US2897657A - Storage and transportation of liquefied gas - Google Patents

Abstract

829,206. Liquefied gas storage vessels. ESSO RESEARCH & ENGINEERING CO. Nov. 21, 1956 [Dec. 13, 1955], No. 35600/56. Class 8(2). [Also in Group XXXIII] Liquefied natural gas is stored during transportation at substantially atmospheric pressure in a vessel 19 surrounded by a jacket 21 of carbon dioxide snow which in turn is surrounded by solid insulation 15 e.g., balsa wood, cork, foam glass or rubber having an inner liquid proof coating 17 and an outer steel container 11 ; the carbondioxide being admitted through a duct 28 and the resulting vapour being vented through a duct 27. Spacing struts 23 are located between the vessel 19 and the solid insulation 15. Vaporized methane may be used to propel the vehicle e.g. a ship (see Group XXXIII) and carbon dioxide vapour may serve as a fire extinguishing medium.

Description

Aug. 4, 1959 w. H. RUPP STORAGE AND TRANSPORTATION 0F LIQUEFIED GAS Filed Dec. 15, 1955 CORK OR BALSA wooo 21 -l5 H? Fig. 2

Walter H. R upp Inventor x945; am; W A w United ties; Patent STORAGE AND TRANSPORTATION OF LIQUE- FIED GAS Walter H. Rupp, Mountainside, NJ., assignor to Esso Research and Engineering Company, a corporation of Delaware Application December 13, 1955, Serial No. 552,780 1 Claim. (Cl. 6245) The present invention relates to a liquefied natural gas vessel and also a process for handling and shipping liquefied natural gas and other liquids of extremely low boiling point.

In the prior art, it has been suggested that very low boiling liquids, e.g. those that boil many degrees below normal atmospheric temperatures, and particularly liquefied natural gas may be transported in an insulated vessel at substantially atmospheric pressure by allowing the liquid to boil, drawing oil the vapors thus formed and using them for fuel, refrigeration, and other purposes. It has also been suggested that in order to promote safety in handling very low boiling materials, a vessel of metal walls, particularly one having steel walls, should be insulated on its interior surface to prevent the metal reaching such extremely low temperatures as to make it brittle and frangible. The present invention is an improvement over the prior art suggestions just mentioned.

According to the present invention, normally gaseous materials, e.g. toxic gases such as ammonia, etc., and especially inflammable vapors such as natural gas, are liquefied and the liquid is stored at low pressure, preferably at or approaching atmospheric pressure in an insulated container which is surrounded by an extremely low melting or low boiling material which is non-toxic, or non-inflammable, such as solid carbon dioxide. The latter, in turn, is placed within an insulation lined vessel which comprises the main structure containing the materials named. This has the advantage that the low melting solids such as carbon dioxide snow, etc., not only provide a secondary insulation barrier but also can be used to reduce fire and/or toxicity hazards and also reduce evaporation losses from the liquefied normally gaseous material.

According to the present invention a vessel, such as a ship having a steel hull, or a barge, or even a railroad tank car, truck tank or the like, is lined interiorly with a thick effective thermal insulating material such as cork, balsa wood, foam rubber or plastic insulator, or combinations of these materials. The insulating materials are secured to the inside surface of the outer Wall. The insulation is preferably coated with an impervious coating which is not soluble in the liquid to be stored in the vessel or in the secondary insulating material such as carbon dioxide. Within the insulated space thus provided, there is mounted in spaced relation to the primary insulation, a thin walled vessel made preferably of metal which is not highly sensitive to temperature changes and which, preferably, does not become substantially brittle at very low temperatures such as 100 F. to 250 F. or lower. The space thus provided between the primary insulation and the inner container or liner is then filled with a loosely packed finely divided solid material of very low boiling point, e.g. solid carbon dioxide. The packing gives additional insulating value and, as it evaporates or sublimes, it gives oif vapors which are nontoxic, non-inflammable and which tend to reduce fire hazard and other hazards.

The material to be shipped is then placed within the inner liner. This material may be a liquefied petroleum gas, anhydrous ammonia, or other liquefied normally gaseous material. For purposes of describing the present invention, reference will be made primarily to a liquefied natural gas. This material usually contains large proportions of methane which boils at about 161 C. or 25 8 F. Natural gas may be liquefied by repeated expansion and cooling processes as is well known in the art. Where convenient, advantage should be taken of the pressure at the gas source which frequently is very substantial. By this means the gas may be liquefied economically.

Since vessels of the character specified above are not built of suflicient strength to withstand high pressures because of economic consideration, the liquefied product ordinarily must be carried at pressures which are not far from atmospheric pressure. In some cases the pressure may be allowed to rise moderately, e.g. to as high as 25 to 50 p.s.i.g. but as a rule, the pressure will be substantially atmospheric or only a few pounds gauge.

Obviously, no insulation system is efficient and liquefied natural gas which boils, for example, around 258 F. will soon warm up to its boiling point and begin to give ofl? vapors. The same is true of materials such as ammonia, etc., which are not so low-boiling. These vapors, in the case of hydrocarbons, may be used as fuel to propel the vessel or any of them may be used as refrigerant first. Obviously, they may also be recompressed, evaporated, cooled, etc., to liquefy them again and return them to the vessel.

By suitable choice of fixed insulating material of appro priate thickness and by suitable spacing of the liner from the insulator to regulate the thickness of the protective carbon dioxide blanket or jacket, the evaporating rate of the carbon dioxide as well as of the liquid natural gas may be controlled substantially as desired. Thus the evaporation rate of carbon dioxide may be arranged to exceed that of the liquefied natural gas or the latter, as suggested above, may be returned to storage by liquefaction in which case the only vapors being lost are those from the carbon dioxide. Obviously, the latter may also be recompressed and cooled to return the carbon dioxide snow to the insulating jacket.

The invention will be more clearly understood by reference to the accompanying drawing. In this drawing Fig. 1 shows a transverse sectional view of a typical tanker vessel in which the invention is incorporated;

Fig. 2 shows an enlarged fragmentary cross section of a modification where a storage vessel is mounted in an insulated compartment with a blanket of CO or the like.

Referring first to Fig. 1, the outer vessel Walls of a tanker vessel or barge are indicatedat 11. These may be of suitable metal such as carbon steel whichis ordinarily employed-for tanker vessels or for railroad cars, truck bodies, and the like. Complete enclosure of the liquid is necessary; hence, a cover member 13 is provided to enclose the compartment to be insulated. The entire walls and bottom of the tank or vessel, as Well as the underside of the cover 13 are lined with an effective porous insulating material 15. This material preferably is a thick layer of balsa wood," for example, 6" to 18" thick. Cork may be used instead of balsa wood or a combination of the two. Other expanded insulating compositions such as foam glass, foam rubber, etc., may also be used. Preferably, they are lined on the inside with a liquid proofing layer 17 although this is not always necessary where the carbon dioxide jacket is employed. The latter is better shown in Fig. 2.

The space between the fixed insulation and an inner liner 19 is indicated at 21. Material to be shipped is contained in space 10 surrounded by liner 19. Liner 19,

or a plurality of them (three are shown in Fig. 1) is held in spaced relation to the insulation by means of struts or other supporting members indicated at 23.

A vent 25 and a liquid feed and withdrawal line 26 are provided from the liner 19 extending through the insulation and through the cover plate or member 13. These allow space inside the tank to be vented or pressured. Several vents may be provided if the vessel is large and they may be connected together in an obvious manner. As indicated above, the evolving vapors escaping through the vents 25 may be used as fuel if they are hydrocarbons, or they may be first used as refrigerant and then used as fuel. On the other hand, they may be recompressed, liquefied and returned to storage so that there are no appreciable losses where the value of the 'gas justifies such procedure.

Likewise, from the carbon dioxide jacket space 21, vents 27 are provided. From these the carbon dioxide vapors may be allowed to escape to the atmosphere. If desired, they may be distributed over the surface of the vessel 11 by applying an extra cover or jacket so as to reduce fire hazards. Alternatively, as indicated above, they may be recompressed, cooled, evaporated, etc. to produce carbon dioxide snow for returning to the insulation layer through one or more filling pipes 28.

Referring now to Fig. 2, similar elements are shown by the same reference characters as in- Fig. 1. Here a cylindrical tank 19 is spaced by means 23 from a thick cork or balsa 'wood liner 15 secured to the inside Wall of an outer vessel 11. The fixed insulation 15 is provided with an impervious coating 17. The space between fixed insulation 15 and the inner vessel 19 is filled with solid CO at 21. This arrangement shows the installation in between structural elements 41, 43 of a vessel or vehicle. Supports 45 are provided for outer vessel 11 and a cover member 47 encloses the top thereof.

The invention described has the following advantages:

A supply of carbon dioxide gas is readily available which can be released in case of a leak or rupture in the natural gas container, or in case of collision of any other damage that might otherwise institute a fire hazard.

As a result of the safety insurance in the presence of large quantities of carbon dioxide, the personnel operating vessels containing natural gas in liquid form are better able to discharge their duties and operate more efficiently.

With the graduated system of insulation, the heat losses from outside the vessel into the liquid natural gas compartments are greatly minimized. As indicated above, any reasonable balance desired may be maintained between evaporation of liquid natural gas and carbon dioxide. Either or both may be used externally, or may be returned to the system.

It will be obvious that the use of a carbon dioxide snow which melts or sublimes at about 112 F. is a very effective insulating buffer and also adds a considerable safety factor. While reference has been made above to shipment of liquid natural gas, and application to ammonia has been mentioned, it is obvious that other materials such as propane, butane, pentane or even gasoline may be shipped in the same manner with advantages. Non-combustible or toxic materials, such as chlorine, etc. may be handled also. The safety of the system makes it more acceptable than some of those suggested in the prior art. The stored material may have a boiling range either below or above that of CO or its boiling range may range above and below that of CO Preferably, the boilingrange of the stored or transported material is below that of CO since this substantially conserves the latter, but the invention is'applicable to materials boiling at any range between absolute zero and ordinary atmospheric temperatures.

It will be appreciated that various changes and modifications may be made within the spirit of the invention and it is intended to cover these so as as they come Within the scope of the following claim and so far as the prior art permits.

What is claimed is:

A method of storage for bulk marine transportation of hydrocarbons such as methane which are normally gaseous at atmospheric temperature and pressure and which have critical temperatures below the sublimation temperature of solid carbon dioxide under atmospheric pressure, which method comprises liquefying said hydrocarbons and cooling them to a temperature below the boiling point thereof at atmospheric pressure; introducing said liquefied hydrocarbons at the reduced temperature into a first confined storage zone disposed within and occupying a substantial portion of the hold region of the hull structure of a marine vessel adapted for the canriage of cargoes in bulk, said hull structure being characterized by an inner liner of a substantially rigid insulation material in spaced relation exteriorly to said first confined storage zone leaving a second confined storage zone between said first storage zone and said insulation material; encasing said first storage zone with a layer of solid carbon dioxide substantially filling said second storage zone; venting said first and said second storage zones to maintain both said liquefied hydrocarbons and said solid carbon dioxide substantially at atmospheric pressure, whereby heat transfer through said hull structure and said liner thereof to said solid carbon dioxide is at least partially compensated by sublimation of the latter, and heat transfer from said solid carbon dioxide to said hydrocarbons is at least partially compensated by vaporization of the latter at atmospheric pressure.

. References Cited in the file of this patent UNITED STATES PATENTS 1,680,873 Lucas-Girardville Aug. 14, 1928 2,148,109 Dana et al. Feb. 21, 1939 2,185,030 Lockwood Dec. 26, 1939 2,475,755 Pearson July 12, 1949 2,712,730 Spangler July 12, 1955

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