Note: Descriptions are shown in the official language in which they were submitted.
This invention relates in particular to the underground storage of
products whose storage temperature as a rule differs from the natural
temperature of the underground surroundings in which the storage is
located. In one aspect it relates to a method of controlling the tempe-
rature of the walls, floor, and ceiling of said underground storage,
this storage often being located in rock, and keeping the temperature of
these sections within a determined range or at a stipulated figure,
using preferably a circulating stream of gas or in some cases a liquid
as a medium, which functions as a vehicle for the transportation of heat
to or the removal of heat from the mentioned storage ~alls, floor, and
ceiling. As a consequence of said temperature control this invention
provides the possibility of establishing a temperature barrier around
the area of the circulation system envisaged in this paper, said barrier
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reducing the ice sublimation process sufficiently for all practical
purposes. In still another aspect this invention relates to a method of
removing water or other substances from or adding the same to the walls,
floor, and ceiling of the underground storage, again using the circu-
lating medium in question as a vehicle, at wish applying pressure or
vacuum, said medium also picking up water vapors from sublimed ice.
The invention furthur relates to a method of recovering products
which possibly could leak out from the underground storage into the said
circulating system and further provides a safety system of controlling
if and to what extent products, in particular volatile combustible
products, are escaping from the storage. In another aspect the object of
this invention is to provide a method of utilizing the temperature
difference between the suggested circulating medium and some other
stream or body with a view to economically recover heat or 'cold' calo-
ries. The invention also provides a new method of supplying sealants
with the aid of said circulating system and also suggests new types
of~ sealants which swell upon contact with the stored products. At the
same time it relates to a safer method of regasification of condensed
gaseous products. It is an object of this invention to provide for
constructing a suitable underground storage for the purposes envisaged,
and it therefore incorporates new types of insulation designs with-
standing very low cryogenic temperatures and suitable for the invention
presented here. Other objects and advantages will be apparant to those
skilled in the art upon study of this disclosure including the detailed
description of the invention and-the appended drawings wherein:
igure 1 is a schematic sectional view in elevation of an horizontal
cylindric or rounded type of underground storage reservoir
according to the invention with a plurality of boreholes for
the circulation system, drilled near and along the rock sur-
face of the cavity, or cast in a concrete wall inside a cavity
in e. 9. silt, clay, or sand (the figure illustrates only the
case of a rock cavity).
gure 2 illustrates a schematic sectional elevation of an horizontal
cylindrical or rounded type of underground storage reservoir
according to a modification of the same invention with a
plurality of circulation channels between the actual rock
storage wall or a cast concrete wall and the inner insulated
storage wall (the figure illustrates only the case of 3 rock
cavity).
igure 3 illustrates a schematic sectional elevation of a vertical
underground storage reservoir with a round or rectangular
bottom according to a modification of the same invention,
showing the plurality of circulation channels, ducts, or
galleries with guiding devices for the circulating medium,
placed between the actual rock storage wall or a cast con-
crete wall and the inner storage wall, all latter surfaces
being equipped with some type of insulation withstanding large
temperature differences (the figure illustrates only the case
of a rock cavity),
igure 4 illustrates a schematic sectional elevation of an vertical
underground storage reservoir according to a modification of
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the same inVention, the plurality circulation channels, ducts,
or galleries with guidin~ devices ~or the circulating medium,
being placed between the inner wall and the concrete wall con-
structed inside of the actual ~uter rock wall or sourroundings
of loosel~aterials such as clay, silt, and sand (the figures
illustrates the case of a concrete outer cavity 29, surrounded
by an insulating material),
Figure 5 shows a schematic sectional plan view of one type of
insulating design used according to the invention. Insulation
is fastened to a system of rods.
`~ Figure 6 shows a schematic sectional plan view of another type
- of insulating design used according to the invention. The in-
sulation is supported by a system of wall laths, which have a ~-
repeated regular wave-formed profile, the crest on each vertical
~; lath in the figure being at the same horizontal level on every
second lath.
Figure 7 Is a sectional elevation along line 1-1 in Figure 6,
and Figures 8a, 8b and 8C are examples showing temperature and
water vapour pressures at two different operating pressures.
The principle of this invention offers advantages when
storing cold as well as hot products underground. As the most
prevalent need of underground storage refers to the storage of
cold, combustible products such as Liquefied Petroleum Gases
(LPG), Liquefied Natural Gas (LNG), Synthetic Natural Gas (SNG),
petrochemical products, and industrial gases, I prefer for
illustrative purposes to select the underground storage of LNG
as a typical example of the use of my invention though the same
principle can for the most part be applied for all types of
products which must be stored at temperatures differing from the
- 30 natural temperatures of the underground environment. For the
~ sake of simplicity mainly the construction of reservoirs in rock
is discussed, though the invention also refers to similar stor-
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ages built of concrete in silt, sand, or a mixture of different
materials.
Pipes for the filling and the removal of liquid or gas
may be conventional and may not be shown in the drawings. The
same goes for some other equipment and instrumentation required.
Corresponding parts have been given the same numerals. The type
of insulation or its design used in ~igures 1-4 has not been
denoted, likewise the detailed attaching of it to the outer or
inner storage wall.
The petroleum industry produces great quantities of
volatile hydrocarbons as a result of processing crude oil and
natural gas. Natural gas is being liquefied at ports of export-
ation, stored there, then shipped overseas, and stored at
terminals at the port of importation. Stand-by storage facili-
ties are located outside consumption centers and along pipelines.
; Such liquids require enormous storage facilities, particularlyduring periods of slack use, for peak-shaving purposes, and on
account of requirements stipulated by the authorities for emerg-
ency cases such as war and embargos.
Other industrial gases require similar facilities.
Great quantities of volatile liquids including propane and
butane have in the past been dissolved from impervious formations,
- stored in earthern storage pits, or in mined underground caverns.
Loss of product, the difficulty of pro-
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viding and maintaining an adequate vapor seal, and excessive heat losses
are some of the problems encountered.
The general tendency is to locate storage facilities for combus-
tible gases underground of the following reasons:
1. LNG fires and similar fires of highly volatile llquids cannot be
extinguished and are therefore left to burn out. Such fires are
also generally accompanied by repeated violent fatal exploslons
with enormous devastations. When storing such products underground,
explosions and other dangers can be prevented, and fires easily
controlled and quickly extinguished. Authorities are therefore
expected to stipulate underground storage location for such pro-
ducts in the future, particularly with regard to public opinion
and other environmental grounds generally presented.
2. Increased protection against wheather, sabotage, and hostile mili-
~ tary operations. -
3. StorOge at constant and low temperature, generally in the range
8-10 centigrade; no exposure to sunl;ght.
4. No space required above ground.
5. Storage under pressure at low cost.
6. A better and improved understandTng lately of the real nature of
forces in rock makes it possible to avail oneself of less fortunate
locations where the underground rock is of inferior quality. Re-
servoirs can also be built in sand, silt, or clay, which problem,
though, will only be mentioned in this paper.
Though storage of LPG in underground rock reservoirs at tempera-
tures in the range of -40C to -50C for a long time has been a success-
ful application the same cannot be said about storage of LNG, SNG, other
cryogenic liquefied products like ethane, ethylene, and other petrochemi-
cals, in such underground caverns because the extremely low temperatures
required to store these cryogenic products at substantially atmospheric
pressure requires an excessive amount of refrigeration on account of
the high heat losses tncurred. Another drawback has been the increased
product losses at these lower temperature levels. The main reason for
the mentioned heat losses is the increased amount of contraction with
subsequent continued incessant cracking of the underground rock, deve-
loping an ever larger seepage of product with time. Further, the inten-
sified rate of sublimation of ice removes the sealing effect of the
surroundings and spoils the insulation of the cavity if any.
The mentioned cracking of the rock can continue for years, steadily
opening up new cracks and constantly furthur away out from the storage
wall. The natural consequence of the cracking of the rock at these
very low temperatures is a continous increase of observed heat influx
from the cavity surroundings to the storaged product body, gas seeping
out in the environment and causing general nuisance and an explosion
danger. There are, of course~always a large number of original cracks
in the rock, and these are opened wider up while new cracks are being
created, sometimes causing large pieces of rock to fall out into the
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storage cavity. Conventional reinforcements and precautions are
therefore always required.
If the temperature of the rock is controlled within the
! predetermined limits by the aid of the multi-purpose system I have
envisaged and which system is located about the surfaces of the
¦ walls, ceiling, and below the floor of the underground storage,
such continued cracking can be totally avoided at the same time
as the stability of the rock material is ensured. By supplying
~ heat the multi-purpose system thus prevents the temperature of
¦ 10 the rock from falling below a desired critical minimum. Difficul-
ties on account of the ice sublimationprocess, such as damage to
the insulation applied, are also halted, which all can be achieved
! with aid of the same multi-purpose circulation system, which
;j constitutes the core of this invention. Water vapors thus moving
j in the direction of the storage may be carried away by the
circulation system with its interconnecting cracks and inter-
`~ spaces, said migration process substantially reduced by the tem-
perature barrier established by temperature control around the
area of the circulating system. By raising the temperature
around the circulation system a change of the temperature gradient
in relation to the temperature of the environs is attained, which
in the presence of sufficient water in the rock pores towards the
outer environs influences the rate of sublimation in the thus
created bottle neck between the circulation system and the
environs. Operatlon at a temperature below OC also implies
generally reduced water vapor pressures and thus reduced sub-
~ limation rates, water vapor pressures above ice being much lower
; than those over water except at OC. Frost heaving and front
lenses often are consequences of not removing water by a device
j 30 such as the one described. Said circulating system consists ofa multitude of comparatively closely spaced circulation channels
along all surfaces of the storage, the channels carrying a liquid
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but preferably a gas such as nitrogen, carbon dioxide, possibly
hydrogen, hydro carbons or even the stored product itself, or one
or several of its components. In some cases ducts, or galleries
with devices to direct the circulating stream, may partly or
completely substitute a plurality of channels or boreholes. These
~ circulation systems can also be used to heat or chill the rock.
¦ which latter operation also will be required when - as described
below - sealing the rock at low temperatures in accordance with
my proposed method. The typical operating range for the temper-
ature barrier of the rock or concrete will depend on the quality
of the rock or concrete but will in many cases vary in the range
-10C to -50C, i.e. about the temperature range used in rock for
many current installations. However, also higher temperatures,
even above OC, may be used.
As rock is a good insulator a very long time, years,
are required before the temperatures have asymptotically reached
their final values. To the extent they can be controlled they
are selected with regard to a number of factors such as rock
3 characteristics, rock material, drainage problems, distribution of
stress in the rock, permeability and porosity of the rock, etc
The operation of the rock storage may be controlled electronically
and in accordance with a predetermined plan.
The controlled movement of water and water vapor in
the rock is of great significance for the successful operation of
the storage.
Water vapor will move in the direction of areas with
~ lower water vapor pressures in accordance with known physical
- laws. If water is partly or totally removed from a particular
area the saturated water vapor pressure at a certain temperature
there cannot be fully developed, and the water vapor pressure in
¦ said area may therefore be lower than in a different area with a
lower temperature, where there is sufficient water available to
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develop the full saturated water vapor pressure for the temper-
ature at this last mentioned point. The porosity of the rock
¦ will, of course, also involve other physical processes of differ-
j ent nature connected with the migration of water which all
influences the general process as put forward. Figure 8a
g illustrates the approximate distribution of temperatures, plotting
¦ only a few points, when keeping the temperature of the circulating
system at a high level and at a lower level (dashed curve). The
3 corresponding water vapor pressures, unsaturated for the dashed
curve except at the far right, are found in Figure 8b. The
effect of using a drying gas is shown in Figure 8c. By lowering
the water vapor pressure curve below OC the amount of water to
; be removed by the drying gas diminishes on account of the lower
water vapor pressures and the reduced water migration rates
encountered at these lower temperatures.
There exists a patented method which suggests a con-
tinuous sealing of cracks opened up, applying a freezing liquid,
which is continuously injected as the rock cracks. I prefer to
start the sealing of natural and potential cracks by first opening
' 20 up these cracks comparatively wide by chilling the rock through
my circulating system to a temperature far below the actual future
operating temperature and then apply a sealing material, using
pressure and partly distributing the sealing agent by said cir-
culating system. At the same time conventional injection of the
same or similar sealing agents may be carried out after a pluralit~ -
-! of auxiliary boreholes have been drilled into the surface from
the cavity. I prefer to select sealants which swell upon getting
in contact with the stored product, though such swelling sealants
not always are imperative. If the product should leak out and
¦ 30 get in touch with a swelling sealing material in a crack the
! swelling sealing agent will automatically close the crack firmer.
In some instances the swelling action may be started by injection
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of water. ~y first injecting a sealing component and then adding
~ a second component and leave the two to react within a closure the
¦ swollen material will act as a very good and elastic seal. The
`~ described method of first opening up the cracks by chilling the
1 wall material and then apply the sealant by injection after which
the cracks are closed again by raising the temperature works as
well with rock material as with concrete.
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There exists a great number of chemical compounds or mixtures
hereof which have the propensity of swelling upon contact with fluids or
gases, the fluids and gases being absorbed, adsorbed, dissolved by these
materials, or forming new structures with them. Some of these materials
are polymers, rubbers, or plastics. The sealant must be selected with
regard to the product stored, and selection of proper material can be
done by the average expert.
I prefer to remove the water in the rock by using a drying gas or
fluid, the latter containing a water absorbing component. These media
are circulated in the proposed system and then continously dried by some
conventional drying agent. When using a circulating gas, water may also
be separated out in condensation, adsorbation, or absorbtion processes,
in some cases after compression. The water removal action may be facil-
itated by first heating the medium. Applying a sealing medium and again
taking advantage of the circulating system the sealant is then applied
in all cracks and spaces in the environment of the circulating system
pr~posed in this invention. A conventional water drainage system will
always be required in all storage designs discussed.
A different mixture, also distributed under pressure through the
proposed circulating system in a similar manner as in the previous case,
contains principally two components, one of which absorbs water while
the other works as a sealant simultaneously. Such products are commer-
cially available. When using the last mentioned mixture the cracks may
all be opened up by chilling and partly closed again by raising the
temperature.
The sealing qualities of the storage cavity walls are at times
dependant on the water content in the rock. Of this reason this inven-
tion also involves the idea of adding water to the circulating stream
when necessary. For the process of sublimation of ice in the rock the
possibility of controlling the water content of the circulating stream
is of utmost importance, because water from the rock tends to migrate
and form ice on the inside wall of the actual storage, thereby having
a tendency of pushing away applied insulation or damaging its valuable
insulating characteristics.
it is also an object of this invention to provide a safety system
which allows a good control of the proper functioning of the storage,
which fact is of prime importance if the cavity contains a volatile
combustible liquid or else a dangerous gas. This can be achieved by
keeping the operating pressure of the circulati-ng system somewhat lower
than the pressure in the actual storage. If product should leak out
from the storage Tt will enter the circulating system where it immedi-
ately can be sensed by a suitable instrument such as a gas chromato-
graph or mass spectrometer. Such a product may then also be recovered,
e.g. through absorbtion or condensation processes. In the case of com-
bustible gases it would involve a direct danger not to use such a
system or a similar device, should the sealing qualities of the cavity
wall prove to be insufficient, needless to mention difficulties which
arise at shut-down or maintanance of the storage.
The selection of a suitable medium to be employed for the circu-
lation system depends very much upon product stored, its storage tem-
perature, operating temperature range of the circulating medium, and
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what type of equipment the medium shall have to pass. A furthur point
is the question if the circulating medium may affect materials contacted
in the system. Among the gases, nitrogen, which is inert and often
employed in start-up operations, is excellent. Another suitable gas may
be carbon dioxide, hydrogen, refinery off-gases, and the product itself,
if volatile. If natural gas is stored, nitrogen is a suitable medium,
and in this case LNG and its components can be separated out completely,
if product should leak into the circulating system, as long as the
product does not contain hydrogen.
A furthur point which always arises is if the operating situation
allows an economical heat exchange between the circulating medium and
some other stream or body.
Underground storage offers the advantage of operating at a higher
pressure at low cost as compared with storage above ground. This may be
important when filling the storage with LNG liquid, when the specific
gravity of the liquid to be filled differs somewhat from the specific
gra'~ity of the storage content. Under such circumstances the pressure in
the reservoir may rise suddenly on account of so called roll-over.
With regard to the same advantage to operate at higher pressures
a further feature of this invention is the suggested use of the reser-
voir as an evaporation chamber. The heat exchange equipment for the
evaporation can be located inside as well as outside the reservoir.
The corresponding heat exchange equipment for this evaporation of liquid
has not been denoted in the drawing and may be conventional.
When storing cryogenic products like LNG the contraction of the
plastic insulations used amounts to about one per cent, while the cor-
responding contraction of the rock for the same temperature interval
will be in the order of one per mille. The contraction differences for
these two different materials therefore call for special types of
insulation designs to be employed along the cavity walls, on wooden
or some other supports along the same walls, or on the walls of a
built-in containing vessel. The basic design principle is to prevent
the insulation from becoming subject to excessive tensile stress.
The insulation designs proposed here are all built up of several layers,
e.g. of polyuretan insulation or similar plastics, along with sealing
membranes, and a heat reflecting aluminium foil. Suitable sealing mem-
branes and suitable insulating materials are known and commercially
available. The designed final compound insulation layer is formed in
such a way that the layer is divided up in equidistant cuplike elements,
resulting in regular parallel rows of such elements, where each element
is equidtstant to any next element. There is an ample amount of insu-
lation material around each element to allow for temperature contrac-
tions, which mainly result in flexural stresses instead of tensile
stresses. The insulation is supported at the centre of each element. The
first mentioned stresses again can be mitigated or relieved during the
initial transition process at start-up by supplying heat to the outside
of the insulation layers, using my proposed circulation system as a heat
source.
The application of such insulation designs can easily be carried
out on comparatively even wall surfaces but will otherwise require a
system of support rods. When supporting the insulation with the ald of
a system of laths with wave-formed profiles the cost will be lower when
the cavtty surface is even and smooth.
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The support rods are fixed in boreholes, drilled tnto the rock, orcast in the concrete wall. These boreholes form a regular symmetric
equidistant pattern, evenly distributed along all walls. Each element of
the insulation is thereafter fastened on these fixed rods, leaving a
'valley' around each rod to allow for temperature contraction. This
design makes it possible to leave the actual rock wall in a rough un-
finished condition.
The system of wooden laths is fixed to the rock walls in such a
manner that the crest of a wave profile on one vertical lath is oppo-
site to the 'valley' of a profile of the next adjacent vertical lath at
the same horizontal level. When cooled the insulating layers will thus
through contraction mainly rest on the crests of all laths, the surplus
length of the insulation round each crest allowing for the temperature
co~traction in conformity with what also happens when the insulation is
fastened on the rods mentioned in the previous paragraph. In the last
mentioned design the elements referred to correspond to the crests in
th~ lath system.
The two insulation designs can be fitted with wooden supports,
if so required; and the circulating medium can be directed between the
insulated inner wall and the actual outer rock or concrete wall. The
designs constitute a built-in container. In the figures is the
plastic insulation cover over bolts and bolt heads omitted.
Referring now to FIGURE 1 of the drawing an horizontal rounded
type of underground reservoir 10 is shown in cross section. A series
of boreholes 11 have been drilled in the rock '6 along the periphery
of the reservoir for the circulation system described, from both ends
of the cavity, or, depending on length of storage, also from niches
between the ends of the reservoir. If a concrete wall has been cast
inside the rock wall or in surrounding loose material like clay or sand,
the system of holes are cast. Small size boreholes 12 have also been
drilled in from the storage (only one such borehole is shown in the
figure) with a view to tighten cracks through the injection of swelling
sealants or other materials after the rock has been cooled down below
the future operating temperature. Other cracks have been mended with
plastics, cement, or similar mixtures, and the outer cavity surface,
depending on the type of insulation used, smoothed. After rock bolts and
insulation supports have been positioned the insulation 13 is fastened.
14 is evaporation space, and 15 withdrawal pipe for gaseous products.
FIGURE 2 illustrates how a circulation system of channels 17,
plàced on the inside of ~he outer cavity wall, may substitute the `-
circulating system of drilled boreholes in the rock wall of the re-
servoir 10 as described in figure 1. The insulation 13 is here fastened
in conformity with what has been outlined in connection with figures 5 ~ -
or 6. Sometimes it will be cheaper to construct galleries with directing
devices for the circulating medium.
The reservoir 10 in FIGURE 3 is a modification of the previous
two storage types described. This storage may be built according to
choice with a rectangular or circular concrete bottom 19, this type
of bottom being equipped with circulation channels 17, preferable in
block elements of balsa wood 18. The circulation system along the
walls consists of a plurality of vertical channels 17 or other gas
stream guiding devices which insure a sufficient contact between
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the streaming medium and the outer and inner wall. While
walls and bottom are equipped with the mentioned standard types
of insulation 13, the ceiling of the reservoir, resting on a
suspended structure 22, is insulated with some pervious loose
insulation like rock wool, which permits the vapors to pass
and the possibility to use the cavity as an evaporation chamber.
Valve 20 is used at start-up.
Figure 4 corresponds to figure 3 and illustrates how
- a reservoir can be built in sand, silt, clay, or similar loose
10 materials, or elsewhere where only inferior rock is available.
The reservoir, including the walls with the built-in circulation
svstem, is cast in concrete 29, using a travelling mould.
Another method is to construct the storage using prefabricated
elements and pre-stressed concrete. Construction in earth
is generally preceded by freezing the surrounding soil before
excavation. When required insulating material, impervious
insulating material, or foamed insulating material 27 may be
filled in round the structure.
Figure 5 shows how the insulation 13 is fastened
20 after a regular pattern of equidistant support rods has been
positoned in the rock wall. 23 are elastomeric membranes,
24 polyurethane foam, 25 aluminium foil, and 26 support rod,
which has been fixed in a hole drilled in the rock or in the
concrete. 28 is an optional support of wood, plywood, or
plastic.
Figure 6 illustrates the utilization of a system of
laths 30 with a configuration of regularly repeated wave-like
profiles.
Figure 7 is a sectional elevation along line 1-1
in figure 6.
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