US2947438A - Internal insulation structure for use with liquefied petroleum products - Google Patents

Description

Aug. 2, 1960 F. A. CLAUSON INTERNAL INSULATION STRUCTURE FOR USE WITH LIQUEF'IED PETROLEUM PRODUCTS Filed Dec. 19, 1957 Tlqzl.

United States Patent INTERNAL INSULATION STRUCTURE FOR USE WITH LIQUEFIED PETROLEUM PRODUCTS Frank A. Clauson, Roslyn Heights, N.Y., assignor to Texaco Inc., a corporation of Delaware Filed Dec. 19, 1957, Ser. No. 703,916

2 Claims. (Cl. 220-15) This invention relates generally to insulation for low temperature refrigerated products and specifically to internal insulation construction for the storage, maintenance and transportation of normally gaseous hydrocarbons in liquid condition.

In domestic petroleum production, utilization of large quantities of petroleum gases is accomplished at nearby facilities, while the transportation of these gases from producing fields to relatively distant points is largely by transcontinental pipelines and to some extent by cargo containers.

Containers built to withstand very high pressures are used in shipment of liquefied petroleum gases for considerable distances. However, the cost of manufacture of the heavy containers, due to the amount of material required, as well as the expense of transportation, restricts the shipment to closeby establishments. At the same time, the size of such containers is limited because of the maximum allowable metal wall thickness permitted without stress relief.

While it is known to transport and store low temperature liquefied gases, such as nitrogen and oxygen, in Dewar type containers consisting of spaced inner and outer receptacles, the problems involved in the construction of such type containers for the shipment of the large quantities of liquefied petroleum gases required to justify their economical transportation prevents their widespread use.

Other means for the transportation of liquefied petroleum gases at extremely low temperatures and at substantially atmospheric pressure have not proven successful in commercial operation, including the use of insulated tanks mounted on barges or in vessels, the tanks being considerably larger than the pressure containers and employing balsa wood for insulation. Because of the amount of such insulation required, both interior and exterior, the usable dimensions and hence the capacities of the tanks are reduced considerably. In addition, there is the danger of low temperature embrittlement of carbon steel tank walls which might occur should the insulation drop off and expose the walls to liquefied petroleum gas. In the absence of the use of high cost alloy steels for constructing the tanks, the shipment of liquefied petroleum gases is restricted by safety standards to the relatively heavier petroleum gases which have the higher boiling points.

The storage and transportation of liquefied petroleum gases in low pressure tanks offers considerable promise if an adequate means of insulating the tank walls were developed. Although there are available satisfactory means 'of external insulation for such stationary tanks, obviously this solution is not practical on the exterior of a tanker. Even on stationary tanks, exterior insulation presents problems of condensation and corrosion beneath the insulation. In extremely low temperature situations, exterior insulation is not desirable because the supporting metal structure must be made of extremely expensive alloys that are not subject to embrittlement and low impact strength at low temepratures.

Internal insulation avoids both the corrosion and embrittlement problems but difiieulty arises in the maintenance of the structural strength of the insulating material. as a result of rapid ebullition within the voids of the insulating material and in the avoidance of sloughing oif of the insulation from the Wall of the container.

Accordingly, it is an object of the present invention to provide a new and improved structure for economic maintenance of low temperature liquefied gases in light weight, low pressure tanks.

Another object of the invention is to provide a novel constructionfor the'storage and/or shipment of low temperature materials, the cost of which is negligible as compared with other means.

Still another object of the invention is to provide a simple internal insulation for the shipment and/ or storage of liquefied petroleum gases in which the dangers of construction failure are virtually eliminated.

And another object of the invention is to provide a novel internal insulation in either a static or mobile apparatus for the maintenance of normally gaseous hydrocarbons in liquid form.

These and other objects, advantages and features of the present invention will become apparent from the following description of the invention and by reference to the accompanying drawings wherein:

Fig. 1 is a partial diagrammatic view of a wall of a container for holding liquefied petroleum gases; and

Fig. 2 is a cross-section taken along the line 2-2 in Fig. 1, disclosing the internal insulation construction in greater detail. 7

In accordance with the illustrated embodiment of my invention, I employ vaporized gas from the cargo of liquefied petroleum gas as a barrier between the liquid and the wall of the container to provide necessary insulation.

Referring to the figures in the drawing, there is disclosed an outer wall W of a container, holding liquefied petroleum gas, (the showing of which is omitted for purposes of clarity) and a series of overlapping thin metallic shields S, which are shown attached, e.g., by

welding, at their top and bottom edges respectively to the outer wall and the immediately adjacent overlapped shield, as at 10 and 11. The attachment along the top edge is complete hermetically and forms a total seal, while the attachment along the bottom edge may be interrupted, as by spot welding of the edge, or, when complete, by the provision of notches 12 therealong or adjacent the bottom edge. The side edges, i.e., the ends of individual pieces of shields, may be fastened to the outer wall, and when the construction is used in a tanker could be welded to the longitudinal ribs of the tanker, or to the contiguous edges of the adjacent shields to form a continuous strip around the interior of the container. The method of attachment of the side edges is considered optional and when fastened to the outer wall, the quantity of heat transferred through the thin metal shields is very small. The shields S are spaced from the outer wall at a distance A, Fig. 2, which may vary to 12 inches, while the distance B, Fig. 2, between the fastening of the top and bottom edges of the shield may vary from 2 to 10 feet, these dimensions varying with the insulation requirement and the thickness of shield available economically, as well as the material used, e.g., alloy steel, sheet iron or foil. Since the shield thickness is small and stresses thereon so low, the problem of low temperature embrittlement is avoided with the shield materials. Although a pronounced angularity is disclosed along the line of fastening of the lower edges to the overlapped shield, such is not required always.

In addition, the insulation spaces or chambers C defined between the outer wall and the overlapping shields may be filled with insulating material M, (shown in Fig.

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