Ammonia synthesis system and method of operation thereof

Abstract

The present disclosure relates to an ammonia synthesis system, a method of operating the same, and an ammonia synthesis method, the ammonia synthesis system comprising: a compressor that compresses a mixed gas; a raw material supply line for supplying the mixed gas to the compressor; an ammonia synthesis reactor into which the mixed gas compressed by the compressor is fed, thereby synthesizing ammonia; an air separation unit that separates nitrogen from air; a first cooler that cools synthesis gas including ammonia discharged from the ammonia synthesis reactor; and a second cooler that exchanges heat between the nitrogen gas separated by the air separation unit and the synthesis gas cooled by the first cooler, and the nitrogen gas subjected to heat exchange in the second cooler is supplied to the raw material supply line.

Description

Technical Field

[0001] The present disclosure relates to an ammonia synthesis system and an operation method thereof. Background Art

[0002] In order to combat climate change and the depletion of oil resources to achieve the goal of reducing greenhouse gas emissions, the necessity of using new renewable energy is increasing. However, the areas that meet the suitable conditions for producing new renewable energy are limited, so it is necessary to find means for storage and transportation. For example, there is a problem of transporting the new renewable energy rich in the equatorial vicinity and southern hemisphere regions to the northern hemisphere with high demand for new renewable energy.

[0003] In addition, new renewable energy has time variability, so an electricity storage device must be accompanied. To solve the problems caused by the regional bias and time variability of new renewable energy, ammonia has attracted much attention as an energy carrier. In particular, ammonia can be liquefied at normal temperature and 8.5 atmospheres, so it has the advantage of being easier to store and transport than hydrogen. Therefore, as an alternative to solve the problems caused by the regional bias and time variability of new renewable energy, it is necessary to pay attention to the scheme of using electricity produced from new renewable energy to produce hydrogen and nitrogen and synthesizing ammonia using the produced hydrogen and nitrogen as raw materials.

[0004] Hydrogen, as the main raw material for ammonia synthesis, can be produced in a water electrolyzer driven by new renewable energy such as solar energy or wind energy. New renewable energy such as solar energy or wind energy has time variability. For example, solar energy cannot be used at night. Therefore, the ammonia synthesis system can never operate at a constant flow rate, and there is a problem of needing to predict and handle the flow rate changes occurring during the production cycle.

[0005] In addition, when the flow rate of a raw material such as hydrogen fed into the ammonia synthesis system decreases, there is a problem that the non-uniformity of the flow rate distribution increases at the front end of the catalytic layer included in the ammonia synthesis reactor.

[0006] Moreover, in the existing ammonia synthesis system, especially in the initial stage of operation, a temperature deviation occurs between the central part and the edge part of the catalytic layer, thus having a problem of reducing the ammonia synthesis yield.

[0007] In addition, when the flow rate of the raw material fed into the ammonia synthesis system changes, for example, when the flow rate of the fed raw material decreases, there is a problem of difficultly stabilizing the operation of the compressor such as the occurrence of a surge phenomenon of the compressor.

[0008] In addition, when the flow rate of the raw material fed into the ammonia synthesis system changes, the ammonia production amount changes with the change of the flow rate of the raw material, thus having a problem of difficultly reducing the energy used in ammonia separation.

[0009] Therefore, it is necessary to develop an ammonia synthesis system that can cope with the flow rate fluctuations occurring during the production cycle, prevent the surge phenomenon of the compressor, and thus operate stably, solve the problem of uneven flow distribution occurring at the front end of the catalyst layer, and the problem of temperature deviation occurring at the center and edge of the catalyst layer at the initial stage of operation, resulting in a decrease in ammonia synthesis yield, and be able to reduce the energy used in ammonia separation. SUMMARY OF THE INVENTION

[0010] According to one aspect of the present disclosure, an ammonia synthesis system that can elastically cope with the flow rate fluctuations occurring during the production cycle can be provided.

[0011] According to another aspect of the present disclosure, an ammonia synthesis system that can maintain a uniform flow distribution at the front end of the catalyst layer included in the ammonia synthesis reactor even when the flow rate of a raw material such as hydrogen fed is reduced can be provided.

[0012] According to still another aspect of the present disclosure, an ammonia synthesis system that can make the temperature deviation between the center and the edge of the catalyst layer uniform at the initial stage of operation, thereby improving the ammonia synthesis yield, can be provided.

[0013] According to one aspect of the present disclosure, an ammonia synthesis system that can preheat the catalyst layer at the initial stage of operation, thereby improving the ammonia synthesis yield at the initial stage of operation, can be provided.

[0014] According to one aspect of the present disclosure, an ammonia synthesis system that can reduce the amount of energy required in the system during operation, thereby saving energy, can be provided.

[0015] According to one aspect of the present disclosure, an ammonia synthesis system that can uniformly use each catalyst layer during operation, thereby extending the catalyst replacement cycle, can be provided.

[0016] In addition, according to another aspect of the present disclosure, an ammonia synthesis system that can prevent the surge phenomenon of the compressor, etc., and thus stably operate the compressor even when the flow rate of the raw material fed into the ammonia synthesis system changes can be provided.

[0017] According to one aspect of the present disclosure, an ammonia synthesis system that can flexibly cope with the separation of ammonia even when the ammonia production amount changes with the change in the flow rate of the raw material fed into the ammonia synthesis system can be provided.

[0018] According to one aspect of the present disclosure, an ammonia synthesis system that can reduce the energy consumed in ammonia separation to cope with the change in the ammonia production amount even when the ammonia production amount changes with the change in the flow rate of the raw material fed into the ammonia synthesis system can be provided.

[0019] The present disclosure provides an ammonia synthesis system, which includes: a compressor that compresses a mixed gas; a raw material supply line that supplies the mixed gas to the compressor; an ammonia synthesis reactor in which the mixed gas compressed in the compressor is introduced to synthesize ammonia; an air separation unit that separates nitrogen from air; a first cooler that cools a synthesis gas including ammonia discharged from the ammonia synthesis reactor; and a second cooler that exchanges heat between the nitrogen separated in the air separation unit and the synthesis gas cooled in the first cooler, and the nitrogen that undergoes heat exchange in the second cooler is supplied to the raw material supply line.

[0020] In an embodiment according to the present disclosure, it may be that the ammonia synthesis system further includes: an air cooler that exchanges heat between the nitrogen separated in the air separation unit and the air introduced into the air separation unit to cool the air, and the nitrogen that undergoes heat exchange in the air cooler is introduced into the second cooler.

[0021] In an embodiment according to the present disclosure, it may be that the ammonia synthesis reactor includes: two or more catalyst layers; a backflow prevention plate that is disposed downstream of each of the catalyst layers other than the lowermost catalyst layer among the two or more catalyst layers to prevent backflow of the mixed gas; a distribution device that is disposed upstream of each of the two or more catalyst layers to distribute the mixed gas to the catalyst layers; and a mixed gas supply line that is arranged to supply the mixed gas to the distribution device.

[0022] In an embodiment according to the present disclosure, it may be that the ammonia synthesis system further includes: a distribution plate that is respectively located between the catalyst layer and the distribution device.

[0023] In an embodiment according to the present disclosure, it may be that the ammonia synthesis system further includes: a plurality of mixed gas flow tubes that are fixed to the lower surface of the distribution plate for the mixed gas to flow through.

[0024] In an embodiment according to the present disclosure, it may be that the mixed gas flow tube has a bottom surface and side surfaces connecting the bottom surface and the distribution plate, a plurality of upper openings are formed at intervals along the circumference on the upper side surface of the mixed gas flow tube, a plurality of middle openings are formed at intervals along the circumference on the middle side surface of the mixed gas flow tube, a plurality of lower openings are formed at intervals along the circumference on the lower side surface of the mixed gas flow tube, and the mixed gas flow tube includes a covering member that is formed to surround at least a partial area of the side surface of the mixed gas flow tube to provide a space for guiding a fluid that flows out of the side surface of the mixed gas flow tube after passing through the upper openings to the side of the middle openings.

[0025] In one embodiment according to the present disclosure, it may be that the mixed gas flow pipe further includes: a partition configured to divide the upper part and the middle part of the mixed gas flow pipe.

[0026] In one embodiment according to the present disclosure, it may be that the ammonia synthesis system further includes: a heat exchanger configured downstream of each of the two or more catalyst layers to remove heat from the effluent of the catalyst layer.

[0027] In one embodiment according to the present disclosure, it may be that each of the mixed gas supply routes includes a flow regulating device.

[0028] In addition, the present disclosure provides an operation method of an ammonia synthesis system, the ammonia synthesis system further including a second cooler bypass route, and the method selectively performs the following modes: a two-stage cooling mode in which the synthesis gas passes through both the first cooler and the second cooler; and a second cooler bypass mode in which the synthesis gas passes only through the first cooler and bypasses the second cooler through the second cooler bypass route.

[0029] In addition, the present disclosure provides an ammonia synthesis method, which includes: S1) a step of compressing a mixed gas in a compressor and then feeding it into an ammonia synthesis reactor; S2) a step of reacting the compressed mixed gas in the ammonia synthesis reactor to generate a synthesis gas including ammonia; S3) a first cooling step of cooling the synthesis gas generated in the step S2); and S4) a step of performing a heat exchange between the synthesis gas cooled in the step S3) and nitrogen separated in an air separation unit, and the nitrogen that has undergone heat exchange in the step S4) is supplied to the compressor.

[0030] In one embodiment according to the present disclosure, it may be that the ammonia synthesis method performs a heat exchange between the nitrogen separated in the air separation unit and the air fed into the air separation unit, and then performs a heat exchange between the nitrogen that has undergone heat exchange and the synthesis gas cooled in the step S4).

[0031] In one embodiment according to the present disclosure, it may be that the ammonia synthesis reactor includes: two or more catalyst layers included in the ammonia synthesis reactor; a backflow prevention plate configured downstream of each of the catalyst layers other than the lowermost catalyst layer among the two or more catalyst layers to prevent backflow of the mixed gas; a distribution device configured upstream of each of the two or more catalyst layers to distribute the mixed gas to the catalyst layer; and a mixed gas supply route arranged to supply the mixed gas to the distribution device.

[0032] The ammonia synthesis system according to one embodiment of the present disclosure can cope with flow rate fluctuations occurring during the production cycle.

[0033] An ammonia synthesis system according to another embodiment of the present disclosure can maintain a uniform flow distribution at the front end of the catalyst layer included in the ammonia synthesis reactor even when the flow rate of a raw material such as hydrogen fed is reduced.

[0034] An ammonia synthesis system according to still another embodiment of the present disclosure equalizes the temperature deviation between the central portion and the edge portion of the catalyst layer in the initial stage of operation, thereby enabling an increase in the ammonia synthesis yield.

[0035] An ammonia synthesis system according to an embodiment of the present disclosure preheats the catalyst layer in the initial stage of operation, thereby enabling an increase in the ammonia synthesis yield in the initial stage of operation.

[0036] An ammonia synthesis system according to an embodiment of the present disclosure can reduce the amount of energy required in the system during operation, thereby saving energy.

[0037] An ammonia synthesis system according to an embodiment of the present disclosure uniformly uses each catalyst layer during operation, thereby enabling an extension of the catalyst replacement cycle.

[0038] In addition, an ammonia synthesis system according to an embodiment of the present disclosure can prevent a surge phenomenon of a compressor, etc., even when the flow rate of the raw material fed to the ammonia synthesis system varies, thereby enabling stable operation of the compressor.

[0039] An ammonia synthesis system according to an embodiment of the present disclosure can synthesize ammonia in an eco-friendly manner.

[0040] An ammonia synthesis system according to an embodiment of the present disclosure can flexibly respond during ammonia separation even when the ammonia production amount varies with the variation in the flow rate of the raw material fed to the ammonia synthesis system, thereby enabling flexibility in process operation.

[0041] An ammonia synthesis system according to an embodiment of the present disclosure can reduce the energy used in ammonia separation to cope with the variation in the ammonia production amount even when the ammonia production amount varies with the variation in the flow rate of the raw material fed to the ammonia synthesis system, and can save the cost consumed in ammonia separation. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 is a schematic diagram showing an ammonia synthesis reactor according to an embodiment of the present disclosure.

[0043] Figure 2 is a schematic diagram showing an ammonia synthesis reactor according to another embodiment of the present disclosure.

[0044] Figure 3 is a perspective view showing a distribution plate and a mixed gas flow pipe according to an embodiment of the present disclosure.

[0045] Figure 4is a perspective view showing the interior of a mixed gas flow tube according to an embodiment of the present disclosure.

[0046] Figure 5 is a perspective view showing the interior of a mixed gas flow tube according to another embodiment of the present disclosure.

[0047] Figure 6 is a view showing a state in which a backflow prevention cover is opened in a backflow prevention plate according to an embodiment of the present disclosure.

[0048] Figure 7 is a view showing a state in which a backflow prevention cover is closed in a backflow prevention plate according to an embodiment of the present disclosure.

[0049] Figure 8 is a process flow diagram showing an ammonia synthesis system according to an embodiment of the present disclosure.

[0050] Reference numerals: 1: ammonia synthesis system, 10: ammonia synthesis reactor, 20, 21: catalyst layer, 30, 31: backflow prevention plate, 301: backflow prevention plate, 302: opening, 303: backflow prevention cover, 304: hinge, 40, 41: distribution device, 50, 51: mixed gas supply line, 60, 61: microwave heating device, 601, 602: microwave guiding part, 70, 71: distribution plate, 72: lower surface, 720: mixed gas flow tube, 722: side surface, 722a: upper part, 722b: middle part, 722c: lower part, 723: upper opening, 725: middle opening, 727: lower opening, 729: partition, 730: covering member, 81: raw material supply line, 82: compressor, 83: first cooler, 84: second cooler, 88: air separation unit, 89: air cooler, 91: synthesis gas, 92: ammonia, 94: nitrogen gas that undergoes heat exchange in the second cooler, 96: nitrogen gas separated in the air separation unit, 97: air cooled in the air cooler, 98: nitrogen gas that undergoes heat exchange in the air cooler. Detailed Description

[0051] Advantages, features, and methods for achieving the same of the present invention will become clear through the embodiments described in detail below. However, the present invention is not limited to the embodiments disclosed below and can be implemented in various different forms. These embodiments are only provided to make the disclosure of the present invention complete and to fully inform those with ordinary knowledge in the technical field to which the present invention pertains of the scope of the invention. The present invention is only defined by the scope of the claims.

[0052] Unless otherwise defined, all terms (including technical terms and scientific terms) used in this specification have the same meaning as commonly understood by those skilled in the technical field to which the present disclosure pertains.

[0053] Unless otherwise specified in the context, the singular forms used in this specification may also include the plural forms.

[0054] The numerical ranges used in this specification include all values within the range including the lower limit value and the upper limit value, the increments logically derived from the form and span of the defined range, all values doubly limited, and all possible combinations of the upper and lower limits within the numerically defined ranges in different forms. Values that may exceed the numerical range due to experimental errors or rounding of numerical values are also included within the defined numerical range unless otherwise defined in the specification of the present invention.

[0055] The term "comprising" mentioned in this specification is an open-ended description, and its meaning is equivalent to expressions such as "having", "containing", "owning", "having the characteristics", etc., and does not exclude factors, materials or processes not additionally listed.

[0056] Unless otherwise defined, the unit of "%" not specifically mentioned as used in this specification means "% by weight".

[0057] Unless otherwise defined, "A to B" in this specification means "above A and below B".

[0058] In this specification, the "recycle stream" refers to a gas including hydrogen and nitrogen, and may further include a small amount of unseparated ammonia.

[0059] In this specification, the "mixed gas" refers to a gas including at least one selected from the group consisting of hydrogen and nitrogen.

[0060] In this specification, the "synthesis gas" refers to a gas including ammonia, unreacted hydrogen and nitrogen.

[0061] In this specification, for convenience, the situations of flow rate changes occurring during the production cycle are roughly divided into 3 types. As described above, they can be divided into the situation of low flow rate, the situation of normal flow rate, and the situation of high flow rate, and can be easily adjusted according to the common sense or judgment of those skilled in the art. It can be that the situation of low flow rate means less than half (50%) compared to the annual average production flow rate (100%), the situation of normal flow rate means more than half (50%) and less than 2 times (200%) of the annual average production flow rate (100%), and the situation of high flow rate means more than 2 times (200%) compared to the annual average production flow rate (100%), but not limited to this.

[0062] Hereinafter, the ammonia synthesis system of the present disclosure will be described in detail. However, it is only an example, and the present disclosure is not limited to the specific embodiments illustrated by the example.

[0063] The present disclosure provides an ammonia synthesis system, which includes: a compressor that compresses a mixed gas; a raw material supply line that supplies the mixed gas to the compressor; an ammonia synthesis reactor in which the mixed gas compressed in the compressor is introduced to synthesize ammonia; an air separation unit that separates nitrogen from air; a first cooler that cools the synthesis gas including ammonia discharged from the ammonia synthesis reactor; and a second cooler that exchanges heat between the nitrogen separated in the air separation unit and the synthesis gas cooled in the first cooler, and the nitrogen that undergoes heat exchange in the second cooler is supplied to the raw material supply line.

[0064] According to the ammonia synthesis system of the present disclosure, while being able to elastically respond to flow rate fluctuations occurring during the production cycle, it can prevent the surge phenomenon of the compressor and thus operate stably. It can solve the problem of uneven flow distribution occurring at the front end of the catalyst layer and the temperature deviation between the central part and the edge part of the catalyst layer occurring in the initial stage of operation, resulting in a reduction in ammonia synthesis yield, and can reduce the energy used in ammonia separation. In particular, the ammonia synthesis system of the present disclosure can prevent the surge phenomenon of the compressor even when the flow rate of the raw material introduced into the ammonia synthesis system changes, thereby stably operating the compressor. This can be achieved by supplying the nitrogen separated in the air separation unit to the raw material supply line.

[0065] In addition, according to the ammonia synthesis system of an embodiment of the present disclosure, even when the ammonia production changes with the change in the flow rate of the raw material introduced into the ammonia synthesis system, it can flexibly respond during ammonia separation, thereby providing flexibility in process operation. Moreover, according to the ammonia synthesis system of an embodiment of the present disclosure, even when the ammonia production changes with the change in the flow rate of the raw material introduced into the ammonia synthesis system, it can reduce the energy used in ammonia separation to cope with it and save the cost consumed in ammonia separation.

[0066] Figure 8 is a process flow diagram showing the ammonia synthesis system according to the present disclosure. Referring to Figure 8 , the mixed gas can be introduced into the compressor 82 through the raw material supply line 81. The mixed gas compressed in the compressor 82 can be introduced into the ammonia synthesis reactor 10. The synthesis gas 91 generated by the reaction in the ammonia synthesis reactor 10 can be introduced into the first cooler 83 for cooling. The cooled synthesis gas is introduced into the second cooler 84 to exchange heat with the nitrogen 96 separated in the air separation unit 88, thereby enabling secondary cooling. Ammonia can condense in the secondary-cooled synthesis gas, thus being separated. The nitrogen introduced into the second cooler 84 can exchange heat with the air introduced into the air separation unit 88 in the air cooler 89. The nitrogen 94 that undergoes heat exchange in the second cooler 84 can be supplied to the raw material supply line 81.

[0067] Specifically, when the flow rate of the synthesis gas including ammonia is high or the ammonia content in the synthesis gas is high, the ammonia synthesis system 1 can cool the synthesis gas once through the first cooler 83 and cool it twice through the second cooler 84, thereby cooling and separating ammonia. Differently, when the flow rate of the synthesis gas including ammonia is low or the ammonia content in the synthesis gas is low, the ammonia synthesis system can be cooled only through the first cooler 83 or the second cooler 84, thereby performing separation. That is, the ammonia synthesis system according to the present disclosure can flexibly respond to the variable ammonia production flow rate during the production cycle, appropriately separate ammonia, and thus can provide process flexibility. Moreover, when the flow rate of the synthesis gas including ammonia is low or the ammonia content in the synthesis gas is low, the operation of the cooler can be adjusted to reduce the energy used in ammonia separation and save the cost consumed in ammonia separation.

[0068] The ammonia synthesis system may further include a raw material heat exchanger at the front end of the first cooler, which exchanges heat between the mixed gas raw material flowing in the raw material supply line and the synthesis gas. In addition, the ammonia synthesis system may further include a steam generation device at the front end of the first cooler, which can recover the thermal energy contained in the synthesis gas. The steam generation device may be a device that exchanges heat between the synthesis gas and water to generate steam. As described above, the ammonia synthesis system can recover the thermal energy contained in the synthesis gas before introducing the synthesis gas into the first cooler. At this time, the temperature of the synthesis gas discharged from the ammonia synthesis reactor may be 200 to 800 °C, 200 to 600 °C, or 300 to 500 °C, but is not limited thereto.

[0069] The ammonia synthesis system may include: a first cooler 83 that cools the synthesis gas once.

[0070] The first cooler can cool the synthesis gas once. Alternatively, the synthesis gas can be cooled once in the first cooler. Additionally, ammonia in the synthesis gas can be condensed in the first cooler to separate ammonia. Specifically, ammonia can be separated by cooling the synthesis gas for gas-liquid separation. The gas-liquid separation can be performed once or more than twice.

[0071] The first cooler can exchange heat between the synthesis gas and a refrigerant to cool it. The refrigerant may include at least one selected from the group consisting of chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs), hydrofluoroolefins (HFOs), fluorinated ether compounds, hydrocarbons, ammonia, water, air, carbon dioxide, and sulfurous acid gas, but is not limited thereto.

[0072] The synthesis gas 91 discharged from the ammonia synthesis reactor 10 may include 1 to 90 vol%, 1 to 50 vol%, 5 to 30 vol%, or 10 to 20 vol% of ammonia relative to the total synthesis gas.

[0073] The gas-liquid separation can be carried out by condensing 10 to 99.99999 vol%, 50 to 99.9999 vol%, 60 to 99.999 vol% or 70 to 99.99 vol% of ammonia included in the synthesis gas, so as to perform the gas-liquid separation.

[0074] The gas-liquid separation can be carried out by condensing ammonia at a temperature of -150 to 200 °C, -150 to 20 °C or -100 to 50 °C. Additionally, the gas-liquid separation can be carried out by condensing ammonia at a pressure of 0.0001 to 30 Mpa, 0.007 to 20.0 Mpa, 1 Mpa to 20.0 Mpa or 3 Mpa to 20.0 Mpa.

[0075] The feed heat exchanger, the steam generation device, the first cooler, the second cooler described later or the air cooler described later can be at least one selected from the group consisting of a spiral heat exchanger, a plate heat exchanger, a double-pipe heat exchanger, a multi-tube cylindrical heat exchanger (shell-and-tube heat exchanger), a multi-layer circular-tube heat exchanger, a scroll tube heat exchanger and a scroll plate heat exchanger, but is not limited thereto.

[0076] In an embodiment according to the present disclosure, the ammonia synthesis system may include an air separation unit 88 for separating nitrogen from air. The air separation unit is especially accompanied in the manufacture of green ammonia that produces hydrogen by electrolyzing water using surplus electricity generated by wind or sunlight. Generally, the air separation unit 88 can be an air separation unit that separates air by liquefaction. The air separation unit can separate oxygen, nitrogen, argon, etc. from air by using the boiling point difference (oxygen: -183 °C, nitrogen: -196 °C, argon: -186 °C).

[0077] In an embodiment according to the present disclosure, the air separation unit may also be composed of a compression unit, a cooling unit, a pretreatment unit, a booster compressor, a liquefaction unit, a distillation unit, a preheater and a turbine, but is not limited thereto.

[0078] In an embodiment according to the present disclosure, the air separation unit can separate nitrogen from air into liquid nitrogen like a common air separation unit (Airseparation unit, ASU).

[0079] Additionally, in an embodiment according to the present disclosure, the air separation unit may also separate nitrogen for discharge after liquefying and separating oxygen and argon with higher boiling points from air. As described above, when the air separation unit does not liquefy nitrogen, the energy consumed for liquefying nitrogen that accounts for about 80% of air can be reduced, so that the energy consumed for separating nitrogen from air can be reduced.

[0080] In an embodiment according to the present disclosure, the ammonia synthesis system may further include: an air cooler 89 that exchanges heat between the nitrogen separated in the air separation unit and the air introduced into the air separation unit, thereby cooling the air. Additionally, in an embodiment according to the present disclosure, the ammonia synthesis system may introduce the nitrogen that has undergone heat exchange in the air cooler into the second cooler. The ammonia synthesis system further includes an air cooler, such that it can first exchange heat between the liquid nitrogen or low-temperature nitrogen discharged from the air separation unit and the air introduced into the air separation unit, reduce the energy consumed for cooling the air in the air separation unit, adjust the temperature of the nitrogen that has undergone heat exchange in the air cooler to not be too low compared to the boiling point of ammonia, and then introduce it into the second cooler, thereby reducing the energy consumed in air cooling and ammonia cooling.

[0081] In an embodiment according to the present disclosure, the ammonia synthesis system may include: a second cooler that exchanges heat between the nitrogen separated in the air separation unit and the synthesis gas cooled in the first cooler. The nitrogen separated in the air separation unit may also be introduced into the second cooler after undergoing heat exchange in the air cooler.

[0082] The second cooler can cool the synthesis gas a second time. It is also possible that the synthesis gas is cooled a second time in the second cooler after being cooled a second time in the first cooler. It is also possible that the synthesis gas is directly cooled in the second cooler without passing through the first cooler. Ammonia in the synthesis gas condenses in the second cooler, thereby separating ammonia. Specifically, ammonia separation can be achieved by cooling the synthesis gas for gas-liquid separation. The gas-liquid separation can be carried out once or more than twice.

[0083] As described above, the ammonia synthesis system according to the present disclosure separates ammonia through two-stage cooling via the first cooler and the second cooler, thereby being able to significantly reduce the cooling load required in the first cooler. Moreover, by undergoing the above two-stage cooling, it can cope with fluctuations in the flow rate of the raw materials, thereby effectively and flexibly responding. For example, when the flow rate of the raw materials introduced into the reactor is low, only the first cooler can be used, so that ammonia is separated by cooling with only the refrigerant. When the flow rate of the raw materials introduced into the reactor is high, the cooling load increases. Therefore, after cooling with the refrigerant in the first cooler, nitrogen can be used to cool and separate ammonia in the second cooler. That is, by coping with fluctuations in the flow rate of the ammonia synthesis raw materials and appropriately distributing the cooling load to each cooler for operation, the energy consumed in ammonia cooling and separation can be reduced, and energy loss can be prevented.

[0084] In the second cooler according to the present disclosure, the heat exchange medium is preferably nitrogen. When liquid nitrogen is used as the heat exchange medium in the second cooler, the cooling air generates liquid nitrogen in the air separation unit, so too much energy is consumed during cooling, and it is difficult to reduce the energy consumed in the overall process. In addition, when liquid nitrogen with a boiling point of -196°C or lower is used in the second cooler, since the boiling point of ammonia is only about -33°C, the temperature of the cooled ammonia is unnecessarily and excessively reduced, and huge energy losses may occur. Moreover, when liquid nitrogen is vaporized, a large amount of energy is absorbed. When cooling is performed in the second cooler, if such a phase conversion process is accompanied, there is a problem that it is difficult to elastically distribute the cooling load to the first cooler and the second cooler during the process operation to cope with the flow rate change of the raw material. On the contrary, when nitrogen is used as the heat exchange medium in the second cooler, it is possible to reduce the energy for liquefying nitrogen in the air separation unit, prevent energy losses caused by unnecessarily reducing the temperature of the cooled ammonia, and has the effect of elastically operating the process in response to the flow rate change of the raw material.

[0085] The temperature of nitrogen can be in the range of -195 to -40°C, but is not limited thereto. As long as it is in the gas phase of nitrogen according to the pressure.

[0086] In the second cooler, the gas-liquid separation can be carried out for 50 to 99.9999 vol%, 60 to 99.999 vol%, or 70 to 99.99 vol% of the ammonia included in the condensed synthesis gas.

[0087] The gas-liquid separation in the second cooler can be carried out by condensing ammonia at a temperature of -150 to 200°C, -150 to 20°C, or -100 to 50°C. In addition, the gas-liquid separation can be carried out by condensing ammonia at a pressure of 0.0001 to 30 Mpa, 0.007 to 20.0 Mpa, 1 Mpa to 20.0 Mpa, or 3 Mpa to 20.0 Mpa.

[0088] The second cooler can be at least one selected from the group consisting of a spiral heat exchanger, a plate heat exchanger, a double-tube heat exchanger, a multi-tube cylindrical heat exchanger (shell-and-tube heat exchanger), a multi-tube heat exchanger, a vortex tube heat exchanger, and a vortex plate heat exchanger, but is not limited thereto.

[0089] The second cooler can be not only located at the rear end of the first cooler but also at the front end of the first cooler. That is, it can also be that after the first cooling in the second cooler, the second cooling is performed in the first cooler to separate ammonia. The ammonia synthesis system can be configured to perform the second cooling in the first cooler after the first cooling in the second cooler.

[0090] In one embodiment according to the present disclosure, nitrogen 94 that undergoes heat exchange in the second cooler can be supplied to the raw material supply line 81. The nitrogen that undergoes heat exchange in the second cooler can be supplied to the raw material supply line through the nitrogen supply line. The ammonia synthesis system can be provided with a buffer tank in the nitrogen supply line. By providing a buffer tank in the nitrogen supply line, it is possible to store the nitrogen that undergoes heat exchange in the second cooler, thereby coping with fluctuations in the feed flow rate of the ammonia synthesis raw materials. For example, when the flow rate of the raw materials fed to the compressor 82 is high, nitrogen may not be supplied to the raw material supply line and is stored in the buffer tank. Then, when the flow rate of the raw materials fed to the compressor is low, a surge phenomenon of the compressor may occur. Therefore, the nitrogen stored in the buffer tank can be supplied to the raw material supply line to prevent this phenomenon. This buffer tank has the advantage of being able to flexibly supply nitrogen to cope with fluctuations in the raw material flow rate, thereby enabling stable operation of the compressor.

[0091] Before being supplied to the raw material supply line, the ammonia synthesis system can recover the energy contained in the nitrogen that undergoes heat exchange in the second cooler from the nitrogen that undergoes heat exchange in the second cooler through further heat exchange or the like. The above energy recovery can be carried out through a heat exchanger or the like, but is not limited thereto.

[0092] In the nitrogen supply line, a flow regulating device can be provided downstream of the buffer tank. By providing a flow regulating device downstream of the buffer tank, it is possible to regulate the flow rate of the nitrogen finally supplied to the raw material supply line. For example, when the flow rate of the raw materials fed is high, the flow regulating device can be closed and nitrogen is not supplied to the raw material supply line but stored in the buffer tank. Then, when the flow rate of the raw materials fed is low, a surge phenomenon of the compressor may occur. Therefore, the flow regulating device can be opened to supply the nitrogen stored in the buffer tank to the raw material supply line to prevent this phenomenon. The flow regulating device has the advantage of being able to flexibly supply nitrogen to cope with fluctuations in the raw material flow rate, thereby enabling stable operation of the compressor.

[0093] In addition, the second cooler can separate the synthesis gas into ammonia and a recycle stream including hydrogen and nitrogen by cooling. The ammonia synthesis system according to the present disclosure can supply the recycle stream including hydrogen and nitrogen separated in the second cooler to the raw material supply line located in front of the compressor through the raw material recycle line. The ammonia synthesis system can be provided with a buffer tank in the raw material recycle line. By providing a buffer tank in the raw material recycle line, it is possible to store the recycle stream flowing in through the raw material recycle line, thereby coping with fluctuations in the feed flow rate of the ammonia synthesis raw materials.

[0094] In addition, in the raw material recycle line, a flow regulating device can be provided upstream of the buffer tank. By providing a flow regulating device upstream of the buffer tank, the flow rate of the recycle stream flowing into the buffer tank can be regulated, thereby enabling flexible response to fluctuations in the flow rate.

[0095] In the raw material recirculation line, a flow regulating device may be provided downstream of the buffer tank. By providing the flow regulating device downstream of the buffer tank, the flow rate of the recycled flow finally supplied to the raw material supply line can be regulated.

[0096] In addition, the ammonia synthesis system may further include: an adsorption device including an adsorbent at the front end or the rear end of the first cooler or the second cooler. The position where the adsorption device is provided can be appropriately selected according to the process conditions.

[0097] The adsorbent may be at least one selected from the group consisting of silica gel, zeolite, and activated carbon, but is not limited thereto, and ordinary adsorbents can be used.

[0098] In an embodiment according to the present disclosure, the ammonia synthesis system may further include: a reactor recirculation line connecting from the raw material recirculation line to the ammonia synthesis reactor.

[0099] The reactor recirculation line may be directly connected to the ammonia synthesis reactor. In addition, the reactor recirculation line may be connected to one of the following mixed gas supply lines or mixer gas supply lines described later. Moreover, the reactor recirculation line may also be connected to the main end of the following mixed gas supply line described later, but is not limited thereto. A flow regulating device may be provided in the reactor recirculation line.

[0100] The ammonia synthesis system according to the present disclosure may further include a second cooler bypass line. The synthesis gas may only be cooled and separated for ammonia in the first cooler through the second cooler bypass line.

[0101] In addition, the ammonia synthesis system may further include a first cooler bypass line. The synthesis gas may be directly fed into the second cooler through the first cooler bypass line without passing through the first cooler, thereby performing cooling and separation of ammonia.

[0102] Specifically, when the flow rate of the synthesis gas including ammonia is high or the ammonia content in the synthesis gas is high, the ammonia synthesis system 1 may cool the synthesis gas 91 once through the first cooler 83 and cool and separate ammonia through the second cooler 84 twice. Differently, when the flow rate of the synthesis gas including ammonia is low or the ammonia content in the synthesis gas is low, the ammonia synthesis system may separate ammonia only through the first cooler 83 or the second cooler 84. That is, the ammonia synthesis system according to the present disclosure can flexibly respond to the variable ammonia production flow rate during the production cycle by having a bypass line, appropriately separate ammonia, and thus can provide process flexibility. Moreover, when the flow rate of the synthesis gas including ammonia is low or the ammonia content in the synthesis gas is low, cooling can be performed only using one cooler, thereby preventing energy loss during cooling. That is, the energy used in ammonia separation can be reduced, and the cost consumed in ammonia separation can be saved.

[0103] In one embodiment according to the present disclosure, the ammonia synthesis reactor 10 may include: two or more catalyst layers, which are included in the ammonia synthesis reactor; anti-backflow plates, which are disposed downstream of each of the catalyst layers other than the lowermost catalyst layer among the two or more catalyst layers to prevent the mixed gas from flowing back; distribution devices, which are disposed upstream of each of the two or more catalyst layers to distribute the mixed gas to the catalyst layers; and a mixed gas supply line, which is arranged to supply the mixed gas to the distribution devices.

[0104] In addition, the ammonia synthesis reactor may further include: microwave heating devices, which irradiate microwaves to each of the two or more catalyst layers.

[0105] Reference Figure 1 and Figure 2 According to one embodiment of the present disclosure, an ammonia synthesis reactor 10 may be provided, which includes: two or more catalyst layers 20, 21; anti-backflow plates 30, 31, which are disposed downstream of each of the catalyst layers other than the lowermost catalyst layer among the two or more catalyst layers 20, 21 to prevent the mixed gas from flowing back; distribution devices 40, 41, which are disposed upstream of each of the two or more catalyst layers 20, 21 to distribute the mixed gas to the catalyst layers 20, 21; mixed gas supply lines 50, 51, which are arranged to supply the mixed gas to the distribution devices 40, 41; and microwave heating devices 60, 61, which irradiate microwaves to each of the two or more catalyst layers 20, 21.

[0106] Hereinafter, as an example of the ammonia synthesis reactor 10 of the present disclosure, an ammonia synthesis reactor including two catalyst layers may be described. Of course, ammonia synthesis reactors including two or more, for example, three, four, five, seven, or ten catalyst layers are included in one embodiment of the present disclosure.

[0107] An ammonia synthesis system according to one embodiment of the present disclosure includes a mixed gas supply line to supply the mixed gas to each of the two or more catalyst layers, so as to be able to cope with the flow rate variation occurring during the production cycle. For example, when the flow rate of the input raw material is high, it can be input through the upper mixed gas supply line 50 to pass through from the uppermost catalyst layer 20, and when the flow rate of the input raw material is low, it can be input through the lower mixed gas supply line 51 to pass through the lower catalyst layer 21 instead of the upper catalyst layer 20, and thus operate. At this time, when the mixed gas is input through the lower mixed gas supply line 51 to pass through the lower catalyst layer 21, the backflow is prevented by the anti-backflow plate 30.

[0108] On the one hand, in the case where the flow rate of the ammonia synthesis system is small as described above, the mixed gas can be fed through the mixed gas supply line 51 located at the lower end and operated to pass through the catalyst layer 21 located at the lower end, so there is no need to maintain the temperature of the entire reactor. Therefore, during operation, the amount of energy required in the system can be reduced as needed, thus saving energy.

[0109] In addition, during the operation of the ammonia synthesis system, each catalyst layer is uniformly used, so that the replacement cycle of the catalyst can be extended. Generally, when the flow rate of the reaction fluid is small, the distribution performance at the upper part of the catalyst layer decreases, resulting in differences in the reaction performance among the catalysts at the same height. The replacement cycle of the catalyst is determined by the reaction performance at the lower end of the catalyst layer. When the distribution performance decreases due to the reduction in flow rate, resulting in a decrease in the reaction performance in some catalyst layer regions at the lower end, there is a problem of a shortened replacement cycle. However, as described in the ammonia synthesis system according to the present disclosure, as long as the passing height of the catalyst layer is adjusted according to the flow rate and the distribution performance in each catalyst layer is improved, the catalyst layer can be used relatively uniformly, thereby extending the replacement cycle of the catalyst.

[0110] In addition, the ammonia synthesis system according to an embodiment of the present disclosure can make the temperature deviation between the central part and the edge part of the catalyst layer uniform at the initial stage of operation by including microwave heating devices 60 and 61, thereby improving the ammonia synthesis yield. Specifically, the microwave heating device can make the temperature deviation between the central part and the edge part of the catalyst layer uniform by irradiating microwaves to the catalyst layer at the initial stage of operation. Moreover, the microwave heating device preheats the catalyst layer that is not sufficiently preheated at the initial stage of operation, thereby being able to improve the ammonia synthesis yield at the initial stage of operation.

[0111] For example, when the flow rate of the fed raw material is small, it can be operated to pass through the catalyst layer 21 located at the lower end instead of the catalyst layer 20 located at the upper end. At this time, the mixed gas is not fed to the catalyst layer 20 located at the upper end, so the temperature of the catalyst layer 20 located at the upper end will decrease over time. Then, when the catalyst layer 20 located at the upper end is used again, since the catalyst layer 20 located at the upper end is in a temperature-lowering state, the ammonia synthesis efficiency may decrease. At this time, the microwave heating device irradiates microwaves to the catalyst layer 20 located at the upper end in the temperature-lowering state, so that excellent ammonia synthesis efficiency can be achieved even when the catalyst layer is reused for operation.

[0112] One or more, two or more, three or more, four or more, five or more, or eight or more microwave heating devices can be provided in each catalyst layer, but it is not limited thereto. The number of microwave heating devices can increase according to the size of the reactor, and the installation position can be adjusted for effective microwave irradiation.

[0113] The ammonia synthesis system may further include microwave guiding parts 601 and 602. The microwave guiding parts can enable the microwaves irradiated from the microwave heating device to reach the catalyst layer more effectively. Of course, the shape or installation position of the guiding parts can be changed according to the microwave waveform.

[0114] In an embodiment according to the present disclosure, the number of catalyst layers may be 2 or more, 3 or more, 4 or more, 5 or more, 6 or more, 7 or more, 10 or more, 20 or less, 10 or less, 8 or less, 7 or less, 6 or less, 5 or less, 4 or less, 3 or less, 2 or less, or an interval value of these numerical values. The number of catalyst layers and the number of distribution devices may be the same.

[0115] In an embodiment according to the present disclosure, the mixed gas may include at least one selected from the group consisting of hydrogen and nitrogen.

[0116] Hydrogen can be produced in a device driven by newly renewable energy. Specifically, the hydrogen can be produced in a water electrolyzer driven by newly renewable energy.

[0117] The newly renewable energy may include at least one selected from the group consisting of solar heat, sunlight, biomass energy, wind power, hydropower, geothermal energy, ocean energy, and waste energy. The newly renewable energy has time variability. For example, solar energy cannot be used at night. Therefore, when hydrogen is produced in a device driven by newly renewable energy, the ammonia synthesis system cannot always operate at a constant flow rate. That is, due to the time variability of the newly renewable energy, an ammonia synthesis system capable of coping with the flow rate fluctuations occurring during the production cycle is required.

[0118] In addition, the mixed gas supplied in the mixed gas supply routes 50 and 51 may be a low-temperature mixed gas. Therefore, the mixed gas supplied in the mixed gas supply routes 50 and 51 serves to cool the mixed gas and can also act as a means for cooling the mixed gas flowing in the ammonia synthesis system. For example, the low-temperature mixed gas can be used as a cooling means for cooling the mixed gas introduced into the catalyst layer.

[0119] The ammonia synthesis system according to an embodiment of the present disclosure may further include distribution plates 70 and 71, which are respectively located between the catalyst layers 20 and 21 and the distribution devices 40 and 41.

[0120] In addition, the ammonia synthesis system according to an embodiment of the present disclosure may further include: a plurality of mixed gas flow tubes 720, which are fixed to the lower surfaces 72 of the distribution plates 70 and 71 for the mixed gas to flow through.

[0121] The ammonia synthesis system further includes a distribution plate and mixed gas flow tubes, so that even if the flow rate of raw materials such as hydrogen introduced is reduced, a uniform flow rate distribution can be maintained at the front end of the catalyst layer included in the ammonia synthesis reactor.

[0122] Reference Figure 3 and Figure 4 The mixed gas flow tube 720 may have a bottom surface and side surfaces 722 connecting the bottom surface and the distribution plate.

[0123] It may be that a plurality of upper openings 723 are formed along the circumference at the side surface of the upper portion 722a of the mixed gas flow tube 720, a plurality of intermediate openings 725 are formed along the circumference at the side surface of the intermediate portion 722b of the mixed gas flow tube 720, and a plurality of lower openings 727 are formed along the circumference at the side surface of the lower portion 722c of the mixed gas flow tube 720. When passing through the upper openings 723, the intermediate openings 725, and the lower openings 727, the flow of the mixed gas occurs. The mixed gas flow tube 720 may include a cover 730, and the cover 730 is formed to surround at least a partial area of the side surface of the mixed gas flow tube 720 to provide a space for guiding the fluid flowing out of the side surface of the mixed gas flow tube 720 after passing through the upper openings 723 toward the side of the intermediate openings 725. The cover 730 may be formed to surround at least one of the group consisting of the upper portion and the intermediate portion of the side surface of the mixed gas flow tube 720.

[0124] The cover 730 guides the fluid flowing out of the side surface of the mixed gas flow tube 720 after passing through the upper openings 723 toward the side of the intermediate openings 725. Thus, a flow that moves toward the outside of the side surface of the mixed gas flow tube 720 and then moves back into the side surface is formed. Through the flow thus formed, the mixing of the fluid is completed more smoothly.

[0125] Reference Figure 5 The mixed gas flow tube 720 may further include a partition 729 configured to divide the upper portion and the intermediate portion of the mixed gas flow tube 720. The partition 729 completely separates the upper portion and the intermediate portion of the mixed gas flow tube 720 so that the fluid cannot move. Therefore, the fluid flowing into the upper portion of the mixed gas flow tube 720 does not directly descend to the intermediate portion due to the partition 729, but flows out through the upper openings 723 into the space between the mixed gas flow tube 720 and the cover 730. Then, the fluid flows into the mixed gas flow tube through the intermediate openings 725 in the space and descends to the lower portion, and thus flows out of the mixed gas flow tube 720 through the lower openings 727. As described above, by forming a flow that flows out of the mixed gas flow tube 720 and then flows back into the inside and then flows out again, the mixing of the fluid can be completed more smoothly, and a uniform flow distribution can be maintained at the front end of the catalytic layer.

[0126] In one embodiment according to the present disclosure, each of the mixed gas supply lines 50 and 51 may include a flow regulating device. The flow regulating device may independently control the flow rate of the mixed gas in each of the mixed gas supply lines. Specifically, the flow regulating device independently adjusts the flow rate of the mixed gas flowing in each of the mixed gas supply lines, so that the flow rate of the mixed gas entering the distribution device remains within the required flow rate range.

[0127] The flow regulating device may be a flow control valve.

[0128] In one embodiment according to the present disclosure, each of the mixed gas supply lines 50 and 51 may be a line branched from one main supply line or main end. Additionally, each of the mixed gas supply lines 50 and 52 may also be supplied from separate supply lines with at least one selected from the group consisting of nitrogen and hydrogen.

[0129] In one embodiment according to the present disclosure, a plurality of openings 302 may be formed in each of the anti-backflow plates 30 and 31, and an anti-backflow cover 303 that is selectively opened according to the gas flow direction may be formed in the plurality of openings 302 formed in each of the anti-backflow plates 30 and 31. The ammonia synthesis system according to the present disclosure includes the anti-backflow plates 30 and 31 formed with the anti-backflow covers 303, so that even if the mixed gas is introduced through the lower mixed gas supply line 51 to pass through the lower catalyst layer 21, the backflow of the mixed gas can be prevented. Additionally, as described above, by implementing a system capable of preventing the backflow of the mixed gas, the amount of energy required in the system can be reduced as needed during operation, thereby saving energy, and each catalyst layer can be used evenly, thereby extending the replacement cycle of the catalyst.

[0130] Reference Figure 6 and Figure 7 , the anti-backflow cover 303 may be coupled to a position on the perimeter of the plurality of openings 302 formed in each of the anti-backflow plates 30 and 31 through a hinge 304. Figure 6 The state where the anti-backflow cover 303 coupled with the hinge 304 is shown open. When the mixed gas flows from the upstream to the downstream of the anti-backflow plates 30 and 31, the anti-backflow cover 303 remains open, so that the mixed gas flows normally. Figure 7 The state where the anti-backflow cover 303 coupled through the hinge 304 is shown closed. When the mixed gas attempts to flow from the downstream to the upstream of the anti-backflow plates 30 and 31, the anti-backflow cover 303 is closed due to the flow of the mixed gas flowing from the downstream to the upstream. Due to this principle, the anti-backflow plates 30 and 31 according to the present disclosure can prevent the backflow of the mixed gas.

[0131] In one embodiment according to the present disclosure, a spring is provided at the hinge 304 joint coupled by the hinge 304, so that an elastic force can be applied in the direction in which the anti-backflow lid 303 approaches the distribution plate.

[0132] In one embodiment according to the present disclosure, the distribution devices 40, 41 may be circular plate-shaped or toroidal, but are not limited thereto, and common gas distribution devices can be used.

[0133] In an ammonia synthesis system according to one embodiment of the present disclosure, ammonia synthesis can be carried out at 1 to 500 bar or 5 to 300 bar.

[0134] In addition, in an ammonia synthesis system according to one embodiment of the present disclosure, ammonia synthesis can be carried out at 100 to 800 °C or 200 to 700 °C.

[0135] An ammonia synthesis system according to one embodiment of the present disclosure may further include: a heat exchanger, which is arranged downstream of each of two or more catalytic layers to remove heat from the effluent of the catalytic layer. The heat exchanger can be arranged to surround the catalytic layer or its periphery. The ammonia synthesis system according to the present disclosure further includes a heat exchanger, so that an additional heat removal unit other than supplying a cooled mixed gas can be provided. Thereby, the ammonia synthesis system can be operated flexibly.

[0136] In addition, the present disclosure can provide an operation method of an ammonia synthesis system. The content repeated with the ammonia synthesis system can be applied equally.

[0137] The present disclosure provides an operation method of an ammonia synthesis system, which is based on the operation method of the ammonia synthesis system according to the first aspect. The ammonia synthesis system further includes a second cooler bypass route. The method selectively performs the following modes: a two-stage cooling mode in which the synthesis gas passes through both the first cooler and the second cooler; and a second cooler bypass mode in which the synthesis gas passes only through the first cooler and bypasses the second cooler through the second cooler bypass route.

[0138] Specifically, when the flow rate of the fed raw material is large and the required cooling load is large, as described in the two-stage cooling mode, it can pass through both the first cooler 83 and the second cooler 84 to perform two-stage cooling, thereby separating ammonia. Then, when the flow rate of the fed raw material is small and the required cooling load is small, it can be operated to pass only through the first cooler 83 and bypass the second cooler.

[0139] That is, the ammonia synthesis system according to the present disclosure is as described above, selectively operating one of the two-stage cooling mode and the second cooler bypass mode, so as to be able to flexibly respond to the variable ammonia production flow during the production cycle, appropriately perform ammonia separation, and thus provide process flexibility. Moreover, when the flow rate of the synthesis gas including ammonia is small or the ammonia content in the synthesis gas is low, excessive cooling can be prevented, thereby reducing the energy used in ammonia separation and saving the cost consumed in ammonia separation.

[0140] In addition, the present disclosure can provide an ammonia synthesis method. Contents repeated with the ammonia synthesis system and its operation method can be applied equally.

[0141] The present disclosure provides an ammonia synthesis method, which includes: S1) a step of compressing a mixed gas in a compressor and then feeding it into an ammonia synthesis reactor; S2) a step of reacting the compressed mixed gas in the ammonia synthesis reactor to generate a synthesis gas including ammonia; S3) a first cooling step of cooling the synthesis gas generated in step S2); and S4) a second cooling step of performing heat exchange between the synthesis gas cooled in step S3) and nitrogen separated in an air separation unit. The nitrogen that undergoes heat exchange in step S4) is supplied to the compressor.

[0142] According to the ammonia synthesis method of the present disclosure, while being able to flexibly respond to the flow rate changes occurring during the production cycle, it can prevent the surge phenomenon of the compressor and thus can be stably operated, can solve the problem of uneven flow distribution occurring at the front end of the catalyst layer and the temperature deviation between the center and the edge of the catalyst layer occurring in the initial stage of operation, which leads to a decrease in ammonia synthesis yield, and can reduce the energy used in ammonia separation. In particular, even if the flow rate of the raw materials fed for the reaction changes, the ammonia synthesis system of the present disclosure can prevent the surge phenomenon of the compressor and the like, thereby stably operating the compressor. This can be achieved by supplying the nitrogen that undergoes heat exchange in the second cooler to the raw material supply route located at the front end of the compressor through a nitrogen supply route.

[0143] In addition, according to an embodiment of the present disclosure, in the ammonia synthesis method, even if the ammonia production volume changes with the change in the flow rate of the raw materials fed for the reaction, it can flexibly respond during ammonia separation, thereby providing flexibility in process operation. Moreover, according to an embodiment of the present disclosure, in the ammonia synthesis method, even if the ammonia production volume changes with the change in the flow rate of the raw materials fed for the reaction, it can also reduce the energy used in ammonia separation and save the cost consumed in ammonia separation.

[0144] In an embodiment according to the present disclosure, the ammonia synthesis method can perform heat exchange between the nitrogen separated in the air separation unit and the air fed into the air separation unit, and then perform heat exchange between the nitrogen that has undergone heat exchange and the synthesis gas cooled in step S4).

[0145] The nitrogen discharged from the air separation unit may also be liquid nitrogen. When discharged as nitrogen gas, it can be at a low temperature below -150°C. In this case, when this liquid nitrogen or nitrogen gas below -150°C is directly used in ammonia cooling, since the boiling point of ammonia is only about -33°C, the temperature of the cooled ammonia may be unnecessarily too low, resulting in energy loss. Therefore, the liquid nitrogen or low-temperature nitrogen gas discharged from the air separation unit can be first heat-exchanged with the air introduced into the air separation unit to reduce the energy consumed in cooling the air in the air separation unit, adjust the temperature of the nitrogen gas that undergoes heat exchange in the air cooler to not be overly low compared to the boiling point of ammonia, and then perform heat exchange with the synthesis gas cooled in step S4), thereby reducing the energy consumed in air cooling and ammonia cooling.

[0146] In an embodiment according to the present disclosure, the ammonia synthesis reactor may include: two or more catalytic layers included in the ammonia synthesis reactor; anti-backflow plates disposed downstream of each of the catalytic layers other than the lowermost catalytic layer among the two or more catalytic layers to prevent backflow of the mixed gas; a distribution device disposed upstream of each of the two or more catalytic layers to distribute the mixed gas to the catalytic layers; and a mixed gas supply line arranged to supply the mixed gas to the distribution device.

[0147] The content described above is only an example of applying the principles of the present disclosure, and other structures may also be included without departing from the scope of the present disclosure.

Claims

1. An ammonia synthesis system, comprising: A compressor for compressing a mixed gas; A raw material supply line for supplying the mixed gas to the compressor; An ammonia synthesis reactor in which the mixed gas compressed in the compressor is introduced to synthesize ammonia; An air separation unit for separating nitrogen from air; A first cooler for cooling the synthesis gas including ammonia discharged from the ammonia synthesis reactor; And A second cooler for exchanging heat between the nitrogen separated in the air separation unit and the synthesis gas cooled in the first cooler, The nitrogen gas that has undergone heat exchange in the second cooler is supplied to the raw material supply line.

2. The ammonia synthesis system according to claim 1, wherein, The ammonia synthesis system further includes: an air cooler for exchanging heat between the nitrogen separated in the air separation unit and the air introduced into the air separation unit to cool the air, The nitrogen gas that has undergone heat exchange in the air cooler is introduced into the second cooler.

3. The ammonia synthesis system according to claim 1, wherein, The ammonia synthesis reactor includes: Two or more catalyst layers; A backflow prevention plate disposed downstream of each of the catalyst layers other than the lowermost catalyst layer among the two or more catalyst layers to prevent backflow of the mixed gas; A distribution device disposed upstream of each of the two or more catalyst layers for distributing the mixed gas to the catalyst layers; and A mixed gas supply line arranged to supply the mixed gas to the distribution device.

4. The ammonia synthesis system according to claim 3, wherein, The ammonia synthesis system further includes: distribution plates respectively located between the catalyst layers and the distribution device.

5. The ammonia synthesis system according to claim 4, wherein, The ammonia synthesis system further includes: a plurality of mixed gas flow tubes fixed to the lower surface of the distribution plate for the mixed gas to flow through.

6. The ammonia synthesis system according to claim 5, wherein, The mixed gas flow tube has a bottom surface and side surfaces connecting the bottom surface and the distribution plate, A plurality of upper opening portions are formed on the upper side surface of the mixed gas flow tube at intervals along the circumference, A plurality of middle portion opening portions are formed on the middle side surface of the mixed gas flow tube at intervals along the circumference, A plurality of lower opening portions are formed on the lower side surface of the mixed gas flow tube at intervals along the circumference, The mixed gas flow tube includes a covering member formed to surround at least a partial area of the side surface of the mixed gas flow tube to provide a space for guiding the fluid flowing out of the side surface of the mixed gas flow tube after passing through the upper opening portions to the middle portion opening portion side.

7. The ammonia synthesis system according to claim 6, wherein, The mixed gas flow tube further includes: a partition plate configured to divide the upper portion and the middle portion of the mixed gas flow tube.

8. The ammonia synthesis system according to claim 1, wherein, The ammonia synthesis system further includes: a heat exchanger disposed downstream of each of the two or more catalyst layers for removing heat from the effluent of the catalyst layer.

9. The ammonia synthesis system according to claim 1, wherein, Each of the mixed gas supply routes includes a flow regulating device.

10. A method for operating an ammonia synthesis system, which is the method for operating the ammonia synthesis system according to claim 1, The ammonia synthesis system further includes a second cooler bypass route, The method selectively performs the following modes: A two-stage cooling mode in which the synthesis gas passes through both the first cooler and the second cooler; and A second cooler bypass mode in which the synthesis gas only passes through the first cooler and bypasses the second cooler through the second cooler bypass route.

11. An ammonia synthesis method, which includes: S1) Compressing a mixed gas in a compressor and thus feeding it into an ammonia synthesis reactor; S2) Reacting the compressed mixed gas in the ammonia synthesis reactor to generate a synthesis gas including ammonia; S3) A first cooling step of cooling the synthesis gas generated in step S2); and S4) A second cooling step of heat-exchanging the synthesis gas cooled in step S3) with nitrogen separated in an air separation unit, The nitrogen that undergoes heat exchange in step S4) is supplied to the compressor.

12. The ammonia synthesis method according to claim 11, wherein, The ammonia synthesis method heat-exchanges the nitrogen separated in the air separation unit with the air fed into the air separation unit, and thus heat-exchanges the nitrogen that has undergone heat exchange with the synthesis gas cooled in step S4).

13. The ammonia synthesis method according to claim 11, wherein, The ammonia synthesis reactor includes: Two or more catalyst layers, which are included in the ammonia synthesis reactor; Backflow prevention plates, which are arranged downstream of each of the catalyst layers other than the lowermost catalyst layer among the two or more catalyst layers to prevent backflow of the mixed gas; Distribution devices, which are arranged upstream of each of the two or more catalyst layers to distribute the mixed gas to the catalyst layers; and Mixed gas supply routes, which are arranged to supply the mixed gas to the distribution devices.

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