Combined pipe frame punching and inerting system for liquefied natural gas cargo hold

Abstract

The invention relates to the field of liquefied natural gas transportation, in particular to a combined pipe frame punching inerting system for a liquefied natural gas cargo hold, and the system flexibly adjusts gas flow in the hold through staggered distributed combined pipe frame structures and staged aperture and direction design of pipelines. The device is characterized in that a plurality of independent pipelines are designed in a combined mode, the first pipeline obliquely extends downwards to the corner of the cabin bottom, and the second pipeline vertically extends downwards and then obliquely extends upwards to the bottom of the other side; gas introduction spray holes with graded apertures are formed, so that uniform introduction and diffusion of gas are promoted; and through multi-direction hole position layout, rapid flowing and uniform distribution of gas in the cabin are ensured. By means of the system, simultaneous inerting of the whole cabin can be achieved, the gas distribution uniformity is remarkably improved, inerting dead angles are eliminated, and the inerting efficiency is improved.

Description

Technical Field

[0001] The 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] As a clean and efficient energy source, liquefied natural gas (LNG) has been in growing demand worldwide in recent years. Many countries around the world have listed natural gas as an important clean energy source, so the proportion of natural gas in international energy supply has also increased year by year, becoming one of the fastest growing energy industries in the world. It is expected that my country's natural gas consumption will reach its peak by 2040.

[0003] Due to limited domestic production capacity, my country needs to import a large amount of natural gas to meet the growing demand. Compared with pipeline imports, offshore liquefied natural gas (LNG) imports are more flexible, with flexible trade, diversified production areas, suitable for peak load regulation, and able to meet rapidly growing demand. LNG transportation is currently the main means of natural gas ocean transportation, which can effectively improve the development and utilization rate of natural gas in marine and desert areas. At the same time, LNG transportation reduces transportation costs and the risks caused by laying pipelines due to insufficient gas sources. The transportation of LNG mainly relies on specially designed LNG ships, which can safely transport liquefied natural gas at ultra-low temperatures (about -163°C). At the same time, the construction and technological innovation of LNG ships have become an important development direction of the shipbuilding industry.

[0004] The liquid cargo tanks of membrane LNG carriers usually adopt a membrane type containment system, which is composed of multiple layers of insulation materials and can effectively prevent the evaporation and leakage of liquefied natural gas. Compared with traditional spherical tanks and independent cargo tanks, membrane cargo tanks have a lighter structure and higher space utilization, which makes them more suitable for the needs of large-scale transportation of liquefied natural gas. In the operation of LNG ships, the inerting process of liquid cargo tanks is crucial. Inerting is to reduce the oxygen content in the cargo tanks, piping systems and primary and secondary insulation layers to below the safe value by introducing inert gases (such as nitrogen). Effective inerting can prevent LNG from mixing with air when it first enters the liquid tank and causing an explosion, ensuring safety.

[0005] At present, many LNG ships use traditional inerting systems, usually with a single pipeline layout. This design cannot effectively cover the entire cabin, resulting in uneven gas distribution, making it impossible to achieve the ideal inerting effect in the corner area, forming an inerting dead corner, and increasing potential safety hazards. In addition, the single pipeline layout cannot be adjusted according to the needs of different areas in the cabin, resulting in gas waste and affecting the inerting efficiency. It usually takes up to 20 hours to reduce the oxygen volume concentration to below 2%, which not only reduces the operating efficiency of the ship, but also increases operating costs.

[0006] Therefore, in view of the shortcomings of the existing technology, 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

[0007] In view of the shortcomings of traditional inerting methods, the purpose of the present invention is to provide a combined pipe rack perforation inerting system for liquefied natural gas cargo tanks. The system increases the flexibility of the system by adding a staggered combined pipe rack structure and adjusting the gas flow in the tank by designing the aperture and direction of the pipeline in stages. The combined pipe rack perforation inerting system can be used in the inerting process of LNG cargo tanks to achieve simultaneous inerting of the entire tank, and has the advantages of more uniform gas distribution, elimination of inerting dead corners, and improved inerting efficiency.

[0008] To achieve the above-mentioned purpose, the technical solution adopted by the present invention is to provide a combined pipe rack perforation inerting system for a liquefied natural gas cargo tank, including a combined pipe rack, wherein the combined pipe rack is composed of two independent pipelines, the first pipeline in the overall structure extends obliquely downward from the tank top to the bottom corner, and the second pipeline extends vertically downward from the tank top and then obliquely upward to the bottom corner on the other side. The first pipeline is designed to extend obliquely downward from the inlet to the bottom corner after passing through a small section of vertical pipeline, and the second pipeline is designed to extend vertically downward from the tank top, connect to the elbow-straight pipe-elbow structure at the bottom of the liquid tank, turn obliquely upward, and extend to the top corner on the other side. The tail end of the pipeline is closed, and spray holes are set on the walls of the two oblique pipelines. The inert gas enters the natural gas tank only through the spray holes on the walls of the two oblique pipelines.

[0009] Furthermore, multiple groups of gas introduction nozzles are designed on each pipeline of the combined pipe rack. The nozzles in each group are evenly spaced along the axial direction of the pipeline, and the nozzles in the same group are evenly distributed along the circumference of the pipeline. The number and aperture of the nozzles are determined by accurate calculation of the cross-sectional area of ​​the pipeline. 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.

[0010] Furthermore, different sections of each pipeline adopt hole configurations in different directions, and three different hole layouts are set. The bottom spray holes are drilled obliquely downward along the axial direction of the pipeline to promote the rapid entry of the 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 spray holes are drilled in the axial vertical direction of 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 spray 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.

[0011] The beneficial effects of the present invention are:

[0012] 1. The present invention provides a combined pipe rack perforation inerting system for natural gas cargo holds. Different from the traditional inerting method of single pipeline air intake and gradual upward inerting from the bottom, the combined pipe rack structure, multiple pipeline paths, and spray holes are used to introduce gas, which significantly improves the coverage and flow efficiency of the inert gas, realizes the inerting of the entire hold at the same time, and can significantly shorten the inerting time.

[0013] 2. The graded aperture design in the present invention adopts the spray holes distributed in an array along the circumference of the pipeline and the multi-level aperture setting that gradually increases from top to bottom to ensure the stability and uniformity of gas flow. The total number of holes and the apertures of each level are calculated in combination with the cross-sectional area of ​​the pipeline. The fine aperture setting optimizes the gas introduction process and improves the overall inerting efficiency.

[0014] 3. The multi-directional hole layout design of the present invention adopts different drilling directions for the nozzles of different pipe sections, 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 the traditional technology that makes it difficult for the inert gas to diffuse to the corners of the liquid tank. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the specific implementation methods of the present invention 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 present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0016] Figure 1 is a schematic diagram of an LNG liquid cargo tank of a combined pipe rack perforated inerting system according to one embodiment of the present invention;

[0017] Figure 2 is a partial view of each pipeline of a combined pipe rack according to an embodiment of the present invention;

[0018] Figure 3 is a partial view of each pipeline of a combined pipe rack according to an embodiment of the present invention;

[0019] Figure 4 is a partial view of each pipeline of a combined pipe rack according to an embodiment of the present invention;

[0020] Figure 5 It is a schematic diagram of the positions of the spray holes of each pipeline of the combined pipe rack according to one embodiment of the present invention, which only illustrates the distribution positions of the spray holes on the pipeline.

[0021] Description of reference numerals:

[0022] 1. Liquefied natural gas cargo hold; 2. Inlet of liquid tank inert gas pipeline; 3. Gas outlet of liquid tank; 4. Straight pipe section of inert gas pipeline; 5. Upper inclined pipe section of combined pipe rack; 6. Lower inclined pipe section of combined pipe rack; 7. Bottom of upper inclined pipeline of combined pipe rack; 8. Spray hole at bottom of upper inclined pipeline; 9. Top of lower inclined pipeline of combined pipe rack; 10. Spray hole at top of lower inclined pipeline; 11. Middle of each pipeline of combined pipe rack; 12. Spray hole at middle of each pipeline. DETAILED DESCRIPTION

[0023] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.

[0025] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0026] 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.

[0027] 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.

[0028] Reference Figures 1 to 5The embodiment of the present invention provides a combined pipe rack perforating 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.

[0029] The combined pipe rack perforation inerting system of the liquefied natural gas cargo hold includes a combined pipe rack, which is composed of two independent pipelines. The first pipeline in the overall structure extends obliquely downward from the top of the tank to the bottom corner, and the second pipeline extends vertically downward from the top of the tank, 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 to the bottom corner after passing through a small section of vertical pipeline, and the second pipeline is designed to extend vertically downward from the top of the tank, connect to the elbow-straight pipe-elbow structure at the bottom of the liquid tank, turn obliquely upward, and extend to the top corner on the other side. The tail end of the pipeline is closed, and spray holes are set on the walls of the two oblique pipelines. Inert gas enters the natural gas tank only through the spray holes on the walls of the two oblique pipelines.

[0030] Multiple groups of gas introduction nozzles are designed on each pipeline of the combined pipe rack. The nozzles in each group are evenly spaced along the axial direction of the pipeline, and the nozzles in the same group are evenly distributed along the circumference of the pipeline. The number and aperture of the nozzles are accurately calculated and determined by the cross-sectional area of ​​the pipeline. 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 the 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.

[0031] Different sections of each pipeline adopt hole configurations in different directions, and three different hole layouts are set. The bottom spray 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 spray holes are drilled in the axial vertical direction of 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 spray 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.

[0032] The diameter and wall thickness of each pipe are 450mm and 14.27mm respectively (the wall thickness standard is SCH40). There are no spray holes on the straight pipe wall of the two pipes, and the lengths of the left and right straight pipe sections are 27750mm and 1500mm respectively.

[0033] The left 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 angles between the above pipe sections and the longitudinal sections of the tank are both 20°. The combined pipe rack inclined pipe section 5 is provided with three levels of spray holes of different diameters and directions, totaling 73 groups. Figure 5As shown, each group of spray holes has 6 spray holes evenly distributed along the circumference of the pipeline. Among them, 22 groups of spray holes 8 with a diameter of 20 mm are set in the bottom 7 of the inclined upper pipeline of the combined pipe rack, and the spray hole direction is 45° obliquely downward along the axial direction of the pipeline. 40 groups of spray holes 12 with a diameter of 14 mm are set in the middle 11 of each pipeline of the combined pipe rack, and the spray hole direction is vertical along the axial direction of the pipeline. Spray holes with a diameter of 10 mm are set in the middle 11 of each pipeline of the combined pipe rack, and the spray hole direction is 45° obliquely upward along the axial direction of the pipeline. The spray hole characteristics are consistent with the spray holes 10 at the top of the inclined downward pipeline.

[0034] The right straight pipe section is connected to the 45° elbow and the 45° combined pipe rack inclined lower pipe section 6 in sequence. The angle between the above pipe sections and the longitudinal sections of the tank at both ends is 20°. The combined pipe rack inclined lower pipe section 6 is provided with three levels of spray holes of different diameters and directions, totaling 77 groups. Figure 5 As shown, each group of spray holes has 6 spray holes evenly distributed along the circumference of the pipeline. Among them, 25 groups of spray holes are set in the bottom of the inclined lower pipeline of the combined pipe rack, and the diameter and direction of the spray holes are consistent with the spray holes 8 at the bottom of the inclined upper pipeline. 12 groups of spray holes 10 at the top of the inclined lower pipeline of the combined pipe rack are set in the top 9 of the inclined lower pipeline, with a diameter of 10mm and a spray hole direction of 45° upward along the axial direction of the pipeline.

[0035] The working principle of the combined pipe rack perforation inerting system is:

[0036] The inert gas with a certain speed from the inert gas generating room enters the straight pipe section 4 and the right straight pipe section of the inert gas pipeline through the inlet 2 of the liquid tank inert gas pipeline. Due to the pressure difference and gravity, the inert gas flows along the straight pipe section, passes through the bend or the straight pipe section, enters the upper inclined pipe section 5 and the lower inclined pipe section 6 of the combined pipe rack, enters the LNG tank through the various levels of spray holes of the pipeline, and diffuses into the air in the tank, discharges the air in the tank upward, and the air is discharged through the liquid tank gas outlet 3. When the oxygen volume concentration in the LNG tank is lower than 2%, the inerting operation can be completed.

[0037] The embodiments of this specific implementation method are all preferred embodiments of the present invention, and are not intended to limit the protection scope of the present invention. Therefore, any equivalent changes made based on the structure, shape, and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A combined pipe rack perforation inerting system for a liquefied natural gas cargo hold, characterized in that: The utility model comprises a combined pipe rack, which is composed of two independent pipes. The first pipe in the overall structure extends obliquely downward from the tank top to the bottom corner, and the second pipe extends vertically downward from the tank top and then extends obliquely upward to the bottom corner on the other side. The first pipe is designed to extend obliquely downward from the inlet to the bottom corner after passing through a small section of vertical pipe, and the second pipe is designed to extend vertically downward from the tank top, connect the elbow-straight pipe-elbow pipe structure at the bottom of the liquid tank, turn obliquely upward, and extend to the top corner on the other side. The tail end of the pipe is closed, and spray holes are arranged on the walls of the two oblique pipes. Inert gas enters the natural gas tank only through the spray holes on the walls of the two oblique pipes.

2. The combined pipe rack perforation inerting system for a liquefied natural gas cargo tank according to claim 1, characterized in that: Multiple groups of gas introduction nozzles are designed on each pipeline of the combined pipe rack. The nozzles in each group are evenly spaced along the axial direction of the pipeline, and the nozzles in the same group are evenly distributed along the circumference of the pipeline. The number and aperture of the nozzles are accurately calculated and determined by the cross-sectional area of ​​the pipeline. 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 the 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.

3. The combined pipe rack perforation inerting system for a liquefied natural gas cargo tank 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 spray 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 spray holes are drilled in the axial vertical direction of 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 spray 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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