Combustion-type ammonia decomposition apparatus and combustion-type ammonia decomposition method

Abstract

To provide a combustion type ammonia decomposition device and a combustion type ammonia decomposition method capable of efficiently producing N2 by supplying NH3 and an oxidizing agent to a combustor to decompose the same into H2 and H2 and refining the same.SOLUTION: This apparatus is provided with a combustor 11 to which ammonia and an oxidizing agent are supplied, a combustion furnace 10 in which the combustor 11 is installed, and a catalyst tank 20 connected to the combustion furnace 10, ammonia decomposition gas is generated in the combustor 11 by using the ammonia and the oxidizing agent, residual ammonia contained in the ammonia decomposition gas introduced into the catalyst tank 20 from the combustion furnace 10 is decomposed in the catalyst tank 20, and the catalyst tank 20 is composed of at least two kinds of catalysts 21 and 22.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a combustion-type ammonia decomposition apparatus and a combustion-type ammonia decomposition method. [Background technology]

[0002] The reaction of decomposing ammonia (NH3) gas into hydrogen (H2) and nitrogen (N2) is promoted under high temperature and low pressure conditions in a chemical equilibrium state. At normal pressure, the decomposition reaction can be easily carried out using a catalytic reaction at 400°C or higher. Known catalysts for NH3 decomposition include metals with NH3 decomposition activity, such as iron (Fe), cobalt (Co), nickel (Ni), and ruthenium (Ru). These catalysts are supported on inorganic supports such as alumina (Al2O3) and zeolite. In industrial applications, Fe catalysts and Ni catalysts, which are relatively inexpensive, are widely used.

[0003] A commonly used method for continuously decomposing NH3 is to externally heat a catalytic reaction tube (cracking tube) packed with a catalyst to thermally compensate for the endothermic reaction accompanying NH3 decomposition. Meanwhile, autothermal reforming (ATR) is also used as an NH3 decomposition technology, in which heat generated by burning part of the raw NH3 (oxidation reaction) is directly utilized to decompose the remaining raw NH3 (non-oxidation reaction) (see, for example, Patent Documents 1 to 4). One combustion method involves using an oxidation catalyst to combust a mixed gas of NH3 and an oxidant on the catalyst surface. While this method has not yet been commercially used, it is being actively developed. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-214225 [Patent Document 2] Patent No. 5483705 [Patent Document 3] Japanese Patent Application Publication No. 2023-76221 [Patent Document 4] Japanese Patent Publication No. 2023-83706 Summary of the Invention [Problem to be solved by the invention]

[0005] H2 gas is attracting attention as a new energy source in the quest to realize a carbon-neutral society. When transporting gas to remote locations, it is generally transported as liquefied or compressed gas. Compressed gas is not suitable for mass transportation, and liquefied H2 gas has a low boiling point, which poses challenges, requiring a great deal of energy to liquefy. NH3 has physical properties similar to propane and a high boiling point, making it easier to transport than H2. In fact, a supply chain has already been established for NH3 as a fertilizer raw material. NH3 is also attracting attention as an H2 carrier, and by decomposing NH3 transported to consumption areas to extract H2, it is expected to be used in a variety of energy sources and as a raw material.

[0006] The present invention has been made in view of the above circumstances, and aims to provide a combustion-type ammonia decomposition apparatus and a combustion-type ammonia decomposition method that are capable of supplying NH3 and an oxidant to a combustor, decomposing them into H2 and N2, and refining them to efficiently produce H2. [Means for solving the problem]

[0007] In order to achieve the above object, the present invention provides the following means. [1] A combustion-type ammonia decomposition apparatus comprising: a combustor to which ammonia and an oxidant are supplied; a combustion furnace in which the combustor is installed; and a catalytic tank connected to the combustion furnace; wherein the combustion furnace generates an ammonia decomposition gas using ammonia and the oxidant; and the catalytic tank decomposes residual ammonia contained in the ammonia decomposition gas introduced from the combustion furnace into the catalytic tank; and the catalytic tank is composed of at least two types of catalysts. [2] The combustion-type ammonia decomposition apparatus according to [1], wherein the oxidant supplied to the combustor has an oxygen concentration of 25 vol% to 100 vol%. [3] The combustion type ammonia decomposition apparatus according to [1] or [2], characterized in that the combustion type ammonia decomposition apparatus is provided with a gas purification device at an outlet of the catalyst tank, and the gas purification device separates nitrogen and hydrogen from the ammonia decomposition gas discharged from the catalyst tank and purifies the gas. [4] A combustion-type ammonia decomposition method using a combustor to which ammonia and an oxidant are supplied, a combustion furnace in which the combustor is installed, and a catalytic tank connected to the combustion furnace, wherein the combustion furnace generates an ammonia decomposition gas using ammonia and the oxidant, and the catalytic tank decomposes residual ammonia contained in the ammonia decomposition gas introduced from the combustion furnace into the catalytic tank, and the catalytic tank is composed of at least two types of catalysts. [5] The combustion-type ammonia decomposition method according to [4], wherein the oxidant supplied to the combustor has an oxygen concentration of 25 vol% to 100 vol%. [6] The combustion type ammonia decomposition method according to [4] or [5], characterized in that a gas purification device is used at the outlet of the catalyst tank, and the gas purification device separates nitrogen and hydrogen from the ammonia decomposition gas discharged from the catalyst tank and purifies the gas. [Effects of the Invention]

[0008] According to the present invention, NH3 and an oxidizer are supplied to a combustor, where they are decomposed into H2 and N2, and then purified to produce H2 efficiently. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a configuration diagram showing an example of a combustion-type ammonia decomposition device. [Figure 2] 1 is a graph showing an example of the relationship between O2 concentration and flame temperature. [Figure 3]1 is a graph showing an example of the relationship between O2 concentration and H2 concentration. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention will be described below based on preferred embodiments.

[0011] The combustion-type ammonia decomposition apparatus 100 shown in FIG. 1 includes a combustor 11 to which NH3 and an oxidizing agent are supplied, a combustion furnace 10 in which the combustor 11 is installed, and a catalyst tank 20 connected to the combustion furnace 10.

[0012] In the combustion furnace 10, NH3 decomposition gas is generated using NH3 and an oxidizer in the combustor 11. In the combustor 11, NH3 is mixed with the oxidizer as fuel to form an NH3 flame 12. This flame 12 can generate high temperatures in the internal space 13 of the combustion furnace 10 in which the combustor 11 is installed.

[0013] Equation (1) shows an example of the reaction formula when NH3 is burned. As shown in equation (2), by supplying less oxidant to the combustor 11 than the amount required for NH3 combustion, NH3 decomposition gas can be generated in the combustion furnace 10. The coefficients β, γ, δ, and ε in equation (2) are determined appropriately depending on the coefficient α and other processing conditions.

[0014] NH3 + 0.75O2 → 1.5H2O + 0.5N2(1) NH3+αO2→βH2O+γH2+δN2+εNH3(2)

[0015] The NH3 decomposition gas contains H2 and N2 produced by the decomposition of NH3, H2O produced by combustion, and unreacted NH3. This mixed gas is supplied to a catalyst tank 20 connected to a combustion furnace 10.

[0016] The combustor 11 is not particularly limited, but may be a burner or the like. The combustor 11 may be provided with separate paths for supplying NH3 and oxidizer. NH3 and the oxidizer may be mixed before the mixed gas starts to burn in the combustor 11. The combustor 11 may combust NH3 on the surface of a combustion catalyst, as in the well-known ATR technology. NH3 may also be combusted while injecting NH3 and an oxidizer from a nozzle without using a combustion catalyst.

[0017] The combustion of NH3 in the combustor 11 may use only NH3 as fuel without using other fuels such as hydrocarbon fuels (oil, natural gas, etc.) or carbonaceous fuels (coal, charcoal, etc.). Also, a portion of H2 that can be produced by decomposition of NH3 may be combusted in the combustor 11 or the combustion furnace 10.

[0018] The combustion furnace 10 forms a combustion chamber for burning NH3. The internal space 13 of the combustion furnace 10 temporarily accommodates NH3 decomposition gas produced by the combustion of NH3. The flow rate of the NH3 decomposition gas introduced from the combustion furnace 10 to the catalyst tank 20 can be set appropriately. The NH3 decomposition gas in the combustion furnace 10 contains N2 and H2O produced by the combustion of NH3, N2 and H2 produced by the combustion of N2, unreacted NH3, etc. When the oxidizing agent contains N2, the NH3 decomposition gas also contains N2 derived from the oxidizing agent.

[0019] In the catalyst tank 20, the remaining NH3 contained in the NH3 decomposition gas introduced into the catalyst tank 20 from the combustion furnace 10 is decomposed. A gas path 14 through which the NH3 decomposition gas passes is provided between the outlet of the combustion furnace 10 and the inlet of the catalyst tank 20. The NH3 decomposition gas introduced into the catalyst tank 20 through the gas path 14 is a high-temperature gas that retains the heat from combustion in the combustion furnace 10. Therefore, in the catalyst tank 20, the heat retained in the NH3 decomposition gas can be used to operate the catalyst, decomposing the undecomposed NH3 into H2 and N2.

[0020] In the illustrated example, a dehumidifier 24 is connected to the outlet of the catalyst tank 20. By removing H2O contained in the NH3 decomposition gas, a gas in which NH3 is decomposed into H2 and N2 can be obtained. The dehumidifier 24 is not particularly limited, but examples thereof include a cooler, a compressor, or other device that condenses and removes moisture by cooling or compressing the gas.

[0021] The catalyst used in the catalyst tank 20 is intended to decompose the NH3 remaining in the NH3 decomposition gas. Because the NH3 decomposition reaction is an endothermic reaction, the high-temperature gas passing through the catalyst tank 20 can be used as a heat source for the catalytic reaction. However, if the gas temperature is too high, the catalyst may be worn out. If the gas temperature drops, the reaction efficiency of the catalyst also decreases.

[0022] Therefore, in the combustion type ammonia decomposition apparatus 100 of this embodiment, the catalyst tank 20 is configured with at least two or more types of catalysts. Examples of the two or more types of catalysts include a first catalyst 21 and a second catalyst 22. Although not particularly shown, a third catalyst, a fourth catalyst, etc. may also be used.

[0023] More specifically, the catalyst packed in the catalyst tank 20 in the illustrated example is made up of a first catalyst 21 that operates at high temperatures and a second catalyst 22 that operates at low temperatures.

[0024] The first catalyst 21 operates at high temperatures, and is therefore sufficiently durable even at the gas temperature immediately after it is introduced from the combustion furnace 10 into the catalyst tank 20. On the other hand, if the gas temperature drops, it will not be able to demonstrate its performance. The second catalyst 22 can operate with low-temperature gas, but has the disadvantage of being worn out when exposed to high-temperature combustion gas.

[0025] Therefore, in the combustion type ammonia decomposition apparatus 100 of this embodiment, by combining these two or more types of catalysts, it is possible to efficiently recover the energy of the high temperature gas generated by the combustor 11 and decompose NH3.

[0026] The first catalyst 21 is preferably packed to an appropriate bed height on the inlet side of the catalyst tank 20. The first catalyst 21 is preferably arranged in the catalyst tank 20 closer to the inlet of the catalyst tank 20 than the second catalyst 22. In other words, in terms of positional relationship along the gas flow path, the first catalyst 21 is preferably positioned closer to the combustion furnace 10 than the second catalyst 22. An example of the first catalyst 21 is a catalyst that operates at about 800 to 1000°C.

[0027] The second catalyst 22 is preferably packed at an appropriate bed height on the outlet side of the catalyst tank 20. The second catalyst 22 is preferably arranged in the catalyst tank 20 closer to the outlet of the catalyst tank 20 than the first catalyst 21. In other words, in terms of its position along the gas flow path, the second catalyst 22 is preferably positioned farther from the combustion furnace 10 than the first catalyst 21. An example of the second catalyst 22 is a catalyst that operates at about 400 to 600°C.

[0028] The same arrangement as in the illustrated example can be carried out when the two or more types of catalysts constituting the catalyst tank 20 further include a third catalyst, etc. It is preferable to arrange the catalysts in such a manner that the type of catalyst that operates at a higher temperature is relatively closer to the inlet of the catalyst tank 20, and the type of catalyst that operates at a lower temperature is relatively closer to the outlet of the catalyst tank 20.

[0029] The catalyst used in the catalyst tank 20 is not particularly limited, and may be appropriately selected from known NH3 decomposition catalysts. Specific examples of the catalyst include transition metal catalysts such as iron (Fe), cobalt (Co), nickel (Ni), vanadium (V), chromium (Cr), manganese (Mn), and molybdenum (Mo); rare earth catalysts such as lanthanum (La), cerium (Ce), and neodymium (Nd); and noble metal catalysts such as ruthenium (Ru), rhodium (Rh), iridium (Ir), palladium (Pd), and platinum (Pt).

[0030] The catalyst used in the catalyst tank 20 is preferably placed in the catalyst tank 20 in a state supported on a carrier. The carrier is not particularly limited, but examples thereof include alumina, silica, zirconia, titania, zeolite, mullite, cordierite, etc. The carrier may be porous with a large specific surface area, and may be, for example, honeycomb-shaped or particulate.

[0031] An oxidant is supplied to the combustor 11. The oxidant supplied to the combustor 11 is preferably an oxidant capable of oxidizing NH3, and may include an oxidant capable of oxidizing H2 produced by decomposition of NH3. From the viewpoint of burning NH3 in a mixed state with the oxidant, an oxidant contained in the gas phase like NH3 is preferred. Specific examples of the oxidant include oxygen (O2) gas or a gas containing O2.

[0032] The oxidant supplied to the combustor 11 preferably has an O2 concentration of 25 vol% to 100 vol%. When O2 gas or a gas containing O2 is used as the oxidant, components other than O2 include nitrogen (N2) and argon (Ar). The O2-containing oxidant may be air obtained from the atmosphere or O2-enriched air. O2-enriched air may be obtained by adding O2 to air or by removing N2 from air.

[0033] Increasing the O2 concentration in the oxidizer makes it possible to increase the temperature of the flame 12 formed in the combustor 11. Furthermore, because the amount of N2 in the oxidizer is reduced, the amount of combustion gas is reduced, making it possible to reduce the volume of the combustion furnace and improve the heating efficiency of the catalyst tank 20. Furthermore, the reduction in N2 contained in the oxidizer increases the H2 concentration at the outlet of the catalyst tank 20. This improves productivity when extracting H2 as a product.

[0034] Fig. 2 is a graph showing an example of the relationship between the O2 concentration in the combustor 11 and the temperature of the flame 12. Fig. 3 is a graph showing an example of the relationship between the O2 concentration of the oxidizer in the combustor 11 and the H2 concentration contained in the NH3 decomposition gas. The horizontal axis of the graph represents the ratio of NH3 to O2 supplied to the combustor 11, and the amount of O2 that can theoretically oxidize all of the NH3 is set to 1. However, even if the amount of O2 is 1, complete combustion does not necessarily occur because there is a possibility that the NH3 decomposition gas will be discharged from the combustion furnace 10 before all of the NH3 is burned in the combustion furnace 10.

[0035] 2 and 3, the oxidant used for comparison is air. Compared to when air is used as the oxidant, when O2 (100 vol%) is used as the oxidant, a higher temperature flame is generated and the O2 concentration (molar fraction) in the NH3 decomposition gas becomes higher.

[0036] The combustion type ammonia decomposition apparatus 100 may be equipped with a gas purification device 30 at the outlet of the catalyst tank 20. The gas purification device 30 separates and purifies N2 and H2 from the NH3 decomposition gas discharged from the catalyst tank 20. The gas purification device 30 in the illustrated example is connected to the outlet of the catalyst tank 20 with a dehumidifier 24 between it and the catalyst tank 20.

[0037] A membrane gas separator, or a pressure swing adsorption (PSA, VPSA, VSA) or temperature swing adsorption (TSA) gas separator / purifier using an adsorbent can be used as the gas purification device 30. Pressure swing adsorption methods can be classified into broadly defined PSA, narrowly defined PSA, VPSA, and VSA, depending on the pressure conditions for adsorption and desorption.

[0038] As described above, a dehumidifier 24 or the like may be disposed between the catalyst tank 20 and the gas purification device 30. In the illustrated example, gas containing moisture flows through a gas path 23 between the catalyst tank 20 and the dehumidifier 24. Gas from which moisture has been removed flows through a gas path 25 between the dehumidifier 24 and the gas purification device 30. In the gas purification device 30, H produced from the NH decomposition gas is separated and can be obtained as a product or a raw material for the product.

[0039] Examples of the gas paths 14, 23, and 25 include pipes, etc. The cross-sectional area, length, etc. of the gas paths 14, 23, and 25 can be appropriately set depending on the gas flow rate between each part connected before and after the gas paths (the combustion furnace 10, the catalyst tank 20, the dehumidifier 24, and the gas purification device 30).

[0040] According to the combustion-type ammonia decomposition apparatus 100 and the combustion-type ammonia decomposition method using the same, NH3 and an oxidizing agent are supplied to a combustor, where they are decomposed into H2 and N2, and then purified to produce H2 efficiently. [Example]

[0041] Examples and comparative examples relating to the present invention will be shown below.

[0042] In the equipment configuration of Figure 1, NH3 gas and O2 gas were introduced into the combustor 11 and combusted, and NH3 decomposition gas was generated in the combustion furnace 10 and then introduced into the catalyst tank 20, and the NH3 conversion rate was evaluated.

[0043] The NH3 conversion rate was defined as the proportion of NH3 decomposed into H2 and N2 in the catalyst tank 20 to the NH3 introduced into the catalyst tank 20. The amount of NH3 gas introduced into the catalyst tank 20 is the amount of NH3 gas remaining unreacted in the combustion furnace 10.

[0044] In Example 1, two types of catalysts, catalyst (A) and catalyst (B), were used in the catalyst tank 20. As catalyst (A), a Ni catalyst was placed on the inlet side of the catalyst tank 20, and as catalyst (B), a Ru catalyst was placed on the outlet side of the catalyst tank 20. The Ni catalyst of catalyst (A) can operate at a higher temperature than the Ru catalyst. The Ru catalyst of catalyst (B) can operate at a lower temperature than the Ni catalyst.

[0045] In Comparative Example 1, Ni catalysts were disposed in both catalyst (A) and catalyst (B), and only one type of catalyst was used.

[0046] The NH3 gas flow rate, O2 gas flow rate, NH3 decomposition gas flow rate, catalyst tank inlet gas temperature, and space velocity (SV) value were the same conditions in Example 1 and Comparative Example 1. Here, the NH3 decomposition gas temperature at the catalyst tank inlet was 1000°C, so if the NH3 decomposition gas was introduced directly into the Ru catalyst, the Ru would volatilize and deactivate the Ru catalyst. Therefore, in the Comparative Example where only the Ru catalyst was used, the NH3 conversion rate was not evaluated.

[0047] [Table 1]

[0048] The evaluation results of the NH3 conversion rate are shown in Table 1. In Example 1, the NH3 conversion rate was 99% or more, and the remaining NH3 gas was effectively decomposed. On the other hand, in Comparative Example 1, the NH3 conversion rate was 74%, and unreacted NH3 remained even after the NH3 decomposition gas passed through the catalyst tank 20.

[0049] The results of Example 1 are thought to be due to the fact that the combination of Ni catalyst and Ru catalyst in the catalyst tank 20 allowed the NH3 decomposition reaction to proceed by fully utilizing the sensible heat of the NH3 decomposition gas introduced into the catalyst tank at 1000°C. The results of Comparative Example 1 are thought to be due to the fact that the use of only Ni catalyst in the catalyst tank 20 reduced the proportion of sensible heat that could be effectively utilized from the NH3 decomposition gas, preventing the NH3 decomposition reaction from proceeding sufficiently. [Explanation of symbols]

[0050] 10...combustion furnace, 11...combustor, 12...flame, 13...internal space, 14, 23, 25...gas path, 20...catalyst tank, 21...first catalyst, 22...second catalyst, 24...dehumidifier, 30...gas purification device, 100...combustion-type ammonia decomposition device.

Claims

1. The system includes a combustor to which ammonia and an oxidant are supplied, a combustion furnace in which the combustor is installed, and a catalyst tank connected to the combustion furnace, In the combustion furnace, ammonia decomposition gas is generated using ammonia and an oxidizer in the combustor, In the catalytic tank, residual ammonia contained in the ammonia decomposition gas introduced into the catalytic tank from the combustion furnace is decomposed, A combustion-type ammonia decomposition apparatus, characterized in that the catalyst tank is composed of at least two types of catalysts.

2. 2. The combustion type ammonia decomposition apparatus according to claim 1, wherein the oxidant supplied to the combustor has an oxygen concentration of 25 vol % to 100 vol %.

3. the combustion type ammonia decomposition apparatus is provided with a gas purification device at an outlet of the catalyst tank, 3. The combustion type ammonia decomposition apparatus according to claim 1, wherein the gas purification device separates nitrogen and hydrogen from the ammonia decomposition gas discharged from the catalyst tank and purifies the gas.

4. A combustion chamber is provided with a combustor to which ammonia and an oxidant are supplied, a combustion furnace in which the combustor is installed, and a catalyst tank connected to the combustion furnace. In the combustion furnace, ammonia decomposition gas is generated using ammonia and an oxidizer in the combustor, In the catalytic tank, residual ammonia contained in the ammonia decomposition gas introduced into the catalytic tank from the combustion furnace is decomposed, 1. A combustion-type ammonia decomposition method, wherein the catalyst tank is composed of at least two types of catalysts.

5. 5. The combustion-type ammonia decomposition method according to claim 4, wherein the oxidant supplied to the combustor has an oxygen concentration of 25 vol % to 100 vol %.

6. A gas purification device is used at the outlet of the catalyst tank, 6. The combustion-type ammonia decomposition method according to claim 4, wherein the gas purification device separates nitrogen and hydrogen from the ammonia decomposition gas discharged from the catalyst tank and purifies the gas.

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