US3159004A

US3159004A - Transportation of liquefied natural gas

Info

Publication number: US3159004A
Application number: US133197A
Authority: US
Inventors: Percival C Keith
Original assignee: Hydrocarbon Research Inc
Current assignee: Hydrocarbon Research Inc
Priority date: 1961-08-22
Filing date: 1961-08-22
Publication date: 1964-12-01
Anticipated expiration: 1981-12-01

Description

Dec. 1, 1964 P.c.KE1TH TRANSPORTATION 0F LIQUEFIED NATURAL GAS Filed Aug. 22, 1961 .,f seb a2 o 74 fle z g CARGO EXPANSDN INVENTQR. Perclvcll C. Kelh United States Patent() 3,159,004 TRANSPGRTATIN F LIQUEFED NATURAL GAS Percival C. Keith, Peapack, NJ., assiguor to Hydrocarbon Research, Inc., New York, NX., a corporation of New .Iersey Filed Aug. 22, i961, Ser. No. 133,197 3 Claims. (Ci. 62-45) This invention relates to the transportation of liquefied natural gas and similar normally gaseous materials which must be maintained at temperature levels below about 40 F. to permit handling at substantially atmospheric pressure. It particularly relates to improvements concerning ship storage whereby the liquefied material may be transported by water carrier.

The liquefaction and storage of natural gas at about 260 F. has been suggested as economical for supplying gas in industrial areas where fluctuating gas demands often exceed the capacity of available facilities. Where, however, the available gas is at remote geographic areas and shipment must be by water borne carrier, many new problems have arisen. Not only is ship transportation relatively slow, thus causing long periods of heat infiltration which tends to vaporize a substantial part of the cargo, but also a ship has substantial turbulence which, in itself, further tends to vaporize the liquid. In a ship, these vapors are an especially serious hazard for they are explosive when mixed with air.

My invention relates primarily to the handling of liquefied natural gas and to the control of vaporization of the liqiud but as hereinafter pointed out, it is also applicable to the handling of other liquefied gases such as propane, oxygen or nitrogen which arefsubject to liquefaction at temperatures in the range of 40 F. to as low as 424 F. and thus subject to objectionable vaporization resulting from ambient heat iniltration.

A principal object of my invention is toprovide a simpliiied liquid storage unit for liquefied gases which unit is suitable for assembly in a ships hold and inrwhich structural stability is combined with safety `against hazardous gases to the end that liquids may be readily stored 'and discharged.

The invention further contemplates storing of the lique- 4lied gases in the sub-cooled state so that under the normal As a specilic feature of the invention, it is proposed to. sub-cool liquefied natural gas to a` temperaturerof about F. below the bubble point so that a container 3,159,004 Patented Dec. 1, 1964 ICC FIG. 1 is a schematic central transverse vertical section taken through a marine vessel.

FIG. 2 is a horizontal cross-section taken substantially on the line 2 2 of FIG. 1.

of liquid when shipped overseas during a customary pei' riod will only be heated to a bubble point which is approximately 260 F. thus avoiding the production Vof any hazardous vapors and making it possible to dispense with a re-liquefaction equipment on board the carrier.

` Further objects and advantages of the invention will appear from the following description of a preferred form `drawing illustrative thereof and in which:

As shown in FIG. l, the vessel 10 which is represented as a marine vessel such as a ship or barge, but which might also be a land Vehicle body, is shown to have a supporting bottom 12, sides 14 and a top deck or flooring 16. While the vessel as shown includes at least a hold encompassed by these walls and the customary bulkheads and extends the full depth below decks, it will be understood that the vessel might be of a multiple deck type and the unit shown might be a typical insulated hold.

Within the defined hold I provide one or more liquid cargo containers or tanks 20 which are preferably made of aluminum. While these tanks may be of a suitable shape, I prefer to use a series of cylindrical tanks in contact one with another as shown in FIG. 2 and conveniently Welded to each other as by means of the stays 22, to become a rigid one piece nest. This assures a common movement of all tanks about a central point and thus does not interfere with expansion or contraction.

The tanks 20, if cylindrical, are provided with dished or hemispherical top and bottom portions with bottom skirt portions 26 which rest on andare Vpermanently afiixed as by welds, not shown, to an aluminum lioor plate 28. This plate, in turn, is provided with a knob 30 which extends into a suitable cooperating slot in the ilooring 32.

vThis flooring which is usually of oak planking is suitably `mounted on insulation such as balsa wood generally shown at 36 carried on the bottom 12 of the hull.

On the side walls of the hold, including the bulkheads, I prefer to use one or more layers of semi-permanent or bonded insulation 36a which consists of foam glass or cork or ,other pre-shaped insulation. This layer is mounted lnpermanent array as by the use of suitable lbinders which hold it against the hull wall. With its celf insulation 36h which may be of rockwool packed in bags of a suitable dimension. The bags themselves are preferably of impervious material and thus serve to decrease gas currents. Such secondary insulation is appropriately held in place to'leave a space 37 between the wall insulation and the tanks which space can be used for an access space to permit an inspection or repair of the outside ofthe tanks 20.V Such a space also becomes an important insulator of the very cold surfaces of the tanks 20. A further space, designated 40 in FIG. 2, between adjacent cylindrical tanks is also large enough for inspection and repair. With rectangular tanks, this internal space is unnecessary.

The hold is completed by an` insulated cover 42 which is supported by skirts 43 on theV upper portions of the tanks 20. The cover includes an aluminum plate 44 covered as by the use of cork or rockwool insulation 45.

3 tanks 2@ in a hold through a lill header 60 with a normally liquefied gaseous material such as natural gas. This header 60 is connected through line 62 to the bottom of one of the tanks of the nest and by the intermediate transfer lines 64- it is possible to fill all of the remaining tanks in the nest. The last tank in the vseries is provided with a discharge line 65 which discharges into surge tank 66. When the liquid .in the surge tank reaches the desired level, all of the tanks in the particular nest are full.

During irl-transit periods, l find it desirable to maintain a circulation of liquid through the tanks to prevent any substantial temperature differences. plished by the use ofl pump 7@ which takes suction by line 65 from the surge tank 66 and through discharge line '72 and ll line 62 can continuously circulate the liquid through the tanks and back through `outlet line 65 to the surge tank. Normally, a turnover of liquid on a daily basis assures uniform temperature of the liquid.

Discharge of the liquid from the tanks is preferably by theruse of a high pressure gas source such as an inert gas, for example, nitrogen or the'same type of gas in storage, for example, natural gas. This may be connected through gas header 74 through gas line '76 to the v.top ofthe surge tank 66. This will impose a head on the liquid in surge tank 66 which in turn will force the liquid out through line 65 into the last tank of the nest thence through lill line 62 to liquidy header 60.

During the `return trip of a ship such as described, it has been found desirable to provide for a recirculation of low temperature gases such as methane or nitrogen or mixtures thereof to assure a uniform low temperature of the tanks. lThis is accomplished by the use of blower S2 which takes suction from the upper part of surge tank 66 through line Sil and then discharges through line SS'and cooler 34 into header 6i). By the same piping 62, tanks 2li., and piping 65, the gases flow back to= the surge tank 66. The `cooler 84% may be nitrogen cooled.

This is accomt Ordinarily provision is made for possible expansion o-f the'liquidin the cargo tanks 20. As the liquid expands into surge tank 66y through line 65, the excess may be drawn olf through pipe 3S to the expansion tank 2.1. Ios- Ysible vapors can be vented through line 9i) back to the surge tank 66. v

The transportation or storage of a normally liquefied gas at about its bubble Vpoint is usually accomplished at atmospheric pressure notwithstanding the constant vapor- In such a Wunit,

ization of gas due to heat` infiltration. especially with an inflammable-gas, there is always a gas discharge which must be burned as 'fuel or reliqueed.

If, however, gas is stored under sub-cooled liquid con- Y ditions, the vapor pressureis of a low absolute valueand the holds, again with the advantage that the actual surface exposed to the gas is extremely small when the total horizontal surface is considered. f

As a result, l nd that the solubility of nitrogen in the liquid methane does not present a technical problem, and, in fact, on revaporization as soonV as the methane is heated to be vaporized for use, the nitrogen is driven oli. It is thus possible to maintain the liquid methane at a temperature condition under which it exerts a vapor pressure less than one atmosphere absolute without in fact having a vacuum present in the chamber.

The degree of sub-cooling can be adjusted to the desired extent but normally a ship voyage of a week would tend to boil ofi about 1.5% of the contents of the tanks resulting from about a 4 F. temperature rise. I prefer, under such conditions, to .sub-cool the methane to about -270' F. which is about 12 F. below the bubbling temperature. This can be accomplished by a iinal stage of liquefaction which can be by heat exchange with liquid nitrogen.

My invention is particularly advantageous for ocean going shipment due to the long period involved and the l advantage of eliminating expensive re-refrigerationequipment. It is also possible, however, tot benefit from my invention in connection with stationary storage vessels where sub-cooling can be accomplished with less energy consumption than `the re-liquefaction can be accomplished.

The pressurizing of the nest of tanks Ztl. not only to discharge liquid but for other purposes, can be Vaccomplished by the use of reenforced tanksand connections. In accordance with the invention, however, I provide only a secondary containment generally shown as a clad shield or cover element 45. This is-necessary only on the outside tanks of the nest and maybe aseries of welded plates. n

Preferably I use a series of WeldY pads or plates 46 attached in thel shop to the tanks. These weld pads'serve notV .only to Vattach the clad cover element l bu-t also the external filler plate or web 47. As the pads 46 are Shop aixed,'the remaining welding of thecover elementl 4S and lillerplate i7 can be accomplished in the'field without in any way weakening the tank structure.

It will be apparent from the foregoing Vdisclosure that modifications may be made'to my invention and I thus desire a broad interpretation `of my invention within the scope and spirit of the disclosure herein and of the claims appended hereinafter.

l. In the method Vfor the safe storage of a highly volatile, low'boiling, liquied, combustible gas inplarge volumes at temperatures below the boiling point wherein the gas is liquefied under substantially atmospheric conditions, the further steps of sub-cooling the liquid yto a temperature substantially below the boiling point wherein nthe vapor pressure conditionV is less than one equipment thathas been used heretofore to reduce the danger, or loss,`oriboth, resulting from heat imiltration to liquefied gases in ship or land storage.

In addition, I floatfonthev liquid a substantially impervious sheet 92 made of a suitable material such as aluminum which nearly covers the exposed liquid. While 7 l small and not objectionable. Y

There is the further advantage that this gas'ftends to Yworkon allof the liquid'inall of the tanks, in all of vpartial pressure substantiallyV atmosphericl and thereby .prevent inflow of air from the surrounding atmosphere andavoidV the formation of a combustible mixture with theliquelied gas. n l2; The method of storage ofa combustible gas as claimed in claim l wherein'the combustible gas is substantially Vliquid methane, the sub-coolingis to a temperature in the order of 270 F. and the blanketing Ygas isl nitrogen;

.V3i The method of storage 0fV a combustible gas as claimed Vin claim 2 including the further step of covering a majorV part of the'exposed surface of the liquid methane with a substantially gas 'impervious surface to ,re-

occlusion.

References Cited in the le of this patent UNITED STATES PATENTS De Motte Mar. 3, 1936 Zuiver July 21, 1936 Willenborg Aug. 4, 1936 Whidden May 8, 1951 McLaughlin June 10, 1952 Payne July 22, 1952 Brandon Sept. 21, 1954 6 Brandon Oct. 11, 1955 Iamsen Oct. 25, 1955 Brandon Ian. 31, 1956 Beckwith Aug.'4, 1959 Murphy May 30, 1961 Wiedemann et a1. May 1, 1962 Aronson July 24, 1962 OTHER REFERENCES Advances in Cryogenic Engineering (Timmerhaus),

Claims

1. IN THE METHOD FOR THE SAFE STORAGE OF A HIGHLY VOLATILE, LOW BOILING, LIQUIFIED, COMBUSTIBLE GAS IN LARGE VOLUMES AT TEMPERATURES BELOW THE BOILING POINT WHEREIN THE GAS IS LIQUEFIED UNDER SUBSTANTIALLY ATMOSPHERIC CONDITIONS, THE FURTHER STEPS OF SUB-COOLING THE LIQUID TO A TEMPERATURE SUBSTANTIALLY BELOW THE BOILING POINT WHEREIN THE VAPOR PRESSURE CONDITION IS LESS THAN ONE ATMOSPHERE ABSOLUTE, CONFINING THE LIQUID IN AN INSULATED STORAGE CONTAINER, INTERCONNECTING THE STORAGE CONTAINER WITH A TANK OF RELATIVELY SMALL HORIZONTAL SURFACE, APPLYING AN INERT AND RELATIVELY LOW SOLUBILITY GAS TO THE SMALL HORIZONTAL SURFACE WHEREBY THE INERT GAS GOES INTO PARTIAL SOLUTION IN THE LIQUID TO THEREBY MAINTAIN A PARTIAL PRESSURE SUBSTANTIALLY ATMOSPHERIC AND THEREBY PREVENT INFLOW OF AIR FROM THE SURROUNDING ATMOSPHERE AND AVOID THE FORMATION OF A COMBUSTIBLE MIXTURE WITH THE LIQUEFIED GAS.