Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Storage installation for lipuified gases
The present invention relates to a storage installation for liquified gases,
such as
LNG, i.e. gases which at temperatures below 0°C boil at atmospheric
pressure
s and which can be liquifled by further cooling.
Such gases may be stored in excavated rock cavities and which constitute a so-
called ground depot. The alternative to such ground depots is tanks laid into
the
ground, entirely above the ground level, or tanks partly above and partly
below the
1o ground level. If the facility is positioned entirely or partly below ground
level, the
storage may be above, at or below the ground- water level. The pressure above
the liquified gas may be about 1 bar abs., normally slightly higher, such as
1,1 bar
abs.. In the liquified gas the pressure, of course, increases downwards from
the
surface of the liquid but the pressure would be lower than in the possibly
1s surrounding ground-water. The low temperature of the gas can be maintained
by
feeding the gas (gaseous phase) above the surface of the liquid to a
refrigerator
to be recondenced to a liquid which is fed back into the tanks, according to
conventional techniques.
2o In rock cavities for this kind of storage it has been attempted to use a
concrete
lining against the rock. The store has been insulated by adhering insulation
onto
the concrete lining, or in some cases, directly onto the rock without the use
of
steel lining. Experiments have shown that due to dissimilar contraction during
the
cooling, adherence problems arise between the different materials, the result
of
2s which being a great risk for the insulation to fall down. Also, if it is
not sealed off
by means of a membrane of special steel, such a storage facility is prone to
leakage, resulting in excessive expenses.
Tanks of steel or tanks of concrete lined with steel have been employed as
tanks
so on or below the ground. Due to the lower temperature level highly costly
special
steel must be used, as steel of a more normal type becomes brittle at low
temperatures. The cost for producing such installations is a serious
disadvantage.
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Through the present invention an installation has been arrived at which solves
the
above problems and which also is considerably cheaper than prior art
facilities for
storing liquified gases at temperatures below about -45°C (in tanks of
steel).
The installation according to the present invention for storing gases in a
cavity
defined by rock or an outer concrete shell comprises a tank for the gas, the
tank
being made of concrete and possibly thermally insulated, the installation
being
characterized in that the tank is entirely or partly surrounded by a mass
filling a
space between the tank and the rock or the concrete shell, the mass itself
being
1o thermally insulating and capable of causing sealing.
The sealing is performed by the mass filling the space or void, either by
means of
the mass as such or by means of one or more membranes which may be placed
within the mass, or on the outer or inner face thereof.
The invention makes it possible to make such an installation either in an
excavated rock cavity , or in loose soil, partly within the loose soil and
partly
above ground level, or entirely above ground level. Here, the expression loose
soil refers to any substance that is not a solid matter, such as earth, sand,
2o shingle, gravel, or a mixture thereof. The loose soil may be arranged
around the
installation, or a depression may be formed in the loose soil in which the
installation is placed. Where an outer shell encapsules the tank, the shell
absorbs
the pressure from within the mass filling the space such that the installation
is
independent from the surrounding medium which, as indicated, may be loose
soil,
partly loose soil and partly. atmospheric air, or atmospheric air exclusively.
When it is to possess sealing capabilities, the mass filling the space may be
clay,
for example, possibly added a thermally insulating material. An exemplary
additive is loose Leca. The addition of such a material may eventually lead to
the
so avoidance of arranging separate thermal insulation on and/or in the tank,
or that
such insulation may be substantially reduced. When being cooled from
0°C to a
certain temperature, clay has the capability of expanding, and hence it will
maintain a tight engagement with the rock or the shell, and with the concrete
tank.
However, to avoid overloading the tank andlor the shell by pressure caused by
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the expansion of the clay, a "crushable material" may be arranged as a shim
between the clay and the tank, or between the clay and the shell, such that
this
"crushable material" crumbles at a certain pressure and prevents the transfer
of a
to high pressure onto the tank andlor shell. If insulation is placed between
the
s mass and concrete this insulation may act as "crushable material".
The mass filling the space may be a natural or a factory-made product. As the
mass itself shall be sealing, its permeability should be extremely small such
that
the mass acts like a membrane sealing off the installation. An exemplary
natural
~o product is clay with a large contents of fine particles. Exemplary factory-
made
products are clay in the form of powder or pellets (bentonite) to which water,
finely
grounded limestone, slag from industrial processes, flight ashes (e.g.
vulcanic),
silica dust, etc., may be added. Although it is not mandatory, it is an
advantage
for the mass to be thermally insulating. Insulation may be arranged in layers
~s inside or outside the tank. Although it is not mandatory, it is also
advantageous
for the mass to be expanding at temperatures below 0°C.
After the starting-up of the installation and when a stable temperature is
present
(in reality, the temperature falls as long as the installation is in
operation), heat
2o may be supplied to the mass. If the mass is clay or a similar material
which
becomes brittle and tends to break up at lower temperatures, heat may be
supplied such that the mass or portions thereof be kept at a temperature
across
the entire or portions of the thickness being higher than the temperature at
which
the mass transforms from being plastic to being brittle. Similarly, if the
mass
2s contains one or more membranes, heat may be supplied to avoid cooling down
of
the membrane or membranes to a temperature where it/they becomeslbecome
brittle or is/are likely to break. The supply of heat makes the choice of
material
for the membrane or membranes less critical. For example, steel of a normal
grade, i.e. not an expensive special steel, may be used.
When the storage facility has been put in operation by being filled with
liquified
gas, slow cooling of the tank, possible insulation, the mass in the space as
well as
the rock or shell around the cold gas takes place and the zero-isotherm is
constantly moved outwards from the storage. In this connection it should be
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noted that insulation may be favourable also in respect of the time that
elapses for
the starting-up. To prepare the installation for storage liquified gas is
supplied,
which due to the heat supply from the surroundings (the concrete tank, the
possible insulation, the surrounding mass and rock or shell) will evaporate.
s Evaporated gas is removed, and condensed gas that is supplied evaporates
such
that the temperature of the surroundings constantly becomes lower. The time it
takes to bring the surroundings down to such a temperature where the
evaporation is minimal and the installation may be regarded as being in stable
operation is substantially shortened by thermal insulation in addition to the
mass.
~o A shortening of the starting-up period is of great economic value due to
the very
large sums of money invested in such facilities.
The insulation material also provides the effect that the mass and rock or
shell are
not subjected to such a low temperature as when insulation is not used. Thus,
15 problems regarding sealing of the storage can be avoided.
The mass between the tank and rock or shell may be of such a kind that it does
not contract nor break up at the temperatures occuring in this regions. In
order to
prevent the temperature from being so low that the mass transforms from a
2o viscous to a brittle behavior with subsequent cracking, or that the
membrane or
membranes becomes/become brittle, heating means, such as tubes, hoses,
heating elements, combined with temperature sensors, may be mounted, such
that heating can be effected to prevent the temperature from being so low that
cracking of the mass occurs, or the membrane or membranes becomes/become
2s brittle. Such heating means are first put in service when the installation
is
approaching its approximate stable operation state, as heating during the
starting-
up would prolong the time for starting-up.
Such an installation exhibits a high grade of safety. Due to the mass and
possible
so ground-water surrounding the tank cracks in the concrete tank, in the
possible
insulation and/or in the shell will not cause any outward leakage of product
or
inward ground-water leakage, either by the fact that the mass does not crack,
or
that the membrane. or membranes performs/perform a sealing function.
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Compared with the use of steel tanks it is, in addition to the economic
savings,
achieved the certainty that cracks which may arise in the concrete tank do not
have any consequences regarding leakage of the product in liquid or gaseous
form, since the surrounding mass, or the mass combined with one or more
s membranes, and possibly the ground-water, will seal against further outbound
leakage.
The thermal insulation of the concrete tank may be external andlor internal.
In
any case, an insulation material must be used which the product does not
~o penetrate into and which does not react with the product, since cracks in
the
concrete tank will occur.
In the following an installation according to the invention will be described
by way
of examples schematically illustrated on the enclosed drawings, on which Figs.
1
to 5 show an installation having a tank located in a cavity excavated in rock,
while
Figs. 6 to 9 show an outer shell around a tank.
Fig. 1 shows a horizontal section through an embodiment of an installation
according to the invention.
2o Fig. 2 shows a vertical section through an installation according to the
invention.
Fig. 3 shows a vertical section through a somewhat different embodiment of an
installation according to the invention.
Fig. 4 shows a horizontal section through an installation according to the
invention, with one membrane located in the mass surrounding the
2s concrete tank.
Fig. 5 shows a vertical section through the installation of Fig. 4.
Fig. 6 shows a horizontal section through another embodiment of an
installation
according to the invention.
Fig. 7 shows a vertical section through the installation of Fig. 6.
so Fig. 8 shows a horizontal section through an installation according to the
invention, with a membrane located in the mass surrounding the concrete
tank.
Fig. 9 shows a vertical section through the installation of Fig. 8.
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Figure 1 may be regarded as a section through each of the insulated tanks
shown
in Figs. 2 and 3.
Fig. 1 shows a concrete tank 2 having a circular cross-section. A layer of
thermal
s insulation 3 is arranged outside the tank 2, and the unit comprising a tank
2 and
the insulation is surrounded by a mass 5 which also bears against the
surrounding
rock 6. In its inner chamber 1 the tank 2 contains liqui~ed gas. Between the
insulation 3 and mass 5 "crushable material" 4 is inserted, this material
being
intended to crack if the outer pressure against the tank 2 exceeds a certain
value,
~o thus preventing the tank 2 to be overloaded because of swelling of the mass
5
when cooled. Apparently the rock wall generally will not be of a regular
shape,
such as that shown, but rather be irregular.
Figs. 2 and 3 show vertical cross-sections through two alternative embodiments
~s which have in common that the cylindrical portion of the tank 2, the
insulation 3,
the "crushable material" 4 and the mass 5 may be disposed as shown in figure
1.
Also, the roof 7 is similarly constructed as the cylindrical portion, except
that the
roof 7 is shown as being dome-shaped. "Crushable elements" 4 are inserted in
the roof 7, too. Contrary to the embodiment of Fig. 2, the embodiment of Fig.
3
2o comprises crushable material underneath the concrete tank.
The embodiment of Fig. 2 comprises a concrete sole 8 having branches 9 (ribs,
posts) down to the rock, and in between these branches there are voids
containing insulation and mass, correspondingly as the wall and roof of the
tank.
2s The sole 8 and branches.9 support the rest of the tank 2.
The embodiment of Fig. 3 comprises, on the other hand, a bottom 10 constructed
with insulation as the rest of the tank, while a mass 5 corresponding to that
surrounding the tank and covering the roof 7 forms the foundation for the
tank.
so Thus, the tank 2 and the insulation 3 are completely surrounded by the mass
5
which also supports the tank. The bottom of the tank 2 and the insulation 3
beneath the bottom are dome-shaped, correspondingly as the roof 7. It is well
known that dome-shaped end portions are far more capable of withstanding
loading from outside than planar end portions, for example.
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The embodiment of Figs. 4 and 5 is similar to the embodiment of Figs. 1 and 3
by
comprising the same elements but differ therefrom by the fact that the mass 5
contains a sealing membrane 11. It should be understood that the membrane
may be located inside or outside the mass and that one or more membranes 11
s may be employed. In this case, the mass 5 may be a liquid permeable
material,
such as sand.
Fig. 6 illustrates a concrete tank 2 having a circular cross-section. A Layer
of
thermal insulation 3 is arranged outside the tank 2, and the unit comprising
the
~o tank 2 and the insulation is surrounded by a mass 5 which also bears
against a
surrounding shell 10 made of concrete. In its inner chamber 1 the tank 2
contains
liquified gas. A "crushable material" 4 is inserted between the insulation 3
and
mass 5, being intended to crack if the outer pressure against the tank 2
exceeds
a certain value, thus preventing overloading of the tank 2 and/or shell 10 due
to
~s the swelling of the mass 5 when cooled. The Fig. illustrates an
installation
surrounded by loose soil 8. The loose soil may be arranged around the
installation, or a depression may be excavated in loose soil in which the
installation is entirely or partly disposed.
2o Fig. 7 is a vertical cross-sectional view through the installation shown in
Fig. 6.
Besides the elements that appear from Fig. 6, Fig. 7 shows a dome-shaped
bottom 6 and a dome-shaped top 7 of the tank 2, a roof covering 12 made of
metal or some other weather proof material, a shell bottom 9 and an upper
shell
collar 11. It is well known that dome-shaped end portions are far more capable
of
2s withstanding loading from outside than planar end portions, for example.
Thus, the installation is located in a depression in the loose soil 8, or the
loose
soil 8 is arranged around the installation, such that only the top 7 and the
roof
covering 12 extend above the loose soil 8.
Even underneath the bottom 6 "crushable elements" 4 are inserted.
The embodiment of Figs. 8 and 9 is similar to the embodiment of Figs. 6 and 7
by
comprising the same elements, but differ therefrom by the fact that the mass 5
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contains a sealing membrane 13. It should be understood that the membrane
may be located outside or inside the mass 5 and that one or more membranes 13
may be employed. In this case, the mass 5 may be a liquid permeable material,
such as sand.
s
The embodiments shown should be regarded as being schematic. A sump or
recession for a loading pump and tubings is not shown, nor is a possible
heating
means illustrated.
~o Several modifications are possible relatively to the examples shown. For
example, insulation may also be mounted internally in the tank 2. It is also
envisaged to add to the mass 5 sufficient insulating material, such as Leca,
such
that the insulation on or in the tank 2 can be omitted, except that the top 7
should
be insulated if it is not covered by the mass 5.
