Method for implementing an ammonia-fuelled fuel cell with dihydrogen recycling, and associated plant

Abstract

The invention relates to a method for implementing an ammonia-burning fuel-cell system (10), which comprises: a) operating a fuel-cell unit (30); b) recovering a dinitrogen- and dihydrogen-rich anode gas stream (40); c) cooling the anode gas stream (40) and condensing the water present in the anode gas stream (40) to form a cooled gaseous anode stream (44); d) separating the cooled gaseous anode stream (44) into a dinitrogen gas stream (18) and a dinitrogen-depleted anode stream (36); and e) injecting the dinitrogen-depleted anode stream (36) into the fuel cell unit (30) so as to recycle the dinitrogen-depleted anode stream (36) in the fuel cell unit (30).

Description

[0001] Method for implementing a fuel cell powered by ammonia with recycling of dihydrogen and associated installation

[0002] The present invention relates to a method for implementing a fuel cell system powered with ammonia, the method comprising a step of recycling the dihydrogen formed during the method and not consumed in the fuel cell.

[0003] The method of the invention is typically implemented in a fuel cell installation allowing the production of an electric current by electrochemical reaction between dihydrogen H2 and the oxygen in the air. In the context of a fuel cell supplied with ammonia, the dihydrogen H2 used as a combustible fluid is generated during the operation of the cell by decomposition of ammonia NHs at the level of the fuel cell, in particular at the level of the anode of the cell.

[0004] The fuel cell typically consists of one or more fuel cells, preferably operating at high temperature and allowing internal cracking of ammonia. Examples include solid oxide fuel cells (or "SOFC" according to the English acronym for "Solid Oxide Fuel Cells").

[0005] These batteries are currently intended primarily for stationary applications with an output power ranging from 1 kW to 2 MW.

[0006] An SOFC element typically consists of four layers, three of which are ceramic. A single stack of these four layers is typically a few millimeters thick. Dozens of these stacks are then stacked in series to form a stack.

[0007] In these batteries, oxygen ions formed on the cathode side are moved through a solid oxide electrolyte at high temperature to react with the combustible gas, particularly hydrogen H2, on the anode side.

[0008] This electrochemical reaction leads to the production of electricity as well as the formation of water, resulting from the electrochemical reaction. Nitrogen, resulting from the decomposition of ammonia, is also recovered at the outlet of the cell, in the form of a mixture with the water formed.

[0009] In order to prevent and / or limit the deterioration of electrochemical cells during their operation, in particular due to the potential differences to which they are subjected, the flow rates of fuel, in particular ammonia, and oxidant, in particular air, are adjusted so that the quantity of dihydrogen H2 in the cell is always in excess, compared to the maximum reaction capacity in the cell. Thus, a significant quantity of unconsumed dihydrogen is recovered at the outlet of the SOFC element. The conversion rate of dihydrogen in a SOFC element is typically around 60%. In other words, approximately 40% of the hydrogen formed is recovered at the outlet of the cell without having reacted with oxygen ions. Similarly, the air leaving the fuel cell is depleted in oxygen but still contains a significant quantity.

[0010] In known installations, the unconsumed dihydrogen is recovered at the outlet of the cell and then burned in a catalytic furnace in order to be recovered in the form of thermal energy. As an example, we can notably mention the process described in US 2021 / 0214849.

[0011] However, the recovery of dihydrogen by combustion is limited. In particular, it does not allow for electrical efficiencies as high as those theoretically permitted by the fuel cell. In addition, the operation of catalytic furnaces regularly leads to the formation of nitrogen oxides (also called "NOx"), which can be complicated to manage. Since nitrogen oxides are polluting for the environment, adaptations to the process are necessary to prevent their release into the atmosphere.

[0012] US 2014 / 007889 describes a method for implementing a fuel cell system powered by ammonia in which the output anode stream is introduced into a post-treatment unit in which the hydrogen H2 is separated from the water and nitrogen. The recovered hydrogen H2 stream is then injected into the fuel cell for recycling. The recovery of the hydrogen H2 is carried out by means of a series of hydrogen pumps allowing the recovery of a high-purity hydrogen H2 stream.

[0013] However, hydrogen pumps are expensive and bulky equipment. Their energy consumption is also high. In particular, the amount of energy required to pump hydrogen is generally only slightly less than the amount of energy recovered by recycling the hydrogen. The energy savings associated with recycling dihydrogen using hydrogen pumps are not significant.

[0014] An aim of the invention is therefore to provide a method for implementing a fuel cell system making it possible to efficiently and reliably recover the dihydrogen H2 present in the anode effluents with a view to recycling it at the inlet of the cell, in particular with the aim of increasing the overall energy performance of the process, while limiting the investment and operating costs of the process. In particular, the aim of the invention is to provide an integrated method which, by minimizing the energy requirement for the recovery of dihydrogen H2, makes it possible to improve the overall energy performance of the electrical power generation unit.

[0015] Another object of the invention is to provide a method of operating a fuel cell system powered with ammonia and the operation of which does not lead to the emission of nitrogen oxides (NOx) in the gaseous discharges.

[0016] To this end, the invention relates to a method for implementing a fuel cell system, comprising the following steps: a) operating a fuel cell unit comprising at least one anode system and at least one cathode system, said fuel cell unit being continuously supplied with an ammonia-rich gas stream injected at the anode system and with a dioxygen-rich gas stream injected at the cathode system; b) recovering at the outlet of the fuel cell unit an anode gas stream rich in nitrogen and hydrogen and a cathode gas stream; c) cooling the anode gas stream and condensing the water present in the anode gas stream to form a cooled gaseous anode stream; d) separating the cooled gaseous anode stream into a nitrogen gas stream and a nitrogen-depleted anode stream;e) injecting at least a portion of the nitrogen-depleted anode stream into the fuel cell unit, in particular at the anode system, so as to recycle said at least a portion of the nitrogen-depleted anode stream into the fuel cell unit, wherein the nitrogen-depleted anode stream has a residual nitrogen content greater than or equal to 5% by volume. The method according to the invention may comprise one or more of the following features, taken in isolation or in any technically possible combination:;

[0017] - the nitrogen-depleted anodic flux has a nitrogen content greater than 10% by volume, preferably greater than 20% by volume, more preferably from 10% to 50% by volume, even more preferably from 15% to 40% by volume, advantageously from 20 to 30% by volume;

[0018] - said at least a portion of the nitrogen-depleted anode stream is injected into the ammonia-rich gas stream to form an ammonia-rich feed stream, said feed stream then being injected into the fuel cell unit, in particular at the anode system;

[0019] - the feed stream has a dihydrogen content greater than or equal to 15% by volume, preferably greater than or equal to 40% by volume, more preferably from 40% to 50% by volume;

[0020] - step d) of separation of the gaseous and cooled anode flow is carried out by membrane separation, by adsorption by pressure inversion, by adsorption by temperature inversion or by adsorption by pressure and temperature inversion;

[0021] - the method comprises between steps c) and d) an intermediate step of compressing the cooled gaseous anode flow, preferably to a pressure greater than or equal to 10 bara, more preferably greater than or equal to 20 bara, typically between 20 bara and 40 bara;

[0022] - the anode gas stream is at least partially cooled during step c) by heat exchange with the ammonia-rich gas stream or feed stream;

[0023] - the oxygen-rich gas flow, before being introduced into the fuel cell unit, is heated at least partially by heat exchange with the cathode gas flow;

[0024] - the process does not include a step of burning, even partial, of the anodic gas flow.

[0025] The invention also relates to a fuel cell installation comprising:

[0026] - a fuel cell unit comprising an inlet for introducing an ammonia-rich gas flow, an inlet for introducing a dioxygen-rich gas flow, an outlet for recovering an anodic gas flow, and an outlet for recovering a cathodic gas flow,

[0027] - a cooling and condensation unit intended to cool and dry the anode gas stream to form a cooled gaseous anode stream,

[0028] - a separation unit intended to separate the cooled gaseous anode stream into a nitrogen gas stream and a nitrogen-depleted anode stream, said separation unit comprising an outlet for recovering the nitrogen-depleted anode stream, said outlet for recovering the nitrogen-depleted anode stream being connected to the inlet for introducing the ammonia-rich gas stream into the fuel cell unit, wherein the separation unit comprises at least one separation module selected from the group consisting of: a membrane separation unit, a pressure reversal adsorption unit, a temperature reversal adsorption unit, a pressure and temperature reversal adsorption unit and any of their combinations.

[0029] The installation according to the invention may comprise the characteristic according to which the separation unit further comprises a compression module, located upstream of said separation module.

[0030] The invention will be better described by reading the following description, given solely by way of example, and made with reference to the attached drawing, in which:

[0031] - figure 1 is a block diagram representing an installation intended for the implementation of a method according to the invention.

[0032] An installation 10 according to the invention is illustrated schematically in Figure 1.

[0033] The installation 10 is intended for the production of an electric current 12 from a gaseous flow of ammonia 14 and a gaseous flow rich in dioxygen 16.

[0034] The installation 10 is also intended for the recovery, as effluents, of a gaseous stream of nitrogen 18 and a gaseous stream depleted in oxygen 20.

[0035] The installation 10 is connected upstream to a first storage unit 22 intended to store the gaseous ammonia 14, as well as to a second storage unit 24 intended to store the gas rich in dioxygen 16.

[0036] Alternatively, the storage unit 22 can be replaced by a gas distribution network making it possible to convey gaseous ammonia 14 into the installation 10 of the invention.

[0037] When the oxygen-rich gas 16 is air, the storage unit 24 can be replaced by a system of pump(s) and compressor(s) making it possible to convey atmospheric air, possibly compressed, into the installation 10 of the invention.

[0038] The ammonia gas stream 14 is predominantly composed of ammonia. Preferably, the ammonia gas stream 14 has an ammonia content greater than or equal to 90% by volume, more preferably greater than or equal to 95% by volume, even more preferably greater than or equal to 97% by volume, advantageously greater than or equal to 98% by volume, more advantageously greater than or equal to 99% by volume.

[0039] Preferably, the ammonia gas 14 consists essentially of ammonia, and possibly impurities.

[0040] According to one embodiment, the ammonia gas stream 14 may comprise impurities in very small quantities, in particular water and traces of oil.

[0041] Preferably, the ammonia gas stream 14 has an impurity content of less than or equal to 10% by volume, more preferably less than or equal to 5% by volume, typically less than or equal to 1% by volume. Preferably, the ammonia gas stream 14 is at a pressure ranging from 1 atm to 5 bara (absolute bars), more preferably from 1 atm to 2 bara (absolute bars).

[0042] The oxygen-rich gas stream 16 typically has a oxygen content of at least 10% by volume, preferably 15% to 25% by volume of oxygen. Advantageously, the oxygen-rich gas stream 16 is an air stream.

[0043] Preferably, the gas stream rich in dioxygen 16 is at a pressure ranging from 1 atm to 5 bara (absolute bars).

[0044] The installation 10 is connected downstream to an installation 26 intended to collect the nitrogen gas stream 18, and to an installation 28 intended to collect the oxygen-depleted gas stream 20 for post-treatment. Alternatively, the nitrogen gas stream 18 and / or the oxygen-depleted gas stream 20 are directly discharged into the atmosphere.

[0045] Preferably, the oxygen-depleted gas stream 20 is directly discharged into the atmosphere at the installation 28.

[0046] Alternatively, the oxygen-depleted gas stream 20 is collected in the installation 28 in order to be conveyed to another installation where it will be consumed or transformed.

[0047] The installation 10 typically comprises a fuel cell unit 30, a cooling and condensation unit 32, and a separation unit 34.

[0048] Before its introduction into the fuel cell unit 30, the ammonia gas stream 14 is mixed with a recycle stream 36 recovered at the outlet of the separation unit 34 to form an ammonia-rich feed stream 38. The nature of the recycle stream 36 is described in detail below.

[0049] The fuel cell unit 30 is intended to produce the electric current 12 from the feed flow 38 and the oxygen-rich gas flow 16 to form at the output on the one hand an anodic gas flow 40 and on the other hand a cathodic gas flow 42.

[0050] The cooling and condensation unit 32 is intended to cool the anode gas flow 40 and to extract at least part of the water therefrom by condensation to form a cooled gaseous anode flow 44.

[0051] Finally, the separation unit 34 is intended to recover at least a portion of the nitrogen present in the cooled gaseous anode flow 44 in the form of the gaseous nitrogen stream 18 and to recover an anode flow depleted in nitrogen 36, also referred to as the recycling flow 36. Preferably, the installation 10 according to the invention comprises, upstream of the fuel cell unit 30, a first heat exchanger system 46 intended to heat the feed flow 38 rich in ammonia, before its introduction into the fuel cell unit 30.

[0052] For the purposes of the invention, a heat exchanger system comprises at least one heat exchanger. A heat exchanger system may thus comprise a single heat exchanger or several heat exchangers associated with each other.

[0053] The first heat exchanger system 46 thus comprises an inlet 48 for introducing the ammonia-rich feed stream 38 and an outlet 50 for recovering a heated combustible stream 52.

[0054] Preferably, the installation 10 further comprises, upstream of the fuel cell unit, a unit 54 for pre-treating the gas flow rich in dioxygen 16. The pre-treatment unit 54 is intended on the one hand to compress and / or dry and / or filter, preferably compress, dry and filter, the gas flow rich in dioxygen 16 and on the other hand to heat the gas flow rich in dioxygen 16 before its introduction into the fuel cell unit 30.

[0055] The pretreatment unit 54 firstly comprises a module 55 intended to compress and / or dry and / or filter, preferably compress, dry and filter the gas flow rich in dioxygen 16 to form at the outlet a pressurized gas flow rich in dioxygen 56. The module 55 thus comprises an inlet 57 for introducing the gas flow rich in dioxygen 16 and an outlet 58 for recovering the pressurized gas flow rich in dioxygen 56.

[0056] Preferably, the pretreatment unit 54 further comprises a second heat exchanger system 60 intended to heat the pressurized gas flow rich in dioxygen 56 before its introduction into the fuel cell unit 30. The second heat exchanger system 60 thus comprises an inlet 62 for introducing the pressurized gas flow rich in dioxygen 56 and an outlet 64 for recovering a heated dioxygen-rich flow 66.

[0057] The fuel cell unit 30 typically comprises at least one anode system 70 and at least one cathode system 72, separated from each other by at least one electrolyte (not shown), in particular a solid electrolyte.

[0058] For the purposes of the invention, an anode (or cathode) system comprises at least one anode (or cathode). A system of anodes (or cathodes) may thus comprise a single anode (or cathode) or several anodes (or cathodes) associated with each other.

[0059] The fuel cell unit 30 comprises an inlet 72 for introducing the heated fuel flow 52. The inlet 72 is intended to bring the heated fuel flow 52 into contact with the anode system 68.

[0060] The fuel cell unit 30 also comprises an inlet 74 for introducing the heated oxygen-rich flow 66. In particular, the inlet 74 is intended to bring the heated oxygen-rich flow 66 into contact with the cathode system 70.

[0061] The fuel cell unit 30 further comprises an outlet 76 for recovering the anode gas flow 40, resulting from the operation of the fuel cell unit 30 and recovered at the level of the anode system 68.

[0062] The fuel cell unit 30 further comprises an outlet 78 for recovering a cathode gas flow depleted in oxygen 42, resulting from the operation of the fuel cell unit 30 and recovered at the level of the cathode system 70.

[0063] The outlet 78 for recovering the cathode gas flow depleted in oxygen 42 is connected to the installation 28, preferably via the pre-treatment unit 54.

[0064] According to one embodiment, the outlet 78 is connected to the pretreatment unit 54 which is itself connected to the installation 28, so that the cathode gas flow depleted in dioxygen 42 undergoes one or more post-treatments before being transferred to the installation 28.

[0065] Preferably, according to this embodiment, the outlet 78 for recovering the cathode gas flow 42 is connected, upstream of the installation 28, to the second heat exchanger system 60 so that the cathode gas flow depleted in dioxygen 42 is cooled there, by heat exchange with a pressurized gas flow rich in dioxygen 56, to form the gas flow depleted in dioxygen 20. The second heat exchanger system 60 then comprises an inlet 79 for introducing the cathode gas flow 42 and an outlet 80 for recovering the gas flow depleted in dioxygen 20.

[0066] According to a further preferred embodiment, the outlet 80 of the second heat exchanger system 60 is connected to a complementary cooling system 81 intended to cool the oxygen-depleted gas flow 20 again, before its transfer to the installation 28. The complementary cooling system 81 then comprises an inlet 82A for introducing the oxygen-depleted gas flow 20 and an outlet 82B for recovering a cooled oxygen-depleted gas flow 83. The outlet 82B of the complementary cooling system 81 is directly connected to the installation 28. The complementary cooling system 81 may contain exchangers making it possible to recover the recovered heat by supplying, for example, a steam generation or Rankine-type electricity generation system or a heat distribution network.Preferably, when there is no thermal integration to recover the heat, the complementary cooling system 81 is composed of coolers such as air coolers or water exchangers to achieve the required cooling level.

[0067] This embodiment is advantageous in that it allows the oxygen-rich gas flow 16 to be heated, before its introduction into the fuel cell unit 30, by thermal integration, without requiring an external energy supply.

[0068] The cooling and condensation unit 32 typically comprises on the one hand a system of heat exchangers 46 and an additional cooling module 84 intended to cool the anode gas flow 40 and to condense at least partially the water present in the anode gas flow 40 resulting from the operation of the fuel cell unit 30, and on the other hand a condensate recovery system 85.

[0069] According to one embodiment, the outlet 76 for recovering the anode gas flow 40 is connected to the first heat exchanger system 46 so that the anode gas flow 40 is cooled there by heat exchange with the feed flow 38 rich in ammonia, to form a pre-cooled anode flow 86. The first heat exchanger system 46 thus comprises an inlet 88 for introducing the anode gas flow 40 as well as an outlet 89 for recovering the pre-cooled anode flow 86.

[0070] Thus, according to this embodiment, the heat exchanger system of the cooling and condensation unit 32 is constituted by the first heat exchanger system 46 described above.

[0071] This embodiment is advantageous in that it allows both heating of the feed stream 38, before its introduction into the fuel cell unit 30, and cooling of the anode gas stream 40, before its introduction into the condensate recovery system 85, by thermal integration without requiring an external energy supply.

[0072] According to an alternative embodiment (not shown), the heat exchanger system of the cooling and condensing unit 32 is separate from the first heat exchanger system 46.

[0073] The additional cooling module 84 is intended to re-cool the pre-cooled anode flow 86 leaving the first heat exchanger system 46 before its introduction into the condensate recovery system 85. In particular, the additional cooling module 84 makes it possible to cool the water present in the pre-cooled anode flow 86 to a temperature low enough to allow condensation.

[0074] The additional cooling module 84 thus comprises an inlet 90 for introducing the pre-cooled anode flow 86 as well as an outlet 91 for recovering a cooled anode flow 92.

[0075] According to a preferred embodiment, the additional cooling module 84 consists of a heat exchanger making it possible to recover, preferably to recover and use, the heat from the pre-cooled anode flow 86. This heat is for example recovered by supplying a steam generation system, a Rankine-type electrical generation system or even a heat distribution network.

[0076] Preferably, the additional cooling module 84 is composed of one or more coolers, notably chosen from air coolers, water exchangers and any of their combinations.

[0077] The condensate recovery system 85 is intended to condense the water present in the cooled anode flow 92 to form, on the one hand, at the bottom of the condensate recovery system 85, a condensate 93 of liquid water, and on the other hand, at the top of the condensate recovery system 85, the gaseous and cooled anode flow 44. The condensate recovery system 85 thus comprises an inlet 94 for introducing the cooled anode flow 92, an outlet 96 for recovering the condensate 93, and an outlet 98 for recovering the gaseous and cooled anode flow 44.

[0078] The installation 10 further comprises an installation 99 for collecting the liquid water condensate 93.

[0079] The separation unit 34 typically comprises on the one hand a compression unit 100, and on the other hand a separation module 102.

[0080] The compression unit 100 is intended to at least partially compress the cooled gaseous anode flow 44 recovered at the outlet 98 of the cooling and condensation unit 32. The compression unit 100 thus comprises an inlet 104 for introducing the cooled gaseous anode flow 44 and an outlet 106 for recovering a compressed cooled gaseous anode flow 108.

[0081] The nature of the compression unit 100 is not particularly limited. Any device known to those skilled in the art and capable of sufficiently compressing the cooled gaseous anode stream 44 for separation may be used. The compression unit 100 consists, for example, of a series of compressors and / or blowers.

[0082] The separation module 102 is intended to partially extract the nitrogen present in the compressed gaseous and cooled anode stream 108 so as to recover on the one hand the gaseous stream of nitrogen 18, and on the other hand the anode stream depleted in nitrogen 36 (also called recycling stream 36). The separation module 102 thus comprises an inlet 110 for introducing the compressed gaseous and cooled anode stream 108, an outlet 112 for recovering the gaseous stream of nitrogen 18 and an outlet 114 for recovering the anode stream depleted in nitrogen 36.

[0083] The separation module 102 typically consists of any equipment known to those skilled in the art and capable of extracting at least partially the nitrogen present in a gaseous mixture of hydrogen and nitrogen.

[0084] The separation module 102 may optionally be supplemented by one or more additional devices chosen from the group: a purification unit (not shown) intended to eliminate possible nitrogen oxides (NOx), a drying device and a superheater. When present, these additional devices are typically placed upstream of the separation module 102, typically between the compression unit 100 and the separation module 102.

[0085] The separation module 102 typically consists of a membrane separation unit, a pressure swing adsorption unit or PSA unit (for “Pressure Swing Adsorption” in English), a temperature swing adsorption unit or TSA unit (for “Temperature Swing Adsorption” in English), a pressure and temperature swing adsorption unit or PTSA unit (for “Pressure-Temperature Swing Adsorption” in English), or any of their combinations.

[0086] These devices are well known to those skilled in the art and will not be described further in the description below.

[0087] Preferably, the outlet 112 for recovering the nitrogen gas stream 18 is connected to the installation 26 so that the nitrogen gas stream 18 is collected there for post-treatment.

[0088] Preferably, the outlet 114 for recovering the nitrogen-depleted anode flow 36 is connected to the inlet 48 of the first heat exchanger system 46 in order to be mixed with the ammonia gas flow 14.

[0089] According to a preferred embodiment, the installation 10 according to the invention does not include hydrogen pumps. This equipment is in fact expensive and bulky. Their operation also requires a significant amount of energy, generally barely less than the amount of energy recovered by recycling hydrogen. The installation according to the invention is thus advantageous in that it makes it possible to do without this expensive, bulky and energy-consuming equipment.

[0090] The currents described in the installation are confused with the pipes that carry them.

[0091] The implementation of a first method according to the invention will now be described.

[0092] The method according to the invention firstly comprises the supply of at least one gaseous flow of ammonia 14, coming from the installation 22 (or from a gas pipe network), and at least one gaseous flow rich in dioxygen 16, coming from the installation 24.

[0093] The ammonia gas stream 14 is first mixed with the nitrogen-depleted anode stream 36 (also called the recycle stream 36) recovered at the outlet 114 of the separation unit 34 to form the ammonia-rich feed stream 38.

[0094] As explained in detail below, the dihydrogen not consumed by the fuel cell unit 30 is recovered and then reinjected upstream of the fuel cell unit 30 in the form of the nitrogen-depleted anode flow 36 in order to be recycled there.

[0095] The ratio in which the ammonia gas stream 14 and the nitrogen-depleted anode stream 36 are mixed depends on the conversion rate of the fuel cell unit 30, which is typically 60%.

[0096] Preferably, the ammonia gas stream 14 and the nitrogen-depleted anode stream 36 are mixed according to a volume ratio ranging from 1:10 to 10:1, more preferably from 5:10 to 1:1, advantageously from 1:2 to 4:5, typically 7:10.

[0097] Preferably, the ammonia-rich feed stream 38 has an ammonia NH3 content of 15% to 75% by volume, more preferably 30% to 60% by volume, advantageously 40% to 50% by volume, typically 45% by volume.

[0098] Preferably, the ammonia-rich feed stream 38 has a dihydrogen H2 content of 15% to 75% by volume, more preferably 30% to 60% by volume, advantageously 40% to 50% by volume, typically 45% by volume.

[0099] Preferably, the ammonia-rich feed stream 38 has a nitrogen N2 content of 0% to 50% by volume, more preferably 5% to 30% by volume, advantageously 10% to 20% by volume, typically 10% by volume.

[0100] The ammonia-rich feed stream 38 is then introduced into the first heat exchanger system 46 in order to be heated there to form a heated combustible stream 52 at the outlet. Preferably, upstream of the first heat exchanger system 46, the ammonia-rich feed stream 38 has a temperature of 5°C to 80°C, more preferably 20°C to 50°C, advantageously 30°C to 40°C, typically equal to 35°C.

[0101] Preferably, the ammonia-rich feed stream 38 is heated at the first heat exchange system 46 to a temperature lower than the temperature of the fuel cell unit 30, more preferably to a temperature 10°C to 300°C lower than that of the fuel cell unit 30, more preferably 50°C to 200°C lower, typically 100°C to 150°C lower.

[0102] The heated fuel stream 52 is then introduced into the fuel cell unit 30.

[0103] Simultaneously, the gaseous flow rich in dioxygen 16 is introduced into the pretreatment unit 54 so as to be on the one hand compressed and / or dried and / or filtered, preferably compressed, dried and filtered, and on the other hand heated before its introduction into the fuel cell unit 30.

[0104] More particularly, the oxygen-rich flow 16 is first introduced into module 55 in order to be compressed and / or dried and / or filtered, preferably compressed, dried and filtered, to form at the outlet a pressurized gas flow rich in oxygen 56.

[0105] The pressurized oxygen-rich gas stream 56 is then introduced into the second heat exchanger system 60 in order to be heated there to form at the outlet 64 the heated oxygen-rich stream 66.

[0106] Preferably, upstream of the second heat exchanger system 60, the pressurized gas flow rich in dioxygen 56 has a temperature of 10°C to 200°C, more preferably of 50°C to 150°C, typically of 75°C to 120°C, typically of 90°C to 95°C.

[0107] Preferably, the pressurized oxygen-rich gas stream 56 is heated at the second heat exchange system 60 to a temperature lower than that of the fuel cell unit 30, more preferably to a temperature 10°C to 300°C lower than the temperature of the fuel cell unit 30, more preferably 50°C to 200°C lower, typically 100°C to 150°C lower.

[0108] The heated oxygen-rich stream 66 is then introduced into the fuel cell unit 30. The oxygen-rich stream 16 and the feed stream 38 are preheated so as to maintain the temperature within the cell unit 30 relatively constant and thus ensure optimal performance.

[0109] The fuel cell unit 30, continuously supplied with the heated fuel stream 52 and the heated oxygen-rich stream 66, is then put into operation.

[0110] For this, the heated fuel stream 52 is introduced into the fuel cell unit 30, at the inlet 72. In particular, the heated fuel stream 52 is injected at the anode system 68.

[0111] The heated oxygen-rich stream 66 is introduced at the inlet 74 of the fuel cell unit 30. In particular, the heated oxygen-rich stream 66 is injected at the cathode system 70.

[0112] Upon entering the fuel cell unit 30, the heated fuel stream 52 undergoes a first catalytic cracking step during which the ammonia present in the heated fuel stream 52 decomposes into nitrogen N2 gas and hydrogen H2 gas. The catalytic cracking of the ammonia is initiated by the high temperature occurring inside the fuel cell unit 30 in the presence of the catalytic materials present in the anode system 68. The temperature inside the fuel cell unit 30 during its operation depends on the nature of the high-temperature fuel cell and the operating choices. In the case of a SOFC type fuel cell, it is typically 500°C to 1100°C, preferably 700°C to 900°C.

[0113] Preferably, all of the ammonia present in the heated fuel stream 52 decomposes into nitrogen N2 gas and hydrogen H2 gas at the fuel cell unit (30).

[0114] On contact with the anode system 68, the dihydrogen H2 then dissociates into protons H + and electrons. The electrons thus released accumulate at the anode system 68 and are transferred to the cathode system 70 of the fuel cell unit 30 by means of an external circuit, the movement of the electrons from the anode system 68 to the cathode system 70 generating the electric current 12.

[0115] The nitrogen N2 present in the fuel cell unit 30, in particular at the anode system 68, is inert at the operating temperatures of the cell unit 30. In particular, the nitrogen N2 is not oxidized and is found entirely in the anode gas flow 40 recovered at the outlet of the fuel cell unit 30.

[0116] At the cathode system 70, the electrons carried via the electric current 12 are fixed by the oxygen O2 present in the heated oxygen-rich flow 66. The oxygen O2 molecules then transform into superoxide ions O 2- by the capture of two electrons.

[0117] Superoxide ions O 2- thus formed then pass through the electrolyte to pass to the side of the anode system 68 at the level of which they react with the protons H + previously generated to form H2O water.

[0118] The anode gas flow 40 and the cathode gas flow 42 are then recovered at the outlet of the fuel cell unit 30.

[0119] The cathode gas flow 42, corresponding to the residual gas flow recovered at the outlet of the cathode system 70, is recovered at the outlet 78 of the fuel cell unit 30. The flow 42 has a reduced dioxygen content compared to the initial heated dioxygen-rich flow 66.

[0120] Typically, the cathode gas stream 42 has a dioxygen content of less than or equal to 20 mol%, preferably 5% to 15 mol%.

[0121] The cathode gas stream 42 is then routed to the installation 28.

[0122] According to one embodiment, before reaching the installation 28, the cathode gas flow 42 is cooled by passing through the second heat exchanger system 60. Thus, the cathode gas flow 42 is cooled by heat exchange with the pressurized gas flow rich in dioxygen 56 to form the gas flow depleted in dioxygen 20.

[0123] The cathode gas flow 42 recovered at the outlet 78 of the fuel cell unit 30 has a temperature close to the temperature of the fuel cell unit 30.

[0124] Thus, in the case of a SOFC type fuel cell, the cathode gas flow 42 recovered at the outlet 78 of the fuel cell unit 30 typically has a temperature of 500°C to 1100°C, preferably of 700°C to 900°C.

[0125] Preferably, the cathode gas stream 42 is cooled to a temperature ranging from 50°C to 250°C, preferably ranging from 100°C to 200°C.

[0126] This embodiment is advantageous in that it makes it possible to heat the oxygen-rich gas flow 16 at the inlet, and to cool the cathode gas flow 42 at the outlet by thermal integration, without requiring an external energy supply.

[0127] According to a further preferred embodiment, before its transfer to the installation 28, the cathode gas stream 42 is cooled in at least two stages. More particularly, the cathode gas stream 42 is cooled a first time at the second heat exchanger system 60 to an intermediate temperature ranging from 200°C to 350°C, preferably from 250°C to 300°C. Then, the oxygen-depleted stream 20 recovered at the outlet 80 of the second heat exchanger system 60 is transferred to a complementary cooling system 81 making it possible to cool the cathode gas stream 42 again to a temperature compatible with the characteristics of the installation 28 to collect the oxygen-depleted stream 20.The oxygen-depleted and cooled gas flow 83 recovered at the outlet 82B of the complementary cooling system 81 typically has a temperature below 200°C, preferably between 100°C and 200°C, advantageously approximately equal to 150°C. This complementary cooling system 81 may contain exchangers making it possible to use the recovered heat by supplying, for example, a steam generation or Rankine-type electricity generation system or a heat distribution network. Preferably, the complementary cooling system 81 is composed of coolers such as air coolers or water exchangers to achieve the required cooling level.

[0128] The anode gas flow 40, corresponding to the residual gas flow recovered at the outlet of the anode system 68, is recovered at the outlet 76 of the fuel cell unit 30. The anode gas flow 40 consists of a mixture of water H2O resulting from the operation of the fuel cell unit 30 but also of nitrogen N2 and unreacted hydrogen H2.

[0129] Preferably, at most 40% by volume of the dihydrogen H2 formed by decomposition of ammonia inside the fuel cell unit 30 is recovered in the anode gas stream 40, more preferably from 20% to 30% by volume.

[0130] Preferably, the anode gas stream 40 has a nitrogen content of 10% to 40% by volume, more preferably 20% to 30% by volume, typically equal to 25% by volume.

[0131] Preferably, the anode gas stream 40 has a water content H2O of 30% to 60% by volume, more preferably of 40% to 50% by volume, typically equal to 45% by volume.

[0132] In the case of a SOFC type fuel cell, the anode gas flow 40, recovered at the outlet 76 of the fuel cell unit 30, typically has a temperature of 500°C to 1,100°C, typically 700°C to 900°C.

[0133] The entire anode gas stream 40 is then introduced into the cooling and condensation unit 32 in order to be cooled there and to eliminate at least a portion, preferably a majority, of the water formed.

[0134] The anode gas stream 40 is first cooled by passing through one or more heat exchanger systems.

[0135] Preferably, the anode gas stream 40 is first introduced into the first heat exchanger system 46 in which it is cooled by heat exchange with the ammonia-rich feed stream 38. A pre-cooled anode stream 86 is recovered at the outlet 89 of the first heat exchanger system 46.

[0136] In the case of a SOFC type fuel cell, the anode gas flow 40, recovered at the outlet 76 of the fuel cell unit 30), typically has a temperature of 500°C to 1100°C, preferably 700°C to 900°C.

[0137] Preferably, the anode gas stream 40 is cooled at the first heat exchanger system 46 to a temperature of 300°C to 500°C, preferably 350°C to 450°C.

[0138] Preferably, the pre-cooled anode flux 86 is then introduced into the additional cooling module 84 in order to be cooled again. A cooled anode flux 92 is recovered at the outlet 91 of the additional cooling module 84.

[0139] Preferably, the pre-cooled anode flux 86 is cooled at the level of the additional cooling module 84 to a temperature less than or equal to 100°C, more preferably between 10°C and 50°C, typically between 30°C and 40°C.

[0140] The cooled anode stream 92 is then introduced into the condensate recovery system 85 in order to remove the water present in the cooled anode stream 92.

[0141] In particular, the cooled anode flow 92 is introduced into the condensate recovery system 85. A liquid water condensate 93 is recovered at the bottom of the condensate recovery system 85 while the gaseous and cooled anode flow 44 is recovered at the top of the condensate recovery system 85.

[0142] Condensate 93 is then sent to installation 99 for post-treatment.

[0143] Preferably, if the fuel cell system operates at a pressure close to atmospheric pressure, the cooled gaseous anode flow 44 has a water content of less than or equal to 10% by volume, more preferably less than or equal to 6% by volume.

[0144] The entirety of the cooled gaseous anode flow 44 is then injected into the separation unit 34 in order to be fractionated there on the one hand into the gaseous nitrogen flow 18 and on the other into the nitrogen-depleted anode flow 36, also referred to as the recycling flow 36.

[0145] Preferably, the cooled gaseous anode flow 44 undergoes a preliminary compression step. For this, the cooled gaseous anode flow 44 is introduced into the compression unit 100 to form the compressed cooled gaseous anode flow 108. Preferably, if the fuel cell system operates at a pressure close to atmospheric pressure, the cooled gaseous anode flow 44 has a pressure of 0.7 bara to 2 bara (absolute bars), more preferably of 1 bara to 1.5 bara (absolute bars).

[0146] Preferably, the cooled gaseous anode flow 44 is compressed at the compression unit 100 to a pressure ranging from 10 bara to 100 bara (absolute bars), more preferably from 20 bara to 40 bara (absolute bars). The final pressure of the cooled gaseous flow 44 depends on the characteristics of the separation module 102.

[0147] The compressed, cooled gaseous anode stream 108 is then introduced into the separation module 102 in order to form, on the one hand, the gaseous nitrogen stream 18 and, on the other hand, the nitrogen-depleted anode stream 36 (recycling stream 36).

[0148] The nitrogen 18 gas stream is then conveyed to installation 26 for post-treatment.

[0149] Preferably, the nitrogen 18 gas stream consists essentially of nitrogen, and possibly impurities.

[0150] More preferably, the gaseous stream of dinitrogen 18 has a dinitrogen content greater than or equal to 99.00% by volume, more preferably between 99.90% and 99.99% by volume.

[0151] According to one embodiment, the gaseous stream of nitrogen 18 may comprise impurities in very small quantities.

[0152] Among the impurities that may be present in the nitrogen 18 gas stream, mention may in particular be made of dihydrogen, ammonia, water, nitrogen oxides (or NOx) or even traces of oil. The presence of a purification unit and / or a drying device, in particular upstream of the separation unit 102, makes it possible to reduce the impurity content.

[0153] Preferably, the gaseous stream of nitrogen 18 has an impurity content of less than or equal to 10% by volume, more preferably less than or equal to 5% by volume, typically less than or equal to 1% by volume.

[0154] Preferably, the nitrogen-depleted anode flow 36 (recycle flow 36) has a hydrogen H2 content greater than or equal to 50% by volume, more preferably greater than or equal to 70% by volume, typically between 70% and 90% by volume, for example between 70% and 80% by volume.

[0155] Preferably, the nitrogen-depleted anode stream 36 (recycle stream 36) has a residual nitrogen N2 content greater than or equal to 10% by volume, more preferably greater than or equal to 20% by volume, typically between 20% and 40% by volume, for example between 20% and 30% by volume. The nitrogen-depleted anode stream 36 is finally injected into the ammonia gas stream 14 in order to be recycled therein into the fuel cell unit.

[0156] According to a preferred embodiment, the method according to the invention does not include a step of implementing one or more hydrogen pumps. The method according to the invention is thus advantageous in that it makes it possible to eliminate the need for hydrogen pumps.

[0157] The installation 10 and the method according to the invention thus allow the production of an electric current 12 by means of a fuel cell unit 30 supplied with ammonia. In addition, the installation 10 and the method according to the invention allow the recovery of unreacted dihydrogen by recycling it in the fuel cell.

[0158] The invention is based on the demonstration that the residual presence of nitrogen N2 in the recycling flow 36 does not affect or only very little affects the operation of the fuel cell unit 30. The nitrogen N2 is in fact a neutral gas for the fuel cell unit 30. At the operating temperatures of the fuel cell unit 30, the nitrogen is in fact inert and does not participate in any reaction likely to occur inside the fuel cell unit 30. An excessive presence of nitrogen within the fuel cell can nevertheless reduce the performance of the fuel cell due to the excessive dilution of the hydrogen fuel in contact with the anode system 68.The separation performance of the separation unit 102 makes it possible to generate a flow 36 whose stoichiometric proportions are as close as possible to the hydrogen / nitrogen stoichiometry of the ammonia gas flow 14 since its decomposition will take place within the anode system 68. Thus, the feed flow 38 resulting from the mixing of the ammonia gas flow 14 and the recycled flow depleted in nitrogen 36 is characterized by a hydrogen / nitrogen ratio very close to that of the ammonia gas flow 14. In fact, the electrochemical performance of the fuel cell system 30 is not affected by this recycle 36.

[0159] Furthermore, the installation 10 and the method according to the invention make it possible to significantly reduce the energy requirement associated with the recycling of dihydrogen H2 by authorizing the injection of a significant portion of the nitrogen N2 recovered at the outlet of the fuel cell unit 30 into the feed stream 38.

[0160] In the prior art processes, the recycle stream consists essentially of dihydrogen H2. In particular, all of the nitrogen present in the anode gas stream has been separated so that the recycle stream is almost free of nitrogen. Separation and purification steps requiring more specific separation equipment and / or a significant energy requirement are then necessary to achieve the required purity.

[0161] In the context of the invention, the residual presence of nitrogen in the recycling stream 36 allows the use of less complex separation equipment. The lower degree of purity permitted by the method of the invention also makes it possible to significantly reduce the energy requirements associated with the post-treatment of the anode gas stream 40 before its recycling.

[0162] The method and the installation of the invention are furthermore advantageous in that they make it possible to recover the excess heat emitted by the fuel cell unit in order to use it. In particular, the anode gas flow 40 recovered at the outlet 76 of the fuel cell unit 30 is cooled in at least two stages, firstly at the first heat exchanger system 46, and secondly at the additional cooling module 84. The first heat exchanger system 46 firstly makes it possible to cool the anode gas flow 40 by heat exchange with the ammonia-rich feed flow 38 to an intermediate temperature ranging from 200°C to 500°C, preferably from 300°C to 450°C. Then, the additional cooling module 84 makes it possible to cool the pre-cooled anode gas flow 86 leaving the first heat exchanger system 46 again.The additional cooling module 84 typically consists of a heat exchanger making it possible to recover, preferably to recover and utilize, the heat from the pre-cooled anode flow 86. This heat is for example recovered by supplying a steam generation system, a Rankine-type electrical generation system or even a heat distribution network.

[0163] When the separation module 102 comprises a membrane separation unit (as described above), it is possible for the gaseous flow of nitrogen 18 recovered at the outlet of the module 102 to be under pressure. Preferably, in this case, the installation 10 according to the invention comprises, between the separation module 102 and the installation 26, a complementary turbine system intended to generate a complementary electric current by expansion of the gaseous flow of nitrogen 18 under pressure.

[0164] The method and the installation according to the invention are also advantageous in that they make it possible to consume in the fuel cell unit 30 at least 80% of the dihydrogen formed by decomposition of ammonia, preferably at least 90%, more preferably at least 95%, typically at least 99% and advantageously all of the dihydrogen formed by decomposition of ammonia.

[0165] Finally, the installation and the method according to the invention are also advantageous in that they allow efficient recycling of fuel which has not been consumed in the fuel cell unit.

Claims

DEMANDS 1. Method of implementing a fuel cell system (10), comprising the following steps: a) starting up a fuel cell unit (30) comprising at least one anode system (68) and at least one cathode system (70), said fuel cell unit (30) being continuously supplied with an ammonia-rich gas stream (14) injected at the anode system (68) and with an oxygen-rich gas stream (16) injected at the cathode system (70); b) recovering from the outlet of the fuel cell unit (30) an anodic gas stream (40) rich in nitrogen and hydrogen and a cathodic gas stream (42); c) cooling the anodic gas stream (40) and condensing the water present in the anodic gas stream (40) to form a cooled gaseous anodic stream (44); d) the separation of the cooled gaseous anodic flux (44) into a nitrogen gas stream (18) and a nitrogen-depleted anodic flux (36);(e) the injection of at least a portion of the nitrogen-depleted anodic flux (36) into the fuel cell unit (30), in particular at the level of the anode system (68), so as to recycle said at least a portion of the nitrogen-depleted anodic flux (36) into the fuel cell unit (30), characterized in that the nitrogen-depleted anodic flux (36) has a residual nitrogen content greater than or equal to 5% by volume.

2. A process according to claim 1, wherein the nitrogen-depleted anodic flux (36) has a nitrogen content greater than 10% by volume, preferably greater than 20% by volume, more preferably from 10% to 50% by volume, even more preferably from 15% to 40% by volume, advantageously from 20% to 30% by volume 3. Method according to claim 1 or according to claim 2, wherein said at least a portion of the nitrogen-depleted anodic flux (36) is injected into the ammonia-rich gaseous flux (14) to form an ammonia-rich feed flux (38), said feed flux (38) being subsequently injected into the fuel cell unit (30), in particular at the anode system (68).

4. A method according to claim 3, wherein the feed stream (38) has a dihydrogen content greater than or equal to 15% by volume, preferably greater than or equal to 40% by volume, more preferably from 40% to 50% by volume.

5. A method according to any one of the preceding claims, wherein step d) of separating the cooled gaseous anodic stream (44) is carried out by membrane separation, by pressure reversal adsorption, by temperature reversal adsorption or by pressure and temperature reversal adsorption.

6. Method according to claim 5, comprising between steps c) and d) an intermediate step of compressing the cooled gaseous anodic flux (44), preferably to a pressure greater than or equal to 10 bara, more preferably greater than or equal to 20 bara, typically between 20 bara and 40 bara.

7. A method according to any one of the preceding claims, wherein the anodic gas stream (40) is at least partially cooled during step c) by heat exchange with the ammonia-rich gas stream (14) or feed stream (38).

8. A method according to any one of the preceding claims, wherein the oxygen-rich gas stream (16), before being introduced into the fuel cell unit (30), is heated at least partially by heat exchange with the cathode gas stream (42).

9. A method according to any one of the preceding claims, characterized in that it does not include a step of burning, even partial, the anodic gas stream (40).

10. Fuel cell installation (10) comprising: - a fuel cell unit (30) comprising an inlet (72) for introducing a gas stream rich in ammonia (14), an inlet (74) for introducing a gas stream rich in dioxygen (16), an outlet (76) for recovering an anodic gas stream (40), and an outlet (78) for recovering a cathodic gas stream (42), - a cooling and condensation unit (32) intended to cool and dry the anodic gas stream (40) to form a cooled, gaseous anodic stream (44), - a separation unit (34) intended to separate the cooled gaseous anodic stream (44) into a nitrogen gas stream (18) and a nitrogen-depleted anodic stream (36), said separation unit (34) comprising an outlet (114) for recovering the nitrogen-depleted anodic stream (36), said outlet (114) for recovering the nitrogen-depleted anodic stream (36) being connected to the inlet (72) for introducing the ammonia-rich gaseous stream (14) into the fuel cell unit (30), characterized in that the separation unit (34) comprises at least one separation module (102) selected from the group consisting of: a membrane separation unit, a pressure reversal adsorption unit, a temperature reversal adsorption unit, a pressure and temperature reversal adsorption unit and any combination thereof.

11. Installation (10) according to claim 10, wherein the separation unit (34) further comprises a compression module (100), located upstream of said separation module (102).

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