US3349572A - Insulation of containers for the storage of liquids which boil at atmospheric or slightly superatmospheric pressure - Google Patents

Description

Oct. 31, 1967 O H. H. R. NIEMANN 3, 9,

INSULATION OF CONTAINERS FOR THE STORAGE OF LIQUIDS WHICH BOIL AT ATMOSPHERIC OR SLIGHTLY SUPERATMOSPHERIC PRESSURE Filed May 10, 1966 2 Sheets-Sheet).

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I I INVENTOR flH/VS H E? Maw/w WHICH H. H. R. NIEMANN INSULATION OF CONTAINERS FOR THE STORAGE OF LIQUIDS BOIL AT ATMOSPHERIC 0R SLIGHTLY SUPER-ATMOSPHERIC PRESSURE 2 Sheets-Sheet 2 Filed May 10, 1966 INVENTOR United States Patent INSULATION 0F CONTAINERS FOR THE STOR- AGE OF LIQUIDS WHICH BOIL AT ATMOS- PHERIC 0R SLIGHTLY SUPERATMOSPHERIC PRESSURE Hans Heinrich Richard Niemann, Hamburg, Germany,

assignor to Minikay A.G., Zurich, Switzerland, a corporation of Switzerland Filed May 10, 1966, Ser. No. 548,998 1 Claim. (CI. 62-55) ABSTRACT OF THE DISCLOSURE An insulating system for single wall containers adapted for the storage or shipping of liquids that boil at approximately atmospheric pressure that includes rigid single wall means that defines the container, a layer of permeable insulating material on the interior of the wall means, a layer of elastic material on the side of the insulating material remote from the wall means and adapted to be contacted by the liquid to be stored in such container. Inner and outer sets of grooves are provided in the insulating material, and the grooves being respectively covered by the elastic material on the one hand and the rigid single wall means on the other, and means are included to selectively circulate dry inert gas either in parallel through both sets of grooves, through only the outer set of grooves during the filling of the container or through the inner set of grooves during the emptying of the container.

This is an improvement in insulation of a type similar to that disclosed and claimed in my earlier application, now Patent No. 3,110,156 dated Nov. 12, 1963.

The invention has as an object to provide for containers as disclosed in the above-mentioned patent an insulation with a constant effect by means of keeping the insulation dry, with substantially less expenditure and quite independently of whether the insulation adjoins the container wall on the inside or the outside or does not adjoin the container Wall at all but instead is disposed at a distance from the container, thus leaving a space, for example for inspection.

According to the invention, channel-like grooves are provided in the insulating material on both surfaces of the insulation for keeping the insulation dry, through which a dry gas is passed having a dew point not so low that ice formation is entirely prevented when a container is filled with a boiling liquid but the dew point being lowered, by drying to such a degree that in the case of an empty container any ice which is formed is conducted out of the insulation by sublimation, and the insulation is dried and kept dry until the next filling of the container occurs.

A relatively small lowering of the dew point of the air passing through the grooves of the insulation can restrict the ice formation in the insulation to a degree which only alters the insulating eifect quite immaterially. For example, if methane is conveyed with a boiling temperature of 162 C. at a dew point of the atmosphere of +28 C., then a dew point of 20 C., i.e. corresponding to a lowerin of the prevailing vapor pressure drop by only 30%, reduces the Water vapor contents of the air being diffused into the insulation by about 95%. A dew point degression of only about 36% of the vapor pressure gradient, i.e. to 40= (1., reduces the water vapor content by about 99.7% to only 0.3% of the content of the atmospheric air being diffused. (The amount of dry gas required at a dew point degression to -40 C. has a volume requiring channel cross-sections which can be a suitable portion of the volume of the insulation. A dew point degression to -162 C., which is necessary for keeping the insulation absolutely dry when the container is filled with methane, requires channel cross-sections so large that they cannot be realized.)

It is not only the very small amount of ice that collects in the insulation while the container is full that is responsible for the slight loss of insulating effect in the present insulation over known insulating systems, but also of equally substantial importance is the form in which the ice is deposited. It is to be noted that the ice forms a thin film adjoining the colder surface of the insulation, the thickness of said film, depending on the duration of the container filling, being predeterminable and controllable by means of the selection of the dew point of the dry gas passing through the channel cross-sections of the insulation. It has been demonstrated that even if a container remained filled for more than a year this ice film could be restricted to a thickness of 1 mm. or less.

The insulation according to the present invention is equally applicable to stationary storage tanks or tanks which are conveyed by means of a land vehicle, as well as by means of a crane or a ship, and especially to large containers built into large tanker vessels.

Other and further objects and advantages will appear from the following description taken with the accompanying drawings in which like characters of reference refer to similar parts in the several views, and in which:

FIGURE 1 shows the section of a ship in which a tank is mounted,

FIGURE 2 is a diagram showing diagramatically one of the sets of channel-like grooves,

FIGURE 3 is a fragmentary section showing the channel-like grooves,

FIGURE 4 shows diagramatically a system by which either or both sets of channel-like grooves may be provided with dry gas, and

FIGURES 5a, 5b and 5c show several arrangements of the insulation of the present invention with respect to the single wall containers and to the enclosure for said containers.

FIGURES l and 2 illustrate the application of an embodiment of the present invention to a tanker. FIGURE 1 shows a vertical section athwart ship of the vessel. The body of the ship has outer skin 1 adjoining tanks 2 for fuel oil or ballast. The inner boundary 3 of the tanks 2 encloses the space for the placement of single-walled containers 4 which are mounted to the body of the ship with supports A. Insulation 5, by way of example, is disposed inside the containers 4. Against the boiling goods to be transported, the insulation is provided with an elastic, joint-tight cladding 6. The insulation is provided on each surface wit-h channel-like grooves 7 on the outside and 8 on the inside, through which passes a dry gas. This gas is conveyed to the channels by means of a conduit 9 and is drawn off via conduit 10.

FIGURE 2 shows schematically the passage of the dry gas through the channel system. For the sake of clearness, the movement of the gas is shown only on the interior surface. Both channel systems are similar.

The gas, fed for example from a generator 11, may be nitrogen. It is conveyed to a drier 12, known per se, which can be in the form of an adsorber or a freezingmixture evaporator or a spiral tube, in Which a small quantity of the transported goods is expanded. The gas is then dried and is fed to the channel system 8 via the distribution lines 9 by means of blower 13. The channels 8 are in diffusion connection with the insulation, and the dry nitrogen passing through them absorbs the moisture penetrating into the insulation in the form of vapor.

3 Subsequently, the gas loaded with moisture (water vapor) is withdrawn through the distribution system 10.

A special embodiment of the invention provides for a regulation of the dew point of the dry gas in such a manner that the ice film building up during the duration of the filling does not block the passage through the channels on the colder surface of the insulation. FIGURE 3 visualizes the ice film 14 forming therewith in the channel cross-section 8, which adjoins directly the colder insulating surface 6. The thickness of the ice film must be less than the depth 15 of the channels 8. The regulation of the dew point of the dry gas is carried out manually or automatically in a known manner by means of thermostats or hydrostats.

It lies within the scope of this invention to selectively feed the dry gas only to the outer channel system 7, and during the emptying only to the inner channel system.

Since water vapor wanders into the insulation not only through ditfusion but also through vagrant convection, it is advantageous (and therefore lies within the scope of the invention) to keep the gas passing through the insulation at a slight overpressure as against the environment. This overpressure acts against penetration of air or of inert gas containing water vapor. It is advantageous to utilize the customary inert protective gas, usually nitrogen, also as dry gas in the channel system of the insulation.

An especially simple and reliably controllable embodiment of the dry-keeping method according to the invention consists in the circulation of a constant-remaining quantity of dry gas, as is shown schematically in FIG- URE 4. Shown there are a feed line 19, a discharge line 20, a gas drier or dehumidifier 12, a conduit 9 to the channel system in the insulation, and a gas exit 10 from the channel system. The gas loaded with water vapor enters drier 12 via 10 and is again fed to the channel system 9 in the form of dry gas by means of blower 13. Switching devices or valves 21 permit the switching over from a feeding of gas to the outer channels 7 to the feeding of gas to the inner channels 8 and also to the simultaneous feeding of both channel systems with dry gas. As shown, the grooves 7 and 8 are connected to the drier in parallel. The circulation of the same quantity of gas in such a circulation process is particularly economical because the gas conveyed to the dehumidifier in this manner, in general, is substantially drier than a gas taken from a gas generator or from the atmosphere.

FIGURES a, 5b and 5c illustrate schematically the applicability of the invention, independently from the arrangement of the insulation, to use in a gas shipping tanker. The insulation arrangement is shown in FIGURE 5a as inside the tank 4; in FIGURE 5b as adjoining the tank on the outside; and in FIGURE 50 as spaced from the tank on the body of the vessel, e.g. the Wall 3 of a ballast tank. The inner channel system 8 and the outer 4 channel system 7 for conveying the dry gas are independent of the arrangement of the insulation 5. In all three cases, a void space is indicated between the tank and the body of the vessel, but this is not required for the applicability and function of the present invention.

The invention is not to be confined to any strict conformity to the showing in the drawings but changes or modifications may be made therein so long as such changes or modifications mark no material departure from the spirit and scope of the appended claim.

What is claimed is:

An insulation system for single wall containers for storing or shipping of liquids that boil at approximately atmospheric pressure comprising rigid single wall means defining a container, a layer of permeable insulating material placed against the interior of said rigid wall means, a layer of elastic material on the side of said insulating material remote from said rigid wall means and adapted to be contacted by the liquid to be stored in such container, said layer of permeable insulating material having a plurality of channels on the interior and exterior sides thereof respectively between the insulating material and the layer of elastic material and between the insulating material and the rigid wall means, said channels defining inner and outer separate sets of intercommunicating passages, a source of inert gas, a gas drying means in communication with said source, said sets of passages having an inlet and outlet for each set, a pair of feed conduits, one feed conduit communicating with the inlet of the inner passages and the other feed conduit of the pair communicating with the inlet of the outer passages, a pair of outlet conduits, one outlet conduit communicating with the outlet of the inner set of passages and the other outlet conduit communicating with the outlet of the outer set of passages, a control valve in each of the inlet and the outlet conduits, conduit means between the control valves of the outlet conduits and the drying means and conduit means between the drying means and the control valves of the inlet conduit, a blower in said lastmentioned conduit means whereby inert gas can be supplied to the drier and forced by the blower to flow in parallel through both sets of passageways and be recirculated through the dried or selectively circulated through the outer set of passages during filling of the container and through the inner set of passages during emptying of the container.

References Cited UNITED STATES PATENTS 2,927,437 3/1960 Rae 62-55 3,110,156 11/1963 Niemann 62-45 3,159,005 12/1964 Reed et a1. 6245 LLOYD L. KING, Primary Examiner.

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