Denitrification tower for natural gas liquefaction device

Abstract

The utility model discloses a denitrification tower for a natural gas liquefaction device. The denitrification tower comprises an aluminum tank body, at least one large opening is formed in the outer wall of the tank body; a manhole pipe is arranged on the large opening; the manhole pipe is formed by rolling and welding a thick aluminum plate; the manhole pipe adopts a cross section full penetration welding seam; and calculating allowable stress values required by the thickness and the length of the manhole pipe, wherein the allowable stress values are the allowable stress values of the manhole pipe welding material. And the aluminum tank body is provided with a large hole, namely a manhole pipe, so that the requirement of on-site filler installation in the denitrification tower can be met. And the manhole pipe is manufactured by adopting an aluminum plate rolling process, so that the production cost of the manhole pipe is reduced, the reinforcement of the manhole pipe can be calculated by adopting an analytical method according to the mechanical indexes of a weld zone, and the strength requirement of the tank body is fully guaranteed. The manhole pipe extends into the tank body and is flush with the inner wall of the tank body, so that the problem that the filler cannot be assembled is effectively avoided; a sealing cover is welded to the tail end of the manhole pipe after milling, and the stability and sealing performance of the connecting structure are improved.

Description

Technical Field

[0001] The utility model belongs to natural gas separation and liquefaction equipment, and particularly relates to a denitrification tower for a natural gas liquefaction device. Background Art

[0002] Generally, the core equipment for natural gas purification and liquefaction is concentrated in the liquefaction cold box, and the equipment and the process pipelines in the cold box are welded. The heat exchanger is made of aluminum alloy. To ensure the reliability of welding and consider economy, the denitrification tower usually also uses aluminum alloy material. The denitrification tower is usually a packed tower, mainly composed of a support, a cylinder body, upper and lower heads, and packing internals, etc. The packing of the conventionally designed denitrification tower is installed integrally at the factory and the tower body is shipped out as a whole. Except for the process pipe openings, no manhole is provided on the tower body. However, in special cases, such as when the installation environment and the hoisting and transportation environment are harsh, it is necessary to install the packing after the denitrification tower is installed on site, so it is also necessary to provide a manhole.

[0003] Chinese patent document with the publication number of CN109675409A discloses a packaging structure for a molecular sieve adsorption tower of an oxygen generator, including an aluminum tank (1), a sealing upper cover (2) and a sealing lower cover (3). The aluminum tank (1) is an aluminum cylindrical barrel structure. Its characteristics are that: the packaging structure further includes a C-shaped snap ring (4), and sealing O-rings (5) are provided on both the sealing upper cover (2) and the sealing lower cover (3). The sealing upper cover (2) is hermetically connected to the inner top of the aluminum tank (1) through the sealing O-ring (5) and fixed by the C-shaped snap ring (4) installed outside the aluminum tank (1); the sealing lower cover (3) is hermetically connected to the inner bottom of the aluminum tank (1) through the sealing O-ring (5) and fixed by the C-shaped snap ring (4) installed outside the aluminum tank (1).

[0004] In the prior art, as in the above patent solution, for an aluminum pressure vessel, for a small opening, the equal area method can be used to calculate the opening reinforcement according to the formula given in the standard; for a large opening (such as a manhole), according to the relevant national standards and specifications (GB / T150-2011), the analytical method needs to be used for calculation. Since large openings are often not provided in aluminum pressure vessels, at the same time, the maximum welding joint coefficient specified in the aluminum container standard can only be taken as 0.95, while the analytical method requires the welding joint coefficient of the nozzle to be taken as 1.0. Therefore, the current national standards and specifications do not give the detailed calculation process and material database of the analytical method.

[0005] In addition, as an interface pipe adapted to a large opening of an aluminum pressure vessel, the cost of an aluminum forging is often relatively high. Content of the Utility Model

[0006] In order to overcome the technical problems in the prior art that no large opening is provided on an aluminum pressure vessel, the cost of an aluminum forged interface pipe adapted to the large opening is relatively high, and the reinforcement of the large opening cannot be calculated according to the current standards; an object of the present invention is to provide a denitrification tower for a natural gas liquefaction device. By using a thick aluminum plate to be rolled and welded to form an interface pipe adapted to the large opening of the aluminum pressure vessel, the forging cost is reduced. At the same time, according to the equivalent allowable stress = the allowable stress of the material * the welding joint coefficient, the welding joint coefficient is taken as 1.0 for reinforcement calculation when performing reinforcement calculation.

[0007] In order to achieve the above object, the present invention is realized by adopting the following technical solutions: A denitrification tower for a natural gas liquefaction device includes an aluminum tank body; at least one large opening is provided on the outer wall of the tank body; a manhole pipe is provided on the large opening; the manhole pipe is formed by rolling and welding a thick aluminum plate; the manhole pipe adopts a full-penetration weld in cross section; wherein, the allowable stress value required for calculating the thickness and length of the manhole pipe is the allowable stress value of the welding material of the manhole pipe.

[0008] The large opening refers to that, relative to the overall diameter or thickness of the tank body, the size of the opening is relatively large, which will have a greater impact on the stress state of the tank body. In the case of the large opening, the phenomenon of stress concentration is more obvious because the opening destroys the original stress distribution and forms a structural discontinuity at the connection between the manhole pipe and the tank body, resulting in a locally high stress area of stress concentration. In order to ensure the safe operation of the tank body, it is usually necessary to reinforce these high stress areas. The reinforcement calculation should be carried out according to relevant specifications such as GB / T 150-2011.

[0009] Since TSG 21-2016 Fixed Pressure Vessel Code quotes GB / T 150-2011, the opening reinforcement of the large opening needs to be calculated by the analytical method. The maximum welding joint coefficient specified in the aluminum container standard can only be taken as 0.95, while the analytical method requires the welding joint coefficient of the manhole pipe to be taken as 1.0; therefore, the manhole pipe formed by rolling plates cannot directly use the analytical method for opening reinforcement calculation.

[0010] Regarding the meaning of the welding joint coefficient, by referring to the data and relevant specifications, it can be known that for a cylinder formed by rolling plates, the strength of the metal in the weld area is generally lower than that of the base metal, so the allowable stress should be multiplied by the welding joint coefficient. Based on this, when calculating the opening reinforcement, the concept of equivalent allowable stress is proposed, that is, equivalent allowable stress = the allowable stress of the material * the welding joint coefficient. At the same time, the welding joint coefficient is taken as 1.0 when performing strength calculation. At this time, the analytical method can be used to perform the opening reinforcement calculation.

[0011] Furthermore, an extension section is provided at the end of the manhole pipe; a cover is welded to the end of the extension section; the extension section is milled, and the thickness after milling is equal to the thickness of the cover; the use of welding can effectively improve the structural strength and sealing effect of the tank body.

[0012] Specifically, the cover is made of aluminum; the cover includes a cylindrical section welded to the manhole pipe and an arc-shaped cap end provided at the end of the cylindrical section.

[0013] Preferably, one end of the manhole pipe located inside the tank body is flush with the inner wall of the tank body.

[0014] Furthermore, the thickness of the manhole pipe satisfies: δet≥max[0.5δe, d*δe / D]; the outer extension length of the manhole pipe satisfies: wherein, δet is the thickness of the manhole pipe; δe is the thickness of the tank body; d is the outer diameter of the manhole pipe; D is the outer diameter of the tank body; lt is the outer extension length of the manhole pipe.

[0015] Furthermore, three large openings arranged longitudinally are provided on the tank body; the distance between the edges of adjacent two large openings is greater than or equal to wherein, Di is the inner diameter of the tank body.

[0016] Specifically, the diameter of the tank body is 900mm; the diameter of the manhole pipe is 490mm; the thickness of the tank body is 18mm; the thickness of the manhole pipe is at least 34mm; the effective outer extension length of the manhole pipe is at least 138mm.

[0017] Specifically, the distance between the intersection line of the manhole pipe and the tank body and the A and B class welds on the tank body is greater than or equal to 150mm.

[0018] Furthermore, the tank body is divided into three layers arranged longitudinally, and each layer respectively includes a positioning grid provided at the bottommost end, a filler provided above the positioning grid, and the manhole pipe provided above the filler.

[0019] Specifically, a gaseous natural gas inlet and a liquid-phase natural gas inlet are provided on the side wall of the middle layer of the tank body; a low-pressure nitrogen outlet is provided at the top of the upper layer of the tank body; a high-pressure nitrogen inlet is provided on the side wall of the upper layer of the tank body.

[0020] Compared with the prior art, the beneficial effects of the present utility model are as follows:

[0021] 1. By providing a large opening, that is, a manhole pipe, on the aluminum tank body, the requirement for on-site installation of fillers in the denitrification tower can be met.

[0022] 2. The manhole pipe is manufactured by using the aluminum plate rolling process. While reducing the production cost of the manhole pipe, the reinforcement of the manhole pipe can be calculated by using the analysis method according to the mechanical indexes of the weld zone, fully ensuring the strength requirements of the tank body.

[0023] 3. The inner extension of the manhole pipe into the tank body is flush with the inner wall of the tank body, effectively avoiding the problem that the packing cannot be assembled; the end of the manhole pipe is welded with a cover after milling, improving the stability and sealing performance of the connection structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a structural schematic diagram of the present utility model;

[0025] Figure 2 is a longitudinal sectional view of the manhole pipe of the present utility model;

[0026] Figure 3 is a transverse sectional view of the manhole pipe of the present utility model.

[0027] In the figure: 11, tank body; 12, large opening; 13, packing; 14, positioning grid; 21, manhole pipe; 211, extension section; 22, cover; 31, gas-phase natural gas inlet; 32, liquid-phase natural gas inlet; 33, low-pressure nitrogen outlet; 34, high-pressure nitrogen inlet. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0028] Next, in combination with the drawings and the specific embodiments, the present utility model will be further described. It should be noted that on the premise of no conflict, the following-described embodiments or technical features can be arbitrarily combined with each other to form new embodiments.

[0029] In the description of the present utility model, it should be noted that for the orientation terms, if there are terms such as "center", "transverse", "longitudinal", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc., the orientation and position relationships indicated are based on the orientation or position relationship shown in the drawings. It is only for the convenience of describing the present utility model 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 cannot be understood as limiting the specific protection scope of the present utility model.

[0030] In addition, if there are terms such as "first" and "second", they are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present utility model, the meaning of "several" is two or more, unless otherwise specifically defined.

[0031] In the present utility model, unless otherwise clearly defined and limited, terms such as "arrangement" and "installation" shall be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may also be a mechanical connection; it can be directly connected, or connected through an intermediate medium, and can be internally connected and communicated between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present utility model can be understood according to specific circumstances.

[0032] See Figures 1-3 , a denitrification tower for a natural gas liquefaction device, including an aluminum tank body 11; at least one large opening 12 is arranged on the outer wall of the tank body 11; a manhole pipe 21 is arranged on the large opening 12; the manhole pipe 21 is formed by rolling and welding thick aluminum plates; the manhole pipe adopts a full penetration weld in cross section; among them, the allowable stress value required for calculating the thickness and length of the manhole pipe 21 is the allowable stress value of the welding material of the manhole pipe 21.

[0033] An extension section 211 is arranged at the end of the manhole pipe 21; a cover 22 is welded at the end of the extension section; the extension section 211 is milled, and the thickness after milling is equal to the thickness of the cover 22; the cover 22 is made of aluminum; the cover 22 includes a cylindrical section welded to the manhole pipe 21 and an arc-shaped cap end arranged at the end of the cylindrical section; one end of the manhole pipe 21 located inside the tank body 11 is flush with the inner wall of the tank body 11.

[0034] The tank body 11 is divided into three layers arranged longitudinally, and each layer respectively includes a positioning grid 14 arranged at the bottommost end, a filler 13 arranged above the positioning grid 14, and the manhole pipe 21 arranged above the filler 13.

[0035] A gas-phase natural gas inlet 31 and a liquid-phase natural gas inlet 32 are arranged on the side wall of the middle layer of the tank body 11; a low-pressure nitrogen outlet 33 is arranged at the top of the upper layer of the tank body 11; a high-pressure nitrogen inlet 34 is arranged on the side wall of the upper layer of the tank body 11.

[0036] The thickness of the manhole pipe satisfies: δet≥max[0.5δe, d*δe / D]; the extension length of the manhole pipe satisfies: Among them, δet is the thickness of the manhole pipe; δe is the thickness of the tank body; d is the outer diameter of the manhole pipe; D is the outer diameter of the tank body; lt is the extension length of the manhole pipe; three large openings arranged longitudinally are arranged on the tank body; the distance between the edges of two adjacent large openings is greater than or equal to Among them, Di is the inner diameter of the tank body.

[0037] Specifically, the wall thickness of the shell and the wall thickness of the manhole pipe satisfy the following conditions:

[0038] And

[0039] And δet ≤ 2δe.

[0040] Where: The opening ratio The opening parameter

[0041] From λ, δet / δe, check the GB / T 150.3 curve group 6-13 to obtain Km and K;

[0042] The outer extension length of the manhole pipe satisfies the following conditions:

[0043] In the formula:

[0044] P is the design pressure, NPa;

[0045] [σ]t is the allowable stress value of the material of the tank body at the design temperature, MPa;

[0046] Di is the inner diameter of the tank body, mm;

[0047] δn is the nominal thickness at the opening of the tank body, mm;

[0048] δe is the effective thickness at the opening of the tank body, mm;

[0049] Cs is the thickness addition of the tank body (equal to the corrosion allowance + thickness negative deviation), mm;

[0050] do is the outer diameter of the manhole pipe, mm;

[0051] δnt is the nominal thickness of the manhole pipe, mm;

[0052] δet is the effective thickness of the manhole pipe, mm;

[0053] Ct is the thickness addition of the manhole pipe (equal to the corrosion allowance + thickness negative deviation), mm;

[0054] lt is the outer extension length of the manhole pipe, mm.

[0055] Specifically, the design pressure of the denitrification tower is 2.3 MPa, and the design temperature is -196 / 65 °C. The inner diameter of the tank is 900 mm, and the material of the tank body is selected as aluminum plate grade 5083-H112 (GB / T 3880). According to the rules of TSG21-2016 and the factory regulations, the allowable stress [σ] of this material is 77 MP. Calculated according to GB / T150.3-2011, the thickness of the plate of the tank body is finally determined to be 18 mm.

[0056] When using the analytical method for opening reinforcement calculation, it is required that the welding joint coefficient is taken as 1. Therefore, first, the opening reinforcement calculation is carried out according to the fact that the manhole pipe joint is made of forging material. The detailed calculation process of the analytical method is not given in the current national standard specifications. At present, the analytical method can be used for opening reinforcement calculation with the help of the SW6 process equipment design software.

[0057] Since there is no relevant data for the above materials in the material database of SW6, it is necessary to first create a new material database, find the relevant data in the JB / T4734-2002 standard and create the target material data. Then, a preliminary calculation is carried out in SW6. Usually, for a pressure vessel, it is calculated according to the actual reinforcement area being 20% more than the required reinforcement area.

[0058] It is calculated that the thickness required for the manhole pipe is at least 34 mm, and the effective outer extension length of the manhole pipe is at least 138 mm. The price of the forging pipe joint material of this specification is relatively high. Considering economy, the manhole pipe joint is designed to be made of thick aluminum plate by rolling and welding.

[0059] According to the specification, the maximum welding joint coefficient of an aluminum pressure vessel can only be taken as 0.95, while the analytical method requires the welding joint coefficient to be taken as 1. Therefore, the manhole pipe joint made of aluminum plate cannot directly use the analytical method for opening reinforcement calculation.

[0060] By consulting the data and relevant specifications, it can be known that for a cylinder made of rolled plate, the metal strength in the weld area is generally lower than that of the base metal. Therefore, the allowable stress [σ] should be multiplied by the welding joint coefficient φ. When calculating the opening reinforcement of the manhole pipe, we propose the concept of equivalent allowable stress accordingly, that is, equivalent allowable stress = allowable stress [σ] of the material * welding joint coefficient φ, and at the same time, the welding joint coefficient φ is taken as 1.0 when performing strength calculation. At this time, the analytical method can be used for opening reinforcement calculation.

[0061] At the same time, it is stipulated that there shall be no type A or B welds within 150 mm from the intersection line of the manhole nozzle and the tank body, and there shall be no any excessive defects on the surface of the tank body within this range; there shall be no any excessive defects in the type A welds of the manhole pipe within 150 mm from the intersection line of the manhole pipe and the tank body.

[0062] Through the concept of equivalent allowable stress proposed above, the opening reinforcement calculation of this large opening can be successfully solved by SW6 using the newly built material database.

[0063] First, determine the outer dimensions of the denitrification tower according to the requirements of the user's design task book and the packing internals drawing. Then select the appropriate material according to the design pressure and design temperature given in the task book and calculate the thickness of the main material. Next, set a support at the bottom of the denitrification tower and a liquid-phase LNG discharge pipe joint at the lower head to facilitate the complete discharge of liquid-phase LNG. Then calculate the opening reinforcement according to the positions of each pipe joint and manhole. The opening reinforcement of the pipe joints other than the manhole can be calculated by the equal area method. For the opening reinforcement of the manhole, use the analysis calculation idea given above for the opening reinforcement design, and make the inner extension of the manhole pipe joint flush with the inner wall of the cylinder to facilitate the installation of the packing internals.

[0064] After calculation, the actual wall thickness of the manhole pipe is 35 mm, which is less than twice the wall thickness of the tank; the minimum outer extension length of the manhole pipe is 135 mm, and the actual outer extension length is 180 mm, meeting the requirements.

[0065] The above are only specific embodiments of the present invention, but the technical features of the present invention are not limited thereto. Any changes or modifications made by those skilled in the art within the scope of the present invention are covered by the patent scope of the present invention.

Claims

1. A denitrification tower for a natural gas liquefaction device, characterized in that: It includes an aluminum tank body; at least one large opening is provided on the outer wall of the tank body; a manhole pipe is provided on the large opening; the manhole pipe is formed by rolling and welding thick aluminum plates; the manhole pipe adopts a full-penetration weld in cross section; wherein, the allowable stress value required for calculating the thickness and length of the manhole pipe is the allowable stress value of the welding material of the manhole pipe.

2. The denitrification tower according to claim 1, characterized in that: An extension section is provided at the end of the manhole pipe; a cover is welded at the end of the extension section; the extension section is milled, and the thickness after milling is equal to the thickness of the cover.

3. The denitrification tower according to claim 2, wherein: The cover is made of aluminum; the cover includes a cylindrical section welded to the manhole pipe and an arc-shaped cap end provided at the end of the cylindrical section.

4. The denitrification tower according to any one of claims 1 to 3, characterized in that: One end of the manhole pipe located inside the tank body is flush with the inner wall of the tank body.

5. The denitrification tower according to any one of claims 1-3, characterized in that: The thickness of the manhole pipe satisfies: δet ≥ max[0.5δe, d*δe / D]; the extension length of the manhole pipe satisfies: wherein, δet is the thickness of the manhole pipe; δe is the thickness of the tank body; d is the outer diameter of the manhole pipe; D is the outer diameter of the tank body; lt is the extension length of the manhole pipe.

6. The denitrification tower according to claim 5, characterized in that: Three of the large openings are arranged longitudinally on the tank body; the distance between the edges of two adjacent large openings is greater than or equal to where Di is the inner diameter of the tank body.

7. The denitrification tower according to claim 5, characterized in that: The diameter of the tank body is 900 mm; the diameter of the manhole pipe is 490 mm; the thickness of the tank body is 18 mm; the thickness of the manhole pipe is at least 34 mm; the effective outer extension length of the manhole pipe is at least 138 mm.

8. The denitrification tower according to claim 7, wherein: The distance between the intersection line of the manhole pipe and the tank body and the A and B class welds on the tank body is greater than or equal to 150 mm.

9. The denitrification tower according to any one of claims 1-3, characterized in that: The tank body is divided into three longitudinally arranged layers, and each layer respectively includes a positioning grid provided at the bottommost end, a filler provided above the positioning grid, and the manhole pipe provided above the filler.

10. The denitrification tower according to claim 9, wherein: A gas-phase natural gas inlet and a liquid-phase natural gas inlet are provided on the side wall of the middle layer of the tank body; a low-pressure nitrogen outlet is provided at the top of the upper layer of the tank body; a high-pressure nitrogen inlet is provided on the side wall of the upper layer of the tank body.

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