Ammonia synthesis system, ammonia synthesis method, and computer program

Abstract

This ammonia synthesis system comprises: a catalytic reactor which accommodates a catalyst and synthesizes ammonia from hydrogen and nitrogen; a separator which separates an ammonia-containing synthesis gas taken out from the catalytic reactor into ammonia and an unreacted gas that contains hydrogen and nitrogen; a supply line which supplies a raw material gas to the catalytic reactor, wherein the raw material gas contains a recycle gas that is at least a portion of the unreacted gas, raw material hydrogen that is supplied from a hydrogen supply source, and raw material nitrogen that is supplied from a nitrogen supply source; and a control unit which controls the ratio of the hydrogen flow rate to the nitrogen flow rate in the supply line.

Description

Ammonia synthesis system, ammonia synthesis method, and computer program

[0001] This invention relates to an ammonia synthesis system, an ammonia synthesis method, and a computer program.

[0002] Ammonia synthesis systems that synthesize ammonia from hydrogen and nitrogen have been known for some time (for example, Patent Documents 1 and 2).

[0003] Japanese Patent Publication No. 2018-203603 Japanese Patent Publication No. 2020-66573

[0004] However, even with prior art such as Patent Documents 1 and 2, there was still room for improvement in the technology for efficiently synthesizing ammonia in ammonia synthesis systems.

[0005] This invention was made to solve the above-mentioned problems and aims to provide a technology that can efficiently synthesize ammonia in an ammonia synthesis system.

[0006] The present invention has been made to solve at least some of the above-mentioned problems and can be realized in the following forms.

[0007] (1) According to one embodiment of the present invention, an ammonia synthesis system is provided. This ammonia synthesis system comprises: a catalytic reactor that houses a catalyst and synthesizes ammonia from hydrogen and nitrogen; a separator that separates the synthesis gas containing ammonia, which is taken out from the catalytic reactor, into ammonia and unreacted gas containing hydrogen and nitrogen; a supply line that supplies the raw material gas, which is at least a portion of the unreacted gas, raw material hydrogen supplied from a hydrogen supply source, and raw material nitrogen supplied from a nitrogen supply source, to the catalytic reactor; and a control unit that controls the ratio of the hydrogen flow rate to the nitrogen flow rate in the supply line.

[0008] In this configuration, the control unit controls the ratio of hydrogen flow rate to nitrogen flow rate in the supply line through which the raw material gas for ammonia flows. This allows for stable ammonia synthesis in the catalytic reactor, thus enabling efficient ammonia synthesis.

[0009] (2) In the ammonia synthesis system of the above form, the system may be provided with a concentration ratio calculation unit that calculates the ratio of hydrogen concentration to nitrogen concentration in any one of the synthesis gas, the unreacted gas, or the recycled gas, and the control unit may control the ratio of hydrogen flow rate to nitrogen flow rate in the supply line by changing at least one of the flow rate of the recycled gas, the flow rate of raw material hydrogen, or the flow rate of raw material nitrogen using the ratio of hydrogen concentration to nitrogen concentration to nitrogen concentration calculated by the concentration ratio calculation unit. With this configuration, the control unit controls the ratio of hydrogen flow rate to nitrogen flow rate in the supply line through which the raw material gas that will be used as a raw material for ammonia flows, using the ratio of hydrogen concentration to nitrogen concentration in the gas taken out from the catalytic reactor. As a result, the ammonia synthesis rate in the catalytic reactor can be fed back into the flow rates of hydrogen and nitrogen contained in the raw material gas, so that ammonia can be synthesized more stably in the catalytic reactor. Therefore, ammonia can be synthesized more efficiently.

[0010] (3) In the ammonia synthesis system of the above form, the control unit may control the ratio of the hydrogen flow rate to the nitrogen flow rate in the supply line from the time the ammonia synthesis system is started until it reaches a steady-state operating state, or from the time it reaches a steady-state operating state until it is stopped. With this configuration, the control unit controls the ratio of the hydrogen flow rate to the nitrogen flow rate in the supply line during the time when ammonia synthesis is relatively unstable, from the time the ammonia synthesis system is started until it reaches a steady-state operating state, or from the time it reaches a steady-state operating state until it is stopped. As a result, ammonia can be synthesized stably while the ammonia synthesis system is in operation, and thus ammonia can be synthesized more efficiently.

[0011] (4) The ammonia synthesis system of the above form may further include a purge line that discharges gases other than the recycled gas from the unreacted gases to the outside of the ammonia synthesis system as a purge gas, and the control unit may control the purge rate, which is the ratio of the total amount of hydrogen flow rate and nitrogen flow rate in the purge line to the total amount of hydrogen flow rate and nitrogen flow rate in the supply line. With this configuration, the control unit controls the purge rate which has a constant relationship with the flow rate of gas taken out of the catalytic reactor, which changes according to the ammonia synthesis rate in the catalytic reactor. As a result the ammonia synthesis rate can be controlled, ammonia can be synthesized stably. Therefore, ammonia can be synthesized efficiently.

[0012] (5) The ammonia synthesis system of the above form further includes a concentration ratio calculation unit that calculates the ratio of hydrogen concentration to nitrogen concentration in any one of the synthesis gas, the unreacted gas, the recycled gas, and the purge gas, and the control unit may control the purge rate by changing at least one of the flow rate of raw hydrogen, the flow rate of raw nitrogen, and the flow rate of recycled gas using the ratio of hydrogen concentration to nitrogen concentration calculated by the concentration ratio calculation unit. With this configuration, the control unit controls the purge rate using the ratio of hydrogen concentration to nitrogen concentration in the gas taken out from the catalytic reactor. This allows the ammonia synthesis rate in the catalytic reactor to be fed back into the flow rate and composition of the raw gas, so that ammonia can be synthesized more stably. Therefore, ammonia can be synthesized more efficiently.

[0013] (6) In the ammonia synthesis system of the above configuration, the control unit may control the purge rate from the time the ammonia synthesis system is started until it reaches a steady-state operating state, or from the time it reaches a steady-state operating state until it is stopped. With this configuration, the control unit controls the purge rate during the time when ammonia synthesis is relatively unstable, from the time the ammonia synthesis system is started until it reaches a steady-state operating state, or from the time it reaches a steady-state operating state until it is stopped. As a result, ammonia can be synthesized stably while the ammonia synthesis system is in operation, and thus ammonia can be synthesized more efficiently.

[0014] (7) The ammonia synthesis system of the above form further comprises a gas temperature control unit for adjusting the temperature of the raw material gas and a catalyst temperature detection unit for detecting the temperature of the catalyst, and the control unit may control the temperature of the catalyst by adjusting the temperature of the raw material gas in the gas temperature control unit using the temperature of the catalyst detected by the catalyst temperature detection unit. With this configuration, the catalyst temperature, which affects the rate of ammonia synthesis, is controlled by adjusting the temperature of the raw material gas by the gas temperature control unit. As a result, the rate of ammonia synthesis can be controlled, and ammonia can be synthesized stably in the catalytic reactor. Therefore, ammonia can be synthesized efficiently.

[0015] (8) In the ammonia synthesis system of the above form, the catalyst housed in the catalytic reactor may be a ruthenium-containing catalyst. With this configuration, the control unit controls the ratio of the hydrogen flow rate to the nitrogen flow rate in the supply line through which the raw material gas flows. This makes it possible to stably synthesize ammonia even with a ruthenium-containing catalyst, which is preferable to synthesize ammonia with a nitrogen-to-hydrogen ratio smaller than 3, which is the stoichiometric ratio in the ammonia synthesis reaction.

[0016] (9) According to another embodiment of the present invention, an ammonia synthesis method is provided for synthesizing ammonia using an ammonia synthesis system. This ammonia synthesis method comprises the steps of: synthesizing ammonia from hydrogen and nitrogen using a catalyst housed in a catalytic reactor; separating the synthesis gas removed from the catalytic reactor into ammonia and unreacted gas containing hydrogen and nitrogen; supplying a raw material gas containing recycled gas, which is at least a portion of the unreacted gas, raw material hydrogen supplied from a hydrogen supply source, and raw material nitrogen supplied from a nitrogen supply source, to the catalytic reactor using a supply line; and controlling the ratio of the hydrogen flow rate to the nitrogen flow rate in the supply line. With this configuration, the ammonia synthesis method using an ammonia synthesis system controls the ratio of the hydrogen flow rate to the nitrogen flow rate in the supply line through which the raw material gas that will be used as raw material for ammonia flows. As a result, ammonia can be synthesized stably in the catalytic reactor, and thus ammonia can be synthesized efficiently.

[0017] (10) According to yet another embodiment of the present invention, a computer program is provided which causes a computer to perform the synthesis of ammonia using an ammonia synthesis system. The computer program causes the computer to perform the following functions: synthesize ammonia from hydrogen and nitrogen using a catalyst housed in a catalytic reactor; separate the synthesis gas extracted from the catalytic reactor into ammonia and unreacted gas containing hydrogen and nitrogen; supply to the catalytic reactor, using a supply line, a recycled gas which is at least a portion of the unreacted gas, raw material hydrogen supplied from a hydrogen supply source, and raw material nitrogen supplied from a nitrogen supply source; and control the ratio of the hydrogen flow rate to the nitrogen flow rate in the supply line. With this configuration, the computer controls the ratio of the hydrogen flow rate to the nitrogen flow rate in the supply line through which the raw material gas that will become the raw material for ammonia flows. As a result, ammonia can be synthesized stably in the catalytic reactor, and thus ammonia can be synthesized efficiently.

[0018] Furthermore, the present invention can be realized in various forms, for example, as a system including an ammonia synthesis apparatus, a control method for such apparatus and system, a computer program for performing ammonia synthesis in such apparatus and system, a server device for distributing the computer program, and a non-temporary storage medium storing the computer program.

[0019] This is a schematic diagram showing the general configuration of the ammonia synthesis system of the first embodiment. This is the first flowchart of the ammonia synthesis method of this embodiment. This is the second flowchart of the ammonia synthesis method of this embodiment. This is a diagram showing the relationship between operating parameters and control items in ammonia synthesis. This is a diagram showing the relationship between the composition of the raw material gas and the catalytic activity of the catalyst. This is a diagram showing the relationship between the gas flow rate and the flow rate ratio in the ammonia synthesis system. This is a diagram explaining the relationship between the system operating time and the ammonia synthesis rate. This is the flowchart of the ammonia synthesis method of the second embodiment. This is a diagram explaining the relationship between the system operating time and the purge rate. This is a schematic diagram showing the general configuration of the ammonia synthesis system of the third embodiment. This is the flowchart of the ammonia synthesis method of the third embodiment.

[0020] <First Embodiment> Figure 1 is a schematic diagram showing the general configuration of the ammonia synthesis system of this embodiment. The ammonia synthesis system 1 shown in Figure 1 uses hydrogen (H ２ ) and nitrogen (N ２ ) and ammonia (NH ３ The system includes a circulation facility for reusing the gas (synthesis gas) after the synthesis of ammonia. As shown in Figure 1, the ammonia synthesis system 1 includes a catalytic reactor 10 for synthesizing ammonia, a separator 20 for separating the ammonia-containing gas into ammonia and non-ammonia gases, a mixer 30 for mixing the non-ammonia gas separated in the separator 20 with raw material hydrogen and raw material nitrogen, which are raw materials for ammonia synthesis, gas sensors 41, 42, 43, and 44 for detecting the gas concentration in each part of the ammonia synthesis system 1, a pressure flow regulator 23a, and a control unit 50 for controlling each part of the ammonia synthesis system 1.

[0021] The catalytic reactor 10 houses a catalyst 11 and synthesizes ammonia from hydrogen and nitrogen. The catalyst 11 is a well-known catalyst such as an Fe-based catalyst or a Ru-based catalyst. In this embodiment, a Ru-based catalyst containing ruthenium is housed within. When the raw material gas, described later, is supplied to the catalytic reactor 10, ammonia is synthesized by the chemical reaction shown in the following formula (1) involving the catalyst 11. In the catalytic reactor 10 of this embodiment, not all of the hydrogen and nitrogen contained in the raw material gas becomes ammonia; therefore, the synthesis gas containing ammonia extracted from the catalytic reactor 10 contains unreacted hydrogen and nitrogen in addition to ammonia. ２ +3H ２ = 2NH ３ ... (1)

[0022] The catalytic reactor 10 and the separator 20 are connected by a synthesis gas line 12. The synthesis gas line 12 includes a first heat exchanger 12a, a second heat exchanger 12b, and a cooler 12c. In the first heat exchanger 12a, heat exchange takes place between the synthesis gas extracted from the catalytic reactor 10 and the raw material gas. The ammonia synthesis reaction shown in equation (1) above is an exothermic reaction, and in the first heat exchanger 12a, the raw material gas is heated using the heat of the synthesis gas.

[0023] The second heat exchanger 12b is located downstream of the first heat exchanger 12a in the synthesis gas line 12. In the second heat exchanger 12b, heat exchange takes place between the synthesis gas after it has passed through the first heat exchanger 12a and the recycled gas, which will be described later. Specifically, in the second heat exchanger 12b, the recycled gas is heated using the heat from the synthesis gas after it has passed through the first heat exchanger 12a. The cooler 12c is located downstream of the second heat exchanger 12b in the synthesis gas line 12. In the cooler 12c, the synthesis gas, whose temperature has decreased compared to when it was taken out of the catalytic reactor 10 due to the heat exchange in the first heat exchanger 12a and the second heat exchanger 12b, is cooled.

[0024] The separator 20 is a so-called gas-liquid separator. In the separator 20, the synthesis gas extracted from the catalytic reactor 10 is cooled and the ammonia contained in the synthesis gas is liquefied. As a result, the synthesis gas is separated into liquid ammonia and gaseous hydrogen and nitrogen. The liquid ammonia is compressed by a compressor (not shown) and stored in tank 21. The gaseous hydrogen and nitrogen are reused for ammonia synthesis in the catalytic reactor 10. The gas containing hydrogen and nitrogen separated from the synthesis gas in the separator 20 is called "unreacted gas".

[0025] The separator 20 and the mixer 30 are connected by a recycling line 22. A purge line 23 is connected to the recycling line 22. The purge line 23 is a line that can discharge at least a portion of the unreacted gas outside the ammonia synthesis system 1. The purge line 23 is equipped with a pressure-flow regulator 23a that can adjust the pressure and flow rate of the gas flowing through the purge line 23. The pressure-flow regulator 23a is electrically connected to a control unit 50 and adjusts the flow rate of the purge gas according to instructions from the control unit 50. Here, the gas that passes through the purge line 23 and is discharged outside the ammonia synthesis system 1 from the unreacted gas is referred to as "purge gas". For convenience, the recycling line 22 from the separator 20 to the point where it connects to the purge line 23 is referred to as recycling line 22a, and the recycling line 22 from the point where it connects to the purge line 23 to the mixer 30 is referred to as recycling line 22b. If we define "recycled gas" as the gas containing hydrogen and nitrogen that is sent to the mixer 30, excluding the purge gas from the unreacted gas, then the aforementioned "unreacted gas" refers to the gas flowing through the recycling line 22a, and "recycled gas" refers to the gas flowing through the recycling line 22b.

[0026] The recycling line 22 is configured such that the downstream side of the point where it connects to the purge line 23 passes through the second heat exchanger 12b. In the second heat exchanger 12b, the recycled gas is heated by heat exchange with the synthesis gas that has passed through the first heat exchanger 12a. In the ammonia synthesis system, the unreacted gas is mixed with trace amounts of argon (Ar) and methane (CH4) in the raw material gas supplied to the catalytic reactor. ４ These may include [unspecified substances]. These inert gases are concentrated by repeatedly recovering and reusing unreacted gases, and a portion of the unreacted gases is discharged outside the ammonia synthesis system as a purge gas.

[0027] Mixer 30 mixes multiple types of gases. In addition to the recycling line 22, mixer 30 is connected to two raw material gas lines 31a and 32a. Raw material gas line 31a is connected to the hydrogen supply unit 31b which supplies raw material hydrogen. Raw material gas line 32a is connected to the nitrogen supply unit 32b which supplies raw material nitrogen. Mixer 30 mixes the raw material hydrogen supplied by the hydrogen supply unit 31b, the raw material nitrogen supplied by the nitrogen supply unit 32b, and the recycled gas supplied by the recycling line 22. Each of the raw material gas lines 31a, 32a and the recycling line 22 is provided with a mass flow controller 31c, 32c, and 24 which can change the mass flow rate of the gas flowing through each gas line. Each of the mass flow controllers 31c, 32c, and 24 is electrically connected to the control unit 50.

[0028] The mixer 30 and the catalytic reactor 10 are connected by a supply line 33. The supply line 33 sends the raw material gas, which includes raw material hydrogen, raw material nitrogen, and recycled gas, mixed in the mixer 30, to the catalytic reactor 10. The raw material gas flowing through the supply line 33 is heated in the first heat exchanger 12a by heat exchange with the synthesis gas taken out from the catalytic reactor 10. A heater 33a and a compressor (not shown) are provided downstream of the first heat exchanger 12a in the supply line 33. The heater 33a is electrically connected to the control unit 50 and, according to instructions from the control unit 50, further heats the raw material gas to raise its temperature to a temperature suitable for the ammonia synthesis reaction. The raw material gas is pressurized so that its pressure is equal to or greater than atmospheric pressure.

[0029] Gas sensors 41, 42, 43, and 44 detect the gas composition at various points in the ammonia synthesis system 1. Gas sensors 41, 42, 43, and 44 are, for example, gas chromatographs. Gas sensor 41 detects the hydrogen and nitrogen concentrations in the raw material gas flowing through the supply line 33. Gas sensor 42 detects the hydrogen and nitrogen concentrations in the synthesis gas flowing through the synthesis gas line 12. Gas sensor 43 detects the hydrogen and nitrogen concentrations in the purge gas flowing through the purge line 23. Gas sensor 44 detects the hydrogen and nitrogen concentrations in the recycled gas flowing through the recycling line 22. In principle, in the ammonia synthesis system 1, the hydrogen and nitrogen concentrations in the synthesis gas, the purge gas, and the recycled gas are all the same, but gas sensors are installed at multiple locations to account for noise such as time lags. Gas sensors 41, 42, 43, and 44 are electrically connected to the control unit 50. However, the location and number of gas sensors installed in the ammonia synthesis system 1 are not limited to those specified above.

[0030] The control unit 50 is a computer including a ROM, a RAM, and a CPU. The control unit 50 is electrically connected to each of the mass flow controllers 31c, 32c, 24, the pressure flow regulator 23a, and the gas sensors 41, 42, 43, 44. The control unit 50 controls each part of the ammonia synthesis system 1 by expanding and executing a computer program stored in a ROM (Read Only Memory), which is not shown, in a RAM (Random Access Memory).

[0031] Next, the details of the ammonia synthesis method using the ammonia synthesis system 1 of the present embodiment will be described. The ammonia synthesis method of the present embodiment is executed immediately after the ammonia synthesis system 1 is started to synthesize ammonia.

[0032] FIG. 2 is a first flowchart of the ammonia synthesis method of the present embodiment. FIG. 3 is a second flowchart of the ammonia synthesis method of the present embodiment. In the ammonia synthesis method of the present embodiment, as optimal operating conditions according to the size and processing capacity of each part of the ammonia synthesis system 1, the flow rate of predetermined raw material hydrogen, the flow rate of predetermined raw material nitrogen, the flow rate of predetermined recycle gas, and the target value r of the ratio of the hydrogen flow rate to the nitrogen flow rate in the raw material gas supplied to the mixer 30 are preset in the control unit 50. ｃ When the ammonia synthesis method shown in FIG. 2 is started, the control unit 50 inputs the flow rate of predetermined raw material hydrogen, the flow rate of predetermined raw material nitrogen, and the flow rate of predetermined recycle gas to the mass flow controllers 31c, 32c, 24. The flow rate of predetermined raw material hydrogen preset in the control unit 50 is, for example, 0.01 to 150000 L / min, the flow rate of predetermined raw material nitrogen is, for example, 0.01 to 500000 L / min, and the flow rate of predetermined recycle gas is, for example, 0.01 to 200000 L / min. Hereinafter, the ratio of the hydrogen flow rate to the nitrogen flow rate in a specific gas is referred to as the "H ２ / N ２ " of that specific gas.

[0033] In the ammonia synthesis method of this embodiment, first, it is determined whether a predetermined time has elapsed since the ammonia synthesis system 1 was started (step S11). In step S11, the control unit 50 determines whether the time elapsed since the ammonia synthesis system 1 was started is equal to or greater than a predetermined time t. The predetermined time t may be a preset time, or it may be a time that changes according to the operating status of the ammonia synthesis system 1. For example, the predetermined time t may be between 1 minute and 100 hours. If it is determined that the time elapsed since the ammonia synthesis system 1 was started is equal to or greater than the predetermined time t (step S11: YES), the process proceeds to step S12. If it is determined that the time elapsed since the ammonia synthesis system 1 was started is less than the predetermined time t (step S11: NO), the determination in step S11 is continued.

[0034] In step S11, if it is determined that the time elapsed since the ammonia synthesis system 1 was started is greater than or equal to a predetermined time t, the raw material gas H ２ / N ２ Step S12 determines whether the hydrogen concentration is within a predetermined range. In step S12, the control unit 50 uses the hydrogen concentration and nitrogen concentration detected by the gas sensors 42, 43, and 44 to determine the H concentration of the raw material gas flowing through the supply line 33. ２ / N ２ The control unit 50 calculates the H of the raw material gas calculated. ２ / N ２ The calculated value r Ｉｎ And the raw material gas H ２ / N ２ Target value r ｃ It is determined whether the absolute value of the difference between the two is less than or equal to a predetermined value a. In this embodiment, the predetermined value a is between 0.001 and 1. Calculated value r Ｉｎ and target value r ｃ If it is determined that the absolute value of the difference is less than or equal to a predetermined value a (Step S12: YES), the process returns to Step S11. Calculated value r Ｉｎ and target value r ｃ If it is determined that the absolute value of the difference is greater than a predetermined value a (step S12: NO), the process proceeds to step S13.

[0035] In step S12, the calculated value r Ｉｎ and target value r ｃ If the absolute value of the difference between the two is determined to be greater than a predetermined value a, then the H of the raw material gas ２ / N ２ Step S13 determines whether the H of the raw material gas is greater than the target value. ２ / N ２ The calculated value r Ｉｎ However, the raw material gas H ２ / N ２ Target value r ｃ Determine whether it is greater than or equal to r. Calculated value r Ｉｎ The target value is r ｃ If it is determined to be greater than (Step S13: YES), proceed to Step S141. Calculated value r Ｉｎ The target value is r ｃ If it is determined to be smaller (step S13: NO), proceed to step S142 (see Figure 3).

[0036] In step S13, the calculated value r Ｉｎ The target value is r ｃ If it is determined to be greater than, the calculated value r Ｉｎ It is determined whether the value is greater than 3 (step S141). In step S141, the control unit 50 determines whether the calculated H of the raw material gas ２ / N ２ The calculated value r Ｉｎ However, it is determined whether or not the stoichiometric ratio is greater than 3 for the ammonia synthesis reaction. Calculated value r Ｉｎ If it is determined that the value is greater than 3 (step S141: YES), proceed to step S151. Calculated value r Ｉｎ If it is determined that the value is less than 3 (step S141: NO), proceed to step S152.

[0037] In step S141, the calculated value r ＩｎIf it is determined that is greater than 3, at least one of the following is performed: "reduce raw hydrogen", "increase raw nitrogen", or "increase recycled gas" (step S151). In step S151, the control unit 50 controls at least one of the mass flow controllers 31c, 32c, and 24 to control the H of the raw gas flowing through the supply line 33. ２ / N ２ The following changes are made. Specifically, when reducing the flow rate of raw hydrogen, the mass flow controller 31c is controlled to reduce the flow rate of raw hydrogen by a predetermined amount Δx. The predetermined amount Δx is, for example, 0.001 to 15000 L / min. When increasing the flow rate of raw nitrogen, the mass flow controller 32c is controlled to increase the flow rate of raw nitrogen by a predetermined amount Δy. The predetermined amount Δy is, for example, 0.001 to 5000 L / min. When increasing the flow rate of recycled gas, the mass flow controller 24 is controlled to increase the flow rate of recycled gas by a predetermined amount Δz. The predetermined amount Δz is, for example, 0.001 to 20000 L / min.

[0038] In step S141, the calculated value r Ｉｎ If it is determined that is less than 3, at least one of the following is performed: "reduce raw hydrogen", "increase raw nitrogen", or "reduce recycled gas" (step S152). In step S152, the control unit 50 controls at least one of the mass flow controllers 31c, 32c, and 24 to control the H of the raw gas flowing through the supply line 33. ２ / N ２ The following changes are made: Specifically, to reduce the flow rate of raw hydrogen, the mass flow controller 31c is controlled to decrease the flow rate of raw hydrogen by a predetermined amount Δx. To increase the flow rate of raw nitrogen, the mass flow controller 32c is controlled to increase the flow rate of raw nitrogen by a predetermined amount Δy. To reduce the flow rate of recycled gas, the mass flow controller 24 is controlled to decrease the flow rate of recycled gas by a predetermined amount Δz.

[0039] In step S13, the calculated value r Ｉｎ The target value is r ｃ If it is determined to be smaller, the calculated value r will be as shown in Figure 3. ＩｎIt is determined whether the value is less than 3 (step S142). In step S142, the control unit 50 determines whether the calculated H of the raw material gas ２ / N ２ The calculated value r Ｉｎ Determine whether the result is less than 3. Calculated value r Ｉｎ If it is determined that the value is less than 3 (step S142: YES), proceed to step S153. Calculated value r Ｉｎ If it is determined that the value is greater than 3 (step S142: NO), proceed to step S154.

[0040] In step S142, the calculated value r Ｉｎ If it is determined that is less than 3, at least one of the following is performed: "increase raw hydrogen", "decrease raw nitrogen", or "decrease recycled gas" (step S153). In step S153, the control unit 50 controls at least one of the mass flow controllers 31c, 32c, and 24 to control the H of the raw gas flowing through the supply line 33. ２ / N ２ The following changes are made: Specifically, to increase the flow rate of raw hydrogen, the mass flow controller 31c is controlled to increase the flow rate of raw hydrogen by a predetermined amount Δx. To decrease the flow rate of raw nitrogen, the mass flow controller 32c is controlled to decrease the flow rate of raw nitrogen by a predetermined amount Δy. To decrease the flow rate of recycled gas, the mass flow controller 24 is controlled to decrease the flow rate of recycled gas by a predetermined amount Δz.

[0041] In step S142, the calculated value r Ｉｎ If it is determined that is greater than 3, at least one of the following is performed: "increase raw hydrogen", "decrease raw nitrogen", or "increase recycled gas" (step S154). In step S154, the control unit 50 controls at least one of the mass flow controllers 31c, 32c, and 24 to control the H of the raw gas flowing through the supply line 33. ２ / N ２The following changes are made: Specifically, to increase the flow rate of raw hydrogen, the mass flow controller 31c is controlled to increase the flow rate of raw hydrogen by a predetermined amount Δx. To decrease the flow rate of raw nitrogen, the mass flow controller 32c is controlled to decrease the flow rate of raw nitrogen by a predetermined amount Δy. To increase the flow rate of recycled gas, the mass flow controller 24 is controlled to increase the flow rate of recycled gas by a predetermined amount Δz.

[0042] Following steps S151, S152, S153, and S154, the raw material gas H flowing through the supply line 33 ２ / N ２ Step S16 determines whether a predetermined time has elapsed since the change. In step S16, the control unit 50 determines whether the time elapsed since the gas flow rate change made in any of steps S151, S152, S153, or S154 is equal to or greater than a predetermined time u. The predetermined time u is, for example, 1 minute to 100 hours. If it is determined that the time elapsed since the gas flow rate change made in any of steps S151, S152, S153, or S154 is equal to or greater than the predetermined time u (Step S16: YES), the process proceeds to step S17. If it is determined that the time elapsed since the gas flow rate change made in any of steps S151, S152, S153, or S154 is less than the predetermined time u (Step S16: NO), the determination in step S16 is continued. In step S16, the control unit 50 uses the gas sensor 41 to detect the hydrogen concentration and nitrogen concentration in the raw material gas flowing through the supply line 33, and determines the H ２ / N ２ You can also verify that the desired ratio is achieved by calculating this.

[0043] In step S16, if it is determined that the time elapsed since the change in gas flow rate is greater than or equal to a predetermined time u, the operating conditions are reset (step S17). In step S17, the control unit 50 inputs the predetermined raw material hydrogen flow rate, predetermined raw material nitrogen flow rate, and predetermined recycled gas flow rate, which are set in advance in the control unit 50 as the optimal operating conditions for the ammonia synthesis system 1, to the mass flow controllers 31c, 32c, and 24.

[0044] After step S17, the process returns to step S11 to determine whether a predetermined time t has elapsed since the operating conditions were reset (step S11). In this embodiment, the ammonia synthesis method involves repeatedly performing steps S11 to S17 shown in Figures 2 and 3 from the start up to the stop down of the ammonia synthesis system 1, thereby synthesizing ammonia.

[0045] Next, the features of the ammonia synthesis system 1 of this embodiment will be described. The ammonia synthesis reaction, which synthesizes ammonia from hydrogen and nitrogen as shown in equation (1), has a conversion rate of about 20% due to the constraint of thermochemical equilibrium concentrations. For this reason, in general ammonia synthesis systems, as in the ammonia synthesis system 1 of this embodiment, unreacted gas is reused (recycled) for ammonia synthesis. For this reason, the relationship between the operational parameters and control items in ammonia synthesis becomes relatively complex.

[0046] Figure 4 shows the relationship between operational parameters and control items in ammonia synthesis. Figure 4 shows the relationship between influencing factors that affect the magnitude of ammonia synthesis in catalytic ammonia synthesis and the operational parameters that can control the magnitude of these influencing factors. As shown in Figure 4, the ammonia synthesis rate in catalytic ammonia synthesis is related to the H₂O₃ content of the raw material gas supplied to the catalytic reactor. ２ / N ２ (Figure 4, "H of raw material gas") ２ It changes depending on any of the following factors: H2 (hydrogen peroxide), the flow rate of the raw material gas (see "Flow Rate of Raw Material Gas" in Figure 4), the temperature of the catalyst (see "Temperature of Catalyst" in Figure 4), and the pressure inside the catalytic reactor (see "Reactor Pressure" in Figure 4). Among these influencing factors, "H2 (hydrogen peroxide) of the raw material gas" is particularly important. ２ The parameters "H / N2" and "raw material gas flow rate" are controllable parameters controlled by the flow rates of raw material hydrogen, raw material nitrogen, and recycled gas. The "catalyst temperature" is a controllable parameter controlled by the temperature of the raw material gas. The "reactor pressure" is controllable by the compressor, etc., and is therefore an operational parameter in itself. If these operational parameters are kept constant during operation, a change in the ammonia synthesis rate will result in a change in the H / N2 of the synthesis gas extracted from the catalytic reactor. ２ / N ２ changes. When the H ２ / N ２ of the synthesis gas changes, the H ２ / N ２ of the recycle gas also changes. As a result, the H ２ / N ２ of the raw material gas also changes, and thus the ammonia synthesis rate further changes.

[0047] FIG. 5 is a diagram showing the relationship between the composition of the raw material gas and the catalytic activity of the catalyst. Here, the characteristics of the Ru-based catalyst used in the ammonia synthesis system 1 of the present embodiment will be described. In FIG. 5, the catalytic activities ARu and ARe that change according to the gas composition of the raw material gas are shown for each of the Ru-based catalyst and the Fe-based catalyst. On the horizontal axis of FIG. 2, the H ２ / N ２ of the raw material gas supplied to the catalytic reactor is shown. The Fe-based catalyst of the ammonia synthesis catalyst industrially used does not greatly depend on the H ２ / N ２ of the raw material gas, so the raw material gas is operated at 3. On the other hand, the Ru-based catalyst, which has been known as a highly active ammonia synthesis catalyst in recent years, is inhibited from adsorbing nitrogen due to poisoning of hydrogen species on the catalyst (hydrogen poisoning), and becomes highly active even when the H ２ / N ２ of the raw material gas is low. Therefore, the raw material gas is preferably operated under the condition that the H ２ / N ２ is less than 3. That is, in ammonia synthesis using a Ru-based catalyst, it is operated below the stoichiometric ratio calculated from the chemical reaction formula shown in formula (1).

[0048] Also, when ammonia synthesis is carried out using a raw material gas with H ２ / N ２ being 3, the H ２ / N ２ of the raw material gas and the H ２ / N ２ of the synthesis gas do not change. On the other hand, when ammonia synthesis is carried out using a raw material gas with H ２ / N ２ being less than 3, the H ２ / N ２ ​​​​H is the raw material gas. ２ / N ２ It becomes smaller than H. ２ / N ２ When ammonia synthesis is performed using a raw material gas with a H content greater than 3, the synthesis gas H ２ / N ２ H is the raw material gas. ２ / N ２ It will be larger than that. Some of the synthesis gas is reused as recycled gas, so the H of the raw gas ２ / N ２ Even if the ammonia synthesis reaction activity changes, the amount of H in the synthesis gas will change. ２ / N ２ This also changes. Therefore, the H of recycled gas ２ / N ２ and the raw material gas H ２ / N ２ This will also change. Therefore, in this embodiment, in order to stably synthesize ammonia, the H of the raw material gas will change. ２ / N ２ It controls it.

[0049] Figure 6 shows the relationship between gas flow rate and flow rate ratio in the ammonia synthesis system. Figure 6 shows the flow rates of hydrogen, nitrogen, and ammonia for each "gas type" in the ammonia synthesis system 1 of this embodiment, and the ratio of hydrogen flow rate to nitrogen flow rate (H ２ / N ２ ) is shown. In Figure 6, the flow rate of the base gas and the ratio of the hydrogen flow rate to the nitrogen flow rate in the recycled gas are shown by the following letters. Of these, the flow rate of raw hydrogen is F. Ｈ２ Flow rate F of raw material nitrogen Ｎ２ , and the flow rate F of the recycled gas Ｒ These are the operating parameters of the ammonia synthesis system 1 in this embodiment (see Figure 4). Using these letters, as shown in Figure 6, the flow rates of hydrogen, nitrogen, and ammonia in the various gases flowing through the ammonia synthesis system 1, and the ratio of the hydrogen flow rate to the nitrogen flow rate in the recycled gas can be expressed. Ｈ２ : Flow rate of raw hydrogen F Ｎ２ : Flow rate of raw nitrogen F Ｒ: Flow rate of recycled gas r Ｒ : Ratio of hydrogen flow rate to nitrogen flow rate in recycled gas α: Flow rate of ammonia synthesized

[0050] The ratio of hydrogen flow rate to nitrogen flow rate in recycled gas (r) Ｒ In principle, the H of synthesis gas ２ / N ２ And, the H of the purge gas ２ / N ２ This is the same. Therefore, the hydrogen concentration and nitrogen concentration of at least one of the unreacted gas, recycled gas, and purge gas are detected, and the flow rate F of the raw hydrogen is determined. Ｈ２ Flow rate F of raw material nitrogen Ｎ２ , the ratio of hydrogen flow rate to nitrogen flow rate in recycled gas r Ｒ By using this, the flow rate α of the ammonia to be synthesized can be calculated by the following equation (2): α = (r Ｒ ×F Ｎ２ -F Ｈ２ ) / (0.5r Ｒ -1.5) ... (2)

[0051] As shown in equation (2), the flow rate α of the synthesized ammonia is equal to the ratio r of the hydrogen flow rate to the nitrogen flow rate in the recycled gas. Ｒ It depends on the H of the raw material gas. Therefore, in the ammonia synthesis system 1 of this embodiment, ２ / N ２ The target of control is the hydrogen and nitrogen concentrations in at least one of the synthesis gas, unreacted gas, recycled gas, and purge gas, and the operating parameters are manipulated using these concentrations. ２ / N ２ This is the target value. This allows for stable ammonia synthesis in the ammonia synthesis system 1.

[0052] Figure 7 illustrates the relationship between the operating time of the ammonia synthesis system and the ammonia synthesis rate. In Figure 7, the relationship between the operating time of the ammonia synthesis system 1 in this embodiment is shown by the solid line SSa1, and the raw material gas H ２ / N ２The relationship between the operating time and the ammonia synthesis rate in a comparative example ammonia synthesis system without control is shown by the dashed line SSa0. As shown in Figure 7, in the comparative example ammonia synthesis system, the ammonia synthesis rate decreases during steady-state operation. This is because, as mentioned above, when using a Ru-based catalyst, the H of the raw material gas ２ / N ２ Because the ratio is smaller than the stoichiometric ratio for ammonia synthesis, as the operating time increases, the H of the raw material gas ２ / N ２ This is because the H of the raw material gas decreases. On the other hand, in the ammonia synthesis system 1 of this embodiment, the H of the raw material gas is adjusted according to the composition of the gas (at least one of the synthesis gas, unreacted gas, recycled gas, and purge gas) taken out from the catalytic reactor 10. ２ / N ２ By controlling this, the rate of ammonia synthesis can be kept constant. This allows for stable ammonia synthesis.

[0053] Furthermore, in the ammonia synthesis system 1 of this embodiment, even during startup and shutdown, when the temperature of the catalyst 11 and the pressure inside the catalytic reactor 10 are intentionally changed, the H of the raw material gas is adjusted according to the composition of the gas extracted from the catalytic reactor 10. ２ / N ２ This controls the process. As a result, ammonia can be stably synthesized even when the ammonia synthesis system 1 is starting up and before it reaches steady-state operation, and also when it is shut down from steady-state operation. Therefore, even under transient operating conditions where the ammonia synthesis system 1 is relatively unstable, hydrogen and nitrogen can be effectively utilized for ammonia synthesis without being wasted.

[0054] As described above, in the ammonia synthesis system 1 of this embodiment, the control unit 50 controls the ratio of the hydrogen flow rate to the nitrogen flow rate in the supply line 33 through which the raw material gas that serves as the raw material for ammonia flows. This allows for stable ammonia synthesis in the catalytic reactor 10, and thus enables efficient ammonia synthesis.

[0055] Furthermore, according to the ammonia synthesis system 1 of this embodiment, the control unit 50 uses the ratio of hydrogen concentration to nitrogen concentration in the synthesis gas extracted from the catalytic reactor 10 to control the ratio of hydrogen flow rate to nitrogen flow rate in the supply line 33 through which the raw material gas, which is the raw material for ammonia, flows. As a result, the ammonia synthesis rate in the catalytic reactor 10 can be fed back into the flow rates of hydrogen and nitrogen contained in the raw material gas, thereby enabling more stable ammonia synthesis in the catalytic reactor 10. Consequently, ammonia can be synthesized even more efficiently.

[0056] Furthermore, according to the ammonia synthesis system 1 of this embodiment, the control unit 50 controls the ratio of hydrogen flow rate to nitrogen flow rate in the supply line 33 during the period from when the ammonia synthesis system 1 is started up until it reaches a steady-state operation, and from the steady-state operation until it is stopped, when ammonia synthesis is relatively unstable. As a result, ammonia can be synthesized stably while the ammonia synthesis system 1 is in operation, and thus ammonia can be synthesized more efficiently.

[0057] Furthermore, according to the ammonia synthesis system 1 of this embodiment, the catalyst 11 housed in the catalytic reactor 10 is a ruthenium-containing catalyst. It is preferable that ammonia synthesis be carried out using a ruthenium-containing catalyst with a nitrogen-to-hydrogen ratio of less than 3, which is the stoichiometric ratio in the ammonia synthesis reaction. However, if the nitrogen-to-hydrogen ratio is different from the stoichiometric ratio, the H of the raw material gas ２ / N ２ This can lead to an instability in ammonia synthesis, as the ratio of hydrogen flow rate to nitrogen flow rate of the gas extracted from the catalytic reactor will differ from that of the catalytic reactor. In the ammonia synthesis system 1 of this embodiment, the control unit 50 controls the ratio of hydrogen flow rate to nitrogen flow rate in the supply line 33 through which the raw material gas flows. This makes it possible to stably synthesize ammonia even with a ruthenium-containing catalyst, where it is preferable to synthesize ammonia using a nitrogen-to-hydrogen ratio smaller than 3, which is the stoichiometric ratio in the ammonia synthesis reaction.

[0058] Furthermore, according to the ammonia synthesis method of this embodiment, the ratio of hydrogen flow rate to nitrogen flow rate in the supply line 33 through which the raw material gas that serves as the raw material for ammonia flows is controlled. As a result, ammonia can be synthesized stably in the catalytic reactor 10, and thus ammonia can be synthesized efficiently.

[0059] Furthermore, according to the computer program of this embodiment, the control unit 50 controls the ratio of the hydrogen flow rate to the nitrogen flow rate in the supply line 33 through which the raw material gas that serves as the raw material for ammonia flows. As a result, ammonia can be synthesized stably in the catalytic reactor 10, and thus ammonia can be synthesized efficiently.

[0060] <Second Embodiment> Figure 8 is a flowchart of the ammonia synthesis method of the second embodiment. The ammonia synthesis system of the second embodiment differs from the ammonia synthesis system of the first embodiment (Figure 1) in that it controls the purging rate.

[0061] The ammonia synthesis system of this embodiment, like the ammonia synthesis system 1 of the first embodiment, comprises a catalytic reactor 10, a separator 20, a mixer 30, gas sensors 41, 42, 43, 44, a pressure flow regulator 23a, and a control unit 50. In the ammonia synthesis system of this embodiment, the control unit 50 uses the hydrogen and nitrogen concentrations detected by the gas sensors 42, 43, 44 to process the H of the raw material gas. ２ / N ２ The purge rate is controlled by controlling the pressure flow regulator 23a in addition to controlling the supply line 33 through which the raw material gas flows. In this embodiment, "purge rate" refers to the ratio of the total hydrogen flow rate and nitrogen flow rate in the purge line 23 through which the purge gas flows to the total hydrogen flow rate and nitrogen flow rate in the supply line 33 through which the raw material gas flows.

[0062] Next, the details of the ammonia synthesis method using the ammonia synthesis system of this embodiment will be described. The ammonia synthesis method of this embodiment is executed in parallel with the ammonia synthesis method of the first embodiment, immediately after the ammonia synthesis system is started up to synthesize ammonia. In the ammonia synthesis method of this embodiment, the optimal operating conditions according to the size and processing capacity of each part of the ammonia synthesis system are the flow rate of a predetermined raw material hydrogen, the flow rate of a predetermined raw material nitrogen, the flow rate of a predetermined recycled gas, and the target value r of the purge rate supplied to the mixer 30. Ｄ These are pre-set in the control unit 50. When the ammonia synthesis method shown in Figure 8 is started, the control unit 50 inputs a predetermined flow rate of raw material hydrogen, a predetermined flow rate of raw material nitrogen, and a predetermined flow rate of recycled gas to the mass flow controllers 31c, 32c, and 24.

[0063] In the ammonia synthesis method of this embodiment, first, it is determined whether a predetermined time has elapsed since the ammonia synthesis system was started, similar to the ammonia synthesis method of the first embodiment (step S21). If it is determined that the time elapsed since the ammonia synthesis system was started is equal to or greater than the predetermined time t (step S21: YES), the process proceeds to step S22. If it is determined that the time elapsed since the ammonia synthesis system was started is less than the predetermined time t (step S21: NO), the determination in step S21 is continued.

[0064] In step S21, if it is determined that the time elapsed since the ammonia synthesis system was started is greater than or equal to a predetermined time t, it is determined whether the purge rate is within a predetermined range (step S22). Here, the method for calculating the purge rate in this embodiment will be described. First, the method for calculating the total amount of hydrogen flow rate and nitrogen flow rate in the supply line 33 through which the raw material gas flows will be described. The total amount of raw material gas flowing through the supply line 33 is the sum of the mass flow rates set in the mass flow controllers 31c, 32c, and 24, respectively. The hydrogen concentration and nitrogen concentration of the raw material gas in the supply line 33 are detected by the gas sensor 41. In this embodiment, these values ​​are used to calculate the total amount of hydrogen flow rate and nitrogen flow rate in the supply line 33 through which the raw material gas flows. On the other hand, the total amount of hydrogen flow rate and nitrogen flow rate in the purge line 23 through which the purge gas flows is calculated using the flow rate set in the pressure flow regulator 23a provided in the purge line 23 and the hydrogen concentration and nitrogen concentration of the purge gas detected by the gas sensor 43. This allows us to calculate the "purge rate," which is the ratio of the total hydrogen flow rate and nitrogen flow rate in the purge line 23 through which the purge gas flows to the total hydrogen flow rate and nitrogen flow rate in the supply line 33 through which the raw material gas flows. In principle, the hydrogen and nitrogen concentrations of the purge gas detected by the gas sensor 43 are the same as the hydrogen and nitrogen concentrations of the synthesis gas detected by the gas sensor 42 and the hydrogen and nitrogen concentrations of the recycled gas detected by the gas sensor 43. Therefore, these values ​​may be used, or the values ​​detected by each of the gas sensors 42, 43, and 44 may be used.

[0065] In step S22, the control unit 50 uses the hydrogen and nitrogen concentrations detected by the gas sensors 41 and 44, the mass flow rates set in the mass flow controllers 31c, 32c, and 24, and the flow rate set in the pressure flow regulator 23a to determine the purge rate r Ｐ The control unit 50 calculates the calculated purge rate r. Ｐ And the pre-set target value r of the purge rate ＤIt is determined whether the absolute value of the difference is less than or equal to a predetermined value a. The calculated purge rate r Ｐ and the target value r of the purge rate Ｄ If it is determined that the absolute value of the difference is less than or equal to a predetermined value a (Step S22: YES), the process returns to Step S21. The calculated purge rate r Ｐ and the target value r of the purge rate Ｄ If it is determined that the absolute value of the difference is greater than a predetermined value a (step S22: NO), the process proceeds to step S23.

[0066] In step S22, the calculated purge rate r Ｐ and the target value r of the purge rate Ｄ If the absolute value of the difference is determined to be less than or equal to a predetermined value a, the calculated purge rate r Ｐ The target value r for the purging rate Ｄ It is determined whether it is greater than or less than (step S23). In step S23, the purge rate r calculated in step S22 is used. Ｐ The target value r for the purging rate Ｄ Determine whether it is greater than or less. Calculate the purge rate r Ｐ The target value r for the purging rate Ｄ If it is determined to be greater (step S23: YES), proceed to step S241. The calculated purge rate r Ｐ The target value r for the purging rate Ｄ If it is determined to be smaller (step S23: NO), proceed to step S242.

[0067] In step S23, the calculated purge rate r Ｐ The target value r for the purging rate Ｄ If it is determined to be greater than the specified value, at least one of the following is performed: "increase raw hydrogen," "increase raw nitrogen," or "decrease recycled gas" (step S241). In step S241, the control unit 50 controls at least one of the mass flow controllers 31c, 32c, and 24 to change the purge rate by changing at least one of the raw hydrogen flow rate, raw nitrogen flow rate, and recycled gas flow rate. The range of increase or decrease in the raw hydrogen flow rate, raw nitrogen flow rate, and recycled gas flow rate is, for example, the same as Δx, Δy, and Δz described in the first embodiment.

[0068] In this embodiment, when at least one of the following is performed in step S241: "increase raw material hydrogen", "increase raw material nitrogen", and "decrease recycled gas", the flow rate of the raw material gas and the H of the raw material gas ２ / N ２ It is preferable to keep the other parameters fixed while only changing the ratio of the flow rate of raw hydrogen, the flow rate of raw nitrogen, and the flow rate of recycled gas. This is because the flow rate of the raw gas and the H of the raw gas ２ / N ２ When this changes, the rate of ammonia synthesis in catalyst 11 changes, which in turn changes the temperature of catalyst 11, and consequently the flow rate of the raw material gas and the H of the raw material gas. ２ / N ２ This is because it could also have an impact.

[0069] In step S23, the calculated purge rate r Ｐ The target value r for the purging rate Ｄ If it is determined to be smaller, at least one of the following is performed: "reduce raw hydrogen," "reduce raw nitrogen," or "increase recycled gas" (step S242). In step S242, the control unit 50 controls at least one of the mass flow controllers 31c, 32c, and 24 to change the purge rate by changing at least one of the raw hydrogen flow rate, raw nitrogen flow rate, and recycled gas flow rate. The range of increase or decrease in the raw hydrogen flow rate, raw nitrogen flow rate, and recycled gas flow rate is, for example, the same as Δx, Δy, and Δz described in the first embodiment.

[0070] In this embodiment, when at least one of the following is performed in step S242: "reduce raw material hydrogen", "reduce raw material nitrogen", and "increase recycled gas", the flow rate of the raw material gas and the H of the raw material gas ２ / N ２ It is preferable to keep the other parameters fixed while only changing the ratio of the flow rate of raw hydrogen, the flow rate of raw nitrogen, and the flow rate of recycled gas. This is because, as mentioned above, the flow rate of the raw gas and the H of the raw gas ２ / N ２ When this changes, the ammonia synthesis rate in catalyst 11 changes, which in turn changes the temperature of catalyst 11, and consequently the flow rate of the raw material gas and the H of the raw material gas. ２ / N ２ This is because it could also have an impact.

[0071] Following steps S241 and S242, it is determined whether a predetermined time has elapsed since the purge rate was changed (step S25). In step S25, the control unit 50 determines whether the time elapsed since the change in the purge rate due to the change in the gas flow rate, which was performed in either step S241 or S242, is equal to or greater than a predetermined time u. If it is determined that the time elapsed since the change in the purge rate, which was performed in either step S241 or S242, is equal to or greater than a predetermined time u (step S25: YES), the process proceeds to step S26. If it is determined that the time elapsed since the change in the purge rate, which was performed in either step S241 or S242, is less than a predetermined time u (step S25: NO), the determination in step S25 is continued.

[0072] In step S25, if it is determined that the time elapsed since the change in the purge rate is greater than or equal to a predetermined time u, the purge rate r Ｐ The target value is r Ｄ It is determined whether or not it has approached the purge rate r (step S26). In step S26, the control unit 50 again determines the purge rate r Ｐ The calculated purge rate r is calculated. Ｐ and the target value r of the purge rate Ｄ The difference between this and the calculated purge rate r confirmed in the previous step S22 is Ｐ and the target value r of the purge rate Ｄ Determine whether the difference is smaller than the calculated purge rate r. Ｐ and the target value r of the purge rate Ｄ If it is determined that the difference is small (step S26: YES), the process returns to step S21 and determines whether a predetermined amount of time has elapsed since the purge rate was changed (step S21). The calculated purge rate r Ｐ and the target value r of the purge rate Ｄ If it is determined that the difference is large (Step S26: NO), proceed to Step S27.

[0073] In step S26, the calculated purge rate r Ｐ and the target value r of the purge rate ＤIf it is determined that the difference between the two values ​​is large, the operating conditions are reset (step S27). In step S27, the control unit 50 inputs predetermined raw material hydrogen flow rate, predetermined raw material nitrogen flow rate, and predetermined recycled gas flow rate, which are set in the control unit 50 as the optimal operating conditions for the ammonia synthesis system 1, to the mass flow controllers 31c, 32c, and 24.

[0074] After step S27, the process returns to step S21 to determine whether a predetermined amount of time has elapsed since the operating conditions were reset (step S21). In this embodiment, the ammonia synthesis method involves repeatedly performing steps S21 to S27 shown in Figure 8 from the start up to the stop down of the ammonia synthesis system, thereby synthesizing ammonia.

[0075] Generally, in ammonia synthesis using an ammonia synthesis system, the purge rate changes when the ammonia synthesis rate and the synthesis gas flow rate change. Specifically, when the ammonia synthesis rate increases, the synthesis gas flow rate decreases, and if the recycle gas flow rate remains constant, the purge rate decreases. Therefore, when the purge rate falls below 0%, the necessary recycle gas flow rate for ammonia synthesis cannot be secured, the raw material gas flow rate decreases, and the ammonia synthesis rate decreases further. On the other hand, when the ammonia synthesis rate decreases, the synthesis gas flow rate increases, and if the recycle gas flow rate remains constant, the purge rate increases. If the purge rate becomes excessively high, it will result in the supply of excess raw material hydrogen and raw material nitrogen. Therefore, in the ammonia synthesis system of this embodiment, the purge rate is controlled by changing at least one of the raw material hydrogen flow rate, raw material nitrogen flow rate, and recycle gas flow rate. This makes it possible to synthesize ammonia stably while suppressing the supply of excess raw material hydrogen and raw material nitrogen, thereby enabling efficient ammonia synthesis.

[0076] Next, the characteristics of the ammonia synthesis method in the ammonia synthesis system of this embodiment will be explained using the relationship between the gas flow rate and the flow rate ratio in the ammonia synthesis system shown in Figure 6. In the ammonia synthesis method in the ammonia synthesis system of this embodiment, the purge rate is r Ｐ Therefore, the relationship with the gas flow rate in the ammonia synthesis system can be expressed by the following equation (3): r Ｐ = (F Ｈ２ +F Ｎ２ -2α) / (F Ｈ２ +F Ｎ２ +F Ｒ ) ... (3) As shown in equation (3), the purge rate r Ｐ The purge rate depends on the flow rate α of the ammonia being synthesized. In other words, if the ammonia synthesis rate changes, the purge rate also changes. Therefore, in the ammonia synthesis system of this embodiment, in order to suppress the excess supply of raw material hydrogen and raw material nitrogen, the purge rate is controlled, and the purge rate is controlled to reach a target value by manipulating the operating parameters (flow rate of raw material hydrogen, flow rate of raw material nitrogen, flow rate of recycled gas) using the hydrogen concentration and nitrogen concentration in at least one of the synthesis gas, unreacted gas, recycled gas, and purge gas.

[0077] Figure 9 illustrates the relationship between the operating time and the purge rate of an ammonia synthesis system. In Figure 9, the relationship between the operating time and the purge rate in the ammonia synthesis system 1 of this embodiment is shown by the solid line Rp1, and the relationship between the operating time and the ammonia synthesis rate in an ammonia synthesis system without purge rate control, as a comparative example, is shown by the dashed line Rp0. As shown in Figure 8, in the comparative example ammonia synthesis system, the purge rate gradually increases during steady-state operation, which may lead to unstable ammonia synthesis. On the other hand, in the ammonia synthesis system of this embodiment, the purge rate is controlled to remain stable, so ammonia synthesis is also performed stably.

[0078] Furthermore, in the ammonia synthesis system of this embodiment, the purge rate is controlled according to the composition of the gas extracted from the catalytic reactor 10, even during startup and shutdown. This allows for continuous and stable ammonia synthesis from the start-up to the shutdown of the ammonia synthesis system. Therefore, even under transient operating conditions where the ammonia synthesis system is relatively unstable, hydrogen and nitrogen can be effectively utilized for ammonia synthesis without being wasted.

[0079] As described above, in the ammonia synthesis system of this embodiment, the control unit 50 controls the purge rate, which has a constant relationship with the flow rate of gas removed from the catalytic reactor 10 and changes according to the ammonia synthesis rate in the catalytic reactor 10. This allows the ammonia synthesis rate to be controlled, enabling stable ammonia synthesis. Therefore, ammonia can be synthesized efficiently.

[0080] Furthermore, in the ammonia synthesis system of this embodiment, the control unit 50 controls the purge rate using the ratio of hydrogen concentration to nitrogen concentration in the gas extracted from the catalytic reactor 10. This allows the ammonia synthesis rate in the catalytic reactor 10 to be fed back into the flow rate and composition of the raw material gas, thereby enabling more stable ammonia synthesis. Consequently, ammonia can be synthesized even more efficiently.

[0081] Furthermore, according to the ammonia synthesis system of this embodiment, the control unit 50 controls the purge rate during the period from when the ammonia synthesis system is started until it reaches a steady-state operation, or from the steady-state operation until it is stopped, when ammonia synthesis is relatively unstable. As a result, ammonia can be synthesized stably while the ammonia synthesis system is in operation, and thus ammonia can be synthesized more efficiently.

[0082] <Third Embodiment> Figure 10 is a schematic diagram showing the general configuration of the ammonia synthesis system of the third embodiment. The ammonia synthesis system of the third embodiment differs from the ammonia synthesis system of the first embodiment (Figure 1) in that it is further equipped with a temperature sensor for detecting the catalyst temperature.

[0083] The ammonia synthesis system 3 of this embodiment, like the ammonia synthesis system 1 of the first embodiment, includes a catalytic reactor 10, a separator 20, a mixer 30, gas sensors 41, 42, 43, 44, a temperature detection unit 45, a pressure flow regulator 23a, and a control unit 50. In the ammonia synthesis system 3, the control unit 50 uses the hydrogen and nitrogen concentrations detected by the gas sensors 42, 43, 44 to process the H of the raw material gas. ２ / N ２ The system controls the temperature of the catalyst 11 using the detection results from the temperature detection unit 45.

[0084] The temperature detection unit 45 detects the temperature of the catalyst 11 housed in the catalytic reactor 10. The temperature detection unit 45 is, for example, a thermocouple and is electrically connected to the control unit 50. The temperature detection unit 45 outputs the detected temperature of the catalyst 11 to the control unit 50.

[0085] Figure 11 is a flowchart of the ammonia synthesis method of the third embodiment. Next, the details of the ammonia synthesis method using the ammonia synthesis system 3 of this embodiment will be described. The ammonia synthesis method of this embodiment is executed in parallel with the ammonia synthesis method of the first embodiment, immediately after the ammonia synthesis system 3 is started up to synthesize ammonia. In the ammonia synthesis method of this embodiment, the control unit 50 sets the optimal operating conditions according to the size and processing capacity of each part of the ammonia synthesis system, including the flow rate of a predetermined raw material hydrogen supplied to the mixer 30, the flow rate of a predetermined raw material nitrogen, the flow rate of a predetermined recycled gas, a predetermined temperature of the raw material gas, and the target temperature T of the catalyst 11. Ｓ The control unit 50 has preset settings for this. When the ammonia synthesis method shown in Figure 11 is started, the control unit 50 controls the heater 33a so that the temperature of the raw material gas reaches a predetermined temperature that has been set in advance.

[0086] In the ammonia synthesis method of this embodiment, first, similar to the ammonia synthesis method of the first embodiment, it is determined whether a predetermined time has elapsed since the ammonia synthesis system 3 was started (step S31). If it is determined that the time elapsed since the ammonia synthesis system was started is equal to or greater than the predetermined time t (step S31: YES), the process proceeds to step S32. If it is determined that the time elapsed since the ammonia synthesis system was started is less than the predetermined time t (step S31: NO), the determination in step S31 is continued.

[0087] In step S31, if it is determined that the time elapsed since the ammonia synthesis system 3 was started is greater than or equal to a predetermined time t, it is determined whether the temperature of the catalyst is within a predetermined range (step S32). In step S32, the control unit 50 determines whether the temperature of the catalyst 11 detected by the temperature detection unit 45 is within a predetermined range T Ｃ And the target temperature T of the catalyst 11, which is set in advance. Ｓ It is determined whether the absolute value of the difference between the detected temperature and the temperature is less than or equal to a predetermined value a. In this embodiment, the predetermined value a is, for example, 0.1°C to 100°C. Ｃ and target temperature T Ｓ If it is determined that the absolute value of the difference is less than or equal to a predetermined value a (step S32: YES), the process returns to step S31. Detected temperature T Ｃ and target temperature T Ｓ If it is determined that the absolute value of the difference is greater than a predetermined value a (step S32: NO), the process proceeds to step S33.

[0088] In step S32, the detected temperature T Ｃ and target temperature T Ｓ If it is determined that the absolute value of the difference between the two is less than or equal to a predetermined value a, then the detected temperature T Ｃ The target temperature is T Ｓ It is determined whether it is greater than or less than (step S33). In step S33, the detection temperature T of the catalyst 11 detected by the temperature detection unit 45 is determined. Ｃ However, the target temperature T of the catalyst 11 is set in advance. Ｓ Determine whether it is greater than or less. Detection temperature T Ｃ The target temperature is T ＳIf it is determined to be greater (step S33: YES), proceed to step S341. Detected temperature T Ｃ The target temperature is T Ｓ If it is determined to be smaller (step S33: NO), proceed to step S342.

[0089] In step S33, the detected temperature T Ｃ The target temperature is T Ｓ If it is determined to be greater than the threshold, the temperature of the raw material gas is lowered (step S341). In step S341, the control unit 50 controls the heater 33a so that the temperature of the raw material gas is lower than the temperature immediately before. As a result, the temperature of the catalyst 11 in the catalytic reactor 10 to which the raw material gas is supplied decreases. The amount of change in the temperature of the raw material gas in step S341 is, for example, 0.01°C to 100°C.

[0090] In step S33, the detected temperature T Ｃ The target temperature is T Ｓ If it is determined that the temperature is smaller, the temperature of the raw material gas is increased (step S342). In step S342, the control unit 50 controls the heater 33a so that the temperature of the raw material gas becomes higher than the temperature immediately before. As a result, the temperature of the catalyst 11 rises in the catalytic reactor 10 to which the raw material gas is supplied. The amount of change in the temperature of the raw material gas in step S342 is, for example, 0.01°C to 100°C.

[0091] Following steps S341 and S342, it is determined whether a predetermined time has elapsed since the temperature of the raw material gas was changed (step S35). In step S35, the control unit 50 determines whether the time elapsed since the temperature change of the raw material gas performed in either step S341 or S342 is equal to or greater than a predetermined time u. If it is determined that the time elapsed since the temperature change of the raw material gas performed in either step S341 or S342 is equal to or greater than a predetermined time u (step S35: YES), the process proceeds to step S36. If it is determined that the time elapsed since the temperature change of the raw material gas performed in either step S341 or S342 is less than a predetermined time u (step S35: NO), the determination in step S35 is continued.

[0092] In step S35, if it is determined that the time elapsed since the temperature change of the raw material gas is greater than or equal to a predetermined time u, the detection temperature of the catalyst 11 T Ｃ The target temperature is T Ｓ Step S36 determines whether it has approached the detection temperature T of the catalyst 11 detected by the temperature detection unit 45. Ｃ and target temperature T Ｓ The difference between this and the detected temperature T confirmed in the previous step S32 is Ｃ and target temperature T Ｓ Determine whether the difference is smaller than the value. Detection temperature T Ｃ and target temperature T Ｓ If it is determined that the difference is small (step S36: YES), the process returns to step S31 to determine whether a predetermined time has elapsed since the temperature of the raw material gas was changed (step S31). Detected temperature T Ｃ and target temperature T Ｓ If it is determined that the difference is large (Step S36: NO), proceed to Step S37.

[0093] In step S36, the detected temperature T Ｃ and target temperature T Ｓ If it is determined that the difference is large, the operating conditions are reset (step S37). In step S37, the control unit 50 controls the heater 33a so that the temperature of the raw material gas reaches a predetermined temperature set in the control unit 50 as the optimal operating condition for the ammonia synthesis system 1.

[0094] After step S37, the process returns to step S31 to determine whether a predetermined amount of time has elapsed since the operating conditions were reset (step S31). In this embodiment, the ammonia synthesis method is carried out by repeatedly performing steps S31 to S37 shown in Figure 11.

[0095] Generally, in ammonia synthesis using an ammonia synthesis system, a change in the flow rate of ammonia synthesized in the catalytic reactor also changes the temperature of the catalyst. This, in turn, causes a further change in the ammonia flow rate. In the ammonia synthesis system of this embodiment, the temperature of the catalyst 11 is controlled by controlling the temperature of the raw material gas, thereby stably synthesizing ammonia. This allows for efficient ammonia synthesis.

[0096] As described above, the ammonia synthesis system 3 of this embodiment controls the temperature of the catalyst 11, which affects the ammonia synthesis rate, by adjusting the temperature of the raw material gas using the heater 33a. This allows the ammonia synthesis rate to be controlled, enabling stable ammonia synthesis in the catalytic reactor 10. Therefore, ammonia can be synthesized efficiently.

[0097] <Modifications of this Embodiment> The present invention is not limited to the above-described embodiments, and can be implemented in various forms without departing from the spirit of the invention. For example, the following modifications are also possible.

[0098] [Modification 1] In the first and second embodiments, the ammonia synthesis method is performed from the start to the stop of the ammonia synthesis system. However, the operating time of the ammonia synthesis system is not limited to this. In both the first and second embodiments, the ammonia synthesis method of each embodiment may be performed only during steady-state operation.

[0099] When an ammonia synthesis system starts or stops, the ammonia synthesis rate changes abruptly. Therefore, if the ratio of hydrogen flow rate to nitrogen flow rate in the supply line and the purge rate are not controlled, recycling operation cannot be performed, and the purge rate becomes 100%, requiring all unreacted hydrogen and nitrogen to be discarded as purge gas. However, by performing these controls when the ammonia synthesis system starts or stops, it becomes possible to reuse unreacted hydrogen and nitrogen contained in the synthesis gas, thereby reducing the supply of excess raw material hydrogen and nitrogen. Consequently, ammonia can be synthesized efficiently.

[0100] [Modification 2] In the second and third embodiments, the ratio of hydrogen flow rate to nitrogen flow rate in the supply line through which the raw material gas flows in the ammonia synthesis method of the first embodiment is controlled, and in parallel with this control, the purge rate and catalyst temperature are controlled. These controls may be performed separately. That is, the control of the purge rate and the control of the catalyst temperature may be performed independently.

[0101] [Modification 3] In the above embodiment, the catalyst was a Ru-based catalyst containing ruthenium. The catalyst used for ammonia synthesis is not limited to this. For example, an Fe-based catalyst may also be used.

[0102] The embodiments of this specification have been described above based on the embodiments and modifications described above. The embodiments described above are for the purpose of facilitating understanding of this specification and do not limit it. This specification may be modified and improved without departing from its spirit and the scope of the claims, and equivalents thereof are included in this specification. Furthermore, any technical features that are not described as essential in this specification may be deleted as appropriate.

[0103] <Application Example 1> An ammonia synthesis system comprising: a catalytic reactor containing a catalyst and synthesizing ammonia from hydrogen and nitrogen; a separator that separates the synthesis gas containing ammonia, taken out from the catalytic reactor, into ammonia and unreacted gas containing hydrogen and nitrogen; a supply line that supplies the raw material gas, which includes recycled gas which is at least a part of the unreacted gas, raw material hydrogen supplied from a hydrogen supply source, and raw material nitrogen supplied from a nitrogen supply source, to the catalytic reactor; and a control unit that controls the ratio of the hydrogen flow rate to the nitrogen flow rate in the supply line. <Application Example 2> The ammonia synthesis system according to Application Example 1 further comprises: a concentration ratio calculation unit that calculates the ratio of the hydrogen concentration to the nitrogen concentration in any one of the synthesis gas, the unreacted gas, and the recycled gas; and the control unit controls the ratio of the hydrogen flow rate to the nitrogen flow rate in the supply line by changing at least one of the flow rate of the recycled gas, the flow rate of the raw material hydrogen, and the flow rate of the raw material nitrogen using the ratio of the hydrogen concentration to the nitrogen concentration calculated by the concentration ratio calculation unit. <Application Example 3> An ammonia synthesis system according to Application Example 1 or Application Example 2, wherein the control unit controls the ratio of the hydrogen flow rate to the nitrogen flow rate in the supply line from the time the ammonia synthesis system is started until it reaches a steady-state operating state, or from the time it reaches a steady-state operating state until it is stopped. <Application Example 4> An ammonia synthesis system according to any one example from Application Example 1 to Application Example 3, further comprising a purge line that discharges gases other than the recycled gas from the unreacted gases to the outside of the ammonia synthesis system as a purge gas, wherein the control unit controls the purge rate, which is the ratio of the total amount of hydrogen flow rate and nitrogen flow rate in the purge line to the total amount of hydrogen flow rate and nitrogen flow rate in the supply line.<Application Example 5> An ammonia synthesis system according to any one of Application Examples 1 to 4, further comprising a concentration ratio calculation unit that calculates the ratio of hydrogen concentration to nitrogen concentration in any one of the synthesis gas, the unreacted gas, the recycled gas, and the purge gas, and a control unit that controls the purge rate by changing at least one of the flow rate of raw hydrogen, the flow rate of raw nitrogen, and the flow rate of recycled gas using the ratio of hydrogen concentration to nitrogen concentration calculated by the concentration ratio calculation unit, an ammonia synthesis system. <Application Example 6> An ammonia synthesis system according to any one of Application Examples 1 to 5, wherein the control unit controls the purge rate from the time the ammonia synthesis system is started until it reaches a steady-state operating state, or from the steady-state operating state until it is stopped, an ammonia synthesis system. <Example 7> An ammonia synthesis system according to any one of Examples 1 to 6, further comprising: a gas temperature control unit for adjusting the temperature of the raw material gas; and a catalyst temperature detection unit for detecting the temperature of the catalyst, wherein the control unit controls the temperature of the catalyst by adjusting the temperature of the raw material gas in the gas temperature control unit using the temperature of the catalyst detected by the catalyst temperature detection unit, thereby controlling the temperature of the catalyst. <Example 8> An ammonia synthesis system according to any one of Examples 1 to 7, wherein the catalyst housed in the catalytic reactor is a ruthenium-containing catalyst. <Application Example 9> An ammonia synthesis method for synthesizing ammonia using an ammonia synthesis system, comprising: a step of synthesizing ammonia from hydrogen and nitrogen using a catalyst housed in a catalytic reactor; a step of separating the synthesis gas removed from the catalytic reactor into ammonia and an unreacted gas containing hydrogen and nitrogen; a step of supplying a raw material gas containing recycled gas which is at least a portion of the unreacted gas, raw material hydrogen supplied from a hydrogen supply source, and raw material nitrogen supplied from a nitrogen supply source to the catalytic reactor using a supply line; and a step of controlling the ratio of hydrogen flow rate to nitrogen flow rate in the supply line.<Application Example 10> A computer program that causes a computer to perform the synthesis of ammonia using an ammonia synthesis system, the computer program that causes the computer to perform the following functions: a function to synthesize ammonia from hydrogen and nitrogen using a catalyst housed in a catalytic reactor; a function to separate the synthesis gas extracted from the catalytic reactor into ammonia and unreacted gas containing hydrogen and nitrogen; a function to supply to the catalytic reactor, using a supply line, a recycled gas which is at least a part of the unreacted gas, raw material hydrogen supplied from a hydrogen supply source, and raw material nitrogen supplied from a nitrogen supply source; and a function to control the ratio of hydrogen flow rate to nitrogen flow rate in the supply line.

[0104] 1, 3... Ammonia synthesis system 10... Catalytic reactor 11... Catalyst 20... Separator 23... Purge line 33... Supply line 31b... Hydrogen supply source 32b... Nitrogen supply source 33a... Heater 42, 43, 44... Gas sensors 45... Temperature detection unit 50... Control unit

Claims

1. An ammonia synthesis system comprising: a catalytic reactor containing a catalyst for synthesizing ammonia from hydrogen and nitrogen; a separator for separating the synthesis gas containing ammonia, taken out from the catalytic reactor, into ammonia and unreacted gas containing hydrogen and nitrogen; a supply line for supplying the raw material gas, which includes recycled gas which is at least a portion of the unreacted gas, raw material hydrogen supplied from a hydrogen supply source, and raw material nitrogen supplied from a nitrogen supply source, to the catalytic reactor; and a control unit for controlling the ratio of hydrogen flow rate to nitrogen flow rate in the supply line.

2. The ammonia synthesis system according to claim 1 further comprises a concentration ratio calculation unit that calculates the ratio of hydrogen concentration to nitrogen concentration in any one of the synthesis gas, the unreacted gas, and the recycled gas, and the control unit controls the ratio of hydrogen flow rate to nitrogen flow rate in the supply line by changing at least one of the flow rate of the recycled gas, the flow rate of raw hydrogen, and the flow rate of raw nitrogen using the ratio of hydrogen concentration to nitrogen concentration calculated by the concentration ratio calculation unit.

3. An ammonia synthesis system according to claim 1 or claim 2, wherein the control unit controls the ratio of the hydrogen flow rate to the nitrogen flow rate in the supply line from the time the ammonia synthesis system is started until it reaches a steady-state operating state, or from the steady-state operating state until it is stopped.

4. The ammonia synthesis system according to claim 1 further comprises a purge line for discharging gases other than the recycled gas from the unreacted gases to the outside of the ammonia synthesis system as a purge gas, and the control unit controls the purge rate, which is the ratio of the total amount of hydrogen flow rate and nitrogen flow rate in the purge line to the total amount of hydrogen flow rate and nitrogen flow rate in the supply line.

5. The ammonia synthesis system according to claim 4 further comprises a concentration ratio calculation unit that calculates the ratio of hydrogen concentration to nitrogen concentration in any one of the synthesis gas, the unreacted gas, the recycled gas, and the purge gas, and the control unit controls the purge rate by changing at least one of the flow rate of raw hydrogen, the flow rate of raw nitrogen, and the flow rate of recycled gas using the ratio of hydrogen concentration to nitrogen concentration calculated by the concentration ratio calculation unit.

6. An ammonia synthesis system according to claim 5, wherein the control unit controls the purge rate from the time the ammonia synthesis system is started until it reaches a steady-state operating state, or from the steady-state operating state until it is stopped.

7. An ammonia synthesis system according to claim 1 or claim 2, further comprising: a gas temperature control unit for adjusting the temperature of the raw material gas; and a catalyst temperature detection unit for detecting the temperature of the catalyst, wherein the control unit controls the temperature of the catalyst by adjusting the temperature of the raw material gas in the gas temperature control unit using the temperature of the catalyst detected by the catalyst temperature detection unit.

8. An ammonia synthesis system according to claim 1 or claim 2, wherein the catalyst housed in the catalytic reactor is a ruthenium-containing catalyst.

9. A method for synthesizing ammonia using an ammonia synthesis system, comprising: a step of synthesizing ammonia from hydrogen and nitrogen using a catalyst housed in a catalytic reactor; a step of separating the synthesis gas removed from the catalytic reactor into ammonia and an unreacted gas containing hydrogen and nitrogen; a step of supplying a raw material gas containing recycled gas which is at least a portion of the unreacted gas, raw material hydrogen supplied from a hydrogen supply source, and raw material nitrogen supplied from a nitrogen supply source to the catalytic reactor using a supply line; and a step of controlling the ratio of the hydrogen flow rate to the nitrogen flow rate in the supply line.

10. A computer program that causes a computer to perform the synthesis of ammonia using an ammonia synthesis system, the computer program that causes the computer to perform the following functions: a function to synthesize ammonia from hydrogen and nitrogen using a catalyst housed in a catalytic reactor; a function to separate the synthesis gas extracted from the catalytic reactor into ammonia and unreacted gas containing hydrogen and nitrogen; a function to supply to the catalytic reactor, using a supply line, a recycled gas which is at least a portion of the unreacted gas, raw material hydrogen supplied from a hydrogen supply source, and raw material nitrogen supplied from a nitrogen supply source; and a function to control the ratio of hydrogen flow rate to nitrogen flow rate in the supply line.

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