US3293011A

US3293011A - Method of handling natural gas

Info

Publication number: US3293011A
Application number: US332204A
Authority: US
Inventors: John D Lewis; Sze Morgan Chuan-Yuan; Carroll O Bennett; Maurice E Brooks; Irvin H Lutz; Howard B Zasloff
Original assignee: Vehoc Corp
Current assignee: Vehoc Corp
Priority date: 1963-12-20
Filing date: 1963-12-20
Publication date: 1966-12-20
Anticipated expiration: 1983-12-20
Also published as: ES307311A1; CA788175A; SE305459B; AT255982B; GB1032080A; FR1434964A; CH502548A; NL6414758A; NO120374B

Description

Dec. 20, 1966 L w s ETAL METHOD OF HANDLING NATURAL G55 3 Sheets-Sheet 1 Filed Dec. 20, 1963 ATTORNEYS Dec. 20, 1966 w s ETAL METHOD OF HANDLING NATURAL GAS 5 Sheets-Shet 2 Filed Dec. 20. 1963 mm 6, A Em A 1 0 EN 8 mm A E \mm mm ATTORNEYS Dec. 20, 1966 L wgs ETAL METHOD OF HANDLING NATURAL GAS 5 Sheets-Sheet 3 Filed Dec. 20, 1963 ATTORNEYS United States Patent Delaware Filed Dec. 20, 1963, Ser. No. 332,204 28 Claims. (Cl. 48-190) This invention relates to the containment and handling of natural gas hydrocarbon mixtures and, more particularly, to a method and apparatus for loading and unloading pressure vessels with a natural gas hydrocarbon mixture while maintaining it in a single-phase state of moderate refrigeration and compression. The inventors, employees of The Lummus Company, made the invention while engaged in development work undertaken by that organization in techniques of natural gas transportation.

In many populated areas throughout the world the demand for natural gas is increasing at a far greater rate than the supply available from pipelines. The industry is responding to this by intensive development in techniques for transporting natural gas by ship so that regions of increased demand remote from sources of supply need not rely solely on pipelines. One of the more important advances in this field has been the concept of maintaining the natural gas cargo mixture in a singlephase state of moderate refrigeration and compression throughout the voyage from the first of the loading steps to the completion of loading. The method generally involves refrigerating the gas but not to the very low cryogenic temperatures characteristic of LNG processes, and compressing the gas but not to the very high pressures characteristic of static storage processes at ambient temperature. By the use of moderate refrigeration and compression, advantage is taken of optimum processing costs per unit of gas transported so that the natural gas cargo can be delivered by ship more economically than by other methods.

It is a primary purpose of the present invention to provide a method and apparatus for carrying out the actual loading and unloading operations for natural gas cargo mixtures maintained in the optimum state of moderate compression and refrigeration described above. One of the most important objects is to insure that the cargo mixture does not depart substantially in pressure or temperature from that operating state at any time during loading and unloading. A further object is to permit of substantially continuous loading and unloading of a ship without significant interruption so that, if desired, the cargo mixture may be directed immediately into pipelines at the dockside facilities to the regions of demand. To achieve this uninterrupted displacement of the cargo, the new method and apparatus are adapted specifically to successive loading and unloading of one ship after another without significant idle time at the ports of embarkation and destination. All of these objects and several others which will be made clear hereinafter, are to be attained under conditions of strict safety and cost control.

Broadly stated, the new method of handling a hydrocarbon mixture in a plurality of pressure vessel means in series is applicable both to the loading and the unloading thereof while the mixture is maintained in a single-phase refrigerated and compressed operating state. In loading the pressure vessel means, a cushion fluid is forced into the first pressure vessel means at a regulated temperature until it is filled at substantially the operating pressure of the hydrocarbon mixture. The hydrocarbon mixture is MCe then forced into the first pressure vessel while the cushion fluid is expelled therefrom at a regulated flow rate so that said first pressure vessel means is filled with the hydrocarbon mixture. Thereafter, the expelled cushion fluid is directed into the next pressure vessel means in the series and it is filled with the hydrocarbon mixture by the foregoing steps. The process is repeated in succession until all of the series of pressure vessel means are filled with the hydrocarbon mixture in the operating state and the cushion fluid is expelled from the last pressure vessel means. In unloading the pressure vessel means by the new method, a displacement fluid at a pressure greater than the operating pressure of the hydrocarbon mixture is forced into the first pressure vessel means while the hydrocarbon mixture is expelled therefrom at a regulated flow rate so that the first pressure vessel means is emptied of the hydrocarbon mixture and filled with displacement fluid. Thereafter, the displacement fluid is directed into the next pressure vessel means in the series to empty it of the hydrocarbon mixture by the foregoing step and the process is repeated in succession until all of the pressure vessel means are emptied of the hydrocarbon mixture and filled with displacement fluid. Finally, at least part of the displacement fluid is removed from all the pressure vessel means in succession.

For carrying out this method, the invention also provides apparatus for handling the hydrocarbon mixture maintained in the single-phase refrigerated and compressed operating state. The apparatus includes a multiplicity of pressure vessel means each including first and second access conduits communicating with the lower and upper regions respectively thereof and means for separately controlling the flow of fluids through each of the access conduits. First and second sub-headers interconnect the first and second access conduits respectively of all of the pressure vessel means. A main header system is included which comprises first main header means interconnecting all of one of the two sub-headers. Second main header means are also included interconnecting all of the other sub-headers.

Preferred embodiments of the method and apparatus of the invention are described hereinbelow with reference to the accompanying drawings, wherein FIG. 1 is a pressure-temperature phase diagram illustrating the limits generally contemplated for the operating state of the hydrocarbon mixture;

FIG. 2 is a schematic layout of a three-header system, including shipboard and dockside facilities, for loading the cargo mixture by gas displacement;

FIG. 2A is a fragmentary schematic layout of dockside facilities to be associated with the shipboard facilities of FIG. 2 for unloading the cargo mixture by gas displacement;

FIG. 3 is a schematic layout of a six-reader system, including shipboard and dockside facilities, for loading the cargo mixture by gas displacement;

FIG. 3A is a fragmentary schematic layout of dockside facilities to be associated with the shipboard facilities of FIG. 3 for unloading the cargo mixture by gas and liquid displacement;

FIG. 4 is a schematic layout of a four-header system, including shipboard and dockside facilities for loading the cargo mixture by liquid displacement; and

FIG. 4A is a fragmentary schematic layout of dockside facilities to be associated with the shipboard facilities of FIG. 4 :for unloading the cargo mixture by liquid displacement.

THE CARGO MIXTURE Various natural gases are suitable for use with the method and apparatus of the invention. In general, they may be described as hydrocarbon .gas mixtures containing at least 50 mol percent methane and at least 75 mol percent methane-plus-ethane, the remainder being heavier hydrocarbons and up to 20 mol percent inert constituents, and having a higher calorific value from 800 B.t.u./s.c.f. to 1800 B.t.u./s.c.=f. The approximate limits of the operating state in which such cargo mixtures are to be maintained in accordance with this invention can best be described with reference to FIG. 1. This phase diagram shows a typical envelope curve within which the gas mixture exists in two-phase state, part liquid and part vapor. Point A indicates the liquification temperature of the mixture at atmospheric pressure, and in absolute terms it might be about 258 F. Point B is the true critical point of the gas at which the various lines of liquid and vapor concentrations within the two-phase region of the envelope convenge. Point C is the cricondenbar point of the gas and it indicates the point of highest pressure, regardless of temperature, at which the twophase condition can exist. Point D is the oricondentherm point of [gas and it indicates the point of highest temperav ture, regardless of pressure, at which the two-phase condition can exist.

When the cargo mixture is moderately refrigerated and compressed to achieve optimum density at minimal compression and refrigeration costs, the mixture is within the region of the FIG. 1 diagram defined by the dotted line E on one side, the dotted lines F and G on the other, and the-interconnecting portion of the envelope curve. The lower temperature limit marked by the dotted line E is the critical temperature of the methane content of the gas, about 116 F., and the maximum temperature indicated by the dotted line F is ambient temperature. The minimum pressure is indicated by the bubble point-dew point line of the envelope and by the dotted line G, the latter being the pressure of the gas at its cricondentherm point D. Thus, the cargo mixture should be refrigerated below ambient temperature but not below the critical temperature of methane, and it should be compressed above the bubble point-dew point-cricondentherm pressure of the mixture.

When the cargo, mixture is refrigerated within this operating range to below its critical point B, it is especially dense and approaches a liquid in its behavior. At temperatures in the operating range above the cricondenbar point C, the mixture is less dense and may therefore be handled diflFerently in a manner to be discussed hereinafter. At temperatures in the operating range between the critical point B and the crioondenbar point C it may be possible to handle the mixture in accordance with any of the techniques disoussedhereinafter.

FIGURE 2 SYSTEM In FIGS. 2 and 2A, a system is illustrated for loading and unloading a cargo mixture by gas displacement. It is particularly suited to a cargo mixture maintained at an operating temperature below the cricondenbar point C thereof as indicated in the FIG. 1 phase diagram, but it is also applicable to a less dense cargo mixture above the cricond-enbar temperature.

The shipboard facilities are to the left of'the dot-das-h line L in FIG. 1 and the shore facilities are to the right thereof. The ship carries a multiplicity of elongated bottles 10,, to 10,, in a plurality of respective batteries 11,, to 11,,. A given ship may include twenty-four batteries of this type disposed laterally in its hold and there may be about one hundred bottles in each battery. Each bottle is made of a suitable alloy resistant to low temperatures and may be three or four feet in diameter and at least about twenty feet long. They are preferably arranged vertically in the hold of the ship. Each bottle in each battery is closed at both ends except for first and second access conduits 12,, to 12,, and 13,, to 13,, which extend through the respective upper ends of the bottles and communicate with the bottom and top regions respectively of the interior thereof. In the FIG. 2 system, constrictions 15,, to 15,, are provided in the respective second access conduits 13 to 13,, of the various bottles to control the flow of fluids into and out of each bottle at a predetermined rate. The constrictions generally vary in size from one bottle to the next in accordance with variations in the size of the bottles and other factors, so that the bottles of relatively large capacity have a relatively large constriction and high flow rate. The object of the flow-control constricti-onsis to insure that all of the bottles in each battery are filled or emptied substantially simultaneously when subjected to the same fluid pressure in their respective second access conduits. Each constriction may be defined by a plate in the appropriate passage with a round orifice tormed in it of a size which may be calculated in accordance with theories of fluid flow well known in the art.

In each of the respective batteries, first sub-headers 17,, to 17,, and second sub-headers 18,, to 18,, interconnect the first and second access conduits 12,, to 1.2,, and 13, to 13,, respectively of allof the bottles. Each subheader may be disposed laterally in the ship over the tops of the bottles in the respective batteries. The system also includes on board the ship a firs-t main header 20 interconnecting all of the first sub-headers 17,, to 17,, for conveying the cargo mixture into and out of the bottles. First valves 21,, to 21,, are located at the respective interconnections between the first main header 20 and the first sub-headers 17,, to 17,,. A second main header 22 interconnects all of the first sub-headers 17,, to 17,, through second valves 23,, to 23,, in a similar manner. Finally, a'

third main header 25 interconnects all of the second subheaders 18,, to 18,, through third valves 26,, to 26,,. The function of the second and third

main headers

22 and 25 is to convey cushion and displacement gas into and out of the bottles. Conventional detection means 27 to 27,, and 28,, to 28,, are located adjacent the bottle-side of the respective first and second valves 21,, to 21,, and 26 to 26,, to recognize and respond to the arrival of an interface between diifering fluids from the bottles of their respective batteries. By interface is meant a sharp or gradual change in the recognizable properties, composition or other characteristics of the fluid passing the detection means. Such detection means, which are commercially available, may operate the various valves in a manner described hereinbelow by any suitable servo system. Also, it will be apparent from the description of the operatlon below that one detection device may suffice at the end of each

main header

20, 22 and 25 where they are attachable to shore facilities.

At one end of each of the

main headers

20, 22 and 25 are

valves

29, 30 and 31 and coupling means 32, 33 and 34 respectively. When the ship is being loaded or unloaded at dockside,

flexible conduits

35, 36 and 37 may be attached to the coupling means 32, 33 and 34 respectively to interconnect the three main headers to the shore When the ship is being loaded, the flexible,

facilities.

conduits

35, 36 and 37 are connected through coupling means 3 8', 39 and 40 to

dockside headers

41, 42 and 43 through

valves

44, 45 and 46 respectively. loading facilities also include a bypass conduit 48 containing a valve 49 between the

headers

42 and 43. Also, they include between those same leaders 42 and 43 a second bypass conduit 51 which includes a heat exchanger 52 between pressure

relief control valves

53 and 54. During unloading at the port of destination, the flexible con-. duits 35, 36 and 37 (or others like them, since counterparts would probably be available at each port) are connected by coupling means 56, 57 and 58 to

headers

59, 60 and 61 through

valves

62, 63 and 64 respectively as shown in FIG. 2A.

When the system of FIGS. 2 and 2A is to be used, a

ship will be returning to the loading facilities with some The dockside residual gaseous mixture in its bottles at a moderately high pressure, perhaps between 100 and 300 p.s.i.g. The temperature of the bottles will be at about the level of the refrigerated cargo mixture carried in the previous voyage, for example 5 R, if adequate insulation surrounds them in the hold of the ship. The system is linked to the dockside facilities by the

conduits

35, 36 and 37 as shown in FIG. 2 while a source of the cargo mixture is in the operating state ready for loading through the header 41. In the header 43 a sup-ply of cushion gas is available at about the operating state pressure of the cargo mixture and at about ambient temperature. The cushion gas usually is less dense at substantially the pressure and temperature of the cargo mixture operating state. The cushion gas is advantageously a leaner natural gas mixture than the cargo mixture but otherwise similar to it in composition or it may be hydrogen, nitrogen or some other gas quite different from the cargo mixture.

At the beginning of the loading cycle, all the shipboard valves 21 to 21, 23, to 23 and 26 to 26 are closed and all the other valves 29 to 31,44 to 4s, 49, 53 and 54 are open. Cushion gas proceeds from its source through the header 43 and the by-pass conduit 48 into the header 42 and the second main header 22. To start the cycle the second valve 23 in the first battery 11 is opened. This causes the cushion gas to pass through i the header 43, the by-pass conduit 48, the header 42, the

conduit 36 and along the second main header 22. Passing through the open valve 23,,, the cushion gas proceeds into the first sub-header 17,, to enter all of the first access conduits 12, of the various bottles in battery 11 The cushion gas fiows into the bottom region of each bottle in this manner and proceeds to fill the respective bottles. Since the pressuring medium is a gas, the flow is automatically distribute-d correctly with more flow going to the larger bottles so that all of the bottles 10 approach capacity at substantially the same time. As the pressure in the bottles 10 rises, heat of compression causes the cushion gas temperature to rise. The temperature of the bottle walls will rise but at .a much slower rate since heat transfer under such conditions is relatively poor. In order to have the cushion gas enter the bottles 10 at the optimum temperature, i.e. perhaps about the refrigerated temperature of the operating state of the cargo mixture, it may be desirable to pass all or part of the cushion gas through the heat exchanger 52 before it enters the ship instead of solely through the bypass conduit 48.

When the pressure of the cushion 'gas in battery 11 has been raised to slightly less than the operating state pressure of the cargo mixture, for example 950 p.s.i.g., the second valve 23 and the by-pass valve 49 are closed while the second valve 23 the third valve 26 and the first valve 21, are opened, since the requisite amount of cushion gas has been put into the system. The cargo mixture, in an operating state of 1000 =p.s.i.g. and 50 F. for example, therefore begins to enter the ship from the header 41 through the flexible conduit 35 and into the first main header 20. It proceeds through the open valve 21 into the first sub-header 17 and hence into the bottom region of the various 'bottles 10 of battery 11 through their respective first access conduits 12 As the dense cargo mixture enters the bottom of the bottles through the first access conduits 12 the compressed cushion gas is forced out of the top of the bottles in the battery 11 through the respective constrictions 15,, and second access conduits 13 into the sub-header 18 The constrictions prevent the cushion gas from escaping from the small bottles in the battery 11 as fast as from the larger bottles, thereby controlling the rate of flow of the dense cargo mixture entering the bottom of the bottles. By suitable correlation of the size of the constrictions 15,, to the volume of the respective bottles, it can be assured that the bottles 10,, in. the battery 11,,

6 are all filled with the dense cargo mixture at the same time.

The cargo mixture entering the bottles 10,, forces the cushion gas out through the second sub-header 18 and into the third main header 25 through the open valve 26,. Since all of the third valves 26 to 26 are closed, the cushion gas proceeds along the third main header 25 through the

valves

31 and 46 and into the header 43 where it started from in the shore facilities. The header 43 is otherwise closed ofiE from the source of cushion gas (not shown) so that the cushion gas can continue on its way only through the

bypass conduits

48 or 51. The by-pass valve 49 may be closed so that the cushion gas passes through the pressure control valve '54 which holds back a pressure on the first battery 11 and thereby maintains the pressure of the cargo mixture entering the bottles 10 of that battery at a constant level. i

If the cushion gas were delivered directly into the bottles 10,, of the next battery 11 in its compressed and therefore warm state, the cushion gas would be heated still further by heat of compression. When the pressure in the battery 11;, rises, the temperature could eventually become excessively high. Therefore, it is desirable for the cushion gas to enter each battery at as low a temperature as practical so that it will not become any warmer than necessary after it is compressed. However, if the cushion gas is too cold when it enters a battery it might chill portions of the bottles thereof to such a low temperature that the bottle Walls would lose their ductility. To guard against these dangers, the cushion gas is passed through the heat exchanger 52 before it is sent back through the header 42 and the

valves

45 and 30 into the second main header 2-2. If the expansion of the cushion gas as it leaves the second control valve 53 cools it to too great an extent, a portion of the cushion gas upstream from the heat exchanger can be drawn oil by the by-pass valve 49 through the by-pass conduit 48 to mix with the cooled cushion gas proceeding through the header 42 back into the second main header 22. Alternatively, the passage of the cushion gas through the first control valve 54 before entering the heat exchanger 52 may elimihate any expansion cooling after the gas leaves the heat exchanger 52. With these alternatives available, either one of the two

control valves

53 or 54 can sufiice in a. given installation without including both of them.

Since the second valve 23 has been opened previously, the cushion gas at its regulated temperature proceeds from the second main header 22 into all the bottles 10 of the battery 11 through the respective first access conduits L2 thereof to fill the second battery 11, in the same manner that it had previously filled the first battery 11 As soon as all of the bottles 10 in the first battery 11,, are filled with the cargo mixture as described, the interface between the denser cargo mixture and the lighter cushion gas reaches the detection device 28,,. When this occurs, the detection device automatically closes the first valve 21 and third valve 26,, in the battery 11 and opens the first valve 21 to direct the cargo mixture into the second battery 11 without interruption. The detection device 28 also closes the second valve 23 and opens the second and third valves of the third battery (not shown) and the third valve 26 of the second battery 11 All of the bottles 10;, in the battery 11 are filled in precisely the same manner as were the bottles 10 in the previous battery 11,,. This continues throughout the ship as one battery after another is filled with the cargo mixture.

Since there was some gas in each battery when the ship arrived at the loading port and this gas is completely displaced by the dense cargo mixture, some of it must be bled oif. This could be done by removing the gas either through the header 43 before the heat exchanger 52 or through the header 42 after the heat exchanger. It could be removed either continuously throughout the loading cycle or at the end of the loading cycle after the pressure of the cargo mixture in the bottles has become as high asdesired. As the last battery .11 on the ship is being filled with the cargo mixture, the cushion gas leaves through the second sub-header 18 the third valve 26 the main header 25, the

valves

31 and 46, and the heat exchanger-52 as before. However, instead of returning to the ship, the detection device 28 in the last battery has the additional function of closing the valve 45 so that the cushion gas exits through the header 42. The header 42 may direct the cushion gas to the next ship immediately, or if no other ship is yet ready to receive it the cushion gas may go to storage facilities on shore or to flare. When the loading cycle is completed in this manner, all the valves are closed and the connecting

conduits

35, 36 and 37 are removed from their associated couplings to permit the ship to proceed on its delivery voyage.

When the ship arrives at the unloading port, it is moored alongside dock facilities such as those shown in FIG. 2A. The

flexible conduits

35, 36 and 37 are attached to the coupling means 56, 57 and 58 of the

headers

59, 60 and 61 respectively. The header 6-1 communicates with a source of displacement gas, the choice of which is similar in all respects to that of the cushion gas used in the loading process. This displacement gas is at [a pressure somewhat higher than that of the cargo mixture in the ship. All the valves 29 to 3.1 and 62 to 64 are initially opened, together with the first and third valves 21,, and 26, in the first battery 11,,.

The displacement gas proceeds into the ship through the third main header 25 and the third valve 26 into the first battery 11,,. It then forces its way through the second sub-header 1 8,, and into each of the bottles through their respective second access conduits 13,,. As the displacement gas enters the bottles 10,, at the top region thereof in this manner at a regulated rate because of the flow control exerted by the constrictions the denser cargo is forced out the bottom of the bottles 10,, through their respective first access conduits .12,,. The cargo mixture proceeds through the first sub-header 17 through the open first valve 21,, and down the first main header 20, so that it exits from the ship through the header 59 in the shore facilities where suitable back pressure is maintained to prevent its decompression. When. the cargo mixture has been removed from all the bottles of the first battery the interface between the displacement gas and the cargo mixture arrives at the detection device 27,, adjacent the first valve 21 and in response thereto the third valve 26 and first valve 21 are closed and the third valve 26,, and first valve 21,,

in the next battery 11 are automatically opened, allowing the displacement gas to push the dense cargo mixture from the second battery 11 At the same time, the second valve 23,, is opened to allow the displacement gas to expand out the bottom of the bottle 10 in the first battery 11,, through the respective first access conduits 12,,, the first sub-header 17 the second valve 23 the second main header 22, the

valves

30 and 63, and the header 60. The displacement gas continues to flow out until the pressure in the first battery 11, is reduced to the desired level for the return voyage, perhaps 100 to 300 p.s.i.g.

When the cargo mixture is displaced out the bottom 3f the bottles as described, some of it may remain in the JOflZOm of a few of the bottles. Such remaining cargo mixture would flash during decompression of the displacement gas and would lower the temperature locally below be permitted design factor for the bottle construction. However, this is avoided because any substantial amount )f the dense cargo mixture left in the bottom of the bottles will be pushed out first before the pressure of the displacenent gas is appreciably reduced. As the displacement gas is removed from the lower region of the bottles the gas remaining in the bottles expands and therefore be comes cooler, and to prevent this remaining gas from becoming too cold it is desirable that the original displacement gas used to push the cargo mixture out of the ships be relatively warm.

FIGURE 3 SYSTEM In FIGS. 3 and 3A, a system is shown which is similar in principle to that of FIGS. 2 and 2A except that in the unloading procedure it provides for removal of the displacement gas at full pressure without expanding it out of the ship after the successive batteries are emptied. Only the unloading operation in the FIGS. 3 and 3A system differs from what has been described previously in regard to FIGS. 2 and 2A, and not the loading operation. Therefore, everything said previously in regard to the loading procedure applies by reference here, and primed reference numerals are used to designate all those elements of the loading means in FIG. 3 which are identical in form and function to their counterparts in FIG. 2.

As shown in FIG. 3, there are certain elements not designated by primed reference numerals which are included in the system for use during unloading and it is to be understood that they have no function whatsoever during loading, the valves among them all being closed during loading operation. These are a fourth main header 70 interconnecting all of the first sub-headers 17 to 17,, through respective fourth valves 71 to 71, 21 fifth main header 72 interconnecting all of the second sub-headers 18 to 18,, through respective fifth valves 73,, to 73,,; a sixth main header 74 interconnecting all of the second sub-headers 18,, to 18,, through respective sixth valves 75,, to 75

valves

77, 78 and 79, coupling means 80, 81 and 82, and

flexible conduits

83, 84 and 85 associated with the four, fifth and sixth main headers respectively; flow-controlling constrictions 87 to 87 in the first access conduits 12,, to 12,, of the respective batteries of bottles; and detection means 88, to 88, and 89,, to 89 adjacent the respective fourth and sixth valves 71 to 71 and 75,,

to 75 designed to actuate various of the valves in response and equipped with

valves

96, 97, 98, 99, and 101 and coupling means 102, 103, 104, 105, 106 and 107 respectively, with a by-pass conduit 108 and by-pass valve 109 connecting the

headers

91 and 92.

To remove the displacement gas from the bottles at full pressure in accordance with the system of FIGS. 3 and 3A, it is forced out with a chilled displacement liquid having a low vapor pressure, such as methanol, acetone, calcium chloride, brine, or heavy naphtha. The latter is particularly advantageou and will serve as an illustrative liquid displacement medium in the following description of the operation of this system. After the displacement liquid has forced out the displacement gas at full pressure, it is replaced in all the bottles by a lowpressure scavenging gas which may be similar in composi tion to the cargo mixture but perhaps somewhat lighter, in a manner discussed hereinbelow.

When the loaded ship arrives in the unloading port,

conduits

83, 84, 85, 35', 36 and 37" are connected to coupling means 102, 103, 104, 105, 106 and 107 respectively on the shore facilities shown in FIG. 3A. To start the unloading operation, all of the valve 77 to 79, 29 to 31', and 96 to 101 are open. The. header 91 transmits to the ship a lean high-pressure displacement gas which i may 'be close to the operating temperature of the cargo mixture since it will remain at fairly constant pressure throughout the unloading cycle. In the first battery 11 the fourth and fifth valves 71 and 73 are opened, and

the displacement gas passes through the header 91 into the fifth main header 72, where it enters the second sub-header 18,, through the fifth valve 73 From the second subheader 18,, the displacement gas passes through the various second access conduits 13, and into all of the bottles of the first battery 11 at the top thereof. This forces the cargo mixture out the bottom of the bottles through the second access conduits 12,, with the flow rate of the displacement gas controlled by the respective constrictions 15,, so that all of the bottles 10 are emptied of cargo substantially simultaneously. As the cargo mixture is removed from the bottles in this manner, it passes from the first sub-header 17 through the fourth valve 71,, and along the main header 70 to the header 90 in the shore facilities Where it is confronted by suificient back pressure to prevent decompression.

As soon as the interface between the displacement gas and cargo mixture reaches the detection device 88,, adjacent the fourth valve 71 after all the bottles 10 in the first battery are emptied of cargo, the fourth valve 71 and the fifth valve 73,, are closed to entrap the displacement gas momentarily in the first battery. At the same time, the sensing device 88 automatically opens the first and fifth valves 21,, and 73 Liquid naphtha pumped into the header 93 in the shore facilities therefore begins to flow through the first main header and into the first battery 11 through the first valve 21,, and the first sub-header 17,,,'. From there, the naphtha enters the bottom region of the bottles 10, in the first battery thereof through the second access conduits 12 to force the displacement gas out of the top of the bottles through the second acces conduits 13 The constrictions 87 in the respective bottles control the entry of naphtha so that all of the bottles are emptied of displacement gas at substantially the same time. The displacement gas is forced from the second sub-header 18 through the fifth valve 75 and into the sixth main header 74. It then proceeds into the header 92 in the shore facilitie where the greater portion of it is directed through the bypass conduit 108 and back into the ship through the header 91. and the fifth main header 72. Since the fifth valve 73 in the second battery 11 was previously opened, the displacement gas enters all of the bottles 1% of the second battery in precisely the same manner as it had entered the bottles of the first battery.

Thus, the liquid naphtha pushes the displacement gas and the latter in turn pushes the cargo from one battery of bottles to the next to remove all of the cargo mixture from the ship. Flow rates may be adjusted so that the cargo mixture has been pushed out of a given battery of bottles at the same time that the displacement gas has been pushed out of the previous battery of bottles by the liquid naphtha. Thus, when the interface of naphtha and displacement gas reaches the detection device 89,, adjacent the sixth valve 75 in the first battery causing it to close the sixth valve 75 and the fifth valve 73 in the next battery, the interface of displacement gas and cargo mixture should have just arrived at the detection device 88 in the next battery. For this reason one detection device in each battery may be made to actuate the valves instead of employing the two detection devices shown.

To remove the naphtha from the bottles, there is a further sequential movement of fiuid through the system which proceeds as all of the steps described above are being carried out. When the interface of naphtha and displacement gas reaches the detection device 89, in the first battery, the sixth valve 75,, and the first valve 21 are closed to entrap the naphtha momentarily in the first battery 11 However, the fifth valve 23,, and the third valve 26, are opened so that the naphtha begins to flow out of the battery 11,, from the bottom of the bottles through the first sub-header 17 and along the second main header 22 to the header 94 on the shore facilities. This reduces the pressure of the naphtha in the bottles to between atmospheric pressure and about 200 p.s.i.g.

A low pressure scavenging gas, chosen with the same standard as the cushion and displacement gases mentioned previously, enters the ship from the header 95 through the third main header 25 and into the second sub-header 18 to the upper regions of the respective bottles 10,,

through their various second access conduits 13 The rate of flow of the scavenging gas into the bottles 10,, should be such that the naphtha is removed from all of the bottles in the battery 11,, substantially simultaneously and also at about the same time the displacement gas is emptied from the next battery 11,, and the cargo mixture is emptied from the battery after that. Thus, the detection devices 89 or the one in the third battery (not shown) corresponding to the devices 88 and 88 may be used to close the second and third valves 23,, and 26,, and to open corresponding valves 23;, and 26 so that the scavenging gas will proceed to empty the naphtha from the next battery 11 From this description of the mannet in which the detecting devices function, it should be apparent that yet another series of them may be located adjacent the second valves 23,, if desired.

While the displacement gas is flowing, for example, into the top of the bottles of battery 11 to push the cargo out of the bottom, the fiow to the individual bottles is controlled primarily by constrictions 15 and 15 and the corresponding constrictions in the next battery. The pressure drop through the constrictions 87 and 87 and the corresponding constrictions in the next battery is relatively low at this time. When the liquid naphtha enters into the bottom of, for example, the bottles of battery 11,, pushing the displacement gas out of the top thereof, the constrictions 87 and 15,, are about equally eifective. When the scavenging gas is entering the top of the bottles of the first battery 11 pushing the liquid naphtha out of the bottom, the distribution to the various bottles is controlled primarily by constrictions 87 and 87 and the corresponding constrictions in the next battery. The pressure drop in constrictions 15 and 15 and the corresponding constrictions in the next battery will be relatively low at that time.

As the naphtha leaves the ship it may be reprocessed and pumped back to high pressure to be returned to the same or the next ship through the header 93 to push displacement gas and cargo mixture out of another battery. A problem to be guarded against is admixture of any of the displacement gas into the liquid naphtha as a result of contact between the two fluids at the interface thereof. When the pressure is subsequently released so that the naphtha may be pushed from the ship with low-pressure scavenging gas, any substantial amount of the displacement gas previously dissolved in the naphtha may flash in the bottles and drop the temperature to a dangerously low level. In order to prevent this it may be desirable to bring the naphtha into the ship at a somewhat higher temperature than the cargo mixture. Alternatively, after the naphtha has pushed all of the displacement gas out of the bottles of the first battery, a small additional amount of naphtha may be sent into the bottles to push out that portion of the naphtha at the top of the bottles which may have been contaminated with an admixture of the displacement gas. This is done before the pressure of the naphtha is released so that the admixture moves out of the ship with the displacement gas rather than with the liquid naphtha.

FIGURE 4 SYSTEM In the system shown in FIGS. 4 and 4A, the hydrocarbon cargo mixture is loaded and unloaded by use of a liquid medium instead of a gas as in the previous systems. The various liquids mentioned previously in regard to the system of FIGS. 3 and 3A may be used here, but again naphtha is employed for illustrative purposes because it is particularly advantageous. The system of FIGS. 4 and 4A is particularly suited to the transportation of relatively lean cargo mixtures at temperatures above its critical point B and particularly above its cricondenbar point C in the operating state shown in FIG. 1. The cargo mixture is much less dense under such conditions than when its temperature is below the critical point B and for that reason there is too great a tendency for the cargo mixture to admix with cushion or displacement gases in direct contact with it as in the systems of FIGS. 2 and 2A or 3 and 3A. Therefore, the FIGS. 4 and 4A system contacts the less refrigerated, and therefore less dense, cargo mixture only with displacement and cushion liquids throughout all the steps of loading and unloading.

The physical arrangement of the system shown in FIGS. 4 and 4A need only be described briefly because it is generally similar to those described previously. Again, the shore facilities are to the right of the dot-dash line marked L and the shipboard facilities are to the left of that line. Bottles 120, to 120,, are arranged in batteries 121 to 121,, throughout the ship. The bottles are connected by first and second access conduits 122,, to 122,, and 123,, to 123,, to first and second sub-headers 124,, to 124,, and 125 to 125,,. Constrictions 126,, to 126,, are located in each of the respective second access conduits 123 to 123,,.

A first main header 128 is connected to the various second sub-headers 125,, to 125,, by first valves 129,, to 129,, associated with detection devices 130 to 130,,. A second main header 131 is connected to the various first sub-headers 124 to 124 by second valves 132,, to 132,,. A third main header 133 is connected to the various first sub-headers 124,, to 124,, by respective third valves 134,, to 134,,. Lastly, a fourth main header 135 is connected to the various second sub-headers 125,, to 125,, by respective fourth valves 136 to 136,, associated with detection devices 137 to 137,,. All of the

headers

128, 131, 133 and 135 terminate with

valves

138, 139, 140 and 141 respectively, together with coupling means 142, 143, 144, 145 by which

respective conduits

146, 147, 148 and 149 may be connected to the shore facilities.

Onshore at the loading port,

headers

151, 152, 153 and 154 terminate in

valves

155, 156, 157 and 158 respectively, together with coupling means 160, 161, 162 and 163 adapted to receive the

respective conduits

146, 147, 148 and 149.

Headers

152 and 153 are interconnected by a by-pass conduit 164 contacting a by-pass valve 165. They also include

valves

166 and 167 respectively on the side of the by-pass conduit 164 remote from the ship and a pressure control valve 168 in the header 153 closer to the ship. At the unloading port, the shore facilities comprise

headers

169, 170, 171, and 172 associated with

valves

173, 174, 175 and 176, together with coupling means 177, 178, 179 and 180 adapted to be connected to the

respective conduits

146, 147, 148 and 149.

When the ship arrives at the loading port, its bottles contain some residual gaseous mixture at atmospheric pressure or somewhat higher. After the shipboard and dockside facilities have been connected as shown in FIG. 4, all of the valves 138 to 141, 155 to 158, 165 and 166 are opened. The first step is to direct a chilled cushion liquid, i.e. naphtha in this embodiment, through the header 152 and second main header 131. The cycle is commenced by opening the second valve 132,, and the fourth valve 136,, in the first battery 121,. As a result, the naphtha passes from the second main header 131 through the second sub-header 124 and into the bottom of each of the bottles 120,, through their respectively first access conduits 122,. As the level of naphtha rises in the various bottles, the residual gas originally in the bottles is expelled through the various constrictions 126,, so that all of the bottles are filled with naphtha at substantially the same time. The expelled residual gas passes through the second sub-header 125 and valve 136,, into the fourth main header 135, from which it passes to the header 154 in the shore facilities.

As soon as the interface of naphtha and residual gas reachesthe detection device 137, adjacent the fourth valve 136,, in the first battery, the second valve 132 and the fourth valve 136 are closed, and valves 129,, 134,, 132,,, and 136,, are opened. The cargo mixture then 12 enters from the header 151 through the first main header 128 and the first valve 129 to fill each of the bottles 120,, from the second sub-header 125,. As the cargo mixture enters at the top of the bottles, the liquid naphtha is forced outthe bottom of each bottle through the respective first access conduits 122,, through the valve 134,, and along the third main header 133 to the header 153 in the shore facilities. Since the valve 167 in the header 153 is closed, the displaced naphtha enters the by-pass conduit 164 and returns to the ship from the header 152 to the second main header 131. From there, it passes,

through the opened second valve 132,, into the first sub header 124,, of the second battery 121,, and on into the respective bottles 120,, through their first access conduits 122,,, displacing the residual gas in the second battery out the fourth valves 136,, and through the fourth main header to shore.

The flow rate of the various fluids is preferably controlled by the constrictions 126,, to 126,, that, for example, all of the bottles 120 are filled with the cargo mixture at the same time all of the bottles 120,, of the secondary battery are filled with liquid naphtha. If not, additional detection devices may be employed in a manner which should be clear from the discussion of the previous system. This process continues until the last battery 121,, of bottles 120,, is filled with the cargo mixture, and at that point the detection device 137,, in the last battery closes the valve and opens the valve 167 in the shore facilities so that the liquid naphtha proceeds out the header 153 to the next ship or to storage instead of being cycled back into the second main header 131. After the couplings 160 to 163 have been disconnected, the ship proceeds on its delivery voyage with all the bottles filled with the cargo mixture and all of the shipboard valves closed.

When the ship arrives at the unloading port, the conduits 146 to 149 are connected to the coupling means 177 to 180 of the headers 169 to 172 on the shore facilities. To commence unloading, all of the valves 138 to 141 and 173 to 176 are first opened. Then, the third.

valve 134,, and the first valve 129,, in the first battery 121,, are opened. Naphtha or one of the other displacement liquids referred to previously is pumped to a pressure somewhat above that in the bottles and enters the third main header 133 through the header 171. It proceeds through the third valve 134 and the first subheader 124 into each of the bottles 120 in the first battery at the bottom thereof. This forces the cargo mixture out of the top of the bottles through their respective second access conduits 123,, and on through the second sub-header 125,, into the first main header 128. The cargo mixture passes from there to the header 169 in the shore facilities.

As soon as the interface of liquid and cargo mixture.

reaches the detection device 130,, adjacent the first valve 129,, the first valve 129,, and the third valve 134,, are closed while the valves 134,,, 129,,, 136,, and 132,, are opened. This permits this displacement liquid to start entering the second battery. of bottles 120,, through the third valve 134,,, the first sub-header 124,,, the various first access conduits 122,, and into the bottom of the bottles 120,,- As a result, the cargo mixture exits from the bottles 120,, through the second access conduits 123,, the second sub-header 125,,, the first valve 129,, and along the first main header 128 to the header 169 in the shore facilities. At the same time, a scavenging gas such as that mentioned in regard to FIG. 3A enters from the header 172 on the shore facilities along the fourth main header 135 through the fourth valve 136,, and the second sub-header 125 into each of the bottles 120 at the top thereof. This forces the liquid naphthaout of the bottom of the bottles through the first sub-header 124,, and the second valve 132,. The naphtha then proceeds along the second main header 131 to the header in the shore facilities. Again, the rate of flow is preferably controlled by the constrictions 126 to 126 so that, for example, the cargo is forced out of the bottles 12% of the second battery 121 at the same time the naphtha is forced out of the bottles 120 of the first battery 121,, by the scavenging gas, so that the detection devices 130 to 130 suflice to operate all the valves in the proper sequence. However, if the batteries do not fill and empty with such precision, additional detection devices may be located adjacent the second valves 132,, to 132 to divide the actuation of the valves in a manner which should be apparent from the description of the previous systems. Unloading proceeds in this manner until all of the bottles are emptied of the cargo mixture and displacement liquid and only residual scavenging gas remains in the ship.

We claim:

1. In the containment of a natural gas hydrocarbon mixture maintained in a refrigerated and compressed single phase operating state, a method of handling the mixture in a plurality of pressure vessel means in series which comprises:

(I) loading said pressure vessel means by the steps of:

(A) forcing a cushion fluid into the first pressure vessel means at a regulated temperature until it is filled with said cushion fluid at substantially the operating pressure of the hydrocarbon mixture,

(B) forcing said hydrocarbon mixture into said first pressure vessel means while expelling said cushion fluid therefrom at a regulated flow rate so that said first pressure vessel means is filled with the hydrocarbon mixture, and

(C) thereafter directing the expelled cushion fluid into the next pressure vessel means in the series and filling it with the hydrocarbon mixture by the foregoing steps and repeating the process in succession until all of the series of pressure vessel means are filled with the hydrocarbon mixture in the openating state and the cushion fluid is expelled from the last pressure vessel means; and

(II) unloading said pressure vessel means by the steps of: v

(A) forcing a displacement fluid at a pressure greater than the operating pressure of the hydrocarbon mixture into the first pressure vessel means while expelling said hydrocarbon mixture therefrom at a regulated flow rate so that said first pressure vessel means is emptied of hydrocarbon mixture and filled with displacement fluid,

(B) thereafter directing the displacement fluid into the next pressure vessel means in the series and emptying it of the hydrocarbon mixture by the foregoing step and repeating the process in succession until all of the series of pressure vessel means are emptied of the hydrocarbon mixture and filled with displacement fluid, and

(C) removing at least part of the displacement fluid from all the pressure vessel means in succession.

2. In the containment of a natural gas hydrocarbon mixture maintained in a substantially uniform refrigerated and compressed singlephase operating state, a method of handling the mixture in a multiplicity of batteries of pressure vessels, said batteries being in series and each containing a plurality of said vessels in parallel, which comprises:

(I) loading said pressure vessels by the steps of:

(A) forcing a cushion fluid into all the vessels of a first battery thereof at a regulated temperature until all vessels of said first battery are filled at substantially the openating pressure of the hydrocarbon mixture,

(B) forcing said mixture into all the vessels of said first battery While expelling said cushion fluid therefrom at a regulated flow rate so that all of said vessels of said first battery are filled with the hydrocarbon mixture substantially simultaneously, and

(C) thereafter directing the expelled cushion fluid into the next battery in the series and filling it with the hydrocarbon mixture by the foregoing steps and repeating the process in succession until all of the vessels are filled with the hydrocarbon mixture in the operating state and the cushion fluid is expelled from the last battery of pressure vessels; and

(II) unloading said pressure vessels by the steps of:

(A) forcing a displacement fluid at a pressure greater than the operating pressure of the hydrocarbon mixture into all the vessels of said first battery while expelling said hydrocarbon mixture therefrom at a regulated flow rate so that all of said vessels of said first battery are emptied of the hydrocarbon mixture and filled with displacement fluid substantially simultaneously,

(B) thereafter directing the displacement fluid into the next battery in the series and emptying it of the "hydrocarbon mixture by the foregoing step and repeating the process in succession until all the pressure vessels are emptied of the hydrocarbon mixture and filled with displacement fluid, and p (C) removing at least part of the displacement fluid from all the batteries in succession.

3. In the containment of a natural gas hydrocarbon mixture maintained in a single-phase state at an operating temperature below ambient but above the critical temperature of methane and an operating pressure above its bubble point-dew point cricondentherm pressures, a method of handling the mixture in a multiplicity of batteries of pressure vessels, said batteries being in series and each containing a plurality of said vessels in parallel,

which comprises:

(1) loading said vessels by the steps of:

(A) forcing a cushion gas simultaneously into the lower region of .tall vessels of a first battery thereof at a regulated temperature so that all vessels of said first battery are filled substantially simultaneously at substantially the operating pressure of the hydrocarbon mixture,

(B) forcing said hydrocarbon mixture simultaneously into the lower region of all vessels of said first battery while expelling said cushion gas from the upper region thereof at a regulated flow rate so that all of said vessels of said first battery are filled with the hydrocarbon mixture substantially simultaneously, and

(C) thereafter directing the expelled cushion gas into the next battery in the series and filling it with the hydrocarbon mixture by the foregoing steps and repeating the process in succession until all of the vessels are filled with the hydrocarbon mixture in the operating state and the cushion gas is expelled from the last battery of vessels; and

(II) unloading said vessels by the steps of:

(A) forcing a displacement gas at a pressure greater than the operating pressure of the hydrocarbon mixture simultaneously into the upper region of all vessels of said first battery while expelling said hydrocarbon mixture from the lower region thereof at a regulated flow rate so that all of said vessels of said first battery are emptied of the hydrocarbon mixture and filled with displacement gas substantially simultaneously,

(B) thereafter directing the displacement gas into the next battery in the series and emptying it of the hydrocarbon mixture by the foregoing step and repeating the process in succession until all the vessels are emptied of the hydrocarbon mixture and filled with displacement gas, and

(C) removing at least part of the displacement gas from all the batteries in succession.

4. The method according to claim 3 wherein during the loading steps the cushion gas is cooled as it is expelled from each battery and directed into the next battery.

5. The method according to claim 3 wherein the displacement gas is removed at the end of the unloading cycle by expanding the greater part of the displacement gas in succession from each battery through the lower region of all the vessels thereof.

6. The method according to claim 3 wherein the displacement gas is removed at the end of the unloading cycle by the following steps:

(A) forcing a displacement liquid simultaneously into the-lower region of all the vessels of each battery in succession while expelling said displacement gas from the upper region thereof at a regulated flow rate so that all the vessels in each successive battery are filled with said liquid substantially simultaneously, and

(B) forcing a scavenging gas at a lower pressure than that of said displacement gas simultaneously into the upper region of all the vessels of each battery in succession while expelling said displacement liquid from the lower region thereof at a regulated flow rate so that all the vessels in each successive battery are filled with said scavenging gas substantially simultaneously.

7. The method according to claim 6 wherein the operating temperaure of the natural gas hydrocarbon mixture is below its cricondenbar temperature, the cushion, displacement and scavenging gases are hydrocarbon mixtures lighter than said natural gas hydrocarbon mixture, and said displacement liquid is naphtha.

8. The method according to claim 7 wherein the naphtha is forced into said vessels at a temperature greater than the operating temperature of the hydrocarbon mixture.

9. The method according to claim 7 wherein excess naphtha is forced into said vessels so that any admixture at the interface with the displacement gas is expelled with said displacement gas.

10. In the containment of a natural gas hydrocarbon mixture maintained in a single-phase state at an operating temperature below ambient but above the critical temperature of methane and an operating pressure above its bubble point-dew point cricondentherm pressures, a method of loading the mixture into a multiplicity of batteries of pressure vessels, said batteries being in series and each containing a plurality of said vessels in parallel, which comprises:

(A) forcing a cushion gas simultaneously into the lower region of all vessels of a first battery thereof at a regulated temperature so that all vessels of said first battery are filled substantially simultaneously at substantially the operating pressure of the hydrocarbon mixture,

(C) thereafter directing the expelled cushion gas into the next battery in the series and filling it '16 with the hydrocarbon mixture by the foregoing steps and repeating the process in succession until all of the vessels are filled with the hydrocarbon mixture in the operating state and the cushion gas is expelled from the last battery of vessels.

11. The method according to claim 10 wherein the cushion gas is cooled as it is expelled from each batter] and directed into the next battery. v

12. The method according to claim 10 wherein the operating temperature of the natural gas hydrocarbon mixture is below its cricondenbar temperature and the cushion gas is a hydrocarbon mixture lighter than said natural gas hydrocarbon mixtures 13. In the containment of a natural gas hydrocarbon mixture maintained in a single-phase state at an operating temperature below ambient but above the critical temperature of methane and an operating pressure above its bubble point-dew point cricondentherm pressures, a method of unloading the hydrocarbon mixture from a multiplicity of batteries of pressure vessels, said batteries being in series and each containing a plurality of said vessels in parallel, which comprises:

(A) forcing a displacement gas at a pressure greater than the operating pressure of the hydrocarbon mixture simultaneously into the upper region of all vessels of said first battery while expelling said hydrocarbon mixture from the lower region thereof at a regulated flow rate so that all of said vessels of said first battery are 14. The method according to claim 13 wherein the.

displacement gas is removed by expanding the greater part of the displacement gas in succession from each battery through the lower region of all the vessels thereof.

15. The method according to claim 13 wherein the displacement gas is removed by the following steps:

(A) forcing a displacement liquid simultaneously into the lower region of all the vessels of each battery in succession while expelling said displacement gas from the upper region thereof at a regulated flow rate so that all the vessels in each successive battery are filled with said liquid substantially simultaneously, and

(B) forcing a scavenging gas at a lower pressure than that of said displacement gas simultaneously into the upper region of all the vessels of each battery in succession while expelling said displacement liquid from the lower region thereof at a regulated flow rate so that all the vessels in each successive battery are filled with said scavenging gas substantially simultaneously,

16. The method according to claim 15 wherein the operating temperature of the natural gas hydrocarbon mixture is below its cricondenbar temperature, the displacement and scavenging gases are hydrocarbon mixtures lighter than said natural gas hydrocarbon mixture, and said displacement liquid is naphtha.

17. The method according to claim 16 wherein the naphtha is forced into said vessels at a temperature greater than the operating temperature of the hydrocarbon mixture.

18. The method according to claim 16 wherein excess naphtha is forced into said vessels so that any admixture at the interface with the displacement gas is expelled with said displacement gas.

19. In the containment of a natural gas hydrocarbon mixture maintained in a single-phase state at an operating temperature below ambient but above the critical temperature of methane and an operating pressure above its bubble point-dew point cricondentherm pressures, a method of handling the cargo mixture in a multiplicity of batteries of pressure vessels, said batteries being in series and each containing a plurality of said vessels in parallel, which comprises:

(1) loading said vessels by the steps of:

(A) forcing a cushion liquid simultaneously into the lower region of all vessels of a first battery thereof at a regulated temperature so that all vessels of said first battery are filled substantially simultaneously at substantially the operating pressure of the hydrocarbon mixture,

(B) forcing said hydrocarbon mixture simultaneously into the upper region of all vessels of said first battery while expelling said cushion liquid from the lower region thereof at a regulated flow rate so that all of said vessels of said first battery are filled with the hydrocarbon mixture substantially simultaneously, and

(C) thereafter directing the expelled cushion liquid into the next battery in the series and filling it with the hydrocarbon mixture by the foregoing steps and repeating the process in succession until all of the vessels are filled with the hydrocarbon mixture in the operating state and the cushion liquid is expelled from the last battery of vessels; and

(II) unloading said vessels by the steps of:

(A) forcing a displacement liquid at a pressure greater than the operating pressure of the hydrocarbon mixture simultaneously into the lower region of all vessels of said first battery while expelling said hydrocarbon mixture from the upper region thereof at a regulated flow rate so that all of said vessels of said first battery are emptied of the hydrocarbon mixture and filled with displacement liquid substantially simultaneously,

(B) thereafter directing the displacement liquid into the next battery in the series and emptying it of the hydrocarbon mixture by the foregoing step and repeating the process in succession until all the vessels are emptied of the hydrocarbon mixture and filled with displacement liquid, and

(C) removing substantially all of the displacement liquid from all the batteries in succession.

20. The method according to claim 19 wherein the displacement liquid is removed at the end of the unloading cycle by forcing a scavenging gas simultaneously into the upper region of all the vessels of each battery in succession while expelling said displacement liquid from the lower region thereof at a regulated flow rate so that all the vessels in each successive battery are filled with said scavening gas substantially simultaneously and substantially at the same time the vessels of the next battery are filled with said displacement liquid.

21. The method according to claim 20 wherein the operating temperature of the natural gas hydrocarbon mixture is above its critical temperature and its operating pressure is above its dew point-cricondentherm pressures, the cushion and displacement liquids are naphtha, and the scavening gas is a hydrocarbon mixture lighter than said natural gas hydrocarbon mixture.

22. The method according to claim 20 wherein the displacement liquid is pumped from each battery in succession and draws said scavening gas in thereafter.

23. In the containment of a natural gas hydrocarbon mixture maintained in a single-phase state at an operating temperature below ambient but above the critical temperature of methane and an operating pressure above its bubble point-dew point-cricondentherm pressures, a meth- 0d of loading the mixture into a multiplicity of batteries of pressure vessels, said batteries being in series and each containing a plurality of said vessels in parallel, which comprises:

(C) thereafter directing the expelled cushion liquid into the next battery in the series and filling it with the hydrocarbon mixture by the foregoing steps and repeating the process in succession until all of the vessels are filled with the hydrocarbon mixture in the operating state and the cushion liquid is expelled from the last battery of vessels.

24. The method according to claim 21 wherein the operating temperature of the natural gas hydrocarbon mixture is above its critical temperature and its operating pressure is above its dew point-cricondentherm pressures, and the cushion liquid is naphtha.

25. In the containment of a natural gas hydrocarbon mixture maintained in a single-phase state at an operating temperature below ambient but above the critical temperature of methane and an operating pressure above its bubble point-dew point-cricondentherm pressures, a method of unloading the mixture from a multiplicity of batteries of pressure vessels, said batteries being in series and each containing a plurality of said vessels in parallel, which comprises:

26. The method according to claim 25 wherein the displacement liquid is removed by forcing a scavening gas simultaneously into the upper region of all the vessels of each battery in succession while expelling said displacement liquid from the lower region thereof at a regulated flow rate so that all the vessels in each successive battery are filled with said scavening gas substantially simultaneously and substantially at the same time the vessels of the next battery are filled with said displacement liquid.

27. The method according to claim 26 wherein the operating temperature of the natural gas hydrocarbon mix- 19 ture is above its critical temperature and its operating References Cited by the Examiner pressure is above its dew point-cricondentherm pressures, UNITED STATES PATENTS the cushion and displacement liquids are naphtha, and g the scavening gas is a hydrocarbon mixture lighter than gig? said natural gas hydrocarbon mixture. 5

28. The method according to claim 26 wherein the displacement liquid is pumped from each battery in suc- MORRIS WOLK Pnmary Exammer cession and draws said scavening gas in thereafter. JAMES H. TAYMAN, JR., Examiner.

Dedication 3,293,011.J0hn D. Lewis, Forest Hills, Mwga n Ohucm-Ywm See, Garden City, Gawoll 0. Bennett, Pelham Manor, and Maurice E. Brooks, Great Neck, N.Y., [min H. Lute, VVestfield, and H award B. Zaslofi, Rockaway, NJ. METHOD OF HANDLING NATURAL GAS. Patent dated Dec. 20, 1966. Dedication filed Sept. 16, 1971, by the assignee, Vehoc Umpomtiom. Hereby dedicates to the Public the entire remaining term of said patent.

[Ofl'icial Gazette Decembe 28, 1971.]

Claims

1. IN THE CONTAINMENT OF A NATURAL GAS HYDROCARBON MIXTURE MAINTAINED IN A REFRIGERATED AND COMPRESSED SINGLE PHASE OPERATING STATE, A METHOD OF HANDLING THE MIXTURE IN A PLURALITY OF PRESSURE VESSEL MEANS IN SERIES WHICH COMPRISES: (I) LOADING SAID PRESSURE VESSEL MEANS BY THE STEPS OF: (A) FORMING A CUSHION FLUID INTO THE FIRST PRESSURE VESSEL MEANS AT A REGULATED TEMPRATURE UNTIL IT IS FILLED WITH SAID CUSHION FLUID AT SUBSTANTIALLY THE OPERATING PRESSURE OF THE HYDROCARBON MIXTURE, (B) FORCING SAID HYDROCARBON MIXTURE INTO SAID FIRST PRESSURE VESSEL MEANS WHILE EXPELLING SAID CUSHION FLUID THEREFROM AT A REGULATED FLOW RATE SO THAT SAID FIRST PRESSURE VESSEL MEANS IS FILLED WITH THE HYDROCARBON MIXTURE, AND (C) THEREAFTER DIRECTING THE EXPELLED CUSHION FLUID INTO THE NEXT PRESSURE VESSEL MEANS IN THE SERIES AND FILLING IT WITH THE HYDROCARBON MIXTURE BY THE FOREGOING STEPS AND REPEATING THE PROCESS IN SUCCESSION UNTIL ALL OF THE SERIES OF PRESSURE VESSEL MEANS ARE FILLED WITH THE HYDROCARBON MIXTURE IN THE OPERATING STATE AND THE CUSHION FLUID IS EXPELLED FROM THE LAST PRESSURE VEESSEL MEANS; AND (II) UNLOADING SAID PRESSURE VESSEL MEANS BY THE STEPS OF: (A) FORCING A DISPLACEMENT FLUID AT A PRESSURE GREATER THAN THE OPERATING PRESSURE OF THE HYDROCARBON MIXTURE INTO THE FIRST PRESSURE VESSEL MEANS WHILE EXPELLING SAID HYDROCARBON MIXTURE THEREFROM AT A REGULATED FLOW RATE SO THAT SAID FIRST PRESSURE VESSEL MEANS IS EMPTTED OF HYDROCARBON MIXTURE AND FILLED WITH DISPLACEMENT FLUID,