Method for Capping Cellular Glass Blocks for the Load Bearing Insulation of Liquefied Gas Storage Tanks

FIG. 1 is a schematic sectional view of a liquefied gas storage tank having a base insulation of cellular glass blocks that are capped with a layer of vermiculite in accordance with the present invention.

FIG. 2 is a schematic view, illustrating in detail the capping layer that is provided between and on the cellular glass block layers of base insulation.

FIG. 3 is a schematic view of the cut face of a cellular glass block, illustrating the vermiculite compressed into the open hemispherical cells of the cellular glass block insulation.

Referring to the drawings and more particularly to FIG. 1 there is illustrated a low temperature or cryogenic storage tank 10 for the storage of liquefied gas such as liquid natural gas (LNG) and liquid oxygen (LOX). Practice of the present invention is not restricted to storage tanks for LNG or LOX, but is applicable to the storage of liquids at elevated temperatures, as for example the storage of hot chemicals. Furthermore, the present invention may be utilized with storage tanks supported above ground as on a pile cap foundation. The cryogenic tank 10 is a double wall vessel having an outer wall 12 spaced from an inner wall 14. The base of the outer wall 12 rests at ground level upon a circular concrete pad 16. The center portion of the concrete pad 16 is backfilled with earth 18 and a layer of sand 20 covers the earth 18 to the upper surface of the concrete pad. The sand layer 20 is provided with a center crown. The concrete pad 16 and the sand pad 20 support a base plate 22 of the outer wall 12. A leveling screed 24 of concrete or sand is poured on the base plate 22 of the outer wall 12 and serves as the base for the first course of cellular glass block insulation.

A ring 26 of cellular glass blocks are laid upon the leveling screed 24 adjacent the outer tank 12 and are arranged in a staggered array on the leveling screed 24. The cellular glass blocks of the insulation ring 26 and the remaining glass blocks utilized for insulation of the base of the cryogenic tank 10 are a shaped cellular glass article made from cellular glass nodules. U.S. Pat. Nos. 2,123,536; 2,611,712; 2,755,524; 2,860,997; 2,955,049 and 2,946,643 teach the making of cellular glass blocks for general insulation. Briefly, the process includes admixing pulverulent glass and a cellulating agent and subjecting the admixture to elevated cellulating temperature in a mold. The admixture softens and the cellulating agent reacts to cellulate the admixture and produce a shaped article of multicellular glass. The insulation blocks are thus formed from the blocks of the closed cell multicellular glass by cutting the block to the desired rectangular dimensions.

The cut face of the glass blocks has a plurality of open hemisherical cells 28 as illustrated in FIG. 3. As each course of the glass block insulation ring 26 is laid upon the leveling screed 24 inorganic particulate material, preferably vermiculite, is spread in a suitable manner over the cut face of the glass block to penetrate and fill the open hemispherical cells 28. In this manner the vermiculite particles form a cap 30 between the layers of cellular glass block 26. Vermiculite is an irreversibly compressible material so that upon application the vermiculite particles compress under preloading to fill the open cells 28 of the cellular glass blocks.

A concrete bearing ring 32 is cast upon the glass block insulation ring 26 and serves as the base for the inner wall 14 of the double wall cryogenic tank 10. With the concrete bearing ring 32 in place a glass block insulation base 34 is set upon the leveling screed 24 within the glass block insulation ring 26. As with the glass block insulation ring 26, a vermiculite capping 30 is applied on the cut face of each of the cellular glass blocks of the insulation base 34 to penetrate and fill the open hemispherical cells thereof.

A sand pad 36 is spread over the capped surface of the upper course of cellular glass block base 34 to approximately the level of the upper surface of the concrete bearing ring 32. With this arrangement the upper surface of the concrete bearing ring 32 and the sand pad 36 receive the base plate 38 for the inner wall 14. Thus, the base plate 38 of the inner wall 14 is insulated by the array of cellular glass blocks 26 and 34 having the vermiculite capping 30. The construction of the cryogenic tank 10 is completed by providing a fiber glass expansion blanket 40 in abutting relationship with the inside surface of the outer wall 12 within the annulus formed by the inner and outer walls 12 and 14. The remaining space between the inner and outer walls 12 and 14 is filled with loose perlite 42 and a 1 p.s.i.g. purge of nitrogen or vaporized natural gas is injected within the annulus.

Referring to FIG. 3, the vermiculite particles are spread over the surface of the cut face of the cellular glass blocks and fill the open hemispherical cells 28. Compression of the vermiculite particles as they are spread over the surface of the cellular glass blocks crushes the particles to form platelet-like structures. Further application and compression of the vermiculite particles binds the platelet-like structures together. In this manner the open cells 28 are completely filled to thereby cap the cellular glass blocks.

Vermiculite is an irreversibly compressible inorganic material and therefore the platelet-like structures will not rebound from the open cells 28. With this arrangement a vermiculite capping 30 of a preselected minimum thickness is applied to each course of the cellular glass block insulation base 26 and 34. The irreversible compressibility of the vermiculite capping 30 assures that the base insulation of the cryogenic tank 10 will not be elastically cycled when the tank is filled and emptied. A limited degree of deformation will take place upon the initial penetration and packing of the vermiculite particles into the open cells 28 of the cellular glass blocks to completely fill the cells and cap the blocks.

The following examples illustrate the present invention but are not intended as limitations thereof.

Compressive strength tests were run for capping of cellular glass block base insulation for liquefied gas in storage tanks using an Instron Universal Testing Machine, Model TTD. Each cellular glass block sample having a cut face forming open hemispherical cells was tested with one of three capping materials: hot asphalt (210.degree.-220.degree. F.) and 0.15 lb./ft..sup.2 felt, Johns-Mansville's 0.32 lb./ft..sup.2 asbestos paper having a thickness of 1/16 inch, and a layer of vermiculite aggregate. A course grade of granular vermiculite where the majority of the weight was between 8 and 50 Tyler standard screen mesh at a thickness in the range between about 3/16 inch to 1/4 inch was applied to the cut surface of the cellular glass block samples by screeding with a frame. Each experimental capping was applied to nine samples.

An average compressive strength for the hot asphalt and felt capping of the insulation samples was measured at about 122 p.s.i. at an average density of about 8.69 lb./ft..sup.3. An average compressive strength for the asbestos paper was measured at about 78 p.s.i. at an average density of about 8.83 lb./ft.sup.3. The vermiculite capping was measured to have an average compressive strength of about 149 p.s.i. at an average density of about 8.95 lb./ft..sup.3 .

The test results indicated the vermiculite capping to be a superior soft inorganic capping material having a high compressive strength and irreversibly compressible upon loading. As the vermiculite capping layer was applied the particles were precompressed under a load of about 42 p.s.i. and consequently crushed to fill the open cell of the cellular glass blocks and bring the particles into intimate contact with the open cells. In this manner the layer of crushed vermiculite functioned to distribute the compressive forces over the surface of the cellular glass blocks.

The effect of temperature on the compressive strength of cellular glass block insulation with vermiculite capping was tested using an Instron Universal Testing Machine, Model TTD, at a constant strain rate using a cross head speed of 0.05 in./min. at both room temperature and at cryogenic temperature. A two layer stack of 9 inch .times. 12 inch .times. 5 inch cellular glass blocks were capped with vermiculite and were measured to have an average compressive strength of about 133.8.p.s.i. at cryogenic temperature. For an identical test sample the compressive strength of the cellular glass block insulation capped with vermiculite at room temperature was measured at an average of about 124.7 p.s.i. From these results it may be concluded that vermiculite possesses superior compressive strength as a capping material for cellular glass block insulation at room temperature and at cryogenic temperature as well. In addition for the above test sample capped with hot asphalt, at room temperature an average compressive strength of 134.1 p.s.i. was measured. This indicates that the compressive strength of the vermiculite capping at room temperature is comparable to that of hot asphalt.

A comparison of the deformation properties between vermiculite capping and alternative capping materials for cellular glass block insulation was conducted using an Instron Universal Testing Machine, Model TTD. Four blocks of 5 inch cellular glass block insulation and five blocks of 4 inch cellular glass block insulation were cut into quadrants. One quadrant of each cellular glass block sample was tested with each of three capping materials: hot asphalt (210.degree.-220.degree. F.); Johns-Manville's 0.32 lb./ft..sup. 2 asbestos paper (single layer, 1/16 inch thick); and a layer of vermiculite aggregate (course grade) at a thickness between about 1/8 inch to 3/16 inch. A frame was used for screeding the layer of vermiculite on the surface of the glass blocks.

The following table illustrates the deformation properties of the various capping materials. It should be noted that the measured deformation includes the penetration and packing of the capping material into the top surface layer of the open hemispherical cells of the cellular glass block insulation as well as elastic/plastic deformations within the capping material and in the elastic deformation of the cellular glass block insulation.

According to the provisions of the patent statutes, I have explained the principle, preferred construction and mode of operation of my invention and have illustrated and described what I now consider to represent its best embodiments. However, it should be understood that the invention may also be practiced otherwise than as specifically illustrated and described .