WO2023021250A1

WO2023021250A1 - Liquid gas storage and/or transport tank intended for a ship

Info

Publication number: WO2023021250A1
Application number: PCT/FR2022/051550
Authority: WO
Inventors: Elodie COUPILLAUD; Sebastien FATET
Original assignee: Gaztransport Et Technigaz
Priority date: 2021-08-16
Filing date: 2022-08-03
Publication date: 2023-02-23
Also published as: FR3126119A1

Abstract

The invention relates to a tank (1) for storing and/or transporting a liquefied gas, the tank (1) comprising at least one main mast (12) and a feed pump (18) which is received in a pump chamber (180) forming part of the main mast (12) and which is configured to pump the liquefied gas received in the tank (1), the tank (1) comprising a purge line (211) configured to convey a purge fluid into the tank (1), characterised in that the main mast (12) has, adjacent to the feed pump (18), an inlet port (2110) through which the purge line (211) opens into the pump chamber (180).

Description

Title of the invention: Liquid gas storage and/or transport tank intended for a ship

The present invention relates to the field of ships equipped with a tank for storing and/or transporting liquid gas such as, for example, liquefied natural gas. The present invention relates more particularly to the field of the tanks fitted to such ships, in which the natural gas in the liquid state is stored.

The liquefied natural gas (also referred to as LNG) present in the tank can in particular be used, at least in part, to ensure the operation of the ship's machinery. In this context, it is known to place a feed pump in the tank, the feed pump being configured to suck the liquefied natural gas and bring it up at the outlet of the tank in the direction of fluid circulation conduits connected by elsewhere to the machines to be fed. The pump can in particular form part of a loading and/or unloading tower comprising a structure with several masts which are fixed to each other by crosspieces.

The use of liquefied natural gas to supply the machines requires continuous operation of the supply pump, which implies that the supply pump must be replaced more frequently than an unloading pump which does not work. only when the liquefied natural gas has to be removed from the tank. In known manner, the retractable feed pump is housed inside one of the masts of the loading and/or unloading tower, which makes it possible, when replacing the pump, to isolate the latter from the rest. of the tank. The mast is then purged and the pump can be removed through the upper part of the mast while the liquefied natural gas is left in the tank.

The mast is associated with a foot valve, located between the pump and the tank, and this foot valve is configured to close the communication between the mast and the tank when the retractable feed pump must be replaced and the internal volume of the mast purged of remaining liquefied natural gas or contaminants that may be present. In order to purge the residual volume of liquefied natural gas present in the mast when replacing the retractable feed pump, it is known to inject into the mast, via an upper end of this mast, a purge fluid, in particular an inert fluid, which allows the evacuation of the residual volume of liquefied natural gas by making it gaseous, the liquefied natural gas thus vaporized then easily evacuating through the opening arranged at the upper end of the mast. However, the existing solutions for injecting this purge fluid are not satisfactory because liquefied natural gas remains at the bottom of the mast, still in liquid form, opposite the opening arranged at the upper end of the mast. The residual quantities of liquefied natural gas in the mast, once this purge operation has been carried out, often remain significant and complicate the operation of replacing said pump.

The object of the present invention is to propose a solution making it possible, in particular, for the replacement of a pump as mentioned above, to evacuate a maximum quantity of residual natural gas remaining in the tank in the vicinity of this pump.

To do this, the subject of the invention is, according to a first aspect, a tank for storing and/or transporting a liquefied gas, the tank comprising at least one main mast and a supply pump which is received in a pump chamber forming part of the main mast and which is configured to pump the liquefied gas contained in the tank, the tank comprising a purge pipe configured to convey, inside the tank, a purge fluid, characterized in that the purge pipe extends mainly, within the tank, outside the main mast and characterized in that the main mast comprises, located in the vicinity of the feed pump, an inlet orifice through which the purge line opens into the pump chamber.

Preferably, the main mast extends substantially over the entire height of the tank and has a lower end in the vicinity of a tank bottom wall.

Preferably, the feed pump is retractable and can be moved inside the main mast as will be detailed later.

It should be noted that the qualification of "main mast" is here attributed to a mast present in the tank in a part of which the feed pump is submerged. retractable, without this mast having dimensions or structural characteristics differentiating it from other masts present in the tank and giving it a preponderant importance in the structure of the tank. In known manner, the main mast can belong to a loading and/or unloading tower.

The retractable feed pump is housed in the main mast and extends, in a working position, into the pump chamber. The pump chamber is here in the form of a tubular portion, for example substantially cylindrical, forming part of the main mast and whose diameter allows the installation of the supply pump inside the cavity that this delimited tubular portion. It should be understood here that the supply pump, when it is in a working position where it is able to pump the fluid stored in the tank, is placed entirely within the pump chamber. The latter has an axial dimension slightly greater than the axial dimension of the feed pump, in order to allow axial displacement of the retractable feed pump of the order of a few tens of centimeters within the pump chamber. By way of example, an axial dimension, or height, of the pump chamber may be of the order of one meter when the main mast housing this pump chamber and the corresponding retractable feed pump may have an axial dimension corresponding to the order of ten meters.

It should be noted that, according to various embodiments, the pump chamber may be in the form of an independent tubular sleeve, attached and fixed to a lower end of the main mast by suitable fixing means, or that it may be an integral part of this mast, forming the lower part of this mast, without precise demarcation with the rest of the mast.

In this way, the inlet orifice can be formed in a peripheral wall of the independent tubular sleeve, or else formed in a peripheral wall of the main mast. Generally, the inlet orifice is formed in a peripheral wall laterally delimiting the pump chamber. These various examples form an integral part of the invention since the pump chamber and the main mast make it possible to extract, when necessary, the retractable supply pump from the main mast via the upper end, opposite to the tank bottom wall and at the lower end of the mast.

As mentioned, according to the invention, the purge pipe extends within the tank while being mainly outside the mast and the main mast is configured so that this purge pipe can open into the pump chamber near the fuel pump. The fact according to the invention of arranging the inlet orifice, through which the purge pipe opens into the main mast, that is to say enters after having circulated mainly outside the main mast, in the vicinity of the lower end of the main mast, in the pump chamber, makes it possible to direct the purge fluid as deeply as possible into the mast without however obstructing the passage within the main mast and therefore without interfering with any maintenance operations of the feed pump for example. The fact of directing the purge fluid as deeply as possible facilitates the transition to the gaseous state of the residual liquefied natural gas located in the lower region of the mast, which is difficult to access with regard to the axial dimension of the main mast when the injection of fluid Purging is carried out through the opening at the upper end of the mast. The introduction of the purge fluid in the vicinity of a lower end of the loading and/or unloading tower allows easier evacuation, towards the upper part of the tank, of the liquefied natural gas which has passed into the gaseous state under the purge fluid action. In other words, the invention allows a form of upward propulsion of the residual liquefied natural gas located in the vicinity of the feed pump, which makes it easier to evacuate this liquefied natural gas.

According to one characteristic, the retractable feed pump and the corresponding pump chamber are located in the vicinity of a lower end of the main mast, close to a bottom wall of the tank.

It is possible to define, for the retractable supply pump, a working position in which it is received in the pump chamber located in the vicinity of a bottom wall of the tank according to the invention, and which is at the opposite an upper end of the mast disposed in the vicinity of an upper wall of the tank according to the invention and adapted to be connected to a fluid circulation conduit also connected to the machinery of the vessel to be supplied.

It follows from the foregoing that, according to the invention, the inlet orifice, through which the purge pipe opens into the mast, is located close to the bottom wall of the tank, and one thus ensures that the liquefied gas residue present in the lower part of the mast, i.e. the fluid sucked in by the supply pump from the tank but not evacuated by the mast and therefore fell back into the bottom of the mast, is well impacted by the injection of the purge fluid, as well as the contaminants which may have deposited at the bottom of the mast.

According to one characteristic of the invention, the purge pipe extends mainly along an outer face of the main mast, that is to say the mast in which the supply pump is housed, up to the inlet opening into the pump chamber. It should be understood here that the purge line mainly extends, within the storage and/or transport tank, according to the axial dimension, or height, along the main mast to the pump chamber.

According to one characteristic of the invention, the main mast is part of a loading and/or unloading tower which also comprises secondary masts connected to each other and to the main mast by a plate placed near the bottom of the tank, the purge pipe comprising at least a first portion which extends along a secondary mast and a second portion which extends along the plate to the main mast.

According to one characteristic of the invention, a foot valve is housed in an airlock located between the pump chamber and the bottom of the tank, the foot valve being configured to be able to assume a position in which the pump chamber is isolated from tank.

The foot valve has, in particular, the role of isolating the pump chamber, and therefore the main mast, from the rest of the tank when replacing the retractable feed pump, that is to say, to on the one hand, to prevent any backflow, into the pump chamber, of liquefied natural gas present in the tank, and, on the other hand, to prevent any passage of purge fluid from the pump chamber to the liquefied natural gas contained in the tank outside the pump chamber.

According to a characteristic of the invention, the foot valve can be housed in an airlock which is in the form of a tubular sleeve, for example substantially cylindrical. The lock may have a diameter substantially equal to the diameter of the pump chamber, and the lock and the main mast in which the pump chamber is formed are fixed together by fixing means that each comprises. According to one example, these fixing means take the form of a first annular flange secured to a lower end of the mast at the level of the pump chamber and a second annular flange secured to an upper end of the airlock, the first annular flange and the second annular flange being fixed together, for example, by screwing.

According to one characteristic of the invention, an additional purge pipe is configured to route a purge fluid into the airlock, via an orifice drilled in a wall of the airlock, the purge pipe and the additional purge pipe being separate.

It should be understood here that within the tank according to the invention, the purge pipe and the additional purge pipe extend respectively between their inlet orifice, respectively formed in the pump chamber and in the airlock, and a connection end to a purge fluid storage tank disposed outside the tank. A suitable connection, formed in the upper wall of the tank, makes it possible to connect the part of the purge pipes present in the tank and the part outside the tank connected to the purge fluid tank. If necessary, the two purge pipes are associated with the same connection formed in the upper wall of the vessel, the purge pipes taking specific paths, if necessary one next to the other, to benefit from the same fixing means within the tank, and the purge pipes distinguishing themselves at the level of their inlet orifice to respectively open into the pump chamber or the airlock.

According to one characteristic of the invention, the purge pipe and the additional purge pipe follow, inside the vessel and over at least a portion of their length, contiguous paths, fastening means being common to the two purge pipes. In other words, according to this exemplary embodiment, the purge pipe and the additional purge pipe, distinct, follow paths close to each other but separated over at least part of their length. The purge pipe and the additional purge pipe may in particular follow, within the tank, paths that are strictly parallel to each other over at least part of their length.

According to one characteristic of the invention, the additional purge pipe comprises at least one portion which extends along the plate of the loading and/or unloading tower and the purge pipe also comprises at least one portion which is extends along the plate of the loading and/or unloading tower, contiguous to the corresponding portion of the additional purge pipe.

According to one characteristic of the invention, the purge pipe is connected to a purge fluid storage tank arranged outside the tank.

According to one characteristic of the invention, the purge fluid is nitrogen in gaseous form.

According to a characteristic of the invention, the purge pipe and the additional purge pipe are connected to the same purge fluid storage tank. It follows that the purge fluid routed into the main mast via the purge line is identical to the purge fluid routed via the additional purge line to the foot valve.

According to one characteristic of the invention, the tank according to the invention comprises means for moving the supply pump within the pump chamber, between a first position, or working position, and a second position, or position purge, wherein the feed pump is disposed remote from the inlet of the purge line in the pump chamber. In the working position of the retractable feed pump, the inlet orifice of the purge pipe in the main mast can face the retractable feed pump. The purge position consists of an intermediate position between the working position and the end upper part of the main mast by which a pump to be replaced is extracted from the main mast. At least one purge operation, i.e. injection of purge fluid, into the main mast is carried out when the supply pump to be replaced is in the intermediate position, to ensure that all of the Residual liquefied natural gas, and any contaminants such as dust, is evacuated before actually replacing the faulty pump.

According to one characteristic of the invention, the foot valve is associated with movable elastic means to give the foot valve a closed position pressed against the opening through which the fluid from the tank is sucked by the supply pump retractable and a release position at a distance from this opening.

According to one characteristic of the invention, the feed pump is carried by a mobile hoist between at least a first stop position in which the feed pump is placed in its first position, or working position, an intermediate position in which the supply pump is placed in its second position, or purge position, and an end position in which the pump is extracted from the mast.

According to another aspect, the invention extends to a method for replacing a feed pump placed in a tank as previously described, the method comprising a first step of moving the feed pump to be replaced between its working position and its purge position, a second step of introducing a purge fluid into the pump chamber through the purge pipe, a third step during which the supply pump to be replaced is removed from the main mast, and a fourth step of inserting a new feed pump into the main mast as far as its purge position and its working position.

According to a preferred embodiment, the second and third steps can be concomitant.

According to one characteristic of the invention, an injection of purge fluid is carried out between the passage from the purge position to the working position of the new pump. According to one characteristic of the invention, a step of closing a lower end of the main mast by moving the foot valve is performed simultaneously with the first step of moving the feed pump to be replaced.

According to one characteristic of the invention, a step of injecting purge fluid into the airlock via the additional purge pipe can be provided during this step of closing by moving the foot valve, in such a way that the volume located between the supply pump or the pump chamber and the foot valve can be emptied of residual liquefied natural gas and contaminants, such as dust, which it contains. Alternatively, the purge fluid injection step can take place after the foot valve closing step.

The invention finally extends to a freight transport ship equipped with a transport and/or storage tank as described above, configured to store a liquefied gas, in which the replacement of the supply pump located in the main mast of the tank is made by a method as explained above.

Other characteristics and advantages of the invention will become apparent through the description which follows on the one hand, and several embodiments given by way of indication and not limiting with reference to the appended diagrammatic drawings on the other hand, on which :

[fig. 1] is a side view of a transport ship showing at least one natural gas tank in liquid state,

[fig. 2] is a schematic general view of a transport and/or storage tank according to the invention,

[fig. 3] is a schematic general view of a loading and/or unloading tower installed in a tank such as that illustrated in figure 2,

[fig. 4] is a schematic close-up perspective view of the plate of a loading and/or unloading tower such as that illustrated in FIG. 3, according to a first embodiment of the invention, [fig. 5] is a schematic close-up perspective view of the plate of a loading and/or unloading tower such as that illustrated in FIG. 3, according to a second embodiment of the invention.

[fig. 6] is a diagrammatic sectional view of a pump chamber showing a feed pump, installed in a mast of a loading and/or unloading tower such as that illustrated by FIG. 3, in its working position , with a foot valve allowing liquefied natural gas to pass between the lower end of the mast and the bottom wall of the tank;

[fig. 7] is a schematic sectional view similar to that of Figure 6 showing the supply pump in its purge position, with the foot valve blocking access to the mast, via the lower end of the mast, to natural gas liquefied.

The features, variants and different embodiments of the invention may be associated with each other, in various combinations, insofar as they are not incompatible or exclusive with respect to each other. In particular, variants of the invention may be imagined comprising only a selection of characteristics described below in isolation from the other characteristics described, if this selection of characteristics is sufficient to confer a technical advantage and/or to differentiate the invention. compared to the prior art.

Furthermore, the same elements will be designated by the same references in the following description and in the various appended figures.

By convention, in the figures, an orthonormal marker (oxyz) is used to describe the elements of the vessel according to the invention. The axis ox corresponds to a longitudinal direction of a ship in which the tank according to the invention is placed, and the axis oy represents a transverse axis perpendicular to the longitudinal direction of the ship. The terms "forward" and "aft" are understood, in the following, with respect to a main direction of movement of the vessel along the longitudinal direction. The axis oz represents a vertical axis perpendicular to the longitudinal and transverse axes and materializes a vertical direction of the tank according to the invention and of the vessel in which it is placed. Terms “Upper” or “top” will designate in what follows the positive direction of the oz axis, the terms “lower” or “bottom” designating the negative direction of the oz axis.

In Figure 1 is shown a transport vessel 100 which comprises in at least one tank of liquefied natural gas, one of these tanks, the tank 1, being here made visible to facilitate understanding. The transport vessel 100 is notably configured to use liquefied natural gas as fuel for the operation of the vessel. The tank 1 is equipped with a loading and/or unloading tower 2 configured to allow the loading and/or the unloading of liquefied natural gas into or from the tank 1, and as will be described below, the tank features a retractable feed pump that is configured to pump liquefied natural gas and direct it towards the ship's machinery.

Figure 2 schematically illustrates a tank 1 for storing and/or transporting a fluid. Tank 1 is equipped with a loading and/or unloading tower 2 as mentioned above. The tank 1 is also anchored in a supporting structure 3 of the ship. The load-bearing structure 3 is, for example, formed by an internal hull of the ship but can more generally be formed from any type of rigid partition having suitable mechanical properties. The tank 1 can be intended for the transport of liquefied natural gas or to receive liquefied natural gas serving as fuel for the propulsion of the ship or for the supply of a heat engine of an electric generator of the ship.

According to the example illustrated here, the fluid contained in tank 1 is liquefied natural gas but it is understood that it could be a different fluid without departing from the context of the present invention. For example, this fluid could be a gaseous mixture comprising mainly methane as well as one or more other hydrocarbons and nitrogen in a small proportion. In what follows, the terms "fluid" and "liquefied natural gas" will be used interchangeably to designate the fluid received in tank 1.

The loading and/or unloading tower 2 is advantageously installed in the vicinity of a side wall 8 of the tank 1, and more particularly in the vicinity of a rear side wall 8 of the tank 1, which makes it possible to optimize the amount of cargo capable of being unloaded by the loading and/or unloading tower 2 insofar as the ships are generally leaning backwards using ballasts in a particular way in particular in order to limit vibrations. In the remainder of the description, the terms “tower” and “loading and/or unloading tower” will be used without distinction to designate the same structure.

The tower 2 extends over substantially the entire height of the tank 1 in the direction of the axis oz, between an upper end 200, placed in the vicinity of an upper wall 9 of the tank, and a lower end 201 placed at the vicinity of a bottom wall 23 of the tank 1.

Figure 3 more precisely illustrates in perspective a loading and/or unloading tower 2 such as that shown in Figure 2.

Referring to Figure 3, the loading and / or unloading tower 2 comprises three masts 11, 12, 13, which are each fixed to each other by crosspieces 14. Each of these masts 11, 12, 13, is hollow and passes through a cover 10 which closes the upper wall of the tank 1. The three masts 11, 12, 13, define, with the crosspieces 14, a prism with a triangular section, without this shape being limiting of the invention.

According to the embodiment more particularly illustrated by Figure 3, the masts 11, 12, 13 are arranged at equal distance from each other, so that the section of the prism is an equilateral triangle, but again it should be noted that this arrangement does not limit the invention.

The tank 1 comprises according to the invention a retractable feed pump 18 housed in one of the masts, this mast being referred to below as a main mast 12. As illustrated in Figure 3, this main mast 12 may have a passage section greater than the corresponding section of the other masts 11, 13, or secondary masts, without this being limiting of the invention since the passage section of the main mast makes it possible to slide the retractable feed pump from a upper opening of the main mast to a lower part, in the vicinity of the lower end 201 of the tower when it comes to positioning the pump at the bottom of the main mast, or in the other direction when it is it's a question of extracting it to replace it notably. The retractable feed pump 18 is configured to pump the liquefied natural gas present in the tank 1 and direct it through the main mast towards the upper end of the latter, in order to bring it out of the tank 1 and to direct it to the ship's machinery through circulation ducts not shown here.

The tank may comprise one or more retractable feed pumps 18. In what follows, the invention will be described for a configuration in which the tank 1 comprises a single retractable feed pump 18, it being understood that the characteristics applied to this retractable feed pump 18 apply to any other retractable feed pump fitted to one of the other masts of tank 1.

The retractable supply pump 18 is housed in a zone of the mast, when it is in the working position, that is to say capable of pumping the liquefied natural gas into the tank, which can be considered as a pump 180. This pump chamber is formed within a mast 12 of the loading and/or unloading tower 2, which therefore forms a main mast in the sense defined above. The retractable feed pump is arranged in this pump chamber so as to extend across the flow of liquefied natural gas likely to ascend the main mast to subsequently supply the ship's machinery.

The pump chamber 180 is located in the lower part of the main mast 12 and it can be considered as an extension of the main mast 12 in the lower part of the latter, in the axial direction of the latter and in the direction of the bottom wall. of the tank.

In the example schematically illustrated in Figure 3, the pump chamber is an integral part of the main mast 12, forming the lower part of this mast, without precise demarcation with the rest of the mast. Provision could be made, without departing from the context of the invention, for the pump chamber to be formed by a tubular sleeve independent of the main mast and attached and fixed to a lower end of this main mast by suitable fixing means. In each case, fluid communication is present between the pump chamber and the upper part of the mast and the dimensions, in particular the passage sections, of the mast and of the pump chamber make it possible to extract the retractable supply pump from the mast by raising it from its working position in the lower part of the mast towards the upper end of the mast, when it is necessary to replace it.

The loading and/or unloading tower 2 comprises a plate 24, which participates in forming the lower end 201 of the tower 2. As shown in FIG. 3, the plate 24 can serve as a support for the retractable feed pump 18 and to the pump chamber 180 in which the supply pump 18 is received. It should however be noted that the representation of the plate in FIG. 3 is a non-limiting schematic representation of the shape of this plate.

FIG. 4 is a close-up schematic view of the lower end 201 of the loading and/or unloading tower 2 of a tank 1 according to a first embodiment of the invention. We find in FIG. 4 the lower end 201 of the loading and/or unloading tower 2, as well as the plate 24 of this tower, and the lower part of the main mast 12, with the pump chamber 180 in which is placed the feed pump 18, not visible in Figure 4.

The tank also comprises a foot valve 19, visible in the schematic representations of Figures 6 and 7, which has the function of allowing or blocking the suction of the liquefied natural gas present in the tank by the retractable feed pump, or in other words, allow or block the passage of fluid at the level of the lower end 120 of the main mast 12. The foot valve 19 is thus movable between a release position, visible in FIG. 6, in which it is at a distance from the lower end 120 of the main mast 12, and a closed position, visible in Figure 7, in which it is pressed against the lower end edge 120 of the main mast. The movement of the foot valve takes place from the release position to the closed position, and vice versa, by a combination of pressure and depression effects created in particular by the movement of the retractable feed pump within the main mast. and elastic return effect, via a set of springs 190 shown schematically in these figures 6 and 7. In an exemplary embodiment, at the level of the pump chamber 180, the main mast 12 may comprise, at its lower end, an annular flange 181 by which the main mast and the pump chamber are connected to a tubular sleeve 182 whose diameter is here substantially identical to the diameter of the pump chamber 180. More precisely the annular flange 181 located at the lower end of the main mast 12 is connected, for example by screwing, to an upper annular flange 183 of the tubular sleeve 182.

The tubular sleeve 182 is hollow, and the cavity that it forms accommodates within it the foot valve mentioned above and which makes it possible to isolate the retractable supply pump 18, as well as the interior volume of the pump chamber 180 and of the main mast 12, of the rest of the interior volume of the tank 1. The aforementioned tubular sleeve 182 therefore forms an airlock within which the foot valve 19 extends. The airlock arranged in the extension of the main mast is located, according to the vertical direction Oz previously defined, between the bottom wall of the storage tank and the pump chamber 180.

According to the invention, the storage tank comprises a purge pipe 211 which is configured to convey purge fluid, from a storage tank not shown in the figures and located outside the tank 1, in the vicinity of the lower end 120 of the main mast 12, and in particular in the pump chamber 180, in which the supply pump 18 is placed. outside the main mast. Only the terminal part of the purge pipe, opposite the storage tank, is housed in, or cooperates with, the main mast, via an inlet orifice formed on the main mast.

More specifically, the invention provides for the purge pipe 211 to emerge within the main mast 12 via an inlet 2110 schematically mentioned in FIG. 4, and arranged as close as possible to the lower end 120 of the main mast. The inlet orifice may in particular open out into the main mast in the vicinity of the retractable supply pump 18 when the latter is in its working position. He It follows from the above that the inlet 2110 is advantageously arranged in the pump chamber, near the lower part of the main mast 12, that is to say near the plate 24 of the tower. loading and/or unloading 2. In other words, the inlet 2110 can be formed in a peripheral wall laterally delimiting the pump chamber.

Two embodiments will more particularly be described with reference to FIGS. 4 and 5, each example being in accordance with the characteristic of the invention according to which an opening is made in the main mast in the vicinity of the lower end of the main mast 12 and a purge pipe is connected to this opening in order to be able to inject purge fluid at the level of the pump chamber, in the lower part of the main mast. These two embodiments differ in the structural elements present in the tank along which the purge line extends.

In a first exemplary embodiment, illustrated in FIG. 4, the purge pipe 211 comprises, from one end for connection to a purge fluid storage tank arranged in the upper part of the tank 1, up to the pump chamber 180, successively:

- a first portion 2111 extending along a secondary mast 11, 13 participating in forming the structure of the loading and/or unloading tower 2, as far as a lower end 2100 of this secondary mast, the first portion 2111 extending in the direction of the axis oz and parallel to the main mast 12 within which the supply pump 18 is placed in the pump chamber 180,

- a second portion 2112 extending between the lower end 2100 of the secondary mast 11, 13 and the lower end 120 of the main mast 12, the second portion 2112 extending in a plane comprising the axes ox and oy and substantially parallel to the plate 24 of the loading and/or unloading tower 2,

- a third portion 2113 which makes it possible to connect the second portion 2112 to the inlet 2110 opening into the main mast 12. The first portion 2111 and the second portion 2112 here form the main portion of the purge pipe which extends outside the main mast 12.

Fixing and anchoring means 215 are provided to freeze the position of the purge pipe 211 within the vessel along the secondary mast and the plate, these fixing and anchoring means being able in particular to take the form of staples made respectively integral with the mast or the plate and shaped to allow the drain pipe to be retained.

In the example illustrated, the tank also includes an additional purge pipe 212, which is configured to convey purge fluid to the vicinity of the foot valve, from the aforementioned storage tank. This additional purge pipe 212 can in particular extend to the interior of the cavity defined by the tubular sleeve 182 forming the airlock in which the foot valve 19 is placed. The additional purge pipe 212 opens into the airlock 182 through an inlet 2120 schematically illustrated in Figure 4.

In this context, the purge pipe 211 and the additional purge pipe 212 are separate, that is to say they penetrate the upper part of the tank 1 through separate orifices, and they travel up to the lower end 120 of the main mast 12, without there being any intersection between them through which the fluid conveyed by one of the pipes could be brought into contact with the fluid conveyed by the other pipe.

More particularly, in the first embodiment illustrated by FIG. 4, the purge pipe 211 and the additional purge pipe 212 follow, between a secondary mast 11, 13, and, respectively, the pump chamber 180 and the airlock 182 , locally contiguous paths.

The purge pipe 211 and the additional purge pipe 212 each notably comprise a first portion 2111, 2121 extending along a secondary mast 11, 13 and a second portion 2112, 2122 extending between the lower end 2100 of the corresponding secondary mast 11, 13 and the lower end 120 of the main mast 12, along the plate 24. According to this embodiment of the invention, the purge pipe 211 and the additional purge pipe 212 therefore have paths that are substantially parallel to each other over a significant portion of their respective lengths. This makes it possible, in particular, to implement fixing and anchoring points 215 common to these two pipes in order to quickly secure the purge pipes in particular to the plate 24 of the loading and/or unloading tower 2 and to the secondary mast 11, 13.

FIG. 5 illustrates a second exemplary embodiment of the invention which differs from what has just been described above by the path of the purge pipe 211. This figure shows the loading and/or unloading tower 2, its lower end 201 and its plate 24, as well as the pump chamber 180, the airlock 182, the secondary mast 11, 13, the purge pipe 211 and the inlet 2110 through which the purge pipe 211 opens into the main mast 12.

According to this second embodiment, the purge pipe 211 comprises only a first portion 2111 which extends along an outer face of the main mast 12, substantially vertically, from the upper wall of the tank 1 to the chamber pump 180 and inlet 2110 formed therein. The purge line can be fixed to the main mast, but as mentioned above, it extends inside the tank outside the mast. Here again, without these being represented here, fixing and anchoring means can be arranged at regular intervals along the main mast to ensure that the purge pipe is held against the external face of the main mast.

As mentioned above for the first embodiment, an additional purge pipe, separate from the purge pipe and connected to the foot valve lock, can be provided. This additional purge pipe can follow the path illustrated in Figure 4 and described above, along a secondary mast and the plate, as shown in Figure 5, or follow the same path along an external face of the main mast to again make common the means of fixing and hooking the two purge pipes. Whatever the embodiment chosen, the presence of the inlet 2110 arranged in the vicinity of a lower end 120 of a mast 12 therefore allows effective and complete evacuation, by a thrust, from the lower part from the main mast 12 towards the upper part of the main mast 12 and of the tank 1, of any residual liquefied natural gas remaining in the lower part of the main mast during a pump replacement operation.

Whatever the embodiment chosen, the invention further provides that the tank 1 includes means for moving the supply pump 18, shown schematically in Figures 6 and 7. Figure 6 illustrates more particularly the pump supply 18 in a working position, in which the pump is able to suck through an opening at the lower end 120 of the main mast 12 the liquefied natural gas present in the tank to direct it through the main mast in the direction of the ship's machinery, and FIG. 7 more particularly illustrates the supply pump 18 in a purge position, that is to say an intermediate position between the working position and a position in which the pump to be replaced has come out by the upper end of the main mast 12.

The means for moving the supply pump 18 are configured to allow the movement of the supply pump 18 between the working position of Figure 6 and the purge position.

These movement means here take the form of a hoist 184 secured to an upper wall of the supply pump 18 and able to assume at least a first stop position in which the supply pump 18 is in its position working and a second position in which the supply pump 18 is in its previously mentioned purge position. The means for moving the feed pump are shown schematically in Figures 6 and 7 and they could have a different shape without departing from the context of the invention, it being noted that it is however advantageous that in accordance with what is illustrated , the displacement means do not obstruct the inlet orifice made in the pump chamber 180. Thus, during a replacement operation of the supply pump 18, the invention provides that, in a first step, the supply pump 18 to be replaced is moved from its working position to its purge position, then , in a second step, the invention provides that the purge fluid is injected into the pump chamber 180 through the inlet 2110 to ensure that the residual liquefied natural gas is expelled upwards at the same time as the pump to be replaced has come out of the main mast 12 in which it is housed.

The fact of moving the supply pump to the purge position simultaneously makes it possible to block the lower end 120 of the mast by depression of the foot valve.

In a third step and then a fourth step, the invention provides for the retractable supply pump to be replaced to be removed from the main mast, then for a new pump 18 to be inserted into the mast to successively assume a purge position and a position of work. An injection of purge fluid, via the purge line, is provided between the passage from the purge position to the working position of the new pump in order to ensure that residues of liquefied natural gas and contaminants are properly evacuated. before the feed pump 18 is put into its final position. The injection of purge fluid into the pump chamber 180 when the feed pump 18 is in its purge position results in an effective emptying of the assembly of the pump chamber 180.

According to various examples, the operation of injecting purge fluid into the pump chamber 180 can be preceded, accompanied, and/or followed by an injection of purge fluid into the airlock 182. The purge pipe 211 and the additional purge pipe 212 being distinct, the purge fluid injection operations in the pump chamber 180 and in the airlock 182 can in fact be carried out independently of one another, simultaneously or not.

The invention, as it has just been described, achieves the goal that it had set itself, and allows the replacement of a defective pump within a gas transport and/or storage tank. natural liquefied, without the need to empty the contents of the tank. The invention makes it possible, by injecting the purge fluid in the lower part of the mast, to evacuate, towards the upper part of the main mast, a greater quantity of liquefied natural gas or of contaminants potentially present in the main mast. when replacing the pump.

Variants not described in this document can be implemented without departing from the context of the invention, provided they have the characteristics described in this document.

Claims

22

1- Tank (1) for storing and/or transporting a liquefied gas, the tank (1) comprising at least one main mast (12) and a supply pump (18) which is received in a pump chamber (180) forming part of the main mast (12) and which is configured to pump the liquefied gas contained in the tank (1), the tank (1) comprising a purge pipe (211) configured to convey, inside the tank (1), a purge fluid, characterized in that the purge pipe (211) extends mainly, within the tank (1), outside the main mast (12) and characterized in that that the main mast (12) comprises, located in the vicinity of the feed pump (18), an inlet orifice (2110) through which the purge pipe (211) opens into the pump chamber (180).

2- tank (1) according to claim 1, characterized in that the drain pipe (211) extends mainly along an outer face of the main mast (12) to the inlet opening into the pump chamber (180).

3- tank (1) according to claim 1, wherein the main mast (12) is part of a loading and / or unloading tower (2) which further comprises secondary masts (11, 13) interconnected and with the main mast by a plate (24) arranged near the bottom of the tank, the drain line (211) comprising at least a first portion (2111) which extends along a secondary mast (11) and a second portion (2112) which extends along the plate (24) to the main mast (12).

4- Tank (1) according to one of the preceding claims, wherein a foot valve (19) is housed in an airlock (182) located between the pump chamber (180) and the bottom of the tank, the valve of foot (19) being configured to be able to assume a position in which the pump chamber is isolated from the tank (1).

5- tank (1) according to the preceding claim, wherein an additional purge pipe (212) is configured to convey a purge fluid into the airlock (182), via an orifice drilled in a wall of the airlock, the purge pipe (211) and the additional purge line (212) being separate. 6- Tank (1) according to the preceding claim, characterized in that the drain pipe (211) and the additional drain pipe (212) follow, inside the tank (1) and on at least a portion of their length, contiguous paths, fastening means being common to the two purge pipes (211, 212).

7- Tank (1) according to any one of the preceding claims, characterized in that the purge pipe (211) is connected to a purge fluid storage tank arranged outside the tank (1).

8- Tank (1) according to any one of the preceding claims, characterized in that the purge fluid is nitrogen in gaseous form.

9- Tank (1) according to any one of the preceding claims, characterized in that it comprises means for moving the supply pump (18) within the pump chamber, between a first position, or position working position, and a second position, or purge position, in which the supply pump (18) is disposed remote from the inlet (2110) of the purge line (211) in the pump chamber (180).

10- A method of replacing a supply pump (18) placed in a tank (1) according to the preceding claim, the method comprising a first step of moving the supply pump (18) to be replaced between its position of work and its purge position, a second step of introducing a purge fluid into the pump chamber (180) through the purge line (211), a third step during which the supply pump to be replaced is removed of the main mast, and a fourth step of inserting a new supply pump within the main mast to its purge position and its working position, the second and third steps possibly being concomitant.

11- Goods transport vessel equipped with a transport and/or storage tank (1) according to any one of claims 1 to 9, configured to store a liquefied gas, in which the replacement of the supply pump (18) located in the main mast (12) of the tank (1) is produced by a method according to claim 10.