Patent Description:
Tanks storing liquefied gases such as LNG and liquefied hydrogen have been conventionally known. For example, Patent Literature <NUM> discloses a liquefied hydrogen carrier including a spherical tank mounted on the hull of the carrier ship to store liquefied hydrogen.

In this liquefied hydrogen carrier ship, the tank is supported by a tubular skirt rising from the floor surface of the hull of the carrier ship. The outer surface of the tank is entirely covered by an insulating layer.

<CIT> discloses an inner tank supporting structure of a double shell storage tank for storing low temperature liquid, low temperature high pressure gas, low temperature liquefied gas and the like.

However, the liquefied hydrogen carrier ship disclosed in Patent Literature <NUM> has the problem of significant heat penetration from the floor surface into the tank through the skirt.

It is therefore an object of the present invention to provide a liquefied gas storage structure that can reduce heat penetration from a floor surface into a tank and a liquefied gas carrier ship including the liquefied gas storage structure.

In order to solve the above problem, a liquefied gas storage structure according to one aspect of the present invention includes: a double-shell tank including a spherical inner shell storing a liquefied gas and an outer shell enclosing the inner shell; a first support member rising from a floor surface and supporting the outer shell; and a second support member supporting the inner shell, wherein: the first support member is a tubular skirt; the second support member is a tubular skirt and has a diameter different from that of the first support member; and the second support member rises from an inner surface of the outer shell at a location different from that of the first support member.

A liquefied gas carrier ship of the present invention includes: a hull; a double-shell tank including a spherical inner shell storing a liquefied gas and an outer shell enclosing the inner shell; a first support member rising from a floor surface of the hull and supporting the outer shell; and a second support member rising from an inner surface of the outer shell at a location different from that of the first support member, the second support member supporting the inner shell.

In the above configuration, the heat penetration route from the floor surface to the inner shell includes the first support member, the portion of the outer shell that is located between the first and second support members, and the second support member. Thus, the length of the heat penetration route can be increased by an amount corresponding to the distance between the portions of the first and second support members that extend along the outer shell. As such, the heat penetration from the floor surface into the double-shell tank can be reduced.

For example, the outer shell may be spherical, the second support member may be joined to the inner shell, and the first support member may be joined to the outer shell.

The second support member may include an upper portion made of the same material as the inner shell, a lower portion made of the same material as the outer shell, and a middle portion made of a material having a lower heat conductivity than the materials of the inner and outer shells. In this configuration, the second support member can easily be joined to the inner and outer shells, and heat transfer through the second support member can be hindered by the middle portion of the second support member.

For example, the material of the inner shell and the upper portion of the second support member may be the same as the material of the outer shell and the lower portion of the second support member.

The upper and lower portions of the second support member may be shorter than the middle portion in an up-down direction. In this configuration, the heat penetration into the double-shell tank can be more reduced than in a configuration where the upper, middle, and lower portions are equal in length.

The floor surface may be a floor surface of a hull, and the first support member may include an upper portion made of the same material as the outer shell, a lower portion made of the same material as the hull, and a middle portion made of a material having a lower heat conductivity than the materials of the outer shell and the hull. In this configuration, the first support member can easily be joined to the outer shell and hull, and heat transfer through the first support member can be hindered by the middle portion of the first support member.

A space between the inner and outer shells may be filled with a boil-off gas generated by evaporation of the liquefied gas. In some cases where the space between the inner and outer shells is filled with a gas, the gas present between the inner and outer shells could be liquefied or solidified depending on the temperature of the liquefied gas stored in the inner shell <NUM>. However, when the gas filling the space is the boil-off gas, liquefaction or solidification of the gas present between the inner and outer shells can be prevented.

For example, the liquefied gas storage structure may further include a heat insulator packed in a space between the inner and outer shells and covering an outer surface of the inner shell and the inner surface of the outer shell.

The liquefied gas storage structure may further include a heat insulator covering an outer surface of the outer shell. In this configuration, the distance from the inner shell to the outer shell and hence the diameter of the outer shell can be smaller than in a configuration where the outer surface of the outer shell is not covered by the heat insulator.

According to the present invention, heat penetration from a floor surface into a double-shell tank can be reduced.

<FIG> shows a liquefied gas carrier ship <NUM> including a liquefied gas storage structure according to one embodiment of the present invention. The liquefied gas carrier ship <NUM> includes a hull <NUM>, a double-shell tank <NUM> mounted on the hull <NUM>, and a tank cover <NUM> forming a holding space <NUM> around the double-shell tank <NUM> together with the hull <NUM>.

In the present embodiment, the holding space <NUM> is filled with nitrogen gas. The holding space <NUM> may be filled with dry air or exhaust gas of an engine for propulsion.

The double-shell tank <NUM> includes an inner shell <NUM> storing a liquefied gas and an outer shell <NUM> enclosing the inner shell <NUM>. For example, the liquefied gas is LNG, liquefied nitrogen, liquefied hydrogen, or liquefied helium.

The inner shell <NUM> is spherical. The inner shell <NUM> need not be spherically symmetric and may have a shape close to a spherically symmetric shape. For example, the inner shell <NUM> may have a shape differing from a spherically symmetric shape in that the inner shell <NUM> bulges upward and/or downward in the direction of <NUM> degrees with respect to the center of the inner shell <NUM>. Alternatively, the inner shell <NUM> may have a shape with a short tubular element interposed between the upper and lower hemispheres.

In the present embodiment, the outer shell <NUM> is also spherical. The center of the outer shell <NUM> coincides with the center of the inner shell <NUM>. Like the inner shell <NUM>, the outer shell <NUM> need not be spherically symmetric and may have a shape close to a spherically symmetric shape. For example, like the inner shell <NUM>, the outer shell <NUM> may have a shape differing from a spherically symmetric shape in that the outer shell <NUM> bulges upward and/or downward in the direction of <NUM> degrees with respect to the center of the outer shell <NUM>. Alternatively, the outer shell <NUM> may have a shape with a short tubular element interposed between the upper and lower hemispheres.

In the present embodiment, the material of the outer shell <NUM> is the same as the material of the inner shell <NUM>. The material of the outer shell <NUM> may be different from the material of the inner shell <NUM>.

A first heat insulator <NUM> is packed in the space between the inner and outer shells <NUM> and <NUM>. The first heat insulator <NUM> entirely covers the inner surface of the outer shell <NUM> and the outer surface of the inner shell <NUM>. Further, the outer surface of the outer shell <NUM> is entirely covered by a second heat insulator <NUM>.

For example, the first heat insulator <NUM> may be a foamed material made of a resin such as polyurethane (PU) or phenolic resin (PF), may be a granular material such as perlite or hollow glass spheres, or may be an inorganic fibrous material such as glass wool.

The second heat insulator <NUM> is, for example, a foamed material made of a resin such as polyurethane or phenolic resin. As described above, the holding space <NUM> is filled with nitrogen gas. Thus, in the case where the second heat insulator <NUM> is a foamed material, the nitrogen gas enters the second heat insulator <NUM> from the holding space <NUM>, and the internal pores of the second heat insulator <NUM> are filled with the nitrogen gas. Nitrogen gas may be fed to the second heat insulator <NUM> from a gas generator (not shown). In the case where the holding space <NUM> is filled with dry air, the internal pores of the second heat insulator <NUM> may also be filled with dry air.

In the present embodiment, the space between the inner and outer shells <NUM> and <NUM> is filled with a boil-off gas generated by evaporation of the liquefied gas stored in the inner shell <NUM>. The space between the inner and outer shells <NUM> and <NUM> may be filled with another gas that is not liquefied at the temperature of the liquefied gas stored in the inner shell <NUM>. Alternatively, the space between the inner and outer shells <NUM> and <NUM> may be a vacuum.

Various methods can be used to fill the space between the inner and outer shells <NUM> and <NUM> with the boil-off gas. For example, an upper portion of the inner shell <NUM> may be provided with a communication hole. Alternatively, although not shown, a delivery pipe through which the boil-off gas is delivered from the inner shell <NUM> to another device may be provided with a branch pipe, and the distal end of the branch pipe may open into the space between the inner and outer shells <NUM> and <NUM>.

A first support member <NUM> is disposed between a floor surface 11a of the hull <NUM> and the outer shell <NUM>, and a second support member <NUM> is disposed between the outer shell <NUM> and the inner shell <NUM>. The first support member <NUM> rises from the floor surface 11a and supports the outer shell <NUM>. The second support member <NUM> rises from the inner surface of the outer shell <NUM> at a location different from that of the first support member <NUM>, and supports the inner shell <NUM>.

In the present embodiment, both the first and second support members <NUM> and <NUM> are tubular skirts having axes extending in the vertical direction. The upper end of the first support member <NUM> is joined to an equatorial portion of the outer shell <NUM> (the equatorial portion is a maximum diameter portion that is farthest from the vertical centerline of the outer shell <NUM>). Likewise, the upper end of the second support member <NUM> is joined to an equatorial portion of the inner shell <NUM> (the equatorial portion is a maximum diameter portion that is farthest from the vertical centerline of the inner shell <NUM>).

As shown in <FIG>, the first support member <NUM> includes an upper portion <NUM>, a middle portion <NUM>, and a lower portion <NUM>. In the example shown, the upper, middle, and lower portions <NUM>, <NUM>, and <NUM> are equal in length in the up-down direction. However, the lengths of these portions may be changed as appropriate.

The upper portion <NUM> is made of the same material as the outer shell <NUM> (an example of the material is aluminum), and the lower portion <NUM> is made of the same material as the hull <NUM> (an example of the material is carbon steel). The middle portion <NUM> is made of a material having a lower heat conductivity than the materials of the outer shell <NUM> and hull <NUM> (an example of the material of the middle portion <NUM> is stainless steel). Although not shown, joints for dissimilar materials are disposed between the upper and middle portions <NUM> and <NUM> and between the middle and lower portions <NUM> and <NUM>. The middle portion <NUM> may be made of the same material as the hull <NUM> or outer shell <NUM>.

Likewise, the second support member <NUM> includes an upper portion <NUM>, a middle portion <NUM>, and a lower portion <NUM>. In the example shown, the upper and lower portions <NUM> and <NUM> are shorter than the middle portion <NUM> in the up-down direction. However, the lengths of these portions may be changed as appropriate.

The upper portion <NUM> is made of the same material as the inner shell <NUM> (an example of the material is aluminum), and the lower portion <NUM> is made of the same material as the outer shell <NUM> (an example of the material is aluminum as mentioned above). The middle portion <NUM> is made of a material having a lower heat conductivity than the materials of the inner and outer shells <NUM> and <NUM> (an example of the material of the middle portion <NUM> is stainless steel). Although not shown, joints for dissimilar materials are disposed between the upper and middle portions <NUM> and <NUM> and between the middle and lower portions <NUM> and <NUM>. The second support member <NUM> may be configured such that the upper, middle, and lower portions <NUM>, <NUM>, and <NUM> of the second support member <NUM> are integral with one another, and may be made of a material having a low heat conductivity over the region of the upper to lower portions <NUM> to <NUM> (an example of the material is stainless steel).

As described above, in the liquefied gas storage structure of the present embodiment, the heat penetration route from the floor surface 11a to the inner shell <NUM> includes the first support member <NUM>, the portion of the outer shell <NUM> that is located between the first and second support members <NUM> and <NUM>, and the second support member <NUM>. Thus, the length of the heat penetration route can be increased by an amount corresponding to the distance between the portions of the first and second support members <NUM> and <NUM> that extend along the outer shell <NUM>. As such, the heat penetration from the floor surface 11a into the double-shell tank <NUM> can be reduced.

Additionally, in the present embodiment, the upper and lower portions <NUM> and <NUM> of the second support member <NUM> are made of the same materials as the inner and outer shells <NUM> and <NUM>, respectively. Thus, the second support member <NUM> can easily be joined to the inner and outer shells <NUM> and <NUM>. Moreover, since the middle portion <NUM> of the second support member <NUM> has a lower heat conductivity than the upper and lower portions <NUM> and <NUM>, heat transfer through the second support member <NUM> can be hindered by the middle portion <NUM>.

Moreover, in the present embodiment, the upper and lower portions <NUM> and <NUM> of the second support member <NUM> are shorter than the middle portion <NUM>. Thus, the heat penetration into the double-shell tank <NUM> can be more reduced than in the case where the upper, middle, and lower portions <NUM>, <NUM>, and <NUM> are equal in length.

Further, in the present embodiment, the upper and lower portions <NUM> and <NUM> of the first support member <NUM> are made of the same materials as the outer shell <NUM> and hull <NUM>, respectively. Thus, the first support member <NUM> can easily be joined to the outer shell <NUM> and hull <NUM>. Moreover, since the middle portion <NUM> of the first support member <NUM> has a lower heat conductivity than the upper and lower portions <NUM> and <NUM>, heat transfer through the first support member <NUM> can be hindered by the middle portion <NUM>.

Additionally, in the present embodiment, the space between the inner and outer shells <NUM> and <NUM> is filled with the boil-off gas. In some cases where the space between the inner and outer shells <NUM> and <NUM> is filled with a gas, the gas present between the inner and outer shells <NUM> and <NUM> could be liquefied or solidified depending on the temperature of the liquefied gas stored in the inner shell <NUM>. However, when the gas filling the space is the boil-off gas as in the present embodiment, liquefaction or solidification of the gas present between the inner and outer shells <NUM> and <NUM> can be prevented.

The present invention is not limited to the embodiment described above, and various modifications can be made without departing from the gist of the present invention.

For example, the liquefied gas storage structure of the present invention need not be included in the liquefied gas carrier ship <NUM>, and may be included in an onshore facility. That is, the floor surface from which the first support member <NUM> rises may be a ground surface.

The space between the inner and outer shells <NUM> and <NUM> need not be packed with the first heat insulator <NUM>. For example, in the case where the space between the inner and outer shells <NUM> and <NUM> is a vacuum, only the outer surface of the inner shell <NUM> may be covered by a layered vacuum heat insulator including a stack of alternating radiation shielding films and spacers.

Further, the outer surface of the outer shell <NUM> need not be covered by the second heat insulator <NUM>, and may be bare as shown in <FIG>. However, in this case, the heat insulation performance needs to be ensured by increasing the distance from the inner shell <NUM> to the outer shell <NUM>. In contrast, when the outer surface of the outer shell <NUM> is covered by the second heat insulator <NUM> as in the embodiment described above, the distance from the inner shell <NUM> to the outer shell <NUM> and hence the diameter of the outer shell <NUM> can be smaller than when the outer surface of the outer shell <NUM> is not covered by the second heat insulator <NUM>.

Claim 1:
A liquefied gas storage structure comprising:
a double-shell tank (<NUM>) including a spherical inner shell (<NUM>) storing a liquefied gas and an outer shell (<NUM>) enclosing the inner shell;
a first support member (<NUM>) rising from a floor surface (11a) and supporting the outer shell; and
a second support member (<NUM>) supporting the inner shell, characterized in that:
the first support member (<NUM>) is a tubular skirt;
the second support member (<NUM>) is a tubular skirt and has a diameter different from that of the first support member (<NUM>); and in that
the second support member (<NUM>) rises from an inner surface of the outer shell (<NUM>) at a location different from that of the first support member (<NUM>).