SYSTEM AND METHOD FOR SYNTHESIS OF CRYOGENICALLY BOUND AMMONIA WITH WASHING WITH LIQUID NITROGEN
Patent Information
- Application Number
- RU2025125754
- Authority / Receiving Office
- RU · RU
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2024-11-20
- Filing Date
- 2025-03-27
- Publication Date
- 2026-09-28
Abstract
Description
A liquid nitrogen washing cryogenic coupling ammonia synthesis system and method
[0001] This application claims priority to Chinese patent application 2024116657623, filed on 2024 / 11 / 20. The entire contents of the aforementioned Chinese patent application are incorporated herein by reference. Technical Field
[0002] This invention relates to an ammonia synthesis system and method using liquid nitrogen washing and cryogenic coupling. Background Technology
[0003] Ammonia is an important inorganic chemical product. The synthesis of ammonia is a reversible exothermic reaction involving three H₂ molecules and one N₂ molecule in a high-temperature, high-pressure reactor containing a catalyst. The reaction equation for ammonia synthesis is as follows: 3H₂ + N₂ → 2NH₃ + Q;
[0004] Because the process is reversible, unreacted raw materials are pressurized and re-enter the reactor via a recirculator. Achieving a higher single-pass conversion rate, thereby reducing the system's circulation volume, not only saves on equipment size and investment but also lowers energy consumption. Improving the single-pass conversion rate of this reaction has become a consensus and direction among industry professionals.
[0005] In practice, the difference in ammonia concentration between the inlet and outlet of the ammonia reactor, i.e., the net ammonia value, is used as the evaluation criterion for this indicator. Achieving a higher net ammonia value involves either increasing the outlet concentration or decreasing the inlet concentration. To increase the outlet concentration, improving the catalyst's reactivity, increasing the system pressure, decreasing the outlet temperature, and reducing the inert gas composition are all effective ways to improve the net ammonia value.
[0006] In current mainstream ammonia synthesis processes, liquid nitrogen scrubbing is commonly used in the removal of impurities such as CO, Ar, and CH4 for economic reasons. The liquid nitrogen scrubbing system includes core components such as a molecular sieve purification unit, a cold box, and a nitrogen scrubbing tower. The molecular sieve adsorption device is used to remove polar impurities such as CO2 and CH3OH from the gas after low-temperature methanol scrubbing. After being cooled stage by stage in the cold box, the gas enters the nitrogen scrubbing tower. In an extremely low environment of -190℃, the significant difference in boiling points between H2 and other components (such as CO, CH4, and Ar) achieves an effect similar to fine separation of multiple components, effectively dissolving CO, CH4, and Ar in liquid nitrogen, thereby reducing the total (CO+CO2) content in the synthesis gas to 16 mg / m³. 3 The system further refines the hydrogen-nitrogen ratio in the syngas to the ideal 3:1 ratio through three steps: fine-tuning of washing nitrogen, preliminary nitrogen mixing, and precise nitrogen mixing. Summary of the Invention
[0007] The present invention aims to solve the problem of how to improve the net ammonia value in the ammonia synthesis process, and thus provides an ammonia synthesis system and method that uses liquid nitrogen washing and cryogenic coupling.
[0008] Currently, in the ammonia synthesis section, no matter how much the cooling capacity of the second ammonia cooler is increased, it is impossible to reach the cooling temperature of the heat exchanger exiting the liquid nitrogen washing section. Reducing the pressure of the liquid ammonia can lower the cold source temperature, but excessively low pressure leads to difficulties in overcoming the resistance drop in the heat exchange equipment. Therefore, increasing the power of the second ammonia cooler has very limited effect. In the liquid nitrogen washing section, the feed gas from the low-temperature methanol wash enters the liquid nitrogen washing system at approximately -50°C. The recovery of this portion of the cooling capacity is generally achieved by sending it to the low-temperature methanol section or air separation. To achieve even lower temperatures, this invention introduces the cooling capacity exiting the heat exchanger in the liquid nitrogen washing section into the ammonia synthesis loop to further cool the process gas exiting the second ammonia cooler. This not only achieves cooling capacity recovery, maintaining a balance in the utilization of cooling capacity throughout the plant, but also improves the separation effect of synthesized ammonia, further increasing the net ammonia value.
[0009] The present invention solves the above-mentioned technical problems through the following technical solution:
[0010] This invention proposes a liquid nitrogen washing cryogenic coupling ammonia synthesis system, which includes: a liquid nitrogen washing module, an ammonia synthesis module, a first pipeline, and a second pipeline; the liquid nitrogen washing module includes a cold box, and the ammonia synthesis module includes an ammonia synthesis device and an ammonia separator;
[0011] The first pipeline connects the ammonia synthesis unit and the cold box, and is used to pass the process gas generated by the ammonia synthesis unit into the cold box for cooling; the second pipeline connects the cold box and the ammonia separator, and is used to pass the process gas cooled by the cold box into the ammonia separator for separation.
[0012] In some of these designs, the cold box is a cold box that receives nitrogen feed gas from the air separation unit.
[0013] It is understood that the air separation section refers to the section in the ammonia synthesis process that provides nitrogen for ammonia synthesis. The main function of the air separation section is to separate oxygen and nitrogen from the air to provide raw materials for the subsequent ammonia synthesis reaction.
[0014] It is understood that the liquid nitrogen washing module can be a conventional module in the art. In some embodiments, the liquid nitrogen washing module includes at least two cold boxes and a nitrogen washing tower, with at least two cold boxes connected in sequence. The first cold box is connected between the ammonia synthesis unit and the ammonia separator via the first pipeline and the second pipeline. This first cold box receives nitrogen feed gas from the air separation section, and the last cold box is connected to the nitrogen washing tower.
[0015] In some specific embodiments, the liquid nitrogen washing module includes three cold boxes and a nitrogen washing tower. The three cold boxes are connected in sequence and are designated as a first cold box, a second cold box, and a third cold box. Each cold box is equipped with a purified gas inlet, a purified gas outlet, a fuel gas inlet, and a fuel gas outlet. The first cold box is also equipped with a nitrogen feed gas inlet, a nitrogen feed gas outlet, a process gas inlet, and a process gas outlet. The second and third cold boxes are each equipped with a hydrogen feed gas inlet, a hydrogen feed gas outlet, a nitrogen feed gas inlet, and a nitrogen feed gas outlet. A second ammonia cooler is connected downstream of the ammonia synthesis unit. One end of the first pipeline is connected to the process gas outlet of the second ammonia cooler, and the other end of the first pipeline is connected to the process gas inlet of the first cold box. One end of the second pipeline is connected to the process gas outlet of the first cold box, and the other end of the second pipeline is connected to the process gas inlet of the ammonia separator. The third cold box is also connected to the nitrogen washing tower.
[0016] In the above scheme, the purified gas and fuel gas from the nitrogen scrubbing tower pass sequentially through the third cold box, the second cold box, and the first cold box, exchanging heat with the nitrogen raw material entering the first cold box and the hydrogen raw material entering the second cold box. By setting up multiple cold boxes for step-by-step cooling, the equipment cost can be reduced compared to a single large cold box.
[0017] It is understood that the structure of the cold box can be a conventional structure in the art, and in some of these solutions, the cold box is a plate-fin heat exchanger.
[0018] In some embodiments, the ammonia synthesis module further includes a compression device, a circulation device, a first ammonia cooler, a second ammonia cooler, and a circulation loop; the compression device and the circulation device are sequentially connected upstream of the ammonia synthesis device; the circulation loop connects the ammonia separator and the circulation device, and the circulation loop is used to return the circulating gas in the ammonia separator to the circulation device; the first ammonia cooler is disposed in the ammonia synthesis device, the second ammonia cooler is connected downstream of the ammonia synthesis device, one end of the first pipeline is connected to the second ammonia cooler, and the other end of the first pipeline is connected to the cold box.
[0019] Furthermore, the ammonia synthesis module also includes a cold gas heat exchanger and a water cooler. A process gas pipeline is provided between the first ammonia cooler and the water cooler. Both the circulation loop and the process gas pipeline pass through the cold gas heat exchanger, so that the circulating gas in the circulation loop and the process gas in the process gas pipeline can exchange heat, making full use of the cooling capacity in the circulating gas.
[0020] In some of these schemes, the liquid nitrogen washing cryogenic coupling ammonia synthesis system further includes a nitrogen distribution module connected between the liquid nitrogen washing module and the ammonia synthesis module, which is used to provide reaction gas to the ammonia synthesis module.
[0021] Furthermore, the nitrogen inlet of the nitrogen distribution module is used to connect to nitrogen from the air separation section.
[0022] In some of these schemes, the liquid nitrogen washing cryogenic coupling ammonia synthesis system may further include an insulated box, in which the liquid nitrogen washing module is integrally housed. The insulated box is equipped with a cold air inlet, through which cold air is supplied to the insulated box to reduce the cold loss of the liquid nitrogen washing module.
[0023] The present invention also proposes a method for ammonia synthesis by liquid nitrogen washing and cryogenic coupling, which includes the following steps: passing the reaction gas into the ammonia synthesis device to perform ammonia synthesis and obtain process gas;
[0024] The process gas is introduced into the cold box of the liquid nitrogen washing section to cool it down. The process gas is cooled down to -77.7°C to room temperature. Further, the process gas is cooled down to -70°C to -10°C.
[0025] After being cooled, the process gas enters the ammonia separator for separation, liquid ammonia is collected, and the separated gas is returned to the ammonia synthesis unit as circulating gas.
[0026] Understandably, the reaction gases generally refer to nitrogen and hydrogen.
[0027] In some of these schemes, the process gas is preferably heated to -20 to -10°C. In this temperature range, the ammonia in the gas phase is already very low. When the temperature is too low, the temperature has little effect on reducing the gas phase fraction of ammonia, but the cost will increase due to the increase in cooling capacity and equipment size. Therefore, this range can better balance the process gas temperature and cost.
[0028] It is understood that the gas after cooling and separation in the nitrogen scrubbing tower generally includes purified gas and combustion gas. Therefore, the liquid nitrogen scrubbing section typically uses purified gas and / or fuel gas flowing through the cold box to cool the process gas. Furthermore, the temperature of the purified gas and / or fuel gas in the liquid nitrogen scrubbing section that exchanges heat with the process gas is preferably -65 to -50°C.
[0029] The composition of the purified gas and the combustion gas is conventional in this field. The purified gas mainly includes H2 and N2, and may contain a small amount of argon. The combustion gas includes CO and CH4, etc.
[0030] In some of these schemes, the ammonia synthesis is preferably carried out using the aforementioned liquid nitrogen washing cryogenic coupling ammonia synthesis system.
[0031] Furthermore, the liquid nitrogen washing cryogenic coupling ammonia synthesis method preferably includes the following steps:
[0032] The reaction gas is passed into the ammonia synthesis unit to perform ammonia synthesis, and process gas is obtained.
[0033] The process gas is introduced into the cold box through the first pipeline to cool the process gas;
[0034] After being cooled, the process gas enters the ammonia separator through the second pipeline for separation, and the separated gas is returned to the ammonia synthesis unit.
[0035] Furthermore, when the liquid nitrogen washing cryogenic coupling ammonia synthesis system is also equipped with the aforementioned cold gas heat exchanger, the temperature of the process gas can be reduced to 40 to -5°C through the cold gas heat exchanger. Theoretically, the lower the temperature after cooling, the better. However, the lower the temperature after cooling, the larger the area of the cold gas heat exchanger needs to be, which is not economically reasonable. Considering both cost and cooling temperature, the temperature of the process gas is optimally reduced to 30°C through the cold gas heat exchanger.
[0036] When the liquid nitrogen washing cryogenic coupling ammonia synthesis system is also equipped with the aforementioned first ammonia cooler, the temperature of the process gas can be reduced to 30-80°C by the first ammonia cooler. Similarly, theoretically, the lower the temperature after cooling, the better. However, the lower the temperature after cooling, the larger the area of the first ammonia cooler needs to be, which is not economically reasonable. Considering both cost and cooling temperature, the optimal temperature is reduced to 15°C.
[0037] When the liquid nitrogen washing cryogenic coupling ammonia synthesis system is also equipped with the aforementioned second ammonia cooler, the temperature of the process gas can be cooled to 15 to -12°C through the second ammonia cooler. Similarly, theoretically, the lower the temperature after cooling, the better. However, the lower the temperature after cooling, the larger the area of the second ammonia cooler needs to be, which is not economically reasonable. Considering both cost and cooling temperature, it is better to cool down to -5°C.
[0038] Furthermore, when the liquid nitrogen washing cryogenic coupling ammonia synthesis system is also equipped with the aforementioned nitrogen distribution module, the hydrogen-nitrogen ratio in the reaction gas is adjusted to 3:1 through the nitrogen distribution module.
[0039] Furthermore, when the liquid nitrogen washing cryogenic coupling ammonia synthesis system is further equipped with the aforementioned liquid nitrogen washing module comprising a first cold box, a second cold box, a third cold box, and a nitrogen washing tower, the method for preparing the reaction gas includes the following steps:
[0040] Nitrogen feed gas from the air separation section enters the first cold box for heat exchange and then enters the second cold box. Hydrogen feed gas from the low-temperature section enters the second cold box. The nitrogen and hydrogen feed gas then pass through the third cold box and the nitrogen scrubbing tower for cooling and separation, resulting in low-temperature purified gas and fuel gas. The purified gas and fuel gas pass through the third, second, and first cold boxes for heat exchange and heating in stages. The purified gas then enters the nitrogen mixing device to mix with the nitrogen from the air separation section, and the hydrogen-nitrogen ratio is adjusted to 3:1 to form the reaction gas.
[0041] It is understood that when the ammonia synthesis is preferably carried out using the aforementioned liquid nitrogen washing cryogenic coupling ammonia synthesis system, the nitrogen feedstock entering the nitrogen feedstock inlet is conventional in the art, such as nitrogen feedstock from the air separation unit, and the nitrogen content in the nitrogen feedstock from the air separation unit is generally above 99.99%. The hydrogen feedstock entering the hydrogen feedstock inlet is also conventional in the art, such as hydrogen feedstock from the low-temperature stage A, and the main component of the hydrogen feedstock from the low-temperature stage A is hydrogen.
[0042] The positive and progressive effects of this invention are as follows:
[0043] This invention introduces the cooling energy from the liquid nitrogen washing section into the ammonia synthesis loop to cool the process gas from the ammonia synthesis unit, thereby reducing the ammonia content of the circulating gas separated from the top of the ammonia separator and increasing the net ammonia value.
[0044] Under the same raw material gas conditions, operating conditions, and ammonia synthesis capacity, the synthesis system of the present invention can reduce the circulating gas volume by 2% to 6%, thereby reducing the size of the equipment in the circulating loop of the ammonia synthesis module by the same amount; calculated by the power of the circulating machine, the energy consumption of the circulating loop can be reduced by 10% to 15%; calculated by the load of the water cooler, the cooling water consumption can be reduced by 6% to 12%. Attached Figure Description
[0045] Figure 1 is a schematic diagram of the liquid nitrogen washing cryogenic coupling ammonia synthesis system described in an embodiment of the present invention.
[0046] Figure 2 is a process gas flow path diagram in the ammonia synthesis system described in an embodiment of the present invention.
[0047] Explanation of reference numerals in the attached drawings: First cold box 1 Second cold box 2 Third cold box 3 Nitrogen washing tower 4 Compressor 5 Ammonia synthesis unit 6 First ammonia cooler 7 Second ammonia cooler 8 Cold gas heat exchanger 9 High-pressure ammonia separator 10 Insulation box 11 Circulation loop 12 Circulator 13 Process gas pipeline 14 First pipeline 15 Second pipeline 16 Nitrogen distribution unit 17. Detailed Implementation
[0048] The present invention will be further illustrated by way of embodiments below, but the present invention is not limited to the scope of the embodiments described herein.
[0049] Example 1
[0050] This embodiment discloses a liquid nitrogen washing cryogenic coupling ammonia synthesis system, which includes a liquid nitrogen washing module, an ammonia synthesis module, a first pipeline 15, and a second pipeline 16. The liquid nitrogen washing module includes a cold box, and the ammonia synthesis module includes an ammonia synthesis device 6 and a high-pressure ammonia separator 10. The first pipeline 15 connects the ammonia synthesis device 6 and the cold box, and is used to pass the process gas generated by the ammonia synthesis device 6 into the cold box for cooling. The second pipeline 16 connects the cold box and the high-pressure ammonia separator 10, and is used to pass the process gas cooled by the cold box into the high-pressure ammonia separator 10 for separation.
[0051] Specifically, the liquid nitrogen washing module in this embodiment includes three cold boxes and a nitrogen washing tower 4. The three cold boxes are connected in sequence and are designated as the first cold box 1, the second cold box 2, and the third cold box 3. All three cold boxes are plate-fin heat exchangers. The first cold box 1 is equipped with a process gas inlet, a process gas outlet, a nitrogen feed gas inlet, a nitrogen feed gas outlet, a purified gas inlet, a purified gas outlet, a fuel gas inlet, and a fuel gas outlet. The second cold box 2 is equipped with a nitrogen feed gas inlet, a nitrogen feed gas outlet, a hydrogen feed gas inlet, a hydrogen feed gas outlet, a purified gas inlet, a purified gas outlet, a fuel gas inlet, and a fuel gas outlet. The third cold box 3 is also equipped with a nitrogen feed gas inlet, a nitrogen feed gas outlet, a hydrogen feed gas inlet, a hydrogen feed gas outlet, a purified gas inlet, a purified gas outlet, a fuel gas inlet, and a fuel gas outlet. The third cold box 3 is also connected to the nitrogen washing tower 4. The purified gas and fuel gas exiting the nitrogen washing tower 4 pass through the three cold boxes in sequence, exchanging heat with the nitrogen feed gas entering the first cold box 1 and the hydrogen feed gas entering the second cold box 2.
[0052] Specifically, the ammonia synthesis module in this embodiment includes a compressor 5, a circulating machine 13, an ammonia synthesis unit 6, a second ammonia cooler 8, a cold gas heat exchanger 9, a high-pressure ammonia separator 10, and a water cooler. The compressor 5, the ammonia synthesis unit 6, the second ammonia cooler 8, and the high-pressure ammonia separator 10 are connected sequentially along the process gas flow direction. The compressor 5 is used to compress the reaction gas. The circulating machine 13 is connected after the compressor 5. The ammonia synthesis unit 6 is used to synthesize ammonia. A first ammonia cooler 7 is provided at the bottom of the ammonia synthesis unit 6. A circulation loop 12 is provided between the high-pressure ammonia separator 10 and the circulating machine 13. The circulation loop 12 is used to return the circulating gas in the high-pressure ammonia separator 10 to the compressor 5. A process gas pipeline 14 is provided between the first ammonia cooler 7 and the water cooler. Both the circulation loop 12 and the process gas pipeline 14 are connected to the cold gas heat exchanger 9, so that the circulating gas in the circulation loop 12 and the process gas in the process gas pipeline 14 exchange heat.
[0053] One end of the first pipeline 15 is connected to the process gas outlet of the second ammonia cooler 8, and the other end of the first pipeline 15 is connected to the process gas inlet of the first cold box 1. One end of the second pipeline 16 is connected to the process gas outlet of the first cold box 1, and the other end of the second pipeline 16 is connected to the process gas inlet of the high-pressure ammonia separator 10.
[0054] Furthermore, the liquid nitrogen washing cryogenic coupling ammonia synthesis system of this embodiment also includes a nitrogen distribution device 17, which is connected between the purified gas outlet of the first cold box 1 and the compressor 5, and is used to provide the ammonia synthesis module with a suitable reaction gas ratio. The nitrogen distribution device 17 is also connected to the air separation section for accessing the nitrogen gas of the air separation section.
[0055] Furthermore, the ammonia synthesis system of cryogenic coupling with liquid nitrogen washing in this embodiment also includes an insulation box 11. The liquid nitrogen washing module is set in the insulation box 11. The insulation box 11 is provided with a cold air inlet. The cold air inlet is used to supplement the cold energy into the insulation box 11 to reduce the cold loss of the liquid nitrogen washing module.
[0056] Example 2
[0057] This embodiment discloses an ammonia synthesis method using liquid nitrogen washing and cryogenic coupling. The ammonia synthesis system described in Example 1 is used for ammonia synthesis. This embodiment takes a synthetic ammonia capacity of 300,000 tons / year as an example. The specific method includes:
[0058] (1) The reaction gas is introduced into ammonia synthesis unit 6 to perform ammonia synthesis, and process gas is obtained; specifically, the following steps are included:
[0059] Nitrogen feed gas from the air separation section enters the first cold box 1 for heat exchange and then enters the second cold box 2. Hydrogen feed gas from the low-temperature section (mainly hydrogen, with small amounts of CO, CH4, Ar, etc.) enters the second cold box 2. The nitrogen and hydrogen feed gas then pass through the third cold box 3 and the nitrogen scrubbing tower 4 for cooling and separation, resulting in low-temperature purified gas (H2 and N2, as well as a small amount of argon) and fuel gas (CO, CH4, etc.). The purified gas and fuel gas pass through the third cold box 3, the second cold box 2, and the first cold box 1 for heat exchange and heating in stages. The purified gas then enters the nitrogen distribution device 17, where it mixes with the nitrogen from the air separation section and the hydrogen-nitrogen ratio is adjusted to 3:1 to form a reaction gas.
[0060] The resulting reaction gas enters compressor 5, and after compression, the gas pressure reaches 14 MPa. It then enters ammonia synthesis unit 6 for reaction, yielding process gas.
[0061] (2) The process gas is introduced into the cold box through the first pipeline 15 to cool the process gas, specifically including the following steps:
[0062] The process gas is cooled to about 30°C after passing through the cold gas heat exchanger 9 and the circulating gas from the high-pressure ammonia separator 10. It then enters the first ammonia cooler 7 and is cooled to about 15°C. After entering the second ammonia cooler 8, it is cooled to about -5°C. Finally, it enters the first cold box 1 and is cooled to -20 to -10°C after exchanging heat with the low-temperature purified gas and fuel gas.
[0063] (3) The cooled process gas enters the high-pressure ammonia separator 10 through the second pipeline 16 for separation, and the separated gas is returned to the compressor 5 as circulating gas.
[0064] The ammonia synthesis results of this embodiment are shown in Table 1.
[0065] Comparative Example 1
[0066] The difference between this comparative example and Example 1 is that the first pipeline 15 and the second pipeline 16 are not provided, and the second ammonia cooler 8 is directly connected to the high-pressure ammonia separator 10. The rest of the system structure, process flow and parameters are the same as those in Examples 1 and 2.
[0067] Taking a synthetic ammonia production capacity of 300,000 tons / year as an example, the results of this comparative study are shown in Table 1.
[0068] Table 1
[0069] In the table above, the inlet ammonia concentration and the outlet ammonia concentration refer to the ammonia concentration at the inlet and outlet of the ammonia synthesis unit, respectively.
[0070] As can be seen, in Example 1, the ammonia content of the circulating gas separated from the top of the ammonia separator is reduced, the net ammonia value is increased, and the circulating gas volume, compressor and circulating machine power are all reduced, thus reducing energy consumption.
[0071] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and various changes or modifications can be made to these embodiments without departing from the principles and essence of the present invention. Therefore, the scope of protection of the present invention is defined by the appended claims.
Claims
1. A system for synthesizing cryogenically bound ammonia with liquid nitrogen flushing, the system comprising: a liquid nitrogen flushing module, an ammonia synthesis module, a first pipeline and a second pipeline; the liquid nitrogen flushing module comprises a cold container, and the ammonia synthesis module comprises an apparatus for synthesizing ammonia and an ammonia separator; The first pipeline connects the ammonia synthesis apparatus to the cold container and serves to introduce the process gas obtained in the ammonia synthesis apparatus into the cold container for cooling; the second pipeline connects the cold container and the ammonia separator and serves to introduce the process gas cooled in the cold container into the ammonia separator for separation.
2. A system for synthesizing cryogenically bound ammonia with liquid nitrogen flushing according to claim 1, characterized in that the cold container is a cold container into which gaseous nitrogen feedstock is supplied from the air separation section.
3. A system for synthesizing cryogenically bound ammonia with liquid nitrogen flushing according to any one of claims 1 and 2, characterized in that the liquid nitrogen flushing module contains at least two cold containers and one nitrogen flushing tower, wherein the at least two cold containers are connected in series as a first cold container and a last cold container, wherein the first cold container is connected between the ammonia synthesis apparatus and the ammonia separator via a first pipeline and a second pipeline, wherein the first cold container is a cold container into which gaseous nitrogen feedstock is supplied from the air separation section, and the last cold container is connected to the nitrogen flushing tower.
4. A system for the synthesis of cryogenically bound ammonia with liquid nitrogen flushing according to any one of claims 1 to 3, characterized in that the liquid nitrogen flushing module comprises three cold containers and one nitrogen flushing tower, wherein the three cold containers are connected in series as a first cold container, a second cold container and a third cold container, each of the cold containers is provided with an inlet for purified gas, an outlet for purified gas, an inlet for fuel gas and an outlet for fuel gas, wherein the first cold container is further provided with an inlet for gaseous nitrogen feedstock, an outlet for gaseous nitrogen feedstock, an inlet for process gas and an outlet for process gas, and both the second cold container and the third cold container are provided with an inlet for gaseous hydrogen feedstock, an outlet for gaseous hydrogen feedstock, an inlet for gaseous nitrogen feedstock and an outlet for gaseous nitrogen feedstock;the second ammonia cooler is connected downstream of the ammonia synthesis apparatus, wherein one end of the first pipeline is connected to the process gas outlet of the second ammonia cooler, and the other end of the first pipeline is connected to the process gas inlet of the first cold container, one end of the second pipeline is connected to the process gas outlet of the first cold container, and the other end of the second pipeline is connected to the process gas inlet of the ammonia separator; the third cold container is additionally connected to a nitrogen flushing tower.
5. A system for synthesizing cryogenically bound ammonia with liquid nitrogen flushing according to any one of paragraphs 1-4, characterized in that the system for synthesizing cryogenically bound ammonia with liquid nitrogen flushing satisfies one or more of the following conditions: 1) cold containers are plate-fin heat exchangers; and 2) the cryogenically bound ammonia synthesis system with liquid nitrogen flushing further comprises an insulating container, wherein the liquid nitrogen flushing module is completely located inside the insulating container, the insulating container is provided with a cold gas inlet, and the cooling energy is supplied through the cold gas inlet to the insulating chamber to reduce cold losses in the liquid nitrogen flushing module.
6. A system for synthesizing cryogenically bound ammonia with liquid nitrogen flushing according to any one of paragraphs 1-5, characterized in that the system for synthesizing cryogenically bound ammonia with liquid nitrogen flushing satisfies one or more of the following conditions: 1) the ammonia synthesis module further comprises a compression apparatus, a circulation apparatus, a first ammonia cooler, a second ammonia cooler and a circulation circuit; the compression apparatus and the circulation apparatus are connected in series upstream of the ammonia synthesis apparatus; the circulation circuit connects the ammonia separator to the circulation apparatus, and the circulation circuit is used to return circulating gas from the ammonia separator to the circulation apparatus; the first ammonia cooler is located in the ammonia synthesis apparatus, the second ammonia cooler is connected downstream of the ammonia synthesis apparatus, one end of the first pipeline is connected to the second ammonia cooler, and the other end of the first pipeline is connected to a cold container; in addition, the ammonia synthesis module further comprises a cold gas heat exchanger and a water cooler, between the first ammonia cooler and the water cooler a process gas pipeline is located, and both the circulation loop and the process gas pipeline pass through the cold gas heat exchanger, which ensures heat exchange between the circulation gas in the circulation loop and the process gas in the process gas pipeline; and 2) the cryogenically bound ammonia synthesis system with liquid nitrogen flushing further includes a nitrogen mixing module, the nitrogen mixing module is connected between the liquid nitrogen flushing module and the ammonia synthesis module, and the nitrogen mixing module is used to supply reaction gas to the ammonia synthesis module; In addition, the nitrogen inlet of the nitrogen mixing module is used to receive nitrogen from the air separation section.
7. A method for synthesizing cryogenically bound ammonia with washing with liquid nitrogen, the method comprising the following steps: introducing a reaction gas into an ammonia synthesis apparatus for synthesizing ammonia, thereby obtaining a process gas; introducing the process gas into the cold container of the washing section with liquid nitrogen to cool the process gas, wherein the process gas is subjected to heat exchange to a temperature in the range of from -77.7°C to the ambient temperature, and, in addition, the process gas is subjected to heat exchange to a temperature in the range of from -70°C to -10°C; and the cooled process gas is fed into the ammonia separator for separation, the liquid ammonia is collected, and the separated gas is returned as cycle gas to the ammonia synthesis apparatus.
8. A method for synthesizing cryogenically bound ammonia with washing with liquid nitrogen according to paragraph 7, characterized in that the process gas is subjected to heat exchange to a temperature in the range from -20°C to -10°C.
9. A method for synthesizing cryogenically bound ammonia with washing with liquid nitrogen according to any one of paragraphs. 7, 8, characterized in that in the liquid nitrogen washing section, purified gas and / or fuel gas passing through a cold container is used to cool the process gas, and the temperature of the purified gas and / or fuel gas, which exchanges heat with the process gas, is in the range from -65°C to -50°C.
10. A method for synthesizing cryogenically bound ammonia with washing with liquid nitrogen according to any of paragraphs 7-9, characterized in that the ammonia synthesis is performed using a system for synthesizing cryogenically bound ammonia with washing with liquid nitrogen according to any of paragraphs 1-6; In addition, the method for cryogenic synthesis of ammonia with washing with liquid nitrogen preferably includes the following steps: introducing the reaction gas into the ammonia synthesis apparatus to synthesize ammonia, thereby obtaining process gas; introducing process gas into the cold container through a first pipeline to cool the process gas; and the cooled process gas is fed into the ammonia separator through a second pipeline for separation and the separated gas is returned to the ammonia synthesis apparatus; and furthermore, when the cryogenically bound ammonia synthesis system with liquid nitrogen flushing is additionally equipped with a liquid nitrogen flushing module according to paragraph 4, the method for producing the reaction gas includes the following steps: sequentially feeding the gaseous nitrogen feedstock from the air separation section into the first cold container for heat exchange and then feeding it into the second cold container, feeding the gaseous hydrogen feedstock from the low methanization section into the second cold container, then sequentially passing the gaseous nitrogen feedstock and the gaseous hydrogen feedstock through the third cold container and the nitrogen washing tower for cooling and separating to obtain a low-temperature purified gas and a fuel gas, sequentially passing the purified gas and the fuel gas through the third cold container, the second cold container and the first cold container for stepwise heat exchange and increasing the temperature, feeding the purified gas into a nitrogen mixing apparatus for mixing with nitrogen from the air separation section and adjusting the ratio of hydrogen and nitrogen to 3:1 to form a reaction gas; and furthermore, when the cryogenically bound ammonia synthesis system with liquid nitrogen flushing is further equipped with a cold gas heat exchanger according to paragraph 6, the temperature of the process gas is reduced by means of the cold gas heat exchanger to 40°C - -5°C, preferably reduced to 30°C; when the cryogenically bound ammonia synthesis system with liquid nitrogen flushing is further equipped with a first ammonia cooler according to claim 6, the temperature of the process gas is reduced by the first ammonia cooler to 30°C-8°C, preferably reduced to 15°C; and when the cryogenically bound ammonia synthesis system with liquid nitrogen flushing is additionally equipped with a second ammonia cooler according to item 6, the temperature of the process gas is reduced by means of the second ammonia cooler to 15°C - -12°C, preferably reduced to -5°C.