Ammonia decomposition system

Abstract

Provided according to exemplary embodiments of the present invention is an ammonia decomposition system capable of minimizing the generation of iron nitride, which is a by-product.

Description

Ammonia decomposition system

[0001] The present invention relates to an ammonia decomposition system.

[0002] In the past, the technology for storing and transporting hydrogen was to compress or liquefy hydrogen at high pressure. However, recently, a technology for storing and transporting hydrogen using ammonia is being reviewed and applied, and this technology using ammonia is attracting attention as it is more efficient than the existing high-pressure or liquefaction technology.

[0003] To transport and use the hydrogen stored in the ammonia, a process is required to decompose the ammonia back into hydrogen. The following reaction formula is used to produce hydrogen by decomposing ammonia.

[0004] [Reaction Formula 1]

[0005] 2NH3→ N2+ 3H2 (△H=46 kJ / mol)

[0006] Figure 1 is a graph showing the thermodynamic equilibrium concentrations of ammonia and hydrogen as a function of temperature and pressure. As shown in Figure 1, the ammonia decomposition reaction described above is an endothermic reaction, and the equilibrium conversion rate increases as the temperature increases. However, since the mole number of reactants is greater than the mole number of products, the equilibrium conversion rate decreases as the pressure increases.

[0007] In order to use hydrogen transported in the form of ammonia, it must go through an ammonia decomposition process to decompose the transported ammonia at the point of use, which requires a catalyst and heat energy for ammonia decomposition.

[0008] Therefore, in order to reduce energy consumption in the ammonia decomposition reaction, it is required to apply a catalyst that operates efficiently even at low temperatures.

[0009] Metal catalysts dispersed on metal oxide supports have been extensively studied as conventional ammonia decomposition catalysts. Figure 2 is a graph showing ammonia decomposition catalyst activity (turnover number). As can be seen from Figure 2, Ru catalysts are known to be the most efficient catalysts, while non-precious metal catalysts such as Ni, Co, and Fe are used.

[0010] Meanwhile, the steel industry is currently developing a hydrogen reduction process that converts the iron ore reducing agent from carbon to hydrogen. The hydrogen reduction process requires a high-temperature reaction to reduce iron ore, and the reduced iron produced thereby can have high thermal energy. When such reduced iron is used as a catalyst for the ammonia decomposition reaction, the energy required for ammonia decomposition can be efficiently supplied, thereby increasing the efficiency of the ammonia decomposition process. However, when reduced iron is used as a catalyst for the ammonia decomposition reaction, the surface of the reduced iron is nitrided, resulting in Fe x N y Problems have arisen with the formation of iron nitride in the structure. Therefore, the development of technologies to address the aforementioned issues is necessary.

[0011] (Patent Document 1) Japanese Patent Publication No. 2023-539511.

[0012] The technical idea of ​​the present invention is to provide an ammonia decomposition system using reduced iron as a catalyst.

[0013] The objectives of the present invention are not limited to the above-described content. Those skilled in the art will have no difficulty understanding the additional objectives of the present invention from the overall description of the present invention.

[0014] According to exemplary embodiments of the present invention, an ammonia decomposition system is provided. The ammonia decomposition system includes a fluidized bed reactor configured to receive ammonia and reduced iron, form a catalyst fluidized bed by discharging the reduced iron downward, and generate hydrogen from the ammonia by contacting the ammonia with the catalyst fluidized bed, wherein a ratio (D / Q) of a supply flow rate (Q) of ammonia to a supply amount (D) of the reduced iron to the fluidized bed reactor is 40 to 300 kg / Nm. 3 is in the range of .

[0015] The ratio (D / Q) of the supply flow rate (Q) of ammonia to the fluidized bed reactor and the supply amount (D) of the reduced iron is 70 to 200 kg / Nm 3 can be controlled to be within the range of .

[0016] The ammonia decomposition system further includes a fluidized reduction reactor connected to the fluidized bed reactor and configured to provide the reduced iron to the fluidized bed reactor, wherein the fluidized reduction reactor can be configured to input and transport fine iron ore, and reduce the fine iron ore by reducing gas supplied countercurrently with respect to the transport direction of the fine iron ore to produce reduced iron.

[0017] The supply temperature of the above reduced iron may be 600°C or higher.

[0018] The discharge temperature of the above reduced iron may be 500°C or higher.

[0019] The average temperature of the hydrogen flowing to the upper portion of the fluidized bed reactor may be 600°C or higher.

[0020] Iron nitride (Fe) contained in the reduced iron emitted above x N y ) may be less than 3% (including 0%) in weight%.

[0021] Iron nitride (Fe) contained in the reduced iron emitted above x N y ) may be, in weight %, 1% or less (including 0%).

[0022] The above ammonia is 2,500 h -1 10,000 h -1 can be supplied at the space velocity of .

[0023] According to exemplary embodiments of the present invention, an ammonia decomposition system capable of minimizing the generation of iron nitride can be provided by controlling the ammonia supply flow rate and the amount of reduced iron.

[0024]

[0025] The various advantageous and beneficial effects of the present invention are not limited to the above-described contents, and will be more easily understood in the course of explaining specific embodiments of the present invention.

[0026] Figure 1 is a graph showing the thermodynamic equilibrium concentrations of ammonia and hydrogen according to temperature and pressure.

[0027] Figure 2 is a graph showing ammonia decomposition catalyst activity (turnover number).

[0028] FIG. 3 is a drawing for explaining an ammonia decomposition system according to exemplary embodiments.

[0029] Figure 4 is a graph comparing and evaluating the ammonia decomposition performance of each catalyst.

[0030] FIG. 5 is a drawing for explaining an ammonia decomposition system according to other exemplary embodiments.

[0031] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings. Prior to this, it should be noted that the terms and words used in this specification and claims should not be construed as limited to their conventional or dictionary meanings. Based on the principle that the inventor can appropriately define the concepts of terms to best explain his or her invention, they should be interpreted in a way that aligns with the technical spirit of the present invention.

[0032] Hereinafter, when describing with reference to drawings, identical or corresponding components are given the same drawing reference numerals and redundant descriptions thereof are omitted.

[0033] In the embodiments below, terms such as first, second, etc. are not used in a limiting sense, but are used for the purpose of distinguishing one component from another.

[0034] In the following embodiments, singular expressions include plural expressions unless the context clearly indicates otherwise.

[0035] In the embodiments below, terms such as “include” or “have” mean that a feature or component described in the specification is present, and do not preclude the possibility that one or more other features or components may be added.

[0036] For convenience of explanation, the sizes of components in the drawings may be exaggerated or reduced. For example, the sizes and thicknesses of each component shown in the drawings are arbitrarily indicated for convenience of explanation, and thus the present invention is not necessarily limited to what is shown.

[0037] If a particular embodiment is capable of being implemented differently, a particular process sequence may be performed in a different order than described. For example, two processes described in succession may be performed substantially simultaneously, or in a reverse order from the described order.

[0038] In addition, when describing the present invention, if it is determined that a detailed description of a related known configuration or function may obscure the gist of the present invention, the detailed description is omitted.

[0039] Additionally, unless otherwise defined, the contents of the alloy composition described below refer to weight percent.

[0040] [Ammonia Decomposition System]

[0041] FIG. 3 is a drawing for explaining an ammonia decomposition system (10) according to exemplary embodiments.

[0042] Referring to FIG. 3, an ammonia decomposition system (10) according to exemplary embodiments may include a fluidized bed reactor (100).

[0043] The fluidized bed reactor (100) can be supplied with ammonia and reduced iron. According to exemplary embodiments, reduced iron is used as a catalyst for the ammonia decomposition reaction.

[0044] Figure 4 is a graph comparing and evaluating the ammonia decomposition performance of each catalyst.

[0045] Referring to Figure 4, ammonia decomposition performance was superior in the order of rubidium (Ru), reduced iron, and nickel (Ni) catalysts. However, rubidium is a precious metal, and its reserves are limited, making it expensive. However, reduced iron has a relatively abundant reserve and a higher energy transfer coefficient for ammonia decomposition than nickel, resulting in superior ammonia decomposition performance compared to nickel catalysts. Thus, by using reduced iron as an ammonia decomposition catalyst, the unit cost of hydrogen production can be lowered, and a relatively high ammonia decomposition capacity can be secured.

[0046] Reduced iron supplied to the fluidized bed reactor (100) is discharged downward from the fluidized bed reactor (100) and can form a catalyst fluidized bed. Reduced iron is used as a catalyst for the ammonia decomposition reaction. Since this reduced iron forms a catalyst fluidized bed and can continuously flow in and out of the fluidized bed reactor (100), the catalyst for the ammonia decomposition reaction can be periodically exchanged. Therefore, unlike a conventional fixed reactor filled with a catalyst, there is no need to stop the reactor for catalyst replacement, so that hydrogen can be continuously produced. Consequently, the hydrogen production efficiency can be improved. As an example, the discharged reduced iron can be provided to a steelmaking process and used as a raw material for steel plates.

[0047] The fluidized bed reactor (100) may be configured to produce hydrogen from ammonia by bringing ammonia into contact with a catalyst fluidized bed. To this end, ammonia may be supplied from below the catalyst fluidized bed, and configured so that the ammonia flows toward the upper portion of the fluidized bed reactor (100). As a result, hydrogen decomposed from ammonia may be distributed in the upper portion of the fluidized bed reactor (100).

[0048] The fluidized bed reactor (100) is not particularly limited as long as a fluidized bed is formed inside the reactor to enable periodic exchange of the catalyst without stopping the operation of the reactor. As a non-limiting example, the fluidized bed reactor (100) may include an ammonia supply portion located at the bottom, a reduced iron discharge portion located above the ammonia supply portion, a reduced iron supply portion located above the ammonia supply portion, and a hydrogen gas discharge portion located at the top. Reduced iron supplied to the reduced iron supply portion forms a catalytic fluidized bed inside the fluidized bed reactor (100) and may be discharged from the reduced iron discharge portion.

[0049] According to exemplary embodiments, the supply temperature of the reduced iron may be 600°C or higher. More specifically, the supply temperature of the reduced iron may be 700°C or higher. The supply temperature of the reduced iron may be 750°C or higher. The supply temperature of the reduced iron may be 800°C or higher. The supply temperature of the reduced iron may be 850°C or higher. Accordingly, the thermal energy required for the ammonia decomposition reaction can be supplied from the reduced iron. In addition, since the fluidized bed reactor (100) continuously supplies and discharges reduced iron, the thermal energy of the reduced iron can be utilized as energy for maintaining the ammonia reaction temperature. As a result, the energy efficiency of the ammonia decomposition process can be improved.

[0050] According to exemplary embodiments, the discharge temperature of the reduced iron may be 500°C or higher. More specifically, the discharge temperature of the reduced iron may be different from the supply temperature of the reduced iron. The discharge temperature of the reduced iron may be substantially equal to the average internal temperature of the fluidized bed reactor (100).

[0051] According to exemplary embodiments, ammonia may be supplied preheated to a temperature of 500°C or higher. More specifically, ammonia may be supplied preheated to a temperature of 500 to 700°C. In this way, by preheating ammonia, the temperature deviation within the fluidized bed reactor (100) can be minimized, and the efficiency of the ammonia decomposition reaction can be improved.

[0052] As a non-limiting example, the average temperature inside the fluidized bed reactor (100) may be 300°C or higher. More specifically, the average temperature inside the fluidized bed reactor (100) may be 400 to 900°C. If the average temperature inside the fluidized bed reactor (100) is less than 300°C, the efficiency of the ammonia decomposition reaction may decrease. In addition, the temperature difference between the part of the fluidized bed reactor (100) where the high-temperature reduced iron flows and other parts may increase, thereby deteriorating the thermal stability of the fluidized bed reactor (100).

[0053] Ammonia is placed in a fluidized bed reactor (100) for 2,500 to 10,000 h for the decomposition reaction of ammonia. -1 It can be injected at a space velocity of 2,500 h. -1 If it is less than 10,000 h, there may be a problem of having to put in too much direct exchange iron. -1 If it exceeds this, a problem may occur in which the efficiency of the ammonia decomposition reaction is excessively reduced.

[0054] Hydrogen produced in the fluidized bed reactor (100) can be captured at the top of the fluidized bed reactor (100) and provided as a reducing agent. The average temperature of the hydrogen flowing to the top of the fluidized bed reactor can be 600°C or higher. More specifically, a mixed gas of nitrogen and hydrogen can be produced by an ammonia decomposition reaction in the fluidized bed reactor (100). This mixed gas can move to the top of the fluidized bed reactor (100). As a result, hydrogen can also flow to the top of the fluidized bed reactor (100). The hydrogen flowing to the top can be recovered in an appropriate manner and discharged to the outside of the fluidized bed reactor (100). As a non-limiting example, hydrogen can be recovered from the mixed gas using any one of a membrane separation method, a pressure swing adsorption (PSA) method, a vacuum swing adsorption (VSA) method, a thermal swing adsorption (TSA) method, and a combination thereof. This allows hydrogen to be produced without producing carbon dioxide, and the process is simple and economical because no separate energy is required to separate hydrogen from ammonia.

[0055] As an example, recovered hydrogen can be supplied to steel mills and used as a reducing agent for iron ore. Furthermore, it can be appropriately utilized by those skilled in the art to control the reducing power of reducing atmosphere gases in various industrial fields.

[0056] FIG. 5 is a drawing for explaining an ammonia decomposition system (20) according to other exemplary embodiments.

[0057] Referring to FIG. 5, the ammonia decomposition system (20) may further include a fluidized bed reactor (200) connected to the fluidized bed reactor (100).

[0058] As a non-limiting example, the fluidized bed reactor (200) may be a fluidized bed reactor used to implement the so-called FINEX process. That is, the fluidized bed reactor (200) may be configured to reduce fine iron ore containing a large amount of iron oxide for the reduction of fine iron ore.

[0059] The fluidized bed reactor (200) may be configured to provide reduced iron to the fluidized bed reactor (100). More specifically, the fluidized bed reactor (200) may be configured to input and transport fine iron ore, and reduce the fine iron ore by reducing gas supplied countercurrently to the transport direction of the fine iron ore to produce reduced iron. This fluidized bed reactor (200) may include two or more stages of fluidized bed reactors that are connected in series.

[0060] By reduction in a multi-stage fluidized bed reactor (200) like this, more than 60 wt% of the iron component in the initially introduced iron ore in the form of iron oxide is reduced to metallic iron, so that so-called direct reduced iron (DRI) can be produced. Direct reduced iron contains more than 93% of the iron component, and at this time, more than 60% of the iron component is in a reduced state. Meanwhile, the remainder contains trace amounts of carbon (C), phosphorus (P), and sulfur (S). This direct reduced iron can be provided as reduced iron, which is a catalyst for the ammonia reaction, to the fluidized bed reactor (100).

[0061] As a non-limiting example, the fluidized bed reactor (200) can be operated under conditions of a pressure of 2 to 8 barg and a temperature of 650 to 900°C. Accordingly, the reduced iron provided from the fluidized bed reactor (200) can contain the thermal energy required for the ammonia decomposition reaction. Since such high-temperature reduced iron can be independently supplied, the ammonia decomposition efficiency of the ammonia decomposition system (20) can be further improved.

[0062] According to exemplary embodiments, the ammonia decomposition system (10, 20) is configured to supply ammonia to the fluidized bed reactor at a flow rate (Q, Nm 3 ) and the ratio (D / Q) of the supply of reduced iron (D, kg) is 40~300kg / Nm 3It can be in the range of . More specifically, the ratio (D / Q) of the feed rate of ammonia (Q) to the feed rate of reduced iron (D) to the fluidized bed reactor is 70 to 200 kg / Nm 3 can be controlled to be within the range of .

[0063] The above D / Q value is 40 kg / Nm 3 If it is less than 300 kg / Nm, the ammonia decomposition performance may deteriorate. In addition, excessive ammonia may be supplied compared to the supplied reduced iron, which may cause excessive iron nitride formation on the surface of the reduced iron. The larger the D / Q value, the more desirable it is, but if the value is less than 300 kg / Nm, 3 If it exceeds, the reduced iron may be supplied excessively, and the temperature of the reduced iron discharged from the fluidized bed reactor may be maintained excessively high. As a result, the overall energy efficiency of the ammonia decomposition system (10,20) may be deteriorated.

[0064] As a non-limiting example, the ammonia feed rate to the fluidized bed reactor can be controlled using conventional fluid feed rate control means. As one example, the ammonia feed rate to the fluidized bed reactor can be controlled using an on-off valve or damper configured to control the fluid feed rate according to the degree of opening and closing, and a volumetric flow meter configured to measure the volumetric flow rate of the ammonia.

[0065] As a non-limiting example, the amount of reduced iron supplied to the fluidized bed reactor can be controlled using conventional solid feed control means. As one example, the amount of reduced iron supplied to the fluidized bed reactor can be controlled using an on-off valve configured to control the amount of solid supplied according to the degree of opening and closing, and a mass flow meter configured to measure the amount of reduced iron supplied.

[0066] As a non-limiting example, the ammonia decomposition system (10,20) adjusts the ammonia supply flow rate and the reduced iron supply flow rate using the measurement results of the above-described volumetric flow meter and mass flow meter, thereby adjusting the ammonia supply flow rate (Q, Nm) to the fluidized bed reactor. 3 ) and the ratio (D / Q) of the supply of reduced iron (D, kg) can be controlled.

[0067] (Example)

[0068] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement them. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0069] (Example 1)

[0070] Ammonia was supplied to flow from the bottom to the top of the fluidized bed reactor. Reduced iron was supplied and discharged to the fluidized bed reactor so that a catalyst fluidized bed was formed above the bottom of the fluidized bed reactor. At this time, the ratio (D / Q) of the ammonia supply flow rate (Q) to the reduced iron supply amount (D) to the fluidized bed reactor was 40 to 60 kg / Nm 3 Controlled by range.

[0071] (Example 2)

[0072] The ratio (D / Q) of the ammonia supply flow rate (Q) and the reduced iron supply amount (D) to the fluidized bed reactor is 70 to 90 kg / Nm 3 The ammonia decomposition reaction was performed in the same manner as in Example 1, except that the range was controlled.

[0073] (Example 3)

[0074] The ratio (D / Q) of the ammonia supply flow rate (Q) and the reduced iron supply amount (D) to the fluidized bed reactor is 120 to 180 kg / Nm 3 The ammonia decomposition reaction was performed in the same manner as in Example 1, except that the range was controlled.

[0075] (Comparative Example 1)

[0076] The ratio (D / Q) of the ammonia supply flow rate (Q) and the reduced iron supply amount (D) to the fluidized bed reactor is 10 to 30 kg / Nm 3 The ammonia decomposition reaction was performed in the same manner as in Example 1, except that the range was controlled.

[0077] Afterwards, the ammonia decomposition rate and the content of iron nitride in the discharged reduced iron were measured and shown in Table 1 below.

[0078] The ammonia decomposition rate is evaluated by analyzing the ammonia, nitrogen, and hydrogen contents at the rear end of the fluidized bed reactor using a mass spectrometer.

[0079] The content of iron nitride is analyzed by XRD and ICP AES after recovering reduced iron after ammonia decomposition.

[0080] Classification Ammonia decomposition rate (%) Iron nitride content (weight %) Example 190~98 1~2 Example 295~98 0.5~1 Example 395~98 0~0.5 Comparative example 165~75 3~5

[0081] Referring to Table 1, in the case of Comparative Example 1, the ratio (D / Q) of the supply flow rate of ammonia (Q) to the supply amount of reduced iron (D) to the fluidized bed reactor was outside the range suggested by the present invention, so the ammonia decomposition rate was inferior and the content of iron nitride was high. In contrast, in Examples 1 to 3, the ratio (D / Q) of the supply flow rate of ammonia (Q) to the supply amount of reduced iron (D) to the fluidized bed reactor satisfied the range suggested by the present invention, so the ammonia decomposition rate was very high and the formation of iron nitride could be minimized.

[0082] The present invention has been described in more detail through drawings and examples. However, the configurations described in the drawings or examples described in this specification are merely embodiments of the present invention and do not represent all of the technical ideas of the present invention. Therefore, it should be understood that various equivalents and modified examples may exist as of the time of this application.

[0083] [Explanation of symbols]

[0084] 10, 20: Ammonia decomposition system

[0085] 100: Fluidized bed reactor

[0086] 200: Fluidized bed reactor

Claims

1. A fluidized bed reactor configured to receive ammonia and reduced iron, discharge the reduced iron downward to form a catalyst fluidized bed, and contact the ammonia with the catalyst fluidized bed to produce hydrogen from the ammonia. The ratio (D / Q) of the supply flow rate (Q) of ammonia to the fluidized bed reactor and the supply amount (D) of the reduced iron is 40 to 300 kg / Nm 3 Ammonia decomposition system in the range of .

2. In paragraph 1, The ratio (D / Q) of the supply flow rate (Q) of ammonia to the fluidized bed reactor and the supply amount (D) of the reduced iron is 70 to 200 kg / Nm 3 An ammonia decomposition system controlled to be within the range of .

3. In paragraph 1, The above ammonia decomposition system, Further comprising a fluidized reduction reactor connected to the fluidized bed reactor and configured to provide the reduced iron to the fluidized bed reactor; In the above fluid reduction, An ammonia decomposition system configured to input and transport fine iron ore, and to reduce the fine iron ore by reducing gas supplied countercurrently to the transport direction of the fine iron ore to produce reduced iron.

4. In paragraph 1, An ammonia decomposition system in which the supply temperature of the above reduced iron is 600℃ or higher.

5. In paragraph 1, An ammonia decomposition system in which the discharge temperature of the above reduced iron is 500℃ or higher.

6. In paragraph 1, An ammonia decomposition system in which the average temperature of the hydrogen flowing to the upper portion of the fluidized bed reactor is 600°C or higher.

7. In paragraph 1, Iron nitride (Fe) contained in the reduced iron emitted above x N y) content, in weight %, less than 3% (including 0%) of an ammonia decomposition system.

8. In paragraph 7, Iron nitride (Fe) contained in the reduced iron emitted above x N y ) content is, in weight %, 1% or less (including 0%) of an ammonia decomposition system.

9. In paragraph 1, The above ammonia decomposition system is supplied by preheating the ammonia to a temperature of 500℃ or higher.

10. In paragraph 1, The above ammonia is 2,500 h -1 Within 10,000 h -1 An ammonia decomposition system which is supplied at a space velocity of .

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