Patent Description:
Incidentally, a liquefied gas carrier that uses liquefied gas, such as liquefied petroleum gas (LPG), liquefied natural gas (LNG), or ammonia, as fuel or cargo is provided with a liquefied gas tank for storing the liquefied gas. Even in such a liquefied gas tank, as in the storage tank disclosed in PTL <NUM>, measures are taken on the assumption that the liquefied gas, which is liquid stored in the liquefied gas tank, leaks to the outside of the liquefied gas tank. For example, since a liquefied gas carrier that carries liquefied gas as cargo often includes a plurality of cargo tanks, a method of introducing liquefied gas having leaked from one cargo tank into the other cargo tank to recover the liquefied gas having leaked has been performed in the related art.

On the other hand, there is a case where a plurality of liquefied gas tanks are not provided in the case of a liquefied gas fueled ship using liquefied gas as fuel unlike in the above-mentioned liquefied gas carrier. In the case of a ship not including such a plurality of liquefied gas tanks, liquid having leaked cannot be introduced from one tank into the other tank unlike the disclosure in PTL <NUM>. For this reason, there is a problem that liquefied gas having leaked cannot be efficiently recovered.

The present disclosure has been made to solve the problem, and an object of the present disclosure is to provide a floating structure that can efficiently recover liquefied gas having leaked from a tank.

In order to solve the problem, a floating structure according to an aspect of the present disclosure includes a floating main structure, a tank that is provided in the floating main structure and includes a tank body capable of storing liquefied gas therein and a heat shield wall covering an outer surface of the tank body, a receiving part that is disposed below the tank to cover the tank from below and includes a receiving surface and a recess recessed from the receiving surface, a pump that is provided in the recess; and a return line that returns the liquefied gas pumped by the pump into the tank body.

According to the present disclosure, it is possible to provide a floating structure that can efficiently recover liquefied gas having leaked from a tank.

A floating structure according to an embodiment of the present disclosure will be described below with reference to the drawings.

The floating structure according to the present embodiment is a liquefied gas fueled ship that uses liquefied gas as fuel. More specifically, the floating structure according to the present embodiment is an ammonia fueled ship that uses ammonia, which is liquefied gas, as fuel. The ammonia fueled ship will be described as an example in the present embodiment as described above, but the type of the floating structure is not limited to a specific one. Examples of the type of the floating structure include a liquefied gas carrier, a ferry, a RO-RO ship, a vehicle carrier, a passenger ship, and the like.

As shown in <FIG>, the floating structure <NUM> includes a floating main structure <NUM>, a superstructure <NUM>, a combustion device <NUM>, a fuel storage unit <NUM>, and a fuel supply system <NUM>.

As shown in <FIG>, the floating main structure <NUM> includes at least ship sides 11A and 11B, a bottom <NUM>, and an upper deck <NUM>.

The ship sides 11A and 11B include a pair of ship side skins that forms left and right ship sides 11A and 11B, respectively. The bottom <NUM> includes a double-bottomed bottom skin that connects these ship sides 11A and 11B. The upper deck <NUM> is provided over the pair of ship side skins.

An outer shell of the floating main structure <NUM> is formed by the ship sides 11A and 11B, the bottom <NUM>, and the upper deck <NUM> to have a box shape in a cross-sectional view orthogonal to a bow-stern direction FA.

Hereinafter, a direction extending from a stern <NUM> of the floating main structure <NUM> to a bow <NUM> thereof will be referred to as "bow-stern direction FA".

The superstructure <NUM> is a structure that is provided to face upward from the upper deck <NUM> in a vertical direction Dv. For example, an accommodation space, a bridge, and the like are provided in the superstructure <NUM>.

The combustion device <NUM> is a device that generates thermal energy by combusting fuel. The combustion device <NUM> is provided in, for example, a compartment, such as an engine room (not shown) provided inside the floating main structure <NUM>. A main engine that propels the floating structure <NUM>, an engine for a generator that supplies electricity to the inside of the ship, a boiler that generates steam as working fluid, and the like can be exemplified as the combustion device <NUM>. The combustion device <NUM> of the present embodiment is a main engine that uses ammonia as fuel.

The fuel storage unit <NUM> stores liquefied ammonia as the fuel of the combustion device <NUM> in a low-temperature state.

The detailed configuration of the fuel storage unit <NUM> will be described later.

The fuel supply system <NUM> is a system that supplies ammonia as fuel to the combustion device <NUM> from the fuel storage unit <NUM>. The fuel supply system <NUM> of the present embodiment is provided in, for example, the floating main structure <NUM>.

The fuel supply system <NUM> includes a supply line <NUM> (another line) and a return line <NUM> (another line). The supply line <NUM> and the return line <NUM> are pipes which are connected to a tank <NUM> and in which ammonia can flow.

The supply line <NUM> connects the tank <NUM> (of which details will be described later) of the fuel storage unit <NUM> and the combustion device <NUM>. Ammonia as fuel flows from the tank <NUM> toward the combustion device <NUM> in the supply line <NUM>. Accordingly, ammonia is introduced into the combustion device <NUM> from the tank <NUM> via the supply line <NUM>.

The supply line <NUM> is provided with a pump (not shown) that pumps ammonia into the combustion device <NUM> from the tank <NUM>, a heat exchanger (not shown) that heats ammonia to be guided to the combustion device <NUM> by the pump and present in the supply line <NUM>, and the like.

The return line <NUM> connects the combustion device <NUM> and the tank <NUM> of the fuel storage unit <NUM>. One end of the return line <NUM> is connected to the combustion device <NUM>, and the other end thereof is connected to the tank <NUM>. Ammonia, which remains without being combusted in the combustion device <NUM>, flows from the combustion device <NUM> toward the tank <NUM> in the return line <NUM>. Accordingly, ammonia sent to the tank <NUM> via the return line <NUM> is supplied into the supply line <NUM> in the tank <NUM> again, and is used for combustion in the combustion device <NUM> again.

One end of a flue gas duct <NUM>, which is a duct for guiding exhaust gas G generated in the combustion device <NUM> to the outside of the floating main structure <NUM>, is connected to the combustion device <NUM>. The other end of the flue gas duct <NUM> penetrates the upper deck <NUM> and extends upward in the vertical direction Dv outside the floating main structure <NUM>. As shown in <FIG>, a portion of the flue gas duct <NUM>, which extends outside the floating main structure <NUM>, is surrounded by a hull structure <NUM> and a funnel <NUM>.

The fuel storage unit <NUM> of the present embodiment is provided in the floating main structure <NUM>.

As shown in <FIG>, the fuel storage unit <NUM> includes the tank <NUM>, a receiving part <NUM>, a pump <NUM>, a return line <NUM>, and a leak detecting unit <NUM>.

Here, the floating main structure <NUM> further includes an inner surface <NUM> that partitions off a hold space R as a space in which the tank <NUM> is accommodated. That is, the tank <NUM> is provided in the hold space R partitioned off by the inner surface <NUM>. The inner surface <NUM> of the present embodiment is formed by, for example, a bulkhead that is provided in the floating main structure <NUM>, or the like. For the convenience of description, the shape and the like of the bulkhead forming the inner surface <NUM> are not shown in <FIG>.

The inner surface <NUM> of the floating main structure <NUM> includes a floor surface 16a that corresponds to a bottom surface portion of the inner surface <NUM>, a top surface 16b that is provided above the floor surface 16a in the vertical direction Dv and faces the floor surface 16a, and side surfaces 16c that connect the floor surface 16a and the top surface 16b in the vertical direction Dv. That is, the top surface 16b corresponds to a ceiling surface portion of the inner surface <NUM>, and the side surfaces 16c correspond to side surface portions of the inner surface <NUM>.

The inner surface <NUM> includes a total of four side surfaces 16c, that is, two side surfaces 16c that face each other in the bow-stern direction FA, and two side surfaces 16c that face each other in a ship width direction Dw extending from one ship side 11A toward the other ship side 11B. One side surface of the two side surfaces 16c facing each other in the ship width direction Dw is not shown in <FIG> due to space limitations.

The two side surfaces 16c facing each other in the bow-stern direction FA stand up in the vertical direction Dv from the respective end portions of the floor surface 16a in the bow-stern direction FA, and are connected to end portions of the top surface 16b in the bow-stern direction FA, respectively. The two side surfaces 16c facing each other in the ship width direction Dw stand up in the vertical direction Dv from the respective end portions of the floor surface 16a in the ship width direction Dw, and are connected to end portions of the top surface 16b in the ship width direction Dw, respectively.

The tank <NUM> is an IMO Type B tank that stores liquefied ammonia as fuel for the combustion device <NUM>. Here, IMO Type B is defined by an International Gas Carrier (IGC) code that is a safety regulation for liquefied gas established by the International Maritime Organization (IMO). Specifically, in the IMO Type B tank, an upper limit of the amount of liquefied gas fuel leaking from the inside of the tank per unit time is calculated on the basis of a predetermined calculation method.

The tank <NUM> includes a tank body <NUM> and a heat shield wall <NUM>.

In <FIG>, for convenience, the supply line <NUM> (another line) that supplies ammonia from the tank <NUM> to the combustion device <NUM> and the return line <NUM> (another line) that returns ammonia from the combustion device <NUM> to the tank <NUM> are shown as the same line.

The tank body <NUM> stores ammonia therein. The tank body <NUM> of the present embodiment is made of, for example, low-temperature steel of which toughness is not reduced even in a low-temperature state, such as nickel steel, stainless steel or an aluminum alloy. The tank body <NUM> of the present embodiment is made of a material of which toughness is not reduced in a temperature range lower than -<NUM> and equal to or higher than -<NUM> that is about -<NUM> which is a temperature at which ammonia is condensed.

The tank body <NUM> includes a ceiling portion <NUM>, a bottom portion <NUM>, and side wall portions <NUM>.

The ceiling portion <NUM> forms a ceiling portion of the tank body <NUM>. The ceiling portion <NUM> includes an upper surface 51a that faces upward in the vertical direction Dv in the hold space R.

The bottom portion <NUM> forms a bottom portion of the tank body <NUM>. The bottom portion <NUM> includes a bottom surface 52a that is provided below the ceiling portion <NUM> in the vertical direction Dv in the hold space R and faces the floor surface 16a.

The side wall portions <NUM> connect the ceiling portion <NUM> and the bottom portion <NUM> in the vertical direction Dv, and form side wall portions of the tank body <NUM>. That is, the side wall portions <NUM> include side surfaces 53a that connect the upper surface 51a of the ceiling portion <NUM> and the bottom surface 52a of the bottom portion <NUM>.

Specifically, the side wall portions <NUM> include four side surfaces 53a that face the four side surfaces 16c of the inner surface <NUM>, respectively.

Accordingly, an outer surface of the tank body <NUM> is formed of the upper surface 51a of the ceiling portion <NUM>, the side surfaces 53a of the side wall portions <NUM>, and the bottom surface 52a of the bottom portion <NUM>.

The heat shield wall <NUM> is a heat insulating member that covers the outer surface of the tank body <NUM>. The heat shield wall <NUM> suppresses natural heat input into the tank body <NUM> from the atmosphere in the hold space R.

The heat shield wall <NUM> includes a heat shield portion <NUM> and a guide portion <NUM>.

The heat shield portion <NUM> covers the entire upper surface 51a and the entire side surfaces 53a of the outer surface of the tank body <NUM> from the outside. The heat shield portion <NUM> insulates the tank body <NUM> so that heat is not conducted to the tank body <NUM> from the atmosphere in the hold space R. That is, the heat shield portion <NUM> fulfills a heat insulating function to prevent natural heat from being input to the tank body <NUM>. The heat shield portion <NUM> of the present embodiment is made of, for example, a material, such as polyurethane foam.

The heat shield portion <NUM> includes a ceiling-heat shield portion 61a and side wall-heat shield portions 61b.

The ceiling-heat shield portion 61a is formed to cover the entire upper surface 51a of the ceiling portion <NUM> of the tank body <NUM> from above in the vertical direction Dv.

The side wall-heat shield portions 61b are formed to cover the entire side surfaces 53a of the side wall portions <NUM> of the tank body <NUM> in the bow-stern direction FA and the ship width direction Dw. The side wall-heat shield portions 61b include contact surfaces 61c that face and are in contact with the side surfaces 53a of the side wall portions <NUM>.

The ceiling-heat shield portion 61a and the side wall-heat shield portions 61b of the present embodiment are integrally formed.

A plurality of side wall grooves 54a, which are recessed from the contact surfaces 61c toward the side surfaces 16c of the inner surface <NUM> and extend in the vertical direction Dv, are formed on the side wall-heat shield portions 61b. Lower end portions of the side wall grooves 54a in the vertical direction Dv reach lower end portions of the side wall-heat shield portions 61b in the vertical direction Dv.

The guide portion <NUM> covers the entire bottom surface 52a of the outer surface of the tank body <NUM> from below in the vertical direction Dv. The guide portion <NUM> is connected to the lower end portions of the side wall-heat shield portions 61b of the heat shield portion <NUM> in the vertical direction Dv, and is formed integrally with the heat shield portion <NUM>.

The guide portion <NUM> fulfills a heat insulating function to prevent natural heat from being input to the tank body <NUM> as with the heat shield portion <NUM>. The guide portion <NUM> of the present embodiment is made of, for example, a material, such as polyurethane foam. The heat shield portion <NUM> and the guide portion <NUM> may not be made of polyurethane foam. Further, the heat shield portion <NUM> and the guide portion <NUM> may be made of different materials.

The guide portion <NUM> includes a guide surface 62a that faces the bottom surface 52a of the bottom portion <NUM> from below in the vertical direction Dv and guides ammonia leaking from the tank body <NUM>.

The guide surface 62a is inclined to be positioned downward in the hold space R from the bow <NUM> toward the stern <NUM> in the bow-stern direction FA. For convenience, a state in which the floating main structure <NUM> does not trim (even trim state) is shown in <FIG>. That is, the guide surface 62a is inclined with respect to an imaginary horizontal plane orthogonal to a direction of gravity.

The guide portion <NUM> includes a plurality of bottom grooves 54b that are recessed from the guide surface 62a toward the floor surface 16a and extend in the ship width direction Dw, and one middle groove 54c that is recessed from the guide surface 62a toward the floor surface 16a in the middle of the guide portion <NUM> and extend in the bow-stern direction FA. The middle groove 54c extends from a side of the guide portion <NUM> closer to the bow <NUM> to a side thereof closer to the stern <NUM> in the bow-stern direction FA. Each of end portions of the middle groove 54c closer to the bow <NUM> and the stern <NUM> in the bow-stern direction FA is connected to a lower end portion of at least one side wall groove in the vertical direction Dv among the plurality of side wall grooves 54a formed on the side wall-heat shield portions 61b.

The bottom grooves 54b extend to be collected at the middle groove 54c from the end portions of the guide portion <NUM> in the ship width direction Dw, and are connected to the middle groove 54c to join the middle groove 54c.

One end of each bottom groove 54b is connected to a lower end portion of the side wall groove 54a, which is formed on the side wall-heat shield portion 61b, in the vertical direction Dv. The other end of each bottom groove 54b is connected to the middle groove 54c.

Accordingly, the side wall grooves 54a of the side wall-heat shield portions 61b, the bottom grooves 54b of the guide portion <NUM>, and the middle groove 54c form a groove <NUM> that continuously extends from the contact surfaces 61c of the side wall-heat shield portions 61b to the guide surface 62a of the guide portion <NUM>.

As a result, even if minute cracks, holes, or the like are generated everywhere in the tank body <NUM> and ammonia leaks to exude from the inside of the tank body <NUM> to the outside of the tank body <NUM> via the minute cracks, holes, or the like, the leaking ammonia is moved from the side surfaces 53a to the bottom surface 52a along the groove <NUM> between the tank body <NUM> and the heat shield wall <NUM>.

A hole portion 62c passing through the guide portion <NUM> from the guide surface 62a downward is formed in the guide portion <NUM>. Specifically, the hole portion 62c is disposed at a portion of an inner wall surface of the middle groove 54c closer to the stern <NUM> in the bow-stern direction FA.

Accordingly, the ammonia, which has leaked from the tank body <NUM> and moved toward the bottom surface 52a along the side wall grooves 54a, directly flows into the middle groove 54c or flows into the middle groove 54c via the bottom grooves 54b. The ammonia having flowed into the middle groove 54c flows in the middle groove 54c along an incline, and then falls downward from the guide portion <NUM> via the hole portion 62c.

The receiving part <NUM> receives and accumulates the ammonia having leaked from the tank <NUM>. The receiving part <NUM> is disposed below the tank <NUM> to cover the entire guide portion <NUM> of the heat shield wall <NUM> from below.

The receiving part <NUM> includes a receiving surface <NUM> and a recess <NUM> that is formed closer to the stern <NUM> than the receiving surface <NUM> in the bow-stern direction FA. The receiving part <NUM> of the present embodiment also serves as the floor surface 16a of the inner surface <NUM> of the floating main structure <NUM>.

In a case where liquefied ammonia having leaked from the guide portion <NUM> of the heat shield wall <NUM> of the tank body <NUM> falls onto the receiving surface <NUM>, the receiving surface <NUM> is a surface as a secondary barrier that receives this liquefied ammonia and guides the received liquefied ammonia to the recess <NUM>.

The secondary barrier of the present embodiment means a barrier that is provided to prevent a member forming the floating main structure <NUM> other than the tank <NUM> from being damaged since the temperature of the member drops in a case where the liquefied ammonia having leaked from the tank body <NUM> is in contact with the member.

The receiving surface <NUM> is made of a material (low-temperature steel) of which toughness is not reduced even in a low-temperature state as with the tank body <NUM>. The top surface 16b and the side surfaces 16c of the inner surface <NUM> of the present embodiment are made of metal or the like other than low-temperature steel. Here, the floating main structure <NUM>, which is sailing, is inclined with respect to the horizontal plane to sink downward in the vertical direction Dv from the bow <NUM> toward the stern <NUM>. That is, the floating main structure <NUM> sails in a stern trim state.

Accordingly, the receiving surface <NUM> is inclined to be positioned downward from the bow <NUM> toward the stern <NUM> in the bow-stern direction FA (an aspect of inclination is not shown). The state of the inclination of the receiving surface <NUM> is not shown in the drawings. Accordingly, the liquefied ammonia having fallen onto the receiving surface <NUM> is moved toward the stern <NUM> along the incline of the receiving surface <NUM>.

The recess <NUM> is a pit (well) as a secondary barrier that is formed to be recessed from the receiving surface <NUM> in the vertical direction Dv. The recess <NUM> is formed to be capable of storing the ammonia having leaked from the tank <NUM>. The recess <NUM> is made of a material (low-temperature steel) of which toughness is not reduced even in a low-temperature state as with the tank body <NUM>. In a case where the liquefied ammonia having leaked is accumulated in the recess <NUM>, the material (low-temperature steel) of the recess <NUM> is cooled and the temperature of the recess <NUM> drops.

The recess <NUM> of the present embodiment includes an opening portion 72a open to the inside of the hold space R. The opening portion 72a is positioned below the hole portion 62c that is provided at an end portion of the guide portion <NUM> closer to the stern <NUM> in the bow-stern direction FA.

Here, the guide surface 62a of the guide portion <NUM> of the heat shield wall <NUM> is inclined to approach the recess <NUM> toward the recess <NUM>.

The pump <NUM> is a diaphragm pump that is provided in the recess <NUM>. The pump <NUM> pumps the ammonia, which is accumulated in the recess <NUM>, to the outside of the recess <NUM>. The drive of the pump <NUM> is controlled by a pump drive device <NUM> that is provided outside the recess <NUM>.

The pump <NUM> of the present embodiment can pump liquefied ammonia of which the amount is larger than the amount of liquefied ammonia leaking from the tank per unit time to the outside of the recess <NUM> per unit time.

Here, since the pump <NUM> is a diaphragm pump that is a type of positive displacement pump, the pump <NUM> can idle. Idling in the present embodiment means that the pump <NUM> continues to perform a normal suction operation even though liquefied ammonia as driving liquid (driving fluid) is not introduced into the pump <NUM>. That is, the pump <NUM> can be operated without causing an abnormality, such as galling or seizure, even in a case where there is no liquefied ammonia in the recess <NUM>.

The return line <NUM> is a pipe returning ammonia, which is accumulated in the recess <NUM> and is to be pumped by the pump <NUM>, into the tank body <NUM>. One end of the return line <NUM> is connected to the pump <NUM>. The other end of the return line <NUM> penetrates the heat shield portion <NUM> of the heat shield wall <NUM> of the tank <NUM> and the ceiling portion <NUM> of the tank body <NUM> to extend into the tank body <NUM>.

Here, the return line <NUM> is not connected to the supply line <NUM> (another line) and the return line <NUM> (another line) that connect the tank <NUM> and the combustion device <NUM>. That is, the ammonia flowing in the return line <NUM> does not directly flow into the supply line <NUM> and the return line <NUM>. That is, the return line <NUM> is provided in the hold space R independently of the supply line <NUM> and the return line <NUM>.

The leak detecting unit <NUM> detects that the liquefied ammonia having leaked from the tank <NUM> is accumulated in the recess <NUM>, and drives the pump <NUM> on the basis of detection information.

The leak detecting unit <NUM> includes a leak sensor <NUM> and a pump drive device <NUM>.

The leak sensor <NUM> is a temperature sensor that is provided on a wall surface of the recess <NUM>. The leak sensor <NUM> acquires the temperature of the wall surface of the recess <NUM> as temperature data at predetermined time intervals, and transmits signals indicating the temperature data to the pump drive device <NUM> that is provided outside the recess <NUM>. The leak sensor <NUM> and the pump drive device <NUM> are connected to each other by wire or wirelessly.

The pump drive device <NUM> is a device that acquires temperature information from the temperature data of the wall surface of the recess <NUM> acquired by the leak sensor <NUM> and controls the drive of the pump <NUM> on the basis of the temperature information.

Specifically, in a case where it is detected that a temperature acquired from the leak sensor <NUM> is equal to or lower than a predetermined threshold value, the pump drive device <NUM> determines that the liquefied ammonia is accumulated in the recess <NUM> and transmits a signal to instruct the pump <NUM> to drive to the pump <NUM>.

In a case where the pump <NUM> receives the signal, which instructs the pump <NUM> to drive, transmitted from the pump drive device <NUM>, the pump <NUM> pumps the liquefied ammonia, which is accumulated in the recess <NUM>, to the tank <NUM> via the return line <NUM>.

The pump <NUM> continues to idle (continues to perform a suction operation) even after pumping the liquefied ammonia accumulated in the recess <NUM>.

The drive of the pump <NUM> of the present embodiment is stopped at a suitable timing by an artificial operation.

In a case where the leak sensor <NUM> detects that the temperature acquired from the leak sensor <NUM> is higher than a predetermined threshold value, the pump drive device <NUM> may determine that liquefied ammonia is not accumulated in the recess <NUM> and transmit a signal for stopping drive (idling) to the pump <NUM>. In this case, the pump <NUM> stops driving when receiving the signal for stopping drive, which is transmitted from the pump drive device <NUM>.

According to the configuration of the floating structure <NUM> according to the embodiment, the ammonia having leaked from the tank <NUM> falls onto the receiving part <NUM> and is accumulated in the recess <NUM> of the receiving part <NUM>. The ammonia accumulated in the recess <NUM> of the receiving part <NUM> is pumped via the return line <NUM> by the pump <NUM> and is returned into the tank body <NUM>. Accordingly, the ammonia, which leaks from the tank <NUM> and is accumulated in the receiving part <NUM>, can be efficiently recovered.

Further, according to the configuration of the floating structure <NUM> according to the embodiment, since the receiving part <NUM> is the floor surface 16a of the inner surface <NUM>, the receiving part <NUM> can be formed without an increase in the number of components of the floating structure <NUM>.

Further, according to the configuration of the floating structure <NUM> according to the embodiment, the pump <NUM> is driven on the basis of the detection information of the leak sensor <NUM>. Accordingly, the ammonia accumulated in the recess <NUM> can be returned into the tank body <NUM> at a suitable timing.

Furthermore, according to the configuration of the floating structure <NUM> according to the embodiment, since the pump <NUM> can pump liquefied ammonia of which the amount is larger than the amount of liquefied ammonia leaking from the tank body <NUM> per unit time to the outside of the recess <NUM> per unit time, the accumulation of ammonia in the recess <NUM> can be suppressed. Accordingly, the evaporation of the ammonia, which is moved into the recess <NUM> from the inside of the tank body <NUM>, in the hold space R can be suppressed.

Moreover, according to the configuration of the floating structure <NUM> according to the embodiment, the liquefied ammonia having leaked from the tank body <NUM> is guided toward the bottom surface 52a of the tank body <NUM> along the groove <NUM> between the tank body <NUM> and the heat shield portion <NUM>. The liquefied ammonia guided toward the bottom surface 52a falls into the recess <NUM> of the receiving part <NUM> via the hole portion 62c that is formed at the middle groove 54c of the guide portion <NUM> of the heat shield wall <NUM>. Accordingly, the ammonia having leaked from the tank body <NUM> can be efficiently guided into the recess <NUM>.

Further, since the guide surface 62a of the guide portion <NUM> is inclined to approach the recess <NUM> toward the recess <NUM>, the falling of the liquefied ammonia onto the receiving surface <NUM> can be suppressed. Accordingly, a region of the secondary barrier, which is made of low-temperature steel, of the receiving surface <NUM> can be reduced, so that cost required to manufacture the floating structure <NUM> can be reduced.

Furthermore, according to the configuration of the floating structure <NUM> according to the embodiment, the supply line <NUM> and the return line <NUM> in which ammonia can flow are connected to the tank <NUM> and the return line <NUM> is independent of the supply line <NUM> and the return line <NUM> serving as other lines. That is, in a case where ammonia accumulated in the recess <NUM> flows toward the tank <NUM>, the ammonia does not flow into the supply line <NUM> and the return line <NUM>. Accordingly, in a case where the pump <NUM> returns ammonia to the tank <NUM> via the return line <NUM>, it is not necessary to stop the flowing of ammonia from the tank <NUM> to the combustion device <NUM> via the supply line <NUM> and the flowing of ammonia from the combustion device <NUM> to the tank <NUM>. Therefore, for example, ammonia having leaked from the tank <NUM> can continue to be returned to the tank <NUM> via the return line <NUM> in a state where the pump <NUM> is constantly driven.

Moreover, according to the configuration of the floating structure <NUM> according to the embodiment, since the pump <NUM> can idle, ammonia having leaked from the tank <NUM> is immediately returned to the tank <NUM> even though the ammonia having leaked from the tank <NUM> is moved into the recess <NUM> of the receiving part <NUM>. Accordingly, the evaporation of the ammonia, which is moved into the recess <NUM>, in the hold space R can be further suppressed.

The embodiment of the present disclosure has been described in detail above with reference to the drawings. However, specific configuration is not limited to the configuration of the embodiment, and additions, omissions, and substitutions of components and other modifications can be made without departing from the scope of the present disclosure. Further, the present disclosure is not limited by the embodiment, and is limited only by the claims.

The floating structure <NUM> has been a ship using ammonia as fuel in the embodiment, but is not limited to the ship using ammonia as fuel. The floating structure <NUM> may use liquefied gas, such as LNG or LPG, as fuel. That is, the tank <NUM> is not limited to the configuration for storing ammonia, and the tank <NUM> may be adapted to store liquefied gas, such as LNG or LPG.

Further, the ceiling portion <NUM> of the tank body <NUM> of the embodiment may include a ceiling portion body that forms the upper surface 51a, and a trunk top that extends upward from the upper surface 51a of the ceiling portion body in the vertical direction Dv. In a case where the ceiling portion <NUM> includes the trunk top and the trunk top is provided outside the hold space R, the ceiling-heat shield portion 61a may not be formed on the trunk top.

Further, the guide surface 62a of the embodiment is inclined to be positioned downward from the bow <NUM> toward the stern <NUM> in the bow-stern direction FA in a state where the floating main structure <NUM> does not trim as shown in <FIG>, but is not limited to this configuration. The guide surface 62a may be adapted to be inclined with respect to the horizontal plane only by a stern trim while the floating main structure <NUM> sails.

Furthermore, the return line <NUM> is provided independently of the supply line <NUM> and the return line <NUM> in the embodiment, but is not limited to this configuration. That is, the return line <NUM> may be connected to the supply line <NUM> or the return line <NUM>. That is, the inside of the pipeline of the return line <NUM> and the inside of the pipelines of the supply line <NUM> and the return line <NUM> may communicate with each other.

Moreover, the pump <NUM> of the embodiment is not limited to a diaphragm pump that is a type of positive displacement pump. The pump <NUM> may be, for example, another positive displacement pump, such as a piston pump, or a non-positive displacement pump.

Further, the supply line <NUM> and the return line <NUM> have been described as other lines in the embodiment, but the other lines are not limited thereto. The other line may be, for example, a cargo line that is connected to the tank <NUM> during bunkering or the like and can supply ammonia, which is supplied from, for example, a bunkering station or the like outside the floating structure <NUM>, into the tank <NUM>. Even in this case, the return line <NUM> is not connected to the cargo line, that is, the return line <NUM> is independent of the cargo line, and the return line <NUM> may be adapted such that ammonia flowing in the return line <NUM> does not flow into the cargo line.

Furthermore, the leak sensor <NUM> of the leak detecting unit <NUM> is a temperature sensor in the embodiment, but is not limited to a temperature sensor. The leak sensor <NUM> may be a level sensor that acquires the height of the liquid surface of the liquefied gas accumulated in the recess <NUM>, a liquefied gas sensor that acquires the concentration of the liquefied gas in the atmosphere inside the hold space R, or the like. In this case, the pump drive device <NUM> of the leak detecting unit <NUM> may acquire detection information from detection data acquired by the leak sensor <NUM> and transmit a signal, which instructs the pump <NUM> to drive, to the pump <NUM> on the basis of the detection information.

Moreover, as shown in <FIG>, the fuel storage unit <NUM> of the floating structure <NUM> may further include a drip pan as a receiving part <NUM> that is disposed below the tank <NUM> to cover the tank <NUM> from below and includes a receiving surface <NUM> and a recess <NUM> recessed from the receiving surface <NUM>. In this case, the floor surface 16a described in the embodiment may not be the receiving part <NUM>. The same effects as described above can be obtained even from this.

For example, the floating structure described in the embodiment is ascertained as follows.

Accordingly, even though the liquefied gas having leaked from the tank <NUM> is moved into the recess <NUM>, <NUM> of the receiving part <NUM>, <NUM>, the liquefied gas is immediately returned to the tank <NUM> by the pump <NUM> that is idling.

Claim 1:
A floating structure (<NUM>) comprising:
a floating main structure (<NUM>);
a tank (<NUM>) that is provided in the floating main structure (<NUM>) and includes a tank body (<NUM>) capable of storing liquefied gas therein;
a receiving part (<NUM>, <NUM>) that is disposed below the tank (<NUM>) to cover the tank (<NUM>) from below and includes a receiving surface (<NUM>, <NUM>) and a recess (<NUM>, <NUM>) recessed from the receiving surface (<NUM>, <NUM>);
a pump (<NUM>) that is provided in the recess (<NUM>, <NUM>); and
a return line (<NUM>) that is connected to the pump (<NUM>), characterized in that
the tank (<NUM>) includes a heat shield wall (<NUM>) covering an outer surface of the tank body (<NUM>), and
the return line (<NUM>) returns the liquefied gas pumped by the pump (<NUM>) into the tank body (<NUM>).