US2896415A

US2896415A - Liquefied gas pressurizing systems

Info

Publication number: US2896415A
Application number: US623675A
Authority: US
Inventors: James J Shanley
Original assignee: Air Products Inc
Current assignee: Air Products Inc
Priority date: 1956-11-21
Filing date: 1956-11-21
Publication date: 1959-07-28
Anticipated expiration: 1976-07-28

Description

Ii i:

J. J. sHANLEY LIQUEFIED GAS PREssuRrzING SYSTEMS' `med Nov. 21. 195e July 28, 1959- INVENTOR nited States Patent O LIQUErmD GAS Pnnssunlzme SYSTEMS James J. Shanley, Bethesda, Md., assignor to Products incorporated, a corporation of Michigan Application November 21, F1956, Serial No. 623,675

11 Claims. (Cl. 62--21) This application is a continuation-impart of application, Serial No. 287,650, filed May 13, 1952, which issued as Patent No. 2,772,545, granted December 4, 1956.

This invention relates to pumping of liquefied gases, in liquid phase. More particularly, it'relates `to methods of and apparatus for transferring a volatile liquid from a supply source at low pressure to a receiving means under a relatively high pressure, such as the liquid product of a gas separation operation in which a gaseous mixture is fractionated to produce a volatile liquid as a product.

As is Well known, volatile liquids held at low pressure, such as liquid oxygen and nitrogen or liquefied petroleum gases, have extensive utility in gaseous phase at relatively high pressure. In lgeneral there are two methods for transferring volatile liquid at low pressure into gaseous form at a relatively high pressure. According to the lirst method the volatile liquid is vaporized at the low pressure and thereafter compressed in gaseous phase to the desired high pressure. Practice of this method requires a gas holder of large over-all dimensions and presents serious gas compression problems, such as lubrication of the compressor and explosion hazards especially in the case of compressing gaseous oxygen. In the second method the volatile liquid is pumped in liquid phase to the desired relatively high pressure and then the high pressure liquid is converted into gaseous form by a suitable vaporizing process. The volatile liquid is pumped in liquid phase to the desired high pressure by means of a mechanical pump usually of the plunger type designed especially for pumping highly volatile liquids. This method requires that the liquid be subcooled before entering the pump and the pump must have special plunger packing and include insulating means to prevent heat infiltration and cold losses. For best performance, provision is made for cooling the liquid conveying end of the pump with a fluid colder than the liquid being pumped to prevent pump stoppages due to vapor lock. While liquid pump arrangements of the foregoing character have proven quite adequate and by far the best system available they are not capable of continuous and uninterrupted performance inasmuch as the moving elements and packing require replacement as in the case of all mechanical machines including moving parts. This is especially the case in pumps of this character where the packing and other elements are designed to minimize heat of friction.

It is therefore an object of the present invention to provide a novel method of and apparatus for pumping volatile liquids without employing moving mechanical elements for producing the pumping force.

Another object is to provide a novel method `of and apparatus for pumping volatile liquids without requiring the use of pump packing or similar materials.

Another object is to provide a novel method of and apparatus for pumping highly volatile liquids which completely eliminates the problem of pump stoppages due to vapor lock or llashing of the liquid during the pumping v PIOCCSS.

' 2,896,415 Patented July 28, 1959 ICC tion to a receiving means under a relatively high pres-V sure.

Still another object is to provide a novel method of and apparatus for transferring in liquid phase a volatile liquid from a fractionating operation to a receiving means under a relatively high pressure by utilizing the influence of gravity and only a small quantity of additional energy that may be obtained from the fractionating operation and readily replaced by merely slightly varying the temperature or pressure of the gaseous mixture feeding the fractionating operation.

Still another object is to provide a novel method of and apparatus for transferring in liquid phase a volatile liquid material from a storage reservoir to a receiver under a relatively high pressure through a transfer zone relatively positioned to Ireceive liquid from the storage reservoir and deliver liquid to the receiver under the influence of gravity.

A still further object of the present invention is to provide a nowel method of and apparatus for fractionating gaseous mixturesv and for providing :a liquid product from the fractionating operation or apparatus in lgaseous phase under a relatively high pressure by pumping the liquid product to a relatively high pressure and passing the high pressure liquid product in heat exchange relation with the gaseous mixture on its way to the fractionating operation or apparatus without employing mechanical pumping apparatus requiring pump packing or equivalent structure, in a substantially continuous operation.

A still further object is to provide a fractionating operation for separating gaseous mixtures including a novel volatile liquid product pumping method and apparatus which effects operation of the fractionating operation to compensate for certain temperature fluctuations which occur during certain phases of operation.

Other objects and features of the present invention will appearmore fully from the following detailed description considered in connection with the accompanying drawing which discloses one embodiment of the invention. It is expressly understood however that the drawing is designed for the purpose of illustration only and not as a definition of the limits of the invention, reference for the latter purpose being had to the appended claims.

The single iigure of the drawing is a diagrammatic view illustrating the present invention in connection with a fractionating operation.

According to the present invention a transfer Zone or vessel is provided for alternately receiving a low pressure volatile liquid from a supply source and for delivering the liquid to a receiving means under a relatively high pressure. The flow of liquid to and from the transfer vessel is determined by alternately establishing predetermined pressure conditions in the transfer vessel and by mounting the supply source, the transfer vessel and the receiving means at such relative elevations for the flow of liquid from` the source to the transfer vessel and from the transfer vessel to the receiving means under the inuence of gravity when the proper relative pressure conditions exist. During one of the predetermined pressure conditions the internal pressure of the transfer vessel is no greater than the low pressure of the supply source, while during the other condition the internal pressure is at least equal to the relatively high pressure of the receiving means. Establishment of the relative high pressure condition determines the time of the pumping stroke or pressurizing action, while the frequency of the occurrence of this condition is, in part, a measure of the pump capacity. Transfer vessel low pressure conditions occur at the same frequency and in proper time relation with the high pressure conditions to allow high speed pumping. The energy required to operate the pump is low inasmuch as the actual transfer of liquid takes place under the influence of gravity while energy is employed only to establish equalized pressure conditions to allow this phenomenon to take place. rlhus when the principles of the present invention are incorporated in a fractionating cycle, as disclosed, very little energy is taken from the cycle for the pumping operationwith a substantially immaterial reduction in fractionatingV efficiency which may be easily compensated for by merely slightly increasing the pressure of the gaseous mixture feeding the cycle, where that is possible. While the invention is disclosed inv connection with a fractionating cycle for the separation of air into its major constituents oxygen and nitrogen, it is to be expressly understood that the principles of the present invention are equally applicable in fractionating apparatus for separating gaseous mixture other than air and may be utilized in cycles other than fractionating cycles.

A pumping system embodying the principles of the present invention is disclosed in the drawing in connection with a fractionating cycle including a primary heat interchanger 1t! and a fractionating column 11. The heat interchanger 1@ includes two banks of

tubes

12, 12 and 13, 13 surrounded by an outer shell 14 to provide'three passageways in heat exchange relation with one another. The fractionating column is of the conventional two stage type including a high pressure zone 15 and a low pressure zone 16, however the present invention may be utilized in connection with single stage fractionating columns. The high and low pressure zones are each provided with a stack of bubbling plates 17 and are separated by a partition 18 and a conventional reiiuxing condenser 19. The gaseous mixture to be fractionated, which may comprise compressed and cooled air free from moisture and other impurities, enters the system through a conduit 20 and passes through the

tubes

12, 12 of the primary heat interchanger in heat exchange relation with cold products of the fractionation cycle. rThe air stream leaves the lower portion of the primary heat interchanger at a substantially lower temperature, and is conducted by way of a conduit 21 through an expansion valve 22, Where its temperature and pressure are reduced, from which it enters the lower end of the high pressure zone 15 at or near its point of liquefaction. In the high pressure zone a preliminary fractionation of the air takes place producing gaseous nitrogen rising into the condenser 19 and a liquid rich in oxygen collecting in a pool 23 in the base of the column. The gaseous nitrogen is liquefied by heat interchange with a pool 24 of boiling liquid oxygen surrounding the condenser. A portion of the liquefied nitrogen collects in a pool 25, While the remainder falls downwardly as reflux for the high pressure Zone. A stream of oxygen rich liquid is removed from the pool 23 by way of a conduit 26, passed through an expansion valve 27 and a pass of a secondary heat interchanger 28 and is introduced by way of a conduit 28a at a medial point in the low pressure zone as feed. A stream of liquid nitrogen is withdrawn from the pool and conducted by a conduit 29'through another pass of the heat interchanger 28 in heat exchange relation with the stream of oxygen rich liquid. Thereafter, the sub-cooled liquid nitrogen is passed through an expansion valve 30 and introduced into the top of the low pressure Zone as reflux by way of a conduit 31. In the low pressure zone the fractionation process is completed producing substantially pure oxygen in liquid phase collecting in the pool 24 above the plate 1S, and gaseous nitrogen which ows upwardly and leaves the column through a conduit 32. The gaseous nitrogen is conducted by the conduit 32 to the shell 14 of the primary interchanger 10, in which it passes in heat exchange relation with the incoming air stream, and leaves the cycle at substantially atmospheric temperature 4 and pressure by Way of a conduit 33 connected to the top of the primary interchanger 10.

In accordance with the principles of the present invention a novel method and apparatus are provided for transferring the liquid oxygen product from the pool 24 to a receiving means under a substantially high pressure with respect to the pressure in the low pressure zone, such as to the

vaporizer section

13, 13 of the heat interchanger 10 in which the liquid oxygen product forfeits cold to the incoming air stream and emerges from the heat interchangerfin gaseous phase under relatively high pressure. For this purpose a pressure or transfer vessel 35 is provided. ',[he transfer vessel may be of cylindrical or rectangular shape to form a closed chamber 36, and is constructed of suitable material to withstand a pressure in the chamber at least equal to the relatively high pressure developed in the receiving means.

The transfer vessel 35 is fed with liquid oxygen from the pool 24 of liquid oxygen collecting in the hase of the low pressure column through a conduit 63 controlled by a pressure responsive inlet valve 41. The transfer vessel is also connected to adjacent the lower ends of tubes 13-13 of the vaporizer section by a conduit 44. The transfer vessel is relatively positioned with respect to the pool 24 of liquid oxygen and the lower end of the heat exchanger 10 so that liquid oxygen can flow, under the influence of gravity, from the pool 24 to the chamber 36 of the transfer vessel and from the chamber 36 to the lower ends of the tubes 13-13 when predetermined relative pressure conditions exist as will be `described more lfully below. A mechanically operated valve 70 is located in the conduit 44 to control communication between the chamber 36 and the tubes 13-13 through the conduit 44. As will be described below, the conduit 44 functions to equalize pressure between the chamber 36-and the tubes 13-13 as well as to provide a pathfor the iiow of liquid oxygen from the chamber 36 to the tubes 13--13. A yconduit 71 is connected between the upper end of the transfer vessel and the vapor space in the ylow pressure zone 16 above the pool 24 of liquid oxygen. Flow through the conduit 71 is controlled by a mechanically actuated valve 72 and a pressure reducing valve 73. '

Ihe valves

70 and 72 are ganged together as indicated by the broken lines 74 and are controlled by a periodic valve operator 50'. The valve operator may comprise any suitable timing device operable to move valve 70 to its open or closed position while simultaneously moving valve 72 to its closed or open position, respectively, at a fixed predetermined frequency, with the period the valves remain in their open or closed position being predetermined.

In operation, liquid oxygen from the poll 24 iiows past the valve41 into the chamber 36 of the transfer vessel when the pressure in the transfer vessel is equal to or lessthan the pressure of the liquid oxygen in the low pressure column, and with the valve 70 closed, the

. chamber 36 will become filled with liquid oxygen. Thereafter, when the periodic valve operator 50 functions to open the valve 70, high pressure existing in the vaporizer section, due to vaporization of liquid oxygen previously pumped to the tubes 13-13, is transmitted to the chamber 36 by way of the conduit 44. Upon a slight increase in pressure of the liquid oxygen in the chamber 36, the valve 41 moves to closed position and isolates the transfer vessel from the column, and after the pressures in the chamber 36 and the tubes 13 are equalized, liquid oxygen will flow, under the influence of gravity, from the transfer vessel to the tubes 13-13 of the vaporizer section under a pressure existing in the vaporizing section. At a time after liquid oxygen has drained from the transfer vessel, the periodic valve operator moves the valve 70 to its closed position and simultaneously opens the valve 72. High pressure vapor present in the chamber 36 then bleeds into the vapor section of the low pressure col-umn 16 through the conduit 71 and the pressure reducing valve 73. The pressure reducing valve 73 lowers the pressure of the oxygen vapor to correspond to the pressure existing in the column above the liquid oxygen pool 24. During this process the temperature of the oxygen vapor is materially reduced and consequently a corresponding quantity of heat is precluded from being introduced into the column. Since the pressure reducing valve 73 bleeds the transfer vessel at a low pressure the valve 72 may be omitted if desired. In such case the periodic valve operator `50 would control only the valve 70. When the pressure in the chamber 36 is reduced to ycorrespond to the pressure in the column 16, the inletvalve 41 moves to open position to again permit the flow of liquid oxygen from the pool 24 into the chamber 36, the valve 41 may be gravity responsive and move to open position at the instant pressure equalization is established between the low pressure column and the chamber 36. After the chamber 36 is again filled with liquid oxygen, the periodic valve operator 50 moves the valve 70 to open position to effect pressure equalization between the chamber 36 and the tubes 13-13 and the ow of liquid oxygen from `the chamber 36 to the tubes 13-13 under the influence of gravity and at the relatively high pressure existin-g in the 'vaporizing section, while at the same time isolating the chamber 36 from the column upon operation of the inlet valve 41. Liquid oxygen introduced into the tubes 13-13 abstracts heat from the incoming air stream flowing through the tubes 12--12 of the heat exchanger and is thereby converted into gaseous phase. The gaseous oxygen may be delivered from the warm end of the heat exchanger 10 by way of a conduit 46 at any desired pressure, as high as 2500 pounds per square inch if desired. The conduit 46 is shown connected'to two

banks

75 and 76 of high pressure gas cylinder 77` through

valves

78 and 79. It may be advantageous in some cases to design the apparatus so that the volume of liquid oxygen fed to the vaporizer section during each transfer or pumping operation is suicient to provide the necessary quantity of gaseous oxygen to ll a bank of cylinders under the desired pressure.

Ordinarily, the period required for liquid oxygen to `flow from the chamber 36 to the tubes 13-13 is less than the time necessary for the high pressure vapor remaining in the chamber 36 after the valve is moved to `closed position to be reduced to the low pressure of the column 16. Consequently the periodic valve operator A5t)` is designed to hold the valve 72 in an open position for a greater portion of its complete cycle. The maximum frequency of pumping operations will in general depend upon the time required to bleed the residual high pressure vapor in the chamber 36 following transfer of liquid from the chamber under relatively high pressure.

lIt is understood that the Volume of the chamber 36 is proportioned in accordance with the over-al1 capacity of the cycle to meet the liquid oxygen demands of the heat exchanger 10. p

The

valves

70 and 72 may be Vsolenoid operated and of the type described in copending application Serial No. 287,650, tiled May 13, 1952, Patent No. 2,772,545, granted December 4, 1956 for Liquified Gas Pressurizing Systems.

There is thus provided by the present invention a novel method of an apparatus for transferring in liquid phase volatile liquids from a supply source where it is held under a low pressure to a receiving means under a relatively high pressure. One of the primary features of the invention comprises the provision of a volatile liquid pumping process Iand apparatus capable of increasing the pressure of highly volatile liquids from `atmospheric pres-` sure up to 2500 pounds per square inch gauge, for ex "ample, without experiencing the common difficulty of flashing and vapor lock and without employing mechanical devices such as plunger type pumps requiring packing material tomaintain a substantially liquid tight system..

The principles of the present invention have special utility in connection with processes for the fractionating of gaseous mixtures, such as air into oxygen and nitrogen, however the invention is clearly not limited to this example, wherein the energy for the pumping process is derived from the nor-mal operation of the fractionating equipment or from products of the process, and wherein the over-all fetliciency of the cycle is substantially unchanged as compared to the efficiency of fractionating equipment employing conventional pumping devices lfor delivering high pressure gaseous oxygen for example.

Although the invention has been shown and described in several different forms, it is to be expressly understood that various changes and substitutions may be made therein without departing from the spirit of the invention. For example, the principles of the present invention are not restricted to use in connection with fractionating systems but may be used to pump any form of volatile liquids. Also, the invention may be employed equally Well with single or double stage fractionating columns and with apparatus for fractionating gaseous mixtures other than air, such as in the processing of natural gas and petroleum oils. Referencetherefore 'will be had to the appended claims for a definition of the Ilimits of the invention.

What is claimed is:

l. The method of transferring in liquid phase a volatile liquid material from `a supply reservoir where it is held at a low pressure to a receiving chamber under a relatively high pressure, which comprises conducting under the influence of gravity volatile liquid material from the supply reservoir to a transfer zone, establishing a pressure in the transfer zone corresponding to the relatively high pressure, conducting volatile liquid material under the influence of gravity in the transfer zone to the receiving chamber, bleeding high pressure vapor from the transfer zone to the ysupply reservoir after volatile liquid has been conducted from the transfer zone to thereby reduce the pressure in the transfer zone to the low pressure and thereafter placing the transfer zone in communication with the supply reservoir.

2. The method of transferring in liquid phase a volatile liquid material from a supply reservoir where it is held at a low pressure to a receiving chamber under a relatively high pressure through a transfer vessel, which meth- `od comprises the steps of transferring under the influence of gravity volatile liquid material at the low pressure from the supply reservoir to the transfer vessel, subjecting liquid material transferred to the transfer vessel to a pressure corresponding to the relatively high pressure of the receiving chamber and simultaneously isolating the transfer vessel from the supply reservoir, transferring under the influence of gravity isolated liquid material at the relatively high pressure from the transfer vessel to the receiving chamber, feeding under reduced pressure high pressure vapor from the transfer vessel to the supply reservoir after liquid material is transferred to the receiving chamber to reduce the pressure in the transfer vessel to the =low pressure, and thereafter placing the transfer vessel in communication with the supply reservoir to receive liquid material from the supply reservoir at the relatively low pressure.

3. The method of transferring in liquid phase a volatile liquid material from a supply reservoir where it is held at a low pressure to a storage chamber under a relatively high pressure through an intermediate transfer vessel, which method comprises conducting under the influence of gravity a stream of liquid material from the supply reservoir to the intermediate transfer vessel at the low pressure, periodically establishing a pressure in the transfer vessel at least equal to the relatively high pressure in the storage chamber, conducting under the influence of :gravity liquid material at the relatively high pressure in the transfer vessel to the storage chamber, and feeding under reduced pressure high pressure Vapor from the transfer vessel to the supply reservoir after liquid material is transferred to the storage chamber to reduce the pressure in the transfer Vessel to at least equal the low pressure in the supply reservoir, the period for establishing a vapor pressure in the -transfer vessel at least equal to the relatively high pressure being longer than the total time required for the transfer of liquid material from the transfer vessel, the reduction of high pressure vapor remaining in the transfer vessel and the transfer of liquid material from the supply reservoir to the transfer vessel.

4. The method of transferring in liquid -phase a vol-atile liquid material from a storage reservoir where it is held at alow pressure to the reservoir of a vaporizer under a relatively high pressure through an intermediate transfer vessel, the vaporizer being operable to deliver Vthe material in gaseous phase under the relativelyV high pressure, which method comprises conducting under the influence of gravity liquid material from the supply reservoir to the transfer vessel, establishing a uid connection between the vaporizer and the transfer vessel to increase the pressure of the liquid material in the transfer Vessel to correspond to the relatively high pressure in the vaporizer, isolating the transfer vessel from the storage reservoir in response to the relatively high pressure in the transfer vessel and conducting under the iniiuence of gravity liquid material at the relatively high pressure from the transfer vessel to the reservoir, terminating the uid connection between the transfer vessel and the vaporizer after the liquid material is conducted to the vaporizer and simultaneously establishing a vapor connection between the transfer vessel and the storage vessel, the vapor connection including a pressure reducing operation.

5. The method of transferring inliquid phase the liquid product of a fractionating operation to a receiving chamber at a relatively high pressure, in which operation a compressed and cooled gaseous mixture is fractionated into a gaseous fraction and a liquid fraction as product, which method comprises conducting under the influence of gravity liquid product from the fractionating operation to an isolated zone, establishing a pressure in the zone corresponding to the relatively high pressure, conducting under the inuence of gravity volatile liquid material at the relatively high pressure in the zone to the receiving chamber, and feeding under4 reduced pressure high pressure vapor from the zone to the fractionating operation after the liquid material is conducted to the receiving chamber to reduce the pressure in the zone to correspond to the pressure of the liquid product and thereafter placing the zone in communication with the fractionating operation to receive liquid productV from the fractionating operation.

6. The method of transferring in liquid phase liquid product of a fractionating operation to a vaporizingprocess under a relatively high pressure through an intermediatetransfer vessel, in which operation a compressed and cooled gaseous mixture is fractionated into a gaseous fraction and a liquid fraction as product and in which process liquid product is converted into gaseous phase at the relatively high pressure by heat exchange with gaseous mixture on its way to the fractionating operation, the method comprising withdrawing liquid product from the fractionating operation and conducting under the influence of gravity liquid product to the transfer vessel at thepressure of the liquid product inthe fractionating operation, establishing a pressure in the trans fer vessel corresponding to therelatively high pressure in the vaporizing process, conducting under the inuence of gravity liquid product at the relatively high pressure in the transfer vessel tothe vaporizing process, feeding under reduced pressure high pressure vapor from the transfer vessel to the fractionating operation `after the liquid product is conducted to the Avaporizer to establish a pressure equalization between the liquid product in the fractionating operation and the transfer vessel.

7. The method of transferring in liquid phase the liquid product of a fractionating operation Vto a vaporizing process under a relatively high pressure througha transfer vessel, in which operation compressed and cooled gaseous mixture is fractionated into gaseous fraction and liquid fraction as product and in which process liquid-product is converted into gaseous phase at the relatively high pressure by heat exchange with gaseous mixture on its kway to the fractionating operation, the method comprising withdrawing liquid product from the'fractionating operation and conducting under the inuence of gravity liquid product to the transfer vessel at the pressure of the liquid product in the fractionating operation, periodically establishing a pressure in the transfer vessel corresponding to the relatively high pressure, conducting under the influence of gravity the liquid product at the relatively high pressure in the transfer vessel to the vaporizing process, feeding under reduced pressure high pressure vapor from the transfer vessel Ito the fractionating operation after the liquid product is conducted to the vaporizing process to equalize the pressure between the liquid product in the fractionating operation and the transfer vessel, the period of the periodic establishment of vapor pressure in the transfer vessel being longer than the total time required to conduct high pressure liquid product to the vaporizing process, to equalize pressure of thetransfer vessel and the fractionating operation and to conduct liquid product from the fractionating operation to the transfer vessel.

8. An apparatus for transferring in liquid phase a volatile liquid material from a supply reservoir where itis held at a low pressure to a receiving chamber under a relatively high pressure, comprising a transfer vessel positioned below the supply reservoir, valvular means operative in response to a pressure differential between the -transfer vessel and the supply reservoir forcontrolling liquid ow under the influence of gravity from the supply reservoir to the transfer vessel, conduit means forming a path between the transfer vessel and the receiving chamber, valve means in the last-named conduit means movable between -an open and closed position, means for alternately moving the valve means between open and closed position, and means including a pressure reducing valve connected between the transfer vessel and the vapor space of the supply reservoir.

9. An apparatus for transferring in liquid phase a volatile liquid material from a supply reservoir where the liquid is held at a low pressure to a receiving chamber under a relatively high pressure, the supply reservoir having a liquid space and a vapor space, comprising a liquid transfer vessel, the transfer Vessel and the receiving chamber vbeing mounted at successively lower elevations with respect to the supply reservoir, first conduit means connected between the liquid space of the supply reservoir and the transfer vessel, second conduit means`conneoted between the transfer Vessel and the receiving chamber, third conduit means connected between the transfer vessel and the vapor space of the supply reservoir, pressure responsive valvular means for controlling liquid iow to the transfer vessel through theiirst conduit means, valve means in the second conduit means movable between open and closed positions to control flow through the second conduit means, a pressure reducing valve in the third conduit means, and means for periodically moving the valve means between open and closed positions.

10. Apparatus for transferring in liquid phase a volatile liquid product from a fractionating operation to a heat interchanger under a relatively high pressure in which heat exchanger the liquid product forfeits cold to a compressed gaseous mixture on its way to the fractionating operation and emerges in gaseous phase under the relatively high pressure, and in which operation the cooled gaseous mixture is fractionated to` produce a volatile liquid at a low pressure as the product, comprising a transfer vessel, means for conducting under the influence of gravity liquid product from the fractionating operation to the transfer vessel at the low pressure and for conducting under the influence of gravity lliquid in the transfer vessel to the heat interchanger at the relatively high pressure, the last-named means including means for periodically establishing a pressure in the transfer' vessel at least equal to the relatively high pressure in the heat interchanger and means for passing under reduced pressure high pressure vapor from the transfer vessel to the fractionating operation after liquid is conducted to the heat interchanger to reduce the pres 10 sure in the transfer vessel to a value at least equal to the pressure of the liquid product in the fractionating operation.

11. Apparatus for transferring in liquid phase a liquid product from the liquid product collecting space of a 15 fractionating operation to a heat interchanger under a relatively high pressure in which heat exchanger the liquid product forfeits cold to a gaseous mixture on its way to the fractionating operation and emerges in gaseous phase under the relatively high pressure, and in which operation the gaseous mixture is fractionated to produce the volatile liquid as a product, comprising a transfer vessel, first conduit means connected between the transfer vessel and the liquid product collecting space of the fractionating operation, second conduit means connected between the transfer vessel and the heatexchanger, third conduit means connected between the transfer vessel and to the fractionating operation above the liquid product collecting space, valvular means in the first conduit means movable to closed position responsively to a pressure in the transfer vessel greater than the pressure of the liquid product in the fractionating operation, a pressure reducing valve in the third conduit means, a valve in the second conduit means, and periodically operable means for controlling the valve in the second conduit means, the periodic operable means alternately moving the valve between open and closed positions.

References Cited in the le of this patent UNITED STATES PATENTS Zenner Apr. 14, 1936 2,052,855 Tworney Sept. l, 1936 2,480,093 Anderson Aug. 23, 1949