US3514913A - Insulating foundation for a low temperature storage tank - Google Patents

Abstract

1,182,578. Liquefied gas storage containers. PITTSBURGH-DES MOINES STEEL CO. 12 July, 1968 [2 Feb., 1968], No. 33297/68. Heading F4P. A cylindrical flat-bottomed inner cold liquefied gas storage tank is supported by a plurality of spaced modules 40, 70'Fig. 4 located between the tank bottom 30 Fig` 1 and the flat bottom 20 of an outer tank and rigidly connected together by planking 90, and the spaces between the modules and that between the cylindrical side walls 32, 22 of the inner and outer tanks are filled with heat insulating material e.g. expanded perlite or mineral wool. The modules 40 which are peripherally arranged beneath the inner tank wall 32 comprise radially extending wood blocks 42, 46, tangential blocks 44 therebetween and top plates 50 all nailed together, whereas modules 70 which support the tank bottom 30 comprise hollow rectangular frames filled with loose insulation 62 and to which are nailed the planks 90. The latter are also nailed to shoulders 56 on modules 40. The exterior of wall 32 is secured by anchor straps 66 which pass between the sector-like space between blocks 40, through a concrete levelling pad (58) Fig. 3, (not shown) and into a concrete foundation 16 supported by piles 14.

Description

June 2, 1970 A. H. NELSO N 3,514,913

INSULATING FOUNDATION FOR A Low TEMPERATURE STORAGE TANK Filed Feb. 2. 1968 2 Sheets-Sheet 1 ARD ELL H. NELSON BY WM We ATTORNEYS A. H. NELSON June 2, 1970 INSULATING FOUNDATION FOR A LOW TEMPERATURE STORAGE TANK Filed Feb. 2. 1968 2 Sheets-Sheet 2 INVENTOR ARDELL H. NELSON ATTORNEY-S United States Patented June 2, 1970 US. Cl. 52249 2 Claims ABSTRACT OF THE DISCLOSURE An inner tank is supported in spaced relationship to an outer tank, the inner tank being supported by a plurality of spaced hollow modules each of which is formed of a plurality of interconnected wooden members. The space between and within the hollow modules as well as the space between the walls of the inner and outer tanks are filled with an insulating material. The various modules supporting the inner tank are interconnected by wooden planking so as to unitize and rigidize the support means for the inner tank.

BACKGROUND OF THE INVENTION This invention relates to the construction of a tank for storing low temperature liquids.- Low temperature storage is defined as storage at a temperature of +32 F. or lower. This invention is more particularly concerned with an insulating foundation system for storage tanks in low temperature service.

When storing substances at atmospheric pressures, it is necessary that low temperatures be used in order for normally gaseous substances to remain in the liquid state. These low temperature liquids are normally stored in heavily insulated tanks. Quite often, these tanks are the flat bottom cylindrical type for economic reasons. When such a flat bottom type of tank is used, it is necessary to provide an insulating foundation under the bottom of the tank. This foundation must have good insulating qualities and also have sufiicient strength to support the weight of the storage tank and its contents. It must also enable easy and economical construction thereof.

Conventional foundation materials for low temperature storage tanks in the past have consisted of air entrained solids such as foamglass, and other materials, such as insulating concerete. Convention-a1 foundation materials and systems presently being used present a number of disadvantages. For example, foamglass may be used for moderate loads, but, it has a high unit cost. If used under conditions of heavy loading, it has a tendency to crush find deflect excessively which in turn creates design probems.

Light aggregate insulating concrete, on the other hand, while being of somewhat lower cost, presents other problems. Excessive heat of hydration can possibly be created by monolithicly placing a large mass of such insulating concrete. In addition, a large mass of such concrete may not have dried sufiiciently within a reasonable time after placement. Care must be taken to avoid excessive Water in mixing insulating concrete since the light Weight particles may be floated thus creating voids which could break down under load from the tank contents.

It is extremely difiicult to dry light aggregate insulating concrete even in very thin sections. Units having a thickness of 4 or 5 inches usually contain between and percent of retained moisture even after extended periods of drying. With this amount of retained moisture, the K value of insulating concrete normally used would be of the order of 1.6 to 1.8 B.t.u. per hour-sq. foot-inch of thickness-degree temperature diflerential. With this high value of thermal conductivity, the thickness of the bottom insulation system must be increased in order to reduce the amount of heat going into the tank. With this increase in thickness, the cost of the insulating system is therefore increased accordingly. Lightweight aggregate insulating units that are sometimes used for insulating foundations must be mnaufactured at special plants to control the quality of the finished product.

SUMMARY OF THE INVENTION In the present invention, the inner tank which is disposed in spaced relation to the outer tank is supported by a plurality of spaced hollow modules having loose fill insulation disposed therebetween and also therewithin. The loose fill insulation which may be expanded perlite or mineral wool and the like, is inexpensive, and the modules are formed of a pluarlity of interconnected wooden mem- 'bers or timbers. Means in the formof planking which comprises a plurality of wooden members is employed for interconnecting the modules with one another to unitize and rigidize the support means for the inner tank. This arrangement is unique and has not been employed in the prior art.

The bottom insulating system described herein has many advantages over prior state of the art. The timber used for both the shell support modules and the bottom support modules has a greater compressive strength than light aggregate concrete, therefore the amount of materials may be reduced accordingly. The ultimate strength of the timber is higher at low temperatures than at atmospheric temperatures. Since this oven dry state (for insulating concrete) is impractical to attain or maintain, the timber used as structural support has a distinct advantage in that it reduces the amount of heat conducted into the tank. The timber used for the shell support modules and the bottom modules is also less expensive than an qeuivalent amount of light aggregate insulating concrete to carry the same load. Since the height of the bottom supoprt modules may be accurately controlled 'by sawing ofi the timber to the proper length, the use of unfinished lumber is possible.

Both the shell support modules and the bottom support modules may be constructed with ease by the use of unskilled personal. This feature permits these components to be assembled anywhere. Since the components in the particular system described herein may be assembled at any construction site, the shipping problems are reduced accordingly. Since the amount of structural support can be reduced by using the timber (when compared to the amount of lightweight aggregate insulating units), the amount of loose fill insulation may he proportionately increased. This further achieves better over-all economy since the thermal conductivity of this loose fill material is better than either timber or lightweight aggregate insulating concrete, and the price of this loose fill insulation material is considerably less than either timer or the lightweight aggregate insulating concrete.

The foundation of the present invention may be employed with tanks of any diameter with relative ease by simply varying the amount and spacing of the various components. The timber making up the shell support modules and the bottom support modules and the bottom planking may be treated to make it both fire retardant and decay resistant. Since the timber units are much stronger than lightweight aggregate insulating concrete units, they may be easily handled without the chipping and breakage problems associated with lightweight insulating concrete. This precludes the possibility of having lightweight insulating concrete units installed as a support system containing hidden cracks which could 'break down under the load imposed by the tank contents.

3 BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevation partly broken away and in section illustrating a low temperature storage tank incorporating the insulating foundation of the present invention;

FIG. 2 is a view on an enlarged scale taken substantially along line 2-2 of FIG. 1 looking in the direction of the arrows, and being broken away for the sake of clarity;

FIG. 3 is an enlarged sectional view of a portion of the structure illustrated in FIG. 1;

FIG. 4 is a top perspective view partly broken away illustrating the arrangement of the modules and planking for supporting the inner tank;

FIG. 5 is a sectional view taken substantially along line 55 of FIG. 3 looking in the direction of the arrows; and

FIG. 6 is a sectional view taken substantially along line 66 of FIG. 4 looking in the direction of the arrows.

DESCRIPTION OF THE PREFERRED EMBODIMENT I Referring now to the drawings wherein like reference characters designate corresponding parts throughout the several views, a low temperature storage tank is indicated generally by reference numeral 10 in FIG. 1, the tank being supported above the ground level indicated by reference numeral 12 by a plurality of piles 14 extending upwardly from the ground. These piles may be supported by friction from contact with the earth and/ or by end bearing on suitable soil strata (not shown) disposed at a suitable distance below the ground level. A support means in the form of a supporting pile cap foundation 16 is provided formed of concrete or similar material having the necessary strength for supporting the weight of the tank.

The storage tank includes an outer tank and an inner tank, the outer tank comprising a bottom wall 20 which is substantially flat, a substantially cylindrical side wall 22 extending upwardly from the bottom wall, and a top wall 24 closing off the upper end of the outer tank, this top wall being generally dome-shaped in configuration as seen in FIG. 1. The walls of the tank are formed of a suitable structural material such as steel or the like adapted to withstand the pressures applied thereto during .use in the tank, the walls being suitably secured to one another as by welding or the like.

The inner tank of the storage tank includes a bottom Wall disposed substantially parallel with the bottom wall 20 of the outer tank, the inner tank also including a substantially cylindrical side wall 32 disposed inwardly of the side wall 22 to define an annular space therebetween. The inner tank also includes a top wall (not shown) which is also generally. of dome-shaped configuration and spaced from the top wall 24 of the outer tank. The space between the side walls of the two tanks as well as the space between the top walls thereof is filled with a loose fill insulation indicated generally by reference numeral 36 as is conventionally employed in low temperature storage tanks. This loose fill insulation may comprise in a typical example a granular material such as expanded perlite or a fibrous insulating material such as mineral wool and the like. Any suitable loose fill insulation may be employed for this purpose.

The inner tank is supported in the position illustrated by a plurality of modules, and as seen most clearly in FIG. 2, a first plurality of spaced shell support modules are indicated generally by reference numeral 40, these shell support modules being disposed in an annular spaced array so as to be disposed substantially beneath the side wall 32 of the inner tank.

Referring now particularly to FIGS. 3 and 4, the construction of the shell sup-port modules is clearly illustrated. Each of these shell support modules comprises a 4- plurality of interconnected timbers or wooden members. While a specific arrangement of timers is illustrated, it will be readily recognized that each of the shell support modules may be built up as desired utilizing a plurality of timbers to afford the desired size and strength.

As illustrated each of the shell support modules 40 includes a first plurality of timbers or blocks 42 disposed in edge-to-edge relationship with one another and extending substantially radially of the storage tank. A second plurality of timbers or blocks 44 are supported on the upper surface of the timbers 42, timbers 44 also being disposed in edge-to-edge relationship with one another and extending substantially tangentially with respect to the storage tank. Each of the shell support modules also includes a third layer of timbers or block 46 disposed in edge-to-edge relationship with one another and supported on timbers 44, the timbers 46 being disposed substant ally parallel with the timbers or block 42. All of these various timbers 42, 44 and 46 are suitably fastened together by means of fasteners 48 extending through the timbers. These fasteners are illustrated comprising elongated nalls, although it should be understood that any suitable fastener means such as bolts or the like may be employed for rigidly securing the timbers together to provide an integrated module.

Each of the modules also includes a wooden timber or flat member 50 secured to the upper surface thereof by a plurality of fasteners such as nails 52, it being noted that the edge 54 of member 50 as seen in FIG. 4 terminates short of the inner edge of the remainder of the module to define a radially inwardly positioned shoulder 56, these inner shoulders on the various modules serving to support the planking hereinafter described.

As seen especially in FIG. 3, a thin concrete levellng base 58 is cast over the bottom Wall 20 of the outer tank and comprises a leveling pad so as to provide a level foundation for the various support modules.

The shell support modules as well as the bottom support modules hereinafter described are supported on the upper surface of this leveling pad so that the inner tank will be properly supported in position. The leveling pad may be formed of regular concrete approximately 6 inches in thickness.

As seen particularly in FIG. 5, adjacent shell support modules 40 are disposed with respect to one another such that the facing ends 4% thereof are spaced apart to define a wedge-shaped space therebetween. A body of Fiberglas or similar material 60 is stiffed or forced into this space so as to be positioned in the location illustrated in FIG. 5 so as to retain loose fill insulation 62 inwardly thereof, this loose fill insulation as described hereinafter completely filling the space between the various bottom support modules of the foundation. This insulation is also disposed within the hollow modules.

The bodies of Fiberglas 60 extend vertically between the leveling pad 20 upon which the shell support modules are supported to the undersurface of the bottom wall 30 of the inner tank which rests upon the upper surface of members 50 of the shell support modules.

A plurality of shell anchor straps (or anchor bolts) 66 are provided, the upper ends of these straps being suitably secured as by welding to the outer surface of the side wall 32 of the inner tank, the shell straps extending down between adjacent spacing shell support modules as seen in FIG. 5, the anchor straps continuing downwardly and having the lower offset ends 68 thereof embedded within the material of the pile cap foundation 16 as seen most clearly for example in FIGS. 1 and 3. It is apparent that the relationship of the anchor straps and the bodies of Fiberglas material as seen in FIG. 5 are such that the anchor straps will tend ot hold the Fiberglas bodies 60 in operative position when subjected to pressure from the inner side thereof by the loose fill insulation bearing thereagainst. The use of anchor bolts in lieu of anchor straps will provide adjustment to compensate for differential contraction of the shell and anchor during cooldown.

As seen most clearly in FIG. 2, a plurality of bottom support modules indicated generally by reference numeral 70 are provided. A large number of these modules are provided in substantially equally spaced relationship beneath the bottom wall of the inner tank. The size and spacing of these bottom support modules will of course vary in accordance with the size of the tank and the load to be supported. Although only certain ones of the bottom support modules 70 are illustrated in FIG. 2, it should be understood that they will be disposed throughout the area beneath the bottom wall of the inner tank in substantially equally spaced relationship.

Referring now to FIGS. 4 and 6, the construction of the bottom support modules may be clearly understood. Each of the bottom support modules 70 is formed of four substantially identical rectangularly shaped timbers or planks 72, 74, 76 and 78 which are interconnected in the manner shown by suitable fasteners 80 comprising spikes, bolts, nails and the like to form hollow post-like sections. It is apparent that the bottom support modules each comprise a hollow construction adapted to receive loose fill therewithin.

Means for interconnecting the modules with one another comprises planking, this planking including a plurality of adjacent timbers 90 disposed in edge-to-edge relationship as seen most clearly for example in FIGS. 3 and 4, these timbers being suitably secured to the respective modules by means of suitable fasteners such as spikes, bolts, nails and the like 92. The outer peripheral edge portion of the over-all planking is supported on the radially inner shoulders 56 of the shell support modules previously described, while the joints between the various lengths of planking aligned with one another are designed to be disposed over one of the bottom support modules. The individual members 90 of the planking are supported on the upper ends of the bottom support modules.

The loose fill insulation 62 previously described is adapted to substantially fill the space between the bottom support modules 70 as well as the space within the hollow interiors thereof, this loose fill insulation extending between the bottom wall 20 of the outer tank and the undersurface of the planking, and also extending between adjacent sheel support modules as previously described in connection with FIG. 5 of the drawings.

It is apparent from the foregoing that there is provided a new and novel insulating foundation for a low temperature storage tank wherein the inner tank is supported by a plurality of spaced hollow modules having loose insulation disposed therebetween, and therewithin, these modules being formed of wooden material to provide the aforementioned advantages. The modules are interconnected with one another by the planking so as to unitize and rigidize the support means for the inner tank.

As this invention may be embodied in several forms without departing from the spirit or essential characteristics thereof, the present embodiment is therefore illustrative and not restrictive, and since the scope of the invention is defined by the appended claims, all changes that fall within the metes and bounds of the claims or that form their functional as well as conjointly cooperative equivalents are therefore intended to be embraced by those claims.

I claim:

1. An insulating foundation for a low temperature storage tank comprising an outer tank including a side wall and a bottom wall, an inner tank including a side wall spaced inwardly of the side wall of said outer tank, insulation provided between said side walls of the inner and outer tanks, said inner tank also including a bottom wall spaced inwardly of the bottom wall of said outer tank, said inner tank being supported by a plurality of spaced modules having insulation disposed therebetween, and means interconnecting said modules with one another to unitize and rigidize the support means for the inner tank, said modules including first a plurality of circumferentially spaced shell support modules of face contacting blocks disposed substantially beneath the side wall of said inner tank, said modules also including a second plurality of spaced bottom support modules of hollow postlike plank-formed sections disposed inwardly of said first modules and substantially beneath the bottom wall of said inner tank.

2. An insulating foundation for a low temperature storage tank comprising an outer tank including a side wall and a bottom wall, an inner tank including a side wall spaced inwardly of the side wall of said outer tank, insulation provided between said side walls of the inner and outer tanks, said inner tank also including a bottom wall spaced inwardly of the bottom wall of said outer tank, said inner tank being supported by a plurality of spaced modules having insulation disposed therebetween, and means interconnecting said modules with one another to unitize and rigidize the support means for the inner tank, said plurality of modules including a first plurality of spaced shell support modules face contacting wooden blocks disposed substantially beneath the side wall of said inner tank and a second plurality of spaced bottom support modules of hollow post-like wooden sections disposed beneath the bottom wall of said inner tank, each of said shell support modules comprising a plurality of interconnected wooden members, the insulation disposed between said modules comprising loose fill insulation substantially filling the space 'between said modules, means for retaining said loose fill insulation in position, said shell support modules defining shoulders thereon, the means for interconnecting said modules with one another comprising a plurality of wooden members defining planking, the edges of said planking being supported on said shoulders, said planking also being supported on the upper ends of said bottom support modules, the planking being rigidly attached to said shell support modules and said bottom support modules, the. bottom wall of said inner tank resting upon and being supported by said planking.

References Cited UNITED STATES PATENTS 2,520,883 8/1950 Kornemann et al. 220-18 3,076,317 2/ 1963 La Fave 52249 3,338,010 8/1967 Waugh 52249 FOREIGN PATENTS 188,513 9/1907 Germany.

FRANK L. ABBOTT, Primary Examiner I. L. RIDGILL, 1111., Assistant Examiner US. Cl. X.R.

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