NZ199710A - Double walled oil tank:oil floats on water on inner tank,which is immersed in water - Google Patents

Description

199710 | Prfci'sly D.zi.. Ah P.'.V....

CorrrJ^ia "cation FiSed: c^„. &b&3> tt/oZJB Pub!icaiioji Dats: ..... 1^.5.... rj ~i ioL(o(s |l '.?» V'_y>. • ;>/ c*«»**«iaaaaaaaat '. - * 1 FEBJ982 >&CEIVED Patents Form No.5 NEW ZEALAND PATENTS ACT 1953 COMPLETE SPECIFICATION "A DOUBLE HULL TYPE OIL TANK SYSTEM WHOSE INNER TANK IS IMMERSED IN WATER" S-,WE NIPPON KOKAN KABUSHIKI KAISHA, of 1-2, 1-chome, Marunouchi, Chiyoda-ku, Tokyo, Japan, a Japanese corporation, hereby declare the invention, for which -I/we pray that a patent may be granted to me/us,,and the method by which it is to be performed, to be particularly described in and by the following statement:— ~ \ (fottovf** bY pa£e 1 19971 t , - lQ- Background of the Invention 1. Field of the Invention This invention relates to a double hull type oil tank system whose inner tank is built in an outer tank 5 filled with water and wherein oil is held in said inner tank in a state floating on the water. 2. Description of the Prior Art When distinguished by the roof structure, the conventional cylindrical oil tanks can be classified into 10 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 is provided with a ventilation 15 valve. The tank itself 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 20 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. 19971 t , 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. (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 technique 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 pontoon. (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 prominently reduced than in the fixed roof type oil tank. However, when the floating roof is made to rise or- fall, then operation losses result from the evaporation of oil deposited on the peripheral wall of the floating roof type oil tank. 199710 III. Problems arising in common to both types of oil tank are (1) the corrosion of the bottom board, (2) the breakage in the proximity of an annular 5 plate due to the irregular sinking of the ground or earthquake shocks, (3) Leakage of oil from the tank due to its sloshing resulting from an earthquake and outbreak of resultant fires.

Summary of the Invention It is accordingly the object of this invention 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 15 to fire, earthquake and weather.

The present invention thus provides a double hull type oil tank system comprising an inner tank immersed in water and an outer tank, and 20 wherein: the peripheral wall of the inner tank has a closed top fitted with an oil inlet-outlet pipe, and the wall of the inner tank is attached to the bottom of the outer tank which is open at the top, the peripheral walls of the inner and outer tanks are connected by coupling members to provide a double hull structure, a water pipe is fitted to the bottom of the outer ' 199710 tank for supplying water to the bottom of the inner tank, the inner tank and the outer tank sharing a common bottom, an overflow pipe is mounted on the upper end portion of the outer tank, a port at the lower end portion of the inner tank effects communication between the inner and outer tanks, and whereby: oil stored in the inner tank floats on water.

Brief Description of the Drawing The figure is a longitudinal sectional view of a double hull type oil tank system embodying this invention, whose inner tank is immersed in water.

Detailed Description of the Preferred Embodiment 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 cleaning 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 ■; 9971 o outer tank 1. This baffle board 8 is intended to deflect the pumped water W crosswise of the outer tank 1 instead of ejecting said water W straight upward. Reference .numeral 10 is an inner steel tank which is 5 formed of a peripheral wall 11 and ceiling 12. This inner tank 10 is set inside of the outer tank 1. The lower end portion of the peripheral wall 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 10 upward inclined toward the center. 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 formed of annular diaphragms whose cross section is shaped like the letter I, 15 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 11a is a hole provided at the lower end of the peripheral wall 11 of the inner 20 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 16. The opening of the inlet-outlet pipe 15 which faces the r.3 ceiling 12 of the inner tank 10 is provided with a Cj I £ <?/ baffle board 8 as in the case of the water pipe 5. !99710 , J H 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 5 outer tank 1. Reference numeral 19 is a level gauge 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, 10 the air-discharging valve 17 is left open, and thereafter 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. 15 Then the pump 16 is actuated to draw off air from the rising portion of the oil inlet-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 20 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 25 baffle board 8, the boundary A between the oil L and water W falls without being disturbed, becouse the oil L is forcefully spread all around by means of said baffle 19971 , & h 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 5 in a state floating on the water W filled in the outer tank 1.

Where the stored oil L is discharged, the water pump 7 is actuated to supply water to the outer tank 1 in a larger amount than that of the discharged oil, 10 thereby causing the water to overflow through the overflow pipe 18. While this condition is maintained, no void space arises, namely, no negative pressure prevails in the inner tank 10, thereby enabling the inner tank 10 to be always immersed in water W. Under this 15 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 20 being disturbed. The second and subsequent steps of filling 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 performed, oil L is first drawn off by the above-mentioned 25 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 199 71 ' * " - 8 - 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 5 and outer tanks 10, 1 may be provided discontinuously, instead of being 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 10 made of concrete, then said connecting member 13 may also be prepared from concrete.

The liquid surrounding the inner tank 10 well serves the purpose, provided it is uninflammable and heavier than oil L to be stored. The liquid need not be 15 limited to water. It is generally sufficient to construct 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 existing oil tank can be 20 easily modified into the type embodying this invention.

The double hull type oil tank system of the invention whose inner tank is immersed in water has the following advantages: (1) The peripheral walls of both inner and outer 25 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 resistance 19971 . d r 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 floating on the water filled in an outer tank. No oil vapors come out of the inner tank, completely eliminating 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 10 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 fully 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 20 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 eliminates the necessity of fitting a weather hood or seal which has hither raised problems with the floating roof « A j 1997 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 filled in the outer tank happens to be frozen in a 5 frigid zone, no difficulties 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 10 from making such a great sloshing as to leak out of said inner tank. 199710 - ii -

Claims (4)

WHAT WE CLAIM IS;

1. A double hull type oil tank system comprising an inner tank immersed in water and an outer tank, and wherein: the peripheral wall of the inner tank has a closed top fitted with an oil inlet-outlet pipe, and the wall of the inner tank is attached to the bottom of the outer tank which is open at the top, the peripheral walls of the inner and outer tanks are connected by coupling members to provide a double hull structure, a water pipe is fitted to the bottom of the outer tank for supplying water to the bottom of the inner tank, the inner tank and the outer tank sharing a common bottom, an overflow pipe is mounted on the upper end portion of the outer tank, a port at the lower end portion of the inner tank effects communication between the inner and outer tanks, and whereby: oil stored in the inner tank floats on water.

2. A double hull type oil tank system whose inner tank is immersed in water and which is constructed by the steps of: fixing the peripheral wall of an inner tank whose closed top is fitted with an oil inlet-outlet pipe, and the wall of the inner tank is attached to the bottom 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 ' 199710 - 12 - hull structure; fitting a water pipe for supplying water to the bottom of 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 in the lower portion of the inner tank to effect communication between the inner and outer tanks; and which is designed to store oil in the inner tank floating on water.

3. A double hull type oil tank system which comprises an inner tank whose peripheral wall is provided at the lower end with a communication hole to an outer tank whose upper portion is left open, said tank system having the inner tank immersed in water and with oil in the inner tank, floating on the water held in the inner tank.

4. A double hull type oil tank system whose inner tank is immersed in water, substantially as hereinbefore described with reference to the accompanying drawing. Baldwin, son & carey . attorneys for the applicants