Deep refrigeration type ammonia synthesis process

Abstract

The invention belongs to the technical field of cryogenic continuous circulating rectification of ammonia gas, and mainly relates to a deep refrigeration type ammonia synthesis process, which comprises the following steps: after pressure increase, a small part of raw material gas enters an annular space of an inner cylinder and an outer cylinder of a synthesis tower, and the rest part is subjected to heat exchange, and then enters the synthesis tower for reaction; synthesis gas is obtained; the synthesis gas exchanges heat to reduce the temperature of the synthesis gas, and the synthesis gas participates in the heat exchange process of the rest part of the raw material gas in the heat exchange process; the synthesis gas subjected to heat exchange enters a combined deep freezer to be condensed into a deep cooling product; ammonia separation is conducted on the cryogenic product to obtain liquid ammonia, and other separated gas enters the combined type cryogenic device again. The temperature of the synthesis gas after the synthesis ammonia reaction is higher, and the raw material gas before the reaction is preheated by utilizing the waste heat of the synthesis gas through multiple times of heat exchange, so that the raw material gas reaches a proper reaction temperature, the energy consumption is reduced, and the energy utilization rate of the whole system is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of cryogenic continuous circulation rectification ammonia technology, and mainly relates to a deep refrigeration type ammonia synthesis process. Background Art

[0002] Ammonia is one of the important inorganic chemical products and occupies an important position in the national economy. In addition to liquid ammonia being directly used as fertilizer, nitrogen fertilizers used in agriculture, such as urea, ammonium nitrate, ammonium phosphate, ammonium chloride, and various nitrogen-containing compound fertilizers, are all based on ammonia. Ammonia synthesis is one of the bulk chemical products, and the world's annual ammonia synthesis output has reached more than 100 million tons. Among them, about 80% of ammonia is used to produce chemical fertilizers, and 20% is used as raw materials for other chemical products.

[0003] In the process of ammonia synthesis, because the ammonia synthesis equation is a reversible equation, a large amount of raw material gas does not fully participate in the reaction and is released. If these raw material gases are treated by direct emission or combustion, it will not only cause environmental pollution, but also pose a threat to human health.

[0004] Based on the above problems, the patent application document with publication number CN118623552A discloses a cryogenic separation system and method for recovering ammonia synthesis purge gas. However, this cryogenic separation system treats various gases by separate recovery, and does not achieve the recycling of these gases, resulting in waste of energy for recovery. At the same time, the equipment for storing these gases will occupy a large amount of space and affect the operation of other work. Summary of the Invention

[0005] The present invention provides a deep refrigeration type ammonia synthesis process to solve the problem that the gas that does not fully participate in the ammonia synthesis reaction in the prior art cannot be recycled.

[0006] To solve the above problems, the present invention adopts the following technical solutions: A deep refrigeration type ammonia synthesis process includes the following steps: Step 1: After the raw material gas is pressurized, a small part of it enters the annular gap between the inner and outer cylinders of the synthesis tower to adjust the temperature of the synthesis tower wall, and the remaining part is heat-exchanged to increase its temperature. Then, the remaining part enters the synthesis tower for reaction to obtain synthesis gas; Step 2: The synthesis gas is heat-exchanged to reduce its temperature. During the heat-exchange process of the synthesis gas, it participates in the heat-exchange process of the remaining part of the raw material gas in Step 1; Step 3: The heat-exchanged synthesis gas enters the combined cryogenic cooler for condensation to reduce the temperature, so that most of the synthesis gas condenses into cryogenic products, and the uncondensed remaining synthesis gas is used as raw material gas to re-perform Step 1; Step 4: The cryogenic product is subjected to ammonia separation to obtain liquid ammonia, and the other gases separated are re-introduced into the combined cryogenic cooler.

[0007] It has the following beneficial effects: The combined cryogenic cooler is used for ammonia synthesis refrigeration, with a lower refrigeration temperature and better ammonia condensation effect; At the same time, the gases that have not fully participated in the ammonia synthesis reaction are discharged from the combined cryogenic cooler, re-pressurized and then participate in the reaction again; The ammonia synthesis reaction is carried out under high temperature and high pressure conditions. The temperature of the syngas after the reaction is relatively high. Through multiple heat exchanges, the waste heat of the syngas is used to preheat the raw material gas before the reaction, so that the raw material gas entering the synthesis tower reaches the appropriate reaction temperature. This not only reduces energy consumption, recycles the raw material gas, but also improves the energy utilization rate of the entire system.

[0008] Further, in Step 2, the syngas undergoes multiple heat exchanges and gradually reduces its temperature.

[0009] It has the following beneficial effects: Before condensing the liquid ammonia, by exchanging heat with other low-temperature media, the temperature of the ammonia gas can be gradually reduced, enabling full utilization of energy and avoiding waste of energy.

[0010] Further, in Step 2, the syngas first exchanges heat in the waste heat boiler, then exchanges heat in the feed water preheater, then exchanges heat with the remaining part in Step 1 in the heat exchanger, and finally exchanges heat in the water cooler and then enters the combined cryogenic cooler.

[0011] It has the following beneficial effects: The condensation of ammonia gas in the combined cryogenic cooler requires reducing its temperature to a certain extent. Since the syngas after the ammonia synthesis reaction contains not only ammonia gas but also nitrogen and hydrogen, the presence of these gases will affect the condensation of ammonia gas. Through multiple heat exchanges, the temperature and pressure can be more precisely controlled, gradually reducing the temperature of the ammonia gas below its dew point temperature, enabling it to be fully condensed into liquid ammonia. Moreover, multiple heat exchanges can make the cooling process more stable, avoid damage to the equipment caused by sharp temperature changes, and at the same time is conducive to improving the purity of the liquid ammonia.

[0012] Further, desalted water is introduced into the feed water preheater to exchange heat with the syngas to reduce the temperature of the syngas; After that, the heated desalted water enters the waste heat boiler to exchange heat with the syngas to further increase the temperature of the desalted water; Circulating water is used in the water cooler to exchange heat with the syngas.

[0013] It has the following beneficial effects: desalted water is water that has been treated to remove scaling ions such as calcium and magnesium. In the heat exchange process of synthetic ammonia, if ordinary water containing more scaling ions is used, as the temperature changes and the salt concentration in the water increases, these ions will easily form scale in the waste boiler and feed water preheater. The thermal conductivity of scale is very poor, which will reduce the heat transfer efficiency in the waste boiler and feed water preheater, increase energy consumption, and even affect the normal operation of the waste boiler and feed water preheater. Desalted water, which contains almost no scaling ions, can effectively avoid the formation of scale, thereby ensuring good heat transfer performance and long-term stable operation of the waste boiler and feed water preheater.

[0014] Furthermore, the cryogenic product enters an ammonia separator to separate the liquid ammonia, and the remaining cryogenic product re-enters the combined cryogenic freezer.

[0015] The method has the following beneficial effects: the gases from which liquid ammonia is not separated are ammonia, hydrogen, and nitrogen, which also contain ammonia. By recycling these gases back into the combined cryogenic refrigerator, the raw gas can be fully utilized, the conversion rate of the raw gas can be improved, and emissions to the environment can be reduced.

[0016] Furthermore, the liquid ammonia enters the heater to be heated, and the heated liquid ammonia enters the storage tank.

[0017] Furthermore, in step 1, the temperature of a small portion of the raw gas entering the annular gap between the inner and outer cylinders of the synthesis tower is 50°C; The temperature of the remaining raw gas entering the synthesis tower is 160°C.

[0018] It has the following beneficial effects: a small portion of the raw gas enters the annular gap between the inner and outer cylinders of the synthesis tower, forming a gas insulation layer between the inner and outer cylinders, which plays a role in cooling and protecting the outer cylinder, keeping the temperature of the outer cylinder within a reasonable range and avoiding it from being affected by excessively high temperatures.

[0019] Furthermore, the temperature of the synthesis gas coming out of the synthesis tower is 430°C. After heat exchange in the waste boiler, the temperature of the synthesis gas drops to 230°C. After heat exchange in the feed water preheater, the temperature of the synthesis gas drops to 170°C.

[0020] Furthermore, the temperature of the synthesis gas entering the heat exchanger is reduced from 170°C to 80°C, and the temperature of the remaining raw gas entering the synthesis tower is increased from 50°C to 160°C.

[0021] Furthermore, after heat exchange in a water cooler, the temperature of the synthesis gas drops from 80°C to 35°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] By reading the following detailed description with reference to the accompanying drawings, the above and other objects, features, and advantages of the exemplary embodiments of the present invention will become readily understandable. In the drawings, several embodiments of the present invention are shown in an exemplary rather than restrictive manner, and the same or corresponding reference numerals represent the same or corresponding parts, where: Figure 1 is a flowchart of the present invention; Figure 2 is a schematic diagram of a combined cryogenic cooler.

[0023] Description of reference numerals: 1, syngas unit; 2, synthesis tower; 3, waste heat boiler; 4, feed water preheater; 5, heat exchanger; 6, water cooler; 7, combined cryogenic cooler; 8, ammonia separator; 9, product ammonia heater; 10, raw material gas; 11, syngas; 12, demineralized water; 13, circulating water; 14, cryogenic product; 15, liquid nitrogen; 16, liquid carbon dioxide; 17, gaseous carbon dioxide; 18, fresh gas; 19, recycle gas. Detailed embodiments

[0024] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Those skilled in the art should know that the embodiments described below are part of the embodiments of the present disclosure, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative efforts fall within the protection scope of the present invention.

[0025] The following specifically introduces various non-restrictive embodiments of the present invention. The number of any element in the drawings is for illustration rather than limitation, and any naming is only for distinction without any restrictive meaning. It should be noted that, without conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0026] As Figure 1 , Figure 2 shown, a deep refrigeration type synthetic ammonia process uses a syngas unit 1, a synthesis tower 2, a waste heat boiler 3, a feed water preheater 4, a heat exchanger 5, a water cooler 6, a combined cryogenic cooler 7, an ammonia separator 8, and a product ammonia heater 9. Among them, the syngas unit 1 is mainly used to compress the raw material gas 10 to make it reach the required pressure. The synthesis tower 2 is used for the synthetic ammonia reaction to generate syngas 11, which contains ammonia, hydrogen, and nitrogen. The waste heat boiler 3, the feed water preheater 4, the heat exchanger 5, and the water cooler 6 are all heat exchangers used to reduce the temperature of the syngas 11. The combined cryogenic cooler 7 is used to reduce the temperature of the syngas 11, so that the ammonia in the syngas 11 condenses into liquid ammonia. The ammonia separator 8 is used to separate the liquid ammonia. The product ammonia heater 9 is used to increase the temperature of the liquid ammonia.

[0027] The raw material gas 10 is discharged after being pressurized by the syngas unit 1. The temperature of the discharged raw material gas 10 is about 50°C. A small part of the raw material gas 10 directly enters the annulus between the inner and outer cylinders of the synthesis tower 2 to adjust the temperature of the tower wall of the synthesis tower 2. The remaining part of the raw material gas 10 enters the heat exchanger 5 for heat exchange to raise the temperature to about 160°C, and then enters the synthesis tower 2 for reaction to obtain syngas 11. At this time, the temperature of the syngas 11 is about 430°C.

[0028] In this embodiment, the raw material gas 10 contains nitrogen, hydrogen, and nitrogen. Most of the hydrogen and nitrogen are fresh gas 18, and nitrogen, a small part of hydrogen and nitrogen are recycled gas 19 provided by the combined cryogenic cooler 7.

[0029] During the ammonia synthesis process, allowing a small part of the raw material gas 10 to enter the annulus between the inner and outer cylinders of the synthesis tower 2 mainly has the following functions: 1. Protect the outer cylinder: The ammonia reaction in the synthesis tower 2 is carried out under high temperature and high pressure conditions, and the temperature of the catalyst bed layer in the tower is relatively high. Without appropriate cooling measures, the outer cylinder of the synthesis tower 2 will generate large thermal stresses due to uneven heating. Being in this state for a long time will affect the material properties and service life of the outer cylinder, and may even cause damage to the outer cylinder. Allowing a small part of the raw material gas 10 to enter the annulus between the inner and outer cylinders can form a gas insulation layer between the inner and outer cylinders, playing a role in cooling and protecting the outer cylinder, keeping the temperature of the outer cylinder within a reasonable range, and avoiding its being affected by excessive temperature.

[0030] 2. Control the temperature distribution: By adjusting the gas flow rate entering the annulus, the temperature distribution in the synthesis tower 2 can be controlled. The gas entering the annulus can absorb a part of the heat transferred from the inner cylinder, preventing local overheating of the inner cylinder and making the temperature of the catalyst bed layer more uniform and stable. This helps to optimize the ammonia synthesis reaction, improve the activity and service life of the catalyst, because the catalyst can only exert the best catalytic effect within an appropriate temperature range, and too high or too low temperature will affect the reaction rate and conversion rate.

[0031] 3. Recover heat: After the raw material gas 10 entering the annulus absorbs heat, its temperature will rise. This part of the hot gas can be recycled, thereby improving the energy utilization rate of the entire ammonia synthesis system and reducing energy consumption.

[0032] After the syngas 11 is synthesized, it is first heat-exchanged in the waste heat boiler 3 and then in the feed water preheater 4 to reduce the temperature of the syngas 11. The waste heat boiler 3 and the feed water preheater 4 simultaneously use the demineralized water 12 for heat-exchanging the syngas 11. The demineralized water 12 is first discharged into the feed water preheater 4. The temperature of the demineralized water 12 before entering the feed water preheater 4 is 100 °C, and it is about 180 °C after heat-exchange. Then it enters the waste heat boiler 3. After heat-exchanging in the waste heat boiler 3, the temperature becomes 220 °C. At the same time, after the syngas 11 is successively heat-exchanged by the waste heat boiler 3 and the feed water preheater 4, the temperature of the syngas 11 successively changes from 430 °C to 230 °C and 170 °C.

[0033] In this embodiment, the waste heat boiler 3 refers to a waste heat boiler, which is a boiler device applied in industrial production. It is mainly used to recover the waste heat generated in the industrial production process and convert it into useful energy such as steam or hot water. The recovered waste heat can be used to preheat other process media, drive steam turbines, etc., improving the efficiency of the production process and the energy utilization rate. And by recovering the waste heat, the thermal pollution caused by the direct discharge of waste heat into the environment is reduced. At the same time, the emissions of greenhouse gases and other pollutants are also reduced, which is beneficial to environmental protection.

[0034] In this embodiment, the waste heat boiler 3 can be one of a shell-and-tube waste heat boiler, a flue-type waste heat boiler or a double-tube waste heat boiler.

[0035] In this embodiment, using the demineralized water 12 for heat-exchange has the following functions: 1. Prevent scaling: The demineralized water 12 is water that has been treated to remove scaling ions such as calcium and magnesium. In the heat-exchange process of synthetic ammonia, if ordinary water containing more scaling ions is used, with the change of temperature and the increase of the salt concentration in the water, these ions are prone to form scale in the waste heat boiler 3 and the feed water preheater 4. The thermal conductivity of scale is very poor, which will reduce the heat transfer efficiency of the waste heat boiler 3 and the feed water preheater 4, increase energy consumption, and even affect the normal operation of the waste heat boiler 3 and the feed water preheater 4. However, since the demineralized water 12 contains almost no scaling ions, it can effectively avoid the formation of scale and ensure the good heat transfer performance and long-term stable operation of the waste heat boiler 3 and the feed water preheater 4.

[0036] 2. Avoid corrosion: Ordinary water may contain corrosive substances such as dissolved oxygen and carbon dioxide, as well as some metal ions. When they come into contact with the waste heat boiler 3 and the feed water preheater 4, corrosion reactions are likely to occur. Corrosion will cause damage to the waste heat boiler 3 and the feed water preheater 4, shorten their service life, increase maintenance costs, and even may lead to safety accidents. The demineralized water 12 has been treated by desalination and deoxygenation, etc., greatly reducing the content of corrosive substances in the water, and can significantly reduce the corrosion of the waste heat boiler 3 and the feed water preheater 4, improving the safety and reliability of the waste heat boiler 3 and the feed water preheater 4.

[0037] 3. Adapt to high-temperature and high-pressure environments: The ammonia synthesis process is carried out under high-temperature and high-pressure conditions. The demineralized water 12 has good thermal stability and chemical stability, and can maintain stable performance under such harsh conditions, without decomposition, deterioration or other adverse reactions due to high temperature and high pressure. Thus, it can reliably undertake the heat exchange task and provide stable temperature conditions for the ammonia synthesis reaction.

[0038] The syngas 11 after heat exchange in the feed water preheater 4 then enters the heat exchanger 5, where it exchanges heat with the remaining part of the above-mentioned raw material gas 10 to reduce the temperature of the syngas 11 from about 170 °C to about 80 °C. The ammonia synthesis reaction is carried out under high-temperature and high-pressure conditions, and the temperature of the syngas 11 after the reaction is relatively high. Through multiple heat exchanges, the waste heat of the syngas 11 after the reaction is used to preheat the raw material gas 10 before the reaction, so that the raw material gas 10 entering the synthesis tower 2 reaches an appropriate reaction temperature. This not only reduces energy consumption but also improves the energy utilization rate of the entire system.

[0039] The syngas 11 after heat exchange in the heat exchanger 5 exchanges heat in the water cooler 6, where the circulating water 13 is used to exchange heat with the syngas 11 to reduce the temperature of the syngas 11 from 80 °C to 35 °C, and the temperature of the circulating water 13 rises from 28 °C to 40 °C. The syngas 11 after heat exchange in the water cooler 6 then enters the combined cryogenic cooler 7.

[0040] The syngas 11 entering the combined cryogenic cooler 7 for condensation has been cooled down through multiple heat exchanges. The ammonia synthesis reaction is carried out under high-temperature and high-pressure conditions, and the temperature of the syngas 11 after the reaction is relatively high. Before condensing the ammonia gas, through multiple heat exchanges and by exchanging heat with other low-temperature media, the temperature of the ammonia gas can be gradually reduced, enabling full utilization of energy and avoiding waste of energy. The condensation of ammonia gas requires reducing its temperature to a certain extent. Since the syngas 11 after the ammonia synthesis reaction contains not only ammonia gas but also nitrogen and hydrogen, the presence of these gases will affect the condensation of ammonia gas. Through multiple heat exchanges, the temperature and pressure can be more precisely controlled, gradually reducing the temperature of the ammonia gas below its dew point temperature to enable it to fully condense into liquid ammonia. Moreover, multiple heat exchanges can make the cooling process more stable, avoid damage to the equipment caused by rapid temperature changes, and also contribute to improving the purity of the liquid ammonia. Through multiple heat exchanges, the heat exchange parameters can be flexibly adjusted to ensure the stable operation of the entire ammonia synthesis system.

[0041] In the combined cryogenic cooler 7, liquid carbon dioxide 16 is used to exchange heat with the syngas 11 to cool and condense it. After heat exchange, the liquid carbon dioxide 16 becomes gaseous carbon dioxide 17. The syngas 11 is condensed, and most of the syngas 11 is condensed to obtain the cryogenic product 14. The uncondensed remaining syngas 11 re-enters the syngas unit 1 as the feed gas 10, can be repressurized and then participate in the ammonia synthesis reaction again, thus realizing recycling.

[0042] In this embodiment, the cryogenic product 14 contains liquid nitrogen 15, nitrogen, hydrogen and nitrogen.

[0043] In this embodiment, the uncondensed remaining syngas 11 contains ammonia, hydrogen and nitrogen.

[0044] The uncondensed remaining syngas 11 can be used as the raw material for the ammonia synthesis reaction. Recycling these uncondensed remaining syngas 11 back to the synthesis tower 2 can realize the full utilization of the feed gas 10, improve the conversion rate of the feed gas 10, and at the same time reduce the emissions to the environment.

[0045] The uncondensed remaining syngas 11 re-enters the syngas unit 1 as the feed gas 10, which can effectively regulate and balance the feed gas 10 and energy in the ammonia synthesis system, ensuring the stable operation of the ammonia synthesis system. Even if there are some fluctuations in the synthesis reaction process, it can buffer and adjust it to a certain extent, so that the whole system will not be affected too much, improving the anti-interference ability and reliability of the system.

[0046] In this embodiment, the combined cryogenic cooler 7 has the following advantages: 1. High-efficiency cooling: The combined cryogenic cooler 7 adopts a combination of multiple cooling technologies or multiple cooling stages, which can achieve a more efficient cooling effect. It can gradually cool the syngas 11 in the ammonia synthesis process to a lower temperature, which is beneficial to the condensation and separation of ammonia and improves the ammonia recovery rate.

[0047] 2. Precise temperature control: The cooling temperature can be precisely controlled by precisely adjusting the parameters of different cooling stages.

[0048] 3. Energy-saving effect: The combined cryogenic cooler 7 can flexibly adjust the cooling load and operating parameters according to different process requirements to achieve energy-saving operation. For example, when operating at partial load, the energy consumption can be reduced by shutting down or adjusting the operation of some cooling units. In addition, the high-efficiency cooling effect also helps to reduce the energy loss caused by insufficient cooling and improve the energy utilization efficiency of the entire ammonia synthesis system.

[0049] 4. Compact structural design: Integrating multiple cooling functions into a combined device reduces the floor area and space requirements of the device. This is highly beneficial for the layout and construction of ammonia synthesis plants, especially in cases where space is limited, as it can enhance the compactness and economy of the plant.

[0050] 5. High reliability and stability: With a combined design, even if a certain cooling unit fails, other units can still continue to operate, ensuring a certain degree of cooling effect and enhancing the reliability and stability of the entire system. At the same time, this design also facilitates the maintenance and repair of the equipment, reducing maintenance costs and downtime.

[0051] 6. Adapt to different process conditions: The ammonia synthesis process may vary due to factors such as raw materials, production scale, and product requirements. The combined cryogenic cooler 7 can be customized and configured according to specific process conditions to adapt to different production needs. It can flexibly adjust the cooling capacity, temperature range, and process flow to meet the special requirements of various ammonia synthesis plants.

[0052] The cryogenic product 14 is discharged to the ammonia separator 8. The ammonia separator 8 separates the liquid ammonia in the cryogenic product 14. After that, the liquid ammonia is discharged to the product ammonia heater 9, and the remaining cryogenic product 14 re-enters the combined cryogenic cooler 7 for condensation. The remaining cryogenic product 14 is ammonia gas, hydrogen gas, and nitrogen gas, and these gases still contain ammonia. Recycling these gases back to the combined cryogenic cooler 7 can achieve the full utilization of the raw material gas 10, improve the conversion rate of the raw material gas 10, and at the same time reduce emissions to the environment.

[0053] In this embodiment, the ammonia separator 8 utilizes the density difference between liquid ammonia and ammonia gas, hydrogen gas, and nitrogen gas. After the gas-liquid mixture flows into the ammonia separator 8, the liquid ammonia settles downward under the action of gravity, while the ammonia gas flows upward to achieve separation.

[0054] The product ammonia heater 9 heats the liquid ammonia to 20 °C, and then the heated liquid ammonia enters the storage tank.

[0055] The working process of the present invention is as follows: After the raw material gas 10 is pressurized by the syngas unit 1, a small part of it enters the annular space between the inner and outer cylinders of the synthesis tower 2 to adjust the temperature of the tower wall of the synthesis tower 2, and the remaining part is heat-exchanged through the heat exchanger 5 to increase its temperature. Then, this remaining part enters the synthesis tower 2 for reaction to obtain the syngas 11.

[0056] After that, the syngas 11 is cooled by heat exchange. During the heat exchange process of the syngas 11, it participates in the heat exchange process of the remaining part of the syngas 11 in the heat exchanger 5.

[0057] The syngas 11 after heat exchange enters the combined cryogenic cooler 7 for condensation to reduce the temperature, so that most of the syngas 11 is condensed into cryogenic products 14, and the uncondensed remaining syngas 11 re-enters the syngas unit 1 as raw material gas 10. After being pressurized, it re-enters the synthesis tower 2.

[0058] The cryogenic products 14 are subjected to ammonia separation to obtain liquid ammonia, and the remaining cryogenic products 14 re-enter the combined cryogenic cooler 7 for re-condensation.

Claims

1. A deep refrigeration type ammonia synthesis process, characterized in that, It includes the following steps: Step 1: After the raw material gas is pressurized, a small part of it enters the annular space between the inner and outer cylinders of the synthesis tower to adjust the temperature of the synthesis tower wall, and the remaining part exchanges heat to increase its temperature. Then, the remaining part enters the synthesis tower for reaction to obtain synthesis gas; Step 2: The synthesis gas exchanges heat to reduce its temperature. During the heat exchange process of the synthesis gas, it participates in the heat exchange process of the remaining part of the raw material gas in Step 1; Step 3: The heat-exchanged synthesis gas enters the combined cryogenic cooler for condensation to reduce the temperature, so that most of the synthesis gas condenses into cryogenic products, and the uncondensed remaining synthesis gas is used as raw material gas to re-perform Step 1; Step 4: The cryogenic products are subjected to ammonia separation to obtain liquid ammonia, and the separated other gases re-enter the combined cryogenic cooler.

2. The deep refrigeration type ammonia synthesis process according to claim 1, characterized in that, In Step 2, the synthesis gas exchanges heat multiple times to gradually reduce the temperature.

3. The deep refrigeration type ammonia synthesis process according to claim 2, characterized in that, In Step 2, the synthesis gas first exchanges heat in the waste heat boiler, then exchanges heat in the feed water preheater, then exchanges heat with the remaining part in Step 1 in the heat exchanger, and finally exchanges heat in the water cooler and then enters the combined cryogenic cooler.

4. The deep refrigeration type ammonia synthesis process according to claim 3, characterized in that, Desalted water is used to enter the feed water preheater to exchange heat with the synthesis gas to reduce the temperature of the synthesis gas; After that, the heated desalted water enters the waste heat boiler to exchange heat with the synthesis gas to further increase the temperature of the desalted water; Circulating water is used in the water cooler to exchange heat with the synthesis gas.

5. The deep refrigeration type ammonia synthesis process according to claim 4, characterized in that The cryogenic products enter the ammonia separator to separate the liquid ammonia, and the remaining cryogenic products re-enter the combined cryogenic cooler.

6. The deep refrigeration type ammonia synthesis process according to claim 5, characterized in that, The liquid ammonia enters the heater for heating, and the heated liquid ammonia enters the storage tank.

7. A deep refrigeration type ammonia synthesis process according to any one of claims 3-6, characterized in that, In Step 1, the temperature of a small part of the raw material gas entering the annular space between the inner and outer cylinders of the synthesis tower is 50°C; The temperature of the remaining part of the raw material gas entering the synthesis tower is 160°C.

8. A deep refrigeration type ammonia synthesis process according to claim 7, characterized in that, The temperature of the synthesis gas coming out of the synthesis tower is 430°C. After heat exchange in the waste heat boiler, the temperature of the synthesis gas drops to 230°C. After heat exchange in the feed water preheater, the temperature of the synthesis gas drops to 170°C.

9. The deep refrigeration type ammonia synthesis process according to claim 8, wherein, The temperature of the synthesis gas entering the heat exchanger drops from 170°C to 80°C, and the temperature of the remaining part of the raw material gas entering the synthesis tower rises from 50°C to 160°C.

10. A deep refrigeration type ammonia synthesis process according to claim 9, characterized in that, After heat exchange in the water cooler, the temperature of the synthesis gas drops from 80°C to 35°C.

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