GB2080359A - Foundation for a Land-based Storage Plant for Liquefied Gas, and a Method of Constructing a Land- based Storage Plant - Google Patents

Abstract

A storage plant with a spherical storage tank for liquefied gas, for installation on land. The spherical storage tank is supported by a skirt inside a surrounding concrete silo. An advantageous way of producing the storage plant is that the concrete silo or a buoyant lower portion thereof is produced in a fitting-out dock together with the spherical tank and thereafter floated to a location in the vicinity of the installation site on land, after which the structure is brought on land by utilizing the lock system principle.

Description

SPECIFICATION Foundation for a Land-Based Storage Plant for Liquefied Gas, and a Method of Constructing a Land-Based Storage Plant The invention pertains to a storage plant with spherically-shaped storage tanks for liquefied gas, for installation on land. The invention also relates to a practical method of producing such a storage plant having spherical storage tanks for liquefied gas, for land installation.

There are a number of conditions which landbased storage tanks for liquefied gas must meet, especially in the case of LNG (liquefied natural gas).

For example, heat transfer into the tank must be minimal, i.e., thick insulation is required.

Moreover, the insulation must be well protected against moisture owing to the large temperature differences. The tanks must also be protected against environmental influences such as temperature variations, earthquakes, wind, precipitation, etc., and land-based storage tanks for liquefied gas should also be protected against other external influences, e.g., "missiles". A further important requirement is that in a number of cases means must be provided to ensure "secondary containment", i.e., to ensure that any liquefied gas which might leak out of the tank will be collected, in the event of a leak or rupture in the primary tank.

These requirements define the level of safety and operational reliability of the plant. In addition to these factors come goals such as cost-saving construction and operation, simple and rapid construction, etc. Recently, the desire for a simple method of building the plant, requiring only a limited crew at the assembly or installation site, has been emphasized. One can obtain this by prefabrication.

A special advantage of using spherical tanks as storage tanks is their high degree of safety and reliability. Much experience is available from the use of such tanks in maritime applications. A particular advantage is that the support of the tank does not require extensive insulation against the ground, as is the case if large, vertical, cylindrical tanks having a flat bottom are utilized.

It is proposed in accordance with the invention that the foundation for the skirt-supported spherical tanks be formed as a buoyant, unified concrete body. The foundation can then be produced in a practical manner at a suitable building site, for example in a dock, and floated to a location in the vicinity of its final destination, where it is then brought on land, either by using skids, or preferably by applying the principle of a system of locks.

A particularly advantageous feature is that the foundation itself can be utilized as a transportation barge. In such case, the entire plant, including spherical tanks, can be built at a dock, set afloat, and floated to a location in the vicinity of the installation site, where it is then brought on land, preferably by utilizing the lock system principle.

The invention is well suited, first and foremost, for use in connection with rather large gas treatment plants, for example LNG plants, petrochemical installations and the like, which because transportation by ship is required are situated along a suitable shoreline.

Preferably, the foundation is made with an integral, upwardiy-extending concrete wall which serves as a load-bearing lower portion of the skirt support. This wall will then also delimit a compartment for collecting any leakage. As external protection, a silo of steel or concrete can be built around the spherical tank. This silo can optionally be constructed and mounted at the same building site as the foundation.

To reduce the draught of the buoyant concrete body, a number of measures may be taken; the most obvious would be to adopt the greatest possible volume of buoyancy by maximizing the surface area, and to select weight-saving solutions for the concrete structure.

The silo will provide protection against wind and weather, and against other external influences, such as flying objects (missiles). The silo can also provide additional protection against moisture in that the atmosphere is held dry. Inside the silo, platforms, ladders and gangways for inspection purposes may be provided. The silo can also serve as a secondary container or collection tank in case of a rupture in the primary tank (the spherical tank). An advantage obtained by using such a silo as the secondary container, when such is required, is that evaporation is limited by the restricted surface of the secondary container, and the damage is held within a limited area. In case of a leak from the primary tank, the space can be rendered inert to reduce the risk of fire and explosion.

The roof of the silo can either be a light framework structure or a cupola having the same strength as the walls, or higher. The spherical tank can either be supported from underneath by a conventional, reinforced skirt, or it may be suspended in a tension-loaded, slightly conical structure, e.g., a combination of a short skirt with suspension stays distributed around the circumference thereof.

The special features of the invention will be apparent from the appurtenant patent claims, and the invention will be explained in greater detail with reference to the accompanying drawings, wherein Figure 1 shows a schematic cross section through a partially-finished storage plant structure in a fitting-out dock, ready to be floated out, Figure 2 shows a schematic cross section through a second embodiment of a storage plant structure in a fitting-out dock, ready to be floated out, Figure 3 shows a third possible embodiment, ready to be floated out from a fitting-out dock, Figure 4 shows how the lock-system principle can be used to elevate and bring on land a structure of the type shown in Figure 3, Figure 5 shows a structure of the type illustrated in Figure 1, placed on the assembly site, its silo having been partially constructed but awaiting completion, Figure 6 shows a structure of the type illustrated in Figure 2, installed on land, Figure 7 shows a structure of the type illustrated in Figure 3, installed on land, Figures 8 and 9 show two possible assemblies of two and three spherical tanks, respectively, in a common concrete silo, Figure 10 illustrates the maximizing of the surface area in order to reduce draught and Figure 11 shows a structure, in cutaway and perspective view, wherein the foundation is a closed box-like body.

In the fitting out dock 1 shown in Figure 1, whose water fill level is designated by the numeral 2, the lower portion 3 of a concrete silo is constructed. In this case, the concrete bottom 4 and a concrete skirt 5 are cast, and a spherical tank 6 is then mounted on the concrete skirt by means of a compression-loaded skirt 7. The skirt 7 and the spherical tank 6 are preferably of the type known from maritime applications, which in professional circles is known as the MRV concept.

In this case, the concrete skirt 5 is advantageously utilized as a wall in the buoyant silo portion 3, such that the structure shown in Figure 1 can be floated out of the fitting-out dock.

Optionally, the silo wall which will later be provided can be begun already at this stage of the construction, as indicated by the dashed lines and designated by numeral 8.

Figure 2 shows how the entire storage plant can be built completely finished in a fitting-out dock 9, whose water level is designated 10. A concrete silo 11 with an integral concrete bottom 12 and cupola 13 is cast in the fitting-out dock, the spherical tank 14 also being installed therein at the same time. The spherical tank 14 is mounted in the concrete silo in the same manner as the embodiment of Figure 1.

Figure 3 shows how a concrete silo 1 5 is constructed in a fitting-out dock 16, whose water level is designated 17. As opposed to the concrete silos shown in Figures 1 and 2, the concrete bottom 1 8 in this case has a crowned configuration, and the rest of the concrete silo is in the form of a vertical cylinder. This type of silo is intended to be provided with a roof or cover in the form of a light framework structure (not illustrated).

In this embodiment, a spherical tank 19 is suspended in the concrete silo 1 5 by means of a tension-loaded, slightly conical skirt structure 20.

The term "skirt structure" in this context should be understood also to comprise combinations of skirts and tension-loaded stays or bolts, or optionally strictly a suspension by means of stays, with the stays distributed around the circumference.

Both the concrete silo and the spherical tank with suspension structure can be produced by means of known per se techniques, so it should not be necessary to go further into detail in this regard. However, it should be mentioned that the spherical tanks may with advantage be made of a suitable steel material, or preferably, of a suitable aluminum alloy. The spherical tank is insulated in a manner known per se, and the insulation is covered by a vapor block in the form of aluminum foil or another suitable material.

After the storage plant structure has been built to the degree shown in Figures 1,2 or 3, respectively, the respective docks 1,9 or 1 6 are filled with water; the structure will then float and; can be floated to a location in the vicinity of the installation site, i.e., the concrete silo or the buoyant portion thereof is utilized as a transportation barge.

Figure 4 shows how a concrete silo with its associated spherical tank can be elevated by a system of locks. The structure illustrated in Figure 4 is identical to that shown in Figure 3. The structure 1 5 is first brought into a lock chamber 21. The lock chamber 21 is then closed and filled with water to the level 22. The lock 23 is opened and the structure 1 5 is floated into the lock 23.

The lock 23 is then closed and fllled with water to the level 24, and the structure is then floated into the upper portion 25 of the lock 23, which in this case represents the installation site. The structure 15 is lowered down into contact with the ground by tapping water from the lock chamber 23.

Figure 5 shows a structure of the type illustrated in Figure 1, placed on an installation site, for example in an upper lock chamber, or in a lock chamber which has a direct connection to the sea. The installation site itself is delimited by a wall 26 and the lock chamber is filled with mass fill 27. The partially-finished wall 8 of the concrete silo is then built up higher as indicated by the dashed lines, so as to produce a finished concrete silo of the type shown in Figure 2, for example. The concrete silo can naturally also be constructed with a cylindrical wall as shown in Figure 3 and provided with a suitable roof or cover, preferably in the form of a light framework structure.

Figures 6 and 7 show structures of the types shown in Figures 2 and 3 respectively, placed on the installation site in the same manner as shown in Figure 5. In Figure 6, a wall is designated 28 and the mass fill material as 29. In Figure 7, the wall is 30 and the mass fill material 31.

Figure 8 shows how two spherical tanks 32, 33 can be assembled inside one concrete silo 34, and Figure 9 shows three spherical tanks 35, 36, 37 placed in a cluster in a common concrete silo 38. These two embodiments can in principle be produced in the same manner as shown, for example, in Figures 1,2 and 3. Reference numerals 39, 40 designate low walls extending upwardly from the bottom of the silo and serving to increase buoyancy.

Figure 10 shows how one can maximize the surface area to reduce the draught of the structure. The expanded surface area 41 with a surrounding low wall 42 provides a maximization of the surface area and reduced draught. The wall 42 defines a compartment 43 which optionally may not be emptied until just prior to installation/lockage. The wall keeps water out during the installation phase. The surface area may be circular, rectangular, oval, etc., adapted to the installation site. In Figure 10, the skirt 44 and tank 45 are merely suggested.

The tank plant shown in Figure 11 is made with a foundation or float body in the form of a closed box or barge 46 of concrete. Extending upwardly from the deck 47 is an integral concrete wall 48 which acts as a load-bearing lower portion of the skirt support, which also comprises the skirt 49. Built around the spherical tank 50 in this instance is a steel silo 51.

In addition to the above-mentioned advantages in connection with the use of a foundation which is constructed as a buoyant body and which later forms part of the storage plant, the invention also makes it feasible to move the plant after its period of service at the installation site is ended, say, after 1 5-25 years. Both concrete and aluminum, for the purpose in question, are very durable materials, and these storage tanks with foundations have an economic lifetime far greater than that of the gas plant itself. Thus, apart from the increasingly important desire, and requirement, that people "clean up after themselves" when the activity is finished, these tanks and silos can also be re-used.

The spherical tanks with a silo constitute one entity, comprising both a primary tank and a secondary tank (when such is required), insulation, protection, inspection and maintenance means, pumps and safety valves, instrumentation, etc., etc. The plant can also be completely prefabricated, that is, including everything mentioned above, and when it is moved to a new site, all secondary and auxiliary systems will be moved along with it. The skirtsupported spherical tank, in addition to not requiring extensive insulation against the ground, will not require means for supplying heat as some systems require, either. Inspections/repairs can be performed immediately, and it is not necessary to wait for months before the tank system/insulation space is gas-free.

A number of the more likely gas plants are located or may come to be located in active earthquake zones. Spherical tanks, for example made of aluminum, supported in non-fixed silos, can withstand extreme vibrations without failing, and the safety of the system against catastrophic consequences of earthquakes will therefore not be dependent upon comprehensive and expensive investigations of the ground in the region for determining earthquake activity.

It should be apparent from the foregoing that the invention provides a "disposable float body" combined with a foundation which functions usefully both during construction and later as a permanent foundation. The float body may be made either as a bottom surface with tank sides, or as an expanded bottom surface with upstanding sides. The float body can be completely closed, or open at the top.

Different structural elements having a different primary function than the limitations of a float body may be used, while at the same time certain of the delimiting surfaces may be reinforced in order to fulfill functions as parts of a highly-ioaded foundation. For example, the bottom can be of crowned configuration, or of a "honeycomb" construction.

Claims (8)

Claims

1. A foundation for one or more skirt-supported spherical tanks for liquefied gas in a storage plant for installation on land, characterized in that the foundation is formed as a buoyant, unified concrete body.

2. A foundation according to claim 1, characterized in that the buoyant concrete body comprises an upwardly-extending, integral concrete wall which serves as a load-bearing lower portion of the skirt support.

3. A method of producing a land-based storage plant having one or more skirt-supported spherical tanks for liquefied gas disposed on a foundation, characterized in that a buoyant, unified concrete body is made, set afloat and floated to a location in the vicinity of the final installation site on land, and is thereafter brought on land and is used as the said foundation.

4. A method according to claim 3, characterized in that the spherical tank or tanks are skirt-supported on the buoyant concrete body prior to the said floating thereof.

5. A method according to claim 3, characterized in that the transfer of the body to the installation site on land is carried out utilizing the principle of a system of locks.

6. A method according to claim 3, characterized in that the buoyant concrete body is cast with an integral, upwardly-extending concrete wall, intended to serve as a load-bearing lower portion of the skirt support for the spherical tank.

7. A method for producing a land based storage plant substantially as hereinbefore described.

8. A foundation for one or more skirt supported spherical tanks substantially as described with reference to the accompanying drawings.