Abstract:
An above-ground, double-walled, tank for holding combustible material and supporting a generator has an outer tank and an inner tank with structural baffles, all made from type 316 stainless steel. An interstitial space formed by the outer tank and inner tank is filled with a fire resistant solution consisting of a fire block gel and water. An internal support system, including structural baffles in the inner tank, provide a structure to support a generator and other equipment on the top of the tank without the use of tank wall stiffeners or external beams. A level detector in the interstitial space detects changes in the level of the fire resistant solution. A water detector in the inner tank detects the presence of water. The fire resistant solution may be removed from the interstitial space for tank inspection and repair.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims priority from U.S. provisional application Ser. No. 60/410,869 filed on Sep. 12, 2002, incorporated herein by reference. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002]     Not Applicable  
       INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC  
       [0003]     Not Applicable  
       BACKGROUND OF THE INVENTION  
       [0004]     1. Field of the Invention  
         [0005]     This invention pertains generally to above ground fuel tanks for generators, and more particularly to a lightweight, low profile base tank with fire resistive, impact resistive and leak protection elements.  
         [0006]     2. Description of Related Art  
         [0007]     Many auxiliary generators that provide remote or backup power are mounted on a base tank as an integrated system. The base tank is required to provide sufficient fuel to the generator system to run for extended periods of time without refueling. Space for installation and access for auxiliary generators is often constrained by site features and facility design, limiting the equipment that may be used for positioning. For a given space, the dimensions and profile of the tank, along with the necessary mounting system for the generator, define the volume of fuel that may be accommodated in a base tank.  
         [0008]     In most applications, aboveground tanks must have secondary containment to prevent fuel leaks to the environment and employ a double wall tank design. Underwriters Laboratory Inc. (UL) 142 standard (incorporated herein by reference) for steel aboveground tanks for flammable and combustible liquids is a safety standard that has been followed to construct commercially available double wall tanks for more than 14 years. A more recent UL 2085 standard for protected aboveground tanks (incorporated herein by reference) specifies limits to the heat transferred to the primary, or inner fuel tank, when exposed to a two-hour hydrocarbon pool fire. This standard further specifies a protection requirement from physical damage including projectile damage.  
         [0009]     Commercially available base tanks constructed to the UL 2085 standard typically use a double wall metal tank with concrete, solidified foam or other solid insulating material in an interstitial space of about six inches to resist the heat of a two hour fire and provide damage and projectile protection. The fire resistant insulation is typically installed before the tank is transported to the site. Increased tank weight increases cost and complexity of installation, however. The relatively large interstitial space required for solid insulating material significantly increases the footprint of the base tank and decreases fuel volume for a given installation space. Furthermore, once installed, solid insulating material cannot be easily removed from the interstitial space for inspection or repair.  
         [0010]     By way of example, U.S. Pat. Nos. 6,422,413 and 5,271,493 to Hall et al., incorporated herein by reference, teach using about six inches of poured concrete as an insulator. The concrete works well as a fire shield, however, the concrete also makes the tank extremely heavy and cumbersome to transport and install. Further, once the concrete has hardened, it cannot be readily removed for tank inspection or repair.  
         [0011]     U.S. Pat. Nos. 6,026,975, 6,257,437 and 6,349,873 to Slater, incorporated herein by reference, disclose Perlite, Vermiculite, fire retardant polymeric foam, ceramic or cementitious materials such as regular concrete, sand or a cementitious material containing a aggregate as an insulator material in the interstitial space. Slater describes a solid insulation, preferably concrete, in an interstitial space, preferably 6 inches to provide the required fire resistance and impact resistance for the UL 2085 standard. Slater does not teach a tank embodiment with an interstitial space of less than 6 inches that meets the UL 2085 standard nor the use of a non-solid fire resistant insulation in the interstitial space.  
         [0012]     Other methods have been employed to provide fire resistance to above-ground fuel tanks. For example, U.S. Pat. Nos. 5,285,920; 5,012,949; 5,038,456 and 4,989,750 to McGarvey et al., incorporated herein by reference, describe above-ground fire resistant tanks that have a sprayed-on exterior fire resistant intumescent material such as Chartek. McGarvey further teaches a double wall tank embodiment with a solid insulation material such as Vermiculite, foamed concrete, Fendolite, Styrofoam or pumice in the double wall space. McGarvey does not, however, teach a combination of exterior fire resistant material, interstitial insulation and support structure necessary to function as a generator base tank. Furthermore, McGarvey does not teach a non-solid insulation material for the interstitial space.  
         [0013]     Although several above-referenced patents suggest materials other than A-36 mild steel for tank walls, such as plastic, fiberglass, or corrosion resistant steel, they do not suggest any particular type of steel that would provide the combined advantage of improved heat conduction, impact resistance, and as corrosion resistance to a water base fire resistant solution in the interstitial space. In fact, the corrosion resistant steels described do not exhibit those properties.  
         [0014]     Furthermore, in order to support a generator on the top of a base tank, there must be a support structure extending from the equipment pad, to the mounts of the generator on the tank. For example, U.S. Pat. Nos. 6,026,975, 6,257,437 and 6,349,873 to Slater, incorporated herein by reference, disclose stiffening members for the top and bottom walls of the inner tank, top and side walls of the outer tank, and support beams along the top outer tank wall. These stiffening members provide support for the generator, however this external support configuration adds significant weight and size to the tank system and can interfere with generator maintenance access. However, none of the patents referenced above suggest the use of baffles in the inner tank as a means of support for the generator.  
         [0015]     Therefore, there is a need for a lightweight low-profile base tank designed to meet the UL 2085 standard and support commercially available generators. Further, the capability to install a fire resistant material in the interstitial space after tank installation and inspect and repair the tank without dismantling is highly beneficial to overcome shortcomings of bulkier and heavier generator base tanks  
       BRIEF SUMMARY OF THE INVENTION  
       [0016]     The present invention satisfied the foregoing needs and overcomes deficiencies in previously developed tanks by providing, according to one aspect of the invention, a lightweight base tank for a generator system comprising an outer tank of type 316 stainless steel and an inner tank of type 316 stainless steel with structural baffles in the inner tank. In one embodiment, the outer tank and inner tank are structurally coupled to form a relative small interstitial space. An intumescent fire resistant coating impregnated with a thermal resistant fiberglass mesh is placed on the outside of the outer tank. After the tank is installed, the interstitial space between the inner tank and outer tank is filled with a fire resistant solution.  
         [0017]     The inventive combination of a type 316 double wall steel tank with an outer intumescent fire resistant coating coupled with a fire resistant solution in the interstitial space exhibits sufficient fire resistance to meet the UL 2085 standard. The physical properties of the type 316 stainless steel combined with the fire resistant solution in the interstitial space also exhibit sufficient resistance to physical and projectile damage to meet the UL 2085 standard.  
         [0018]     In one embodiment, generator mounts on the top of the outer tank are supported in part by structural baffles in the inner tank and interstitial spacers between the inner tank and outer tank. No external columns, beams or stiffeners are necessary to support a generator.  
         [0019]     The fire resistant solution can be removed for inspection or repair of the tank at the site. A leak detection system with a level sensor is located in the interstitial space and can detect a leak in the outer tank or in the inner tank. A water detection system may also be located in the inner tank to detect leaks. An antifreeze solution is optionally added to the fire resistant solution to protect the solution from freezing in cold climates.  
         [0020]     One aspect of the invention is a light weight base tank for a generator using type 316 stainless steel for the walls of the inner tank and the walls of the outer tank. In one mode of this aspect, the thickness of the outer tank walls is about one-quarter inch. In another mode of this aspect, the thickness of the inner tank walls is about three-sixteenths of an inch.  
         [0021]     Another aspect is a base tank having type 316 stainless steel for tank walls for beneficial heat conductance, projectile resistance and corrosion resistance.  
         [0022]     A further aspect is a base tank with baffles configured in an inner tank for heat conduction and internal support. In one mode of this aspect, the baffles are made of type 316 stainless steel. In another mode, the baffles couple opposite side walls of the inner tank and couple the top wall and bottom wall of the inner tank.  
         [0023]     Another aspect is a base tank with a coating of intumescent paint on the outer tank. In one mode of this aspect, a thermal resistant fiberglass mesh is embedded in the coating of intumescent paint. In another mode the intumescent paint is Thermolag 3000™.  
         [0024]     A further aspect is a base tank with an interstitial space between the inner tank and the outer tank of about two inches or less for side and bottom walls and about four inches or less for top walls. In beneficial mode of this aspect, the interstitial space between the side walls and bottom walls of the inner tank and the outer tank is about one inch.  
         [0025]     A still further aspect is a lightweight low profile base tank that meets the UL 2085 standard.  
         [0026]     Another aspect is a base tank with a fire resistant solution installed in the interstitial space between the inner tank and the outer tank. In one mode of this aspect, the fire resistant solution is installed after the base tank is in place. In another mode, the fire resistant solution can be removed to inspect or repair the base tank while the base tank remains in place. In a further mode, the base tank can be put back in service after a fire by replacing the fire resistant solution.  
         [0027]     A further aspect is a fire resistant solution consisting of at least two percent fire blocking gel and at least eighty-eight percent water. In one mode, the fire resistant solution is BARRICADE™. In another mode, the fire resistant solution can be modified to prevent freezing during cold temperatures. In a further mode, the fire resistant solution contains up to ten percent propylene glycol to prevent freezing.  
         [0028]     Another aspect is a lightweight low profile base tank with an internal support structure that includes baffles in the inner tank. In one mode of this aspect, a plurality of generator mounts are coupled directly to the top of the outer tank with no external support beams. In another mode, tubular generator supports couple the top of the inner tank to the top of the outer tank and align with the baffles in the inner tank and the generator mounts on top of the outer tank  
         [0029]     A further aspect is a base tank with a leak detection system with a level sensor in the interstitial space to detect loss of a fire resistant solution.  
         [0030]     A still further aspect is a base tank with a water detection system in the inner tank to detect water, or a solution containing water, leaking into the inner tank from the interstitial space.  
         [0031]     Further aspects of the invention will be brought out in the following portions of the specification, wherein the detailed description is for the purpose of fully disclosing preferred embodiments of the invention without placing limitations thereon. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)  
       [0032]     The invention will be more fully understood by reference to the following drawings which are for illustrative purposes only:  
         [0033]      FIG. 1  is a perspective view of the exterior of a base tank for a generator according to the present invention.  
         [0034]      FIG. 2  is a partial cross-section view of the base tank shown in  FIG. 1  taken through lines  2 - 2 .  
         [0035]      FIG. 3  is partial cross-section view of the base tank shown in  FIG. 1  taken through lines  3 - 3 .  
         [0036]      FIG. 4  is a side view of an alternative embodiment of the generator mount configuration shown in  FIG. 1 , wherein two baffles are employed.  
         [0037]      FIG. 5  is side view of a base tank according to the present invention shown with a generator, related components, and enclosure mounted on top shown in phantom. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0038]     Referring more specifically to the drawings, for illustrative purposes the present invention is embodied in the apparatus generally shown in  FIG. 1  through  FIG. 5 . It will be appreciated that the apparatus may vary as to configuration and as to details of the parts, and that the method may vary as to the specific steps and sequence, without departing from the basic concepts as disclosed herein. All joints are typically made with welds unless otherwise specified.  
         [0039]      FIG. 1  is a perspective view of the exterior of a fire resistant base tank assembly  10  before a fire resistant coating (shown in  FIG. 2  and  FIG. 3 ) is applied. Details of tank components such as ports for instrumentation, fuel supply, fuel return and venting, brackets for lifting and securing, and tank cut outs for electrical connections, as are known in the art, are omitted for clarity. Base tank assembly  10  comprises an outer tank  20  and an inner tank  50  which are positioned and configured as will be more fully described below.  
         [0040]     Outer tank  20  has a top wall  22 , two side walls  24 , two end walls  26 , and a bottom wall  28 . Outer tank  20  is preferably made from type 316 stainless steel or equivalent and, in a particular embodiment, the walls are one-quarter inch thick. A pair of base members  30 , coupled to side walls  24 , are provided to support tank  10  when it is placed on an equipment pad (not shown). Base members  30  preferably have reinforcement tabs  32  coupled to side walls  24 . In one embodiment, base members  30  and reinforcement tabs  32  are made from one-half inch stainless steel. A center support  36 , extending between end walls  26 , is coupled to the outside of bottom wall  28  and centered between base members  30  to provide further support to bottom wall  28  on the equipment pad. In one particular embodiment, center support  36  is one-half inch thick stainless steel. A plurality of generator mounts  38  are coupled to top wall  22  and are shown in further detail in  FIG. 2  through  FIG. 4 .  
         [0041]     An access port  40 , level detector  42 , fuel port  44 , and water detector  46  are also provided as will be described further with reference to  FIG. 2  and  FIG. 3 .  FIG. 2  is a partial side sectional view of the base tank assembly  10  in  FIG. 1 , and  FIG. 3  is a partial end sectional view of the base tank assembly  10  in  FIG. 1 . Access port  40 , level detector  42 , fuel port  44  and water detector  46  are repositioned in these views for clarity.  
         [0042]     Inner tank  50  has a top wall  52 , two side walls  54 , two end walls  56  and a bottom wall  58 . Inner tank  50  is preferably made of type 316 stainless steel or equivalent and, in a particular embodiment, is three-sixteenths inches thick. Inner tank  50  is fluidly connected to one or more fuel ports  44  which can be used for filling, venting, fuel supply, fuel return or measurement. Water detector  46  has a sensor  48  positioned in inner tank  50  adjacent bottom wall  58  to detect the presence of water.  
         [0043]     Inner tank  50  is positioned within outer tank  20  to form an interstitial space  60  which is fluidly connected to access port  40 . Interstitial space  60  has a top space  62  defined by top walls  22  and  52 , two side spaces  64  defined by side walls  24  and  54 , two end spaces  66  defined by end walls  26  and  56 , and a bottom space  68  defined by bottom walls  28  and  58 . In one mode, top space  62  is at least about four inches between top wall  22  and top wall  52 , side spaces  64  are about one to two inches between side walls  24  and  54 , end spaces  66  are one to two inches between end walls  26  and  56 , and bottom space  68  is about one to two inches between bottom walls  28  and  58 . In the preferred embodiment, side spaces  64 , end spaces  66  and bottom space  68  are about one inch between walls.  
         [0044]     One or more access ports  40  are fluidly connected to interstitial space  60  and can be used for filling, venting, measurement or removal of a fluid. Level detector  42  is fluidly connected to interstitial space  60  and detects a change in level of a fluid in interstitial space  60 .  
         [0045]     The bottom wall  58  of inner tank  50  is supported by and coupled to bottom wall  28  of outer tank  20  by spacer tube  70 . Spacer tube  70  is preferably made of type 316 stainless steel or equivalent and extends the width of end walls  56  of inner tank  50 . In one particular embodiment, spacer tube  70  is one inch by one inch box tubing. Other spacers with cross sections as channels, angles or hats, as are known in the art, may also be used.  
         [0046]     The top wall  52  of inner tank  50  is supported by and coupled to bottom wall  58  of inner tank  50  by tank baffles  72  having one or more holes  86  therethrough for fuel flow. Tank baffles  72  also couple the side walls  54  of inner tank  50 . Tank baffles  72  are spaced as necessary for support, but preferably not greater than approximately twenty-four inches apart and are structurally aligned with spacer tubes  70 . Tank baffles  72  are preferably made of type 316 stainless steel or equivalent.  
         [0047]     The top wall  22  of outer tank  20  is supported in part by, and coupled to, top wall  52  of inner tank  50  by a plurality of tubular generator supports  74 . Tubular generator supports  74  are positioned to support generator mounts  38  and are structurally aligned with one or more baffles  72 . Tubular generator supports  74  may also be used to support top wall  22  in locations not associated with generator mounts  38 . In one beneficial embodiment, tubular generator supports  74  are an eight inch by eight inch box tubing of one-quarter inch thick plate stainless steel about four inches long.  
         [0048]     A generator system (as shown in  FIG. 5 ) can be supported on tank assembly  10  without external columns, stiffening members or beams by the beneficial configuration and coupling of base elements  30 , center support  36 , bottom wall  28 , spacer tubes  70 , bottom wall  58 , tank baffles  72 , top wall  52  tubular generator supports  74 , top wall  22  and generator mounts  38 .  
         [0049]     Top wall  22  of outer tank  20  is also supported in part by an interstitial baffle  76  that couples top wall  22  of outer tank  20  to top wall  52  of inner tank  50  and is further aligned with a tank baffle  72 . Interstitial baffle  76  typically couples to side walls  24  and is adapted with openings (not shown) for the flow of fluid. In a beneficial embodiment, interstitial baffle  76  is made of one-quarter inch stainless steel or the like. In one beneficial embodiment, there is at least one interstitial baffle  76  for each pair of generator mounts  38 .  
         [0050]     The outside surface of top wall  22 , side walls  24 , and end walls  26  of outer tank  20  are covered by a layer of fire resistant fiberglass mesh  80 . The fiberglass mesh  80  is in turn covered by a coat of intumenscent paint  82 . In one particular method of installation, a first coat of intumescent paint  82  is applied to the walls of tank  20 . The fiberglass mesh  80  is applied while the first coat of intumescent paint  82  is still wet. A second coat of intumenscent paint  82  is the applied over fiberglass mesh  80 , effectively embedding the fiberglass mesh  80  within a thick coating of intumescent paint  82 . In a preferred embodiment, the intumescent paint  82  is Thermolag 3000™. In a preferred embodiment, the thickness of the fiberglass mesh  80  with the intumescent paint  82  on the outside walls of tank  20  is about one-eight inch.  
         [0051]     Interstitial space  60 , defined by the opposing walls of outer tank  20  and inner tank  50 , is filled with a fire resistant solution  84  through an access port  40 , preferably after site installation of tank assembly  10 . Fire resistant solution  84  comprises, in part, a compound that will significantly reduce the movement of a fluid, such as water, by convection when exposed to heat. A fire block gel, such as BARRICADE™, exhibits this property. Fire resistant solution  84  preferably comprises at least two percent fire block gel mixed with at least about eighty-eight percent water. Up to about ten percent propylene glycol may be added to fire resistant solution  84  to provide freeze protection.  
         [0052]     The specific use of type 316 stainless steel for outer tank  20 , coated with fire resistant fiberglass mesh  80  and intumescent paint  82 , combined with fire resistant solution  84  in interstitial space  60  and the use of type 316 stainless steel for inner tank  50  and tank baffles  72 , results in base tank  10  having a two-hour fire rating and resisting physical damage sufficient to meet the UL 2085 standard.  
         [0053]     Referring now to  FIG. 4 , an alternative embodiment of a support configuration for a generator mount  38  is shown. In this embodiment, a pair of baffles  72  are coupled to top wall  52  and aligned to provide support to tubular generator support  74  coupled to top wall  52 . In this way, additional structural support for generator mount  38  is provided through top wall  22 .  
         [0054]      FIG. 5  illustrates a generator system  100  mounted on a base tank assembly  10  with generator mounts  38  and without external brackets, beams or stiffeners. Connections, controls, panels and relief valves, known in the art, have been omitted for clarity. Alignment of baffles  72  and alignment of tubular generator supports  74 , are illustrated for the particular mounting configuration shown. Generator system  100  includes a motor  102 , a generator  104 , a radiator  106 , and an exhaust system  108 , shown partially in phantom. In this embodiment, an optional enclosure  110  is also supported by base tank assembly  10  without external brackets, beams or stiffeners. Enclosure doors and panels have been omitted for clarity. Enclosure  110  includes an exhaust fan  112 , an exhaust vent  114  and an air intake  116 . Enclosure  110  is preferably lined with a soundproofing material  118 , shown in phantom, for sound attenuation.  
         [0055]     As can be seen, therefore, the present invention comprises a base tank for storing flammable and combustible liquids and supporting a generator. In the preferred embodiment, the base tank has an inner tank and outer tank. A plurality of baffles couple opposing side walls of the inner tank and further couple the bottom wall of the inner tank to the top wall of the inner tank. The inner tank is positioned in relation to the outer tank such that an interstitial space is defined between said walls of said outer tank and said walls of said inner tank, which is filled with a fire resistant solution. Preferably the fire resistant solution comprises at least about 2 percent fire blocking gel, such as BARRACADE™, and at least about 88 percent water. More preferably, the fire resistant solution comprises up to about 10 percent propylene glycol. Also, the walls of the inner and outer tanks are preferably fabricated from type 316 stainless steel having a thickness at least about {fraction (3/16)} inch.  
         [0056]     The walls of the outer tank are preferably coated or covered with a fire resistant material. Preferably, the fire resistant material comprises fire resistant fiberglass mesh coated with an intumescent paint, and more preferably, the intumescent paint comprises a ⅛ th  inch coating of Thermolag 3000™.  
         [0057]     In a further preferred embodiment, the interstitial space adjoining said sidewalls of said inner tank and adjoining said bottom wall of said inner tank is about 2 inches or less, and the interstitial space adjoining said top wall of said inner tank is about 4 inches or less. More preferably, the interstitial space adjoining said sidewalls of said inner tank and adjoining said bottom wall of said inner tank is about 1 inch.  
         [0058]     Optionally, the base tank can include means for supporting a generator. Preferably, said means comprises (i) a plurality of base support members adapted to couple the bottom wall of the outer tank to an equipment pad and further adapted to support the weight of said base tank and a generator, (ii) a plurality of interstitial spacers configured to support the bottom wall of the inner tank on the bottom wall of the outer tank where the interstitial spacers are structurally coupled to the base support members and further adapted to support the weight of said inner tank and a generator, (iii) where the baffles in the inner tank are structurally coupled to the interstitial spacers and where the baffles are further adapted to support the weight of a generator, (iv) a plurality of tubular generator supports adapted to couple the top wall of the inner tank to the top wall of the outer tank in the interstitial space, (v) wherein the tubular generator supports are structurally aligned with the baffles and further adapted to support the weight of a generator, and (vi) a plurality of generator mounts coupled to the top wall of the outer tank, where the generator mounts are structurally coupled to the tubular generator supports and the generator mounts are further adapted to support the weight of a generator. Preferably, the baffles are spaced apart at a spacing of about 24 inches or less.  
         [0059]     As a further option, a level detector configured to detect change of level of the fire resistant solution in the interstitial space can be included. Another optional aspect of the invention is a water detector configured to detect the presence of water in the inner tank.  
         [0060]     Although the description above contains many details, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments of this invention. Therefore, it will be appreciated that the scope of the present invention fully encompasses other embodiments which may become obvious to those skilled in the art, and that the scope of the present invention is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather “one or more.” All structural, chemical, and functional equivalents to the elements of the above-described preferred embodiment that are known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the present claims. Moreover, it is not necessary for a device or method to address each and every problem sought to be solved by the present invention, for it to be encompassed by the present claims. Furthermore, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims. No claim element herein is to be construed under the provisions of 35 U.S.C. 112, sixth paragraph, unless the element is expressly recited using the phrase “means for.”