04/773580

06/08/1971

11/05/1968

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General American Transportation Corporation (Chicago, IL)

220/560.120

220/901, 220/565

F17C3/02; F17C3/00; B65D25/18

220/9A,10,15,26,18

3352443	Internal suspended insulating ceiling for storage tanks	November 1967	Sattelberg et al.
3419174	Method and apparatus for liquefied gas storage	December 1968	Engdahl

Leclair, Joseph R.

Garrett, James R.

What I claim is

1. A cryogenic storage tank comprising a closed shell having an insulated bottom and a substantially vertical cylindrical insulated sidewall and a domed roof supported by said sidewall, ceiling support structure mounted on said sidewall adjacent to the upper end thereof, a supporting column centrally positioned with respect to said shell bottom and extending upwardly above the intended maximum capacity level of the tank, a plurality of supporting struts extending upwardly and outwardly from said column adjacent to the top thereof, a support ring mounted on said struts adjacent to the upper ends thereof, and an insulated ceiling having an essentially imperforate outer portion surrounding a foraminous inner portion and mounted on said ceiling support structure and said support ring, said imperforate outer portion extending between said sidewall and said support ring and disposed above the intended maximum capacity level of the tank, said foraminous inner portion overlying the central portion of said support ring to allow passage of vapors therethrough for equalizing the pressure on the opposite sides of said ceiling while preventing convective circulation therebetween, whereby said insulated bottom and said insulated sidewall and said insulated ceiling define an enclosed insulating container for cryogenic materials.

2. A cryogenic storage tank comprising an inner shell having an insulated bottom and a substantially vertical cylindrical sidewall and a roof supported by said sidewall, an outer shell surrounding said sidewall and spaced therefrom and joined thereto adjacent to the upper and lower ends thereof and defining therewith a vaportight annular apace, insulation filling said annular space to a level slightly below the upper end thereof to provide a purge space above said insulation, ceiling support structure mounted on said sidewall adjacent to the upper end thereof, a substantially vertical supporting column centrally positioned with respect to said inner shell bottom and extending upwardly above the intended maximum capacity level of the tank, and an insulated ceiling having an essentially imperforate outer portion surrounding a foraminous inner portion and mounted upon said ceiling support structure and said supporting column, said ceiling overlying the area enclosed by said sidewall and disposed above the intended maximum capacity level of the tank and dividing the tank into a lower storage space and upper vapor space, said foraminous inner portion allowing passage of vapor between said storage space and said vapor space for equalizing the pressure on the opposite sides of said ceiling while preventing convective circulation therebetween, said sidewall having a plurality of communicating openings therethrough between said vapor space and said purge space for maintaining said purge space at a sufficient pressure to prevent infiltration of outside air.

3. A cryogenic storage tank comprising an inner shell having an insulated bottom and a substantially vertical cylindrical sidewall and a roof supported by said sidewall, an outer shell surrounding said sidewall and spaced therefrom and joined thereto adjacent to the upper and lower ends thereof and defining therewith a vaportight annular space, insulation filling said annular space to a level slightly below the upper end thereof to provide a purge space above said insulation, a tension ring disposed adjacent to the upper end of said sidewall and having a diameter slightly less than the diameter of said sidewall, a plurality of circumferentially spaced supporting means mounting said tension ring on said sidewall adjacent to the upper end thereof, a supporting column centrally positioned with respect to said inner shell bottom and extending upwardly above the intended maximum capacity level of the tank, a a plurality of supporting struts extending upwardly and outwardly from said supporting column adjacent to the top thereof, a support ring mounted on said struts adjacent to the upper ends thereof, a plurality of radially extending joist members respectively supported at the outer ends thereof by said tension ring and respectively supported at the inner ends thereof by said support ring, an essentially imperforate deck supported by said joist members above the intended maximum capacity level of the tank and closing the area between said sidewall and said support ring and dividing the tank into a lower storage space and an upper vapor space, a foraminous member supported by said support ring and covering the opening therein to permit equalization of the pressure on the opposite sides of said ceiling, and a body of heat insulating material supported upon and covering said deck and said foraminous member, said sidewall having a plurality of communicating openings therethrough between said vapor space and said purge space for maintaining said purge space at a sufficient pressure to prevent infiltration of outside air.

4. A cryogenic storage tank comprising a closed shell having an insulated bottom and a substantially vertical cylindrical insulated sidewall and a domed roof supported by said sidewall, ceiling support structure mounted on said sidewall adjacent to the upper end thereof, a supporting column centrally positioned with respect to said shell bottom and extending upwardly above the intended maximum capacity level of the tank, a pair of crown plates covering the top of said supporting column and being fastened together at the peripheries thereof, the bottom one of said crown plates being attached to the top of said column, a plurality of supporting struts attached at the bottom ends thereof to the upper one of said crown plates and extending upwardly and outwardly therefrom, a support ring mounted on said struts adjacent to the upper ends thereof, and an insulated ceiling having an essentially imperforate outer portion surrounding a foraminous inner portion and mounted on said ceiling support structure and said support ring, said imperforate outer portion extending between said sidewall and said support ring and disposed above the intended maximum capacity level of the tank, said foraminous inner portion overlying the central portion of said support ring to allow passage of vapors therethrough for equalizing the pressure on the opposite sides of said ceiling while preventing convective circulation therebetween, whereby said insulated bottom and said insulated sidewall and said insulated ceiling define an enclosed insulating container for cryogenic materials.

5. A cryogenic storage tank comprising a closed shell having an insulated bottom and a substantially vertical cylindrical insulated sidewall and a domed roof supported by said sidewall, ceiling support structure mounted on said sidewall adjacent to the upper end thereof, a supporting column centrally positioned with respect to said shell bottom and extending upwardly above the intended maximum capacity level of the tank, a plurality of supporting struts extending upwardly and outwardly from said column adjacent to the top thereof, a support ring mounted on said struts adjacent to the upper ends thereof, said support ring having a substantially L-shaped radial cross section including a vertically downwardly extending flange and a horizontally outwardly extending flange, the inner surface of said downwardly extending flange being attached to the upper ends of said supporting struts, and an insulated ceiling having an essentially imperforate outer portion surrounding a foraminous inner portion and mounted on said ceiling support structure and on the outwardly extending flange of said support ring, said imperforate outer portion extending between said sidewall and said support ring and disposed above the intended maximum capacity level of the tank, said foraminous inner portion overlying the central portion of said support ring to allow passage of vapors therethrough for equalizing the pressure on the opposite sides of said ceiling while preventing convective circulation therebetween, whereby said insulated bottom and said insulated sidewall and said insulated ceiling define an enclosed insulating container for cryogenic materials.

6. A cryogenic storage tank comprising a closed shell having an insulated bottom and a substantially vertical cylindrical insulated sidewall and a domed roof supported by said sidewall, a cylindrical tension ring disposed adjacent to the upper end of said sidewall and having a diameter slightly less than the inner diameter of said sidewall, a plurality of circumferentially spaced-apart supporting means mounting said tension ring on said sidewall adjacent to the upper end thereof, a plurality of hanger members spaced around the periphery of said tension ring and extending downwardly therefrom, a substantially vertical supporting column centrally positioned with respect to said shell bottom and extending upwardly above the intended maximum capacity level of the tank, and an insulated ceiling supported by said hanger members and said supporting column and overlying the area enclosed by said sidewall and disposed above the intended maximum capacity level of the tank, whereby said insulated bottom and said insulated sidewall and said insulated ceiling define an enclosed insulating container for cryogenic materials.

7. The cryogenic storage tank set forth in claim 6, wherein each of said circumferentially spaced supporting means includes a pair of straplike radially extending members overlapping each other and joined together at one end and connected at their opposite ends to said tension ring and said sidewall, respectively.

8. The cryogenic storage tank set forth in claim 6, wherein each of said circumferentially spaced supporting means and hanger members comprises a relatively thin straplike member having a rectangular cross section of minimal area to minimize the conduction of heat therealong.

9. The cryogenic storage tank set forth in claim 6, and further comprising an annular closure ring having a substantially Z-shaped radial cross section and attached at its lower end to said ceiling adjacent to the outer edge thereof and at its upper end to said sidewall for closing the space between said sidewall and the outer edge of said ceiling.

10. A cryogenic storage tank comprising a closed shell having an insulated bottom and a substantially vertical cylindrical insulated sidewall and a domed roof supported by said sidewall, a tension ring disposed adjacent to the upper end of said sidewall and having a diameter slightly less than the inner diameter of said sidewall, a plurality of circumferentially spaced supporting means mounting said tension ring on said sidewall adjacent to the upper end thereof, a supporting column centrally positioned with respect to said shell bottom and extending upwardly above the intended maximum capacity level of the tank, a plurality of supporting struts extending upwardly and outwardly from said column adjacent to the top thereof, a support ring mounted on said struts adjacent to the upper ends thereof, a plurality of radially extending joist members respectively supported at the outer ends thereof by said tension ring and respectively supported at the inner ends thereof by said support ring, an essentially imperforate deck supported by said joist members above the intended maximum capacity level of the tank and closing the area between said sidewall and said support ring, a foraminous member supported by said support ring and covering the opening therein to permit equalization of the pressure on the opposite sides of said deck, and a body of heat insulating material supported upon and covering said deck and said foraminous member.

11. The cryogenic storage tank set forth in claim 10, and further comprising a screen overlying said foraminous member and covering the opening in said support ring.

12. The cryogenic storage tank set forth in claim 10, wherein said support ring is an angle member having a substantially L-shaped radial cross section having one flange extending vertically downwardly and another flange extending horizontally outwardly and wherein the inner surface of said downwardly extending flange is attached to the upper ends of said supporting struts and wherein said outwardly extending flange supports said foraminous member and said screen and the inner ends of said joist members.

13. The cryogenic storage tank set forth in claim 10, wherein each of said joist members includes a lower chord, an upper chord spaced vertically therefrom and connected thereto at the ends thereof and a bar bent into a series of W-shapes and attached between said lower chord of said upper chord.

14. A cryogenic storage tank comprising, an inner shell having an insulated bottom and a substantially vertical cylindrical sidewall and a roof supported by said sidewall, an outer shell surrounding said sidewall and spaced therefrom and joined thereto adjacent to the upper and lower ends thereof and defining therewith a vaportight annular space, insulation filling said annular space to a level slightly below the upper end thereof to provide a purge space above said insulation, ceiling support structure mounted on said sidewall adjacent to the upper end thereof, a substantially vertical supporting column centrally positioned with respect to said inner shell bottom and extending upwardly above the intended maximum capacity level of the tank, and an insulated ceiling mounted on said ceiling support structure and said supporting column and overlying the area enclosed by said sidewall and disposed above the intended maximum capacity level of the tank for dividing the tank into a lower storage space and an upper vapor space, said sidewall having a plurality of communicating openings therethrough between said vapor space and said purge space for maintaining said purge space at a sufficient pressure to prevent infiltration of outside air.

15. The cryogenic storage tank set forth in claim 14, wherein said sidewall includes a compression ring attached at the upper edge thereof and wherein said communicating openings are situated in said compression ring.

16. The cryogenic storage tank set forth in claim 14, wherein said outer shell includes a compression ring attached thereto adjacent to the upper end thereof for holding said outer shell firmly in place against said insulation.

This invention relates to insulated storage tanks, and especially to tanks designed for storage of cryogenic liquids. More particularly, this invention is concerned with improved tanks which have good insulating characteristics.

It is an important object of this invention to provide a cryogenic storage tank including an internally disposed false ceiling which is supported by the sidewall of the tank and by a supporting column.

It is another object of this invention to provide a cryogenic storage tank including an internally disposed false ceiling which is supported at its periphery by a tension ring which is attached to the sidewall of the tank adjacent to the upper end thereof.

A further object of this invention is to provide a cryogenic storage tank of the character described including an insulated false ceiling having an essentially imperforate outer portion surrounding a foraminous inner portion and supported by the sidewall of the tank and by a supporting column and overlying the area enclosed by the sidewall and disposed above the intended maximum capacity level of the tank and dividing the tank into a lower storage space and an upper vapor space, the foraminous inner portion allowing passage of vapors between the storage space and the vapor space for equalizing pressure on the opposite sides of the ceiling while preventing convective circulation therebetween.

Yet another object of this invention is to provide a cryogenic storage tank of the character described including an internally disposed false ceiling supported by the sidewall of the tank and by a supporting column centrally positioned with respect to the sidewall and extending upwardly above the intended maximum capacity level of the tank, the column including a plurality of supporting struts extending upwardly and outwardly therefrom adjacent to the top thereof and a support ring mounted on said struts, the ring supporting the center portion of the ceiling.

Still another object of this invention is to provide a cryogenic storage tank of the character described including an internally disposed false ceiling supported by the sidewall of the tank and by a supporting column centrally positioned with respect to the sidewall and extending upwardly above the intended maximum capacity level of the tank, wherein the ceiling includes a plurality of radially extending joist members respectively supported at the outer ends thereof by the sidewall of the tank and respectively supported at the inner ends thereof by the column and an essentially imperforate deck supported by the joist members and enclosing the area between the sidewall and the column and a foraminous member supported by the column to permit equalization of the pressure on the opposite sides of the ceiling.

Another object of this invention is to provide a cryogenic storage tank of the character described including an internally disposed false ceiling supported by the sidewall of the tank and by a supporting column for dividing the tank into a lower storage space and an upper vapor space wherein the tank has an outer shell surrounding the sidewall and spaced therefrom and joined thereto adjacent to the upper and lower ends thereof and defining therewith a vaportight annular space, the annular space being filled with insulation to a level slightly below the upper end thereof to provide a purge space above the insulation, and wherein the sidewall has a plurality of connecting openings therethrough between the upper vapor space of the tank and the purge space for maintaining the purge space at a sufficient pressure to prevent infiltration of outside air.

The invention, both as to its arrangement and method of operation together with further objects and advantages thereof, will best be understood by reference to the following specification taken in connection with the accompanying drawings in which:

Fig. 1 is a view in vertical section of a cryogenic storage tank constructed in accordance with the present invention;

FIG. 2 is an enlarged fragmentary view in horizontal section taken along the line 2-2 in FIG. 1;

FIG. 3 is a further enlarged fragmentary view of a vertical cross section of a portion of the supporting column structure and the inner portion of the ceiling structure of the tank of FIG. 1;

FIG. 4 is a fragmentary view in vertical cross section of the upper portion of the sidewall and the outer portion of the ceiling and ceiling support structure of the tank of FIG. 1; and

FIG. 5 is a view similar to FIG. 4 illustrating a second embodiment of the invention including a double-sidewall construction, there being shown the upper portion of the double sidewall and the outer portion of the ceiling and the ceiling support structure.

Referring now to the drawings, and in particular to FIGS. 1 through 4 thereof, there is shown a cryogenic storage tank generally designated 100. The tank 100 includes a flat generally circular bottom 101 surrounded by a substantially vertical cylindrical sidewall 102 having a substantially circular cross section. The tank 100 is covered by a domed roof generally designated 103 having a radius of curvature approximately equal to the diameter of the sidewall 102. The roof 103 includes a plurality of rafter members 104 spanning the area enclosed by the sidewall 102 and supported thereon adjacent to the upper end thereof. The rafter members 104 are covered by and support roof plates 105 which terminate at a boundary spaced a small distance from the sidewall 102. In the preferred embodiment, the bottom 101, the sidewall 102 and the roof 103 are made of metal, preferably steel. The tank 100 is supported at its bottom by an annular wall foundation 106 having a spread base portion 108. The foundation 106 is preferably made of concrete or other suitable foundation material. Holddown straps (not shown), preferably made of steel, may be attached to the sidewall 102 near the bottom thereof and anchored in the foundation 106 to counteract the lifting forces of the vapors within the tank 100.

Stored within the tank 100 is a cryogenic liquid generally designated by the numeral 110, which liquid 110 may typically be liquified natural gas, butane, ammonia, helium, hydrogen, etc., or other liquid suitably stored at a temperature less than approximately 30° F.

The underside of the bottom 101 of the tank 100 is covered with a layer of suitable insulation material 112. The outer surface of the sidewall 102 is also covered with insulating material, preferably arranged in two layers 113 and 114. A vapor barrier (not shown) is normally provided on the underside of the bottom insulation 112. Suitable materials for this purpose would be roofing felt asphalt impregnated and hot-mopped with asphalt.

A supporting column 115 is provided and preferably is shaped as a hollow cylinder, is centrally positioned with respect to the bottom 101 and is supported thereby and extends vertically upwardly therefrom above the intended maximum capacity level of the tank 100. Disposed between the bottom 101 of the tank 100 and the bottom of the supporting column 115 is a baseplate 116 having an area substantially greater than the cross-sectional area of the column 115 to spread the load supported by the column 115 across a wider area of the bottom 101. At the top of the column 115 is a pair of crown plates 117 to be described more fully hereinafter. Attached to the crown plates 117 and extending upwardly and outwardly therefrom is a plurality of supporting struts 118 attached at their upper ends to a support ring 120. The support ring 120 has an annular shape and is formed from a rolled angle member having a generally L-shaped cross section to be described more fully hereinafter.

Attached to the upper edge of the sidewall 102 is an annular sidewall compression ring 122 having an inner surface coplanar with the inner surface of the sidewall 102. Attached to the upper end of the sidewall compression ring 122 is an annular roof compression ring 124. The ring 124 overlaps and is attached to the outer periphery of the roof plates 105 and covers the space separating the periphery of the roof plates 105 from the upper edge of the sidewall compression ring 122.

A tension ring 125 having a diameter slightly less than the diameter of the sidewall compression ring 122 is disposed within the sidewall 102 adjacent to the upper end of the sidewall compression ring 122. The tension ring 125 is connected to and supported by the sidewall compression ring 122 by means of a plurality of circumferentially spaced-apart support clip members generally designated 126. Attached to the outer surface of the tension ring 125 at points spaced around the periphery thereof is a plurality of support hanger members 128 which extend vertically downwardly from the tension ring 125. The members 128 are preferably thin straplike metal plates having a small rectangular cross section to decrease heat conduction therealong.

Disposed within the sidewall 102 adjacent to the upper end thereof is a false ceiling structure generally designated 130. The ceiling structure 130 includes a plurality of radially disposed web bar joist members 131 each including a web bar 132, an upper chord member 133 and a lower chord member 134. The lower chord member 134 is an elongated rod or bar having a length approximately equal to the radial distance between the support hanger members 128 and the periphery of the support ring 120. The upper chord member 133 is an elongated rod or bar extending longitudinally vertically above and substantially parallel to the lower chord member 134 and being bent downwardly at each end thereof to contact the corresponding end of the lower chord member 134. The web bar 132 is bent into a series of W-shapes, the bottoms of which are attached to the lower chord member 134 and the tops of which are connected to the upper chord member 133. The joist members 131 are supported at their inner ends by the support ring 120 and at their outer ends by the support hanger members 128. Attached to the undersides of and supported by the lower chord members 134 is a horizontally disposed annular ceiling deck 135, preferably comprising a series of interconnected metal plates or corrugated metal sheets. The deck 135 encloses the area between the support members 128 and the outer periphery of the support ring 120. At the outer periphery of the deck 135 and connected between the deck 135 and the sidewall 102 is a deck closure ring 136 having a substantially Z-shaped radial cross section and closing the annular space between the sidewall 102 and the outer periphery of the deck 135. Overlying the deck 135 and covering and supported by the ceiling structure 130 is a layer of insulation material 138, this insulation material 138 also overlying covering the closure ring 136. The ceiling structure 130, therefore, divides the interior space of the tank 100 into a lower storage space 140 and an upper dome vapor space 145.

Overlying the support ring 120 and covering the opening therein is a perforated crown plate 150 that is generally circular in outline. The purpose of the crown plate 150 is to allow the passage of vapors between the storage space 140 and the dome vapor space 145, as will be more fully explained hereinafter. The crown plate 150 is also covered by the insulation material 138 which is sufficiently porous to permit the passage of vapors therethrough.

The sidewall insulation comprising the inner layer 113 and the outer layer 114 is surrounded by an external weather covering 155 held in place by a plurality of vertically spaced tension bands 156 as shown in FIG. 4. The top surface of the insulation layers 113 and 114 and of the sidewall compression ring 122 and the outer surface of the roof compression ring 124 are all covered by a suitable watertight sealing material 157, as indicated in FIG. 4, the material 157 being compatible with the sidewall insulation.

On the inner surface of the sidewall compression ring 122 near the upper end thereof is attached a rolled bar member 158 to facilitate the welding of the roof compression ring 124 to the upper end of the sidewall compression ring 122.

Referring now more particularly to FIG. 4, there is attached to the bottom ends of the support hanger members 128 an annular member generally designated 160 and having an inverted T-shaped cross section. The member 160 includes a vertical flange 162, an inwardly directed and horizontally extending lateral flange 163 and an outwardly directed and horizontally extending lateral flange 164. The vertical flange 162 is connected to the support hanger members 128 at the lower ends thereof. There is provided on the inner surface of the sidewall 102 near the upper end thereof a second rolled bar member 165 to facilitate the attachment of the closure ring 136 to the sidewall 102. The upper end 166 of the Z-shaped closure ring 136 is attached to the rolled bar member 165 and the lower end 168 of the closure ring 136 is attached to the upper surface of the lateral flange 164 of the member 160. The outer edge 169 of the deck 135 is bent slightly downwardly from the plane of the deck 135 and is attached to the flange 163 of the member 160 at the lower surface thereof. The upper surface of the lateral flange 163 supports the inner ends 170 of the joist members 131.

Referring now to FIG. 3, the crown plates 117 are substantially disc shaped and have a diameter slightly greater than the diameter of the supporting column 115. The crown plates 117 are placed one on top of the other and are fastened together at their peripheries by a plurality of circumferentially spaced bolts 172. The lower one of the crown plates 117 is welded to the column 115 at the upper edge thereof and the upper one of the crown plates 117 is welded to the bottom ends 173 of the supporting strut members 118. The strut members 118 are preferably angle members having a substantially L-shaped cross section. The top ends 174 of the strut members 118 are attached to the support ring 120. The support ring 120 has a substantially L-shaped cross section including a downwardly directed vertically extending flange 175 and an outwardly directed horizontally extending flange 176, the inner surface of the flange 175 being connected to the upper ends 174 of the strut members 118. The inner edge 178 of the deck 135 is bent slightly downwardly from the plane of the deck 135 so that the edge 178 is coplanar with the flange 176 of the support ring 120 and is butt welded to the flange 176.

The perforated crown plate 150 overlies the support ring 120 to allow vapor passage through openings or perforations 180 in the crown plate 150. The number and size of the perforations 180 are designed to prevent a pressure differential between the opposite sides of the ceiling 130 greater than the combined weight of the false ceiling 130 and the supported insulation 138 distributed over the ceiling. Furthermore, the openings 180 are so designed as to limit the equalizing velocities of vapors passing therethrough to a low value to reduce convection currents in the dome vapor space 145. A circular screen 182 overlies the crown plate 150 and prevents compaction of any loose fibrous or free flowing insulation in the perforations 180. The perforated plate 150 and the screen 182 each have a diameter slightly greater than the outer diameter of the flange 176 of the support ring 120. The inner ends 184 of the joist members 131 overlap the outer edge of the screen 182 and of the flange 176 and are supported thereby.

The support clips 126, by which the tension ring 125 is attached to the sidewall compression ring 122, are each comprised of two members 185 and 186 which overlap at one end and are fastened together by a suitable fastening means 187 such as bolts or rivets. The other end of the member 185 is connnected to the outer surface of the tension ring 125 and the other end of the member 186 is connected to the inner surface of the sidewall compression ring 122. Each of the members 185 and 186 is preferably a thin metal plate having a rectangular cross section as small as strength requirements will allow to reduce heat conduction therealong.

In operation, the insulated false ceiling 130 separates the relatively warm dome vapor space 145 from the cryogenic storage space 140. This serves to improve the insulating characteristics of the tank 100 by preventing transfer of heat by radiation from the roof 103 to the surface of the stored liquid 110 since such radiation is blocked by the thermal insulation material 138. The ceiling 130 is also effective to prevent heat transfer to the stored liquid 110 by convection currents in the vapors present in the dome vapor space 145. It will also be noted that since the ceiling 130 is supported entirely by the sidewall 102 and the supporting column 115, there are no direct thermally conductive paths between the ceiling 130 and the roof 103. Since the ceiling 130 is designed only to support the insulation material 138 and not to withstand gas pressure which may build up on either side thereof, the perforated plate 150 is provided over the support ring 120 to permit passage of vapors therethrough, thereby equalizing the pressures on the opposite sides of the ceiling 130 to avoid damage thereto.

Referring now to FIG. 5, there is shown another embodiment of the invention including a double-sidewall construction. A cryogenic tank, generally designated 200, is shown having an inner sidewall 202, roof rafter members 204 supported by the sidewall 202 and roof plates 205 covering and supported by the rafters 204. A sidewall compression ring 222 is attached to the sidewall 202 at the upper edge thereof and a roof compression ring 224 is connected to the sidewall compression ring 222 at the upper end thereof and to the outer periphery of the roof plate 205. A tension ring 225 having a diameter slightly less than the diameter of the sidewall 202 is disposed within the tank 200 adjacent to the upper end of the sidewall compression ring 222 and is connected to the compression ring 222 by a plurality of circumferentially spaced clip members 226. A plurality of support hanger members 228 are spaced about the periphery of the tension ring 225 and are attached to the outer surface thereof and depend downwardly therefrom. A false ceiling structure 230, including a plurality of radially extending joist members 231 and a deck 235 is supported at its periphery by the hanger members 228. A deck closure ring 236 is connected between the sidewall 202 and the outer periphery of the ceiling 230 thereby closing the annular space therebetween. A layer of thermal insulation material 238 covers and is supported by the ceiling 230 and the closure ring 236. The ceiling 230 divides the tank 200 into a lower storage space 240 and an upper dome vapor space 245.

An outer cylindrical shell 290 surrounds the sidewall 202 and is spaced therefrom a predetermined distance. The outer shell 290 will normally be connected to the sidewall 202 at the bottom thereof by a connecting portion not shown. An outer shell compression ring 292 is attached to the outer shell 290 at the upper edge thereof. The ring 292 has an L-shaped cross section including a downwardly directed vertically extending flange 293 which is connected to the upper edge of the outer shell 290 and an inwardly directed horizontally extending flange 294. The outer shell 290 cooperates with the sidewall 202 to define a vaportight annular space 295. An annular cover plate 296 is connected at its outer edge to the flange 294 of the compression ring 292 and at its inner edge to the upper end of the sidewall compression ring 222, thereby covering the annular space 295. The annular space 295 is filled with a thermal insulation material 298 to a level slightly below the upper end thereof but above the level of the ceiling 230. There is thereby defined a purge space 300 above the insulation 298. A plurality of openings 305 are provided in the sidewall compression ring 222 above the level of the annular space insulation 298 thereby providing communication between the purge space 300 and the dome vapor space 245. A sufficient number of the openings 305 is provided to allow the pressure of the purge space 300 to be maintained slightly greater than the outside atmospheric pressure.

In operation, the tank 200 of FIG. 5 is very similar to the tank 100 of FIGS. 1 to 4. The false ceiling 230 serves to insulate the stored liquid from the heat of the dome vapor space 245 in the same manner as does ceiling 130 of tank 100. But in the tank 200, the communicating openings 305 allow the pressure of annular space 295 to be maintained slightly greater than the outside atmospheric pressure to thereby prevent infiltration of outside air into the annular space 295.

The insulation provided along the sidewalls 102 and 202 of the tanks 100 and 200, respectively, and along the bottom 101 of the tank 100 and above the false ceilings 130 and 230 of the tanks 100 and 200, respectively may be of any suitable type. It has been found, for example, that the insulation 112 of the bottom 101 may advantageously be perlitic concrete or perlite-filled asphalt. In the single wall embodiment of FIGS. 1 through 4, the sidewall insulation layers 113 and 114 may comprise precast blocks of foam glass. Also any of several foamed or frothed materials may be used, such as sprayed-on urethane resin or epoxy resin, a foamed or frothed in place urethane resin, or a polystyrene resin such as that sold under the trade name "Styrofoam." Where a permeable insulation such as "Styrofoam," urethane resin or epoxy resin is used an external vapor barrier is required which may be light aluminum sheeting with sealed joints or compatible mastic and reinforcing fabric. In the double wall embodiment of FIG. 5 the annulus insulation 298 may consist of perlite, vermiculite, a silica aerogel such as that sold under the trade name "Santocell" or other free flowing lightweight material having low heat conduction characteristics. The ceiling insulation 138 and 238 is preferably of a fibrous type such as rock wool or glass fibers, however, free flowing insulation could be used.

Means for supplying heat to the underside of the tank will normally be required if the storage temperature is below the freezing point of water in order to prevent frost heave of the ground beneath the tank. This may be electrical wiring or a circulated heating medium. Such heating means may not be necessary if the depth of the tank bottom 101 within the ground and the thickness of bottom insulation 112 are such that the 32° F. isotherm always falls within insulation 112 and above the bottom vapor barrier.

From the foregoing it can be seen that there has been described a cryogenic storage tank 100 comprising a flat bottom 101, a substantially vertical cylindrical sidewall 102 and a domed roof 103 supported by the sidewall 102 and having a false ceiling 130 disposed beneath the roof 103 and above the intended maximum capacity level of the tank and supported at its periphery by support means connected to the sidewall and at its center by a supporting column 115 extending upwardly from the bottom of the tank, the bottom 101, the sidewall 102 and the false ceiling 130 being covered with thermal insulation material 138 and defining an enclosed insulated container for cryogenic materials.

The supporting column 115 is centrally positioned with respect to the sidewall of the tank and has a plurality of supporting struts 118 attached thereto at the upper end thereof and extending upwardly and outwardly therefrom, the supporting struts 118 being attached at their upper ends to a support ring 120 which supports the center portion of the false ceiling 130. The false ceiling 130 includes a substantially imperforate outer portion surrounding a foraminous inner portion, the foraminous inner portion overlying the support ring 120 and covering the opening therethrough to allow passage of vapors to equalize the pressure on the opposite sides of the ceiling.

There has also been disclosed a cryogenic storage tank 200 having an outer shell 290 surrounding a sidewall 202 and spaced therefrom and connected thereto adjacent to the upper and lower ends thereof and defining therewith an annular space 295, the annular space 295 being filled with insulation material 298 to a level below the upper end thereof but above the level of a false ceiling 230, thereby providing a purge space 300 above the annular space insulation 298. A plurality of openings 305 is provided in the sidewall 202 above the level of the false ceiling 230 for communicating the purge space 300 with the domed vapor space 245 to maintain the annular space 295 at a pressure sufficient to prevent infiltration of outside air into said space.

While there has been described what is at present considered to be the preferred embodiments of the invention, it will be understood that various modifications may be made therein, and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.