Ammonia decomposition system

Abstract

Provided is an ammonia decomposition system capable of suppressing the amount of waste heat.　The present invention provides an ammonia decomposition system equipped with a raw material supply line, a reactor, a discharge line, and a heat exchange unit. The raw material supply line is configured so that the ammonia supplied to the reactor as a raw material flows through the raw material line. The discharge line is configured so that a mixed gas containing a product gas discharged from the reactor and unreacted ammonia that has not been decomposed in the reactor flows through the discharge line. The heat exchange unit is configured so that the heat of the mixed gas in the discharge line is transferred to the ammonia in the raw material supply line.

Description

Ammonia decomposition system

[0001] The present invention relates to an ammonia decomposition system for obtaining hydrogen from ammonia.

[0002] Ammonia has attracted attention as one type of hydrogen carrier. Accordingly, various ammonia decomposition technologies have been developed as techniques for obtaining hydrogen from ammonia serving as a hydrogen carrier.

[0003] Patent Document 1 discloses an ammonia decomposition technology using an ATR reactor (autothermal reformer).

[0004] Japanese Patent No. 7319965

[0005] Since the ammonia decomposition reaction is an endothermic reaction, a large amount of heat is required to allow the reaction to proceed favorably. For this reason, it is preferable to effectively recover discharged heat and prevent wasteful heat discard from the ammonia decomposition system.

[0006] The present invention has been made in view of such circumstances, and provides an ammonia decomposition system capable of reducing the amount of waste heat.

[0007] The present invention provides the following: [1] An ammonia decomposition system comprising a raw material supply line, a reactor, a discharge line, and a heat exchange unit, wherein the raw material supply line is configured to carry ammonia as a raw material supplied to the reactor, the reactor is configured to decompose the ammonia supplied from the raw material supply line to produce a product gas containing hydrogen and nitrogen, the discharge line is configured to carry a mixed gas containing the product gas discharged from the reactor and unreacted ammonia that was not decomposed in the reactor, and the heat exchange unit is configured to transfer the heat of the mixed gas in the discharge line to the ammonia in the raw material supply line. [2] The ammonia decomposition system according to [1], wherein the heat exchange unit is configured to recover the heat of the mixed gas in the discharge line into a heat transfer fluid and transfer the heat of the heat transfer fluid to the ammonia in the raw material supply line. [3] An ammonia decomposition system according to [1], wherein the heat exchange unit comprises a plurality of heat storage units capable of storing supplied heat, and is configured to recover the heat of the mixed gas in the discharge line into the plurality of heat storage units and selectively transfer the heat from the plurality of heat storage units to the ammonia in the raw material supply line, and each of the plurality of heat storage units is configured to independently dissipate and store heat. [4] An ammonia decomposition system according to [1], wherein the reactor is a self-thermal decomposition reactor, the raw material supply line is configured to pass through ammonia and oxygen as raw materials supplied to the self-thermal decomposition reactor, and the self-thermal decomposition reactor is configured to decompose the remainder of the ammonia using heat obtained by oxidizing a portion of the ammonia supplied from the raw material supply line to produce a product gas containing hydrogen and nitrogen. [5] An ammonia decomposition system according to any one of [1] to [4], further comprising an ammonia recovery unit, the ammonia recovery unit is configured to separate the unreacted ammonia from the mixed gas.An ammonia decomposition system according to [6] [5], wherein the ammonia recovery unit is configured to separate the unreacted ammonia from the mixed gas, liquefy the separated ammonia, and return it to the raw material supply line. An ammonia decomposition system according to [7] [5], wherein the ammonia recovery unit is configured to separate the unreacted ammonia from the mixed gas by absorbing it into an absorbent liquid, raise the pressure of the absorbent liquid in which the unreacted ammonia has been absorbed to a level higher than the pressure of the raw material supply line, separate the unreacted ammonia from the absorbent liquid, and return it to the raw material supply line. An ammonia decomposition system according to [8] [5], wherein the ammonia recovery unit comprises a removal unit, a distillation unit, and a recovery line, wherein the removal unit is configured to absorb the unreacted ammonia from the mixed gas into an absorbent liquid, the distillation unit is configured to distillate and separate ammonia from the absorbent liquid, the recovery line is configured to return the ammonia separated in the distillation unit to the raw material supply line, and the pressure of the distillation unit is set based on the amount of unreacted ammonia. An ammonia decomposition system according to [9] [5], wherein the ammonia recovery unit comprises a first removal unit and a second removal unit, wherein the first removal unit is configured to remove the unreacted ammonia from the mixed gas as first ammonia water in which the unreacted ammonia has been absorbed by contacting the unreacted ammonia in the mixed gas with water, and the second removal unit is configured to remove the unreacted ammonia from the mixed gas as second ammonia water in which the unreacted ammonia has been absorbed by contacting the unreacted ammonia in the mixed gas after it has passed through the first removal unit with water, and the ammonia decomposition system according to

[10] [9], wherein the ammonia recovery unit comprises a first distillation unit and a second distillation unit, wherein the first distillation unit is configured to distillate and separate ammonia from the first ammonia water, and the second distillation unit is configured to distillate and separate ammonia from the second ammonia water,An ammonia decomposition system according to

[11] and [9], wherein the ammonia recovery unit comprises a multi-stage distillation unit, the multi-stage distillation unit is configured to distill and separate ammonia from the first ammonia water and the second ammonia water, and is configured to receive the first ammonia water at a stage higher than the second ammonia water.

[0008] In the ammonia decomposition system of the present invention, the heat of the high-temperature (for example, around 400 to 700°C) mixed gas sent from the reactor to the discharge line is transferred to the ammonia in the raw material supply line by the heat exchange unit. Therefore, it is possible to suppress the amount of waste heat in the ammonia decomposition system.

[0009] Figure 1 is a diagram showing the schematic configuration of the ammonia decomposition system 1 of the first embodiment. Figure 2 is a diagram showing a more detailed configuration of the ammonia recovery unit 6 of Figure 1. Figure 3 is a diagram showing a modified configuration of the ammonia recovery unit 6 of Figure 2. Figure 4 is a diagram showing a modified configuration of the heat exchange unit 5 of Figure 1. Figure 5A is a diagram showing another modified configuration of the heat exchange unit 5 of Figure 1. Figure 5B is a diagram showing another modified configuration of the heat exchange unit 5 of Figure 1. Figure 6 is a diagram showing a modified configuration of the ammonia recovery unit 6 of Figure 1. Figure 7 is a diagram showing a modified configuration of the ammonia recovery unit 6 of Figure 6. Figure 8 is a diagram showing another modified configuration of the ammonia recovery unit 6 of Figure 1. Figure 9 is a diagram showing the schematic configuration of the ammonia decomposition system 1A of the second embodiment. Figure 10A shows an example configuration in which a cooling unit 40 is provided upstream of the heat exchange unit 5 of the discharge line 4, Figure 10B shows an example configuration in which high-temperature water discharged from the bottom of the distillation column 63 is introduced into the absorption column 62, and Figure 10C shows an example configuration in which ammonia is preheated at multiple locations in the raw material supply line 2.

[0010] Embodiments of the present invention will be described below. The various features shown in the embodiments below can be combined with each other. Furthermore, each feature constitutes an independent invention.

[0011] <Ammonia Decomposition System 1 of the First Embodiment> As shown in Figure 1, the ammonia decomposition system 1 comprises a raw material supply line 2, a reactor 3, a discharge line 4, a heat exchange unit 5, and an ammonia recovery unit 6. The raw material supply line 2 is configured to connect the oxygen supply unit 21 and the ammonia supply unit 22 to the reactor 3, respectively. The oxygen supply unit 21 is configured to supply oxygen from a tank for high-pressure oxygen gas. The ammonia supply unit 22 is configured to supply ammonia from a tank for liquid ammonia at approximately -33°C. The raw material supply line 2 is configured to allow oxygen and ammonia, which are raw materials supplied to the reactor 3, to flow through it. In this embodiment, as will be described later, since the reactor 3 is of the self-thermal decomposition type, the raw materials flowing through the raw material supply line 2 are ammonia and oxygen, but it is not limited to this.

[0012] The raw material supply line 2 is provided with a first confluence point 2A and a second confluence point 2B. At the first confluence point 2A, the recovery line 7 of the ammonia recovery unit 6 is connected. Therefore, at the first confluence point 2A, ammonia from the ammonia supply unit 22 and ammonia from the ammonia recovery unit 6 merge. At the second confluence point 2B, oxygen from the oxygen supply unit 21 and ammonia from the ammonia supply unit 22 merge. Note that the ammonia decomposition system 1 does not necessarily have to be equipped with an ammonia recovery unit 6. For example, if a certain amount of ammonia contamination is acceptable depending on the application of the hydrogen product, and the unreacted ammonia contained in the product gas from the reactor 3 is less than the acceptable amount of ammonia contamination, the ammonia decomposition system 1 does not need to be equipped with an ammonia recovery unit 6. However, especially when a self-thermal decomposition type reactor is used as the reactor 3, the product gas may contain a certain amount of water, and it may be necessary to remove this water. In this case, when the water is removed, highly water-soluble ammonia is also removed and recovered along with the water.

[0013] <Reactor 3> Reactor 3 is configured to decompose ammonia supplied from the raw material supply line 2 and produce a product gas containing hydrogen and nitrogen. In this embodiment, reactor 3 is a self-thermal decomposition type reactor. Reactor 3 is configured to obtain the heat of ammonia decomposition by reacting a portion of the ammonia with oxygen. Reactor 3 is configured to decompose the remaining ammonia using the heat obtained by oxidizing a portion of the ammonia supplied from the raw material supply line 2 and produce a product gas containing hydrogen and nitrogen.

[0014] The catalyst used in reactor 3 is not particularly limited, but for example, transition metal catalysts such as Fe, Co, Ni, and Mo can be used. Transition metal catalysts can be used as alloys, nitrides, carbides, oxides, or composite oxides. The metal catalyst can be supported on a high specific surface area support (e.g., a porous body) such as alumina, silica, zirconia, or titania. In addition to transition metal catalysts, it is also possible to use catalysts made of noble metals such as Ru, Rh, Ir, Pd, and Pt.

[0015] <Discharge Line 4 and Heat Exchange Unit 5> The discharge line 4 is configured to carry a mixed gas containing the product gas discharged from the reactor 3 and unreacted ammonia that was not decomposed in the reactor 3. In this embodiment, the mixed gas flowing through the discharge line 4 is a high-temperature gas at approximately 400 to 700°C.

[0016] The heat exchange unit 5 is configured to transfer heat from the mixed gas in the discharge line 4 to the ammonia in the raw material supply line 2. In the heat exchange unit 5, the ammonia from the ammonia supply unit 22 is preheated before being introduced into the reactor 3. For example, it is preferable that the ammonia is preheated to about 350 to 650°C in the heat exchange unit 5. By preheating the ammonia from the ammonia supply unit 22 in the heat exchange unit 5 before being introduced into the reactor 3, the thermal efficiency of the system improves as the temperature approaches that of the mixed gas flowing through the discharge line 4.

[0017] <Ammonia Recovery Unit 6> The ammonia recovery unit 6 is configured to separate unreacted ammonia from the mixed gas and return it to the raw material supply line 2. In this embodiment, the ammonia recovery unit 6 has a gas-liquid separation tank 61, an absorption tower 62, a distillation tower (also called a decontamination tower) 63, and a recovery line 7. Here, the distillation tower 63 corresponds to the distillation unit of the present invention.

[0018] The gas-liquid separator 61 is configured to separate aqueous ammonia from the product gas in the mixed gas. The aqueous ammonia separated here is produced when unreacted ammonia is absorbed by water in the mixed gas (which functions as an absorbent). For convenience, the aqueous ammonia obtained in the gas-liquid separator 61 is referred to as first aqueous ammonia. The first aqueous ammonia is sent to the distillation column 63 through the first liquid line 60A. In this embodiment, the gas-liquid separator 61 corresponds to the removal unit or first removal unit of the present invention. It is also possible to replace the gas-liquid separator 61 with a column such as an absorption column.

[0019] The absorption tower 62 is configured to further separate ammonia from the product gas separated in the gas-liquid separation tank 61. The absorption tower 62 is configured to absorb unreacted ammonia contained in the product gas into an absorbent liquid (for example, water). For convenience, the ammonia water obtained in the absorption tower 62 is referred to as second ammonia water. The second ammonia water is sent to the distillation tower 63 through the second liquid line 60B. In this embodiment, the absorption tower 62 corresponds to the removal unit or second removal unit of the present invention. The product gas from which ammonia has been removed in the absorption tower 62 is sent to the product line 8 and recovered as appropriate.

[0020] The distillation column 63 is configured to distill and separate ammonia from the first aqueous ammonia and the second aqueous ammonia (absorbent solution containing ammonia). The distillation column 63 is connected to the recovery line 7. The recovery line 7 is configured to return the ammonia separated by distillation in the distillation column 63 to the first confluence point 2A of the raw material supply line 2.

[0021] In this embodiment, the distillation column 63 is a multi-stage distillation column and corresponds to the multi-stage distillation section of the present invention. The distillation column 63 preferably includes, for example, a bottom evaporator using high-pressure steam and a top condenser using cooling water. The distillation column 63 is configured to distillate and separate ammonia from the first ammonia water and the second ammonia water, respectively. The distillation column 63 is also configured to receive the first ammonia water at a higher stage than the second ammonia water. Typically, the ammonia concentration in the first ammonia water is higher than that in the second ammonia water. Therefore, by introducing the first ammonia water and the second ammonia water separately to optimal positions in the distillation column 63, it becomes possible to distillate and separate them more efficiently compared to when the first ammonia water and the second ammonia water are introduced into the distillation column 63 in a mixed state. As a result, it becomes possible to reduce the energy required to operate the distillation column 63.

[0022] With the above configuration, the heat exchange unit 5 effectively preheats the raw ammonia using the heat from the mixed gas in the discharge line 4, thus suppressing the wasteful discharge of heat. Furthermore, since unreacted ammonia is effectively recovered in the ammonia recovery unit 6, it becomes possible to reduce the energy required for operation.

[0023] The configuration of the ammonia recovery unit 6 will be explained in more detail using Figure 2. In this embodiment, as shown in the figure, a heat exchanger 64, a gas-liquid separation tank 65, and a pump 66 are provided in the recovery line 7 extending from the distillation column 63 to the first confluence point 2A. The heat exchanger 64 is configured to recover the cold energy of the liquid ammonia flowing through the raw material supply line 2 and cool the ammonia gas flowing through the recovery line 7. For example, if the temperature of the ammonia gas (approximately 0.5 to 1.0 MPaG) flowing through the recovery line 7 is approximately 40°C, it is cooled to approximately 10°C in the heat exchanger 64. On the other hand, the liquid ammonia flowing through the raw material supply line 2 is heated from -33°C to approximately 20°C. These pressures and temperatures are examples, and the pressures and temperatures of the gas and liquid will vary depending on the operating environment, such as the amount of ammonia recovered. In this example, ammonia detectors 68 are provided in the first liquid line 60A and the second liquid line 60B. The ammonia detectors 68 are configured to detect the ammonia concentration. The amount of unreacted ammonia can be determined by the detection value of the ammonia detector 68. The pressure of the distillation column 63 may be set based on the amount of unreacted ammonia detected by the ammonia detector 68. For example, the amount of unreacted ammonia may fluctuate due to the deterioration of the catalyst in the reactor 3. If the pressure of the distillation column 63 is set according to the detection value of the ammonia detector 68, it is possible to maintain the ammonia pressure in the recovery line 7 within a suitable range even if the amount of unreacted ammonia increases or decreases.

[0024] The gas-liquid separation tank 65 is configured to separate the ammonia in the recovery line 7 into ammonia gas and liquid ammonia. For example, in this case, about 99% becomes liquid ammonia and about 1% becomes ammonia gas. These compositions vary depending on the amount of ammonia recovered and the temperature and pressure conditions of the recovery line 7. The pump 66 pressurizes the liquid ammonia separated in the gas-liquid separation tank 65 and sends it to the first confluence point 2A.

[0025] The liquid ammonia in the raw material supply line 2 is often adjusted to a pressure of about 1 to 10 MPaG. Therefore, the ammonia sent from the recovery line 7 to the first confluence point 2A also needs to be adjusted to a pressure of about 1 to 10 MPaG. As in this embodiment, by liquefying the ammonia gas in the recovery line 7, it becomes possible to increase the pressure using the pump 66 instead of a compressor. As a result, it becomes possible to reduce the power required to increase the pressure of the ammonia in the recovery line 7 by more than 90% compared to when a compressor is used. In addition, the pressure of the liquid ammonia may be adjusted to match the operating pressure of the gas turbine generator that introduces the hydrogen produced after the cracking reaction.

[0026] In this example, approximately 1% of the ammonia gas separated in the gas-liquid separation tank 65 is not returned to the raw material supply line 2, but it is also possible to return the ammonia gas to the raw material supply line 2. In that case, as shown in Figure 3, it is preferable to provide a third confluence point 2C downstream of the heat exchange section 5 of the raw material supply line 2. The gas-liquid separation tank 65 and the third confluence point 2C are connected by a preliminary recovery line 7A. The preliminary recovery line 7A is equipped with a compressor 67 to adjust the pressure of the ammonia gas to match that of the raw material supply line 2. The compressor 67 only needs to have the function of pressurizing the small amount of gas separated in the gas-liquid separation tank 65, so the energy required to operate the compressor 67 is small.

[0027] <First Modified Example of Heat Exchange Unit 5> In the above-described embodiment, an example was described in which heat is directly exchanged between the mixed gas in the discharge line 4 and the ammonia in the raw material supply line 2, but the invention is not limited to this. For example, the heat exchange unit 5 may be configured to recover the heat from the mixed gas in the discharge line 4 into a heat transfer fluid and to transfer the heat from the heat transfer fluid to the ammonia in the raw material supply line 2.

[0028] Specifically, as shown in Figure 4, the heat exchange unit 5 may include a first heat exchanger 51, a second heat exchanger 52, a heat transfer fluid tank 53, and a circulation line 55. The heat transfer fluid tank 53 contains a heat transfer fluid. Examples of heat transfer fluids include, but are not limited to, molten metal, molten salt, heat transfer oil, water (high-temperature steam), etc. The heat transfer fluid sent from the heat transfer fluid tank 53 to the circulation line 55 is heated in the first heat exchanger 51 by receiving heat from the mixed gas in the discharge line 4. Furthermore, the heated heat transfer fluid is heated in the second heat exchanger 52 to the ammonia in the raw material supply line 2, and then stored in the heat transfer fluid tank 53.

[0029] By performing heat exchange via a heat transfer fluid in this manner, heat can be transferred more efficiently compared to direct heat exchange (gas-to-gas heat exchange) between the mixed gas in the discharge line 4 and the ammonia gas in the raw material supply line 2. For example, the heat transfer coefficient increases, allowing for a reduction in the size (heat transfer area) of the heat exchanger. Furthermore, performing heat exchange via a heat transfer fluid makes it possible to control the temperature of the heat exchange section 5. Since high-temperature ammonia can be corrosive to metals, using a heat transfer fluid instead of high-temperature ammonia for heat exchange can prevent corrosion of the heat exchanger.

[0030] <Second Modification of Heat Exchange Unit 5> The heat exchange unit 5 may be configured to include a plurality of heat storage units capable of storing supplied heat, recover the heat of the mixed gas in the discharge line 4 into the plurality of heat storage units, and selectively transfer the heat from the plurality of heat storage units to the ammonia in the raw material supply line 2. Figures 5A and 5B show an example in which the heat exchange unit 5 includes a first heat storage unit 56A and a second heat storage unit 56B, as well as a first flow path switching mechanism 57A and a second flow path switching mechanism 57B. The first heat storage unit 56A and the second heat storage unit 56B are each configured to independently dissipate and store heat. Furthermore, by switching the first flow path switching mechanism 57A and the second flow path switching mechanism 57B, the first heat storage unit 56A and the second heat storage unit 56B can be selectively used for heat storage or heat dissipation. For example, a flow path switching mechanism such as a four-way valve can be used as the first flow path switching mechanism 57A and the second flow path switching mechanism 57B. Figure 5A shows an example in which the heat from the mixed gas in the discharge line 4 is stored in the first heat storage unit 56A and released from the second heat storage unit 56B to the ammonia in the raw material supply line 2. Figure 5B shows an example in which heat is released from the first heat storage unit 56A to the ammonia in the raw material supply line 2 and the heat from the mixed gas in the discharge line 4 is stored in the second heat storage unit 56B. By adopting such a configuration, it becomes possible to stably supply heat to the ammonia in the raw material supply line 2 by appropriately using the heat from the first heat storage unit 56A and the second heat storage unit 56B.

[0031] <First Modified Example of Ammonia Recovery Unit 6> The ammonia recovery unit 6 may be configured to absorb unreacted ammonia from the mixed gas into an absorbent solution, raise the pressure of the absorbent solution containing the absorbed unreacted ammonia to a level higher than the pressure of the raw material supply line 2, separate the unreacted ammonia from the absorbent solution, and return it to the raw material supply line 2. Specifically, as shown in Figure 6, the ammonia recovery unit 6 may be equipped with pumps 67A and 67B for pressurizing the absorbent solution (first ammonia water, second ammonia water) containing the absorbed unreacted ammonia. By pressurizing the ammonia water using pumps 67A and 67B, the pressure necessary to return it to the raw material supply line 2 can be secured with relatively little power. Here, the operation of pumps 67A and 67B is controlled so that the operating pressure of the distillation column 63 is higher than the pressure of the raw material supply line 2.

[0032] In this modified configuration, for example, a gas-liquid separator 69A is provided in the recovery line 7. In the gas-liquid separator 69A, water is separated from the ammonia gas separated in the distillation column 63. The ammonia gas separated in the gas-liquid separator 69A, while maintaining a high pressure, passes through the recovery line 7 and merges with the ammonia gas in the raw material supply line 2 at the third confluence point 2C. As a result, a gas booster and heat exchanger are not required in the recovery line 7, resulting in a simpler equipment configuration. Meanwhile, the water separated in the gas-liquid separator 69A is returned to the distillation column 63 by a pump 69B.

[0033] Figure 6 shows an example where ammonia gas is returned to the raw material supply line 2 via the recovery line 7. However, as shown in Figure 7, the ammonia gas may be liquefied in the recovery line 7 before being returned to the raw material supply line 2. Furthermore, if the cold energy of the liquid ammonia is not used or is in excess in the heat exchanger 64, it can be used as a substitute for cooling water for the top condenser of the distillation column 63 or to cool the absorbent liquid of the absorption column 62. This makes it possible to improve thermal efficiency.

[0034] <Second Modification of Ammonia Recovery Section 6> As shown in Figure 8, instead of the distillation column 63 described above, a first distillation column 63A and a second distillation column 63B may be provided independently of each other. In this case, the first distillation column 63A corresponds to the first distillation section of the present invention, and the second distillation column 63B corresponds to the second distillation section. The first distillation column 63A is configured to distillate and separate ammonia from the first ammonia water separated in the gas-liquid separation tank 61. The second distillation column 63B is configured to distillate and separate ammonia from the second ammonia water separated in the absorption column 62. By adopting such a configuration, it becomes possible to recover ammonia under more efficient operating conditions and distillation column designs compared to when the first ammonia water and the second ammonia water are mixed and distilled together. The ammonia separated and recovered in the first distillation column 63A and the second distillation column 63B can be returned to the raw material supply line 2 after being combined at the confluence point 7B, for example. However, the ammonia separated and recovered in the first distillation column 63A and the second distillation column 63B may be returned to the raw material supply line 2 via separate routes. It is also possible to use the ammonia separated and recovered in the first distillation column 63A and the second distillation column 63B for different purposes, such as returning one of the ammonias to the raw material supply line 2 and using the other as fuel.

[0035] <Ammonia Decomposition System 1A of the Second Embodiment> In the first embodiment, a self-thermal decomposition reactor 3 was used, but as a second embodiment, an example in which an externally heated reactor 3A is used for the ammonia decomposition system 1A will be described. As shown in Figure 9, the ammonia decomposition system 1A comprises a raw material supply line 2, a reactor 3A, a discharge line 4, a heat exchange unit 5, and an ammonia recovery unit 6. When an externally heated reactor 3A is used, the oxygen supply unit 21 described above is not required. The raw material supply line 2 is configured to allow ammonia, which is supplied to the reactor 3A, to flow through it. In the reactor 3A, the ammonia decomposition reaction is promoted using heat obtained from a heating device such as a burner.

[0036] As described above, the present invention can be applied even when using an externally heated reactor 3A. In Figure 9, unreacted ammonia is absorbed by a single absorption tower 62, but the invention is not limited to this. By providing multiple absorption towers 62, the absorption treatment of unreacted ammonia can be performed in multiple stages, as in the first embodiment.

[0037] <Other Embodiments> ・As shown in Figure 10A, a cooling unit 40 may be provided upstream of the heat exchange unit 5 in the discharge line 4 to reduce the temperature of the mixed gas. When water cooling is performed in the cooling unit 40 using water, steam can be obtained. The generated steam can be used in each part of the ammonia decomposition system 1. In addition, by reducing the temperature of the mixed gas before introducing it to the heat exchange unit 5, the corrosiveness (nitriding and hydrogen erosion) of ammonia and hydrogen in the mixed gas can be reduced, making the heat exchange unit 5 less susceptible to corrosion. In particular, by reducing the temperature of the fluid, corrosiveness can be reduced, eliminating the need to construct the heat exchange unit 5 with a material that has high corrosion resistance, thus reducing costs. ・As shown in Figure 10B, high-temperature water discharged from the bottom of the distillation column 63 may be introduced into the absorption column 62. In this case, the liquid introduced into the distillation column 63 may be preheated by performing heat exchange as appropriate on the introduction line. - Whether there is one or more distillation columns 63, the ammonia water produced from the bottom of the distillation column 63 can be supplied to, for example, an absorption column 62 for use. The amount supplied to the absorption column 62 is adjusted according to the amount of ammonia that is allowed to be mixed into the product line 8, and any excess or deficiency is discharged or supplied from the ammonia recovery unit 6. This adjusts the appropriate circulation amount of absorbent liquid within the ammonia recovery unit 6 and minimizes the heat consumption of the evaporator at the bottom of the distillation column 63. - As shown in Figure 10C, ammonia may be preheated as appropriate at multiple points in the raw material supply line 2. - In the above embodiment, oxygen is not preheated, but a configuration may be adopted in which oxygen is preheated using the heat of the mixed gas, a heat transfer medium from which heat has been recovered from the mixed gas, or both. - An example of absorbing unreacted ammonia with water has been described, but the absorbent liquid for absorbing unreacted ammonia may be something other than water.

[0038] 1: Ammonia decomposition system, 1A: Ammonia decomposition system, 2: Raw material supply line, 2A: First confluence point, 2B: Second confluence point, 2C: Third confluence point, 3: Reactor, 3A: Reactor, 4: Discharge line, 5: Heat exchange section, 6: Ammonia recovery section, 7: Recovery line, 7A: Preliminary recovery line, 7B: Confluence point, 8: Product line, 21: Oxygen supply section, 22: Ammonia supply section, 40: Cooling section, 51: First heat exchanger, 52: Second heat exchanger, 53: Heat transfer medium tank, 55: Circulation line, 56A: First heat storage section, 56B: Second heat storage section, 57A: First flow path switching mechanism, 57B: Second flow path switching mechanism, 60A: First liquid line, 60B: Second liquid line, 61: Gas-liquid separator, 62: Absorption tower, 63: Distillation tower, 63A: First distillation tower, 63B: Second distillation tower, 64: Heat exchanger, 65: Gas-liquid separator, 66: Pump, 67: Compressor, 67A: Pump, 67B: Pump, 68: Ammonia detector, 69A: Gas-liquid separator, 69B: Pump

Claims

1. An ammonia decomposition system comprising a raw material supply line, a reactor, a discharge line, and a heat exchange unit, wherein the raw material supply line is configured to carry ammonia as a raw material supplied to the reactor, the reactor is configured to decompose the ammonia supplied from the raw material supply line to produce a product gas containing hydrogen and nitrogen, the discharge line is configured to carry a mixed gas containing the product gas discharged from the reactor and unreacted ammonia that was not decomposed in the reactor, and the heat exchange unit is configured to transfer the heat from the mixed gas in the discharge line to the ammonia in the raw material supply line.

2. An ammonia decomposition system according to claim 1, wherein the heat exchange unit is configured to recover the heat of the mixed gas in the discharge line into a heat transfer fluid and to transfer the heat of the heat transfer fluid to the ammonia in the raw material supply line.

3. An ammonia decomposition system according to claim 1, wherein the heat exchange unit comprises a plurality of heat storage units capable of storing supplied heat, is configured to recover the heat of the mixed gas in the discharge line into the plurality of heat storage units, and selectively transfer the heat from the plurality of heat storage units to the ammonia in the raw material supply line, and each of the plurality of heat storage units is configured to independently dissipate and store heat.

4. An ammonia decomposition system according to claim 1, wherein the reactor is a self-thermal decomposition reactor, the raw material supply line is configured to carry ammonia and oxygen as raw materials supplied to the self-thermal decomposition reactor, and the self-thermal decomposition reactor is configured to decompose the remainder of the ammonia using heat obtained by oxidizing a portion of the ammonia supplied from the raw material supply line to produce a product gas containing hydrogen and nitrogen.

5. An ammonia decomposition system according to any one of claims 1 to 4, further comprising an ammonia recovery unit, wherein the ammonia recovery unit is configured to separate the unreacted ammonia from the mixed gas.

6. An ammonia decomposition system according to claim 5, wherein the ammonia recovery unit is configured to separate the unreacted ammonia from the mixed gas, liquefy the separated ammonia, and then return it to the raw material supply line.

7. An ammonia decomposition system according to claim 5, wherein the ammonia recovery unit is configured to separate the unreacted ammonia from the mixed gas by absorbing it into an absorbent liquid, to raise the pressure of the absorbent liquid in which the unreacted ammonia has been absorbed to a level higher than the pressure of the raw material supply line, and to separate the unreacted ammonia from the absorbent liquid and return it to the raw material supply line.

8. An ammonia decomposition system according to claim 5, wherein the ammonia recovery unit comprises a removal unit, a distillation unit, and a recovery line, wherein the removal unit is configured to absorb the unreacted ammonia from the mixed gas into an absorbent liquid, the distillation unit is configured to distill and separate ammonia from the absorbent liquid, the recovery line is configured to return the ammonia separated in the distillation unit to the raw material supply line, and the pressure of the distillation unit is set based on the amount of unreacted ammonia.

9. An ammonia decomposition system according to claim 5, wherein the ammonia recovery unit comprises a first removal unit and a second removal unit, the first removal unit is configured to remove the unreacted ammonia from the mixed gas as first ammonia water in which the unreacted ammonia has been absorbed by contacting the unreacted ammonia in the mixed gas with water, and the second removal unit is configured to remove the unreacted ammonia from the mixed gas as second ammonia water in which the unreacted ammonia has been absorbed by contacting the unreacted ammonia in the mixed gas after it has passed through the first removal unit with water.

10. An ammonia decomposition system according to claim 9, wherein the ammonia recovery unit comprises a first distillation unit and a second distillation unit, the first distillation unit is configured to distillate and separate ammonia from the first ammonia water, and the second distillation unit is configured to distillate and separate ammonia from the second ammonia water.

11. An ammonia decomposition system according to claim 9, wherein the ammonia recovery unit comprises a multi-stage distillation unit, the multi-stage distillation unit is configured to distill and separate ammonia from the first ammonia water and the second ammonia water, and is configured to receive the first ammonia water at a stage higher than the second ammonia water.

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