US2933902A

US2933902A - Transportation of liquefied gases

Info

Publication number: US2933902A
Application number: US552421A
Authority: US
Inventors: Frank A Howard
Original assignee: Exxon Research and Engineering Co
Current assignee: ExxonMobil Technology and Engineering Co
Priority date: 1955-12-12
Filing date: 1955-12-12
Publication date: 1960-04-26
Anticipated expiration: 1977-04-26
Also published as: GB829915A

Abstract

829,915. Storing liquefied gases. ESSO RESEARCH & ENGINEERING CO. Nov. 21, 1956 [Dec. 12, 1955], No. 35599/56. Class 8(2) [Also in Group XXXIII] A transportable vessel for storing liquefied hydrocarbons of low boiling point e.g. methane at substantially atmospheric pressure comprises an inner container 23 lined with heat insulating material 25 e.g. balsa wood having a liquid-proof lining 29 and submerged in a tank 8 of hydrocarbon liquid of much higher boiling point e.g. petroleum capable of absorbing gas in either the liquid or gaseous phase leaking from the inner container 23. The container 23 which has a vent 33 and a liquid inlet and discharge duct 31 is held by saddles 17, 19, 21 within the tank 8 which also has a vent 39 and a supply and discharge line 37. A plurality of such vessels may be located in the hold of a ship (see Group XXXIII) the engines of which may be fuelled by vented gas. Reference has been directed by the Comptroller to Specification 766,128.

Description

April 26, 1960 F. A. HOWARD 2,933,902

TRANSPORTATION oF LIQUEFIED GAsEs Filed nec. 12, 1955 By ,/M, dwamttomey reliquefied and returned tok storage.

2,933,902 l TRANSPORTATION F LIQUEFIED GASES Frank A. Howard, New York, N.Y., assignor to Esso Research and Engineering Company, a corporation of Delaware Application December 12, 1955, Serial No. 552,421

6 Claims. (cl. sz-.45)

` asmethane, natural gas which is largely methane, ethane,

ethylene and the like, have enormously high vapor pressures at ordinary atmospheric temperatures. In fact, some of these cannot be liquefied at any pressure at ordinary temperatures. I t is obvious that the shipment of such llow boiling materials in pressure vessels is not commercially feasible, particularly where large quantities are to be shipped and their economic value is relatively low.

. It has also been proposed in the prior art yto liquefy normally gaseous materials of the type mentioned and to transport them in vessels maintained merely at atmospheric pressure. Obviously, even'with the best of thermal insulation, part of the products are bound to evaporate during transportation to any substantialdistance. yThe free evaporation of these materials involves considerable hazard although they obviously may be used for refrigeration, as engine fuel, or they maybe recompressed and Evenv when 'the gases are so disposed of, there are still substantial hazards involved in transporting liquefied gas in equipment and by processes known to the prior art.

According to the present invention, the difficulties mentioned are largely overcome by transporting the liquefied gas in thermally insulated tanks or vessels which are submerged, or at least partially submerged, in liquids of `much higher boiling range. For example, natural gas may be liquifed and stored in a well-insulated tank which in turn is kept submerged in a tanker or vessel filled with a material, e.g. crude oil or gasoline, which will absorb "large quantities of the gas. Under these conditions, any -incidental leakage of the liquefied gas or of the products evaporating therefrom is caused to pass into vvthe liquid medium surrounding the insulated tank. Natural gas,

i.e. the lower hydrocarbons, can be absorbed to a substantial extent in a large body of heavier hydrocarbons.

The surrounding liquid 'preferably is one which does not .have a flash specification; otherwise ifgasleaks into it, .it may have to be reprocessed. .Moreovenaccording 'to yanother feature of the invention, the gasesV which may escape into the heavier yoil in excess of its Acapacity to ,absorb them, can be-readily controlled and, if necessary, they may be bled off at a safe point4 from the vessel :or .carrier .so as Ato minimizetire and other hazards.

Ainsulating material is indicated at 25 and is suitably bondoil tankeris indicated at 1.

or bonding layer 27 also is .proof.`

`atenafd Appr. 26,1960

The invention will be Ymore clearly understood by referring to presently preferred specific embodiments thereof. It will be understood, however, that the invention is not necessarily limited thereto.

Referring to the accompanying drawings,

Figure l shows a typical longitudinal sectional view of a vessel or tanker adapted to carry liquefied normally gaseous material such as liqueed natural gas, certain parts being broken away.

Figure 2 shows a transverse section of the vessel of Fig. l, taken substantially along the line 2 2 of Fig. l.

Figure 3 shows an enlarged cross-section of a liquefied gas tank immersed in a liquid filled tank of common type, this view being taken substantially along line 3--3 of Fig. 2.

Referring rst to Fig. 1, an outer vessel such as an It hasl a bow portion 2, containing

tanks

3, 4, 5, and a middle section 6 con'- taining further tanks 7, 8, 9. The stern section 10 contains the engine and crew compartments, etc. The vessel itself is constructed so as to be substantially liquidtight and it preferably has a deck 11 which also ismore or less liquid-tight. Suitable vents and means of access into the inner parts of the vessel may be provided as will be obvious to those skilled in the art. Suitable struc` tural elements 13,' 15 are provided for supporting tanks 7, 8, 9, from the vessel walls.

Suitably mounted in the lowerV part of one or more of the tanks, 8, 9, etc. and at the sides thereof are saddles orsupporting members 17, 19 and 21, best shown in Fig.` 3. These are so arranged as to provide adequate support for an inner, vessel 23. The latter is lined with an effective heat-insulating material such as cork, balsa wood or the like,l,applied in a layer which may be from two or three inches to a foot or more in thickness. This ed to the vessel 23 by means of an adhesive or bonding layer 27. The 4vessel 23 is impervious `to gas and is pref- 'Aerably made of steel or other suitable material.

The insulating material 25 may be impregnated to make it `impermeable to gas or liquid contained therein, and it is preferably coated on its inner face with a lining or layer 29 of liquid-proof and gas-tight material. Theadhesive preferably gas and liquid- Inlet means for supplying liquefied gases, to the tank 23 are indicated at 31 and an outlet 33 is provided for gases which evaporate and collect in the upper part of the tank at 35. g

A feed line 37 is vprovided for supplying oil to, and removing it from the outer tank. Although inner tanks are shown placed only in two tanks 8, 9, of the tanker vessel, Fig. l, it will be obvious that all of the cargo tanks of the vessel may be provided with such -if desired.

In use, the inner tank 23 is filled with the liquefied gas to be transported. 'Since it is well insulated thermally, the amount of evaporation taking place therein is kept low. The outer vessel 11 is filled with a heavier material vsuch as crude oil, gasoline, etc., as previously mentioned,

or some other material boiling well above normal atmospheric pressures. v

It willbe understood, of course, that normally there are no gases escaping from the inner tank into the 'outer compartment. vThe normally evaporating gases are carriedoff through outlet 33. vFrom this outlet, theylmay g be taken to the engine room to supply fuel to the power plant orthey may be first used for refrigeration and then burned 'as fuel; Alternativ'ely,'they maybe recompressed and liquefied and returned to the vessel through the line 31. In general, the inner tank will have its own independent inlet and outlet connections which pass through the cover or top wall of the outer tank in which the inner container is located.

The shape of the inner tank may be varied and it need not be built to withstand substantial pressure. As indicated in` Fig. 3, a horizontal cylindrical tankffor/liq'uetied methane, etc. can be carried in smooth saddles'which conform on their bottom to thebottom of the ordinary cargo tank. In all cases", it is desirable to haveV the inner tank supported at some distance abovefth bottorn of the outer tank. This permits inspection and cleaning of all of the opposed surfaces of bothv the inner tank and the outer tank. A.

In order to provide forescape of gas from the outer 'tanks such as 8, Fig. 3, in case of a large volume leakage of gas from the inner tank which the oil cannot fully absorb, a vent 39 is provided. This connects. to avent line 41 which preferably extends to the rear of the. vesf sel where it will direct escaping gas away from the vessel as indicated at 43. Obviously, a flare may be provided here, if needed, to burn escaping'gas, especiallywhen the vessel is not in motion s o as to diffuse escaping gas rapidly enough for safety. p

Whilefthe-above description has suggested the storage and transportation at atmospheric pressure, it will 'be understood that the same principles may be applied to transportation of gases which are kept liquid under pressure. Thus, propane, butane and mixtures thereof, even containing some proportions of ethane, may be kept liquid without venting them to the surface. As indicated above, such materials may be stored'in the inner tank. If a leak develops in the inner tank, no harm is done since the escaping materials are soluble inthe oil which surrounds it. y

The arrangement described has several advantages. Since it makes full use of the cargo space available, capital costs are low per unit of total Vliquid cargo capacity. Where gases are to be maintained at very low temperature to keep them liquid, the use ofthe internal insulation such as balsa wood reduces the heattransfer n rate to such a low figure that it makes little or no dif.- ference whether the external wall of the inner tank is exposed to air or to a liquid oil or oil'L product. In either case, the submersion .of the inner tank in oil, or gasoline, etc., increases safety. ,'Ihe pressure of the outer body Vof oil helps resist internal pressure within the. inner tank. In addition, the oil is available to absorb substantial quantities of escaping gases, ras previously pointed out. For'this reason, the production of eX- plosive mixtures in empty confined spaces within the vessel, is eliminated. When the outer or hull tank is not used for oil, it may be filled with water to maintain this same safety against explosion."V

It'will be noted that the total volumetric capacity of the moulded hull of a bulk oil carrier remains almost unaffected by fitting it with the internal tanks. Hence, Acapacity for total shipment is kept high. A carrier of this type is highly flexible as to the service to which it can be pnt. Thus, insteadfof carrying only liquefied gases or in combination with oil products, the vessel can'. be used for a full load ofalmost any form of liquid product. When demand for the liquefied gas is low, the inner tank may be filled with crudev oil, gasoline or other oil products. Hence, the full capacity of the vessel maybe utilized regardless of the products to be carried. The invention is applicableto. railroad tank cars, truckfmounted tanks, barges, etc. as well as to lareeoil tankers. 1

A ,1t.-wi11bc obvious Vthat numerous `variations mayv be these in the following claims so far as the state of the 'prior art permits.

What is claimed is: l y

1. A container for liquefied materials which are gaseous at atmospheric temperatures and pressures, comprising an outer substantially liquid-tight container shell whichin turn comprises at least a portion of the structure of a bulk transport container, an inner substantially gas-tight container shell supported within said outer shell and disposed therein with the outer surface portions of said inner shell in spaced relation to the inner surface portions of said outer shell, whereby to define a first storage compartment substantially surrounding said inner shell, 'a' liner of substantial thickness and of a solid, thermal insulation material secured to the inner surface portions of said inner shell in gas-tight relationv thereto, said liner defining a second storage compartment within itself and including an inner surface portion of a material'y substantially impervious to said liquefied materials, a body of liquid disposedV in said first storage compartment submerging said inner shell, said liquid having a boiling point at atmospheric pressures which is substantially above the normal range of atmospheric temperatures, means for introducing said liquid into said first -storag'e.compartment, means for introducing said liquefied' materials into said second storage compartment,

fied gaseous hydrocarbon material, and wherein said body of liquid in said first storage compartment comprises a hydrocarbon liquid having the capacity to absorb at least a portion of said liquefied gaseous hydrocarbon material.

3. A container according to claim 2 wherein said liqueed gaseous hydrocarbon material is liquefied natural gas, and said body of hydrocarbon liquid in said first storage compartment comprises a hydrocarbon'liquid boiling at atmospheric pressure in the boiling temperature range 4of gasoline and higher.

4. A container according to vclaim 1 wherein said bulk transport container comprises a marine vessel.

5. A container for liquefied materials which are gaseous at atmospheric temperatures and pressures, comprising an outer substantially liquid-tight container shell which in turn comprises at leasta portion of the structure of a bulk transport container, an innerfsubstantially gas-tight container shell supported Within said outer shell and disposed therein with the outer surface portions of said inner shell in spaced relation to the inner surface portions of said outer shell, whereby to define a first storage compartment substantially surrounding said inner shell, a liner of substantial thickness and of a solid, thermal insulation material secured to the inner surface portions of said inner shell in substantially continuous contact therewith, said liner defining a second storage compartment within itself, a body of liquid disposed in said first storage cornpartment submerging said inner shell, said liquid comprising a hydrocarbon liquid having at least some capacity to absorb liquefied natural gases and having a boiling point at atmospheric pressures which is substantially above the normal range of atmospheric temperatures be- Ving at least in the boiling temperature range of gasoline andihigher, means for introducing said liquid into said first storagecompartment, means' for introducing said' liquefied materials .into said second storage compartment, means forventing vapors from said first storage compartment including leakage. from Ysaid second storage compartment, means for venting vapors from said second storage compartment, and means: for. disposalat'a distance from each References Cited in the le of this patentv UNITED STATES PATENTS Moody Feb.` 5, 1867 Cabot May 18, 1915 10 Lucas-Girardville A-ug. 14, 1928 Backstrom Jan. 31, 1939 Dana et al. Feb. 21,` 1939 Kornemann et al Aug. 18, 1942 Winternitz Apr. 22, 1952 McLaughlin June 10, 1952 Reich Dec. 15, 1953 Loveday May 11, 1954 Bergstrom Aug. 31, 1954 fMorrison July 9, 1957 Loveday May 13, 1958 Johnson Dec. 9, 1958