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(11) | EP 0 269 586 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Internal protection system for tanks, particularly underground tanks for fuel and the like |
| (57) The invention provides for the use of a liner (6) of flexible, elastic plastics material
unattackable by the liquid material to be contained in the tank (1). The plastics liner (6) is inserted into the tank through the manhole (5) or possibly through a connection if sufficiently large. The liner (6) adapts to the inner shape of the tank (1) by virtue of the flexibility and elasticity of the material of which is manufactured. The liner (6) is kept substantially adhering to the inner walls of the tank (1) by flexible hoop elements (7) which are applied to the interior of the liner (6) after it has been inserted into the tank (1), or by pressurisable tubes which are preformed in said liner (6) and are pressurised after the liner (6) has been inserted into the tank (1). In this latter case, a double wall liner can be provided, and the interspace pressurised to monitor any loss of seal. The tubes can also be filled with expanded synthetic material. |
[0001] This invention relates to an internal protection system for tanks, particularly underground tanks for fuel and the like.
[0002] Tanks of this type are mainly constructed of mild steel plate, their geometry comprising dished ends and a cylindrical shell formed from rolled sheet or a helically welded coiled strip. To protect these tanks from attack by corrosive agents present in the soil in which are buried, the outer walls are coated with tar or a special glass fibre and resin coating. In some cases, to protect against pollution the tanks are formed with a double wall, the sealed interspace being below atmospheric pressure and the soundness of the wall being checked by monitoring the vacuum of the air in the interspace.
[0003] In structures of this kind constructed in accordance with the state of the art, in addition to the wall corrosion problems there is the problem of handling the dregs or sediments which form with time during the use of the tank. The dregs consist of impurities of greater density than the fuel, which deposit by gravity. These dregs are often agitated during refilling of the tank, and as they require a certain time for redeposition they tend to mix with the fuel withdrawn from the tank and fed to the final user. Feeding "dirty" fuel to the final user causes problems in internal combustion engines or in burners of heating installations, and requires operators to use costly means for filtering or handing the fuel (decantation). Moreover, the presence of dregs or sediments in tanks of this type leads to corrosion of the inner tank wall, which can result in fuel leakage, with negative consequences due to the polluting effect of the fuel and the irrecoverable cost of the quantity lost.
[0004] Other problems arise from the need to remove the drags or sediments, this operation involving the use of solvents, mechanical means, high pressure cleaning lances operating with hot water and steam etc.
[0005] These and other problems are solved by the present invention which provides an internal protection system for tanks, particularly for underground tanks for fuel and the like, comprising the use of a liner of flexible, elastic plastics material unattackable by the liquid material to be contained in the tank. The plastics liner is inserted into the tank through the manhole or possibly through a connection if sufficiently large. The liner adapts to the inner shape of the tank by virtue of the flexibility and elasticity of the material of which it is manufactured, and is kept substantially adhering to the inner walls of the tank by flexible hoop elements which are applied to the interior of the liner after it has been inserted into the tank, or by pressurisable tubes which are preformed in said liner and are pressurised after the liner has been inserted into the tank. In this latter case, according to a modified embodiment the pressurisable tubes are associated with a double wall liner, and the interspace between the two walls can be pressurised with positive or negative pressure relative to atmospheric in order to monitor any loss of seal. The tubes can also be filled with expanded synthetic material.
[0006] Preferred embodiments of the present invention are described hereinafter by way of non-limiting example with reference to the figures of the accompanying drawings in which:
Figure 1 is a partly sectional overall view of a generic tank provided with the inner liner according to the invention;
Figure 2 is a section on the line II-II of Figure 1;
Figure 3 is a detail of the structure of Figures 1 and 2;
Figure 4 is a diagrammatic illustration of a tank liner kit according to the invention;
Figure 5 is a diagrammatic view of a second embodiment of the present invention;
Figure 6 shows the arrangement of a separator baffle for a tank or the like in two intercommunicating parts according to the invention, shown applied to the second embodiment;
Figures 7 and 7a show a further embodiment of a liner comprising tubes which can be pressurised or filled with expanded material, and/or a double wall which can be pressurised with positive or negative pressure relative to normal atmospheric pressure; and
Figure 8 is a modification of the liner of Figure 7.
[0007] The drawings, and in particular Figures 1 to 3, show a generic tank 1 of underground type to which the present invention can be applied.
[0008] As shown in Figure 1, the tank 1 is provided with a cylindrical wall 2, two dished ends 3 and 4, and a manhole 5.
[0009] The inner liner 6 is inserted into the tank 1 through the manhole 5. The inner liner 6 is constructed of flexible and yieldable elastic material unattackable either by the dregs or sediments, or by the fuel to be contained in the tank. The liner can be constructed for example of plasticised PVC of thickness between 0.5 and 0.7 mm.
[0010] The plastics liner does not need to be constructed with a shape which perfectly corresponds to the interior of the tank to be protected, as the characteristics of the chosen material allow said liner 6 to adapt to the interior of the tank 1. The liner 6 is kept adhering against the interior of the tank 1 by an arrangement of hoop elements 7, 8, 9 which prevent the liner 6 becoming flabby when empty. Figure 2 shows a generic hoop 7 extending over most of the cylindrical wall of the tank 1 and fixed in suitable pockets 8, as shown in Figure 3. This figure shows part of the liner 6 in which a pocket element 8 is formed by welding to receive a hoop 7, which is constructed preferably of plastics material unattackable by the contents of the tank in question. The hoops 7 are installed after the liner 6 has been inserted into the tank 1.
[0011] Figure 4 shows by way of example an inner liner kit for tanks of the said type, it comprising a folded liner 6ʹ, a plurality of hoops 7ʹ of which only one is shown, and a container 9 for the liner 6ʹ.
[0012] By using the liner according to the invention, any leakages due to perforation of the constituent sheet metal of the tank are eliminated. The liner according to the invention can also be applied to already working tanks containing dregs or sediments, so avoiding the need for their removal and at the same time resulting in a reconditioned structure.
[0013] In addition, with the liner according to the invention the dregs or sediments which deposit in the liner 6 can be removed together with the old liner, so considerably simplifying the reinstatement procedures.
[0014] Figures 5 and 6 show a second embodiment of the present invention. As shown in these figures, the inner liner 12 is inserted into a tank 10 through the manhole 11 as previously described. In this embodiment, instead of the hoop elements and pockets there are provided tubular ribs 13 which can be pressurised through a connector 14 fitted with a valve. When the tubular ribs 13 are pressurised they cause the liner 12 to adhere to the inner structure of the tank 10.
[0015] Figure 6 shows a modified embodiment of the structure of Figure 5, using the same reference numerals for corresponding parts, and in which the interior of the tank 10 is divided into two compartments ZC and ZA by a baffle 15 preferably constructed of the same material as the liner 12. The compartments ZC and ZA indicate the filling region and withdrawal region for the fuel or the like. In this respect, apertures 16 positioned in the bottom of the baffle 15 enable the tank 10 to be filled by feeding the charge into the region ZC with reduced turbulence, and thus reduced fuel turbidity deriving from the lifting of dregs or sediments in the region ZA, from which the non-agitated fuel is withdrawn for consumption.
[0016] The aforesaid embodiment, which comprises the separation baffle 15 with relative apertures 16, can obviously also be used with the same advantages in the structure shown in Figure 1, as is apparent to an expert of the art.
[0018] With reference to Figures 7 and 7a, the tank 17 is provided in its interior with a double-walled liner, the walls of which are indicated by 18 and 19 respectively, and the interspace by 20. In this embodiment the tubes 21 can be either pressurised or filled with a convenient material chosen from the various materials which expand on polymerisation, to form a cell structure of greater or lesser rigidity depending on the type of starting material used.
[0019] In this embodiment a valve 22 is provided for inflation purposes or for injection of the expandable plastics material, together with a valve 23 for feeding into the interspace 20 a gaseous medium at a pressure higher or lower than atmospheric, in order to be able to monitor the fluid-tightness of the liner by the methods used for double-shell metal tanks.
[0020] Again with reference to Figures 7 and 7a, a further embodiment is provided in which said interspace 20, conveniently pressurised, itself causes the outer wall 18 of the liner to adhere to the inner surface of the metal tank 17, any leakages being verified by monitoring the positive inflation pressure of said interspace 20.
[0021] Figure 8 shows a further modification to the construction shown in Figures 7 and 7a, in which tubular ribs 13ʹ are provided extending along a plurality of directrices of the substantially cylindrical tank, these being indicated by way of example as 13ʹa, 13ʹb, 13ʹc etc., and also along the end surfaces, they being pressurised by a pneumatic circuit 14ʹ.
1. An internal protection system for tanks, particularly for underground tanks for
fuel and the like, characterised by providing a liner (6) of flexible, elastic plastics
material unattackable by the liquid material to be contained in the tank (1) and having
a shape substantially corresponding to the shape of the interior of said tank (1),
inserting said liner (6) into the tank (1) through the manhole (5; 11) or other convenient
aperture, and applying means for urging the liner (6) towards the inner walls of the
tank (1).
2. A system according to claim 1, characterised in that said means for urging the
liner (6) towards the inner walls of the tank (1) consist of plastics hoops (7, 8,
9) insertable into suitable pockets (8) provided in the liner (6).
3. A system according to claim 1, characterised in that said means for urging the
liner (6) towards the inner walls of the tank (1) comprise a plurality of tubular
elements (13) integral or associated with the interior of said liner (6), said tubular
elements (13) being pressurised after installation and during the operation of the
tank (1).
4. A system according to claim 3, characterised in that the liner (6) associated with
the pressurisable tubular elements (21) is constructed as a double walled structure
with an interspace (20), said interspace (20) not communicating with the interior
of the inner liner wall (19) or with the exterior of the outer liner wall (18).
5. A system according to claim 4, characterised in that the interspace (20) can be
pressurised in a controllable manner with preferably inert gas to a pressure higher
or lower than normal atmospheric pressure in order to be able to monitor the occurrence
of any leakages.
6. A system according to any of claims 3 to 5, characterised in that the pressurisable
tubular elements (13; 21) are filled by injecting plastics material of the type which
expands on polymerisation to form a rigid structure.
7. A system according to claim 3, characterised in that the plurality of tubular elements
(13ʹ) is disposed along directrices of the cylindrical form of the tank (1).
8. A system according to claim 7, characterised by further comprising a second plurality
of tubular elements (24) integral or associated with the interior of the liner (6)
which are disposed along directrices of the cylindrical form of the tank (1) and are
interposed between the tubular elements (13′) of the first plurality, the tubular
elements (24) of the second plurality being pressurisable by a circuit (25) different
from that (14ʹ) relative to the first plurality after installation and during tank
operation, in order to provide improved adherence of the liner (6) against the inner
surface of the tank.
9. A system according to claim 8, characterised in that the tubular elements (24)
of the second plurality can be pressurised in a controllable manner with preferably
inert gas to a pressure higher or lower than normal atmospheric pressure in order
to be able to monitor the occurrence of any leakages.
10. A system according to any one of the preceding claims, characterised in that the
liner (6) is provided with a flexible baffle (15) constructed preferably of the same
material as the liner (6), said baffle (15) dividing the tank (1) into two regions
(ZC, ZA), namely a filling (ZC) and a withdrawal (ZA) region, which communicate through
apertures (16) provided in the lower part of the baffle (15).
11. A system according to any one of the preceding claims, characterised in that the
liner (6) is constructed of sheet material in the form of plasticised PVC.