EP0069051B1 - Reservoir for storing deep cooled liquids - Google Patents

Description

The invention relates to a container for the storage of frozen liquids, in particular liquefied gases, consisting of an all-round closed reinforced concrete or prestressed concrete outer container and an inner steel container open at the top with the insertion of an insulating material, which serves to hold the liquid, the insulating material in the also open annular space between the two containers consists of a granulate on a mineral basis. Such a container is known from the article _" prestressed concrete container for liquefied natural gas" in the magazine Beton, issue 28/1978, pages 163 ff.

In recent times, the use of natural gas as an energy source in the private sector and the economy has become increasingly important. In addition to transporting the gas from remote locations to customers through pipelines, the transport also takes place after the gas has been liquefied by sea. The liquefied gas then requires corresponding storage devices at the customer, whereby prescribed safety conditions must be met.

As a rule, a steel inner container open at the top is used to hold the liquefied gas, the steel inner container being completely surrounded by a reinforced concrete outer container with the interposition of an insulating material.

Extensive safety precautions must be taken to operate such containers. On the one hand, the outer container must be earthquake-proof, on the other hand, it must also be able to withstand loads in the event of a gas cloud explosion. For the inner container, however, the load case must also be countered that it suddenly tears open. Since steel tends to become brittle at the low temperatures at which liquefied gas is stored, material defects in the steel can actually cause an initially small crack to expand into a continuous crack. The result of this is that the frozen liquid gas emerges from the crack and pours into the annular gap between the steel inner container and the reinforced concrete outer container and flows into the annular gap from the exit point in both directions.

If we first consider the simplified case that there is no insulating material in the annular gap, the flow of the liquid runs in both directions within the annular gap until the two partial flows meet approximately on the diametrically opposite side of the fracture point, and model tests have shown that then at this point of the encounter, a pressure acts on the reinforced concrete container, which is locally up to six times the hydrostatic pressure, so that the reinforced concrete outer container can be subjected to impermissible loads.

This excessive hydrostatic pressure can, however, also occur in the liquid gas containers which have been customary hitherto and in which insulation is arranged between the steel inner container and the reinforced concrete outer container. This insulation usually consists of expanded pearlite. The starting material is a volcanic silicate rock, in which the bound water is converted into steam by briefly heating to about 1000 °, so that the glass melt is inflated to a multiple of its original volume.

While between the bottom of the steel inner container and the reinforced concrete outer container, the insulation consists of foam glass, which is able to withstand the static pressure of the steel inner container and the liquid gas contained therein, the pearlite granulate serves for insulation in the annular space between the two containers, which has the advantage of a high Insulation ability, non-flammable and relatively inexpensive.

However, like any heat-insulating material, the pearlite granulate has a very low specific weight, which means that if the steel inner container is torn open, the insulation of the liquid which then emerges would not provide any appreciable resistance and would be displaced upward out of the annular gap by the liquid gas which escapes, so that the same consequences would then occur as if there was no insulating material between the two containers.

To counteract this, two solutions would be conceivable. One of these solutions would be to replace the pearlite material with another insulating material that counteracts the expansion of the liquid gas if the inner container breaks. This would be possible, for example, by foaming the intermediate space with a plastic that is sufficiently resistant when foamed. However, there are technical and economic considerations. Plastic foams are flammable and therefore unsuitable for this reason alone. Furthermore, no technical method is known for producing a homogeneous foam lining of this size, because the ring gap has a thickness of approximately 1 m with a circumference of approximately 300 m in containers of common size. In addition, a complete lining of the annular gap would prevent access to the steel inner container, for example for control purposes. The costs of the plastic material and its introduction into the annular gap would also be considerably greater than when using the pearlite granulate, which has the advantage of being non-combustible because it is based on minerals.

Based on the use of such a mineral granulate, one could think of closing the annular gap on its upper side in order to prevent the insulation material from being displaced if the inner container breaks. Such a closure is however out not possible for several reasons. On the one hand, this would create an undesirable cold bridge, since a direct connection between the steel inner container and the reinforced concrete outer container would be created. In addition, an external pressure equalization would then be prevented, which is necessary, for example, when the frozen liquid gas is filled into the steel inner container.

The invention has for its object to avoid inadmissible local pressure stresses of the reinforced concrete outer container for a container of the type mentioned in the event of a crack in the steel inner container.

The object is achieved according to the invention in that at least one annular blocking body is arranged between the reinforced concrete outer container and the steel inner container, which is attached to the reinforced concrete outer container or to the steel inner container and leaves a space between the two containers.

As a result of the measure according to the invention, in the event of a sudden opening of the steel inner container, the emerging liquid cannot abruptly displace the light granulate, so that the flow velocity of the emerging liquid is greatly reduced and the two partial flows on the side opposite the exit point are no longer gushing can meet.

Here, since the blocking body does not establish a connection between the two containers, the formation of a cold bridge is prevented and an unhindered pressure equalization is permitted.

By choosing the size of the space left by the blocking body in the annular gap and possibly through holes or slots in the blocking body, it can be achieved that the pressure load on the prestressed concrete container is never greater than the hydrostatic load at any point.

A locking body is preferably arranged parallel to the floor at the level of the upper edge of the steel inner container, but further locking bodies can also be provided in levels below the upper edge of the steel inner container.

However, a locking body can also be attached to the roof dome of the reinforced concrete outer container, which extends approximately parallel to the container axis in the direction of the upper end of the steel inner container.

• Fig. 1 eine Querschnittsdarstellung eines Behälters zur Einlagerung von Flüssiggas;
• Fig. 2 einen Ausschnitt aus Fig. 1 in vergrössertem Massstab und
• Fig. 3 eine andere Ausführungsform zur Anbringung des Sperrkörpers.

The invention is explained in more detail below with reference to exemplary embodiments shown in the drawing. In the drawing:

• Figure 1 is a cross-sectional view of a container for storing liquid gas.
• Fig. 2 shows a detail of Fig. 1 on an enlarged scale and
• Fig. 3 shows another embodiment for attaching the locking body.

Fig. 1 shows a reinforced concrete outer container, which consists of a base plate 1, a wall 2 and a roof dome 3. Inside the outer container, an inner container 5 made of steel is arranged separated by insulation 4, which is open at the top and serves to hold liquefied natural gas. In such a container with a capacity of 50,000 m ³ , the wall thickness of the steel inner container 5 is about 14-30 mm, the thickness of the insulation 4 is about 1 m and the wall thickness of the reinforced concrete outer container is about 50 cm. The insulation under the bottom of the steel container consists of foam glass, which is able to withstand the static load on the container 5 filled with liquid gas, while the insulation on the ceiling consists of mineral wool. The annular gap between the two containers is filled with a granulate of pearlite. The non-combustible perlite granulate has the advantage that it can be easily introduced into the annular gap, but that it can also be removed just as easily by suction for inspection purposes or for necessary repair work.

In order to prevent the partial streams emerging from the gap on both sides of the container from suddenly appearing in the gap between the two containers on the side opposite the exit point and displacing the pearlite granules, displacement according to the invention is now at least in accordance with the invention An annular locking body 6 is provided in the vicinity of the upper end of the steel inner container 5, FIG. 2 showing a possible embodiment and fastening form for such a locking body.

There, the locking body 6 is designed as an annular disc which is fastened to the wall 2 of the reinforced concrete outer container with the aid of crossbars 9. The attachment can be done by means of screws 10 and bolts 11 anchored in reinforced concrete. On the inside of the reinforced concrete wall 2 there is a sheet metal cladding 12 in the usual way, while on the outside of the steel inner container 5 there is also a mineral fiber mat 13, which serves as a compressible buffer layer when the inner container 5 expands.

The radial dimensions of the disk 6 are smaller than the distance between the outside of the sheet metal cladding 12 and the outside of the mineral fiber mat 13, so that an intermediate space 14 remains through which pressure compensation can take place. If necessary, holes or slots 15 can also be additionally made in the annular disk 6.

If the load case of the sudden opening of the steel inner container occurs, the liquid gas then escaping would be strongly prevented from flowing rapidly in the space between the containers, since the blocking body 6 ensures that the pearlite granules only to a limited extent through the space 14 and possibly the holes or Slots 15 can emerge, so that the space between the Containers only slowly seeped and a gushing collision of partial liquid flows is prevented. When the liquid gas penetrates into the interspace, evaporation gases can also escape through the interspace 14 and, if appropriate, the holes or slots 15. Model tests have shown that the covered surface of the space between the containers should be about 50% to 90% of the total surface.

In Fig. 1 it is indicated that, if necessary, further locking bodies 7 and 8 can also be provided in levels below the upper edge of the container, which are of the same design as the steel body shown in Fig. 2.

Of course, other embodiments of the locking body are also conceivable, and the attachment can also take place on the steel inner container.

For example, according to FIG. 3, it is possible to fasten the locking body 6 to the roof dome 3, the locking body extending approximately parallel to the container axis and extending to the upper end of the steel inner container 5. The space for the limited passage of the pearlite granules in the event of bursting is here formed by one or more openings 15 in the blocking body 6 above the insulation above the steel inner container 5. Here, the end of the locking body 6 overlaps the upper end of the steel inner container 5. Instead, however, the locking body could also be attached to the upper end of the steel inner container 5 and then form a distance from the roof dome 3.

Claims (8)

1. Reservoir for storing deep cooled fluids, especially liquified gases, comprising a completely closed exterior container (2) of steel reinforced concrete or prestressed concrete and an inner steel container (5) for receiving the fluid, said steel container being open at the top and placed into the outer container with an insulating material inserted therebetween, whereby the insulating material within the ring shaped space being formed between the two containers and being also open at the top, consists of a granulated material on mineral base, characterized in that between the exterior container (2) of steel reinforced concrete and the inner steel container (5) there is provided at least one ring shaped barrier member (6) which is fastened either to the exterior container (2) of steel reinforced concrete or to the inner steel container (5) with a space left between the two containers.

2. Reservoir according to claim 1, characterized in that one barrier member (6) is arranged in parallel to the bottom at a height of the upper edge of the inner steel container (5).

3. Reservoir according to claim 2, characterized in that further barrier members (7, 8) are arranged in planes beneath the upper edge of the container.

4. Reservoir according to any of the preceding claims, characterized in that the barrier members (6, 7, 8) consist of ring shaped disks.

5. Reservoir according to claim 1, characterized in that one barrier member (6) is fastened to the roof dome (3) and extends substantially in parallel to the container axis towards the upper end of the inner steel container (5).

6. Reservoir according to any of claims 1 to 4, characterized in that the space is formed owing to smaller dimensions of the barrier members (6) than the space between the containers.

7. Reservoir according to any of claims 1 to 6, characterized in that the barrier members (6) are provided with holes or slots (15).

8. Reservoir according to any of the preceding claims, characterized in that the barrier members (6, 7, 8) are reinforced by cross bars.

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