Rim Seal Flammable Liquid Storage Tank

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

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.

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. Tankincludes a hollow cylindrical housinghaving a closed lower end, an open upper end, and a cylindrical sidewall. The open upper endis sealed by a buoyant roof or cover, having a circular contour matching the dimensions of the interior of housing. Rooffloats on the flammable liquid L contained within the housing, 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.

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.

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

The rim seal for a flammable liquid storage tankserves 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.andB show an exemplary liquid storage tank similar to storage tankof. The liquid storage tank shown inincludes a hollow cylindrical tankhaving a closed lower end, an open upper end, and a cylindrical sidewall. A floating roofis received within the hollow cylindrical tank. The floating roofhas a circular contour and is adapted to float on the liquid L received within the hollow cylindrical tank. The rim sealis positioned within, and extends across, a gap G formed between an outer circumferential edgeof the floating roofand an inner surfaceof the cylindrical sidewallof the hollow cylindrical tank. It should be understood that the relative thicknesses of the floating roofand the cylindrical sidewallare shown for exemplary purposes only.

The rim sealincludes a plurality of buoyant membersadapted to float on the liquid L received within the liquid storage tank. The plurality of buoyant membersare received within a closed flexible membrane. The buoyant membersare formed from a material which is resistant to hydrocarbon degradation and which is flame retardant. As a non-limiting example, as shown in, each of the buoyant membersmay have a coreand an outer layerformed on an outer surface of the core. The outer layermay be formed from a heat-reactive intumescent material. Although shown as being solid, it should be understood that coremay 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, 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 membersform a vapor-impermeable barrier. Alternatively, the intumescent layermay be replaced with a flame-retardant material, thus providing protection for the core. 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 memberscan 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 layermay 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.

The closed flexible membranemay 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, membranecan be formed from, or coated with, polyethylene, nitrile rubber, fluorine rubber (also known as fluoro-rubber) or the like. The membranemay further include a stiffening component that keeps the membranesecured tightly to the circumferential edgeof the floating roof. Alternatively, a stiffening component can be separate and attached to a mounting flange of the floating roof.

As shown in, as the size of the gap G decreases, the buoyant membersare pushed together in the radial or horizontal direction, moving within the membranesuch that they are stacked on top of one another. As the gap G widens, the buoyant membersspread out again within the membraneunder the force of gravity. It should be understood that the spherical shape of buoyant membersinandB is shown for exemplary purposes only and that the buoyant membersmay have any suitable shape. As a non-limiting example, each of the buoyant membersmay be round, allowing the buoyant membersto move easily with respect to one another. As a further non-limiting example, each of the buoyant membersmay have a spherical, ovoidal, ellipsoidal or oblate spheroidal shape. Although each of the each of the buoyant membersmay have any suitable size and shape, as a non-limiting example, each of the buoyant membersmay 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 membersshould be lighter than the hydrocarbon liquid L stored within the storage tank, allowing buoyant membersto 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 membershave a specific gravity of 0.1, then five layers of stacked buoyant members are expected to submerge the bottom layer of buoyant membersabout halfway beneath the surface of the crude oil. In practice, the layers of buoyant memberswill form a seemingly random three-dimensional packing arrangement. Thus, as a non-limiting example, each of the buoyant membersmay 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 membranewere to tear, causing the flammable liquid L to enter the interior of membrane, the buoyant memberswould 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 membersallows for a stacked, interlocking arrangement, as shown inwhen the rim sealis compressed, with the buoyant membersnaturally settling under the force of gravity into a vapor suppressing layer. In both the compressed configuration ofand the non-compressed configuration of, the natural settling of the buoyant memberswithin the membranecauses the buoyant membersto push outwards, horizontally, thus ensuring that the rim sealmakes contact with both inner surfaceand the circumferential edgeof floating roof. The vapor barrier layer formed by the stacked buoyant membersform 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 memberscreate interstitial vapor pockets, trapping vapors therein and preventing the release thereof into the area above the rim sealin sufficient quantity to allow combustion.

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

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

Returning to, a bumpermay be mounted on the floating roofand project outwardly therefrom, into the gap G. The bumperprevents the floating rooffrom making direct contact with the inner surfaceof sidewalland also crushing the buoyant members. The bumpermaintains a minimal space between the circumferential edge of floating roofand the inner surfaceof sidewall, which is filled with the rim seal. It should be understood that bumperis shown for exemplary purposes only and may have any suitable shape, relative dimensions and overall configuration. For the non-limiting example discussed above, the bumpermay extend beyond the circumferential edgeof floating roofa distance of about 4 inches, thus contacting the inner surfaceof sidewallwhen the rim sealis in the compressed configuration of.

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.