US2972873A - System for loading and unloading liquefied gases from tankers - Google Patents

Description

J. R. PEET ETAL Feb. 28, 1961 Filed Jan; 2, 1959 2 Sheets-Sheet 1 Inventors omzommfim H A? H A I o? 3 0 3 5 w 217 S 2% 2% 8w 0 a J .H. .N. A .M. M w 5 m. m 8* 8w 8m flwl mw n 00 .N. a My a aom fi N? N WWW LEW w 3 .N. we .Nbdm w 3v 2w 8m 2m 3? 5 g 5 g g Q Q mm B a a? 2v 3m em A v ST and 3? Q 8 (0C r O \J 2 mm 8w n8 AV E a John R. Peef, George Cloypole, Arnold Fink and Christopher E. Loeser ,Feb. 28, 1961 .1. R. PEET ETAL 2,972,873

SYSTEM FOR LOADING AND UNLOADING LIQUEFIED GASES FROM TANKERS Filed Jan. 2, 1959 Arnold Fink and Christopher E. Loeser Inventors 3,? Attorney SYSTEM FOR LOADING AND UNLOADING LIQUEFED GASES FROM TANKERS John R. Peet, Westfield, George Claypole, Sparta, Arnold Fink, Rahway, and Christopher E. Loeser, Scotch Plains, N.J., assignors to Esso Research and Engineering Company, a corporation of Delaware Filed Jan. 2, 1959, Ser. No. 784,714

3 Claims. (Cl. 62-51) This invention relates to a system for loading and discharging liquefied gases from tanks and the removal of residual vapors. More specifically, the invention relates to the unloading of liquefied petroleum gases stored in a plurality of container bottles carried on a tanker vessel.

Previous methods for loading and discharging liquefied petroleum gases into or from container bottles or tanks employ a complete circuit arrangement which includes a liquid line, a return vapor equalization line, pumps and compressors. In previous methods of loading, the loading pipe extends from the top to the bottom of the tank and liquid is pumped through this line. Displaced vapor is drawn off the top of the tank by a compressor and the vapor is blown back through the vapor equalization line to the shore storage containers. An alternative procedure is the use of the compressor alone to create the differential pressure for loading.

The previous methods of discharging or unloading liquefied petroleum gases are the reverse of the loading procedure just described. For example, a pump draws liquid from the container bottles or tanks on board a ship, while discharged liquid is replaced by vapors recirculated from the receiving tanks through the vapor equalization lines. On completion of liquid discharge, the compressor operation is reversed and vapor is evacuated from the tanks. The vapor is forced back to the shore containers or tanks.

There are many disadvatnages of the previous methods. In the first place, the vapor equalization lines can be very expensive when the distance to the shore facilities from the tanker is great, as is usually the case. Also, the high cost of compressor capacity limits the liquid discharge to low rates. Another time consuming disadvantage is that vapor removal cannot be commenced until the liquid discharge is completed, and this adds several hours to turnaround time.

According to the present invention, liquefied gases are discharged from tanks at much higher rates than with previous methods. In the first place, no return vapor equalization line between the tanks and the shore storage vessels normally is required or used. With the present invention a group of tanks may be emptied of liquefied gas and then, while a second group of tanks is being emptied, residual vapor in the first group of emptied tanks can be removed or evacuated simultaneously. With the present invention, higher discharge rates of liquefied gases are obtained at a lower cost than with previous methods or systems. All of the equipment of the present invention is self-contained on the tanker, thus allowing complete flexibility of operation.

The piping between the several tanks is so arranged that the tanks in the tanker are connected in groups, and any group can be charged or discharged in any sequence. The liquefied gas in one or more tanks is heated, and the heated vapor is used to overpressure a Patented Feb. as, real selected group of tanks to force liquefied gas from this group to an inboard pump, and then to a cavern or receiving tank or tanks on shore or in any other location. This eliminates the need for a compressor to'do this job. Upon completion of liquefied gas discharge from one group, another group of tanks is selected for liquefied gas discharge, and vapor removal can commence from the emptied group of tanks concurrently with liquefied gas discharge from the next selected group of tanks. This reduces the unloading and turnaround time. Residual vapors are withdrawn from the discharged tanks, compressed, condensed, and the condensate pumped directly into the main discharge line.

As indicated above, it is an object of this invention to provide a substantially self-contained system for loading and unloading liquefied, gaseous materials into and from a series of storage containers therefor. A further object is to provide a method and means for handling liquefied, gaseous material with a minimum requirement for conventional accessory equipment and facilities, including vapor equalization lines, compressors and the like. It is also an object of the present invention to provide a method and means for discharging the liquefied content of one group of a series of storage containers, while simultaneously discharging the residual vapor content of another group of containers in the same series, and by way of a single discharge connection to the system. A particular object of the present invention is to provide a simplified method and means for loading and unloading tanker vessels employed for the transportation of liquefied gaseous materials such as liquefied petroleum gases (L.P.G.), including propane and butane, and mixtures thereof with other gaseous materials.

The present invention and its object may be more fully understood from the following description, when it is read in conjunction with and with reference to the accompanying drawings, in which:

Fig. 1 illustrates schematically a representative storage system, according to the present invention, adapted for the storage and handling of liqufied butane on a tanker vessel;

Fig. 2 is a vertical section taken through a container bottle such as is schematically represented in Fig. l; and

Fig. 3 provides an enlarged, schematic showing of the vapor and liquid pump, compressor and condenser system illustrated by Fig. 1, including its connection in the conduit system shown by Fig. 1, and additionally including a showing of operating control means.

In Fig. 1, the numeral 1 designates the hull of a tanker vessel having a deck surface 1a. For reference, the vessel is oriented by the terms: Stern, Bow, Starboard, and Port, suitably applied to the drawing.

As shown, the storage system comprises a plurality or series of individual storage vessels, represented in the drawing by small circles. The vessels here contemplated are of a generally conventional form known as bottles. They may be disposed either vertically or horizontally, depending upon the design and structure of the tanker, and rigidly secured therein. Also, contemplating conventional practice in ship construction, the hull will be divided into a series of compartments by means of transverse and longitudinal bulkheads. In Fig. 1, the location of transverse bulkheads is indicated by arrows applied at right angles to the starboard and port hull lines. Between these arrows, also for reference, the transverse compartments are designated consecutively toward the bow, by the Roman numerals I, II, III, and IV.

The compartmented spaces between bulkheads are intended to accommodate separate groups of storage containers or bottles. In this description, the several groups illustrated will be referred to by the numbers of the compartments in which located. The number of bottles in each group will be determined by the size thereof, and the compartment space available. To simplify illustration, each group, except Group I, has been limited to a total of six containers, of which four are disposed in pairs on either side of the center or keel line, and two are oppositely disposed adjacent the respective starboard and port sides of the hull. The center containers substantially correspond to and may be disposed in the conventional main tanks of a tanker, while the side containers correspond to and may be disposed in the wing tanks. The containers of Group I are of the former category, the wing containers or bottles having been omitted to provide space for operating equipment, including pumps, compressors, condensers, etc.

In applying reference numbers to the respective container bottles in each group, the first numeral in each number indicates the group location, while the second numeral, if odd, indicates a port location or, if even, a starboard location. Thus, the two bottles located in the first compartment are numbered 11 and 12, while the six bottles in the second compartment are numbered 21, 23, and 25 on the port side, and 22, 24, and 26 on the starboard side.

Each of the container bottles is provided with vapor and liquid conduit connections. In Fig. 1, these connections are designated by bottle number plus the letter a for vapor or the letter b for liquid. Thus, the numerals 21a and 21b designate the respective vapor and liquid conduit connections to a center line bottle 21 which is on the port side in compartment II. Each bottle is additionally provided with pressure relief valves adapted to relieve pressures in excess of a safe operating pressure for the system. These valves are preferably adapted to be connected by manifolds for safe discharge of released vapors. The relief valves and the related manifolds have been omitted from the showing of Fig. 1, however, as their nature and location are of common knowledge, and are not essential to the present disclosures.

Starboard and port liquid manifolds for discharge and loading of liquefied gas from and into the respective bottles are designated in Fig. 1' by the numerals 2 and 3, respectively. These manifolds are continuous to the extent of the cargo compartments of the vessel. At their after ends, they communicate, through valves 2a and 3a respectively, with corresponding starboard and port pumps 50 and 51 respectively, at respective pump suction inlets 52 and 53 thereof. Discharge outlets 54and 55 of the respective pumps are connected through a common header 56 and branch connections 57 and 58 to each of two shore connection conduits 59 and 60, through valves 57a and 58a. By means of valves 56a, 56b, and 560, the pumps 50 and 51 may be separately connected to either or both shore connections 59 and 60. As shown, the shore connection conduits 59 and 60 are disposed transversely of the ship, and are provided with valves 59a, 59b, 60a, and 60b, whereby to permit loading or unloading at either or both port and starboard sides.

In addition to the liquid manifolds 2 and 3, vapor manifolds 4 and are also provided. These vapor manifolds extend longitudinally of the hull 1 communicating at their after ends, through valves 4a and 5a respectively, with a common transverse header conduit 61. The conduit 61 is adapted for connection at opposite ends to the suction inlets of compressors 62 and 63, respectively. Valves 61a, 61b, and 610 in the header 61 permit alternate or simultaneous connection of the compressors to either or both the manifolds 4 and 5.

As shown in Fig. l, the discharge outlets of the respective compressors 62 and 63 are connected, through inlet conduits 64 and 65, to the inlets of condensers 72 and 71. In addition, valved bypass conduits 66 and 67 connect the header 61 to the respective condenser inlet conduits 64 and 65. The respective condensers 71 and 72 also have outlet conduit connections 73 and 74 to the suction inlets 52 and 53 of the respective pumps 50 and 4 51. Recycle conduit connections 76 and 77 between the pump discharge conduits and the respective condenser inlets 64 and 65 avoid undesired evacuation of the condensers.

The manifolds 4 and 5 are additionally cross-connected by a series of conduits 101, 201, 301, and 401, respectively, including valves 101a and b, 201a and [9, 301a and b, and 401a and b. Each of these cross-connecting conduits is provided with a corresponding manifold branch 102, 202, 302 and 402, respectively. Each manifold branch is associated with and connected to the vapor lines of a single group of container bottles. Thus, the conduits 102, 202, 302, and 402 are connected to the vapor lines for Groups I, II, III, and IV, respectively.

In addition to the connection of the short conduits 59 and 60 to branch conduits 57 and 58 respectively, the conduit 59 is also provided for connection with the manifolds 3 and 4, by way of conduit connections 81 and 83, while the conduit 60 is provided for connection with manifolds 5 and 2 by way of conduit connections 82 and 84. Corresponding valves 81a, 82a, 83a, and 84a in the respective connections, control use thereof during loading and unloading liquefied gases into and from the several groups of container bottles. Also as shown in Fig. 1, the container bottles 11 and 12 are provided with valved inlet and outlet connections and 92, and 91 and 93, respectively. These connections communicate with internal coils (not shown in Fig. 1) which permit heating of these containers.

As previously indicated, all the container bottles or vessels in a given series will have substantially identical structural and operating characteristics. An exception to the rule will be the inclusion of a heating element, preferably the internal coils referred to above, disposed in a selected number of bottles. Fig. 2 provides a more detailed view of atypical container bottle, including a heating element. The container bottle as shown is representative of the bottles designated in Fig. l by the numerals 11 or 12. Ornitting the heating element, the bottle shown is representative of any of the others in the series.

As shown in Fig. 2, the bottle 12 is a typical pressureresistant container for liquefied gaseous materials having a sidewall 112, and domed upper and lower end walls 114 and 116. The upper end wall 114 provides a necked portion 118 opening through a flanged end 120 adapted to receive a cover 122 in fluid-tight, pressure-retaining relation. The cover 122 provides a means for mounting conduit connections such as the liquid and vapor conduits 12a and 12b. The cover 122, as shown, also provides a mount for a pressure-relief valve such as designated by the numeral 124. In shipboard service especially, the valve 124 normally would communicate with a vent line common to one or more of the other bottles in a given group or series.

In a typical installation of the character'represented, the necked portion of each container bottle would extend from the below deck compartmented space through the deckplates in sealed, fluid-tight relation thereto. Also, provision normally would be made to load higher boiling liquid materials, such a fuel oil, kerosene and the like in the compartment space surrounding each container bottle.

As noted above, the container bottle 12, while representative of a typical bottle, has been modified by the inclusion of a heating element 126. As shown, this element is a steam heating coil connected at opposite ends to the inlet and outlet conduits 90 and 92 extended through the container bottle wall.

In operation of a system such as illustrated by Fig. 1, loading of the series of container vessels may proceed simultaneously or by groups. Also, loading may be accomplished by introduction of the liquefied gaseous material through either or both the vapor lines and liquid lines, as for example the conduits 4 and 5, and the conduits 2 and 3. Loading through the vapor lines 4 and 5, at least for the purpose of this description, may be termed a top loading technique, while loading through the liquid lines 2 and 3 may be termed a bottom loading technique. In either technique, the conduits 59 and 60 are connected to a supply source as through the valves 59a and 60a, or and 60b. Where desirable, a combination of top and bottom loading techniques may be employed.

If toploading is to be performed, valves 57a, 58a, 81a, 84a, 2a and 3a would be closed, as would valves 61a and 610, and/or 4a and 5a. In addition, the individual valves in each liquid conduit, such as the lines 21b, 22b, etc., connecting the individual container bottles to the conduits 2 and 3 also would be closed. At the same time, valves 82a and $30, 101:: and 101b, 201a and 201b, 301a and 301b, 401a and 4011), as well as the individual valves in each vapor conduit, such as the lines 21a, 22a, etc., connecting individual container bottles to the conduits 4 and 5 through the several manifolds 102, 202, 302 and 402, would be opened. In this fashion, liquid flow paths are established thorugh the conduits 59, 82, 4, 101, 201, 301, 401, 102, 202, 302, 402 and the several vapor conduits connecting the individual container bottles with the manifolds 102, 202, 302, and 402. At the same time, a second flow path is established through the conduits 60, 83, and 5, whereby delivery through the conduit 4 is duplicated by delivery through the conduit 5, or whereby delivery to certain groups of container vessels may be made through one of said conduits 4 and 5 while the other provides delivery to another group. For example, by closing valves 101a, 201a, 301b, and 40112, delivery to the container vessels aft of the conduits 59 and 60 would be made by way of conduits 60, $3, and 5, while delivery to the container vessels forward of conduits 59 and 60 would be made by Way of conduits 59, 8-2, and 4.

The employment of a top loading techniquesubstantially eliminates the need for balance lines in order to prevent pressure build up in the containers during the loading operation. When loading from the bottom, as the level of liquid in a container rises, vapors of the material are compressed, and the temperature of the vapors is increased. In turn, the temperature of the liquid surface increases to produce further vaporization of the liquefied gas. In the conventional system, the pressure produced must be relieved either by venting to the atmosphere or by returning the vapors to the source. In the one instance, valuable product is lost; in the other, high investment and operating costs are entailed. By top loading, the liquefied gas introduced dissolves some of the vapors in the vapor space, and also cools the surface of the liquid supplied to the container vessel so as to reduce vaporization therefrom, whereby to maintain pressure in the containers below that at which venting would be required.

Where, for any reason, the bottom loading technique is desired, the procedure will rquire action to avoid development of excess pressures in the container. This may be accomplished in one of two ways. In the one instance, pressure may be vented to the suction of the shipboard compressor equipment described above, or in the other instance the vented vapors may be returned to the supply source from which loading is accomplished by way of conventional balance line conduit connections.

In the first instance, both loading conduits 59 and 60 may be employed for connection to shoreside conduits delivering liquefied gas from a supply source. Valves 82a and 83a are closed, as are valves 2a and 3a, and valves 57a and 58a. The valves in the individual conduit connections between the conduits 2 and 3 are opened, including lines 11b, 12b, 21b, 22b, etc., as are the respective valves 81a and 84a in the conduits 81 and 84, respec tively. Initially, all remaining valves will be closed also.

With flow started under pressure of shoreside pumps,

liquefied gas will flow through the conduits 59-and 60 and thence through the respective conduits? and 2 by way of conduit connections 81 and 84, respectively. From conduits 2 and 3 the liquefied'material will pass through the individual conduits 11b, 12b, 21b, 22b, e'tc., into the container bottles 11, 12, 22, etc. As loading proceeds, pressure will develop in each of the container bottles. At a pressure of about pounds per square inch absolute (for butane) the valves in the individual vapor conduits connections to the several manifolds 101, 202, 302, and 402 are opened. Also, dependent upon the loading rate, ambient temperature, and rate of pressure increase in the individual bottles, either or both recompression systems, including the compressors 61 and 62, are

connected to the manifolds, through vapor conduits 4 and 5, by opening the suitable valves in conduits 101, 201, 301, and 401;:as well as valves 61a and/or 61b, and 4a and/or 5a. The conduits 4 and/or 5 are thus placed in communication with either or both of the compressors 62 and 63. If one compressor is to handle the vented gas from the system, either valve 61a or 61b may be closed, while valve 610 is opened. Other alternatives for distributing flow to the compressors 61 and 62, by selective control of valves in the several vapor conduits and manifold connections should be evident from the system as illustrated. Preferably, operation of the compressors 62 and 63 is controlled automatically, as by pressure controllers in the line 61 or 4, whereby compressor operation is initiated at such times as the pressure in these lines is not substantially less than the vapor pressure of the liquefied gas at the operating temperatures. In any event, the compressors are operated so as to avoid pressures in the container bottles in excess of the set safety valve relief pressure.

From the compressors 62 and/ or 63, the compressed gas is passed through the related condensers 71 and/or 72, and thence, as a liquid, to the proper pump 51 and/or 52. From the pumps, the liquefied gas is returned to one or both the conduits 59 and 60, by way of the con duits 57 and 58, valves 56a and/or 561), and 57a and/0r 58a being opened. Of course, the pressure applied to the liquefied gas at pumps 51 and/or 52 must be suflicient to maintain a pressure in the lines 57 and/or 58 adequate to discharge the liquefied gas into lines 59' and 60 without any substantial revaporization.

In a combined top loading and bottom loading operation, the valves 57a, 58a, 2a and 3a would remain closed. All other valves including those in the distribution lines 81, 82, 83 and 84, connected to the conduits 59 and 60 would be opened. Flow through the liquid and vapor conduit connections would be adjusted by manipulation of the various valves so as substantially to maintain a balanced system Without need for employment of either balance line connections to the shore-side supply source, or exhaust to a recompression and condensation system. If desired, however, by additional piping connections (not shown) to the vent lines communicating with the pressure relief valves, such as the valve 124 of Fig. 2, provision might be made for employment of the compressors as required.

In such a combination procedure, the liquefied gas delivered to the respective container bottles by way of the vapor lines 11a, 12a, 22a, etc., at least partially overcomes effects produced through compression of vapors in the vapor space of the several container bottles as a result of rising liquid levels therein.

Unloading of the series of container bottles, in a shipboard system such as illustrated by Figs. 1 and 2, is accomplished in such manner as to maintain the trim and stability of the carrier vessel. Best results are obtained by simultaneously discharging the contents of transverse groups of bottles disposed in a common thwartship area of the vessel.

For the purpose of illustration, it will be assumedthat a ship, constructed substantially as described above, is

7 berthed starboard side to, and that the cargo to be unloaded consists of gas oil in the tank compartments housing the several groups of container bottles, and a liquefied petroleum gas, such as liquefied n-butane, in the series of gas container bottles. Also for the purpose of illustration, certain other assumptions will be made, namely, that summer temperature conditions exist at the unloading berth, wherein the surrounding sea water is at a temperature of about 80 F., and the gas oil cargo envelope has an attained temperature of about 150 F. Under such conditions, it may also be assumed that the liquefied gas in the container bottles will be at a temperature substantially equal to that of the gas oil envelope. At a temperature of 150 F., it may be assumed further, that the gas cargo will be contained in liquid form at substantially its equilibrium vapor pressure of about 120 pounds per square inch absolute.

At any given temperature existing in the contents of the container bottles, in order to retain the contents substantially in liquid form, a pressure must be maintained thereon which is substantially equal to the equilibrium vapor pressure of the contents at the given temperature. In the container bottles such a pressure is established by a suitable setting of the safety valve release pressure, consonant with the maximum temperatures anticipated for storage, and the structural characteristics of the containers.

To avoid flashing of the liquefied material at such temperatures during discharge and transmission to the inlets 52 and 53 of the pumps 50 and 51, however, the liquefied materials must be delivered to the inlets at a pressure slightly above the equilibrium pressure at the temperature in the container bottles. This may be accomplished by increasing the container pressure by an amount at least equal to the total static pressure values of:

(a) A column of the liquefied material equal to the height of the pump inlets above the inlets of the liquid In a typical system as represented by the drawings, an

overpressure of about 27 p.s.i.a. may be assumed as sub-,

stantially equal to the static pressure values to be overcome.

In the system as represented by the drawings, unloading is accomplished by connection of the lines 59 and 60 in fluid-tight relation to suitable shore-side receivingtransmission lines. The latter may include auxiliary pump equipment, adapted to maintain any desired pressure on the liquefied materials discharged. With the conduits 59 and 60 thus connected, the valves 59a and 60a are opened. Assuming all other valves to be closed, at this time, or immediately before, the valves in the lines 90 and 92, and 91 and 93, are also opened, admitting a heat exchange fiuid such as hot water or steam to the heat exchange coils in the container bottles 12 and 11, respectively. Under the operating condition assumed, saturated steam at about 150 pounds per square inch gauge pressure is employed at a rate of about 11,000 pounds per hour. As shown in Fig. 2, control valves in the lines and 92, respectively, are provided. The valves in these lines are actuated in response to pressures within the bottles 11 and 12, whereby to establish and maintain a predetermined pressure therein during the unloading operation, by regulating flow of the heat exchange fluid through the heating coils such as the coil 126 in the bottle 12. The predetermined pressure thus maintained, substantially will exceed the existing equilibrium vapor pressure of the liquefied material in the remaining container bottles by an amount substantially equal to the total static pressure values mentioned above. In the system now contemplated, the pressure in bottles :11 and 12 would be maintained at about 150 p.s.i.a.

At this pressure then, the valves in the vapor lines 11a and 12a from the respective container bottles 11 and 12 are opened, as are the valves in the vapor lines connected with a first group of the other container bottles in the series. For example, if the Group II container bottles were to be discharged, valves 101a and b, 201a and b, and the valves in lines 21a, 22a, 23a, 24a, 25a and 26a all would be opened. With communication thus established between the bottles 11 and 12 and the bottles 21, 22, 23, 24, 25 and 26, through the lines 102, 101, 201, and 202, pressure in the bottles 21 to 26 inclusive would be increased to that in the bottles 11 and 12.

At this point, the valves in liquid lines 21b, 22b, 23b, 24b, 25b and 26b would be opened, placing the respective container bottles 21 to 26 inclusive in communication with the main liquid lines 2 and 3. At the same time, the valves 2a and 3a would be opened and the pumps 50 and 51 put in service. Valves 62c, 63c, 64a, 65a, 66a, 67a, 74a, 75a, 76a and 77:: would remain closed. Valves 56a, 56b, and valves 58a and 57a would be opened. The discharge of the liquefied material from the container bottles 21 to 26 inclusive would now proceed at a rate determined by the supply rate of pressurized gas from the containers 11 and 12. This, in the system contemplated, with steam supplied to the heating coils at the rate of 11,000 pounds per hour, would be about 51,000 cubic feet per hour. At such steam supply rate, liquefied material would be supplied to the pumps at a rate sufiicient to permit a pump discharge rate of about 10,000 barrels per hour.

Liquefied material is discharged from the container bottles being unloaded until the level of liquefied material is lowered to approximately the inlet of the liquid discharge pipe. Preferably this level is such that vaporization of the remaining liquefied material at ambient temperatures will, at all times, maintain a positive pressure in the container bottles, which is above atmospheric pressure. For an n-butane cargo, retention of about 0.6% of the original contents of liquefied material will ordinarily suffice to maintain such pressure at the ambient temperatures likely to be encountered under the most severe atmospheric and sea water temperature conditions.

Having reduced the contents of each of the container bottles in the Group II to the predetermined level, the valves in the respective vapor and liquid lines connecting each bottle into the vapor and liquid mains are closed and the bottles in another group are connected into these mains. At this time, the container bottles of the initially evacuated Group II contain a relatively small amount or liquefied material held under a gas phase pressure and temperature approximately equal to the temperature and pressure of the vapors in either or both the container bottles 11 and 12.

In connecting the second group of container bottles into the mains for discharging their liquid contents, the original connections employed for discharging liquid from the Group II bottles, are altered somewhat in order to provide for simultaneous recovery of vapors from the Group II container bottles, while discharging liquid from another group. For example, if liquid in the container bottles of Group IV is to be discharged simultaneously with vapors remaining in the bottles of Group II, either of the vapor mains 4 and 5 will be employed as a vapor recovery main, to evacuate vapor from the container bottles in Group II, While the other is employed as a pressure main in order to overpressure the container bottles in Group IV.

If, for example, the vapor main 4 is used to recover vapor from the Group II bottles, and the vapor main 5 is used to overpressure the Group IV bottles, valves 101a and 20112 will be closed. Valve 201a will remain open. Valve 4011) will be opened, while valve 401a will remain closed. Valve 5a will remain closed, while valve 4a will be opened.

Either or both of the compressor-condenser systems may be employed for the purpose of delivering re -liquefied gas to the liquid mains 2 and 3. For simplicity, however, the operation will be described with reference to the employment of the starboard system alone. this description, use of the port system is restricted to that of the pump 51 for the purpose of handling the liquefied material delivered from the container bottles 41, 43, and 45 by way of the liquid line 3. In such an operation, the valves 2a, 3a, 56a, 56b, 57a, and 53a are opened, while valves 560, 81a, and 84a are closed. Valves 82a and 83a remain closed also.

With such a connection system, then, the valves 41a, 42a, 43a, 44a, 45a, and 46a in the lines connecting the Group IV container bottles 41 to 46, inclusive, to the manifold 401 are opened. This places these bottles in communication with the bottles 11 and/or 12 through the main vapor line 5, valve 101b being open. At about the same time the valves 41b, 42b, 43b, 44b, 45b, and 46b in the liquid lines connecting the Group IV container bottles 41 to 46, inclusive, with the main liquid lines 2 and 3 are also opened, as are the valves 21a, 22a, 23a, 24a, 25a, and 26a in the vapor lines connecting the Group II container bottles with the manifold or branch line 202. Flow of liquid from the overpressured container bottles in Group IV then proceeds substantially in the manner previously described with reference to the discharge of liquid from those in Group II.

At the same time, the overpressured bottles in Group II will discharge vapors, under the existing pressure in these bottles, into the manifold 202 and thence, through the line 201 and Valves 201a and 4a, into the conduit 61. If, as assumed in this example, the gas discharged from the container bottles in Group II is to be handled solely by the starboard compressor-condenser system, the valve 61a will be open, while valves 61b and 61c Will remain closed.

Initially, the gaseous contents of the container bottles, 21 to 26 of Group II, will be at substantially the pressure and temperature induced therein during the preceding liquid discharge operation. According to the conditions assumed above, the pressure would be about 147 p.s.i.a, and the temperature about 170 F. At this pressure, the gaseous butane may be liquefied at a temperature of about 165 F. Thus, with condenser water supplied through the coil 72a at about 80 F. the butane gas may be condensed at the container pressure .until that pressure is reduced to about 60 p.s.i.a. Above 60 p.s.i. a. pressure, the valves 62c and 64a will be kept closed, and the valve 66a open. Butane gas from the containers will thus by-pass the compressor 62 through the conduit 66, to enter the condenser 72 by Way of the conduit 64. Condensate is discharged from the condenser 72 into the conduit 2, which also carries liquefied butane from the container bottles 41 to 46 inclusive.

In addition to the gaseous butane passed into the line 64 by way of the conduit 66, controlled amounts of liquid butane may also be passed into the line 64 from the conduit 56 by way of the conduit '76 and the control valve 76a therein. By so doing, a certain solution or condensation eifect is attained upstream fromthe condenser itself. Also, a controlled liquid level may be maintained in the condenser, whereby to avoid passing uncondensed vapors directly into the conduit 2.

When as a result of continued evacuation, the pressure on the vapors from the container bottles 21 to 26, inclusive, drops to a level below that required to permit condensation at the condenser Water temperature, and to discharge condensate from the condenser 72 into the conduit 2, the valve 66a is closed, valves 62a and Ma opened, and the compressor 62 activated. The compressor thus takes suction from the conduit 61 and the container bottles 21 to 26, inclusive, in order to continue evacuation thereof. By meansof the compressor, pressure on the gaseous butane is established at that level 10 required :for condensation at the condenser water temperature, and for condensate discharge.

Evacuation of the container bottles is continued in this fashion until the residue of vapor and/ or liquid in each of the bottles is contained at a pressure of about 30 p.s.i.a. and a. temperature of about F. Under this temperature and pressure, there will remain in the container bottles a quantity of vapor and liquid such as to maintain therein a positive pressure about atmospheric, but below the designed safe pressure for the bottles, at all temperatures between about 35 and F. Such temperatures will be within the maximum and minimum ambient temperatures which may be anticipated in the operational environment of the transport vessel.

Evacuation of the several groups of bottles comprising the facilities of a given ship or vessel is then continued in a similar fashion until all the bottles, including those employed in the fashion of bottles 11 and 1-2, retain only such remainder of vapor and/or liquid as may be required to maintain the desired positive pressure therein. Normally, this remainder will be between about 0.5 and 0.7 percent of the original cargo.

A preferred embodiment of the compressor-condenser system contemplated according to the present system is shown in Fig. 3. In this figure, like parts are designated by the same numeral as in Figs. 1 and 2. As shown in Fig. 3, the compressor pump 62 is driven by means such as a steam turbine 68, having inlet and outlet steam lines 68a and 68b, respectively. A valve 70 in the inlet line 68a is a motorized control valve, ac uated automatically by a pressure control means 7th: in the line 4, through means such as the electrical connection 7%. If desired, however, electrical actuating means may be replaced by a pressurized air system including an air driven valve motor, all as commonly known.

Also in the preferred system as shown in Fig. 3, a condensate drum 30 is introduced into the system, illustrated by Fig. 1, downstream from the condenser 72, being connected to the condenser by way of an inlet conduit 72b. The conduit 74 of Fig. 1, then, is connected to the inlet 80a of a pump 86; The pump discharge, in turn, communicates with the main cargo conduit 58 by means of the conduit 88.

Motorized valve 88a in the discharge conduit 88 is provided for actuation through electrical connection 2a by means of a liquid level control means 92 activated by the liquid level in the drum 80. The control means 92, as shown, also is provided for connection to the motor drive (not shown) for the pump 86. This connection is designated by the numeral 92b. As previously noted, the electrical control system as shown may be replaced by a pressurized fiuid system if desired.

The amplified compressor-condenser system illustrated by Fig. 3 includes a representative showing of the manner in which this system may be substantially completely automated by the use of the pressure responsive and liquid level control means. As shown in Fig. 3, a control means 70a is provided to sense pressures existing in the conduit 4. This control means as shown is designed to actuate electrically a motorized valve 70 whereby to control the steam supplied through the steam line 68a to the steam turbine 68, which drives the compressor 62. The pressure control 70a is adapted to actuate the motorized valve 70 so as to drive the turbine 68 at whatever speed may be required to produce a compressor discharge pressure suitable to obtain condensation of vapors at that pressure and at the temperature of the cooling water passed through the condenser 72. Thus, as the difierence between the pressure of vapors in conduit 4 and the required condensation pressure changes, the control means 70a will function to adjust the steam supply to turbine 68 as required to maintain a substantially constant compressor discharge pressure at any preselected level; V

This control function is performed by the means 70a only within a preselected range of pressures existing in the conduit 4. For instance, in the operating example provided above, wherein the vapors to be evacuated are initially at a pressure of about 147 p.s.i.a., and a temperature of about 170 F., and where the condenser water temperature is at about 80 F., the control would be set to energize the turbine 68 by initially opening the valve 7i) at a pressure in the conduit 61 of about 60 p.s.i.a. Then as the vapors are evacuated from the container bottles, and the pressure in conduit 4 is reduced, the control 70a would actuate the valve 70, gradually to increase the speed of the turbine 68, and thereby to maintain a substantially constant pressure on the discharge of the compressor 62. With the condenser water temperature at about 80 E, this discharge pressure would be not less than about 60 p.s.i.a. Finally, when the pressure in the conduit 4 falls to a level selected for the purpose of retaining a residue of the cargo material in the container bottles, the control 70a functions to close the valve 70 and shut down the turbine and compressor. In the example contemplated, the shutdown pressure would be about 30 p.s.i.a.

If desired, the valves 4a, 61a, 620, 64a, and 66a may also be of the motorized variety, and also actuated by the control means 78a, or additional similar means. In the drawing, such connection of the aforesaid valves to the control 760 is illustrated. In such instance the valves 62c and 640 will be arranged to be closed at pressures above the selected upper limit for actuation of the valve 70, and to be opened synchronously with the initial actuation thereof. Likewise, the valve 61a and/or 4a may be actuated by the control means 70a, or similar means whereby to close these values when pressure in the conduits 61 and/ or 4 decreases to a level below that which has been preselected to retain any desired residue of cargo material in the container bottles.

Also represented in the showing of Fig. 3, is means for automatically controlling introduction of condensate into the main liquid conduit 58. The condensate drum is connected, through conduit 8001, pump 86, and conduit 88 with the conduit 58. A liquid level control means is provided in conjunction with the drum 88 so as to respond to preselected upper and lower liquid levels which may be encountered in the drum, whereby to actuate a motorized control valve 88a in conduit 88, and the drive means for the pump 86. Either electrical, as shown, or pressurized fluid means may be utilized to energize the respective pump and valve actuating means. As in conventional installations, the liquid level control means is adapted to energize both the valve 880 and the pump drive means when the condensate level exceeds a preselected upper lirnit, and to de-energize the valve and pump at a preselected lower limit.

What is claimed is:

1. In a tank ship, including a plurality of individual 7 storage vessels adapted to contain a liquefied gas under superatmospheric pressure, each said storage vessel having first and second conduit connections communicating respectively with the upper and lower interior portions of said vessel, and wherein said storage vessels are disposed in fore and aft, substantially parallel rows; a shipboard system for loading and unloading said storage vessels comprising, at least one main liquid cargo conduit for loading and unloading said storage vessels, said conduit disposed athwartship and adapted for communicating connection with a shoreside conduit system, at least one cargo pump in said shipboard system, said pump having a valved discharge conduit connection to said main liquid cargo conduit, and a pump inlet conduit including a valve adjacent said pump; a plurality of valved branch conduit connections communicating between said pump inlet conduit and the respective second conduit connections of said storage vessels, and with said main cargo conduit upstream from said valve adjacent the pump;v at least one fore and aft header conduit having valved connections to said main liquid cargo conduit and to said pump inlet conduit, said header conduit including a compressor-condenser system upstream from said valved connection to said pump inlet conduit; 2. series of manifold conduits each having a plurality of valve communicating branch conduits at least equal in number to the number of said vessel rows, respectively connected to at least one vessel in each said rows by way of said vessel first conduit, and also to said fore and aft header conduit upstream from said header conduit valved connection to said pump inlet conduit, whereby said container vessels are interconnected through said several manifold conduits in a corresponding series of thwartship groups; and heat exchange means in at least one storage vessel, in said plurality of vessels, adapted to vaporize a liquefied gas contained therein, whereby to overpressure said vessel, and through said manifolds and said header conduits to overpressure said other storage vessels.

2. In a tank ship, a shipboard system, according to claim 1, for loading and unloading said storage vessels, wherein said compressor-condenser system comprises, a compressor, inlet and outlet conduit connections to said compressor, a driving motor for said compressor, a bypass conduit connection between said compressor inlet and outlet conduit connections, motorized valves in each said inlet and outlet connections downstream and upstream respectively from said by-pass conduit, a means to energize said compressor driving motor, and pressure control means in said header conduit adapted to actuate said driving motor energizing means and simultaneously to actuate said motorized valves in said inlet, outlet and bypass conduit connections whereby said energizing means is actuated to drive said compressor at speeds nversely related to a preselected range of pressure values in said header conduit, said speeds increasing as said pressure value decreases, and to de-energize said driving motor above and below said preselected range, and also whereby to actuate said valves in said inlet, outlet and by-pass conduit connections to open said inlet and outlet valves at the upper level and to close said valves at any level outside said preselected range of pressure values, and to open and close said by-pass valve at pressure values respectively above and below the upper level of said preselected range of values.

3. A method for discharging a liquefied gas from a group of storage vessels in which said liquefied gas is contained, and wherein said group of storage vessels belong to an associated series of liquefied gas containers, comprising heating the liquefied gas contained in a first vessel in said series to a temperature at which the vapor pressure of said liquefied gas is at least equal to the statlc pressure of a column of said liquefied gas having a height greater than that of any vessel in said series; vaporizing said liquefied gas and maintaining said vapor pressure by continued heating; placing said first vessel in communication with a first group of other storage vessels in said series at a pressure level above the pressure level of liquefied gas therein; simultaneously discharging the liquefied gas in said first group of other storage vessels therefrom substantially under the pressure exerted thereon by vapors of the heated liquefied gas contained in said first vessel; evacuating vapors from a previously discharged second group of other storage vessels; condensing said evacuated vapors, and combining the resulting condensate with the liquefied gas discharged from said first group of other storage vessels.

References Cited in the file of this patent UNITED STATES PATENTS 1,753,785 Heylandt Apr. 8, 1930 2,435,332 Van Vleet et a1 Feb. 3, 1948 2,487,863 Garretson Nov. 15, 1949 2,670,605 Van Zandt et al Mar. 2, 1954

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