GB2124743A

GB2124743A - Low temperature storage tank

Info

Publication number: GB2124743A
Application number: GB8315344A
Authority: GB
Inventors: Tsutomu Tomita
Original assignee: Kawasaki Heavy Industries Ltd; Kawasaki Jukogyo KK
Current assignee: Kawasaki Heavy Industries Ltd; Kawasaki Motors Ltd
Priority date: 1982-06-05
Filing date: 1983-06-03
Publication date: 1984-02-22
Also published as: JPS58214093A; GB2124743B; GB8315344D0

Abstract

A double shell low temperature storage tank (A) including an outer tank member (11) and an inner tank member (12) for containing in the inner tank member LNG, LPG and other liquids of low temperature. The inner tank member is hermetically sealed, and a internal dike (17) is mounted between the outer tank member and the inner tank member. The internal dike has a top portion preferably located substantially in the vicinity of the designed liquid level in the inner tank member. A space defined by the inner tank member and the internal dike may be used as a void space (18), or an insulator layer may be provided between the inner tank member and the internal dike in the same manner as an insulator layer is provided between the outer tank member and the internal dike. <IMAGE>

Description

SPECIFICATION Double shell low temperature storage tank with internal dike This invention relates to a double shell low temperature storage tank suitable for storing at low temperature in a liquid state LNG, LPG, etc., which are normally gaseous elements.

In a double shell low temperature storage tank installation, when rupture of an inner tank member should occur, the liquid stored therein at low temperature would flow out and would be vaporized upon contact with parts of higher temperature between the inner tank member and an outer tank member. The gas produced in this fashion would raise pressure in the outer tank and cause buckling of the inner tank member with domed roof and rupture of the outer tank member to take place. This would subsequently increase the volume and intensity of the stream of liquid flowing out of the inner tank and due to thermal shock would cause the outer tank member to collapse, resulting in a large volume of liquid stored at low temperature flowing out of the tank and causing a consequent catastrophic disaster to occur.

In order to prevent a large volume of liquid stored at low temperature in a double shell low temperature storage tank from flowing out of the tank and spreading over a wide area in the event of the occurrence of an accident such as the one described hereinabove, it has hitherto been an usual practice to set up a dike on the ground in enclosing relationship to the double shell low temperature storage tank to confine the liquid spill size by the dike and avoid occurrence of subsequent disasters in the surrounding region.

The solution of the problem that has hitherto been adopted has generally been considered unsatisfactory. The provision of a dike could avoid the liquid from the ruptured tank spreading and flooding the surrounding area outside the dike. However, the liquid contained inside the dike would be vaporized and flow out of the dike. Thus there would be the risk of such vapor exploding outside the dike, thereby destroying the region surrounding the tank. Even if such an accident as vapor explosion could be avoided, the liquid collected inside the dike would raise a problem with regard to the recovery of the liquid collected inside the dike.

Since the provision of a dike is not a satisfactory solution to the problem, the need to provide a double shell low temperature storage tank of improved construction capable of avoiding the occurrence of above said accidents has been keenly felt, and programs have been underway in many quarters to provide improvements in or relating to double shell low temperature storage tanks.

Proposals have hitherto been made, to obviate the disadvantage of the prior art described above, to use low temperature storage tanks having triple side walls as deschribed in US Patent Specification No.

3,416,325 and Japanese Laid-Open Patent No. Sho 54-127022, for example. In the former, a moisture barrier is mounted outside an outer wall means and an inner wall means to provide a void space between the outer and inner tank means and fill a space between the outer tank means and the moisture barrier with an insulating material. The void space is maintained in communication with the inner tank means via an opening at the top of the inner tank means, and an inner roof plate supporting an insulating material is disposed above the inner tank means and spaced radially inwardly of the uppermost portion of the outer tank means.In the latter as shown in Figure 1,an intermediate tank 2 with domed roof is interposed between an inner tank 4 and an outer tank 1, and a space defined between the outer tank 1 and the intermediate tank 2 is filled with an insulating material 3, while a void space is defined between the intermediate tank 2 and the inner tank 4. The inner tank 4 which is a liquid storage tank of an open top type is in communication with the void space 6 via an opening at the top thereof. A body of level concrete 5 is interposed between a bottom plate of the inner tank 4 and a bottom plate of the intermediate tank 2, and a bottom insulating layer is provided between the bottom plate of the intermediate tank 2 and a bottom plate of the outer tank 1.

In the two low temperature storage tanks of the prior art of the aforesaid construction, in the event that the inner tank is ruptured, the liquid contained in the inner tank can be held in check by the wall disposed inwardly of the body of insulating material, so that urgent but safe operation can be attained and release of a large volume of inflammable gas into the atmosphere can be avoided. In addition, the need to provide a dike for avoiding liquid spills can be eliminated. However, the low temperature storage tanks of the aforesaid construction would be faced with the following probiems which would have serious consequences, as presently to be described.

(a) The arrangement whereby the inner tank and the void space are maintained in communication with each other at their upper portions would cause a portion of the liquid that has been vaporized to flow from the inner tank to the void space. Particularly in the case of a tank shown in Figure 1, such vapor would permeate the body of level concrete and stay therein at all times, to thereby create a dangerous atmosphere when the tank is purged out or repaired because air would be introduced from outside in such occasions. Particularly when repair of the tank is carried out, the use of an welding machine, a gas cutting machine, etc., might pose the danger of explosion of the vapor remaining in the level concrete.

(b) Vapor might be cooled in the void space and the body of level concrete and reliquefied to a condensate. The condensate produced in this way is often heavy (C4H10, C5H12 difficultly vaporize even at room temperature). Thus when the tank is purged out for inspection, the condensate would remain in the body of level concrete and tend to create a dangerous atmosphere in the same manner as described in paragraph (a).

(c) The condensate, when its volume increases, would be collected also in the void space and exert an external pressure over the inner tank. This would cause buckling of the liquid storing inner tank to occur or result in lifting up its bottom plate and/or in breaking of anchors due to buoyancy acting on the inner tank. To avoid this trouble, a submerged pump may, for example, be mounted in the void space to discharge the condensate therefrom. However, it would be impossible to remove all the condensate from the void space and instability would result if a pump barrel were suspended from the roof. The provision of a pump would be accompanied by the structural defect that openings for installing the pump barrel should be formed, to obtain necessary design strength, in shoulders of the outer tank member and the intermediate tank member where stresses of complex form tend to develop.

(d) When earthquakes occur, sloshing of the liquid stored in the tank would occur and might overflow the inner tank shell into the void space, thereby increasing the disadvantage described in paragraph (c). To increase the height of the inner tank shell to avoid the overflow due to the sloshing would be uneconomical.

(e) Since the liquid storing inner tank is open at the top, a portion of the liquid in the inner tank would be vaporized and flow into the void space at all times. In such a double shell low temperature storage tank in which the inner tank is of open top type, it would be impossible to detect gas leaks at the outer surface of the inner tank. Thus when unpredictable crack occurs in the inner tank, it would be impossible to sense it beforehand and the inner tank might suffer sudden unstable breakdown without any indications or signs, because the crack would grow due to cyclic loadings to become as long as critical crack length of the material without being detected and countermeasured.

According to the present invention there is provided a double shell low temperature storage tank comprising: an inner tank member and an outer tank member, said inner tank member being adapted to store therein a liquid at low temperature; wherein the inner tank member is hermetically sealed and an internal dike is provided between the inner tank member and the outer tank member to restrict the size of liquid spills within the tank. This tank is high in reliability and safety and can be constructed with ease.

For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to Figures 2 to 15 of the accompanying drawings, in which Figure 2 is a fragmentary vertical sectional front view of one embodiment of a double shell low temperature storage tank with internal dike; and Figures 3 to 75 are fragmentary sectional views of other embodiments incorporating therein partial alterations of design.

Figures 2 to 15 show in detail a preferred embodiment of the double shell low temperature storage tank with internal dike in conformity with the invention with modifications thereof. Referring to Figure 2, the double shell low temperature storage tank generally designated by A comprises an outer tank member 11, an inner tank member 12 which is hermetically sealed, an insulator layer 13 formed as of perlite having inert gas, such as nitrogen gas, sealed therein, a foundation 14, suitably protected from soil freezing, a bottom plate 11 a of the outer tank member 11, a bottom plate 12a of the inner tank member 12, a bottom insulator layer 15 formed of perlite concrete or cellular glass and a body of level concrete 16, such as concrete or perlite concrete.

The invention provides, in the double shell low temperature storage tank A of the aforesaid construction, an internal dike 17 between the outer tank member 11 and the inner tank member 12. The internal dike 17 may be formed of 9% nickei steel, stainless steel, aluminum killed steel, aluminum alloy and other low temperature resistant metal materials, concrete or a combination thereof, depending on temperatures of stored liquids.

The insulator layer 13 is interposed between the internal dike 17 and the outer tank member 11, and the internal dike 17 and the inner tank member 12 define therebetween a void space 18 for separating the internal dike 17 from the inner tank member 12.

The void space 18 has a width which, although it may vary depending on the size of the tank, should be 60 cm at a minimum for reasons of construction.

The void space 18 has a cover 19 over its top, to avoid inflow of the insulating material, such as perlite, into the void space 18. A sealing member 20 formed of gas permeable material, such as glass wool, is mounted between an outer peripheral edge of the cover 19 and an upper end of the internal dike shell 17 to equalize the pressure outside the internal dike 17 and the pressure inside thereof. Preferably the internal dike 17 has a height which is substantially in the vicinity of the designed liquid level. 17a is a bottom plate ofthe internal dike 17.

The foregoing description describes the basic construction of the double shell low temperature storage tank with internal dike according to the invention. Various modifications may be incorporated therein as presently to be described. Figure 3 shows one of such modifications in which the body of level concrete 16 is dispensed with and the bottom plate 12a of the inner tank member 12 and the bottom plate 17a of the internal dike 17 are superposed one over the other. The bottom plates 12a and 17a may be joined together as by welding, depending on the design.

Figure 4 shows an inner tank member shell plate 12b welded to the internal dike bottom plate 17a. In this constructional form the inner tank bottom plate 1 2a may be attached to an inner surface of a lower end portion of the inner tank shell plate 12b and the body of level concrete 16 is interposed between the inner tank bottom plate 12a and the internal dike bottom plate 17a.

In Figure 5, a connector plate 12c is joined by welding to an outer peripheral edge of the inner tank bottom plate 12a and the internal dike bottom plate 17a to define a sealed space between the inner tank member bottom plate 12a and the internal dike bottom plate 1 7a for sealing the body of level concrete 16 therein.

Figure 6 shows an outer periphery of the inner tank member bottom plate 1 2a extended and joined as by welding to an inner shell surface of the internal dike 17. The body of level concrete 16 is sealed in a space defined between the bottom plates 12a and 17a. In this case, a corrugation or the like may be attached to one of the bottom plates 12a and 17a so as to absorb the difference in thermal behaviour between the internal dike bottom plate 17a and the inner tank bottom plate 12a.

Figure 7 uses a connector plate 12d of L-shape in cross section interposed between the inner tank 12 and the internal dike 17. The connector plate 12d is joined as by welding at its upper end to an outer surface of the inner tank shell 12b and at its lower end to a top surface of the internal dike bottom plate 17a.

In Figure 8, a multiplicity of partition plates 21 are provided radially on an inner surface of the internal dike 17. The partition plates 21 may be located on an outer surface of the internal tank member 12 in place of the inner surface of the internal dike 17. In the tank construction according to the invention, there is no risk of unstable breakdown of the inner tank member occurring on a large scale because sensing of gas leaks can be effected between the inner and outer tank members 12 and 11. However, should rupture of the inner tank member 12 occur, the liquid would flow circumferentially in torrents within the void space 18 and cause a dynamic liquid pressure of high magnitude to occur. The modification shown in Figure 8 enables this trouble to be prevented.

Figure 9 shows a liquid spills recovery pipe 22 opening at one end in the void space 18 and extending through the bottom insulator layer 15. The liquid spills recovery pipe 22 is extended outwardly of the tank A and provided with a blank flange 23 at its outer end whole a valve 24 is mounted therein, to collect liquid spills.

Figure 10 shows a constructional form in which the internal dike bottom plate 17a and the outer tank member bottom plate 1 la are placed directly one over the other in superposed relation or the two bottom plates 17a and 1 lea are joined together as by welding after being placed one over the other in superposed relation. In this constructional form, the bottom insulator layer 15 is located on the internal dike bottom plate 17a.

In Figure 11, the constructional form shown in Figure 10 is provided with the liquid spills recovery pipe 22 having the valve 24 of the constructional form shown in Figure 9.

Figure 12 shows a constructional form which is a modification of the constructional form shown in Figure 10 in which the wall of the internal dike 17 and the bottom plate 17a thereof differ from each other in temperature. To cope with this situation, the constructional form shown in Figure 12 provides a corrugation 17b or the like on the bottom plate 17a of the internal dike 17 in the void space 18 for adjusting the thermal contraction behaviors of 17 and 17a. 13a designates a body of insulating material, such as perlite.

In Figure 13, the internal dike 17 share the outer tank member bottom plate 11 a formed of a material suitable for use in temporary urgent low temperature storage of spill liquid and the bottom insulator layer 15 is provided on the outer tank member bottom plate 1 la for supporting the inner tank member 12 thereon. In this constructional form, a portion of the outer tank bottom plate 11 a within the internal dike shell 17 region usually has a normal temperature which becomes lower than normal when the liquid contained in the inner tank member 12 spills out, thereby causing contraction of the bottom plate. Meanwhile no contraction occurs in the wall of the outer tank member 11. To cope with this situation, a corrugation 11 b or the like for absorbing the difference in thermal contraction behavior between the wall of the outer tank member 11 and the internal dike 17 is provided.Shear plates for avoiding sliding movement of the inner tank member 12 may be provided in the bottom insulator layer 15.

In Figure 14, the constructional form shown in Figure 13 is provided with the liquid spills recovery pipe 22 having the valve 24 of the constructional form shown in Figure 9.

Figure 15 shows a constructional form in which a body of insulating material 13b such as perlite is filled in a space which is a void space in the preceding constructional forms. The provision of the body of insulating material 1 3b eiiminates the need to provide the cover 19 while reducing the external insulating load applied to the outer surface of the internal dike 17. In this constructional form, the space corresponding to the void space 18 has a relatively high temperature, so that when the liquid contained in the inner tank member 12 flows out, boil-off gas would be produced in large volumes therein. This would make it necessary to provide the outer tank member 11 with a gas relief valve (safety valve) of increased capacity.However, the volumes of boil-off gas which would be produced when the liquid contained in the inner tank of the prior art flowed out directly into the outer tank, and the gas relief valve necessary for the constructional form shown in Figure 15 could be smaller in capacity than that used with the low temperature storage tank of the prior art. In all the constructional forms of the invention described hereinabove, the temperature of the internal dike 17 is normally substantially much lower than ambient temperature so that the internal dike 17 has little possibility of suffering damage due to thermal shock caused by contact with the liquid, and the outer tank will never be damaged because it never gets in contact with low temperature liquid spills.

In the embodiments shown in Figures 2 to 14, the internal dike 17 and the cover 19 may be connected together to make the void space 18 an independent space which is hermetically sealed.

In all the embodiments shown in Figures 2 to 15, the outer tank member 11 and inner tank member 12 may, of course, be formed not only of metal, such as steel, aluminum, etc., but also of nonmetallic material, such as concrete. Other material than perlite may, of course, be used as an insulating material for the side, roof and bottom of the tank.

From the foregoing description, it will be appreciated that the double shell low temperature storage tank with internal dike of the aforesaid construction can achieve the following effects. The void space has a temperature which is substantially equal to that of the liquid contained in the inner tank member. This eliminates the danger of sudden production of boil-off gas within the outer tank in the event of the liquid flowing out of the inner tank member by some accident, and avoids an inordinate pressure rise between the inner and outer tank members. This is conducive to elimination of the danger of rupture of the outer tank member and the possibilities of the occurrence of buckling of the inner tank member, to say nothing of the internal dike. The internal dike effectively arrests the outflow of the liquid, so that not only the outer tank member will not suffer damage but also vapor will be prevented from flowing out of the tank in large volumes, because the outer tank remains undamaged, and explosing upon contact with atmosphere. The liquid spill checked by the internal dike is not released from the tank to outside and can be readily recovered without the risk of dispersion and explosion of vapor. An additional feature is that since the stored liquid and vapor are separated from the body of insulating material in normal operation, there is no risk of an inflammable atmosphere being formed during purge out inspections in the body of insulating material as has hitherto been the case with the prior art.

Claims

1. A double shell low temperature storage tank comprising: an inner tank member and an outer tank member, said inner tank member being adapted to store therein a liquid at low temperature; wherein the inner tank member is hermetically sealed and an internal dike is provided between the inner tank member and the outer tank member to restrict the size of liquid spills within the tank.

2. A double shell low temperature storage tank as claimed in claim 1, wherein said internal dike includes a top portion located substantially in the vicinity of the designed liquid level in the inner tank member.

3. A double shell low temperature storage tank as claimed in claim 1, wherein said inner tank member and said internal dike define therebetween a void space.

4. A double shell low temperature storage tank as claimed in claim 1, wherein said internal dike is located in an insulator material layer interposed between the inner tank member and the outer tank member.

5. Adoubleshell lowtemperature storage tank substantially as hereinbefore described with reference to any of the embodiments illustrated in Figures 2 to 15 of the accompanying drawings.