Liquefied gas storage tank system and design and manufacturing method thereof

Abstract

Provided are a pressure design method capable of reducing the thickness, weight and cost of a liquefied gas storage tank; a manufacturing method of a liquefied gas storage tank system; and a liquefied gas storage tank system obtained thereby.

Description

Technical Field

[0001] The invention relates to a liquefied gas storage tank system of a ship, and a pressure design method and a manufacturing method of the liquefied gas storage tank system. Background Art

[0002] Generally, liquefied gas storage tanks of maritime structures such as ships are used to transport or store liquefied gas. Among these liquefied gases, liquefied natural gas (LNG) and liquefied petroleum gas (LPG) are stored in liquefied gas storage tanks at extremely low temperatures of -160°C and -45°C, respectively. In liquefied gas storage tanks, the thickness of pressure vessel type C-type liquefied gas storage tanks is designed for each part of the tank (such as head, shell, saddle, dome, storage tank, etc.) according to the purpose of use, by reflecting the design conditions of internal pressure and external pressure. That is, the thickness is designed for each part so as to fully withstand the internal design pressure and external design pressure, and each part of the C-type liquefied gas storage tank is manufactured according to the thickness. The internal pressure and external pressure of the liquefied gas storage tank are designed by reflecting each item defined in the International Code of safety for ships using Gases or other low-flashpoint Fuels (IGF Code). Summary of the invention

[0003] [Technical issues]

[0004] In addition to its internal pressure, the C-type liquefied gas storage tank also bears its external pressure. Therefore, when performing pressure design for the C-type liquefied gas storage tank, the design internal pressure Pi and the design external pressure Pe should be considered separately. That is, after calculating the internal pressure thickness Ti that withstands the design internal pressure Pi and the external pressure thickness Te that withstands the design external pressure Pe, the thickness of each part of the liquefied gas storage tank is designed by using the larger of the two calculated values.

[0005] However, under conventional pressure design, the design internal pressure Pi (0.7MPa(g) to 0.75MPa(g)) is even higher than the design external pressure Pe (0.02MPa(g) to 0.045MPa(g)) (i.e., the internal pressure thickness Ti is even greater than the external pressure thickness Te), so the final thickness of the liquefied gas storage tank is determined by the design internal pressure Pi, and the fluctuation of the design external pressure Pe does not affect the final thickness of the liquefied gas storage tank. Even if the design external pressure changes, the resulting change in the external pressure thickness Te is smaller than the change in the internal pressure thickness Ti, so the change in the design external pressure is not related to the weight and thickness of each part of the liquefied gas storage tank.

[0006] Therefore, normally, when designing the external pressure, all the external pressure items defined in the IGF Rules are habitually reflected without question. In the design external pressure, all the external pressure items defined in the IGF Rules are fully reflected, and although the reflected value is greater than the value usually set for each item defined in the IGF Rules, the internal pressure is still large, so even if the external pressure is designed to deviate from the generally recognized value, the external pressure does not affect the thickness and weight of the liquefied gas storage tank, and the thickness of each part of the liquefied gas storage tank is determined by the design internal pressure. That is, normally, in the design of the liquefied gas storage tank, since the external pressure has nothing to do with the thickness and weight of the liquefied gas storage tank (this may be a matter recognized as technical common sense when designing and manufacturing the liquefied gas storage tank), the design external pressure is not a target of concern, and furthermore, it is inconceivable to reduce the thickness and weight of the liquefied gas storage tank by reducing the design external pressure.

[0007] However, the present inventors have provided a new technology that can reduce the thickness and weight of a liquefied gas storage tank by a new solution that deviates from the technical common sense or prejudice or consensus when designing and manufacturing a liquefied gas storage tank as described above. The present inventors have provided a new technology that enhances the design and manufacturing competitiveness of a liquefied gas storage tank by optimizing the thickness of each part of the liquefied gas storage tank.

[0008] [Technical solution]

[0009] The new technology capable of reducing the thickness and weight of the liquefied gas storage tank provided by the inventor is based on the technical concept of determining the thickness of the liquefied gas storage tank based on the design external pressure, which runs counter to the traditional technical common sense, prejudice or consensus. Therefore, the design external pressure can be reduced by removing some of the items constituting (defining) the design external pressure or reducing the values ​​of some items, and as a result, the thickness and weight of the liquefied gas storage tank can be reduced.

[0010] Without being bound by any particular theory, the inventors have revealed that even when the design internal pressure is still greater than the design external pressure, the thickness and weight of the liquefied gas storage tank are determined as follows when the design internal pressure is within a specific range.

[0011] (1) Conditions where the design internal pressure is about 0.65 MPa(g) or higher (about 6.5 bar(g) or higher) (e.g., about 0.65 MPa(g) to 0.70 MPa(g)):

[0012] Similar to the prior art, the thickness and weight of the liquefied gas storage tank are determined by the design internal pressure and are independent of changes in the design external pressure (eg, changes between approximately 0.045 MPa(g) and 0.020 MPa(g)).

[0013] (2) The design internal pressure is less than about 0.65 MPa(g) (less than about 6.5 bar(g)):

[0014] The reduction in design external pressure reduces the thickness and weight of the liquefied gas storage tank.

[0015] (i) When the design internal pressure is greater than about 0.45 MPa(g) (i.e., when the design internal pressure is greater than 0.45 MPa(g) and less than about 0.65 MPa(g)): the thickness and weight of the liquefied gas storage tank are determined by both the design external pressure and the design internal pressure. For example, in the case where the design external pressure is in the range of about 0.045 MPa(g) to 0.03 MPa(g), when the design internal pressure is about 0.55 MPa(g), the thickness and weight of the liquefied gas storage tank are completely determined by the change in the design external pressure, but when the design external pressure is in a range less than the above range (e.g., in the range of about 0.03 MPa(g) to 0.02 MPa(g)), the change in the design external pressure within this range is not related to the thickness and weight of the liquefied gas storage tank, and the thickness and weight of the liquefied gas storage tank are determined by the design internal pressure;

[0016] (ii) When the design internal pressure is equal to or less than about 0.45 MPa(g):

[0017] The thickness and weight of the liquefied gas storage tank are completely determined by the design external pressure.

[0018] The fluctuation of the design external pressure within the range of approximately 0.045MPa(g) to 0.02MPa(g) determines the thickness and weight of the liquefied gas storage tank.

[0019] Accordingly, in the case of condition (2) for the design internal pressure (i.e., when the design internal pressure is less than about 0.65 MPa(g)), the thickness and weight of the liquefied gas storage tank can be reduced by reducing the design pressure (design internal pressure / design external pressure). For example, when the design internal pressure is less than about 0.65 MPa(g), the design external pressure is reduced to reduce the thickness and weight of the liquefied gas storage tank. When the design external pressure is calculated, some of the items that constitute the design external pressure are removed or the values ​​of the items are reduced, thereby reducing the thickness and weight of the liquefied gas storage tank.

[0020] For example, when operating a liquefied gas storage tank, vacuum pressure may be generated. Accordingly, when designing a liquefied gas storage tank, a minimum value of about 0.025 MPa(g) for the vacuum pressure term P1 considering the vacuum pressure inside the liquefied gas storage tank should be considered as at least one external pressure term in addition to other terms for external pressure (P2: set pressure of pressure relief valves (PRV) for a completely enclosed space containing a pressure vessel or a component of a pressure vessel, P3: compression caused in or on the shell due to the weight and contraction of insulation, the weight of the shell including corrosion allowance, and various other external pressure loads that the pressure vessel can withstand, and P4: external pressure caused by the head of the pressure vessel or a part of the pressure vessel on the exposed deck). Accordingly, the external pressure will be designed to be at least about 0.040 MPa(g). Here, the vacuum pressure term considering the vacuum pressure inside the liquefied gas storage tank is at least about 0.025 MPa(g), and accounts for half or more of the design external pressure of 0.040 MPa(g).

[0021] Therefore, under condition (2) for the design internal pressure (i.e., when the design internal pressure is less than approximately 0.65 MPa(g)), the vacuum pressure inside the liquefied gas storage tank is reduced or eliminated, that is, in the external pressure constituting items P1 to P4, the vacuum pressure item P1 is removed or reduced, which allows the design external pressure to be reduced, thereby reducing the thickness and weight of the liquefied gas storage tank.

[0022] Therefore, one aspect of the present invention provides a pressure design method, a method for manufacturing a liquefied gas storage tank system, and the liquefied gas storage tank system obtained thereby, which can reduce the thickness of the liquefied gas storage tank, reduce the weight of the liquefied gas storage tank and reduce the cost of the liquefied gas storage tank.

[0023] Further, another aspect of the present invention provides a liquefied gas storage tank system that effectively responds to both positive and negative pressures, simplifies facilities for responding to the positive and negative pressures, and reduces costs.

[0024] According to an embodiment of the present invention, a liquefied gas storage tank system includes: a liquefied gas storage tank, which is designed by a designed internal pressure and a designed external pressure under designed internal conditions, and the designed internal conditions at least allow the designed external pressure to determine the thickness of the liquefied gas storage tank; and a vacuum relief valve, which is connected to the liquefied gas storage tank and releases the vacuum pressure generated inside the liquefied gas storage tank.

[0025] A pressure design method for manufacturing a liquefied gas storage tank according to an embodiment of the present invention includes: determining whether the design internal pressure is within a reference pressure range, within which the thickness of the liquefied gas storage tank is determined by at least the design external pressure; and when the design internal pressure is within the reference pressure range, determining the design external pressure by removing or reducing the vacuum pressure item defined for the vacuum pressure inside the liquefied gas storage tank from the pressure item defining the design external pressure.

[0026] A method for manufacturing a liquefied gas storage tank according to an embodiment of the present invention includes: manufacturing the liquefied gas storage tank under design internal pressure conditions according to a determined design internal pressure and a determined design external pressure, wherein the design internal pressure conditions at least allow the design external pressure to determine the thickness of the liquefied gas storage tank; and connecting a pressure control valve for controlling the internal pressure of the liquefied gas storage tank to the liquefied gas storage tank.

[0027] [Beneficial Effects]

[0028] According to the embodiments of the present invention, the thickness of the liquefied gas storage tank can be reduced, and the weight of the liquefied gas storage tank can be reduced and the cost of the liquefied gas storage tank can be reduced.

[0029] Further, according to an embodiment of the present invention, it is possible to effectively respond to both positive pressure and vacuum pressure within a liquefied gas storage tank, and facilities for responding to positive pressure and vacuum pressure can be simplified and costs can be reduced.

[0030] Furthermore, according to an embodiment of the present invention, the liquefied gas stored in the liquefied gas storage tank can be prevented from flowing back to the outside, and both the positive pressure and the vacuum pressure within the liquefied gas storage tank can be effectively responded to, and the facilities for responding to the positive pressure and the vacuum pressure can be simplified and the cost can be reduced.

[0031] The problems and effects to be solved by the present invention are not limited to the above-mentioned purposes and effects. According to the following description, those skilled in the art to which the present invention belongs will be able to clearly understand other technical problems and effects not mentioned. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The design external pressure range imposed on the thickness and weight of the liquefied gas storage tank is schematically shown, and the design external pressure range is obtained according to the research results of the inventors based on a new scheme related to the pressure design of the liquefied gas storage tank.

[0033] Figure 2 A pressure design method for determining the thickness of a liquefied gas storage tank according to an embodiment of the present invention is schematically illustrated.

[0034] Figure 3 Schematically shows the Figure 2 Manufacturing method of liquefied gas storage tank system designed for pressure.

[0035] Figure 4 A liquefied gas storage tank system according to an embodiment of the present invention is schematically shown.

[0036] Figure 5 A combination of a vacuum relief valve and a liquefied gas storage tank according to an embodiment of the present invention is shown.

[0037] FIG. 6 is a diagram for schematically describing the operation of the vacuum relief valve according to the embodiment of the present invention.

[0038] Figure 7 A liquefied gas storage tank system according to another embodiment of the present invention is schematically shown.

[0039] Figure 8 The figure schematically shows a liquefied gas storage tank system according to another embodiment of the present invention.

[0040] Fig. 9 The figure schematically shows a liquefied gas storage tank system having an isolation valve according to an embodiment of the present invention.

[0041] Fig.10 The figure schematically shows a liquefied gas storage tank system according to another embodiment of the present invention.

[0042] Fig.11 Shows Fig.10 The combined relationship between the positive pressure derivation valve, the liquefied gas storage tank and the vacuum pressure analysis source.

[0043] Fig.12 is a graph for describing the effect according to the embodiment of the present invention.

[0044] Fig.13 The figure schematically shows a liquefied gas storage tank system according to another embodiment of the present invention.

[0045] Fig.14 The figure schematically shows a liquefied gas storage tank system according to another embodiment of the present invention.

[0046] Fig.15 The figure schematically shows a liquefied gas storage tank system according to another embodiment of the present invention.

[0047] Fig.16 and 17 To show the basis Fig.15 A diagram of an operating state of a liquefied gas storage tank system of an embodiment, and Fig.16 The vacuum relief valve performs pressure derivation operation. Fig.17The state in which the vacuum relief valve performs a vacuum extraction operation is shown. DETAILED DESCRIPTION

[0048] The advantages and features of the present invention, and the methods for achieving these advantages and features will be more clearly understood from the embodiments described in detail below with reference to the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, and the present invention is defined only by a series of claims. Even if not defined, all terms (including technical terms or scientific terms) used herein have the same meaning as the general technology generally accepted in the prior art to which the present invention belongs. The general description of known configurations can be omitted to avoid blurring the main points of the present invention. In the accompanying drawings of the present invention, the same figure numerals are used for the same or corresponding parts. In order to help understand the present invention, some parts in the figure may be exaggerated or reduced.

[0049] The terms used herein are only used to describe specific embodiments and are not intended to limit the inventive concept. As used herein, the singular forms "one, an", "the" also include plural forms unless the context clearly indicates otherwise. It should be further understood that the terms "include" and / or "comprise" when used in this specification specify the presence of the features, integers, steps, operations, elements and / or parts, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, parts and / or groups thereof.

[0050] It should be understood that although the terms "first", "second", "third", etc. may be used herein to describe various elements and components, these elements and components should not be limited by these terms. These terms are only used to distinguish one element or component from another element or component. Therefore, without departing from the teachings of the present inventive concept, the first pipe and the first pipe portion in one embodiment may be referred to as the second pipe and the second pipe portion, respectively, in another embodiment.

[0051] For the purposes of this specification and the appended claims, unless otherwise indicated, all numerals representing quantities, percentages or ratios and other numerical values ​​used in the specification and claims should be understood to be modified by the term "about" in all cases. The use of the term "about" applies to all numerical values, whether or not explicitly indicated. This term generally refers to a numerical range that a person of ordinary skill in the art would consider to be a reasonable deviation amount (i.e., having an equivalent function or result) of the listed numerical values. For example, this term can be interpreted as including deviations of ±10%, alternatively ±5%, alternatively ±1%, alternatively ±0.5%, and alternatively ±0.1% of a given numerical value, as long as such deviations do not change the final function or result of the value. Therefore, unless otherwise indicated, the numerical parameters set forth in this specification and the appended claims are approximate values, which can vary according to the desired characteristics sought to be obtained by the present invention.

[0052] The present invention relates to a liquefied gas storage tank system and provides a technology capable of reducing the thickness of the liquefied gas storage tank, reducing the weight of the liquefied gas storage tank and reducing the cost of the liquefied gas storage tank.

[0053] The thickness of a liquefied gas storage tank depends on the design pressures for the internal and external pressures of the liquefied gas storage tank, and an embodiment of the present invention provides a method for reducing the thickness or weight of the liquefied gas storage tank by reducing the design pressure value of the external pressure of the liquefied gas storage tank, thereby reducing the thickness or weight of the liquefied gas storage tank by adopting a technical approach that enables some of the items constituting the external pressure to be removed or minimized when designing the external pressure of the liquefied gas storage tank.

[0054] In addition to its external pressure, the C-type liquefied gas storage tank must also withstand its internal pressure. That is, after calculating the internal pressure thickness Ti for the design internal pressure Pi and the external pressure thickness Te for the design external pressure Pe by independently considering the design internal pressure Pi and the design external pressure Pe, the pressure of the C-type liquefied gas storage tank is designed by using the larger of the two calculated values.

[0055] Generally speaking, the design internal pressure of a Type C liquefied gas storage tank (about 0.7MPa(g) to 0.75MPa(g) (about 7bar(g) to 7.5bar(g))) is, for example, at least 16 to 17 times or more the design external pressure (about 0.045MPa(g) on ​​average). Therefore, the design thickness of each part of the liquefied gas storage tank (for example, the head, shell, saddle, dome, storage tank, etc.) is determined by the design internal pressure. That is, under the conventional design internal pressure (0.7MPa(g) to 0.75MPa(g)), the thickness and weight of the liquefied gas storage tank are determined according to the design internal pressure, regardless of the size of the design external pressure. Normally, since changes in the design external pressure will not affect the thickness and weight of the liquefied gas storage tank, all external pressure items defined in the IGF rules will be habitually reflected in the design external pressure without any doubt.

[0056] When designing a liquefied gas storage tank, it is technical common sense, prejudice or consensus that the design external pressure has nothing to do with the thickness and weight of the liquefied gas storage tank, so the design external pressure is not the focus, and furthermore, it is inconceivable to promote the reduction of the thickness and weight of the liquefied gas storage tank by changing the design external pressure (for example, reducing the design external pressure).

[0057] However, the inventors have provided a new technology that can reduce the thickness and weight of liquefied gas storage tanks through a new solution that deviates from technical common sense or industry prejudice or consensus. The inventors have provided a new technology that enhances the design and manufacturing competitiveness of liquefied gas storage tanks by optimizing the thickness of each part of the liquefied gas storage tank.

[0058] The new technology capable of reducing the thickness and weight of the liquefied gas storage tank provided by the inventor is based on the technical concept of determining the thickness of the liquefied gas storage tank based on the design external pressure, which runs counter to the traditional technical common sense, prejudice or consensus. Therefore, the design external pressure can be reduced by removing some of the items constituting the design external pressure or reducing the values ​​of some items, and as a result, the thickness and weight of the liquefied gas storage tank can be reduced.

[0059] Without being bound by any particular theory, the inventors have revealed that even when the design internal pressure is still greater than the design external pressure, when the design internal pressure is within a specific range, a reduction in the design external pressure also reduces the thickness and weight of the liquefied gas storage tank. The correlation between the design pressure and the thickness and weight of the liquefied gas storage tank derived by the inventors is as follows.

[0060] (1) Conditions where the design internal pressure is about 0.65 MPa(g) or higher (about 6.5 bar(g) or higher) (e.g., about 0.65 MPa(g) to 0.70 MPa(g)):

[0061] Fluctuations in the design external pressure within the range of approximately 0.045 MPa(g) to 0.02 MPa(g) do not affect the thickness and weight of the liquefied gas storage tank, and the thickness and weight of the liquefied gas storage tank are completely determined by the design internal pressure.

[0062] (2) The design internal pressure is less than about 0.65 MPa(g) (less than about 6.5 bar(g)):

[0063] The reduction in design external pressure reduces the thickness and weight of the liquefied gas storage tank.

[0064] (i) When the design internal pressure is greater than about 0.45 MPa(g) under the condition that the design internal pressure is less than about 0.65 MPa(g) (i.e., when the design internal pressure is greater than 0.45 MPa(g) and less than about 0.65 MPa(g)):

[0065] The thickness and weight of the liquefied gas storage tank are determined by both the design external pressure and the design internal pressure. That is, the thickness and weight of the liquefied gas storage tank are determined by the design external pressure in the design external pressure within a specific range, and the thickness and weight of the liquefied gas storage tank are determined by the design internal pressure in the design external pressure range of the design external pressure or a smaller design internal pressure. For example, in the case where the design external pressure is in the range of about 0.045MPa(g) to 0.03MPa(g), when the design internal pressure is about 0.55MPa(g), the thickness and weight of the liquefied gas storage tank are completely determined by the change in the design external pressure, but when the design external pressure is within a range less than the above range (for example, a range of about 0.03MPa(g) to 0.02MPa(g)), the change in the design external pressure within this range is not related to the thickness and weight of the liquefied gas storage tank, and the thickness and weight of the liquefied gas storage tank are determined by the design internal pressure.

[0066] (ii) When the design internal pressure is less than about 0.65 MPa(g) and the design internal pressure is about 0.45 MPa(g):

[0067] The thickness and weight of the liquefied gas storage tank are completely determined by the design external pressure.

[0068] The fluctuation of the design external pressure within the range of approximately 0.045MPa(g) to 0.02MPa(g) determines the thickness and weight of the liquefied gas storage tank.

[0069] That is to say, under the condition that the design internal pressure is still greater than the design external pressure, as the design internal pressure decreases, the factors determining the thickness and weight of the liquefied gas storage tank change in the order of design internal pressure, design external pressure and design internal pressure, and design external pressure.

[0070] Accordingly, in the case of condition (2) for the design internal pressure (ie, when the design internal pressure is less than about 0.65 MPa(g)), the thickness and weight of the liquefied gas storage tank can be reduced by lowering the design pressure.

[0071] For example, when the design internal pressure is less than about 0.65MPa(g), the vacuum pressure item P1 in the external pressure components P1 to P4 is removed or reduced, thereby reducing the design external pressure and correspondingly reducing the thickness and weight of the liquefied gas storage tank. The removal or reduction of the vacuum pressure item P1 of the design external pressure can be compensated by installing a vacuum pressure relief valve in the liquefied gas storage tank. Accordingly, when the design internal pressure is less than about 0.65MPa(g), a vacuum pressure relief valve is installed in the liquefied gas storage tank, which has the unexpected result of reducing the thickness and weight of the liquefied gas storage tank. In other words, when the design internal pressure is less than about 0.65MPa(g), the vacuum pressure relief valve may have the effect of reducing the thickness and weight of the liquefied gas storage tank.

[0072] Accordingly, when designing a liquefied gas storage tank, a minimum value of about 0.025 MPa(g) for the vacuum pressure item P1 considering the vacuum pressure inside the liquefied gas storage tank should be regarded as at least one external pressure item in addition to other items for external pressure (P2: set pressure of a pressure relief valve (PRV) for a completely enclosed space containing a pressure vessel or a component of a pressure vessel, P3: compression in or on the shell due to the weight and contraction of insulation, the weight of the shell including corrosion allowance, and other various external pressure loads that the pressure vessel can withstand, and P4: external pressure due to the head of the pressure vessel or a part of the pressure vessel on the exposed deck). Accordingly, the external pressure will be designed to be at least about 0.040 MPa(g). Here, the vacuum pressure item of at least about 0.025 MPa(g) considering the vacuum pressure inside the liquefied gas storage tank accounts for half or more of the design external pressure of 0.040 MPa(g).

[0073] Here, the inventors note that the vacuum pressure term considering the vacuum pressure inside the liquefied gas storage tank is at least about 0.025MPa (g) and accounts for half or more of the design external pressure. Therefore, in an embodiment of the present invention, when the vacuum pressure-related term is removed from the term constituting the design external pressure or the vacuum pressure-related term is minimized, the effect of reducing the thickness and weight of the liquefied gas storage tank can be maximized. At the same time, since the removal / reduction of the vacuum pressure term under the design pressure requires the prevention of the situation where vacuum pressure is generated when operating the liquefied gas storage tank, the liquefied gas storage tank according to an embodiment of the present invention has a device for removing / reducing the vacuum pressure that may be generated therein. For example, a vacuum relief valve (that is, a vacuum pressure reducing valve) is used to remove / reduce the vacuum pressure inside the liquefied gas storage tank. The vacuum relief valve is configured to operate to open automatically when the pressure inside the liquefied gas storage tank is a predetermined pressure, thereby preventing the inside of the liquefied gas storage tank from becoming a vacuum. For example, when a vacuum pressure of about 0.005MPa (g) is generated inside the liquefied gas storage tank, the vacuum relief valve can be configured to open automatically. In this case, it can be understood that the value of the vacuum pressure term constituting the design external pressure is about 0.005 MPa(g).

[0074] Furthermore, in the present invention, the reduced portion of the value of the vacuum pressure item constituting the design external pressure is reflected as other items of the design external pressure, for example, item P3 (compression generated in or on the shell due to the weight and shrinkage of the insulation, the weight of the shell including the corrosion allowance, and various other external pressure loads that the pressure vessel can withstand), item P4 (external pressure generated due to the head of the pressure vessel or a part of the pressure vessel on the exposed deck), etc., so as to improve the manufacturing flexibility of the liquefied gas storage tank.

[0075] The content disclosed in this specification provides a method for reducing the thickness and weight of a liquefied gas storage tank by reducing the design pressure value of the external pressure of the liquefied gas storage tank. Therefore, the embodiment of the present invention will be particularly effectively applicable to situations where the thickness of the liquefied gas storage tank is mainly determined by the external pressure.

[0076] The condition where the thickness of the liquefied gas storage tank is determined by the design external pressure may include a case where the design internal pressure is within a predetermined range e (e.g., less than about 0.65 MPa(g)), and as the design internal pressure decreases, the influence of the design external pressure on the thickness of the liquefied gas storage tank gradually increases, and when the design internal pressure is about 0.45 MPa(g), the thickness of the liquefied gas storage tank is completely determined by the design external pressure. Therefore, for example, the embodiments of the present invention can be effectively applied to a case where the design pressure of the internal pressure of the liquefied gas storage tank is less than about 0.65 MPa(g).

[0077] Considering that the design external pressure of the liquefied gas storage tank is at least about 0.020 MPa(g) and the design internal pressure is less than about 0.65 MPa(g), a specific embodiment of the present invention provides a method for manufacturing a liquefied gas storage tank.

[0078] Hereinafter, the method will be described with reference to the accompanying drawings.

[0079] Figure 1 The design external pressure range imposed on the thickness and weight of the liquefied gas storage tank is schematically shown, and the design external pressure range is obtained according to the research results of the inventors based on a new scheme related to the pressure design of the liquefied gas storage tank. Figure 1 It shows the weight change (unit: %) (vertical axis) of the liquefied gas storage tank depending on the change of the design external pressure Pe (0.045MPa(g)->0.02MPa(g)) (horizontal axis) when the design internal pressure Pi changes differently, such as about 0.45MPa(g), about 0.55MPa(g), and about 0.65MPa(g).

[0080] exist Figure 1 In the figure, the reference weight is set relative to the weight change of the liquefied gas tank and the case where the design external pressure is 0.045 MPa(g) is displayed as 100%. For example, 90% means that the weight of the liquefied gas tank is reduced by about 10% compared with the case where the design external pressure is 0.045 MPa(g).

[0081] refer to Figure 1 , it can be verified that within a specific range of design internal pressure, as the design external pressure changes (that is, as the design external pressure decreases), the weight of the liquefied gas storage tank also changes (decreases).

[0082] Specifically, it can be seen that when the design internal pressure is about 0.65 MPa(g) or greater than 0.65 MPa(g), even if the design external pressure changes (that is, even if the design external pressure decreases from about 0.045 MPa(g) to about 0.02 MPa(g)), the weight of the liquefied gas storage tank does not change. That is, when the design internal pressure is about 0.65 MPa(g) or greater than 0.65 MPa(g), the thickness and weight of the liquefied gas storage tank completely depend on the design internal pressure.

[0083] However, it can be seen that when the design internal pressure is about 0.45MPa(g) or lower than 0.45MPa(g), the weight of the liquefied gas storage tank decreases in proportion to the decrease in the design external pressure. That is, it can be verified that as the design external pressure decreases from 0.045MPa(g)->0.04MPa(g)->0.035MPa(g)->0.030MPa(g)->0.025MPa(g)->0.020MPa(g), the weight of the liquefied gas storage tank gradually decreases from 100%->99%->92%->88%->84%->80%. For example, when the design internal pressure is about 0.45 MPa(g), when the design external pressure is reduced from about 0.045 MPa(g) to about 0.025 MPa(g), the weight of the liquefied gas storage tank is reduced by about 16%, and when the design external pressure is reduced to about 0.020 MPa(g), the weight of the liquefied gas storage tank is reduced by about 20%.

[0084] Meanwhile, when the design internal pressure is lower than about 0.65 MPa(g) but higher than about 0.45 MPa(g), the weight of the liquefied gas storage tank is affected by the design external pressure within a specific range. Within the range of the design external pressure of about 0.045 MPa(g) to 0.030 MPa(g), the weight of the liquefied gas storage tank decreases as the design external pressure decreases. However, when the design external pressure is within the range of 0.030 MPa(g) to 0.020 MPa(g), the liquefied gas storage tank does not change in response to the decrease in the design external pressure.

[0085] refer to Figure 1 It can be seen that when the design internal pressure is equal to or greater than 0.65MPa(g), the change of the design external pressure will not affect the weight of the liquefied gas storage tank, but when the design internal pressure is less than about 0.65MPa(g), the weight of the liquefied gas storage tank decreases with the change of the design external pressure (as the design external pressure decreases).

[0086] That is to say, the inventors obtained an unexpected and surprising result, namely, when the design internal pressure is within a specific range, the design external pressure will affect the thickness of the liquefied gas storage tank and then affect the weight of the liquefied gas storage tank, which is different from the general technical common sense known in the industry.

[0087] Therefore, when the inventors utilize the Figure 1 When the technical ideas or inventive concepts verified in the above are verified, the weight of the liquefied gas storage tank can be reduced and the cost can be reduced. Figure 1is described in detail. When the design internal pressure is set to be less than 0.65MPa(g), the design external pressure can be reduced, thereby reducing the thickness of the liquefied gas storage tank in response to the reduction in the design external pressure and thus reducing the weight of the liquefied gas storage tank. In particular, since the external pressure component P1 (about 0.025MPa(g), taking into account the vacuum pressure that may be generated when operating the liquefied gas storage tank) is half or more of the total external pressures P1 to P4 (about 0.045MPa(g) on ​​average), simply removing or reducing the vacuum pressure component P1 from the design external pressure component can reduce the weight of the liquefied gas storage tank over a large range. Further, since the vacuum pressure term in the design external pressure is considered in view of the situation in which vacuum pressure is generated inside the liquefied gas storage tank, excluding the vacuum pressure-related term requires that vacuum pressure should not be generated inside the liquefied gas storage tank, and this can be achieved by providing a vacuum relief valve in the liquefied gas storage tank.

[0088] For example, when it is assumed that the design internal pressure is set to about 0.45 MPa(g) and a vacuum relief valve is installed in the liquefied gas storage tank, the vacuum pressure-related item P1 among the items constituting the design external pressure may be reduced, and by considering the operating tolerance of the vacuum relief valve, the design external pressure can be reduced by about 0.020 MPa(g). As a result, the weight of the liquefied gas storage tank can be reduced by about 16%, as shown in FIG. Figure 1 as shown in .

[0089] On the contrary, if Figure 1 It can be determined that when the design internal pressure is about 0.65MPa(g) or greater than 0.65MPa(g), the thickness and weight of the liquefied gas storage tank completely depend on the design internal pressure. Accordingly, unlike the embodiment of the present invention, when the conventional design internal pressure is designed to be 0.7MPa(g) to 0.75MPa(g), although the design external pressure is reduced by installing a vacuum pressure relief valve, the weight of the liquefied gas storage tank may not be reduced. Therefore, under conventional circumstances, reducing the weight of the liquefied gas storage tank by connecting a vacuum pressure relief valve to the liquefied gas storage tank exceeds technical common sense and rules of thumb and is unthinkable.

[0090] The embodiments of the present invention provide a method for pressure designing to determine the thickness of a liquefied gas storage tank based on the basic concept or technical idea of ​​the present invention described above, and a method for manufacturing a liquefied gas storage tank system accordingly.

[0091] Figure 2 A pressure design method for determining the thickness of a liquefied gas storage tank according to an embodiment of the present invention is schematically illustrated.

[0092] In step S11, the design internal pressure P is determined in the pressure design related to the thickness of the liquefied gas storage tank. d_int , and determine the design internal pressure P d_intIs it the reference pressure value or within the reference pressure range P ref Within this reference pressure range, the design external pressure P d_ext To determine the thickness of the liquefied gas storage tank. In step S10, for example, in the embodiment, the reference pressure range P ref In step S11, the reference pressure range may be, for example, equal to or greater than about 0.45 MPa(g) and less than about 0.65 MPa(g), for example, equal to or greater than about 0.45 MPa(g) and less than about 0.55 MPa(g), for example, equal to or greater than about 0.45 MPa(g) and less than about 0.50 MPa(g), for example, equal to or greater than about 0.45 MPa(g) and less than 0.60 Pa.

[0093] In step S13, when the design internal pressure P d_int In the reference pressure range P ref When the vacuum pressure P is considered, the vacuum pressure inside the liquefied gas tank vac From the definition (construction) design external pressure P d_ext The design external pressure P is excluded or minimized from the pressure term d_ext Normally, the vacuum pressure P that constitutes one item of the design external pressure is vac The minimum value can be 0.025MPa(g), and except for the vacuum pressure P vac The other external pressure items other than 0.015 MPa (g) can be 0.015 MPa (g). However, according to an embodiment of the present invention, in step S13, the vacuum pressure P can be removed. vac Or reduce the vacuum pressure to 0.005 MPa (g) (ie, vacuum pressure P vac The minimum reduction can be 0.02MPa(g)) - this means that the design external pressure is reduced by 0.02MPa(g) compared with the conventional design external pressure, and the thickness of the liquefied gas storage tank can be reduced in response to the reduction amount. As a result, the weight of the liquefied gas storage tank can be reduced.

[0094] Therefore, according to an embodiment of the present invention, the determined design external pressure P ext The minimum design internal pressure can be about 0.020MPa(g). d_int The maximum value may be about 0.65 MPa (g). In one embodiment, the design external pressure P ext For example, it can be a minimum of about 0.020 MPa(g), equal to or greater than about 0.020 MPa(g) and less than about 0.045 MPa(g), equal to or greater than about 0.020 MPa(g) and equal to or less than about 0.030 MPa(g), and equal to or greater than about 0.020 MPa(g) and equal to or less than about 0.040 MPa(g).

[0095] In the implementation scheme, the design internal pressure P d_int It can be less than about 0.65MPa(g). Design internal pressure P d_int It can be, for example, equal to or greater than about 0.45 MPa(g) and less than about 0.65 MPa(g), for example, equal to or greater than about 0.45 MPa(g) and less than about 0.55 MPa(g), for example, equal to or greater than about 0.45 MPa(g) and less than about 0.50 MPa(g), and for example, equal to or greater than about 0.45 MPa(g) and less than 0.60 MPa(g).

[0096] Furthermore, the design internal pressure P d_int can be set to various pressure ranges between 0.45 and 0.65 (including 0.45 but excluding 0.65) (unit: MPa(g)) as the lower limit and upper limit, respectively. ext It can be set to various pressure ranges between 0.02 and 0.045 (including 0.02 but excluding 0.045) (unit: MPa(g)), which are the lower limit value and the upper limit value, respectively.

[0097] Under the condition that there will be no numerical conflict in the pressure design of liquefied gas storage tanks, any set of design internal pressure P can be selected. d_int Value or range and design P ext The value or range is used as the design internal pressure and design external pressure.

[0098] In reference Figure 2 In the method described for designing a storage tank, the design internal pressure P d_int Can be equal to the reference pressure range P ref , this reference pressure range becomes a reference for determining the weight of the liquefied gas storage tank by designing the external pressure.

[0099] Next, refer to Figure 3 , will describe the Figure 2 A method for manufacturing a liquefied gas storage tank system according to an embodiment of the present invention is based on a pressure design.

[0100] In step S21, according to Figure 2 The design internal pressure P determined by the pressure design d_int and design external pressure P d_ext To manufacture a liquefied gas storage tank (to withstand the design pressure). As described above, according to the embodiment, the thickness of the liquefied gas storage tank can be reduced in response to the reduced or removed vacuum pressure item (external pressure value) in the items constituting the design external pressure in the pressure design, and the weight of the liquefied gas storage tank can be reduced in response to the reduced thickness.

[0101] At the same time, since the vacuum pressure item is excluded from the items constituting the design external pressure, it should be ensured that the vacuum is not generated in the liquefied gas storage tank. For this reason, in step S23, a device for preventing / eliminating the generation of vacuum (vacuum pressure) is prepared. For example, as a device for preventing / eliminating the generation of vacuum pressure, a vacuum relief valve can be prepared.

[0102] In step S25, a device for preventing / removing the generation of vacuum pressure is connected to the liquefied gas storage tank. For example, the device for preventing / removing the generation of vacuum pressure is connected to the upper part of the liquefied gas storage tank. In the manufacturing method of the liquefied gas storage tank according to the present embodiment, it is easy to prevent the generation of vacuum inside the liquefied gas storage tank only by connecting the vacuum relief valve to the liquefied gas storage tank. In the manufacturing method of the liquefied gas storage tank, the order of step S21 and step S23 is not important, even if step S21 and step S23 are performed in a predetermined order. Figure 5 The scheme of connecting the device for preventing / removing the generation of vacuum pressure to the liquefied gas storage tank can be understood from the following related description.

[0103] Figure 4 The liquefied gas storage tank system according to an embodiment of the present invention is schematically shown. The liquefied gas storage tank system according to this embodiment can be referred to Figure 3 The method described is used to manufacture.

[0104] refer to Figure 4 , the liquefied gas storage tank system 1000 includes a liquefied gas storage tank 100 and a vacuum pressure generation prevention device / vacuum pressure relief device 10. Specifically, as a vacuum pressure generation prevention device / vacuum pressure relief device, a vacuum pressure relief valve 10 is provided in the liquefied gas storage tank 100. The liquefied gas storage tank 100 includes an internal space for storing liquefied gas, and can be configured to include a pressure vessel type C-type tank with a cylindrical structure having a circular cross-section and an insulator covering the outside of the C-type tank. The C-type tank can contain liquefied gas in an ultra-low temperature state, such as liquefied natural gas (LNG), liquefied petroleum gas (LPG), etc. The liquefied gas storage tank 100 can be supported by a supporting device installed in the hull. The supporting device can be configured to include one or more supporting devices that support the C-type liquefied gas storage tank in a fixed state and a supporting device that can slidably support the C-type tank to respond to the thermal contraction / expansion of the C-type liquefied gas storage tank.

[0105] The vacuum relief valve 10 can be connected to the upper part of the liquefied gas storage tank 100. The vacuum relief valve 10 includes a first inlet 10A and a second inlet 10B. The first inlet 10A of the vacuum relief valve 10 is connected to communicate with the internal fluid at the upper part of the liquefied gas storage tank 100. The second inlet 10B of the vacuum relief valve 10 is exposed to a vacuum relief source (e.g., atmosphere or air), or an inert gas connected to the vacuum relief source. For example, one end of the second inlet 10B of the vacuum relief valve 10 is opened to communicate with the atmosphere or air, or an inert gas. Therefore, according to the present embodiment, when vacuum pressure is generated in the internal space of the liquefied gas storage tank 100, the vacuum relief valve 10 is in an open state (a state in which the first inlet and the second inlet are connected to the inside of the liquefied gas storage tank 100, and as a result, liquid can flow), and therefore, the atmosphere or inert gas connected to the second inlet 10B is introduced into the liquefied gas storage tank 100 through the first inlet 10A to release (remove) the vacuum pressure (vacuum state) of the internal space of the liquefied gas storage tank 100. In the present embodiment, the first inlet 10A and the second inlet 10B of the vacuum relief valve 10 may be respectively referred to as an inlet and an outlet based on the direction in which a fluid (e.g., atmosphere) flows through the vacuum relief valve 10 during operation.

[0106] Meanwhile, for example, the vacuum pressure may be a pressure of 0 MPa(g) (0 bar(g)) or less. The vacuum relief valve 10 may be configured to be automatically opened to release the vacuum pressure when the internal pressure is less than a set pressure relative to the vacuum pressure. As an example, the vacuum relief valve 10 may be automatically opened when the pressure of the liquefied gas storage tank 100 decreases and becomes, for example, 0 barg. Alternatively, when the difference between the internal pressure and the external pressure of the liquefied gas storage tank 100 is approximately 0.005 MPa(g), that is, when the internal pressure of the liquefied gas storage tank 100 is approximately 0.005 MPa(g) lower than the atmospheric pressure, the vacuum relief valve 10 may be automatically opened, which is consistent with the vacuum pressure P vac In reference Figure 2 This corresponds to the case where the pressure design method described in the reference is reduced to 0.005 MPa (g). Figure 2 In the pressure design method, when manufacturing a liquefied gas storage tank by designing the vacuum pressure item of the designed external pressure from the traditional 0.025MPa(g)×0.002MPa(g) to 0.005MPa(g), when the internal pressure of the liquefied gas storage tank is approximately 0.005MPa(g) lower than the atmospheric pressure, the vacuum relief valve connected to the liquefied gas storage tank is configured to open automatically.

[0107] Will refer to Figure 5 The detailed structure of the vacuum relief valve 10 and the connection with the liquefied gas storage tank 100 are described.

[0108] refer to Figure 5, the vacuum relief valve 10 may be configured to include: a valve body 10C, which defines a second inlet 10B (inlet) and a first inlet 10A (outlet); a valve plate 10D; a valve cover 10E; a valve nozzle 10F; and a valve plate guide G. The second inlet 10B and the first inlet 10A are configured to change the flow direction of a fluid (such as a gas), for example, to change the flow direction of the fluid by about 90 degrees. The first inlet 10A is connected to the liquefied gas storage tank 100 to be in fluid communication with the liquefied gas storage tank 100. For example, the first inlet 10A may be connected to the liquefied gas storage tank 100 through a pipe. The second inlet 10B is in communication with external air, atmosphere, or inert gas. For example, when vacuum pressure is generated in the liquefied gas storage tank 100, the external air, atmosphere, or inert gas introduced into the second inlet 10B (inlet) may be introduced into the liquefied gas storage tank 100 through the first inlet 10A (outlet), and as a result, the vacuum pressure inside the liquefied gas storage tank 100 is released.

[0109] The valve plate 10D is disposed inside the valve body 10C and is configured to close the second inlet 10B (inlet) (in this case, the valve is in a closed state). The valve cover 10E closes the upper portion of the valve body 10C on the side opposite to the second inlet 10B. The valve plate guide 10G is fixedly coupled to the valve cover 10E, the valve plate 10D is movably coupled to the valve plate guide 10G (vertically movable), and in an idle state, the valve plate 10D is configured to close the second inlet 10B. As an example, the valve nozzle 10F may be coupled to the inner wall of the second inlet 10B, and in this case, the valve plate 10D closes one end of the valve nozzle 10F in the valve body 10C to close the second inlet 10B.

[0110] The valve plate 10D is configured to move between one end of the valve nozzle 10F and the valve cover 10E according to the internal pressure condition of the liquefied gas storage tank 100. The area ds of the bottom surface of the valve plate 10D (the portion exposed to the second inlet 10B) and the self-weight of the valve plate 10D are set according to a predetermined pressure range or pressure value. That is, when a vacuum pressure of a predetermined range or value is generated inside the liquefied gas storage tank 10, the thickness (self-weight) and area of ​​the bottom surface are set accordingly, so that the valve plate 10D seated on the valve nozzle 10F is lifted upward toward the valve cover 10E.

[0111] When the pressure of the liquefied gas fuel tank 100 is high, a force is applied in the downward direction (direction of gravity) through the dead weight of the valve plate 10D and the high pressure of the fuel tank 100 (see the arrow on the screen), and as a result, the valve plate 10D sits on the valve nozzle 10F to keep the valve plate in a closed state.

[0112] However, when the internal pressure of the liquefied gas fuel tank 100 decreases and reaches the vacuum pressure (see FIG. 6A ), the atmospheric force applied to the area ds becomes greater than the dead weight of the valve plate 10D, and therefore, the atmosphere lifts the valve plate 10C upward (toward the valve cover 10E) to put it in an open state (a state in which a fluid passage is formed between the first inlet 10A and the second inlet 10B). When the valve is opened, the atmosphere or air is introduced into the liquefied gas fuel tank 100, and as a result, the internal pressure of the liquefied gas fuel tank 100 increases and the vacuum pressure is released.

[0113] When the internal pressure of the fuel gas tank 100 is increased by introducing the atmosphere and the vacuum pressure is released (see Figure 6B), the force applied in the downward direction (in the gravity direction, toward the second inlet 10B) becomes greater than the force applied to the area ds of the bottom surface of the valve plate 10D by the dead weight of the valve plate 10D and the high pressure of the fuel gas tank 100. As a result, the valve plate 10D moves downward toward the valve nozzle 10F and sits on the valve nozzle 10F again, and the valve plate is thereby closed.

[0114] The predetermined pressure range or pressure value inside the liquefied gas tank 100 for opening the valve plate 10D may be, for example, a range of about 0.025 MPa(g) to 0.000 MPa(g), or, for example, about -0.040 MPa(g). The predetermined pressure value may be, for example, about 0.050 MPa(g).

[0115] Figure 5 The structure of the vacuum relief valve 10 in FIG. 6 is shown only as an example, and if the vacuum relief valve 10 automatically opens / closes according to the internal pressure condition of the liquefied gas storage tank 100 to perform the operation of reducing / releasing the vacuum pressure, there is no limitation on its detailed structure. For example, the structure of the vacuum relief valve 10 may be implemented as a structure in which the valve plate 10D is directly seated on the first inlet 10A in the valve body 10C to close the first inlet 10A.

[0116] Figure 7 Another embodiment of a liquefied gas storage tank system 1000 is shown. In this embodiment, a vacuum relief valve 10 is installed on a pipe 200 connecting the liquefied gas storage tank 100 and a vent mast 300 adjacent to the upper portion of the liquefied gas storage tank 100. Specifically, a first inlet 10A of the vacuum relief valve 10 according to the present embodiment is fluidly connected to the liquefied gas storage tank 100 through a pipe portion 200A of the pipe 200 at the upper portion of the liquefied gas storage tank 100, and a second inlet 10B is fluidly connected to the vent mast 300 through a pipe portion 200B of the pipe 200. Therefore, when the internal pressure of the liquefied gas storage tank 100 is a vacuum pressure of a predetermined range or a predetermined value, the vacuum relief valve 10 opens and introduces atmospheric air into the liquefied gas storage tank 100 through the vent mast 300 to release (remove / reduce) the internal vacuum pressure.

[0117] In the present embodiment, the pipe 10 (i.e., the pipe section 200B) between the vent mast 300 and the vacuum relief valve 10 is filled with nitrogen and an inert gas, and as a result, the introduction of a pollution source from the atmosphere into the vacuum relief valve 10 can be blocked through the bent mast 300. Further, for such a purpose, a filter may also be provided inside the pipe section 200B.

[0118] exist Figure 7 In the embodiment of the present invention, the atmosphere is used to release the internal vacuum pressure of the liquefied gas storage tank 100, but as Figure 8 As shown, an inert gas (such as nitrogen) may be used. Figure 8 In this embodiment, the second inlet 10B of the vacuum relief valve 10 is connected to the inert gas storage tank 400 through the pipeline portion 200'B. In this embodiment, the pressure of the inert gas storage tank 400 can also be set to about 0.7MPa(g) to 1.0MPa(g). In order to prevent the liquefied gas storage tank 100 from flowing back to the inert gas storage tank 400, a check valve can also be provided in the pipeline portion 200'B between the vacuum relief valve 10 and the inert gas storage tank 400.

[0119] In the above embodiment, in order to maintain and repair the vacuum relief valve 10 between the vacuum relief valve 10 and the liquefied gas storage tank 100, the following can be done: Fig. 9 The isolating valve 20 is shown to be provided. As isolating valve 2, a manually operated ball valve can be used.

[0120] In all or some embodiments, when the internal pressure of the liquefied gas storage tank is a positive pressure within a predetermined range or a predetermined value, a positive pressure relief valve (or pressure reducing valve) for releasing the internal positive pressure may be further provided. Fig.10 It is schematically shown in FIG.

[0121] Fig.10 FIG. 1 is a diagram schematically showing a liquefied gas storage tank system according to another embodiment of the present invention. The liquefied gas storage tank system 1000 according to this embodiment includes a positive pressure relief valve 30 in addition to the liquefied gas storage tank 100 and the vacuum pressure relief valve 10 .

[0122] In the case of the present embodiment, the rear end portion 200B of the pipe 200 connected to the ventilation mast 300 is branched into a pipe portion 200B1 connected to the vacuum relief valve 10 at a branch point 200P and a pipe portion 200B2 connected to the positive pressure relief valve 30. Meanwhile, the positive pressure relief valve 30 includes a first inlet 10'A connected to the pipe portion 200B2 and a second inlet 10'B connected to the liquefied gas storage tank 100 through a pipe portion 200C.

[0123] Since the vacuum relief valve 10 is Figures 4 to 9The vacuum relief valve 10 in the described embodiments is substantially the same in structure, connection type, and function, and a description thereof will be omitted.

[0124] The positive pressure relief valve 30 according to the embodiment operates at a pressure (e.g., a positive pressure value or a positive pressure range) higher than the vacuum pressure of the predetermined range or value in which the vacuum relief valve 10 operates. That is, when the internal pressure of the liquefied gas storage tank 100 exceeds the predetermined pressure range or pressure value set relative to the positive pressure, the positive pressure relief valve 30 is set to automatically open. Therefore, the positive pressure relief valve 30 according to the present embodiment adopts the same structure as the vacuum relief valve 10, but can be implemented as a valve different in connection type, valve plate thickness, and size, which will be referred to in detail. Fig.11 Give a description.

[0125] refer to Fig.11 In the embodiment, the positive pressure relief valve 30 is configured to include a valve body 10C, a first inlet 10'A, a second inlet 10'B, a valve plate 10'D, a valve cover 10E, a valve nozzle 10F, and a valve plate guide 10G. In the present embodiment, the second inlet 10'B (inlet) (inlet opened / closed by the valve plate 10D) of the positive pressure relief valve 30 is configured to be in fluid communication with the liquefied gas storage tank 100, and the first inlet 10'A (outlet) is configured to be in fluid communication with the vent mast 300. Therefore, when the interior of the liquefied gas storage tank 100 is at a predetermined positive pressure or a positive pressure range, the valve plate 10'D is pressure-elevated and opened, and as a result, the interior of the liquefied gas storage tank 100 is communicated with the external atmosphere to release the predetermined positive pressure inside the liquefied gas storage tank 100. For example, when the pressure in the liquefied gas storage tank 100 reaches, for example, 100 mbarg, the deadweight (thickness) and bottom area (ds′) of the valve plate 10 ′D of the positive pressure relief valve 30 may be set so that the positive pressure relief valve 30 opens.

[0126] In this embodiment, when the dead weight (thickness) and bottom area ds of the valve plate of each vacuum relief valve 10 and positive pressure relief valve 30 are appropriately set to automatically open / close in response to a predetermined vacuum pressure range (value) and a predetermined positive pressure range (value) inside the liquefied gas storage tank 100, respectively.

[0127] As described above, according to the present embodiment, it is possible to respond to vacuum pressure when negative pressure is generated in the liquefied gas storage tank 100, and it is possible to respond to positive pressure when positive pressure is generated by the vacuum relief valve 10 and the positive pressure relief valve 30.

[0128] Even in reference Fig.10 and Fig.11In the embodiment of the present invention, the valves 10 and 30 can be connected to the inert gas storage tank 400 instead of the vent mast 300. Further, an isolation valve for maintenance and repair can be provided between the vacuum relief valve 10 and the liquefied gas storage tank 100 and / or between the positive pressure relief valve 30 and the liquefied gas storage tank 100 (see Fig. 9 ).

[0129] Next, you can Fig.12 The effect of the implementation scheme according to the present invention is verified in the embodiment. Fig.12 When manufacturing a liquefied gas storage tank with a capacity of 1750m3, when the design external pressure changes to 0.02MPa(g) to 0.045MPa(g) while the design internal pressure is fixed at 0.49MPa(g), the design weight change of the liquefied gas storage tank is expressed in %. Fig.12 According to an embodiment of the present invention, when the vacuum pressure item is reduced from 0.025MPa(g) to 0.005MPa(g) and the design external pressure is reduced from 0.040MPa(g) to 0.020MPa(g), the weight of the liquefied gas storage tank can be reduced by 15%.

[0130] Hereinafter, other embodiments of the present invention will be referred to Figures 13 to 17 In the embodiments described below, the vacuum relief valve and the positive pressure relief valve can also be used in conjunction with the reference Figures 1 to 12 The vacuum relief valve and positive pressure relief valve of the described embodiments are similarly configured.

[0131] According to another embodiment of the present invention, a liquefied gas storage tank system may include: a liquefied gas storage tank; a vacuum relief valve, which releases the vacuum pressure inside the liquefied gas storage tank (removes the vacuum pressure state) when a vacuum is generated in the internal space of the liquefied gas storage tank; and an inert gas supply pipeline, which supplies an inert gas (such as nitrogen) to the internal space of the liquefied gas storage tank when the vacuum relief valve removes the vacuum state.

[0132] According to this embodiment, the thickness of the liquefied gas storage tank can be reduced by effectively responding to the vacuum pressure of the liquefied gas storage tank, and the weight of the liquefied gas storage tank can be reduced and the cost of the liquefied gas storage tank can be reduced, and oxygen in the atmosphere can be prevented from entering the liquefied gas storage tank through a pipe equipped with a vacuum relief valve (which may cause a fire) to prevent a fire and ensure safety.

[0133] Fig.13 FIG. 2 is a schematic diagram schematically showing a liquefied gas storage tank system according to an embodiment of the present invention. Fig.13 The liquefied gas storage tank system 1000 may include a liquefied gas storage tank, a vacuum relief valve 510 , an inert gas storage tank 520 , an inert gas supply line 530 , and a check valve 540 .

[0134] The liquefied gas storage tank 100 may include an inner space for storing liquefied gas. The C-type tank 20 may contain therein liquefied gas in an ultra-low temperature state such as liquefied natural gas (LNG), liquefied petroleum gas (LPG), etc.

[0135] The liquefied gas storage tank 100 may include a pressure vessel type C-type tank 25 having a cylindrical structure with a circular cross section and an insulator 35 covering the outside of the C-type tank 25. The liquefied gas storage tank 100 may be supported by support devices 45 and 55 installed in the hull 65.

[0136] At least one of the supporting devices 45 and 55 may support the C-type liquefied gas storage tank in a fixed state, and the other supporting device 55 may slidably support the C-type tank 25 to respond to thermal contraction / expansion of the C-type liquefied gas storage tank.

[0137] The vacuum relief valve 510 may be disposed at the upper portion of the liquefied gas storage tank 100. The vacuum pressure reducing valve 510 may be installed on the inert gas supply line 530. When vacuum pressure is generated in the internal space of the liquefied gas storage tank, the vacuum relief valve 510 may release (remove) the vacuum pressure (vacuum state) of the internal space of the liquefied gas storage tank. In an embodiment, the vacuum pressure may be a pressure of about 0 MPa (g) or less. The vacuum relief valve 510 may be set to be automatically opened to release the vacuum pressure when the internal pressure is less than a set pressure relative to the vacuum pressure.

[0138] The inert gas storage tank 520 may supply the inert gas through the inert gas supply line 530. In an embodiment, the inert gas may include nitrogen (N 2 ). The inert gas storage tank 520 may be set to a pressure of about 0.7 MPa(g) to 1.0 MPa(g) so that the inert gas is supplied to the liquefied gas storage tank 100 through the inert gas supply line 530 in a natural flow manner.

[0139] The inert gas supply line 530 may supply the inert gas to the inner space of the liquefied gas storage tank 100 when the vacuum state is removed by the vacuum relief valve 510. A check valve 540 may be provided in the inert gas supply line 530 so as to prevent the liquefied gas stored in the liquefied gas storage tank 100 from flowing back to the inert gas storage tank 520. The check valve 540 may be installed between the vacuum relief valve 510 and the inert gas storage tank 520.

[0140] According to an embodiment of the present invention, by applying the vacuum relief valve 510 and the inert gas supply line 530 to refill the pressure, the thickness of the liquefied gas storage tank 100 and the weight of the liquefied gas storage tank 100 can be reduced and the cost of the liquefied gas storage tank can be reduced, and the pressure can be refilled into the liquefied gas storage tank 100 by supplying an inert gas (such as nitrogen) to prevent the oxygen (O 2 ) (which may cause ignition in the atmosphere) is introduced into the liquefied gas storage tank 100 and prevents the occurrence of fire. In addition, the liquefied gas can be prevented from flowing back to the inert gas storage tank 520 by the check valve 540.

[0141] Fig.14 Schematically shows a liquefied gas storage tank system according to another embodiment of the present invention. Fig.14 When describing an implementation scheme of the present invention, repeated description of parts that are the same as or corresponding to the above-mentioned implementation scheme may be omitted. Fig.14 The embodiment is different from the above embodiment in that the liquefied gas storage tank system 1000 further includes a vent line 560 and a positive pressure relief valve 550.

[0142] When a positive pressure higher than the reference pressure is generated in the liquefied gas storage tank 100, a vent line 560 may be provided to remove the positive pressure in the liquefied gas storage tank 100. The positive pressure relief valve 550 may be provided in the vent line 560. The positive pressure relief valve 510 may be set to be automatically opened when the internal pressure of the liquefied gas storage tank 100 exceeds a pressure set relative to the positive pressure. Fig.14 In the embodiment, the vacuum relief valve 510 and the positive pressure relief valve 550 may control the internal pressure of the liquefied gas storage tank 100 in response to the vacuum pressure and the positive pressure of the liquefied gas storage tank 100 .

[0143] Fig.15 The diagram schematically shows a liquefied gas storage tank system according to another embodiment of the present invention. Fig.16 and Fig.17 To show the basis Fig.15 A diagram of an operating state of a liquefied gas storage tank system of an embodiment, and Fig.16 shows the state in which the negative pressure derivation valve performs a pressure derivation operation, and Fig.17 The diagram shows a state in which the negative pressure derivation valve performs a vacuum derivation operation.

[0144] In the description Figures 15 to 17 In the embodiment of the present invention, repeated description of the parts that are the same as or corresponding to the above-mentioned embodiment can be omitted. Figures 15 to 17The embodiment of the present invention is different from the above-mentioned embodiment in that, in the liquefied gas storage tank system 1000, a vacuum relief valve 510a is installed in the ventilation pipeline 560, and when a negative pressure is generated in the liquefied gas storage tank 100, the vacuum relief valve is operated to remove the negative pressure, and when a positive pressure is generated in the liquefied gas storage tank 100, the vacuum relief valve is also operated to remove the positive pressure, and the liquefied gas storage tank system 1000 also includes a first control valve, a second control valve 589 and a pressure measurer 590.

[0145] The pressure measurer 590 may measure the vapor pressure in the liquefied gas storage tank 100. The first control valve 570 may be installed between the check valve 540 in the inert gas supply line 530 and the inert gas storage tank 520. As a result, since the check valve 540 may prevent the liquefied gas from leaking to the first control valve 570, the first control valve 570 may be implemented as a control valve for room temperature, and the cost of the first control valve 570 may be reduced.

[0146] The first control valve 570 may be opened / closed according to the vapor pressure in the liquefied gas storage tank 100 measured by the pressure measurer 590. The second control valve 580 may be installed at the rear end of the vacuum relief valve 110a in the vent line 160. The second control valve 180 may be opened / closed according to the vapor pressure in the liquefied gas storage tank 100 measured by the pressure measurer 590.

[0147] When the vapor pressure in the liquefied gas storage tank 100 measured by the pressure measuring device 590 exceeds the first reference pressure, the first control valve 570 may be blocked and the second control valve 580 may be opened. For example, when the pressure of the liquefied gas storage tank 100 exceeds 0 MPa (g), the first control valve 570 is blocked and the second control valve 580 is opened to discharge the positive pressure in the liquefied gas storage tank 100 to the atmosphere. In this case, the vacuum relief valve 510a performs the function of a positive pressure relief valve to release the positive pressure of the liquefied gas storage tank 100.

[0148] When the vapor pressure in the liquefied gas storage tank 100 measured by the pressure measurer 590 is equal to or lower than a second reference pressure lower than the first reference pressure, the first control valve 570 may be opened and the second control valve 580 may be blocked. For example, when the pressure of the liquefied gas storage tank 100 is 0 barg, the second control valve 580 is blocked to prevent the introduction of air to the external ventilation side, and the vacuum relief valve 510a may perform a vacuum release function.

[0149] When the pressure of the liquefied gas storage tank 100 reaches a set pressure (e.g., 100 mbarg) for pressure release, an inert gas (e.g., nitrogen) is supplied from the inert gas storage tank 120 through the inert gas supply line 530 and introduced into the liquefied gas storage tank by opening the first control valve 570. As a result, the vacuum pressure of the liquefied gas storage tank 100 can be effectively released, and risks such as fire due to the introduction of oxygen from the atmosphere are prevented.

[0150] Further, according to Figures 15 to 17 In the embodiment of the present invention, the vacuum relief valve 110a can perform the vacuum release function and can also release the excessive positive pressure generated in the liquefied gas storage tank 100 through the vent line 560. Further, even if the valve erroneously operates and opens due to a local or temporary pressure drop around the vacuum relief valve 510a in the liquefied gas storage tank 100, the first control valve 570 remains closed under normal operation, so that the inert gas (such as nitrogen (N2)) can be prevented from entering the liquefied gas storage tank 100. 2 )) is unnecessarily introduced into the liquefied gas storage tank 100.

[0151] The above embodiments are proposed to help understand the present invention. It should be understood that the scope of the present invention is not limited, and various modified embodiments belong to the scope of the present invention. The protection scope of the present invention should be determined by the technical ideas of the claims. It should be understood that the protection scope of the present invention is not limited to the textual description of the claims themselves, but actually affects the invention category with uneven technical value.

[0152] [Industrial Applicability]

[0153] For example, the embodiments of the present invention may be effectively applied to a case where the design pressure for the internal pressure of a liquefied gas storage tank is less than about 0.65 MPa(g).

Claims

1. A liquefied gas storage tank system, comprising: A liquefied gas storage tank, wherein the liquefied gas storage tank is designed by a design internal pressure and a design external pressure under a design internal pressure condition, wherein the design internal pressure condition at least allows the design external pressure to determine the thickness of the liquefied gas storage tank; as well as a vacuum relief valve that is coupled to the liquefied gas storage tank and releases vacuum pressure generated inside the liquefied gas storage tank, Wherein, the liquefied gas storage tank is a C-type liquefied gas storage tank.

2. The liquefied gas storage tank system according to claim 1, wherein: The liquefied gas storage tank is designed with a design internal pressure of less than 0.65 MPa(g).

3. The liquefied gas storage tank system according to claim 2, wherein: The liquefied gas storage tank is designed with a design internal pressure equal to or greater than 0.45 MPa(g) and less than 0.65 MPa(g), and a design external pressure equal to or greater than 0.020 MPa(g) and less than 0.045 MPa(g).

4. The liquefied gas storage tank system according to claim 2, wherein: The liquefied gas storage tank is designed with a design internal pressure equal to or greater than 0.45 MPa(g) and equal to or less than 0.55 MPa(g), and a design external pressure equal to or greater than 0.020 MPa(g) and equal to or less than 0.025 MPa(g).

5. The liquefied gas storage tank system according to any one of claims 1 to 4, wherein: The first inlet of the vacuum relief valve is connected to communicate with the interior of the liquefied gas storage tank through a first pipe, and the second inlet is connected to communicate with a vent mast or an inert gas storage tank through a second pipe, or the second inlet is directly connected to the atmosphere.

6. The liquefied gas storage tank system according to claim 5, further comprising: A positive pressure relief valve is provided to release a positive pressure higher than a reference pressure generated inside the liquefied gas storage tank.

7. The liquefied gas storage tank system according to claim 6, wherein: The second inlet of the positive pressure relief valve is connected to communicate with the interior of the liquefied gas storage tank through a third pipe, the first inlet of the positive pressure relief valve is connected to communicate with the ventilation mast or the inert gas storage tank through a fourth pipe, or the first inlet of the positive pressure relief valve is directly connected to the atmosphere, or is connected to the second pipe connected to the second inlet of the vacuum relief valve.

8. A pressure design method for manufacturing a liquefied gas storage tank, the pressure design method comprising: Determining whether the design internal pressure is within a reference pressure range, wherein the thickness of the liquefied gas storage tank is determined at least by the design external pressure within the reference pressure range; as well as When the design internal pressure is within the reference pressure range, the design external pressure is determined by removing or reducing a vacuum pressure term defined for the vacuum pressure inside the liquefied gas storage tank from a pressure term defining the design external pressure.

9. The pressure design method for manufacturing a liquefied gas storage tank according to claim 8, wherein: The reference pressure range is less than 0.65 MPa(g).

10. The pressure design method for manufacturing a liquefied gas storage tank according to claim 9, wherein: The reference pressure range is equal to or greater than 0.45 MPa(g) and less than 0.65 MPa(g).

11. The pressure design method for manufacturing a liquefied gas storage tank according to any one of claims 8 to 10, wherein: The designed internal pressure is equal to or greater than 0.45 MPa(g) and less than 0.65 MPa(g), and The determined design external pressure is equal to or greater than 0.02 MPa(g) and equal to or less than 0.030 MPa(g).

12. A method for manufacturing a liquefied gas storage tank, the method comprising: Under the design internal pressure condition, manufacturing the liquefied gas storage tank according to the determined design internal pressure and the determined design external pressure, wherein the design internal pressure condition at least allows the design external pressure to determine the thickness of the liquefied gas storage tank; as well as A pressure control valve is connected to the liquefied gas storage tank, wherein the pressure control valve controls the internal pressure of the liquefied gas storage tank. Wherein, the liquefied gas storage tank is a C-type liquefied gas storage tank.

13. The method for manufacturing a liquefied gas storage tank according to claim 12, wherein: The determined design internal pressure is less than 0.65 MPa(g), and the determined design external pressure is equal to or greater than 0.020 MPa(g).

14. The method for manufacturing a liquefied gas storage tank according to claim 13, wherein: The determined design internal pressure is equal to or greater than 0.45 MPa(g) and less than 0.65 MPa(g), and The determined design external pressure is equal to or greater than 0.02 MPa(g) and less than 0.045 MPa(g).

Images