UNDERGROUND LIQUID STORAGE

Abstract: Storage system, comprising a plurality of mutually spaced, separate storage tanks (1) located in a surrounding substrate and below the substrate surface, filled with oil (6) floating on ballast water (5) and with a roof (7) movable up and down and a system to maintain the oil surface at a constant level below the surface of the surrounding substrate by adding water to a storage tank from which oil is removed, while the storage tanks are connected to a common buffer reservoir (12).

Description: Underground liquid storage The invention is concerned with a storage system, particularly for liquid. Although herafter the invention is discussed? by way of storage of crude oil, it is appreciated that the invention is not limited to said field of application. E.g. storage of other chemical liquid is also feasible. Also storage of solid elements is feasible. "Concrete" also means here other poured and cured stone like material. "Substrate" means here the liquid (such as water) or solid (such as soil) material surrounding the storage tank. "Filling material" means here any liquid or solid matter or mixtures thereof, with which the storage tank is filled. From practise it is already known from long ago, to store crude oil in e.g. a harbour area within a plurality of spaced storage tanks standing next to each other above the ground and shaped like upright, thin walled steel cylinders with a fill height of about 10 meters and a diameter of about 30 meters. The object of the invention is to improve this known storage. This object is met by the storage system according to the annexed claim 1. In this way, the following advantages are obtained compared to the known storage system above the ground: With unchanged (fire) safety the storage tanks can stand closer to each other, such that the required surface is smaller; Alternative construction materials, such as concrete, come available; The storage tanks can be designed with a substantial larger height, such that the storage capacity can be increased while the used substrate surface is unchanged; - It is not required to take account of the risk of bursting of the storage tanks, such that a surrounding dike is not required. The storage tanks preferably have one or more of the following features: they are each at least substantially equally shaped and/or dimensioned (e.g. a diameter and a height of more than 15 meters and/or a volume of at least 25,000 m 3 ) ; they are arranged according to an at least substantially regular pattern as viewed from above; they are at least substantially cylindrical; they are at least substantially upright; their upper edge ends at least substantially at the same level as the surrounding substrate; they have at least substantially liquid tight and/or gas tight external walls; they have a fixed bottom wall and from there upward extending, at least substantially liquid teigth and/or gas tight to said bottom wall connected fixed side walls at least substantially liquid teigth and/or gas tight connected to each other; The side walls are thin walled; they are located in a sandy substrate (i.e. no undeformable substrate, such as rock, but a preferably granule like substrate that is easy to dig, such as sand, clay, peat, gravel or a mixture thereof and possibly added thereto other preferably small granule components such as minerals and/or ground water); at least over their complete height below substrate level their side walls bear against the surrounding substrate; they have a top wall movable in height, preferably at least substantially liquid tight and/or gas tight connecting to the side walls; At least substantially all of them are at least partly filled with the same storage goods, such as (crude) oil; At least substantially all of them are at least partly filled with the same ballast material, such as water; the bottom wall is made of concrete mixed with weightening material, such as ore, to increase the specific weight and resistance against buoyancy capacity of the liquid surrounding the storage tank; the bottom wall is made from concrete with on top of it a layer of bulk stone to increase the resistance against buoyancy capacity of the liquid surrounding the storage tank; the bottom wall is below the (ground) water level, preferably at least 10 meters below (ground) water level; if made from concrete, at least the upper part of the side walls contains armouring; the top edge of the side walls is made from structural concrete. It is appreciated that according to the present invention the storage goods are preferably at least substantially completely stored below substrate level, such that the storage tanks can be arranged with a closer spacing without decreasing the (fire) safety. However, the invention features that a part, preferably a small part, of the storage tank projects above substrate level. On the one hand this is acceptable from the point of (fire) safety, as long as it is sure that the storage goods are not stored in this part of the storage tank projecting above the substrate level. On the other hand it is expected that when storing above substrate level over a height that is substantially smaller than the usual fill height of 10 meters with known storage tanks standing completely above the ground (to be axpected one or several meters but preferably not more than about three meters), the (fire) safety is at Tieast substantially not decreased. It is prefered if in each storage tank the level of the fill material is at least substantially continuously close to the surface of the surrounding substrate and/or (ground) water level or the upper edge of the storage tank, or is substantantially continuous, e.g. fluctuating over a height smaller than about 10%, more preferably smaller than about 5% of the height of the side walls of the storage tank (which means in practise mostly that said fluctuation is no more than one or several meters). The storage system can therefor be equipped with convenient level detection and/or level adjustment means to e.g. automatically supply to and/or remove from the storage tank fill material if a change of fill material level is detected in said storage tank, and this possibly only after exceeding a predetermined treshold difference value. The level adjustment means can have at least one fill material feed and/or discharge line, extending externally from and debouching into the storage tank. The storage tank is e.g. filled with a first fill material, that can serve as ballast material, such as a first liquid, such as water, and a therefrom separated (e.g. in that the first liquid floats on the second liquid, or vice versa) or easily separatable (e.g. solid matter) second fill material, which can be a storage good, such as a second liquid, such as (crude) oil, wherein when the second fill material is fed to the storage an at least substantially equally large volume of the first fill material is discharged therefrom, and vice versa. In this connection it is prefered that the storage tank is provided with a first feed and/or discharge means, such as a line, coming externally from the storage tank and (possibly at a first, low level above the bottom wall) supplying or discharging fill material (e.g. the first liquid) to respectively from (e.g. debouching in) the storage tank, such as debouching in the liquid of largest specific weight, and a second feed and/or discharge means, such as a line, coming externally from the storage tank and (possibly at a second, higher level above the bottom wall) supplying or discharging fill material (e.g. the second liquid) to respectively from (e.g. debouching in) the storage tank, such as debouching in the liquid of smaller specific weight. This maintaining of fill material level in the storage tank offers several advantages. One is that the fill material offers counter pressure to the substrate surrounding the storage tank, such that the storage tank structure always bears low loads, such that structural saving are possible. E.g. the side walls can be designed such that they have merely a separating and no bearing function. On the other hand the liquid and/or gas sealing of the top side of the storage tank (e.g. when applying a top wall floating on the liquid) can be designed more reliable. In stead of or in addition to the second fill material (such as the second liquid) the storage tanks can contain storage godds in solid shape, such as containers that can be filled with liquid. It is e.g. feasible that the storage tank contains a plurality of sealed bags, filled with the second liquid which can be removed from the storage tank by e.g. a hoist. Particularly in case of storage goods in solid shape one can imagine that the first liquid surrounds said storage goods at least substantially on all sides. According to an alternative application of storage of goods in solid shape, a heavy ballast material, such as ore, is poured onto the bottom wall, to avoid buoyancy of the storage tank. The storage goods are present within the space above said ballast material. If the side walls are designed strong enough such that they can resist the surrounding (ground) water pressure, it is not required that the space within the storage tank above the bottom wall is filled with the counter pressure generating liquid, such that the storage goods in solid shape can be stored dry. The storage tanks preferably has at a distance above the bottom wall a top wall located above and preferably bearing on the fill material, such as the storage goods, and which connects liquid and/or gas tight to the side walls, preferably through sealing means. To make sure that the top wall can move up and down without loosing the sealing, it is prefered that the sealing means are sealin- gly active over a height area of the storage tank. For a reliable sealing, mutually at least substantially liquid and/or gas tight connected sealing side walls can at least substantially liquid and/or gas tight connect to the radial circumference of the top wall floating on the liquid in the storage tank and extending at a distance from the storage tank side walls over a substantial height of at least 25%, preferably 50%, more preferably 75% of the storage tank height towards the bottom wall and projecting into the fill material (particularly the liquid in the storage tank). This embodiment is further more detailed by a prefered embodiment shown in the drawings. To maximally save the environment it is prefered that the storage tanks are connected via a line system to a preferably common reservoir, sealed from the environment and wherein first fill material, such as the ballast li- quid, coming from the storage tanks is stored temporarily to be refed into the storage tanks at a later mement in time. In this way it is not required that the first fill material, such as water, which is removed by refilling the storage tank with storage goods, such as oil, is directly drained to e.g. the open water of the sewer. Said reservoir preferably has such a capacity that only under extreme conditions not all first fill material coming from the storage tanks can be stored therein. In such extreme situation a small volume of the first fill material from the storage tanks must be drained, after cleaning, for which the reservoir is connected to a purification device. To avoid or minimising leaking of contents of a stora- ge tank into the environment without putting high demands on the liquid tightness of walls of the storage tank, it is prefered that of each storage tank the part below substrate level is at least substantially surrounded by liquid, e.g. ground water, at least substantially to the fill material level and/or substrate level. In this connection it is prefered that at least substantially at any location along the height of the storage tank at or below the fill material level the fill material pressure is lower than the substrate material pressure. This requirement is at least sufficed, if the liwuid level within the storage tank as at the same level as, or below the level of the liquid surrounding the storage tank, wherein said level difference is preferably at least 25 cm, more preferably at least about 50 cm, such as about 1 meter. To be able to check the leak tightness of the storage tank in a reliable manner it is prefered to provide around the storage tanks and below the subtstrate level suction means, such as suction nozzles connected to suction lines. To increase the reliability of the leak detection the location of these suchtion means is preferably such that all or almost all liquid (such as ground water) flowing along the storage tank passes these suction means. Without undue burden, this location can be found by trail and error. These suction means are preferably connected to a reservoir in which the sucked away liquid can be collected. Preferably each storage tank has a means to remove settlement (so called sludge) therefrom without the requirement that the storage tank must be deactivated. According to a prefered embodiment means are provided to remove a layer present on top of the bottom wall. These means can comprise one or more of the following; at least a suction nozzle debouching in the storage tank close to the bottom wall and to suck up said layer; at least one jet nozzle debouching in the storage tank close to the bottom wall (e.g. within the upper face thereof or just therebelow or thereabove) with which said layer can be forced towards at least on predetermined location (such as the location of the suction nozzle) ; a sufficiently slanting (e.g. at least 0.5°) embodiment of the upper face of the bottom wall, such that gravity at least promotes to force said layer towards at least one predetermined location (such as the location of the suction nozzle). Now the invention is further illustrated by virtue of non-limiting embodiments, refering to the enclosed dra- wings, in which: Fig. 1 is a top view of the invented storage system; Fig. 2 is a sectional side view of one of the storage tanks of the inventive storage system; and Fig. 3 is a view according to fig. 2 of an alternati- ve. The storage system shown in fig. 1 comprises a plurality of mutually spaced storage tanks 1 in a regular pattern. As fig. 2 shows, each storage tank 1 stands upright in a hole in the ground 2. The storage tank 1 has a storage space delimited by a bottom wall 3 and therefrom upward extending side walls 4 ending just above the ground surface 2. The lower part of the storage tank 1 is filled with water 5 and on top of it oil 6 floats. The level of the oil 6 is just below the ground water level 8. On top of the oil 6 a top wall 7 floats, with which the storage space of the storage tank 1 is closed at its top side. To ensure the liquid and gas tight sealing between the top wall 7 and the side walls 4, an easily deformable part 9 extends between the top wall 7 and the side walls and is fixed to both the top wall 7 and the side walls 4. This deformable part 9 allows some movement up and down of the top wall 7 such that it can follow the small fluctuations of the level of the oil 6. In this example the part 9 is an easily pleada- ble web. According to an alternative this part 9 can be a very elastic stretchable web. In stead of the deformable part 9 a narrow slide fitting as a sealing means between the side walls 4 and the top wall 7 can be provided over the (limited) height part over which the top wall 7 moves up and down. A feed and/or discharge line 10 for the water 5 debouches into the storage tank 1 at a low level. A feed and/or discharge line 11 for oil 6 debouches into the storage tank 1 at a high level and is designed to move with the top wall 7. The line 10 is connected to a buffer reservoir 12 which connecs through a line 13 to a water purification device 14 from which water can be drained. A level detector (not shown) detects the level of the top wall 7 and generates a corresponding signal to a level control unit (not shown). Depending on the detected level of the top wall 7, water from the buffer reservoir 12 is fed to the storage tank 1 or is discharges therefrom to keep the top wall 7 within the desired level range. Fig. 3 shows how sealing side walls 15 extend downward from the top wall 7 and end at a short distance above the bottom wall 3. The space between the side walls 4 and the top wall 7/sealing side walls 15 is filled with water 5. As a consequence, it is no longer required that the line 10 debouches into the storage tank 1 at a low level. According to another embodiment the top wall 7 is located at a fixed distance from the bottom wall 3. Also further alternatives belong to the invention. It is e.f. feasible that the storage system consists of one single storage tank as described above.

Claims: CLAIMS 1. Storage system, comprising a plurality of at least two, preferably at least three, such as four or at least five or at least six, mutually spaced separate storage tanks (1) located in surrounding substrate (2, 8), said tanks (1) being present over at least 50%, preferably at least 75%, more preferably at least about 90% of their height, such as completely, below substrate level, wherein preferably the distance between two adjacent storage tanks measures about 75 meters, preferably 50 meters, more preferably 30 meters, to a maximum, or is less than half the diameter of a storage tank. 2. System according to claim 1, wherein the storage tanks are located in a sandy soil substrate. 3. System according to claim 1 or 2, wherein the storage tanks bear against surrounding substrate, such as ground water, over at least their complete height below substrate level. 4. System according to claim 1, 2 or 3, wherein the storage tanks comprise a top wall (7) movable up and down, preferably floating on the fill material within the storage tank and/or comprising sealing means (9, 15) to avoid undesired escape of storage goods (6) along the top wall. 5. System according to claim 4, wherein a wall (15) extends downward from said top wall (7) to delimit below the top wall a storage room spaced from the storage tank side wall (4) . 6. System according to claim 1, 2, 3, 4 or 5, comprising a system for maintaining the surface of the fill material within the storage tanks at an at least substantial constant level, preferably such that at at least substantially each level de pressure exerted by the fill material within the storage tanks on the storage tank wall (3, 4) is lower than the pressure exerted on the storage tanks by the substrate surrounding the storage tanks. 7. System according to claim 7, wherein the fill material surface within the storage tanks is at the same level as, or lower than, the surface of the substrate surrounding the storage tank, wherein said level difference is preferably at least 25 cm, more preferably at least about 50 cm, such as a meter, 8. System according to claim 6 or 7 , wherein said level maintaining system is designed to feed ballast material, such as water, to a storage tank from which storage goods, such as crude oil, is removed, or vice versa. 9. System according to claim 1, 2, 3, 4, 5, 6, 7 or 8, wherein the storage tanks contain a first liquid and on top of it a second liquid. 10. System according to claim 1, 2, 3, 4, 5, 6, 7, 8 or 9, wherein the storage tanks are connected to a preferably common ballast material (5) buffer reservoir (12), preferably connected to a discharge of superfluous ballast materi- al through a purification device (14).

Inventors: VAN T ZELFDE WILLEM DANIEL ANT, VAN 'T ZELFDE, WILLEM, DANIEL, ANTHONY
Applicants: T ZELFDE WILLEM DANIEL ANTHONY, WEGER ARCHITECTEN EN INGENIEUR, DE WEGER ARCHITECTEN- EN INGENIEURSBUREAU BV, VAN 'T ZELFDE, WILLEM, DANIEL, ANTHONY
Application year: 2000
Main classification: B65D88
IPC codes: B65D88