LNG distribution vehicle with sub-tank

Abstract

The application relates to the field of LNG distribution vehicles, and discloses a primary and secondary tank of an LNG distribution vehicle, which comprises a tank body and a pipeline system, the tank body comprises a primary tank and a secondary tank, one or more primary tanks are contained in the secondary tank, the primary tank is fixedly connected with the secondary tank through a connecting piece, and the pipeline system comprises liquid passing pipelines, self-pressurizing pipelines and air passing pipelines connected with the primary tank and the secondary tank respectively. The primary and secondary tank of the LNG distribution vehicle is provided, the tank body is arranged in an inner-outer sleeving mode of the primary tank and the secondary tank, and the self-pressurizing time is shortened.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of LNG distribution vehicles, in particular to a primary and secondary tank of an LNG distribution vehicle for distributing small terminals. BACKGROUND

[0002] With the wide application of LNG (liquefied natural gas), the number of LNG customers is increasing. Small customers increase significantly, and small customers have less LNG consumption but a large base, which requires suitable dedicated LNG distribution vehicles to distribute to small customer terminals. Since the main component of LNG is methane, its combustion has very little air pollution, which can meet the requirements of adjusting the energy structure in China, so the development space of LNG distribution vehicles in China is huge.

[0003] The existing LNG distribution vehicles can be divided into large and small types according to the capacity. The tank capacity of small LNG distribution vehicles is generally 4m 3 , 9m 3 or 15m 3 , and the tank capacity of large LNG distribution vehicles is generally about 50m 3 . In order to realize the honeycomb service, the small LNG distribution vehicles usually need to unload multiple times. With the increase of unloading times, the LNG liquid level in the tank gradually decreases, and the pressure in the tank also decreases. In order to realize differential pressure conveying, the tank needs to be self-pressurized, and after reaching the rated pressure difference, unloading can be carried out. However, after multiple unloading, the self-pressurization time of the tank will increase, resulting in an increase in the overall operation time.

[0004] In order to solve the above technical problems, as shown in Figure 1 , the prior art divides the tank into left tank 2 and right tank 3 by partition plate 1, but the above tank will have process problems during manufacturing. The partition plate 1 needs to be full-welded during welding, which causes welding self-stress problems, resulting in poor overall sealing ability and poor fatigue strength. SUMMARY

[0005] The present application mainly solves the technical problems of the prior art that the self-pressurization time of the tank will increase after multiple unloading and that the overall sealing ability and fatigue strength will be poor when the tank is divided by a partition plate. A primary and secondary tank of an LNG distribution vehicle is provided, in which the tank is set as an inner and outer sleeve to shorten the self-pressurization time.

[0006] In order to solve the above technical problems and achieve the above purposes, the application provides a LNG distribution vehicle's primary and secondary tanks, characterized in that it comprises a tank body and a pipeline system, the tank body comprises a primary tank and a secondary tank, the secondary tank is contained in the secondary tank, the primary tank is connected with the secondary tank through a connecting piece, and the pipeline system comprises a liquid pipeline, a self-pressurizing pipeline and a gas pipeline connected with the primary tank and the secondary tank respectively.

[0007] In an implementation, the connecting piece is arranged in a containing cavity between the secondary tank and the primary tank, the connecting piece is arranged at the bottom of the primary tank, and the connecting piece is a base enclosed by a plurality of connecting plates.

[0008] In an implementation, the connecting plate is densely provided with through holes.

[0009] In an implementation, the liquid pipeline comprises an upper liquid pipeline branch for inputting liquefied natural gas and a lower liquid pipeline branch for inputting or outputting liquefied natural gas, the upper liquid pipeline branch is arranged at the top of the tank body, and the lower liquid pipeline branch is arranged at the bottom of the tank body.

[0010] In an implementation, the upper liquid pipeline branch comprises a first liquid pipeline, a second liquid pipeline and an upper liquid pipeline main pipe, the first liquid pipeline and the second liquid pipeline are both communicated with the upper liquid pipeline main pipe, the first liquid pipeline is connected with the primary tank, the second liquid pipeline is connected with the secondary tank, a first liquid valve is arranged on the first liquid pipeline, a second liquid valve is arranged on the second liquid pipeline, and an upper liquid valve is arranged on the upper liquid pipeline main pipe.

[0011] In an implementation, the lower liquid pipeline branch comprises a third liquid pipeline, a fourth liquid pipeline and a lower liquid pipeline main pipe, the third liquid pipeline and the fourth liquid pipeline are both communicated with the lower liquid pipeline main pipe, the third liquid pipeline is connected with the primary tank, the fourth liquid pipeline is connected with the secondary tank, a third liquid valve is arranged on the third liquid pipeline, a fourth liquid valve is arranged on the fourth liquid pipeline, and a lower liquid valve is arranged on the lower liquid pipeline main pipe.

[0012] In an implementation, the third liquid valve, the fourth liquid valve and the lower liquid valve are all connected with a control module, a liquid level meter for detecting the storage of liquefied natural gas in the tank is arranged in the primary tank and / or the secondary tank, the liquid level meter is connected with the control module, and the control module is used for controlling whether the lower liquid pipeline main pipe is communicated with the third liquid pipeline or the fourth liquid pipeline.

[0013] In an embodiment, the self-pressurization pipeline comprises an upper pressurization branch, a lower pressurization branch and a pressurization main pipe, the upper pressurization branch is arranged at the top of the tank body, the lower pressurization branch is arranged at the bottom of the tank body, the upper pressurization branch is connected with the lower pressurization branch through the pressurization main pipe, the pressurization main pipe is provided with a vaporizer, the upper pressurization branch comprises a first pressurization pipe connected with the mother tank and a second pressurization pipe connected with the child tank, the first pressurization pipe is provided with a first pressurization valve, the second pressurization pipe is provided with a second pressurization valve, the lower pressurization branch comprises a third pressurization pipe connected with the mother tank and a fourth pressurization pipe connected with the child tank, the third pressurization pipe is provided with a third pressurization valve, and the fourth pressurization pipe is provided with a fourth pressurization valve.

[0014] In an embodiment, the vent pipeline comprises a first vent pipe, a second vent pipe and a vent main pipe, the first vent pipe and the second vent pipe are both communicated with the vent main pipe, the first vent pipe is connected with the top of the mother tank, the second vent pipe is connected with the top of the child tank, and the first vent pipe and the second vent pipe are both provided with a combined safety valve.

[0015] In an embodiment, the mother tank and the child tank are both provided with a pressure gauge for detecting the internal pressure.

[0016] Compared with the prior art, the mother-child tank of the LNG distribution vehicle has the following beneficial effects:

[0017] 1. The mother tank is sleeved outside the child tank, so when the liquefied natural gas in the child tank is used up and then the liquefied natural gas in the mother tank is used, because the child tank occupies part of the space of the mother tank, the mother tank does not need to repeatedly pressurize the part of the space in the child tank when self-pressurizing, thereby achieving the purpose of saving time, and of course the liquefied natural gas in the mother tank can be used preferentially or the liquefied natural gas in the mother tank and the child tank can be used alternately.

[0018] 2. The mother tank is directly connected with the child tank in a spot welding manner through the connecting piece, and the overall manufacturing process is more simple.

[0019] Therefore, the application has the characteristics of saving time and convenient manufacturing. BRIEF DESCRIPTION OF DRAWINGS

[0020] FIG. 1 is a structural schematic diagram of the prior art; Figure 1 FIG. 2 is a structural schematic diagram of the application;

[0021] FIG. 3 is a structural schematic diagram of the prior art; Figure 2 FIG. 4 is a structural schematic diagram of the application;

[0022] FIG. 5 is a structural schematic diagram of the prior art; Figure 3 FIG. 6 is a line schematic diagram of the application.

[0023] The figure label explanation: 1, partition; 2, left tank body; 3, right tank body; 4, sub tank; 5, mother tank; 6, connecting piece; 7, through hole; 8, first through liquid pipe; 9, second through liquid pipe; 10, upper through liquid main pipe; 11, first through liquid valve; 12, second through liquid valve; 13, upper through liquid main valve; 14, third through liquid pipe; 15, fourth through liquid pipe; 16, lower through liquid main pipe; 17, third through liquid valve; 18, fourth through liquid valve; 19, lower through liquid main valve; 20, control module; 21, liquid level gauge; 22, booster main pipe; 23, vaporizer; 24, first booster pipe; 25, second booster pipe; 26, third booster pipe; 27, fourth booster pipe; 28, first vent pipe; 29, second vent pipe; 30, vent main pipe; 31, combined safety valve; 32, pressure gauge; 33, first booster valve; 34, second booster valve; 35, third booster valve; 36, fourth booster valve. DETAILED DESCRIPTION

[0024] In order to make the purpose, features and advantages of the present application more obvious and easy to understand, the technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0025] In the prior art, the self-pressurization time in the tank after multiple unloading increases, and the overall sealing ability and fatigue strength are poor when the tank body is divided by the partition 1.

[0026] Therefore, the present application provides a sub-mother tank of an LNG distribution vehicle, which comprises a tank body and a pipeline system. The tank body comprises a sub tank 4 and a mother tank 5, the mother tank 5 contains one or several sub tanks 4, the sub tank 4 is connected to the mother tank 5 through a connecting piece 6, and the pipeline system comprises a through liquid pipeline, a self-pressurization pipeline and a vent pipeline connected to the sub tank 4 and the mother tank 5 respectively.

[0027] Embodiment:

[0028] Figure 2 and Figure 3 An embodiment of the sub-mother tank of the LNG distribution vehicle of the present application is shown.

[0029] The LNG distribution vehicle comprises a vehicle frame and a tank body, the tank body is arranged on the vehicle frame, and the tank body is filled with liquefied natural gas, so as to realize liquefied natural gas distribution for small terminal equipment. In the specific embodiments of the present application, the LNG distribution vehicle specifically refers to a small LNG distribution vehicle with small capacity, and preferably, the capacity of the small LNG distribution vehicle is 4m 3 or 9m 3 or 15m3 The small LNG distribution vehicle is used for distribution of small terminal equipment with small storage capacity. The small LNG distribution vehicle needs to be unloaded many times during distribution, and self-pressurization is needed after each unloading for next differential pressure delivery.

[0030] Please refer to Figure 2 The mother- daughter tank 5 of the LNG distribution vehicle includes a tank body and a pipeline system. The tank body is divided into a daughter tank 4 and a mother tank 5 according to the inclusion relationship. The mother tank 5 contains several daughter tanks 4 to form a mother- daughter structure. In this embodiment, when the daughter tank 4 is several, the daughter tanks 4 can be freely arranged in the mother tank 5, or can be arranged in the form of layer-by-layer nesting from the outside to the inside.

[0031] In this embodiment, the tank body can also include one daughter tank 4 and one mother tank 5. The daughter tank 4 is arranged in the mother tank 5 and occupies a certain capacity of the mother tank 5. The daughter tank 4 and the mother tank 5 are both used for storing liquefied natural gas. In the preferred state, the capacity of the whole tank body is 13m 3 , wherein the capacity of the daughter tank 4 is 4m 3 , and the capacity of the mother tank 5 is 9m 3 The above capacity is only one combination of the present application, and the present application is not limited to the above combination.

[0032] In the specific embodiment of the present application, the pipeline system includes a liquid pipeline, a self-pressurization pipeline and a venting pipeline. The liquid pipeline is connected with the daughter tank 4 or the mother tank 5, thereby inputting or outputting liquefied natural gas to or from the mother tank 5 or the daughter tank 4. The self-pressurization pipeline is connected with the daughter tank 4 or the mother tank 5, thereby inputting the liquefied natural gas in the mother tank 5 or the daughter tank 4 after gasification to the mother tank 5 or the daughter tank 4, so as to increase the pressure in the mother tank 5 or the daughter tank 4, thereby creating conditions for differential pressure delivery of the liquefied natural gas. The venting pipeline is connected with the mother tank 5 or the daughter tank 4, thereby automatically discharging gaseous natural gas through the venting pipeline when the pressure in the mother tank 5 or the daughter tank 4 is too high, so as to stabilize the gas pressure in the tank body and prevent overpressure.

[0033] The daughter tank 4 is connected with the mother tank 5 through the connecting piece 6, so as to fix the relative position between the daughter tank 4 and the mother tank 5 and avoid relative displacement of the daughter tank 4 during transportation.

[0034] When it is needed to deliver liquefied natural gas outward, the liquefied natural gas in the daughter tank 4 is first delivered outward through the liquid pipeline, and then the liquefied natural gas in the mother tank 5 is delivered outward through the liquid pipeline after the liquefied natural gas in the daughter tank 4 is used up. Since the daughter tank 4 occupies part of the space of the mother tank 5, the part of the space of the daughter tank 4 is excluded when the mother tank 5 is pressurized, so it is not necessary to repeatedly pressurize the space in the daughter tank 4, thereby achieving the purpose of saving time.

[0035] Of course, the liquefied natural gas in the mother tank 5 can also be preferentially transported out through the liquid passage multiple times until the liquefied natural gas in the mother tank 5 is used up, and then the liquefied natural gas in the daughter tank 4 is transported out through the liquid passage. Since the daughter tank 4 occupies part of the space of the mother tank 5, when the daughter tank 4 is pressurized, the part of the space of the mother tank 5 is excluded, so it is not necessary to repeatedly pressurize the space in the mother tank 5, thereby achieving the purpose of saving time.

[0036] Moreover, the natural gas in the mother tank 5 and the daughter tank 4 can also be alternately used, so that the gas pressures in the daughter tank 4 and the mother tank 5 are kept relatively balanced.

[0037] In the specific embodiments of the present application, the mother tank 5 comprises a main tank body and a head, the main tank body is a semi-closed tank body with an opening at one end, the daughter tank 4 enters into the main tank body from the opening and is connected with the mother tank 5 through the connecting piece 6, and the head is weldedly connected with the main tank body and is full-welded between the head and the main tank body, thereby achieving the closed arrangement of the mother tank 5.

[0038] In the specific embodiments of the present application, the connecting piece 6 is arranged in the containing cavity between the mother tank 5 and the daughter tank 4, the containing cavity is used to store the liquefied natural gas, and the connecting piece 6 is arranged at the bottom of the daughter tank 4, thereby enhancing the firmness, and the connecting piece 6 is a base enclosed by a plurality of connecting plates.

[0039] In order to enhance the flowability of the liquefied natural gas and avoid the waste of the space in the connecting piece, the through holes 7 are densely arranged on the connecting plates, and the shape of the through holes 7 is preferably circular.

[0040] In the specific embodiments of the present application, the daughter tank 4 and the mother tank 5 are both cylindrical tank bodies, the mother tank 5 and the daughter tank 4 are both provided with a central axis, and the mother tank 5 and the daughter tank 4 are coaxially arranged.

[0041] In the specific embodiments of the present application, the liquid passage comprises an upper liquid passage branch and a lower liquid passage branch, the upper liquid passage branch is arranged at the top of the tank body, the lower liquid passage branch is arranged at the bottom of the tank body, the upper liquid passage branch is used to input the liquefied natural gas, and the lower liquid passage branch can be used to input and output the liquefied natural gas. The daughter tank 4 or the mother tank 5 can be divided into a gaseous natural gas layer and a liquid natural gas layer arranged in the upper and lower parts according to the state of the natural gas. When the liquefied natural gas is input through the upper liquid passage branch, the gaseous natural gas layer enters the liquid natural gas layer, thereby liquefying the gaseous natural gas in the gaseous natural gas layer. The lower liquid passage branch is arranged at the bottom of the tank body, so that when the natural gas is output, the output of the liquid natural gas is more convenient due to the gravity of the liquid natural gas itself.

[0042] In the specific embodiments of the present application, the upper liquid passage pipeline includes a first liquid passage 8, a second liquid passage 9 and a liquid passage main pipe. The first liquid passage 8 and the second liquid passage 9 are both in communication with the upper liquid passage main pipe 10. The first liquid passage 8 is connected with the mother tank 5, and the connection point between the first liquid passage 8 and the mother tank 5 is arranged at the top of the mother tank 5. The second liquid passage 9 is connected with the child tank 4, and the connection point between the second liquid passage 9 and the child tank 4 is arranged at the top of the child tank 4. The first liquid passage 8 is provided with a first liquid passage valve 11, which is used to control whether the first liquid passage 8 inputs liquefied natural gas to the mother tank 5. The second liquid passage 9 is provided with a second liquid passage valve 12, which is used to control whether the second liquid passage 9 inputs liquefied natural gas to the child tank 4. The upper liquid passage main pipe 10 is provided with an upper liquid passage main valve 13, which is used to control whether the entire upper liquid passage pipeline can input liquefied natural gas to the tank body.

[0043] In the specific embodiments of the present application, the lower liquid passage branch includes a third liquid passage 14, a fourth liquid passage 15 and a lower liquid passage main pipe 16. The third liquid passage 14 and the fourth liquid passage 15 are both in communication with the lower liquid passage main pipe 16. The third liquid passage 14 is connected with the mother tank 5, and the connection point between the third liquid passage 14 and the mother tank 5 is arranged at the top of the mother tank 5. The fourth liquid passage 15 is connected with the child tank 4, and the connection point between the fourth liquid passage 15 and the child tank 4 is arranged at the top of the child tank 4. The third liquid passage 14 is provided with a third liquid passage valve 17, which is used to control whether the third liquid passage 14 inputs or outputs liquefied natural gas to the mother tank 5. The fourth liquid passage 15 is provided with a fourth liquid passage valve 18, which is used to control whether the fourth liquid passage 15 inputs or outputs liquefied natural gas to the child tank 4. The lower liquid passage main pipe 16 is provided with a lower liquid passage main valve 19, which is used to control whether the entire lower liquid passage pipeline can input or output liquefied natural gas to the tank body.

[0044] In the specific embodiments of the present application, the child tank 4 and / or the mother tank 5 is provided with a liquid level meter 21 for checking the storage of liquefied natural gas in the tank. The liquid level meter 21 includes a child tank liquid level meter and a mother tank liquid level meter. The child tank liquid level meter is used to detect the storage of liquefied natural gas in the child tank 4, and the mother tank liquid level meter is used to detect the storage of liquefied natural gas in the mother tank 5. The liquid level meter 21 is preferably a differential pressure liquid level meter, which is an instrument that calculates the level of a substance in a container (differential pressure) by measuring the pressure difference at two different points of the container. The two detection points of the mother tank liquid level meter are respectively located at the top and the bottom of the mother tank 5, and the two detection points of the child tank liquid level meter are respectively located at the top and the bottom of the child tank 4.

[0045] Please refer to Figure 3The liquid level meter 21 is connected with the third liquid passage valve 17 and the fourth liquid passage valve 18 through the control module 20, and the control module 20 is used for controlling whether the lower liquid passage main pipe 16 is communicated with the third liquid passage pipe 14 or the fourth liquid passage pipe 15. When the liquid level meter 21 detects that the liquefied natural gas storage in the sub-tank 4 or the mother tank 5 is insufficient, the control module 20 controls the third liquid passage valve 17 or the fourth liquid passage valve 18 to select the remaining sub-tank 4 or the mother tank 5 to deliver natural gas.

[0046] In the specific embodiment of the present application, the self-pressurization pipeline includes an upper pressurization branch, a lower pressurization branch and a pressurization main pipe 22. The upper pressurization branch is arranged at the top of the tank body, and the lower pressurization branch is arranged at the bottom of the tank body. The upper pressurization branch is connected with the lower pressurization branch through the pressurization main pipe 22, and a vaporizer 23 is arranged on the pressurization main pipe 22. The liquefied natural gas in the lower pressurization branch is output, gasified and pressurized through the vaporizer 23, and then the gasified and pressurized gaseous natural gas is delivered into the tank body, so as to realize self-pressurization in the tank.

[0047] The upper pressurization branch includes a first pressurization pipe 24 and a second pressurization pipe 25. The first pressurization pipe 24 is connected with the mother tank 5, and the connection point of the first pressurization pipe 24 with the mother tank 5 is arranged at the top of the mother tank 5. The second pressurization pipe 25 is connected with the sub-tank 4, and the connection point of the second pressurization pipe 25 with the sub-tank 4 is arranged at the top of the sub-tank 4. A first pressurization valve 33 is arranged on the first pressurization pipe 24, and the first pressurization pipe 24 is used for controlling whether the mother tank 5 is communicated with the pressurization main pipe 22. A second pressurization valve 34 is arranged on the second pressurization pipe 25, and the second pressurization pipe 25 is used for controlling whether the sub-tank 4 is communicated with the pressurization main pipe 22.

[0048] The lower pressurization branch includes a third pressurization pipe 26 and a fourth pressurization pipe 27. The third pressurization pipe 26 is connected with the mother tank 5, and the connection point of the third pressurization pipe 26 with the mother tank 5 is arranged at the bottom of the mother tank 5. The fourth pressurization pipe 27 is connected with the sub-tank 4, and the connection point of the fourth pressurization pipe 27 with the sub-tank 4 is arranged at the bottom of the sub-tank 4. A third pressurization valve 35 is arranged on the third pressurization pipe 26, and the third pressurization valve 35 is used for controlling whether the lower pressurization branch is communicated with the mother tank 5. A fourth pressurization valve 36 is arranged on the fourth pressurization pipe 27, and the fourth pressurization valve 36 is used for controlling whether the lower pressurization branch is communicated with the sub-tank 4.

[0049] In the specific embodiment of the present application, the gas passage pipeline includes a first gas passage pipe 28, a second gas passage pipe 29 and a gas passage main pipe 30. The first gas passage pipe 28 and the second gas passage pipe 29 are both communicated with the gas passage main pipe 30. The first gas passage pipe 28 is connected with the top of the mother tank 5, and the second gas passage pipe 29 is connected with the top of the sub-tank 4. A combined safety valve 31 is arranged on the first gas passage pipe 28 and the second gas passage pipe 29. A rated gas pressure value is arranged in the combined safety valve. When the gas pressure in the sub-tank 4 or the mother tank 5 is greater than the rated gas pressure value, the combined safety valve 31 is used for exhausting gas.

[0050] In the specific embodiments of the present application, the mother tank 5 and the sub-tank 4 are both provided with pressure gauges 32, which include a mother tank 5 pressure gauge 32 arranged in the mother tank 5 and a sub-tank 4 pressure gauge 32 arranged in the sub-tank 4, the mother tank 5 pressure gauge 32 being used to detect the pressure in the mother tank 5, and the sub-tank 4 pressure gauge 32 being used to monitor the pressure in the sub-tank 4.

[0051] In the description of the present application, the description of the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. In addition, different embodiments or examples described in the present application and the features of different embodiments or examples can be combined and combined by those skilled in the art without contradiction.

[0052] In addition, the terms "first", "second" are only for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined with "first", "second" can explicitly or implicitly include at least one of the features. In the description of the present application, the meaning of "a plurality of" is two or more, unless otherwise specifically limited.

[0053] The above is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art can easily think of changes or replacements within the technical scope disclosed in the present application, which should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A sub-containers for LNG distribution vehicles, characterized in that, The application relates to a liquefied natural gas tank and pipeline system, which comprises a tank body and a pipeline system. The tank body comprises a sub-tank (4) and a mother tank (5), the mother tank (5) contains one or several sub-tanks (4), the sub-tank (4) is fixedly connected with the mother tank (5) through a connecting piece (6), and the mother tank (5) and the sub-tank (4) are alternately used so that the gas pressure in the mother tank (5) and the sub-tank (4) is relatively balanced. The pipeline system comprises a liquid passing pipeline, a self-pressurizing pipeline and a gas passing pipeline which are respectively connected with the sub-tank (4) and the mother tank (5). The liquid passing pipeline comprises an upper liquid passing branch for inputting liquefied natural gas and a lower liquid passing branch for inputting or outputting liquefied natural gas, the upper liquid passing branch is arranged at the top of the tank body, and the lower liquid passing branch is arranged at the bottom of the tank body. The connecting piece (6) is arranged in a containing cavity between the mother tank (5) and the sub-tank (4), the connecting piece (6) is arranged at the bottom of the sub-tank (4), and the connecting piece (6) is a base which is enclosed by several connecting plates.

2. The sub-containers of an LNG delivery vehicle according to claim 1, characterized in that, The connecting plates are densely provided with through holes (7).

3. The sub-containers of an LNG delivery vehicle according to claim 1, characterized in that, The upper liquid passing branch comprises a first liquid passing pipe (8), a second liquid passing pipe (9) and an upper liquid passing main pipe (10), the first liquid passing pipe (8) and the second liquid passing pipe (9) are communicated with the upper liquid passing main pipe (10), the first liquid passing pipe (8) is connected with the mother tank (5), the second liquid passing pipe (9) is connected with the sub-tank (4), a first liquid passing valve (11) is arranged on the first liquid passing pipe (8), a second liquid passing valve (12) is arranged on the second liquid passing pipe (9), and an upper liquid passing main valve (13) is arranged on the upper liquid passing main pipe (10).

4. The sub-mother tank of the LNG delivery vehicle according to claim 3, characterized in that, The lower liquid passing branch comprises a third liquid passing pipe (14), a fourth liquid passing pipe (15) and a lower liquid passing main pipe (16), the third liquid passing pipe (14) and the fourth liquid passing pipe (15) are communicated with the lower liquid passing main pipe (16), the third liquid passing pipe (14) is connected with the mother tank (5), the fourth liquid passing pipe (15) is connected with the sub-tank (4), a third liquid passing valve (17) is arranged on the third liquid passing pipe (14), a fourth liquid passing valve (18) is arranged on the fourth liquid passing pipe (15), and a lower liquid passing main valve (19) is arranged on the lower liquid passing main pipe (16). The third liquid passing valve (17), the fourth liquid passing valve (18) and the lower liquid passing main valve (19) are connected with a control module (20), a liquid level meter (21) for detecting the storage amount of liquefied natural gas in the tank is arranged in the sub-tank (4) and / or the mother tank (5), the liquid level meter (21) is connected with the control module (20), and the control module (20) is used for controlling whether the lower liquid passing main pipe (16) is communicated with the third liquid passing pipe (14) or the fourth liquid passing pipe (15).

5. The sub-containers of an LNG delivery vehicle according to claim 1, characterized in that, The self-pressurization pipeline comprises an upper pressurization branch, a lower pressurization branch and a pressurization main pipe (22), the upper pressurization branch is arranged at the top of the tank body, the lower pressurization branch is arranged at the bottom of the tank body, the upper pressurization branch is connected with the lower pressurization branch through the pressurization main pipe (22), a carburetor (23) is arranged on the pressurization main pipe (22), the upper pressurization branch comprises a first pressurization pipe (24) connected with the mother tank (5) and a second pressurization pipe (25) connected with the child tank (4), a first pressurization valve (33) is arranged on the first pressurization pipe (24), a second pressurization valve (34) is arranged on the second pressurization pipe (25), the lower pressurization branch comprises a third pressurization pipe (26) connected with the mother tank (5) and a fourth pressurization pipe (27) connected with the child tank (4), a third pressurization valve (35) is arranged on the third pressurization pipe (26), and a fourth pressurization valve (36) is arranged on the fourth pressurization pipe (27).

6. The sub-containers of an LNG delivery vehicle according to claim 1, characterized in that, The vent pipeline comprises a first vent pipe (28), a second vent pipe (29) and a vent main pipe (30), the first vent pipe (28) and the second vent pipe (29) are both communicated with the vent main pipe (30), the first vent pipe (28) is connected with the top of the mother tank (5), the second vent pipe (29) is connected with the top of the child tank (4), and a combined safety valve (31) is arranged on the first vent pipe (28) and the second vent pipe (29).

7. The sub-containers of an LNG delivery vehicle according to claim 1, characterized in that, The mother tank (5) and the child tank (4) are both provided with a pressure gauge (32) for detecting the internal pressure.

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