Liquid gas storage and / or transportation tanks for ships

Abstract

The present invention relates to a tank (1) for storing and / or transporting liquefied gas, characterized in that the tank (1) comprises at least one main strut (12) and a feed pump (18) housed in a pump chamber (180) forming part of the main strut (12), the feed pump (18) being configured to pump the liquefied gas contained in the tank (1), the tank (1) comprising a purge line (211) configured to convey a purge fluid into the tank (1), the main strut (12) having an inlet port (2110) adjacent to the feed pump (18) through which the purge line (211) opens into the pump chamber (180).

Description

[Technical field]

[0001] The present invention relates to the field of ships equipped with tanks for storing and / or transporting liquid gas, such as liquefied natural gas, and in particular to the field of tanks equipped on such ships in which natural gas is stored in liquid form. [Background technology]

[0002] The liquefied natural gas (also called LNG) present in the tank can in particular be used, at least in part, to provide for the operation of the ship's machinery. In this respect, it is known to arrange a feed pump in the tank, which is configured to suck in the liquefied natural gas and to make it rise towards a fluid circulation duct to the outlet of the tank, which is also connected to the machinery to be fuelled. The pump may in particular be part of a loading tower, which comprises a structure with several columns attached to each other by cross members.

[0003] The use of liquefied natural gas to supply machinery requires continuous operation of the feed pump, which means that the feed pump must be replaced more frequently than a discharge pump, which operates only when liquefied natural gas needs to be removed from the tank. As is known, a retractable feed pump is housed in one of the columns of the loading tower, which allows the pump to be isolated from the rest of the tank during replacement. The column is then purged and the pump can be removed through the upper part of the column while the liquefied natural gas remains in the tank.

[0004] The strut is assigned a foot valve arranged between the pump and the tank, which is configured to close the communication between the strut and the tank when the retractable feed pump has to be replaced and the internal volume of the strut has to be purged of residual liquefied natural gas or possible contaminants.

[0005] In order to purge the residual volume of liquefied natural gas present in the column during replacement of a retractable feed pump, it is known to inject a purge fluid, in particular an inert fluid, into the column through the upper end of said column, which makes it possible to evacuate the residual volume of liquefied natural gas by turning it into a gaseous form and then easily discharging the gaseous liquefied natural gas through an opening arranged at the upper end of the column. However, the existing means for injecting this purge fluid are not satisfactory, since the liquefied natural gas still remains in liquid form at the bottom of the column opposite the opening arranged at the upper end of the column. Once the purge operation has been carried out, the residual amount of liquefied natural gas in the column often remains large, complicating the operation of replacing said pump. Summary of the Invention [Problem to be solved by the invention]

[0006] The object of the invention is to propose a solution which makes it possible to remove the maximum amount of residual natural gas remaining in the tank close to a pump, in particular as described above, in order to replace said pump. [Means for solving the problem]

[0007] To this end, according to a first aspect, the invention relates to a tank for storing and / or transporting liquefied gas, the tank comprising at least one main strut and a feed pump accommodated in a pump chamber forming part of the main strut, the feed pump being configured to pump the liquefied gas contained in the tank, the tank comprising a purge line configured to convey a purge fluid into said tank, characterized in that within the tank, the purge line extends mainly outside the main strut and that the main strut has, close to the feed pump, an inlet port through which the purge line opens into the pump chamber.

[0008] Preferably, the main strut extends substantially the full height of the tank and has a lower end adjacent the bottom wall of the tank.

[0009] Preferably the feed pump is retractable and may be moved within the main strut, as described in more detail below.

[0010] It should be noted that in this specification the term "main column" refers to a column present in the tank, part of which column has a retractable feed pump immersed therein, which column does not have structural dimensions or features that differentiate it from other columns present in the tank and give it a dominant importance in the structure of the tank. As is known, the main column may belong to the loading tower.

[0011] The retractable feed pump is accommodated in the main strut and extends in the working position into the pump chamber, where the pump chamber is in the form of a tubular section forming part of the main strut, for example being substantially cylindrical. The diameter of the pump chamber allows the feed pump to be arranged in the cavity defined by this tubular section. Here, it should be understood that the feed pump is arranged completely in the pump chamber when it is in the working position in which it is able to pump the fluid stored in the tank. The pump chamber has an axial dimension that is slightly larger than that of the feed pump in order to allow an axial movement of the retractable feed pump in the pump chamber of the order of several tens of centimeters. By way of example, the axial dimension or height of the pump chamber may be of the order of one meter, while the main strut accommodating this pump chamber and the corresponding retractable feed pump may have corresponding axial dimensions of the order of 10 meters.

[0012] It should be noted that according to different embodiments, the pump chamber may be in the form of an independent tubular sleeve joined and attached to the lower end of the main strut by suitable attachment means, or the pump chamber may be an integral part of the strut forming the lower part of said strut without a precise boundary with the rest of the strut.

[0013] Thereby, the inlet port can be formed in the peripheral wall of a separate tubular sleeve or in the peripheral wall of the main strut, generally in the peripheral wall that laterally defines the pump chamber.

[0014] These different examples form an integral part of the invention when the pump chamber and main column need to be adapted to pull out the retractable feed pump outside the main column, via the bottom tank wall and the upper end of the column opposite the lower end.

[0015] As mentioned above, according to the invention, the purge lines, while extending into the tank, are mainly on the outside of the strut, and the main strut is configured in such a way that said purge lines can open into the pump chamber in the vicinity of the feed pump. According to the invention, the inlet port where the purge lines open into the main strut, i.e. where the purge lines enter after having gone mainly around the outside of the main strut, is located in the pump chamber close to the lower end of the main strut, so that the purge fluid can be sent as deep as possible into the strut, without obstructing the passage in the main strut and thus, for example, without interfering with maintenance operations of the feed pump. Sending the purge fluid as deep as possible facilitates the conversion of the residual liquefied natural gas in the lower region of the strut to a gaseous state. If the injection of the purge fluid is carried out through an opening provided at the upper end of the strut, the lower region of the strut is difficult to access in relation to the axial dimension of the main strut. The introduction of the purge fluid close to the lower end of the loading tower allows the liquefied natural gas, which has been converted into a gaseous state by the action of the purge fluid, to be easily discharged towards the upper part of the tank. In other words, the present invention allows for the upward propulsion of residual liquefied natural gas located in proximity to the feed pump, which facilitates the discharge of this liquefied natural gas.

[0016] According to one feature, the retractable feed pump and corresponding pump chamber are located adjacent the bottom wall of the tank, adjacent the lower end of the main strut.

[0017] It is possible to define an operating position for the retractable feed pump, in which it is housed in a pump chamber arranged according to the invention in the vicinity of the bottom wall of the tank, opposite an upper end of the strut arranged in the vicinity of the top wall of the tank according to the invention, and which can be connected elsewhere to a fluid circulation duct connected to the machinery of the ship to be supplied with fuel.

[0018] Therefore, in view of the above, according to the invention, the inlet port through which the purge line opens into the support is located near the bottom wall of the tank, thus ensuring that the liquefied gas residues present in the lower part of the support, i.e. the fluid sucked from the tank by the feed pump but not discharged through the support and therefore falling to the bottom of the support, are actually affected by the injection of purge fluid, as well as contaminants that may settle at the bottom of the support.

[0019] According to one feature of the invention, the purge line extends primarily along the outer surface of the main column, i.e. the column in which the feed pump is housed, to an inlet opening to the pump chamber, where it should be understood that the purge line extends primarily along the axial dimension or height of the main column to the pump chamber within the storage and / or transport tank.

[0020] According to one aspect of the invention, the main strut is part of a loading tower, the loading tower further comprising a plurality of secondary struts, the secondary struts being connected to each other and to the main struts by a plate located adjacent to the tank bottom, and the purge line having at least a first portion extending along the secondary strut and a second portion extending along the plate to the main strut.

[0021] According to one aspect of the invention, a foot valve is housed in an airlock disposed between the pump chamber and the bottom of the tank, the foot valve being configured to be capable of assuming a position in which the pump chamber is isolated from the tank.

[0022] In particular, the foot valve must isolate the pump chamber, and thus the main strut, from the rest of the tank during replacement of the retractable feed pump, i.e. on the one hand, the discharge of the liquefied natural gas present in the tank into the pump chamber must be prevented, and on the other hand, the passage of purge fluid from the pump chamber to the liquefied natural gas contained in the tank outside the pump chamber must be prevented.

[0023] According to one aspect of the invention, the foot valve can be accommodated in an airlock of tubular sleeve, for example of substantially cylindrical form. The airlock can have a diameter substantially equal to that of the pump chamber, the airlock and the main column in which the pump chamber is formed being attached to each other by means of attachment means provided on each. According to one example, said attachment means take the form of a first annular flange rigidly connected to the lower end of the column in the pump chamber and a second annular flange integrated into the upper end of the airlock, the first and second annular flanges being attached to each other, for example by means of a screw fastening.

[0024] According to one feature of the invention, an additional purge line is configured to convey purge fluid into the airlock through an orifice drilled in the wall of the airlock, the purge line and the additional purge line being separate from each other.

[0025] It should now be understood that in the tank, according to the invention, a purge line extends between an inlet port formed in the pump chamber and an end for connection to a purge fluid storage tank arranged outside the tank, and an additional purge line extends between an inlet port formed in the airlock and an end for connection to a purge fluid storage tank arranged outside the tank. Suitable connections formed in the top wall of the tank make it possible to connect the part of the purge line present in the tank with the part outside the tank, which is connected to the purge fluid tank. If necessary, the two purge lines are assigned identical connections formed in the top wall of the tank, which follow a specific path, where one purge line adjoins the other if appropriate in order to benefit from identical mounting means in the tank, and which differ from each other in the inlet port opening into the pump chamber or into the airlock, respectively.

[0026] According to one feature of the invention, the purge line and the additional purge line follow adjacent paths in the tank and over at least a portion of their length, the attachment means being common to the two purge lines. In other words, according to this embodiment, the purge line and the additional separate purge line follow paths adjacent to each other, but separate paths over at least a portion of their length. The purge line and the additional purge line can in particular follow paths strictly parallel to each other in the tank and over at least a portion of their length.

[0027] According to one feature of the invention, the additional purge line has at least one portion extending along the plate of the loading tower, and the purge line also has at least one portion extending along the plate of the loading tower adjacent to a corresponding portion of the additional purge line.

[0028] According to one aspect of the invention, a purge line is connected to a purge fluid storage tank located outside the tank.

[0029] According to one aspect of the invention, the purge fluid is gaseous nitrogen.

[0030] According to one feature of the invention, the purge line and the additional purge line are connected to the same purge fluid storage tank, so that the purge fluid delivered through the purge line into the main strut is the same as the purge fluid delivered through the additional purge line to the foot valve.

[0031] According to one feature of the invention, the tank according to the invention comprises means for moving the feed pump in the pump chamber between a first or working position and a second or purging position, in which the feed pump is located away from the inlet port of the purge line to the pump chamber. In the working position of the retractable feed pump, the inlet port of the purge line in the main strut can be opposite the retractable feed pump. The purge position is in an intermediate position between the working position and the upper end of the main strut, where the pump to be replaced is retracted from the main strut. At least one purge operation, i.e. an injection of purge fluid into the main strut, is carried out when the feed pump to be replaced is in the intermediate position, which makes it possible to ensure that all residual liquefied natural gas and suitable contaminants, e.g. dust, are evacuated before an efficient replacement of the failed pump can be carried out.

[0032] According to one feature of the invention, the foot valve is assigned movable elastic means, which allows the foot valve to have a sealing position in which it is pressed against the opening through which the fluid is sucked out of the tank by the retractable feed pump, and a released position in which it is spaced away from this opening.

[0033] According to one feature of the invention, the feed pump is transported by a movable hoist between at least a first stop position where the feed pump is located in its first or operating position, an intermediate position where the feed pump is located in its second or purge position, and an end position where the pump is withdrawn from the support.

[0034] According to another aspect, the present invention relates to a method for replacing a feed pump arranged in a tank as described above, comprising a first step of moving the feed pump to be replaced between its working position and a purge position, a second step of introducing a purge fluid into the pump chamber by a purge line, a third step of removing the feed pump to be replaced from the main post, and a fourth step of inserting a new feed pump into the main post into the purge position and into the working position.

[0035] According to a preferred embodiment, the second and third steps can be carried out simultaneously.

[0036] In accordance with one aspect of the invention, a purge fluid injection is performed during switching of the new pump from the purge position to the on position.

[0037] According to one feature of the invention, the step of closing the lower end of the main strut by movement of the foot valve is performed simultaneously with the first step of moving the feed pump to be replaced.

[0038] According to one feature of the invention, during this step of closing by movement of the foot valve, a step of injecting a purge fluid into the airlock via an additional purge line may be provided, so as to expel residual liquefied natural gas and any contaminants such as dust that it may contain from the volume located between the feed pump or pump chamber and the foot valve. Alternatively, the purge fluid injection step can be performed after the step of closing the foot valve.

[0039] Finally, the invention relates to a cargo ship equipped with a transport and / or storage tank as described above adapted for storing liquefied gas, in which the replacement of a feed pump arranged in the main strut of the tank is carried out by the method as described above.

[0040] Other characteristics and advantages of the present invention will become apparent from the following description and from some illustrative embodiments, given by way of example and without limitation with reference to the accompanying schematic drawings in which: [Brief description of the drawings]

[0041] [Figure 1] FIG. 1 is a side view of a transport vessel showing at least one tank of natural gas in liquid form. [Diagram 2] FIG. 1 is a schematic overview of a transport and / or storage tank according to the invention. [Diagram 3] FIG. 3 is a schematic overview of a loading tower installed in a tank such as the tank shown in FIG. 2. [Figure 4] FIG. 4 is a schematic perspective view showing an enlarged plate of a handling tower such as the one shown in FIG. 3 according to a first embodiment of the invention; [Diagram 5] FIG. 4 is a schematic perspective view showing an enlarged plate of a handling tower such as the one shown in FIG. 3 according to a second embodiment of the invention; [Figure 6] FIG. 4 is a schematic cross-sectional view of a pump chamber showing a feed pump in its operating position installed in a column of a loading tower such as that shown in FIG. 3, together with a foot valve allowing liquefied natural gas to pass between the lower end of the column and the bottom wall of the tank. [Figure 7] FIG. 7 is a schematic cross-sectional view similar to FIG. 6 showing the feed pump in a purge position, with the foot valve blocking the strut's access to liquefied natural gas through the strut's lower end. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0042] The features, variants and different embodiments of the invention can be combined with each other in various combinations, as long as the embodiments are not mutually exclusive or exclusive. In particular, it is possible to envisage a variant of the invention comprising only one selected feature of the multiple features described below, separately from the other features described, provided that this selection of features is sufficient to provide a technical advantage and / or to differentiate the invention from the prior art.

[0043] Moreover, in the following description and in the various accompanying drawings, like elements are designated with like reference numerals.

[0044] By convention, in the drawings, a Cartesian coordinate system (oxyz) is used to represent the elements of the tank according to the invention. The ox axis corresponds to the longitudinal direction of the ship in which the tank according to the invention is arranged, and the oy axis is a transverse axis perpendicular to the longitudinal direction of the ship. The terms "forward" and "aft" are understood below with respect to the main direction of the ship's motion in the longitudinal direction. The oz axis represents the vertical axis perpendicular to the longitudinal and transverse axes and embodies the vertical direction of the tank according to the invention and of the ship in which it is arranged. In the following, the terms "upper" or "higher" refer to the positive direction of the oz axis and the terms "lower" or "bottom" refer to the negative direction of the oz axis.

[0045] Figure 1 shows a transport vessel 100 equipped with at least one tank of liquefied natural gas, one of which, namely tank 1, is visible in Figure 1 for ease of understanding. The transport vessel 100 is configured in particular to use liquefied natural gas as fuel for the operation of the vessel. The tank 1 comprises a loading tower 2 configured to allow the loading and / or unloading of liquefied natural gas into and / or from the tank 1, which, as will be explained below, comprises a retractable feed pump configured to pump and deliver the liquefied natural gas to the vessel's machinery.

[0046] Figure 2 shows diagrammatically a tank 1 for storing and / or transporting fluids. The tank 1 is equipped with a loading tower 2 as described above. The tank 1 is also anchored to a support structure 3 on board the ship. The support structure 3 may for example be formed by the inner hull of the ship, but more generally from any type of rigid partition wall having suitable mechanical properties. This tank 1 may be for transporting liquefied natural gas, or for containing liquefied natural gas that serves as fuel for propelling the ship, or for fuelling the heat engine of the ship's generator.

[0047] According to the example shown, the fluid contained in tank 1 is liquefied natural gas, but it is understood that it may be a fluid different from liquefied natural gas without departing from the context of the present invention. For example, the fluid may be a gaseous mixture containing mainly methane with small proportions of one or more other hydrocarbons and nitrogen. In the following, the terms "fluid" and "liquefied natural gas" are used interchangeably to denote the fluid contained in tank 1.

[0048] The loading tower 2 is advantageously installed close to the side wall 8 of the tank 1, more particularly close to the rear side wall 8 of the tank 1, which makes it possible to optimize the amount of cargo that can be unloaded by the loading tower 2, insofar as the ship is generally tilted aft with ballast, in particular to limit vibrations. In the remainder of this specification, the terms "tower" and "loading tower" will be used interchangeably to denote the same structure.

[0049] The tower 2 extends substantially over the entire height of the tank 1 along the oz-axis between an upper end 200 located adjacent to the upper wall 9 of the tank and a lower end 201 located adjacent to the bottom wall 23 of the tank 1.

[0050] FIG. 3 shows a more accurate perspective view of a loading tower 2 such as the tower shown in FIG.

[0051] 3, the loading tower 2 comprises three columns 11, 12, 13, which are attached to each other by cross members 14. Each of these columns 11, 12, 13 is hollow and passes through a cover 10 that closes the top wall of the tank 1. The three columns 11, 12, 13 define a prism with a triangular cross section by the cross members 14, although this shape is not limiting to the invention.

[0052] According to an embodiment shown in more detail in FIG. 3, the pillars 11, 12, 13 are arranged equidistant from one another so that the cross section of the prism is an equilateral triangle, but it should be noted here that this arrangement is not a limitation of the invention.

[0053] According to the invention, the tank 1 comprises a retractable feed pump 18 housed in one of the columns, which will be referred to below as the main column 12. As shown in FIG. 3, said main column 12 may have a larger passage cross-section than the corresponding cross-sections of the other columns 11, 13 or of the secondary columns, without limiting the invention, as long as the passage cross-section of the main column allows the retractable feed pump to slide from its upper opening to the lower part close to the lower end 201 of the tower, if it is required to position the pump at the bottom of the main column, or in another direction, especially if it is required to withdraw the pump to replace it. The retractable feed pump 18 is configured to pump the liquefied natural gas present in the tank 1 through the main column to the upper end of this column, in order to leave the tank 1 and send it to the ship's machinery through a circulation line, not shown.

[0054] The tank may be equipped with one or more retractable feed pumps 18. In the following, the invention is described in a configuration in which the tank 1 is equipped with a single retractable feed pump 18. It is to be understood that the characteristics that apply to this retractable feed pump 18 also apply to any of the other retractable feed pumps mounted on one of the other supports of the tank 1.

[0055] The retractable feed pump 18 is accommodated in a defined area of ​​the pillar when the pump is in the working position, i.e. when it is able to pump the liquefied natural gas in the tank, which defined area can be considered as the pump room 180. The pump room is formed in the pillar 12 of the loading tower 2, which pillar 12 therefore forms the main pillar in the above defined sense. The retractable feed pump is arranged in the pump room so as to extend through the flow of liquefied natural gas which can then rise up the main pillar to supply the ship's machinery.

[0056] The pump chamber 180 is located in the lower part of the main strut 12 and can be considered as an extension of the main strut 12 in the axial direction of the main strut towards the bottom wall of the tank.

[0057] In the example shown diagrammatically in FIG. 3, the pump chamber, while being an integral part of the main column 12, forms the lower part of this column and does not define a precise boundary with the rest of the column. Without departing from the context of the invention, it may be provided that the pump chamber is formed by a tubular sleeve independent of the main column and attached to the lower end of this column by suitable attachment means. In any case, there is fluid communication between the pump chamber and the upper part of the column, and the dimensions of the column and the pump chamber, in particular the passage cross-section, make it possible to pull the retractable feed pump out of the column in case of pump replacement, by lifting it from its working position in the lower part of the column to the upper end of the column.

[0058] The loading 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 the pump chamber 180 in which the feed pump 18 is housed. However, it should be noted that the representation of the plate shown in Fig. 3 is a non-limiting schematic view of the shape of this plate.

[0059] Figure 4 is a schematic view of an enlarged view of the lower end 201 of the loading tower 2 of the tank 1 according to the first embodiment of the invention. Figure 4 shows the lower end 201 of the loading tower 2, the plate 24 of said tower as well as the lower part of the main strut 12, the pump chamber 180 in which the feed pump 18 is located is not visible in Figure 4.

[0060] The tank further comprises a foot valve 19, which can be seen in the schematic diagrams of Figures 6 and 7. The foot valve 19 serves to allow or block the suction of the liquefied natural gas present in the tank by the retractable feed pump, or in other words to allow or block the passage of fluid at the lower end 120 of the main strut 12. The foot valve 19 is therefore movable between a release position, shown in Figure 6, in which it is spaced away from the lower end 120 of the main strut 12, and a sealing position, shown in Figure 7, in which it is pressed against the edge 120 of the lower end of the main strut. The movement of the foot valve from the release position to the sealing position or from the sealing position to the release position is achieved by a combination of pressure and suction effects, caused in particular by the movement of the retractable feed pump in the main strut, and an elastic return effect via a set of springs 190, shown diagrammatically in Figures 6 and 7 above.

[0061] In one embodiment, in the pump chamber 180, the main strut 12 may have an annular flange 181 at its lower end, by which the main strut and the pump chamber are connected to a tubular sleeve 182, the diameter of which in this embodiment is substantially the same as the diameter of the pump chamber 180. More specifically, the annular flange 181 arranged at the lower end of the main strut 12 is connected to an upper annular flange 183 of the tubular sleeve 182, for example by a screw fastening.

[0062] The tubular sleeve 182 is hollow and forms a cavity in which the aforementioned foot valve is accommodated, which cavity allows the retractable feed pump 18 and the internal volume of the pump chamber 180 and the main strut 12 to be isolated from the rest of the internal volume of the tank 1. The aforementioned tubular sleeve 182 thus forms an airlock into which the foot valve 19 extends. The airlock, which is arranged in the extension of the main strut, is located between the bottom wall of the storage tank and the pump chamber 180 in the vertical direction oz defined above.

[0063] According to the invention, the storage tank is equipped with a purge line 211. The purge line 211 is arranged to convey a purge fluid from a storage tank (not shown) arranged outside the tank 1 into a pump chamber 180 adjacent to the lower end 120 of the main strut 12, in particular in which the feed pump 18 is arranged. For this purpose, the purge line 211 is mainly outside the main strut, while it extends into the tank 1. Only the end part of the purge line opposite the storage tank is accommodated in the main strut or cooperates with the main strut via an inlet port formed in the main strut.

[0064] More specifically, the invention provides that the purge line 211 opens into the main column 12 through an inlet port 2110, shown diagrammatically in FIG. 4, which is arranged as close as possible to the lower end 120 of the main column. The inlet port may open into the main column close to the retractable feed pump 18, in particular when the latter is in the operating position. Due to the above, the inlet port 2110 is advantageously arranged in the pump chamber close to the lower part of the main column 12, i.e. close to the plate 24 of the loading tower 2. In other words, the inlet port 2110 may be formed in a peripheral wall that laterally defines the pump chamber.

[0065] Two exemplary embodiments are described in more detail with respect to figures 4 and 5. Each example relates to a feature of the invention according to which an opening is formed in the main strut close to the lower end of the main strut 12 and a purge line is connected to said opening so as to be able to inject purge fluid in the pump chamber at the lower part of the main strut. These two embodiments differ from each other by the structural elements present in the tank along which the purge line runs.

[0066] In a first exemplary embodiment shown in FIG. 4, the purge line 211 has, in succession, the following portions from an end connected to a purge fluid storage tank located at the top of the tank 1 to the pump chamber 180:

[0067] A first portion 2111 extending along the secondary columns 11, 13 participating in forming the structure of the loading tower 2 to the lower end 2100 of said secondary columns, said first portion 2111 extending in the direction of the oz axis and parallel to the main column 12 in which the feed pump 18 is arranged in the pump chamber 180.

[0068] A second portion 2112 extending between the lower end 2100 of the secondary column 11, 13 and the lower end 120 of the main column 12, the second portion 2112 extending in a plane containing the ox axis and the oy axis and being substantially parallel to the plate 24 of the loading tower 2.

[0069] A third portion 2113 making it possible to connect the second portion 2112 to an inlet port 2110 opening into the main strut 12 .

[0070] The first portion 2111 and the second portion 2112 form the main portion of the purge line that extends outside the main strut 12 .

[0071] Attachment and anchoring means 215 are provided for fixing the position of the purge line 211 along the secondary struts and plates within the tank, said attachment and anchoring means may in particular take the form of clips integral with the struts or plates, respectively, and shaped to enable holding the purge line.

[0072] In the illustrated example, the tank also has an additional purge line 212, which is arranged to convey a purge fluid from the aforementioned storage tank to the vicinity of the foot valve. This additional purge line 212 may extend in particular into the cavity defined by the tubular sleeve 182 forming the airlock in which the foot valve 19 is located. The additional purge line 212 opens into the airlock 182 through an inlet port 2120, which is shown diagrammatically in FIG. 4.

[0073] In this regard, the purge line 211 and the additional purge line 212 are separate from each other, i.e., the purge line 211 and the additional purge line 212 enter the upper part of the tank 1 through separate orifices and pass to the lower end 120 of the main strut 12, and there are no intersections between the purge line 211 and the additional purge line 212 where fluid carried by one of these lines would come into contact with fluid carried by the other line.

[0074] More specifically, in the first exemplary embodiment shown in FIG. 4, the purge line 211 and the additional purge line 212 follow locally adjacent paths between the secondary column 11 and the pump chamber 180 and between the secondary column 13 and the airlock 182, respectively.

[0075] In particular, the purge line 211 and the additional purge line 212 each have a first portion 2111, 2121 extending along the secondary pillars 11, 13 and a second portion 2112, 2122 extending along the plate 24 between the lower end 2100 of the corresponding secondary pillar 11, 13 and the lower end 120 of the main pillar 12.

[0076] Thus, according to this exemplary embodiment of the invention, the purge line 211 and the additional purge line 212 have paths that are substantially parallel to one another over a large portion of their respective lengths, which in particular makes it possible to implement a common attachment and anchoring point 215 for these two lines for rapid fixation of the purge lines, in particular to the plate 24 of the loading tower 2 and the secondary columns 11, 13.

[0077] Figure 5 shows a second embodiment of the invention, which differs from the one described above by the path of the purge line 211. This figure shows the loading tower 2, its lower end 201 and its plate 24 as well as the pump chamber 180, the airlock 182, the secondary columns 11, 13, the purge line 211 and the inlet port 2110 through which the purge line 211 opens into the main column 12.

[0078] According to this second exemplary embodiment, the purge line 211 only comprises a first portion 2111 which extends substantially vertically along the outer surface of the main strut 12 from the top wall of the tank 1 to the pump chamber 180 and an inlet port 2110 formed therein. The purge line may be attached to the main strut, but runs outside the strut into the tank, in accordance with what has been described above. Again, not shown, mounting and anchoring means may be arranged at regular intervals along the main strut, which ensures retention of the purge line against the outer surface of the main strut.

[0079] As described above with respect to the first exemplary embodiment, an additional purge line may be provided, separate from the purge line and connected to a port on the foot valve, which may follow a route as shown in Figure 4 and described above along the secondary struts and plates as shown in Figure 5, or may follow the same route as the purge line along the outer surface of the main strut, allowing the two purge lines to share common fastening and mounting means.

[0080] Therefore, regardless of the embodiment selected, the presence of the inlet port 2110 located close to the lower end 120 of the tower 12 allows for effective and complete drainage of any residual liquefied natural gas remaining in the lower portion of the main column during pump replacement operations by pushing it up from the lower portion of the main column 12 towards the upper portion of the main column 12 and tank 1.

[0081] Regardless of the exemplary embodiment chosen, the invention further provides that the tank 1 comprises means for moving a feed pump 18, which is shown diagrammatically in figures 6 and 7. Figure 6 shows more specifically the feed pump 18 in a working position, in which the pump is able to suck the liquefied natural gas present in the tank through an opening provided in the lower end 120 of the main strut 12, and thus to send it through the main strut towards the machinery of the ship. Figure 7 shows more specifically the feed pump 18 in a purging position, i.e. an intermediate position between the working position and the position in which the pump to be replaced is taken out through the upper end of the main strut 12.

[0082] The means for moving the feed pump 18 is configured to allow movement of the feed pump 18 between an operating position and a purge position, as shown in FIG.

[0083] In the present embodiment, these movement means take the form of a hoist 184 fixed to the upper wall of the feed pump 18 and can take at least a first rest position, in which the feed pump 18 is in its working position, and a second position, in which the feed pump 18 is in the above-mentioned purging position. The means for moving the feed pump are shown diagrammatically in Figures 6 and 7 and these means may have different forms without departing from the spirit of the invention. However, it should be noted that, according to what is shown, it is advantageous for the movement means not to block the inlet opening provided in the pump chamber 180.

[0084] Therefore, during the operation of replacing the feed pump 18, the present invention provides that in a first step, the feed pump 18 to be replaced is moved from its operating position to the purge position, and then, in a second step, the present invention provides for injecting purge fluid into the pump chamber 180 via the inlet port 2110, thereby ensuring that the residual liquefied natural gas is driven upwards and at the same time the pump to be replaced is removed from the main support 12 in which it is housed.

[0085] Simultaneously, the feed pump is moved to the purge position, allowing the foot valve to suction to block the lower end 120 of the strut.

[0086] In a third step and a subsequent fourth step, the invention provides that the retractable feed pump to be replaced is removed from the main column and then the new pump 18 is inserted into the column, successively assuming the purge and working positions. Injection of purge fluid through the purge line occurs during the switchover of the new pump from the purge position to the working position, thereby ensuring that liquefied natural gas residues and contaminants are properly discharged before the feed pump 18 is finally put into operation. Injection of purge fluid into the pump chamber 180 when the feed pump 18 is in its purge position effectively empties the pump chamber 180 assembly.

[0087] According to various different examples, the act of injecting purge fluid into pump chamber 180 can be preceded, accompanied and / or followed by the act of injecting purge fluid into airlock 182. Because purge line 211 and additional purge line 212 are distinct, the act of injecting purge fluid into pump chamber 180 and the act of injecting purge fluid into airlock 182 can in fact be performed independently of each other, simultaneously or non-simultaneously.

[0088] The invention, as mentioned above, achieves the set goal and allows the replacement of a defective pump in a tank for transporting and / or storing liquefied natural gas without the need to empty the tank's contents. In fact, the invention allows the evacuation of large amounts of liquefied natural gas or contaminants potentially present in the main strut during replacement of the pump to the upper part of the main strut by injecting a purge fluid into the lower part of the strut.

[0089] Variations not described in this specification can be implemented without departing from the context of the invention, provided they have the characteristics described in this specification.

Claims

1. A liquid gas storage and / or transport tank (1), comprising at least one main strut (12) and a feed pump (18) housed in a pump chamber (180) forming part of the main strut (12), the feed pump (18) configured to pump liquefied gas contained in the tank (1), the tank (1) comprising a purge line (211) configured to convey a purge fluid into the tank (1), Within the tank (1), the purge line (211) extends mainly outside the main strut (12); and The main strut (12) has an inlet port (2110) adjacent to the feed pump (18), through which the purge line (211) opens into the pump chamber (180). A tank (1).

2. 2. The tank (1) according to claim 1, characterized in that the purge line (211) extends mainly along the outer surface of the main strut (12) to the inlet opening to the pump chamber (180).

3. 2. The tank (1) according to claim 1, wherein the main strut (12) is part of a loading tower (2), the loading tower (2) further comprising secondary struts (11, 13), the secondary struts (11, 13) being connected to each other and to the main strut by a plate (24) arranged adjacent to the tank bottom, and the purge line (211) comprising at least a first portion (2111) extending along the secondary strut (11) and a second portion (2112) extending along the plate (24) to the main strut (12).

4. 4. The tank (1) according to claim 1, wherein a foot valve (19) is accommodated in an air lock (182) arranged between the pump chamber (180) and the bottom of the tank, the foot valve (19) being configured to be able to take a position in which the pump chamber is isolated from the tank (1).

5. 5. The tank (1) of claim 4, wherein an additional purge line (212) is configured to convey purge fluid into the airlock (182) through an orifice drilled in a wall of the airlock (182), and the purge line (211) and the additional purge line (212) are separate from each other.

6. 6. The tank (1) according to claim 5, characterized in that the purge line (211) and the additional purge line (212) follow adjacent paths within the tank (1) and over at least part of their length, and that the attachment means are common to the two purge lines (211, 212).

7. 4. Tank (1) according to any one of claims 1 to 3, characterized in that the purge line (211) is connected to a purge fluid storage tank arranged outside the tank (1).

8. Tank (1) according to any one of claims 1 to 3, characterized in that the purge fluid is gaseous nitrogen.

9. 4. The tank (1) according to claim 1, further comprising means for moving the feed pump (18) within the pump chamber between a first or operating position and a second or purge position, wherein in the purge position the feed pump (18) is positioned away from the inlet port (2110) of the purge line (211) into the pump chamber (180).

10. 10. A method for replacing a feed pump (18) disposed in a tank (1) according to claim 9, comprising: a first step of moving the feed pump (18) to be replaced between its operating position and a purge position; a second step of introducing a purge fluid into the pump chamber (180) through the purge line (211); a third step of removing the feed pump to be replaced from the main strut; and a fourth step of inserting a new feed pump into the main strut to its purge position and operating position, wherein the second step and the third step can be performed simultaneously.

11. 11. A cargo ship equipped with a transport and / or storage tank (1) according to claim 1, adapted for storing liquefied gas, wherein replacement of the feed pump (18) arranged in the main strut (12) of the tank (1) is carried out by a method according to claim 10.

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