Method for treating frozen blockage of air separation plate type heat exchanger and quickly recovering production of air separation plate type heat exchanger

Abstract

The invention belongs to the technical field of air separation equipment, and particularly discloses an air separation plate heat exchanger freezing and blocking treatment and rapid recovery method which comprises the steps that S1, whether a plate heat exchanger is frozen and blocked or not is judged according to the air side outlet temperature, the air side pressure and the air flow; s2, if the judgment result in the step S1 is freezing and blocking, freezing and blocking treatment of the plate heat exchanger is conducted remotely through a DCS control panel; s3, opening a liquid air blow-off valve and an air blow-off valve, blowing the pipeline by using a medium to check whether the dredging of the pipeline is qualified or not, if so, carrying out the step of recovering production, and if not, repeating the step S2; and S4, if the pipeline dredging detected in the S3 is qualified, starting to recover the operation process. According to the steps, water inlet and carbon dioxide freezing and blocking accidents of the plate heat exchanger of the air separation cold box can be treated in a short time, the production interruption time is effectively shortened, and the cost loss caused by production interruption is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of air separation equipment, and in particular to a method for processing freezing and blocking of an air separation plate heat exchanger and for rapidly resuming production. Background Art

[0002] During the operation of the air separation equipment, the cold box plate heat exchanger has a high heat exchange efficiency and can fully recover the cold in the reflux gas and transfer it to the forward flow air and other fluids that need to be cooled. This can greatly reduce the energy consumption of the air separation equipment and improve the economy of the entire system, playing a vital role in the oxygen production system.

[0003] However, due to various reasons, water ingress and carbon dioxide freezing accidents may occur in the plate heat exchanger, such as: water cooling tower leakage, molecular sieve adsorber failure, pipeline rupture or leakage, improper operating parameter settings, improper purification system switching operation, inadequate maintenance, etc. These water and carbon dioxide will freeze at the cold end of the plate heat exchanger, reducing the amount of positive air flow, resulting in the oxygen, nitrogen, and dirty nitrogen low-temperature gases in the cold box tower as reflux gas. Due to insufficient heat exchange, the outlet temperature of the tower is below zero, which will cause the outlet product gas delivery pipeline (stainless steel pipe for oxygen, carbon steel pipe for nitrogen and dirty nitrogen) to become low-temperature brittle and shrink, which will seriously affect the normal operation of the air separation equipment and the product gas delivery network, resulting in production interruption. Summary of the invention

[0004] The purpose of the present invention is to provide a method for treating freezing and blocking of an air separation plate heat exchanger and for quickly resuming production, so as to solve the problem that the outlet temperature is lower than zero degrees due to insufficient heat exchange, resulting in low-temperature brittleness and cold shrinkage deformation of the outlet product gas transmission pipeline, affecting the normal operation of the air separation equipment and the product gas transmission pipeline network, and causing production interruption.

[0005] In order to achieve the above-mentioned purpose, the basic scheme provided by the present invention is: a method for treating freezing and blocking of an air separation plate heat exchanger and quickly resuming production, comprising:

[0006] S1: Determine whether the plate heat exchanger is frozen or blocked based on the air side outlet temperature, air side pressure and air flow rate. The judgment criteria are as follows:

[0007] When the temperature of oxygen, nitrogen and dirty nitrogen out of the tower is 15℃-22℃, the air side pressure is 0.5Mpa, and the air flow rate is 65500m 3 / h, it is judged that the pipeline is operating normally.

[0008] When the temperature of oxygen, nitrogen and polluted nitrogen out of the tower is below 15℃, the air side pressure value is higher than 0.55Mpa, and the air flow rate is less than 60000m 3 / h, it is judged that the pipeline is frozen;

[0009] S2: If the result of S1 is freezing, the plate heat exchanger is remotely processed through the DCS control panel;

[0010] S3: Open the liquid air purge valve and the air purge valve, and use the medium to purge the pipeline to check whether the pipeline is unblocked. If it is qualified, resume production. If it is unqualified, repeat step S2;

[0011] S4: If the pipeline is found to be unblocked in S3, the operation process is resumed.

[0012] The working principle of the present invention is to detect the air side outlet temperature, air side pressure and air flow. If the temperature is between 15-22℃, the pressure value is 0.55Mpa and the flow rate is 65500m 3 , the pipeline is judged to be normal, otherwise it is judged that the pipeline is frozen; after judging that freezing occurs, the opening and closing of the process valve is remotely controlled through the DCS control panel, and the frozen part is treated by the medium in the pipeline, and the medium in the pipeline is air and liquid gas; after the treatment is completed, the pipeline is purged with air to check whether the pipeline is unblocked and qualified. If unqualified, it is reprocessed, and if qualified, the recovery process is carried out.

[0013] The beneficial effects of the present invention are that it can handle water ingress and carbon dioxide freezing blockage accidents in the air separation cold box plate heat exchanger in a relatively short period of time, reduce production interruption time, and effectively remove moisture and carbon dioxide by heating and blowing off the plate heat exchanger alone, thereby ensuring the normal operation of the air separation equipment and improving the reliability and stability of the equipment. Compared with the traditional treatment of water ingress or carbon dioxide accidents in the plate heat exchanger of the air separation system, this solution takes a shorter time, has a simple and fast operation method, and restores normal production conditions by 60 hours less than the previous treatment method.

[0014] Solution 2, which is the preferred basic solution, the freezing and blocking treatment in step S2 is as follows:

[0015] (1) Reduce the exhaust pressure of the air compressor from 0.5Mpa to 0.45Mpa. At the same time, completely close the oxygen control valve at a speed of 20° / min and completely close the nitrogen control valve at a speed of 20° / min;

[0016] (2) Stop the operation of the purification system electric heater power control cabinet and suspend the purification system operation program;

[0017] (3) Increase the valve opening of the liquid air throttle valve to 80% and adjust the flow rate to 5.5m 3 / h, the liquid air in the lower tower of the fractionation tower is pumped into the upper tower of the fractionation tower, and the liquid air level height of the lower tower of the fractionation tower is maintained between 90-110mm according to the detection of the differential pressure level gauge;

[0018] (4) Completely close the flow control valve into the distillation tower and other process valves at a speed of 20° / min. According to the pressure transmitter detection:

[0019] If the measured exhaust pressure of the air compressor is equal to 0.45Mpa, the flow control valve of the distillation tower and other process valves are set at 20

[0020] ° / min speed closing;

[0021] If the measured exhaust pressure of the air compressor is higher than 0.45Mpa, the flow control valve into the distillation tower and other process valves are adjusted to close at a speed of 15° / min;

[0022] (5) Adjust the opening of the air bypass regeneration gas valve to 40% so that the regeneration gas flow rate reaches 18500m 3 / h, and then start the purification system electric heater power control cabinet to activate and regenerate the purification molecular sieve system;

[0023] (6) Detect the gas moisture content and the cold blow peak value of molecular sieve regeneration according to the online instrument of the purification system:

[0024] If the online dew point meter after the molecular sieve analyzes the value ≤2ppm and the cold blowing peak value of the molecular sieve regeneration is ≥120℃, the molecular sieve has completed the analysis of moisture and carbon dioxide and can be put into operation. The air pipeline entering the tower is heated and purged.

[0025] If the online dew point meter analysis value after the molecular sieve is ≥2ppm and the cold blow peak value of the molecular sieve regeneration is ≤100℃, the molecular sieve cannot completely resolve moisture and carbon dioxide, and the number of purification system operation cycles needs to be increased until the analysis value meets the requirements and the tower inlet air pipeline is heated and purged.

[0026] Scheme 3, which is the preferred option of Scheme 2, is to purge the pipeline in (6) as follows:

[0027] a. After judging that the molecular sieve to be purified is qualified for activation and regeneration, fully open the flow control valve into the fractionation tower at a speed of 10° / min, drain the liquid air in the lower tower of the fractionation tower, and after the liquid air level is completely drained, adjust the valve opening of the liquid air purge valve and the valve opening of the air purge valve, and heat and purge the pipelines from the cooling tower → the plate heat exchanger → the lower tower of the fractionation tower in turn;

[0028] b. Determine whether the purge is qualified based on the air temperature:

[0029] If the air temperature entering the lower tower is 10°C or above, the heated purge is qualified;

[0030] If the air temperature entering the lower tower does not reach 10°C or above, the heating and purging is unqualified and it is necessary to return to S2 to check whether there is a problem in the freezing and blocking treatment step, make adjustments and repeat the heating and purging work.

[0031] Option 4 is the preferred option of Option 3. The adjustment method for the liquid air purge valve and the air purge valve in option a is as follows:

[0032] Increase the opening of the liquid air blow-off valve to 65% and control the flow rate to 4800m 3 / h,

[0033] Increase the air blow-off valve opening of the plate heat exchanger to 50% and control the flow rate to 4000m 3 / h;

[0034] Solution 5: This is the preferred basic solution. The steps for resuming production in S4 are as follows:

[0035] (1) The flow control valve into the distillation tower, the liquid air purge valve and the plate heat exchanger air purge valve are completely closed at a speed of 20° / min, the expansion air bypass dirty nitrogen valve is fully opened, and the valve opening of the dirty nitrogen to water cooling tower is adjusted to 35%. The air inlet pipeline flow rate is 12000m 3 / h;

[0036] (2) Start the expander to reduce the air pressure from 750Kpa to 55Kpa, and then enter the plate heat exchanger through the expanded air bypass nitrogen valve, and cool the temperature of the plate heat exchanger to -173°C;

[0037] (3) After the expander outlet temperature drops to -173°C, the flow control valve into the fractionation tower is fully opened at a speed of 15° / min according to the exhaust pressure of the air compressor, so that the positive flow air enters the lower tower of the fractionation tower after heat exchange through the plate heat exchanger;

[0038] (4) Adjust the opening of the liquid air purge valve to 35%, and then completely close the liquid air purge valve after liquid flows out;

[0039] (5) Adjust several valves:

[0040] Adjust the oxygen flow control valve opening to 36% and control the oxygen flow to 3800m 3 / h;

[0041] Adjust the opening of the nitrogen vent remote control valve to 40%, the nitrogen delivery regulating valve to the fully open position, and the nitrogen flow regulating control valve to 15% in sequence, and control the nitrogen flow rate out of the tower to 24000m 3 / h;

[0042] Adjust the dirty nitrogen gas inlet cooling tower from manual to automatic, and set the control pressure to 12.5Kpa;

[0043] (6) The valve of the expanded air bypass dirty nitrogen valve is completely closed to allow the expanded air to enter the upper tower of the fractionation tower to participate in distillation, and then the valve of the air bypass regeneration gas valve is completely closed to switch the purified regeneration gas to the dirty nitrogen gas out of the cold box. During this process, the electric heater equipment is turned off;

[0044] (7) The air separation system enters the purification stage.

[0045] Scheme 6, which is the preferred embodiment of Scheme 5, the purification steps in (7) are as follows:

[0046] a. When the upper tower resistance value of the fractionation tower is 3.5Kpa and the lower tower resistance value is 7.5Kpa, it means that the distillation working conditions of the upper and lower towers of the fractionation tower have been established. At this time, the liquid nitrogen reflux valve is fully opened, and the opening of the regulating liquid nitrogen throttle valve is adjusted to 44%, and the upper tower resistance value of the fractionation tower is controlled to reach 7Kpa and the lower tower resistance value of the fractionation tower is controlled to reach 15Kpa;

[0047] b. According to the detection of the analytical instrument, when the online oxygen purity analysis value reaches 85%, adjust the liquid nitrogen throttle valve to adjust the upper and lower tower pressures:

[0048] Control the pressure in the lower tower: adjust the valve opening of the liquid nitrogen throttle valve to 38% so that the flow rate of liquid nitrogen flowing into the upper tower of the fractionation tower is 28.6m 3 / h, the pressure of the lower tower of the distillation tower after being affected by liquid nitrogen is 454Kpa;

[0049] Stabilize the upper tower pressure: After the liquid nitrogen enters the upper tower of the fractionation tower, the pressure in the upper tower of the fractionation tower rises from 35Kpa to 40Kpa. The opening of the liquid nitrogen throttle valve is controlled at 42.5%, so that the upper tower pressure of the fractionation tower is maintained at 45Kpa, ensuring the stable operation of the air separation system;

[0050] c. When the liquid nitrogen throttle valve opening is 42%, the oxygen output is 13000m 3 , oxygen purity reaches 99.6%, nitrogen output is 2700m 3 , the purity of nitrogen reaches 99.9997%, and then the oxygen and nitrogen are switched from the venting pipeline to the oxygen output pipeline and the nitrogen output pipeline respectively;

[0051] d. Adjust the opening of the expansion air bypass nitrogen valve to 18% to control the expansion air bypass flow rate at 1730m 3 / h;

[0052] e. After the distillation tower is operating stably, put the automatic control instrument into operation and resume gas supply. DETAILED DESCRIPTION

[0053] The present invention is further described in detail below through specific embodiments:

[0054] Example

[0055] A method for treating freezing and blocking of an air separation plate heat exchanger and for quickly resuming production, comprising:

[0056] S1: Determine whether the plate heat exchanger is frozen or blocked based on the air side outlet temperature, air side pressure and air flow rate. The judgment criteria are as follows:

[0057] When the temperature of oxygen, nitrogen and dirty nitrogen out of the tower is 15℃-22℃, the air side pressure is 0.5Mpa, and the air flow rate is 65500m 3 / h, it is judged that the pipeline is operating normally;

[0058] When the temperature of oxygen, nitrogen and polluted nitrogen out of the tower is below 15℃, the air side pressure value is higher than 0.55Mpa, and the air flow rate is less than 60000m 3 / h, it is judged that the pipeline is frozen;

[0059] If the molecular sieve online dew point meter analysis value of the purification system is ≥5ppm and the cold blow peak value of the molecular sieve regeneration is ≤100℃, it can be judged that the moisture content of the molecular sieve adsorber exceeds the standard before the air passes through the molecular sieve and enters the plate heat exchanger during the adsorption cycle, causing the plate heat exchanger to freeze and block due to excessive air moisture content;

[0060] S2: If the result of S1 is freezing, the plate heat exchanger is remotely processed through the DCS control panel;

[0061] (1) Reduce the exhaust pressure of the air compressor from 0.5Mpa to 0.45Mpa. At the same time, completely close the oxygen control valve at a speed of 20° / min and completely close the nitrogen control valve at a speed of 20° / min;

[0062] (2) Stop the operation of the purification system electric heater power control cabinet and suspend the purification system operation program;

[0063] (3) Increase the valve opening of the liquid air throttle valve to 80% and adjust the flow rate to 5.5m 3 / h, the liquid air in the lower tower of the fractionation tower is pumped into the upper tower of the fractionation tower, and the liquid air level height of the lower tower of the fractionation tower is maintained between 90-110mm according to the detection of the differential pressure level gauge;

[0064] (4) Completely close the flow control valve into the distillation tower and other process valves at a speed of 20° / min. According to the pressure transmitter detection:

[0065] If the measured exhaust pressure of the air compressor is equal to 0.45Mpa, the flow control valve into the distillation tower and other process valves are closed at a speed of 20° / min;

[0066] If the measured exhaust pressure of the air compressor is higher than 0.45Mpa, the flow control valve into the distillation tower and other process valves are adjusted to close at a speed of 15° / min;

[0067] (5) Adjust the opening of the air bypass regeneration gas valve to 40% so that the regeneration gas flow rate reaches 18500m 3 / h, and then start the purification system electric heater power control cabinet to activate and regenerate the purification molecular sieve system;

[0068] (6) Detect the gas moisture content and the cold blow peak value of molecular sieve regeneration according to the online instrument of the purification system:

[0069] If the online dew point meter after the molecular sieve analyzes the value ≤2ppm and the cold blowing peak value of the molecular sieve regeneration is ≥120℃, the molecular sieve has completed the analysis of moisture and carbon dioxide and can be put into operation. The air pipeline entering the tower is heated and purged.

[0070] If the online dew point meter after the molecular sieve analyzes the value ≥ 2ppm and the cold blowing peak value of the molecular sieve regeneration is ≤ 100℃, the molecular sieve cannot completely analyze the water and carbon dioxide. It is necessary to increase the number of purification system operation cycles until the analysis value reaches the requirement and heat and purge the air pipeline entering the tower. The purge steps are as follows:

[0071] a. After judging that the molecular sieve to be purified is qualified for activation and regeneration, fully open the flow control valve into the fractionation tower at a speed of 10° / min, and drain the liquid air in the lower tower of the fractionation tower. After the liquid air level is completely drained, adjust the valve opening of the liquid air purge valve and the valve opening of the air purge valve, and heat and purge the flow from the cooling tower to the plate heat exchanger to the lower tower of the fractionation tower in turn;

[0072] b. Determine whether the purge is qualified based on the air temperature:

[0073] If the air entering the lower tower temperature rises slowly from -173°C to 10°C or above, the heating and purging is considered qualified;

[0074] If the air inlet temperature of the lower tower does not reach 10°C or above, it is judged that the heating and purging is unqualified, and it is necessary to return to S2 to check whether there is a problem in the freezing and blocking treatment step, and repeat the heating and purging work after adjustment;

[0075] S3: Open the liquid air purge valve and the air purge valve, and use the medium to purge the pipeline to check whether the pipeline is unblocked. If it is qualified, resume production. If it is unqualified, repeat step S2;

[0076] S4: If the pipeline is found to be unblocked in S3, the operation process will be resumed:

[0077] (1) The flow control valve into the distillation tower, the liquid air purge valve and the plate heat exchanger air purge valve are completely closed at a speed of 20° / min, the expansion air bypass dirty nitrogen valve is fully opened, and the valve opening of the dirty nitrogen to water cooling tower is adjusted to 35%. The air inlet pipeline flow rate is 12000m 3 / h;

[0078] (2) Start the expander to reduce the air pressure from 750Kpa to 55Kpa, and then enter the plate heat exchanger through the expanded air bypass nitrogen valve, and cool the temperature of the plate heat exchanger to -173°C;

[0079] (3) After the expander outlet temperature drops to -173°C, the flow control valve into the fractionation tower is fully opened at a speed of 15° / min according to the exhaust pressure of the air compressor, so that the positive flow air enters the lower tower of the fractionation tower after heat exchange through the plate heat exchanger;

[0080] (4) Adjust the opening of the liquid air purge valve to 35%, and then completely close the liquid air purge valve after liquid flows out;

[0081] (5) Adjust several valves:

[0082] Adjust the oxygen flow control valve opening to 36% and control the oxygen flow to 3800m 3 / h;

[0083] Adjust the nitrogen venting remote control valve opening to 40%, the nitrogen delivery regulating valve to fully open, and the nitrogen flow regulating control valve to 15% in sequence, and control the nitrogen flow rate out of the tower to 24000m 3 / h;

[0084] Adjust the dirty nitrogen gas inlet cooling tower valve from manual to automatic, and set the control pressure to 12.5Kpa;

[0085] (6) The valve of the expanded air bypass dirty nitrogen is completely closed to allow the expanded air to enter the upper tower to participate in distillation, and then the valve of the air bypass regeneration gas valve is completely closed to switch the purified regeneration gas to the dirty nitrogen gas out of the cold box. During this process, the electric heater equipment is turned off;

[0086] (7) The air separation system enters the purification stage:

[0087] a. When the resistance value of the upper tower of the fractionation tower is 3.5Kpa and the resistance value of the lower tower of the fractionation tower is 7.5Kpa, it means that the distillation working conditions of the upper and lower towers of the fractionation tower have been established. At this time, the liquid nitrogen reflux valve is fully opened, and the opening of the regulating liquid nitrogen throttle valve is adjusted to 44%, and the resistance value of the upper tower of the fractionation tower is controlled to reach 7Kpa and the resistance value of the lower tower of the fractionation tower is controlled to reach 15Kpa;

[0088] b. According to the detection of the analytical instrument, when the online oxygen purity analysis value reaches 85%, start to adjust the liquid nitrogen throttle valve to adjust the upper and lower tower pressures of the distillation tower:

[0089] Control the pressure in the lower tower: adjust the valve opening of the liquid nitrogen throttle valve to 38% so that the flow rate of liquid nitrogen flowing into the upper tower of the fractionation tower is 28.6m 3 / h, the pressure of the lower tower of the distillation tower after being affected by liquid nitrogen is 454Kpa;

[0090] Stabilize the upper tower pressure: After the liquid nitrogen enters the upper tower of the fractionation tower, the pressure in the upper tower of the fractionation tower rises from 35Kpa to 40Kpa. The opening of the liquid nitrogen throttle valve is controlled at 42.5%, so that the upper tower pressure of the fractionation tower is maintained at 45Kpa, ensuring the stable operation of the air separation system;

[0091] c. When the liquid nitrogen throttle valve opening is 42%, the oxygen output is 13000m 3 , oxygen purity reaches 99.6%, nitrogen output is 2700m 3 , the purity of nitrogen reaches 99.9997%, and then the oxygen and nitrogen are switched from the venting pipeline to the oxygen output pipeline and the nitrogen output pipeline respectively;

[0092] d. Adjust the opening of the expansion air bypass nitrogen valve to 18% to control the expansion air bypass flow rate at 1730m 3 / h;

[0093] e. After the distillation tower is operating stably, put the automatic control instrument into operation and resume gas supply.

[0094] The above is only an embodiment of the present invention, and the common knowledge such as the known specific structure and characteristics in the scheme is not described in detail here. It should be pointed out that for those skilled in the art, several deformations and improvements can be made without departing from the structure of the present invention, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A method for treating freezing and blocking of an air separation plate heat exchanger and for rapidly resuming production, characterized in that: The following steps are involved: S1: Determine whether the plate heat exchanger is frozen or blocked based on the air side outlet temperature, air side pressure and air flow rate. The judgment criteria are as follows: When the temperature of oxygen, nitrogen and dirty nitrogen out of the tower is between 15℃ and 22℃, the air side pressure is 0.5Mpa, and the air flow rate is 65500m 3 / h, it is judged that the pipeline is operating normally; When the temperature of oxygen, nitrogen and polluted nitrogen out of the tower is below 15℃, the air side pressure is higher than 0.55Mpa, and the air flow rate is less than 60000m 3 / h, it is judged that the pipeline is frozen; S2: If the result of S1 is freezing, the plate heat exchanger is remotely processed through the DCS control panel; S3: Open the liquid air purge valve and the air purge valve, and use the medium to purge the pipeline to check whether the pipeline is unblocked. If it is qualified, resume production. If it is unqualified, repeat step S2; S4: If the pipeline is found to be unblocked in S3, the operation process is resumed.

2. A method for treating freezing and blocking of an air separation plate heat exchanger and for rapid resumption of production according to claim 1, characterized in that: The freezing and blocking treatment method in step S2 is as follows: (1) Reduce the exhaust pressure of the air compressor from 0.5Mpa to 0.45Mpa. At the same time, completely close the oxygen control valve at a speed of 20° / min and completely close the nitrogen control valve at a speed of 20° / min; (2) Stop the operation of the purification system electric heater power control cabinet and suspend the purification system operation program; (3) Increase the valve opening of the liquid air throttle valve to 80% and adjust the liquid air flow rate to 5.5m 3 / h, the liquid air in the lower tower of the fractionation tower is pumped into the upper tower of the fractionation tower, and the liquid air level height of the lower tower is maintained between 90-110mm according to the detection of the differential pressure level gauge; (4) Completely close the flow control valve into the distillation tower and other process valves at a speed of 20° / min. According to the pressure transmitter detection: If the measured exhaust pressure of the air compressor is equal to 0.45Mpa, the flow control valve into the distillation tower and other process valves are closed at a speed of 20° / min; If the measured exhaust pressure of the air compressor is higher than 0.45Mpa, the flow control valve into the distillation tower and other process valves are adjusted to close at a speed of 15° / min; (5) Adjust the opening of the air bypass regeneration gas valve to 40% so that the regeneration gas flow rate reaches 18500m 3 / h, and then start the purification system electric heater power control cabinet to activate and regenerate the purification molecular sieve system; (6) Detect the gas moisture content and the cold blow peak value of molecular sieve regeneration according to the online instrument of the purification system: If the online dew point meter analysis value after the molecular sieve is ≤2ppm and the cold blowing peak value of the molecular sieve regeneration is ≥120℃, the molecular sieve has completed the analysis of moisture and carbon dioxide and can be put into operation, and the air pipeline entering the tower is heated and purged; If the online dew point meter analysis value after the molecular sieve is ≥2ppm and the cold blow peak value of the molecular sieve regeneration is ≤100℃, the molecular sieve cannot completely resolve moisture and carbon dioxide, and the number of purification system operation cycles needs to be increased until the analysis value meets the requirements and the tower inlet air pipeline is heated and purged.

3. A method for treating freezing and blocking of an air separation plate heat exchanger and for rapid resumption of production according to claim 2, characterized in that: The purge process of the pipeline in (6) is as follows: a. After judging that the molecular sieve to be purified is qualified for activation and regeneration, fully open the flow control valve into the fractionation tower at a speed of 10° / min, drain the liquid air in the lower tower of the fractionation tower, and after the liquid air level is completely drained, adjust the valve opening of the liquid air purge valve and the valve opening of the air purge valve, and heat and purge the pipelines from the cooling tower → the plate heat exchanger → the lower tower of the fractionation tower in turn; b. Determine whether the purge is qualified based on the air temperature: If the air temperature entering the lower tower is 10°C or above, the heated purge is qualified; If the air temperature entering the lower tower does not reach 10°C or above, the heating and purging is unqualified and it is necessary to return to S2 to check whether there is a problem in the freezing and blocking treatment step, make adjustments and repeat the heating and purging work.

4. A method for treating freezing and blocking of an air separation plate heat exchanger and for rapid resumption of production according to claim 3, characterized in that: The adjustment method for the liquid air blow-off valve and the air blow-off valve in a is: Increase the opening of the liquid air blow-off valve to 65% and control the flow rate to 4800m 3 / h; Increase the air blow-off valve opening to 50% and control the flow rate to 4000m 3 / h.

5. The method for treating freezing and blocking of an air separation plate heat exchanger and quickly resuming production according to claim 1, characterized in that: The steps to resume operation in S4 are as follows: (1) The flow control valve into the distillation tower, the liquid air purge valve and the plate heat exchanger air purge valve are completely closed at a speed of 20° / min, the expansion air bypass dirty nitrogen valve is fully opened, and the valve opening of the dirty nitrogen to water cooling tower is adjusted to 35%. The air inlet pipeline flow rate is 12000m 3 / h; (2) Start the expander to reduce the air pressure from 750Kpa to 55Kpa, and then enter the plate heat exchanger through the expanded air bypass nitrogen valve, and cool the temperature of the plate heat exchanger to -173°C; (3) After the expander outlet temperature drops to -173°C, the flow control valve into the fractionation tower is fully opened at a speed of 15° / min according to the exhaust pressure of the air compressor, so that the positive flow air enters the lower tower of the fractionation tower after heat exchange through the plate heat exchanger; (4) Adjust the opening of the liquid air purge valve to 35%, and then completely close the liquid air purge valve after liquid flows out; (5) Adjust several valves: Adjust the oxygen flow control valve opening to 36% and control the oxygen flow to 3800m 3 / h; Adjust the opening of the nitrogen venting remote control valve to 40%, the nitrogen delivery regulating valve HV-102 to fully open, and the nitrogen flow regulating control valve to 15%, and control the nitrogen flow rate out of the tower to 24000m 3 / h; Adjust the dirty nitrogen gas inlet cooling tower valve from manual to automatic, and set the control pressure to 12.5Kpa; (6) The valve of the expanded air bypass dirty nitrogen valve is completely closed to allow the expanded air to enter the upper tower of the fractionation tower to participate in distillation, and then the valve of the air bypass regeneration gas valve is completely closed to switch the purified regeneration gas to the dirty nitrogen gas out of the cold box. During this process, the electric heater equipment is turned off; (7) The air separation system enters the purification stage.

6. A method for treating freezing and blocking of an air separation plate heat exchanger and for rapid resumption of production according to claim 5, characterized in that: (7) The purification steps are as follows: a. When the upper tower resistance value of the fractionation tower is 3.5Kpa and the lower tower resistance value is 7.5Kpa, it means that the distillation working conditions of the upper and lower towers of the fractionation tower have been established. At this time, the liquid nitrogen reflux valve is fully opened, and the opening of the regulating liquid nitrogen throttle valve is adjusted to 44%, and the upper tower resistance value of the fractionation tower is controlled to reach 7Kpa and the lower tower resistance value of the fractionation tower is controlled to reach 15Kpa; b. According to the detection of the analytical instrument, when the online oxygen purity analysis value reaches 85%, adjust the liquid nitrogen throttle valve to control the pressure of the upper and lower towers of the distillation tower: Control the pressure in the lower tower: adjust the valve opening of the liquid nitrogen throttle valve to 38% so that the flow rate of liquid nitrogen flowing into the upper tower of the fractionation tower is 28.6m 3 / h, the pressure of the lower tower of the distillation tower after being affected by liquid nitrogen is 454Kpa; Stabilize the upper tower pressure: After the liquid nitrogen enters the upper tower of the fractionation tower, the pressure in the upper tower of the fractionation tower rises from 35Kpa to 40Kpa. The opening of the liquid nitrogen throttle valve is controlled at 42.5%, so that the upper tower pressure of the fractionation tower is maintained at 45Kpa, ensuring the stable operation of the air separation system; c. When the liquid nitrogen throttle valve opening is 42%, the oxygen output is 13000m 3 , oxygen purity reaches 99.6%, nitrogen output is 2700m 3 , the purity of nitrogen reaches 99.9997%, and then the oxygen and nitrogen are switched from the venting pipeline to the oxygen output pipeline and the nitrogen output pipeline respectively; d. Adjust the opening of the expansion air bypass nitrogen valve to 18% to control the expansion air bypass flow rate at 1730m 3 / h; e. After the distillation tower is operating stably, put the automatic control instrument into operation and resume gas supply.