Ammonia synthesis system

Abstract

To provide a technology capable of efficiently synthesizing ammonia.SOLUTION: An ammonia synthesis system for synthesizing ammonia comprises a reactor containing a catalyst for promoting a synthesis reaction for synthesizing ammonia from a reaction gas containing hydrogen and nitrogen, and a control part for controlling a H2 / N2 ratio which is the ratio of hydrogen to nitrogen in the reaction gas supplied to the reactor, the control part controlling the H2 / N2 ratio according to the degree of deterioration of the catalyst.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an ammonia synthesis system. [Background technology]

[0002] Conventionally, there has been known an ammonia synthesis system that synthesizes ammonia by supplying a reaction gas containing nitrogen (N2) and hydrogen (H2) to a reactor containing a catalyst. As such an ammonia synthesis system, for example, Patent Document 1 discloses an ammonia synthesis system that cools an intermediate product gas using a purge gas or a cooler. In addition, Patent Document 2 discloses an ammonia synthesis system that performs ammonia synthesis by setting the concentration of ammonia gas in the circulation gas used for ammonia synthesis to 3% by volume or more. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-203603 A [Patent Document 2] JP 2020-66573 A Summary of the Invention [Problem to be solved by the invention]

[0004] The ratio of hydrogen to nitrogen in the reaction gas supplied to the catalyst (H2 / N2 ratio) is one of the parameters that determine the ammonia synthesis rate. The H2 / N2 ratio appropriate for promoting the ammonia synthesis rate varies depending on, for example, the degree of catalyst deterioration. However, the ammonia synthesis systems in Patent Documents 1 and 2 do not take into consideration the control of the H2 / N2 ratio, and there is room for improvement.

[0005] The present invention has been made to solve at least a part of the above-mentioned problems, and has an object to provide an ammonia synthesis system capable of efficiently synthesizing ammonia. [Means for solving the problem]

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

[0007] (1) According to one aspect of the present invention, there is provided an ammonia synthesis system comprising a reactor containing a catalyst that promotes a synthesis reaction for synthesizing ammonia from a reaction gas containing hydrogen and nitrogen, and a control unit that controls an H2 / N2 ratio, which is a ratio of hydrogen to nitrogen in the reaction gas supplied to the reactor, and the control unit controls the H2 / N2 ratio in accordance with a degree of deterioration of the catalyst.

[0008] The H2 / N2 ratio in the reaction gas suitable for synthesizing ammonia tends to become smaller as the catalyst deteriorates. With this configuration, the H2 / N2 ratio in the reaction gas can be controlled according to the degree of deterioration of the catalyst. Therefore, ammonia can be synthesized more efficiently than in a configuration in which a reaction gas with an H2 / N2 ratio adjusted without considering the degree of deterioration of the catalyst is supplied to the reactor. In other words, as the catalyst deteriorates, the H2 / N2 ratio in the reaction gas approaches a suitable value at which the activity of the catalyst is further promoted, thereby reducing the input energy required for producing ammonia.

[0009] (2) In the ammonia synthesis system of the above aspect, the control unit may control the H2 / N2 ratio using at least one of the ammonia concentration in the reaction gas discharged from the reactor and the temperature of the catalyst as an indicator of the degree of deterioration of the catalyst. For example, if the ammonia concentration in the post-reaction gas when a reaction gas with a certain H2 / N2 ratio is supplied to a catalyst is lower than the ammonia concentration in the post-reaction gas when the reaction gas with the same H2 / N2 ratio is supplied to an undegraded catalyst, the catalyst can be considered to be degraded. In addition, since the ammonia synthesis reaction is an exothermic reaction, if the temperature of the catalyst when a reaction gas with the same H2 / N2 ratio is supplied to a catalyst is lower than the temperature of the catalyst when a reaction gas with the same H2 / N2 ratio is supplied to the catalyst, the catalyst can be considered to be degraded. Therefore, according to this configuration, the ammonia concentration in the post-reaction gas and the temperature of the catalyst are used as indicators of catalyst degradation, so that the H2 / N2 ratio can be controlled while accurately grasping the degree of catalyst degradation. As a result, a reaction gas with an H2 / N2 ratio according to the catalyst degradation can be supplied to the reactor, so that ammonia can be synthesized more efficiently.

[0010] (3) In the ammonia synthesis system of the above aspect, the control unit executes a reduction control to reduce the H2 / N2 ratio when the ammonia concentration at a first reference time point is equal to or lower than a comparative concentration obtained by multiplying the ammonia concentration at a comparison time point prior to the first reference time point by a predetermined rate, or when the temperature of the catalyst at the first reference time point is equal to or lower than a comparative temperature obtained by multiplying the temperature of the catalyst at the comparison time point by a predetermined rate, and when the ammonia concentration at a second reference time point after last executing the reduction control is higher than the ammonia concentration at the first reference time point, or when the temperature of the catalyst at the second reference time point is higher than the temperature of the catalyst at the first reference time point. In this case, a maintenance control is executed to maintain the H2 / N2 ratio after the last reduction control was executed, and if the ammonia concentration at the second reference time point is equal to or lower than the ammonia concentration at the first reference time point, or if the temperature of the catalyst at the second reference time point is equal to or lower than the temperature of the catalyst at the first reference time point, a regression control is executed to return the H2 / N2 ratio to the H2 / N2 ratio before the last reduction control was executed, and the time point after the maintenance control or the regression control is executed is regarded as the new first reference time point, and the ammonia concentration at the first reference time point is compared with the comparison concentration and the temperature of the catalyst at the first reference time point is compared with the comparison temperature again. According to this configuration, by executing the decrease control, the regression control, or the maintenance control according to the ammonia concentration in the reaction gas and the temperature of the catalyst, the H2 / N2 ratio in the reaction gas can be brought closer to a value suitable for ammonia synthesis, and therefore ammonia can be synthesized more efficiently.

[0011] The present invention can be realized in various aspects, for example, in the form of an ammonia synthesis system, an ammonia production plant, an ammonia production apparatus, an apparatus and system including these, an ammonia production method, an ammonia synthesis method, a computer program for executing these apparatus and methods, a server device for distributing this computer program, and a non-transitory storage medium storing the computer program. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is an explanatory diagram illustrating the configuration of an ammonia synthesis system according to a first embodiment. [Diagram 2] FIG. 2 is an explanatory diagram showing the flow of reaction gas supplied into the reactor. [Diagram 3] FIG. 11 is an explanatory diagram for explaining an activation temperature. [Figure 4] FIG. 1 is an explanatory diagram showing the concentration of ammonia synthesized using a general Ru catalyst. [Diagram 5] 4 is a flowchart showing an example of a procedure for an H2 / N2 ratio control process. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] First Embodiment 1 is an explanatory diagram illustrating the configuration of an ammonia synthesis system 1 according to one embodiment of the present invention. The ammonia synthesis system 1 is a system that synthesizes ammonia from a reaction gas containing hydrogen and nitrogen. The ammonia synthesis system 1 includes a control unit 5, a mixer 10, a first heat exchanger 20, a heater 30, a reactor 40, a second heat exchanger 50, a cooler 60, a gas-liquid separator 70, and a storage tank 80.

[0014] The mixer 10 mixes hydrogen supplied from a hydrogen tank (not shown) and nitrogen supplied from a nitrogen tank (not shown) to generate a reaction gas containing hydrogen and nitrogen. The reaction gas generated in the mixer 10 is sent toward the reactor 40. The reaction gas is compressed by the mixer 10 or a compressor (not shown) separate from the mixer 10, and then sent toward the reactor 40. Ammonia is synthesized in the reactor 40 using this reaction gas. Note that the synthesis reaction of synthesizing ammonia from the reaction gas containing hydrogen and nitrogen is an exothermic reaction.

[0015] A first heat exchanger 20 and a heater 30 are disposed between the mixer 10 and the reactor 40. The first heat exchanger 20 exchanges heat between the reaction gas sent from the mixer 10 to the reactor 40 and the post-reaction gas sent from the reactor 40. In detail, the post-reaction gas heated by the synthesis reaction in the reactor 40 heats the reaction gas sent from the mixer 10 to the reactor 40 in the first heat exchanger 20. The reaction gas heated in the first heat exchanger 20 is further heated by the heater 30.

[0016] In the reactor 40, ammonia is synthesized using the reaction gas supplied from the mixer 10. The reactor 40 contains a catalyst 45 therein for promoting a synthesis reaction for synthesizing ammonia from the reaction gas. The reaction gas sent from the reactor 40 to the first heat exchanger 20 contains the synthesized ammonia and unreacted hydrogen and nitrogen. The ammonia concentration, hydrogen concentration and nitrogen concentration in the reaction gas are detected by a gas sensor (not shown, installed in the pipe or in a branched pipe) provided in a pipe for flowing the reaction gas from the reactor 40 to the first heat exchanger 20. In addition, the temperature of the catalyst 45, which varies due to the supply of the heated reaction gas and the heat generated by the synthesis reaction, is detected by a temperature sensor such as a thermocouple provided in the reactor 40. The control unit 5 controls the H2 / N2 ratio, which is the ratio of hydrogen to nitrogen in the reaction gas supplied to the reactor 40, by adjusting the amount of hydrogen and the amount of nitrogen supplied to the mixer 10.

[0017] The reacted gas discharged from the reactor 40 passes through the first heat exchanger 20 and the second heat exchanger 50, is cooled by the cooler 60, and then reaches the gas-liquid separator 70. The gas-liquid separator 70 separates liquid ammonia from the reacted gas by cooling the reacted gas. The separated liquid ammonia is stored in the storage tank 80. Meanwhile, the reacted gas from which the liquid ammonia has been separated contains unreacted hydrogen and nitrogen, and unseparated ammonia. For this reason, the reacted gas from which the liquid ammonia has been separated passes through the second heat exchanger 50 and the compressor 90 as a recycled gas, and is then supplied to a pipe for flowing the reacted gas from the mixer 10 to the reactor 40. In detail, the recycled gas is heated in the second heat exchanger 50 by the reacted gas discharged from the reactor 40 (reached the second heat exchanger 50 via the first heat exchanger 20), and is then compressed by the compressor 90 and supplied to a pipe through which the reacted gas flows. On the other hand, the recycled gas that is not sent to the second heat exchanger 50 is purged to the outside of the ammonia synthesis system 1. When a gas sensor (not shown, installed in the pipe or in a branched pipe) is provided in any of the pipes through which the recycled gas flows, it is possible to estimate the ammonia concentration in the post-reaction gas based on the difference between the hydrogen concentration and nitrogen concentration in the recycled gas detected by the gas sensor and the hydrogen concentration and nitrogen concentration in the reaction gas.

[0018] FIG. 2 is an explanatory diagram showing the flow of the reaction gas from when it is supplied to the inside of the reactor 40 until it is discharged. The reactor 40 has an inner pipe 41 and an outer pipe 42. The inner pipe 41 has a cylindrical shape and accommodates a catalyst 45 therein. The outer pipe 42 has a cylindrical shape and covers the inner pipe 41. In addition to the configuration described in FIG. 1, the ammonia synthesis system 1 includes an upstream heater 43 and a downstream heater 44. The upstream heater 43 is provided downstream of the heater 30 in a pipe (not shown) that connects the mixer 10 and the reactor 40. The downstream heater 44 is provided in a pipe (not shown) that connects the downstream end of the outer pipe 42 and the upstream end of the inner pipe 41.

[0019] The reaction gas sent from the mixer 10 toward the reactor 40 is heated by the upstream heater 43 and then supplied to the inside of the outer pipe 42 (and outside the inner pipe 41), and then reaches the downstream heater 44. The reaction gas is then heated by the downstream heater 44 and supplied to the inside of the inner pipe 41, passes through the catalyst 45, and is then discharged from the reactor 40 as a reacted gas.

[0020] FIG. 3 shows the results of measuring the temperature change over time of the catalyst 45 after the supply of the reaction gas to the reactor 40 is started. In FIG. 3, the horizontal axis indicates the elapsed time (h), and the vertical axis indicates the temperature (°C) of the catalyst 45. Each of the curves L1 to L6 shown in FIG. 3 shows the change over time of the temperature of the catalyst 45 when reaction gases with various H2 / N2 ratios are supplied to the reactor 40. The larger the number in the symbol indicating each curve, the larger the H2 / N2 ratio of the reaction gas supplied to the reactor 40. That is, among the curves L1 to L6, the curve L6 shows the result when the reaction gas with the largest H2 / N2 ratio is supplied to the reactor 40.

[0021] As shown in FIG. 3, when the supply of the reaction gas to the reactor 40 is started, the catalyst 45 starts to rise in temperature due to the synthesis reaction of ammonia, which is an exothermic reaction. After that, as the temperature continues to rise, when the temperature exceeds a certain temperature (the temperature indicated by the open diamond), the temperature of the catalyst 45 starts to rise suddenly. This sudden rise is caused by the catalyst 45 being activated by the continued temperature rise, which further promotes the synthesis reaction of ammonia. Here, the certain temperature corresponds to the activation temperature at which the catalyst 45 is considered to be activated. The open diamonds shown on the curves L1 to L6 indicate activation temperatures that are preset based on experimental results, etc. In the ammonia synthesis system 1, the operation from the start of the supply of the reaction gas to the reactor 40 to the time when the temperature of the catalyst 45 is raised to the activation temperature is called pre-activation operation, and the operation after the temperature of the catalyst 45 reaches the activation temperature is called post-activation operation.

[0022] Fig. 4 is an explanatory diagram showing the ammonia concentration synthesized when a reaction gas (containing hydrogen and nitrogen) is supplied to a reactor (not shown) containing a general Ru catalyst. In Fig. 4, the horizontal axis indicates the H2 / N2 ratio in the reaction gas, and the vertical axis indicates the ammonia concentration (%) in the post-reaction gas discharged from the reactor. The value on the horizontal axis increases toward the right side of the drawing. The value on the vertical axis is the average value of the ammonia concentration in the post-reaction gas after the temperature of the Ru catalyst reaches or exceeds the activation temperature (see Fig. 3) and is saturated while the supply of the reaction gas to the reactor is continued.

[0023] The solid line La shows the ammonia concentration in the post-reaction gas when reaction gases with various H2 / N2 ratios are supplied to an undegraded Ru catalyst before the ammonia equilibrium concentration is reached. Here, the ammonia equilibrium concentration refers to the ammonia concentration in the reactor when the ammonia synthesis reaction and its reverse reaction are in equilibrium under the temperature and pressure conditions in the reactor. The dashed line Lb shows the ammonia concentration in the post-reaction gas when reaction gases with various H2 / N2 ratios are supplied to a aged Ru catalyst before the ammonia equilibrium concentration is reached. Here, aging refers to keeping the target catalyst at 500°C for 9 hours, which is a process performed to degrade the catalyst. Note that the temperature of the reaction gas supplied to the Ru catalyst is the same in each of the solid line La and dashed line Lb.

[0024] When the Ru catalyst deteriorated (shifted from solid line La to dashed line Lb), the ammonia concentration in the post-reaction gas decreased regardless of the H2 / N2 ratio of the reaction gas. For example, when the reaction gas with the same H2 / N2 ratio was supplied, the ammonia concentration in the post-reaction gas decreased by 20% due to deterioration when comparing points Pa1 and Pb1, and the ammonia concentration in the post-reaction gas decreased by 24% due to deterioration when comparing points Pa2 and Pb2. Also, as shown by the solid line La, in the case of an undeteriorated Ru catalyst, the ammonia concentration in the post-reaction gas tended to be higher the closer the H2 / N2 ratio in the reaction gas supplied was to the value shown by point Pa2. On the other hand, as shown by the dashed line Lb, in the case of an endured Ru catalyst, the ammonia concentration in the post-reaction gas tended to be higher the closer the H2 / N2 ratio in the reaction gas supplied was to the value shown by point Pb1. Since the H2 / N2 ratio value shown at point Pb1 is smaller than the H2 / N2 ratio value shown at point Pa2, it can be said that the H2 / N2 ratio value in the reaction gas that is suitable for the ammonia concentration in the post-reaction gas decreases as the catalyst deteriorates.

[0025] From the results shown by the solid line La and the broken line Lb in FIG. 4, in the ammonia synthesis system 1, the control unit 5 controls the H2 / N2 ratio in the reaction gas supplied to the reactor 40 in accordance with the degree of deterioration of the catalyst 45 during post-activation operation. In detail, in the ammonia synthesis system 1, when a reaction gas (assumed to be reaction gas G1) having a certain H2 / N2 ratio is supplied to the reactor 40 during post-activation operation, if the ammonia concentration in the actual post-reaction gas is lower than the lower limit of the assumed ammonia concentration range and this state continues for a preset set time or more, the control unit 5 adjusts the amount of hydrogen and the amount of nitrogen supplied to the mixer 10 so that the reaction gas G2 having a lower H2 / N2 ratio than the reaction gas G1 is supplied to the reactor 40. In this embodiment, the greater the difference between the lowest ammonia concentration in the actual post-reaction gas during the set time and the lower limit of the assumed ammonia concentration range, the greater the reaction gas G2 having a lower H2 / N2 ratio is supplied to the reactor 40. The expected ammonia concentration range is obtained by the control unit 5 referring to a map in which the value of the H2 / N2 ratio in the reaction gas is associated with the ammonia concentration range in the post-reaction gas when the reaction gas of each H2 / N2 ratio is supplied to the undegraded catalyst 45. The expected ammonia concentration range may also be obtained by the control unit 5 referring to data in which the value of the H2 / N2 ratio in the reaction gas is associated with the ammonia concentration range in the post-reaction gas when the reaction gas of each H2 / N2 ratio is actually finally supplied to the catalyst 45.

[0026] In the ammonia synthesis system 1, when a reaction gas (referred to as reaction gas G1) having a certain H2 / N2 ratio is supplied to the reactor 40 during post-activation operation, if the temperature of the actual catalyst 45 is lower than the lower limit of the assumed temperature range of the catalyst 45 and this state continues for a preset time or longer, the control unit 5 adjusts the amount of hydrogen and the amount of nitrogen supplied to the mixer 10 so that a reaction gas G2 having a smaller H2 / N2 ratio than the reaction gas G1 is supplied to the reactor 40. In this embodiment, the greater the difference between the lowest value of the actual catalyst 45 temperature during the set time and the lower limit of the assumed temperature range of the catalyst 45, the greater the reaction gas G2 having a smaller H2 / N2 ratio is supplied to the reactor 40. The assumed temperature range of the catalyst 45 is acquired by the control unit 5 by referring to a map in which the value of the H2 / N2 ratio in the reaction gas and the temperature range of the catalyst 45 when each reaction gas having a H2 / N2 ratio is supplied to the catalyst 45 that is not deteriorated are associated with each other. In addition, the expected temperature range of catalyst 45 may be obtained by the control unit 5 by referring to data that corresponds the value of the H2 / N2 ratio in the reaction gas to the temperature range of catalyst 45 when the reaction gas of each H2 / N2 ratio was last actually supplied to catalyst 45.

[0027] In this way, when the actual ammonia concentration in the reacted gas is lower than the lower limit of the assumed ammonia concentration range during post-activation operation and this state continues for a preset time or more, or when the actual temperature of the catalyst 45 is lower than the lower limit of the assumed temperature range of the catalyst 45 and this state continues for a preset time or more, the control unit 5 controls the H2 / N2 ratio in the reacted gas to be smaller. That is, the control unit 5 controls the H2 / N2 ratio using the ammonia concentration in the reacted gas discharged from the reactor 40 and the temperature of the catalyst 45 as indicators of the deterioration degree of the catalyst 45.

[0028] As shown in FIG. 4, the H2 / N2 ratio in the reaction gas suitable for ammonia synthesis tends to decrease as the catalyst deteriorates. In this regard, according to the ammonia synthesis system 1 of the first embodiment, the H2 / N2 ratio in the reaction gas can be controlled according to the deterioration degree of the catalyst 45. Therefore, ammonia can be synthesized more efficiently than in a mode in which a reaction gas having an H2 / N2 ratio adjusted without considering the deterioration degree of the catalyst 45 is supplied to the reactor 40. In other words, as the catalyst 45 deteriorates, the H2 / N2 ratio in the reaction gas approaches a suitable value at which the activity of the catalyst 45 is further promoted, and thus the input energy required for ammonia production can be reduced.

[0029] In the ammonia synthesis system 1 of the first embodiment, the H2 / N2 ratio is controlled using the ammonia concentration in the post-reaction gas sent from the reactor 40 and the temperature of the catalyst 45 as indicators of the deterioration degree of the catalyst 45. For example, if the ammonia concentration in the post-reaction gas when a reaction gas with a certain H2 / N2 ratio is supplied to a catalyst is lower than the ammonia concentration in the post-reaction gas when the reaction gas with the same H2 / N2 ratio is supplied to the catalyst, the catalyst can be considered to be deteriorated. In addition, since the ammonia synthesis reaction is an exothermic reaction, if the temperature of the catalyst when a reaction gas with the same H2 / N2 ratio is supplied to the catalyst is lower than the temperature of the catalyst when the reaction gas with the same H2 / N2 ratio is supplied to the catalyst, the catalyst can be considered to be deteriorated. Therefore, according to the ammonia synthesis system 1 of the first embodiment, the ammonia concentration in the post-reaction gas and the temperature of the catalyst 45 are used as indicators of catalyst deterioration, so that the H2 / N2 ratio can be controlled while accurately grasping the deterioration degree of the catalyst 45. As a result, the reaction gas having an H2 / N2 ratio according to the deterioration of the catalyst 45 can be supplied to the reactor 40, so that ammonia can be synthesized more efficiently.

[0030] <Second embodiment> The ammonia synthesis system of the second embodiment is the same as the ammonia synthesis system 1 of the first embodiment, except that the control method of the H2 / N2 ratio in the reaction gas by the control unit 5 is different from that of the ammonia synthesis system 1 of the first embodiment.

[0031] 5 is a flow chart showing an example of the procedure of the H2 / N2 ratio control process. The H2 / N2 ratio control process is executed after the temperature of the catalyst 45 becomes saturated after reaching the activation temperature (see FIG. 3) or higher during post-activation operation. The control unit 5 judges whether the temperature of the catalyst 45 becomes saturated based on whether the temperature change of the catalyst 45 becomes 1° C. / 5 min or less after the temperature of the catalyst 45 becomes the activation temperature or higher. It is assumed that the control unit 5 has been supplying the reaction gas having a preset H2 / N2 ratio to the reactor 40 before the H2 / N2 ratio control process is started.

[0032] When the H2 / N2 ratio control process is started, the control unit 5 first determines whether or not a set period Δt has elapsed since the start of the H2 / N2 ratio control process (step S11). The set period Δt is set between 5 minutes and 100 hours. If the set period Δt has not elapsed (step S11: NO), the control unit 5 repeats the process of step S11 until the set period Δt has elapsed.

[0033] After the set period Δt has elapsed (step S11: YES), the control unit 5 sets the time when the set period Δt has elapsed as a first reference time point, and calculates the ammonia concentration A n+1 is higher than the comparative concentration CC, and the temperature T n+1 is higher than the comparative temperature CT (step S12). The comparative concentration CC is the concentration obtained by multiplying the ammonia concentration in the post-reaction gas at a comparative time point a predetermined period (≦set period Δt) before the first reference time point by a predetermined ratio S. The comparative temperature CT is the concentration obtained by multiplying the temperature of the catalyst 45 at the comparative time point by a predetermined ratio U. The predetermined ratio S and the predetermined ratio U are each set to a value within the range of 0.5 to 1.0. The ammonia concentration A in the post-reaction gas at the first reference time pointn+1 is higher than the comparative concentration CC, or the temperature T n+1 If is higher than the comparison temperature CT (step S12: YES), the control unit 5 executes the process of step S11 again.

[0034] Ammonia concentration A in the post-reaction gas at the first reference point n+1 is equal to or lower than the comparative concentration CC, or the temperature T n+1 is equal to or lower than the comparison temperature CT (step S12: NO), that is, when it is deemed that the catalyst 45 may have deteriorated, the control unit 5 executes a reduction control to reduce the H2 / N2 ratio in the reaction gas (step S13). Specifically, the control unit 5 executes the reduction control by executing at least one of a reduction in the amount of hydrogen and an increase in the amount of nitrogen supplied to the mixer 10.

[0035] After executing the reduction control (step S13), the control unit 5 determines whether or not the set period Δu has elapsed (step S14). The set period Δu is set between 5 minutes and 100 hours. If the set period Δu has not elapsed (step S14: NO), the control unit 5 repeats the process of step S14 until the set period Δu has elapsed.

[0036] After the set period Δu has elapsed (step S14: YES), the control unit 5 sets the time point after the last execution of the reduction control (the time point after the set period Δu has elapsed since the last execution of the reduction control in FIG. 5) as a second reference time point, and calculates the ammonia concentration A n+2 is the ammonia concentration A in the post-reaction gas at the first reference point. n+1 and determining whether the temperature T n+2 is the temperature T of the catalyst 45 at the first reference point in time. n+1 It is determined whether it is higher than (step S15).

[0037] Ammonia concentration A in the post-reaction gas at the second reference point n+2is the ammonia concentration A in the post-reaction gas at the first reference point. n+1 or the temperature T n+2 is the temperature T of the catalyst 45 at the first reference point in time. n+1 If the ammonia concentration A in the post-reaction gas at the second reference point is higher than the ammonia concentration A in the post-reaction gas at the second reference point, that is, if the efficiency of the ammonia synthesis reaction is improved by reducing the H2 / N2 ratio in the reaction gas by the reduction control, the control unit 5 executes a maintenance control to maintain the H2 / N2 ratio in the reaction gas after the last reduction control is executed (step S16). n+2 is the ammonia concentration A in the post-reaction gas at the first reference point. n+1 or less, or the temperature T n+2 is the temperature T of the catalyst 45 at the first reference point in time. n+1 If it is equal to or less than this (step S15: NO), that is, if the efficiency of the ammonia synthesis reaction is reduced by reducing the H2 / N2 ratio in the reaction gas by the reduction control, a regression control is executed (step S17) to return the H2 / N2 ratio in the reaction gas to the H2 / N2 ratio in the reaction gas before the last reduction control was executed. Thus, in step S15, the ammonia concentration A in the reaction gas after the reduction control is executed is n+2 and the catalyst temperature T n+2 The ammonia concentration A in the post-reaction gas before the reduction control is performed n+1 and the catalyst temperature T n+1 Therefore, it is preferable to set the set period Δu in step S14 to a period longer than the period required from when the reaction gas with the H2 / N2 ratio that has changed due to the execution of the reduction control starts to be supplied to the reactor 40 until the temperature of the catalyst 45 is saturated.

[0038] After performing the maintenance control or regression control (step S16 or S17), the control unit 5 again executes the process of step S11. At this time, the control unit 5 judges whether or not a set period Δt has elapsed since the maintenance control or regression control was performed (step S11). If a positive judgment is obtained in step S11, the control unit 5 again executes the process of step S12. That is, the control unit 5 regards the time point after the maintenance control or regression control is performed (the time point when the set period Δt has elapsed since the last maintenance control or regression control was performed in FIG. 5) as a new first reference time point, and again calculates the ammonia concentration A in the post-reaction gas at the first reference time point. n+1 and the comparison concentration CC and the temperature T n+1 and the comparison temperature CT (step S13). For this reason, it is preferable to set the set period Δt in step S11 to a period longer than the period required from when the reaction gas with the H2 / N2 ratio that has changed due to the execution of the regression control starts to be supplied to the reactor 40 until the temperature of the catalyst 45 is saturated. The H2 / N2 ratio control process shown in FIG. 5 is terminated when the control unit 5 receives a signal indicating an end instruction.

[0039] In the ammonia synthesis system of the second embodiment described above, the H2 / N2 ratio is controlled using the ammonia concentration in the reacted gas and the temperature of the catalyst 45 as indicators of the deterioration degree of the catalyst 45 (for example, step S12). Moreover, according to the ammonia synthesis system of the second embodiment, the H2 / N2 ratio in the reacted gas can be brought closer to a value suitable for ammonia synthesis by executing reduction control, regression control, or maintenance control according to the ammonia concentration in the reacted gas and the temperature of the catalyst 45. Therefore, ammonia can be synthesized more efficiently.

[0040] <Modifications of this embodiment> The present invention is not limited to the above-described embodiment, and can be embodied in various forms without departing from the spirit and scope of the invention. For example, the following modifications are also possible.

[0041] [Variation 1] The above embodiment is merely an example, and the configuration and control of the ammonia synthesis system can be modified in various ways. For example, the ammonia synthesis system may not include the gas-liquid separator 70 and the storage tank 80, and another system connected to the ammonia synthesis system may include the gas-liquid separator 70 and the storage tank 80. The ammonia synthesis system may not include the mixer 10, and hydrogen supplied from the hydrogen tank and nitrogen supplied from the nitrogen tank may be mixed in a pipe connected to the reactor 40.

[0042] [Variation 2] In the above embodiment, one catalyst 45 is accommodated in the reactor 40, but this is not limited thereto. For example, two catalysts may be accommodated in the reactor 40. In such a case, the catalysts are assumed to be arranged in series inside the reactor 40. Of course, three or more catalysts may be accommodated in the reactor 40.

[0043] [Variation 3] In the above embodiment, the control unit 5 controls the H2 / N2 ratio in the reaction gas supplied to the reactor 40 in accordance with the deterioration degree of the catalyst 45 during the post-activation operation, but this is not limited thereto. In addition to or instead of the post-activation operation, the control unit 5 may control the H2 / N2 ratio in the reaction gas supplied to the reactor 40 in accordance with the deterioration degree of the catalyst 45 during the pre-activation operation (operation from when the supply of the reaction gas to the reactor 40 is started until the temperature of the catalyst 45 is raised to the activation temperature). At this time, the same parameters as those during the post-activation operation (such as the ammonia concentration in the post-reaction gas and the temperature of the catalyst 45) are used as indicators of the deterioration degree of the catalyst 45.

[0044] [Variation 4] In the above embodiment, the control unit 5 controls the H2 / N2 ratio using the ammonia concentration in the post-reaction gas discharged from the reactor 40 and the temperature of the catalyst 45 as indicators of the deterioration degree of the catalyst 45, but this is not limited thereto. For example, the control unit 5 may control the H2 / N2 ratio using only one of the ammonia concentration in the post-reaction gas discharged from the reactor 40 and the temperature of the catalyst 45 as an indicator of the deterioration degree of the catalyst 45. Furthermore, in addition to the ammonia concentration in the post-reaction gas and the temperature of the catalyst 45, or instead of the ammonia concentration in the post-reaction gas and the temperature of the catalyst 45, the control unit 5 may control the H2 / N2 ratio using the accumulated usage time from the first use of the catalyst 45 in the synthesis reaction to the present, the temperature history of the catalyst 45 during use, and the H2 / N2 ratio history in the reaction gas supplied during use as indicators of the deterioration degree of the catalyst 45. The above-mentioned usage time refers to the time during which the reaction gas is supplied to the reactor 40.

[0045] Although the present aspect has been described above based on the embodiment and modified examples, the above-mentioned embodiment of the aspect is intended to facilitate understanding of the present aspect and does not limit the present aspect. The present aspect may be modified or improved without departing from the spirit and scope of the claims, and equivalents are included in the present aspect. Furthermore, if a technical feature is not described as essential in this specification, it may be deleted as appropriate. [Explanation of symbols]

[0046] 1. Ammonia synthesis system 5. Control section 10…Mixer 20...First heat exchanger 30...heater 40…Reactor 41…Inner piping 42…Outside piping 43...Upstream heater 44…Downstream heater 45…Catalyst 50…Second heat exchanger 60...Cooler 70…Gas-liquid separator 80…Storage tank 90…Compressor

Claims

1. An ammonia synthesis system for synthesizing ammonia, comprising: A reactor containing a catalyst that promotes a synthesis reaction for synthesizing ammonia from a reaction gas containing hydrogen and nitrogen; H, which is the ratio of hydrogen to nitrogen in the reaction gas supplied to the reactor 2 / N 2 A control unit for controlling the ratio, The control unit adjusts the temperature of the catalyst according to a degree of deterioration of the catalyst. 2 / N 2 Ratio controlled, ammonia synthesis system.

2. 2. The ammonia synthesis system according to claim 1, The control unit uses at least one of the ammonia concentration in the post-reaction gas discharged from the reactor and the temperature of the catalyst as an index of the degree of deterioration of the catalyst, 2 / N 2 Ratio controlled, ammonia synthesis system.

3. The ammonia synthesis system according to claim 1 or 2, The control unit is If the ammonia concentration at the first reference time point is equal to or lower than a comparative concentration obtained by multiplying the ammonia concentration at a comparison time point prior to the first reference time point by a predetermined ratio, or if the temperature of the catalyst at the first reference time point is equal to or lower than a comparative temperature obtained by multiplying the temperature of the catalyst at the comparison time point by a predetermined ratio, H 2 / N 2 Execute a reduction control to reduce the ratio; If the ammonia concentration at the second reference point after the last execution of the reduction control is higher than the ammonia concentration at the first reference point, or if the temperature of the catalyst at the second reference point is higher than the temperature of the catalyst at the first reference point, H 2 / N 2 Execute maintenance control to maintain the ratio; If the ammonia concentration at the second reference time point is equal to or lower than the ammonia concentration at the first reference time point, or if the temperature of the catalyst at the second reference time point is equal to or lower than the temperature of the catalyst at the first reference time point, H 2 / N 2 The ratio is set to H before the last reduction control is executed. 2 / N 2 Run regression control back to the ratio A time point after the maintenance control or the regression control is executed is regarded as a new first reference time point, and the ammonia concentration at the first reference time point is compared with the comparison concentration and the temperature of the catalyst at the first reference time point is compared with the comparison temperature again.

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