variant 218 illustrated in [Fig. 17], the transport and circulation of the catalyst contained in the upper reaction layer 262 are solely due to the SNG flow rate from layer 221. No additional fluid is directly added. Thus, the characteristics of the catalyst in the upper reaction layer 262 and the cross-sectional area of ​​this layer 262 are determined with respect to the flow rate exiting layer 221, to achieve the same velocity criteria as before. In this variant 219, the upper layer 262 also consists of a transported bed which alone controls the temperature of this layer 262.For this purpose, the transported catalyst is separated from the SNG by the separator 248, then cooled by a cooled fluid (preferably, cooled SNG from the device 240 which includes a heat exchanger, not shown) in a cooler 253, before recirculating to the upper reaction layer 262. The cooling fluid used in the cooler 253 rejoins the SNG stream via the separator 248.

[0110] To control the temperature TIC2, a valve 255 positioned on the pipe going from the device 240 to the cooler 253 is controlled by a temperature sensor 254 measuring the temperature inside the separator 248.

[0111] Figures 19 and 20 represent the evolution of the PCS and the mole fraction of H2, after the removal of water and carbon dioxide, during the change of configuration, from one of the first four variants 215 to 218, jointly shown on the left, to the fifth variant 219, shown on the right, for a TIC2 temperature equal to 270°C. For variant 219 illustrated in [Fig. 17], the characteristics of the SNG are a result of the mixture between the SNG exiting layer 222 and the fluid used for cooling the catalyst in the cooler 253. In the illustrated example, the fluid being a recycling of SNG brought to specifications, its contact with the catalyst in the cooler 253 leads to a slight modification of the chemical equilibria.

[0112] In terms of the H2 composition of the SNG, a decrease can be observed with variant 219 shown in [Fig. 17], compared to the variants shown in Figures 12, 13, 14, and 17. Indeed, its content decreases from approximately 1.4% to 1.1%, reflecting improved conversion efficiency. This higher conversion also results in an increase in the HHV, the Wobbe index, and the CH4 content. Thus, to meet the same natural gas network injection specifications, this variant could operate at a slightly higher temperature, thereby reducing the required TR recycling rate and the associated drawbacks.

[0113] Third embodiment

[0114] The third embodiment relates to a catalytic methanation device, within the same reactor, with several reaction layers of fluidized bed catalyst, which implements a coupling between a lower reaction layer of dense fluidized bed catalyst cooled by an immersed exchanger, in the reaction layer and at least one upper reaction layer of transported fluidized bed catalyst cooled by an external loop, as illustrated in its variants, in Figures 21 and 22.

[0115] The gas flow velocity within the upper catalytic layer 322 exceeds the transport velocity of the catalyst present in this layer 322. To achieve a fluidized bed in the upper reaction layer 322, several options are possible, including: - Use a catalyst with different physical properties than the catalyst present in the first layer 321; these properties may be, for example, a smaller particle size and / or a lower density, - A reduction in the reactor cross-section on the upper reaction layer 322, allowing for increased gas velocities, or - A combination of these approaches.

[0116] The transported catalyst is separated (for example, by a cyclone, a filter, or by gravity) from the gas exiting reactor 320 and cooled (for example, by a fluid / solid heat exchanger or by injecting a cooler fluid). The order of these two steps can be reversed. In the first variant 315 shown in [Fig. 21], a heat exchanger 352 precedes a separator 348. Conversely, in the second variant 316 shown in [Fig. 22], the separator 348 precedes the heat exchanger 352. The catalyst cooled then recirculates to the upper layer 322 of the methanation reactor 320, thus allowing this layer 322 to be operated at a temperature TIC2 lower than that of the previous layer (in the direction of movement of the gas flow).

[0117] The advantage of this third embodiment is that it reduces the amount of heat to be removed from the second reaction layer 322 by relocating this cooling function to the outside of the reactor 320. This advantage is sometimes essential due to the size of the heat exchangers dedicated to cooling the lower reaction layer 321, especially when the option of a pin bundle introduced from the top of the reactor is chosen.

[0118] As illustrated in Figures 21 and 22, the methanation device, 315 or 316 depending on the variant, comprises, within the same reactor 320, a cascade of isothermal fluidized catalytic layers whose setpoint temperatures decrease with TICn+l <TICn, n étant le numéro de la couche réactionnelle, dans le sens de déplacement du flux gazeux.

[0119] In Figures 21 and 22, only two catalyst reaction layers, here catalytic layers, 321 and 322, are shown to limit the complexity of representing the methanation device. The following description therefore relates only to two catalyst reaction layers, 321 and 322. However, the invention is not limited to this number and can be extended to more than two catalyst reaction layers, following the general rule of decreasing temperatures between these layers, in the direction of the flow of gas to be converted (from bottom to top in Figures 21 and 22).

[0120] A methanation device 315 is shown in [Fig. 21], in which the reactor 320 includes a heat exchanger 325 in the lower layer 321. The device 315 further includes an inlet 323 for syngas and steam or CO2 and hydrogen, an outlet 324 for SNG, and a cooling circuit connected to the heat exchanger 325. This cooling circuit includes a heat exchanger 326 that removes heat from the lower layer 321 to the outside of the device 315, a valve 327, and a pump or compressor 328. The flow rate through the valve 327 is controlled by a temperature measurement TIC1 taken by a sensor 337 in the lower layer 321. Alternatively (not shown) or in addition, the temperature of the heat transfer fluid passing through the heat exchanger 325 is controlled by this temperature measurement.

[0121] Connected successively to the outlet 324 of SNG are a heat exchanger 352, the gas and solids separator 348, and a catalyst recirculation line 350 from the separator 348 to the upper reaction layer 322. The flow rate of the heat transfer fluid through the heat exchanger 352 is controlled by a TIC2 temperature measurements performed by a sensor 354 in the upper layer 322.

[0122] A stream containing a mixture of syngas and steam or CO2 and hydrogen, conveyed by a pipe 323, feeds the reactor 320 from below through a distributor 335 (for example, a perforated plate, a nozzle, a metal sinter, etc.) in order to fluidize a first reaction layer of catalytic particles 321 with a particle size between 100 and 1500 µm, and preferably between 150 and 500 µm. Upon contact with the catalyst of the lower reaction layer 321, at temperature TIC1, the CO or CO2 is hydrogenated to produce a methane-rich SNG according to the Sabatier methanation reactions. The heat released by the conversion is extracted from the gas / solid reaction medium by means of the heat exchanger 325 immersed in it. Thus, the catalytic particles transfer their energy by convection and conduction to a heat transfer fluid circulating in the heat exchanger 325.

[0123] In its variant 315 illustrated in [Fig. 21], the injection of cold fluid not only cools the catalyst reaction layer 322 located above a distributor 336, but also carries the catalyst into the outlet 324. This solid catalyst is separated from the SNG in the gas / solid separator 348 and then returned to the layer 322 via the pipe 350. In this case, the layer 322 operates in a transported fluidization regime and, together with the gas / solid separation and the return leg (also called "Standpipe") 350, forms a transported fluidized bed. The main advantage of this variant 315 lies in the intensification of energy and mass exchange between the solid and fluid phases. The key factor remains the control of the TIC2 temperature by the injection of the cold fluid via the catalyst outlet pipe 350 from the separator 348.

[0124] A valve 353 controlled by the temperature measured by a sensor 354 in the second reaction layer 322 controls the flow of heat transfer fluid in the exchanger 352.

[0125] The particle size and / or diameter of the layer 222 is adapted to achieve speeds at least greater than Ut (Terminal free fall speed of catalyst particles) and preferably between one and three times Ut, or even more, but preferably between one and a half and two and a half times Ut.

[0126] In its variant 316 illustrated in [Fig.22], and unlike variant 315 illustrated in [Fig.21], the separator 348 precedes the heat exchanger 352.

[0127] In terms of conversion efficiency, changes in PCS, Wobbe index, H2 mole fraction and CH4 mole fraction, the results obtained by implementing the fourth embodiment are very similar to those achieved with the first embodiment.

[0128] Fourth embodiment

[0129] The fourth embodiment relates to a catalytic methanation device comprising, within the same reactor, several reaction layers of fluidized bed catalyst, which implements a coupling between a lower reaction layer of dense fluidized bed catalyst cooled by an immersed heat exchanger, and at least one reaction layer of fixed bed catalyst, as illustrated in its variants in [Fig. 23]. The first reaction layer is fluidized and isothermal and accommodates an immersed heat exchange surface. The second reaction layer is an adiabatic fixed bed. Between these two layers, no fluid is injected into the SNG produced by the first layer to cool it. On the contrary, a cooling system is positioned upstream of each reaction layer. These latter catalytic layers, whether dense or bubbling fluidized beds, fixed bed, or transported bed, operate in an adiabatic thermal regime. The diagram in [Fig.

[23] shows the operating principle of such a design by applying it to a configuration with two reaction layers of catalyst. In these variants, the cooling is represented as heat exchangers. A first heat exchanger 125 is immersed in the first reaction layer of catalyst in a fluidized bed 421. A second heat exchanger 430 is dedicated to cooling the top of the first reaction layer of catalyst 421, before the gas flow enters the downstream layer 422. These forced heat exchangers 125 and 430 can, for example, each be: - a bundle of tubes; . - a coil placed at the center or periphery of the catalyst reaction layer; - a cooled wall or - a combination of these types of heat exchangers.

[0130] Furthermore, instead of a specifically dedicated exchanger 430 and if the exchanger 125 is of the vertical plunging tube type, the passage through the sky of layer 421 can also ensure the cooling of the gas before its supply in layer 422.

[0131] For greater heat exchange efficiency, these tubes may, for example, have elements such as fins, corrugations, or any other means known to those skilled in the art for improving heat transfer in this passage through the top of layer 421. Finally, a last cooling method is to allow natural cooling through energy losses at the walls. However, choosing these last two options implies a more uncertain temperature control of the second layer 422, which is no longer effectively regulated by a TCI2 measurement as shown in [Fig. 23].

[0132] In the first variant 415, the elements of the device 116 illustrated in [Fig.5] are found, except for the heat exchanger 130. A heat exchanger 430 is positioned, in the reactor 420, in the sky of the lower reaction layer 421, below the distributor 136 and the upper reaction layer 422.

[0133] In an alternative (not shown), the second reaction layer of catalyst forms a fixed bed. In this case, the temperature measuring sensor used to regulate the flow rate of the heat transfer fluid in the exchanger 430 is positioned in the top of the second reaction layer.

[0134] With this embodiment, the specification of 2% residual H2 is achieved for a TIC2 temperature close to that of other embodiments (approximately 275°C). However, under these conditions, the PCS remains below the minimum permissible value for injection into the networks. A lower TIC2 temperature is therefore required to maintain this property.

[0135] A variant of a cooling means for a reaction layer 553 is shown in [Fig. 24]. This reaction layer can be any of the reaction layers of the methanation device of the invention. In this variant, a rising-bed catalyst cooling reactor 551 cools the catalyst coming from and returning to the methanation reactor 558. Thus, the heat produced by methanation is extracted from the reaction zone 553 and released through the solid catalyst transported to an external zone without the need for an immersed heat exchanger in the reaction zone 553 of the methanation reactor 558.

[0136] In the following description, reaction layer 553 is assumed to be the first reaction layer, in the direction of gas flow. The reaction gas flow is then syngas and / or a mixture of CO2 and H2, possibly supplemented by water vapor. If device 550 is used to cool a reaction layer other than the first, the reaction gas flow is mainly composed of SNG already produced by the preceding reaction layer(s). This SNG then consists mainly of CH4, CO2, and H2O, and to a lesser extent of CO (in the case of an application to the pyrogasification process) and H2. A portion, depending on the temperature and pressure conditions, of these "excesses" of H2 and CO are converted into SNG in this reaction layer.In the case of the power-to-methane process, H2 reacts with CO2 and, in the case of the pyrogasification process, H2 reacts primarily with excess CO from the previous reaction layer, then with CO2 if the CO concentration is sufficiently low (<1000 ppmv) and the residual hydrogen content is greater than the chemical equilibrium content under the pressure and temperature conditions of said next reaction layer.

[0137] In [Fig.24], in the device 550, we observe a methanation reactor 558 comprising a dense or bubbling fluidized bed 553 through which a reaction flow enters through the inlet 556 at the bottom of this reactor 558, and the cooling reactor 551 with transported bed catalyst.

[0138] In this device 550, the reaction flow feeds the dense or bubbling fluidized bed 553 containing a catalyst. The velocity of the reaction gas flow is preferably between three and seven times the minimum fluidization velocity of the catalyst. The produced SNG then passes into at least one other reaction layer 568, symbolized by a dashed box, and then exits the reactor through a pipe 559 at the top of the reactor 558. To control the temperature of the reaction layer 553, the catalyst circulates between the methanation reactor 558 and the transported fluidized bed cooling reactor 551. For this purpose, an inclined channel 554 (or a siphon) connects the lower parts of the two reactors 558 and 551, allowing a continuous flow of the catalyst from the methanation reactor 558 to the cooling reactor 551.

[0139] In the bottom of the cooling reactor 551, at least one fluid is injected through at least one pipe 564 to cool the catalyst and ensure its fluidization and subsequent transport to the top of the cooling reactor 551. Generally, and as shown in [Fig. 24], to ensure a gas seal between the cold and hot poles of the cooling reactor 551, this reactor 551 has a dense or bubbling zone at the bottom, above a distributor overlooking the outlet of the injection pipe 564. An injection through a pipe 565, positioned further downstream in the reactor 551, is necessary for the cooling of the catalyst, on the one hand, and its transport, on the other hand, if the horizontal cross-section of the reactor 551 is not sufficiently small to achieve the transport velocities (1.2 to 2 times the terminal free-fall velocity of the solid particles to be transported).In the device 550, fluid injection is staged via three pipes 564, 565, and 566. Several fluids of different types can be used to perform the two functions: cooling and transport. In [Fig. 24], on the one hand, liquid water is injected into the cooling reactor 551 via a pump 562 and pipe 566, and on the other hand, SNG, N2, or CO2 is injected into the cooling reactor 551 via a compressor or blower 563 and pipes 564 and 565. In normal operation, the cooling fluid is not air, oxygen, or H2, but during the catalyst activation or passivation phases, these fluids can also be used to enable: - regenerate the catalyst by burning the coke that can be formed during methanation reactions and be present in the catalytic bed (injection of water or air). - reactivate the catalyst in case of loss of catalytic activity (H2 injection).

[0140] At the top of the cooling reactor 551, the cooled catalyst is separated from the gas stream by a solids and gas separator 552, before being recirculated into the methanation reactor 558, via a pipe 555. This circulation of catalyst, cooled in the cooling reactor 551, allows the temperature of the reaction zone 553 to be controlled to a temperature setpoint. The flow rate of the pump 562 and the compressor or booster 563 is controlled according to the temperature measured in the reaction zone 553 by a sensor 561. The gas exiting the separator 552 is conveyed, by a pipe 567 to a heat exchanger 560 which cools it and allows the separation of the condensed water, if any, in liquid form, on the one hand, and of the SNG, N2 or CO2, in gaseous form, on the other hand, into at least one tank 557 supplying the pump 562 and the compressor or booster 563.

[0141] Initially, a reservoir 557 preferably contains liquid water and a gaseous headspace. The gaseous headspace is circulated to, on the one hand, allow the transport of the catalyst and, on the other hand, cool the catalyst. If, for example, at maximum circulation of the compressor 563, the target temperature in the reaction layer 553 (measured by the temperature sensor 561) is exceeded, liquid water is injected through the pipe 566, in addition to the gaseous headspace. In other operating modes, the cooling reactor 551 operates, in a steady state controlled by the temperature of the reaction layer 553, with a gas injection to ensure transport and a water injection providing the majority of the cooling.The advantage of this latter method of operation is to reduce the gas volumes to be managed in the separator 552, the pipe 567 and the heat exchanger 560, because very little liquid water is needed to extract a lot of heat from the catalyst, due to the evaporation of this liquid water in contact with the hot catalyst (thanks to the high value of the latent heat of vaporization of water).

[0142] The methanation device 550 includes, for at least one reaction layer 553, a means for extracting catalyst 554 from this reaction layer and a cooling reactor 551 having a fluidized bed, a zone of which operates in transport regime, this cooling reactor being provided with at least one inlet, 564, 565, 566 of cooling fluid, a pipeline 555 injecting the cooled catalyst exiting this cooling reactor into the methanation reactor 558.

Claims

Demands

1. Methanation device (115, 116, 215, 216, 217, 218, 219, 315, 316, 415, 420), characterized in that it comprises, within the same methanation reactor (120, 220, 320, 420) through which a gas flow passes between an inlet (123, 223, 323) and an outlet (124, 224, 324) of this reactor, successively in the direction of movement of the gas flow, at least two reaction layers (121, 122, 221, 222, 252, 262, 321, 322, 421, 422) of catalyst, the first of which (121, 221, 321, 421) forms a fluidized bed, and, between two successive reaction layers, a separation means (136, 236, 336) physically separating said two reaction layers, the device further comprising cooling means (125 to 128, 130 to 134, 160, 161, 165, 166, 225 to 228, 239 to 243, 247 to 251, 253, 255, 325 to 328, 348, 350, 352 to 354, 430) for each of the reaction layers and, for each reaction layer, a control means (127, 132, 137, 138, 227, 237,238, 241, 249, 254, 255, 327, 337, 353, 354) of the temperature of said reaction layer, said control means being configured to maintain a decreasing temperature between successive reaction layers in the direction of gas flow.

2. Methanation device (115, 116, 215 to 219, 315, 316, 415) according to claim 1, wherein at least the first reaction layer (121, 221, 321, 421), in the direction of gas flow movement, forms a dense or bubbling fluidized catalytic bed.

3. Methanation device (115, 116, 215 to 219, 315, 316, 415) according to any one of claims 1 or 2, wherein each reaction layer (121, 122, 221, 222, 252, 262, 321, 322, 421, 422) comprises a catalyst for converting pyrogaseous hydrocarbon and water syngas into methane.

4. Methanation device (115, 116, 215 to 219, 315, 316, 415) according to any one of claims 1 or 2, wherein each reaction layer (121, 122, 221, 222, 252, 262, 321, 322, 421, 422) comprises a catalyst for converting a mixture of hydrogen and carbon dioxide into methane.

5. Methanation device (115, 116, 215 to 219, 315, 316, 415) according to any one of claims 1 to 4, wherein at least two reaction layers contain catalysts that differ in their physico-chemical properties.

6. Methanation device (115, 116, 215 to 219, 315, 316, 415) according to any one of claims 1 to 5, wherein at least two reaction layers comprise a catalyst identical in its physico-chemical properties.

7. A methanation device (115, 116, 215 to 219, 315, 316, 415) according to any one of claims 1 to 6, wherein the cooling means (125 to 128, 130 to 134, 160, 161, 165, 166, 225 to 228, 239 to 243, 247 to 251, 253, 255, 325 to 328, 348, 350, 352 to 354, 430) of each of the reaction layers (121, 122, 221, 222, 252, 262, 321, 322, 421, 422) are configured so that more than three quarters of the cooling capacity of the cooling means are found in the first reaction layer (121, 221, 321, 421) through which the gas flow passes.

8. Methanation device (115, 116, 215 to 219, 315, 316, 415) according to any one of claims 1 to 7, wherein said control means (127, 132, 137, 138, 227, 237, 238, 241, 249, 254, 255, 327, 337, 352, 353, 354, 561, 563, 564) are configured to maintain a temperature difference, between the first reaction layer (121, 221, 321, 421) and the last reaction layer (122, 222, 252, 262, 322, 422), greater than or equal to 5 °C.

9. Methanation device (115, 116, 215 to 219, 315, 316, 415) according to any one of claims 1 to 8, wherein said control means (127, 132, 137, 138, 227, 237, 238, 241, 249, 254, 255, 327, 337, 352, 353, 354, 561, 563, 564) are configured to maintain a temperature of the first reaction layer (121, 221, 321, 421) greater than or equal to 300 °C and a temperature of the last reaction layer (122, 222, 252, 262, 322, 422) less than or equal to 295 °C.

10. Methanation device (115, 116, 215 to 219, 315, 316, 415) according to any one of claims 1 to 9, wherein at least one reaction layer (121, 122, 221, 222, 252, 262, 321, 322, 421, 422) forms an isothermal fluidized catalyst bed and at least one heat exchanger (125, 130, 161, 165, 166, 225, 325) present in one of the reaction layers is absent from another reaction layer.

11. A methanation device (115, 116, 215 to 219, 315, 316, 415) according to any one of claims 1 to 10, comprising, for at least one reaction layer (121, 122, 221, 222, 321, 421), a temperature sensor (137, 138, 237, 337) of said reaction layer, wherein the temperature control means (127, 132, 227, 327) of said reaction layer is configured to control the flow rate and / or temperature of the heat transfer fluid passing through at least one of said heat exchangers (125, 130, 160, 161, 165, 166, 225, 325) present in said reaction layer at the temperature measured by the temperature sensor in said reaction layer.

12. Methanation device (215, 216, 217, 218) according to any one of claims 1 to 11, wherein the cooling means (239 to 243, 249) of at least the last reaction layer (222, 252, 262), in the direction of movement of the gas flow, comprise a heat exchanger (239, 249) configured to cool the gas flow exiting the methanation reactor (220) to provide a cooled gas flow and an injection (242, 243, 247) of this cooled gas flow into said reaction layer or between said reaction layer and the previous reaction layer (221).

13. Methanation device (215, 216, 217, 218) according to claim 12, which further comprises a device (240) for bringing the gaseous flow exiting the reactor (220) to specifications, the cooled gaseous flow coming from this device for bringing to specifications.

14. Methanation device (217) according to any one of claims 12 or 13, wherein the last reaction layer (252) forms a fixed catalytic bed and the injection (242) of the cooled gas stream is carried out between said last reaction layer and the previous reaction layer (221).

15. Methanation device (218, 219, 315, 316) according to any one of claims 1 to 11, wherein said last reaction layer (262, 322) forms a fluidized bed in transported regime, the methanation device further comprising, at the outlet of the reactor (220, 320), a gas and solids separator (248, 348) configured to extract the transported catalyst particles, and a recirculation line (250, 350) for injecting these particles into said last reaction layer.

16. Methanation device (219, 315, 316) according to claim 15, further comprising, on the recirculation pipeline (250, 350), a cooler (253, 352) configured to cool said catalyst particles before their injection into said last reaction layer (262, 322).

17. Methanation device (550) according to any one of claims 1 to 11, 15 or 16, further comprising, for at least one reaction layer (553), a means for extracting catalyst (554) from this reaction layer and a cooling reactor (551) comprising a fluidized bed, a zone of which operates in transported mode, this cooling reactor being provided with at least one inlet (564, 565, 566) of cooling fluid, a pipeline (555) injecting the cooled catalyst exiting this cooling reactor into the methanation reactor (558).

18. Methanation device (415) according to any one of claims 1 to 9, wherein, in the direction of movement of the gas flow, the first reaction layer (421) forms a dense isothermal fluidized bed and at least the last reaction layer (422) forms a fixed adiabatic bed, the cooling means (430) comprising a heat exchanger (430) before said last reaction layer, in the sky of the previous reaction layer (421).

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