Ammonia production systems, ammonia synthesis reactors, ammonia recovery units, and heat recovery units

Abstract

Provided are an ammonia production system, an ammonia synthesis reactor, an ammonia recovery vessel, and a heat recovery vessel that have good production efficiency and can tolerate fluctuations in the supply quantity of raw material gas. The ammonia production system comprises an ammonia synthesis reactor that subjects a raw material gas to a synthesis reaction to generate ammonia, an ammonia recovery vessel that recovers the ammonia from a mixed gas containing the ammonia generated by the ammonia synthesis reactor, and a heat recovery vessel that recovers the heat energy of the ammonia synthesis reactor by generating thermoelectric power by the temperature difference between the heat of the ammonia synthesis reaction from the ammonia synthesis reactor and the coolness of the post-recovery gas discharged from the ammonia recovery vessel.

Description

Technical Field

[0001] The present disclosure relates to an ammonia production system for synthesizing ammonia, an ammonia synthesis reactor, an ammonia recovery unit, and a heat recovery unit.

Background Art

[0002] Currently, ammonia is expected to see an increase in future demand as a hydrogen carrier and as a clean fuel that does not produce carbon dioxide when burned. Therefore, there is a need to efficiently produce ammonia.

[0003] When using hydrogen derived from renewable energy as a raw material for ammonia synthesis, considering the dispersed and local distribution of renewable energy, the ammonia production facility will be a small-scale, decentralized production facility rather than a conventional large-scale production facility. When the production facility is miniaturized, the exposed area increases and the heat release amount increases, resulting in a generally known efficiency decrease. It is important to reduce this efficiency decrease.

[0004] Patent Document 1 discloses a microchannel process device that can efficiently perform heat exchange between multiple processes and is applicable to ammonia synthesis reactions.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In recent years, ammonia has been produced using hydrogen derived from renewable energy such as sunlight, wind power, wave power, and geothermal energy. Ammonia produced by such a manufacturing method that does not emit carbon dioxide is called green ammonia or the like.

[0007] Hydrogen derived from renewable energy sources has the property of having a variable supply. However, conventional ammonia production processes do not take into account fluctuations in the supply of raw material gases, and when the supply fluctuates, production efficiency may decrease.

[0008] The purpose of this disclosure is to provide an ammonia production system, an ammonia synthesis reactor, an ammonia recovery unit, and a heat recovery unit that offer good production efficiency when applied not only to conventional ammonia production facilities but also to small-scale distributed facilities, and that can tolerate fluctuations in the supply of raw material gas. [Means for solving the problem]

[0009] An ammonia production system according to one aspect of the present disclosure comprises: an ammonia synthesis reactor that generates ammonia by synthesizing raw material gases; an ammonia recovery unit that recovers ammonia from a mixed gas containing the ammonia generated by the ammonia synthesis reactor; and a heat recovery unit that recovers the thermal energy of the ammonia synthesis reactor by generating thermoelectric power from the temperature difference between the heat of the ammonia synthesis reaction in the ammonia synthesis reactor and the cold heat of the recovered gas discharged from the ammonia recovery unit.

[0010] An ammonia synthesis reactor according to one aspect of this disclosure includes a case having a supply port for supplying ammonia raw material gas, Arranged inside the aforementioned case It comprises a heat exchange section having a tubular structure, The tubular structure has a first end which is an opening provided inside the case, a second end opposite to the first end, a first region located on the first end side where a catalyst layer is formed with a catalyst that promotes the ammonia synthesis reaction, and a second region located on the second end side where the catalyst layer is not formed, and the case and the tubular structure are, From the aforementioned supply port The supplied raw material gas , inside the case and the outer surface of the tubular structure arranged Passing through the catalyst layer End of the first section flow The first channel and ,before The mixed gas containing ammonia produced by the synthesis reaction Flowing in from the aforementioned first end, Inside the tubular structure Through the first and second regions to the second end The second flow channel, of composition death The above heat exchange section This causes heat exchange to occur between the raw material gas flowing through the first channel and the mixed gas flowing through the second channel.

[0011] An ammonia recovery device according to one aspect of the present disclosure is an ammonia recovery device for recovering ammonia from a mixed gas containing ammonia, comprising: a case; a heat exchange section having a plurality of tubular structures that allow the mixed gas to flow from outside the case into the inside of the case; and a cooler that provides cooling to the first end of the tubular structure located inside the case, wherein the case has a recovery port for recovering the ammonia that has been cooled and liquefied by the cooler, and is configured as a third flow path through which the mixed gas flows from outside the case to the first end of the tubular structure located inside the case, and a fourth flow path through which the recovered gas flows from the first end to an outlet for discharging the recovered gas after ammonia recovery, wherein the tubular structure causes heat exchange to occur between the mixed gas flowing through the third flow path and the recovered gas flowing through the fourth flow path.

[0012] A heat recovery device according to one aspect of the present disclosure includes a heat conduction unit that is in contact with a part of an ammonia synthesis reactor that synthesizes raw material gases to produce ammonia and transmits the heat of the ammonia synthesis reaction, and a thermoelectric element that generates electricity from the temperature difference between the cold heat of the recovered gas discharged from an ammonia recovery unit that recovers ammonia from a mixed gas containing ammonia produced by the ammonia synthesis reactor and the heat of the synthesis reaction transmitted by the heat conduction unit. [Effects of the Invention]

[0013] According to this disclosure, the manufacturing efficiency is high and fluctuations in the supply of raw material gas can be tolerated. [Brief explanation of the drawing]

[0014] [Figure 1] A schematic diagram showing the overall configuration of an ammonia production system according to an embodiment of this disclosure. [Figure 2] Perspective view showing the structure of an ammonia synthesis reactor. [Figure 3] Cross-sectional view of an ammonia synthesis reactor [Figure 4] A diagram showing the equilibrium curve of ammonia. [Figure 5] Figure illustrating the structure of a conventional multi-stage synthesis reactor [Figure 6] Figure for explaining temperature control in a conventional multi-stage synthesis reactor [Figure 7] Figure showing the structure of an ammonia recovery unit [Figure 8] Cross-sectional view of an ammonia recovery unit [Figure 9] Schematic diagram showing the structure of a heat recovery unit

Mode for Carrying Out the Invention

[0015] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. However, detailed descriptions that are more than necessary, for example, detailed descriptions of well-known matters and redundant descriptions of substantially the same configurations may be omitted in some cases.

[0016] <Overall Configuration> FIG. 1 is a schematic diagram showing the overall configuration of an ammonia production system 100 according to an embodiment of the present disclosure.

[0017] As shown in FIG. 1, the ammonia production system 100 includes an ammonia synthesis reactor 1, an ammonia recovery unit 2, and a heat recovery unit 3.

[0018] The ammonia synthesis reactor 1 generates a synthesis reaction of ammonia based on hydrogen gas and nitrogen gas, which are raw material gases, and generates ammonia gas. In this embodiment, it is assumed that hydrogen gas is generated using renewable energy. That is, it is assumed in advance that the supply amount of hydrogen gas may fluctuate greatly temporarily.

[0019] The ammonia synthesis reactor 1 sends out a mixed gas containing the generated ammonia gas and unreacted hydrogen gas and nitrogen gas to the ammonia recovery unit 2.

[0020] Ammonia recovery unit 2 liquefies and recovers the ammonia component contained in the mixed gas by cryogenic separation. Ammonia recovery unit 2 discharges the remaining gas (hereinafter referred to as post-recovery gas) from which the ammonia component has been recovered.

[0021] The heat recovery unit 3 generates thermoelectric power using the temperature difference between the heat obtained from the ammonia synthesis reaction in the ammonia synthesis reactor 1 and the cold heat of the recovered gas discharged from the ammonia recovery unit 2, recovering thermal energy as electricity. The electricity generated by the heat recovery unit 3 is effectively used in each component of the ammonia production system 100, or in hydrogen production equipment or nitrogen production equipment that produce the raw material gas.

[0022] (Ammonia synthesis reactor 1) Figure 2 is a perspective view showing the structure of ammonia synthesis reactor 1. Figure 3 is a cross-sectional view of ammonia synthesis reactor 1.

[0023] As shown in Figure 2 or Figure 3, the ammonia synthesis reactor 1 comprises a case 11, a heat exchange section 12, and a heater 13. The heat exchange section 12 has a plurality of tubular structures 121. The outside of the case 11 is covered with insulating material to minimize heat loss.

[0024] Case 11 is a case in which a raw material gas is introduced into the interior and an ammonia synthesis reaction is carried out using a catalyst. In the example shown in Figure 2, Case 11 has a cylindrical shape and two bottom surfaces. In Figure 2, the outer shape of Case 11 is shown with a dashed line so that the inside of Case 11 can be seen.

[0025] A tubular structure 121 of the heat exchange section 12 penetrates one of the bottom surfaces. In the following description, of the two bottom surfaces of case 11, the one through which the tubular structure 121 penetrates will be referred to as the upper surface 111. The other bottom surface will be referred to as the lower surface 112. The upper surface 111 and the lower surface 112 face each other. In this embodiment, as shown in Figures 2 and 3, the ammonia synthesis reactor 1 is installed with the upper surface 111 of case 11 facing upwards and the lower surface 112 facing downwards. However, the installation orientation of the ammonia synthesis reactor in this disclosure is not limited to the examples shown in Figures 2 and 3, and it may be installed in other orientations.

[0026] The upper surface 111 is provided with a supply port 113 for supplying raw material gas. The lower surface 112 is provided with a heater 13. The heater 13 is embedded, for example, inside the lower surface 112. Furthermore, the outer surface of the lower surface 112 is in contact with the heat conduction section 31 of the heat recovery unit 3, which will be described later.

[0027] While it is preferable for case 11 to be cylindrical in shape to withstand the high pressure inside, various shapes can be used as long as they can withstand the high pressure inside.

[0028] The heat exchange section 12 is configured to perform heat exchange between the raw material gas and the mixed gas containing the generated ammonia. The multiple tubular structures 121 of the heat exchange section 12 are made of a material with high thermal conductivity, such as SUS (Stainless Used Steel). The number of tubular structures 121 is, for example, about 30 to 50. The number of tubular structures 121 and the diameter of each are not limited, but the diameter and number of tubular structures 121 may be adjusted so that the total cross-sectional area of ​​the tubular structures 121 is approximately equal to the area of ​​the parts of the case 11 excluding the tubular structures 121 in the cross-section of the ammonia synthesis reactor 1 in a plane parallel to the upper surface 111 or the lower surface 112.

[0029] In the examples shown in Figures 2 and 3, the tubular structure 121 is shown to have a cylindrical shape, but is not limited to this. The tubular structure 121 may be formed to have, for example, multiple folds in order to ensure a larger surface area in order to improve the efficiency of heat exchange.

[0030] The thickness of the tubular structure 121 is preferably formed to be, for example, 1 mm or less. This is because a thinner structure is preferable from the viewpoint of thermal conductivity.

[0031] Of the upper and lower ends of the tubular structure 121, the lower end, the first end 123, faces the upper surface of the lower surface 112 of the case 11 and is positioned away from the lower surface 112. The distance at which the first end 123 is separated from the lower surface 122 can be set to an appropriate distance based on, for example, the amount of catalyst described later. On the other hand, the upper end, the second end 124, is located outside the case 11 and is connected to the piping leading to the ammonia recovery unit 2.

[0032] As shown in Figure 3, a catalyst that promotes the ammonia synthesis reaction is placed between the first end 123 and the bottom surface 112. Note that the catalyst is not shown in Figure 2. In addition, the inside of the tubular structure 121 above the first end 123 is also filled with catalyst. Inside the tubular structure 121, the catalyst is filled from the first end 123 up to a predetermined position (height). That is, the catalyst is filled inside the tubular structure 121 and also spreads out from the first end 123 onto the bottom surface 112. As an example of a catalyst, a transition metal catalyst is used in the part that is close to the bottom surface 112 and is relatively hot, and a ruthenium catalyst is used in the part inside the tubular structure 121 that is away from the bottom surface 112 and is relatively cold.

[0033] To prevent the catalyst from unintentionally spreading inside the case 11, a catalyst stopper, such as a protrusion, may be installed at a predetermined position above the bottom surface 112. This stopper is configured to allow gas to pass through but not the catalyst, and can be fixed, for example, to the inner wall surface of the case 11 or the outer wall surface of the tubular structure 121.

[0034] Furthermore, the height of the catalyst inside the tubular structure 121 is set to a sufficient height, for example, based on experiments conducted beforehand, so that the temperature at the upper end of the catalyst reaches approximately 300°C.

[0035] With this configuration, the ammonia synthesis reaction based on the raw material gas proceeds in the ammonia synthesis reactor 1 as follows.

[0036] The raw material gas flowing in from the supply port 113 flows downward along the outer surface of the tubular structure 121 to the first end. The flow path from the supply port 113 to the first end 123 is referred to as the first flow path. The raw material gas supplied from the supply port 113 is assumed to be at approximately room temperature (around 20°C). In this disclosure, the pressure inside the case 11 is not particularly limited, but for example, since hydrogen gas, which is part of the raw material gas, becomes high pressure (8 MPa) during manufacturing, the pressure inside the case 11 should be set to approximately 10 MPa, which is close to this pressure.

[0037] As the raw material gas travels along the first flow path, it exchanges heat with the mixed gas inside the tubular structure 121 via the surface of the tubular structure 121, gradually becoming hotter. When the raw material gas reaches the vicinity of the first end 123, it comes into contact with the catalyst, and the ammonia synthesis reaction is promoted. Since the ammonia synthesis reaction is an exothermic reaction, the temperature rises near the first end 123 where the synthesis reaction is active.

[0038] The raw material gas that reaches the first end 123, and the mixed gas containing ammonia gas generated from the raw material gas, flow upward inside the tubular structure 121. The flow path through which the mixed gas flows from the first end 123 inside the tubular structure 121 is designated as the second flow path. As the mixed gas flows through the second flow path, heat is transferred to the raw material gas flowing through the first flow path via the tubular structure 121. As a result, the temperature of the mixed gas gradually decreases as it moves through the second flow path. In this way, the heat exchange section 12 facilitates heat exchange between the raw material gas flowing through the first flow path and the mixed gas flowing through the second flow path. Here, the flow of the raw material gas in the first flow path and the flow of the mixed gas in the second flow path are opposing flows, enabling efficient heat exchange between the raw material gas and the mixed gas.

[0039] At the first end portion 123, which is the return section from the first flow path to the second flow path, heat exchange by the heat exchange section 12 is most advanced, and therefore the ambient temperature around the first end portion 123 is the highest in the case 11. For example, the catalyst temperature around the first end portion 123 is expected to be, for example, 600°C. Also, since the catalyst is in contact with the bottom surface 112, the bottom surface 112 itself is expected to reach a high temperature of about 600°C.

[0040] The temperature of the mixed gas inside the tubular structure 121 decreases as it moves through the second flow path, and it is expected that the temperature near the terminal end of the catalyst inside the tubular structure 121 will be around 300°C. Furthermore, when the mixed gas moves through the second flow path and is discharged to the outside from the second end 124, which is the upper end of the tubular structure 121, the temperature will drop to, for example, around 100°C.

[0041] Thus, around the first end 123, which is the lower end of the tubular structure 121, the catalyst temperature reaches a high temperature of 600°C. On the other hand, at the terminal end of the catalyst inside the tubular structure 121, the catalyst temperature is expected to drop to around 300°C. The temperature inside the tubular structure 121 changes continuously from 600°C to 300°C as you move upward from the first end 123 side. Figure 4 shows the equilibrium curve of the ammonia synthesis reaction. The arrows in Figure 4 show the relationship between the temperature change from 600°C to 400°C and the concentration change along the equilibrium concentration curve, as an example of temperature and concentration changes in the ammonia synthesis reaction in the ammonia synthesis reactor 1. In this way, the ammonia synthesis reactor 1 can produce ammonia along the equilibrium curve of the ammonia synthesis reaction.

[0042] The raw material gas supplied into case 11 comes into contact with the 600°C catalyst at the first end 123 while its temperature rises due to heat exchange. As shown in Figure 4, the equilibrium concentration is relatively low at the high temperature of 600°C, so an equilibrium state is easily achieved.

[0043] Furthermore, at a high temperature of 600°C, the equilibrium concentration is low, which suppresses the synthesis reaction and slows down the reaction rate. This naturally prevents the synthesis reaction from proceeding too far around the first end 123, causing localized temperatures to become excessively high (significantly exceeding 600°C).

[0044] As the mixed gas rises inside the tubular structure 121, the temperature decreases due to heat exchange, and near the upper end of the catalyst, it drops to about 300°C, allowing for high-concentration reactions to occur there.

[0045] Thus, in the ammonia synthesis reactor 1 according to this embodiment, by using the first end 123 of the tubular structure 121 as a folded portion, the flow of the raw material gas in the first channel outside the tubular structure 121 and the flow of the mixed gas in the second channel inside the tubular structure 121 are made to face each other, thereby enabling efficient heat exchange between the raw material gas and the mixed gas. With this configuration, the temperature around the first end 123 can be made the highest inside the reactor, and the temperature can be continuously decreased as one moves upward.

[0046] Here, even if the supply of hydrogen, which is part of the raw material gas, temporarily decreases significantly, heat is transferred from the mixed gas inside the tubular structure 121 to the raw material gas inside the case 11, so no significant change in temperature occurs near the first end 123.

[0047] In this way, the temperature in various parts of the ammonia synthesis reactor 1 is naturally suppressed to prevent large fluctuations. As a result, even if the supply amount of hydrogen, which is part of the raw material gas, changes significantly temporarily, the ammonia synthesis reaction can be stably continued.

[0048] In the ammonia synthesis reactor 1, the following operations are performed when the ammonia synthesis reaction is started. Raw material gas is supplied into the case 11 from the supply port 113, and the heater 13 provided on the bottom surface 112 is activated to raise the catalyst temperature around the first end 123. As the ammonia synthesis reaction becomes more active, the temperature around the first end 123 rises. The temperature inside the tubular structure 121 also rises, and heat begins to be transferred to the raw material gas outside the tubular structure 121. This further increases the temperature around the first end 123. As a result, the reactor can autonomously reach a steady state in which the temperature around the first end 123 is between 600°C and 650°C, and the temperature near the upper end of the catalyst inside the tubular structure 121 is between 250°C and 300°C. Thus, the heater 13 is used only at the start of operation, and there is no need to supply new energy from the heater 13 after the start of the synthesis reaction. Therefore, the ammonia synthesis reactor 1 of this disclosure can be operated in an energy-saving and efficient manner.

[0049] For example, if it is predicted that the supply of hydrogen will be cut off in the medium to long term due to weather forecasts, the operation of the ammonia synthesis reactor 1 may be stopped. Even if ammonia production is temporarily stopped, once the supply of raw material gas is resumed, operation can be easily restarted by simply supplying the raw material gas into the case 11 and activating the heater 13, as described above.

[0050] [Comparison with conventional technology] The advantages of the ammonia synthesis reactor 1 according to this embodiment will be explained by comparing it with a conventional multi-stage synthesis reactor.

[0051] Figure 5 illustrates the structure of a conventional multi-stage ammonia synthesis reactor 200. The multi-stage ammonia synthesis reactor 200 shown in Figure 5 is equipped with three reactors 201, 202, and 203, each filled with a catalyst. Each reactor 201, 202, and 203 also has a temperature control function, and the temperature of the inlet (hereinafter referred to as the inlet temperature) and the outlet (hereinafter referred to as the outlet temperature) of the catalyst are controlled to be constant. Note that the inlet temperature and outlet temperature may be different.

[0052] Figure 6 shows the relationship between the temperature control of the multi-stage ammonia synthesis reactor 200 shown in Figure 5 and the equilibrium curve of the ammonia synthesis reaction. In Figure 6, the inlet temperature of the upstream reactor 201 is shown as T1 and the outlet temperature as T2, the inlet temperature of reactor 202 as T3 and the outlet temperature as T4, and the inlet temperature of the downstream reactor 203 as T5 and the outlet temperature as T6.

[0053] As shown in Figure 6, in the conventional multi-stage ammonia synthesis reactor 200 shown in Figure 5, equilibrium at the target temperature (300°C to 400°C) is achieved at the outlet temperature of the downstream reactor while controlling the inlet and outlet temperatures of each reactor 201, 202, and 203 to be constant.

[0054] As shown in Figure 5, in the conventional multi-stage ammonia synthesis reactor 200, the inlet and outlet temperatures must be controlled to a constant level. In this case, when the supply of hydrogen, which is part of the raw material gas, increases or decreases, localized high temperatures may occur, or the expected amount of ammonia may not be produced. To cope with fluctuations in the hydrogen supply, the operator of the multi-stage ammonia synthesis reactor 200 must perform skilled temperature control, resulting in high control costs (labor costs, effort).

[0055] The ammonia synthesis reactor 1 according to this embodiment has the advantage of eliminating the need for the operator to perform temperature control, compared to the multi-stage ammonia synthesis reactor 200 shown in Figure 5. Furthermore, since the temperature can be continuously lowered from the first end 123 of the tubular structure 121 to near the upper end of the catalyst inside the tubular structure 121, the rate of the ammonia synthesis reaction can be increased along the equilibrium curve. As a result, ammonia can be produced more efficiently in the relatively low-temperature portion than in the conventional multi-stage ammonia synthesis reactor 200 shown in Figure 5.

[0056] (Ammonia recovery unit 2) Next, the ammonia recovery unit 2 will be described. The ammonia recovery unit 2 liquefies and separates ammonia by cryogenic separation by cooling the mixed gas discharged from the ammonia synthesis reactor 1 described above. Figure 7 is a diagram showing the structure of the ammonia recovery unit 2. Figure 8 is a cross-sectional view of the ammonia recovery unit 2.

[0057] As shown in Figures 7 and 8, the ammonia recovery unit 2 comprises a case 21, a heat exchange unit 22, and a cooler 23. The outside of the case 21 is covered with an insulating material. The heat exchange unit 22 has a plurality of tubular structures 221.

[0058] Case 21 is the case into which a mixed gas containing ammonia is introduced from ammonia synthesis reactor 1. In the example shown in Figure 7, case 21 has a cylindrical shape and two bottom surfaces. Note that in Figure 7, the outer shape of case 11 is shown with a dashed line so that the inside of case 11 can be seen.

[0059] A tubular structure 221 of the heat exchange section 22 penetrates one of the bottom surfaces. In the following description, of the two bottom surfaces of the case 21, the one through which the tubular structure 221 penetrates will be referred to as the upper surface 211. The other bottom surface will be referred to as the lower surface 212. The upper surface 211 and the lower surface 212 face each other. In this embodiment, the ammonia recovery unit 2 is installed so that the upper surface 211 of the case 21 is on the top and the lower surface 212 is on the bottom.

[0060] The upper surface 211 is provided with an outlet 213 for discharging the remaining gas (hereinafter referred to as "recovered gas") from which the ammonia component has been recovered from the mixed gas. The lower surface 212 is provided with a recovery port 214 for recovering liquefied ammonia. A cooler 23 is also provided on the lower surface 212. In the example shown in Figure 8, multiple coolers 23 are provided, but only one cooler may be provided.

[0061] While the case 21 is preferably cylindrical in shape to withstand high pressure, this disclosure is not limited to this, and various shapes may be adopted.

[0062] The heat exchange section 22 is configured to perform heat exchange between the mixed gas and the recovered gas. The tubular structure 221 is made of a material with high thermal conductivity, such as SUS. The number of tubular structures 221 is, for example, about 30 to 50. The number and diameter of the tubular structures 221 are not limited, but for example, in the cross-section of the ammonia recoverer 2 in a plane perpendicular to the long axis of the tubular structure 121, the total cross-sectional area of ​​the tubular structures 221 is approximately equal to the area of ​​the part of the case 21 excluding the tubular structures 221.

[0063] Of the upper and lower ends of the tubular structure 221, the lower end, the first end 223, faces the upper surface of the lower surface 212 of the case 21 and is positioned slightly away from the lower surface. On the other hand, the upper end, the second end 224, is located outside the case 21 and is connected to the piping that passes through the heat recovery unit 3.

[0064] Thus, the ammonia recovery unit 2 has the same configuration as the ammonia synthesis reactor 1 shown in Figures 2 and 3, except that it does not have a catalyst inside and that a cooler 23 is located on the bottom surface instead of a heater 13.

[0065] With this configuration, the recovery of ammonia components from the mixed gas in the ammonia recovery unit proceeds as follows.

[0066] The mixed gas discharged from the ammonia synthesis reactor 1 flows into the ammonia recovery unit 2 from the second end 224, which is the upper end of the tubular structure 221. The temperature of the mixed gas flowing into the ammonia recovery unit 2 is assumed to be, for example, around room temperature. The mixed gas flowing in from the second end 224 flows downward through the inside of the tubular structure 221. The flow path through which the raw material gas flows from the second end 224 to the first end 223 is designated as the third flow path. During this process, heat exchange occurs with the recovered gas inside the case 21 (outside the tubular structure 221) via the surface of the tubular structure 221, and the temperature decreases as the gas moves along the third flow path.

[0067] The temperature around the first end 223, which is the lower end of the tubular structure 221, is cooled to below the condensation point of ammonia (for example, around -60°C to -70°C) by a cooler 23 provided on the lower surface 212. As a result, the ammonia component contained in the mixed gas condenses. The condensed and liquefied ammonia is recovered from a recovery port 214 provided on the lower surface 212.

[0068] After the ammonia component is recovered, the recovered gas, which includes hydrogen gas, nitrogen gas, and unrecovered ammonia gas, flows upward inside the case 21 along the outer surface of the tubular structure 221. The flow path through which the recovered gas flows from the first end 223 to the outlet 213 inside the case 21 is designated as the fourth flow path. During this process, the recovered gas exchanges heat with the mixed gas inside the tubular structure 221, and its temperature increases as it travels along the fourth flow path. By the time it is discharged from the outlet 213 on the top surface 211, its temperature will be close to room temperature (approximately 0-20°C).

[0069] Thus, in the ammonia recovery unit 2 according to this embodiment, by making the turning point of the heat exchange process of the heat exchange unit 22 the first end portion 223, which is the lower end of the tubular structure 221, the heat exchange efficiency inside and outside the tubular structure 221 can be maximized. As a result, the cooling energy required for the chiller 23 to maintain the temperature around the first end portion 223 below the condensation point of ammonia can be minimized. This makes it possible to improve the overall ammonia production efficiency of the ammonia production system 100.

[0070] While the pressure inside the ammonia recovery unit 2 is not particularly limited, maintaining a relatively high pressure can suppress the ammonia concentration in the recovered gas, thus enabling relatively low-energy operation.

[0071] (Heat recovery unit 3) Next, we will describe the heat recovery unit 3 shown in Figure 1. Figure 9 is a schematic diagram showing the structure of the heat recovery unit 3.

[0072] As shown in Figure 9, the heat recovery unit 3 includes a heat conduction unit 31, a gas pipe 32, a water pipe 33, a thermoelectric element 34, a state transition unit 35, a heat exchanger 36, and an insulating material 37.

[0073] The heat conduction section 31 is in contact with a part of the ammonia synthesis reactor 1, for example, the bottom surface 112. Not only is it in contact, but as shown in Figure 9, the heat conduction section 31 may also penetrate into the interior of the bottom surface 112, which has a predetermined thickness. As mentioned above, it is assumed that the bottom surface 112 of the ammonia synthesis reactor 1 will reach a high temperature of 600°C or higher. The heat conduction section 31 is made of a metal with high thermal conductivity and transfers the heat from the bottom surface 112 to the thermoelectric element 34. In the example shown in Figure 9, four heat conduction sections 31 are provided, but the number of heat conduction sections 31 is not limited to this. The area around the heat conduction section 31 is covered with an insulating material 37. This allows the heat generated by the ammonia synthesis reactor 1 to be efficiently transferred to the thermoelectric element 34.

[0074] The gas piping 32 is connected to the outlet 213 of the ammonia recovery unit 2, and recovered gas at a temperature of approximately 0°C to 20°C flows through it. A portion of the gas piping 32 is in contact with the thermoelectric element 34. As a result, the coldness of the recovered gas flowing through the gas piping 32 is transferred to the thermoelectric element 34, and at least a portion of the heat transferred from the ammonia synthesis reactor 1 to the thermoelectric element 34 is transferred to the recovered gas flowing through the gas piping 32 via the thermoelectric element 34.

[0075] Furthermore, another portion of the gas piping 32 is in contact with the heat exchanger 36. The heat exchanger 36 performs heat exchange between the gas piping 32 and the water piping 33. Any known method can be appropriately adopted for the heat exchange in the heat exchanger 36.

[0076] The water pipe 33 is connected to a hydrogen production device that supplies hydrogen to the ammonia synthesis reactor 1. The hydrogen production device produces hydrogen, for example, by electrolyzing water using renewable electricity. The water pipe 33 is in contact with the heat exchanger 36. The temperature of the water flowing inside the water pipe 33 rises due to the heat transferred by the heat exchanger 36. Generally, in a hydrogen production device that produces hydrogen by electrolyzing water, a higher water temperature improves the hydrogen production efficiency. Therefore, by recovering heat from the ammonia synthesis reactor 1 through the water pipe 33, the overall energy efficiency of the ammonia production system 100 can be improved.

[0077] The thermoelectric element 34 is an element that generates electricity from the temperature difference between the heat (600°C) from the lower surface 112 of the ammonia synthesis reactor 1 transmitted by the heat conduction section 31 and the cold temperature (0°C to 20°C) of the recovered gas inside the gas piping 32. When the temperature difference between the high-temperature side and the low-temperature side is as large as 600°C, thermal energy can be recovered with an efficiency of, for example, around 10%. Furthermore, as described above, the thermoelectric element 34 transmits the heat transmitted from the ammonia synthesis reactor 1 to the gas piping 32.

[0078] The state transition unit 35 transitions the state of the heat conduction unit 31 based on the internal temperature of the ammonia synthesis reactor 1. Specifically, the state transition unit 35 has a moving mechanism such as a motor and rails, and when the internal temperature of the ammonia synthesis reactor 1 is less than 600°C, the heat conduction unit 31 is moved away from the ammonia synthesis reactor 1 (detached state), and when the internal temperature becomes 600°C or higher, the heat conduction unit 31 is moved into contact with the ammonia synthesis reactor 1 (contact state). The internal temperature of the ammonia synthesis reactor 1 can be obtained, for example, by a sensor provided around the first end 123 of the ammonia synthesis reactor 1.

[0079] The heat exchanger 36 is installed between the gas piping 32 and the water piping 33. The heat exchanger 36 transfers the heat transferred to the recovered gas flowing through the gas piping 32 (heat transferred from the ammonia synthesis reactor 1 via the thermoelectric element 34) to the water flowing through the water piping 33.

[0080] With this configuration, if the ammonia synthesis reactor 1 reaches a temperature exceeding 600°C, the heat conduction section 31 can remove heat from the ammonia synthesis reactor 1. This prevents the catalyst in the ammonia synthesis reactor 1 from becoming deactivated due to excessive heat. Furthermore, if the internal temperature of the ammonia synthesis reactor 1 is below 600°C, the heat conduction section 31 is deactivated and does not remove heat, thereby preventing the internal temperature of the ammonia synthesis reactor 1 from rising.

[0081] The electricity generated by the thermoelectric element 34 is effectively utilized in various parts of the ammonia production system 100. For example, the electricity from the thermoelectric element 34 may be used to operate the chiller 23 of the ammonia recovery unit 2. Alternatively, the electricity from the thermoelectric element 34 may be supplied to a hydrogen production device and used for the electrolysis of water. Furthermore, the electricity from the thermoelectric element 34 may be supplied to a nitrogen production device that supplies nitrogen to the ammonia synthesis reactor 1 and used for nitrogen production.

[0082] Furthermore, the heat from the ammonia synthesis reactor 1 is transferred to the water flowing through the water pipe 33 via the thermoelectric element 34, gas pipe 32, and heat exchanger 36. This increases the temperature of the water supplied to the hydrogen production apparatus, thereby improving the hydrogen production efficiency.

[0083] <Mechanism of action, effect> As described above, the ammonia production system 100 according to the embodiment of this disclosure includes a heat recovery unit 3 that recovers the thermal energy of the ammonia synthesis reactor by generating thermoelectric power from the temperature difference between the heat of the ammonia synthesis reaction from the ammonia synthesis reactor 1 and the cold heat of the recovered gas discharged from the ammonia recovery unit 2. This allows for efficient recovery of thermal energy within the ammonia production system 100, thereby achieving overall energy savings.

[0084] The ammonia synthesis reactor 1 has a heat exchange section 12 that facilitates heat exchange between a first channel and a second channel facing each other. The catalyst temperature around the first end 123 of the tubular structure 121, which corresponds to the folded section, can be made the highest in the case 11, and as the catalyst proceeds through the second channel in the tubular structure 121, the temperature can be continuously decreased while maintaining the equilibrium state of the ammonia synthesis reaction. This enables energy-saving and efficient ammonia production. Furthermore, with this structure, even if the supply amount of hydrogen, which is part of the raw material gas, fluctuates, the reaction proceeds in a direction that maintains the equilibrium state, thus naturally suppressing temperature changes inside the case 11. This reduces the control costs of the ammonia synthesis reactor 1.

[0085] The ammonia recovery unit 2, like the ammonia synthesis reactor 1, has a heat exchange section 22 that allows heat exchange to occur between the opposing third and fourth flow channels. Therefore, the temperature around the first end 223 of the tubular structure 221, which corresponds to the folded section, can be efficiently lowered, and ammonia contained in the mixed gas can be efficiently recovered.

[0086] The heat recovery unit 3 has a thermoelectric element 34 that generates thermoelectric power from the temperature difference between the heat from the ammonia synthesis reactor 1 and the recovered gas discharged by the ammonia recovery unit 2. This allows for the effective recovery of thermal energy within the ammonia production system 100. Furthermore, it has a state transition unit 35 that moves the heat conduction unit 31 to avoid heat recovery when the operating temperature of the ammonia synthesis reactor 1 is relatively low. This allows for energy recovery without reducing the efficiency of the ammonia synthesis reactor 1. [Industrial applicability]

[0087] This disclosure is useful for application to ammonia synthesis plants, and is also useful for all chemical processes in which the target reaction is exothermic and the product liquid is recovered, similar to the ammonia synthesis reaction.

[0088] All disclosures in the specification, drawings, and abstract contained in the Japanese application 2022-194928, filed on December 6, 2022, are incorporated herein by reference. [Explanation of Symbols]

[0089] 100 Ammonia Production System 1. Ammonia synthesis reactor 2. Ammonia recovery unit 3. Heat recovery unit 11 cases 111 Top surface 112 Bottom surface 113 Supply port 12 Heat exchange section 121 Tubular structure 123 First end 124 Second end 13. Heating device 200 Multistage Ammonia Synthesis Reactor 21 cases 211 Top surface 212 Bottom surface 213 Outlet 214 Collection port 22 Heat exchange section 221 Tubular structure 223 First end 224 Second end 23 Cooler 31 Heat conduction section 32 Gas piping 33 Water Piping 34 Thermoelectric elements 35 State transition section

Claims

1. An ammonia synthesis reactor that produces ammonia by synthesizing raw material gases, An ammonia recovery unit recovers the ammonia from the mixed gas containing the ammonia produced by the ammonia synthesis reactor, A heat recovery unit recovers the thermal energy of the ammonia synthesis reactor by generating thermoelectric power from the temperature difference between the heat of the ammonia synthesis reaction in the ammonia synthesis reactor and the cold energy of the recovered gas discharged from the ammonia recovery unit. An ammonia production system equipped with the following features.

2. A case having a supply port for supplying ammonia raw material gas, A heat exchange section having a tubular structure is arranged inside the case, Equipped with, The tubular structure has a first end which is an opening provided inside the case, a second end opposite to the first end, a first region located on the first end side where a catalyst layer is formed with a catalyst that promotes the ammonia synthesis reaction, and a second region located on the second end side where the catalyst layer is not formed. The case and the tubular structure comprise a first flow path through which the raw material gas supplied from the supply port flows to the first end, passing through the catalyst layer located inside the case and outside the tubular structure; and a second flow path through which a mixed gas containing ammonia produced by the synthesis reaction flows in from the first end and flows to the second end, passing through the first and second regions inside the tubular structure. The heat exchange unit causes heat exchange to occur between the raw material gas flowing through the first channel and the mixed gas flowing through the second channel. Ammonia synthesis reactor.

3. The catalyst temperature at the first end reaches a temperature of 600°C or higher and 650°C or lower. The ammonia synthesis reactor according to claim 2.

4. The catalyst is filled inside the tubular structure from the first end to a predetermined position. The heat exchange section continuously lowers the catalyst temperature inside the tubular structure from the first end to the predetermined position. The ammonia synthesis reactor according to claim 3.

5. The catalyst temperature at the predetermined position reaches a temperature of 250°C or higher and 300°C or lower. The ammonia synthesis reactor according to claim 4.

6. The flow of the raw material gas in the first channel and the flow of the mixed gas in the second channel are opposite to each other. The ammonia synthesis reactor according to claim 2.

7. The case has a bottom surface provided opposite the first end, The catalyst is positioned between the first end and the bottom surface. A heater is provided on the bottom surface to transfer heat to the catalyst. The ammonia synthesis reactor according to claim 2.

8. An ammonia recovery device for recovering ammonia from a mixed gas containing ammonia, The case and, A heat exchange section having multiple tubular structures that allow the mixed gas to flow from the outside of the case into the inside of the case, A cooling device that provides cooling to the first end of the tubular structure, which is placed inside the case, Equipped with, The case has a recovery port for recovering the ammonia that has been cooled and liquefied by the refrigerator, The case is configured with a third flow path through which the mixed gas flows from the outside of the case to the first end of the tubular structure located inside the case, and a fourth flow path through which the recovered gas flows from the first end to an outlet for discharging the recovered gas after ammonia recovery. The tubular structure allows heat exchange to occur between the mixed gas flowing through the third channel and the recovered gas flowing through the fourth channel. Ammonia recovery unit.

9. The flow of the mixed gas in the third channel and the flow of the recovered gas in the fourth channel are opposite to each other. The ammonia recovery device according to claim 8.

10. A heat conduction section that contacts a part of an ammonia synthesis reactor that synthesizes raw material gases to produce ammonia, and transmits the heat of the ammonia synthesis reaction, A thermoelectric element that generates electricity based on the temperature difference between the cold heat of the recovered gas discharged from an ammonia recovery unit that recovers the ammonia from the ammonia-containing mixed gas produced by the ammonia synthesis reactor, and the heat of the synthesis reaction transmitted by the heat conduction unit. A heat recovery unit equipped with a heat recovery system.

11. The system further includes a state transition unit that moves the heat conduction unit between a contact state, where it is in contact with the ammonia synthesis reactor, and a detached state, where it is separated from the ammonia synthesis reactor, based on the internal temperature of the ammonia synthesis reactor. The heat recovery device according to claim 10.

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