RIM SEAL FLAMMABLE LIQUID STORAGE TANK

Abstract

A rim seal for a flammable liquid storage tank is provided. The rim seal forms a vapor impermeable barrier with passive fire-suppressing capabilities provided by layers of buoyant members that suppress flammable vapors to prevent fires. The buoyant and fire-retardant members are contained within a closed flexible membrane. The closed flexible membrane contains one or more layers of the buoyant members. The closed flexible membrane and the buoyant members therein extend across the gap formed between an outer circumferential edge of a floating roof and the inner wall of the liquid storage tank. The buoyant members form the layers under the influence of gravity. The buoyant members are formed from a material which is resistant to hydrocarbon degradation, and which is flame retardant and vapor suppressing. The layers of the buoyant members form a passive fire protective barrier between the flammable liquid in the storage tank and the atmosphere.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Patent Application No. 63/648,776, filed on May 17, 2024.

BACKGROUND

Field

The disclosure of the present patent application relates to storage tanks for flammable liquids, and particularly to a rim seal for a flammable liquid storage tank which serves as a vapor barrier and provides fire-suppressing capabilities for the gap between the floating roof of the storage tank and the storage tank's inner wall.

Description of Related Art

Flammable liquids, such as oil, gasoline and the like, must be stored in specialized storage tanks due to the flammable vapor that forms above the liquid surface. A common type of storage tank, often used in the petrochemical industry, is the “floating roof” tank. A typical floating roof tank is illustrated in FIG. 3. Tank 100 includes a hollow cylindrical housing 112 having a closed lower end 110, an open upper end 116, and a cylindrical sidewall 118. The open upper end 116 is sealed by a buoyant roof or cover 114, having a circular contour matching the dimensions of the interior of housing 112. Roof 114 floats on the flammable liquid L contained within the housing 112, thus preventing the buildup of flammable vapor and exposure thereof to the environment, and also to external hazards, such as sparks.

It is common for the floating roof to have a diameter which is smaller than the inner diameter of the storage tank, resulting in a gap between the floating roof and the inner wall of the storage tank. To prevent evaporative loss through the gap, it is common to apply a rim seal between the outer edge of the floating roof and the inner wall of the storage tank. Typical rim seals are formed from an open cell foam material which expands and compresses as the size of the gap changes. The size of the gap can change due to the horizontal movement of the floating roof within the storage tank, and also due to a non-constant diameter of the inner wall of the storage tank. In the latter case, as the floating roof rises and falls, dependent on the level of flammable liquid stored therein, the size of the gap can increase or decrease.

The open cell foam material is typically contained within an envelope or membrane. If the envelope or membrane tears, the typical open cell foam material used to make rim seals often absorbs the flammable liquid, resulting in degradation of the foam and removing its ability to form a tight seal. Due to the constant rising and falling of the floating roof, the friction between the envelope or membrane and the inner wall of the storage tank makes such tears more and more likely throughout the life of the storage tank.

Any failure of the rim seal can result in flammable vapors escaping through the gap, and the escaped vapors can create a flammable vapor mixture which poses significant safety risks from a fire. Often times, storage tanks have a fire foam system mounted to the top of each tank's rim to address fires in the rim seal area, however, such systems require detection, activation and deployment of water-based firefighting foams. The water-based foams commonly contain hazardous materials, including perfluoroalkyl and polyfluoroalkyl substances (PFAS). However, if the firefighting foam fails, there are no additional safety measures in place to prevent accidental ignition of the vapor. Thus, passive fire protection in the rim seal for a flammable liquid storage tank solving the aforementioned problems is desired.

SUMMARY

The rim seal for a flammable liquid storage tank serves as a vapor barrier that provides a vapor impermeable barrier layer with fire-suppressing capabilities for the gap between the floating roof of the storage tank and the storage tank's inner wall. The rim seal includes a plurality of buoyant members adapted to float on a liquid received within the liquid storage tank. The plurality of buoyant members are received within a closed flexible membrane. The closed flexible membrane and the plurality of buoyant members received therein are adapted to be received within, and extend across, a gap formed between an outer circumferential edge of the floating roof and an inner surface of a sidewall of the liquid storage tank. The buoyant members are formed from a material which is resistant to hydrocarbon degradation, which is flame retardant and which, together in layers, provide vapor suppression. The flame retardant nature of the buoyant members is due to the stacking of multiple layers of the buoyant members cause sufficient vapor suppression to prevent ignition of flammable liquids.

A liquid storage tank including the rim seal is also provided. The liquid storage tank is a hollow cylindrical tank having a closed lower end, an open upper end, and a cylindrical sidewall. The floating roof is received within the hollow cylindrical tank. The floating roof has a circular contour and is adapted to float on the liquid received within the hollow cylindrical tank. The rim seal is positioned within, and extends across, a gap formed between an outer circumferential edge of the floating roof and an inner surface of the cylindrical sidewall of the hollow cylindrical tank.

These and other features of the present subject matter will become readily apparent upon further review of the following specification.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a partial, environmental diagrammatic view of a rim seal for a flammable storage tank, with the rim seal shown in a non-compressed configuration.

FIG. 1B is a partial, environmental diagrammatic view of the rim seal for a flammable storage tank, with the rim seal shown in a compressed configuration.

FIG. 2 is a side view in section of a buoyant member of the rim seal for a flammable storage tank.

FIG. 3 is a perspective view of a conventional storage tank with a floating roof.

Similar reference characters denote corresponding features consistently throughout the attached drawings.

DETAILED DESCRIPTION

The rim seal for a flammable liquid storage tank 10 serves as a vapor barrier that provides a vapor impermeable barrier layer with fire-suppressing capabilities for the gap between the floating roof of the storage tank and the storage tank's inner wall. FIGS. 1A and 1B show an exemplary liquid storage tank similar to storage tank 100 of FIG. 3. The liquid storage tank shown in FIGS. 1A and 1B includes a hollow cylindrical tank 12 having a closed lower end, an open upper end 16, and a cylindrical sidewall 18. A floating roof 14 is received within the hollow cylindrical tank 12. The floating roof 14 has a circular contour and is adapted to float on the liquid L received within the hollow cylindrical tank 12. The rim seal 10 is positioned within, and extends across, a gap G formed between an outer circumferential edge 26 of the floating roof 14 and an inner surface 20 of the cylindrical sidewall 18 of the hollow cylindrical tank 12. It should be understood that the relative thicknesses of the floating roof 14 and the cylindrical sidewall 18 are shown for exemplary purposes only.

The rim seal 10 includes a plurality of buoyant members 24 adapted to float on the liquid L received within the liquid storage tank. The plurality of buoyant members 24 are received within a closed flexible membrane 22. The buoyant members 24 are formed from a material which is resistant to hydrocarbon degradation and which is flame retardant. As a non-limiting example, as shown in FIG. 2, each of the buoyant members 24 may have a core 30 and an outer layer 32 formed on an outer surface of the core 30. The outer layer 32 may be formed from a heat-reactive intumescent material. Although shown as being solid, it should be understood that core 30 may also be in the form of a hollow shell or the like. In the event of a fire within the storage tank, the intumescent layer 32, which is heat reactive, expands to create an insulating layer in the uppermost layers of shells while also protecting the underlying members from the heat, thus ensuring that buoyant members 24 form a vapor-impermeable barrier. Alternatively, the intumescent layer 32 may be replaced with a flame-retardant material, thus providing protection for the core 30. Heat-reactive, expanding foam materials that are non-reactive with petroleum products and that can withstand relatively high temperatures are well known, and any suitable heat-reactive intumescent material (or, alternatively, flame retardant material) may be utilized.

As further non-limiting examples, the buoyant members 24 can be made of, or coated with, glass, ceramic, plastic, resin, composite or the like. The selection of material should provide for operating temperature tolerances between about −200° F. and 140° F. The intumescent layer 32 may be formed from a material selected not only to swell when exposed to extreme heat, but to also form a carbon crust that insulates and prevents heat transfer to the underlying buoyant members 24.

The closed flexible membrane 22 may be made of any suitable type of flexible material either formed from, or coated with, a material which is chemically compatible with the stored flammable liquid L; i.e., a material which will not dissolve, degrade or otherwise react with the liquid L. As non-limiting examples, membrane 22 can be formed from, or coated with, polyethylene, nitrile rubber, fluorine rubber (also known as fluoro-rubber) or the like. The membrane 22 may further include a stiffening component that keeps the membrane 22 secured tightly to the circumferential edge 26 of the floating roof 14. Alternatively, a stiffening component can be separate and attached to a mounting flange of the floating roof 14.

As shown in FIGS. 1A and 1B, as the size of the gap G decreases, the buoyant members 24 are pushed together in the radial or horizontal direction, moving within the membrane 22 such that they are stacked on top of one another. As the gap G widens, the buoyant members 24 spread out again within the membrane 22 under the force of gravity. It should be understood that the spherical shape of buoyant members 24 in FIGS. 1A and 1B is shown for exemplary purposes only and that the buoyant members 24 may have any suitable shape. As a non-limiting example, each of the buoyant members 24 may be round, allowing the buoyant members 24 to move easily with respect to one another. As a further non-limiting example, each of the buoyant members 24 may have a spherical, ovoidal, ellipsoidal or oblate spheroidal shape. Although each of the each of the buoyant members 24 may have any suitable size and shape, as a non-limiting example, each of the buoyant members 24 may have a diameter in the range of about 0.01 inches to about 4.0 inches, with a tolerance of ±10%.

The specific gravity of the buoyant members 24 should be lighter than the hydrocarbon liquid L stored within the storage tank, allowing buoyant members 24 to float on liquid L and form layers. For example, if a crude oil with a specific gravity of 0.9 is stored in the storage tank and the buoyant members 24 have a specific gravity of 0.1, then five layers of stacked buoyant members are expected to submerge the bottom layer of buoyant members 24 about halfway beneath the surface of the crude oil. In practice, the layers of buoyant members 24 will form a seemingly random three-dimensional packing arrangement. Thus, as a non-limiting example, each of the buoyant members 24 may have a specific gravity in the range of about 0.01 to about 0.5, with a tolerance of ±10%, in order to be effective. In use, if membrane 22 were to tear, causing the flammable liquid L to enter the interior of membrane 22, the buoyant members 24 would float on top of the surface of liquid L, thus suppressing the flammable vapors from volatizing into the air.

A rounded shape for each of the of the buoyant members 24 allows for a stacked, interlocking arrangement, as shown in FIG. 1B when the rim seal 10 is compressed, with the buoyant members 24 naturally settling under the force of gravity into a vapor suppressing layer. In both the compressed configuration of FIG. 1B and the non-compressed configuration of FIG. 1A, the natural settling of the buoyant members 24 within the membrane 24 causes the buoyant members 24 to push outwards, horizontally, thus ensuring that the rim seal 10 makes contact with both inner surface 20 and the circumferential edge 26 of floating roof 14. The vapor barrier layer formed by the stacked buoyant members 24 form a vapor suppressing blanket effect for the surface of liquid L, minimizing possible liquid-vapor contact within the storage tank. Spaces between the stacked buoyant members 24 create interstitial vapor pockets, trapping vapors therein and preventing the release thereof into the area above the rim seal 10 in sufficient quantity to allow combustion.

As further seen in FIGS. 1A and 1B, a layer of resilient foam 31 may also be received within the closed flexible membrane 22. As a non-limiting example, the layer of resilient foam 31 may be a reticulated foam. Although shown as being positioned beneath the buoyant members 24, it should be understood that the layer of foam 31 may also be positioned on top of the buoyant members 24 within flexible membrane 22, or may be positioned both below and on top of the buoyant members 24.

It should be understood that the rim seal 10 may have any suitable size and relative dimensions. As a non-limiting example, the rim seal 10 may be sized and shaped to form a seal across the gap G ranging between about 12 inches (in the non-compressed configuration of FIG. 1A) and 4 inches (in the compressed configuration of FIG. 1B). A corresponding exemplary height of the rim seal 10 in the compressed configuration of FIG. 1B is about 12 inches.

Returning to FIGS. 1A and 1B, a bumper 34 may be mounted on the floating roof 14 and project outwardly therefrom, into the gap G. The bumper 34 prevents the floating roof 14 from making direct contact with the inner surface 20 of sidewall 18 and also crushing the buoyant members 24. The bumper 34 maintains a minimal space between the circumferential edge of floating roof 14 and the inner surface 20 of sidewall 18, which is filled with the rim seal 10. It should be understood that bumper 34 is shown for exemplary purposes only and may have any suitable shape, relative dimensions and overall configuration. For the non-limiting example discussed above, the bumper 34 may extend beyond the circumferential edge 26 of floating roof 14 a distance of about 4 inches, thus contacting the inner surface 20 of sidewall 18 when the rim seal 10 is in the compressed configuration of FIG. 1B.

It is to be understood that the rim seal for a flammable liquid storage tank is not limited to the specific embodiments described above, but encompasses any and all embodiments within the scope of the generic language of the following claims enabled by the embodiments described herein, or otherwise shown in the drawings or described above in terms sufficient to enable one of ordinary skill in the art to make and use the claimed subject matter.

Claims

1. A rim seal for a flammable liquid storage tank, comprising:

a plurality of round, buoyant members adapted to float on a liquid received within a liquid storage tank, the round, buoyant members being formed from a material which is resistant to hydrocarbon degradation; and

a closed flexible membrane, the plurality of round, buoyant members being received therein, wherein the closed flexible membrane is formed from a material that does not dissolve in the liquid,

wherein the closed flexible membrane and the plurality of round, buoyant members received therein are adapted to be received within, and extend across, a gap formed between an outer circumferential edge of a floating roof and an inner surface of a sidewall of the liquid storage tank.

2. (canceled)

3. (canceled)

4. The rim seal for a flammable liquid storage tank as recited in claim 1, wherein a shape of each of the round, buoyant members is selected from the group consisting of spherical, ovoidal, ellipsoidal and oblate spheroidal.

5. The rim seal for a flammable liquid storage tank as recited in claim 1, further comprising a layer of resilient foam received within the closed flexible membrane.

6. The rim seal for a flammable liquid storage tank as recited in claim 5, wherein the layer of resilient foam comprises reticulated foam.

7. The rim seal for a flammable liquid storage tank as recited in claim 1, wherein each of the round, buoyant members comprises a core and an outer layer formed on an outer surface of the core, the outer layer comprising a heat-reactive intumescent material.

8. The rim seal for a flammable liquid storage tank as recited in claim 1, wherein each of the round, buoyant members is formed from a material selected from the group consisting of glass, ceramic, plastic, resin and a composite material.

9. The rim seal for a flammable liquid storage tank as recited in claim 1, wherein each of the round, buoyant members has a diameter in the range of about 0.01 inches to about 4.0 inches.

10. The rim seal for a flammable liquid storage tank as recited in claim 1, wherein each of the round, buoyant members has a specific gravity in the range of about 0.01 to about 0.5.

11. A liquid storage tank with a rim seal, comprising:

a hollow cylindrical tank having a closed lower end, an open upper end, and a cylindrical sidewall;

a floating roof received within the hollow cylindrical tank, the floating roof having a circular contour and being adapted to float on a liquid received within the hollow cylindrical tank; and

a rim seal, comprising:

a plurality of round, buoyant members adapted to float on the liquid received within the hollow cylindrical tank, the round, buoyant members being formed from a material which is resistant to hydrocarbon degradation; and

a closed flexible membrane, the plurality of round, buoyant members being received therein, wherein the closed flexible membrane is formed from a material that does not dissolve in the liquid,

wherein the rim seal is positioned within, and extends across, a gap formed between an outer circumferential edge of the floating roof and an inner surface of the cylindrical sidewall of the hollow cylindrical tank.

12. (canceled)

13. (canceled)

14. The liquid storage tank with a rim seal as recited in claim 11, wherein a shape of each of the round, buoyant members is selected from the group consisting of spherical, ovoidal, ellipsoidal and oblate spheroidal.

15. The liquid storage tank with a rim seal as recited in claim 11, further comprising a layer of resilient foam received within the closed flexible membrane.

16. The liquid storage tank with a rim seal as recited in claim 15, wherein the layer of resilient foam comprises reticulated foam.

17. The liquid storage tank with a rim seal as recited in claim 11, wherein each of the round, buoyant members comprises a core and an outer layer formed on an outer surface of the core, the outer layer comprising a heat-reactive intumescent material.

18. The liquid storage tank with a rim seal as recited in claim 11, wherein each of the round, buoyant members is formed from a material selected from the group consisting of glass, ceramic, plastic, resin and a composite material.

19. The liquid storage tank with a rim seal as recited in claim 11, wherein each of the round, buoyant members has a diameter in the range of about 0.01 inches to about 4.0 inches, and wherein each of the buoyant members has a specific gravity in the range of about 0.01 to about 0.5.

20. The liquid storage tank with a rim seal as recited in claim 11, further comprising a bumper mounted on the floating roof and projecting outwardly therefrom.