GB2089014A - Liquefied gas storage tanks - Google Patents

Abstract

In storage tanks for liquids including relatively large, stationary tanks on land for the storage of liquefied gases (e.g. natural gas, ethylene and ammonia) at or below ambient temperature and at or above atmospheric pressure, as well as to small transporting tanks (e.g. for road tankers) and fuel tanks for motor vehicles, the side and end walls are provided by a single tier of connected lobes 2, 3, in that said lobes extend in one common direction over the tank, in that the end walls of the tank comprise curved knuckles closing off the ends of the part-cylindrical lobes, and in that a separating plate 9 is provided at each lobe connection to strengthen the tank against internal pressure, all of said plates defining an opening so that the tank provides a single storage compartment capable of storing liquid under pressure with virtually no additional stiffening or strengthening members. <IMAGE>

Description

SPECIFICATION Storage tank for liquefied gases The invention relates to tanks for the storage of liquids and has application to relatively large, stationary storage tanks on land for the storage of gases such as natural gas, petroleum gas, ethane/ethylene and noxious gases such as ammonia and chlorine, liquefied at or below ambient temperature and at or above atmospheric pressure, as well as to small transporting tanks (e.g. for road tankers) and to fuel tanks for motor vehicles.

In U.l < . Patent Application No. 7939108 there is described a tank particularly of large dimensions and for land storage which is generally of the kind in which the walls are formed by a multiplicity of connected, parallel, part-cylindrical lobes presenting outwardly convex arcuate surfaces.

The storage tank is characterised in that the side and end walls thereof are provided by a single tier of connected lobes, in that said lobes extend in one common direction over the tank, in that the end walls of the tank comprise part-spherical knuckles closing off the ends of the part-cylindrical lobes, and in that a separating plate is provided at each lobe connection to strengthen the tank against internal pressure, one or more of said plates being liquid tight so as to divide the tank into separate storage compartments.

Such an arrangement provides a tank which is particularly useful for liquefied gases stored at atmospheric pressure, or at relatively small pressures (typically liquefied natural gas at 50 p.s.i.) particularly in the case where a liquid tight separating plate is provided at each lobe connection. This is because in the event of a fracture of a weld or the wall of the tank, the leak will be localised to one or two of the separate storage compartments, and the liquid tight separating plates can withstand the relatively small pressure differentials which can arise when one or more compartments becomes depressurised.

In accordance with the present invention a storage tank for the storage of liquid at or above atmospheric pressure of the kind in which the walls are formed by a multiplicity of connected parallel, part-cylindrical lobes presenting outwardly convex arcuate surfaces, is characterised in that the side and end walls thereof are provided by a single tier of connected lobes, in that said lobes extend in one common direction over the tank, in that the end walls of the tank comprise curved knuckles closing off the ends of the part-cylindrical lobes, and in that a separating plate is provided at each lobe connection to strengthen the tank against internal pressure, all of said plates defining an opening so that the tank provides a single storage compartment capable of storing liquid under pressure with virtually no additional stiffening or strengthening members.

In the case where the storage tank is intended to be for land storage, the connection between each adjacent pair of lobes is preferably provided by welding to two arms of a generally "Y" shaped insert, the third arm constituting or providing an outer peripheral part of the respective separating plate.

In the case where the storage tank is intended for use as a fuel tank for motor vehicles, preferably each separating plate is of a planar form with an aperture therein, the respective adjacent lobe ends being welded directly to opposite faces of said plate.

Thus, in one application, the present invention provides a modified arrangement of land storage tank which can be used as required to accommodate different gases, which gases may vary widely in their storage pressure and temperature conditions. For example, the storage tank in accordance with the present invention may be capable of storing a range of liquefied gas between the extremes of liquefied natural gas which is preferably stored at approximately -1 650C and atmospheric pressure to propane which is preferably stored at ambient temperature and approximately 250 p.s.i.

In another application the present invention provides a storage tank which is particularly useful as a fuel tank for motor vehicles designed or converted for running on liquefied gas. For example, one generally used fuel is liquefied petroleum gas which, of course, needs to be stored at ambient temperature and thus requires a storage pressure of approximately 300 p.s.i.

In order that the invention may be readily understood and further features made apparent, two exemplary embodiments constructed in accordance therewith will now be described with reference to the accompanying drawings in which: Figure 1 is a part-sectional longitudinal elevation of a storage tank, intended to be of relatively large dimensions for land storage.

Figure 2 is a view on the line Il-lI of Figure 1, Figure 3 is a plan view of the tank of Figure 1, Figure 4 is a sectional elevation of a storage tank intended for use as a fuel tank for motor vehicles, Figure 5 is a fragmentary view on the line V-V of Figure 4, and Figure 6 is a general isometric view of the tank of Figure 4.

Referring to Figures 1 to 3 of the drawings, the land storage tank 1 as shown is of rectangular plan and is intended for the bulk storage of a range of liquefied gases at pressures varying from atmospheric up to approximately 250 p.s.i.

The tank 1 is made of a metal appropriate for its intended range of operating temperaturess.

Thus, for example, if it is to accommodate a liquefied gas at a very low temperature, e.g.

liquefied natural gas at approximately 60 C, the metal used would be 9% nickel steel, stainless steel, or an appropriate aluminium alloy to avoid the possiblity of cold embrittlement. The tank comprises top, bottom, side and end walls A,B,C and D respectively consisting of a multiplicty of outwardly convex, part-cylindrical parallel lobes 2, 3 connected together to extend along the length of the tank. The overall plan dlrmensions can be varied to suit the space in which the tank is to be located and can be square in plan or its longitudinal or transverse dimension can be made significantly greater by increasing the length of the lobes 2 and 3, cr respectively by constructing the tank with a greater number of intermediate lobes 3.Thus, in accordance with this invention, only one tier a lobes is provided, thereby eliminating any need to provide a framework, plates, or the like to inter-connect more than one tier or lobes. In this embodiment, the two side walls lobes C, in cross-section as shown (see Figure 1) ) each have an arc of about 2400, whilst each intermediate lobe 3 has top and bottom wall arcs of about 600 emanating from the median horizontal plane of the tank.The end walls D of this ten embodiment are in the form of part-spherical knuckles 4 which close-off the ends of the longitudinally extending lobes 2 and 3. Alternatively, If the maximum intended operating pressure allows, the end walls D can be appropriately cussed part obes. The lobes 3 and the knuckles 4, in their transverse direction, each have the same radius of curvature, the chord length of each or the intermediate lobes 3 is thus the same, so that they can each be made as a modular construction with the tank walls being of a common wall thickness, thereby avoiding costly and time consuming stress calculations etc. for each new tank installation.

Over the height of each knuci'.le 4, the vertical radius of curvature may be equal to or greater than its transverse radius of curvature. With regard to the side lobes 2, referring to the right-hand lobe in Figure 1 , the left-hand part referenced E is equivalent to half an intermediate lobe 3, whilst its right-hand part, referenced F, has a vertical radius of curvature of the knuckle o; at its vertical centreline.

At the intersection lines of the lobes, i.e. the "nodes" between adjacent lobe arcs, preferably three-armed insert rings 5 a generally Y-cross section are used for the welded joints between said lobe arcs. Such a joint is described in detail in our said co-pending Patent Application No.

7938108, each insert ring comprising arms 6 and 7 appropriately spaced to be in alignment with respective edges of the top and bottom lobes 2, 3 and ;he edges of the IcnuckLes 4, for buti-welding, and the third arm 8 ex-i -n-1ing perpendicular to its respective tank well so as .o project inwardly into the tank interior. An important feature of this invention is that a separating plate 9 is provided at each lobe interconnecdon. This plate may be constituted by an e: --ension of the length of each arm 8 of the insert rings 5.However, preferably, as shown each plate 9 is a separate member which is butt-welded around its periphery to the free edge a a said arm 8 of the respective insert ring. Thus, the plates 9 perform the functions of providing internal ties for the tank, particularly against tension forces, supporting the tank vvhen empty and, in the case where thr tank itself supports a roof structure, supporting the tank against compressive loads due to said roof structure.

In this embodiment, in accordance with the present invention, the spaces defined within the lobes 2, 3 are in communication so as to provide a single overall storage compartment and this interconnection is provided by openings 10 extending through said plates 9. In most applications the separating plates 9 are of simple, planar form. However, in those applications where it is necessary to strengthen the tank e.g. against externally applied compressive loads, etc.

preferably vertically extending stiffening members 11 (see shown dotted in Figure 2) may be welded to said plates.

Referring again to Figures 1 and 2, it can be readily seen that the long tank provides a low profile and it can therefore be readily sited within a safety containing dyke at least partly below ground level, thermally insulated, and, if required, provided with a roo, structure supported directly on top of the tank substantially as described in detail in our said co-pending Patent Application No.7938108.

As mentioned above, a feature of this tank is its low profile which enables it to be economically located substantially or wholly below ground.

Aiso, the design is such that the tank is flexible transversely and slidable longitudinally to absorb thermal contraction/expansion in use, and to accommodate any subsidence in the foundations.

A further important feature of the tank is that, as distinct from the liquid tight separating plate/separate storage compartment arrangement of our said co-pending Patent Application No.

7938108 one overall storage compartment is provided; thus, a simple filling and emptying arrangement can also be provided.

Referring now to Figures 4 to 6, for a storage tank of relatively small dimensions for use as a fuel tank for a motor vehicle, the general arrangement is very similar to the land storage tank described above and like parts have been given the same reference numerals. However, because of its relatively small size, insert rings 5 are not desirable, because of welding/construction difficulties. Instead, as shown particularly in Figure 4, the adjacent lobe ends are welded directly onto the opposite faces of the respective separating plate 9. Also, as shown in Figure 4, instead of having a separate base support arrangement, this can be provided merely by extending the lower edges of the support plates 9 and welding foot members 12 thereto. To provide support for a covering panel or the like, the upper edges 1 3 of the plates can be similarly extended as shown. The upper and lower extensions to the plates 9 also provide some measure of protection to the tanks against physical impact and enable the tanks to be stacked for storage and transport. An appropriate filling connection 14, and feed connection (not shown) are provided and, if desired, lifting holes 1 can readily be provided in the upper plate extensions 13 (see Figure 5).

Particular advantages for such a fuel tank are that its dimensions can be readily adapted according to space requirements. It requires a relatively small wall thickness compared to the more normally used circular cylindrical tank and is therefore lighter, and due to its smaller plate radius, it is of relatively small height. Also, because of the smaller plate radius compared with a circular tank, it can absorb relatively large external loads or shocks e.g. resulting from a collision, thereby enhancing its safety.

It will be appreciated that a storage tank for the bulk transport of liquefied gas, e.g. for a road tanker, could also be constructed in accordance with this invention.

Claims (4)

1. A storage tank for the storage of liquid at or above atmospheric pressure of the kind in which the walls are formed by a multiplicity of connected parallel, part-cylindrical lobes presenting outwardly convex arcuate surfaces, characterised in that the side and end walls thereof are provided by a single tier of connected lobes, in that said lobes extend in one common direction over the tank, in that the end walls of the tank comprise curved knuckles closing off the ends of the part cylindrical lobes, and in that a separating plate is provided at each lobe connection to strengthen the tank against internal pressure, all of said plates defining an opening so that the tank provides a single storage compartment capable of storing liquid under pressure with virtually no additional stiffening or strengthening members.

2. A storage tank according to Claim 1, intended for land storage, characterised in that the connection between each adjacent pair of lobes is provided by welding to two arms of a generally "Y" shaped insert, the third arm providing an outer peripheral part of the respective separating plate.

3. A storage tank according to Claim 1, intended for use as a fuel tank for motor vehicles, characterised in that each separating plate is of planar form and defines an aperture, and in that respective adjacent lobe ends are welded directly to opposite faces of each said plate.

4. A storage tank for the storage of liquid at or above atmospheric pressure constructed, arranged and adapted for use substantially as hereinbefore described with reference to and as shown in Figures 1 to 3, or 4 to 6 of the accompanying drawings.