US 3338010 A
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w. H. WAUGH 3,338,010 INSULATION FOUNDATION FOR LOW TEMPERATURE AND CRYOGENIC STORAGE TANKS Filed Dec. 22, 1964 /NVENTOR United States Patent O INSULATION FOUNDATION FOR LOW TEM- PERATURE AND CRYOGENIC STORAGE TANKS Whitney H. Waugh, Glen Ellyn, Ill., assigner to Chicago Bridge & Iron Company, Oak Brook, Ill., a corporation of Illinois Filed Dec. 22, 1964, Ser. No. 420,388 2 Claims. (Cl. 52-249) This invention relates to the foundation for a tank adapted for storage of liquid cryogens.
Liquid cryogens or frost producing substances such as liquefied oxygen, liquefied hydrogen, liqueed methane and similar liquefied gases have extensive industrial and defense applications. In storing these liquid cryogens at atmospheric pressures, it is necessary that extremely low temperatures be used in order for the normally gaseous materials to remain in the liquid state. Under these conditions the following temperatures are used: hydrogen 423 F., oxygen 297 F., and methane 258 F. Accordingly, the storage of liquid cryogens has an important part in the application of such cryogens for both industrial and defense purposes.
Normally, it is desirable to store liquid cryogens in ilat bottom cylindrical storage tanks because the initial cost of such tanks is substantially less than the initial cost of storage tanks having a more complicated configuration, such as spheres or the like. In order to prevent excessive transfer of heat into the cryogen stored in a cylindrical tank, it is necessary to insulate the tank from the surrounding atmosphere and also from the supporting ground. Moisture and other foreign substances must be kept away from the insulating materials in order to maintain the insulating effectiveness of such materials, and it is therefore desirable to install the cryogenic storage tank inside a larger tank or housing which serves as a moisture barrier yand also serves as a retaining chamber for the insulating materials. The annular space between the shells and roofs of the inner and outer tanks can then be filled with a loose fill of an inexpensive, granular, insulating material such as expanded perlite at a cost far below the cost of other suitable rigid and impermeable insulating material applied to the exterior shell and root surface of the cryogenic storage tank where no outer tank is utilized. In order to obtain the economy of construction that is inherent in the use of the double-walled, at bottom tank, it is necessary to provide an insulating material between the bottom of the cryogenic storage tank and the bottom of the outer tank which not only has excellent insulating properties but also is of suicient strength to support the weight of the cryogenic storage tank and its contents.
.Conventional foundation materials for cryogenic storage tanks in the past have consisted of air entrained solids such as foamed glass, and other materials. Such materials are satisfactory because they not only have the strength necessary to support the weight of the cryogenic tanks and its contents, but also are inorganic, a requirement which must be met in the case of the storage of liquid oxygen, for example.
The conventional foundation materials have presented a number of disadvantages. For example, foamed glass, although used successfully, has a very high unit cost. Insulating concrete, on the other hand, while being of somewhat lower cost, presents other problems inherent in pouring a large mass of concrete. Excessive heat of hydration can be created by monolithically placing a large mass of concrete and also such concrete may not have dried suiliciently within a reasonable time after placement because of its large mass. Furthermore, if an extremely light type of insulating concrete having excellent insulating properties is used, such as foamed cement, it is sometimes difficult to place it monolithically without encountering excessive slumping which destroys much of the insulating effectiveness.
n According to this invention, there is provided a foundat1on for a Hat bottom liquid cryogenic storage tank which combines the economic advantages of the use of granular when mass concrete is used.
An illustrative form of my invention is presented in the accompanying drawings, in which:
FIGURE 1 is a vertical cross-sectional View of a fiat bottom cylindrical cryogenic storage tank built in accordance with this invention;
FIGURE 2 is a horizontal cross-sectional view taken through the section 2 2 of FIGURE l;
FIGURE 3 is a side elevational view showing in greater detail structural features of the invention; and
FIGURE 4 is a plan View of FIGURE 3.
Referring to FIGURE l, it can be seen that the cryogenic tank consists of an inner storage vessel indicated generally at lll, having Hat bottom 1I, cylindrical shell 12, and roof I3, all of metallic material having proper structural qualities at the extremely low temperatures of the stored product, such as stainless steel or aluminum. Inner vessel I0, containing the cryogenic liquid L, is surrounded by an outer shell or vessel 14 having a shape similar to inner vessel l0. Outer shell or vessel I4 has cylindrical shell I6 and roof 17.
Outer vessel 14 is also provided with a fiat bottom or leveling pad 18 which rests upon a prepared grade I9 which may comprise sand, gravel, dirt, a concrete slab on piles or other suitable foundation. Leveling pad i8 is formed of poured concrete and may be of a thickness of from about three to six inches depending upon the structural requirements for the tank.
A plurality of concrete blocks 20 having cylindrical voids or cavities 21, and having a substantially greater height than width, are pla-ced on the leveling pad IS with their longitudinal axes vertically disposed. The height of the blocks are generally about l5 to 40% greater than the width, and more preferably about 20 to 25% greater. The concrete lblocks are preformed which eliminates pouring a large mass of concrete on the job site for the foundation. The blocks in place on the leveling pad act substantially as a hollow structural column and maintain inner vessel 10 in spaced relation from the bottom of outer vessel 14 and provide insulation. In the preferred embodiment, the concrete blocks are preferably cylindrical in shape having a -concentric core or void, but where desired, the Iblocks may have a different cross-section such as square, rectangular or other polygon-a1 shape. The blocks may be placed upon the leveling pad in either a substantially triangular pattern or a substantially square pattern depending upon such factors as the quantity of perlite required structurally to support the inner tank and the product load. As shown in FIGURE 2, blocks Ztla of smaller width or diameter than blocks Ztl may be used at each edge to transition into the concentric outer row. The blocks can `be in contact with each other or spaced apart so that the maximum advantage is taken of the eiciency of the loose fill perlite, which again depends upon the amount of perlite concrete required.
In service, the voids 21 of the concrete blocks as well as any space between the blocks are filled with a loose lill of an inexpensive granular or fibrous insulating material such as expanded perlite 22. A suitable cap 23, such as a reinforced concrete cap, is placed on top of each block Zti to support the flat bottom 11 of the inner vessel and to distribute the load to the concrete blocks. (See FIGURES 3 and 4.) Where desired, a wooden iiooring may be provided for capping the blocks and for providing a support for fiat bottom 11 of inner vessel 10. In this illustrative embodiment, annular space 24 between the shelves and roofs of the inner vessel 10 and outer vessel 14 also is filled with a loose ll of an inexpensive granular insulating material such as expanded perlite 22.
A thin concrete cap is shown between the top of the concrete blocks 20 and the bottom 11 of the inner storage vessel. In order to provide a short span slab for bridging the cavities, the concrete cap or wooden flooring should be about 3 to 6 inches thick. It should be understood, however, that under certain circumstances the concrete cap or wooden flooring may be dispensed with, particularly where the voids are of sufficiently small cross-sectional area as to .permit the tank bottom to bridge over the cavities or voids without excessive deflection and where adequate provision has been taken to prevent moisture from getting into the insulation-filled voids.
Annular ring 26 surrounds inner vessel 10 and is welded at its inner marginal edge to the vessel. A plurality of spaced braces Z7 further aids in supporting the annular ring. A plurality of spaced anchor bolts 28 extend through the annular ring and leveling pad 18 into a concrete ring wall or pile cap 29. The hooked end 36 of anchor bolt 26 is anchored in concrete ring wall or pile cap 29, such that upon tightening of bolt member 31, the inner vessel 10 is secured in place. The anchor bolts are regularly spaced so that they pass between the concrete blocks.
Where the prepared grade contains substantial quantities of moisture or where the tank is located in a geographical area in which proper drainage is diiiicult or irnpossible, it is preferable to use a porous grade material such as gravel or crushed stone and to locate the tank grade at an elevation sufficiently high to be above the level of any ground water. In these installations the heat transfer between the supporting grade 19 and the cryogenic liquid L will be such that, unless the grade is heated or ventilated in some way, it will freeze. The result could be a damaged tank. Freezing of the prepared grade can be avoided by providing duct Work or conduit system 32 through which a heat transfer medium can be circulated. Such freezing can occur because of heat transfer from the grade through the insulating material into the cryogenic tank. This Ventilating or heat transfer means is schematically shown in the form of tubing through which heated water can be circulated if necessary. In some instances it may be sufficient for the ducts of the heat exchange system to be merely left open to the atmosphere to permit natural circulation.
In a specific embodiment of this invention for use with a cylindrical storage tank utilized in the storage of liquefied methane at about 258 F. and atmospheric pressure having an outer vessel 60 feet in diameter fabricated from 1A: inch thick lmild steel plate and an inner storage vessel 52 `feet in diameter and 48 feet high fabricated from aluminum and insulated with expanded perlite granules disposed in the annular space. A concrete leveling pad 4 inches thick is provided for the outer vessel. Cylindrical concrete `blocks having a concentric core, and measuring 32 inches in outside diameter, 24 inches for the inside diameter and 35 inches in length, are placed upon the leveling pad and spaced about 12 inches apart. The cylindrical cores and space between blocks are filled withr granular expanded perlite insulation. Reinforced structural concrete caps measuring 44 inches by 88 inches and 4 inches thick are pla-ced directly over two cylindrical blocks so that when all the caps are in position, the bottom of the inner vessel will be resting on a substantially continuous slab or plate, and the bottom of the vessel therefore will not be required to span any voids or cavities.
For the pur-pose of rmaximum economy, the ratio of the horizontal cross-sectional area of the voids to the horizontal cross-sectional area of the concrete yblock should be a maximum consistent with the load-carrying ability 5 of the block. Each different combination of materials, i.e., granular and load-bearing, will demand a different ratio of cross-sectional areas dependent on the insulating and strength properties of each as well as the cost of each. Generally, however, cross-sectional area ratios within the range of about 1:1 to 30:1 are preferred.
Light-weight concretes having densities of about 28 to 40 pounds per cubic foot are used in the construction of the foundation. Light-weight aggregates can be used to produce the light-weight product or preferably conventional proprietary aeration techniques can be used to control the desired density of the concrete used.
A further advantage is that the concrete blocks can be preformed at the factory and shipped to the job site or the blocks can Abe cast locally thereby reducing substantially the costs of the finished system. In this manner, the blocks are completely dry ybefore being installed, and there is no disadvantage attendant with the liberation of heat or hydration produced during the hardening of the concrete. In addition, the large number of voids presents a much larger surface area for drying, which assures a drying of the mass of concrete within a relatively short time. This is particularly true if the cores are removed as soon as practicable after the concrete has set up.
In the foregoing illustrative embodiment, granular expanded -perlite was employed as the insulating material in the cavities of the cored tank foundation. Other loose ll insulation can lbe employed including expanded vermiculite, inorganic aerogels such as silica aerogel, granulated cork, shredded foamed polystyrene, shredded wood pulp, etc. Preferably, the insulation should have a particle size of less than about 1A; inch and K factor of less than about 0.25 B.t.u.-in./hr./ft.2/ F.
While a specific embodiment of this invention has been shown, it should be understood that the detail in which it has been shown is for the purposes of clarity only, and no undue limitations in the scope of the claims should be implied therefrom.
1. In a cryogenic storage tank having an outer vessel and an inner vessel disposed within and spaced from said outer vessel and having a substantially hat bottom, a foundation comprising:
la leveling pad disposed as the bottom of said outer vessel;
a plurality of concrete blocks disposed on said leveling pad, said blocks being contiguous to each other; each of said blocks having a void extending longitudinally throughout said block;
said blocks disposed on said pad having their longitudinal axes vertically arranged;
means for covering said top of said blocks disposed on said pad; and,
said voids in said blocks and the space between said blocks being filled with a loose iill of dry insulating 60 material.
2. The foundation according to claim 1 wherein said concrete blocks are cylindrical blocks each having a concentric core.
References Cited UNITED STATES PATENTS 2,520,883 8/ 1950 Kornemann et al 220-18 3,076,317 2/1963 La Fave 52-249 FOREIGN PATENTS 686,955 5/ 1964 Canada.
188,573 9/ 1907 Germany.
14,649 8/1892` Great Britain.
FRANK L. ABBOTT, Primary Examiner.
I. L. RIDGILL, Assistant Examiner.