Combustion-type ammonia decomposition device

Abstract

NH3 and an oxidizing agent are supplied to a combustion-type ammonia decomposition unit, and the heat of combustion generated in the combustor is utilized to the maximum extent for the decomposition heat of NH3 into N2 and H2. Furthermore, the decomposition gas is purified to efficiently produce H2. [Solution] The combustion-type ammonia decomposition apparatus 101 comprises a combustor 11 composed of a burner, a combustion furnace 12 in which the combustor 11 is installed, a heating furnace 14 following the combustion furnace 12, and a catalyst tank 15 following the heating furnace 14. In the combustion furnace 12, NH3 and an oxidizer supplied to the combustor 11 are combusted, and the combustion gas containing N2 and water vapor generated in the combustion furnace 12 is supplied to the subsequent heating furnace 14. In the heating furnace 14, NH3 supplied separately to the heating furnace 14 is heated and decomposed by the combustion gas, and the decomposition gas produced by the decomposition of NH3 in the heating furnace 14 is supplied to the subsequent catalyst tank 15. In the catalyst tank 15, the remaining NH3 contained in the decomposition gas is decomposed using a catalyst 16.

Description

Technical Field

[0001] The present invention relates to an ammonia decomposition apparatus that decomposes ammonia gas into nitrogen and hydrogen using a combustion flame.

Background Art

[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 NH3 decomposition reaction can be easily carried out by using a catalytic reaction at 400 °C or higher. As catalysts for NH3 decomposition, metals having NH3 decomposition activity such as iron (Fe), cobalt (Co), nickel (Ni), ruthenium (Ru), etc. are known. These catalysts are supported on inorganic carriers such as alumina (Al2O3) and zeolite. Industrially, Fe catalysts and Ni catalysts, which are relatively inexpensive, are widely used.

[0003] As a reaction apparatus for continuously performing NH3 decomposition, a method is generally adopted in which a catalytic reaction tube (cracking tube) filled with a catalyst is heated from the outside to compensate for the heat of the endothermic reaction accompanying NH3 decomposition. On the other hand, autothermal decomposition (ATR: Auto Thermal Reformer), which directly uses the heat generated by burning (oxidation reaction) a part of the raw material NH3 and decomposes the remaining raw material NH3 (non-oxidation reaction), is also used as an NH3 decomposition technique (for example, see Patent Documents 1 to 5).

[0004] Regarding Patent Documents 1 to 4, as a combustion method, a method of burning a mixed gas of NH3 and an oxidizing agent on the catalyst surface using an oxidation catalyst is disclosed. Regarding Patent Document 5, a method is disclosed in which a part of the supplied ammonia is oxidatively burned using a burner of a combustor, and the generated combustion heat is used for the decomposition reaction of the remaining ammonia.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] In Patent Document 5, the decomposition gas temperature after the catalytic tank reaction downstream of the combustor is high, at over 700°C, resulting in significant energy loss and a decrease in the conversion efficiency from NH3 to H2. Furthermore, all of the NH3 is supplied to the combustor's burner, and the NH3 burns using the burner in an oxygen (O2)-deficient state, leading to problems with reduced ignition and combustion stability.

[0007] In order to realize a carbon-neutral society, H2 gas is attracting attention as a new energy source. When transporting H2 gas to distant locations, it is common to transport it as liquefied H2 gas or compressed H2 gas. However, compressed H2 gas is unsuitable for large-scale transport, and liquefied H2 gas has the challenge of requiring a large amount of energy to liquefy due to the low boiling point of H2.

[0008] On the other hand, NH3 has physical properties similar to propane and a high boiling point, making it easier to transport than H2. In fact, a supply chain for NH3 as a raw material for fertilizer has already been established. NH3 is also attracting attention as an H2 carrier, and by decomposing NH3 transported to consumption sites to extract H2, it is expected to have various applications as an energy source and raw material.

[0009] Therefore, the present invention aims to supply NH3 and an oxidizing agent to a combustion-type ammonia decomposition device, maximize the use of the combustion heat generated in the combustor for the decomposition heat of NH3 into N2 and H2, and further purify the decomposition gas to efficiently produce H2. [Means for solving the problem]

[0010] To achieve the above objective, the present invention provides the following means. [1] A combustion-type ammonia decomposition apparatus comprising a combustor composed of a burner, a combustion furnace in which the combustor is installed, a heating furnace following the combustion furnace, and a catalyst tank following the heating furnace, wherein in the combustion furnace ammonia and an oxidizing agent supplied to the combustor are combusted, the combustion gas containing nitrogen and water vapor generated in the combustion furnace is supplied to the following heating furnace, in the heating furnace ammonia supplied separately to the heating furnace is heated and decomposed by the combustion gas, the ammonia decomposition gas produced by the decomposition of ammonia in the heating furnace is supplied to the following catalyst tank, and in the catalyst tank residual ammonia contained in the ammonia decomposition gas is decomposed using a catalyst. [2] The combustion-type ammonia decomposition apparatus according to [1], characterized in that the oxidizing agent supplied to the combustor is an oxidizing agent with an oxygen concentration of 25 vol% to 100 vol%. [3] The combustion ammonia decomposition apparatus according to [1] or [2], wherein the combustion ammonia decomposition apparatus comprises a gas purification device following the catalyst tank, wherein nitrogen and hydrogen are separated and purified from the ammonia decomposition gas discharged from the catalyst tank in the gas purification device, and the unpurified ammonia decomposition gas containing hydrogen from the separated and purified gas is supplied to the combustor. [4] The combustion ammonia decomposition apparatus according to any one of [1] to [3], wherein the combustion ammonia decomposition apparatus comprises a condenser following the catalyst tank and a purifier following the condenser, wherein in the condenser, unreacted ammonia and ammonia-containing water are separated from the ammonia decomposition gas discharged from the catalyst tank, and in the purifier, ammonia and water are separated from the ammonia-containing water. [5] The combustion ammonia decomposition apparatus according to any one of [1] to [4], further comprising an oxidant flow control valve for controlling the flow rate of an oxidant supplied to the combustor, and a gas analyzer for analyzing the composition of the combustion gas introduced from the combustion furnace to the heating furnace in order to determine the flow rate of the oxidant, and further comprising an ammonia flow control valve for controlling the flow rate of ammonia supplied to the combustor, and a thermometer for measuring the temperature of the ammonia decomposition gas introduced from the heating furnace to the catalyst tank in order to determine the flow rate of ammonia. [Effects of the Invention]

[0011] According to the present invention, by supplying NH3 and an oxidizing agent to a combustion-type ammonia decomposition device, the heat of combustion generated in the combustor is utilized as the heat of decomposition from NH3 to N2 and H2, and the decomposition gas is further purified to efficiently produce H2. [Brief explanation of the drawing]

[0012] [Figure 1] This is a diagram illustrating a combustion-type ammonia decomposition apparatus according to the first embodiment. [Figure 2] This is a diagram illustrating a combustion-type ammonia decomposition apparatus according to a second embodiment. [Figure 3] This is a diagram illustrating a combustion-type ammonia decomposition apparatus according to the third embodiment. [Figure 4] This graph shows an example of the relationship between O2 concentration and flame temperature. [Figure 5] This graph shows an example of the relationship between O2 concentration and H2 concentration.

Mode for Carrying Out the Invention

[0013] Hereinafter, the present invention will be described based on preferred embodiments.

[0014] <First Embodiment> FIG. 1 illustrates a combustion-type ammonia decomposition apparatus according to the first embodiment. The combustion-type ammonia decomposition apparatus 101 of the present embodiment includes a combustor 11, a combustion furnace 12 in which the combustor 11 is installed, a heating furnace 14 following the combustion furnace 12, and a catalyst tank 15 following the heating furnace 14.

[0015] The combustor 11 is composed of a burner. When an oxidant close to the theoretical oxygen amount is supplied to the burner, the burner forms a stable flame 13. Further, at least NH3 is supplied to the combustor 11 as fuel. In the combustor 11, fuel containing NH3 and an oxidant are mixed to form a stable flame 13.

[0016] A combustion NH3 supply path 21 and an oxidant supply path 22 are connected to the combustor 11. In the combustor 11 shown in the figure, the combustion NH3 supply path 21 and the oxidant supply path 22 are provided separately. The mixing of NH3 and the oxidant may be carried out before the mixed gas starts to burn in the combustor 11. In the example shown in the figure, the oxidant in the oxidant supply path 22 is indicated as "OX.".

[0017] In the combustor 11, it is possible to stably burn mainly NH3 as fuel without using other fuels such as hydrocarbon fuels (petroleum, natural gas, etc.) and carbon-based fuels (coal, charcoal, etc.). Also, a part of H2 that can be generated by the decomposition of NH3 may burn in the combustor 11 or the combustion furnace 12. More specifically, although described later, off-gas containing H2 or NH3 may be supplied to the combustor 11 as a part of the fuel.

[0018] The oxidizing agent supplied to the combustor 11 is preferably an oxidizing agent capable of oxidizing NH3, and may also include an oxidizing agent capable of oxidizing H2 produced by the decomposition of NH3. From the viewpoint of burning NH3 in a mixed state with the oxidizing agent, an oxidizing agent that is contained in the gas phase, similar to NH3, is preferred. Specific examples of oxidizing agents include O2 gas or gases containing O2.

[0019] Equation (1) shows an example of an oxidation reaction of a mixed gas containing NH3, H2, N2, and O2.

[0020] NH3(g)+αH2(g)+βN2(g)+(0.75+0.5α)O2(g) →(1.5+α)H2O(g)+(0.5+β)N2(g) (1)

[0021] The flame 13 formed from the combustor 11 can generate high temperatures inside the combustion furnace 12 in which the combustor 11 is installed. The combustor 11 can also be burned using only NH3 as fuel. Equation (2) shows the reaction equation between NH3 and O2, and this reaction is an exothermic reaction with ΔH = -317 kJ / mol.

[0022] NH3(g)+0.75O2(g)→1.5H2O(g)+0.5N2(g) (2)

[0023] The combustion furnace 12 forms the combustion chamber where NH3 burns. The combustion gas produced by the combustion of NH3 is temporarily contained within the combustion furnace 12. The reaction that proceeds within the combustion furnace 12 is not limited to the combustion (oxidation reaction) of NH3, but may also include the decomposition (non-oxidation reaction) of NH3. The combustion gas in the combustion furnace 12 may include gases produced by the combustion of NH3 (N2 and H2O), gases produced by the decomposition of NH3 (N2 and H2), unreacted NH3, etc. If the oxidizing agent contains N2, that N2 will also be included in the combustion gas.

[0024] When the fuel containing NH3 and the oxidizer supplied to the combustor 11 are burned, high-temperature combustion gas is generated in the combustion furnace 12. The temperature of the combustion gas can be, for example, 700°C or higher, more preferably 1000°C or higher, although this depends on the combustion conditions, which will be described in more detail later. The combustion gas contains N2 generated by the combustion or decomposition of NH3 and water vapor generated by the combustion of NH3. The combustion gas generated in the combustion furnace 12 is introduced into the heating furnace 14 that follows the combustion furnace 12. A combustion gas supply path 24 is provided between the combustion furnace 12 and the heating furnace 14 in the illustrated example.

[0025] The heating furnace 14 is supplied with NH3 from a decomposition NH3 supply route 23, which is separate from the combustion NH3 supply route 21 for the combustor 11. The NH3 supplied to the heating furnace 14 from the decomposition NH3 supply route 23 is mixed with the combustion gas supplied from the combustion furnace 12, causing the NH3 to be heated and decomposed to produce NH3 decomposition gas. The NH3 decomposition gas is a mixture of NH3, N2, and H2, as shown on the right-hand side of equation (3). In the following explanation, the NH3 decomposition gas may sometimes be simply referred to as "decomposition gas".

[0026] NH3(g)→1.5(1-γ)H2(g)+0.5(1-γ)N2(g) +γNH3(g) (3)

[0027] The heating furnace 14 forms a reaction chamber for the thermal decomposition of NH3. The atmosphere inside the heating furnace 14 may have a lower proportion of O2 and a higher proportion of NH3 compared to the combustion furnace 12. This allows for suppression of NH3 combustion (oxidation reaction) in the heating furnace 14 compared to the combustion furnace 12. Furthermore, if H2 is present in the heating furnace 14, the combustion of H2 can also be suppressed.

[0028] In the heating furnace 14, heat is transferred from the combustion gas to NH3, and as the temperature of NH3 rises, NH3 decomposition (non-oxidation reaction) proceeds. The NH3 decomposed in the heating furnace 14 may be NH3 supplied from the decomposition NH3 supply path 23 without passing through the combustion furnace 12, or NH3 contained in the combustion gas supplied from the combustion furnace 12. A catalyst 16, such as the catalyst tank 15 described later, is not required to be placed in the heating furnace 14. Because the temperature of NH3 is high in the heating furnace 14, the decomposition of NH3 can proceed in chemical equilibrium without the use of a catalyst 16.

[0029] The decomposition gas generated in the heating furnace 14 is supplied to the catalyst tank 15 which follows the heating furnace 14. In the decomposition gas supply path 25, the decomposition gas may contain NH3, N2, H2O, and H2. Since the decomposition gas introduced into the catalyst tank 15 still maintains a high temperature, the sensible heat of this gas activates the catalyst 16, allowing the undecomposed remaining NH3 to be decomposed into N2 and H2. As a result, at the outlet of the catalyst tank 15, gas decomposed into N2 and H2 can be obtained, as shown on the right-hand side of equation (4).

[0030] NH3(g)→1.5H2(g)+0.5N2(g) (4)

[0031] The NH3 decomposition reaction shown in equations (3) and (4) is an endothermic reaction, and it is known that in equation (4), ΔH = +46.11 kJ / mol. As the reaction in equation (4) proceeds, the temperature of the decomposition gas at the outlet of the catalyst tank 15 decreases.

[0032] The catalyst 16 is not particularly limited, but may be appropriately selected from known NH3 decomposition catalysts. Specific examples of NH3 decomposition catalysts 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 precious metal catalysts such as ruthenium (Ru), rhodium (Rh), iridium (Ir), palladium (Pd), and platinum (Pt).

[0033] It is preferable to place the catalyst 16 in the catalyst tank 15 while supported on a carrier. The carrier is not particularly limited, but examples include alumina, silica, zirconia, titania, zeolite, mullite, cordierite, etc. The carrier may be porous with a large specific surface area, for example, in a honeycomb or particulate form.

[0034] In the catalyst tank 15, unreacted NH3 contained in the decomposition gas introduced from the heating furnace 14 is decomposed into N2 and H2 at a temperature lower than the temperature inside the heating furnace 14. As a result, the proportion of residual NH3 and the proportion of H2 in the decomposition gas discharged from the catalyst tank 15 can be reduced compared to the decomposition gas introduced from the heating furnace 14.

[0035] In this embodiment, the catalyst 16 is activated by the sensible heat of the decomposition gas supplied from the heating furnace 14, so there is no need to perform thermal compensation for the endothermic reaction by heating from outside the catalyst tank 15, as in the external heating method. However, if the temperature is too high, the catalyst 16 may be worn down. From the viewpoint of avoiding energy loss, the temperature of the decomposition gas may decrease due to the endothermic reaction associated with the NH3 decomposition reaction, but heat dissipation to the outside from the heating furnace 14 and the catalyst tank 15 (including the decomposition gas supply path 25 in the illustrated example) is suppressed. The flow of decomposition gas from the heating furnace 14 to the catalyst tank 15 (flow rate, residence time, etc.) can be designed as appropriate. For example, while the temperature of the decomposition gas is high, the NH3 decomposition reaction may proceed in thermal equilibrium within the heating furnace 14, and when the temperature of the decomposition gas decreases, the NH3 decomposition reaction may proceed using the catalyst 16 within the catalyst tank 15.

[0036] Furthermore, in this embodiment, it is preferable that the oxidizing agent supplied to the combustor 11 has an O2 concentration of 25 vol% to 100 vol%. When using O2 gas or an O2-containing gas as the oxidizing agent, other components besides O2 include N2, argon (Ar), etc. The O2-containing oxidizing agent 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.

[0037] The graph in Figure 4 shows an example of the relationship between the O2 concentration supplied to the combustor 11 and the temperature of the flame 13. The graph in Figure 5 shows an example of the relationship between the O2 concentration and the H2 concentration. The horizontal axis of the graphs represents the ratio of NH3 to O2 supplied to the combustor 11, with the amount of O2 that can theoretically oxidize all of the NH3 being set to 1. However, even if the amount of O2 is 1, complete combustion is not guaranteed because decomposition gas may be released from the combustion furnace 12 before all of the NH3 is burned in the combustion furnace 12.

[0038] As shown in Figure 4, increasing the O2 concentration in the oxidizer makes it possible to increase the temperature of the flame 13 formed in the combustor 11. On the other hand, since the amount of N2 in the oxidizer decreases, the amount of combustion gas decreases, and as a result, it becomes possible to reduce the volume of the combustion furnace 12. In addition, the heating and decomposition efficiency of NH3 in the heating furnace 14 is also improved.

[0039] Furthermore, increasing the O2 concentration of the oxidizing agent reduces the amount of N2 in the decomposition gas, which in turn increases the H2 concentration at the inlet of the catalyst tank 15. This improves the gas separation efficiency when H2 is extracted as a product in the gas purification device 33.

[0040] In Figures 4 and 5, the oxidizing agent used in the proportional ratio is air. When O2 (100 vol%) is used as the oxidizing agent, a higher temperature flame is generated and the O2 concentration (mole fraction) in the decomposition gas is higher compared to when air is used as the oxidizing agent.

[0041] It is desirable that the flow rate of NH3 supplied from the decomposition NH3 supply path 23 to the heating furnace 14 be such that the predetermined oxygen ratio m (see equation (5)) is in the range of 0.15 to 0.3.

[0042] m = (Amount of O2 in the oxidizer actually supplied to the combustor / Theoretical amount of O2 required to completely combust the entire amount of ammonia and ammonia decomposition gas supplied) (5)

[0043] The denominator of the oxygen ratio m shown in equation (5) represents the O2 flow rate required for the stoichiometric complete combustion of the total amount of NH3 supplied to the combustor 11 or heating furnace 14 and the decomposition gas produced in the combustion furnace 12. The numerator of the oxygen ratio m represents the O2 flow rate in the oxidizer actually supplied to the combustor 11. In other words, the oxygen ratio m is expressed as the ratio of the theoretical O2 flow rate (denominator of the fraction) to the actual O2 flow rate (numerator of the fraction).

[0044] By supplying NH3 and an oxidizing agent so that the oxygen ratio m falls within the above range, the temperature of the decomposition gas after the reaction is completed in the catalyst tank 15 following the heating furnace 14 can be set to between 250°C and 700°C, allowing the NH3 decomposition reaction using the catalyst 16 to proceed. Furthermore, as described above, sufficient heat is generated in the combustion furnace 12 to raise the temperature of the NH3 supplied to the heating furnace 14, and the NH3 decomposition reaction can proceed in the heating furnace 14 without using the catalyst 16, while the O2 concentration is reduced by the supply of NH3. This reduces energy loss unrelated to the NH3 decomposition reaction, and as a result, it is possible to increase the conversion efficiency from NH3 to H2.

[0045] The catalyst tank 15 can use at least two or more catalysts 16 with different physical or chemical properties. By using catalysts 16, NH3 can be decomposed into H2 and N2 at a high rate even at low temperatures below 700°C. The catalyst 16 is not particularly limited, but catalysts containing nickel (Ni) and catalysts containing ruthenium (Ru) can be preferably used.

[0046] A gas purification device 33 may be installed following the catalyst tank 15. By installing the gas purification device 33 at the outlet of the catalyst tank 15, N2 and H2 can be separated and purified from the decomposition gas discharged from the catalyst tank 15. The gas purification device 33 can be a membrane type purifier or a pressure swing type separator / purifier using an adsorbent.

[0047] As the gas purification apparatus 33, a membrane gas separator or a pressure swing type (PSA, VPSA, VSA) or temperature swing type (TSA) gas separator / purifier using an adsorbent can be used. In the pressure swing type adsorption method, PSA in the broad sense can be distinguished into PSA in the narrow sense and VPSA, VSA depending on the pressure conditions of adsorption and desorption.

[0048] In this embodiment, the primary objective is to purify the decomposition gas using H2 as the product gas. Therefore, if, for example, a pressure swing type separation and purification device is used, due to the principle of the device, unpurified decomposition gas (off-gas) containing H2 will be generated. Thus, this unpurified off-gas may be mixed with NH3 and used as part of the fuel for the combustor 11. Of the gas separated and purified by the gas purification device 33, the off-gas containing H2 is preferably supplied to the combustor 11 while being stored in the buffer tank 34 as needed.

[0049] In the illustrated gas purification apparatus 33, a product H2 recovery path 33a and an off-gas recovery path 33b are provided on the outlet side. A buffer tank 34 follows the off-gas recovery path 33b. Furthermore, off-gas containing H2 can be supplied from the buffer tank 34 to the combustor 11 via an off-gas supply path 35.

[0050] If the condenser 31, described later, is not located between the outlet of the catalyst tank 15 and the inlet of the gas purification device 33, the decomposition gas may be directly introduced from the catalyst tank 15 to the gas purification device 33. In this case, NH3 and H2 may be purified from the decomposition gas using an adsorbent such as zeolite. In addition, a water removal agent that chemically reacts with water may be used on the decomposition gas discharge path 26 connected to the outlet of the catalyst tank 15 to remove water from the decomposition gas. The gas purification device 33 may be equipped with separate devices for adsorbing and purifying NH3 and adsorbing and purifying H2. Unreacted NH3 recovered by the NH3 adsorption and purification device can be used as fuel for the combustor 11. The device for adsorbing and purifying H2 is the same as when separating product H2 and off-gas in the gas purification device 33.

[0051] In this embodiment, water is generated when a fuel containing at least NH3 and possibly H2 is burned in the combustor 11 and combustion furnace 12. Therefore, it is preferable to remove the water when separating N2 and H2 in the gas purification device 33. Thus, it is preferable to provide a condenser 31 at the outlet of the catalyst tank 15 where the temperature of the decomposition gas decreases to remove the water. In the illustrated example, the condenser 31 follows the decomposition gas discharge path 26 connected to the outlet of the catalyst tank 15. In the decomposition gas discharge path 26, the decomposition gas may contain H2, N2, H2O, and NH3.

[0052] A scrubber or the like can be used in the condenser 31 following the catalyst tank 15. The scrubber sprays water onto the decomposition gas to cool it and produce liquid-phase water in which water vapor in the decomposition gas and sprayed water are mixed. In addition, although the condenser 31 is not particularly limited, a device that removes moisture by condensing it through cooling, compression, etc. of the gas, such as a cooler or compressor, may also be used.

[0053] In the condenser 31, unreacted NH3 and water containing NH3 are separated from the decomposition gas discharged from the catalyst tank 15. Since undecomposed NH3 dissolves in the water when it is condensed, it is preferable to install a purifier 32 following the condenser 31 to separate and purify the water from the NH3.

[0054] In the purifier 32, NH3 and water are separated from the water containing NH3. An adsorbent such as zirconium phosphate, which can absorb and desorb NH3 dissolved in water, can be used in the purifier 32. The water separated in the purifier 32 can be reused as water to condense water vapor in the gas using a scrubber in the condenser 31. The NH3 separated in the purifier 32 can be used as fuel for the combustor 11.

[0055] In the illustrated example, the outlet side of the condenser 31 is provided with a first discharge path 31a, which mainly discharges unreacted NH3 and H2O, and a second discharge path 31b, which mainly discharges H2 and N2. The gas in the second discharge path 31b may contain unreacted NH3 that did not dissolve completely in the water in the first discharge path 31a. In the illustrated example, a purifier 32 follows the first discharge path 31a, and a gas purification device 33 follows the second discharge path 31b.

[0056] In the condenser 31, under conditions where H2O condenses, NH3 may dissolve in H2O to produce aqueous ammonia. Condensed liquid water may be supplied to the condenser 31 to dissolve NH3 in the decomposition gas and to cool the H2O in the decomposition gas. In this case, liquid water or aqueous ammonia may be introduced into the purifier 32 through the first discharge path 31a.

[0057] When liquid water containing dissolved ammonia is introduced into the purifier 32, the NH3 dissolved in the water is separated into water and NH3 in the purifier 32. The purifier 32 is not particularly limited, but examples include a tower filled with an adsorbent such as zeolite. NH3 in water is separated into ammonium (NH4) + They may be adsorbed onto the adsorbent as ions.

[0058] The method for recovering unreacted NH3 adsorbed on the adsorbent in the purifier 32 is not particularly limited, and any appropriate method can be used. For example, depending on the characteristics of the adsorbent, a method of desorption and recovery using a vacuum pump, heater, etc., can be used. Furthermore, the adsorption capacity of the adsorbent is regenerated by the desorption of unreacted NH3 from the adsorbent.

[0059] The NH3 separated from the water in the purifier 32 is recovered via the NH3 recovery path 32a. The water remaining after the separation of NH3 is recovered via the H2O recovery path 32b. The water discharged from the H2O recovery path 32b may be purified and reused as needed. For example, the water supplied to separate unreacted NH3 from the decomposition gas in the condenser 31 may be circulated between the condenser 31 and the purifier 32.

[0060] The various routes mentioned above, such as the combustion NH3 supply route 21, oxidizer supply route 22, decomposition NH3 supply route 23, combustion gas supply route 24, decomposition gas supply route 25, decomposition gas discharge route 26, first discharge route 31a, second discharge route 31b, NH3 recovery route 32a, H2O recovery route 32b, product H2 recovery route 33a, off-gas recovery route 33b, and off-gas supply route 35, can be pipes, etc. The cross-sectional area and length of each route can be appropriately set according to the composition and flow rate of the fluid flowing through the route, the properties of the parts connected before and after the route, etc.

[0061] In this embodiment, the objective is to efficiently extract H2 by heating NH3 in a heating furnace 14, decomposing NH3 in a catalyst tank 15, and purifying the decomposed gas in a gas purification device 33. For this reason, it is undesirable if O2 is present in the high-temperature gas generated in the combustion furnace 12, as this reduces the efficiency of NH3 decomposition (non-oxidation reaction).

[0062] Therefore, it is preferable to install a gas analyzer 42 at the outlet of the combustion furnace 12 to measure the O2 concentration in the combustion gas and to control the flow rate of the oxidizer supplied to the combustor 11 with an oxidizer flow rate control valve 41. The gas analyzer 42 analyzes the composition of the combustion gas introduced from the combustion furnace 12 to the heating furnace 14 in order to determine the flow rate of the oxidizer supplied to the combustor 11. It is desirable that the oxygen concentration in the combustion gas at the outlet of the combustion furnace 12 be 0.2% or less.

[0063] Furthermore, in this embodiment, since the NH3 heated in the heating furnace 14 is decomposed in the catalyst tank 15, the inlet gas temperature of the catalyst tank 15 is an important parameter for operating the catalyst 16. Therefore, a thermometer 52 is installed at the inlet of the catalyst tank 15, and the NH3 flow rate supplied to the combustor 11 is controlled by an NH3 flow rate control valve 51 so that the inlet gas temperature is maintained at the optimal temperature. The thermometer 52 measures the temperature of the decomposition gas introduced from the heating furnace 14 to the catalyst tank 15 in order to determine the flow rate of NH3 supplied to the combustor 11.

[0064] The combustor 11 can also be supplied with H2 and NH3 contained in the decomposition gas generated by the gas purification device 33 as fuel. Therefore, by controlling the flow rate of NH3 in order to control the inlet gas temperature of the catalyst tank 15, the flow rate of NH3 supplied as fuel can be minimized.

[0065] <Other Embodiments> This embodiment is not limited to the configuration shown in Figure 1. For example, as shown in Figures 2-3, the arrangement of the combustion furnace 12, heating furnace 14, catalyst tank 15, gas analyzer 42, and thermometer 52 can be different from that shown in Figure 1. In the configuration shown in Figure 1, the combustion furnace 12, heating furnace 14, and catalyst tank 15 are each composed of separate furnace bodies or containers.

[0066] In both the configuration shown in Figure 1 and configurations different from Figure 1, the combustion furnace 12 generates sufficient heat through combustion, the heating furnace 14 allows the NH3 decomposition reaction to proceed without using the catalyst 16, and the catalyst tank 15 allows the NH3 decomposition reaction to proceed even at a lower temperature than in the heating furnace 14 by using the catalyst 16. Furthermore, for configurations different from Figure 1 (such as the second embodiment in Figure 2 and the third embodiment in Figure 3), the condenser 31, purifier 32, gas purification device 33, buffer tank 34, and off-gas supply path 35 can be used in the same way as in the configuration shown in Figure 1.

[0067] In the combustion-type ammonia decomposition apparatus 102 shown in Figure 2, the combustion furnace 12 and the heating furnace 14 are formed within the same furnace body 112. In this case, the gas analyzer 42 can be placed in the boundary region between the combustion furnace 12 and the heating furnace 14 within the same furnace body 112. Also, in the configuration shown in Figure 2, similar to the configuration in Figure 1, a thermometer 52 is placed in the decomposition gas supply path 25 between the heating furnace 14 and the catalyst tank 15.

[0068] In the combustion-type ammonia decomposition apparatus 103 shown in Figure 3, the combustion furnace 12, the heating furnace 14, and the catalyst tank 15 are formed within the same furnace body 113. In this case, a gas analyzer 42 is positioned in the boundary region between the combustion furnace 12 and the heating furnace 14 within the same furnace body 113, and a thermometer 52 is positioned in the boundary region between the heating furnace 14 and the catalyst tank 15 within the same furnace body 113.

[0069] Although not specifically shown in the figures, in this embodiment, a combustion gas supply path 24 is provided between the combustion furnace 12 and the heating furnace 14, and a configuration in which the heating furnace 14 and the catalyst tank 15 are formed within the same furnace body is also conceivable. In this case, a gas analyzer 42 may be placed in the combustion gas supply path 24 between the combustion furnace 12 and the downstream furnace body (heating furnace 14 and catalyst tank 15), and a thermometer 52 may be placed in the boundary region between the heating furnace 14 and the catalyst tank 15 within the same furnace body.

[0070] If the combustion gas supply path 24 is omitted between the combustion furnace 12 and the heating furnace 14, the heating furnace 14 region may follow the combustion furnace 12 region within the same furnace body 112, 113. The boundary region between the combustion furnace 12 and the heating furnace 14 within the same furnace body 112, 113 may have the same cross-sectional area as the combustion furnace 12 region or the heating furnace 14 region with respect to the gas flow direction, or it may have a different cross-sectional area than the combustion furnace 12 region or the heating furnace 14 region. It is preferable that the gas flow direction is generally from the combustion furnace 12 towards the heating furnace 14, and that backflow from the heating furnace 14 towards the combustion furnace 12 is suppressed.

[0071] If the boundary region between the combustion furnace 12 and the heating furnace 14 has the same cross-sectional area as the regions of the combustion furnace 12 and heating furnace 14 before and after it, the gas analyzer 42 may be positioned at an appropriate location in the boundary region between the combustion furnace 12 and the heating furnace 14 in the direction of gas flow. Depending on the situation, the position of the gas analyzer 42 in the direction of flow within the same furnace body may be changeable. Examples of positions for the gas analyzer 42 in the boundary region between the combustion furnace 12 and the heating furnace 14 include a position closer to the combustion furnace 12, a position closer to the heating furnace 14, or a position intermediate between the two.

[0072] When the same furnace body 112, 113 contains both a combustion furnace 12 and a heating furnace 14, the decomposition NH3 supply path 23 is provided in the region of the heating furnace 14. As described above, when the NH3 supplied from the decomposition NH3 supply path 23 is mixed with the combustion gas supplied from the combustion furnace 12, it is preferable that the combustion (oxidation reaction) of NH3 in the heating furnace 14 is suppressed compared to the combustion furnace 12. By appropriately setting the composition of the combustion gas in the combustion furnace 12 and the ratio of NH3 supplied to the heating furnace 14 relative to the combustion gas, the gas composition and gas temperature after the NH3 is supplied from the decomposition NH3 supply path 23 can be adjusted, lowering the oxidizer concentration and gas temperature in the heating furnace 14 compared to the combustion furnace 12, thereby suppressing the combustion (oxidation reaction) of NH3.

[0073] If the decomposition gas supply path 25 is omitted between the heating furnace 14 and the catalyst tank 15, the region of the catalyst tank 15 may follow the region of the heating furnace 14 within the same furnace body 113. The boundary region between the heating furnace 14 and the catalyst tank 15 within the same furnace body 113 may have the same cross-sectional area as the region of the heating furnace 14 or the region of the catalyst tank 15 with respect to the gas flow direction, or it may have a different cross-sectional area than the region of the heating furnace 14 or the catalyst tank 15. It is preferable that the gas flow direction is generally from the heating furnace 14 toward the catalyst tank 15, and that backflow from the catalyst tank 15 toward the heating furnace 14 is suppressed.

[0074] If the boundary region between the heating furnace 14 and the catalyst tank 15 has the same cross-sectional area as the regions of the heating furnace 14 and catalyst tank 15 before and after it, the thermometer 52 may be placed at an appropriate position in the boundary region between the heating furnace 14 and the catalyst tank 15 in the direction of gas flow. Depending on the situation, the position of the thermometer 52 in the direction of flow within the same furnace body may be changeable. Examples of positions for the thermometer 52 in the boundary region between the heating furnace 14 and the catalyst tank 15 include a position closer to the heating furnace 14, a position closer to the catalyst tank 15, or a position intermediate between the two.

[0075] Although the present invention has been described above based on preferred embodiments, the present invention is not limited to the embodiments described above, and various modifications are possible without departing from the spirit of the invention. Modifications include adding, substituting, omitting, or otherwise changing the components in each embodiment. It is also possible to combine components used in two or more embodiments as appropriate. [Explanation of Symbols]

[0076] 11... Combustor, 12... Combustion furnace, 13... Flame, 14... Heating furnace, 15... Catalyst tank, 16... Catalyst, 21... NH3 supply route for combustion, 22... Oxidizer supply route, 23... NH3 supply route for decomposition, 24... Combustion gas supply route, 25... Decomposition gas supply route, 26... Decomposition gas discharge route, 31... Condenser, 31a... First discharge route, 31b... Second discharge route, 32... Purifier, 32a... NH3 recovery route, 32b... H2O recovery route, 33... Gas purification device, 33a... Product H2 recovery route, 33b... Off-gas recovery route, 34... Buffer tank, 35... Off-gas supply route, 41... Oxidizer flow control valve, 42... Gas analyzer, 51... NH3 flow control valve, 52... Thermometer, 101, 102, 103... Combustion-type ammonia decomposition device, 112, 113... Furnace body.

Claims

1. The system comprises a combustor consisting of a burner, a combustion furnace in which the combustor is installed, a heating furnace following the combustion furnace, and a catalyst tank following the heating furnace. In the aforementioned combustion furnace, ammonia and oxidizer supplied to the combustor are burned, and the combustion gas containing nitrogen and water vapor generated in the combustion furnace is supplied to the subsequent heating furnace. In the aforementioned heating furnace, ammonia supplied to the heating furnace is heated and decomposed by the combustion gas, and the ammonia decomposition gas produced by the decomposition of ammonia in the heating furnace is supplied to the subsequent catalyst tank. A combustion-type ammonia decomposition apparatus characterized in that, in the catalyst tank, residual ammonia contained in the ammonia decomposition gas is decomposed using a catalyst.

2. The combustion-type ammonia decomposition apparatus according to claim 1, characterized in that the oxidizing agent supplied to the combustor is an oxidizing agent having an oxygen concentration of 25 vol% to 100 vol%.

3. The combustion-type ammonia decomposition apparatus includes a gas purification apparatus following the catalyst tank, In the gas purification apparatus, nitrogen and hydrogen are separated and purified from the ammonia decomposition gas discharged from the catalyst tank. The combustion-type ammonia decomposition apparatus according to claim 1 or 2, characterized in that, of the separated and purified gases, the unpurified ammonia decomposition gas containing hydrogen is supplied to the combustor.

4. The combustion-type ammonia decomposition apparatus comprises a condenser following the catalyst tank and a purifier following the condenser, In the condenser, unreacted ammonia and water containing ammonia are separated from the ammonia decomposition gas discharged from the catalyst tank. The combustion-type ammonia decomposition apparatus according to claim 1 or 2, characterized in that the purifier separates ammonia and water from the water containing ammonia.

5. The combustion-type ammonia decomposition apparatus comprises an oxidant flow control valve for controlling the flow rate of oxidant supplied to the combustor, and a gas analyzer for analyzing the composition of the combustion gas introduced from the combustion furnace to the heating furnace in order to determine the flow rate of the oxidant. Furthermore, the combustion-type ammonia decomposition apparatus is characterized by comprising an ammonia flow control valve for controlling the flow rate of ammonia supplied to the combustor, and a thermometer for measuring the temperature of the ammonia decomposition gas introduced from the heating furnace to the catalyst tank in order to determine the flow rate of ammonia, as described in claim 1 or 2.

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