Hydrogen production methods

Abstract

A hydrogen production method for producing hydrogen by decomposing ammonia in multiple stages, comprising: a first preheating step for preheating an ammonia raw material; a first decomposition step for decomposing the ammonia raw material preheated in the first preheating step in a first temperature range; a second preheating step for preheating the ammonia raw material that has been partially decomposed in the first decomposition step again; and a second decomposition step for decomposing the ammonia raw material preheated in the second preheating step in a second temperature range that is higher than the first temperature range, wherein the nitriding temperature is determined as the temperature at which the piping material undergoes nitriding based on the material of the piping through which the pipe passes from the outlet of the first preheating step to the inlet of the first decomposition step, the temperature of the ammonia raw material in the piping, and the ammonia concentration in the piping, and the first temperature range is a temperature range lower than the nitriding temperature.

Description

Technical Field

[0007] ,

[0001] The present invention relates to a hydrogen production method.

Background Art

[0002] As a technology for converting renewable energy into an energy carrier, a technology for producing hydrogen (H2) by electrolyzing water using electric power generated by renewable energy has been proposed. However, hydrogen has a low boiling point and is not easily liquefied, and there are problems in transportation, storage, etc. Ammonia (NH3) has been proposed as an energy carrier because it contains many hydrogen atoms (H) in its molecule. For example, Patent Document 1 describes a method for producing hydrogen by decomposing ammonia in the presence of a catalyst.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Patent Document 1 describes that in a reaction tube for cracking ammonia gas, when the upstream catalyst layer is more active than the downstream catalyst layer, nitridation of the metal tube is suppressed.

[0005] An object of the present invention is to provide a hydrogen production method capable of suppressing nitridation of piping when ammonia is decomposed in multiple stages to produce hydrogen.

Means for Solving the Problems

[0006] As a result of intensive studies to solve the above problems, the present inventors have completed the present invention with the following configuration.

[0007] ​[1] A hydrogen production method for producing hydrogen by decomposing ammonia in multiple stages, comprising: a first preheating step for preheating an ammonia raw material; a first decomposition step for decomposing the ammonia raw material preheated in the first preheating step in a first temperature range; a second preheating step for preheating the ammonia raw material that has been partially decomposed in the first decomposition step again; and a second decomposition step for decomposing the ammonia raw material preheated in the second preheating step in a second temperature range at a temperature higher than the first temperature range, wherein when the nitriding temperature is determined as the temperature at which the piping material undergoes nitriding based on the material of the piping through which the pipe passes from the outlet of the first preheating step to the inlet of the first decomposition step, the temperature of the ammonia raw material in the piping, and the ammonia concentration in the piping, the first temperature range is a temperature range lower than the nitriding temperature. [2] The hydrogen production method according to [1], characterized in that the temperature of the ammonia raw material at the inlet of the first decomposition step is 400°C or lower. [3] The hydrogen production method according to [1] or [2], characterized in that a ruthenium-containing catalyst is used in the first decomposition step. [4] A hydrogen production method according to any one of the items [1] to [3], characterized in that when the nitride concentration is determined as the ammonia concentration nitrided by the material of the piping and equipment, based on the material of the piping and equipment from the outlet of the first decomposition step to the inlet of the second decomposition step, the temperature of the ammonia raw material in the piping or equipment, and the ammonia concentration in the piping and equipment, the first decomposition step decomposes the ammonia raw material to an ammonia concentration lower than the nitride concentration.

[0008] [5] The hydrogen production method according to any one of [1] to [4], characterized in that the first decomposition step is carried out by an isothermal reaction. [6] The hydrogen production method according to [5], characterized in that a decomposition furnace is used in the second decomposition step, and the heat source for the first decomposition step carried out in the isothermal reaction is the waste heat of the decomposition furnace. [7] The hydrogen production method according to [5] or [6], characterized in that the temperature of the first decomposition step carried out in the isothermal reaction is 400°C or lower. [8] A method for producing hydrogen according to any one of [5] to [7], characterized in that the temperature of the first decomposition step carried out in the isothermal reaction is 350°C or higher.

[0009] [9] The hydrogen production method according to [1], characterized in that the first decomposition step is carried out in multiple stages, with a reheater installed between each stage, and the ammonia raw material is heated in the reheater.

[10] The hydrogen production method according to [9], characterized in that in the first decomposition step of the multiple stages, the temperature of the ammonia raw material at the inlet of a later stage is higher than the temperature of the ammonia raw material at the inlet of an earlier stage.

[11] The hydrogen production method according to [9] or

[10] , characterized in that in the multiple stages of the first decomposition step, the first stage is an isothermal reaction and the other stages are adiabatic reactions.

[12] The hydrogen production method according to [9] or

[10] , characterized in that all of the steps in the multi-stage first decomposition step are adiabatic reactions.

[0010]

[13] The hydrogen production method according to any one of [1] to

[12] , characterized in that the first decomposition step is characterized in that the ammonia decomposition rate in the reactor that first decomposes the undecomposed ammonia raw material is 15 mol% or less.

[14] A method for producing hydrogen according to any one of [1] to

[13] , characterized in that the second decomposition step is decomposition by external heating.

[15] A hydrogen production method according to any one of [1] to

[14] , characterized in that it has a third decomposition step downstream of the second decomposition step. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a hydrogen production method that can suppress nitriding of piping when producing hydrogen by decomposing ammonia in multiple stages. [Brief explanation of the drawing]

[0012] [Figure 1]This is an explanatory diagram illustrating the hydrogen production method of the first embodiment. [Figure 2] This is an explanatory diagram illustrating a comparative form of hydrogen production method. [Figure 3] This is an explanatory diagram illustrating a hydrogen production method according to a second embodiment. [Modes for carrying out the invention]

[0013] The following describes embodiments for carrying out the present invention.

[0014] First, the hydrogen production method of the first embodiment will be described with reference to Figure 1. This hydrogen production method produces hydrogen by decomposing ammonia in multiple stages. The ammonia decomposition system 50 shown in Figure 1 is a system that decomposes ammonia in multiple stages. In the ammonia decomposition reaction, ammonia generally decomposes into nitrogen and hydrogen, as in 2NH3 → N2 + 3H2.

[0015] The ammonia decomposition method used in hydrogen production includes a first preheating step S1 for preheating the ammonia raw material, a first decomposition step S2 for decomposing the ammonia raw material preheated in the first preheating step S1 in a first temperature range, a second preheating step S3 for preheating the ammonia raw material that has been partially decomposed in the first decomposition step S2 again, and a second decomposition step S4 for decomposing the ammonia raw material preheated in the second preheating step S3 in a second temperature range that is higher than the first temperature range.

[0016] The first and second temperature ranges may each be temperature ranges with a wide temperature range. Depending on the difference in location where each decomposition process (first decomposition process S2 or second decomposition process S4) is performed, the temperature gradient, temporal fluctuations, changes in operating conditions, etc., the width of the temperature range may be expanded or narrowed.

[0017] When the temperature in the second temperature range is higher than that in the first temperature range, it is preferable to compare at least the representative values of each temperature range and ensure that the representative value of the second temperature range is higher than that of the first temperature range. The representative value can be at least one selected from the inlet temperature, outlet temperature, maximum temperature, minimum temperature, average temperature, etc. Also, if there is no overlap between the temperature ranges of the first temperature range and the second temperature range, the minimum value of the second temperature range may be higher than the maximum value of the first temperature range.

[0018] In the case of the ammonia decomposition system 50 in the illustrated example, the first preheating step S1 is performed using a vaporizer 12 that vaporizes liquefied ammonia and heat exchangers 14 and 16 that preheat the ammonia gas vaporized in the vaporizer 12 by heat exchange with a heat medium. The first decomposition step S2 is performed using a pre-decomposer 20. The second preheating step S3 is performed using a preheater 22. The second decomposition step S4 is performed using a decomposition furnace 24.

[0019] Liquefied ammonia is supplied to the vaporizer 12 via a supply line 11. Ammonia gas is transported between the vaporizer 12 and the heat exchanger 14 via a pipe 13. Ammonia gas is transported between the heat exchangers 14 and 16 via a pipe 15. Ammonia gas is transported between the heat exchanger 16 and the pre-decomposer 20 via a pipe 17. Ammonia raw material is transported between the pre-decomposer 20 and the preheater 22 via a pipe 21. Ammonia raw material is transported between the preheater 22 and the decomposition furnace 24 via a pipe 23.

[0020] The decomposition gas generated by decomposing the ammonia raw material in the decomposition furnace 24 is recovered from the ammonia decomposition system 50 via a recovery line 25 and led to a subsequent processing system (not shown).

[0021] When implementing the hydrogen production method, a decomposition gas treatment unit (not shown) is provided at the end of the recovery line 25. In the decomposition gas treatment unit, nitrogen, unreacted ammonia, moisture, etc. can be separated by adsorption, distillation, cooling, etc. to produce hydrogen as a product. The unreacted ammonia in the decomposition gas can be used as fuel, etc. as off-gas, etc.

[0022] In the decomposition furnace 24, ammonia is decomposed using a combustor such as a burner. In the combustor, a fuel gas and an oxidizer are introduced, and the fuel gas is burned. The fuel gas is not particularly limited, but examples include gases containing ammonia, methane, hydrogen, etc. Examples of oxidizers include oxygen or air, or gases containing oxygen. The combustion of the fuel gas generates high-temperature exhaust gas in the decomposition furnace 24. An ammonia decomposition catalyst may be used in the decomposition furnace 24 as needed.

[0023] The type of decomposition furnace 24 is not particularly limited, but examples include external heating type and auto-thermal type (ATR type). The decomposition furnace 24 in the illustrated example is an external heating type in which the reaction tube section through which the ammonia raw material flows and the heating furnace section into which the fuel gas and combustion air are introduced are provided separately. Although not specifically shown, in the case of the ATR type, a portion of the ammonia raw material is used as fuel gas.

[0024] The waste heat from the decomposition furnace 24, such as the exhaust gas from the combustor, can be used as a heat source in the ammonia decomposition system 50. For example, the preheater 22 may use the waste heat from the decomposition furnace 24 as its heat source.

[0025] Figure 2 illustrates an ammonia decomposition system 60 used in a comparative hydrogen production method. In this ammonia decomposition system 60, a preheater 18 is also provided before the pre-decomposition unit 20. For example, the temperature of the preheaters 18 and 22 rises to about 400-700°C or 450-600°C. When the temperature of the pre-decomposition unit 20 rises to about 350-550°C, the temperatures of the pipes 17, 19, 21, and 23 provided before and after the preheaters 18 and 22 also rise, causing nitridation of the pipe material, which raises concerns about reduced durability and shortened lifespan.

[0026] Therefore, in the ammonia decomposition system 50 of this embodiment, a preheater 18 is not provided before the pre-decomposer 20. As the heat source for the first preheating step S1, a heat source with a temperature range lower than the waste heat from the decomposition furnace 24 may be used.

[0027] In the hydrogen production method of this embodiment, the nitriding temperature is determined by the material of the piping 17 through which the material passes from the outlet of the first preheating step S1 to the inlet of the first decomposition step S2, the temperature of the ammonia raw material in the piping 17, and the ammonia concentration in the piping 17. Examples of nitriding temperatures include temperatures of 400°C or lower, and even temperatures of 350°C or lower.

[0028] Furthermore, the first temperature range in the first decomposition process S2 is a temperature range lower than the nitriding temperature. This suppresses nitriding in piping, equipment, etc., from the outlet of the first preheating process S1 to the inlet of the first decomposition process S2. Examples of the first temperature range include a temperature range of 400°C or lower, and even a temperature range of 350°C or lower.

[0029] The temperature of the ammonia raw material at the inlet of the first decomposition step S2 is preferably 400°C or lower. The catalyst used in the first decomposition step S2 is a catalyst that is active in the ammonia decomposition reaction in the first temperature range described above. The specific catalyst is not particularly limited, but for example, a ruthenium (Ru)-containing catalyst can be used as a catalyst that is highly active at low temperatures.

[0030] The preheating method in the first preheating step S1 is not particularly limited, but it is preferable to gradually increase the temperature of the ammonia raw material in a temperature range below the first temperature range described above. Since the temperature range below the first temperature range is lower than the nitriding temperature, nitriding in the piping, equipment, etc. in the first preheating step S1 is suppressed.

[0031] For example, the temperature may be raised to about 80°C in the vaporizer 12, about 100°C in the heat exchanger 14, and to about the same temperature as the inlet of the first decomposition step S2 in the heat exchanger 16. In the heat exchanger 16, the ammonia raw material may be preheated using a heat source with a temperature of about 200 to 350°C.

[0032] In the hydrogen production method of this embodiment, the nitriding concentration is determined as the ammonia concentration at which the materials of the piping and equipment undergo nitriding, based on the materials of the piping 21, 23 and equipment such as the preheater 22 from the outlet of the first decomposition step S2 to the inlet of the second decomposition step S4, and the temperature and ammonia concentration of the ammonia raw material in these piping and equipment.

[0033] The ammonia concentration used to determine the nitriding concentration may be either the proportion (mole fraction) of ammonia in the ammonia raw material, or the pressure (partial pressure) of ammonia in the ammonia raw material. When each component in the ammonia raw material is denoted by the subscript i, the mole fraction of each component is Xi, the partial pressure of each component is Pi, and the total pressure of the ammonia raw material is P, then generally Pi = XiP holds true.

[0034] In the first decomposition step S2, it is preferable to decompose the ammonia raw material to an ammonia concentration lower than the nitriding concentration. This makes it possible to suppress nitriding of materials in the piping 21, 23 and equipment such as the preheater 22 from the outlet of the first decomposition step S2 to the inlet of the second decomposition step S4.

[0035] When referring to an ammonia concentration lower than the nitriding concentration, the ammonia concentration can be expressed as either the mole fraction or the partial pressure of ammonia, as mentioned above. An example of a nitriding concentration expressed as mole fraction is 50 mol% or less. When considering the effect of total pressure, the partial pressure of ammonia may be used as the reference.

[0036] Among the ammonia decomposition systems 50, materials such as alloys are used for piping, equipment, etc.

[0037] The thermal decomposition method for ammonia in the first decomposition step S2 includes isothermal reactions, adiabatic reactions, or methods that combine these.

[0038] When an isothermal reaction is used in the first decomposition step S2, heat must be supplied from outside the reactor because the decomposition of ammonia is an endothermic reaction. For example, waste heat from the decomposition furnace 24 may be used as the heat source for the pre-decomposition unit 20. The temperature of the first decomposition step, which is carried out by an isothermal reaction, is preferably 400°C or lower, and more preferably 350°C or higher.

[0039] When an adiabatic reaction is used in the first decomposition step S2, heat must be supplied from outside the reactor because the decomposition of ammonia is an endothermic reaction. If the first decomposition step S2 is a single stage, or in the first stage of a multi-stage first decomposition step S2, the thermal energy contained in the ammonia raw material preheated in the first preheating step S1 is used for the decomposition reaction.

[0040] When the first decomposition step S2 is performed in multiple stages, a reheater may be installed between each stage, and the ammonia raw material may be heated in the reheater. This suppresses the temperature drop of the ammonia raw material even when an adiabatic reaction is adopted in the second or subsequent stages. Furthermore, when the first decomposition step S2 is performed in multiple stages, it is also possible to perform an isothermal reaction in at least one stage, or in all stages.

[0041] An example of a reactor in each stage is a pre-decomposition unit 20. An example of a reheater is a preheater 22. When an adiabatic reaction is used in the first decomposition step S2, the waste heat from the decomposition furnace 24 may be used as the heat source for the reheater. For example, a combination of a pre-decomposition unit 20 and a preheater 22 placed downstream of the pre-decomposition unit 20 may be repeated in series two or more times to form a configuration such as pre-decomposition unit 20 / preheater 22 / pre-decomposition unit 20 / preheater 22 / decomposition furnace 24. Here, the symbol / represents piping between the equipment. In this example, the pre-decomposition unit 20 is an example of equipment that performs the first decomposition step S2, and the decomposition furnace 24 is an example of equipment that performs the second decomposition step S4.

[0042] In the multi-stage first decomposition step S2, it is preferable that the temperature of the ammonia raw material at the inlet of a later stage is higher than the temperature of the ammonia raw material at the inlet of an earlier stage. Since the ammonia concentration decreases in later stages, nitriding can be suppressed even if the temperature is higher than in earlier stages.

[0043] In the multi-stage first decomposition step S2, the first stage may be an isothermal reaction, while the other stages may be adiabatic reactions. In this case, even if the preheating temperature of the ammonia raw material by the first preheating step S1 is relatively low in the first stage, the ammonia decomposition reaction can proceed in the pre-decomposer 20 while receiving thermal energy from the outside. This makes it possible to suppress nitriding of piping, equipment, etc. in the first stage of the first preheating step S1 or the first decomposition step S2.

[0044] Furthermore, in the multi-stage first decomposition step S2, all stages may be adiabatic reactions. Similar to how the ammonia raw material is heated in the reheater from the second stage onward, the ammonia raw material is heated in the first preheating step S1 in the first stage, so that the ammonia decomposition reaction can proceed while suppressing nitridation of piping, equipment, etc. In the case of an adiabatic reaction, the apparatus can generally be simplified and costs can be reduced compared to an isothermal reaction.

[0045] In the first decomposition step S2, it is preferable that the ammonia decomposition rate in the reactor that first decomposes the undecomposed ammonia raw material is 15 mol% or less. An example of a reactor is a pre-decomposition reactor 20. If the first decomposition step S2 has multiple stages, the ammonia decomposition rate in the first stage may be 15 mol% or less. If the first decomposition step S2 does not have multiple stages, the ammonia decomposition rate in the entire first decomposition step S2 may be 15 mol% or less.

[0046] Next, with reference to Figure 3, the hydrogen production method of the second embodiment will be described. This hydrogen production method is the same as the second embodiment except that it has a third decomposition step S5 downstream of the second decomposition step S4. In the first preheating step S1, the first decomposition step S2, and the second preheating step S3, nitriding in piping, equipment, etc. is suppressed, as in the first embodiment described above.

[0047] In the second embodiment, specifically, a decomposer 27 is provided downstream of the decomposition furnace 24 via piping 26, and a recovery line 25 is provided downstream of the decompositioner 27. The recovery line 25 in the second embodiment is connected to a decomposition gas processing unit (not shown) for producing hydrogen, similar to the recovery line 25 in the first embodiment.

[0048] The thermal decomposition method for ammonia in the third decomposition step S5 may be an isothermal reaction, an adiabatic reaction, or a combination of both. The decomposer 27 that performs the third decomposition step S5 may be a device that uses a catalyst to thermally decompose ammonia. The decomposer 27 that performs the third decomposition step S5 may be the same type as the pre-decomposer 20 that performs the first decomposition step S2.

[0049] By performing the third decomposition step S5, the load on the second decomposition step S4 can be reduced. Furthermore, even if the temperature of the first preheating step S1 or the first decomposition step S2 is lowered to suppress nitriding of piping, equipment, etc. in the first preheating step S1 or the first decomposition step S2, the ammonia decomposition process can be more easily constructed by distributing a portion of the load of the second decomposition step S4 to the third decomposition step S5. In addition, by lowering the temperature of the waste heat and decomposition gas from the second decomposition step S4, it is possible to easily improve efficiency through heat recovery.

[0050] Although not specifically shown in the diagram, when the third decomposition step S5 is performed, a heat exchanger may be provided between the decomposition furnace 24 and the decomposition unit 27 to adjust the temperature of the decomposition gas discharged from the decomposition furnace 24. If the temperature of the decomposition gas is higher than the temperature required for the ammonia decomposition reaction in the decomposition unit 27, a portion of the thermal energy of the decomposition gas may be recovered as a heat source, power source, etc. Even when the third decomposition step S5 is not performed, a heat exchanger or the like may be provided downstream of the decomposition furnace 24 to recover a portion of the thermal energy of the decomposition gas as a heat source, power source, etc. [Industrial applicability]

[0051] This invention can be used in a method for producing hydrogen using an ammonia decomposition system. [Explanation of Symbols]

[0052] S1...First preheating process, S2...First decomposition process, S3...Second preheating process, S4...Second decomposition process, 11...Supply line, 13,15,17,19,21,23,26...Piping, 12...Vaporizer, 14,16...Heat exchanger, 18,22...Preheater, 20...Pre-decomposition unit, 24...Decomposition furnace, 25...Recovery line, 27...Decomposition unit, 50,51,60...Ammonia decomposition system.

Claims

1. A hydrogen production method that produces hydrogen by decomposing ammonia in multiple stages, The first preheating step involves preheating the ammonia raw material, A first decomposition step in which the ammonia raw material preheated in the first preheating step is decomposed in a first temperature range, A second preheating step is performed to preheat the ammonia raw material, which has been partially decomposed in the first decomposition step, The process includes a second decomposition step in which the ammonia raw material preheated in the second preheating step is decomposed in a second temperature range where the temperature is higher than the first temperature range. A hydrogen production method characterized in that, when the nitriding temperature is determined as the temperature at which the piping material undergoes nitriding based on the material of the piping through which the material passes from the outlet of the first preheating step to the inlet of the first decomposition step, the temperature of the ammonia raw material in the piping, and the ammonia concentration in the piping, the first temperature range is set to a temperature range lower than the nitriding temperature, and the temperature of the ammonia raw material at the inlet of the first decomposition step is set to 400°C or lower, thereby suppressing the nitriding of the piping.

2. The hydrogen production method according to claim 1, characterized in that a ruthenium-containing catalyst is used in the first decomposition step.

3. The hydrogen production method according to claim 1, wherein when the nitride concentration is determined as the ammonia concentration nitrided by the material of the piping and equipment from the outlet of the first decomposition step to the inlet of the second decomposition step, the temperature of the ammonia raw material in the piping or equipment, and the ammonia concentration in the piping and equipment, the first decomposition step decomposes the ammonia raw material to an ammonia concentration lower than the nitride concentration.

4. The hydrogen production method according to claim 1, characterized in that the first decomposition step is carried out by an isothermal reaction.

5. The hydrogen production method according to claim 4, characterized in that a decomposition furnace is used in the second decomposition step, and the heat source for the first decomposition step, which is carried out in the isothermal reaction, is the waste heat of the decomposition furnace.

6. The hydrogen production method according to claim 4, characterized in that the temperature of the first decomposition step carried out in the isothermal reaction is 400°C or lower.

7. The hydrogen production method according to claim 4, characterized in that the temperature of the first decomposition step carried out in the isothermal reaction is 350°C or higher.

8. The hydrogen production method according to claim 1, characterized in that the first decomposition step is carried out in multiple stages, with a reheater installed between each stage, and the ammonia raw material is heated in the reheater.

9. The hydrogen production method according to claim 8, characterized in that, in the first decomposition step of the multiple stages, the temperature of the ammonia raw material at the inlet of a later stage is higher than the temperature of the ammonia raw material at the inlet of an earlier stage.

10. The hydrogen production method according to claim 8, characterized in that in the multiple stages of the first decomposition step, the first stage is an isothermal reaction and the other stages are adiabatic reactions.

11. The hydrogen production method according to claim 8, characterized in that all of the steps in the multiple-stage first decomposition step are adiabatic reactions.

12. The hydrogen production method according to claim 1, characterized in that the first decomposition step is characterized in that the ammonia decomposition rate in the reactor that first decomposes the undecomposed ammonia raw material is 15 mol% or less.

13. The hydrogen production method according to claim 1, characterized in that the second decomposition step is decomposition by external heating.

14. The hydrogen production method according to claim 1, characterized in that it has a third decomposition step downstream of the second decomposition step.

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