Method and associated plant for implementing an ammonia-fueled fuel cell with dihydrogen recirculation - Patents.com

Abstract

The present invention is a method for implementing an ammonia-burning fuel cell system (10) comprising: a) operating a fuel cell unit (30); b) recovering a dinitrogen-rich and dihydrogen-rich anode gas stream (40); c) cooling the anode gas stream (40) and condensing water present in the gaseous anode 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) for recirculation within the fuel cell unit (30).

Description

[Technical field]

[0001] The present invention relates to a method for implementing an ammonia-burning fuel cell system, the method including a step for recycling dihydrogen formed during the method that is not consumed in the fuel cell.

[0002] The method of the invention is typically implemented in a fuel cell plant that allows the production of electric current by electrochemical reaction between dihydrogen H2 and dioxygen from the air. In the context of an ammonia-fueled fuel cell, the dihydrogen H2 used as fuel fluid is generated during cell operation by decomposition of ammonia NH3 in the fuel cell, in particular at the cell anode. [Background technology]

[0003] A fuel cell typically consists of one or more fuel cells, preferably operating at high temperatures and allowing the internal decomposition of ammonia. Examples that may be cited include the solid oxide fuel cell (SOFC).

[0004] These batteries are currently designed primarily for stationary applications, with output powers ranging from 1 kW to 2 MW.

[0005] SOFC devices are generally constructed from four layers, three of which are ceramic. A single stack of these four superimposed layers is typically only a few millimeters thick. Dozens of these stacks are then stacked in series to form the stack.

[0006] In these cells, oxygen ions formed on the cathode side migrate through a solid oxide used as a high-temperature electrolyte and react with a fuel gas, in particular dihydrogen H2, on the anode side.

[0007] This electrochemical reaction results in the production of electricity as well as the formation of water, which is a by-product of the electrochemical reaction. Dinitrogen resulting from the decomposition of ammonia is also collected at the stack outlet in a mixture with the water formed.

[0008] In particular, to prevent and / or limit damage during the operation of the electrochemical cell due to the potential difference to which it is subjected, the flow rates of the fuel, in particular ammonia, and the oxidant, in particular air, are adjusted so that the amount of dihydrogen H2 in the cell always exceeds the maximum reaction capacity in the cell. As a result, a significant amount of unconsumed hydrogen is recovered from the SOFC element. The conversion rate of dihydrogen in the SOFC element is typically about 60%. In other words, about 40% of the hydrogen formed is recovered from the cell without reacting with oxygen ions. Similarly, the air leaving the fuel cell contains a reduced, but still significant amount of oxygen.

[0009] In known plants, the unconsumed dihydrogen is recovered at the stack outlet and then combusted in a catalytic converter to recover it in the form of thermal energy. An example is the method described in US Patent Application Publication No. 2021 / 0214849.

[0010] However, the use of dihydrogen by combustion is limited; in particular, it does not achieve electrical efficiencies as high as those theoretically allowed by fuel cells. Furthermore, the operation of catalytic furnaces usually results in the formation of nitrogen oxides (also known as "NOx"), which can be difficult to control. Nitrogen oxides are pollutants for the environment, so adaptations to methods are necessary to prevent their release into the atmosphere.

[0011] US Patent Application Publication No. 2014 / 007889 describes a method for implementing an ammonia-fueled fuel cell system in which the anode output stream is fed to an aftertreatment unit where H2-dihydrogen is separated from water and dinitrogen. The H2-dihydrogen stream thus recovered is then injected into the fuel cell for recirculation. Recovery of H2-dihydrogen is achieved by a series of hydrogen pumps that allow recovery of a high purity H2-dihydrogen stream.

[0012] However, hydrogen pumps are expensive and bulky devices. 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 hydrogen. The energy gain associated with recycling dihydrogen using a hydrogen pump is negligible. Summary of the Invention

[0013] One object of the present invention is therefore to provide a method for implementing a fuel cell system that allows efficient and reliable recovery of the H2-dihydrogen present in the anode effluent for recirculation at the cell inlet, with the aim in particular of increasing the overall energy performance of the method while limiting its investment and operating costs.

[0014] In particular, it is an object of the present invention to provide an integrated method for improving the overall energy performance of a power generating unit by minimizing the energy requirements for H2-dihydrogen recovery.

[0015] Another object of the present invention is to provide a method for implementing an ammonia burning fuel cell system, the operation of which does not result in the emission of nitrogen oxides (NOx) in the exhaust gas.

[0016] To this end, the present invention provides a method for implementing a fuel cell system, comprising: 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 in the anode system and a dioxygen-rich gas stream injected in the cathode system; b) recovering a dinitrogen-rich and dihydrogen-rich anode gas stream and a cathode gas stream at the outlet of the fuel cell unit; c) cooling the anode gas stream and condensing water present in the anode gas stream to form a cooled anode gas stream; d) separating the cooled anode gas stream into a dinitrogen gas stream and a dinitrogen-depleted anode stream; e) injecting at least a portion of the dinitrogen-depleted anode stream into the fuel cell unit, in particular into the anode system, for recirculating said at least a portion of the dinitrogen-depleted anode stream to the fuel cell unit, The method according to the invention comprises the following features, taken alone or according to any technically feasible combination: the dinitrogen-depleted anode stream has a dinitrogen content of more than 10% by volume, preferably more than 20% by volume, more preferentially between 10% by volume and 50% by volume, even more preferentially between 15% by volume and 40% by volume, advantageously between 20% by volume and 30% by volume, - said at least a portion of the dinitrogen-depleted anode stream is injected into an ammonia-rich gas stream to form an ammonia-rich feed stream, said feed stream then being injected into the fuel cell unit, in particular the anode system, the feed stream has a dihydrogen content of at least 15% by volume, preferably at least 40% by volume and more preferentially between 40% by volume and 50% by volume, step d) of separating the cooled anode gas stream is carried out by membrane separation, pressure swing adsorption, temperature swing adsorption, or pressure-temperature swing adsorption, the method comprises, between steps c) and d), an intermediate step of compressing the cooled anode gas stream, preferably to a pressure of at least 10 bara, more preferentially at least 20 bara, typically between 20 bara and 40 bara, - the anode gas stream is at least partially cooled in step c) by heat exchange with an ammonia-rich gas stream or a feed stream, - the dioxygen-rich gas stream is at least partially heated by heat exchange with the cathode gas stream before being introduced into the fuel cell unit; the method does not include a step of combusting the anode gas stream, or even a step of partial combustion.

[0017] The present invention relates to a fuel cell unit including an inlet for introducing an ammonia-rich gas stream, an inlet for introducing a dioxygen-rich gas stream, an outlet for recovering an anode gas stream, and an outlet for recovering a cathode gas stream; a cooling and condensation unit for cooling and drying the anode gas stream to form a cooled anode gas stream; a separation unit for separating the cooled anode gas stream into a dinitrogen gas stream and a dinitrogen-depleted anode stream, the separation unit including a dinitrogen-depleted anode stream recovery outlet, said dinitrogen-depleted anode stream recovery outlet being connected to an inlet for introducing an ammonia-rich gas stream into the fuel cell unit, The present invention further relates to a fuel cell plant, wherein the separation unit comprises at least one separation module selected from the group consisting of a membrane separation unit, a pressure swing adsorption unit, a temperature swing adsorption unit, a pressure-temperature swing adsorption unit, and any combination thereof.

[0018] The plant according to the invention may comprise the feature that the separation unit further comprises a compression module positioned upstream of said separation module. [Brief description of the drawings]

[0019] The invention will be better understood on reading the following description, given purely by way of example and made with reference to the following drawings, in which: [Figure 1] 1 is a block diagram showing a plant for implementing the method according to the invention; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] A plant 10 according to the invention is illustrated diagrammatically in FIG.

[0021] The plant 10 is designed to produce an electric current 12 from an ammonia gas stream 14 and a dioxygen rich gas stream 16 .

[0022] The plant 10 is also designed to recover as effluents a dinitrogen gas stream 18 on the one hand and a dioxygen-depleted gas stream 20 on the other hand.

[0023] The plant 10 is connected upstream to a first storage unit 22 for storing the ammonia gas 14 and a second storage unit 24 for storing the dioxygen rich gas 16 .

[0024] Alternatively, the storage unit 22 may be replaced by a gas distribution network for supplying ammonia gas 14 to the plant 10 of the present invention.

[0025] When the dioxygen-rich gas 16 is air, the storage unit 24 may be replaced by a system of pumps and compressors for supplying optionally compressed atmospheric air to the plant 10 of the present invention.

[0026] The ammonia gas stream 14 is mainly composed of ammonia. Preferably, the ammonia gas stream 14 has an ammonia content of at least 90% by volume, more preferentially at least 95% by volume, even more preferentially at least 97% by volume, advantageously at least 98% by volume, more advantageously at least 99% by volume.

[0027] Preferably, the ammonia gas 14 consists essentially of ammonia and possibly impurities.

[0028] In one embodiment, the ammonia gas stream 14 may contain very small amounts of impurities, particularly water and traces of oil.

[0029] Preferably, the ammonia gas stream 14 has an impurity content of less than or equal to 10% by volume, more preferentially less than or equal to 5% by volume, typically less than or equal to 1% by volume.

[0030] Preferably, the ammonia gas stream 14 is at a pressure in the range of 1 atm to 5 bara (bar absolute), more preferentially 1 atm to 2 bara (bar absolute).

[0031] The dioxygen rich gas stream 16 typically has a dioxygen content of at least 10% by volume of dioxygen, preferably between 15% and 25% by volume of dioxygen. Advantageously, the dioxygen rich gas stream 16 is an air stream.

[0032] Preferably, the dioxygen rich gas stream 16 is at a pressure in the range of 1 atm to 5 bara (bars absolute).

[0033] Plant 10 is connected downstream to a plant 26 for collecting dinitrogen gas stream 18, and to a plant 28 for collecting dioxygen-depleted gas stream 20 for further treatment. Alternatively, dinitrogen gas stream 18 and / or dioxygen-depleted gas stream 20 are released directly into the atmosphere.

[0034] Preferably, the dioxygen depleted gas stream 20 is discharged directly to the atmosphere at the plant 28 .

[0035] Alternatively, the dioxygen-depleted gas stream 20 may be collected at the plant 28 and sent to another plant for consumption or processing.

[0036] The plant 10 typically includes a fuel cell unit 30 , a cooling and condensing unit 32 , and a separation unit 34 .

[0037] Prior to being introduced 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 more detail below.

[0038] The fuel cell unit 30 is designed to generate an electric current 12 from a feed stream 38 and a dioxygen rich gas stream 16 to form an anode gas stream 40 and a cathode gas stream 42 .

[0039] The cooling and condensation unit 32 is designed to cool the anode gas stream 40 and extract at least a portion of the water by condensation to form a cooled anode gas stream 44 .

[0040] Finally, separation unit 34 is designed to recover at least a portion of the dinitrogen present in the cooled anode gas stream 44 in the form of dinitrogen gas stream 18 and recover a dinitrogen-depleted anode stream 36, also referred to as recycle stream 36.

[0041] Preferably, the plant 10 according to the invention comprises, upstream of the fuel cell unit 30 , a first heat exchanger system 46 designed to heat the ammonia-rich feed stream 38 before its introduction into the fuel cell unit 30 .

[0042] For the purposes of the present invention, a heat exchanger system includes at least one heat exchanger. Thus, a heat exchanger system can include a single heat exchanger or multiple heat exchangers associated with each other.

[0043] Thus, the first heat exchanger system 46 includes an inlet 48 for receiving the ammonia-rich feed stream 38 and an outlet 50 for recovering the heated fuel stream 52 .

[0044] Preferably, upstream of the fuel cell unit, the plant 10 further comprises a unit 54 for pre-treating the dioxygen-rich gas stream 16. The pre-treatment unit 54 is designed, on the one hand, to compress and / or dry and / or filter, preferably to compress, dry and filter, the dioxygen-rich gas stream 16 and, on the other hand, to heat the dioxygen-rich gas stream 16 before its introduction into the fuel cell unit 30.

[0045] Pre-treatment unit 54 includes a module 55 designed to first compress and / or dry and / or filter, preferably compress, dry and filter, dioxygen-rich gas stream 16 to form a pressurized dioxygen-rich gas stream 56. Module 55 therefore includes an inlet 57 for introducing dioxygen-rich gas stream 16 and an outlet 58 for recovering pressurized dioxygen-rich gas stream 56.

[0046] Preferably, the pretreatment unit 54 further comprises a second heat exchanger system 60 designed to heat the pressurized dioxygen-rich gas stream 56 prior to introduction into the fuel cell unit 30. The second heat exchanger system 60 therefore comprises an inlet 62 for introducing the pressurized dioxygen-rich gas stream 56, and an outlet 64 for recovering the heated dioxygen-rich stream 66.

[0047] The fuel cell unit 30 typically includes at least one anode system 70 and at least one cathode system 72 separated from each other by at least one electrolyte (not shown), particularly a solid electrolyte.

[0048] For the purposes of the present invention, an anode (or cathode) system includes at least one anode (or cathode). Thus, an anode (or cathode) system can include a single anode (or cathode) or multiple anodes (or cathodes) associated with each other.

[0049] The fuel cell unit 30 includes an inlet 72 for introducing the heated fuel stream 52. The inlet 72 is designed to bring the heated fuel stream 52 into contact with the anode system 68.

[0050] The fuel cell unit 30 further includes an inlet 74 for introducing the heated dioxygen-rich stream 66. In particular, the inlet 74 is designed to bring the heated dioxygen-rich stream 66 into contact with the cathode system 70.

[0051] The fuel cell unit 30 further includes an outlet 76 for collecting the anode gas stream 40 resulting from operation of the fuel cell unit 30 and collected from the anode system 68 .

[0052] The fuel cell unit 30 further includes an outlet 78 for recovering the dioxygen-depleted cathode gas stream 42 resulting from operation of the fuel cell unit 30 and recovered from the cathode system 70 .

[0053] An outlet 78 for recovering the dioxygen-depleted cathode gas stream 42 is preferably connected to the plant 28 via the pre-treatment unit 54 .

[0054] In one embodiment, the outlet 78 is connected to a pre-treatment unit 54 which is in turn connected to the plant 28 so that the dioxygen-depleted cathode gas stream 42 undergoes one or more post-treatments before being transported to the plant 28.

[0055] Preferably, the outlet 78 for recovering the cathode gas stream 42 is connected to a second heat exchanger system 60 upstream of the plant 28, so that the dioxygen-depleted cathode gas stream 42 is there cooled by heat exchange with the pressurized dioxygen-rich gas stream 56 to form the dioxygen-depleted gas stream 20. The second heat exchanger system 60 then includes an inlet 79 for introducing the cathode gas stream 42, and an outlet 80 for recovering the dioxygen-depleted gas stream 20.

[0056] In an even more preferred embodiment, the outlet 80 of the second heat exchanger system 60 is connected to an auxiliary cooling system 81 designed to further cool the dioxygen-depleted gas stream 20 before transferring it to the plant 28. The auxiliary cooling system 81 in turn includes an inlet 82A for introducing the dioxygen-depleted gas stream 20 and an outlet 82B for recovering the cooled dioxygen-depleted gas stream 83. The outlet 82B of the auxiliary cooling system 81 is connected directly to the plant 28.

[0057] The auxiliary cooling system 81 may contain heat exchangers that allow the recovered heat to be used to feed, for example, a Rankine steam or power generation system, or a heat distribution network. Preferably, in the absence of heat integration for heat recovery, the auxiliary cooling system 81 consists of coolers such as air coolers or water exchangers to achieve the required cooling level.

[0058] This method is advantageous in that it allows the dioxygen rich gas stream 16 to be heated by heat integration before being introduced into the fuel cell unit 30 without the need for an external energy input.

[0059] The cooling and condensation unit 32 typically includes, on the one hand, a heat exchanger system 46 and an auxiliary cooling module 84 designed to cool the anode gas stream 40 and at least partially condense water present in the anode gas stream 40 resulting from the operation of the fuel cell unit 30, and, on the other hand, a condensate recovery system 85.

[0060] In one embodiment, the outlet 76 for recovering the anode gas stream 40 is connected to a first heat exchanger system 46 such that the anode gas stream 40 is cooled therein by heat exchange with the ammonia-rich feed stream 38 to form a pre-cooled anode stream 86. The first heat exchanger system 46 therefore includes an inlet 88 for introducing the anode gas stream 40 and an outlet 89 for recovering the pre-cooled anode stream 86.

[0061] Therefore, according to this embodiment, the heat exchanger system of the cooling and condensing unit 32 is constituted by the first heat exchanger system 46 described above.

[0062] This method is advantageous in that it allows for heat integration without requiring external energy input to heat the feed stream 38 prior to introduction into the fuel cell unit 30 and to cool the anode gas stream 40 prior to introduction into the condensate recovery system 85.

[0063] In 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 .

[0064] The auxiliary cooling module 84 is designed to further cool the pre-cooled anode stream 86 exiting the first heat exchanger system 46 before it is introduced into the condensate recovery system 85. In particular, the auxiliary cooling module 84 cools the water present in the pre-cooled anode stream 86 to a temperature low enough to allow condensation.

[0065] Thus, the auxiliary cooling module 84 includes an inlet 90 for introducing the pre-cooled anode stream 86 and an outlet 91 for withdrawing the cooled anode stream 92 .

[0066] In a preferred embodiment, the auxiliary cooling module 84 consists of a heat exchanger for recovering, preferably recovering and recycling, heat from the pre-cooled anode stream 86. This heat is recovered, for example, by feeding it to a steam generation system, a Rankine type power generation system, or a heat distribution network.

[0067] Preferably, the auxiliary cooling module 84 includes one or more coolers selected from an air cooler, a water exchanger, and any combination thereof, among others.

[0068] Condensate recovery system 85 is designed to condense water present in cooled anode stream 92 to form liquid water condensate 93 at the bottom of condensate recovery system 85 and cooled anode gas stream 44 at the top of condensate recovery system 85. Condensate recovery system 85 therefore includes an inlet 94 for introducing cooled anode stream 92, an outlet 96 for collecting condensate 93, and an outlet 98 for collecting cooled anode gas stream 44.

[0069] The plant 10 further comprises a system 99 for collecting the liquid-water condensate 93 .

[0070] The separation unit 34 typically includes a compression unit 100 and a separation module 102 .

[0071] The compression unit 100 is designed to at least partially compress the cooled anode gas stream 44 recovered at the outlet 98 of the cooling and condensing unit 32. The compressor unit 100 therefore includes an inlet 104 for receiving the cooled anode gas stream 44 and an outlet 106 for recovering a compressed, cooled anode gas stream 108.

[0072] The nature of the compression unit 100 is not particularly limited. Any device known to those skilled in the art that is capable of compressing the cooled anode gas stream 44 sufficiently for separation may be used. The compression unit 100 may consist, for example, of a series of compressors and / or blowers.

[0073] The separation module 102 is designed to partially extract the dinitrogen present in the compressed, cooled anode gas stream 108 to recover the dinitrogen gas stream 18 on the one hand and the dinitrogen-depleted anode stream 36 (also known as the recycle stream 36) on the other hand. The separation module 102 therefore comprises an inlet 110 for introducing the compressed, cooled anode gas stream 108, an outlet 112 for recovering the dinitrogen gas stream 18, and an outlet 114 for recovering the dinitrogen-depleted anode stream 36.

[0074] The separation module 102 is typically comprised of any equipment known to those skilled in the art that is capable of at least partially extracting the dinitrogen present in a gaseous mixture of dihydrogen and dinitrogen.

[0075] The separation module 102 may optionally be supplemented by one or more additional equipment items selected from the group of a purification unit (not shown) for removing any nitrogen oxides (NOx), a drying device, and a superheater. If present, this additional equipment is typically located upstream of the separation module 102, typically between the compression unit 100 and the separation module 102.

[0076] Separation module 102 typically includes a membrane separation unit, a pressure-swing adsorption (PSA) unit, a temperature-swing adsorption (TSA) unit, a pressure-temperature-swing adsorption (PTSA) unit, or any combination thereof.

[0077] This equipment is well known to those skilled in the art and will not be described further below.

[0078] Preferably, the outlet 112 for recovering the dinitrogen gas stream 18 is connected to a plant 26 so that the dinitrogen gas stream 18 can be collected there for further processing.

[0079] Preferably, the outlet 114 for recovering the dinitrogen-depleted anode stream 36 is connected to the inlet 48 of the first heat exchanger system 46 for mixing with the ammonia gas stream 14 .

[0080] According to a preferred embodiment, the plant 10 according to the invention does not include hydrogen pumps. Such equipment is expensive and bulky. They also require a significant amount of energy to operate, generally slightly less than the energy recovered by recycling the hydrogen. The system according to the invention is therefore advantageous in that it does away with this expensive, cumbersome, energy-intensive equipment.

[0081] The flows described in the plant are combined with the pipes that transport them.

[0082] Next, an implementation of the first method according to the present invention will be described.

[0083] The method according to the invention first involves supplying at least one ammonia gas stream 14 from a plant 22 (or a gas pipe network) and at least one dioxygen-rich gas stream 16 from a plant 24 .

[0084] The ammonia gas stream 14 is first mixed with a dinitrogen-depleted anode stream 36 (also known as recycle stream 36 ) recovered at the outlet 114 of the separation unit 34 to form an ammonia-rich feed stream 38 .

[0085] As will be explained in more detail below, hydrogen not consumed by fuel cell unit 30 is recovered and reinjected upstream of fuel cell unit 30 in the form of dinitrogen-depleted anode stream 36 for recirculation.

[0086] The ratio in which the ammonia gas stream 14 and the dinitrogen depleted anode stream 36 are mixed depends on the conversion rate of the fuel cell unit 30, and is typically 60%.

[0087] Preferably, the ammonia gas stream 14 and the dinitrogen-depleted anode stream 36 are mixed in a volume ratio in the range of 1:10 to 10:1, more preferentially 5:10 to 1:1, advantageously 1:2 to 4:5, typically 7:10.

[0088] Preferably, the ammonia-rich feed stream 38 has an ammonia NH3 content of between 15% and 75% by volume, more preferentially between 30% and 60% by volume, advantageously between 40% and 50% by volume, typically 45% by volume.

[0089] Preferably, the ammonia rich feed stream 38 has a dihydrogen H2 content of between 15% and 75% by volume, more preferentially between 30% and 60% by volume, advantageously between 40% and 50% by volume, typically 45% by volume.

[0090] Preferably, the ammonia-rich feed stream 38 has a dinitrogen N2 content of between 0% and 50% by volume, more preferentially between 5% and 30% by volume, advantageously between 10% and 20% by volume, typically 10% by volume.

[0091] The ammonia-rich feed stream 38 is then introduced into a first heat exchanger system 46 where it is heated to form a heated fuel stream 52 .

[0092] Preferably, upstream of the first heat exchanger system 46, the ammonia-rich feed stream 38 has a temperature of between 5°C and 80°C, more preferentially between 20°C and 50°C, advantageously between 30°C and 40°C, typically 35°C.

[0093] Preferably, the ammonia-rich feed stream 38 is heated in the first heat exchange system 46 to a temperature lower than the temperature of the fuel cell unit 30, more preferentially to a temperature between 10°C and 300°C lower, more preferentially to a temperature between 50°C and 200°C lower, typically to a temperature between 100°C and 150°C lower than the temperature of the fuel cell unit 30.

[0094] The heated fuel stream 52 is then introduced into the fuel cell unit 30 .

[0095] At the same time, the dioxygen rich gas stream 16 is introduced into a pretreatment unit 54 where it is compressed and / or dried and / or filtered, preferably compressed, dried and filtered, and heated before being introduced into the fuel cell unit 30.

[0096] More specifically, the dioxygen-rich stream 16 is first introduced into module 55 where it is compressed and / or dried and / or filtered, preferably compressed, dried and filtered to form a pressurized dioxygen-rich gas stream 56 at the outlet.

[0097] The pressurized dioxygen-rich gas stream 56 is then introduced into a second heat exchanger system 60 where it is heated to form a heated dioxygen-rich stream 66 at an outlet 64 .

[0098] Preferably, upstream of the second heat exchanger system 60, the dioxygen-rich pressurized gas stream 56 has a temperature of between 10°C and 200°C, more preferentially between 50°C and 150°C, typically between 75°C and 120°C, typically between 90°C and 95°C.

[0099] Preferably, the dioxygen-rich pressurized gas stream 56 is heated in the second heat exchange system 60 to a temperature lower than the temperature of the fuel cell unit 30, more preferentially to a temperature between 10°C and 300°C lower than the temperature of the fuel cell unit 30, more preferentially to a temperature between 50°C and 200°C lower, typically to a temperature between 100°C and 150°C lower.

[0100] The heated dioxygen rich stream 66 is then introduced into the fuel cell unit 30 .

[0101] The dioxygen-rich stream 16 and the feed stream 38 are preheated to maintain a relatively constant temperature inside the stack unit 30, thus ensuring optimum performance.

[0102] The fuel cell unit 30, which is continuously supplied with the heated fuel stream 52 and the heated dioxygen-rich stream 66, is then put into operation.

[0103] To do this, the heated fuel stream 52 is introduced into the fuel cell unit 30 at an inlet 72. In particular, the heated fuel stream 52 is injected into the anode system 68.

[0104] The heated dioxygen rich stream 66 is introduced into an inlet 74 of the fuel cell unit 30. In particular, the heated dioxygen rich stream 66 is injected into a cathode system 70.

[0105] Upon entering the fuel cell unit 30, the heated fuel stream 52 undergoes a first catalytic cracking step during which ammonia present in the heated fuel stream 52 decomposes into dinitrogen gas N2 and hydrogen gas H2. The catalytic cracking of ammonia is initiated by the high temperature inside the fuel cell unit 30 in the presence of catalytic material in the anode system 68. The temperature inside the fuel cell unit 30 during operation depends on the type of high temperature fuel cell and the operational choices made. For SOFC fuel cells this is typically between 500°C and 1100°C, preferably between 700°C and 900°C.

[0106] Preferably, all of the ammonia in the heated fuel stream 52 is decomposed in the fuel cell unit (30) into dinitrogen gas, N2, and hydrogen gas, H2.

[0107] Upon contact with the anode system 68, the H2 hydrogen is converted to H +The protons and electrons are released and stored in the anode system 68 and transported to the cathode system 70 of the fuel cell unit 30 by an external circuit, and the movement of electrons from the anode system 68 to the cathode system 70 generates the electric current 12.

[0108] Dinitrogen N2 present in the fuel cell unit 30, and particularly in the anode system 68, is inert at the operating temperatures of the fuel cell unit 30. In particular, nitrous oxide N2 is not oxidized and remains entirely in the anode gas stream 40 that is recovered at the outlet of the fuel cell unit 30.

[0109] In the cathode system 70, the electrons carried by the current 12 are fixed by dioxygen O2 present in the heated dioxygen-rich stream 66. The dioxygen molecule O2 is then converted to a superoxide ion O2 by the capture of two electrons. 2- is converted to

[0110] The resulting superoxide ion O 2- then pass through the electrolyte to the anode system 68 where they react with the previously generated protons H + It reacts with to form water, H2O.

[0111] The anode gas stream 40 and the cathode gas stream 42 are then recovered at the outlet of the fuel cell unit 30 .

[0112] A cathode gas stream 42, which corresponds to the residual gas stream recovered at the outlet of the cathode system 70, is recovered at an outlet 78 of the fuel cell unit 30. Stream 42 has a reduced dioxygen content compared to the original heated dioxygen-rich stream 66.

[0113] Typically, the cathode gas stream 42 has a dioxygen content of less than 20 mol %, preferably between 5 mol % and 15 mol %.

[0114] The cathode gas stream 42 is then conveyed to the plant 28 .

[0115] In one embodiment, the cathode gas stream 42 is cooled by passing through a second heat exchanger system 60 before reaching the plant 28. In this manner, the cathode gas stream 42 is cooled by heat exchange with the pressurized dioxygen-rich gas stream 56 to form the dioxygen-depleted gas stream 20.

[0116] The cathode gas stream 42 recovered at the outlet 78 of the fuel cell unit 30 has a temperature close to that of the fuel cell unit 30 .

[0117] Thus, for a SOFC fuel cell, the cathode gas stream 42 recovered at the outlet 78 of the fuel cell unit 30 typically has a temperature of between 500°C and 1100°C, preferably between 700°C and 900°C.

[0118] Preferably, the cathode gas stream 42 is cooled to a temperature in the range of 50°C to 250°C, preferably 100°C to 200°C.

[0119] This method is advantageous in that it allows the dioxygen rich gas stream 16 at the inlet to be heated and the cathode gas stream 42 at the outlet to be cooled by heat integration without requiring external energy input.

[0120] According to an even more preferred method, the cathode gas stream 42 is cooled in at least two stages before being transferred to the plant 28. In particular, the cathode gas stream 42 is first cooled in a second heat exchanger system 60 to an intermediate temperature between 200° C. and 350° C., preferably between 250° C. and 300° C. The dioxygen-depleted stream 20 recovered at an outlet 80 of the second heat exchanger system 60 is then transferred to an auxiliary cooling system 81 for further cooling of the cathode gas stream 42 to a temperature compatible with the characteristics of the plant 28 for collecting the dioxygen-depleted stream 20. The cooled dioxygen-depleted gas stream 83 recovered at an outlet 82B of the auxiliary cooling system 81 typically has a temperature below 200° C., preferably between 100° C. and 200° C., advantageously around 150° C. This auxiliary cooling system 81 may contain a heat exchanger making it possible to stabilise the recovered heat, for example by feeding it to a Rankine-type steam or power generation system or to a heat distribution network. Preferably, the auxiliary cooling system 81 comprises a cooler, such as an air cooler or a water exchanger, to achieve the required cooling level.

[0121] An anode gas stream 40, which corresponds to the residual gas stream recovered at the outlet of the anode system 68, is recovered at an outlet 76 of the fuel cell unit 30. The anode gas stream 40 is composed of a mixture of water, HO, and unreacted dinitrogen, N, and dihydrogen, H, resulting from the operation of the fuel cell unit 30.

[0122] Preferably, at most 40% by volume, and more preferentially 20% to 30% by volume, of the dihydrogen H2 formed by ammonia decomposition inside the fuel cell unit 30 is recovered in the anode gas stream 40.

[0123] Preferably, the anode gas stream 40 has a dinitrogen content of between 10% and 40% by volume, more advantageously between 20% and 30% by volume, typically 25% by volume.

[0124] Preferably, the anode gas stream 40 has a water H2O content of between 30% and 60% by volume, more preferentially between 40% and 50% by volume, typically 45% by volume.

[0125] In the case of a SOFC fuel cell, the anode gas stream 40 recovered at the outlet 76 of the fuel cell unit 30 typically has a temperature in the range of 500°C to 1100°C, typically in the range of 700°C to 900°C.

[0126] The entire anode gas stream 40 is then introduced into the cooling and condensing unit 32 where it is cooled and at least a portion, and preferably most of the water formed is removed.

[0127] The anode gas stream 40 is first cooled by passing through one or more heat exchanger systems.

[0128] Preferably, the anode gas stream 40 is first introduced into the first heat exchanger system 46 where it is cooled by heat exchange with the ammonia-rich feed stream 38. A pre-cooled anode stream 86 is recovered at an outlet 89 of the first heat exchanger system 46.

[0129] In the case of a SOFC fuel cell, the anode gas stream 40 recovered at the outlet 76 of the fuel cell unit 30 typically has a temperature of between 500°C and 1100°C, preferably between 700°C and 900°C.

[0130] Preferably, the anode gas stream 40 is cooled in the first heat exchanger system 46 to a temperature between 300°C and 500°C, preferably between 350°C and 450°C.

[0131] Preferably, the pre-cooled anode stream 86 is then introduced into the auxiliary cooling module 84 for further cooling. The cooled anode stream 92 is collected from the outlet 91 of the auxiliary cooling module 84.

[0132] Preferably, the pre-cooled anode stream 86 is cooled in the auxiliary cooling module 84 to a temperature below 100°C, more preferentially between 10°C and 50°C, typically between 30°C and 40°C.

[0133] The cooled anode stream 92 is then introduced into a condensate recovery system 85 to remove water present in the cooled anode stream 92 .

[0134] In particular, cooled anode stream 92 is introduced into condensate recovery system 85. Liquid water condensate 93 is collected at the bottom of condensate recovery system 85, while cooled anode gas stream 44 is collected at the top of condensate recovery system 85.

[0135] The condensate 93 is then sent to a plant 99 for further treatment.

[0136] Preferably, when the fuel cell system operates at about atmospheric pressure, the cooled anode gas stream 44 has a water content of less than 10% by volume, more preferentially less than 6% by volume.

[0137] The entire cooled anode gas stream 44 is then injected into the separation unit 34 where it is split into a dinitrogen gas stream 18 and a dinitrogen-depleted anode stream 36 , also known as a recycle stream 36 .

[0138] Preferably, the cooled anode gas stream 44 undergoes a pre-compression step. To accomplish this, the cooled anode gas stream 44 is fed to a compressor unit 100 to form a compressed and cooled anode gas stream 108.

[0139] Preferably, when the fuel cell system operates at about atmospheric pressure, the cooled anode gas stream 44 has a pressure of between 0.7 bara and 2 bara (bars absolute), more preferentially between 1 bara and 1.5 bara (bars absolute).

[0140] Preferably, the cooled anode gas stream 44 is compressed in the compressor unit 100 to a pressure in the range of 10 bara to 100 bara (bar absolute), more preferentially 20 bara to 40 bara (bar absolute). The final pressure of the cooled gas stream 44 depends on the characteristics of the separation module 102.

[0141] The compressed and cooled anode gas stream 108 is then introduced into the separation module 102 to form the dinitrogen gas stream 18 on the one hand and the dinitrogen-depleted anode stream 36 (recycle stream 36) on the other hand.

[0142] The dinitrogen gas stream 18 is then sent to a plant 26 for further treatment.

[0143] Preferably, the dinitrogen gas stream 18 consists essentially of ammonia and possibly impurities.

[0144] More preferentially, the dinitrogen gas stream 18 has a dinitrogen content of greater than or equal to 99.00% by volume, more preferentially between 99.90% by volume and 99.99% by volume.

[0145] In one embodiment, the dinitrogen gas stream 18 may contain very small amounts of impurities.

[0146] Impurities that may be present in the dinitrogen gas stream 18 include dihydrogen, ammonia, water, nitrogen oxides (or NOx), and traces of oil. The presence of purification and / or drying units, especially upstream of the separation unit 102, reduces the impurity content.

[0147] Preferably, the dinitrogen gas stream 18 has an impurity content of less than 10% by volume, more preferentially less than 5% by volume, typically less than 1% by volume.

[0148] Preferably, the dinitrogen-depleted anode stream 36 (recycle stream 36) has a dihydrogen H content of 50% by volume or more, more preferentially 70% by volume or more, typically between 70% by volume and 90% by volume, for example between 70% by volume and 80% by volume.

[0149] Preferably, the dinitrogen-depleted anode stream 36 (recycle stream 36) has a residual dinitrogen N2 content of 10 vol.% or more, more preferentially 20 vol.% or more, typically 20 vol.% to 40 vol.%, for example 20 vol.% to 30 vol.%.

[0150] Finally, the dinitrogen depleted anode stream 36 is injected into the ammonia gas stream 14 where it is recycled to the fuel cell unit.

[0151] According to a preferred embodiment, the method according to the invention does not include the step of using one or more hydrogen pumps. Therefore, the method according to the invention is advantageous in that it eliminates the need for a hydrogen pump.

[0152] The plant 10 and the method according to the invention therefore enable the production of an electric current 12 by the fuel cell unit 30 supplied with ammonia. In addition, the plant 10 and the method described herein enable the recycling of unreacted dihydrogen back to the fuel cell.

[0153] The invention is based on the fact that the presence of dinitrogen N2 residues in the recycle stream 36 has little or no effect on the operation of the fuel cell unit 30. Dinitrogen N2 is a neutral gas for the fuel cell unit 30. At the operating temperature of the fuel cell unit 30, dinitrogen is inert and does not participate in any reactions that may occur inside the fuel cell unit 30. However, too much nitrogen in the fuel cell can reduce the performance of the fuel cell by excessively diluting the dihydrogen fuel when it contacts the anode system 68. The separation performance of the separation unit 102 allows that when the decomposition of the ammonia gas stream 14 occurs in the anode system 68, a stream 36 is produced whose stoichiometric ratio is as close as possible to the hydrogen / dinitrogen stoichiometry of the ammonia gas stream 14. In this way, the feed stream 38 resulting from the mixture of the ammonia gas stream 14 and the dinitrogen-depleted recycle stream 36 is characterized by a hydrogen-nitrogen ratio that is very close to the hydrogen-nitrogen ratio of the ammonia gas stream 14. In fact, the electrochemical performance of the fuel cell system 30 is not affected by this recirculation 36 .

[0154] In addition, the plant 10 and method according to the present invention significantly reduces the energy requirements associated with the recycling of dihydrogen H2 by allowing a significant proportion of the dinitrogen N2 recovered at the outlet of the fuel cell unit 30 to be injected into the feed stream 38.

[0155] In prior art processes, the recycle stream is essentially dihydrogen H2. In particular, any dinitrogen present in the anode gas stream is separated so that the recycle stream is substantially free of dinitrogen. Separation and purification steps requiring more specialized separation equipment and / or high energy requirements are then necessary to achieve the required purity.

[0156] In the context of the present invention, the presence of residual dinitrogen in the recycle stream 36 means that less complex separation equipment can be used. The lower purity made possible by the method of the present invention also makes it possible to significantly reduce the energy requirements associated with post-treatment of the anode gas stream 40 before recycle.

[0157] A further advantage of the method and system is that it allows the recovery and reuse of excess heat released by the fuel cell unit. In particular, the anode gas stream 40 recovered at the outlet 76 of the fuel cell unit 30 is cooled in at least two stages, on the one hand by the first heat exchanger system 46 and on the other hand by the auxiliary cooling module 84. The first heat exchanger system 46 cools the anode gas stream 40 to an intermediate temperature between 200° C. and 500° C., preferably between 300° C. and 450° C., by heat exchange with the ammonia-rich feed stream 38. The auxiliary cooling module 84 then cools the pre-cooled anode gas stream 86 leaving the first heat exchanger system 46. The auxiliary cooling module 84 typically consists of a heat exchanger for recovering, preferably recovering and reusing, heat from the pre-cooled anode stream 86. This heat is recovered, for example, by feeding it to a steam generation system, a Rankine type power generation system or a heat distribution network.

[0158] If the separation module 102 comprises a membrane separation unit (as described above), it is possible that the dinitrogen gas stream 18 recovered at the outlet of the module 102 is under pressure. Preferably, in this case, the plant 10 according to the invention comprises, between the separation module 102 and the plant 26, a complementary system of turbines designed to generate a complementary electric current by the expansion of the pressurized dinitrogen gas stream 18.

[0159] The method and plant according to the invention are also advantageous in that they enable at least 80%, preferably at least 90%, more preferentially at least 95%, typically at least 99%, and advantageously all of the dihydrogen formed by decomposition of ammonia to be consumed in the fuel cell unit 30.

[0160] Finally, the systems and methods described in this invention are also advantageous in that they allow for efficient recirculation of fuel not consumed in the fuel cell unit.

Claims

1. A method for implementing a fuel cell system (10) comprising: a) operating 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 a dioxygen-rich gas stream (16) injected at the cathode system (70); b) recovering a dinitrogen-rich and dihydrogen-rich anode gas stream (40) and a cathode gas stream (42) at the outlet of said fuel cell unit (30); c) cooling the anode gas stream (40) and condensing water present in the anode gas stream (40) to form a cooled anode gas stream (44); d) separating the cooled anode gas stream (44) into a dinitrogen gas stream (18) and a dinitrogen-depleted anode stream (36); e) injecting at least a portion of the dinitrogen-depleted anode stream (36) into the fuel cell unit (30), in particular into the anode system (68), for recirculation of said at least a portion of the dinitrogen-depleted anode stream (36) to said fuel cell unit (30); The method of claim 1, wherein the dinitrogen-depleted anode stream (36) has a residual dinitrogen content of 5% by volume or greater.

2. 2. The method of claim 1, wherein the dinitrogen-depleted anode stream (36) has a dinitrogen content of more than 10 vol.%, preferably more than 20 vol.%, more preferentially between 10 vol.% and 50 vol.%, even more preferentially between 15 vol.% and 40 vol.%, advantageously between 20 vol.% and 30 vol.%.

3. 3. The method of claim 1 or 2, wherein at least a portion of the dinitrogen-depleted anode stream (36) is injected into the ammonia-rich gas stream (14) to form an ammonia-rich feed stream (38), which is then injected into the fuel cell unit (30), in particular the anode system (68).

4. 4. The method according to claim 3, wherein said feed stream (38) has a dihydrogen content of at least 15% by volume, preferably at least 40% by volume, more preferentially between 40% and 50% by volume.

5. The method of any one of claims 1 to 4, wherein step d) of separating the cooled anode gas stream (44) is carried out by membrane separation, pressure swing adsorption, temperature swing adsorption, or pressure-temperature swing adsorption.

6. 6. The method according to claim 5, comprising an intermediate step between steps c) and d) of compressing the cooled anode gas stream (44), preferably to a pressure of at least 10 bara, more preferentially at least 20 bara, typically between 20 bara and 40 bara.

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

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

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

10. A fuel cell plant (10), comprising: a fuel cell unit (30) comprising an inlet (72) for introducing an ammonia-rich gas stream (14), an inlet (74) for introducing a dioxygen-rich gas stream (16), an outlet (76) for recovering an anode gas stream (40), and an outlet (78) for recovering a cathode gas stream (42); - a cooling and condensation unit (32) for cooling and drying said anode gas stream (40) to form a cooled anode gas stream (44); a separation unit (34) for separating the cooled anode gas stream (44) into a dinitrogen gas stream (18) and a dinitrogen-depleted anode stream (36), said separation unit (34) comprising a recovery outlet (114) for recovering the dinitrogen-depleted anode stream (36), said dinitrogen-depleted anode stream (36) being connected to the inlet (72) for introducing the ammonia-rich gas stream (14) into the fuel cell unit (30), The fuel cell plant (10), wherein the separation unit (34) comprises at least one separation module (102) selected from the group consisting of a membrane separation unit, a pressure swing adsorption unit, a temperature swing adsorption unit, a pressure-temperature swing adsorption unit, and any combination thereof.

11. The plant (10) of claim 10, wherein the separation unit (34) further comprises a compression module (100) positioned upstream of the separation module (102).

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