Tank bottom leakage repairing method for double-metal-wall low-temperature storage tank

Abstract

The invention relates to a tank bottom leakage repairing method for a double-metal-wall low-temperature storage tank. A thin film isolation plate is installed at the proper position of an annular space of an inner tank and an outer tank, and an upper cavity and a lower cavity which are independent are formed in the outer tank. The film isolation plate prevents the boil-off gas on the upper portion of the outer tank from entering a tank bottom heat insulation system on the lower portion of the outer tank, and therefore the medium boil-off gas is prevented from leaking and escaping. And compared with dismantling and rebuilding of the low-temperature storage tank, the repairing period is shorter, and the manufacturing cost is lower. The arrangement of the arched part of the thin film isolation plate can provide corresponding displacement compensation when the inner tank radially contracts in a cold state, that is, when the width of the annular space cavity is increased due to the radial contraction in the cold state of the inner tank, the height of the arched part of the thin film isolation plate is reduced and the width is increased so as to provide corresponding displacement compensation; and the two side edges of the film isolation plate can be always fixed and sealed with the side walls of the inner and outer tanks.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of low-temperature liquefied gas storage tank, in particular to a tank bottom leakage repair method of double-metal-wall low-temperature storage tank. BACKGROUND

[0002] The low-temperature storage tank can store low-temperature liquefied gas such as LNG (Liquefied Natural Gas), low-temperature ethylene, LPG, low-temperature ethane, low-temperature ammonia, low-temperature propane, low-temperature propylene, low-temperature butane, etc. under near atmospheric pressure. The low-temperature storage tank has large storage volume, small land occupation and low cost of storing low-temperature medium per unit volume. At the same time, due to the low storage pressure of the low-temperature storage tank, the safety is good, and it is the preferred tank type for receiving stations, peak shaving stations and petrochemical device tank farms. The structure of the low-temperature storage tank is generally a vertical flat-bottomed cylindrical storage tank, which can be divided into single-container tanks, double-container tanks, full-container tanks and membrane tanks. Among them, the double-metal-wall storage tank is a common tank type.

[0003] The double-metal-wall low-temperature storage tank includes an inner tank and an outer tank. The inner tank is used to store low-temperature liquefied gas. The outer tank includes a tank bottom, a tank wall and a tank top, and is a completely closed structure. An annular gap cavity is formed between the inner tank and the outer tank, and the annular gap cavity is filled with thermal insulation material. In normal operation, the outer tank maintains a slight positive pressure, which blocks the intrusion of external humid air into the thermal insulation system of the inner tank, so that the cold preservation layer between the inner tank and the outer tank is in a dry state, which reduces the thermal conductivity of the cold preservation material and improves the thermal insulation performance. At the same time, it also plays a good anticorrosion protection role for the tank body, thereby prolonging the service life of the storage tank.

[0004] The large-scale construction and application of low-temperature storage tanks abroad began in the 1970s, and in China, it began in the late 20th century, and has been in operation for several decades. After years of operation, the outer tank bottom plate of the double-metal-wall low-temperature storage tank is often corroded and perforated due to environmental corrosion. The corrosion perforation leakage of the outer tank bottom plate causes water vapor to enter the tank, thereby causing the water content and oxygen content of the tank insulation layer to exceed the specification requirements, the performance of the thermal insulation material of the storage tank is severely degraded, and the medium evaporation rate of the storage tank increases sharply, which seriously affects the operating efficiency and safety of the low-temperature storage tank. In this case, the storage tank is usually rebuilt, which results in a long repair period and huge investment. SUMMARY

[0005] The present application provides a tank bottom leakage repair method of a double-metal-wall low-temperature storage tank for storing low-temperature liquefied gas selected from one of LNG, low-temperature ethylene, LPG, low-temperature ethane, low-temperature ammonia, low-temperature propane, low-temperature propylene, low-temperature butane, which comprises: The annular gap cavity of the storage tank is divided into two independent sub-cavities distributed along the height of the inner and outer tank walls by using a thin film isolation plate. The film isolation plate is arranged in the annular gap cavity of the storage tank, and one side edge of the film isolation plate is fixed and sealed to the outer tank sidewall by welding, and the other side edge of the film isolation plate is fixed and sealed to the inner tank sidewall by welding, so that the film isolation plate divides the annular gap cavity of the storage tank into two independent sub-cavities distributed along the height of the inner and outer tank walls; the film isolation plate comprises at least one arch portion, and the extension direction of the arch portion surrounds the inner tank.

[0006] In some embodiments, before the film isolation plate is arranged in the annular gap cavity of the storage tank, the height position of the film isolation plate, the thickness and / or material of the film isolation plate are determined in advance; The number, height, width and / or distance from the edge of the film isolation plate of the arch portion on the film isolation plate are determined by a finite element calculation method, the model used in the finite element calculation method comprises the inner tank, the outer tank, the annular gap cavity of the storage tank and the film isolation plate, and the load used in the finite element calculation method comprises temperature load and pressure load; The temperature field distribution of the film isolation plate is analyzed to determine whether the temperature of the connection part between the film isolation plate and the outer tank is higher than the lower limit value of the temperature of the outer tank material.

[0007] In some embodiments, a support assembly is arranged in the annular gap cavity of the storage tank, the support assembly is used to support the film isolation plate, the support assembly comprises two support rings, one of the support rings is fixed to the inner wall of the outer tank by welding, the other support ring is fixed to the outer wall of the inner tank by welding, and the two side edges of the film isolation plate are welded to the upper sides of the two support rings respectively.

[0008] In some embodiments, the support assembly further comprises a support plate, a support block and dry sand, which are sequentially supported and arranged at the bottom of the film isolation plate from top to bottom.

[0009] In some embodiments, after the film isolation plate is arranged in the annular gap cavity of the storage tank, the following steps are further included: By installing the N2 ring pipe at the bottom of the annular gap of the storage tank, nitrogen gas is continuously injected into the lower cavity, and a slight positive pressure is maintained to prevent water vapor from entering the bottom of the storage tank through the leakage point of the tank bottom, so as to ensure that the storage tank can be continuously and safely used normally.

[0010] In some embodiments, the low-temperature liquefied gas is LNG.

[0011] The tank bottom leakage repair method of the double-metal-wall low-temperature storage tank can make the upper sub-cavity communicate with the inner tank, and the evaporation gas generated by the medium stored in the inner tank can enter the upper sub-cavity, and the two sub-cavities are isolated by the film isolation plate, so that the gas in the upper sub-cavity cannot enter the lower sub-cavity, and the gas leakage from the perforation of the outer tank bottom is blocked.

[0012] Since the width of the annular cavity may increase when the inner tank is radially contracted in cold state, the film isolation plate comprises at least one arch portion, and the extension direction of the arch portion is arranged around the inner tank. The arch portion can provide displacement compensation when the inner tank is radially contracted in cold state, that is, when the width of the annular cavity increases due to the radial contraction of the inner tank in cold state, the height of the arch portion decreases while the width increases to provide displacement compensation, so that the two side edges of the film isolation plate can always be fixed and sealed with the side wall of the inner tank and the side wall of the outer tank.

[0013] It should be understood that the above general description and the following detailed description are only exemplary and explanatory, and cannot limit the application. BRIEF DESCRIPTION OF DRAWINGS

[0014] The drawings incorporated into the specification and forming part of the specification, show embodiments consistent with the application, and together with the specification, serve to explain the principles of the application.

[0015] Figure 1 is a sectional view of a double-metal-wall low-temperature storage tank; Figure 2 is a schematic view of the outer tank bottom perforation leakage of a double-metal-wall low-temperature storage tank; Figure 3 is a schematic view of a double-metal-wall low-temperature storage tank provided with a film isolation plate; Figure 4 is a partial enlarged view of the film isolation plate region in the embodiment of the application; Figure 5 is a schematic view of the leakage repair method of a double-metal-wall low-temperature storage tank in the embodiment of the application.

[0016] REFERENCE NUMERALS: 1-inner tank, 101-inner tank top, 102-inner tank bottom plate, 104-inner tank side wall, 2-outer tank, 201-outer tank top, 202-outer tank side wall, 3-thermal insulation material, 4-supporting table, 5-perforation, 6-film isolation plate, 601-arch portion, 7-supporting ring, 8-foamed glass brick, 9-dry sand. DETAILED DESCRIPTION

[0017] The present disclosure will now be discussed with reference to several embodiments. It should be appreciated that these embodiments are discussed solely for the purpose of enabling those with ordinary skill in the art to better understand and therefore practice the present disclosure and are not intended to limit the scope of the present disclosure in any way.

[0018] As used herein, the terms "comprises," "comprising," "includes," "including," "has," "having," "contains," "containing," or any other similar words, are intended to be interpreted broadeningly and in a non-exclusive manner; the terms "embodiment" and "one embodiment" are to be interpreted as "at least one embodiment"; the term "another embodiment" is to be interpreted as "at least one other embodiment"; the terms "first," "second," etc. can refer to different or identical objects; the term "set" is not limited to direct connections or indirect connections, nor to specific connection manners. Other explicit and implicit definitions can also be included below.

[0019] Some specific numerical values or numerical ranges can be involved in the following description. It should be understood that these numerical values and numerical ranges are only exemplary, which can be beneficial to put the idea of the present disclosure into practice. However, the description of these examples is not intended to limit the scope of the present disclosure in any way. These numerical values or numerical ranges can be set otherwise according to specific application scenarios and requirements.

[0020] Referring to Figure 1 The double-metal wall tank includes an inner tank 1 for containing low-temperature liquefied gas and an outer tank 2 including an outer tank bottom, an outer tank sidewall, and an outer tank top 201. An annular gap cavity is formed between the inner tank 1 and the outer tank 2, and the annular gap cavity is filled with insulation material 3. The outer side of the bottom of the outer tank 2 is provided with a support platform 4 to support the double-metal wall low-temperature tank; wherein the support platform 4 is a concrete platform. In normal operation, the inner tank 2 is filled with medium vapor and maintains a slight positive pressure, which blocks the intrusion of external humid air into the insulation system of the inner tank 1, so that the cold insulation layer between the inner tank 1 and the outer tank 2 is in a dry state, which reduces the thermal conductivity of the insulation material and improves the insulation performance. At the same time, it also plays a good anticorrosion protection role for the tank body, thereby prolonging the service life of the tank. The double-metal wall low-temperature tank is used for storing low-temperature liquefied gas, and the low-temperature liquefied gas is selected from one of LNG, low-temperature ethylene, LPG, low-temperature ethane, low-temperature ammonia, low-temperature propane, low-temperature propylene, and low-temperature butane. Exemplarily, the low-temperature liquefied gas is LNG.

[0021] In the structure of the double-metal wall low-temperature tank, corrosion perforation 5 leakage of the outer tank bottom caused by environmental corrosion is a more common accident. For example, Figure 2As shown, the outer tank side wall and the inner tank side wall 104 are insulated by the thermal insulation material 3, and the outer tank bottom and the inner tank bottom plate 102 are also provided with the thermal insulation material 3. The corrosion perforation 5 of the outer tank bottom leaks water vapor into the tank, thereby causing the water content and oxygen content of the thermal insulation layer in the tank to exceed the specification requirements, the performance of the thermal insulation material 3 of the storage tank is seriously degraded, the medium evaporation rate of the low-temperature storage tank is sharply increased, and the operation efficiency and safety of the low-temperature storage tank are seriously affected. In the prior art, in view of the perforation 5 leakage problem of the outer tank bottom, the storage tank is generally disassembled and rebuilt, which results in a long repair period and huge investment. The repair method based on the application can avoid the leakage of medium evaporation gas from the outer tank bottom and the invasion of external water vapor from the leakage of the outer tank bottom, thereby avoiding the case that the operation efficiency of the storage tank is low, and the repair period is short and the cost is low.

[0022] In view of the above situation, the application provides a tank bottom leakage repair method for a double-metal-wall low-temperature storage tank, which comprises the following steps: S1: The thin film isolation plate 6 is used to divide the storage tank annular gap cavity into two independent sub-cavities distributed along the height of the inner and outer tank walls. The thin film isolation plate 6 is arranged in the storage tank annular gap cavity, and one side edge of the thin film isolation plate 6 is fixed and sealed to the outer tank side wall 202 by welding, and the other side edge of the thin film isolation plate 6 is fixed and sealed to the inner tank side wall 104 by welding, so that the thin film isolation plate 6 divides the storage tank annular gap cavity into two independent sub-cavities distributed along the height of the inner and outer tank walls. The thin film isolation plate 6 comprises at least one arch portion 601, and the extension direction of the arch portion 601 surrounds the inner tank.

[0023] By using the above technical solution, the thin film isolation plate 6 is arranged in the storage tank annular gap cavity, and the thin film isolation plate 6 divides the annular gap cavity into two independent sub-cavities distributed along the height of the outer tank 2. The upper sub-cavity can be in communication with the inside of the inner tank 1, and the evaporation gas generated by the medium stored in the inner tank 1 can enter the upper sub-cavity, and the thin film isolation plate 6 isolates the two sub-cavities, thereby preventing the gas in the upper sub-cavity from entering the lower sub-cavity, and further preventing the gas from leaking out of the perforation 5 of the outer tank bottom.

[0024] Since the width of the annular gap cavity may increase when the inner tank 1 contracts radially in a cold state, the thin film isolation plate 6 comprises at least one arch portion 601, and the extension direction of the arch portion 601 surrounds the inner tank 1. The position of the arch portion 601 and the upper and lower surfaces of the arch portion 601 are both protruded in the same direction. The arrangement of the arch portion 601 can provide displacement compensation when the inner tank 1 contracts radially in a cold state, that is, when the width of the annular gap cavity increases due to the radial contraction of the inner tank 1 in a cold state, the height of the arch portion 601 decreases while the width increases to provide displacement compensation, so as to ensure that the two side edges of the thin film isolation plate 6 can always be fixed and sealed to the inner tank side wall 104 and the outer tank side wall 202.

[0025] In some embodiments, such as Figure 5 As shown, before step S1, the following step is also included: S01: Determine the position, height, thickness, and / or material of the membrane isolation plate 6 in advance; In this step, the height of the membrane partition 6 can be determined based on the construction opening, the pipeline layout within the annular cavity, and the anchor strip arrangement. However, the height and position of the membrane partition 6 must not affect the normal operation of the bimetallic wall storage tank. The membrane partition 6 can be made of stainless steel to facilitate processing and reduce costs.

[0026] Since the perforation 5 is located at the bottom of the outer tank, it is only necessary to isolate the annular cavity in the vicinity of the bottom of the outer tank. Therefore, the height of the membrane isolation plate should be minimized. Based on this, the distance between the membrane isolation plate 6 and the top 201 of the outer tank is greater than the distance between the membrane isolation plate 6 and the bottom of the outer tank; that is, the membrane isolation plate 6 is positioned closer to the bottom of the outer tank than the top 201. This prevents gas from entering the lower sub-cavity from the upper sub-cavity, thus preventing gas leakage from the perforation 5 at the bottom of the outer tank. It also ensures the insulation effect of the upper sub-cavity around the inner tank 1, preventing significant loss of cooling energy from the medium inside the inner tank 1.

[0027] Since the membrane isolation plate 6 needs to bear the pressure of the gas in the upper sub-cavity and the weight of the insulation material, the membrane isolation plate 6 needs to have a certain load-bearing capacity. Based on this, in this embodiment, the thickness of the membrane isolation plate 6 is 1.2mm-2.0mm.

[0028] To adapt to low-temperature media environments and high temperature gradient conditions, the membrane isolation plate 6 can be a metal plate. Specifically, the membrane isolation plate 6 can be a stainless steel plate; for example, austenitic stainless steel, such as S30408 ​​or S30403, can be selected.

[0029] The number, shape, and position of the arches 601 in the thin-film separator 6 have a significant impact on the amount of compensation displacement of the thin-film separator 6. In some embodiments, such as Figure 5 As shown, before step S1, step S02 is also included: using the finite element method to determine the number, height, width and / or distance from the edge of the membrane isolation plate 6 to the arched portion 601 on the membrane isolation plate 6. The model used in the finite element method includes the inner tank 1, the outer tank 2, the annular cavity and the membrane isolation plate 6. The loads used in the finite element method include temperature load and pressure load.

[0030] In some embodiments, such as Figure 5 As shown, before step S1, the following step is also included: S03: Analyzing the temperature field distribution of the thin film insulation plate 6 to determine whether the temperature of the connection part between the thin film insulation plate 6 and the outer tank 2 is higher than the lower limit of the temperature of the material of the outer tank 2. Due to the large temperature difference between the inner tank 1 and the outer tank 2, the finite element temperature field analysis is performed on the inner and outer tanks 2 and the insulation system to determine the temperature field distribution of the thin film insulation plate 6, so as to determine the temperature value of the connection part with the outer tank 2, and avoid the cold brittleness effect on the material of the outer tank 2 caused by the low temperature of the inner tank 1 through the thin film insulation plate 6.

[0031] In some embodiments, in step S1, a support assembly is further arranged in the annular gap cavity of the storage tank, and the support assembly includes two support rings 7, one of which is fixed to the inner wall of the outer tank, and the other is fixed to the outer wall of the inner tank 1, and the two side edges of the thin film insulation plate 6 are respectively arranged on the upper side of the two support rings 7. That is, the two side edges of the thin film insulation plate 6 are respectively supported by the two support rings 7, so that the thin film insulation plate 6 is more stable and is convenient to arrange in the annular gap cavity. Specifically, one of the support rings 7 is fixed to the inner wall of the outer tank by welding, and the other is fixed to the outer wall of the inner tank 1 by welding. The two side edges of the thin film insulation plate 6 are partially overlapped with the two support rings 7 and are fixed by welding, while ensuring the sealing between the two side edges of the thin film insulation plate 6 and the support rings 7, and further ensuring the fixation and sealing of the two side edges of the thin film insulation plate 6 with the outer tank side wall 202 and the inner tank side wall 104. The material of the support ring 7 can include low-temperature steel or austenitic stainless steel resistant to medium temperature.

[0032] In some embodiments, the support assembly includes a support plate arranged at the bottom of the thin film insulation plate 6, which can uniformly support the thin film insulation plate 6 to buffer the pressure of the thin film insulation plate 6 and ensure the stability of the thin film insulation plate 6. Specifically, the support plate can be plywood.

[0033] In some embodiments, the support assembly further includes a support block arranged at the lower side of the support plate, which can include foam glass bricks 8, hard polyurethane foam plates, etc. The foam glass bricks 8 have good compression resistance and good heat insulation performance. Therefore, in this embodiment, the foam glass bricks 8 are used to support the thin film insulation plate 6 and the support plate to ensure the insulation of the upper and lower sub-cavities. The foam glass bricks 8 are brittle materials, and in order to avoid the top of the foam glass bricks 8 being damaged due to excessive local pressure, a layer of support plate is laid at the lower part of the thin film insulation plate 6 to buffer the pressure of the thin film insulation plate 6.

[0034] In order to ensure the flatness of the bottom of the support block, dry sand 9 can be laid on the lower side of the support block to level it, so as to ensure the horizontal positioning of the support block, the support plate and the thin film insulation plate 6, and prevent the thin film insulation plate 6 from being inclined, which causes the upper and lower two sub-cavities to be not completely insulated.

[0035] In some embodiments, asFigure 5 As shown, after the thin film isolation plate is arranged in the annular cavity of the low-temperature storage tank, the low-temperature storage tank further comprises: The N2 ring pipe installed at the bottom of the low-temperature storage tank continuously injects nitrogen and maintains a slight positive pressure to prevent water vapor from entering the bottom of the storage tank through the leakage point of the tank bottom, so that the storage tank can be continuously and safely used. Specifically, the N2 ring pipe fills nitrogen into the lower sub-cavity, fills dry nitrogen into the lower sub-cavity and forms a positive pressure, thereby preventing external water vapor from entering the outer tank 2 through the perforation 5 of the outer tank bottom, preventing the water content and oxygen content of the insulation layer in the tank from exceeding the specification requirements, and avoiding the situation that the running efficiency of the storage tank is low due to the leakage of the tank bottom.

[0036] In addition, the content of the medium evaporation gas in the lower sub-cavity can be monitored in real time to monitor whether the thin film isolation plate 6 leaks, thereby ensuring the normal operation of the bimetallic wall low-temperature storage tank.

[0037] In some embodiments, pressure sensors can be arranged in the upper and lower two independent sub-cavities, and an adjusting valve is arranged at the gas filling port of the lower sub-cavity. By adjusting the flow of dry gas at the gas filling port of the lower sub-cavity, the pressure difference between the upper and lower sub-cavities is controlled, and the pressure in the upper sub-cavity is ensured to be greater than the pressure in the lower sub-cavity.

[0038] Any reference to direction or position in the description of the embodiments herein is only for the purpose of facilitating description and cannot be understood as any limitation on the scope of protection of the present application. The description of the preferred embodiments may involve a combination of features, which may exist independently or in combination, and the present application is not particularly limited to the preferred embodiments. The scope of the present application is defined by the claims.

[0039] The above is only a preferred embodiment of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for repairing a bottom leak in a bimetallic wall cryogenic storage tank, wherein the bimetallic wall cryogenic storage tank is used to store cryogenic liquefied gas, wherein the cryogenic liquefied gas is selected from one of LNG, cryogenic ethylene, LPG, cryogenic ethane, cryogenic liquid ammonia, cryogenic propane, cryogenic propylene, and cryogenic butane, characterized in that, The repair method includes: A thin-film separator is used to divide the annular cavity of the storage tank into two independent sub-cavities that are distributed along the height of the inner and outer tank walls; The membrane partition plate is disposed within the annular cavity of the storage tank, and one edge of the membrane partition plate is fixed and sealed to the outer tank sidewall by welding, while the other edge of the membrane partition plate is fixed and sealed to the inner tank sidewall by welding, so that the membrane partition plate divides the annular cavity of the storage tank into two independent sub-cavities distributed along the height of the inner and outer tank walls; the membrane partition plate includes at least one arched portion, and the extension direction of the arched portion is arranged around the inner tank.

2. The method for repairing bottom leakage of a bimetallic wall cryogenic storage tank according to claim 1, characterized in that, Before installing the membrane isolation plate in the annular cavity of the storage tank, the height, position, thickness and / or material of the membrane isolation plate are determined in advance. The number, height, width and / or distance from the edge of the membrane partition plate are determined by the finite element method. The model used in the finite element method includes the inner tank, outer tank, tank annular cavity and membrane partition plate. The loads used in the finite element method include temperature load and pressure load. The temperature field distribution of the thin-film separator is analyzed to determine whether the temperature at the connection between the thin-film separator and the outer tank is higher than the lower limit of the temperature of the outer tank material.

3. The method for repairing bottom leakage of a bimetallic wall cryogenic storage tank according to claim 1, characterized in that, A support assembly is provided inside the annular cavity of the storage tank. The support assembly is used to support the membrane isolation plate. The support assembly includes two support rings. One of the support rings is fixed to the inner wall of the outer tank by welding, and the other support ring is fixed to the outer wall of the inner tank by welding. The two side edges of the membrane isolation plate are respectively welded to the upper sides of the two support rings.

4. The method for repairing bottom leakage of a bimetallic wall cryogenic storage tank according to claim 1, characterized in that, The support assembly also includes a support plate, a support block, and dry sand, which are arranged sequentially from top to bottom at the bottom of the membrane isolation plate.

5. The method for repairing bottom leakage of a bimetallic wall cryogenic storage tank according to claim 1, characterized in that, After installing a thin-film isolation plate in the annular cavity of the storage tank, the following is also included: By continuously injecting nitrogen through an N2 ring pipe installed in the annular gap at the bottom of the storage tank and maintaining a slight pressurization, water vapor is prevented from entering the bottom of the storage tank through the leak point, ensuring that the storage tank can be used continuously, safely and normally.

6. The method for repairing bottom leakage of a bimetallic wall cryogenic storage tank according to claim 1, characterized in that, The cryogenic liquefied gas is LNG.

Images