Dual fuel tanker LNG supply pipe sub-shielding system and working method

Abstract

A secondary shielding system of a dual-fuel oil tanker LNG supply pipe and a working method thereof belong to the field of liquefied natural gas storage and transportation. The system comprises a fuel supply inner pipe, an outer fuel supply pipe arranged outside the fuel supply inner pipe, and an insulation layer arranged outside the outer fuel supply pipe; a pressure and temperature gauge is arranged on the outer fuel supply pipe to detect the pressure and temperature of the medium in the outer pipe; a safety valve and a check valve are arranged on the outer fuel supply pipe, the safety valve is connected to an LNG tank, and the check valve is connected to a gas vent mast. By adding an insulation layer to the LNG fuel supply outer pipe, low-temperature damage to the ship body caused by liquefied natural gas is prevented, a pressure and temperature gauge is arranged above the LNG fuel supply outer pipe to detect the pressure and temperature of the medium in the outer pipe in real time, and the safety valve and the check valve realize effective treatment of the leaked fuel.

Description

Technical Field

[0001] This invention relates to a secondary shielding system and its operating method for a dual-fuel tanker LNG supply pipeline, belonging to the field of liquefied natural gas storage and transportation. Background Technology

[0002] According to the latest requirements of the Maritime Safety Committee, secondary protection is needed for the supply pipeline from the liquefied natural gas (LNG) tank to the equipment room. Because LNG is cold, flammable, and explosive, a leak could cause the ship's structure to become brittle and crack instantly due to the low temperature, and a large amount of vaporized natural gas could trigger an explosion and fire. Existing technologies for secondary shielding devices on LNG supply pipelines for dual-fuel tankers mainly include ventilated double-layer pipes, nitrogen-filled shielding, and vacuum-insulated double-layer pipes. The ventilated double-layer pipe type uses a double-layer pipe structure, with the annular space using mechanical ventilation to vent leaked fuel gas to the atmosphere. This technology requires small-displacement, high-back-pressure, and explosion-proof mechanical fans, but there are few manufacturers of such fans, resulting in high costs and unfavorable space layout on the ship. In vacuum-insulated double-layer tube designs, the annular space of the double-layer tube is under vacuum, requiring extremely high airtightness and stringent insulation processing for the fuel tubes, resulting in high design and construction costs. Nitrogen-filled shielding systems, while using nitrogen at a certain pressure to suppress fuel leakage, experience pressure drops over time, making real-time monitoring of fuel tube leaks impossible. Furthermore, once a leak occurs, it is difficult to address the leaked fuel in real time. Therefore, designing a secondary shielding system that is thermally insulated, low-cost, and capable of real-time handling of leaked fuel is essential. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention provides a secondary shielding system and operating method for the LNG supply pipe of a dual-fuel tanker. By adding an insulation layer to the outer LNG fuel supply pipe, the system prevents liquefied natural gas from causing low-temperature damage to the hull. A pressure thermometer is installed above the outer LNG fuel supply pipe to monitor the pressure and temperature of the medium in the outer pipe in real time. Safety valves and check valves enable effective handling of leaked fuel.

[0004] The technical solution adopted in this invention is: a secondary shielding system for the LNG supply pipe of a dual-fuel tanker, the system comprising an inner fuel supply pipe, an outer fuel supply pipe, and an outer insulation layer.

[0005] A pressure and temperature gauge is installed on the fuel supply outer pipe to detect the pressure and temperature of the medium in the outer pipe;

[0006] A safety valve and a check valve are installed on the fuel supply pipeline. The safety valve is connected to the LNG tank, and the check valve is connected to the venting mast.

[0007] An inner tube support is provided between the inner fuel supply tube and the outer fuel supply tube, and an outer tube support is provided between the outer fuel supply tube and the outer side of the insulation layer. The outer tube support is a structure consisting of two semi-circular interlocking rings, a first half-ring and a second half-ring, which are fixed by bolts. The base of the outer tube support is fixed on the oil tanker, and a slide rail is provided on the base along the length of the tube. One end of the support connector is fixedly installed below the first half-ring, and the other end is fixedly installed with a support slider. The support slider moves along the support slide rail in the length of the tube.

[0008] Furthermore, it also includes a pressure reducing valve, with the fuel supply pipe connected to the pressure reducing valve via a check valve.

[0009] Furthermore, a drain valve is installed at the lowest point of the fuel supply pipe to drain condensate.

[0010] Furthermore, an inner pipe support is provided between the inner fuel supply pipe and the outer fuel supply pipe.

[0011] Furthermore, the thickness of the insulation layer is 80mm ± 10mm.

[0012] A method for operating a secondary shielding system for a dual-fuel tanker LNG supply pipeline includes the following steps:

[0013] S1. Install the inner tube support to support the fuel supply inner tube, and insert the fuel supply inner tube into the fuel supply outer tube; first complete the butt welding of the fuel supply inner tube, perform non-destructive testing on the inner tube weld, and after the testing is qualified, wrap the outer tube HALF half tube in half over the outside of the inner tube to complete the splicing and welding, forming a double-layer structure of inner and outer tubes.

[0014] S2. Assemble the outer pipe support: Fasten the first half ring and the second half ring to the outside of the fuel supply outer pipe and the insulation layer, and tighten them with the outer pipe support bolts; align the support slider with the support base slide rail so that the outer pipe can slide and deform along the length of the pipeline.

[0015] S3. Install a pressure thermometer, safety valve, check valve, pressure reducing valve, and residual discharge valve in sequence on the fuel supply external pipe, and complete the pipeline connection.

[0016] S4. Open the check valve and related pipelines, and fill the fuel supply pipe with the medium through the pressure reducing valve to inertize and replace the space between the inner and outer pipes, expelling air and water vapor. After inertization, maintain the nitrogen pressure at 0.3MPa±0.05MPa, close the relevant valves to the vent mast, so that the nitrogen forms a closed pressure-maintaining environment to prevent outside air and water vapor from entering the interlayer. Monitor the nitrogen pressure and temperature in real time with a pressure thermometer to confirm that the pressure maintenance is stable.

[0017] S5. Normal LNG transport operation phase: liquefied natural gas is transported through the fuel supply inner pipe. During system operation, pressure and temperature gauges continuously monitor nitrogen pressure and temperature to ensure stable operation of the jacket. A small amount of condensate in the jacket collects at the lowest point of the fuel supply outer pipe and is periodically drained by opening the residual vent valve.

[0018] S6. LNG Leakage Emergency Handling Stage: If there is a slight leak in the fuel supply pipe, and the LNG evaporates and vaporizes, causing the interlayer pressure to rise but not to 2.5 MPa, the gas will preferentially be discharged to the venting mast through the check valve; if the leakage increases and the interlayer pressure rises to the safety valve set pressure of 2.5 MPa, the safety valve will open automatically, and the leaked LNG and gas will flow back to the LNG tank.

[0019] S7. System maintenance and pressure holding stage: Regularly check the nitrogen pressure using a pressure thermometer. If the pressure is too low, add nitrogen through the pressure reducing valve to restore the pressure to 0.3MPa. Regularly open the drain valve to discharge condensate.

[0020] S8. System overhaul phase: During overhaul, first release the nitrogen pressure, and then inspect and maintain the inner and outer pipes, valves, and supports.

[0021] The beneficial effects of this invention are as follows: This system adopts a double-layer pipeline with a semi-split outer pipe structure. During construction, the inner pipe welding and flaw detection can be completed first, and then the outer pipe can be assembled and welded. This not only leaves sufficient construction space and ensures that the inner pipe weld is qualified and the pipeline sealing meets the standards, but also reduces the difficulty of installing double-layer pipelines and improves construction efficiency and pipeline welding quality. The inner and outer pipes are supported and isolated by a composite bracket, which, together with a sliding outer pipe bracket, can prevent the inner and outer pipes from contacting each other when the pipeline is deformed, and can also adapt to the thermal expansion and contraction displacement of the pipeline, thus extending the service life of the pipeline. The interlayer is pressurized with nitrogen at 0.3MPa±0.05MPa, which completely isolates it from external air and moisture, preventing the formation of condensate and flammable mixtures. Combined with real-time monitoring by pressure and temperature gauges, and a dual pressure relief and reflux structure with safety valves and check valves, it can vent gas to the vent mast in case of minor LNG leaks and return the medium to the LNG tank in case of overpressure, forming a multi-level safety protection system that significantly improves the safety of LNG transportation and avoids safety hazards caused by leaks. The 80mm thick insulation layer effectively blocks heat transfer, significantly reducing LNG heat absorption and evaporation, and lowering fuel consumption. The entire system is equipped with residual discharge valves, pressure reducing valves, and other valves, which can periodically drain condensate and replenish nitrogen in a timely manner. It is easy to operate and maintain, can operate stably for a long time, and fully meets the safety requirements for LNG transportation in dual-fuel tankers. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the secondary shielding system for a dual-fuel tanker LNG supply pipeline.

[0023] Figure 2 This is a side view of the inner tube support.

[0024] Figure 3 This is a side view of the outer tube support.

[0025] Figure 4 This is a schematic diagram of the installation of a secondary shielding system for a dual-fuel tanker LNG supply pipeline.

[0026] In the diagram: 1. Fuel supply inner pipe, 2. Fuel supply outer pipe, 3. Insulation layer, 4. Pressure thermometer, 5. Safety valve, 6. Check valve, 7. Pressure reducing valve, 8. Residual discharge valve, 9. Inner pipe support, 10. Outer pipe support, 10a. Support base, 10b. Support slide, 10c. Support slider, 10d. Support connector, 10e. First half ring, 10f. Second half ring, 11. Inner pipe medium, 12. Outer pipe medium, 13. Outer pipe support bolt, 14. Inner pipe weld, 15. Outer pipe half-pipe. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0029] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps described in these embodiments do not limit the scope of the invention. It should also be understood that, for ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following figures denote similar items; therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0030] In the description of this invention, it should be understood that the orientation or positional relationship indicated by directional terms such as "front, back, up, down, left, right", "horizontal, vertical, horizontal" and "top, bottom" is generally based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing this invention and simplifying the description. Unless otherwise stated, these directional terms do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the scope of protection of this invention. The directional terms "inner" and "outer" refer to the inner and outer contours relative to the outline of each component itself.

[0031] For ease of description, spatial relative terms such as "above," "over," "on the upper surface of," "above," etc., are used herein to describe the spatial positional relationship of a device or feature as shown in the figures to other devices or features. It should be understood that spatial relative terms are intended to encompass different orientations in use or operation besides the orientation of the device as described in the figures. For example, if the device in the figures is inverted, a device described as "above" or "above" other devices or structures would subsequently be positioned as "below" or "under" other devices or structures. Thus, the exemplary term "above" can include both "above" and "below." The device may also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatial relative descriptions used herein will be interpreted accordingly.

[0032] Furthermore, it should be noted that the use of terms such as "first" and "second" to define components is merely for the purpose of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore should not be construed as limiting the scope of protection of this invention.

[0033] The technical solution of the present invention will be clearly and completely described below through specific embodiments.

[0034] A secondary shielding system for a dual-fuel tanker LNG supply pipeline includes an inner fuel supply pipe 1, an outer fuel supply pipe 2, and an outer insulation layer 3. A pressure thermometer 4 is installed on the outer fuel supply pipe 2 to detect the pressure and temperature of the medium 12 in the outer pipe. A safety valve 5 and a check valve 6 are installed on the outer fuel supply pipe 2. The safety valve 5 is connected to the LNG tank, and the check valve 6 is connected to the vent mast.

[0035] An inner pipe support 9 is provided between the inner fuel supply pipe 1 and the outer fuel supply pipe 2. An outer pipe support 10 is provided between the outer fuel supply pipe 2 and the outer side of the insulation layer 3. The outer pipe support 10 consists of two semi-circular interlocking structures: a first semi-ring 10e and a second semi-ring 10f, which are fixed by outer pipe support bolts 13. The support base 10a of the outer pipe support 10 is fixed to the oil tanker, and a slide rail along the pipe length direction is provided on the support base 10a. One end of the support connector 10d is fixed below the first semi-ring 10e, and the other end is fixed to the support slider 10c. The support slider 10c moves along the support slide rail 10d in the pipe length direction. It also includes a pressure reducing valve 7, which is connected to the outer fuel supply pipe 2 via a check valve 6. A residual discharge valve 8 is provided at the lowest point of the outer fuel supply pipe 2 to discharge condensate. An inner pipe support 9 is provided between the inner fuel supply pipe 1 and the outer fuel supply pipe 2.

[0036] The thickness of insulation layer 3 is 80mm ± 10mm.

[0037] Example 1

[0038] Figure 1 This paper illustrates a secondary shielding system for a dual-fuel tanker LNG supply pipeline. The system comprises an inner fuel supply pipe 1, an outer fuel supply pipe 2, and an insulation layer 3. An inner pipe support 9 is installed between the inner and outer fuel supply pipes 1 and 2. This inner pipe support 9 is composite, ensuring that the inner and outer pipes do not contact each other during pipeline deformation. An outer pipe support 10 is installed between the outer fuel supply pipe 2 and the insulation layer 3. This outer pipe support 10 is divided into two parts, connected by outer pipe support bolts 13. The outer pipe support 10 is sliding, allowing for overall pipeline deformation and movement. The inner pipe medium 11 is liquefied natural gas (LNG), and the outer pipe medium 12 is nitrogen at a pressure of approximately 0.3 MPa. The nitrogen ensures that atmospheric air cannot enter and that water vapor cannot be generated. The insulation layer 3 is approximately 80 mm thick, minimizing heat transfer and LNG evaporation.

[0039] A pressure and temperature gauge 4 is installed on the fuel supply outer pipe 2 to detect the pressure and temperature of nitrogen gas, ensuring the stability of the system operation.

[0040] A safety valve 5 and a check valve 6 are installed on the fuel supply outer pipe 2. When the fuel supply inner pipe 1 leaks, the LNG gas evaporated in the fuel supply outer pipe 2 can be discharged to the venting mast through the check valve 6. When the leakage increases, the LNG in the fuel supply outer pipe 2 flows to the LNG tank through the safety valve 5.

[0041] The fuel supply outer pipe 2 is connected to the pressure reducing valve 7 via the check valve 6. When the pressure of the medium 12 in the outer pipe decreases, nitrogen is replenished through this valve to ensure the stability of the system.

[0042] A drain valve 8 is installed at the lowest point of the fuel supply outer pipe 2. When there is condensate between the inner and outer pipes, it is discharged through the drain valve 8.

[0043] When using the above technical solution, the following steps are included:

[0044] S1. Install the inner tube support 9 to support the fuel supply inner tube 1, and insert the fuel supply inner tube 1 into the fuel supply outer tube 2; first complete the butt welding of the fuel supply inner tube 1, and perform non-destructive testing on the inner tube weld 14. After the testing is qualified, wrap the outer tube HALF half tube 15 in half around the outside of the inner tube to complete the splicing and welding, forming a double-layer structure of inner and outer tubes.

[0045] S2. Assemble the outer pipe support 10: Fasten the first half ring 10e and the second half ring 10f to the outside of the fuel supply outer pipe 2 and the insulation layer 3, and tighten them with the outer pipe support bolts 13; make the support slider 10c cooperate with the support base 10a slide rail so that the outer pipe can slide and deform along the length of the pipeline.

[0046] S3. Install pressure thermometer 4, safety valve 5, check valve 6, pressure reducing valve 7, and residual discharge valve 8 sequentially on the fuel supply external pipe 2, and complete the pipeline connection.

[0047] S4. Open the check valve 6 and related pipelines, and fill the fuel supply outer pipe 2 with outer pipe medium 12 through pressure reducing valve 7 to inertize and replace the space between the inner and outer pipes, and remove air and water vapor; after inertization, maintain the nitrogen pressure at 0.3MPa±0.05MPa, close the relevant valves to the vent mast, so that the nitrogen forms a closed pressure-maintaining environment to prevent outside air and water vapor from entering the interlayer; monitor the nitrogen pressure and temperature in real time through pressure thermometer 4 to confirm that the pressure maintenance is stable;

[0048] S5. Normal LNG transport operation phase: Fuel supply inner pipe 1 transports liquefied natural gas. During system operation, pressure thermometer 4 continuously monitors nitrogen pressure and temperature to ensure stable operation of the jacket. A small amount of condensate in the jacket collects at the lowest point of fuel supply outer pipe 2 and is periodically discharged by opening the residual discharge valve 8.

[0049] S6. LNG Leakage Emergency Handling Stage: If there is a slight leak in the fuel supply inner pipe 1, and the LNG evaporates and vaporizes, causing the interlayer pressure to rise but not to 2.5MPa, the gas will preferentially be discharged to the venting mast through the check valve 6; if the leakage increases and the interlayer pressure rises to the safety valve set pressure of 2.5MPa, the safety valve 5 will open automatically, and the leaked LNG and gas will flow back to the LNG tank.

[0050] S7. System maintenance and pressure holding stage: Regularly check the nitrogen pressure using pressure thermometer 4. If the pressure is too low, add nitrogen through pressure reducing valve 7 to restore the pressure to 0.3MPa; regularly open drain valve 8 to drain condensate.

[0051] S8. System overhaul phase: During overhaul, first release the nitrogen pressure, and then inspect and maintain the inner and outer pipes, valves, and supports.

[0052] By monitoring parameters such as the pressure of the medium filling the outer pipe in real time using a pressure thermometer, it is possible to indirectly determine whether there is a leak in the LNG supply pipe and to promptly investigate and repair it, preventing the leak from expanding further. By wrapping the fuel supply pipe with insulation material, it is possible to effectively reduce the amount of external heat entering the supply pipe, reduce the vaporization rate of LNG, thereby helping to maintain the LNG in a low-temperature liquid state, reduce energy loss, and improve energy utilization efficiency.

[0053] Although embodiments of this patent have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention, the additional scope of which is defined by the appended claims and their equivalents.

Claims

1. A secondary shielding system for a dual-fuel tanker LNG supply pipeline, the system comprising an inner fuel supply pipeline (1), characterized in that: The inner fuel supply pipe (1) is provided with an outer fuel supply pipe (2), and the outer fuel supply pipe (2) is provided with an insulation layer (3). A pressure thermometer (4) is installed on the fuel supply outer pipe (2) to detect the pressure and temperature of the medium (12) in the outer pipe; A safety valve (5) and a check valve (6) are installed on the fuel supply pipe (2). The safety valve (5) is connected to the LNG tank and the check valve (6) is connected to the venting mast. An inner tube support (9) is provided between the inner fuel supply tube (1) and the outer fuel supply tube (2). The outer fuel supply tube (2) is connected to the outer tube support (10) of the insulation layer (3). The outer tube support (10) is a structure in which two semi-circular parts, the first half ring (10e) and the second half ring (10f), are fastened together and fixed by the outer tube support bolt (13). The support base (10a) of the outer tube support (10) is fixed on the oil tanker. A slide rail along the length of the tube is provided on the support base (10a). One end of the support connector (10d) is fixedly provided below the first half ring (10e), and the other end of the support slider (10c) is fixedly provided. The support slider (10c) moves along the support slide rail (10d) in the length of the tube.

2. The secondary shielding system for a dual-fuel tanker LNG supply pipeline according to claim 1, characterized in that: It also includes a pressure reducing valve (7), and the fuel supply pipe (2) is connected to the pressure reducing valve (7) via a check valve (6).

3. The secondary shielding system for a dual-fuel tanker LNG supply pipeline according to claim 2, characterized in that: A drain valve (8) is installed at the lowest point of the fuel supply pipe (2) to drain condensate.

4. The secondary shielding system for a dual-fuel tanker LNG supply pipeline according to claim 3, characterized in that: An inner tube support (9) is provided between the inner fuel supply tube (1) and the outer fuel supply tube (2).

5. The secondary shielding system for a dual-fuel tanker LNG supply pipeline according to claim 4, characterized in that: The thickness of the insulation layer (3) is 80mm ± 10mm.

6. The operating method of the secondary shielding system for a dual-fuel tanker LNG supply pipeline according to any one of claims 1-4, characterized in that, Includes the following steps: S1. Install the inner tube support (9) to support the fuel supply inner tube (1), insert the fuel supply inner tube (1) into the fuel supply outer tube (2); first complete the butt welding of the fuel supply inner tube (1), perform non-destructive testing on the inner tube weld (14), and after the testing is qualified, wrap the outer tube HALF half tube (15) in half around the outside of the inner tube to complete the splicing and welding, forming a double-layer structure of inner and outer tubes; S2. Assemble the outer pipe support (10): Fasten the first half ring (10e) and the second half ring (10f) to the outside of the fuel supply outer pipe (2) and the insulation layer (3), and tighten them with the outer pipe support bolts (13); make the support slider (10c) cooperate with the support base (10a) slide rail so that the outer pipe can slide and deform along the length of the pipeline; S3. Install pressure thermometer (4), safety valve (5), check valve (6), pressure reducing valve (7), and residual discharge valve (8) in sequence on the fuel supply external pipe (2), and complete the pipeline connection; S4. Open the check valve (6) and related pipelines, and fill the fuel supply outer pipe (2) with the outer pipe medium (12) through the pressure reducing valve (7) to inertize and replace the space between the inner and outer pipes, and discharge air and water vapor; after inertization, maintain the nitrogen pressure at 0.3MPa±0.05MPa, close the relevant valves of the venting mast, so that the nitrogen forms a closed pressure-maintaining environment and prevents outside air and water vapor from entering the interlayer; monitor the nitrogen pressure and temperature in real time through the pressure thermometer (4) to confirm that the pressure is stable; S5. Normal LNG transport operation stage: The fuel supply inner pipe (1) transports liquefied natural gas. During system operation, the pressure thermometer (4) continuously monitors the nitrogen pressure and temperature to ensure stable operation of the jacket. A small amount of condensate in the jacket collects at the lowest point of the fuel supply outer pipe (2) and is discharged periodically by opening the residual discharge valve (8). S6. LNG Leakage Emergency Handling Stage: If there is a slight leak in the fuel supply inner pipe (1), the LNG evaporates and vaporizes, causing the interlayer pressure to rise but less than 2.5MPa. The gas will preferentially pass through the check valve (6) to the venting mast. If the leakage increases and the interlayer pressure rises to the safety valve setting pressure of 2.5MPa, the safety valve (5) will open automatically, and the leaked LNG and gas will flow back to the LNG tank. S7. System maintenance and pressure holding stage: Regularly check the nitrogen pressure using a pressure thermometer (4). If the pressure is too low, replenish nitrogen through the pressure reducing valve (7) to restore the pressure to 0.3MPa. Regularly open the drain valve (8) to drain the condensate. S8. System overhaul phase: During overhaul, first release the nitrogen pressure, and then inspect and maintain the inner and outer pipes, valves, and supports.

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