Low-temperature adiabatic cylinder vacuum high-temperature heat sealing method

Abstract

The application discloses a low-temperature adiabatic gas cylinder vacuum high-temperature heat sealing method, which comprises the following steps: S1, vacuum sealing vacuum degree index; S2, vacuumizing equipment operation preparation; S3, nitrogen replacement; S3, pre-vacuumizing; S5, main vacuumizing; S6, vacuum degree stabilization and standing; and S7, high-temperature heat sealing. Before high-temperature heat sealing, the application determines the dynamic vacuum degree index p 12 and the static vacuum degree index p 22 of vacuum sealing. Then, a plurality of low-temperature adiabatic gas cylinders sealed by high-temperature heat sealing are subjected to a plurality of performance test experiments. The main vacuumizing of the existing normal-temperature sealing needs 7-9 days, and the two high-temperature heat sealing indexes of the application need only 3-5 days for high-temperature main vacuumizing at 160-180 DEG C, the activity of gas molecules in the interlayer is greatly improved, the sealing period is greatly reduced, the performance of the gas cylinder is better than that of the normal-temperature sealing, and the problem of vacuum degree deviation caused by product batch dispersion is solved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of low-temperature adiabatic gas cylinders, and particularly relates to a low-temperature adiabatic gas cylinder vacuum high-temperature heat sealing method. BACKGROUND

[0002] Liquefied natural gas, liquid nitrogen, liquid hydrogen, liquid oxygen and other low-temperature liquid containers use vacuum interlayers and aluminum foil cladding layers to isolate heat conduction, heat convection and heat radiation, maintain the long-time low-temperature state of the liquid, and reduce the heat absorption volatilization leakage loss of the low-temperature liquid. Therefore, the long-time high vacuum degree maintenance of the low-temperature liquid container is the technical key of the low-temperature liquid container product.

[0003] The poor vacuum maintenance is a direct cause of the increase of the evaporation rate of the liquid gas, and the main causes affecting the vacuum degree of the gas cylinder vacuum interlayer are the slow outgassing of the materials in the interlayer and the leakage rate at the joints and welds. In the production process of the gas cylinder, the helium mass spectrometer leak detector can be used to monitor the interlayer leakage rate to ensure that the gas cylinder leakage rate meets the standard requirements. The existing process technology cannot obtain the direct interlayer outgassing rate, and reducing the outgassing rate of the materials in the interlayer is the key to improving the vacuum performance of the gas cylinder, and the batch dispersion of the product easily causes the problem of vacuum degree deviation.

[0004] The Chinese invention patent with the publication number CN 108799820 B discloses a kind of low-temperature adiabatic gas cylinder high-efficiency vacuumizing method, which strictly limits the heating temperature for vacuumizing gas cylinder to 140-160 ℃, controls the heating time to 44-48 h, and stops vacuumizing when the vacuum degree of the gas cylinder is lower than 4 × 10 -2 Pa, and seals the vacuum port of the gas cylinder. However, the sealing process of this scheme is still carried out at a relatively low temperature, and the required time is 7-9 days, still having the problem of too long time. In addition, there are also the problems of low vacuum degree, short vacuum maintenance time and poor comprehensive performance of the gas cylinder. SUMMARY

[0005] The purpose of the present application is to provide a low-temperature adiabatic gas cylinder vacuum high-temperature heat sealing method with short vacuumizing cycle, high vacuum degree, long vacuum maintenance time and good comprehensive performance of the gas cylinder, aiming at the defects of the existing vacuumizing process technology.

[0006] To achieve the above-mentioned purpose, the low-temperature adiabatic gas cylinder vacuum high-temperature heat sealing method designed by the present application has the following specific steps:

[0007] S1, determine the high-temperature heat sealing vacuum degree index: select a plurality of low-temperature adiabatic gas cylinders with normal temperature sealing, connect the gas cylinder interlayer with the vacuumizing equipment, heat the inner container of the gas cylinder to 160-180 ℃, and maintain for 3-5 h; start the vacuumizing equipment, and vacuumize the equipment pipeline to 2 × 10 -4Pa, measure the vacuum degree pi of each low-temperature adiabatic cylinder at the time when the dynamic vacuum degree is stable, and obtain the average value p 11 , on the basis of which the high-temperature heat-sealing dynamic vacuum degree index p 11 is weighted 12 ; turn off the vacuumizing equipment, stand still for 20-30 min, measure the vacuum degree p2 of each low-temperature adiabatic cylinder at the time when the static vacuum degree is stable, and obtain the average value p 21 , on the basis of which the high-temperature heat-sealing static vacuum degree index p 21 is weighted 22 ;

[0008] S2, high-temperature heat-sealing preparation: take a plurality of low-temperature adiabatic cylinders to be heat-sealed, first vacuumize the equipment pipeline, when the pressure of the equipment pipeline reaches 800-1000 Pa, connect the cylinder interlayer to the vacuumizing equipment, confirm that there is no leakage at each connection part of the equipment, then vacuumize the equipment pipeline and the cylinder interlayer, when the pressure of the equipment pipeline reaches 800-1000 Pa again, continue to vacuumize the cylinder interlayer, and at the same time, heat the inner container of the cylinder and maintain the high temperature at 160-180℃;

[0009] S3, hot nitrogen replacement: when the pressure of the equipment pipeline is less than or equal to 10 Pa, stop vacuumizing, replace the cylinder interlayer with hot nitrogen, control the nitrogen filling set pressure to be less than or equal to 8x10 4 Pa; then stop the hot nitrogen replacement, stand still for 2-4 h; repeat the process of vacuumizing the cylinder interlayer, heating the inner container of the cylinder to maintain the high temperature at 160-180℃, and hot nitrogen replacement for several times;

[0010] S4, pre-vacuumizing: after the hot nitrogen replacement is completed, heat the cylinder interlayer under the condition of maintaining the high temperature at 160-180℃ of the inner container of the cylinder;

[0011] S5, main vacuumizing: when the pressure of the equipment pipeline is less than or equal to 10 Pa, continue to maintain the high temperature at 160-180℃ of the inner container of the cylinder, heat the cylinder interlayer for main vacuumizing;

[0012] S6, vacuum degree stabilization and standing still: detect the dynamic vacuum degree of the above low-temperature adiabatic cylinder, when it is lower than the dynamic vacuum degree index p 12 , stop the main vacuumizing, and stand still for 20-30 min;

[0013] S7, high-temperature heat-sealing: detect the static vacuum degree of the low-temperature adiabatic cylinder after standing still, when it reaches the static vacuum degree index p 22 , timely heat-seal the low-temperature adiabatic cylinder under the high temperature; otherwise, return to step S5, and continue to re-perform the main vacuumizing until the static vacuum degree of all the low-temperature adiabatic cylinders is lower than the static vacuum degree index p22 , the heat sealing is completed.

[0014] Further, the p 11 is weighted on the basis of the p 12 , and the weight coefficient of the p 21 is 0.7-0.9. 22 is weighted on the basis of the p

[0015] Further, the p 11 is weighted on the basis of the p 12 , and the weight coefficient of the p 21 is 0.8. 22 is weighted on the basis of the p

[0016] Further, in the steps, the inner liner of the heating gas cylinder is maintained at a high temperature of 170-180 DEG C. Thus, the activity of the gas molecules in the gas cylinder interlayer is further improved.

[0017] Further, in the step S3, the step S3, the number of times of the hot nitrogen replacement is 3-5, and the nitrogen filling is completed within 10-15 min.

[0018] Further, in the step S4, the vacuum degree of the low-temperature adiabatic gas cylinder interlayer is ensured to reach 6-10 Pa through real-time monitoring.

[0019] Compared with the prior art, the present application has the following advantages:

[0020] 1) The values of the dynamic vacuum degree index and the static vacuum degree of the existing normal-temperature sealing are generally 10 -4 orders of magnitude, and the normal-temperature main pumping needs 7-9 days. The two vacuum degree indexes of the present application are 10 -1 orders of magnitude, and the high-temperature main pumping only needs 3-5 days at a high temperature of 160-180 DEG C, because the activity of the gas molecules in the interlayer is greatly improved, and the sealing period is greatly reduced.

[0021] 2) The dynamic vacuum degree index and the static vacuum degree of the vacuum sealing are determined by the low-temperature adiabatic gas cylinder high-temperature sealing at 160-180 DEG C, the average value of a plurality of gas cylinders is selected as the comparison data, and the problem of the vacuum degree deviation caused by the product batch discreteness is solved.

[0022] 3) The high-temperature heat-sealed gas cylinder is subjected to leak air rate measurement, static evaporation rate measurement and vacuum maintenance time test, and the performance of the gas cylinder is better than that of the normal-temperature sealing, the vacuum maintenance effect of the gas cylinder is better, the product quality is improved, and remarkable economic benefits are brought. DETAILED DESCRIPTION

[0023] The low-temperature adiabatic gas cylinder vacuum high-temperature heat-sealing method designed in the application first determines the dynamic vacuum degree index p 12 and the static vacuum degree index p 22 of the high-temperature heat sealing by using a plurality of normal-temperature sealing combined low-temperature adiabatic gas cylinders, and then uses the two measured vacuum degree indexes to heat seal the low-temperature adiabatic gas cylinder in a high-temperature state.

[0024] The specific steps of the low-temperature adiabatic gas cylinder vacuum high-temperature heat-sealing method are as follows:

[0025] S1, determining the high-temperature heat-sealing vacuum degree index

[0026] Three low-temperature adiabatic gas cylinders of the same size with a diameter of 600 mm and a volume of 450 L are selected, the interlayer of the gas cylinder is connected with a vacuumizing device, and the inner barrels of the three gas cylinders are heated to 160, 170 and 180 DEG C respectively by hot air and maintained for 3, 4 and 5 h respectively; the vacuumizing device is started, and the pipeline of the device is vacuumized to 2*10 -4 Pa, the vacuum degree p1 of each low-temperature adiabatic gas cylinder at the time when the dynamic vacuum degree is stable is measured, and the average value p 11 0.60 Pa is obtained, and the dynamic vacuum degree index p 11 of the high-temperature heat sealing is obtained by weighting on the basis of p 12 .

[0027] The high-temperature heat sealing is a new type of vacuum high-temperature heat sealing method. According to the ideal gas state equation, the higher the temperature of the gas, the greater the pressure of the gas. The high-temperature heat sealing index is different from the normal-temperature sealing index, and how to select the optimal high-temperature heat sealing index becomes the key of the process technology: if the sealing index is too low, the low-temperature vacuum degree of the gas cylinder will be unqualified; if the sealing index is too high, the vacuum degree index requirement cannot be met or additional economic cost is increased. The application is mainly to obtain the optimal high-temperature heat sealing index.

[0028] In the embodiment, the weight coefficients of the dynamic vacuum degree indexes of the three gas cylinders are taken as 0.7, 0.8 and 0.9 respectively as the subsequent high-temperature heat sealing index, and the dynamic vacuum degree indexes p 12 are 0.42 Pa, 0.48 Pa and 0.54 Pa respectively.

[0029] After the vacuumizing equipment is closed again, the low-temperature adiabatic cylinders are left for 20-30 minutes, and the vacuum degrees p2 of each low-temperature adiabatic cylinder at the time when the static vacuum degree is stable are measured to be 1.29, 1.27 and 1.28 Pa respectively, and the average value p 21 is 1.28 Pa, and the high-temperature heat sealing static vacuum degree index p 21 is obtained by weighting on the basis of p 22 In this embodiment, the weight coefficients of the static vacuum degree indexes of the three low-temperature adiabatic cylinders are respectively taken as 0.7, 0.8 and 0.9 to be the subsequent high-temperature heat sealing indexes, and the static vacuum degree indexes p 22 are respectively 0.90, 1.02 and 1.15 Pa.

[0030] In this embodiment, three low-temperature adiabatic cylinders of another normal-temperature sealing joint are selected, the diameters of which are 850 mm, the volumes of which are 1000 L, and other parameters are kept consistent, and the obtained dynamic vacuum degree index p 12 and the static vacuum degree index p 22 are basically consistent.

[0031] In the following, three specific embodiments are combined to respectively perform high-temperature heat sealing on products of the same specification by using the above three different dynamic vacuum degree indexes p 12 and the static vacuum degree indexes p 22 respectively, the selected products are low-temperature adiabatic cylinders of vehicle-mounted liquefied natural gas (LNG) with a diameter of 850 mm and a volume of 1000 L, and the performance test is performed on the low-temperature adiabatic cylinders of high-temperature heat sealing to compare the test results.

[0032] In the following, three specific embodiments are combined to respectively perform high-temperature heat sealing on products of the same specification by using the above three different dynamic vacuum degree indexes p 12 and the static vacuum degree indexes p 22 respectively, the selected products are low-temperature adiabatic cylinders of vehicle-mounted liquefied natural gas (LNG) with a diameter of 850 mm and a volume of 1000 L, and the performance test is performed on the low-temperature adiabatic cylinders of high-temperature heat sealing to compare the test results.

[0033] Embodiment 1

[0034] S2, preliminary preparation before high-temperature heat sealing

[0035] Two low-temperature adiabatic gas cylinders to be high-temperature heat-sealed are connected with a vacuumizing device, the front-stage pump and the pre-extraction valve are first opened to extract the pipeline of the device, when the pressure of the pipeline of the device reaches 800 Pa, after confirming that the hand valves and the push-pull valves of the connecting parts of the device have no leakage, all the push-pull valves and the hand valves connecting the two low-temperature adiabatic gas cylinders are opened to extract the pipeline of the device and the gas cylinder interlayer, when the pressure of the pipeline of the device reaches 800 Pa again, the Roots pump is opened to start extracting the gas cylinder interlayer, at this time, the low-extraction vacuum system is run, the air blower is opened to ventilate, the heater switch is opened, and the extraction of the gas cylinder interlayer is continuously maintained, at the same time, the inner container of the gas cylinder is heated and maintained at a high temperature of 160 DEG C. In the three embodiments of the present application, the vacuumizing device has a low-extraction vacuum system and a high-extraction vacuum system. The front-stage pump and the Roots pump are mechanical pumps selected by the low-extraction vacuum system; the diffusion pump is a molecular pump selected by the high-extraction vacuum system, and the pressure is extracted to below 10 Pa to reach the opening condition of the diffusion pump, when the diffusion pump is opened, the Roots pump is closed. The air blower and the heater are heat sources used in the embodiment, and are always in an opened state until sealing.

[0036] S3, hot nitrogen replacement

[0037] After the pressure of the pipeline of the device is less than or equal to 10 Pa, the extraction is stopped, the hot nitrogen replacement of the gas cylinder interlayer is carried out, the nitrogen filling set pressure is controlled to be not more than 8x10 4 Pa; then the hot nitrogen replacement is stopped, and the process of extracting the gas cylinder interlayer, heating the inner container of the gas cylinder to maintain a high temperature of 160 DEG C, and hot nitrogen replacement is repeated three times.

[0038] In the embodiment, the nitrogen filling is completed within 10-15 min each time.

[0039] S4, pre-extraction

[0040] After the hot nitrogen replacement is completed, the pre-extraction valve and the Roots pump of the device are in an opened state, at this time, the low-extraction vacuum system is run, and the gas cylinder interlayer is heated and pre-extracted under the condition of maintaining the high temperature of 160 DEG C of the inner container of the gas cylinder.

[0041] In the embodiment, the heating temperature of the hot air in the inner container during the pre-extraction is 160 DEG C. The vacuum degree in the vacuum interlayer of the low-temperature adiabatic gas cylinder is guaranteed to be 6-10 Pa during the pre-extraction, and when the vacuum degree is less than 6 Pa, the pre-extraction period will greatly increase, therefore, the value is preferably 6-10 Pa.

[0042] S5, main extraction

[0043] After the equipment pipeline pressure is ≤10Pa, open the front-stage valve, close the Roots pump, and turn on the diffusion pump. After stabilizing for 25 minutes, confirm that the pre-vacuuming is qualified, close the pre-vacuuming valve, open the main pumping valve of the vacuum equipment, and heat the two low-temperature insulated gas cylinders for main pumping. In the three embodiments of the present invention, when the equipment pipeline pressure is pumped to below 10Pa, when the gas cylinder turns on the diffusion pump, the Roots pump will be turned off and the high vacuum system will be operated. In this embodiment, the front-stage valve is the control system of the vacuum system. Only when the front-stage valve is turned on can the diffusion pump vacuum the equipment. The diffusion pump is used for vacuuming, and the diffusion pump has high power, and belongs to the main pumping system of this embodiment. The front-stage valve is the control system of the vacuum equipment. Only when the front-stage valve is turned on can the diffusion pump vacuum the equipment.

[0044] S6, vacuum degree stable and stand still

[0045] When the dynamic vacuum degree of the two cryogenic insulation cylinders reaches p 12 When the dynamic vacuum degree p of the two gas cylinders is 0.42Pa, measure the dynamic vacuum degree p of the two gas cylinders at this time. 13 They are 0.27 and 0.13Pa respectively, both of which are lower than 0.42Pa, meeting the requirements. Then close the manual valve and the push-pull valve, stop the main pumping, let it stand for 20 minutes, and keep heating the two low-temperature insulated gas cylinders.

[0046] S7, high temperature heat sealing

[0047] After retesting the vacuum of the two cryogenic insulated gas cylinders for half an hour, the static vacuum p3 of the two cylinders were 0.67 and 0.53 Pa respectively, both of which were lower than p 22 If the static vacuum p3 of both cylinders is not lower than 0.9 Pa, and the vacuum level of both cylinders is confirmed to be qualified, the cylinders are promptly heat-sealed at a high temperature of 160°C. If the static vacuum level p3 of both cylinders is not lower than 0.9 Pa, the process returns to step S4 and repeats the main vacuum pumping until the static vacuum level of all cryogenically insulated cylinders is lower than 0.9 Pa.

[0048] After the heat sealing is completed, the main pumping valve, the diffusion pump, the fore valve, the fore pump, the blower and the heater are closed.

[0049] When the push-pull valve is not closed, the gas cylinder and the equipment are in a connected state, and the equipment is constantly pumping air from the interlayer. The vacuum degree at this time is the vacuum degree exchanged between the equipment and the interlayer, which we call dynamic vacuum degree; after closing the push-pull valve, the equipment no longer pumps air from the interlayer, and the gas cylinder is only exchanged inside the interlayer. After standing for half an hour, it is a static vacuum degree. Usually, the static vacuum degree can more accurately reflect the vacuum degree of the gas cylinder than the dynamic vacuum degree.

[0050] After the heat sealing is completed, the main pumping valve, the diffusion pump, the fore valve, the fore pump, the blower and the heater are closed.

[0051] The two heat-sealed low-temperature adiabatic cylinders were tested for performance:

[0052] First, the two cylinders were tested for leakage rate according to Q = ΔP(t)VK / Δt, which were 6.3 x 10 -8 Pa·m 3 / s and 9.8 x 10 -8 Pa·m 3 / s, respectively, both of which were better than the standard requirement of 6 x 10 -7 Pa·m 3 / s. In the above formula: Q is the leakage rate of the vacuum interlayer of the tested piece, with a unit of Pa·m 3 / s;

[0053] ΔP(t) / Δt is the rate of change of vacuum degree of the interlayer space, with a unit of Pa / s, i.e. the ratio of the change amount ΔP(t) of the vacuum degree of the interlayer space to the time Δt required to produce the change;

[0054] V is the geometric volume of the vacuum interlayer of the tested piece, with a unit of m 3 ;

[0055] K is the correction coefficient of the interlayer volume, which is 0.9 for vacuum multilayer insulation.

[0056] The two cylinders were filled with the same weight of liquid nitrogen for cold test, and were left standing for more than 48 hours. The low-temperature vacuum degrees of the two cylinders were tested, which were 9.7 x 10 -3 Pa and 5.6 x 10 -3 Pa, respectively, both of which were better than the standard requirement of 2 x 10 -2 Pa.

[0057] The static evaporation rates of the two cylinders were tested, which were 1.76% / d and 1.74% / d, respectively, both of which were better than the standard requirement of 2.15% / d.

[0058] The two cylinders were filled with liquid nitrogen at 90% of the rated volume for maintenance time test, and were left standing for 15 days. The ratio of the pressure of the two cylinders to the take-off pressure of the safety valve was tested. The pressure of the two normal-temperature sealing cylinders was about 70% of the take-off pressure of the safety valve, and the pressure of the two high-temperature heat-sealing cylinders was about 50% of the take-off pressure of the safety valve.

[0059] Example 2

[0060] S2, preliminary preparation before high-temperature heat sealing

[0061] Take three low-temperature adiabatic gas cylinders to be high-temperature heat-sealed, connect the gas cylinder interlayer with the vacuumizing equipment, first open the pre-pump and the pre-evacuation valve to vacuumize the equipment pipeline, when the pressure of the equipment pipeline reaches 900 Pa, confirm that the hand valves and push-pull valves of the equipment connection parts have no leakage, then open all the push-pull valves and hand valves connected with the three low-temperature adiabatic gas cylinders to vacuumize the equipment pipeline and the gas cylinder interlayer, when the pressure of the equipment pipeline reaches 900 Pa again, open the Roots pump to start vacuumizing the gas cylinder interlayer, at this time, run the low-evacuation vacuum system, then open the air blower to ventilate, open the heater switch and continue to maintain the vacuumization of the gas cylinder interlayer, at the same time, heat the inner liner of the gas cylinder and maintain it at a high temperature of 170℃.

[0062] S3, hot nitrogen replacement

[0063] After the pressure of the equipment pipeline is less than or equal to 10 Pa, stop vacuumizing, replace the gas cylinder interlayer with hot nitrogen, control the nitrogen filling set pressure to be less than or equal to 8x10 4 Pa, then stop the hot nitrogen replacement, stand still for 3 hours, and repeat the process of vacuumizing the gas cylinder interlayer, heating the inner liner of the gas cylinder to maintain a high temperature of 170℃, and hot nitrogen replacement for three times.

[0064] In this embodiment, the nitrogen filling is completed within 10-15 minutes each time.

[0065] S4, pre-evacuation

[0066] After the hot nitrogen replacement is completed, the pre-evacuation valve and the Roots pump of the equipment are in the open state, at this time, run the low-evacuation vacuum system, heat the gas cylinder interlayer to pre-evacuate under the condition of maintaining the high temperature of 170℃ of the inner liner of the gas cylinder.

[0067] In this embodiment, the heating temperature of the hot air in the inner liner during the pre-evacuation is 170℃.

[0068] In this embodiment, the vacuum degree in the vacuum interlayer of the low-temperature adiabatic gas cylinder during the pre-evacuation is 6-10 Pa, when the vacuum degree is less than 6 Pa, the pre-evacuation period will greatly increase, therefore, the value is preferably 6-10 Pa.

[0069] S5, main evacuation

[0070] After the pressure of the equipment pipeline is less than or equal to 10 Pa, open the pre-stage valve, close the Roots pump, open the diffusion pump, after stabilizing for 25 minutes, confirm that the pre-evacuation is qualified, close the pre-evacuation valve, open the main evacuation valve of the vacuumizing equipment, heat the three low-temperature adiabatic gas cylinders for main evacuation.

[0071] S6, vacuum degree stabilization and standing still

[0072] When the dynamic vacuum degrees of the three low-temperature adiabatic gas cylinders all reach p 120.48 Pa, the dynamic vacuum degrees p of the three gas cylinders at this time are measured 13 0.37 Pa, 0.41 Pa and 0.33 Pa respectively, which are all lower than 0.48 Pa, meeting the requirements, then the hand valve and the push-pull valve are closed, the main pumping is stopped, and the three low-temperature adiabatic gas cylinders are kept being heated for 20 min.

[0073] S7, high-temperature heat sealing

[0074] The vacuum degrees of the three low-temperature adiabatic gas cylinders after the re-measurement for 30 min are measured, the static vacuum degrees p3 of the three gas cylinders are 0.63 Pa, 0.75 Pa and 0.59 Pa respectively, which are all lower than 1.02 Pa, confirming that the vacuum degrees of the three gas cylinders are qualified, then the gas cylinders are heat sealed at 170℃ in a high-temperature state in time. If the static vacuum degrees p3 of the three gas cylinders are not all lower than 1.02 Pa, otherwise, return to step S4, continue to repeat the main pumping, until the static vacuum degrees of all the low-temperature adiabatic gas cylinders are less than 1.02 Pa. 22

[0075] After the heat sealing is completed, the main pumping valve, the diffusion pump, the pre-stage valve, the pre-stage pump, the air blower and the heater are closed.

[0076] The performance of the three heat-sealed low-temperature adiabatic gas cylinders is tested:

[0077] First, the leak air rates of the three gas cylinders are calculated according to Q = ΔP(t) VK / Δt, which are 9.6 x 10 -8 Pa·m 3 / s, 5.6 x 10 -8 Pa·m 3 / s and 1.2 x 10 -7 Pa·m 3 / s respectively, which are all better than the standard requirement of 6 x 10 -7 Pa·m 3 / s.

[0078] The cold test is conducted on the three gas cylinders filled with the same weight of liquid nitrogen, and the low-temperature vacuum degrees of the three gas cylinders are detected after being kept for 48 hours, which are 4.8 x 10 -3 Pa, 7.4 x 10 -3 Pa and 9.2 x 10 -3 Pa respectively, which are all better than the standard requirement of 2 x 10 -2 Pa.

[0079] The static evaporation rates of the three gas cylinders are tested, which are 1.88% / d, 1.92% / d and 1.67% / d respectively, which are all better than the standard requirement of 2.4% / d.

[0080] ​Three cylinders were filled with liquid nitrogen to 90% of the rated volume for maintenance time test. After 15 days, the pressure of the three cylinders sealed at room temperature was about 70% of the relief pressure of the safety valve, and the pressure of the three cylinders sealed at high temperature was about 50% of the relief pressure of the safety valve.

[0081] Example 3

[0082] S2, preparation before high-temperature heat sealing

[0083] Four low-temperature adiabatic cylinders to be sealed at high temperature were connected to the vacuumizing equipment through the interlayer. First, the pre-pump and the pre-evacuation valve were opened to evacuate the equipment pipeline. When the pressure of the equipment pipeline reached 1000 Pa, it was confirmed that there was no leakage in the hand valve and the push-pull valve of each connection part of the equipment. Then, all the push-pull valves and hand valves connected to the four low-temperature adiabatic cylinders were opened to evacuate the equipment pipeline and the cylinder interlayer. When the pressure of the equipment pipeline reached 1000 Pa again, the Roots pump was started to evacuate the cylinder interlayer. At this time, the low-evacuation system was operated, the air blower was started to ventilate, the heater switch was started, and the cylinder interlayer was continuously evacuated while the inner liner was heated and maintained at a high temperature of 180°C.

[0084] S3, hot nitrogen replacement

[0085] When the pressure of the equipment pipeline was less than or equal to 10 Pa, the evacuation was stopped, and the cylinder interlayer was replaced with hot nitrogen. The nitrogen filling pressure was controlled to be less than or equal to 8x10 4 Pa. Then, the hot nitrogen replacement was stopped, and the cylinder interlayer was left for 3 hours. The process of evacuating the cylinder interlayer, heating the inner liner to maintain a high temperature of 180°C, and replacing the hot nitrogen was repeated three times. In this embodiment, the nitrogen filling was completed within 10-15 minutes each time.

[0086] S4, pre-evacuation

[0087] After the hot nitrogen replacement was completed, the pre-evacuation valve and the Roots pump of the equipment were in the open state. At this time, the low-evacuation system was operated, and the cylinder interlayer was heated for pre-evacuation under the condition of maintaining the inner liner at a high temperature of 180°C.

[0088] In this embodiment, the heating temperature of the hot air in the inner liner during pre-evacuation was 180°C.

[0089] In this embodiment, the vacuum degree in the vacuum interlayer of the low-temperature adiabatic cylinder during pre-evacuation was 6-10 Pa. When the vacuum degree was less than 6 Pa, the pre-evacuation period would be greatly increased, so the value was preferably 6-10 Pa.

[0090] S5, main evacuation

[0091] After the equipment pipeline pressure is ≤10Pa, open the front stage valve, close the Roots pump, start the diffusion pump, stabilize for 25 minutes, confirm that the pre-vacuuming is qualified, close the pre-vacuuming valve, open the main vacuum valve of the vacuum equipment, and heat the four low-temperature insulated gas cylinders for main vacuuming.

[0092] S6, vacuum degree stable and stand still

[0093] When the dynamic vacuum degree of the four cryogenic insulation cylinders reaches p 12 When the dynamic vacuum degree p of the four gas cylinders is 0.54Pa, measure the dynamic vacuum degree p of the four gas cylinders at this time. 13 They are 0.43Pa, 0.36Pa, 0.41Pa and 0.32Pa respectively, all of which are lower than 0.54Pa, meeting the requirements. Then close the manual valve and the push-pull valve, stop the main pumping, let it stand for 20 minutes, and keep heating the four low-temperature insulated gas cylinders.

[0094] S7, high temperature heat sealing

[0095] After retesting the vacuum of the four cryogenic insulated gas cylinders after standing for half an hour, the static vacuum p3 of the four gas cylinders were 0.68Pa, 0.55Pa, 0.72Pa and 0.59Pa respectively, and the values ​​were all lower than p 22 If the static vacuum p3 of all four cylinders is not lower than 1.15 Pa, the process returns to step S4 and repeats the main vacuum pumping until the static vacuum of all cryogenically insulated cylinders is less than 1.15 Pa.

[0096] After the heat sealing is completed, the main pumping valve, the diffusion pump, the fore valve, the fore pump, the blower and the heater are closed.

[0097] The four heat-sealed cryogenic insulated gas cylinders were subjected to performance tests:

[0098] The gas leakage rate of the four gas cylinders was calculated according to Q = ΔP(t)VK / Δt, which were 7.6×10 -8 Pa·m 3 / s, 8.2×10 -8 Pa·m 3 / s, 1.1×10 -7 Pa·m 3 / s, 6.7×10 -8 Pa·m 3 / s, which are better than the standard requirement of 6×10 -7 Pa·m 3 / s.

[0099] Four cylinders were filled with the same weight of liquid nitrogen for cold test, and were placed for more than 48 hours. The low temperature vacuum degrees of the four cylinders were detected, which were 5.3*10 -3 Pa, 4.6*10 -3 Pa, 6.6*10 -3 Pa, and 7.8*10 -3 Pa, all of which were better than the standard requirement of 2*10 -2 Pa.

[0100] The static evaporation rates of the four cylinders were tested, which were 1.23% / d, 1.37% / d, 1.26% / d, and 1.13% / d, all of which were better than the standard requirement of 1.8% / d.

[0101] The four cylinders were filled with liquid nitrogen at 90% of the rated volume for maintenance time test. After being placed for 15 days, the ratios of the pressures of the warm sealing and high temperature sealing cylinders to the trip pressure of the safety valve were compared. The pressure of the four warm sealing cylinders was about 70% of the trip pressure of the safety valve, and the pressure of the four high temperature sealing cylinders was about 50% of the trip pressure of the safety valve.

[0102] In the above three embodiments, when the high temperature of 170-180℃ was maintained in the heating cylinder liner, the sealing effect was better than that at 160℃.

[0103] In addition, it can be obtained that the dynamic vacuum degree index p 12 was 0.42-0.58Pa. Through test, when the dynamic vacuum degree index p 12 >0.58Pa, the vacuum maintenance effect of the sealed cylinder was relatively poor, which was not suitable as an index. When the dynamic vacuum degree index p 12 <0.42Pa, the vacuum maintenance effect of the sealed cylinder was basically the same as that when p

[0104] was 0.42-0.58Pa, but the required vacuumizing time was increased by 1-2 days. According to the comparison, the effect of embodiment 2 in the three embodiments was better, and the value thereof was preferably 0.48Pa.

[0105] Similarly, when the static vacuum degree index p 22 <0.9Pa, the vacuum maintenance effect of the sealed cylinder was basically the same as that when p 22 >1.15Pa, the performance of the sealed cylinder was relatively poor, and there was a potential risk in the vacuum maintenance of the cylinder, which was not suitable as an index. Through comparison, the effect of embodiment 2 in the three embodiments was better, and the value thereof was preferably 1.02Pa.

[0106] The dynamic vacuum degree index and static vacuum degree of vacuum sealing are determined by high temperature heat sealing of low temperature adiabatic gas cylinder at 160-180 DEG C, the average value of multiple gas cylinders except two can be selected as comparison data, and the problem of vacuum degree deviation caused by product batch dispersion is solved.

[0107] The dynamic vacuum degree index and static vacuum degree of vacuum sealing of existing normal temperature sealing are generally 10 -4 orders of magnitude, and normal temperature main pumping needs 7-9 days, and the two vacuum degree indexes of the application, high temperature main pumping only needs 3-5 days at 160-180 DEG C due to the great improvement of activity of gas molecules in the interlayer, which greatly reduces the sealing period compared with 7-9 days of the prior art.

Claims

1. A vacuum high-temperature heat sealing method for low-temperature insulated gas cylinders, characterized in that: The following steps are involved: S1. Determine the vacuum index of high-temperature heat sealing: select several low-temperature insulated gas cylinders that are suitable for room-temperature sealing, connect the gas cylinder interlayer to the vacuum pumping equipment, and heat the gas cylinder liner to 160-180℃ for 3-5 hours; turn on the vacuum pumping equipment and evacuate the equipment pipeline to 2×10 -4 Pa below, measure the vacuum degree p1 of each cryogenic insulation gas cylinder when the dynamic vacuum degree is stable, and calculate the average value p 11 , in the p 11 The dynamic vacuum index p of high temperature heat sealing is obtained by weighting 12 ; Turn off the vacuum equipment and let it stand for 20 to 30 minutes. Measure the vacuum degree p2 of each low-temperature insulation gas cylinder when the static vacuum degree is stable, and calculate the average value p 21 , in the p 21 The static vacuum index p of high temperature heat sealing is obtained by weighting 22 ; S2. Preliminary preparation for high-temperature heat sealing: Take several low-temperature insulated gas cylinders to be heat-sealed at high temperatures, first evacuate the equipment pipeline, and when the equipment pipeline pressure reaches 800-1000Pa, connect the cylinder interlayer to the vacuum equipment. After confirming that there are no leaks at all the connection parts of the equipment, evacuate the equipment pipeline and the cylinder interlayer again. When the equipment pipeline pressure reaches 800-1000Pa again, continue to evacuate the cylinder interlayer and heat the cylinder liner at the same time, and maintain a high temperature of 160-180℃. S3. Hot nitrogen replacement: When the equipment pipeline pressure is ≤10Pa, stop vacuuming and replace the cylinder interlayer with hot nitrogen. Control the nitrogen filling setting pressure not to exceed 8×10 4 Pa; then stop the hot nitrogen replacement and let it stand for 2 to 4 hours; then repeat the process of vacuuming the cylinder interlayer, heating the cylinder liner to maintain a high temperature of 160 to 180 ° C, and replacing it with hot nitrogen several times; S4. Pre-vacuuming: After the hot nitrogen replacement is completed, the cylinder interlayer is heated and pre-vacuumed while maintaining the high temperature of the cylinder liner at 160-180°C; S5. Main vacuuming: When the equipment pipeline pressure is ≤10Pa, continue to maintain the high temperature of 160-180℃ in the gas cylinder liner and heat the gas cylinder interlayer for main vacuuming; S6, vacuum degree stable static: detect the dynamic vacuum degree of the above-mentioned low-temperature insulation gas cylinder, when it is lower than the dynamic vacuum degree index p 12 When the temperature is high, stop the main pumping and let it stand for 20 to 30 minutes; S7, high temperature heat sealing: detect the static vacuum degree of the low temperature insulation gas cylinder after standing, when it reaches the static vacuum degree index p 22 Otherwise, return to step S5 and continue to re-evacuate the main vacuum until the static vacuum degree of all the cryogenic insulation gas bottles is lower than the static vacuum degree index p 22 , heat sealing is completed.

2. The vacuum high-temperature heat sealing method for cryogenic insulated gas cylinders according to claim 1, characterized in that: In the p 11 The dynamic vacuum index p of high temperature heat sealing is obtained by weighting 12 The weight coefficient is 0.7 to 0.

9. 21 The static vacuum index p of high temperature heat sealing is obtained by weighting 22 The weight coefficient is 0.7 to 0.

9.

3. The vacuum high-temperature heat sealing method for cryogenic insulated gas cylinders according to claim 1, characterized in that: In the p 11 The dynamic vacuum index p of high temperature heat sealing is obtained by weighting 12 The weight coefficient is 0.8, in the p 21 The static vacuum index p of high temperature heat sealing is obtained by weighting 22 The weight coefficient is 0.

8.

4. The vacuum high-temperature heat sealing method for a cryogenically insulated gas cylinder according to claim 1, 2 or 3, characterized in that: In each of the steps, the inner liner of the heating cylinder is maintained at a high temperature of 170-180°C.

5. The vacuum high-temperature heat sealing method for a cryogenically insulated gas cylinder according to claim 1, 2 or 3, characterized in that: In step S3, the hot nitrogen replacement is performed 3 to 5 times, and each time the nitrogen filling is completed within 10 to 15 minutes.

6. The vacuum high-temperature heat sealing method for a cryogenically insulated gas cylinder according to claim 1, 2 or 3, characterized in that: In step S4, the vacuum degree of the interlayer of the cryogenic insulation gas cylinder is ensured to reach 6-10 Pa through real-time monitoring.