A combined pipe rack perforation inerting system for liquefied natural gas cargo tanks

Abstract

The present invention relates to the field of liquefied natural gas transportation, and in particular to a combined pipe rack perforation inerting system for liquefied natural gas cargo holds. This system flexibly adjusts the gas flow within the hold through a staggered combined pipe rack structure and a phased aperture and direction design for the pipes. Its core features include: a combined design of multiple independent pipes, with the first pipe extending diagonally downward to a corner of the hold bottom, and the second pipe extending vertically downward and then diagonally upward to the bottom of the other side; gas introduction nozzles with graded apertures to promote uniform gas introduction and diffusion; and a multi-directional hole layout to ensure rapid gas flow and uniform distribution within the hold. This system allows for simultaneous inerting of the entire hold, significantly improving the uniformity of gas distribution, eliminating inerting dead zones, and increasing inerting efficiency.

Description

Technical Field

[0001] The present invention relates to the field of liquefied natural gas transportation, and in particular to a combined pipe rack perforation inerting system for a liquefied natural gas cargo hold. Background Art

[0002] Liquefied natural gas (LNG), a clean and efficient energy source, has seen growing global demand in recent years. LNG transportation is currently the primary means of long-distance natural gas transportation, effectively increasing the utilization rate of natural gas in marine and desert areas. It also reduces transportation costs and the risks associated with laying pipelines due to insufficient gas sources. LNG transportation primarily relies on specially designed LNG carriers capable of safely transporting LNG at ultra-low temperatures (approximately -163°C). LNG carrier construction and technological innovation have become key development areas for the shipbuilding industry.

[0003] The cargo tanks of membrane LNG carriers typically utilize a membrane containment system, constructed from multiple layers of insulation material, that effectively prevents evaporation and leakage of liquefied natural gas (LNG). Compared to traditional spherical and independent cargo tanks, membrane tanks offer a lighter structure and higher space efficiency, making them more suitable for large-scale LNG transportation. The inerting process of the cargo tanks is crucial in the operation of LNG carriers. Inerting involves the introduction of inert gases (such as nitrogen) to reduce the oxygen content within the cargo tanks, piping systems, and between primary and secondary insulation layers to below a safe level. Effective inerting prevents explosions caused by LNG mixing with air upon initial entry into the tanks, thus ensuring safety.

[0004] Currently, many LNG carriers utilize traditional inerting systems, typically using a single pipeline layout. This design fails to effectively cover the entire tank, resulting in uneven gas distribution. This prevents ideal inerting in corners, creating dead zones and increasing potential safety hazards. Furthermore, the single pipeline layout cannot be adjusted to meet the needs of different areas within the tank, leading to gas waste and reduced inerting efficiency. Reducing the oxygen concentration to below 2% by volume typically takes up to 20 hours, reducing the ship's operational efficiency and increasing operating costs.

[0005] Therefore, in view of the shortcomings of existing technologies, a more efficient and flexible inerting system design is needed to improve the safety and economy of LNG ships during the inerting process of liquid cargo tanks. Summary of the Invention

[0006] To address the shortcomings of traditional inerting methods, the present invention provides a modular pipe rack perforation inerting system for liquefied natural gas (LNG) cargo tanks. This system utilizes a staggered modular pipe rack structure and, through phased design of pipe apertures and orientation, adjusts gas flow within the tank, enhancing system flexibility. Application of the modular pipe rack perforation inerting system during the inerting process of LNG cargo tanks allows for simultaneous inerting of the entire tank, resulting in more uniform gas distribution, elimination of dead zones, and improved inerting efficiency.

[0007] To achieve the above-mentioned objectives, the technical solution adopted by the present invention is to provide a combined pipe rack perforation inerting system for liquefied natural gas cargo tanks, including a combined pipe rack, which is composed of two independent pipelines. The first pipeline in the overall structure extends obliquely downward from the tank roof to the bottom corner, and the second pipeline extends vertically downward from the tank roof and then extends obliquely upward to the bottom corner on the other side. The first pipeline is designed to extend obliquely downward from the inlet through a small vertical pipeline to the bottom corner, and the second pipeline is designed to extend vertically downward from the tank roof, connect to a bend-straight-bend structure at the bottom of the liquid tank, and then turn obliquely upward to extend to the top corner on the other side. The tail ends of the pipelines are closed, and nozzles are provided on the walls of the two oblique pipelines. Inert gas enters the natural gas tank only through the nozzles on the walls of the two oblique pipelines.

[0008] Furthermore, multiple groups of gas introduction nozzles are designed on each pipe of the combined pipe rack. The nozzles in each group are evenly spaced along the axial direction of the pipe, and the nozzles in the same group are distributed at equal angles along the circumference of the pipe. The number and aperture of the nozzles are determined by accurate calculation of the cross-sectional area of ​​the pipe. The aperture design adopts a step-by-step increase from top to bottom, and three levels of aperture are set. The bottom aperture is larger to promote initial gas introduction, the middle aperture is moderate to maintain the stability of gas flow, and the top aperture is smaller to enhance the gas diffusion effect.

[0009] Furthermore, different sections of each pipeline adopt hole configurations in different directions, and three different hole layouts are set. The bottom nozzle holes are drilled obliquely downward along the axial direction of the pipeline to promote the rapid entry of inert gas into the cabin, which helps to push the air in the cabin to flow upward and ensure that the inert gas can effectively diffuse to the bottom and corners of the cabin; the middle nozzle holes are drilled in the axial direction perpendicular to the pipeline to promote the mixing and replacement of the overall gas in the cabin and ensure that the inert gas is evenly distributed throughout the cabin; the top nozzle holes are drilled obliquely upward along the axial direction of the pipeline to enhance the rising power of the inert gas at the top and ensure that the inert gas can effectively diffuse to the top and corners of the cabin.

[0010] The beneficial effects of the present invention are:

[0011] 1. The present invention provides a combined pipe rack perforation inerting system for natural gas cargo tanks. Unlike the traditional inerting method of a single pipe intake and gradual upward inerting from the bottom, the system introduces gas through a combined pipe rack structure, multiple pipe paths, and nozzles. This significantly improves the coverage and flow efficiency of the inert gas, achieves simultaneous inerting of the entire tank, and can significantly shorten the inerting time.

[0012] 2. The graded aperture design of this invention utilizes nozzles arranged in an array along the pipe's circumference, with a multi-stage aperture arrangement that gradually increases from top to bottom, ensuring stable and uniform gas flow. The total number of holes and the apertures of each stage are calculated based on the pipe's cross-sectional area. This refined aperture arrangement optimizes the gas introduction process and improves overall inerting efficiency.

[0013] 3. The multi-directional hole layout design of the present invention adopts different drilling directions for the nozzles in different pipe sections, which optimizes the gas flow path, flexibly responds to the needs of the liquid tank, and avoids the gas waste caused by the single pipeline layout in traditional technology that makes it difficult for the inert gas to diffuse to the corners of the liquid tank. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the specific implementation methods of the utility model or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the utility model. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0015] Figure 1 Schematic diagram of an LNG cargo tank of a combined pipe rack perforated inerting system according to one embodiment of the present invention;

[0016] Figure 2 This is a partial diagram of each pipeline of the combined pipe rack according to one embodiment of the present invention;

[0017] Figure 3 This is a partial diagram of each pipeline of the combined pipe rack according to one embodiment of the present invention;

[0018] Figure 4 This is a partial diagram of each pipeline of the combined pipe rack according to one embodiment of the present invention;

[0019] Figure 5 This is a schematic diagram of the orientation of the nozzle holes of each pipeline of the combined pipe rack according to one embodiment of the present invention, which only illustrates the distribution position of each nozzle hole on the pipeline.

[0020] Description of reference numerals:

[0021] 1. Liquefied natural gas cargo hold; 2. Liquid tank inert gas pipeline inlet; 3. Liquid tank gas outlet; 4. Straight inert gas pipeline section; 5. Upper inclined section of combined pipe rack; 6. Lower inclined section of combined pipe rack; 7. Bottom of the upper inclined pipeline of the combined pipe rack; 8. Spray hole at the bottom of the upper inclined pipeline; 9. Top of the lower inclined pipeline of the combined pipe rack; 10. Spray hole at the top of the lower inclined pipeline; 11. Middle of each pipeline of the combined pipe rack; 12. Spray hole at the middle of each pipeline. DETAILED DESCRIPTION

[0022] The following is a clear and complete description of the technical solution of the present invention in conjunction with the accompanying drawings. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0023] In the description of this utility model, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicating positions or relationships, are based on the positions or relationships shown in the accompanying drawings and are intended solely to facilitate the description of this utility model and simplify the description. They do not indicate or imply that the devices or components referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limitations on this utility model. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0024] In the description of this utility model, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; mechanical connections, electrical connections; direct connections, indirect connections through an intermediate medium, and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in this utility model based on the specific circumstances.

[0025] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0026] As introduced in the background technology, the traditional LNG liquid cargo tank inerting system inerts the liquid tank through a single pipeline. During the inerting process, there are problems such as uneven gas distribution, easy formation of inerting dead corners, and low inerting efficiency. In order to solve the above technical problems, the present application proposes a combined pipe rack perforation inerting system for LNG liquid cargo tanks, which has the advantages of simultaneous inerting of the entire field, flexible gas flow, and high inerting efficiency.

[0027] Reference Figures 1 to 5 An embodiment of the present invention provides a combined pipe rack perforation inerting system for a liquefied natural gas cargo tank. The liquefied natural gas cargo tank 1 mainly includes a liquid tank inerting pipeline inlet 2, a liquid tank gas outlet 3, an inert gas pipeline straight pipe section 4, a combined pipe rack upper inclined pipe section 5, and a combined pipe rack lower inclined pipe section 6.

[0028] The combined pipe rack perforation inerting system for liquefied natural gas cargo holds includes a combined pipe rack, which is composed of two independent pipelines. The first pipeline in the overall structure extends obliquely downward from the tank roof to the bottom corner, and the second pipeline extends vertically downward from the tank roof and then extends obliquely upward to the bottom corner on the other side. The first pipeline is designed to extend obliquely downward from the inlet through a small vertical pipeline to the bottom corner, and the second pipeline is designed to extend vertically downward from the tank roof, connect to the elbow-straight pipe-elbow structure at the bottom of the liquid tank, and then turn obliquely upward to extend to the top corner on the other side. The tail end of the pipeline is closed, and nozzles are provided on the walls of the two oblique pipelines. Inert gas enters the natural gas liquid tank only through the nozzles on the walls of the two oblique pipelines.

[0029] Multiple groups of gas introduction nozzles are designed on each pipe of the combined pipe rack. The nozzles in each group are evenly spaced along the axial direction of the pipe, and the nozzles within the group are distributed at equal angles along the circumference of the pipe. The number and aperture of the nozzles are determined by accurate calculation of the cross-sectional area of ​​the pipe. The aperture design adopts a step-by-step increase from top to bottom, with three levels of aperture. The bottom aperture is larger to promote initial gas introduction, the middle aperture is moderate to maintain the stability of gas flow, and the top aperture is smaller to enhance the gas diffusion effect.

[0030] Different sections of each pipeline adopt hole configurations in different directions, and three different hole layouts are set. The bottom nozzle holes are drilled obliquely downward along the axial direction of the pipeline to promote the rapid entry of inert gas into the cabin, which helps to push the air in the cabin to flow upward and ensure that the inert gas can effectively diffuse to the bottom and corners of the cabin; the middle nozzle holes are drilled in the axial direction perpendicular to the pipeline to promote the mixing and replacement of the overall gas in the cabin and ensure that the inert gas is evenly distributed throughout the cabin; the top nozzle holes are drilled obliquely upward along the axial direction of the pipeline to enhance the rising power of the inert gas at the top and ensure that the inert gas can effectively diffuse to the top and corners of the cabin.

[0031] The diameter and wall thickness of each pipe are 450mm and 14.27mm respectively (wall thickness standard is SCH40). There are no nozzle holes on the walls of the straight pipe sections of the two pipes. The lengths of the left and right straight pipe sections are 27750mm and 1500mm respectively.

[0032] The left side of the inert gas straight pipe section 4 is connected in sequence to a 90° elbow, a 500mm straight pipe, and a 45° combined pipe rack inclined pipe section 5. The angle between the above pipe sections and the longitudinal section of the tank is 20°. The combined pipe rack inclined pipe section 5 is equipped with three levels of nozzles of different diameters and directions, totaling 73 groups. Figure 5As shown, each group of nozzles consists of six nozzles evenly distributed along the circumference of the pipe. Twenty-two groups of nozzles 8 are located in the bottom 7 of the upper slanted pipes on the combined pipe rack. These nozzles have a diameter of 20 mm and are oriented at a 45° angle downward along the pipe axis. Forty groups of nozzles 12 are located in the middle 11 of each pipe on the combined pipe rack. These nozzles have a diameter of 14 mm and are oriented perpendicular to the pipe axis. Each nozzle in the middle 11 of the combined pipe rack has a diameter of 10 mm and is oriented at a 45° angle upward along the pipe axis. These nozzle characteristics are consistent with the nozzles 10 at the top of the lower slanted pipes.

[0033] The right straight pipe section is connected in sequence to the 45° elbow and the 45° combined pipe rack inclined lower pipe section 6. The angle between the above pipe sections and the longitudinal section of the tank is 20°. The combined pipe rack inclined lower pipe section 6 is equipped with three levels of nozzles of different diameters and directions, totaling 77 groups. Figure 5 As shown, each group of spray holes has six nozzles evenly distributed along the circumference of the pipe. Twenty-five groups of spray holes are provided in the bottom of the lower slanted pipe of the combined pipe rack. Their diameter and orientation are consistent with the spray holes 8 at the bottom of the upper slanted pipe. Twelve groups of spray holes 10 are provided in the top of the lower slanted pipe of the combined pipe rack. These 10mm diameter nozzles are oriented at a 45° angle upward along the pipe axis.

[0034] The working principle of the combined pipe rack punching inerting system is:

[0035] Inert gas from the inert gas generator at a constant velocity enters the inert gas pipeline's straight section 4 and right-hand straight section through the tank inert gas pipeline inlet 2. Due to pressure differentials and gravity, the inert gas flows along the straight sections, passes through the bends or straight sections, and enters the combined pipe rack's upper and lower sections 5 and 6, respectively. It then enters the LNG tank through the various nozzles on the pipeline and diffuses into the air inside the tank, discharging the air upward. The air is then discharged through the tank gas outlet 3. The inerting operation is complete when the oxygen concentration in the LNG tank falls below 2% by volume.

[0036] The embodiments of this specific implementation method are all preferred embodiments of the present utility model, and are not intended to limit the scope of protection of the present utility model. Therefore, any equivalent changes made based on the structure, shape, and principle of the present utility model should be included in the scope of protection of the present utility model.

Claims

1. A combined pipe rack perforation inerting system for a liquefied natural gas cargo hold, characterized in that: The combined pipe rack is composed of two independent pipes. The first pipe in the overall structure extends obliquely downward from the top of the tank to the corner of the bottom, and the second pipe extends vertically downward from the top of the tank, and then extends obliquely upward to the bottom corner of the other side. The design of the first pipe is to extend obliquely downward from the inlet through a small vertical pipe to the bottom corner. The design of the second pipe is to extend vertically downward from the top of the tank, connect the elbow-straight pipe-elbow structure at the bottom of the liquid tank, and then turn obliquely upward to extend to the top corner of the other side. The tail end of the pipe is closed. The two oblique pipes Nozzles are set on the wall, and inert gas enters the natural gas tank only through the two inclined pipe wall nozzles; multiple groups of gas introduction nozzles are designed on each pipe of the combined pipe rack. The nozzles in each group are evenly spaced along the axial direction of the pipe, and the nozzles in the same group are distributed at equal angles along the circumference of the pipe. The number and aperture of the nozzles are determined by accurate calculation of the cross-sectional area of ​​the pipe. The aperture design adopts a step-by-step increase from top to bottom, and three levels of aperture are set. The bottom aperture is larger to promote initial gas introduction, the middle aperture is moderate to maintain the stability of gas flow, and the top aperture is smaller to enhance the gas diffusion effect.

2. The combined pipe rack perforation inerting system for a liquefied natural gas cargo hold according to claim 1, characterized in that: Different sections of each pipeline adopt hole configurations in different directions, and three different hole layouts are set. The bottom nozzle holes are drilled obliquely downward along the axial direction of the pipeline to promote the rapid entry of inert gas into the cabin, which helps to push the air in the cabin to flow upward and ensure that the inert gas can effectively diffuse to the bottom and corners of the cabin; the middle nozzle holes are drilled in the axial direction perpendicular to the pipeline to promote the mixing and replacement of the overall gas in the cabin and ensure that the inert gas is evenly distributed throughout the cabin; the top nozzle holes are drilled obliquely upward along the axial direction of the pipeline to enhance the rising power of the inert gas at the top and ensure that the inert gas can effectively diffuse to the top and corners of the cabin.

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