US20130341333A1

US20130341333A1 - Storage tank with internal floor

Info

Publication number: US20130341333A1
Application number: US13/927,684
Authority: US
Inventors: William Roy HERDMAN; Wayne Geyer
Original assignee: Steel Tank Institute
Current assignee: Steel Tank Institute
Priority date: 2012-06-26
Filing date: 2013-06-26
Publication date: 2013-12-26

Abstract

The present disclosure relates to a storage tank which includes a sloped internal plate(s) fabricated within a bottom portion of the tank to form an internal sloping floor. The storage tank may further include at least one optional sump and/or optional support saddle extending out from the tank body. The tank may include internal lining that covers at least a portion of the interior of the tank. A draw-off pipe may be included for removing water, sludge, or other undesirable elements collected at the base of the internal sloping floor.

Description

CROSS REFERENCE TO PRIOR APPLICATIONS

This application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application No. 61/664,526, filed Jun. 26, 2012, titled “STORAGE TANK WITH INTERNAL FLOOR,” the disclosure of which is hereby expressly incorporated herein by reference in its entirety.

FIELD OF THE DISCLOSURE

The present disclosure relates to a storage tank for storing fluids that is configured to facilitate removal of certain components from the storage tank, such as, for example, water, sludge, and the like.

BACKGROUND OF THE DISCLOSURE

Fuel and other products are typically delivered and stored for commercial use in underground storage tanks (“USTs”) and above ground storage tanks (“ASTs”), either metallic or nonmetallic in nature. Water can be inadvertently introduced into the USTs and ASTs where fuel is being stored due to many factors. Water can be introduced during the fuel transfer process or can enter the tank during tank operations and maintenance activities, through damaged fill boxes, gaskets, loose fittings or plugs, and any tank orifice that is not water and/or vapor tight, or through poor practices. Water can also form as condensation due to temperature fluctuations in the tank or air entering in the tank vents, and since water is heavier than fuel, water settles to the bottom of the tank with time.
Water in the tank is not desirable as it can cause bacteria and other microbes to congregate and feed on the fuel, causing microbial contamination and degradation of the storage unit. The presence of water in fuel oil can cause oxidation and create sludge, eventually clogging fuel filters, lines, nozzles and screens and disrupting fueling operations and possibly causing system malfunction. Water in fuel can potentially cause serious or catastrophic operational problems in airplanes and/or other vehicles.
Further, with the advent of new types or formulations of fuels, the presence of water becomes more problematic. For example, with fuels such as, e.g., ultra-low sulfur diesel fuel, and renewable fuels such as, e.g., ethanol blended fuels and biodiesel fuel blends, it has become even more critical to collect and remove water from fuel storage tanks for efficient and safe fuel dispensing operations. Ethanol blended fuels, for example, can hold much water and once saturated, may cause phase separation with two distinct layers: a top mostly gasoline layer and a bottom layer mix of ethanol and water and sludge. New fuel formulations that are less tolerant of water may result in more clogged filters, phase separation, more sludge buildup and microbial activity at the water-fuel surface area.
Current industry solutions for keeping water out of storage tanks include: preventive operations and maintenance practices; measuring the water levels at the bottom of the tank using tank bottom sampling tools such as tank gauge hardware from, e.g., Veeder-Root, and pumping the water out at various access points from the tank; draining and thoroughly cleaning the tank internally via non-entry tank cleaning or physical entry tank cleaning; and placing ASTs on a sloped foundation during installation to more easily collect and remove the water at a collection point or sump. Further, coating and/or lining can be installed in the tank to prevent tank degradation.
USTs are installed relatively level and the water and/or sludge may be located along the entire length of the tank. However, over time, groundwater and other environmental conditions may slightly lift one end of the UST higher than the other, causing a slope and pooling of water and/or sludge in one area of the UST. Related attached piping such as a fill pipe and draw-off pipe is usually set level with the tank. One challenge with using current tank gauging hardware, such as, for example a Veeder-Root probe, is that the probe may be detecting water levels only at the high end of the tank and may not detect any water residing in the lower end of the tank. Removing water and other foreign matters to acceptable amounts may not be possible due to the water and residue being located in unknown areas along the bottom of the tank. Over time, with water accumulation, come sludge formation, corrosion, and the like, the UST may lose its integrity.
Further, it is common in the industry for fuel delivery personnel to check fuel levels in USTs by dropping a measuring drop stick into the USTs. The measuring drop stick is typically a small, rectangular, wooden stick calibrated to measure liquid levels, such as before and after fuel is delivered into a tank. Frequently, the measuring rods have steel tips that, through repeated use, tend to impact the floor of the USTs and wear the floor.
There is a need for an improved and more efficient way to remove water or sludge from ASTs and USTs that does not require any special equipment to detect and/or remove the unwanted water and foreign matters from the tanks.

SUMMARY OF THE DISCLOSURE

A fuel storage tank storage tank is described herein. The fuel storage tank may include an internal sloping floor welded to a bottom portion of the fuel storage tank, a collection point located at a low end of the at least one sloped plate, the collection point configured to collect water and sludge forming in the tank, and a draw-off pipe configured to provide access to the collection point for removing the water from the tank.
The internal sloping floor may be configured to create an internal slope to a grade of about 1% to greater than 5%.
The collection point may be located on the bottom floor of the fuel storage tank.
The collection point may comprise a sump built into the fuel storage tank at the collection point.
The fuel storage tank may include a horizontal cylindrical tank or a vertical, cylindrical tank. The fuel storage tank may include an underground fuel storage tank, or an above-ground fuel storage tank. The tank configuration may be rectangular as well as cylindrical. The tank may be single wall or multiple wall construction.
The fuel storage tank may include a first compartment, a second compartment, and/or additional compartments wherein each of the first compartment and the additional compartments comprise a collection point and an internal sloping floor.
The internal sloping floor may be made of a material that comprises one or more of carbon steel, stainless steel, or duplex stainless steel.
The fuel storage tank may include a manway configured to provide access to the interior of the fuel storage tank.
The draw-off pipe may be configured to allow manual collection of water and sludge from the collection point. The draw-off pipe may be configured to allow automatic removal of water from the collection point via the collection device.
The internal sloping floor of the fuel storage tank may have a thickness of about 10 gauge or more.
The draw-off pipe may be configured to terminate about two inches above the floor of the fuel storage tank at the collection point. Alternatively, the draw-off pipe may be configured to terminate on the floor of the fuel storage tank at the collection point, with access openings in the wall of the bottom of the pipe to allow free flow collection of the water and sludge.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a further understanding of the disclosure, are incorporated in and constitute a part of this specification, illustrate embodiments of the disclosure and, together with the detailed description, serve to explain the principles of the disclosure. No attempt is made to show structural details of the disclosure in more detail than may be necessary for a fundamental understanding of the disclosure and the various ways in which it may be practiced.

FIG. 1 shows a cross-sectional side view of an example of a storage tank having a secondary tank bottom (or internal sloping floor) constructed according to the principles of the disclosure.

FIG. 2 shows a cross-sectional partial side end view of another example of a storage tank having a secondary tank bottom (or internal sloping floor) with an optional support mechanism and an optional sump, constructed according to the principles of the disclosure.

FIG. 3 shows a cross-sectional partial side end view of yet another example of a storage tank having a secondary tank bottom (or internal sloping floor) with an optional sump and an optional tank lining, constructed according to the principles of the disclosure.

FIG. 4 shows a cross-sectional front view of an example of a storage tank comprising an optional tank lining and/an optional internal coating, constructed according to the principles of the disclosure.

FIG. 5 shows a cross-sectional side view of an example of a multi-compartment storage tank having a secondary tank bottom (or internal sloping floor) constructed according to the principles of the disclosure.

FIG. 6 shows a process for fabricating a secondary tank bottom and/or fabricating a storage tank with a secondary tank bottom (internal sloping floor), according to the principles of the disclosure.

DETAILED DESCRIPTION OF THE DISCLOSURE

The embodiments of the disclosure and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments and examples that are described and/or illustrated in the accompanying drawings and detailed in the following attached description. It should be noted that the features illustrated in the drawings are not necessarily drawn to scale, and features of one embodiment may be employed with other embodiments as the skilled artisan would recognize, even if not explicitly stated herein. Descriptions of well-known components and processing techniques may be omitted so as to not unnecessarily obscure the embodiments of the disclosure. The examples used herein are intended merely to facilitate an understanding of ways in which the disclosure may be practiced and to further enable those of skill in the art to practice the embodiments of the disclosure. Accordingly, the examples and embodiments herein should not be construed as limiting the scope of the disclosure, which is defined solely by the appended claims and applicable law. Moreover, it is noted that like reference numerals represent similar parts throughout the several views of the drawings.
The terms “including,” “comprising,” and variations thereof, as used in this disclosure, mean “including, but not limited to,” unless expressly specified otherwise.
The terms “a,” “an,” and “the,” as used in this disclosure, means “one or more,” unless expressly specified otherwise.
FIG. 1 shows a cross-sectional side view of a storage tank 100 having an internal sloping floor 102 constructed according to the principles of the disclosure. In this non-limiting example, a horizontal tank 100 comprises a cylindrical body, dished tank heads 104, and various access holes such as at least one draw-off pipe 106, one or more optional vent and test pipes 108, and a manway 110. When used, the optional vent and test pipe 108 may be used to test the space between the sloping internal floor 102 and the primary tank wall bottom to verify, for example, that no water or fuel exists in the space. In some aspects, draw-off pipe 106 may be configured to monitor water levels. While flanged flat tank heads 104 are shown in this example, the tank 100 may include other types of tank heads, such dished tank heads 105, hemispherical tank heads, toroconical tank heads, or tank heads having any other shape without departing from the scope or spirit of the disclosure. Internal sloping floor 102 may be fabricated or installed in the tank 100 during or after construction of the tank, and may be comprised of one or more plates. The internal sloping floor 102 may have a longer side (“higher side”) on the higher end and a shorter side (“lower side”) on the lower end to fit snugly within the cylindrical body of the tank. The internal sloping floor 102 may be sloped to create a grade of, for example, about 1% to greater than 5% at the bottom of the tank to ensure proper drainage to a collection point, such as collection point 112 and/or 118. According to one embodiment of the tank, the internal sloping floor 102 may be sloped to create a grade of, for example, about 2%. A higher (or lower) grading, from greater than 5% to about 45%, for example, may also be implemented for faster drainage, depending on the particular application and/or tank shape. By providing an internal sloping floor 102, the need to install the entire tank 100 at a slope is avoided.
Optional collection plates (or striker plates) 120, 122 may be included at the collection points 112, 118, respectively. Optional collection plates 120, 122 may be, for example, about twelve inches (12″) in width, and while shown inside the tank in this example, may be located outside of the tank. The dimensions of the optional collection plates may vary, as understood by those having ordinary skill in the art, depending on the tank diameter and tank application in order to ensure enough floor space to capture and contain the water and/or sludge at the collection points 112 and/or 118, while minimizing fabrication costs.
When more than one plate is used to create internal sloping floor 102, the plates may be attached together either using fillets around the plates to bind the plates, or fully welding the plates together and to the tank shell to provide a hermetic (or air-tight) seal, so as to prevent gases and/or liquids from entering the cavity or region between the internal (or “false”, or second) floor 102 formed by the plates and the floor of the tank. Plates may be lap welded (overlapping areas welded) as shown at 114 and/or butt welded (edge-to-edge welding) as shown at 116. If lap welded, the low end of the lap should be positioned downstream of the intended flow pathway of the water from the higher end of the lap joint in order to ensure a drainage path to the collection point without obstructions. A lip may be provided on the edge of each plate in order to provide additional rigidity to the floor.
Alternatively (or additionally), the plates may be fastened to the tank 100 using fasteners, such as, for example, bolts, nuts, screws, pins, rods, clamps, tongue-and-grove mechanisms, or the like. In this regard, a sealant (such as, e.g., epoxy, rubber gaskets, silicone gaskets, and the like) may be used between the plate(s) and the tank 100 walls to provide a hermetic (or air-tight) seal, so as to prevent gases and/or liquids from entering the cavity or region between the internal (or “false”, or second) floor 102 formed by the plates and the floor of the tank.
The plates forming the internal sloping floor 102 may be fully seal welded to the body of the tank 100, so as to provide a hermetic (or air-tight) seal between the internal sloping floor and the tank floor. The plates may have a thickness that is effective to form a floor and retain and provide structural support for the fuel, such as, for example, about 10 gauge, or greater. The dimensions of the plates may vary, as understood by those having ordinary skill in the art, and as such, the plates may be less than 10 gauge thickness.
The body of the tank, tank heads, as well as the plates forming the internal sloping floor 102 may be made from a hard, durable material, such as, for example, carbon steel, stainless steel, other metal alloys, or non-metallic materials, such as fiberglass reinforced plastic. The steel composition may provide an additional barrier to corrosion from the water and microbial activity. The bottom of the tank may include lining that covers a portion of or the complete interior of the tank. The lining may cover between 0% and 100% of the tank interior. A liner may be composed of for example, carbon steel, stainless steel, other metal alloys, epoxy, fiberglass or some other appropriate material known in industry for such use, depending on the liquid to be stored in the tank. The internal sloping floor 102 may also extend upwards along and overlapping of the shell and head of the tank, as desired, to create a liner extending upwards along the inner tank wall. Extending the floor in this manner can provide a more economical alternative to fabricating the tank completely from metal such as stainless steel. This construction may also reduce galvanic action between, for example, a stainless steel liner and a carbon steel tank. The floor at the collection point (112 and/or 118) may also serve as the location for gauging of the liquid levels.
Access to the collection points, such as collection point 112 may be provided via the draw-off pipe 106, which may be installed within a fill pipe that extends to nearly the bottom of the tank 100, near the collection point 112. The draw-off pipe 106 may extend nearly to the bottom of the tank, for example, approximately 2″ from the bottom at the collection point, though other lesser (or greater) lengths may be used. Alternatively, the draw-off pipe may be configured to terminate on the floor of the fuel storage tank at the collection point, with access openings in the wall of the bottom of the pipe to allow free flow collection of the water and sludge. The draw-off pipe 106 may be approximately the same diameter as the fill pipe or may be substantially smaller in diameter. In this manner, the water and/or sludge may be removed using a vacuum or other automated suction (negative pressure) device, or a manual pump, placed at or inside the opening of the draw-off pipe 106 for proper disposal or treatment of unwanted materials by fuel service personnel. The draw-off pipe 106 may be composed of, for example, carbon steel, stainless steel, aluminum, other metal alloys, polyvinyl chloride, epoxy, fiberglass or other appropriate material known in industry for such use. If an additional collection point 118 is used, an additional draw-off pipe 126 located above collection point 118 may be provided for removing water and/or sludge in a manner similar to that of draw-off pipe 106.
Steel tank 100 may be comprised of an outer wall, shown partially at 124. Communication between the interstice (or interstitial space) 123 between the outer wall 124 and the primary tank, and the space between the internal sloping floor 102 of primary tank and the floor of the primary tank may be accommodated by including an opening 125 in the floor of the primary tank. Such communication may be used to monitor and test the tightness of the floor.
FIG. 1 is an example of a UST, but the tank design may be modified and adjusted for use as an AST, if desired. ASTs are built to comply with safety code requirements that are different from those set for USTs. ASTs can be installed vertically or horizontally. An AST may have any shape, including, e.g., a rectangular shape. The disclosed plate(s) creating an internal sloping floor may be fabricated into all such embodiments of ASTs. Horizontal tanks and rectangular tanks are typically fabricated with at least two supports along the bottom of the tank. The tanks may include emergency venting to comply with fire safety codes. Additional engineering may be carried out with regard to these supports and/or sumps, as will be appreciated by those having ordinary skill in the art. Also, liners and floor space may require additional venting measures to satisfy safety codes.
FIG. 2 shows a cross-sectional partial side end view of another example of a storage tank that is configured according to the principles of the disclosure. The storage tank seen in FIG. 2 may be configured with optional support mechanisms 202 and an optional sump 204 constructed. In this embodiment of the disclosure, a fitting or access may be constructed at the bottom of the tank to provide access to a collection point so that the water and/or sludge may be more readily extracted. As seen in FIG. 2, an optional sump or reservoir area 204 may be built into the tank. The sump 204 may be in the form of a projection such as a basin that extends out from the tank body, and may include an optional drainage pipe extending from the sump 204 to draw the unwanted materials away from the bottom of the tank in lieu of using a draw-off pipe located at the top of the tank, such as draw-off pipe 106 shown in FIG. 1.
Sumps fabricated with the body of the tank expand the tank space available to capture unwanted materials. However, some construction safety codes may require a minimum of about 0.25″ thick striker plate under fill and/or gauge openings, so the inner floor at this location may need to be constructed thicker to accommodate such code requirements. Tanks constructed as described herein may preclude the need for striker plates due to the addition of the internal sloping floor.
FIG. 2 shows the use of multiple internal plates to comprise the floor, with one set of plates lap welded, as seen at 206, and another set of plates butt welded, as seen at 208.
The bottom of the tank may also be constructed with loose or fixed support saddles, angles, pipes, skids, runner box or comparable tank support mechanisms 202 in order to facilitate the collection of the water and/or sludge to be removed at the sump 204. The welds for the support mechanism 202 should be located, for example, about 3″ or more from the welds for the sump 204, though greater or shorter distances are envisioned depending on the circumstances.
FIG. 3 shows another example of a cross-sectional side end view of the disclosure with optional sump 302 and optional tank lining 304 constructed according to the principles of the disclosure. In this embodiment, metal lining of carbon or stainless steel may be fabricated at the collection point over the sump 302. The welds of the sump 302 may be located, e.g., at least 6″ or more from the tank head 306.
FIG. 4 shows a cross-sectional front view of the disclosure with additional tank lining 404 and optional internal coating 406 constructed according to the principles of the disclosure. In this embodiment, optional internal coating may be applied to all or partial inside surface areas of the tank to better preserve the integrity and lifespan of the tank. The coating may be comprised of epoxies or polyurethanes, depending on the particular use of the tank. Additional lining 404 may also be used as necessary to preserve the integrity of the tank.
FIG. 5 shows a multi-compartment tank 500 incorporating flow control features. Tank 500 may comprise a first compartment 510 and a second compartment 520, separated by a steel wall, or bulkhead, 504. While only two compartments are shown in FIG. 5, additional compartments may be included. In some aspects, each compartment may be configured to hold a different liquid. For example, the first compartment 510 may be configured to store a first type of fuel (e.g., unleaded gasoline) while the second compartment 520 may be configured to store a second type of fuel (e.g., diesel fuel).
First compartment 510 may be configured with an internal sloping floor 514 within the compartment terminating at collection point 512, which may include an optional collection plate or striker plate 516 that may be internal or external to the tank. A draw-off pipe 516 may be provided above collection point 512 to facilitate collection of water and/or sludge in a manner similar to draw-off pipe 106 described above with respect to FIG. 1. Similarly, second compartment 520 may be configured with an internal sloping floor 524 within the compartment terminating at collection point 522, which may include an optional collection plate or striker plate 526 that may be internal or external to the tank. A draw-off pipe 526 may be provided above collection point 522 to facilitate collection of water and/or sludge collected in second compartment 520.
FIG. 6 shows a process for fabricating a storage tank with internal sloping floor, according to the principles of the disclosure. The process (600) begins upon receiving of a tank body (620), welding of one tank head to one end of the tank body (640), welding one or more plates inside the tank body and to the tank head to form an internal sloping floor (660), welding the other tank head to the other open end of the tank body (680), and welding the one or more plates to the other tank head (690). In accordance with aspects of the disclosure, the internal sloping floor may be configured with a lower end terminating above a collection point at the bottom of the tank. The tank may include a draw-off pipe installed above the collection point for removing water, sludge, or other undesirable elements from the tank. The inner floor may be formed in the tank so as to form a hermetic (or air-tight) seal between the inner floor and the tank floor.
While principles of the disclosure have been described above in reference to manufacturing a new tank, the principles may also be used to retrofit existing storage tanks in-situ. For example, internal plates may be added to an existing storage tank in accordance with the principles described above to create an internal sloping floor within the existing storage tank.
For instance, one or both of the tank heads may be removed from an existing storage tank (e.g., cutting the tank head off from the tank body) and carrying out the process shown in FIG. 6. Or, a cut-out at the top of the tank can be made to enable tank entry using safe practices known those having ordinary skill in the art, to carry out the process shown in FIG. 6 while an underground tank is still buried.
Although process steps, method steps, algorithms, or the like, may be described in a sequential order, such processes, methods and algorithms may be configured to work in alternate orders. In other words, any sequence or order of steps that may be described does not necessarily indicate a requirement that the steps be performed in that order. The steps of the processes, methods or algorithms described herein may be performed in any order practical. Further, some steps may be performed simultaneously.
When a single device or article is described herein, it ill be readily apparent that more than one device or article may be used in place of a single device or article, where more than one device or article is described herein, it will be readily apparent that a single device or article may be used in place of the more than one device or article. The functionality or the features of a device may be alternatively embodied by one or more other devices which are not explicitly described as having such functionality or features.
While the disclosure has been described in terms of exemplary embodiments, those skilled in the art will recognize that the disclosure can be practiced with modifications in the spirit and scope of the appended claims. These examples given above are merely illustrative and are not meant to be an exhaustive list of all possible designs, embodiments, applications or modifications of the disclosure. For example, various numbers of plates may be used, various shapes, sizes, materials, etc., may be used for each of the components described or contemplated herein,

Claims

What is claimed:

1. A fuel storage tank comprising a tank floor, comprising:

an internal sloping floor welded to a portion of the fuel storage tank near said tank floor or bottom;

a collection point located at a low end of the internal sloping floor, the collection point configured to collect water or sludge; and

a draw-off pipe configured to provide access to the collection point fir removing the water or sludge from the tank.

2. The fuel storage tank of claim 1, wherein the internal sloping floor is configured to create an internal slope to a grade of about 1% to greater than 5%.

3. The fuel storage tank of claim 1, wherein the collection point is located on said tank floor or bottom.

4. The fuel storage tank of claim 1, wherein the collection point comprises a sump built into the fuel storage tank at the collection point.

5. The fuel storage tank of claim 1, wherein the fuel storage tank includes a horizontal cylindrical tank, vertical cylindrical tank or rectangular tank.

6. The fuel storage tank of claim 1, wherein the fuel storage tank includes an underground or in-ground fuel storage tank, and wherein the fuel storage tank comprises a material made of one or more of carbon steel, stainless steel, duplex stainless steel, non-metallic fiberglass reinforce plastic, polyethylene, and concrete.

7. The fuel storage tank of claim 1, wherein the fuel storage tank includes an above-ground fuel storage tank, and wherein the fuel storage tank comprises a material made of one or more of carbon steel, stainless steel, duplex stainless steel, non-metallic fiberglass reinforce plastic, polyethylene, and concrete.

8. The fuel storage tank of claim 1, further comprising:

a first compartment; and

one or more additional compartments,

wherein each additional compartment comprises one or more additional collection points and one or more additional internal sloping floors.

9. The fuel storage tank of claim 1, wherein the internal sloping floor comprises a material made of one or more of carbon steel, stainless steel, duplex stainless steel, and non-metallic materials.

10. The fuel storage tank of claim 9, wherein the internal sloping floor comprises at least a non-metallic material, the non-metallic material comprising fiberglass reinforced plastic, polyethylene, or concrete.

11. The fuel storage tank of claim 1, further comprising:

a manway that provides access to an interior portion of the fuel storage tank.

12. The fuel storage tank of claim 1, wherein the draw-off pipe is configured to allow manual collection of the water or sludge from the collection point.

13. The fuel storage tank of claim 1, wherein the draw-off pipe is configured to allow automatic removal of the water or sludge from the collection point via a collection device.

14. The fuel storage tank of claim 1, wherein the internal sloping floor has a thickness of at least 10 gauge.

15. The fuel storage tank of claim 1, wherein the internal sloping floor has a thickness of less than 10 gauge.

16. The fuel storage tank of claim 1, wherein the draw-off pipe is configured to terminate about two inches above the tank floor at the collection point.

17. The fuel storage tank of claim 1, wherein the draw-off pipe is configured to terminate on the floor of the fuel storage tank at the collection point, and wherein the fuel storage tank further comprises one or more access openings in the wall of the bottom of the draw-off pipe for free-flow collection of the water and sludge.

18. The fuel storage tank of claim 1, wherein the fuel storage tank comprises a single wall tank; a horizontal cylindrical tank, a rectangular tank; a vertical cylindrical tank; a multiple containment tank; a double wall tank, a jacketed tank, or a double bottom tank.

19. The filet storage tank of claim 18, wherein the fuel storage tank comprises an external tank wall, and wherein the tank floor includes an opening for communication between an interstice between the tank floor and the external tank wall, and a space between the internal sloping floor and the tank floor.

20. The fuel storage tank of claim 1, wherein the fuel storage tank is an existing fuel storage tank, and wherein the internal sloping floor is added in-situ.

21. A fuel storage tank having an inner wall with a portion of the inner wall forming a tank floor, the fuel storage tank comprising:

an internal sloping floor hermetically affixed to a portion of the inner wall, forming an air-tight cavity between the internal sloping floor and said tank floor; and

a collection point located at a low end of the internal sloping floor, the collection point configured to allow water or sludge to collect and to be removed from the tank.

22. The fuel storage tank of claim 21, wherein the internal sloping floor includes an internal slope having a grade of about 1% to eater than 5%.

23. The fuel storage tank of claim 21, further comprising:

a first compartment; and

one or more additional compartments,

wherein each additional compartment comprises an additional collection point and an additional internal sloping floor.

24. The fuel storage tank of claim 21, wherein the internal sloping floor includes a thickness of at least 10 gauge.

25. The fuel storage tank of claim 21, wherein the internal sloping floor includes a thickness of less than 10 gauge.

26. A fuel storage tank having an inner wall with a portion of the inner wall forming a tank floor, the fuel storage tank comprising:

an internal sloping floor hermetically affixed to a portion of the inner wall, forming an air-tight cavity between the internal sloping floor and said tank floor;

a collection point located at a low end of the internal sloping floor, the collection point configured to allow water or sludge to collect and to be removed from the tank; and

a draw-off pipe configured to provide access to the collection point for removing the water or sludge from the tank.