A device and control method for automatic pressurization using circulating back fluid

Abstract

The application discloses a device and a control method for automatic pressurization by recycling back liquid, relates to the field of LNG and energy recovery, and aims at solving the problems of high cost, high energy consumption and incapability of filling during pressurization of the existing pressurization technology. The liquid inlet of the pressurization vaporizer is connected to the back liquid pipeline of the LNG liquid filling machine and the front end liquid leading pipeline of the LNG low-temperature submerged liquid pump respectively, the temperature transmitter is used for monitoring the temperature of the gas outlet of the pressurization vaporizer, and it is selected whether the recycling back liquid is directly returned to the storage tank or is returned to the storage tank after being vaporized by the pressurization vaporizer. When the filling is continuously performed, the LNG low-temperature submerged liquid pump is used for leading the liquid to the front end of the pressurization vaporizer to be vaporized, so that the storage tank is pressurized. The application does not affect the filling operation during pressurization, and has the characteristics of low power consumption, high efficiency and low cost.

Description

Technical Field

[0001] This invention relates to the field of LNG and energy recovery, and in particular to a device and control method for automatically pressurizing circulating return liquid. Background Technology

[0002] Statistics show that during LNG refueling operations, when the daily refueling volume reaches 15 tons / day or more, the liquid in the LNG cryogenic storage tank will flow out too quickly, and the pressure in the LNG cryogenic storage tank will drop below 0.2 MPa. This will affect the pressure after the pump (pressure after the pump P3 = storage tank pressure P1 + submersible pump pressurization P2), thereby affecting the speed of vehicle refueling or making it impossible to fill the vehicle's gas tank. It is necessary to promptly and quickly pressurize the LNG cryogenic storage tank.

[0003] In addition, for LNG cryogenic submerged pumps to operate normally, the pump pool inlet needs to meet a certain required net positive suction head (NPSH). Various factors can affect the LNG cryogenic submerged pump's NPSH, including: the relative height difference between the LNG cryogenic storage tank and the pump pool, the layout, pipe diameter, bends, and slope of the process pipelines. This will affect the LNG cryogenic storage tank's ability to supply liquid to the cryogenic pump pool. Insufficient liquid supply will cause phenomena such as cavitation, insufficient pressurization, and no-load operation of the LNG cryogenic submerged pump during the filling process, affecting the normal operation and service life of the LNG cryogenic submerged pump. To overcome this problem, it is also necessary to perform timely and rapid pressurization operations on the LNG cryogenic storage tank.

[0004] Currently, the traditional pressurization method used in LNG refueling stations involves pressurizing the LNG cryogenic storage tanks separately when refueling operations are stopped. This means that when refueling volumes are large (e.g., daily refueling exceeding 15 tons), switching from standby mode to the saturation adjustment process for pressurization disrupts the operation of the refueling equipment. Refueling cannot be carried out during pressurization; it must wait until pressurization is complete before refueling can begin. For example, Chinese patent document CN111536413A discloses a device that directly utilizes the cold energy of LNG to drive an LNG high-pressure pump for vaporization. This device uses a plug pump and cylinders to dynamically adjust the pressure of each CNG storage tank. When the high-pressure tank pressurizes the low-pressure tank, it draws in LNG. After the high-pressure tank loses pressure, the LNG enters the vaporizer and vaporizes, then repressurizes the high-pressure tank. In addition to stopping the refueling operation during pressurization, this scheme requires the continuous injection of new cryogenic LNG to pressurize the high-pressure storage tank. It needs to ensure a sufficient source of cryogenic LNG and requires high-strength embolized pumps and cylinders for support. The hardware cost of the equipment is high, and the cryogenic LNG needs to be vaporized, resulting in high energy consumption. Summary of the Invention

[0005] The purpose of this invention is to provide a device and control method for automatic pressurization using circulating return liquid, addressing all or part of the problems mentioned above. Through low-cost pipeline design, it efficiently utilizes the high-temperature liquid of the circulating return liquid for automatic pressurization, reducing the need for pressurization using low-temperature liquid, thereby solving the problems of high cost, high energy consumption, and inability to add liquid during pressurization in existing pressurization technologies.

[0006] The technical solution adopted in this invention is as follows:

[0007] An automatic pressurization device utilizing circulating liquid return includes an LNG cryogenic storage tank, at least one LNG cryogenic submersible pump, a booster vaporizer, at least one LNG dispenser, a temperature transmitter, and a PLC, wherein the temperature transmitter is connected to the outlet of the booster vaporizer.

[0008] The outlet of the LNG cryogenic storage tank is connected to the first inlet of each LNG cryogenic submersible pump via a first pipeline; the first outlet of each LNG cryogenic submersible pump is connected to the inlet of at least one LNG dispenser via a second pipeline; the return outlet of each LNG dispenser is connected to the top and bottom of the LNG cryogenic storage tank via a third pipeline, and a regulating valve T1 is installed on the main line of the third pipeline; the inlet of the booster vaporizer is connected to the inlet end of the regulating valve T1 via a fourth pipeline, the outlet of the booster vaporizer is connected to the outlet end of the regulating valve T1 via a fifth pipeline, and the inlet of the booster vaporizer is also connected to the first inlet of at least one of the LNG cryogenic submersible pumps via a sixth pipeline;

[0009] The first pipeline is connected in series with a first manual valve and a first electric valve; the second pipeline is connected in series with a second manual valve and a second electric valve; the branch of the third pipeline connecting to the top of the LNG cryogenic storage tank is connected in series with a third manual valve and a third electric valve, and the branch of the third pipeline connecting to the bottom of the LNG cryogenic storage tank is connected in series with a fourth manual valve and a fourth electric valve; a fifth manual valve is installed on the return port of each LNG dispenser; a fifth electric valve is installed on the fourth pipeline; a sixth manual valve is installed on the fifth pipeline; and a seventh manual valve is installed on the sixth pipeline.

[0010] The regulating valve T1, each electrical valve, and the temperature transmitter are respectively connected to the PLC.

[0011] Furthermore, the first, second, third, and fifth manual valves are normally open; the fourth manual valve is normally closed.

[0012] Furthermore, the inlet of the booster vaporizer is connected to the liquid phase valve of the LNG tanker via a seventh pipeline; the outlet of the booster vaporizer is connected to the gas phase valve of the LNG tanker via an eighth pipeline; and the outlet valve of the LNG tanker is connected to the outlet end of the regulating valve T1 via a ninth pipeline.

[0013] Furthermore, at least one of the LNG cryogenic submersible pumps has its second inlet connected to the ninth pipeline, and its second outlet is connected to the first inlet of the LNG cryogenic storage tank via the tenth pipeline.

[0014] The present invention also provides a control method for automatic pressurization using circulating return liquid, which is based on the above-mentioned device for automatic pressurization using circulating return liquid, and the control method includes:

[0015] When the LNG cryogenic storage tank needs to be pressurized to saturation, in standby or refueling mode, the PLC controls the regulating valve T1 to be completely closed, controls the fifth and third electric valves to be opened, and controls the fourth electric valve to be closed; the sixth manual valve is manually opened and the seventh manual valve is closed, so that the return liquid from each of the LNG dispensers enters the pressurizer vaporizer through the third and fourth pipelines for pressurization, and then flows into the LNG cryogenic storage tank through the fifth and third pipelines for pressurization.

[0016] Furthermore, when the automatic pressurization function is enabled, the PLC automatically executes the corresponding pressurization control strategy based on the temperature feedback from the temperature transmitter when the temperature reaches the corresponding threshold.

[0017] Furthermore, based on the temperature feedback from the temperature transmitter, the PLC automatically executes the corresponding pressurization control strategy when the temperature reaches a corresponding threshold, including:

[0018] When the LNG cryogenic storage tank needs to be pressurized to saturation, the PLC controls the pressurization based on the temperature feedback from the temperature transmitter as follows:

[0019] When the temperature is below -20 degrees Celsius, the PLC controls the opening of the regulating valve T1 to increase, so that all or most of the return liquid from the LNG dispenser flows directly into the LNG cryogenic storage tank through the third pipeline.

[0020] When the temperature rises back to 0 degrees Celsius, the PLC controls the opening of the regulating valve T1 to decrease, thereby increasing the amount of LNG return liquid flowing into the booster vaporizer for pressurization.

[0021] Furthermore, control methods also include:

[0022] When the LNG cryogenic storage tank does not require saturation pressurization, the PLC controls the fifth electrical valve to close and controls the regulating valve T1 to fully open.

[0023] Furthermore, control methods also include:

[0024] During continuous refueling, the PLC automatic pressurization function is deactivated. The PLC controls the fifth electrical valve to close and controls the regulating valve T1 to fully open. At least one of the seventh manual valves is manually opened, so that the LNG cryogenic submersible pump front end priming liquid flows into the pressurizer for pressurization, and then flows into the LNG cryogenic storage tank through the fifth pipeline and the third pipeline for pressurization.

[0025] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0026] 1. This invention allows for manual operation of the configuration system to control the pressurization process at any time during refueling or standby, without affecting the refueling operation of the vehicle.

[0027] 2. This invention utilizes a PLC-based response strategy to the temperature feedback from the temperature transmitter. This strategy enables the return liquid from the LNG dispenser to be directly returned to the LNG cryogenic storage tank at low temperatures, and the return liquid to be promptly diverted to the booster vaporizer for pressurization at high temperatures. This maximizes the use of the cold energy from the LNG dispenser's return liquid to pressurize the LNG cryogenic storage tank, thereby reducing system power consumption and improving the vaporization efficiency of the booster vaporizer.

[0028] 3. This invention fully utilizes the high-temperature return liquid from the LNG dispenser for pressurization, minimizing the use of cryogenic liquid from the LNG cryogenic storage tank for pressurization, thus reducing energy consumption. Furthermore, it avoids the adverse effect of saturated gas in the return pipe directly returning to the LNG cryogenic storage tank, which could cause the liquid temperature inside the tank to rise.

[0029] 4. This invention only requires simple pipelines and valves that meet standard requirements to achieve closed-loop control of pressurization, resulting in low hardware costs. Attached Figure Description

[0030] The present invention will be described by way of example and with reference to the accompanying drawings, wherein:

[0031] Figure 1 This is an example of an automatic pressurization device that utilizes circulating return liquid for pressurization.

[0032] Figure 2 This is an example of an automatic pressurization device that utilizes circulating return liquid to pressurize cryogenic liquid. Detailed Implementation

[0033] All features disclosed in this specification, or steps in all methods or processes disclosed herein, may be combined in any way, except for mutually exclusive features and / or steps.

[0034] Any feature disclosed in this specification (including any appended claims and abstract) may be replaced by other equivalent or similar features, unless specifically stated otherwise. That is, unless specifically stated otherwise, each feature is merely one example of a series of equivalent or similar features.

[0035] Example 1

[0036] This embodiment uses the design of two LNG cryogenic submersible pumps and two LNG dispensers as an example to introduce a device that utilizes automatic pressurization through circulating liquid return. See appendix. Figure 1 It includes an LNG cryogenic storage tank S1, a first LNG cryogenic submersible pump M1, a second LNG cryogenic submersible pump M2, a booster vaporizer H1, a first LNG dispenser K1, a second LNG dispenser K2, a temperature transmitter TT, and a PLC. The temperature transmitter TT is connected to the outlet of the booster vaporizer H1.

[0037] The outlet of the LNG cryogenic storage tank is connected to the inlet of the first LNG cryogenic submersible pump M1 and the second LNG cryogenic submersible pump M2 via two first pipelines. A first manual valve and a first electric valve are connected in series on the first pipelines. Specifically, the first pipeline connecting the first LNG cryogenic submersible pump M1 is connected in series with manual valve V106 and electric valve GV006, while the first pipeline connecting the second LNG cryogenic submersible pump M2 is connected in series with manual valve V105 and electric valve GV005.

[0038] The first outlet of the first LNG cryogenic submersible pump M1 is connected to the inlet of the first LNG dispenser K1 via a second pipeline, and the first outlet of the second LNG cryogenic submersible pump M2 is connected to the inlet of the second LNG dispenser K2 via a second pipeline. A second manual valve and a second electric valve are connected in series on the second pipeline. Specifically, a manual valve V210 and an electric valve GV009 are connected in series on the second pipeline between the first LNG cryogenic submersible pump M1 and the first LNG dispenser K1, and a manual valve V208 and an electric valve GV008 are connected in series on the second pipeline between the second LNG cryogenic submersible pump M2 and the second LNG dispenser K2.

[0039] The return ports of the first LNG dispenser K1 and the second LNG dispenser K2 are both connected to the LNG cryogenic storage tank S1 via a third pipeline. This third pipeline has two branches near the dispenser end: one connects to the first LNG dispenser K1 and is equipped with a manual valve V209; the other connects to the second LNG dispenser K2 and is equipped with a manual valve V207 (manual valves V209 and V207 constitute the fifth manual valve). Similarly, the third pipeline has two branches near the LNG cryogenic storage tank S1: one connects to the top of the LNG cryogenic storage tank S1 and is connected in series with a manual valve V103 and an electric valve GV003 (i.e., the third manual valve and the third electric valve); the other connects to the bottom of the LNG cryogenic storage tank S1 and is connected in series with a manual valve V104 and an electric valve GV004 (i.e., the fourth manual valve and the fourth electric valve). A regulating valve T1 is installed on the main line of the third pipeline. By adjusting the opening of the regulating valve T1, the flow rate through the regulating valve T1 can be controlled.

[0040] The inlet of the booster vaporizer H1 is connected to the inlet of the regulating valve T1 via a fourth pipeline. An electric valve GV007 (i.e., the fifth electric valve) is installed on this fourth pipeline. The outlet of the booster vaporizer H1 is connected to the outlet of the regulating valve T1 via a fifth pipeline. A manual valve V203 (i.e., the sixth manual valve) is installed on this fifth pipeline. The inlet of the booster vaporizer H1 is also connected to the first inlet of the first LNG cryogenic submersible pump M1 via a sixth pipeline. A manual valve V205 (i.e., the seventh manual valve) is installed on this sixth pipeline.

[0041] Each electric valve (GV001~GV009), regulating valve T1, and temperature transmitter TT are connected to the PLC. The temperature transmitter TT monitors the temperature at the outlet of the booster vaporizer H1 and transmits it to the PLC in real time. The PLC controls the opening or closing status of each valve (electric valve and regulating valve T1) according to the boosting strategy to be executed.

[0042] As mentioned earlier, the third pipeline is connected to both the top and bottom of the LNG cryogenic storage tank S1. The pipeline connected to the top can directly inject high-temperature gas into the top of the LNG cryogenic storage tank S1, achieving a rapid pressurization effect. However, when the pipeline connected to the bottom injects high-temperature gas into the bottom of the LNG cryogenic storage tank S1, the heat of the high-temperature gas is absorbed by the cryogenic liquid inside the LNG cryogenic storage tank S1 before the high-temperature gas reaches the top of the LNG cryogenic storage tank S1. This results in a relatively slower pressurization speed, and the temperature of the cryogenic liquid inside the LNG cryogenic storage tank S1 will increase. In this invention, rapid pressurization is required. Therefore, when controlling pressurization, the pipeline connected to the top of the LNG cryogenic storage tank S1 is selected. Based on this design concept, manual valve V104 (i.e., the fourth manual valve) is set to a normally closed state, while the first manual valve (manual valves V105 and V106), the second manual valve (manual valves V208 and V210), the third manual valve (manual valve V103), and the fifth manual valve (manual valves V207 and V209) are set to a normally open state.

[0043] Furthermore, the apparatus in this embodiment also considers pressurizing the LNG tanker. In this embodiment, the inlet of the pressurizing vaporizer H1 is connected to the liquid phase valve V211 of the LNG tanker via a seventh pipeline, and the outlet of the pressurizing vaporizer H1 is connected to the gas phase valve V212 of the LNG tanker via an eighth pipeline. The outlet valve V213 of the LNG tanker is connected to the outlet of the regulating valve T1 via a ninth pipeline. The liquid flowing out of the liquid phase valve V211 of the LNG tanker enters the pressurizing vaporizer H1 via the seventh pipeline, is vaporized, and then flows into the LNG tanker via the gas phase valve V212 of the LNG tanker through the eighth pipeline to achieve pressurization. Under pressure, the unloaded LNG liquid is unloaded into the LNG cryogenic storage tank S1 via the outlet valve V213 through the ninth pipeline and the third pipeline.

[0044] The second inlets of the first LNG cryogenic submersible pump M1 and the second LNG cryogenic submersible pump M2 are connected via the ninth pipeline. The second outlet of the first LNG cryogenic submersible pump M1 is connected to the first inlet of the LNG cryogenic storage tank S1 via a tenth pipeline, on which a manual valve V101 and an electric valve GV001 are connected in series. The second outlet of the second LNG cryogenic submersible pump M2 is connected to the first inlet of the LNG cryogenic storage tank S1 via another tenth pipeline, on which a manual valve V102 and an electric valve GV002 are connected in series.

[0045] The device designed above connects the inlet of the booster vaporizer H1 to the return liquid pipeline of each LNG dispenser. Utilizing high-temperature circulating return liquid, and with PLC-controlled pipeline selection and monitoring of the outlet temperature of the booster vaporizer H1, automatic pressurization control is achieved. The high-temperature return liquid vaporization process has low energy consumption, thus exhibiting low energy consumption characteristics. Furthermore, the PLC's pipeline selection does not affect the refueling pipeline and can be performed during refueling, meaning that pressurization can be achieved during refueling using circulating return liquid, thereby improving refueling efficiency.

[0046] As for Figure 1 , Figure 2 Manual valves V201 and V202 are manually opened when unloading LNG liquid via the LNG cryogenic submersible pump. At this time, the cryogenic LNG liquid from the LNG tanker is unloaded into the LNG cryogenic storage tank S1 through two tenth pipelines. Manual valve V206 is only opened when filling two LNG dispensers using one LNG cryogenic submersible pump. Manual valve V204 is used during precooling.

[0047] Example 2

[0048] This embodiment describes the control method for automatic pressurization of circulating liquid return, based on the device for automatic pressurization of circulating liquid return in Embodiment 1.

[0049] like Figure 1 The diagram shows an example of pressurization using circulating return fluid, where the thick line represents the pressurization flow path.

[0050] When the LNG cryogenic storage tank S1 needs to be saturated and pressurized, in standby or refueling mode, the PLC controls the regulating valve T1 to be completely closed, controls the opening of electrical valves GV007 (fifth electrical valve) and GV003 (third electrical valve), and controls the closing of electrical valve GV004 (fourth electrical valve); the manual valve V203 (sixth manual valve) is opened and the manual valve V205 (seventh manual valve) is closed, so that the return liquid from the first LNG dispenser K1 and the second LNG dispenser K2 enters the pressurizer vaporizer H1 through the manual valves V209 / V207, the third pipeline and the fourth pipeline for pressurization, and then flows into the LNG cryogenic storage tank S1 through the fifth pipeline and the third pipeline for pressurization.

[0051] In addition, the PLC also has an automatic pressurization function, which responds to the temperature at the outlet of the pressurizer vaporizer H1 to execute an automatic pressurization strategy. The PLC's automatic pressurization function is activated when enabled and deactivated when disabled. When the automatic pressurization function is enabled, the PLC automatically executes the corresponding pressurization control strategy based on the temperature feedback from the temperature transmitter TT, when the temperature reaches the corresponding threshold.

[0052] In some embodiments, the PLC automatically executes a corresponding pressurization control strategy based on the temperature feedback from the temperature transmitter when the temperature reaches a corresponding threshold, including:

[0053] When the LNG cryogenic storage tank needs to be pressurized to saturation, the PLC controls the pressurization based on the temperature feedback from the temperature transmitter as follows:

[0054] When the temperature is below -20 degrees Celsius (which can be adjusted to other nearby temperatures based on experience, and is considered an equivalent replacement), the opening of the PLC-controlled regulating valve T1 increases. Due to the air resistance of the booster vaporizer H1, very little liquid will flow into the booster vaporizer H1, causing all or most of the return liquid from the two LNG dispensers to flow directly into the LNG cryogenic storage tank S1 through the third pipeline.

[0055] As time progresses and the temperature recovers to 0 degrees Celsius (or any other temperature), the PLC controls the opening of regulating valve T1 to decrease, thereby increasing the amount of return liquid from the two LNG dispensers flowing into the booster vaporizer H1 for pressurization. In this way, the temperature collected by the temperature transmitter TT is fed back to the PLC in real time, enabling dynamic control of the pressurization regulation by the PLC to ensure that the vaporization efficiency of the booster vaporizer H1 operates at its optimal state.

[0056] Additionally, when LNG cryogenic storage tank S1 does not require saturation pressurization, the PLC-controlled electro-valve GV007 (the fifth electro-valve) is closed, and the control regulating valve T1 is fully open. The return liquid from the two LNG dispensers is then directly returned to LNG cryogenic storage tank S1 via the third pipeline.

[0057] Furthermore, when the LNG filling volume at the site is large, both LNG dispensers are in continuous filling mode. At this time, the process pipeline remains in a cryogenic liquid state, and the LNG dispensers do not require large-scale pre-cooling before filling. The amount of LNG returning from the dispensers that enters the booster vaporizer H1 for vaporization and pressurization is limited; that is, using the circulating return liquid for pressurization cannot achieve the desired effect. In this situation, the PLC automatic pressurization function should be disabled. Figure 2 As shown, the PLC controls the electrical valve GV007 (the fifth electrical valve) to be closed, and controls the regulating valve T1 to be fully open; the manual valve V205 (the seventh manual valve) is manually opened, causing the priming liquid from the front end of the first LNG cryogenic submersible pump M1 to flow into the booster vaporizer H1 for pressurization, and then flow into the LNG cryogenic storage tank S1 through the fifth and third pipelines for further pressurization. Automatic pressure regulation reduces the load on the LNG cryogenic submersible pump, lowers energy consumption, and also reduces abnormal wear on the LNG cryogenic submersible pump, thus lowering maintenance costs.

[0058] The above embodiments are all illustrated using two LNG cryogenic submersible pumps and two LNG dispensers as examples. Those skilled in the art should understand that, under the same principle, other numbers of LNG cryogenic submersible pumps and LNG dispensers can be designed; the numbers do not need to be equal, but obviously the number of LNG dispensers will not be less than the number of LNG cryogenic submersible pumps, that is, at least one LNG dispenser can be connected to one LNG cryogenic submersible pump. This invention is not limited to the specific embodiments described above. This invention extends to any new feature or any new combination disclosed in this specification, as well as any new method or process step or any new combination disclosed.

Claims

1. A device for automatic pressurization using circulating return liquid, characterized in that, It includes an LNG cryogenic storage tank, at least one LNG cryogenic submersible pump, a booster vaporizer, at least one LNG dispenser, a temperature transmitter, and a PLC, wherein the temperature transmitter is connected to the outlet of the booster vaporizer. The outlet of the LNG cryogenic storage tank is connected to the first inlet of each LNG cryogenic submersible pump via a first pipeline. The first outlet of each LNG cryogenic submersible pump is connected to the inlet of at least one LNG dispenser via a second pipeline; the return outlet of each LNG dispenser is connected to the top and bottom of the LNG cryogenic storage tank via a third pipeline, and a regulating valve T1 is installed on the main line of the third pipeline; the inlet of the booster vaporizer is connected to the inlet end of the regulating valve T1 via a fourth pipeline, the outlet of the booster vaporizer is connected to the outlet end of the regulating valve T1 via a fifth pipeline, and the inlet of the booster vaporizer is also connected to the first inlet of at least one of the LNG cryogenic submersible pumps via a sixth pipeline; The first pipeline is connected in series with a first manual valve and a first electric valve; the second pipeline is connected in series with a second manual valve and a second electric valve; the branch of the third pipeline connecting to the top of the LNG cryogenic storage tank is connected in series with a third manual valve and a third electric valve, and the branch of the third pipeline connecting to the bottom of the LNG cryogenic storage tank is connected in series with a fourth manual valve and a fourth electric valve; a fifth manual valve is installed on the return port of each LNG dispenser; a fifth electric valve is installed on the fourth pipeline; a sixth manual valve is installed on the fifth pipeline; and a seventh manual valve is installed on the sixth pipeline. The regulating valve T1, each electrical valve, and the temperature transmitter are respectively connected to the PLC.

2. The device for automatic pressurization using circulating return liquid as described in claim 1, characterized in that, The first, second, third, and fifth manual valves are normally open; the fourth manual valve is normally closed.

3. The device for automatic pressurization using circulating return liquid as described in claim 1, characterized in that, The inlet of the booster vaporizer is also connected to the liquid phase valve of the LNG tanker via a seventh pipeline; the outlet of the booster vaporizer is also connected to the gas phase valve of the LNG tanker via an eighth pipeline; and the outlet valve of the LNG tanker is connected to the outlet end of the regulating valve T1 via a ninth pipeline.

4. The device for automatic pressurization using circulating return liquid as described in claim 3, characterized in that, The second inlet of at least one of the LNG cryogenic submersible pumps is connected to the ninth pipeline, and the second outlet of the LNG cryogenic submersible pump is connected to the first inlet of the LNG cryogenic storage tank via the tenth pipeline.

5. A control method for automatic pressurization using circulating return liquid, characterized in that, This control method is based on the device for automatic pressurization using circulating return liquid as described in any one of claims 1 to 4, and the control method includes: When the LNG cryogenic storage tank needs to be pressurized to saturation, in standby or refueling mode, the PLC controls the regulating valve T1 to be completely closed, controls the fifth and third electric valves to be opened, and controls the fourth electric valve to be closed; the sixth manual valve is manually opened and the seventh manual valve is closed, so that the return liquid from each of the LNG dispensers enters the pressurizer vaporizer through the third and fourth pipelines for pressurization, and then flows into the LNG cryogenic storage tank through the fifth and third pipelines for pressurization.

6. The control method for automatic pressurization using circulating return liquid as described in claim 5, characterized in that, When the automatic pressurization function is enabled, the PLC automatically executes the corresponding pressurization control strategy based on the temperature feedback from the temperature transmitter when the temperature reaches the corresponding threshold.

7. The control method for automatic pressurization using circulating return liquid as described in claim 6, characterized in that, Based on the temperature feedback from the temperature transmitter, the PLC automatically executes the corresponding pressurization control strategy when the temperature reaches a certain threshold, including: When the LNG cryogenic storage tank needs to be pressurized to saturation, the PLC controls the pressurization based on the temperature feedback from the temperature transmitter as follows: When the temperature is below -20 degrees Celsius, the PLC controls the opening of the regulating valve T1 to increase, so that all or most of the return liquid from the LNG dispenser flows directly into the LNG cryogenic storage tank through the third pipeline. When the temperature rises back to 0 degrees Celsius, the PLC controls the opening of the regulating valve T1 to decrease, thereby increasing the amount of LNG return liquid flowing into the booster vaporizer for pressurization.

8. The control method for automatic pressurization using circulating return liquid as described in claim 5, characterized in that, Also includes: When the LNG cryogenic storage tank does not require saturation pressurization, the PLC controls the fifth electrical valve to close and controls the regulating valve T1 to fully open.

9. The control method for automatic pressurization using circulating return liquid as described in claim 6, characterized in that, Also includes: During continuous refueling, the PLC automatic pressurization function is deactivated. The PLC controls the fifth electrical valve to close and controls the regulating valve T1 to open fully. At least one of the seventh manual valves is manually opened, so that the LNG cryogenic submersible pump front end priming liquid flows into the booster vaporizer for pressurization, and then flows into the LNG cryogenic storage tank through the fifth pipeline and the third pipeline for pressurization.

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