Storage tank and gas replacement method

Abstract

The invention provides a storage tank and a gas replacement method, and the method comprises the steps: introducing a second gas from a gas inlet of the storage tank under the condition that a gas outlet of the storage tank is opened, and discharging a first gas from the gas outlet; when the volume fraction of the second gas in the storage tank is larger than or equal to the first preset volume fraction, the exhaust port is controlled to be closed; when the gas pressure of the storage tank is larger than or equal to the preset pressure, the gas inlet is controlled to be closed; and when the closing duration of the air inlet is larger than or equal to the first preset duration, the exhaust port is controlled to be opened, the combined replacement mode gives full play to the advantages of high inflation and deflation replacement efficiency and more thorough pressure replacement at the same time, and the overall replacement efficiency is improved while the system safety is ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of industrial production, and in particular to a storage tank and a gas replacement method. Background Art

[0002] During industrial production or scientific experiments, for safety reasons or product protection, it is necessary to replace the initial gas in related pipelines, containers, or confined spaces with inert or other gases. Gas replacement is widely used in many fields, including chemical, cryogenic, and aerospace. Examples include replacement of natural gas pipelines for commissioning, replacement of cryogenic piping and pipelines such as aerospace liquid hydrogen filling systems, manned space capsules and aerospace solid lubrication membrane products, and low dew point control for ground-based atmospheric pressure thermal environment testing. Different industries and fields require different replacement methods.

[0003] However, the existing gas replacement method generally adopts a method of repeatedly filling and deflating the storage tank, which has a low replacement efficiency. Summary of the Invention

[0004] Aiming at the problem of low gas filling and discharging efficiency in the prior art, the present invention proposes a storage tank and a gas replacement method.

[0005] In a first aspect, the present invention provides a gas replacement method, which is applied to a storage tank storing a first gas, and the method comprises:

[0006] When the exhaust port of the storage tank is open, the second gas is introduced from the gas inlet of the storage tank, and the first gas is discharged from the exhaust port;

[0007] When the volume fraction of the second gas in the storage tank is greater than or equal to the first preset volume fraction, controlling the exhaust port to close;

[0008] When the gas pressure in the storage tank is greater than or equal to the preset pressure, the air inlet is controlled to close;

[0009] When the closing time of the air inlet is greater than or equal to the first preset time, the exhaust port is controlled to open.

[0010] Optionally, when the closing time is greater than or equal to the target time, after controlling the exhaust port of the storage tank to open, the method further includes:

[0011] When the volume fraction is less than the second preset volume fraction, the exhaust port is controlled to be closed, and the second gas is introduced from the air inlet until the volume fraction is greater than or equal to the second preset volume fraction.

[0012] Optionally, when the exhaust port of the storage tank is open, after the second gas is introduced from the gas inlet of the storage tank, the method further comprises:

[0013] Recording the duration of the second gas being introduced into the air inlet;

[0014] When the inflation time is greater than or equal to the second preset time, the exhaust port is controlled to be closed;

[0015] When the gas pressure in the storage tank is greater than or equal to the preset pressure, the air inlet is controlled to close;

[0016] When the closing time of the air inlet is greater than or equal to the first preset time, the exhaust port is controlled to open.

[0017] Optionally, the second preset time period is determined by inputting the volume of the storage tank and the first preset volume fraction into a pre-built time period determination model.

[0018] Optionally, the volume of the storage tank is greater than or equal to a preset volume.

[0019] Optionally, the storage tank includes a storage tank body and at least one branch pipeline.

[0020] Optionally, the storage tank includes a storage tank body and at least one blind leg.

[0021] Optionally, when the exhaust port of the storage tank is open, introducing the second gas from the gas inlet of the storage tank comprises:

[0022] When the exhaust port of the storage tank is open, the second gas is introduced into the storage tank from the gas inlet at a preset flow rate.

[0023] In a second aspect, the present invention provides a storage tank, wherein a first gas is stored in the storage tank, and the storage tank replaces the first gas with a second gas through any gas replacement method as described in the first aspect.

[0024] Optionally, the volume of the storage tank is greater than or equal to a preset volume.

[0025] The present invention provides a storage tank and a gas replacement method, which have the following technical effects:

[0026] In this embodiment, the air inlet and exhaust port of the storage tank are opened simultaneously to perform blowout and replacement. When the volume fraction of the second gas reaches a first preset volume fraction, the exhaust port is closed to increase the pressure in the storage tank, so that the gas in the storage tank is fully replaced under a certain pressure. Finally, after a preset time, the exhaust port is opened to release the pressure so that the gas in the storage tank meets the replacement requirements. This combined replacement method fully utilizes the advantages of high replacement efficiency of simultaneous filling and discharging of gases and more thorough pressure replacement, thereby improving the overall replacement efficiency while ensuring system safety.

[0027] It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The accompanying drawings, which constitute part of the present invention, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0029] Figure 1 A first flow chart of a gas replacement method provided by an exemplary embodiment of the present invention;

[0030] Figure 2a A schematic diagram of gas distribution in a storage tank when the inflation time is 300 seconds, provided by an exemplary embodiment of the present invention;

[0031] Figure 2b A schematic diagram of gas distribution in a storage tank when the inflation time is 600s provided in an exemplary embodiment of the present invention;

[0032] Figure 2c A schematic diagram of gas distribution in a storage tank when the inflation time is 900s provided in an exemplary embodiment of the present invention;

[0033] Figure 2d A schematic diagram of gas distribution in a storage tank when the inflation time is 1200s provided in an exemplary embodiment of the present invention;

[0034] Figure 2e A schematic diagram of gas distribution in a storage tank when the inflation time is 1500s provided in an exemplary embodiment of the present invention;

[0035] Figure 2f A schematic diagram of gas distribution in a storage tank when the inflation time is 1800s provided in an exemplary embodiment of the present invention;

[0036] Figure 3 A second flow chart of a gas replacement method provided by an exemplary embodiment of the present invention;

[0037] Figure 4a A schematic diagram of gas distribution in a storage tank when the number of replacements is 1, provided as an exemplary embodiment of the present invention;

[0038] Figure 4b A schematic diagram of gas distribution in a storage tank when the number of replacements is 2, provided by an exemplary embodiment of the present invention;

[0039] Figure 4c A schematic diagram of gas distribution in a storage tank when the number of replacements is three, provided by an exemplary embodiment of the present invention;

[0040] Figure 4d A schematic diagram of gas distribution in a storage tank when the number of replacements is 4, provided as an exemplary embodiment of the present invention;

[0041] Figure 4eA schematic diagram of gas distribution in a storage tank when the number of replacements is 5, provided as an exemplary embodiment of the present invention;

[0042] Figure 5 A schematic diagram of nitrogen concentration changes provided by an exemplary embodiment of the present invention;

[0043] Figure 6 A schematic diagram of pipeline gas distribution provided by an exemplary embodiment of the present invention. DETAILED DESCRIPTION

[0044] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments. It should be noted that, in the absence of conflict, the embodiments and features of the embodiments of the present invention can be combined with each other.

[0045] The following detailed description is an exemplary description and is intended to provide further detailed description of the present invention. Unless otherwise indicated, all technical terms used in the present invention have the same meaning as those generally understood by those skilled in the art to which the present invention belongs. The terms used in the present invention are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention.

[0046] An exemplary embodiment of the present invention provides a gas replacement method. Figure 1 , applied to a storage tank storing a first gas, the method comprising:

[0047] S101. When the exhaust port of the storage tank is open, the second gas is introduced from the air inlet of the storage tank, and the first gas is discharged from the exhaust port.

[0048] The first gas is the gas originally stored in the storage tank, while the second gas is the target gas to be stored in the storage tank. A storage tank refers to a device used to store various gases. It includes a storage tank body and at least one branch pipeline and / or a storage tank includes a storage tank body and at least one blind leg. The volume of the storage tank is greater than or equal to a preset volume. The value of the preset volume can be set according to actual conditions and can be a larger volume or a smaller volume. This embodiment is preferably suitable for storage tanks with larger volumes. This embodiment is preferably applied to large storage tanks, which have many branch pipelines and blind legs and are not easy to replace.

[0049] In addition, in order to facilitate gas exchange, the exhaust port of the storage tank is generally set at the top of the storage tank, while the air inlet of the storage tank is generally set at the bottom of the storage tank.

[0050] In this embodiment, replacement gas is introduced into the tank through the inlet at the bottom of the tank, while the exhaust port is simultaneously opened, causing the tank to be simultaneously inflated and deflated (purging and replacement). Figure 2 shows the changes in the flow field within the tank, the gas flow rate, and the gas volume fraction over time during the purge process. Figure 2 is based on a simulation using Fluent (a simulation software).

[0051] In one embodiment, step S101 further includes:

[0052] When the exhaust port of the storage tank is open, the second gas is introduced into the storage tank from the gas inlet at a preset flow rate.

[0053] The preset flow rate is set based on the balance between the air supply capacity and the air consumption. The larger the preset flow rate, the shorter the replacement time.

[0054] S102: When the volume fraction of the second gas in the storage tank is greater than or equal to a first preset volume fraction, control the exhaust port to be closed.

[0055] Among them, the volume fraction of the second gas can be collected by a gas concentration sensor built into the storage tank, or it can be determined by simulating the volume, shape, and filling and discharging of the storage tank. When the volume of the storage tank is fixed, the longer the filling time of the second gas is, the greater the volume fraction of the second gas in the storage tank. The first preset volume fraction can be set according to actual conditions.

[0056] In this embodiment, while simultaneous inflation and deflation alone can achieve high displacement efficiency, this often results in poor displacement efficiency for tanks with blind legs or branch pipes. Therefore, in step S103, when the gas pressure is greater than or equal to a preset pressure, pressure-based displacement is employed. This involves closing the tank's exhaust port while maintaining gas flow through the intake port to purge uncovered blind legs or branch pipes.

[0057] S103: When the gas pressure in the storage tank is greater than or equal to the preset pressure, the air inlet is controlled to be closed.

[0058] In this embodiment, since the exhaust port of the storage tank is closed and the air inlet is open, if gas is continuously introduced into the storage tank, the gas pressure in the storage tank will rise. When the preset pressure is reached, the air inlet is closed, and the gas molecules can move under the internal pressure to cover the blind pipe or branch pipe. The preset pressure can be set according to actual needs.

[0059] In one embodiment, in addition to determining whether the storage tank meets the stop condition for simultaneous inflation and deflation based on the volume fraction of the second gas, it can also be determined based on the inflation time. Figure 3After step S101, the method further includes:

[0060] S201, recording the inflation time of the second gas introduced into the air inlet.

[0061] S202: When the inflation time is greater than or equal to a second preset time, the exhaust port is controlled to be closed.

[0062] Among them, during the filling and discharging process, when the volume of the storage tank is fixed, the filling time and the volume fraction of the second gas in the storage tank are positively correlated. The following table takes the volume of the storage tank as 105m 3 , take the second gas as nitrogen for inflation as an example:

[0063] Inflation time / s Volume fraction of nitrogen 300 85.81％ 600 90.61％ 900 94.41％ 1200 96.94％ 1500 98.32％ 1800 99.03％

[0064] Table 1 - Changes in nitrogen volume fraction during simultaneous inflation and deflation

[0065] Therefore, the table can be used to determine the first preset volume fraction required for both the inflation and deflation phases, and then the second preset duration of the tank can be determined based on the nitrogen volume fraction. For example, if the volume fraction of the second gas is replaced with 94.41%, a purge time of 900 seconds is required. The inflation duration can also be determined based on the volume fraction of the second gas initially stored in the tank and the first preset volume fraction. For example, if the initial nitrogen volume fraction in the tank is 85.81%, a purge time of 900 (1200-300) seconds is required to replace the nitrogen volume fraction with 96.94%.

[0066] In one specific embodiment, in addition to determining the second preset duration using the schematic method shown in the table above, the second preset duration can also be determined by inputting the volume of the storage tank and the first preset volume into a pre-established duration determination model. The duration determination model is obtained by fitting the first preset integral and the second preset duration under a certain volume, and includes, but is not limited to, a learning model and algorithm thereof, and can be selected based on actual circumstances.

[0067] In this embodiment, the duration of simultaneous inflation and deflation can be set to give full play to the advantage of high efficiency of blowing and replacement by simultaneous inflation and deflation. In addition, since this method has a high replacement efficiency, under certain circumstances, the second preset time can be appropriately extended to achieve more thorough replacement. However, when there are many branch pipes or blind pipes in the structure of the storage tank, this method cannot effectively cover more areas, and the second preset time should be appropriately reduced.

[0068] S104: When the closing time of the air inlet is greater than or equal to the first preset time, control the exhaust port to open.

[0069] In the pressure-based replacement method, when the gas pressure is greater than or equal to a preset pressure, the air inlet and exhaust ports are closed and the tank is left to rest for a first preset period of time, allowing the second gas to fully exchange within the tank and completely cover the tank's blind legs or branch pipes. After the rest period is complete (i.e., the air inlet is closed for a period greater than or equal to the first preset period), the exhaust port is opened to release the pressure in the tank, allowing the volume fraction of the second gas in the tank to fully cover the entire volume, meeting the replacement requirements.

[0070] In addition, although the pressure replacement method has a high coverage rate, the replacement efficiency of pressure replacement is low, and multiple inflation and deflation are required to pass the test. Moreover, a single inflation generally takes a long time, resulting in a longer total replacement time and a longer working time of the supporting equipment for replacement. There are many safety hazards. Therefore, in this embodiment, blow-off replacement is performed first, and then pressure replacement is performed.

[0071] In one embodiment, if the volume fraction of the second gas in the storage tank still does not meet the replacement requirement after one pressure replacement, the pressure replacement can be repeated. The specific method further includes:

[0072] When the volume fraction is less than the second preset volume fraction, the exhaust port is controlled to be closed, and the second gas is introduced from the air inlet until the volume fraction is greater than or equal to the second preset volume fraction.

[0073] The second preset volume fraction is the volume fraction of the second gas required to meet the replacement requirement, and can be set according to actual needs.

[0074] The volume of the storage tank is 105m3 3 As an example, the second gas is nitrogen. The first gas is set to be air, and the initial nitrogen volume fraction is about 78%. Pressure replacement is performed. The gas distribution after each pressure replacement is as follows: Figure 4a-4e See also the table below:

[0075] Number of replacements Volume fraction of nitrogen 1 94.39％ 2 98.31％ 3 99.52％ 4 99.85％ 5 99.92％

[0076] Table 2 - Changes in nitrogen volume fraction under pressure displacement

[0077] Based on the results, the volume fraction of the second gas after each positive pressure displacement, given a given tank volume, can be determined, thereby determining the number of pressure displacements required. For example, if the nitrogen content is required to be above 96%, two displacements are required. The number of pressure displacements can also be determined based on the volume fraction of the second gas initially stored in the tank and a second predetermined volume fraction to accommodate different initial conditions. For example, if the initial nitrogen content of the tank is 95%, one displacement is required to reach a nitrogen content of 98%.

[0078] Generally speaking, the number of pressure replacements in this embodiment is the difference between the total number of pressure replacements (M) performed alone and the number of replacements (N) corresponding to the volume fraction of the second gas after the purge replacement. Taking nitrogen as an example, the volume fraction of the replaced gas after 900s of purge replacement is 94.41%, which is better than the volume fraction of 94.39% after one positive pressure replacement. The purge replacement effect corresponds to one pressure replacement, N = 1. If the volume fraction of the second gas is to be increased to above 99%, if the total number of pressure replacements (M) performed alone is 3, then in this embodiment, after 900s of purge replacement, the number of positive pressure replacements performed is MN = 2 (the actual mixing amount can reach above 99.52%).

[0079] The following is a detailed explanation using the replacement of long and narrow pipelines such as natural gas pipelines or gas supply pipelines as an example:

[0080] Natural gas pipeline replacement generally uses inert gases such as nitrogen and carbon dioxide to reduce the oxygen concentration to a safe value (usually <2%); then natural gas is used to replace it until the purity meets the standard (methane concentration >90%). For long pipelines, due to the large number of branches and the length of the pipeline, they are generally divided into several sections and replaced section by section to avoid mutual influence and reduce overall risk. However, in actual operation, there are still many branch pipelines without emission outlets; and the efficiency of segmented replacement is low. In this case, the replacement method provided in this embodiment can be used to improve efficiency.

[0081] Depending on the use scenario of the pipeline, the inner diameter of the natural gas transmission pipeline is 100mm-300mm, etc. Taking the DN300 (pipeline parameters) pipeline as an example, the replacement length of the medium and low pressure pipeline is generally set to 0.6km; for nitrogen replacement, the replacement pressure is 0.1MPa; the inlet and outlet ports are both set to 50mm. When blowing and replacing, the nitrogen concentration changes with time as shown in the following curve: Figure 1 As shown. It can be seen that after 370s of blowing, the average nitrogen concentration can reach 98.5%, and the subsequent blowing replacement efficiency decreases significantly, so the blowing is stopped at this time. Continue to perform positive pressure replacement. After multiple replacements, the nitrogen content is higher than 99%. The replacement is completed. If positive pressure replacement is used throughout the process, it will take 2240s and the gas consumption will be 665m 3 Under the combined replacement, the time saved is 1310s and the nitrogen consumption is saved by 345m 3 , nitrogen and gas concentration changes can be found in Figure 5 and Figure 6 .

[0082] This embodiment proposes a combined replacement method of first blowing and then positive pressure replacement to give full play to the advantages of high initial efficiency of blowing and thorough positive pressure replacement, thereby improving the overall replacement efficiency while ensuring thorough replacement and system safety.

[0083] An exemplary embodiment of the present invention further provides a storage tank, which stores a first gas. The storage tank replaces the first gas with a second gas through any gas replacement method as described in the first aspect, and the volume of the storage tank is greater than or equal to a preset volume.

[0084] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered by the scope of protection of the claims of the present invention.

Claims

1. A gas replacement method, characterized in that: Applied to a storage tank storing a first gas, the method comprises: When the exhaust port of the storage tank is open, the second gas is introduced from the gas inlet of the storage tank, and the first gas is discharged from the exhaust port; When the volume fraction of the second gas in the storage tank is greater than or equal to a first preset volume fraction, controlling the exhaust port to close; When the gas pressure in the storage tank is greater than or equal to a preset pressure, controlling the gas inlet to close; When the closing time of the air inlet is greater than or equal to a first preset time, the exhaust port is controlled to open.

2. The gas replacement method according to claim 1, wherein: After controlling the exhaust port of the storage tank to open when the closing time is greater than or equal to the target time, the method further includes: When the volume fraction is less than a second preset volume fraction, the exhaust port is controlled to be closed, and a second gas is introduced from the gas inlet until the volume fraction is greater than or equal to the second preset volume fraction.

3. The gas replacement method according to claim 1, wherein: After the second gas is introduced from the gas inlet of the storage tank while the exhaust port of the storage tank is open, the method further comprises: Recording the duration of the second gas being introduced into the air inlet; When the inflation time is greater than or equal to a second preset time, controlling the exhaust port to close; When the gas pressure in the storage tank is greater than or equal to a preset pressure, controlling the gas inlet to close; When the closing time of the air inlet is greater than or equal to a first preset time, the exhaust port is controlled to open.

4. The gas replacement method according to claim 3, wherein: The second preset duration is determined by inputting the volume of the storage tank and the first preset volume fraction into a pre-built duration determination model.

5. The gas replacement method according to claim 1, wherein: The volume of the storage tank is greater than or equal to a preset volume.

6. The gas replacement method according to claim 1, wherein: The storage tank includes a storage tank body and at least one branch pipeline.

7. The gas replacement method according to claim 1, wherein: The storage tank includes a storage tank body and at least one blind pipe.

8. The gas replacement method according to claim 1, wherein: The step of introducing the second gas from the gas inlet of the storage tank when the exhaust port of the storage tank is open comprises: When the exhaust port of the storage tank is open, the second gas is introduced into the storage tank from the gas inlet at a preset flow rate.

9. A storage tank, characterized in that: The storage tank stores a first gas, and the storage tank replaces the first gas with a second gas through the gas replacement method according to any one of claims 1 to 8.

10. The storage tank according to claim 9, characterized in that The volume of the storage tank is greater than or equal to a preset volume.

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