GB2108647A

GB2108647A - Improvements in tanks

Info

Publication number: GB2108647A
Application number: GB08132392A
Authority: GB
Inventors: John Malcolm Dixon
Original assignee: CAPPER NEILL INTERNATIONAL LIM
Current assignee: CAPPER NEILL INTERNATIONAL LIM
Priority date: 1981-10-27
Filing date: 1981-10-27
Publication date: 1983-05-18
Also published as: GB2108647B; EP0078134A1

Description

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GB 2 108 647 A 1

SPECIFICATION Improvements in tanks

The invention relates to tanks of the type used for storing liquid at low temperatures, the tanks 5 being double-walled and comprising an inner primary container, an outer secondary container and a layer of thermal insulation between the two containers to provide an inner container and an outer container whereby should the inner 10 container fail the outer container would prevent spillage of cold liquid.

Such tanks will be referred to hereinafter as "tanks of the kind described".

Commonly, the outer storage container has a 15 base of concrete and walls either of steel or concrete, the inner primary container being commonly of steel. Problems arise in the event of a leak in the wall of the inner primary container in that the liquid can penetrate the base insulation, 20 which is normally of cellular foamed glass in block form, there being practical difficulties in sealing the edge of the base insulation because of its construction and the thermal movements of the inner container. In the event of penetration of the 25 base insulation, the foundations of the tank couid be chilled and also, upon entering the relatively warm base insulation the leaking liquid would vaporise to generate a pressure that could lift the base of the inner primary container to cause stress 30 in the structure.

According to the invention there is provided a tank of the kind described comprising continuous . skirt means extending downwardly with respect to and in the region of the periphery of the base of 35 the inner container, and continuous flange means extending upwardly from the base of the outer container and radially within the skirt means, the free edge of the skirt means being lower than the free edge of the flange means to provide a vapour 40 lock between the base insulation and the space between the inner and outer walls of the tank in the event of a leak from the wall of the inner container to limit the amount of liquid reaching the base insulation.

45 The skirt means may extend from the base of the inner container or alternatively, the tank may comprise a rigid sheet member, for example of steel, extending beneath the base of the inner container, the skirt means extending downwardly 50 from the periphery of the rigid sheet member.

The tank may be cylindrical and the skirt means and flange means annular. The skirt means may be of a diameter greater than the diameter of the inner container.

55 The outer container may have a bund wall surrounding the inner container or may have a wall surrounding the inner container and a roof covering the inner container.

By way of example, embodiments of a tank 60 according to the invention, and modifications thereto will now be described with reference to the accompanying drawings, in which:—

Figure 1 shows a complete tank according to the invention;

Figure 2 shows an enlarged scale and in section detail of the base periphery of the tank of Figure 1;

Figure 3 illustrates a bracket arrangement for holding the inner container of Figures 1 and 2 to the foundations;

Figure 4 illustrates a base edge detail of a modified tank of the type shown in Figures 1, 2 and 3;

Figure 5 shows a second embodiment of a tank;

Figure 6 shows a base corner detail on an enlarged scale of the tank of Figure 5;

Figure 7 shows a base edge detail of a further embodiment of a tank according to the invention, and

Figure 8 shows a further embodiment of a tank.

As shown in Figures 1 and 2, a tank generally indicated at 10 has an inner primary container 11 of steel with a base 12 and an outer secondary container 13 defined by an outer concrete wall 14 supporting a vapour barrier 15 arid a base 16 of concrete which also supports the vapour barrier 15. A peripheral foundation 17 is provided for the outer wall 14 and tendons 18 in the outer wall 14 prestress the wall 14. A heating conduit 1 9 extends through the concrete base of the outer secondary container.

Supported on the outer container wall 14 is a dome roof 20 from which is suspended a flat deck 21 and contained between the deck 21 and the roof 20 is roof insulation material 22.

Beneath the inner container base 12 is a bedding layer 23 of sand and beneath the bedding layer of sand 23 is a barrier sheet 24 of steel having a skirt 25 extending downwardly and continuously around the periphery of the barrier sheet 24. Between the barrier sheet 24 and the vapour barrier 15 lies a base insulation layer 26' of foamed glass in block form, or other suitable insulation material, surrounded by a ring of lightweight insulating concrete blocks 26 and, radially inwardly of the skirt 25, a flange 27 extends continuously and upwardly from the vapour barrier 15. The vapour barrier 15 and the flange 27 are conveniently of steel so that the flange 27 can be secured to the vapour barrier by welding although other means may be used.

The flange 27 extends above the base of the skirt 25 with the result that, if a leak occurs in the wall 1 of the inner container causing liquid to occupy the space between the wall 11 and the vapour barrier 15, when liquid begins to permeate the base insulation it is warmed and produces a vapour pressure which causes the combination of the skirt 25 and flange 27 to act as a vapour lock to prevent further entry of liquid from the space between the wall 11 and the vapour barrier 1 5 into the base insulation. In this way, wide spread contamination of the base insulation by the liquid is prevented.

As shown in Figure 2, a layer 28 of wall foam insulation is provided on the inside of the vapour barrier 15.

A further advantage of the barrier 24 is that a leak occurring in the base 12 of the inner

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container will not contaminate the base insulation directly, the liquid being forced to travel over the barrier 24 and into the peripheral space between the vapour barrier 15 and the flange 27. A 5 significant leak in the base 12 will not cause significant contamination of the base insulation because of the vapour lock caused by the skirt 25 and flange 27 arrangement previously explained.

A further advantage of the vapour lock 10 arrangement is that since the liquid level in the inner container would always be greater or equal to the liquid in the annular space between the wall 11 and the vapour barrier 1 5, there would be no danger of vapour pressure in the base insulation 15 lifting the inner container base 12. The vapour pressure beneath the barrier 24 cannot exceed the pressure caused by liquid contained in the inner container 11.

Figure 3 shows a bracket arrangement for 20 securing the inner container to the foundations. A bolt 29 is set in the foundations and passes through the vapour barrier 15 and the barrier sheet 24, sealing welds being made between the bolt 29 and the vapour barrier and barrier sheet. A 25 nut 30 applies pressure to a flange 31 secured to the inner container to hold down the inner container for example to resist forces from events such as earthquakes.

Figure 4 illustrates a base edge detail of a 30 modified tank of the type shown in Figures 1, 2 and 3. In the modification of Figure 4, barrier sheet 24' extending further out beyond the periphery of the inner container than was the case in the embodiment of Figures 1 to 3 and the liquid 35 barrier is extended close to outer containment wall 14'. This arrangement reduces the area over the base slab that cold temperatures could apply and could ease design on the concrete beneath the outer containment wall 14'.

40 Figures 5 and 6 shows a second embodiment of a tank according to the invention, the overall arrangement being similar to the embodiment of Figures 1 to 3 with an inner container 40 having a base 41 and an outer container 42 having a base 45 43. In this embodiment, the inner container and the outer container 42 are of steel or other suitable metal. In the annular space between the walls of the inner and outer containers 40 and 42 there is insulation, for example perlite. 50 Between the base 41 of the inner container and the base 43 of the outer container is a base insulation 44, for example of foamed glass, above which is a barrier, for example of steel, 45 similar to the barrier 24 of the first embodiment. The 55 barrier 45 has a cylindrical skirt 46 depending therefrom and a flange 47 extends upwardly from the base 43 of the outer container to provide a vapour barrier in the same way that the skirt 25 and flange 27 in the first embodiment provide a 60 vapour barrier. A bolt arrangement generally indicated at 48 secures the outer container 42 to a foundation ring 49.

A base edge detail of a third embodiment of a container according to the invention is shown in 65 Figure 7. In this embodiment, there is no separate barrier similar to the barrier 24 in the embodiment of Figures 1 to 3 or 45 in the embodiment of Figures 5 and 6. Instead, inner container 50 has a base 51 which extends outwardly beyond the inner container wall and is turned down at its periphery to provide a skirt 52. The skirt 52 forms a vapour barrier with a flange 53 extending upwardly from the base 54 of an outer container, the remaining features of the tank being similar to those of Figures 1 to 3. Thus the embodiment of the Figure 7 provides a vapour barrier for protection from a wall leakage only, there being no continuous liquid barrier under the base 51 of the inner container 50 to prevent a leak in the base 51 contaminating base insulation 55.

A further embodiment of a tank, generally indicated at 60, is shown in Figure 8.

The tank 60 has an inner container 61 conveniently of steefwith a dome roof. An insulation layer 62 covers the wall and roof of the inner container 61.

The inner container 61 is seated, in a similar way to the embodiment of Figure 3, on a base insulation layer 63, suitably of foamed glass with a barrier 64 of steel of other suitable material between the base insulation 63 and the base of inner container 61. The barrier 64 has a downturned peripheral skirt 65 and a flange 66 extends from outer base 67, the skirt 65 and flange 66 providing a vapour lock in the way hereinbefore described.

Instead of a complete outer container as with previous embodiments, a bund wall 68 extends around the outside of the inner container 61 to prevent widespread liquid spillage in the event of a leak.

it will be appreciated that specific materials have been specified when describing the preferred embodiments, but that alternative suitable materials to those specified may be used.

Advantages associated with the various embodiments are as follows:—

All embodiments have the advantage that a leak in the wall of the inner container wili not contaminate the main base slab due to the vapour lock formed between the skirt and flange.

The embodiments having a separate barrier sheet under the base of the inner container provide a secondary barrier against a leak in the base of the inner container that enables such a leak to be easily monitored in the vapour space. For a small leak since there was no penetration of liquid into the base insulation it may not necessitate any rectification or checking of the base insulation or foundation. This is considered important since for such large constructions containing dangerous products there would normally be great concern in the event of a small leak on such complex structures that could result in considerable downtime and expense in checking the consequences. The checking of a small inner container base leak could also be an advantage during hydro static testing of the inner container. The likeliest time for such a leak is during the first liquid fill when, without it being

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obvious, it could otherwise do irreparable damage by saturating the base insulation.

As the base of the outer container located beneath the base insulation will not be subject to 5 cold temperatures instead of having a material suitable for the product temperature, it could be made from less expensive carbon steel.

The embodiments incorporating a radiused transition corner joint such as shown in Figure 2 10 which is designed to absorb all movements from concrete wall/foundation slab and also from thermal influences, since the outer base vapour barrier is not subject to cold temperature, the thermal movement generated on this corner joint 15 is reduced.

The embodiments with a barrier sheet also have the advantage that during construction exposure of the base insulation to weather is prevented before the inner container is located. 20 Since the integrity of the base insulation is retained, the foundation heating to prevent ground freezing would still be functional.

Claims

1. A tank of the kind described comprising 25 continuous skirt means extending downwardly with respect to and in the region of the periphery of the base of the inner container, and continuous flange means extending upwardly from the base of the outer container and radially within the skirt 30 means, the free edge of the skirt means being lower than the free edge of the flange means to provide a vapour lock between the base insulation and the space between the inner and outer walls of the tank in the event of a leak from the wall of

35 the inner container to limit the amount of liquid reaching the base insulation.

2. A tank as claimed in Claim 1 wherein the skirt means extends from the base of the inner container.

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3. A tank as claimed in Claim 1 comprising a rigid sheet member extending beneath the base of the inner container, the skirt means extending downwardly from the periphery of the rigid sheet member.

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4. A tank as claimed in any preceding claim wherein the flange means is annular and the tank cylindrical.

5. A tank as claimed in Claim 4 wherein the skirt means is of a diameter greater than the

50 diameter of the inner container.

6. A tank as claimed in any preceding claim wherein the outer container has a wall surrounding the wall of the inner container and a roof extending over the inner container.

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7. A tank as claimed in any one of Claims 1 to 5 wherein the outer container has a bund wall surrounding the wall of the inner container.

8. A tank substantially as hereinbefore described with reference to and as shown in

60 Figures 1, 2, and 3, or in Figure 4, or in Figure 5 and 6, or in Figure 7 or in Figure 8 of the accompanying drawings.

Printed for Her Majesty's Stationery Office by the Courier Press, Leamington Spa, 1983. Published by the Patent Office 25 Southampton Buildings, London, WC2A 1AY, from which copies may be obtained.