TANK FOR STORING PETROLEUM PRODUCTS AND FLOATING ELEMENT FOR SAID TANK

Abstract

Present invention relates to the field of a storage tank design and can be used in the construction of tanks for storing light ends and, preferably, for storing gasoline. The claimed tank for storing petroleum products consists of a body, a roof and a floating protective cover comprised of a plurality of floating elements in the form of solids of revolution having the same shape. In the tank, a portion of the floating elements of the protective cover is situated below the surface of the liquid, and a portion is situated in the gas space of the tank. The distinguishing feature of the proposed invention is the floating elements, which differ from one another in shape and size by not more than 5%. Furthermore, the floating elements that make up the floating protective cover have a centre of flotation that is offset from their geometric centre. All of the elements of the protective cover are made of non-sparking metal. The technical result of the invention is that of reducing the rate of evaporation of the liquid and the concentration of vapors, suppressing the process of combustion and preventing the possibility of electrostatic buildup and spark discharge between the floating elements.

Claims

1. A petroleum product storage tank, which consists of a body, a shell and a floating protective coating consisting of numerous floating elements as rotation bodies of the same shape, some part of which are located below a liquid surface in the tank and some of themin the tank gas space characterized in that the floating elements in size and shape differ from each other for not more than 5%, the floating elements have a center of flotation offset from their geometric centre, and all floating elements are made of non-sparkling metal.

2. The tank according to claim 1 characterized in that the floating elements located in the gas space form not less than four layers.

3. The tank according to claim 1 characterized in that the floating elements located within the liquid form not less than one and a half layers.

4. The tank according to claim 1 characterized in that in its upper part, a grid with a cell less than the floating element diameter is installed.

5. The tank according to claim 1 characterized in that in its lower part above the liquid discharge-load level a grid with a cell smaller than the floating element diameter is installed.

6. The tank according to claim 1 characterized in that in its upper part an internal collaring is also made.

7. The floating element for the tank according to claim 1 made as a rotation body characterized in that it is made of aluminum or its alloy.

8. The floating element according to claim 3 characterized in that it is made with the ceramic coating of aluminum oxide or stainless steel.

9. The floating element according to claim 3 characterized in that the ratio of maximum diameter of the rotation body to its wall thickness is at least 60.

10. The floating element according to claim 3 characterized in that it is made with the minimum diameter not less than 10 mm.

11. The floating element according to claim 3 characterized in that it is made with the maximum diameter not more than 60 mm.

12. The floating element according to claim 3 characterized in that it has a spheroid, ellipsoid or egg-shaped form.

Description

[0025] The invention essence is clarified by drawings where

[0026] on FIG. 1, the general appearance of a covered tank is provided; where it is denoted: 1the tank, 2the tank cover, 3the floating protective coating consisting of numerous floating elements 4, 5the liquid (petroleum products), 6the liquid surface, 7the gas space, 8the grid, 9the collaring, 12the lower grid.

[0027] on FIG. 2 and FIG. 3section A of FIG. 1;

[0028] on FIG. 4,5,6,7cross section of some possible forms of the floating elements; where it is denoted: 10the flotation center of a floating element, 11the geometric center of the floating element 4.

[0029] on FIG. 8the flow charts of liquid evaporation rate in the tank are provided depending on its configuration: 13a curve for a tank without floating elements, 14a curve for a rigid pontoon tank, 15a curve for a tank with a floating protective coating from numerous floating elements.

[0030] The petroleum product storage tank 1 contains a cover 2, a floating protective coating 3 consisting of numerous floating elements 4 some of which are located in liquid 5, i.e. below liquid surface 6, and some of them above liquid surface 6, i.e. in gas space 7 (FIG. 1). In the upper part of the tank, a grid 8 (FIG. 2) or a collaring 9 (FIG. 3) are installed. Flotation center 10 of the floating elements 4 is offset from their geometric centre 11 (FIG. 4, 5, 6, 7). In the lower part of the tank above a drainage-load level, the upper grid 12 is made with a perforation cell smaller than the floating element diameter 4.

[0031] The tank 1 with the cover 2 and the floating protective coating 3 acts in the following way.

[0032] When the floating elements 4 are filled in to the tank 1 with the liquid 5 (petroleum products), as well when the liquid 5 is loaded and discharged, they, being chaotically distributed in the tank, are placed in several layers forming the floating protective coating 3 with dense packing.

[0033] In the event of oscillation of liquid surface 6 in loads and discharges or explosion, the floating protective coating 3 consisting of the numerous floating elements 4 as rotation bodies of the same shape functions by the principle of tank duckweed. In the event of possible lighting strike or collapse of the cover constructions 2 within the tank 1, the floating elements 4 may diverge, even fly apart within the tank 1. But then chaotically returning, they are placed to the structure with dense packaging (floating protective coating 3) thereby they extinguish evaporation and evolving fire locus, as well significantly phlegmatize combustion process. To prevent the discharge of the floating elements 4 beyond the tank 1 in the event of explosion, in its upper part, the grid 8 or the collaring 9 are installed. The grid 8 has a cell smaller than the floating element diameter 4. The collaring 9 is installed as it is shown on FIG. 3, by the periphery of the upper part of the tank 1. It allows to localize and extinguish fire quickly and with the lack of risk of new explosions. To reduce the risk of penetration of the floating elements to drainage holes, in the lower part of the tank above liquid discharge-load, the grid 5 is made with a perforation cell smaller than a floating element diameter.

[0034] To reduce the concentration of liquid vapors in the gas space 7 of the tank 1 and provide phlegmatization of combustion process as the protective coating 3, the floating elements 4 are used which are made as rotation bodies, with the flotation center 10 offset from their geometric centre 11. E.g., as FIG. 4, 5, 6, 7 show, the floating element 4 may have a spherical, ellipsoid or egg-shaped form. Further considerations would be made in relation to the floating elements 4 having spherical form. However, it should be understood that such considerations also cover other rotation bodies. With the tank discharge and loading, the spherical floating elements 4 may touching each other turn about its geometrical center and touching the liquid 5 have a liquid film on its surface. The film may evaporate and vapors will penetrate to the gas space of the tank 7. To prevent this the spherical floating elements 4 are made so that their gravity center 10 is offset from their geometric centre 11 (FIG. 4-8). Hereby the spherical floating elements 4 will be constantly oriented in relation to the liquid surface 6 and in the event of the tank discharge-load may only fluctuate slightly in relation to their position. So a dry surface of the spherical floating element 4 will not be immersed to the liquid 5, and, respectively, have a liquid film. Moreover, hydrophobic coating may be applied to the surface of the floating element 4, which prevents a capillary effect. It will significantly reduce evaporation.

[0035] To prevent static electricity and possible spark discharge in the mass of the spherical floating elements 4, these elements should be made from non-sparkling metal, mainly from aluminum or its alloys. In this case, the necessary buoyancy of the elements 4 of the floating protective coating 3 may be provided. The criterion for selection of the floating element size 4 is the ratio:

n=D/t,

[0036] where Dthe external diameter of the spherical floating element 4,

[0037] twall width of the spherical floating element 4.

[0038] The ratio of the floating element diameter n D to its wall thickness t should be at least 60. The preferred ratio is n=80 . . . 110. The larger ratio is undesirable as the floating wall element 4 will be too thin and not resistant to mechanic exposures. For the same reasons, the minimum diameter of the floating diameter D should be at least 10 mm. The maximum diameter of the floating element D should be not more than 60 mm. In this case the size of a cell formed by the surfaces of the floating elements 4, densely located will be less than the critical value, i.e. sufficient to break a chain reaction (explosion) of stoichiometric petroleum product and air mixture (see Semenov N. N., Chain reactions, M., Nauka, 1986). In other words, vapor-air mixture within such a cell will not explode being exposed to any ignition source (static electricity spark, lightning strike, open fire exposure, etc.).

[0039] Our studies have shown that a minimum number of layers of the floating elements 4 located in gas space to reduce the dramatically flammable liquid evaporation 5 and, respectively, entry of liquid vapors to the gas space 7 of the tank 1 should be at least four. Hereby combustion in the gas space 7 of the tank 1, even if it occurs for any reasons, would be phlegmatic. It is explained by the fact that the liquid evaporation rate 5 would be minimized due to overlapping of the liquid surface 6 and the gas space 7 above the surface 6 with several layers of the floating elements 4.

[0040] Our calculations and tests have shown that the number of layers of the floating elements 4 located in the liquid 5 is of the same importance. After possible explosion in the gas space 7 and spread of the floating elements 4 located in the gas space 7, they first, being emerged, overlap the liquid surface 6 and thereby phlegmatize combustion. And as the tests have shown the floating elements 4 scattered in the tank 1 completely recover the floating protective coating 3. The number of layers of the floating elements 4 in the liquid 5 should be at least one and a half.

[0041] Reduction of evaporation rate is well illustrated by the diagram of relationship between the level of excessive pressure and achievement time in the tank 1 in which pressure is released (FIG. 8), where 13a curve for a tank without the floating elements, 14a curve for a rigid pontoon, 15a curve for a tank with the floating protective coating 3 from the numerous floating elements 4. The diagram on FIG. 8 shows that with the presence of the floating protective coating 3 in which the floating elements 4 are placed in several layers, an excessive pressure is achieved for a longer time.

[0042] To prevent the surface corrosion of the floating elements 4, a layer of aluminum or its alloys should be applied to their surface. The preferred coating composition for the floating elements is Al.sub.2O.sub.3. Our studies have shown that the ceramic surface coating of the floating elements 4 makes effective corrosive protection of metallic surface for the overwhelming majority of petroleum products both of original manufacture and having various types of additives. The studies have shown high corrosive resistance of such coating in relation to a variety of flammable liquids and for benzenes it fully protects the surface of the floating aluminum elements 4 from corrosion.

[0043] So the assigned goal and the technical result are achieved.