Film type storage tank residual liquid recovery device and method

Abstract

The invention discloses a film type storage tank residual liquid recovery device and method, and the device comprises a low-temperature liquid storage device, the feeding port of the low-temperature liquid storage device is connected to a film type storage tank through a first pipeline, and the first pipeline is provided with a first valve; the post-treatment equipment is connected to the discharge port of the low-temperature liquid storage device through a second pipeline and a third pipeline, a second valve is arranged on the second pipeline, and a third valve is arranged on the third pipeline; the vacuum pump is arranged on the third pipeline and is arranged between the third valve and the post-treatment equipment; the gas inlet end of the line sweeping gas pipeline is communicated with a line sweeping gas source, and the gas outlet end of the line sweeping gas pipeline is communicated with the first pipeline and is close to the first valve; and the liquid level meter and the thermometer are arranged in the low-temperature liquid storage device and are respectively used for detecting the liquid level and the temperature in the low-temperature liquid storage device. The device can fully recover the residual liquid in the film type storage tank and effectively reduce the waste amount of the residual liquid.

Description

Technical Field

[0001] The present invention belongs to the field of petrochemical material storage, and in particular relates to a device and method for recovering residual liquid from a membrane type storage tank. Background Art

[0002] my country's oil and natural gas resources are relatively scarce. With the rapid development of its chemical industry in recent years, the consumption of liquefied hydrocarbons has continued to rise. Currently, the main methods used worldwide for aboveground storage of liquefied hydrocarbons include ambient pressure storage, semi-refrigerated storage, and fully refrigerated storage. my country's large-scale cryogenic storage tank technology is becoming increasingly mature and is being used more widely. Among them, membrane tanks, due to their economic and technical advantages such as large effective tank capacity, low cost, short construction period, and long service life, are expected to have extremely promising future development prospects.

[0003] Membrane-type storage tanks can allow for multiple rewarming operations due to their thin stainless steel inner walls and the absence of temperature gradient constraints. Therefore, when performing tank inspections, maintenance, and storage material replacement operations, there is a need to discharge the residual liquid in the tank. The full discharge and recovery of residual liquid in the tank can not only reduce material waste, but also greatly save operating time compared to the natural evaporation rewarming method, facilitate the inspection and maintenance of the tank, and the replacement of stored materials, thereby extending the service life of the tank, improving utilization, and reducing related cost investment. However, the openings of the membrane-type storage tank pipelines are all set at the top of the tank, and are limited by the cavitation margin of the submersible pump in the tank. At present, there is no method in China that can completely discharge and recover the residual liquid in the tank. Therefore, how to quickly discharge and recover the residual liquid in the membrane-type storage tank has important practical research significance and value. Summary of the Invention

[0004] The purpose of the present invention is to provide a safe, reliable and waste-avoiding film-type storage tank residual liquid recovery device and method.

[0005] In order to achieve the above object, the present invention provides a membrane type storage tank residual liquid recovery device, comprising:

[0006] A low-temperature liquid storage device, wherein the feed port of the low-temperature liquid storage device is connected to the membrane-type storage tank via a first pipe, and a first valve is provided on the first pipe;

[0007] a post-processing device connected to the discharge port of the cryogenic liquid storage device through a second pipeline and a third pipeline, wherein the second pipeline is provided with a second valve and the third pipeline is provided with a third valve;

[0008] a vacuum pump, provided on the third pipeline and between the third valve and the post-processing equipment;

[0009] a sweeping gas pipeline, wherein the inlet end of the sweeping gas pipeline is connected to the sweeping gas source, and the outlet end of the sweeping gas pipeline is connected to the first pipeline and is close to the first valve;

[0010] A liquid level meter and a thermometer are provided in the low-temperature liquid storage device and are used to detect the liquid level and temperature in the low-temperature liquid storage device respectively.

[0011] Preferably, the first pipe is in an inverted U-shape, and the first pipe is inserted into the membrane type storage tank from the top of the membrane type storage tank and extends to the bottom of the membrane type storage tank.

[0012] Preferably, the first valve is close to the top of the membrane type storage tank;

[0013] The feed port is located at the bottom of the low-temperature liquid storage device, the discharge port is located at the top of the low-temperature liquid storage device, and the second valve and the third valve are close to the discharge port;

[0014] A sweeping gas valve is provided on the sweeping gas pipeline.

[0015] Preferably, the membrane type storage tank residual liquid recovery device further comprises a moving device for moving the low-temperature liquid storage device, and a liquid drain port is provided at the bottom of the low-temperature liquid storage device.

[0016] Preferably, the first pipe is subjected to cold-insulation treatment.

[0017] Preferably, the membrane type storage tank residual liquid recovery device also includes a controller, which is electrically connected to the liquid level gauge, thermometer, first valve, second valve, third valve, and vacuum pump, and is used to control the operation of the first valve, second valve, third valve, and vacuum pump according to the liquid level detected by the liquid level gauge and the temperature detected by the thermometer.

[0018] Preferably, when the temperature drops below a predetermined temperature and the liquid level starts to rise, the controller controls the vacuum pump to stop operating, controls the second valve to open, and controls the third valve to close.

[0019] Preferably, after the controller controls the vacuum pump to stop operating, when the rising speed of the liquid level is lower than a predetermined speed, the controller controls the third valve to open, controls the second valve to close, and controls the vacuum pump to start operating.

[0020] Another aspect of the present invention provides a method for recovering residual liquid from a membrane-type storage tank, using the aforementioned residual liquid recovery device for a membrane-type storage tank, the method comprising:

[0021] Open the second valve and the third valve, and close the first valve;

[0022] Passing a sweep gas until the sweep gas completely replaces the air in the first pipeline, the cryogenic liquid storage device, the second pipeline, the third pipeline, and the vacuum pump;

[0023] Open the first valve, close the second valve, and start the vacuum pump to perform a vacuum operation;

[0024] When the residual liquid enters the low-temperature liquid storage device, the second valve is opened, the vacuum pump is stopped, and the third valve is closed;

[0025] When the rising speed of the liquid level is lower than a predetermined speed, the third valve is opened, the second valve is closed, and the vacuum pump is started again;

[0026] When the residual liquid in the membrane type storage tank is fully discharged, the vacuum pump is turned off, and the first valve, the second valve and the third valve are closed.

[0027] Preferably, the recovery device further comprises a controller, which is electrically connected to the liquid level gauge, the thermometer, the first valve, the second valve, the third valve, and the vacuum pump, and is used to control the operation of the first valve, the second valve, the third valve, and the vacuum pump according to the liquid level and temperature detected by the liquid level gauge and the thermometer;

[0028] When the temperature drops below a predetermined temperature and the liquid level begins to rise, the controller determines that residual liquid has entered the low-temperature liquid storage device, controls the vacuum pump to stop operating, controls the second valve to open, and controls the third valve to close;

[0029] After the controller controls the vacuum pump to stop operating, when the rising speed of the liquid level is lower than a predetermined speed, the controller controls the third valve to open, controls the second valve to close, and controls the vacuum pump to start operating.

[0030] The beneficial effects of the present invention are as follows: the membrane-type storage tank residual liquid recovery device and method of the present invention fully discharge the residual liquid in the membrane-type storage tank into the low-temperature liquid storage device through pressure difference and siphon action, and further discharge it into the post-processing equipment for treatment, thereby fully recovering the residual liquid that cannot be directly pumped out of the membrane-type storage tank, effectively reducing the amount of residual liquid waste. In addition, compared with the traditional natural evaporation method, the membrane-type storage tank residual liquid recovery device and method of the present invention can achieve rapid rewarming of the membrane-type storage tank, providing convenience for the inspection and maintenance of the membrane-type storage tank after the residual liquid is discharged and the replacement of stored materials, extending the service life of the storage tank, improving the utilization rate, and reducing related costs.

[0031] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The above and other objects, features and advantages of the present invention will become more apparent through a more detailed description of exemplary embodiments of the present invention with reference to the accompanying drawings, wherein like reference numerals generally represent like components throughout the exemplary embodiments of the present invention.

[0033] Figure 1 A structural diagram of a membrane-type storage tank residual liquid recovery device according to an embodiment of the present invention is shown.

[0034] Figure 2 A structural diagram of a membrane-type storage tank residual liquid recovery device according to another embodiment of the present invention is shown.

[0035] Description of Reference Numerals

[0036] 1. Membrane storage tank; 2. Low-temperature liquid storage device; 3. Vacuum pump; 4. Post-processing equipment; 5. Thermometer; 6. Liquid level gauge; 7. First valve; 8. Second valve; 9. Third valve; 10. Sweep gas valve. DETAILED DESCRIPTION

[0037] The preferred embodiments of the present invention will be described in more detail below. Although the preferred embodiments of the present invention are described below, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. Instead, these embodiments are provided to make the present invention more thorough and complete and to fully convey the scope of the present invention to those skilled in the art.

[0038] In this disclosure, unless otherwise indicated, terms such as "first," "second," and "third" are used solely to distinguish between components and do not imply a specific order of connection. In this disclosure, directional terms such as "upper," "lower," "top," and "bottom" generally refer to the top and bottom, or top and bottom, of a device in normal use. "Inside" and "outside" refer to the outline of a device.

[0039] The present invention provides a membrane type storage tank residual liquid recovery device, comprising:

[0040] A low-temperature liquid storage device, wherein the feed port of the low-temperature liquid storage device is connected to the membrane type storage tank through a first pipeline, and a first valve is provided on the first pipeline;

[0041] The post-processing equipment is connected to the discharge port of the low-temperature liquid storage device through a second pipeline and a third pipeline, the second pipeline is provided with a second valve, and the third pipeline is provided with a third valve;

[0042] a vacuum pump, provided on the third pipeline and between the third valve and the post-processing equipment;

[0043] a line-sweeping gas pipeline, wherein the air inlet end of the line-sweeping gas pipeline is connected to the line-sweeping gas source, and the air outlet end of the line-sweeping gas pipeline is connected to the first pipeline and is close to the first valve;

[0044] The liquid level gauge and the thermometer are arranged in the low-temperature liquid storage device and are used to detect the liquid level and temperature in the low-temperature liquid storage device respectively.

[0045] The operating process of the membrane-type storage tank residual liquid recovery device is as follows: Before starting the line sweep, open the second and third valves and close the first valve. Sweep gas is introduced and the line sweeping begins until the sweep gas completely replaces the air in the first pipeline, the cryogenic liquid storage device, the second pipeline, the third pipeline, and the vacuum pump. After the line sweeping is completed, open the first valve, close the second valve, and simultaneously start the vacuum pump to evacuate the air. The operation of the vacuum pump causes the pressure in the first pipeline and the cryogenic liquid storage device to continuously decrease. When the pressure difference between the downward inflection point of the first pipeline along the direction of residual liquid flow and the pressure inside the membrane-type storage tank is greater than the static pressure of the residual liquid in the upward flow direction of the first pipeline, the residual liquid in the tank can flow to the downward inflection point of the first pipeline under the action of the pressure difference. Thereafter, under the dual action of the pressure difference and gravity, it further flows to the cryogenic liquid storage device for storage. A thermometer and liquid level gauge are used to monitor the liquid inflow into the cryogenic liquid storage device. When it is determined that the residual liquid has entered the low-temperature liquid storage device, the second valve is opened, the vacuum pump is shut down, and the third valve is closed. The remaining residual liquid can continue to enter the low-temperature liquid storage device through siphon action, and the gas in the low-temperature liquid storage device enters the post-processing equipment through the second pipeline. During the drainage process after stopping the vacuum pump, when the rising speed of the liquid level drops significantly, the third valve is opened, the second valve is closed, and the vacuum pump is started again to assist in drainage. When the pressure change rate of the diaphragm-type storage tank (pressure measurement can be achieved using a pressure gauge installed on the diaphragm-type storage tank) increases significantly, it means that the residual liquid in the tank has been fully discharged. At this time, the vacuum pump is shut down, and the first valve, second valve, and third valve are closed, and the residual liquid recovery process is completed.

[0046] The membrane-type storage tank residual liquid recovery device of the present invention fully discharges the residual liquid in the membrane-type storage tank into the low-temperature liquid storage device through pressure difference and siphon action. The sweep gas and BOG (Boil-Off Gas, flash gas) mixed gas originally filled in the system are discharged into the post-processing facility, thereby effectively solving the problem of difficult discharge of residual liquid in the membrane-type storage tank, and providing new possibilities for rapid rewarming, completion of inspection and maintenance, material replacement storage, and residual liquid recovery and reuse.

[0047] The vacuum pump is used to extract gas, thereby establishing a pressure differential between the membrane storage tank and the cryogenic liquid storage device. The vacuum pump can be a centrifugal vacuum pump. Post-processing equipment is used to treat the mixed gas consisting of sweep gas and BOG pumped by the vacuum pump and discharged through a second pipeline after the pump is shut down. The cryogenic liquid storage device can be a cryogenic liquid tank truck or other cryogenic liquid storage device. The number of tank trucks required and the size of the cryogenic liquid storage device can be determined based on actual operational requirements.

[0048] In one example, the first pipe is in an inverted U shape, and the first pipe is inserted into the membrane type storage tank from the top and extends to the bottom of the membrane type storage tank, so as to facilitate complete discharge of residual liquid in the storage tank.

[0049] In one example, the first valve is located near the top of the membrane-type storage tank to facilitate the sweep gas to fully expel air from the first pipeline. The feed port is located at the bottom of the cryogenic liquid storage device, the discharge port is located at the top of the cryogenic liquid storage device, and the second and third valves are located near the discharge port.

[0050] In one example, a sweep gas valve is provided on the sweep gas pipeline to facilitate controlling the flow of sweep gas into the sweep gas pipeline according to actual needs.

[0051] In one example, the membrane type storage tank residual liquid recovery device further includes a mobile device for moving the low temperature liquid storage device. A drain port is provided at the bottom of the low temperature liquid storage device to facilitate the discharge of residual liquid in the low temperature liquid storage device, thereby further realizing residual liquid recovery.

[0052] In one example, the first pipe is subjected to a cold insulation treatment to prevent the residual liquid from vaporizing due to heat exchange with the environment during flow. The cold insulation treatment can use, for example, a cold insulation material (such as polyisocyanurate, foam glass, silica aerogel felt, etc.) to effectively isolate the temperature inside the pipe from the external environment.

[0053] In one example, the sweep gas is nitrogen, or other suitable inert gas. The first valve, the second valve, and the third valve may be gate valves.

[0054] In one example, a membrane-type storage tank residual liquid recovery device further includes a controller electrically connected to a liquid level gauge, a thermometer, a first valve, a second valve, a third valve, and a vacuum pump. The controller is configured to control the operation of the first valve, the second valve, the third valve, and the vacuum pump based on the liquid level detected by the liquid level gauge and the temperature detected by the thermometer. More specifically, when the temperature detected by the thermometer drops below a predetermined temperature and the liquid level detected by the liquid level gauge begins to rise, indicating that residual liquid has begun to enter the low-temperature liquid storage device, the controller controls the vacuum pump to stop operation, controls the second valve to open, and controls the third valve to close, thereby allowing the residual liquid to continue to flow into the low-temperature liquid storage device under siphoning. After the controller controls the vacuum pump to stop operation, if the rate of increase of the liquid level detected by the liquid level gauge falls below a predetermined rate, the controller controls the third valve to open, controls the second valve to close, and controls the vacuum pump to start operation to assist in liquid drainage. When the residual liquid in the storage tank has been fully drained, the controller controls the vacuum pump to stop operation and controls the first, second, and third valves to close, thereby concluding the residual liquid recovery process.

[0055] The present invention also provides a method for recovering residual liquid from a membrane-type storage tank, using the aforementioned residual liquid recovery device for a membrane-type storage tank. The method comprises:

[0056] Open the second valve and the third valve, and close the first valve;

[0057] Pass the sweep gas until the sweep gas completely replaces the air in the first pipeline, the cryogenic liquid storage device, the second pipeline, the third pipeline, and the vacuum pump;

[0058] Open the first valve, close the second valve, and start the vacuum pump to perform the vacuum operation;

[0059] When the residual liquid enters the low-temperature liquid storage device, the second valve is opened, the vacuum pump is shut down, and the third valve is closed;

[0060] When the rising speed of the liquid level is lower than the predetermined speed, the third valve is opened, the second valve is closed, and the vacuum pump is started again;

[0061] When the residual liquid in the membrane type storage tank is fully discharged, turn off the vacuum pump and close the first valve, the second valve and the third valve.

[0062] In one example, the recovery device further includes a controller electrically connected to a liquid level gauge, a thermometer, a first valve, a second valve, a third valve, and a vacuum pump, and configured to control the operation of the first valve, the second valve, the third valve, and the vacuum pump based on the liquid level and temperature detected by the liquid level gauge and the thermometer. When the temperature drops below a predetermined temperature and the liquid level begins to rise, the controller determines that residual liquid has entered the low-temperature liquid storage device, controls the vacuum pump to stop operating, controls the second valve to open, and controls the third valve to close. After the controller controls the vacuum pump to stop operating, if the rate of increase of the liquid level falls below a predetermined rate, the controller controls the third valve to open, the second valve to close, and controls the vacuum pump to start operating.

[0063] Example 1

[0064] Figure 1 FIG1 shows a structural diagram of a membrane type storage tank residual liquid recovery device according to an embodiment of the present invention. Figure 1 As shown, the membrane type storage tank residual liquid recovery device includes:

[0065] A low-temperature liquid storage device 2, the feed port of which is connected to the membrane type storage tank 1 via a first pipe, and a first valve 7 is provided on the first pipe;

[0066] The post-processing equipment 4 is connected to the discharge port of the low-temperature liquid storage device 2 through a second pipeline and a third pipeline, respectively. The second pipeline is provided with a second valve 8, and the third pipeline is provided with a third valve 9;

[0067] A vacuum pump 3 is provided on the third pipeline and between the third valve 9 and the post-processing device 4;

[0068] A sweeping gas pipeline, the inlet end of which is connected to the sweeping gas source, and the outlet end of which is connected to the first pipeline and close to the first valve 7;

[0069] The liquid level meter 5 and the thermometer 6 are provided in the low-temperature liquid storage device 2 and are used to detect the liquid level and temperature in the low-temperature liquid storage device respectively.

[0070] The vacuum pump 3 is a centrifugal vacuum pump used to extract gas from the cryogenic liquid storage device 2 and the first pipeline to establish a pressure differential between the membrane storage tank 1 and the cryogenic liquid storage device 2. The post-processing equipment 4 is used to process the mixed gas consisting of sweep gas and BOG pumped by the vacuum pump 3 and discharged through the second pipeline after the pump is stopped. A sweep gas valve 10 is provided on the sweep gas pipeline, and the sweep gas is nitrogen.

[0071] The working process of the membrane-type storage tank residual liquid recovery device according to this embodiment is as follows: Before starting the line sweeping, open the second valve 8 and the third valve 9, and close the first valve 7. The line sweeping gas is introduced and the line sweeping begins until the line sweeping gas completely replaces the air in the first pipeline, the low-temperature liquid storage device 2, the second pipeline, the third pipeline, and the vacuum pump 3. After the line sweeping is completed, open the first valve 7, close the second valve 8, and start the vacuum pump 3 to perform the air extraction operation. The operation of the vacuum pump 3 causes the pressure in the first pipeline and the low-temperature liquid storage device 2 to continuously decrease. When the pressure difference between the downward inflection point of the first pipeline along the direction of residual liquid flow and the membrane-type storage tank 1 is greater than the static pressure of the liquid column of the residual liquid in the upward flow direction of the first pipeline, the residual liquid in the storage tank can flow to the downward inflection point of the first pipeline under the action of the pressure difference. Then, under the dual action of the pressure difference and gravity, it further flows to the low-temperature liquid storage device 2 for storage. The thermometer and liquid level gauge are used to monitor the liquid inflow into the low-temperature liquid storage device 2. When it is determined that the residual liquid has entered the low-temperature liquid storage device 2, the second valve 8 is opened, the vacuum pump 3 is stopped, and the third valve 9 is closed. The remaining residual liquid can continue to enter the low-temperature liquid storage device 2 through siphon action, and the gas in the liquid storage device enters the post-processing equipment 4 through the second pipeline. During the drainage process after stopping the vacuum pump, when the rising speed of the liquid level drops significantly, the third valve 9 is opened, the second valve 8 is closed, and the vacuum pump 3 is started again to assist in drainage. When the pressure change rate of the membrane-type storage tank increases significantly, it means that the residual liquid in the storage tank has been fully discharged. At this time, the vacuum pump 3 is turned off, and the first valve 7, the second valve 8 and the third valve 9 are closed, and the residual liquid recovery process is completed.

[0072] Example 2

[0073] Figure 2 FIG. 1 shows a structural diagram of a membrane type tank residual liquid recovery device according to another embodiment of the present invention. Figure 2 As shown, the only difference between this embodiment and embodiment 1 is that the low-temperature liquid storage device 2 is a low-temperature liquid tank truck to achieve the mobility of the low-temperature liquid storage device.

[0074] While various embodiments of the present invention have been described above, the above description is intended to be illustrative, not exhaustive, and not limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A membrane type storage tank residual liquid recovery device, characterized in that: include: A low-temperature liquid storage device, wherein the feed port of the low-temperature liquid storage device is connected to the membrane-type storage tank via a first pipe, and a first valve is provided on the first pipe; a post-processing device connected to the discharge port of the cryogenic liquid storage device through a second pipeline and a third pipeline, wherein the second pipeline is provided with a second valve and the third pipeline is provided with a third valve; a vacuum pump, provided on the third pipeline and between the third valve and the post-processing equipment; a line-sweeping gas pipeline, wherein the air inlet end of the line-sweeping gas pipeline is connected to the line-sweeping gas source, and the air outlet end of the line-sweeping gas pipeline is connected to the first pipeline and is close to the first valve; A liquid level meter and a thermometer are provided in the low-temperature liquid storage device and are used to detect the liquid level and temperature in the low-temperature liquid storage device respectively.

2. The membrane type storage tank residual liquid recovery device according to claim 1 is characterized in that: The first pipe is in an inverted U-shape, and the first pipe is inserted into the membrane type storage tank from the top of the membrane type storage tank and extends to the bottom of the membrane type storage tank.

3. The membrane type storage tank residual liquid recovery device according to claim 1, characterized in that: The first valve is close to the top of the membrane type storage tank; The feed port is located at the bottom of the low-temperature liquid storage device, the discharge port is located at the top of the low-temperature liquid storage device, and the second valve and the third valve are close to the discharge port; A sweeping gas valve is provided on the sweeping gas pipeline.

4. The membrane type storage tank residual liquid recovery device according to claim 1, characterized in that: It also includes a moving device for moving the low-temperature liquid storage device, and a liquid discharge port is provided at the bottom of the low-temperature liquid storage device.

5. The membrane type storage tank residual liquid recovery device according to claim 1, characterized in that: The first pipe is subjected to cold-insulation treatment.

6. The membrane type storage tank residual liquid recovery device according to claim 1, characterized in that: It also includes a controller, which is electrically connected to the liquid level meter, thermometer, first valve, second valve, third valve, and vacuum pump, and is used to control the operation of the first valve, second valve, third valve, and vacuum pump based on the liquid level detected by the liquid level meter and the temperature detected by the thermometer.

7. The membrane type storage tank residual liquid recovery device according to claim 6, characterized in that: When the temperature drops below a predetermined temperature and the liquid level starts to rise, the controller controls the vacuum pump to stop operating, controls the second valve to open, and controls the third valve to close.

8. The membrane type storage tank residual liquid recovery device according to claim 7, characterized in that: After the controller controls the vacuum pump to stop operating, when the rising speed of the liquid level is lower than a predetermined speed, the controller controls the third valve to open, controls the second valve to close, and controls the vacuum pump to start operating.

9. A method for recovering residual liquid from a membrane type storage tank, characterized in that: Utilizing the membrane type storage tank residual liquid recovery device according to any one of claims 1 to 8, the method comprises: Open the second valve and the third valve, and close the first valve; Passing a sweep gas until the sweep gas completely replaces the air in the first pipeline, the cryogenic liquid storage device, the second pipeline, the third pipeline, and the vacuum pump; Open the first valve, close the second valve, and start the vacuum pump to perform a vacuum operation; When the residual liquid enters the low-temperature liquid storage device, the second valve is opened, the vacuum pump is stopped, and the third valve is closed; When the rising speed of the liquid level is lower than a predetermined speed, the third valve is opened, the second valve is closed, and the vacuum pump is started again; When the residual liquid in the membrane type storage tank is fully discharged, the vacuum pump is turned off, and the first valve, the second valve and the third valve are closed.

10. The method for recovering residual liquid from a membrane type storage tank according to claim 9, characterized in that: The recovery device further includes a controller electrically connected to the liquid level gauge, the thermometer, the first valve, the second valve, the third valve, and the vacuum pump, and configured to control the operation of the first valve, the second valve, the third valve, and the vacuum pump according to the liquid level and temperature detected by the liquid level gauge and the thermometer; When the temperature drops below a predetermined temperature and the liquid level begins to rise, the controller determines that residual liquid has entered the low-temperature liquid storage device, controls the vacuum pump to stop operating, controls the second valve to open, and controls the third valve to close; After the controller controls the vacuum pump to stop operating, when the rising speed of the liquid level is lower than a predetermined speed, the controller controls the third valve to open, controls the second valve to close, and controls the vacuum pump to start operating.

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