Treatment method for reducing gas emptying during driving of liquid nitrogen washing device

Abstract

The invention discloses a treatment method for reducing gas emptying during driving of a liquid nitrogen washing device. The treatment method comprises the steps that a medium-pressure liquid nitrogen pump in an air separation backup system is started, liquid nitrogen in a liquid nitrogen storage tank is pressurized to 1.5 MPa, and the liquid nitrogen is conveyed to a hydrogen separation tank through a pipeline which is made of 06Cr9Ni 10 and has the specification of DN50 * 8mm so as to supplement system cooling capacity. Through a series of operations of starting a medium-pressure liquid nitrogen pump to convey liquid nitrogen to supplement cold energy, accurately regulating and controlling related parameters of a nitrogen washing tower, controlling the temperature and pressure of each link, reasonably adjusting the opening degree of a valve and the like, CO at a liquid nitrogen washing outlet quickly reaches the standard, the starting time is remarkably shortened, the gas emptying amount is reduced, the production efficiency is improved, and the production cost is reduced. The ammonia synthesis device can produce liquid ammonia in advance, the production cost is reduced, and meanwhile pollution to the environment is relieved.

Description

Technical Field

[0001] The present invention relates to the technical field of coal-based synthetic ammonia, and in particular to a method for reducing gas venting during the start-up of a liquid nitrogen washing device. Background Art

[0002] The coal-to-ammonia project's liquid nitrogen scrubbing unit primarily removes trace impurities such as carbon dioxide, carbon monoxide, argon, and methane from the feed gas from the low-temperature methanol scrubbing process, providing synthesis gas with a hydrogen-nitrogen ratio of 3:1 for the ammonia synthesis process. The feed gas from the low-temperature methanol scrubbing process first enters a molecular sieve adsorber to remove trace methanol and carbon dioxide, preventing them from freezing in the cold box and potentially clogging cryogenic equipment and pipelines. Two adsorbers, each equipped with molecular sieves, operate in a 24-hour cycle, while the other is regenerated. Switching is automated by a program controller.

[0003] Currently, the startup of a liquid nitrogen scrubbing unit requires seven hours of process adjustments to reduce CO2 emissions to within target levels. During this time, approximately 60,000 m³ / h of hydrogen and 20,000 m³ / h of medium-pressure nitrogen are forced to be flared, increasing production costs and polluting the environment. To address this issue, a more efficient liquid nitrogen scrubbing unit solution was proposed to shorten startup time and reduce gas venting. Summary of the Invention

[0004] Aiming at the problems of long process adjustment time and large gas venting volume during the start-up of existing liquid nitrogen washing devices, which lead to increased production costs and environmental pollution, the present invention provides a treatment method for reducing gas venting during the start-up of liquid nitrogen washing devices, which has the advantages of shortening the start-up time, reducing production costs, and reducing environmental pollution.

[0005] The technical solution of the present invention is:

[0006] Regarding the method of reducing gas venting during the start-up of the liquid nitrogen washing device, the medium-pressure liquid nitrogen pump in the air separation backup system is started, and the liquid nitrogen in the liquid nitrogen storage tank is pressurized to 1.5MPa. It is transported to the hydrogen separation tank through a 06Cr9Ni10 material and DN50*8mm pipe to supplement the system cooling capacity. The nitrogen washing amount of the nitrogen washing tower is adjusted according to the amount of hydrogen entering the tower. The liquid nitrogen added to the hydrogen separation tank is used as the fuel gas amount, and the nitrogen washing amount temperature is controlled to be ≦-187℃. Liquid nitrogen is added to the liquid nitrogen tank, and the temperature of the raw gas entering the nitrogen washing tower is adjusted to be ≦-184℃. The hydrogen temperature at the outlet of the nitrogen washing tower is controlled between -192℃ and -196℃, so that the CO at the outlet of the liquid nitrogen washing can reach the indicator range within 1 hour. The liquid nitrogen pump is pre-cooled during startup, and 4.0Mpa nitrogen is used to purify the liquid nitrogen washing device. Set up each device for cooling treatment, control the cooling rate ≤ 15℃, wait until the temperature of the low-temperature synthesis gas pipeline drops to -188℃, and when the liquid level of the hydrogen separation tank and nitrogen tower is ≥ 75%, perform the liquid accumulation end operation, start the liquid nitrogen pump, adjust the reflux valve opening to control the outlet pressure at 1.3-1.5MPa, and pressurize the system. After the system pressure reaches 3.0MPa, open the synthesis gas delivery valve, accurately adjust the opening of multiple valves, control the raw gas flow rate and pressure, as well as the nitrogen washing volume of the nitrogen washing tower, fuel gas flow rate, recovered hydrogen flow rate, low-temperature raw gas pipeline temperature and other parameters to ensure The temperature of the raw gas entering the nitrogen washing tower is ≥-183℃, and the temperature of the medium-pressure nitrogen entering the nitrogen washing tower is ≥-185℃. In the initial stage of startup, when the cooling capacity of the nitrogen washing tower does not match the raw gas volume, resulting in a drop in the liquid level of the nitrogen washing tower and the hydrogen separation tank, open the liquid nitrogen pump outlet valve and the hydrogen separation tank nitrogen supply valve, adjust the nitrogen supply valve opening, control the hydrogen separation tank liquid level within 40%-85%, maintain the fuel gas flow and the recovered hydrogen flow, and ensure that the temperature of the relevant cooler is within the normal index range. When the CO at the outlet of the liquid nitrogen washing device is qualified, open the synthesis gas nitrogen supply valve and adjust the opening to control the hydrogen content of the synthesis gas at 7 4-75%, and notify the downstream ammonia synthesis unit to connect gas. As the hydrogen separation tank replenishes liquid nitrogen cooling capacity, the nitrogen washing tower liquid level rises. When the nitrogen washing tower liquid level is ≥60%, adjust the opening of the washing nitrogen discharge valve to discharge the excess washing nitrogen into the hydrogen separation tank; when the hydrogen separation tank liquid level is ≥60%, gradually adjust the opening of the hydrogen separation tank nitrogen replenishment valve until it is closed. The temperature of the raw gas entering the nitrogen washing tower is controlled by adjusting the opening of the liquid nitrogen tank nitrogen replenishment valve, and the temperature of the medium-pressure nitrogen entering the nitrogen washing tower is controlled by adjusting the washing nitrogen pressure reducing valve. During the molecular sieve switching process, the above temperatures are controlled at the lower limit of the index in advance.

[0007] The working principle of the above technical solution is as follows:

[0008] During startup of the liquid nitrogen scrubbing unit, insufficient system cooling capacity is a key factor leading to prolonged gas venting and process adjustments. By starting the medium-pressure liquid nitrogen pump to deliver liquid nitrogen to the hydrogen separation tank, the system cooling capacity can be quickly replenished, allowing the system to reach cooling equilibrium more quickly. Adjusting the nitrogen scrubbing volume of the nitrogen scrubbing tower based on the amount of hydrogen entering the tower and controlling the temperature parameters can more accurately achieve gas separation and purification, allowing the CO at the liquid nitrogen scrubbing outlet to quickly reach the target range, reducing the long process adjustments and gas venting required due to substandard CO. Pre-cooling the liquid nitrogen pump, using 4.0 MPa nitrogen to cool accumulated liquid, and controlling the system pressure, valve opening, and parameters are all aimed at ensuring smooth startup of the unit and avoiding cooling capacity loss and gas venting due to improper operation. Dynamic adjustment of the liquid level and temperature during startup is a real-time optimization of operations based on the unit's operating status, ensuring that the unit is always in an efficient and stable operating state.

[0009] In a further technical solution, a medium-pressure liquid nitrogen pump pressurizes the liquid nitrogen to 1.5MPa and transports it to the hydrogen separation tank through pipes of specific materials and specifications. This design ensures the stability and efficiency of liquid nitrogen transportation. The pipes of specific materials can adapt to low-temperature environments and reduce cooling loss, thus solving the technical problems of leakage and large cooling loss that may occur during liquid nitrogen transportation in the existing technology.

[0010] In a further technical solution, when adjusting the nitrogen washing amount of the nitrogen washing tower, the liquid nitrogen added to the hydrogen separation tank is used as the fuel gas, and the temperature of the nitrogen washing amount is controlled to be ≤-187°C. This rationally utilizes the added liquid nitrogen, which not only ensures the supply of fuel gas, but also improves the gas separation effect through precise temperature control, solving the technical problems of unstable fuel gas supply and poor gas separation effect in the prior art.

[0011] In a further technical solution, liquid nitrogen is added to the liquid nitrogen tank, the temperature of the raw gas entering the nitrogen scrubber is adjusted to ≤-184°C, and the temperature of the hydrogen at the outlet of the nitrogen scrubber is controlled between -192°C and -196°C. Through precise temperature control, the device operates under more suitable temperature conditions, thereby improving the CO removal efficiency and solving the technical problem in the prior art of substandard CO removal due to improper temperature control and the need for large amounts of venting gas for adjustment.

[0012] In a further technical solution, the liquid nitrogen pump is pre-cooled during startup, and 4.0Mpa nitrogen is used to cool the device and the cooling rate is controlled to be ≤15°C. Pre-cooling the liquid nitrogen pump can avoid damage to the pump due to sudden temperature changes. The reasonable cooling rate ensures the safety and stability of the equipment, and solves the technical problems in the prior art that equipment is damaged due to excessively rapid cooling or failure to pre-cool the pump, which affects the startup progress.

[0013] In a further technical solution, when liquid accumulation occurs, the liquid accumulation is stopped when the liquid levels in the hydrogen separation tank and the nitrogen tower are ≥ 75%, the liquid nitrogen pump is started and the outlet pressure is controlled at 1.3-1.5MPa. The clear liquid accumulation end conditions and pressure control range ensure the stability and reliability of subsequent operations, and solve the technical problems of unstable operation of the device caused by irregular liquid accumulation operation and inaccurate pressure control in the existing technology.

[0014] In a further technical solution, the synthesis gas delivery valve is opened after the system is pressurized to 3.0MPa, and the openings of multiple valves are precisely adjusted to control various parameters, ensuring that the synthesis gas can be smoothly delivered. At the same time, through precise parameter control, the device can quickly reach a stable operating state during the start-up process, solving the technical problems in the existing technology caused by improper system pressure control and inaccurate valve adjustment, resulting in poor synthesis gas delivery and large fluctuations in device operation.

[0015] In a further technical solution, relevant valves are opened to supplement cooling capacity at the initial stage of startup, and the liquid level in the hydrogen separation tank is controlled within 40%-85%. The cooling capacity is supplemented in time and the liquid level is stabilized, thereby maintaining the fuel gas flow rate and the recovered hydrogen flow rate, ensuring the normal temperature of the cooler, and solving the technical problems of insufficient cooling capacity and large liquid level fluctuations in the initial stage of startup and abnormal operation of the device.

[0016] In a further technical solution, when the CO at the outlet of the liquid nitrogen scrubbing device meets the requirements, the synthesis gas nitrogen replenishment valve is opened to control the hydrogen content of the synthesis gas to 74-75%. This ensures that the quality of the synthesis gas meets the requirements of the downstream ammonia synthesis unit, avoids subsequent production problems and gas venting caused by substandard synthesis gas quality, and solves the technical problem of poor synthesis gas quality control in the prior art.

[0017] In a further technical solution, the valve opening is adjusted according to the changes in the liquid levels of the nitrogen scrubber and the hydrogen separation tank, and the lower temperature limit is controlled in advance when the molecular sieve is switched, thereby achieving dynamic optimization of the operating status of the device, avoiding gas venting and device performance degradation caused by changes in liquid level and temperature, and solving the technical problems of untimely response to the operating status of the device and inflexible adjustment in the existing technology.

[0018] The beneficial effects of the present invention are:

[0019] 1. In order to solve the problems of long start-up time, large gas venting volume, high production cost and serious environmental pollution in the liquid nitrogen washing device in the prior art, the present application sets a series of operations such as starting a medium-pressure liquid nitrogen pump to deliver liquid nitrogen to supplement cooling capacity, accurately controlling the relevant parameters of the nitrogen washing tower, controlling the temperature and pressure of each link, and reasonably adjusting the valve opening. The liquid nitrogen washing outlet CO is quickly brought to the standard, the start-up time is significantly shortened, and the gas venting volume is reduced. This not only improves production efficiency and enables the ammonia synthesis unit to produce liquid ammonia in advance, but also reduces production costs and alleviates environmental pollution.

[0020] 2. In order to solve the problems existing in the prior art in liquid nitrogen transportation, fuel gas supply, gas separation and synthesis gas quality control, the present application adopts measures such as setting up pipelines of specific materials and specifications to transport liquid nitrogen, using the supplementary liquid nitrogen as the fuel gas volume and controlling the temperature, accurately controlling the temperature of the hydrogen entering the nitrogen scrubber and at the outlet, and controlling the hydrogen content of the synthesis gas after the CO is qualified. The above measures achieve stable and efficient liquid nitrogen transportation, stable fuel gas supply, improved gas separation effect and synthesis gas quality that meets the requirements of downstream equipment, and solve the problems of liquid nitrogen leakage, large cooling capacity loss, unstable fuel gas supply, poor gas separation and difficult synthesis gas quality control.

[0021] 3. By setting up pre-cooling of the liquid nitrogen pump during startup, controlling the cooling rate, clarifying the conditions for the end of liquid accumulation, adjusting the valve opening according to the liquid level change, and controlling the lower temperature limit in advance when switching the molecular sieve, it is possible to avoid damage to the equipment due to sudden temperature changes, ensure stable operation of the equipment, stable and reliable subsequent operations, and dynamically optimize the operating status of the device. This solves the problems in the existing technology such as equipment damage due to excessively rapid cooling, irregular liquid accumulation operations, improper liquid level and temperature control, unstable device operation, untimely response to operating status, and inflexible adjustment, which are caused by the excessively rapid cooling, irregular liquid accumulation operations, and improper liquid level and temperature control. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the overall process of an embodiment of the present invention.

[0023] Description of reference numerals:

[0024] 1. Liquid nitrogen wash feed gas inlet valve; 2. Molecular sieve A inlet valve; 3. Molecular sieve A; 4. Molecular sieve A outlet valve; 5. Molecular sieve B outlet valve; 6. Molecular sieve B; 7. Molecular sieve B inlet valve; 8. Feed gas inlet valve to cold box; 9. Low-pressure nitrogen outlet valve; 10. 4.0 MPa nitrogen pipeline; 11. 4.0 MPa nitrogen inlet valve to cold box; 12. Fuel gas outlet valve; 13. Recovered hydrogen outlet valve; 14. High-pressure nitrogen cooler; 15. 1# feed gas cooler; 16. 2# feed gas cooler; 17. Cryogenic nitrogen pipeline; 18. Liquid nitrogen tank; 19. Liquid nitrogen tank nitrogen replenishment valve; 20. Liquid nitrogen tank nitrogen replenishment pipeline; 21. Liquid nitrogen storage tank; 22. Liquid nitrogen pump reflux pipeline; 23. Liquid nitrogen pump reflux valve; 24. Liquid nitrogen pump inlet valve; 25. Liquid nitrogen pump; 26. Liquid nitrogen pump outlet valve; 27. Cryogenic hydrogen recovery pipeline; 28. Cryogenic fuel gas pipeline; 29. ​​Synthesis gas nitrogen supply valve; 30. Synthesis gas outlet valve for liquid nitrogen washing unit; 31. Cryogenic synthesis gas pipeline; 32. Liquid nitrogen regulating valve for nitrogen washing tower; 33. Cryogenic feed gas pipeline; 34. Nitrogen washing tower; 35. Washing nitrogen discharge valve; 36. Hydrogen separator; 37. Nitrogen supply valve for hydrogen separator; 38. Washing nitrogen pressure reducing valve; 39. Cryogenic hydrogen recovery pressure reducing valve; 40. Hydrogen separator nitrogen supply pipeline. DETAILED DESCRIPTION

[0025] The embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0026] Example:

[0027] like Figure 1As shown, the method for reducing gas venting during the start-up of the liquid nitrogen washing device includes a comprehensive inspection and confirmation of the equipment before start-up, such as the medium-pressure liquid nitrogen pump 1, liquid nitrogen storage tank 2, hydrogen separation tank 3, nitrogen washing tower 4, liquid nitrogen tank 6, etc., to ensure that the equipment is not damaged, there is no leakage, and all connection parts are firm; check the connection of the pipeline 5 to ensure its good sealing; debug the valve to ensure that the switch is flexible and the opening control is accurate; check the instrument system to ensure accurate measurement and sensitive control. At the same time, ensure that the liquid nitrogen storage tank 2 and the liquid nitrogen tank 6 have sufficient liquid nitrogen reserves, and use nitrogen to replace the system to exhaust air. When starting, open the reflux valve 9 of the liquid nitrogen pump 1 for pre-cooling, and use 4.0Mpa nitrogen to enter the nitrogen tower 8 through the cooling equipment. Adjust the valve to control the cooling rate of each equipment to ≤15℃. When the temperature of the low-temperature synthesis gas pipeline 7 drops to -188℃, the nitrogen tower 8 is filled with liquid, and the liquid level is ≥75%, start the liquid nitrogen pump 1, and adjust the opening of the reflux valve 9 to make the outlet pressure between 1.3- 1.5MPa, open the relevant valves to pressurize the system to 3.0MPa, then open the synthesis gas delivery valve 10, accurately adjust the multi-valve control raw gas flow, pressure and other parameters to ensure that the raw gas and medium-pressure nitrogen enter the nitrogen washing tower 4 at the standard temperature. In the early stage of startup, when the liquid level drops due to the mismatch between the cooling capacity and the raw gas volume, open the liquid nitrogen pump 1 outlet valve 12 and the hydrogen separation tank 3 nitrogen supply valve 13 to supply cooling capacity, control the hydrogen separation tank 3 liquid level at 40%-85%, maintain the fuel gas and recovery When the hydrogen flow rate and the temperature of the cooler 14 are normal and the outlet CO is qualified, the synthesis gas nitrogen supply valve 15 is opened to control the hydrogen content of the synthesis gas at 74-75% and notify the downstream gas connection. As the liquid level changes, when the liquid level of the nitrogen washing tower 4 is ≥60%, the washing nitrogen discharge valve 17 is adjusted, and the liquid level of the hydrogen separation tank 3 is ≥60%, the nitrogen supply valve 13 is gradually closed. The inlet tower temperature is controlled by adjusting the nitrogen supply valve 18 of the liquid nitrogen tank 6 and the washing nitrogen pressure reducing valve 19. The lower temperature limit is controlled in advance when the molecular sieve 20 is switched.

[0028] In another embodiment, the equipment can be inspected before start-up using more advanced non-destructive testing technologies, such as ultrasonic testing and magnetic particle testing, to inspect the key components of the medium-pressure liquid nitrogen pump 1 and the welds of the pipeline 5 to ensure that there are no potential defects inside the equipment, thereby further improving the safety and reliability of equipment operation. At the same time, during the liquid nitrogen storage and system replacement process, real-time monitoring of the liquid nitrogen purity and nitrogen gas purity can be added to ensure that the quality of the medium entering the system meets the requirements.

[0029] In another embodiment, the pre-cooling process of the liquid nitrogen pump 1 can adopt a segmented pre-cooling method, first performing preliminary pre-cooling with a lower liquid nitrogen flow rate, and then gradually increasing the liquid nitrogen flow rate to a normal pre-cooling flow rate after the pump body temperature drops to a certain level. This can avoid the pump body from generating large thermal stress due to excessive pre-cooling speed, thereby extending the service life of the pump. During the equipment cooling process, different cooling rates can be set according to the material and structural characteristics of different equipment to achieve more precise temperature control.

[0030] In another embodiment, during liquid accumulation operation, an automatic liquid level control system can be used to automatically adjust the amount of liquid nitrogen replenished according to the changes in the liquid levels of the hydrogen separation tank 3 and the nitrogen tower 8, ensuring that the liquid level is stable at around 75%, thereby reducing errors and labor intensity in manual operation. At the same time, after starting the liquid nitrogen pump 1, an intelligent control system can be introduced to automatically adjust the opening of the reflux valve 9 according to changes in system pressure and flow, so that the outlet pressure is more stable.

[0031] In another embodiment, when controlling the temperature of the raw gas and medium-pressure nitrogen entering the nitrogen scrubbing tower 4, advanced temperature sensors and intelligent adjustment algorithms can be used to monitor temperature changes in real time and quickly adjust the openings of the nitrogen replenishment valve 18 of the liquid nitrogen tank 6 and the scrubbing nitrogen pressure reducing valve 19. At the same time, a temperature prediction model can be established to predict temperature change trends based on historical data and current operating conditions, so that adjustments can be made in advance to improve the accuracy and timeliness of temperature control.

[0032] In another embodiment, when the liquid level drops during the initial start-up, in addition to opening the relevant valves to replenish the cooling capacity, the liquid level changes in the nitrogen scrubber 4 and the hydrogen separation tank 3 can be analyzed in real time to determine whether the cause of the liquid level drop is insufficient cooling capacity or other factors. If insufficient cooling capacity is the cause, the liquid nitrogen replenishment method can be further optimized, such as adopting a multi-point replenishment method to make the cooling capacity distribution more uniform. At the same time, a liquid level early warning system can be established to issue an alarm in time when the liquid level approaches the lower limit or upper limit, reminding the operator to take action.

[0033] In another embodiment, when the CO at the outlet of the liquid nitrogen scrubbing device is qualified, an online gas analyzer can be used to monitor the composition changes of the synthesis gas in real time when controlling the hydrogen content of the synthesis gas. The opening of the synthesis gas nitrogen replenishment valve 15 can be automatically adjusted based on the analysis results. At the same time, a data sharing and linkage control system can be established with the downstream ammonia synthesis device 16 to adjust the quality and flow of the synthesis gas in real time according to the needs of the downstream device, thereby improving the coordination and efficiency of the entire production system.

[0034] In another embodiment, when adjusting the valve opening as the liquid level changes, an intelligent valve actuator can be used to achieve precise control and rapid response of the valve opening. At the same time, a valve status monitoring system can be established to monitor parameters such as the valve switch status, opening size, and operating time in real time, so as to promptly detect valve failures and perform repairs to ensure stable operation of the device.

[0035] In another embodiment, during the switching process of the molecular sieve 20, in addition to controlling the lower limit of the tower inlet temperature in advance, the switching time and sequence of the molecular sieve 20 can also be optimized. By establishing a performance evaluation model for the molecular sieve 20, the switching time and sequence can be reasonably arranged according to the adsorption capacity and regeneration status of the molecular sieve 20, thereby reducing the impact of the switching process on the operation of the device and improving the stability and reliability of the device.

[0036] In another embodiment, the entire startup process can use a digital monitoring and management system to monitor and record the operating parameters, valve status, temperature, pressure, liquid level, etc. of the equipment in real time. Through big data analysis and artificial intelligence algorithms, the operating status of the device can be evaluated and predicted, potential problems can be discovered in advance, and corresponding measures can be taken to deal with them, thereby realizing intelligent operation and management of the device.

[0037] The working principle of the above technical solution is as follows: through comprehensive pre-start preparation, ensure that the equipment is in good condition and the medium quality meets the requirements, laying the foundation for the stable start-up of the device. The pre-cooling of the liquid nitrogen pump 1 and the equipment cooling process are to make the equipment adapt to the low temperature environment and avoid equipment damage due to rapid temperature changes. The liquid accumulation operation is to store enough cold capacity to ensure the stability of subsequent operation. During the start-up process, the system's cold capacity balance, pressure balance and gas separation effects are achieved by precisely controlling various parameters and valve openings. The dynamic adjustment of liquid level and temperature is optimized in real time according to the actual operating status of the device to ensure that the device is always in an efficient and stable operating state. The application of advanced detection technology, intelligent control system and digital management system can improve the degree of automation, control accuracy and reliability of the device, reduce errors and labor intensity of manual operation, and promptly discover and deal with potential problems, thereby achieving the purpose of reducing gas venting during the start-up of the liquid nitrogen washing device.

[0038] The above-described embodiments merely represent specific implementations of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, and all such variations and improvements fall within the scope of protection of the present invention.

Claims

1. Regarding the method for reducing gas venting during the start-up of the liquid nitrogen washing device, it is characterized by: The method includes starting a medium-pressure liquid nitrogen pump (1) in an air separation backup system, pressurizing the liquid nitrogen in a liquid nitrogen storage tank (2) and then transporting it to a hydrogen separation tank (3) to supplement the system's cooling capacity, adjusting the nitrogen washing amount of a nitrogen washing tower (4) according to the amount of hydrogen entering the tower, and controlling relevant temperature parameters so that the CO at the liquid nitrogen washing outlet quickly reaches a target range.

2. The method for reducing gas venting during the start-up of a liquid nitrogen washing device according to claim 1 is characterized in that: The medium-pressure liquid nitrogen pump (1) pressurizes the liquid nitrogen to 1.5 MPa and transports it to the hydrogen separation tank (3) through the pipeline (5). The pipeline (5) is made of 06Cr9Ni 10 material and has a specification of DN50*8mm.

3. The method for reducing gas venting during the start-up of a liquid nitrogen washing device according to claim 1 is characterized in that: When adjusting the nitrogen washing amount of the nitrogen washing tower (4), the liquid nitrogen added to the hydrogen separation tank (3) is used as the fuel gas amount, and the nitrogen washing amount temperature is controlled to be ≤-187°C.

4. The method for reducing gas venting during the start-up of a liquid nitrogen washing device according to claim 1 is characterized in that: Liquid nitrogen is added to the liquid nitrogen tank (6), the temperature of the raw gas entering the nitrogen washing tower (4) is adjusted to ≤-184°C, and the temperature of the hydrogen gas at the outlet of the nitrogen washing tower (4) is controlled between -192°C and -196°C.

5. The method for reducing gas venting during the start-up of a liquid nitrogen washing device according to claim 1 is characterized in that: When starting up, the liquid nitrogen pump (1) is pre-cooled, and 4.0 MPa nitrogen is used to cool down the equipment of the liquid nitrogen washing device, and the cooling rate is controlled to be ≤15°C. After the temperature of the low-temperature synthesis gas pipeline (7) drops to -188°C, the liquid accumulation operation is performed.

6. The method for reducing gas venting during the start-up of a liquid nitrogen washing device according to claim 5 is characterized in that: During liquid accumulation, when the liquid levels of the hydrogen separation tank (3) and the nitrogen tower (8) are greater than or equal to 75%, the liquid accumulation ends, the liquid nitrogen pump (1) is started, and the opening of the reflux valve (9) is adjusted to control the outlet pressure at 1.3-1.5 MPa.

7. The method for reducing gas venting during the start-up of a liquid nitrogen washing device according to claim 1 is characterized in that: The system is pressurized, and after the system pressure reaches 3.0 MPa, the synthesis gas delivery valve (10) is opened. By accurately adjusting the openings of multiple valves, the flow rate and pressure of the raw gas, as well as the nitrogen washing amount of the nitrogen washing tower (4), the fuel gas flow rate, the recovered hydrogen flow rate, the temperature of the low-temperature raw gas pipeline (11) and other parameters are controlled to ensure that the temperature of the raw gas entering the nitrogen washing tower (4) is ≥-183°C and the temperature of the medium-pressure nitrogen entering the nitrogen washing tower (4) is ≥-185°C.

8. The method for reducing gas venting during the start-up of a liquid nitrogen washing device according to claim 1 is characterized in that: At the initial start-up, when the liquid levels of the nitrogen washing tower (4) and the hydrogen separation tank (3) drop due to the mismatch between the cooling capacity of the nitrogen washing tower (4) and the raw gas volume, the outlet valve (12) of the liquid nitrogen pump (1) and the nitrogen supply valve (13) of the hydrogen separation tank (3) are opened, and the opening of the nitrogen supply valve (13) is adjusted to control the liquid level of the hydrogen separation tank (3) within 40%-85%, maintain the fuel gas flow rate and the recovered hydrogen flow rate, and ensure that the temperature of the relevant cooler (14) is within the normal index range.

9. The method for reducing gas venting during the start-up of a liquid nitrogen washing device according to claim 8 is characterized in that: When the CO at the outlet of the liquid nitrogen washing device is qualified, the synthesis gas nitrogen replenishment valve (15) is opened, the opening is adjusted to control the hydrogen content of the synthesis gas to 74-75%, and the downstream ammonia synthesis device (16) is notified to receive gas.

10. The method for reducing gas venting during the start-up of a liquid nitrogen washing device according to claim 1 is characterized in that: As the hydrogen separation tank (3) replenishes liquid nitrogen cooling capacity, the liquid level of the nitrogen washing tower (4) rises. When the liquid level of the nitrogen washing tower (4) is greater than or equal to 60%, the opening of the washing nitrogen discharge valve (17) is adjusted to discharge excess washing nitrogen into the hydrogen separation tank (3); when the liquid level of the hydrogen separation tank (3) is greater than or equal to 60%, the opening of the nitrogen replenishment valve (13) of the hydrogen separation tank (3) is gradually adjusted until it is closed; the temperature of the raw gas entering the nitrogen washing tower (4) is controlled by adjusting the opening of the nitrogen replenishment valve (18) of the liquid nitrogen tank (6), and the temperature of the medium-pressure nitrogen entering the nitrogen washing tower (4) is controlled by adjusting the washing nitrogen pressure reducing valve (19). During the switching process of the molecular sieve (20), the above temperature is controlled at the lower limit of the index in advance.

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