JP7494314B2 - Liquefied gas storage tank system, its design and manufacturing method - Google Patents

Description

The present invention relates to a liquefied gas storage tank system for a ship, its pressure design method, and manufacturing method.

Generally, liquefied gas is transported or stored in liquefied gas storage tanks on offshore structures such as ships. Among these liquefied gases, liquefied natural gas (LNG) and liquefied petroleum gas (LPG) are stored in liquefied gas storage tanks at cryogenic temperatures of approximately -160°C and -45°C, respectively. Among liquefied gas storage tanks, the pressure vessel type C-type liquefied gas storage tank has its thickness designed for each part, such as the head, shell, saddle, dome, and sump, reflecting the design conditions of internal pressure and external pressure depending on the purpose of use. In other words, the thickness of each part is designed to fully withstand the designed internal pressure and external pressure, and each part of the C-type liquefied gas storage tank is manufactured according to that thickness. The internal and external pressures of liquefied gas storage tanks are designed to reflect each item defined in the IGF Code (International Code of safety for ships using Gases or other low-flashpoint Fuels).

C-Type liquefied gas storage tanks must not only withstand internal pressure, but also external pressure. Therefore, when designing the pressure of a C-Type liquefied gas storage tank, the design internal pressure (Pi) and the design external pressure (Pe) are considered independently. In other words, after calculating the internal pressure thickness (Ti) that can withstand the design internal pressure (Pi) and the external pressure thickness (Te) that can withstand the design external pressure (Pe), the larger of the two values is used to design the thickness of each part of the liquefied gas storage tank.

However, under conventional pressure design, the design internal pressure (Pi) (0.7-0.75MPa(g)) is much higher than the design external pressure (Pe) (0.02-0.045MPa(g)) (i.e. the internal pressure thickness (Ti) is much higher than the external pressure thickness (Te)), and the final thickness of the liquefied gas storage tank is determined by the design internal pressure (Pi), so fluctuations in the design external pressure (Pe) do not affect the final thickness of the liquefied gas storage tank. Even if the design external pressure is changed, the resulting change in the external pressure thickness (Te) cannot affect the internal pressure thickness (Ti), so changes in the design external pressure are unrelated to the thickness and therefore weight of each part of the liquefied gas storage tank.

Conventionally, when designing the external pressure, all the external pressure items defined in the IGF Code were habitually reflected without any doubt. Even if all the external pressure items defined in the IGF Code were reflected in the design external pressure, and a value higher than the value normally set for each item defined in the IGF Code was reflected, the internal pressure would still be large, and even if the external pressure was designed at a value that deviates from normal perception, the external pressure would not affect the thickness and weight of the liquefied gas storage tank, and the thickness of each part of the liquefied gas storage tank would be determined by the design internal pressure. In other words, in the design of liquefied gas storage tanks, since the external pressure is unrelated to the thickness and weight of the liquefied gas storage tank (it can also be said to be an item accepted by technical common sense in the design and manufacture of liquefied gas storage tanks), the design external pressure was not a subject of interest, and furthermore, the reduction in the thickness and weight of the liquefied gas storage tank through the reduction in the design external pressure was unimaginable.

However, the present inventors provide a new technology that breaks away from technical common sense, prejudices, or conventional wisdom in the design and manufacture of liquefied gas storage tanks as detailed above, and can reduce the thickness and weight of liquefied gas storage tanks in a new way. The present inventors provide a new technology that enhances the competitiveness of the design and manufacture of liquefied gas storage tanks by optimizing the thickness of each part of the liquefied gas storage tank.

The new technology provided by the inventors that can reduce the thickness and weight of liquefied gas storage tanks breaks away from conventional technical common sense, prejudices, or conventional wisdom, and is based on the technical idea that the design external pressure determines the thickness of a liquefied gas storage tank. Therefore, by removing some of the items that make up (define) the design external pressure, or by reducing their values, the design external pressure can be reduced, which will allow the thickness and weight of the liquefied gas storage tank to be reduced.

Without being bound by any particular theory, the inventors have found that when the design internal pressure is still sufficiently larger than the design external pressure and is within a specific range, the thickness and weight of a liquefied gas storage tank are determined as follows:
(1) The condition that the design internal pressure is approximately 0.65 MPa(g) or more (approximately 6.5 bar(g) or more) (for example, approximately 0.65 to 0.70 MPa(g)):
As in the past, the thickness and weight of a liquefied gas storage tank are determined by the design internal pressure regardless of changes in the design external pressure (for example, changes between approximately 0.045 and 0.020 MPa(g)).
(2) The design internal pressure is less than approximately 0.65 MPa(g) (less than approximately 6.5 bar(g)):
The reduction in design external pressure reduces the thickness and weight of the liquefied gas storage tank.
(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, when the design internal pressure is about 0.55 MPa(g), if the design external pressure is in the range of about 0.045 to 0.03 MPa(g), the thickness and weight of the liquefied gas storage tank are determined entirely by the change in the design external pressure within that range, but if the design external pressure is in a smaller range, for example, in the range of about 0.03 to 0.02 MPa(g), the change in the design external pressure within that range is unrelated 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.
(ii) When the design internal pressure is approximately 0.45 MPa(g) or less:
The thickness and weight of a liquefied gas storage tank are determined entirely by the design external pressure.
The design external pressure fluctuation, which is in the range of approximately 0.045 to 0.02 MPa(g), determines the thickness and weight of the liquefied gas storage tank.

Therefore, in the case of condition (2) for the above design internal pressure (i.e., when the design internal pressure is less than approximately 0.65 MPa(g)), the thickness and weight of the liquefied gas storage tank can be reduced by lowering the design pressure (design internal pressure/design external pressure). For example, when the design internal pressure is less than approximately 0.65 MPa(g), the thickness and weight of the liquefied gas storage tank can be reduced by lowering the design external pressure. When designing the external pressure, by eliminating some of the items that make up the design external pressure or reducing their values, the thickness and weight of the liquefied gas storage tank can be reduced as a result.

For example, negative pressure (vacuum pressure) may occur inside a liquefied gas storage tank during operation. Therefore, the external pressure when designing a liquefied gas storage tank must be at least approximately 0.025 MPa (g) as the negative pressure item (P1) that takes into account the negative pressure inside the liquefied gas storage tank, and taking into account other external pressure items other than the negative pressure item (P2: set pressure of the pressure outlet valve of the compartment that completely encloses the pressure vessel or a part of it, P3: weight of insulation material and weight of copper pipe including extra thickness due to shrinkage and corrosion, and compressive force of copper plate due to other external pressures expected to be received by the pressure vessel, etc., P4: external pressure due to the head of the pressure vessel or a part of it on the exposed deck), the external pressure will be designed to be approximately 0.040 MPa (g) at a minimum. Here, the negative pressure item that takes into account the negative pressure inside the liquefied gas storage tank is approximately 0.025 MPa (g) at a minimum, which accounts for more than half of the external pressure design pressure.

Therefore, in the case of condition (2) for the above design internal pressure (i.e., when the design internal pressure is less than approximately 0.65 MPa(g)), by eliminating/reducing the generation of negative pressure in the liquefied gas storage tank, i.e., by eliminating or reducing the negative pressure item P1 among the external pressure components, e.g., P1 to P4, the external pressure design pressure can be lowered and the thickness and weight of the liquefied gas storage tank can be reduced accordingly.

In response to this, one aspect of the present invention provides a liquefied gas storage tank design, a method for manufacturing a liquefied gas storage tank system, and a liquefied gas storage tank system resulting therefrom, which can reduce the thickness of the liquefied gas storage tank and can save the weight and cost of the liquefied gas storage tank.

Another aspect of the present invention provides a liquefied gas storage tank system that can effectively handle both positive and negative pressures in a liquefied gas storage tank and can simplify the equipment required to handle positive and negative pressures, thereby reducing costs.

A liquefied gas storage tank system according to one embodiment of the present invention includes a liquefied gas storage tank designed with a design internal pressure and a design external pressure under a design internal pressure, the thickness of which is determined by at least the design external pressure, and a negative pressure outlet valve connected to the liquefied gas storage tank to eliminate negative pressure generated inside the liquefied gas storage tank.

A pressure design method for manufacturing a liquefied gas storage tank according to one embodiment of the present invention includes: determining whether the design internal pressure is within a standard pressure range determined by at least the design external pressure when the thickness of the liquefied gas storage tank is within the standard pressure range, and calculating the design external pressure by removing or reducing the negative pressure item that takes into account the negative pressure inside the liquefied gas storage tank from the pressure items that define the design external pressure when the design internal pressure is within the standard pressure range.

A method for manufacturing a liquefied gas storage tank system according to one embodiment of the present invention includes: manufacturing a liquefied gas storage tank with a selected design internal pressure and a selected design external pressure under design internal pressure conditions such that the thickness of the liquefied gas storage tank is determined by at least the design external pressure, and coupling a pressure control valve to the liquefied gas storage tank for adjusting the internal pressure of the liquefied gas storage tank.

According to an embodiment of the present invention, the thickness of the liquefied gas storage tank can be reduced, and the weight and cost of the liquefied gas storage tank can be reduced.

Furthermore, according to an embodiment of the present invention, it is possible to effectively respond to both positive and negative pressures in a liquefied gas storage tank, and it is possible to simplify the equipment for responding to positive and negative pressures, thereby reducing costs.

Furthermore, according to the embodiment of the present invention, it is possible to prevent the liquefied gas stored in the liquefied gas storage tank from flowing back to the outside, it is possible to effectively respond to both positive and negative pressures within the liquefied gas storage tank, and it is possible to simplify the equipment for responding to positive and negative pressures, thereby reducing costs.

The problems and advantages that the present invention aims to solve are not limited to the problems and advantages mentioned above. Other technical problems and advantages not mentioned will be clearly understood by those with ordinary skill in the art to which the present invention pertains from the following description.

FIG. 1 shows a schematic diagram of a design external pressure range for a liquefied gas storage tank according to thickness and weight, which is derived from the results of the inventors' research based on a new method related to pressure design for a liquefied gas storage tank. FIG. 2 illustrates a schematic diagram of a pressure design method for determining the thickness of a liquefied gas storage tank according to one embodiment of the present invention. FIG. 3 shows a schematic diagram of a method for manufacturing a liquefied gas storage tank system according to the pressure design of FIG. FIG. 4 illustrates a schematic of a liquefied gas storage tank system according to one embodiment of the present invention. FIG. 5 shows a negative pressure outlet valve and its combination with a liquefied gas storage tank according to one embodiment of the present invention. FIG. 6 is a diagram for explaining the operation of a negative pressure outlet valve according to an embodiment of the present invention. FIG. 7 illustrates a schematic diagram of a liquefied gas storage tank system according to another embodiment of the present invention. FIG. 8 is a schematic diagram of a liquefied gas storage tank system according to still another embodiment of the present invention. FIG. 9 is a schematic diagram of a liquefied gas storage tank system having an isolation valve according to an embodiment of the present invention. FIG. 10 is a schematic diagram of a liquefied gas storage tank system according to still another embodiment of the present invention. FIG. 11 shows the connection relationship between the positive pressure outlet valve of FIG. 10 and the liquefied gas storage tank and negative pressure relief source. FIG. 12 is a graph for explaining the effect of one embodiment of the present invention. FIG. 13 is a schematic diagram of a liquefied gas storage tank system according to still another embodiment of the present invention. FIG. 14 is a schematic diagram of a liquefied gas storage tank system according to still another embodiment of the present invention. FIG. 15 is a schematic diagram of a liquefied gas storage tank system according to still another embodiment of the present invention. Figures 16 and 17 are diagrams showing the operating state of the liquefied gas storage tank system according to the embodiment of Figure 15, where Figure 16 shows a state in which the negative pressure outlet valve performs a pressure outlet operation, and Figure 17 shows a state in which the negative pressure outlet valve performs a vacuum outlet operation.

Other advantages and features of the present invention, and methods for achieving the same, will become apparent from the following detailed description of the embodiments in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, and the present invention is only defined by the scope of the claims. Even if not defined, all terms (including technical or scientific terms) used herein have the same meaning as generally accepted by the general art in the prior art to which this invention belongs. General descriptions of known structures may be omitted so as not to obscure the gist of the present invention. The same reference numerals are used as much as possible for the same or corresponding structures in the drawings of the present invention. Some structures may be somewhat exaggerated or shrunk in the drawings to facilitate understanding of the present invention.

The terms used in this application are merely used to describe certain embodiments and are not intended to limit the present invention. The singular includes the plural unless specifically expressly stated to exclude the plural. In this application, the terms "comprise", "have" or "comprise" are intended to specify the presence of features, numbers, steps, operations, components, ingredients, parts, components, or combinations thereof described in the specification, and should be understood as not precluding the presence or additional possibility of one or more other features, numbers, steps, operations, components, ingredients, parts, components, or combinations thereof.

Furthermore, although terms such as first, second, etc. may be used herein to describe various components, it will be understood that the components are not limited to such terms. Such terms are merely used to distinguish one component from another. For example, a configuration referred to as 'first piping' or 'first piping portion' in one embodiment may be referred to as 'second piping' or 'second piping portion', respectively, in another embodiment.

For purposes of this specification and claims, unless otherwise stated, all numbers used in the specification and claims, including quantities, percentages or ratios, and other numerical values, should be understood in all cases to be modified by the term "approximately". The use of the term "approximately" applies to all numerical values, whether or not they are explicitly indicated on the label. This term generally refers to a range of numbers that one of ordinary skill in the art can expect to vary a reasonable amount from the stated numerical values (i.e., having the same function or result). For example, this term can be interpreted to include ±10% deviations, alternatively ±5% deviations, alternatively ±1% deviations, alternatively ±0.5% deviations, and alternatively ±0.1% deviations for a given numerical range that do not alter the ultimate function, effect, or result of the numerical range. Thus, unless indicated to the contrary, the numerical parameters presented in this specification and claims are approximations that can vary depending on the desired properties obtained by the present invention.

The subject matter disclosed in this specification relates to a liquefied gas storage tank system and provides a technology that can reduce the thickness of a liquefied gas storage tank and reduce the weight and cost of the liquefied gas storage tank.

The thickness of a liquefied gas storage tank depends on the design pressure for the internal and external pressures of the liquefied gas storage tank, and the embodiments of the present invention provide a method for reducing the design pressure value for the external pressure of a liquefied gas storage tank and the thickness and weight of the liquefied gas storage tank through a technical idea that can eliminate or minimize some of the items that make up the external pressure when designing the external pressure of a liquefied gas storage tank, thereby lowering the design pressure value for the external pressure of the liquefied gas storage tank.

C-Type liquefied gas storage tanks must not only withstand the internal pressure, but also the external pressure. Therefore, the design internal pressure (Pi) and design external pressure (Pe) are considered independently, and the internal pressure thickness (Ti) that can withstand the design internal pressure (Pi) and the external pressure thickness (Te) that can withstand the design external pressure (Pe) are calculated, and then the larger of the two values is used to perform the pressure design for the C-Type liquefied gas storage tank.

Generally, the design internal pressure of a C-Type liquefied gas storage tank is, for example, approximately 0.7 to 0.75 MPa(g) (approximately 7 to 7.5 bar(g)), which is at least 16 to 17 times higher than the design external pressure (approximately 0.045 MPa(g) on average). Therefore, the design internal pressure determines the design thickness of each part of the liquefied gas storage tank, such as the head, shell, saddle, dome, and sump. In other words, under the conventional design internal pressure (0.7 to 0.75 MPa(g)), the thickness and weight of a liquefied gas storage tank were determined by the design internal pressure regardless of the magnitude of the design external pressure. Conventionally, because changes in the design external pressure do not affect the thickness and weight of a liquefied gas storage tank, all external pressure items defined in the IGF Code were habitually reflected without any doubt when designing the external pressure.

In the design of liquefied gas storage tanks, the idea that the design external pressure is unrelated to the thickness and weight of the liquefied gas storage tank is a kind of technical common sense, prejudice, or conventional wisdom in the design and manufacture of liquefied gas storage tanks, and the design external pressure was not a matter of concern. Furthermore, it was unimaginable to measure the reduction in thickness and weight of a liquefied gas storage tank through a change in the design external pressure (e.g. a reduction in the design external pressure).

However, the inventors provide a new technology that breaks away from such industry technical common sense, prejudices, or conventional wisdom and can reduce the thickness and weight of liquefied gas storage tanks in a new way. The inventors provide 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.

The new technology provided by the inventors that can reduce the thickness and weight of liquefied gas storage tanks breaks away from conventional technical common sense, prejudices, or conventional wisdom, and is based on the technical idea that the design external pressure determines the thickness of a liquefied gas storage tank. Therefore, the design external pressure can be reduced by removing some of the items that make up the design external pressure or by reducing their values, which will allow the thickness and weight of the liquefied gas storage tank to be reduced.

The present inventors have not been bound by any particular theory, but have found that even if the design internal pressure is still sufficiently higher than the design external pressure, when the design internal pressure is within a certain range, a decrease in the design external pressure 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 present inventors is as follows:
(1) The condition that the design internal pressure is approximately 0.65 MPa(g) or more (approximately 6.5 bar(g) or more) (for example, approximately 0.65 to 0.70 MPa(g)):
Fluctuations in the design external pressure range of approximately 0.045 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 entirely determined by the design internal pressure.
2) The condition that the design internal pressure is less than approximately 0.65 MPa(g) (less than approximately 6.5 bar(g)):
The reduction in design external pressure reduces the thickness and weight of the liquefied gas storage tank.
(i) When the design internal pressure is greater than approximately 0.45 MPa(g) under the condition that the design internal pressure is less than approximately 0.65 MPa(g) (i.e., when the design internal pressure is greater than 0.45 MPa(g) and less than approximately 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. That is, in a certain range of the design external pressure, the thickness and weight of the liquefied gas storage tank are determined by the design external pressure, and in the range of the design external pressure below that, the thickness and weight of the liquefied gas storage tank are determined by the design internal pressure. For example, when the design internal pressure is about 0.55 MPa(g), if the design external pressure is in the range of about 0.045 to 0.03 MPa(g), the thickness and weight of the liquefied gas storage tank are determined entirely by the change in the design external pressure in that range, but if the design external pressure is in a smaller range, for example, in the range of about 0.03 to 0.02 MPa(g), the change in the design external pressure is not related to the thickness and weight of the liquefied gas storage tank in that range, and the thickness and weight of the liquefied gas storage tank are determined by the design internal pressure;
(ii) When the design internal pressure is less than approximately 0.65 MPa(g) and the design internal pressure is approximately 0.45 MPa(g) or less:
The thickness and weight of a liquefied gas storage tank are determined entirely by the design external pressure.
The design external pressure fluctuation, which is in the range of approximately 0.045 to 0.02 MPa(g), determines the thickness and weight of the liquefied gas storage tank.

In other words, when the design internal pressure remains sufficiently greater than the design external pressure, as the design internal pressure decreases, the factors determining the thickness and weight of a liquefied gas storage tank change in the order of design internal pressure -> design external pressure and both design internal pressures -> design external pressure.

Therefore, in the case of condition (2) for the design internal pressure above (i.e., when the design internal pressure is less than approximately 0.65 MPa(g)), the thickness and weight of the liquefied gas storage tank can be reduced by lowering the design pressure.

For example, when the design internal pressure is less than approximately 0.65 MPa(g), the design external pressure can be lowered by removing or reducing the negative pressure item P1 among the external pressure configuration items P1 to P4 during external pressure design, and the thickness and weight of the liquefied gas storage tank can be reduced accordingly. The removal or reduction of the negative pressure item P1 of the design external pressure can be compensated for, for example, by installing a negative pressure outlet valve in the liquefied gas storage tank. Therefore, if a negative pressure outlet valve is installed in the liquefied gas storage tank when the design internal pressure is less than approximately 0.65 MPa(g), this will cause the unexpected result of reducing the thickness and weight of the liquefied gas storage tank. In other words, it is believed that the negative pressure outlet valve has the effect of reducing the thickness and weight of the liquefied gas storage tank when the design internal pressure is less than approximately 0.65 MPa(g).

During operation of a liquefied gas storage tank, negative pressure (vacuum pressure) may occur inside the tank. Therefore, when designing a liquefied gas storage tank, the external pressure must be considered to be at least approximately 0.025 MPa (g) for the negative pressure item (P1) that takes into account the negative pressure inside the liquefied gas storage tank. Taking into account other external pressure items other than the negative pressure item (P2: set pressure of the pressure outlet valve of the compartment that completely encloses the pressure vessel or a part of it, P3: weight of insulation and weight of copper pipe including extra thickness due to shrinkage and corrosion, and compressive force of copper plate due to other external pressures expected to be received by the pressure vessel, etc., P4: external pressure due to the head of the pressure vessel or a part of it on the exposed deck), the external pressure will be designed to be at least approximately 0.040 MPa (g). Here, the negative pressure item that takes into account the negative pressure inside the liquefied gas storage tank is at least approximately 0.025 MPa (g), which accounts for more than half of the external pressure design pressure.

Here, the inventors particularly noted that the negative pressure item considering the negative pressure inside the liquefied gas storage tank is a minimum of approximately 0.025 MPa (g), which accounts for more than half of the external pressure design pressure. Therefore, in one embodiment of the present invention, by removing or minimizing the negative pressure-related items among the items constituting the design external pressure, the effect of reducing the thickness and weight of the liquefied gas storage tank can be maximized. Meanwhile, since removing/reducing the negative pressure items at the design pressure requires preventing the occurrence of negative pressure during operation of the liquefied gas storage tank, the liquefied gas storage tank according to one embodiment of the present invention is provided with a means for removing/reducing the negative pressure that may occur inside. For example, a vacuum relief valve (in other words, a vacuum relief valve) can be used to remove/reduc the negative pressure inside the liquefied gas storage tank. The negative pressure relief valve is configured to operate to automatically open when the pressure inside the liquefied gas storage tank is at a predetermined pressure so that the inside of the liquefied gas storage tank does not become a vacuum (negative pressure). For example, when a negative pressure of approximately 0.005 MPa(g) occurs inside a liquefied gas storage tank, the negative pressure outlet valve can be configured to automatically open. In this case, it will be understood that the value of the negative pressure item that constitutes the design external pressure is approximately 0.005 MPa(g).

In addition, in the present invention, a portion of the reduction in the negative pressure item value that constitutes the design external pressure can be reflected in other items of the design external pressure, such as P3 item (weight of the insulation material and shrinkage, weight of the copper tube including the extra thickness due to corrosion, and compressive force of the copper plate due to other external pressures expected to be received by the pressure vessel, etc.) and P4 item (external pressure due to the head of the pressure vessel or part of it on the exposed deck), thereby increasing the manufacturing flexibility of the liquefied gas storage tank.

The contents disclosed in this specification provide a method for reducing the thickness and weight of a liquefied gas storage tank by lowering the design pressure value of the liquefied gas storage tank relative to the external pressure, and the embodiments of the present invention will be particularly useful in cases where the thickness of a liquefied gas storage tank is primarily determined by the external pressure.

The conditions under which the thickness of a liquefied gas storage tank is determined by the design external pressure may include cases where the design internal pressure is within a predetermined range, for example, less than approximately 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 becomes greater, and when the design internal pressure is less than approximately 0.45 MPa(g), the thickness of the liquefied gas storage tank is entirely determined by the design external pressure. Therefore, the embodiments of the present invention can be usefully applied to cases where the design pressure for the internal pressure of a liquefied gas storage tank is, for example, less than approximately 0.65 MPa(g).

One embodiment of the present invention therefore provides a method for manufacturing a liquefied gas storage tank that takes into account that the design external pressure of the liquefied gas storage tank is a minimum of approximately 0.020 MPa(g) and the design internal pressure is less than approximately 0.65 MPa(g).

The following is a detailed explanation with reference to the drawings.

Figure 1 shows a schematic diagram of the design external pressure range for the thickness and weight of a liquefied gas storage tank, which the inventors derived as a result of their research based on a new method related to pressure design for liquefied gas storage tanks. Figure 1 shows the change in weight (in %) (vertical axis) of a liquefied gas storage tank according to the change in design external pressure (Pe) (0.045MPa(g) -> 0.02MPa(g)) (horizontal axis) when the design internal pressure (Pi) is varied to approximately 0.45MPa(g), approximately 0.55MPa(g), and approximately 0.65MPa(g).

In Figure 1, the weight change of the liquefied gas storage tank is shown as 100% with a reference weight set for a design external pressure of 0.045 MPa (g). For example, 90% means that the weight of the liquefied gas storage tank has decreased by approximately 10% compared to when the design external pressure is 0.045 MPa (g).

Referring to Figure 1, it can be seen that within a certain range of design internal pressure, the weight of a liquefied gas storage tank changes (decreases) as the design external pressure changes (i.e., as the design external pressure decreases).

Specifically, when the design internal pressure is approximately 0.65 MPa(g) or higher, even if the design external pressure changes (i.e., even if the design external pressure decreases from approximately 0.045 MPa(g) to approximately 0.02 MPa(g), there is no change in the weight of the liquefied gas storage tank. In other words, when the design internal pressure is approximately 0.65 MPa(g) or higher, the thickness and weight of the liquefied gas storage tank are entirely dependent on the design internal pressure.

However, when the design internal pressure is approximately 0.45 MPa(g) or less, it can be seen that the weight of the liquefied gas storage tank decreases in proportion to the decrease in the design external pressure. In other words, it can be seen that as the design external pressure decreases from 0.045 MPa(g) -> 0.04 MPa(g) -> 0.035 MPa(g) -> 0.030 MPa(g) -> 0.025 MPa(g) -> 0.020 MPa(g), the weight of the liquefied gas storage tank decreases accordingly by 100% -> 99% -> 92% -> 88% -> 84% -> 80%. For example, when the design internal pressure is approximately 0.45 MPa(g), if the design external pressure decreases from approximately 0.045 MPa(g) to approximately 0.025 MPa(g), the weight of the liquefied gas storage tank decreases by approximately 16%, and when the design external pressure decreases to approximately 0.020 MPa(g), the weight of the liquefied gas storage tank decreases by approximately 20%.

On the other hand, when the design internal pressure is lower than approximately 0.65 MPa(g) but higher than approximately 0.45 MPa(g), the weight of the liquefied gas storage tank is affected by the design external pressure within a certain range of the design external pressure. When the design external pressure is in the range of approximately 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 in the lower range of 0.030 MPa(g) to 0.020 MPa(g), the weight of the liquefied gas storage tank does not change even if the design external pressure decreases.

From Figure 1, it can be seen that when the design internal pressure is 0.65 MPa(g) or more, changes in the design external pressure do not affect the weight of the liquefied gas storage tank, but when the design internal pressure is less than approximately 0.65 MPa(g), the weight of the liquefied gas storage tank decreases as the design external pressure changes (as the design external pressure decreases).

In other words, the inventors have derived the unexpected and surprising result that, contrary to common technical knowledge known in the industry, within a given range of design internal pressure, the design external pressure affects the weight of a liquefied gas storage tank according to its thickness.

Therefore, by utilizing the technical idea or inventive concept presented by the inventors, which can be seen in Figure 1, it is possible to reduce the weight of a liquefied gas storage tank and save costs. This will be explained in detail with reference to Figure 1 again. When the design internal pressure is made less than 0.65 MPa(g), if the design external pressure is reduced, the weight can be reduced correspondingly according to the thickness of the liquefied gas storage tank. In particular, among the components (P1 to P4) that make up the design external pressure, the item (P1 (approximately 0.025 MPa(g)) that takes into account the negative pressure that can occur during operation of the liquefied gas storage tank is more than half of the total external pressure components (approximately 0.045 MPa(g) on average), so by eliminating or reducing one negative pressure item (P1) in the design external pressure, the weight of the liquefied gas storage tank can be reduced to a large extent. In addition, since the negative pressure item in the design external pressure is considered in consideration of the negative pressure generation situation inside the liquefied gas storage tank, the elimination of negative pressure-related items in the external pressure design requires that negative pressure not be generated inside the liquefied gas storage tank, which can be realized by equipping the liquefied gas storage tank with a negative pressure outlet valve.

For example, if the design internal pressure is set to approximately 0.45 MPa(g) and a negative pressure outlet valve is installed in a liquefied gas storage tank, the negative pressure-related item (P1) among the items that make up the design external pressure can be reduced, and the design external pressure can be reduced by approximately 0.020 MPa(g) taking into account the operating tolerance of the negative pressure outlet valve, which means that the weight of the liquefied gas storage tank can be reduced by approximately 16%, as shown in Figure 1.

On the other hand, as can be seen from Figure 1, when the design internal pressure is approximately 0.65 MPa(g) or more, the thickness and weight of the liquefied gas storage tank are entirely dependent on the design internal pressure, so unlike the embodiments of the present invention, when the design internal pressure is conventionally designed at 0.7 to 0.75 MPa(g), the weight of the liquefied gas storage tank cannot be reduced even by installing a negative pressure outlet valve to reduce the design external pressure. Therefore, in the conventional case, the configuration of reducing the weight of a liquefied gas storage tank by combining a negative pressure outlet valve with the liquefied gas storage tank was unexpected as it deviated from technical common sense or empirical rules.

One embodiment of the present invention provides a method for manufacturing a liquefied gas storage tank system by performing pressure design to determine the thickness of a liquefied gas storage tank based on the basic concept or technical idea of the present invention described above.

Figure 2 shows a schematic diagram of a pressure design method for determining the thickness of a liquefied gas storage tank according to one embodiment of the present invention.

In step S11, a design internal pressure (Pd_int) is determined by pressure design associated with the thickness of the liquefied gas storage tank, and it is determined whether the determined design internal pressure (Pd_int) is a reference pressure value or a reference pressure range (Pref) determined by the thickness of the liquefied gas storage tank according to the design external pressure (Pd_ext). In step S10, the reference pressure range (Pref) may be, for example, less than about 0.65 MPa(g) in one embodiment. In step S11, the reference pressure range (Pref) may be, for example, from about 0.45 MPa(g) to less than about 0.65 MPa(g), for example, from about 0.45 MPa(g) to less than about 0.55 MPa(g), for example, from about 0.45 MPa(g) to less than about 0.50 MPa(g), for example, from about 0.45 MPa(g) to less than about 0.60 Pa.

If the design internal pressure (Pd_int) falls within the reference pressure range (Pref) in step S13, the design external pressure (Pd_ext) is determined by eliminating or minimizing the negative pressure (Pvac) that takes into account the negative pressure inside the liquefied gas storage tank among the pressure items that define (constitute) the design external pressure (Pd_ext). Conventionally, the negative pressure (Pvac), which is one item that constitutes the design external pressure, is a minimum of 0.025 MPa(g), and the other external pressure items may be 0.015 MPa(g). However, according to one embodiment of the present invention, the negative pressure (Pvac) is eliminated or reduced to 0.005 MPa(g) in step S13 (i.e., the negative pressure (Pvac) can be reduced by a minimum of about 0.02 MPa(g) - this means that it is reduced by about 0.02 MPa(g) compared to the conventional design external pressure, and the thickness of the liquefied gas storage tank can be reduced accordingly, thereby reducing the weight of the liquefied gas storage tank).

Therefore, according to one embodiment of the present invention, the determined design external pressure (Pext) may be a minimum of approximately 0.020 MPa(g) and the design internal pressure (Pd_int) may be a maximum of approximately 0.65 MPa(g). In one embodiment, the design external pressure (Pext) may be, for example, a minimum of approximately 0.020 MPa(g), approximately 0.020 MPa(g) or more and less than approximately 0.045 MPa(g), approximately 0.020 MPa(g) or more and approximately 0.030 MPa(g) or less, or approximately 0.020 MPa(g) or more and approximately 0.040 MPa(g) or less.

In one embodiment, the design internal pressure (Pd_int) may be less than approximately 0.65 MPa(g). The design internal pressure (Pd_int) may be, for example, equal to or greater than approximately 0.45 MPa(g) and less than approximately 0.65 MPa(g), for example, equal to or greater than approximately 0.45 MPa(g) and less than approximately 0.55 MPa(g), for example, equal to or greater than approximately 0.45 MPa(g) and less than approximately 0.50 MPa(g), for example, equal to or greater than approximately 0.45 MPa(g) and less than approximately 0.60 MPa(g).

In addition, the design internal pressure (Pd_int) can be set to various pressure ranges (unit: MPa(g)) with upper and lower limit values being any value between 0.45 and 0.65 (including 0.45 but not including 0.65). Similarly, the design external pressure (Pext) can be set to various pressure ranges (unit: MPa(g)) with upper and lower limit values being any value between 0.02 and 0.045 (including 0.02 but not including 0.045).

The design internal pressure (Pd_int) values or ranges and the design external pressure (Pext) values or ranges can be determined as the design internal pressure and the design external pressure by forming a set in various combinations within a range that is not mutually exclusive in the pressure design of a liquefied gas storage tank.
In the liquefied gas storage tank design method described with reference to FIG. 2, the design internal pressure (Pd_int) may be equal to a reference pressure range (Pref) on which the design external pressure is based to determine the weight of the liquefied gas storage tank.

Next, referring to Figure 3, a method for manufacturing a liquefied gas storage tank system according to one embodiment of the present invention using the pressure design of Figure 2 will be described.

In step S21, a liquefied gas storage tank is manufactured (to withstand the design pressure) according to the design internal pressure (Pd_int) and design external pressure (Pd_ext) determined by the pressure design in FIG. 2. As explained in detail above, according to this embodiment, the thickness of the liquefied gas storage tank can be reduced in accordance with the negative pressure items (external pressure values) that are reduced or removed from the items that make up the design external pressure in the pressure design, and the weight of the liquefied gas storage tank is reduced accordingly.

Meanwhile, it is necessary to prevent the occurrence of a vacuum in the liquefied gas storage tank due to the negative pressure item that is excluded from the items that make up the design external pressure, and for this purpose, a means for preventing/eliminating vacuum (negative pressure) occurrence is prepared in step S23. For example, a vacuum relief valve may be provided as a means for preventing/eliminating negative pressure occurrence.

In step S25, the negative pressure generation prevention/elimination means is coupled to the liquefied gas storage tank. For example, the negative pressure generation prevention/elimination means is coupled to the top of the liquefied gas storage tank. In the liquefied gas storage tank manufacturing method of this embodiment, prevention of vacuum generation inside the liquefied gas storage tank can be easily implemented by simply coupling a negative pressure outlet valve to the liquefied gas storage tank. The order of steps S21 and S23 in the liquefied gas storage tank system manufacturing method is not important and may be performed in any order. The method of coupling the negative pressure generation prevention/elimination means and the negative pressure generation prevention/elimination means to the liquefied gas storage tank can be understood from FIG. 5 and the related description below.

Figure 4 shows a schematic diagram of a liquefied gas storage tank system according to one embodiment of the present invention. The liquefied gas storage tank system of this embodiment can be manufactured by the method described with reference to Figure 3.

Referring to FIG. 4, the liquefied gas storage tank system 1000 includes a liquefied gas storage tank 100 and a negative pressure generation prevention/elimination means 10. More specifically, the liquefied gas storage tank 100 is provided with a negative pressure outlet valve (Vacuum Relief Valve) 10 as a negative pressure generation prevention/elimination means. The liquefied gas storage tank 100 has an internal space for storing liquefied gas and may be configured to include a pressure vessel type C-Type tank having a conical structure with a circular cross section, and an insulating material that wraps the outside of the C-Type tank. The C-Type tank can store liquefied gas in an ultra-low temperature state such as liquefied natural gas (LNG) and liquefied petroleum gas (LPG) inside. The liquefied gas storage tank 100 may be supported by support devices installed on the hull. The support devices may include one or more support devices that support the C-Type liquefied gas storage tank in a fixed state, and a support device that can slidably support the C-Type tank to accommodate thermal contraction/expansion of the C-Type liquefied gas storage tank.

The negative pressure outlet valve 10 can be coupled to the top of the liquefied gas storage tank 100. The negative pressure outlet valve 10 includes a first inlet/outlet 10A and a second inlet/outlet 10B. The first inlet/outlet 10A of the negative pressure outlet valve 10 is coupled to the top of the liquefied gas storage tank 100 in a manner that allows fluid communication with its interior. The second inlet/outlet 10B of the negative pressure outlet valve 10 is exposed to a negative pressure relieving source, such as the atmosphere, air, or an inert gas, and is connected to the negative pressure relieving source. For example, the second inlet/outlet 10B of the negative pressure outlet valve 10 has an open end that is connected to the atmosphere, air, or an inert gas. Therefore, according to this embodiment, when negative pressure (vacuum pressure) occurs in the internal space of the liquefied gas storage tank 100, the negative pressure outlet valve 10 is in an open state (a state in which the first inlet/outlet connected to the inside of the liquefied gas storage tank 100 is connected to the second inlet/outlet, allowing fluid to flow), and thus the atmosphere or inert gas connected to the second inlet/outlet 10B is introduced into the liquefied gas storage tank 100 through the first inlet/outlet 10A, thereby eliminating (removing) the negative pressure (vacuum state) in the internal space of the liquefied gas storage tank 100. In this embodiment, the first inlet/outlet 10A and the second inlet/outlet 10B of the negative pressure outlet valve 10 can be referred to as an inlet and an outlet, respectively, based on the direction in which a fluid such as atmosphere flows through the negative pressure outlet valve 10 during operation.

Meanwhile, the negative pressure may be, for example, a pressure of 0 MPa(g) (0 bar(g)) or less. The negative pressure outlet valve 10 may be configured to automatically open and release the negative pressure when the internal pressure of the liquefied gas storage tank 100 does not reach a pressure set in relation to the negative pressure. For example, the negative pressure outlet valve 10 may automatically open when the pressure of the liquefied gas storage tank 100 decreases to 0 bar(g). Alternatively, the negative pressure outlet valve 10 may automatically open when the difference between the pressure inside the liquefied gas storage tank 100 and the external pressure is about 0.005 MPa(g), i.e., when the pressure inside the liquefied gas storage tank 100 is about 0.005 MPa(g) lower than the atmospheric pressure, which corresponds to the case where the negative pressure (Pvac) decreases to 0.005 MPa(g) in the pressure design method described above with reference to FIG. 2. That is, when manufacturing a liquefied gas storage tank according to an embodiment in which the negative pressure item of the design external pressure (Pd_ext) is designed to be 0.005 MPa(g), which is reduced by about 0.002 MPa(g) from the conventional 0.025 MPa(g) in the pressure design method described with reference to FIG. 2, the negative pressure outlet valve connected to the liquefied gas storage tank is configured to be automatically operated when the pressure inside the liquefied gas storage tank is approximately 0.005 MPa(g) lower than atmospheric pressure.

Referring to Figure 5, the detailed structure of the negative pressure discharge valve 10 and its connection to the liquefied gas storage tank 100 will be explained.

Referring to FIG. 5, the negative pressure outlet valve 10 may be configured to include a valve body 10C, a valve plate 10D, a valve cover 10E, a valve nozzle 10F, and a valve plate guide 10G that define a second inlet/outlet 10B (inlet) and a first inlet/outlet 10A (outlet). The second inlet/outlet 10B and the first inlet/outlet 10A are configured to switch the flow direction of a fluid such as a gas, for example, by approximately 90 degrees. The first inlet/outlet 10A is coupled to be in fluid communication with the liquefied gas storage tank 100. For example, the first inlet/outlet 10A may be coupled to the liquefied gas storage tank 100 through a pipe. The second inlet/outlet 10B is in communication with the outside air, atmosphere, or inert gas. For example, when negative pressure occurs inside the liquefied gas storage tank 100, the external air, atmosphere, or inert gas flowing into the second inlet/outlet 10B (inlet) can flow into the liquefied gas storage tank 100 through the first inlet/outlet 10A (outlet), thereby relieving the negative pressure inside the liquefied gas storage tank 100.

A valve plate 10D is disposed inside the valve body 10C and closes the second port 10B (inlet port) (in this case, the valve is in a closed state). A valve cover 10E closes the upper part of the valve body 10C on the opposite side of the second port 10B. A valve plate guide 10G is fixedly connected to the valve cover 10E, and the valve plate 10D is movably connected (up and down) to the valve plate guide 10G and is disposed so as to close the second port 10B in the rest state. As an example, a valve nozzle 10F can be connected to the inner wall of the second port 10B, in which case the valve plate 10D can close one end of the valve nozzle 10F in the valve body 10C to close the second port 10B.

The valve plate 10D is configured to move between one end of the valve nozzle 10F and the valve cover 10E depending on the internal pressure conditions of the liquefied gas storage tank 100. The area (ds) and weight (thickness) of the underside of the valve plate 10D (the portion exposed to the second inlet/outlet 10B side) are determined according to a preset pressure range or pressure value. That is, when a negative pressure of a predetermined range or value is generated inside the liquefied gas storage tank 100, the thickness (weight) and area (ds) of the underside are determined so that the valve plate 10D seated on the valve nozzle 10F can be lifted upward toward the valve cover 10E.

When the pressure in the liquefied gas fuel tank 100 is high, a force acts downward (in the direction of gravity) due to the weight of the valve plate 10D itself and the high pressure in the fuel tank 100 (see the arrow in the drawing), so that the valve plate 10D is seated on the valve nozzle 10F and the valve plate is maintained in a closed state.

However, when the internal pressure of the liquefied gas fuel tank 100 decreases and reaches negative pressure (see FIG. 6A), the force of atmospheric pressure acting on the area (ds) becomes greater than the weight of the valve plate 10D itself, so the atmosphere lifts the valve plate 10C upward (towards the valve cover 10E) and the valve plate 10C enters an open state (a fluid passage is formed between the first inlet/outlet 10A and the second inlet/outlet 10B). When the valve is opened, atmosphere or air flows into the liquefied gas fuel tank 100, which increases the pressure inside the liquefied gas fuel tank 100 and eliminates the negative pressure.

When the pressure inside the liquefied gas fuel tank 100 increases due to the inflow of atmospheric air and the negative pressure is eliminated (see Figure 6B), the downward force (in the direction of gravity, toward the second inlet/outlet 10B) caused by the weight of the valve plate 10D itself and the high pressure of the liquefied gas fuel tank 100 becomes greater than the force acting on the area (ds) of the underside of the valve plate 10D, and therefore the valve plate 10D moves downward toward the valve nozzle 10F and settles again on the valve nozzle 10F, closing the valve plate.

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

The structure of the negative pressure outlet valve 10 in Figures 5 and 6 is merely an example, and there are no limitations on the detailed structure as long as it is automatically opened and closed according to the pressure conditions inside the liquefied gas storage tank 100 to reduce/eliminate the negative pressure. For example, it can be embodied in a structure in which the valve plate 10D is properly seated on the first inlet/outlet 10A in the valve body 10C to close the first inlet/outlet 10A.

Figure 7 shows another embodiment of the liquefied gas storage tank system 1000. In this embodiment, the negative pressure outlet valve 10 is installed adjacent to the top of the liquefied gas storage tank 100 on the piping 200 connecting the liquefied gas storage tank 100 and the vent mast 300. Specifically, the first inlet/outlet 10A of the negative pressure outlet valve 10 in this embodiment is fluidly connected to the liquefied gas storage tank 100 through the piping portion 200A of the piping 200 at the top of the liquefied gas storage tank 100, and the second inlet/outlet 10B is fluidly connected to the vent mast 300 through the piping portion 200B of the piping 200. Therefore, when the internal pressure of the liquefied gas storage tank 100 is within the above-mentioned predetermined range or a predetermined negative pressure value, the negative pressure outlet valve 10 is opened, and the atmosphere is introduced into the inside of the liquefied gas storage tank 100 through the vent mast 300 to derive (remove/reduce) the negative pressure inside.

In this embodiment, the piping 200 between the vent mast 300 and the negative pressure exhaust valve 10, i.e., the piping portion 200B, can be charged with an inert gas such as nitrogen gas to prevent contamination from the atmosphere from flowing into the negative pressure exhaust valve 10 through the vent mast 300. A filter can also be provided inside the piping portion 200B for this purpose.

In the embodiment of FIG. 7, the atmosphere is used to extract the negative pressure inside the liquefied gas storage tank 100, but as shown in FIG. 8, an inert gas such as nitrogen gas can be used. Referring to FIG. 8, in this embodiment, the second inlet/outlet 10B of the negative pressure extraction valve 10 is connected to the inert gas storage tank 400 through the piping portion 200'B. In this embodiment, the pressure of the inert gas storage tank 400 can be set to about 0.7 to 1.0 MPa(g). A check valve can be provided in the piping portion 200'B between the negative pressure extraction valve 10 and the inert gas storage tank 400 to prevent backflow from the liquefied gas storage tank 100 to the inert gas storage tank 400.

In the embodiments described above, an isolation valve 20 may be provided between the negative pressure outlet valve 10 and the liquefied gas storage tank 100 as shown in FIG. 9 for maintenance and repair of the negative pressure outlet valve 10. A manually operated ball valve may be used as the isolation valve 20.

In some or all of the above-mentioned embodiments, when the pressure inside the liquefied gas storage tank is within a predetermined range or a predetermined value of positive pressure, a positive pressure relief valve (or pressure relief valve) for delivering the internal positive pressure may be further provided, as shown diagrammatically in FIG. 10.

Figure 10 is a schematic diagram of 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 further comprises a positive pressure outlet valve 30 in addition to the liquefied gas storage tank 100 and negative pressure outlet valve 10 described above.

In this embodiment, the rear end portion 200B of the pipe 200 connected to the vent mast 300 branches at a branch point 200P into a pipe portion 200B1 connected to the negative pressure outlet valve 10 and a pipe portion 200B2 connected to the positive pressure outlet valve 30. Meanwhile, the positive pressure outlet valve 30 has a first inlet/outlet 10'A connected to the pipe portion 200B2 and a second inlet/outlet 10'B connected to the liquefied gas storage tank 100 through the pipe portion 200C.

The negative pressure outlet valve 10 of this embodiment is substantially the same in structure, connection form, and function as the negative pressure outlet valve 10 of the embodiment described with reference to Figures 4 to 9, so a description thereof will be omitted.

The positive pressure outlet valve 30 of this embodiment operates at a pressure higher than the predetermined range or value of the negative pressure at which the negative pressure outlet valve 10 operates, for example, a positive pressure value or positive pressure range. That is, the positive pressure outlet valve 30 is set to automatically open when the internal pressure of the liquefied gas storage tank 100 exceeds a predetermined pressure range or pressure value set in relation to the positive pressure. Therefore, the positive pressure outlet valve 30 of this embodiment adopts the same structure as the negative pressure outlet valve 10, but can be embodied as a valve with different connection forms and valve plate thicknesses and sizes, which will be described with reference to FIG. 11.

11, the positive pressure outlet valve 30 in this embodiment is similar to the structure of the negative pressure outlet valve 10 described with reference to FIGS. 4 to 9, and is configured to include a valve body 10C, a first inlet/outlet 10'A, a second inlet/outlet 10'B, a valve plate 10'D, a valve cover 10E, a valve nozzle 10F, and a valve plate guide 10G. In this embodiment, the second inlet/outlet 10'B (inlet) (inlet/outlet opened/closed by the valve plate 10D) of the positive pressure outlet valve 30 is coupled to be fluidly connected to the liquefied gas storage tank 100, and the first inlet/outlet 10'A (outlet) is configured to be fluidly connected to the vent mast 300. Therefore, when the inside of the liquefied gas storage tank 100 reaches a predetermined positive pressure or a positive pressure range, the valve plate 10'D is lifted by the pressure and opened, thereby communicating the inside of the liquefied gas storage tank 100 with the outside atmosphere, so that a predetermined positive pressure inside the liquefied gas storage tank 100 can be delivered. For example, when the pressure inside the liquefied gas storage tank 100 reaches, for example, 100 mbarg, the weight (thickness) and the area (ds') of the lower surface of the valve plate 10'D of the positive pressure outlet valve 30 can be set so that the positive pressure outlet valve 30 is in an open state.

In this embodiment, the weight (thickness) and underside area (ds) of each valve plate of the negative pressure outlet valve 10 and the positive pressure outlet valve 30 are appropriately set so that they are automatically opened and closed in accordance with the predetermined negative pressure range (value) and the predetermined positive pressure range (value) inside the liquefied gas storage tank 100, respectively.

As described above, according to this embodiment, the negative pressure outlet valve 10 and the positive pressure outlet valve 30 can of course respond to negative pressure when negative pressure occurs within the liquefied gas storage tank 100, but can also respond to positive pressure when positive pressure occurs.

In the embodiment described with reference to Figures 10 and 11, the valves 10 and 30 can also be connected to the inert gas storage tank 400 instead of the vent mast 300. In addition, an isolation valve (see Figure 9) can be further provided between the negative pressure outlet valve 10 and the liquefied gas storage tank 100 and/or between the positive pressure outlet valve 30 and the liquefied gas storage tank 100 for maintenance and repair.

Next, the effects of the embodiments of the present invention can be seen in Figure 12. Figure 12 is a diagram showing the change in design weight of a liquefied gas storage tank in ^percentage when the design external pressure is changed from 0.02 to 0.045 MPa(g) with the design internal pressure fixed at 0.49 MPa(g) when manufacturing a liquefied gas storage tank with a capacity of 1,750 m3. Referring to Figure 12, according to one embodiment of the present invention, when the negative pressure item is reduced from 0.025 MPa(g) to 0.005 MPa(g) and the design external pressure (P _ext ) is reduced from 0.040 MPa(g) to 0.020 MPa(g), the weight of the liquefied gas storage tank can be reduced by 15%.

Below, other embodiments of the present invention will be described with reference to Figs. 13 to 17. In the embodiments described below, the vacuum relief valve and the pressure relief valve may be configured in the same manner as the vacuum relief valve and the positive pressure relief valve of the embodiments described with reference to Figs. 1 to 12.

A liquefied gas storage tank system according to another embodiment of the present invention may include a liquefied gas storage tank, a vacuum relief valve that relieves the negative pressure (removes the negative pressure state) in the internal space of the liquefied gas storage tank when a negative pressure (vacuum pressure) occurs in the internal space of the liquefied gas storage tank, and an inert gas supply line that supplies an inert gas such as nitrogen to the internal space of the liquefied gas storage tank while the vacuum state is being removed by the negative pressure relief valve.

According to this embodiment, the thickness of the liquefied gas storage tank can be reduced by effectively dealing with the negative pressure in the liquefied gas storage tank, thereby reducing the weight and cost of the liquefied gas storage tank, and the negative pressure outlet valve can be installed in the line to prevent atmospheric oxygen, which can cause ignition, from flowing into the liquefied gas storage tank, thereby preventing the occurrence of a fire and ensuring safety.

Figure 13 is a diagram showing a schematic diagram of a liquefied gas storage tank system according to one embodiment of the present invention. Referring to Figure 13, the liquefied gas storage tank system 1000 according to an embodiment of the present invention may include a liquefied gas storage tank 100, a negative pressure outlet valve 510, an inert gas storage tank 520, an inert gas supply line 530, and a check valve 540.

The liquefied gas storage tank 100 may have an internal space for storing liquefied gas. The C-Type tank 20 may store liquefied gas in an ultra-low temperature state, such as liquefied natural gas (LNG) and liquefied petroleum gas (LPG).

The liquefied gas storage tank 100 may include a pressure vessel type C-Type tank 25 having a conical structure with a circular cross section, and insulation material 35 that wraps around the outside of the C-Type tank 25. The liquefied gas storage tank 100 may be supported by support devices 45, 55 installed on the hull 65.

Of the support devices 45, 55, one or more of the support devices 45 support the C-Type liquefied gas storage tank in a fixed state, and the other one or more of the support devices 55 can slidably support the C-Type tank 25 to accommodate thermal contraction/expansion of the C-Type liquefied gas storage tank.

The vacuum relief valve 510 may be provided on the top of the liquefied gas storage tank 100. The vacuum relief valve 510 may be installed on the inert gas supply line 530. The vacuum relief valve 510 may eliminate (remove) the negative pressure (vacuum state) in the internal space of the liquefied gas storage tank when a negative pressure (vacuum pressure) occurs in the internal space of the liquefied gas storage tank. In an embodiment, the negative pressure may be a pressure of approximately 0 MPa (g) or less. The negative pressure relief valve 510 may be set to automatically open when the internal pressure of the liquefied gas storage tank 100 does not reach a pressure set in relation to the negative pressure.

The inert gas storage tank 520 may supply the inert gas through an inert gas supply line 530. In an embodiment, the inert gas may include nitrogen (N ₂ ) gas. The inert gas storage tank 520 may be set at a pressure of about 0.7 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 by natural flow.

The inert gas supply line 530 can supply inert gas to the internal space of the liquefied gas storage tank 100 while the vacuum state is removed by the negative pressure discharge valve 510. A check valve 540 can be provided in the inert gas supply line 530 to prevent the liquefied gas stored in the liquefied gas storage tank 100 from flowing back into the inert gas storage tank 520. The check valve 540 can be installed between the negative pressure discharge valve 510 and the inert gas storage tank 520.

According to the embodiment of the present invention, the pressure can be compensated for by applying the negative pressure outlet valve 510 and the inert gas supply line 530, and the thickness of the liquefied gas storage tank 100 can be reduced to reduce the weight and cost of the liquefied gas storage tank 100. The pressure inside the liquefied gas storage tank 100 can be compensated for by supplying an inert gas such as nitrogen, and the occurrence of a fire can be prevented by preventing oxygen (O ₂ ), which may cause ignition, from flowing into the atmosphere inside the liquefied gas storage tank 100. In addition, the check valve 540 can prevent the liquefied gas from flowing back into the inert gas storage tank 520.

Figure 14 is a schematic diagram of a liquefied gas storage tank system according to another embodiment of the present invention. In describing the embodiment of Figure 14, duplicated descriptions of components that are the same as or correspond to the previously described embodiments may be omitted. The liquefied gas storage tank system 1000 according to the embodiment of Figure 14 differs from the previously described embodiments in that it further includes a vent line 560 and a positive pressure outlet valve 550.

The exhaust line 560 may be provided to remove the positive pressure in the liquefied gas storage tank 100 when a positive pressure higher than a reference pressure occurs in the liquefied gas storage tank 100. The positive pressure outlet valve 550 may be provided in the exhaust line 560. The positive pressure outlet valve 510 may be set to automatically open when the internal pressure of the liquefied gas storage tank 100 exceeds a pressure set in association with the positive pressure. According to the embodiment of FIG. 14, the internal pressure of the liquefied gas storage tank 100 can be controlled in response to both the negative pressure and positive pressure of the liquefied gas storage tank 100 by the negative pressure outlet valve 510 and the positive pressure outlet valve 550.

Figure 15 is a diagram showing a schematic diagram of a liquefied gas storage tank system according to another embodiment of the present invention. Figures 16 and 17 are diagrams showing the operating state of the liquefied gas storage tank system according to the embodiment of Figure 15, where Figure 16 shows a state in which the negative pressure outlet valve performs a pressure outlet operation, and Figure 17 shows a state in which the negative pressure outlet valve performs a vacuum outlet operation.

In describing the embodiments of Figures 15 to 17, duplicated descriptions of components that are the same as or correspond to the previously described embodiments may be omitted. The liquefied gas storage tank system 1000 according to the embodiment of Figures 15 to 17 differs from the previously described embodiments in that a negative pressure outlet valve 510A is installed in the exhaust line 560 to remove positive pressure when positive pressure is generated in the liquefied gas storage tank 100, and also operates to remove positive pressure when positive pressure is generated in the liquefied gas storage tank 100, and further includes a first control valve 570, a second control valve 580, and a pressure gauge 590.

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

The first control valve 570 can be opened and closed according to the vapor pressure in the liquefied gas storage tank 100 measured by the pressure gauge 590. The second control valve 580 can be installed at the rear end of the negative pressure outlet valve 110A in the exhaust line 160. The second control valve 180 can be opened and closed according to the vapor pressure in the liquefied gas storage tank 100 measured by the pressure gauge 590.

When the vapor pressure in the liquefied gas storage tank 100 measured by the pressure gauge 590 exceeds the first reference pressure, the first control valve 570 can be closed and the second control valve 580 can be opened as shown in FIG. 16. For example, when the pressure in the liquefied gas storage tank 100 exceeds 0 MPa(g), the first control valve 570 can be closed and the second control valve 580 can be opened to release the positive pressure in the liquefied gas storage tank 100 to the atmosphere. At this time, the negative pressure outlet valve 510A performs the function of a positive pressure outlet valve to relieve the positive pressure in the liquefied gas storage tank 100.

When the vapor pressure in the liquefied gas storage tank 100 measured by the pressure gauge 590 is equal to or lower than a second reference pressure that is lower than the first reference pressure, the first control valve 570 can be opened and the second control valve 580 can be closed, as shown in FIG. 17. For example, when the pressure in the liquefied gas storage tank 100 is 0 barg, the second control valve 580 is closed to prevent air from flowing into the external exhaust side, and the negative pressure outlet valve 510A can perform a vacuum outlet function.

When the pressure in the liquefied gas storage tank 100 reaches the set pressure for vacuum extraction (e.g., 100 mbarg), the first control valve 570 is opened to supply inert gas (e.g., nitrogen gas) from the inert gas storage tank 120 through the inert gas supply line 530 and flow into the liquefied gas storage tank 100, thereby effectively eliminating the negative pressure in the liquefied gas storage tank 100 and preventing the risk of fires and other accidents caused by the inflow of oxygen from the atmosphere.

In addition, according to the embodiments of Figures 15 to 17, the negative pressure outlet valve 110A performs a vacuum outlet function and can also respond to excessive positive pressure generated in the liquefied gas storage tank 100 in the exhaust line 560. Even if the valve malfunctions and opens due to a local or temporary pressure drop around the negative pressure outlet valve 510A in the liquefied gas storage tank 100, the first control valve 570 maintains a closed state in a normal operation state, so that it is possible to prevent inert gases such as nitrogen ( _N2 ) from flowing into the liquefied gas storage tank 100 unnecessarily.

The above examples are presented to aid in understanding the present invention, and do not limit the scope of the present invention, and it should be understood that various modified examples from these examples also fall within the scope of the present invention. It should be understood that the scope of protection of the present invention should be determined by the technical ideas of the claims, and that the scope of protection of the present invention is not limited to the literal description of the claims themselves, but extends to inventions of substantially equivalent technical value.

Embodiments of the present invention can be usefully applied when the design pressure for the internal pressure of a liquefied gas storage tank is, for example, less than approximately 0.65 MPa(g).

Claims (14)

A liquefied gas storage tank designed with a design internal pressure and a design external pressure under a design internal pressure condition, the thickness of the liquefied gas storage tank being determined by at least the design external pressure; and
A C-Type liquefied gas storage tank system including a negative pressure outlet valve coupled to the liquefied gas storage tank to eliminate negative pressure generated inside the liquefied gas storage tank. The C-Type liquefied gas storage tank system according to claim 1, characterized in that the liquefied gas storage tank is designed with a design internal pressure of less than approximately 0.65 MPa (g). The C-Type liquefied gas storage tank system according to claim 2, characterized in that the liquefied gas storage tank is designed with a design internal pressure of approximately 0.45 MPa(g) or more and less than approximately 0.65 MPa(g) and a design external pressure of approximately 0.020 MPa(g) or more and less than approximately 0.045 MPa(g). The C-Type liquefied gas storage tank system as described in claim 2, characterized in that the liquefied gas storage tank is designed with a design internal pressure of approximately 0.45 MPa(g) or more and approximately 0.55 MPa(g) or less and a design external pressure of approximately 0.020 MPa(g) or more and approximately 0.025 MPa(g) or less. The C-Type liquefied gas storage tank system according to any one of claims 1 to 4, characterized in that the first inlet/outlet of the negative pressure outlet valve is connected to communicate with the inside of the liquefied gas storage tank through a first pipe, and the second inlet/outlet is connected to communicate with a vent mast or an inert gas storage tank through a second pipe, or directly communicates with the atmosphere. The C-Type liquefied gas storage tank system according to claim 5, further comprising a positive pressure outlet valve for eliminating a positive pressure generated inside the liquefied gas storage tank that is higher than a reference pressure. The C-type liquefied gas storage tank system according to claim 6, characterized in that the second inlet/outlet of the positive pressure discharge valve is connected to communicate with the inside of the liquefied gas storage tank through a third pipe, and the first inlet/outlet of the positive pressure discharge valve is connected to communicate with a vent mast or an inert gas storage tank through a fourth pipe, or is directly connected to the atmosphere, or is connected to the second pipe connected to the second inlet/outlet of the negative pressure discharge valve. In the pressure design method for manufacturing liquefied gas storage tanks,
Determine whether the design internal pressure is within a standard pressure range determined by the design external pressure of the thickness of the liquefied gas storage tank;
When the design internal pressure is within the reference pressure range, a negative pressure item that takes into account the negative pressure inside the liquefied gas storage tank is removed or reduced from pressure items that define the design external pressure to determine the design external pressure. The pressure design method for a liquefied gas storage tank according to claim 8, characterized in that the reference pressure range is less than approximately 0.65 MPa (g). The pressure design method for a liquefied gas storage tank according to claim 9, characterized in that the reference pressure range is equal to or greater than approximately 0.45 MPa (g) and less than approximately 0.65 MPa (g). The design internal pressure is equal to or greater than approximately 0.45 MPa(g) and less than approximately 0.65 MPa(g),
A pressure design method for a liquefied gas storage tank according to any one of claims 8 to 10, characterized in that the determined design external pressure is equal to or greater than approximately 0.020 MPa(g) and equal to or less than approximately 0.030 MPg(a). As a method of manufacturing a liquefied gas storage tank, the method comprises:
Manufacture the liquefied gas storage tank according to the determined design internal pressure and the determined design external pressure under the design internal pressure conditions, so that the thickness of the liquefied gas storage tank is determined at least by the design external pressure;
a pressure control valve coupled to the liquefied gas storage tank for controlling an internal pressure of the liquefied gas storage tank; The liquefied gas storage tank manufacturing method described in claim 12, characterized in that the determined design internal pressure is less than approximately 0.65 MPa (g) and the determined design external pressure is approximately 0.020 MPa (g) or more. The determined design internal pressure is equal to or greater than approximately 0.45 MPa(g) and less than approximately 0.65 MPa(g),
The method for manufacturing a liquefied gas storage tank according to claim 13, characterized in that the determined design external pressure is equal to or greater than approximately 0.020 MPa(g) and less than approximately 0.045 MPg(a).