A method for external insulation of LNG ultra-low temperature liquid tank

Abstract

The present invention discloses an external thermal insulation method for an LNG ultra-low temperature liquid tank, comprising: (1) spraying polyurethane rigid foam on the outside of the liquid tank to form an insulation layer, and then grinding the surface to be flat and smooth; (2) cutting expansion joints at stress release positions on the surface of the polyurethane rigid foam; (3) applying a glass fiber reinforced plastic protective layer on the outer surface of the grinded polyurethane rigid foam insulation layer; (4) placing polyurethane prefabricated foam strips at the expansion joints, and fixing and pasting glass fiber reinforced plastic prefabricated parts. The present invention can effectively release stress, ensure that the insulation layer is stable and does not crack during long-term transportation, and improve the thermal insulation performance.

Description

Technical Field

[0001] The invention relates to the technical field of chemical thermal insulation, and in particular to an external thermal insulation method for an LNG ultra-low temperature liquid tank. Background Art

[0002] Refrigerated liquefied natural gas refers to gas that is partially in liquid form due to low temperature during transportation, and its critical temperature is generally not higher than -50°C. Natural gas becomes liquid after being compressed and cooled to its freezing point (-161.5°C). Usually, liquefied natural gas is stored in low-temperature storage tanks at -161.5 degrees Celsius and around 0.1MPa. Its main component is methane, which is transported by special ships or tank trucks and re-gasified when used.

[0003] With the continuous expansion of my country's energy demand, the consumption market of refrigerated liquefied gas represented by LNG has increased rapidly. In 2021, my country imported 81.4 million tons of LNG, becoming the world's largest importer of liquefied natural gas (LNG). In the process of LNG transportation, thermal insulation of the outer surface of the tank is a key process. At present, the main insulation method is to lay an insulation layer on the outside of the tank. The main insulation layer is urethane rigid foam, which is 30cm thick. Glass fiber mesh cloth is added every 5cm to maintain its structural stability. A waterproof protective layer is laid on the outside, which can be a sprayed polyurea coating or a brushed fiberglass reinforced plastic.

[0004] However, after spraying the ultra-low temperature resistant polyurethane rigid foam insulation layer on the outside of the tank, the insulation layer and the external waterproof protective layer are prone to cracking. If the waterproof protective layer is sprayed with polyurea coating, the appearance is not smooth enough, and the coating strength is not enough, and it is easy to be damaged by external impact. If the waterproof protective layer is made of fiberglass, although the appearance is smooth, it is more likely to crack. Figure 1 shown. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides an external insulation method for an LNG ultra-low temperature liquid tank.

[0006] The complete technical solution of the present invention includes:

[0007] A method for external thermal insulation of an LNG ultra-low temperature liquid tank, characterized in that it comprises the following steps:

[0008] (1) After spraying polyurethane rigid foam on the outside of the tank to form an insulation layer, polish the surface to make it smooth;

[0009] (2) Cut expansion joints at the stress release area on the surface of the polyurethane rigid foam;

[0010] (3) Apply a fiberglass protective layer on the outer surface of the polished polyurethane rigid foam insulation layer.

[0011] (4) Place prefabricated polyurethane foam strips at the expansion joints and fix and glue the FRP prefabricated parts.

[0012] The cutting depth of the expansion joint is 1 / 2 of the polyurethane rigid foam insulation layer.

[0013] In step 4, the sprayed polyurethane rigid foam and the prefabricated polyurethane foam strips are included below, and the prefabricated foam strips are pressed tightly by the prefabricated fiberglass parts on both sides. The prefabricated fiberglass parts are fixed to the bottom fiberglass and the outer fiberglass by stainless steel screws.

[0014] The advantages of the present invention over the prior art are as follows: after the ultra-low temperature resistant polyurethane rigid foam insulation layer is sprayed on the outside of the liquid tank, the insulation layer and the external waterproof protective layer are prone to cracking. The present invention can effectively release stress by cutting expansion joints at the stress release position on the surface of the polyurethane rigid foam, thereby achieving stability of the insulation layer without cracking during long-term transportation, thereby improving the thermal insulation performance. At the same time, a reasonable design is made in the selection of the location of the expansion joint, taking into account both strength and stress release effects, and can be well applied to LNG of different specifications. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Schematic diagram of cracks on the surface of the liquid tank.

[0016] Figure 2 This is a front view of the liquid tank after heat insulation treatment of the present invention.

[0017] Figure 3 for Figure 2 Top view.

[0018] Figure 4 This is a schematic diagram of the connection between the can body and the can.

[0019] Figure 5 This is a cross-section diagram of the tank body.

[0020] Figure 6 This is the on-site picture of the liquid tank after insulation treatment.

[0021] Figure 7 This is a physical picture of the connecting parts. DETAILED DESCRIPTION

[0022] The following will clearly and completely describe the technical solutions in the embodiments of the present application in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only for illustration and are not intended to limit the present application.

[0023] A method for external thermal insulation of an LNG ultra-low temperature liquid tank comprises the following steps:

[0024] (1) After the exterior of the tank is sprayed with polyurethane rigid foam, the surface is polished to make it smooth.

[0025] (2) If Figure 2-3 As shown, expansion joints are cut at the stress release position on the surface of the polyurethane rigid foam, and the cutting depth is 1 / 2 of the insulation layer. The location of the expansion joint takes into account the internal stress caused by the inconsistent thermal expansion coefficients of the rigid polyurethane foam material and the tank body, as well as the internal stress caused by the temperature change of the rigid polyurethane foam material itself. In terms of location selection, it includes the first annular expansion joint 3 near the can 1 on both sides, the second annular expansion joint 41 and the third annular expansion joint 42 on both sides of the tank, and the fourth annular expansion joint 5 located in the center of the tank body. On the other side of the tank body, the first, second, and third annular expansion joints are also symmetrically arranged relative to the fourth annular expansion joint. It also includes a first horizontal expansion joint 6 surrounding the tank body;

[0026] The first annular expansion joint is close to the connection between the can body and the can. Due to the change in cross section, the location is in the stress concentration area. However, it is found in the actual process that the expansion joint cannot be directly opened on the connection surface between the can body and the can, because cutting will cause the strength of this area to decrease and the hard polyurethane foam material is easy to break. Therefore, it is chosen to deviate from the connection surface by a distance, such as Figure 4 As shown in the figure, since LNG has different specifications, such as 50 cubic meters, 80 cubic meters, 100 cubic meters, etc., it is necessary to make unified regulations for LNG of different sizes for the convenience of operation. After a large amount of field data collection and analysis, the selection is generally as follows, namely: , L is the distance between the first annular expansion joint and the connection surface, R is the radius of curvature at the connection surface, k is the coefficient, and the value range is 0.1~0.12. The above method will take into account both strength and stress release effects, and provide a good specification for on-site operation and construction.

[0027] Because the positions of various places are different, a support frame 8 is placed under the tank body, so a second horizontal expansion joint 7 is provided between the second and third annular expansion joints. The plane formed by the second horizontal expansion joint and the central axis of the LNG tank has an angle of 15° with the horizontal plane. Figure 5 shown.

[0028] In particular, in order to improve stability, the width of the cut expansion joints at various locations is limited, specifically, the first expansion joint: the second expansion joint: the third expansion joint: the fourth expansion joint = 0.8:1:1:1.

[0029] (3) Apply a fiberglass protective layer on the outer surface of the polished polyurethane rigid foam insulation layer (reserving expansion joints).

[0030] (4) Place polyurethane prefabricated foam strips at the expansion joints and fix and glue the FRP prefabricated parts; including the sprayed polyurethane rigid foam at the bottom, the polyurethane prefabricated foam strips, and the prefabricated foam strips are pressed tightly by FRP prefabricated parts on both sides. The FRP prefabricated parts are fixed to the bottom FRP and the outer FRP by stainless steel screws, such as Figure 7 shown.

[0031] The actual LNG ultra-low temperature liquid tank after the overall insulation treatment is as follows Figure 6 shown.

[0032] The above applications are only some implementation methods of the present application. For those skilled in the art, several modifications and improvements can be made without departing from the creative concept of the present application, and these all belong to the protection scope of the present application.

Claims

1. A method for external insulation of an LNG ultra-low temperature liquid tank, characterized in that: The steps include: (1) After spraying polyurethane rigid foam on the outside of the tank to form an insulation layer, polish the surface to make it smooth; (2) Cut expansion joints at the stress release area on the surface of the polyurethane rigid foam; It includes a first annular expansion joint near the cans on both sides, a second annular expansion joint and a third annular expansion joint located on both sides of the can, and a fourth annular expansion joint located in the center of the can body. On the other side of the can body, the first, second and third annular expansion joints are also symmetrically arranged relative to the fourth annular expansion joint; and it also includes a first horizontal expansion joint surrounding the can body; The first annular expansion joint is arranged on the can body and deviates from the connection surface between the can body and the can by a certain distance, specifically: Wherein, L is the distance between the first annular expansion joint and the connection surface, R is the radius of curvature at the connection surface, and k is the coefficient, ranging from 0.1 to 0.12; A support frame is placed under the tank body, and the support frame is arranged between the second and third annular expansion joints. A second horizontal expansion joint is arranged between the second and third annular expansion joints. The plane formed by the second horizontal expansion joint and the central axis of the LNG tank has an angle of 15° with the horizontal plane. The specific widths of the cut expansion joints at various locations are: first expansion joint: second expansion joint: third expansion joint: fourth expansion joint = 0.8:1:1:1; (3) Apply a glass fiber reinforced plastic protective layer on the outer surface of the polished polyurethane rigid foam insulation layer; (4) Place prefabricated polyurethane foam strips at the expansion joints and fix and glue the FRP prefabricated parts.

2. The external insulation method of an LNG ultra-low temperature liquid tank according to claim 1, characterized in that: The cutting depth of the expansion joint is 1 / 2 of the polyurethane rigid foam insulation layer.

3. The external insulation method of an LNG ultra-low temperature liquid tank according to claim 1, characterized in that: In step (4), the following steps are included: spraying polyurethane rigid foam at the bottom, prefabricated polyurethane foam strips, and prefabricated foam strips are pressed tightly on both sides by glass fiber reinforced plastic prefabricated parts.

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