Method and related plant for implementing an ammonia-fueled fuel cell with dihydrogen recirculation.

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 combustion fuel cell system, the method comprising a step for recycling dihydrogen formed during the method that is not consumed in the fuel cell.

[0002] The method of the present invention is typically implemented in a fuel cell plant that enables generation of electric current by an electrochemical reaction between dihydrogen H2 and dioxygen from air. In the context of ammonia-fueled fuel cells, the dihydrogen H2 used as fuel fluid is produced during cell operation by decomposition of ammonia NH3 in the fuel cell, particularly at the cell anode. [Background Art]

[0003] Fuel cells typically consist of one or more fuel cells, and preferably operate at high temperature to enable internal decomposition of ammonia. Examples that may be cited include solid oxide fuel cells (SOFC).

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

[0005] An SOFC element is generally composed of four layers, three of which are ceramic. A single stack composed of these four superimposed layers is typically only a few millimeters thick. Dozens of these stacks are then superimposed in series to form a stack assembly.

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

[0007] This electrochemical reaction results in the generation of electricity and the formation of water, a byproduct of the electrochemical reaction. Dinitrogen produced from the decomposition of ammonia is also recovered at the stack outlet as a mixture with the formed water.

[0008] In particular, to prevent and / or limit damage to the electrochemical cell during operation caused by the potential difference it experiences, the flow rates of the fuel, especially ammonia, and the oxidizer, especially air, are adjusted so that the amount of dihydrogen (H2) in the cell always exceeds the maximum reaction capacity within the cell. As a result, a considerable 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 still contains a considerable amount of oxygen, although it has been depleted.

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

[0010] However, the use of dihydrogen by combustion is limited. In particular, it does not achieve the high electrical efficiency theoretically permissible by fuel cells. Furthermore, the operation of catalytic reactors typically results in the formation of nitrogen oxides (also known as "NOx"), which can be difficult to control. Since nitrogen oxides are pollutants to the environment, adaptations are needed to prevent their release into the atmosphere.

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

[0012] 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 recirculating hydrogen. The energy gain associated with recirculating hydrogen dihydrogen using hydrogen pumps is negligible. [Overview of the project]

[0013] Therefore, one object of the present invention is to provide a method for implementing a fuel cell system that enables efficient and reliable recovery of H2-dihydrogen present in the anode effluent for recirculation at the battery inlet, and in particular, to increase the overall energy performance of the method while limiting the investment and operating costs of the method.

[0014] In particular, an object of the present invention is to provide an integrated method for improving the overall energy performance of a power generation 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 combustion fuel cell system whose operation does not result in the emission of nitrogen oxides (NOx) in the exhaust gas.

[0016] For this purpose, the present invention provides a method for implementing a fuel cell system, the following: a) Operating a fuel cell unit comprising at least one anode system and at least one cathode system, wherein the fuel cell unit is continuously supplied with an ammonia-rich gas flow injected into the anode system and a dioxygen-rich gas flow injected into the cathode system; b) A step of recovering the nitrogen-rich and hydrogen-rich anode gas streams and cathode gas streams at the outlet of the fuel cell unit, c) A step of cooling the anode gas flow and condensing the water present in the anode gas flow to form a cooled anode gas flow, d) A step of separating the cooled anode gas flow into a dinitrogen gas flow and a dinitrogen-reduced anode flow, e) The step of injecting at least a portion of the nitrogen-depleted anode flow into the fuel cell unit, particularly into the anode system, in order to recirculate at least a portion of the nitrogen-depleted anode flow to the fuel cell unit, The present invention relates to a method for a nitrogen-reduced anode flow having a residual nitrogen content of 5 volume% or more. The method according to the present invention, either alone or in any technically feasible combination, has the following characteristics: - The nitrogen-reduced anode flow has a nitrogen content of more than 10 vol%, preferably more than 20 vol%, more preferably 10 vol% to 50 vol%, even more preferably 15 vol% to 40 vol%, and advantageously 20 vol% to 30 vol%. -At least a portion of the nitrogen-reduced anode flow is injected into the ammonia-rich gas flow to form an ammonia-rich supply flow, which is then injected into the fuel cell unit, particularly the anode system. - The supply flow has a dihydrogen content of 15% by volume or more, preferably 40% by volume or more, more preferably 40% to 50% by volume. - Step d) of separating the cooled anode gas stream is performed by membrane separation, pressure swing adsorption, temperature swing adsorption, or pressure-temperature swing adsorption. - The method includes an intermediate step between step c) and step d) in which the cooled anode gas flow is compressed to a pressure of preferably 10 bara or more, more preferably 20 bara or more, typically 20 bara to 40 bara. - The anode gas flow is at least partially cooled in step c) by heat exchange with the ammonia-rich gas flow or the feed flow. -The dioxygen-rich gas flow is at least partially heated by heat exchange with the cathode gas flow before being introduced into the fuel cell unit. the method may include one or more selected from among not comprising the step of combusting the anode gas stream, and not even comprising the step of partial combustion.

[0017] The present invention relates to a fuel cell unit comprising an inlet for introducing an ammonia-rich gas stream, an inlet for introducing an oxygen-rich gas stream, an outlet for recovering an anode gas stream, and an outlet for recovering a cathode gas stream; a cooling and condensing 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-reduced anode stream, wherein the separation unit comprises a dinitrogen-reduced anode stream recovery outlet, and the dinitrogen-reduced anode stream recovery outlet is connected to the inlet for introducing the ammonia-rich gas stream into the fuel cell unit, and 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 present invention may have the feature that the separation unit further comprises a compression module positioned upstream of the separation module. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The present invention will be better understood upon reading the following description, which is given purely by way of example and made with reference to the following drawings. [Figure 1] Fig. 1 is a block diagram showing a plant for carrying out the method according to the present invention. DESCRIPTION OF EMBODIMENTS

[0020] A plant 10 according to the present invention is schematically illustrated in Fig. 1.

[0021] Plant 10 is designed to generate an electric current 12 from an ammonia gas flow 14 and a dioxygen-rich gas flow 16.

[0022] Plant 10 is also designed to recover a dinitrogen gas stream 18 on the one hand and a dioxygen-reduced gas stream 20 on the other hand as spillovers.

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

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

[0025] When the oxygen-rich gas 16 is air, the storage unit 24 can optionally be replaced by a system of pumps and compressors for supplying compressed 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 90% by volume or more, more preferably 95% by volume or more, even more preferably 97% by volume or more, advantageously 98% by volume or more, and more advantageously 99% by volume or more.

[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 trace amounts of oil.

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

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

[0031] The dioxygen-rich gas flow 16 typically has a dioxygen content of at least 10 volume%, preferably 15 to 25 volume%, of dioxygen. Advantageously, the dioxygen-rich gas flow 16 is an airflow.

[0032] Preferably, the oxygen-rich gas flow 16 is at a pressure in the range of 1 atm to 5 bara (absolute bar).

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

[0034] Preferably, the oxygen-depleting gas flow 20 is directly discharged into the atmosphere at the plant 28.

[0035] Alternatively, the oxygen-reduced gas stream 20 is collected at plant 28 and sent to another plant for consumption or processing.

[0036] Plant 10 typically comprises a fuel cell unit 30, a cooling and condensing unit 32, and a separation unit 34.

[0037] Before being introduced into the fuel cell unit 30, the ammonia gas stream 14 is mixed with the recirculated stream 36 recovered at the outlet of the separation unit 34 to form an ammonia-rich supply stream 38. The properties of the recirculated stream 36 are described in detail below.

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

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

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

[0041] Preferably, the plant 10 according to the present invention includes a first heat exchanger system 46 upstream of the fuel cell unit 30, which is designed to heat the ammonia-rich supply flow 38 before introducing it into the fuel cell unit 30.

[0042] For the purposes of the present invention, the heat exchanger system includes at least one heat exchanger. Therefore, the heat exchanger system may include a single heat exchanger or a plurality of heat exchangers associated with one another.

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

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

[0045] The pretreatment unit 54 includes a module 55 designed to first compress and / or dry and / or filter, preferably compress, dry and filter, a dioxygen-rich gas flow 16 to form a pressurized dioxygen-rich gas flow 56. Therefore, the module 55 includes an inlet 57 for introducing the dioxygen-rich gas flow 16 and an outlet 58 for recovering the pressurized dioxygen-rich gas flow 56.

[0046] Preferably, the pretreatment unit 54 further includes a second heat exchanger system 60 designed to heat the pressurized dioxygen-rich gas flow 56 before introducing it to the fuel cell unit 30. Thus, the second heat exchanger system 60 includes an inlet 62 for introducing the pressurized dioxygen-rich gas flow 56 and an outlet 64 for recovering the heated dioxygen-rich flow 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). Therefore, an anode (or cathode) system may include a single anode (or cathode) or a plurality of anodes (or cathodes) associated with one another.

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

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

[0051] The fuel cell unit 30 further includes an outlet 76 for recovering the anode gas flow 40 that arises from the operation of the fuel cell unit 30 and is recovered from the anode system 68.

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

[0053] An outlet 78 for recovering the oxygen-depleted cathode gas flow 42 is preferably connected to the plant 28 via a pretreatment unit 54.

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

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

[0056] In a 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 flow 20 before transferring it to the plant 28. The auxiliary cooling system 81 then includes an inlet 82A for introducing the dioxygen-depleted gas flow 20 and an outlet 82B for recovering the cooled dioxygen-depleted gas flow 83. The outlet 82B of the auxiliary cooling system 81 is connected directly to the plant 28.

[0057] The auxiliary cooling system 81 may house a heat exchanger that allows the recovered heat to be used, for example, to supply a Rankine steam or power generation system or a heat distribution network. Preferably, if there is no heat integration for heat recovery, the auxiliary cooling system 81 consists of a cooler, such as an air cooler or a water exchanger, to achieve the required cooling level.

[0058] This method is advantageous in that it allows the oxygen-rich gas flow 16 to be heated by thermal integration before being introduced into the fuel cell unit 30, without requiring an external energy input.

[0059] The cooling and condensing 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 flow 40 and at least partially condense 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.

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

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

[0062] This method is advantageous in that it allows the supply flow 38 to be heated before being introduced into the fuel cell unit 30 and the anode gas flow 40 to be cooled before being introduced into the condensate recovery system 85 by thermal integration that does not require an external energy input.

[0063] In an alternative embodiment (not shown), the heat exchanger system of the cooling and condensing unit 32 is separated from the first heat exchanger system 46.

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

[0065] Therefore, the auxiliary cooling module 84 includes an inlet 90 for introducing a pre-cooled anode flow 86 and an outlet 91 for recovering the cooled anode flow 92.

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

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

[0068] The condensate recovery system 85 is designed to condense water present in the cooled anode flow 92 to form liquid water condensate 93 at the bottom of the condensate recovery system 85 and to form a cooled anode gas flow 44 at the top of the condensate recovery system 85. Therefore, the condensate recovery system 85 includes 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 cooled anode gas flow 44.

[0069] Plant 10 further comprises a system 99 for collecting 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 flow 44 recovered at the outlet 98 of the cooling and condensing unit 32. Therefore, the compressor unit 100 includes an inlet 104 for introducing the cooled anode gas flow 44 and an outlet 106 for recovering the compressed and cooled anode gas flow 108.

[0072] The properties of the compression unit 100 are not particularly limited. Any device known to those skilled in the art that can sufficiently compress the cooled anode gas flow 44 for separation may be used. The compressor unit 100 consists, for example, a series of compressors and / or blowers.

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

[0074] The separation module 102 typically consists of any apparatus known to those skilled in the art that can at least partially extract 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 a group of purification units (not shown), drying devices, and superheaters for the removal of any nitrogen oxides (NOx). 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] The 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 device 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 the plant 26, so that the dinitrogen gas stream 18 can be collected there for post-treatment.

[0079] 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 for mixing with the ammonia gas flow 14.

[0080] According to a preferred embodiment, the plant 10 according to the present invention does not include a hydrogen pump. Such equipment is expensive and bulky. They also require a considerable amount of energy to operate, generally slightly less than the energy recovered by recirculating hydrogen. Therefore, the system according to the present invention is advantageous in that it eliminates the need for this expensive, cumbersome, and 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 present invention first includes supplying at least one ammonia gas stream 14 from plant 22 (or gas pipe network) and at least one dioxygen-rich gas stream 16 from plant 24.

[0084] The ammonia gas flow 14 is first mixed with the nitrogen-reduced anode flow 36 (also known as the recirculation flow 36) recovered at the outlet 114 of the separation unit 34 to form an ammonia-rich supply flow 38.

[0085] As described in detail below, hydrogen not consumed by the fuel cell unit 30 is recovered and reinjected upstream of the fuel cell unit 30 in the form of a nitrogen-depleted anode flow 36 for recirculation.

[0086] The mixing ratio of the ammonia gas flow 14 to the nitrogen-depleted anode flow 36 depends on the conversion rate of the fuel cell unit 30 and is typically 60%.

[0087] Preferably, the ammonia gas stream 14 and the nitrogen-depleted anode stream 36 are mixed in a volume ratio ranging from 1:10 to 10:1, more preferably 5:10 to 1:1, favorably 1:2 to 4:5, typically 7:10.

[0088] 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, and typically 45% by volume.

[0089] 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, favorably 40% to 50% by volume, and typically 45% by volume.

[0090] 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, favorably 10% to 20% by volume, and typically 10% by volume.

[0091] Next, the ammonia-rich supply flow 38 is introduced into the first heat exchanger system 46, where it is heated to form a heated fuel flow 52.

[0092] 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, favorably 30°C to 40°C, and 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 preferably to a temperature 10°C to 300°C lower than the temperature of the fuel cell unit 30, more preferably to a temperature 50°C to 200°C lower, and typically to a temperature 100°C to 150°C lower.

[0094] Next, the heated fuel flow 52 is introduced into the fuel cell unit 30.

[0095] Simultaneously, the oxygen-rich gas stream 16 is introduced into the 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 flow 16 is first introduced into module 55, where it is compressed and / or dried and / or filtered, preferably, to form a pressurized dioxygen-rich gas flow 56 at the outlet.

[0097] Next, the pressurized dioxygen-rich gas flow 56 is introduced into a second heat exchanger system 60, where it is heated to form a heated dioxygen-rich flow 66 at the outlet 64.

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

[0099] Preferably, the oxygen-rich pressurized gas flow 56 is heated in the second heat exchange system 60 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 the temperature of the fuel cell unit 30, more preferably to a temperature 50°C to 200°C lower, and typically to a temperature 100°C to 150°C lower.

[0100] Next, the heated oxygen-rich flow 66 is introduced into the fuel cell unit 30.

[0101] The oxygen-rich flow 16 and the supply flow 38 are preheated to maintain a relatively constant temperature inside the laminated unit 30, thus ensuring optimal performance.

[0102] A fuel cell unit 30, to which a heated fuel flow 52 and a heated oxygen-rich flow 66 are continuously supplied, then operates.

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

[0104] The heated oxygen-rich flow 66 is introduced into the inlet 74 of the fuel cell unit 30. In particular, the heated oxygen-rich flow 66 is injected into the cathode system 70.

[0105] Upon entering the fuel cell unit 30, the heated fuel flow 52 undergoes a first catalytic cracking step, during which the ammonia present in the heated fuel flow 52 is decomposed into nitrogen 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 a catalyst material in the anode system 68. The temperature inside the operating fuel cell unit 30 depends on the type of high-temperature fuel cell and the operation selection made. For SOFC fuel cells, this is typically 500°C to 1100°C, preferably 700°C to 900°C.

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

[0107] When it comes into contact with anode system 68, hydrogen H2 becomes H +The protons dissociate into electrons. The electrons released are stored in the anode system 68 and transferred by an external circuit to the cathode system 70 of the fuel cell unit 30. The movement of electrons from the anode system 68 to the cathode system 70 generates the electric current 12.

[0108] The dinitrogen (N2) present in the fuel cell unit 30, particularly in the anode system 68, is inert at the operating temperature of the fuel cell unit 30. In particular, nitrous oxide (N2) is not oxidized and remains completely in the anode gas stream 40 recovered at the outlet of the fuel cell unit 30.

[0109] In the cathode system 70, electrons carried by the current 12 are fixed by dioxygen O2 present in the heated dioxygen-rich flow 66. Subsequently, the dioxygen molecule O2 captures two electrons to form a superoxide ion O 2- It will be converted.

[0110] The superoxide ion O formed as a result 2- They then proceed through the electrolyte to the anode 68, where they are converted into the previously generated proton H + It reacts with to form water (H2O).

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

[0112] 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. Flow 42 has a reduced dioxygen content compared to the initial heated dioxygen-rich flow 66.

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

[0114] Next, the cathode gas stream 42 is transported to plant 28.

[0115] In one embodiment, the cathode gas flow 42 is cooled by passing through a second heat exchanger system 60 before reaching the plant 28. In this way, the cathode gas flow 42 is cooled by heat exchange with a pressurized dioxygen-rich gas flow 56 to form a dioxygen-depleted gas flow 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] Therefore, in the case of an SOFC fuel cell, the cathode gas stream 42 recovered at the outlet 78 of the fuel cell unit 30 typically has a temperature of 500°C to 1100°C, preferably 700°C to 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 oxygen-rich gas flow 16 at the inlet to be heated and the cathode gas flow 42 at the outlet to be cooled by thermal integration that does not require external energy input.

[0120] In a 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 of 200°C to 350°C, preferably 250°C to 300°C. The dioxygen-reduced stream 20 recovered at the outlet 80 of the second heat exchanger system 60 is then transferred to an auxiliary cooling system 81 to further cool the cathode gas stream 42 to a temperature suitable for the characteristics of the plant 28 for collecting the dioxygen-reduced stream 20. The cooled dioxygen-reduced gas stream 83 recovered at the outlet 82B of the auxiliary cooling system 81 typically has a temperature of less than 200°C, preferably 100°C to 200°C, and advantageously about 150°C. The auxiliary cooling system 81 may include a heat exchanger that allows the recovered heat to be stabilized by supplying it to, for example, a Rankine steam system, a power generation system, or a heat distribution network. Preferably, the auxiliary cooling system 81 consists of a cooler such as an air cooler or a water exchanger to achieve the required cooling level.

[0121] The anode gas flow 40, which corresponds 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 water H2O produced from the operation of the fuel cell unit 30, as well as a mixture of unreacted dinitrogen N2 and dihydrogen H2.

[0122] Preferably, up to 40% by volume, more preferably 20% to 30% by volume, of the dihydrogen H2 formed by ammonia decomposition inside the fuel cell unit 30 is recovered into the anode gas stream 40.

[0123] Preferably, the anode gas stream 40 has a nitrogen content of 10% to 40% by volume, more favorably 20% to 30% by volume, typically 25% by volume.

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

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

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

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

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

[0129] In the case of an SOFC fuel cell, the anode gas stream 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.

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

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

[0132] Preferably, the pre-cooled anode flow 86 is cooled in the auxiliary cooling module 84 to a temperature of 100°C or less, more preferably 10°C to 50°C, typically 30°C to 40°C.

[0133] Next, the cooled anode flow 92 is introduced into the condensate recovery system 85 to remove any water present in the cooled anode flow 92.

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

[0135] Next, the condensate 93 is sent to the plant 99 for post-processing.

[0136] Preferably, when the fuel cell system operates at approximately atmospheric pressure, the cooled anode gas flow 44 has a water content of 10% by volume or less, more preferably 6% by volume or less.

[0137] Next, the entire cooled anode gas flow 44 is injected into the separation unit 34, where it is split into a dinitrogen gas flow 18 and a dinitrogen-reduced anode flow 36, also known as the recirculation flow 36.

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

[0139] Preferably, when the fuel cell system operates at approximately atmospheric pressure, the cooled anode gas flow 44 has a pressure of 0.7 bara to 2 bara (absolute bar), more preferably 1 bara to 1.5 bara (absolute bar).

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

[0141] The compressed and cooled anode gas flow 108 is then introduced into the separation module 102, where it forms a dinitrogen gas flow 18 on one hand and a dinitrogen-reduced anode flow 36 (recirculating flow 36) on the other.

[0142] Next, the nitrogen gas stream 18 is sent to the plant 26 for post-treatment.

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

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

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

[0146] Possible impurities present in the nitrogen gas stream 18 include dihydrogen, ammonia, water, nitrogen oxides (or NOx), and trace amounts of oil. In particular, the presence of a refining and / or drying unit upstream of the separation unit 102 reduces the impurity content.

[0147] Preferably, the nitrogen gas stream 18 has an impurity content of 10% by volume or less, more preferably 5% by volume or less, and typically 1% by volume or less.

[0148] Preferably, the nitrogen-reduced anode flow 36 (recirculating flow 36) has a dihydrogen H2 content of 50% by volume or more, more preferably 70% by volume or more, typically 70% to 90% by volume, for example, 70% to 80% by volume.

[0149] Preferably, the nitrogen-reduced anode flow 36 (recirculating flow 36) has a residual nitrogen N2 content of 10% by volume or more, more preferably 20% by volume or more, typically 20% to 40% by volume, for example, 20% to 30% by volume.

[0150] Finally, the nitrogen-depleted anode flow 36 is injected into the ammonia gas flow 14, where it is recirculated to the fuel cell unit.

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

[0152] Therefore, the plant 10 and method according to the present invention enable the generation of electric current 12 by a fuel cell unit 30 supplied with ammonia. In addition, the plant 10 and method described herein enable the recirculation of unreacted dihydrogen back into the fuel cell.

[0153] The present invention is based on the fact that the presence of dinitrogen (N2) residue in the recirculating flow 36 has little to 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 comes into contact with the anode system 68. The separation performance of the separation unit 102 allows that when the decomposition of the ammonia gas flow 14 occurs in the anode system 68, a flow 36 is produced in which the stoichiometric ratio is as close as possible to the hydrogen / dinitrous stoichiometry of the ammonia gas flow 14. In this way, the feed flow 38 resulting from the mixture of the ammonia gas flow 14 and the dinitrogen-reduced recirculating flow 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 recirculation 36.

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

[0155] In prior art methods, the recirculated flow is essentially dihydrogen (H2). In particular, all dinitrogen present in the anode gas flow is separated so that the recirculated flow is substantially free of dinitrogen. Then, more specialized separation equipment and / or high energy requirements are needed for separation and purification processes to achieve the required purity.

[0156] In light of the present invention, the presence of dinitrogen residue in the recirculated flow 36 means that less complex separation equipment can be used. The lower purity achievable by the method of the present invention also makes it possible to significantly reduce the post-treatment and associated energy requirements of the anode gas flow 40 before recirculation.

[0157] A further advantage of this method and system is that excess heat released by the fuel cell unit can be recovered and reused. 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, on the one hand by a first heat exchanger system 46 and on the other hand by an auxiliary cooling module 84. The first heat exchanger system 46 cools the anode gas flow 40 to an intermediate temperature of 200°C to 500°C, preferably 300°C to 450°C, by heat exchange with the ammonia-rich supply flow 38. The auxiliary cooling module 84 then cools the pre-cooled anode gas flow 86 exiting the first heat exchanger system 46. The auxiliary cooling module 84 typically consists of a heat exchanger that recovers heat from the pre-cooled anode flow 86, preferably for recovery and reuse. This heat is recovered, for example, by supplying it to a steam generation system, a Rankine power generation system, or a heat distribution network.

[0158] If the separation module 102 includes a membrane separation unit (as described above), the nitrogen gas flow 18 recovered at the outlet of module 102 can be under pressure. Preferably, in this case, the plant 10 according to the present invention includes a complementary system of turbines between the separation module 102 and plant 26, designed to generate a complementary current by the expansion of the pressurized nitrogen gas flow 18.

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

[0160] Finally, the system and method described in this invention are also advantageous in that they enable the efficient recirculation of fuel that was not consumed in the fuel cell unit.

Claims

1. A method for implementing a fuel cell system (10), the following: a) A step of operating a fuel cell unit (30) comprising at least one anode system (68) and at least one cathode system (70), wherein the fuel cell unit (30) is continuously supplied with an ammonia-rich gas flow (14) injected into the anode system (68) and a dioxygen-rich gas flow (16) injected into the cathode system (70), b) A step of recovering the nitrogen-rich and hydrogen-rich anode gas flow (40) and cathode gas flow (42) at the outlet of the fuel cell unit (30), c) A step of cooling the anode gas flow (40) and condensing the water present in the anode gas flow (40) to form a cooled anode gas flow (44), d) A step of separating the cooled anode gas flow (44) into a dinitrogen gas flow (18) and a dinitrogen-reduced anode flow (36), e) The process includes the step of injecting at least a portion of the nitrogen-depleted anode flow (36) into the fuel cell unit (30) in order to recirculate at least a portion of the nitrogen-depleted anode flow (36) into the fuel cell unit (30), A method characterized in that the nitrogen-depleted anode flow (36) has a residual nitrogen content of 5% by volume or more.

2. The method according to claim 1, wherein the nitrogen-reduced anode flow (36) has a nitrogen content of more than 10% by volume.

3. The method according to claim 1 or 2, wherein at least a portion of the nitrogen-depleted anode flow (36) is injected into the ammonia-rich gas flow (14) to form an ammonia-rich supply flow (38), and the supply flow (38) is then injected into the fuel cell unit (30).

4. The method according to claim 3, wherein the supply flow (38) has a dihydrogen content of 15% by volume or more.

5. The method according to claim 1, wherein step d) for separating the cooled anode gas flow (44) is performed by membrane separation, pressure swing adsorption, temperature swing adsorption, or pressure-temperature swing adsorption.

6. The method according to claim 5, further comprising an intermediate step between steps c) and d) in which the cooled anode gas flow (44) is compressed to a pressure of 10 bara or more.

7. The method according to claim 1, wherein the anode gas flow (40) is at least partially cooled in step c) by heat exchange with the ammonia-rich gas flow (14) or the supply flow (38).

8. The method according to claim 1, wherein the dioxygen-rich gas flow (16) is at least partially heated by heat exchange with the cathode gas flow (42) before being introduced into the fuel cell unit (30).

9. The method according to claim 1, characterized in that it does not include a step of burning the anode gas flow (40), nor does it even include a step of partial combustion.

10. A fuel cell plant (10), - A fuel cell unit (30) including an inlet (72) for introducing an ammonia-rich gas flow (14), an inlet (74) for introducing a dioxygen-rich gas flow (16), an outlet (76) for recovering an anode gas flow (40), and an outlet (78) for recovering a cathode gas flow (42), - A cooling and condensing unit (32) for cooling and drying the anode gas flow (40) to form a cooled anode gas flow (44), - A separation unit (34) for separating the cooled anode gas flow (44) into a dinitrogen gas flow (18) and a dinitrogen-reduced anode flow (36), wherein the separation unit (34) includes a recovery outlet (114), and the dinitrogen-reduced anode flow (36) recovery outlet (114) for recovering the dinitrogen-reduced anode flow (36) is connected to the inlet (72) for introducing the ammonia-rich gas flow (14) into the fuel cell unit (30), The fuel cell plant (10) is characterized in that the separation unit (34) includes 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, and the nitrogen-reduced anode flow (36) has a residual nitrogen content of 5 volume% or more.

11. The plant (10) according to claim 10, further comprising a compression module (100) located upstream of the separation unit (34) of the separation module (102).

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