US 3655086 A
Tanks for the storage of liquefied gases at cryogenic temperatures are disclosed. The disclosed tanks comprise two concentric shells with dished ends. The internal shell is fabricated from layers of glass fabric with organosiloxane treatment. A layer of high tensile wire fabric is incorporated as one of the integral laminae of the internal and external shells. The internal shell is covered with an insulating layer of flexible and rigid urethane foam. This foam is fabricated in contoured or flat blocks of suitable size and shape to conform to the inner shell. The blocks may be separated from the inner shell by multiple layers of metallized polyethylene terephthalate (Mylar), or other material which will reflect radiant heat.
Description (OCR text may contain errors)
United States-Patent Trenner 1151 3,655,086 [451 Apr. 11, 1972 [s41 RECEPTACLES .FOR THE STORAGE 0F LIQUEFIED GASES AT CRYOGENIC TEMPERATURES 3,367,527 2/1968 Darlington ..220/9F 3,411,656 11/1968 Jackson ..114/74AX FOREIGN PATENTS OR APPLICATIONS 1,289,071 2/1969 Germany ..220/9 F Primary Examiner-Joseph R. Leclair Assistant Examiner-James R. Garrett Attorney-Kimmel, Crowell & Weaver 1 1 ABSTRACT Tanks for the storage of liquefied gases at cryogenic temperatures are disclosed. The disclosed tanks comprise two concentric shells with dished ends. The internal shell is fabricated from layers of glass fabric with organosiloxane treatment. A layer of high tensile wire fabric is incorporated as one of the integral laminae of the internal and external shells. The internal shell is covered with an insulating layer of flexible and rigid urethane foam. This foam is fabricated in contoured or flat blocks of suitable size and shape to conform to the inner shell.
The blocks may be separated from the inner shell by multiple layers of metallized polyethylene terephthalate (Mylar), or other material which will reflectradiant heat.
9 Claims, 6 Drawing Figures FIBERGLASS & PLASTIC RIGID URET'HANE FOAM METALLIZED MYLAR- FLEXIBLE URETHANE FOAM METALLIZED MYLAR.
FLEXIBLE URETHANE FOAM METALLIZ'ED MYLAR- PLASTIC WITH FIBERGLASS - Inventor: Lew Trenner, Englewood,Colo.
 Assigneez Cryotan, lnc., Canyon, Tex. 221 Filed: Oct. 9, 1970 Y  Appl. No.: 79,441
 U.S.Cl. ..220/9 LG  lnt.Cl ..B65d 25/18  Field of Search ..220/9 LG, 9 D, 9 F, 9 A; 1 14/74 A  References Cited UNITED STATES PATENTS.
2,728,702 12/1955 Simon et a1. ..220/9 F UX 2,731,374 1/1956 I DeReus ....220/9 AUX 3,009,600 11/1961 Matsch ..220/9 LG 3,013,922 12/1961 Fisher 20/9 F UX 3,170,828 2/ 1965 Irvine .220/9 F X 3,261,087 7/1966 Schlumberge 220/9 LG X PMENTEUAPR 1 1 m2 SHEET 2 OF 2 FIG. 4
/N I E N TOR LEW TRENNE/l RECEPTACLES FOR THE STORAGE OF LIQUEFIED GASES AT CRYOGENIC TEMPERATURES BACKGROUND OF THE INVENTION The invention relates to the storage of liquefied gases at cryogenic temperatures, and more particularly, to tanks for the storage of liquefied gases at cryogenic temperatures.
Extremely large quantities of natural gas such as methane can be stored in relatively small spaces by storing the gas in its liquid state. This may require extremely low temperatures. Liquid natural gas (LNG) so stored can be used for the purposes of municipal or industrial peak saving of local or regional fuel gas supplies.
In addition to providing receptacles for storing the liquefied gases, the tanks or receptacles must be so designed so as to withstand the environment in which they are located. Large tanks of such liquefied gas could ideally serve the fuel needs of the communities on the highly populated East and West coasts of the United States and other countries where elevated temperatures are frequent (e.g. desert areas of the Middle East countries). These tanks could be held in tank farms located under the ocean or buried below the surface of the ground. However, in order to store tanks in sea water or underground, the tanks must be so constructed as to be completely unaffected by immersion in sea water or by subsoil conditions of widely varying pH, soil bacteria, fungus, etc. Thus, suitable tanks for the storage of cryogenic liquids must not only be able to withstand the extremely low temperatures but must also be able to withstand the environment in which they are located.
Many prior art attempts have been made to solve both the storage and environmental problems noted above. These prior art attempts have not been entirely satisfactory. The tanks thus far devised are either heavy and bulky or extremely expensive. In addition, there is considerable temperature leakage in many of the storage tanks now available on the market.
SUMMARY OF THE INVENTION Receptacles or tanks are constructed in accordance with this invention by using a mandrel or an external mold to lay up external and internal walls of two concentric shells with dished ends. The walls of the shells are fabricated by laying up layers of glass fabric with an organosiloxane treatment. A layer of high tensile wire fabric is incorporated as one of the integral laminae of the layers. The internal shell is thus built up by using processes which are generally well known in the art. Instead of building up layers of the glass fabric, the internal shell can be fabricated from prefabricated plates. If prefabricated plates are used, the reinforcing wire is allowed to protrude from each peripheral edge of suchplates, so that they may be incorporated into the bond edge which is the junction between two or more plates. By this method, the wire becomes continuous to all intents and purposes.
After the internal shell is completed, it is covered with a layer of rigid and flexible urethane foam. This foam is in contoured or flat blocks of suitable size and shape to conform to the inner shell. The blocks may be separated from the tank by multiple layers of metallized polyethylene terephthalate (Mylar) so that the blocks may move freely with cycling temperatures of the tank. The combination of rigid and flexible foam forms a monolithic layer of insulation. The flexible foam forms a monolithic layer of insulation. The flexible foam serves the function of keeping the overall integrity of the insulating wall and at the same time allowing for free motion of the overall insulating layer.
Several facts become obvious to anyone attempting to build a tank suitable for cryogenic purposes. If there is to be no thermal leak, the insulation must be continuous in one form or another, and without gaps or voids which could be responsible for such thermal leaks. Another fact to be considered is that any matter in any phase, will expand and contract with temperature changes.
Perkins (U.S. Pat. No. 3,379,330) provides overlapping shingles or panels which permit expansion and contraction of the tank, but a natural result of such movement would be the grinding effect which each panel or shingle would have upon the other. Perkins refers to the unavoidable heat short" (line 58, column 3) that he encounters, so he seals the space between the panels" (line 61, column 3) and substantially negates the purpose of his slip joints.
Barker (U.S. Pat. No. 3,317,074) admits that the insulation he proposes does not possess sufficient strength to overcome the stresses of contraction and the insulation is likely to crack when suddenly cooled. He solves this problem" (lines 49 through 53, column 1) by using tension threads or other supports of low conductivity extending through the insulation to tie the inner liner to the supporting external metal shell (lines 63 to 65, column 1). It is quite clear that no supporting tension threads of any material can prevent expansion or contraction with sufficient thermal shift and something will have to give.
Pratt (U.S. Pat. No. 3,298,345) also recognizes the problem of expansion and contraction and solves it by saying that panels are so supported and secured as to be relatively immobilized against gross distortion of shape resulting from sub- ;tantial temperature differentials lines 2, 3, 4 and 5, column Others have tried to prevent contraction and expansion by firmly bonding insulation to a rigid structure such as the hull of a steel ship, but it is obvious that anything which tends to impede expsnsion and contraction can only contribute to the break-up of the insulation.
The only dependable practice in the face of irresistable expansion and contraction, is to provide for it and thus develop a systemwhich will accommodate it.
Rigid polyurethane foam is admirably suited for both the insulating and load bearing qualities it possesses, but in continuous lengths encountered in large tanks, it will crack into fissures at cryogenic temperatures if any attempt is made to prevent such contraction. If it is used as loose insulation, that is not bonded to either inner or outer sheel of the tank, it will become too short upon freezing and allow a thermal leak.
This invention uses blocks or partially channeled grids of rigid urethane foam, and the channels between the discreet or partially discreet blocks are filled with flexible urethane foam. At 75 F, a rigid polyester foam blown with fluorocarbon gas will have a tensile strength of approximately p.s.i. and a flexible polyether foam blown with the same gas, will have a tensile strength of only an approximate 15 p.s.i. at the same temperature. However, at minus 325 F the tensile strength of these foams almost meet. The rigid foam develops a tensile strength of 55 p.s.i. and the flexible foam develops a tensile strength of 45 p.s.i.
Elongation of the different foams are even more remarkably adapted to my method. At minus 325 F a rigid polyester foam has approximately two percent elongation and a flexible polyether foam about 4 to 5 percent elongation. At 75 F the rigid polyester foam is not substantially different, but the flexible polyether becomes 210 percent.
Insulating characteristics of the two foams are substantially the same at cryogenic temperatures and before the lowest temperature encountered in use is reached, the flexible grid permits carefully controlled expansion and contraction of the :cold side or sides adjacent to the inner tank without fracturmg.
When this insulating structure is completed, the external shell is built on the internal tank and its insulation as a mandrel following the techniques employed for the internal shell as described above. That is, layers of glass fabric pregnated with organosiloxane are used to cover the insulating layer. A layer of high tensile wire fabric is also included in the external shell structure. Of course, means must be provided to fill and exhaust the tank. In addition, manholes or other access openings may be provided.
BRIEF DESCRIPTION OF THE DRAWINGS The details of the invention will become readily apparent from the following detailed description when read in conjunction with the annexed drawings in which:
FIG. I shows a cylindrical tank with the ends removed and constructed in accordance with this invention;
FIG. 2 is a cross section of the tank of FIG. 1;
FIG. 3 is an enlarged view of a section of the tank showing the material used in fabricating the tank and showing one embodiment of the insulating layer of this invention;
FIG. 4 shows a second embodiment of the insulating layer;
FIG. 5 shows a modification of the insulating layer of FIG. 4 so constructed as to conform to a cylindrical tank and FIG. 6 shows a third construction of the insulating layer.
DESCRIPTION OF THE INVENTION Referring to the drawings, FIG. 1 shows a section of a cylindrical tank constructed in accordance with this invention, FIG. 2 shows a cross section of the tank of FIG. I and FIG. 3 is anenlarged view of a section of the tank showing a first embodiment of an insulating layer utilized in the construction of the shell 5. An inner tank is first formed by utilizing layers of Polyglas fiber with an organosiloxane treatment. The inner shell 5 thus is constructed of laminated layers of Polyglas fiber and plastic. Included in this structure is a layer of high tensile wire fabric integrally incorporated in the laminae. After the inner shell has been constructed, it is covered with layers of flexible foam sandwiched between sheets of metallized Mylar as more clearly shown in FIG. 3.
As shown in FIG. 3, the outer surface 9 of the inner shell is covered with layers of flexible urethane foam 11 sandwiched between sheets of metallized Mylar 13. While only two such layers are shown in FIG. 3, several layers of the flexible foam and Mylar can be wrapped around the internal shell. The outer layer of Mylar 13 is covered with a layer of rigid urethane foam 15. The structure just described is not sufficiently strong to support the weight of the inner tank. Therefore, cylindrical rods 7 of rigid urethane foam are utilized to increase the strength of the structure. I-Ioles are drilled through the rigid plastic foam, and laminated structure of Mylar and flexible plastic foam and the inner shell 5. The rigid rods 7 pass through the holes in the inner shell as clearly shown in FIGS. 1 and 2. The holes are made sufficiently small so that little or no temperature leak will occur around the rigid rods 7.
After the structure just described has been completed, the outer surface 3 of the rigid plastic foam layer 15 is covered with layers of Polyglas fiber with an organosiloxane treatment. That is, layers of fiberglass and plastic constructed in the same manner that the inner shell wall was constructed. Included in this lamination of fiberglass is another layer of wire fabric made of wire having a high tensile strength.
Thus, the tank just described actually consists of two concentric shells. While not shown the ends of the tank may be dished-shaped. The inner shell or first tank consists of laminations of fiberglass and plastic reinforced with a layer of wire fabric made up of high tensile strength wire. Covering this inner shell is an insulating layer made of laminations of flexible plastic foam and Mylar. The outer layer of Mylar is covered with a rigid plastic foam. Finally, the second or outer shell 17 is constructed of laminations of fiberglass and plastic reinforced with a layer of wire fabric which is used to cover the outer surface of the rigid plastic foam. Rigid plastic foam rods are utilized to impart strength to the tank.
FIGS. 4, 5 and 6 show alternate embodiments of the insulating layer provided between the inner and outer tank shells. Referring to FIG. 4, the inner shell wall is again designated with the numeral 5. As shown in this figure, the inner shell comprises laminations of fiberglass and plastic with a layer of wire fabric having a high tensile strength integrally formed with the laminae of fiberglass and plastic. The layer of wire fabric is designated with the numeral 23 in this figure. The outer shell 17 is also constructed of laminations of fiberglass and plastic with the reinforcing wires 23. To provide insulation a block of rigid plastic foam 19 is utilized. Channels 21 are cut through the block of rigid plastic foam 19. These channels are cut to a depth of approximately two thirds of the depth of the rigid foam block. These channels are filled with a flexible plastic foam. The structure thus formed is a monolithic sheet of foam plastic insulation.
I have found that six inches of foam plastic serves as suitable insulation for the inner shell. Thus, if block 19 is six inches in depth the channels 21 will be approximately four inches in depth. This combination of rigid and flexible plastic foam forms an insulating layer that is not adversely affected by the cycling of the tank. The foam plastic will of course contract under the extreme low temperature. However, with a combination of flexible and rigid plastic foam the contraction and expansion does not destroy the insulating layer.
The inner shell is completely covered with blocks of the insulating layer of rigid and flexible plastic foam. The insulating layer is then of course covered with the outer shell made of fiberglass and plastic with reinforcing wire as described above. A layer of metallized Mylar (not shown) is preferably placed between the outer surface of the inner shell and the insulating layer and the inner surface of the outer shell and the insulating layer. The smooth surface of the Mylar permits shifting of the insulating layer during the temperature recycling of the tank.
FIG. 5 shows an insulating layer constructed in accordance with the construction of the insulating layer of FIG. 4. However, in this case the blocks are formed to fit around the cylindrical tank such as shown in FIG. 1. In FIG. 5 the inner shell is not shown. The channels 21 must be so cut in an insulating layer fabricated as shown in FIG. 5 that the edges of the rigid foam on the sides of the channels 21 do not touch each other at the cold side.
FIG. 6 shows an alternate technique for constructing the insulating layer between the inner and outer shells of the tank. The wall 5 of the inner shell is again shown as being constructed of laminations of fiberglass and plastic with a layer of wire fabric integrally formed with the laminations of fiberglass and plastic. Similarly, the outer shell 17 is formed of laminations of fiberglass and plastic with the wire fabric 23 integrally formed into the outer shell wall. In this embodiment individual blocks 25 of rigid plastic foam are joined together by strips 27 of flexible plastic foam. These blocks of rigid plastic foam joined together by flexible plastic foam form a blanket between the inner and outer shells of the tank. Multiple layers of metallized Mylar 29 are placed between the inner surface of the outer shell and the insulating layer and between the outer surface of the inner shell and the insulating layer. These multiple layers of metallized Mylar provide an additional radiant heat barrier and the slick surface of the Mylar sheets also permits movement of the blanket of blocks without abrasion to the surface of this insulation blanket.
While the inner and outer shells have been described as being made up of layers of fiberglass and plastic with reinforcing wires, the shells can also be fabricated out of plates made fiberglass and plastic with reinforcing wire. If the shells are so constructed, the terminal ends of the reinforcing wires extend beyond the edges of the plates. The wires can then be incorporated into the juncture between two or more plates in such a manner that the wire becomes continuous to all intents and purposes.
The cryogenic tanks just described provide ideal receptacles for the storage of liquid natural gas such as methane and other low temperature liquids. Plastic foams are remarkable insulators. Therefore, cryogenic liquids can be stored in tanks constructed in accordance with my invention for an extremely long time. In fact, tests have indicated that tanks constructed in accordance with my invention will have a resultant K factor of approximately 0.13 (that is to say, 0.13 btu per hour per degree temperature differential from the inside of the tank to the outside of the tank per square foot thickness); or an overall factor of less than 1% per month. My storage tanks also provide ideal receptacles for the storage of liquid natural gas in large tank farms. The tank fanns can be located underground or under the ocean. Salt water and subsoil acidity have no adverse affects on my tanks.
An additional benefit derived from tanks constructed in accordance with my invention is their relative light weight. Thus, the tanks can be prefabricated and shipped by conventional means of transportation. Conventional metal tanks of any appreciable size cannot be readily prefabricated and transported to the site of use. In fact tanks constructed in accordance with my invention can be prefabricated of such size that they cannot be readily transported by railroad car. in such a case, a tank could be filled with helium to render it to minimal or negative weight and then transported by helicopter. Clearly, such a method cannot be used with conventional metal tanks.
While the invention has been described with reference to preferred embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made in the embodiments described without departing from the spirit and scope of this invention.
What is claim is:
l. A tank for the storage of cryogenic liquids comprising: an inner shell constructed of layers of fiberglass impregnated with plastic and reinforced with high tensile steel wires; a layer of insulating material fabricated from rigid plastic foam and flexible plastic foam covering the outer surface of said inner shell; and an outer tank constructed of layers of fiberglass impregnated with plastic and reinforced with steel wires, said outer shell covering said insulating layer.
2. The storage tank as described in claim 1 wherein said insulating layer comprises blocks of rigid urethane foam joined together with flexible urethane foam.
3. A storage tank as defined in claim 1 wherein said inner and outer shells are fabricated from plates of laminated layers of glass fabric impregnated with plastic with reinforcing wires formed integrally with the laminated glass fiber and plastic.
4. The tank as described in claim 1 wherein said insulating layer comprises layers of flexible plastic foam sandwiched between layers of polyethylene terephthalate, said layers of flexible plastic foam and polyethylene terephthalate being wrapped around said inner shell; and a layer of rigid plastic foam covering said layers of flexible plastic foam and said polyethylene terephthalate.
5. A storage tank as described in claim 4 wherein holes are drilled through said insulating layer and said inner shell and rigid plastic foam rods are inserted through said holes.
6. A storage tank as described in claim 1 wherein said insulating layer comprises plates of rigid urethane foam containing channels that are filled with flexible urethane foam, said plates being placed around said inner shell in such a manner that the channeled portion of the rigid urethane foam plates face said inner shell.
7. The storage tank as described in claim 6 wherein said channels are cut to within one-third of the total thickness of said rigid urethane foam plates and said rigid foam plates are-