EP0796211A1

EP0796211A1 - Variable volume sealed container for storing liquids

Info

Publication number: EP0796211A1
Application number: EP95941762A
Authority: EP
Inventors: Lorena Grundrich
Original assignee: Individual
Current assignee: Individual
Priority date: 1994-12-13
Filing date: 1995-12-05
Publication date: 1997-09-24
Anticipated expiration: 2015-12-05
Also published as: DE69505272D1; AU4307496A; EP0796211B1; WO1996018559A1; CA2205000A1; FR2727943A1; DE69505272T2; JPH11506408A; ATE171918T1; FR2727943B1

Abstract

Variable volume container composed of essentially rigid elements ensuring superior airtightness and a sealed environment, in particular for preserving liquids and preventing any contact with the air. A lower element (1) of the container comprises a tank (14) into which is poured a liquid of variable volume to be stored (15), and a sealing envelope (16) surrounding the tank and containing a steady volume of a second liquid (17). An upper element (2) comprises a cover (20) which floats on the stored liquid, and a vertical skirt (24) which dips into the sealing envelope. The upper element (2) rises and descends with the level of stored liquid and traps an intermediate gas (29) between the two liquids (15 and 17). The container of the invention is useful for storing and/or carrying liquid products, in particular, beverages, hydrocarbons, waste water and farm effluents.

Description

WATERPROOF TANK WITH VARIABLE VOLUME FOR THE STORAGE OF A LIQUID

The present invention relates to a sealed variable volume tank for storing a liquid.

Such a tank can be intended for the storage and possibly for the transport of all kinds of liquid products, in particular those whose contact with the atmosphere must be avoided, for example for reasons of hygiene, conservation, security and protection of the environment. This is the case in particular for drinks or other liquid food products such as drinking water, mineral water, milk, or hydrocarbons presenting risks of evaporation, pollution or explosion, or even liquids which must be kept away from air to avoid their oxidation, such as fruit juices or wine, or to avoid the emission of odors as is the case with slurry.

In such cases, the use of a constant volume tank can cause problems because of the volume of gases which varies in the tank when the volume of the stored liquid varies. It is then necessary to specially treat the volumes of gas entering or leaving the tank, or to store them separately if it is for example an inert gas. The use of a variable volume tank such as a flexible tank makes it possible to avoid most of these problems, but may present other well-known difficulties, related to the materials, the stability and the durability of the flexible walls. .

Document FR-A-2 385 612 describes a tank for the storage of hydrocarbons at almost constant volume. This tank has around the upper part of the tank a sealing cavity containing water. It also includes a floating roof which rests directly on the hydrocarbon and extends beyond the wall of the tank to end in a peripheral part which plunges into the sealing cavity. This reservoir is at constant volume thanks to an increase in the volume of water on which the hydrocarbon rests to compensate for the decrease in the volume of hydrocarbon. Thus, the floating roof moves very little. Its sliding along the tank is also limited by the length of the heating devices used to thin the hydrocarbon. This reservoir has drawbacks, in particular the mixing the water with the hydrocarbon and the impossibility of completely emptying the tank since it is necessary to maintain a constant volume.

The patent US-A-1 823 256 also describes a tank for hydrocarbons almost constant volume comprising in its upper part an annular cavity filled with water. The tank also has a floating cover supported on the hydrocarbon and extended by a vertical skirt which plunges into said cavity. This device works thanks to a balance established between the hydrocarbon and the EA which are in contact in the annular cavity. The seal is therefore not respected. In addition, the annular cavity being limited in height prevents the floating roof from sliding downwards and from remaining in contact with the fluid if the level drops. This arrangement therefore has the drawbacks of bringing the water into contact with the stored fluid and always requiring a constant volume.

The present invention aims to avoid these drawbacks, by creating a variable volume tank which consists of essentially rigid elements, ensures excellent tightness with respect to the atmosphere and great security with respect to the risks of pollution of the product or environment and allows, if necessary, to keep the stored liquid away from contact with air.

To this end, the invention relates to a reservoir of the type indicated in the preamble, characterized in that it comprises a lower element, forming a tank open upwards and arranged to contain a variable volume of the liquid to be stored, called the first liquid. , and an upper element mounted on the lower element so as to ensure a tight closure of the tank and to slide vertically when the volume of first liquid varies, in that the lower element comprises, around the tank, a jacket seal open upwards and containing a second liquid between two peripheral walls, in that the upper element comprises a floating cover, pressing on the first liquid directly or through a gas, and a vertical skirt integral with the cover and immersed in the second liquid in the sealing jacket, and in that an intermediate gas is retained captive in the upper element by free surfaces respec tives of the first and second liquid.

Thus, the upper element of the tank can move up and down like the bell of a gasometer, but these movements are directly dictated by the variations in the level of the first liquid stored in the tank. At the same time, the upper element, the construction of which can be entirely rigid, guarantees an appropriate and lasting seal against the atmosphere, thanks to its skirt permanently immersed in the second liquid. Finally, the presence of an intermediate volume of gas acting as a buffer between the free surfaces of the first and of the second liquid inside the upper element, and which can have a substantially constant volume, makes it possible on the one hand to avoid any contact between the two liquids and, on the other hand, to avoid contact of the first liquid with air or oxygen, if this intermediate gas is a neutral gas, for example nitrogen.

In a particularly advantageous embodiment when the first liquid presents a danger of environmental pollution, the sealing jacket also extends below the tank so as to completely surround the tank, except upwards.

Preferably, said peripheral walls comprise an inner peripheral wall, separating the sealing jacket from the interior of the tank, and an outer peripheral wall having an upper edge situated lower than an upper edge of the inner peripheral wall.

In a preferred form, the floating cover may have a bottom and a peripheral wall extending upwards from this bottom and sealingly connected to an upper edge of the skirt. The bottom of the floating cover can rest directly on the first liquid. The bottom of the floating cover can be convex down or convex up.

For applications where it is desirable to avoid contact between the cover and the first liquid, provision may be made for the intermediate gas to extend between the first liquid and the bottom of the floating cover and support the upper element.

In a first embodiment of the means for filling and emptying the tank, these may comprise at least one pipe passing under the tank and opening into the tank through a bottom thereof. In another form, these can comprise at least one pipe mounted on the upper element and opening into the tank through the floating cover.

Other characteristics and advantages of the present invention will appear in the following description of various exemplary embodiments, presented without implied limitation with reference to the appended drawings, in which:

FIG. 1 is a schematic view in vertical section of a first embodiment of a tank according to the invention, when the tank is full,

FIG. 2 represents the reservoir of FIG. 1 when it is practically empty,

FIG. 3 represents a variant of the embodiment according to FIG. 1, where the intermediate gas buffer also extends between the upper element and the stored liquid,

FIG. 4 represents another variant of the embodiment according to FIG. 1,

FIG. 5 is a view similar to FIG. 2 and represents a variant of double-jacketed tank offering increased security,

FIGS. 6 to 8 are schematic plan views showing different possible forms of a tank according to the invention, and

- Figure 9 is a schematic view in vertical section of two twin tanks.

Referring to Figures 1 and 2, the reservoir shown mainly consists of a stationary lower element 1 and an upper element 2 mounted on the lower element so that it can slide vertically along the double arrow A The two elements 1 and 2 are of rigid construction, preferably metallic, they are preferably cylindrical, but other shapes are possible as will be described later. The lower element 1 has a slightly conical sealed bottom 10, an inner peripheral wall 11 connected to the bottom 10, an outer peripheral wall 12 and an annular bottom 13 sealingly connecting the walls 11 and 12. The bottom 10 and the wall 11 together form a cylindrical tank 14 containing a variable volume of a first liquid 15 which is the liquid to be stored in the tank. Around the tank 14, the walls 11 and 12 and the annular bottom 13 together define a narrow annular sealing jacket 16, which does not communicate with the interior of the tank and in which is placed a constant volume of a second liquid 17 serving as sealing liquid. The external peripheral wall 12 has an upper edge 18 situated a little lower than the upper edge 19 of the internal peripheral wall 11, in order to prevent any risk of accidental spillage of the sealing liquid 17 inside the tank 14.

The upper element 2 has a cover 20 which closes most of the upper opening of the tank 14 and floats on the first liquid 15 contained in this tank. The cover 20 comprises a circular bottom 21 and a cylindrical peripheral wall 22. The bottom 21 is convex downwards, for example conical, to avoid retaining gas under it II can be provided with an inspection hatch 23 closing so waterproofs a manhole intended for access for maintenance work. The peripheral wall 22 is surrounded externally by a cylindrical skirt 24 to which it is tightly connected by an upper ring 25 which can support a roof 26 (shown diagrammatically) if the tank is used in the open air. The skirt 24 slides inside the jacket 16, where its lower edge 27 is permanently immersed in the sealing liquid 17, which prevents any passage of gas in one direction or the other between the interior and outside the tank. The wall 22, the ring 25 and the skirt 24 define an annular chamber 28 in which an intermediate volume of gas 29 is retained, this gas being in contact with the upper surface 30 of the first liquid 15 and the upper surface 31 of the second liquid 17 inside the chamber 28. The intermediate gas 29 can for example be air or a neutral gas such as nitrogen. It is preferably at a pressure close to atmospheric pressure, so that the free surface 32 of the second liquid 17 outside the skirt 24 is substantially at the same level as the surface 31 of this same liquid inside of the skirt. The chamber 28 can be connected to a decompression sniffer 34, making it possible to adjust the pressure of the intermediate gas 29 and being able to be connected to a supply or accumulation tank for this gas (not shown). Known level detection means can be installed in the sealing jacket 16 to monitor the levels of the surfaces 31 and 32. In the example of FIGS. 1 and 2, the liquid to be stored 15 is introduced into the tank 14 and withdrawn from this tank via a pipe 35 connected to the bottom point 36 of the bottom 10 of the tank and provided with a valve 37 or d other means of control. When the volume of the stored liquid 15 is increased or decreased, the upper element 2 moves to the same extent as the upper surface 30 of this liquid, while its skirt 24 slides in the outer jacket 16 where it can be guided by guide members such as slides or rollers (not shown). Thus, these guide members are protected from the stored liquid 15 and can be lubricated by the sealing liquid 17. The level and the volume of the stored liquid 15 are therefore visible directly from the position of the upper element 2. To support the upper element 2, the pressure to be exerted by the stored liquid 15 on the bottom 21 of the cover

20 does not need to be high, given the large surface of the cover. In large metal tanks, a pressure of less than 10 kPa (0.1 bar) is sufficient, i.e. the cover 20 sinks slightly into the stored liquid 15, depending on the surface and the weight of the cover float. An overpressure of the intermediate gas in the annular chamber 28 is not necessary.

If the upper element 2 must withstand significant forces due to the wind, it can be envisaged to guide it by sliding in an external structure comprising vertical posts fixed to the outside of the external wall 12. This structure can then support the roof possible 26. Instead of this structure, it is also possible to envisage a central guide post, extending from the bottom of the tank and overlapped by a sealed protuberant part provided in the center of the cover 20.

In the position shown in Figure 2, the tank 14 is practically empty and the bottom

21 of the cover can rest on the bottom 10 of corresponding shape of the tank. For maintenance work, it is possible to empty the tank by gravity, lift the upper element 2 by injecting compressed air through the pipe 35 or the sniffer 34, then hang this element 2 on the upper edge. 19 of the lower element by means of appropriate locks, which makes it possible to release the air pressure and to open the hatch 23 to access the tank.

When the tank is emptied, in order to avoid creating a vacuum between the bottom 10 of the tank and the bottom 21 of the cover, a mechanical system (not shown) is provided to ensure the closing of a flap or valve (not shown) mounted on the pipe 35 in order to stop the flow of the liquid. One can also provide an indirect control device for closing this valve by means of an end-of-stroke detector which indicates the bottom of the tank and electrically controls the closing of the valve.

The example shown in Figure 3 is similar to that of Figure 1, except that a mattress 40 of the intermediate gas 29 is held between the stored liquid 15 and the bottom 21 of the cover in order to prevent contact between them In this case, the bottom 21 is preferably flat or convex upwards. The intermediate gas 29 is subjected to the pressure supporting the upper element 2, for example 10 kPa with may ηιm _; which corresponds to a difference in level of a maximum of one meter between the surfaces 30 and 31 of the sealing liquid 17 if it has the density of water.

In the example of FIG. 4, the filling or withdrawal of the liquid from below by means of the pipe 35, according to FIGS. 1 and 2, is replaced by a filling or pumping of the stored liquid from above, by means of 'a pipe 42 mounted on the upper element 2 and opening into the tank through the bottom 21 of the cover, which is convex upwards in this case. For the rest, the construction and the operation of the tank are the same as in the example of FIGS. 1 and 2.

In the variant illustrated in FIG. 5, the sealing jacket 16 also extends under the bottom 10 of the tank, by virtue of a second sealed flat bottom 44 located at a small distance below the bottom 10. This results a double safety envelope all around the tank. This provision is especially useful to guarantee the maintenance and control of the seal between the tank and the environment in the case of storage of polluting liquids, such as hydrocarbons. The second liquid 17 can be a non-polluting liquid, such as water, and any leakage of the first liquid into the second will be easily detected. The double jacket also offers a more secure seal in the opposite direction, between the environment and the inside of the tank. In all cases, it is possible to choose and control at will the composition of the intermediate gas 29 which is in contact with the two liquids.

The plan shape of the tank according to the invention can be arbitrary, depending on the specific conditions such as its size, the materials used, the space available and whether the tank is buried or not. Figures 6 to 8 show some examples of plan shapes. The circular shape of the elements 1 and 2 according to Figure 6 is generally preferred from the construction point of view. The bottom of the cover 20 can be conical, but also curved, faceted or even flat. In the rectangular shape shown in FIG. 7, the bottom of the cover 20 is preferably pyramidal, as in the oval shape with two straight sides in FIG. 8.

In the cases where they have certain right sides, two or more reservoirs according to the invention can be juxtaposed and associated as shown in FIG. 9, so that their sealing sleeves 16 have a common part 16 'between the respective interior walls. 11 of the two tanks. It follows that the vertical outer envelope is formed by an outer wall 12 common to the two reservoirs, and that the sealing liquid is also common to them. This does not pose a level problem since the level of the liquid stored in each tank can vary without modifying the level of the sealing liquid.

Reservoirs according to the invention can be produced in any size and with any waterproof material, and can be used for all kinds of applications, especially those which require a tight separation between the stored liquid and the atmosphere. Apart from the applications already mentioned for the storage of liquid food products, hydrocarbons or chemicals, an interesting application may be that of the storage and transport of mineral water in order to deliver it in bulk to consumers. In countries where regulations prohibit two successive packages of these waters before retailing, the use of a tank according to the invention would make it possible to avoid the high costs of transporting and storing bottled water.

The present invention is not limited to the embodiments described, but extends to any modification and variant obvious to a person skilled in the art.

Claims

claims

1. Watertight variable volume tank for the storage of a Uquide, comprising a lower element (1), forming a tank (14) open upwards and arranged to contain a variable volume of the Uquide to be stored, known as the first Uquide (15 ), and an upper element (2) mounted on the lower element so as to ensure a tight closure of the tank and to slide vertically when the volume of the first Uquide varies, characterized in that the lower element (1) comprises, around the tank (14), a sealing jacket (16) extending over the entire height of the tank, open upwards and containing a second Uquide (17) between two peripheral walls (11, 12), in that the upper element (2) comprises a floating cover (20), resting on the first Uquide directly or through a gas, and a vertical skirt (24) of the cover, extending over a height substantially equal to the height of the tank and plunging into the cond Uquide (17) in the sealing jacket (16), and in that an intermediate gas (29) is retained captive in the upper element by respective free surfaces (30, 31) of the first and second Uquide .

2. Tank according to claim 1, characterized in that the sealing jacket (16) also extends below the tank (14) so as to completely surround the tank, except upwards.

3. Tank according to claim 1 or 2, characterized in that said peripheral walls comprise an inner peripheral wall (11), separating the sealing jacket (16) from the interior of the tank (14), and a peripheral wall outdoor

(12) having an upper edge (18) located lower than an upper edge (19) of the inner peripheral wall (11).

4. Tank according to one of the preceding claims, characterized in that the floating cover (20) has a bottom (21) and a peripheral wall (22) extending upwards from this bottom and tightly connected to an upper edge of the skirt (24).

5. Tank according to claim 4, characterized in that the bottom (21) of the floating cover (20) rests directly on the first Uquide (15).

6. Tank according to claim 4, characterized in that the bottom (21) of the floating cover (20) is convex downwards.

7. Tank according to claim 4, characterized in that the bottom (21) of the floating cover (20) is convex upwards.

8. Tank according to claim 4, characterized in that the intermediate gas (29) extends between the first Uquide (15) and the bottom (21) of the floating cover and supports the upper element (2).

9. Tank according to one of the preceding claims, characterized in that means for filling and emptying the tank comprise at least one pipe (35) passing under the tank and opening into the tank (14) through a bottom ( 10) of it

10. Tank according to claim 5, characterized in that means for filling and emptying the tank comprise at least one pipe (42) mounted on the upper element (2) and opening into the tank (14) through the floating cover (20).