US2986011A

US2986011A - Cold liquid storage tank

Info

Publication number: US2986011A
Application number: US805159A
Authority: US
Inventors: John A Murphy
Original assignee: Conch International Methane Ltd
Current assignee: Conch International Methane Ltd
Priority date: 1959-04-09
Filing date: 1959-04-09
Publication date: 1961-05-30
Anticipated expiration: 1978-05-30
Also published as: GB869130A; FR1253564A; DE1191245B; NL112946C; DE1191245C2; ES256985A1; BE589567A

Abstract

869,130. Tankers. CONCH INTERNATIONAL METHANE Ltd. March 17, 1960 [April 9, 1959], No. 9471/60. Class 113. [Also in Group XXVIII] Liquified methane tanks 22 are arranged in pairs in the hold of a double-hulled ship and adjacent pairs are separated by transverse coffer dams 18 which together with the inner surfaces of the walls of the inner hull 14 are lined with heat insualting material 20. Specifications 854,705, 854,706 and 854,707 are referred to.

Description

May 3o, 1961 J. A. MURPHY 2,986,011

COLD LIQUID STORAGE TANK Filed April 9. 1959 FIG, l 7p ,y ,y

United States Patent() COLD LIQUID STORAGE TANK John A. Murphy, New York, N.Y., assignor to Couch International Methane Limited, a corporation of Bahama Islands Filed Apr. 9, 1959, Ser. No. 805,159

9 Claims. (Cl. 62-55) This invention relates to the storage and transportation of a liquid adapted to be maintained at subatmo'spheric temperatures, and it relates more particularly to the construction and arrangement of insulated tanks of large capacity for use in the storage and transportation of a liquid which is adapted to be maintained at extremely low temperatures, such as at or below the boiling point temperature of a liquefied gas such as natural gas.

While this invention will be described with reference to the storage and transportation of liquefied natural gas, it will be understood that the concepts of construction and arrangement of a liquid storage tank can be adapted for use with other liquefied gases having a boiling point considerably below ambient temperature at atmospheric pressure. The interest in the storage and transportation of liquefied natural gas stems from the fact that such natural gas is available in amounts far in excess of the requirements in areas wherein it is located so that it is either flared olf and wasted, or else re-introduced into the ground at considerable expense. On the other hand, there are large areas remote from the source of excess supply of natural gas, wherein such natural gas is not available to the extent that such areas are starved for fuel and must resort to the expensive methods of manufacturing gas from coal or the like.

The objective is to make the excess gas at a source of plentiful supply available to the areas where deficiencies exist, thereby to make economical utilization of the less expensive natural gases otherwise wasted while conserving the supply of coal and the cost of manufacturing gas therefrom. Where the source of plentiful supply is connected by land with the area where a deficiency exists, and where the demand in such is sufiicient, the natural gas can be transferred by pipeline from one area to the other while being maintained in the gaseous state. The principal problem arises where the source of plentiful supply is separated by water or by great distances from the area where deficiencies exist, such that pipeline transmission becomes impractical.

The program which has been developed resides in the liquefaction of the natural gas at the source of plentiful supply whereby the gas is reduced in volume by a ratio of 600 to l. The liquefied gas can be transported in suitable containers from the source of plentiful supply to the area where deficiencies exist so that the liquefied gas can be reconverted from the liquefied to the gaseous state for use. One of the principal problems resides in the construction and arrangement vof suitable containers or tanks for use in the storage and transportation of such liquefied natural gases. For practical operation, it becomes desirable to provide means fo'r the storage and transportation of large volumes of liquefied gas. This means that tanks of suiiicient Wall thicknes for housing the liquid under pressure for transportation at reasonable temperature cannot be employed, at least from a practical or economical standpoint. Thus, it becomes important to provide for the transportation and storage of the liqueed natural gas in large tanks maintained at about atmospheric pressure or preferably slightly above, thus indieating storage temperature at about 258 F. (the boiling point of liquefied methane at atmospheric pressure) or slightly above, depending upo'n the amount of heavier hydrocarbons present in the liquefied natural gas. Usually, the temperature of storage and transportation of the liquefied natural gas, which is composed mostly of methane, will be within the range of about -240 F. to 258 F.

One arrangement for the storage and transportation of liquefied natural gas in large volume has been described in the copending application of Henry, Serial No. 582,965, wherein the liquefied natural gas is housed in large metal tanks fitted within the hold space of a ship formed with an outer metal hull and an inner metal hull which is separated from the outer hull to define wing tanks therebetween. The hold space is completely insulated by a low heat transfer material attached to' the inner surfaces of the inner hull to minimize heat loss into the tanks mounted within the insulated hold space.

Because of the Wide dimensional changes which take place in the tanks due to expansion and contraction in response to temperature change, it is desirable to support the tanks Within the hold space in a manner which permits free relative movement between the tanks and the ships structure while embodying means for stabilizing the positions of the tanks within the insulated hold space to maintain proper control notwithstanding the pitching and the rolling of the ship. In the aforementioned Henry application, such means are provided by the use of keys and keyways in the bottom side and the top side of the tank and the adjacent sturcture of the ship.

Access to the interior of the tank lfor loading and unloading, vapor relief, iluid level control and the like, is achieved through a trunk of smaller dimension extending upwardly from the top side of the tank through a suitable opening provided in the deck of the ship. All of the inlet and outlet pipes, pressure control means, vapor outlets and the like, extend from the trunk into the tank.

This type of construction and arrangement is capable of considerable improvement from the standpoint of cost of construction and operation, and from the standpoint of safety and stability. For one thing, many of the elements are exposed to temperature changes in use ranging from ambient temperature of about -100 F., when installed, or when the tanks are empty, to about -258 F. when the tanks are cooled down and contain liquid therein. Thus, when the outlet pipe extends downwardly through the trunk to the bottom of the tank and the pump is located on the trunk, a substantial proportion of the elements of the pump are subject to extreme temperature change whereby differences in expansion or contraction, or solidification of material, may cause seizure of the elements or cause elements of the pump to freeze, thereby to interfere with the operation of the pump and delivery of liquid from the storage tank. Such stoppages necessitate complete drainage of the liquid from the tank so that the tank can be heated up to free the elements or inerted to enable a person to enter the tank for replacement and repair.

If the main delivery pump becomes frozen or otherwise incapable of operation, means must be provided in the form of a blow-case pump located in the bottom of the tank for removal of liquid by the slow process of alternating pressure for liquid displacement with release of pressure for enabling liquid to ow into the blow-case.

ItV will be apparent also that, in the construction of a trunk of smaller dimension than the tank, only limited space is available in which to make the various connections and welds, thereby to increase the expense of construction andv interfere with the perfection of the welds.

I have devised a construction and arrangement whereby many of the aforementioned characteristics can be alleviated to the end that a more desirable tank can be constructed for more efiicient and economical storage and transportation of a liquefied natural gas, and it is an object of this invention to provide a construction and arrangement of a tank for accomplishing same.

More specifically, it is an object of this invention to t produce a new and improved construction and arrangement in a tank for the storage and transportation of a liquid which is to be maintained at extremely cold temperature; which embodies means for stabilizing the tank within an insulated space; which embodies means to eliminate the possibility of seizure or freezing of the delivery pump; which enables substantially complete drainage of the liquid from the tank; which enables the tank to be inerted and heated more eflciently and more rapidly for access thereto; which eliminates the necessity for auxiliary means to effect removal of liquid from the tank; which enables replacement or repair of the pump to be effected in a simple and eicient manner; which markedly reduces the number of pipes or other elements extending upwardly through the trunk thereby to minimize the number of welds to be made within the limited space; and which is effective markedly to reduce the number of pumps and, with it, the number of units with which problems of operation and repair can be raised and which embodies additional reinforcements to enable tanks of large capacity to be constructed for the more economical storage and transportation of a liquefied gas.

These and other objects and advantages of this invention will hereinafter appear and for purposes of illustration, but not of limitation, an embodiment, of the invention is shown in the accompanying drawing, in which- Figure l is a schematic sectional elevational view of a ship embodying the practice of this invention;

Figure 2 is an enlarged sectional elevational view schematically setting forth the construction and arrangement of a tank embodying the features of this invention; and

Figure 3 is a schematic elevational view of the arrange-- ment of a cluster of tanks.

In Figure 1, illustration is made of a ship constructed with an outer hull 12 and an inner hull 14 spaced inwardly a short distance from the outer hull but interconnected therewith to provide a rigid construction having an open space 16 therebetween which may be subdivided into wing tanks through which ballast water can be circulated for proper operation of the ship or through which heat exchange fluid can be introduced for maintaining proper control of temperature of the inner hull, or to protect transfer of cold to the outer hull.

The hold space Within the inner hull can be further subdivided into separate hold spaces by cofferdams 18 extending crosswise of the ship.

The inner surfaces of the walls of the inner hull and the cotferdams are lined with a relatively thick layer 20 of thermal insulating material to provide insulated hold spaces in which one or more tanks 22 can be located for Vthe storage and transportation of the liquefied gas 24. The liquid storage tank is constructed of aluminum, stainless steel or the like metal which is capable of retaining its strength and ductility when reduced to temperatures in the range of liquefied gas, and of a strength sufficient to retain the hydrostatic load under conditions of use. The inner and outer hull of the ship may be `constructed of conventional ships steel although certain advantages are to be derived when the inner hull 14 is constructed of a metal or material, the strength of which is not adversely affected by the cold of the liquid, thereby to enable the inner hull to function as a secondary container in the event of failure of any of the containers 22. The insulation is composed of a material of low heat `conductivity but it is preferred to construct the floor 26 of an insulation material having structural strength, such as balsa,

4 quippo or the like wood to support the tanks on the surfaces thereof, as will hereinafter be explained.

The tanks 22 may be of cylindrical or curvilinear shape in cross-section, but it is preferred to make use of tanks of prismatic shape, such as of square or rectangular shape, for fuller utilization of the insulated space available in the ship. It will be understood that the construction described can be adapted for use in other transportation means or even for land storage of the liquefied gas, although more of the problems arise in ship transportation and storage, as will hereinafter appear.

In Figure 2, illustration is made of the construction and arrangement of a tank 22 embodying the features of this invention and dimensioned to have a capacity to hold many thousands of barrels of liquid. The tank of round, square, rectangular, triangular or other prismatic shape, has a top wall 28, a bottom wall 30, and side walls 32 secured one to the other in sealing relation to provide a concealed space therebetween. Extending vertically through the central access of the tank is a column 34, preferably in the form of a tubular member of cylindrical or polygonal shape, dimensioned to have a height greater than the height of the liquid-holding portion of the tank to project a short distance below and above the top and bottom walls to provide a bottom extension 36 and a top extension 38. The column is dimensioned in cross-section to provide a space suicient to permit passage of men and equipment downwardly therethrough. The walls 40 defining the column are constructed of a metal similar to that of the tank walls 2S, 30 and 32, and the walls of the column are joined to the adjacent walls of the tank, as by welding or the like, to provide a sealing relationship therebetween and to isolate the interior of the column from the liquid in the tank.

The inner surface of the column is covered with a layer 42 of insulation material to minimize the rate of transmission of heat or cold, thereby to minimize heat loss into the liquid and to permit heating up of the column for enabling a person to operate therein. It will be apparent that considerably less insulation is required on the walls of the column by comparison with the insulation of the hold space since access to the interior of the column will be required on very few occasions and, on such occasions, warm air can be circulated through the column to provide a safe temperature without excessive heat loss into the tank. The pump 44 for the displacement of liquid from the tank is located within the column, preferably adjacent the bottom thereof, and the drive 46, in the form of an electrical motor or turbine drive or the like, can be located adjacent the pump for operation thereof. A pipe 48 connects the inlet of the pump with the outlet opening 50 at the bottom of the liquid storage space of the tank for transmission of liquid from the storage space to the pump. The pipe is provided with a `flexible coupling S2 to permit expansions and contractions due to temperature change and it is also adapted to be provided with a valve l5'4 capable of remote control for opening and closing. The outlet of the pump communicates with a pipe for discharge of liquid from the tank through a section of pipe 56 which extends upwardly from the pump through the column to beyond the liquid storage space. From there it may continue upwardly through the top of the column, but it is preferred to have the outlet pipe extend through the side wall of the column at a level to be protected by the insulation 58 covering the tank. Similarly, many of the elements previously extending downwardly through the trunk may now extend through the column for passage laterally through the column into the liquid storage space of the tank. The top of the column is provided with a manhole 60 for access to the interior thereof. The portions 38 and 36 of the column can function as means for stabilization of the tank within the insulated space.

vIt will be apparent that there are a number .of advantages in the construction and arrangement of the tank which embodies the features of this invention.

The portion 36 of the column which extends downwardly beyond the bottom wall 30 of the tank can function as a key adapted to be received in a keyway 62 provided in the insulating floor 26 on which the tank is supported. The key and keyway sections dene the stabilized position of the tank while permitting outer portions of the tank to shift in the direction toward and away from the keyway in response to expansions and contractions due to temperature change.

The portion 38 `of the column extending upwardly beyond the top wall of the tank is similarly capable of functioning as a key adapted to be received within the keyway 64 provided in the top wall of the insulation or other bracket, thereby to stabilize the position at the top of the tank. The portion of the extension 38 adapted to be received in operative engagement in the keyway 64 is dimensioned to have a length greater than the amount of contraction calculated to take place when the tank is reduced in temperature from about 100 F. to 258 F. so that the tank will be free to expand or contract vertically relative to the ships structure without disengagement of the key from the keyway, thereby to permit independent movement of the tank in all directions in response to expansion `and contraction without movement of the tank from a predetermined position.

The interior of the insulated column will normally be at a temperature considerably higher than that of ther liquid in the tank so that less trouble will be encountered in the loperation of the pump due to seizure or freezing responsive to temperature change. In the event that interference with operation does develop, the pump can be removed from the assembly without the necessity of tirst removing all of the liquid from the tank and thereafter inerting the tank after it has reached ambient tempera- Similarly, in the event of inoperation due to diiii-V substantially complete drainage of liquid from the tank This provides for complete removal of liquid to enable utilization of the tank for other purposes during the return voyage without loss of product and without waste of time for complete elimination of the liquefied gas. It also enables removal of the liquid from the tank to a level beyond that heretofore achieved even by the blow-case pump, thereby to eliminate the need for such auxiliary pumping means and the corresponding supporting equipment and piping.

Because of the location of the pump and parts Within the column, the wide tempenature gradient heretofore existing when parts were submerged in the liquid lwhile other parts were outside the liquid storage space is substantially completely avoided, thereby to minimize the possibilities of freezing or seizure due to temperature change or temperature gradient. Similarly, protection of the pump and parts from the extreme cold of the liquid in the storage space permits the use of less expensive pumping systems and less expensive or more economical drive systems with various locations available therefor.

Since most `of the connections with the liquid storage space of the tank can be led through the column to the top of the tank, the number of pipes (not shown) adapted to extend upwardly through the trunk of the tank and the number of welds can be materially reduced to simplify the construction of the tank and to enable a stronger and better tank to be fabricated at lesser cost. Such additional piping (not shown) may include the inlet pipes for filling the tanks, vapor pipes forventing the tanks and the like. Y

'I'he column 40 need not be provided in each and every one of the tanks. It will be suicient if only one or two of the tanks loc-ated within an insulated hold space is provided with a column construction of the type described.

Under such circumstances, the tanks may be interconnected one to another adjacent thereto by pipes or passages 70 provided with remote control valves 72 whereby ow of liquid into and out of one tank will operate to control liquid level in adjacent tanks, such that all tanks can be drained or lled from one or more columnar tanks of the type embodying the features of this invention. This construction is schematically illustrated in Figure 3.

By arrangement of the column in an internal portion of the cross-section of the tank, very little of the volumetric capacity of the tank is lost. To the contrary, it has been found that the centralized column operates materially to increase the strength of the tank such that tanks of still larger capacity can be constructed, thereby actually to reduce the cost and increase the utilization of available space for the storage and transportation of liquid.

The central column can be used as a support for stilieners, as represented by horizontally disposed beams or plates 74 secured at their outer edges to the column walls in vertically spaced-apart relation. Such stiieners serve to increase the strength and rigidity of the entire tank structure and they are capable also of functioning as swashbuckle plates, thereby to permit the design of tanks of much larger capacity.

In order to avoid destructive eiiects which might arise from impacts on the column and tank responsive to the rocking and rolling movements of the ship, it has `been found desirable to retard the rocking movements of the tank as by the use of snubbers or other means which will militate against impacts by the elements of the tank and rigid surfaces which might be employed for stabilizing the position of the tank. Such snubbing or retarding means are best located to engage the upper portion of the tank since movement of the lower portion is resisted suiiiciently effectively by the `frictional forces existing between the bottom of the tank and the top surface of the iloor or insulation upon which it rests. In theillustrated modification, such snubbing or retarding action can be imparted by the coil springs 80, a plurality of'whichare.

arranged in laterally spaced-apart relation Vin a cornpressed state with the outer end secured to a bracket 8'2 depending from an adjacent portion of the ship structure while the inner end bears against the outer wall of the column. retarding movement may be similarly disposed to engage the trunk instead of the column. Instead of coil springs of the vtype described, the rocking movement of the tank may be slowed as by means of a resilient member packed between the column and the rigid supporting structure, as illustrated by a foamed rubber or the like.

While description is made of the location of the column along the vertical central axis of the tank, it will be understood that the column can be oiset from the center but, when the column functions also as the key for the tank, such column position will constitute the stabilized position from which the outer portions of the tank can expand or contract.

It will be apparent from the foregoing that I have provided a new and improved tank structure and arrangement which is capable of more eiiicient construction and use in the storage and transportation of a liquid which has to be maintained at extremely low temperature and which can be adapted for arrangement in an insulated hold space of a ship or other transportation means or for land storage.

It will be understood that changes may be made in the details of construction, arrangement and operation with- In the use of a trunk, the resilient means for out `departing from the spirit of the invention, especially as defined in the following claims.

I claim:

1. A tank of large capacity `for the storage of a liquid at a temperature considerably below ambient temperature comprising within a rigid support a housing of large capacity, a column extending downwardly through a central portion of the housing from the top to the bottom and free of any rigid attachment to the support, the walls of the housing and column being formed of a structurally strong uid and vapor impervious material which retains strength and ductility at the temperature of the cold liquid and which are joined in sealing relationship to isolate the interior of the column from the remainder of the housing wherein thel liquid is stored, an insulation lining the inner surface of the column, uid displacement means located within the base of the column, a passage communicating the base of the housing with the uid displacement means for the removal of liquid from the housing, another passage communicating the fluid displacement means with a receiver for the liquid outside of the housing and means for actuating said uid displacement means for the transfer of liquid from the housing to the receiver, and an insulated loor for support of the housing, said column being dimensioned to extend beyond the `bottom wall of the housing and the oor is provided -with a recessed portion dimensioned to receive the portion of the column extending beyond the bottom Awall of the housing to tix the position of the housing on the iloor.

2. A tank as claimed in claim 1 which includes means for enabling heat to be introduced into the column to raise the temperature therein to safe temperature for habitation.

3. A tank as claimed in claim l which includes means to enable removal of the displacement means from the base of the column.

4. A tank as claimed in claim l in which additional housings are present for the storage of liquid and which includes means communicating the bottom portions of the other housings with the bottom portion of the housing having the column therethrough.

5. A tank as claimed in claim 1 in which the column extends through the vertical central portion of the housing.

6. A tank of large capacity for the storage of a liquid at a temperature considerably below ambient temperature Within a rigid support comprising a housing of large capacity, a column extending downwardly through aY central portion of the housing from the top to the bottom and dimensioned to have a height greater than the height of the housing to have portions extending beyond Athe top and bottom walls of the housing, the Walls of the housing and the column being formed of a structurally strong, uid and vapor impervious material which retains strength and ductility at the temperature of the cold liquid and which are joined in sealing relationship to isolate the interior of the column from the remainder of the housing wherein the liquid is stored, an insulation lining the inner surface of the column, fluid displacement means located within the base of the column, a passage communicating the base ofthe housing with the fluid displacementmeans for removal of liquid from the housing, another passage communicating the uid displacement means with a receiver for the liquid outside of the housing, means for actuating said uid displacement means for the transfer of Aliquid from the housing to the receiver, and a support upon which the bottom wall of the housing rests having a recessed portion dimensioned to receive the portion of the column extending beyond the bottom wall of the housing to key the housing to the support to stabilize the position thereof on the support.

7. A tank as claimed in claim 6 which includes means operatively engaging the portion of the column extending upwardly beyond the top wall of the housing to hold the column against relative crosswise movement while permitting relativevertical movement responsive to expansion and contraction due to temperature change.

8. A tank of large capacity for the storage of a liquid at a temperature considerably below ambient temperature within a `rigid `support comprising a housing of large capacity, a column extending downwardly through a central portion of the housing from the top to the bottom and free of any rigid attachment to the support, the column being dimensioned Vto have a length greater than the length of the housing to provide a portion which extends upwardly from 'the top wall of the housing, the walls of thehousing Vand column being formed of a structurally strong fluid and vapor impervious material which retains strength and ductility at the temperature of the cold liquid and which are joined'in sealing relationship to isolate the interior of the column from the remainder ofthe housing wherein the liquid is stored, an insulation lining the inner surface of thecolummuid displacement means located within the base Aof the column, a passage communicating the base of the housing with the uid displacement means Vfor the removal of liquid from the housing, another passage vcommunicating the uid displacement means with a receiver for the liquid outside of the housing, means for actuating said Vluid displacement means for the transfer of liquid from the housing to the receiver, and means operatively engaging the lateral walls of the upwardly extending portion resiliently to urge the Vcolumn towards 'a centralized position.

9. A tank as claimed in claim8 which includes means in the portion of the column extending upwardly beyond the top wall of the housing for gaining access to the interior thereof.

References Cited in the le of this patent UNITED STATES PATENTS 1,947,515 Blackburn Feb. 20, 1934 2,600,015 McLaughlin June 10, 1952 FOREIGN PATENTS 121,513 Great Britain Dec. 17, 1918 1,034,499 Germany May 9, 1956