Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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This invention relates to a double hull type oil
tank system whose inner tank is built in an outer tank
filled with water and wherein oil is held in said inner
tank in a state floating on the water.
When distinguished by the roof structure, the con-
ventional cylindrical oil tanks can be classiEied into
the fixed roof type and the floating roof type. These
two conventional types of cylindrical oil tank are
accompanied with the undermentioned drawbacks.
I. Fixed roof type oil tank
(1) The tank roof i5 provided with a ventilation
valve. The tank itsel~ performs breathing when oil is
taken into or out of the tank and also due to changes in
ambient temperature, leading to heavy vapor loss of the
stored oil and the resultant environmental pollution.
(2) When oil is discharged, air brought into the
tank through the ventilation valve is mixed with oil gas
vapor, resulting in the danger of the tank being filled
with explosive gasses.
(3) The fixed roof type oil tank generally
involves a higher construction cost, and moreover a
longer construction period, and is unavailable as a
large capacity tank.
II. Floating roof type oil tank
This floating roof type oil tank has been developed
by eliminating the above-mentioned drawbacks, but is
still accompanied~with the following difficulties.
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(1) Problems are raised regarding the construction
of a weather hood intended to prevent rain from seeping
into interspaces between the periphery of the roof of
the floating tank and the peripheral wall thereof. Many
devices have been proposed to suppress the occurrence of
such difficultly. To date, however, no reliable tech-
nique has been established for the full prevention of
rain intrusion.
(2) Similar difficulties to those described in
Item (1) above arise regarding to a construction of
sealing a space between the peripheral wall of the
floating tank and pontoonO
(3) The floating roof type oil tank is safer from
a fire than the fixed roof type, and yet is accompanied
with the danger of the so-called rim fire taking place
between the pontoon and the peripheral wall of the oil
tank.
(4) Vapor losses of the stored oil are more promi-
nently reduced than in the fixed roof type oil tank.
However, when the floating roof is made to rise or fallt
then operation losses result from the evaporati~n of oil
deposited on the peripheral wall of the floating roof
type oil tank.
III. Problems arising in common to both types of oil
tank are
(1) the corrosion of the bottom board,
(2) the breakage of the proximity of an annular
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plate due to the irregular sinking of the yround or
earthqnake shocks,
(3) Leaka~e of oil from the tank due to its
sloshing resultiny from an earthquake and outbreak of
resultant fires.
It is accordingly the objèct of this in~ention to
provide a double hull type oil tank system whose inner
tank is immersed in water, and which eliminates the
vapor loss of stored oil and is improved in resistance
to fire, earthquake and weather.
To attain the above~mentioned object, this inven-
tion provides an oil tank system which is constructed by
the steps of:
fixing the peripheral wall of an inner tank whose
lS ceiling is fitted with an oil inlet-outlet pipe to the
bottom board of an outer tank which is open at the top;
connecting the peripheral walls of the inner and
outer tanks by coupling members to provide a double-hull
structure;
fitting a water pipe surrounding the inner tank to
the lower end portion of the outer tank;
mounting an overflow pipe on the upper end portion
of the outer tank;
drilling a port at the lower end portion of the
inner tank to effect communication between the inner and
outer tanks;
and which is designed to store oil in the inner
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tank in a s~ate floatin~ on the water filled in the
outer ~ank.
This invention can be more ~ully understood Erom
the following detailed description when taken in con-
junction with the accompanying drawings, in which:
The figure is a longitudinal sectional view of a
double hull type oil tank system embodying this inven-
tion, whose inner tank is immersed in water.
Description is now given with reference to the
accompanying drawing of a double hull type oil tank
system embodying this invention whose inner tank is
immersed in water. Reference numeral 1 denotes an outer
steel tank which is formed of a bottom board 2 and
peripheral wall 3, is open at the top and is set on a
base mound 4. The bottom board 2 is downward inclined
toward the center. Reference numeral 5 is a water pipe
connected to the center of the bottom board 2 in order
to enable water W to be delivered from a water storage
tank 6 to the outer tank 1 by means of a pump 7. The
pipe 5 is also used to draw off water applied in clean-
ing the inside of the outer tank 1. Reference numeral 8
is a baffle board so positioned as to face the opening
of the water pipe 5 directed to the interior of the
outer tank 1. This baffle board 8 is intended to de~
flect the pumped water W crosswise of the outer tank 1
instead of ejecting said water W straight upward. Re-
ference numeral 10 is an inner steel tank which is
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formed of a peripheral walL :L1 and ceiling 12. This
inner tank 10 is set inside of the outer tank 1. The
lower end portion o-f the peripheral ~all 11 of said
inner tank 10 is fixed to the bottom board 2 of the
outer tank 1. The ceiling 12 of the inner tank 10 is
upward inclined toward the enter. The peripheral wall
11 of the inner tank 10 and the peripheral wall 3 of the
outer tank 1 are connected together at upper and lower
portions by connecting members 13 ormed of annular dia-
phragms whose cross section is shaped like the letter I,thereby providing a double hull type oil tank system.
The web section of the connecting diaphragm member 13 is
drilled with a hole 13a allowing for the passage of
water W. Reference numeral lla is a hole provided at
the lower end of the peripheral wall 11 of the inner
tank 10 to effect communication between the inner and
outer tanks 10 and 1. Reference numeral 15 denotes an
oil inlet-outlet pipe connected to the center of the
ceiling 12 of the inner tank 10. Oil L is let to flow
through said inlet-outlet pipe 15 by means of a pump 1~.
The opening of the inlet-outlet pipe 15 which faces the
ceiling 12 of the inner tank 10 is provided with a
baffle board 8 as in the case of the water pipe 5.
Reference numeral 17 is an air-discharging valve set at
the highest position of the oil inlet-oulet pipe 15.
Reference numeral 18 is an overflow pipe of water W laid
at the upper end portion of the peripheral wall 3 of the
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outer tank 1. Reference numeral lg is a level gauye
disposed at the lower end portion of the peripheral wall
11 of the inner tank 10 to detect a boundary A between
the oil L and water W within the inner tank 10.
While oil L is first taken into the inner tank 10,
the air-discharging valve 17 is left open, and there-
after water W is supplied from the water storage tank 6
to the outer tank 1 by the pump 7, until the water W
overflows from the outer tank 1, thereby causing the
inner tank 10 to be completely immersed in water W.
Then the pump 16 is actuated to draw off air from the
rising portion of the oil in]et-outlet pipe 15. With
the air-discharging valve 17 shut, oil L is taken into
the inner tank 10 with pressure. As a result, the water
W left in the inner tank 10 is forced out by the oil L
introduced with pressure. The boundary A between the
oil L and water W within the inner tank 10 gradually
falls. The water W thus discharged is returned to the
storage tank 6 through the overflow pipe 18. Since the
open end of the oil inlet pipe 15 is provided with a
baffle board 8, the boundary A between the oil L and
water W falls without being disturbed, becuase the oil L
is forcefully spread all around by means of said baffle
board 8 instead of being ejected straight downward.
When the level gauge 19 detects that the boundary A has
fallen to the prescribed level, then the pump 16 is
stopped. Thus the oil L is stored in the inner tank 10
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in a state floating on the ~ater W filled in the outer
tank 1.
Where the stored oil L is cJischaryed, the water
pump 7 is actuated to supply water to the outer tank 1
in a larger amount than that of the discharged oil,
thereby causing the water to overflow through the
overflow pipe 1~. While this condition is maintained,
no void space arises, namely, no negative pressure pre-
vails in the inner tank 10, thereby enabling the inner
tank lO to be always immersed in water W. Under this
condition, the pump 16 is started to discharge oil
through the oil pipe 15. In this case, too, the open
end of the water pipe 5 fitted with the baffle board 8
enables the boundary A between the oil L and water W
within the inner tank 10 to progressively rise without
being disturbed. The second and subsequent steps of
~illing and discharging oil L are taken in the same
manner as described above. Where the maintenance and
cleaning of the inner and outer tanks 10, 1 are per-
formed, oil L is first drawn off by the above-mentioned
process, and then the water left in the outer tank 1 is
drained through the water pipe 5.
The inner and outer tanks 10 and 1 need not be made
of a steel plate, but instead may be prepared from
concrete. Further, both tanks 10 and 1 may be built
underground regardless of the material. The connecting
member 13 for bonding the peripheral walls of both inner
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ancl outer tanks 10, 1 may be provided discontinuously,
instead of beiny mounted all along the peripheral wall
of the inner tank 10. Moreover, the cross section of
said connecting member 13 need not be shaped like the
letter I. Where both inner and outer tanks 10, 1 are
made of concrete, then said connecting member 13 may
also be prepared from concret.
The liquid surrounding the inner tank 10 well ser-
ves the purpose, provided it is uninflammable and
heavier than oil L to be stored. The liquid need not be
limited to water. It is generally sufficient to con-
struct a single water storage tank 6 for each oil
storage base consisting of a group of oil tanks. Water
used to surround the oil tank may be supplied from a
lake, river, or sea. The exi.sting oil tank can be
easily modified into the type embodying this invention.
The double hull type oil tank system of the inven-
tion whose inner tank is immersed in water has the
following advantages:
(1) The peripheral walls of both inner and outer
tanks are bonded together by connecting means to provide
a double hull type. Therefore, the subject oil tank
system has a sufficiently great rigidity, or registance
to wind forces to dispense with the fitting of a wind
girder as has been required for the conventional oil
tank.
(2) Oil is stored in an inner tank in a state
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floatin~ on the water filled in an outer tank. No oil
vapors come out of the inner tank, completely elimi-
nating the vapor loss of the stored oil. Consequently,
problems do not arise which might result from the leak
of oil vapors or explosive caused by oil vapors mixed
with air.
(3) The inner tank which is completely surrounded
with water is very effectively protected from the spread
of an external fire or its own fire damage.
(4) The inner tank is full surrounded by water
heavier than oil. Should, therefore, the inner tank be
damaged, oil only floats on the water held in the outer
tank, and does not leak from the oil tank system. In
case the outer tank is damaged, for example, by an
earthquake shock, the liquid which is first drawn out is
water held in the outer tank. Therefore, the leakage of
oil can be effectively prevented by taking such measures
as transpose the oil of said defective tank to another
safe tank before the ultimate efflux of oil.
(5) The double hull type oil tank system of the
invention whose inner tank is immersed in water elimina-
tes the necessity of fitting a weather hood or seal
which has hither raised problems with the floating roof
type oil tank. Further, no consideration has to be
taken with regard to the seepage of rain into said oil
tank system. Even where the surface portion of the
water f illed in the outer tank happens to be froæen in a
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frigid zone, no dificul.ties arise in the operation of
the subject oil tank system.
(6) should the double hull -type oil tank system as
a whole be shaken vigorously at the occurrence of an
earthquake, the oil held in the inner tank is prevented
from making such a great sloshing as to leak out of said
inner tank.
