PLANT FOR TREATING A HYDROGEN GAS STREAM BY STAGED CATALITIC COMBUSTION

Abstract

INSTALLATION FOR TREATING A HYDROGEN GAS STREAM BY STAGED CATALITIC COMBUSTION E Installation (14) for treating a gas stream (16) comprising successive stages (26, 28, 30) adapted to burn hydrogen from the gas stream, each of the stages (26, 28, 30) comprising: - a source (38, 40, 42) of a gaseous oxidant stream, - a catalytic burner (50, 52, 54) adapted to admit an inlet stream (56, 58, 60), the oxidant stream, and to produce a flue gas stream (62, 64, 66), - an exchanger (68, 70, 72) for cooling the flue gas stream and obtaining an outlet stream (74, 76, 78). The inlet stream of a first stage comprises the gas stream to be treated, the inlet stream of each of the other stages comprising the outlet stream of the previous stage. In the stages, except the last, the catalytic burner burns only a fraction of the hydrogen present in the inlet stream, the outlet stream still comprising hydrogen.The installation produces at least one water flow (18) from the outlet flow of at least one of the stages. Figure for abstract: Figure 2.

Description

Title of the invention: INSTALLATION FOR TREATING A HYDROGEN GAS STREAM BY STAGED CATALITIC COMBUSTION

[0001] The present invention relates to an installation suitable for eliminating by combustion a gaseous flow to be treated comprising at least 75% hydrogen by volume.

[0002] The invention also relates to a naval platform, in particular an underwater vehicle, comprising such an installation.

[0003] The invention also relates to a treatment method implementing such an installation.

[0004] The gas flow to be treated is, for example, pure hydrogen from the operation of a fuel cell on board a naval platform, or produced by a chemical reaction.

[0005] By "elimination" is meant the transformation, preferably total, of hydrogen into one or more products which can be stored in the naval platform or released into its environment.

[0006] Currently, to achieve this elimination of hydrogen, it is known to use a catalytic burner supplied with ventilation air. Such a solution is used to treat diluted hydrogen discharges from batteries or a propulsion system, in order to maintain a hydrogen concentration below the lower explosive limit in the naval platform. However, this solution is not suitable for treating a gas with a high hydrogen content. There is a risk of reaching a high temperature in the burner catalyst, which can cause damage to the equipment, a fire or an explosion in the event of a hydrogen concentration above the lower explosive limit at the burner inlet. This technology is therefore not safe enough to be used in a naval platform such as an underwater vehicle.

[0007] To achieve this elimination, it would be possible to use a fuel cell and produce electricity from the hydrogen to be eliminated and oxygen. This solution may seem interesting from the point of view of size, but it must be navalized and adapted to reduce the risks in order to allow its approval. However, the approval constraints are higher for such equipment than for a fuel cell used for propulsion. Such a solution is therefore not currently considered sufficiently reliable in the particularly restrictive environment of an underwater vehicle, including including in exceptional environmental situations and after a shock.

[0008] To achieve the elimination of hydrogen, a mechanical compressor similar to those used to treat carbon dioxide emissions could be used. However, this type of compressor cannot be used as is with hydrogen. The external sealing of this type of equipment is often poor. In addition, the reliability of this type of component does not appear sufficient to ensure safe operation. Furthermore, this technology does not appear appropriate from the point of view of acoustic and vibration discretion. It could also pose a problem of size.

[0009] There are also metal hydride compressors that can remove hydrogen on a laboratory scale. However, the level of maturity of this technology is still low and does not allow its deployment on a naval platform to be considered reliably.

[0010] An aim of the invention is therefore to provide an installation suitable for treating a hydrogen-rich gas flow overcoming all or part of the above drawbacks, i.e. presenting sufficient guarantees in terms of reliability, discretion, reduced size and safety.

[0011] To this end, the invention relates to an installation suitable for treating a gas flow to be treated comprising at least 75% hydrogen by volume, the installation comprising a plurality of successive stages suitable for burning hydrogen from the gas flow to be treated, each of the stages comprising:

[0012] - a source of a gaseous oxidant flow comprising at least 21% oxygen in volume,

[0013] - a catalytic burner adapted to admit an inlet flow comprising hydrogen, to admit the flow of oxidant, and to produce a flow of fumes, and

[0014] - an exchanger for cooling the flow of fumes by heat exchange with a fluid refrigerant and obtain an output flow,

[0015] the inlet flow of a first stage of said plurality comprising the gaseous flow to be treated, the inlet flow of each of the other stages of said plurality respectively comprising the outlet flow of a previous stage of said plurality,

[0016] the installation being configured so that, in the stages of said plurality except the last stage, the catalytic burner burns only a fraction of the hydrogen present in the inlet flow, the outlet flow still comprising hydrogen,

[0017] the installation being further adapted to produce at least one flow of water from the outlet flow of at least one of the stages of said plurality.

[0018] According to particular embodiments, the installation comprises one or more of the following characteristics, taken in isolation or in all combinations: technically possible:

[0019] - said plurality of stages consists of two or three stages;

[0020] - the installation comprises a regulation system configured to regulate, in each of the stages of said plurality, a flow rate of the oxidant flow such that a temperature of the flue gas flow is lower than a maximum temperature between 800°C and 900°C;

[0021] - the regulation system is further configured to regulate, in each of the stages of said plurality, a flow rate of the refrigerant fluid such that a temperature of the outlet flow is greater than a minimum temperature between 100°C and 150°C;

[0022] - the regulation system is further configured to regulate, in the last stage of said plurality, a flow rate of the oxidant flow such that the flue gas flow of the last stage of said plurality comprises less than 1.0% hydrogen by volume;

[0023] - the installation further comprises: a source of a gas flow comprising at least 98% nitrogen by volume, the catalytic burner of the first stage of said plurality being adapted to admit the gas stream to dilute the flue gas stream of said catalytic burner; and a separator adapted to admit the outlet stream of the last stage of said plurality, and to produce the water stream and a gas stream comprising at least 90% nitrogen by volume, the catalytic burner of the first stage of said plurality being adapted to admit said gas stream;

[0024] - the refrigerant fluid comprises sea water or fresh water; and

[0025] - the installation comprises a pipe system adapted to admit the fluid refrigerant and passing the refrigerant fluid successively through the exchanger of each of the stages of said plurality in an inverse succession compared to a succession defined by the smoke flows.

[0026] The invention also relates to a naval platform, in particular an underwater vehicle, comprising at least one installation as described above.

[0027] The invention also relates to a method for treating a gas flow to be treated comprising at least 75% hydrogen by volume, the method implementing an installation and comprising the following steps:

[0028] - combustion of hydrogen from the gas flow to be treated in the stages of said plurality,

[0029] - in each of the stages of said plurality, except the last stage of said plurality, admission of the inlet flow and the oxidant flow into the catalytic burner and production of the flue gas flow, the catalytic burner burning only a fraction of the hydrogen present in the inlet flow, the outlet flow still comprising hydrogen,

[0030] - in the last stage of said plurality, admission of the inlet flow and the flow of oxidant in the catalytic burner and production of the smoke flow,

[0031] - in each of the stages of said plurality, cooling of the flow of fumes in the exchanger by heat exchange with the refrigerant fluid and obtaining the outlet flow,

[0032] - production of the water flow from the outlet flow of at least one of the stages of said plurality.

[0033] The invention will be better understood on reading the following description, given solely by way of example and with reference to the appended drawings, in which:

[0034] [Fig-1] [Fig.l] is a schematic view of a naval platform according to the invention,

[0035] [Fig.2] [Fig.2] is a schematic view of an installation according to the invention, included in the naval platform shown in [Fig.l], and

[0036] [Fig.3] [Fig.3] is a schematic view of an installation according to the invention, constituting a variant of the installation shown in Figures 1 and 2.

[0037] With reference to [Fig.l], a naval platform 10 according to the invention is described.

[0038] The naval platform 10 is preferably an underwater vehicle.

[0039] Alternatively, the naval platform 10 is a surface vessel.

[0040] In use, the naval platform 10 is surrounded by sea water 12.

[0041] The naval platform 10 comprises an installation 14 according to the invention.

[0042] According to a variant not shown, the naval platform 10 comprises several installations similar to the installation 14.

[0043] The installation 14 is adapted to treat a gaseous flow to be treated 16, comprising at least 75% hydrogen by volume, and to produce at least one flow of water 18.

[0044] In the example, the installation 14 is also adapted to admit a refrigerant fluid 20, advantageously consisting of a sample of sea water 12, and to discharge an effluent 22 consisting of the refrigerant fluid 20 after its use in the installation.

[0045] As visible in [Fig.2], the gas flow to be treated 16 comes from a source 24, for example:

[0046] - a fuel cell advantageously belonging to the propulsion system (not shown) of naval platform 10, or

[0047] - a storage of hydrogenated fuel, advantageously intended for supplying the propulsion system, and likely to produce a release of hydrogen.

[0048] The installation 14 comprises a plurality of successive stages 26, 28, 30 adapted to burn the hydrogen of the gas flow to be treated 16. The installation 14 advantageously comprises a regulation system 32, and a source 34 of a gas flow 36 comprising at least 98% nitrogen by volume. The installation 14 advantageously comprises a separator 38 adapted to evacuate the water flow 18, and comprises a recycling loop 40.

[0049] As a variant (not shown), the installation 14 comprises for example several se parators adapted to evacuate several flows of water from combustion in several of the stages 26, 28, 30, or even in all the stages.

[0050] According to still other variants (not shown), the installation 14 comprises a separator adapted to evacuate a flow of water resulting from the combustion in one of the stages 26, 28 (i.e. not in the last stage 30).

[0051] The installation 14 advantageously comprises a system of pipes 41 for admitting the refrigerant fluid 20 and rejecting the effluent 22.

[0052] As will be seen, stages 26, 28, 30 are adapted to carry out a staged combustion of hydrogen, and are successive from the point of view of the fumes. Stage 26 is therefore a first stage. Stage 28 is a second stage. Stage 30 is a third and final stage in the example shown in [Fig.3].

[0053] Each of the stages 26, 28, 30 comprises a source 38, 40, 42 of a gaseous oxidant flow 44, 46, 48 comprising between 21% and 100% oxygen by volume. Each of the stages 26, 28, 30 comprises a catalytic burner 50, 52, 54 adapted to admit an inlet flow 56, 58, 60 comprising hydrogen, to admit the oxidant flow 44, 46, 48, and to produce a flue gas flow 62, 64, 66. Each of the stages also comprises an exchanger 68, 70, 72 to cool the flue gas flow 62, 64, 66 by heat exchange with the refrigerant fluid 20 and obtain an outlet flow 74, 76, 78.

[0054] The inlet flow 56 of the first stage 26 is constituted in the example by the gas flow to be treated 16.

[0055] The input flows 58, 60 of the other stages 28, 30 are for example constituted respectively by the output flows 74, 76 of the preceding stages 26, 28.

[0056] According to a particular embodiment, not shown, the sources 38, 40, 42 are one and the same source.

[0057] According to a particular embodiment, a refrigerant circuit can be dedicated to each stage and not common to the entire installation.

[0058] According to a particular embodiment, the refrigerant circuit can supply stage 68, then stage 70 and stage 72 in this order.

[0059] The catalytic burners 50, 52, 54 are for example made up of tubes containing supported or bulk catalysts, containing elements known for their ability to carry out the hydrogen oxidation reaction. Advantageously, these elements can be metals from the family of supported platinoids and rare earths.

[0060] According to a particular embodiment, the catalyst consisting of the same elements is coated directly on the channels of the exchangers 68, 70, 72. In this case, the catalytic burners 50, 52, 54 and the exchangers 68, 70, 72 respectively form a single piece of equipment.

[0061] The installation 14 is configured so that, in all stages except the last stage 30, that is to say in stages 26 and 28, the catalytic burners 50, 52 burn only a fraction of the hydrogen present in the inlet flows 56, 58, the outlet flows 62, 64 still comprising hydrogen. In other words, the catalytic burners 50, 52, that is to say all except the last one, are intended to achieve a partial combustion of the hydrogen present in the inlet flows 56, 58. This is obtained by the fact that the quantity of oxygen supplied by the oxidant flows 44, 46 is deliberately insufficient for all the hydrogen present in the inlet flows 56, 58 to be burned.

[0062] In the example, the catalytic burner 50 of the first stage 26 is further adapted to admit the nitrogen-rich gas flow 36 to dilute the flue gas flow 62, and / or a gas flow 57 coming from the separator 38.

[0063] Advantageously, in the catalytic burner 54 of the last stage 30, the combustion of the hydrogen present in the inlet flow 60 is complete, the quantity of oxygen present in the oxidant flow 48 being sufficient for this, and advantageously just sufficient for this. In other words, the oxygen is found for example in the stoichiometric proportion in the oxidant flow 48.

[0064] The regulation system 32 is advantageously configured to regulate, in each of the stages 26, 28, 30, the flow rate of the oxidant flow 44, 46, 48 so that the temperature of the smoke flow 62, 64, 66 is lower than a maximum temperature of between 800°C and 900°C.

[0065] Preferably, the installation 14 is configured so that, in each stage, the oxidant is completely consumed.

[0066] The regulation system 32 is further advantageously configured to regulate, in each of the stages 26, 28, 30, the flow rate of the refrigerant fluid 20 so that the temperature of the outlet flow 74, 76, 78 is greater than a minimum temperature of between 100°C and 150°C.

[0067] The regulation system 32 is for example also configured to regulate, in the last stage, i.e. stage 30, the flow rate of the oxidant flow 48 so that the smoke flow 66 comprises less than 1.0% hydrogen by volume, and advantageously less than 0.1% hydrogen by volume, and even more advantageously less than 1 ppm hydrogen by volume.

[0068] The separator 38 is adapted to admit the outlet flow 78 from the last stage 30 and to produce the water flow 18 and a gas flow 80 comprising at least 90% nitrogen by volume. The separator 38 is for example of the float purger type.

[0069] As a variant, the separator 38 is for example a separator tank equipped with level measurements controlling purge valves.

[0070] Advantageously, the gas flow 80 comprises at least 99% nitrogen and water in volume, the combustion carried out in the catalytic burner 54 being complete or almost complete.

[0071] The recycling loop 40 comprises for example a recirculator 82 adapted to recirculate the gas flow 80, and a heater 84, advantageously electric to heat the gas flow 80 and preheat the installation 14 during the start-up phase.

[0072] The gas flow 80 is for example admitted into the catalytic burner 50 via the recycling loop 40 in the form of the gas flow 57, with or without the addition of the gas flow 36.

[0073] Advantageously, the installation 14 comprises a purge system (not shown), for example located on the gas flow 80, and adapted to carry out a purge in the edge, in particular in the event of overpressure. This purge system is for example controlled by the regulation system 32 and a pressure measurement in the installation 14.

[0074] The pipe system 41 is for example adapted to admit the refrigerant fluid 20 and pass it successively into the exchangers 72, 70, 68 of the stages 30, 28, 26 in an inverse succession with respect to the succession defined by the smoke flows 62, 64, 66.

[0075] The operation of the installation 14 will now be described, which also illustrates a method according to the invention.

[0076] The hydrogen contained in the gas flow to be treated 16 is gradually burned in stages 26, 28, 30.

[0077] In each of the stages, except the last stage 30, that is to say in each of the stages 26, 28, the inlet flow 56, 58 and the oxidant flow 44, 46 are admitted into the catalytic burners 50, 52 which produce the smoke flows 62, 64. The catalytic burners 50, 52 burn only a fraction of the hydrogen present in the inlet flows 56, 58, so that the outlet flows 74, 76 still comprise hydrogen.

[0078] In the last stage 30, the inlet flow 60 and the oxidant flow 48 are admitted into the catalytic burner 50 which produces the smoke flow 66 advantageously free of hydrogen.

[0079] In each of the stages 26, 28, 30, the flow of fumes 62, 64, 66 is cooled in the exchanger 68, 70, 72 by heat exchange with the refrigerant fluid 20 to obtain the outlet flows 74, 76, 78.

[0080] In the example, the inlet flow 56 of the first stage 26 is the gas flow to be treated 16. The outlet flow 74 of the first stage 26 becomes the inlet flow 58 of the second stage 28. The outlet flow 76 of the second stage 28 becomes the inlet flow 60 of the third and final stage 30.

[0081] The water flow 18 is produced from the outlet flow 78 of the last stage 30, in the example by the separator 38.

[0082] Advantageously, the regulation system 32 regulates the installation 14 so that the temperature of the smoke flows 62, 64, 66 does not exceed the maximum temperature between 800°C and 900°C, and advantageously so that the oxygen content at any point in the loop complies with the values ​​ensuring the safety of the installation. To do this, the regulation system 32 adjusts the flow rate of the oxidant flows 44, 46, 48, and the flow rate of the gas flow 80.

[0083] For each of the catalytic burners 50, 52, 54, the temperature of the fumes and / or the oxygen content downstream thereof can be lowered by reducing the flow rate of the oxidant flow 44, 46, 48, respectively, or by increasing the flow rate of the gas flow 80, i.e. by increasing the dilution of the fume flows 62, 64, 66.

[0084] The regulation system 32 advantageously regulates the temperature of the outlet flows 74, 76, 78 at temperatures above the minimum temperature of between 100°C and 150°C. To increase this temperature, the regulation system 32 reduces the flow rate of the refrigerant fluid 20 in the pipes. Conversely, to reduce this temperature, the regulation system 32 increases the flow rate of refrigerant fluid 20 in the pipes.

[0085] Optionally, according to a variant not shown, an additional exchanger is interposed between the exchanger 72 and the separator 38 to cool the outlet flow 78.

[0086] According to yet another variant, not only the refrigerant fluid 20, but another refrigerant fluid (not shown) is passed through the exchanger 72, so as to increase the refrigeration capacity in the last stage 30.

[0087] According to yet another variant, already described above, the exchangers 68, 70, 72 are made independent of each other, so as to be able to admit different refrigerant flows into each of these exchangers, and to adjust the refrigeration capacity of each of the stages, in particular by adapting the flow rate of refrigerant passing through each of the exchangers.

[0088] The compressor 82 circulates the gas flow 80 in the recycling loop 40. The source 34 makes it possible to provide an inert gas supplement via the gas flow 36 admitted into the catalytic burner 50.

[0089] Advantageously, when starting the installation 14, it is placed under non-pressurized nitrogen thanks to the gas flow 36 and the recirculation loop 40. The heater 84 heats the gas flow 80 in order to bring the catalytic burners 50, 52, 54 to a temperature for initiating the catalytic combustion of the hydrogen.

[0090] In normal operation, oxygen is introduced in sub-stoichiometry in all stages except the last stage 30. In these stages, the oxidation reaction occurs, leading to the transformation of a portion of the hydrogen present in the inlet flows 56, 58 into water vapor and leads to a release of heat. The oxygen is advantageously completely consumed by these reactions. The flow rate of oxygen supplied via the oxidant flows 44, 46 is for example controlled from the temperature of the smoke flows 62, 64 or by the flow rate of hydrogen at the inlet of each of the stages, calculated from the measurements of the flow rates of the gas flow 36 and the gas flow 80 and the hydrogen content at the inlet of each of the stages. At the outlet of each of the stages, the oxygen content is preferably measured and this measurement is used by the regulation system 32 to adjust the quantity of oxidant sent to each of the stages.

[0091] The temperature of the smoke flows 62, 64, 66 being kept lower than the maximum temperature, this avoids degradation of the catalysts present in the catalytic burners 50, 52, 54.

[0092] At the outlet of each of the stages 26, 28, 30, the exchangers 68, 70, 72 supplied by the refrigerant fluid 20 make it possible to lower the temperature of the outlet flows 74, 76, 78 to a temperature higher than the minimum temperature, which prevents condensation of water in these flows.

[0093] Alternatively, at the outlet of the exchanger 72, an additional exchanger (not shown) makes it possible to further cool the flow 78. The regulation system 32 adjusts the refrigerant flow rate of this additional exchanger in order to allow the separator 38 to produce the water flow 18.

[0094] In the example, the catalytic combustion and cooling operations are repeated three times. At the outlet of the last stage, i.e. stage 30 in the example, there is advantageously no more hydrogen or oxygen in the flue gas stream 66. The water produced by the successive combustions is completely or partially separated from the gases in the separator 38. The gas stream 80 is advantageously made up of nitrogen and water, and circulates via the recirculation loop 40 in order to dilute the reactants in each of the catalytic burners 50, 52, 54.

[0095] Advantageously, the installation 14, except for the compressor 82 and the heater 84, can be manufactured in a single piece by additive manufacturing.

[0096] Thanks to the characteristics described above, the installation 14 makes it possible to eliminate hydrogen from the gas flow to be treated 16 in a reliable, discreet and safe manner, with reduced bulk. The lack of oxygen, in particular in stages 26 and 28, makes it possible to avoid the explosion of the mixture by ensuring a hydrogen content higher than the upper explosive limit.

[0097] The reaction temperature of the gases, that is to say in particular the temperature of the smoke flows 62, 64, 66 is limited by staging the reaction in order to minimize the quantity of energy released in each of the stages. This staging is achieved by introducing the oxidant as a limiting reactant at each stage.

[0098] Advantageously, the reactive mixture seen by the catalytic burners 50, 52, 54 is diluted thanks to recirculation loop 40.

[0099] The reaction temperature is also limited by the refrigeration carried out at the outlet of the catalytic burners 50, 52, 54.

[0100] After the last stage 30, the hydrogen and oxygen possibly recirculate in the recirculation loop 40 and are only present in trace form, in quantities of less than 1 ppm by volume respectively. A system for measuring these constituents in the recirculation loop advantageously makes it possible to control their contents to ensure the safety of the installation.

[0101] With reference to [Fig. 3], an installation 114 is described which constitutes a variant of the installation 14 shown in FIGS. 1 and 2. The installation 114 is analogous to the installation 14. Similar elements bear the same numerical references and will not be described again. Only the differences will be described in detail below.

[0102] Installation 114 does not include floor 30 of installation 14, but only floors 26 and 28.

[0103] Stage 28 is therefore the last stage of the installation 114. The output flow 76 is admitted into the separator 38.

[0104] Stage 28 of installation 114 has all the properties of stage 30 of installation 14. In particular, the catalytic burner 52 achieves advantageously complete combustion of the hydrogen still present in the inlet flow 58.

[0105] The exchangers 68, 70 are independent of each other. The exchanger 68 receives a refrigerant fluid 22A, for example sea water, and discharges an effluent 22. The exchanger 70 receives the refrigerant fluid 20, for example sea water, and discharges an effluent 22A.

[0106] The exchangers 68, 70 can therefore be adjusted independently of one another so as to adapt the refrigeration capacity of each of the stages, which are not linked by the same refrigerant flow rate.

[0107] The installation 114 operates in a similar manner to the installation 14 and has substantially the same advantages.

[0108] Example:

[0109] The following example concerns the variant described above, with two stages 26, 28. The gas flow to be treated 16 is pure hydrogen and has a flow rate of 0.6470 kg / h.

[0110] The oxidant flows 46, 48 consist of pure oxygen and have flow rates of 2.600 kg / h and 2.535 kg / h respectively.

[0111] Upstream of the catalytic burner 50 of the first stage 26, the mixture of the gas flow to be treated 16, the oxidant flow 44 and the recirculated gas flow 80 is at a pressure of 1,400 bar and a temperature of 43.4°C. Its flow rate is 93.21 kg / h. In this mixture, the volume fraction of hydrogen is 0.08, that of oxygen is 0.02, that of nitrogen of 0.88, and that of water of 0.03.

[0112] The flue gas stream 62 has a temperature of 402.3°C. Its hydrogen molar fraction is 0.04 and that of oxygen is 0.0000.

[0113] The smoke flow 64 has a temperature of 537.5°C. Its mole fraction of nitrogen is 0.86 and its mole fraction of water is 0.14. In this stream, the mole fraction of hydrogen and oxygen is 0.0000.

[0114] The water stream 18 has a temperature of 40.0°C and a flow rate of 5.782 kg / h. Its water mole fraction is 1.0000.

[0115] The gas stream 80, or recycled gas 57, is at a pressure of 1.4 bar, a temperature of 40.0°C and its flow rate is 89.96 kg / h. Its molar fraction of nitrogen is 0.95 and its molar fraction of water is 0.05. Its molar fraction of hydrogen and oxygen is 0.00.

[0116] The total oxygen consumption is 5.14 kg / h.

Claims

Claims

1. An underwater vehicle (10) comprising an installation (14; 114) adapted to treat a gaseous flow to be treated (16) comprising at least 75% hydrogen by volume, and to produce at least one water flow (18), the installation (14; 114) comprising a plurality of successive stages (26, 28, 30; 26, 28) adapted to burn hydrogen from the gaseous flow to be treated (16), each of the stages (26, 28, 30; 26, 28) comprising: - a source (38, 40, 42; 38, 40) of a gaseous oxidant flow (44, 46, 48; 44, 46) comprising at least 21% oxygen by volume, - a catalytic burner (50, 52, 54; 50, 52) adapted ... to admit an inlet flow (56, 58, 60; 56, 58) comprising hydrogen, to admit the flow of oxidant (44, 46, 48; 44, 46), and to produce a flow of fumes (62, 64, 66; 62, 64), and - an exchanger (68, 70, 72; 68, 70) to cool the flow of fumes (62, 64, 66;62, 64) by heat exchange with a refrigerant fluid (20) and obtain an outlet flow (74, 76, 78; 74, 76), the inlet flow (56) of a first stage (26) of said plurality comprising the gaseous flow to be treated (16), the inlet flow (58, 60; 58) of each of the other stages (28, 30; 28) of said plurality respectively comprising the outlet flow (74, 76; 74) of a previous stage of said plurality, the installation (14; 114) being configured so that, in the stages (26, 28, 30; 26, 28) of said plurality except the last stage (30), the catalytic burner (56, 58; 56) burns only a fraction of the hydrogen present in the inlet flow (56, 58, 60; 56, 58), the outlet stream (74, 76; 74) further comprising hydrogen, the installation (14; 114) being further adapted to produce at least the water stream (18) from the outlet stream (74, 76, 78; 74, 76) of at least one of the stages (26, 28, 30; 26, 28) of said plurality.;

2. An underwater vehicle (10) according to claim 1, wherein said plurality of stages (26, 28, 30; 26, 28) consists of two or three stages.

3. Underwater vehicle (10) according to claim 1 or 2, comprising a regulation system (32) configured to regulate, in each of the stages (26, 28, 30; 26, 28) of said plurality, a flow rate of the oxidant flow (44, 46, 48; 44, 46) so that a temperature of the smoke flow (62, 64, 66; 62, 64) is lower than a temperature maximum between 800°C and 900°C.

4. An underwater vehicle (10) according to claim 3, wherein the control system (32) is further configured to control, in each of the stages (26, 28, 30; 26, 28) of said plurality, a flow rate of the refrigerant fluid (20) such that a temperature of the outlet flow (74, 76, 78; 74, 76) is greater than a minimum temperature of between 100°C and 150°C.

5. An underwater vehicle (10) according to claim 3 or 4, wherein the regulation system (32) is further configured to regulate, in the last stage (30; 28) of said plurality, a flow rate of the oxidant flow (48; 46) such that the flue gas flow (66; 64) of the last stage (30; 28) of said plurality comprises less than 1.0% hydrogen by volume.

6. An underwater vehicle (10) according to any one of claims 1 to 5, further comprising: - a source (34) of a gas stream (36) comprising at least 98% nitrogen by volume, the catalytic burner (50) of the first stage (26) of said plurality being adapted to admit the gas stream (36) to dilute the flue gas stream (62) of said catalytic burner (50), and - a separator (38) adapted to admit the outlet stream (78; 76) of the last stage (30; 28) of said plurality, and to produce the water stream (18) and a gas stream (80) comprising at least 90% nitrogen by volume, the catalytic burner (50) of the first stage (26) of said plurality being adapted to admit said gas stream (57).

7. An underwater vehicle (10) according to any one of claims 1 to 6, wherein the coolant (20) comprises sea water (12) or fresh water.

8. An underwater vehicle (10) according to any one of claims 1 to 7, comprising a system of pipes (41) adapted to admit the refrigerant fluid (20) and to pass the refrigerant fluid (20) successively into the exchanger (68, 70, 72; 68, 70) of each of the stages (26, 28, 30; 26, 28) of said plurality in a reverse sequence relative to a sequence defined by the smoke flows (62, 64, 66; 62, 64).

9. Method for treating a gaseous flow to be treated (16) comprising at least 75% hydrogen by volume, the method implementing an underwater vehicle (10) according to any one of claims 1 to 8 and comprising the following steps: - combustion of hydrogen from the gas flow to be treated (16) in the stages (26, 28, 30; 26, 28) of said plurality, - in each of the stages (26, 28, 30; 26, 28) of said plurality, except the last stage (30; 28) of said plurality, admission of the inlet flow (56, 58, 60; 56, 58) and of the oxidant flow (44, 46, 48; 44, 46) into the catalytic burner (50, 52, 54; 50, 52) and production of the flue gas flow (62, 64, 66; 62, 64), the catalytic burner (50, 52, 54; 50, 52) burning only a fraction of the hydrogen present in the inlet flow (56, 58, 60; 56, 58), the outlet flow (74, 76, 78; 74, 76) still comprising hydrogen, - in the last stage (30; 28) of said plurality, admission of the inlet flow (60; 58) and of the oxidant flow (48; 46) into the catalytic burner (54; 52) and production of the smoke flow (62; 64), - in each of the stages (26, 28, 30; 26, 28) of said plurality, cooling of the flow of fumes (62, 64, 66; 62, 64) in the exchanger (68, 70, 72; 68, 70) by heat exchange with the refrigerant fluid (20) and obtaining the outlet flow (74, 76, 78; 74, 76), - producing the water flow (18) from the outlet flow (74, 76, 78; 74, 76) of at least one of the stages of said plurality.

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