US 3076317 A
Description (OCR text may contain errors)
Feb. 5, 1963 l. v. LA FAvE 3,076,317
INSULATING FOUNDATION-FOR CRYOGENIC STORAGE TANK Filed Sept. 26, 1960 Fig. I
n INVENTOR. /van V. Lal-'ave Merriam, .9m/'M Marsha/l ATTORNEYS 3,076,317 Patented Feb. 5, 1963 3,076,317 INSULATING FOUNDATION FOR CRYOGENIC i STORAGE TANK Ivan V. La Fave, Homewood, Ill., assignor to Chicago Bridge & Iron Company, Chicago, Ill. FiledSept. 26, 1960, Ser. No. 58,524 2 Claims. (Cl. 61`36) This invention relates to the construction of a tank adapted Ifor storage of liquid cryogens. It is more particularly concerned with a foundation for storage tanks employed in this service.
Liquid cryogens `or frost vproducing substances such as liquefied oxygen, liquefied hydrogen, liquefied 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 ythe liquid state. Under these conditions the following temperatures are used: hydrogen -`423 F., oxygen -297 F.,Aand 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 hat 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 eectiveness of such material-aand it is therefore desirable to install the cryogenic storage tank inside a larger tank or housing which serves as a moisture barrier and 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 roof 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 streng-th 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, including the fact that excessive heat of hydration can be created by rnonolithically placing a large mass of concrete and also the fact that such concrete may not have dried sufficiently within a reasonable time after placement because of its large mass. Furthermore, if an extremely light type of insulating concrete having excellent insulating properties isused, such as foamed cement, it is sometimes diflicult to place it monolithically without encountering excessive slumping which destroys much of the insulating effectiveness.
According to this invention, there is provided a foundation for a flat bottom liquid cryogenic storage tank which combines the economic advantages of the use of granular or Ifibrous insulating material such as perlite or mineral wool with the structural advantage of using insulating concrete, and at the same time overcomes the disadvantages relating to excessive heat of hydration and Y excessively Ilong drying times when mass concrete is used.
An illustrative form of my invention is presented in the accompanying drawings, in which:
FIGURE l is a vertical cross-sectional view of a flat bottom cylindrical cryogenic storage tank built in accordance with this invention; and
FIGURE 2 is a horizontal cross-sectional view taken through the section 2 2 of FIGURE l. Y
Referring to FIGURE l, it can be seen that the cryogenie tank consists of an inner storage vessel 10 having flat bottom 11, cylindrical shell 12, and roof 13, al1 of metallic material having proper structural qualities at the extremely low temperatures of the stored product, such as stainless steel or aluminum. Inner vessel 10, containing the cryogenic liquid L, is surrounded by an outer shell or vessel 14 having a shape similar to inner vessel 10. Outer shell or vessel 14 has fiat bottom 15, cylindrical shell 16, and roof 17. To maintain inner vessel 10 in spaced relation from the bottom of outer vessel 14 and provide insulation having suitable bearing a cored, lightweight concrete foundation 18 is placed upon flat bottom 1S of the outer vessel 14. A large number of cylindrical voids 19 are provided in this foundation. In service, these voids are filled with a loose Iiill of an inexpensive granular or brous insulating material such asexpanded perlite. A concrete cap -20 is placed above the foundation 18 to support the iiat bottom` 11V of the outer vessel 14 element of the cryogenic tank. In this illustrative embodiment, annular space 21 between the shells and roofs of the inner vessel 10 and outer vessel 14 is filled with a loose lill of an in,- expensive granular insulating material such as expanded perlite 2,2.
Flat bottom 15 of the outer housing rests upon a prepared grade 23 which can consist of sand, gravel, dirt, a concrete slab on piles, or other suitable foundation. Where the prepared grade contains substantial quantities of moisture or where the tank is located in a geographical area in which proper drainage is difficult or impossible, it is preferable to use a porous grade material such as gravel or crushed stone and to locate the tank grade at an elevation suiiiciently high to be above the level of any ground water. In these installations the heat transfer between the supporting grade 23 and the cryogenic liquid L will be such that, vunless 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 24 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 24 is schematically shown in the form of tubing through which heated water can be circulated if necessary. In some instances it may be suflicient 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 mild 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 conventional insulating concrete foundation 60 inches thick is provided within the outer housing. A plurality of voids are provided for holding the loose iill of granular expanded perlite insulation. The foundation slab after the granular insulation has been placed is covered with a concrete cap upon which is positioned the inner storage vessel.
For the purpose of maximum economy, the ratio of the horizontal cross-sectional area of the voids to the horizontal cross-sectional area of the bottom supporting material should be a maximum consistent with the loadcarrying ability of the bottom supporting material. Each different combination of materials, i.e., granular and loadbearing, 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 5 to 40 pounds per cubic foot are used in the construction of the foundation. Lightweight aggregates can be used to produce the lightweight product or preferably conventional proprietary aeration techniques can be used to control the desired density of the concrete used.
In the drawings, the voids are shown as cylindrical, but they may as well have polygonal cross-sections. By designing the supporting foundations for the cryogenic tank to have a large number of voids, as shown in the drawings, the total mass of the foundation concrete is measurably lessened, and there is consequently a measurable reduction in the heat of 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 be 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 0.4 B.t.u./ sq. ft./hr./inch.
In FIGURE 1 a thin concrete cap is shown between the top of the poured concrete foundation 18 and the bottom 11 of the inner storage vessel. In order to provide a short span slab for bridging the cavities the concrete cap should be about 4 to 6 inches thick. It should be understood, however, that under certain circumstances the concrete cap may be dispensed with, particularly where the voids are of sufiiciently small cross-sectional area as to permit the tank bottom to bridge over the cavities or voids without excessive deection and where adequate provision has been taken to prevent moisture from getting into the insulation-filled voids.
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.
What is claimed is:
l. A cryogenic storage tank comprising an outer vessel including a substantially flat bottom resting on a graded foundation, an inner storage vessel disposed within and spaced from said outer vessel and having a substantially flat bottom, and a foundation for said inner vessel disposed between said bottom of said inner vessel and said bottom of said outer vessel which substantially covers the bottom of said outer vessel, said foundation comprising a lightweight concrete slab having a plurality of individual cylindrical cavities penetrating substantially the thickness of said slab and a thin concrete cap covering said slab, said cavities being tlled with a loose lill of dry insulating material.
2. A cryogenic storage tank comprising an outer vessel including a substantially at bottom resting on a graded foundation, an inner storage vessel disposed within and spaced from said outer vessel and having a substantially at bottom, a foundation for said inner vessel disposed between said bottom of said inner vessel and said bottom of said outer vessel which substantially covers the bottom of said outer vessel, said foundation comprising a lightweight concrete slab having a plurality of individual cylindrical cavities penetrating substantially the thickness of said slab and a thin concrete cap covering said slab, said cavities being lled with a loose ll of dry insulating material, and a heat transfer system disposed in the graded foundation below said bottom of said outer vessel for supplying heat to the graded foundation.
References Cited in the file of this patent UNITED STATES PATENTS 2,520,883 Kornemann et al. Aug. 29, 1950 2,777,295 Bliss et al. Ian. l5, 1957 2,959,318 Clark et al. Nov. 8, 1960 FOREIGN PATENTS 840,952 Great Britain July 13, 1960