US2999366A - Insulated cryogenic storage tank - Google Patents

Description

Sept 1951 l. v. LA FAVE ETAL 2,999,366

INSULATED CRYOGENIC STORAGE TANK Filed Dec. 19, 1958 2 sheetswsheet 1 s 1/ Fig. .1

l 5 //3 22 GP \U\ A I l n l i. 3 Fl. 4

INVENTORS 1 Ivan V. Lal-ave BY Ivan L WIssm/fler Merriam, Larch 8 Smifl;

A T TOR/V5 YS Sept. 12, 1961 v. LAFAVE ETAL 2,999,366

INSULATED CRYOGENIC STORAGE TANK Filed Dec. 19, 1958 2 Sheets-Sheet 2 Fig. 2 I 67 INVENTORS Ivan 1 [.aFave BY Ivan L. Wissmi/ler Merriam, Larch 8 .Sm/fll A T TOR/V5 Y5 2,999,366 INSULATED CRYOGENIC STORAGE TANK Ivan V. La Fave, Oak Lawn, and Ivan L. Wissmiller,

Chicago, 11]., assignors to Chicago Bridge & Iron Company, Chicago, 11]., a corporation of Illinois Filed Dec. 19, 1958, Ser. No. 781,675 7 Claims. (Cl. 62-45) This invention relates to insulated cryogenic storage tanks. It is more particularly directed to methods and apparatus for preventing excessive consolidation of the insulating material employed in the construction of tanks used for the storage of liquids at extremely low temperatures.

In recent years, both industrial and military uses for liquid cryogens such as liquefied oxygen, liquefied hydrogen, and liquefied methane have made it necessary to develop large capacity storage containers meeting the peculiar service conditions which are imposed by the extremely low temperatures resulting from the atmospheric pressure storage conditions at which such cryogenic materials preferably are maintained. One of the most difiicult problems to overcome is the prevention of excessive heat gain in the stored liquid cryogen. In order to prevent excessive heat gain it is necessary to provide etficient thermal insulation between the cryogenic liquid and the surrounding atmosphere.

It has been found that efiective insulation can be maintained in cryogenic storage tanks by constructing tanks comprising an inner vessel surrounded in spaced relationship by an outer vessel. The inner vessel is constructed of a metal having those metallurgical properties which are necessary to prevent it from becoming brittle at the low service temperatures at which it must function. The outer vessel, fabricated from a suitable material of construction, acts as a retaining wall for the purpose of retaining insulating material within the annular space formed between the inner and outer vessels and also serves as a moisture barrier to prevent moisture or vapors from coming into contact with the insulating materials, freezing, and thereby destroying the effectiveness of the insulating materials.

When such a double vessel, storage tank is provided, a relatively inexpensive, light, insulating material such as expanded perlite can be used in the annular space bebetween the inner and outer vessels. The use of such a light insulating material in the past has, however, been complicated by the wide range of thermal movement of the inner vessel, particularly during any warming cycle which occurs when the tank has become empty. For example, if the insulating material is placed in the space between the walls at a time when both the inner and outer walls are at ambient temperature, as soon as an extremely low temperature liquid is placed inside the inner vessel, its wall contracts, increasing the width or thickness of the space between the inner wall and the outer wall. Loose insulating material therefore will have a tendency to flow downward into the wider space created by the thermal contraction of the inner wall, leaving a void of such material at the top of the space between the walls. Afer the tank has been emptied, the inner tank wall commences to warm up and thermal expansion takes place. This thermal expansion reduces the width or thickness of the space between the inner and outer walls, and has the effect of compressing or compacting the insulating material. In the case of expanded perlite, this compression can cause a crushing of the material into much finer particles, decreasing its volume thereby causing excessive consolidation and reducing its insulating value.

A repetition of the cooling and warming cycle will cause a continued trituration of the insulation and resulting packing so that the size of the void in the space be- 2,999,366 Patented Sept. 12, 1961 tween the walls near the top of the tank increases and more and more insulating material is crushed in other areas. If this condition is permitted to continue through.

several cycles resistance of the insulating material to the crushing forces caused by thermal expansion of the inner tank causes high buckling stresses in the inner tank shell which may be sufficient to cause a structural failure.

The annular space between the inner and outer vessels of the tank containing the insulation has a relatively constant thickness when the inner tank is at constant tem perature. When the inner tank is full of cryogenic liquid According to this invention there is provided an ap-j paratus and a method for preventing compaction of the insulating material used as insulation in the annular space of a double-walled cryogenic storage tank. The invention will be described in conjunction with the appended drawings in which:

FIGURE 1 is a partially cut away elevation view of a flat bottom, cylindrical, double-walled, cryogenic stor-' age tank employing the insulating technique of this invention;

FIGURE 2 is a partially cut away elevation view of a spherical storage tank built in accordance with this invention;

embodiment employed in distributing the fluidizing gas in the annular space in the tank shown in FIGURE 1; and

FIGURE 4 is a fragmentary schematic view of an alternate insulation fluidizing technique.

In FIGURE 1 there is shown a double-walled, cylin-. drical, flat-bottom, cryogenic storage vessel '10 compris-.

ing outer housing 11 having flat bottom 12,, cylindrical wall shell 13 and roof 14, and inner vessel 15 concentrically fabricated within outer vessel 11 to provide an annular space 16. Inner vessel 15 consists of flat bottom 17, cylindrical shell wall 15;, and roof 19. Inner vessel 15 is supported by insulating load-bearing pad 20 which rests on fiat bottom 12 of outer vessel 11. A light weight, liowable insulating material such as. expanded perlite 21 fills the space between sidewalls 13 and 18 and roofs 14 and 19. Air inlet nozzles 22 are provided in the outer cylindrical shell at an elevation at or slightly above the level of the inner flat bottom 23 and are connected by means of a manifold 25 shown schematically. An air outlet nozzle 24 is located at the top of the roof.

In order to provide a closed system for the circulation of the fluidizing gas stream during use in the warming phase of the loading and unloading cycle, a piping ar-' rangement schematically shown in FIGURE 1 can be used. The fluidizing gas steam leaving annulus 16 through nozzle 24 is transported via line 30 to a convential desiccator 31 which serves to provide a dry gas stream which is pumped through line 32 by means of pump 33. It is then distributed by means of suitablev manifold system 25 to inlet nozzles 22. Make-up for any losses in fluidizing stream is introduced through line 34. Dry nitrogen furnished from an auxiliary tank may provide the make-up gas. It could also be air passed through a desiccator. Suitable filter means (not shown) are provided at the outlet nozzles to prevent loss of insulation.

FIGURE 3 is a fragmentary view of an alternative In order to prevent the air flow from channeling, it is sometimes desirable to use a slightly different embodiment of the simple air inlet means: shown in FIGURE 1. FIGURE 3 shows a variation in which an annular perforated manifold pipe 48 is located in space 16 between sidewalls 13 and 18 at or just above the level of the inner flat bottom 17 to which air is supplied through an air inlet nozzle 41 which is connected to pump 33.

An alternative fluidizing technique which is employed in order to facilitate the fiuidization of the insulationtank 69 employing the instant invention comprising an outer spherical housing 61 supported by columns 62 and an inner spherical storage vessel 63 supported by suitable means, such as hanger bars 64 from the outer shell 61. Conventional piping connections for filling and einptying the sphere are not shown. The space between the inner and outer spherical shells is filled with a flowable light weight insulating material such as perlite 65. An air inlet nozzle 66 is provided at the bottom of the outer spherical shell and an air outlet nozzle 6"] is provided at the top. Additional inlets similar to those shown in FIGURE 4 may be used at difierent levels in the insulation space.

From the illustrative embodiments it is seen that compaction of the insulating material in the annular space between walls 13 and '18 of FIGURE 1 or 61 of FIG- URE 2, during thewarming phase of a loading and unloading cycle, can be prevented. It has been discovered that air can be blown through the spaces from the bottom to the top, and that the insulating material is sulficiently light that, if adequate quantities of air are blown through the space, a portion of the particles may be lifted or fluidized so as to prevent any insulating material from becoming crushed or compacted as the inner vessel walls thermally expand as they warm up. Vents 67 and 24 permit the escape of air from the space at the top of the tanks if non-circulating gas systems are used; or the circulation system shown in FIGURE 1 can be employed.

The insulating materials which are preferably employed are non-cohesive or substantially free-flowing, light weight, thermal insulators having a particle size sufiiciently small so as to prevent convection losses through circulation of air through the packed mass. Preferably, granular insulation having a particle size of less than about /6 inch is used. The particulate insulation should be substantially non-friable and have a k'factor of less than about 0.4 B.t.u./sq. ft./hr./inch. To avoid combustion problems encountered in the storage of liquid oxygen, inorganic substances such as expanded pcrlite, expanded vermiculite, inorganic aerogels such as silica aerogel, and the like can be used. Other insulation which can be used includes granulated cork, shredded foamed polystyrene, etc. Although granular insulation is used in the illustrative embodiments other types of insulation, such as fibrous materials, including shredded wood or bark, fiber glass waste or mineral wool can be used which can consolidate and cause excessive passive lateral pressure.

To effect the fluidization of the insulation a dry gaseous medium can be used such as nitrogen, carbon dioxide, air, or the like. The deleterious effect of frosting of the inner tank is prevented by dehumidifying the fiuidizing gas to produce a substantially bone dry gas. Conventional dehumidification or desiccation apparatus can be used to provide a fluidizing gas having the desired dryness.

Fluidizing conditions such as gas velocity, average size of particles, range of particle size, etc. are selected such that a dense phase of fluidized particles is produced with a minimum amount of total entrainment of the insulation particles in the exiting gas stream and substantially no net movement of the particles. For example, in a storage tank employed in the storage of liquefied methane an outer cylindrical, steel vessel 73 feet in diameter and an inner concentric, cylindrical aluminum vessel 67 feet in diameter has an annular space 3 feet wide. With this space filled with granular expanded perlite particles having a density of 5 pounds per cubic foot, bone dry air introduced into the annular space through a distribution ring fabricated from 6 inch pipe having /4 inch holes spaced at tniervals of 6 inches along the top surface in suthcient amounts to produce a gas velocity of about 0.3 foot per second through the annular space will provide satisfactory fluidization. In general, however, forv the light weight particle sizes employed gas velocities within the range of about 0.1 to 1.0 foot per second will produce good fluidization.

Under normal conditions the fiuidization of the particulate insulation within the annular space between the inner storage vessel and the outer housing will occur.

during the warming phase of the loading and unloading storage cycle and is therefore carried out intermittently. This intermittent operation requires suitable conventional flow control means, not shown, to be provided for effecting the periodic flow of fluidizing medium through the system. Because the cooling or loading and warming or unloading phases of the storage cycle are not carried out at frequent intervals, it is generally unnecessary to provide automatic controls which initiate and terminate the fiuidizing of the insulation. Accordingly, the

operation of pump 33 can be controlled by conventional, -manually operated means.

It is to be understood, however, that the fluidization of the particulate insulation does not have to be carried out during each warming phase of the storage cycle. Certain insulations are not as susceptible to compaction as other particulate insulation material and several storage cycles can occur without the need for fluidizing the particulate insulation material during each warming phase to avoid or eliminate compaction of the insulation. In carrying out the fluidization, even though it is preferred to initiate the fluidization at the beginning of the warming phase of the storage cycle, the particulate insulation material can be fluidized during any period of the warming cycle and can even be fluidized after the warming cycle has been completed to find up any insulation which has become compacted.

In fabricating the inner and outer vessels conventional materials of construction, preferably low carbon steel, are used for the latter. The inner vessel, however, must be constructed from materials which do not become brittle in the low temperature service to which they are exposed. Metals such as aluminum, stainless steel, cupro-nickel, and others have desirable properties over substantially the entire temperature range. Steel alloys, however, have to be notch tough (Charpy Impact Test of about not less than 15 foot-pounds keyhole at the lowest expected operating temperature of the material), e.g. 18-8 stainless steel, 9% nickel alloy steel, and others.

The instant invention has particular application in the storage of normally gaseous liquefied materials at temperatures near the boiling point of the material and at substantially atmospheric pressure. If desired, however, the instant invention can also be utilized in providing storage facilities in which the fluid contents of the inner storage vessel are maintained. at pressures other than atmospheric.

. Particular embodiments of this invention have been shown and described in this application for purposes of clarity, but variations may be made by persons skilled in the art without departing from the spirit or scope of this invention, and no undue limitations should be implied from the embodiments shown and described in determining the scope of the appended claims.

What is claimed is: v

l. The method of preventing compaction of particles of light weight insulating material disposed within an annular space provided by an outer housing and a spaced inner metallic storage vessel, said inner vessel being employed in the cryogenic storage of liquefied, normally gaseous materials and being subject to thermally induced contraction and expansion during the filling and emptying of said inner vessel, which comprises suspending portions of said insulating material in a upwardly flowing gas in a dense phase with no net movement of said insulating material during periods when areas of the inner vessel are Warming to ambient atmospheric temperature and thermally expanding during the emptying of said inner storage vessel, the velocity of said flowing gas being sufficient only to suspend said insulating material.

2. The method of preventing compaction of particles of light weight insulating material disposed within an annular space provided by an outer housing and a spaced inner metallic storage vessel, said inner vessel being employed in the cryogenic storage of liquefied, normally gaseous materials and being subject to thermally induced contraction and expansion during the filling and emptying of said inner vessel, which comprises introducing a substantially water-free, gaseous fluidizing medium at peripherally spaced inlets in said annular space to induce a dense phase fluidization of said insulating material during periods when areas of the inner vessel are Warming to ambient atmospheric temperature and thermally expanding during the emptying of said inner storage vessel, said fiuidizing medium being introduced at a velocity sufiicient to avoid deleterious losses of insulating material through entrainment in said fiuidizing medium.

3. The method of preventing compaction of particles of light weight insulating material disposed Within an annular space provided by an outer housing and a spaced inner metallic storage vessel, said inner vessel being employed in the cryogenic storage of liquefied, normally gaseous materials and being subject tothermally induced contraction and expansion during the filling and emptying of said inner vessel, which comprises introducing substantially water-free air at spaced inlets in said annular space to induce a dense phase fluidization of said insulating material during periods when areas of the inner vessel are warming to ambient atmospheric temperature and thermally expanding during the emptying of said inner storage vessel, said fiuidizing medium being introduced at a velocity sufiicient to avoid deleterious losses of insulating material through entrainment in said fluidizing medium.

4. The method of preventing compaction of particles of light weight insulating material disposed within an annular space provided by an outer housing and a spaced inner metallic storage vessel, said inner vessel being employed in the cryogenic storage of liquefied, normally gaseous materials and being subject to thermally induced contraction and expansion during the filling and emptying of said inner vessel, which comprises introducing substantially water-free air at spaced inlets in said annular space to induce a dense phase fluidization of said insulating material during periods when areas of the inner vessel are warming to ambient atmospheric temperature and thermally expanding during the emptying of said inner storage vessel, said fluidizing medium being introduced at a velocity suificient to avoid deleterious losses of insulating material through entrainment in said fiuidizing medium, and venting said air from said annular space.

5. An insulated tank for the cryogenic storage of liquids comprising an inner fluid-tight storage vessel, an outer housing spaced apart from said inner vessel to provide an annular space, a light weight fluidizable insulating material substantially filling said annular space, gas distribution means including peripherally spaced inlet nozzles penetrating said outer housing adjacent the bottom thereof and terminating within said annular space, and gas outlet means penetrating said outer housing located in the top portion of said annular space, and means for supplying a gaseous fiuidizing medium to said gas distribution means from a source exterior to said tank.

6. An insulated tank for the cryogenic storage of liquids comprising an inner fluid-tight storage vessel, an outer housing spaced apart from said inner vessel to provide an annular space, a light weight fluidizable insulating material substantially filling said annular space, gas distribution means including an annular ring disposed Within said annular space and circumscribing said inner vessel, gas inlet means penetrating said outer housing and interconnected to said annular ring, and gas outlet means penetrating said outer housing located above the bottom of said annular space, means for supplying a gaseous fluidizing medium to said gas distribution means from a source exterior to said tank.

7. An insulated tank for the cryogenic storage of liquids comprising an inner fluid-tight storage vessel, an outer housing spaced apart from said inner vessel to provide an annular space, a light weight fluidizable insulating material substantially filling said annular space, gas distribution means including an annular ring disposed Within said annular space and circumscribing said inner vessel, gas inlet means penetrating said outer housing and interconnected to said annular ring, gas outlet means penetrating said outer housing located in the top portion of said annular space, and means for supplying substantially Water-free gas to said gas distribution means, from a source exterior to said tank.

References Cited in the file of this patent UNITED STATES PATENTS 1,825,022 Sommers Sept. 29, 1931 1,936,214 Sommers Nov. 21, 1933 2,148,109 Dana et al. Feb. 21, 1939 UNITED STATES PATENT OFFICE CERTIFICATION OF CORRECTION Patent No, 2 9995366 September 12 1961 Ivan V; La Fave et al.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 3 line 35 after "61" insert and 63 column 4 line 17 for "tniervals" read intervals column 5 line 16 for "a" read an Signed and sealed this 24th day of April 1962,

(SEAL) Attest:

ESTON 6 JOHNSON DAVID L, LADD Attesting Officer Commissioner of Patents

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