US2730870A

US2730870A - Method and apparatus for pumping volatile liquids

Info

Publication number: US2730870A
Application number: US168190A
Authority: US
Inventors: Arthur E Steele
Original assignee: Air Products Inc
Current assignee: Air Products Inc
Priority date: 1950-06-15
Filing date: 1950-06-15
Publication date: 1956-01-17
Anticipated expiration: 1973-01-17

Description

Jan. 17, 1956 STEELE; 2,730,870

METHOD AND APPARATUS FOR PUMPING VOLATILE LIQUIDS Filed June 15, 1950 INVENTOR mmluk E. STEELE BY M A. ATTORNEY United States Patent 2,73 0,870 METHOD AND APPARATUS FOR PUMPING VOLATILE LIQUIDS Arthur E. Steele, McKeesport, Pa., assignor to Air Prod" uets Incorporated, a corporation of Michigan Application June 15, 1950, Serial No. 168,190

17 Claims. (Cl. 62-122) This invention relates to the pumping in liquid phase of liquefied gases and more particularly to the pumping of liquid oxygen or nitrogen.

An important object of the present invention is to or pipe lines at a high pressure, thereby avoiding the necessity of a gaseous product compressing system.

A still further object of the invention is to provide a method and means for withdrawing a stream of a liquid product from a fractionating column and for subcooling the product by utilizing a stream of a cold fluid under a higher pressure for pressurizing the product stream.

A still further object of the invention is to provide a method and means for subcooling the propellent stream of fluid before it is utilized to pressurize the stream to be.

pumped.

A still further object of the invention is to provide a method and means for subcooling a stream of liquid product to be pumped wherein a portion of the pumped fluid is cooled and utilized as the pressurizing stream of fluid to subcool the stream of liquid product to be pumped.

A still further object of the invention is to provide a method and means for starting up the pumping system of the present invention in which a stream ofcold fluid, under pressure, from the system is utilized as the pressurizing stream until such timeas the pumped fluid can be so utilized.

In the preparation and use of certain liquids having extremely low boiling points at atmospheric pressure, it is often highly economical and desirable to transfer them from one point to another in the liquid rather than in the gaseous condition. It is also common practice to store oxygen, nitrogen and other so-called permanent gases, in.

the liquefied form, to transport the liquid through pipe lines, and to bring it back to the gaseous condition at the point at which it is to be used or placed in pressure cylinders for final distribution. In such cases the stored liquefied gas is usually at slightly above atmospheric pressure while the conditions of use or distribution may require that the gasified liquid be at a very high pressure, often up to or over 2500 pounds per square inch. In such service, it is extremely desirable to apply'the finally required pressure to the liquid rather than to a gaseous stream, as both the cost of power and the weight and complexity of apparatus required in the former case are small fractions of the corresponding figures in the latter.

The step of pumping liquid oxygen or nitrogen has proven in practice to be one of great difliculty. The liquid is, in the nature of the case, at its boiling point at the existing pressure. From this, it follows that any reduc tion in pressure, such as is occasioned by liquid inertia and friction in the pump auction, or any increase in enthalpy due to heat leakage into the pump body or to 2,730,870 Patented Jan. 17, 1956 ice 2 frictional heat transmitted into the liquid, will cause the evolution of gas which locks the suction and puts the pump out of commission. A further cause of vapor lock is back leakage through the discharge valve, the high pressure leakage liquid partially flashing to the gaseous state.

it has previously been proposed to prevent the gas locking of the pump by subcooling the liquid stream to be pumped to a temperature below its boiling point at the pressure existing in the pump cylinder during the suction stroke. Various methods of accomplishing the subcooling step have been proposed.

The present invention has solved the problem by a novel method and means whereby a small portion of the pumped liquid under a relatively high pressure is cooled and then injected into the stream flowing to the pump so as to increase the pressure of the stream to be pumped without raising its temperature thereby in effect subcooling the stream.

Referring to the drawings:

Figure l is a diagrammatic view of one form of the invention, and

Figure 2 is a similar view of a modified. form of the invention.

Referring to the drawings, the system shown in Figure 1 includes a heat interchanger iii having two banks of

tubes

11, 11 and 12, 12 within an outer shell 13 to provide three passageways therethrough in heat exchange relationship with one another. The fractionating column indicated generally byreference numeral M, is: conventional and any preferred form of fractionating column may be used. The form of column disclosed consists of a high pressure section 15 and a low pressure section 16, each supplied with astack of bubbling plates 17 separated by a partition 18 which includes the conventional downwardly draining condenser 19, the condensate from which drains into the high pressure section of the column. Compressed air enters the interehanger 10 through feed pipe 20, passes through tubes 11, 11 and then through conduit 21 to boiling coil 22 submerged in a pool of boiling crude oxygen 23 in the base of the high pressure section. The air flows from the coil 22 through conduit 24 and expansion valve 25 into the high pressure section of the column at a medial height. In this section of the column, the feed air is fractionated into a substantially pure gaseous nitrogen rising into the condenser 19 which is immersed in a pool of boiling pure oxygen 26 collecting in the base of the low pressure section of the column. As the upper section of the column is maintained at a materially lower pressure than the lower section, the condenser acts as a reboiler for the pure oxygen surrounding it. As a result, the nitrogen rich gas rising in the condenser is liquefied, part falling into the pool 27 and part falling onto the top plate of the lower section 15 where it acts as reflux for the lower section. Liquefied nitrogen from pool 27 is transferred through conduit 28 and expansion valve 29 to the top of the upper section in which it acts as reflux. The crude oxygen product formed in the high pressure seetionof the column collects in the pool 23 in the base of the column. The crude oxygen eollecting in the pool 23 is transferred through conduit 3t,

32 and expansion valve 33 to the low pressure stage of i erzso ero coil 37 in heat exchanger 36, to be described hereafter. The nitrogen product stream is then conducted through conduit 38 to the shell of the interchanger where it' gives up :its cold .totthe feed. air, leaving the-:interchanger 10.-th'rough: conduit! 39.. r

The-pure oxygen? product formeddn-thedow pressure sectiemof, the;colummcollectsin thezpool 26.:at the;l.o.wer' end thereof:- and. is w-ithdrawnt ine liquid; form; through: conduit 41. The oxygen product stream is conducted:

'via. conduitAl; to; the.intake..-chamber, of an injector 42 Wheree acold stream of:-:liq.uid under'pressure to; be described hereafteris; injected; into. the. oxygen product stream;.. The combined streams; issuing from' the dis? charge; side. of, injector;.- 42; passes; through, conduit; 43: and is conducted to the suctiunevalver ld-ofttherliquidt pump: 45-1'na, which the; stream 1 is 1 pumped to the desired pressure. The; pump 45rmay, be-any pump capablezof;

handlinga liquid-.- at .highpressure, but. ishere; illustrated.- as; a. single, acting; plunger: plunp, Preferably, ,the pump; 45. is.similar. to that describednin PatenttNo. 2,439,957.,

dated. April. 20,- l9,48; toC., Anderson. The prime mover by which power is applied to thepump; to reeipro cate the plunger is indicated at. 4.6. Onthe'compression stroke. of. the pump plunger; the: liquid oxygen passes through the discharge valve 47, and flows through

conduits

48,49 andacontrol valve.- tottheptubes 12, 1-2 of interchanger 10, in which the'stream is brought to atmospheric temperatureandjgaseous condition and is discharged, through conduit 51 whence it. is delivered. to; pressure.cylinders-won other.- pressurervesselstnot shown), or topipe linesin which his transported under pressure ina gaseous state.

'A.' portion of the pumped liquid oxygen flowing; through. conduit 48.-is diverted at point 52 to conduit 53, controlvalve 54-and pressure regulator 55m the coil 37- in; exchanger. 36. In. passing through coil 37 in heat exchange. with the, colder gaseous; nitrogen stream flowing through the shell thereof. as'previously described, the. pumpedoxygen streamis, cooled to such an extent that flashing into vapor; in the injector ishprevented. The pressure regulating, valve 55: maintains the propellent stream flowing through conduit 56.to the'injector 42* at a constantpressure. The. propellent stream entering the nozzleof injector 42.is thusa subcooledstream under av relatively highpressure which by virtueofits' velocity component, raises the pressure of the. stream to be pumped flowing in'conduit ll, ,withoutappreciably. changing ;its temperature; The stream flowing from the dischargeend of theiinjector-inconduit 43,has-a temperature sufiiciently lower than. its normal: boiling point. at that pressure-so; that. there will be=substantially no ,flashing of the oxygen; intovapor during the. subsequent pumping;

operation.

In:.star,ting.;up,.the-pump, until sutficrent. discharge pressure, has: been developed by the pump, a different pro pellent. stream -musti be, utilized; In the; embodiment showntin Figure; l, a portion of the crudev liquid. oxygenfloW-ingin conduit 31 is divertedrat p0int.5,8. thr.ough conduit.59-and controlvalve to the coil 37- in heat exchanger '3i6; The crude oxygen streamis there cooled by heat exchange with: the. gaseous nitrogen streamv flOWllJg through the shell of the exchanger to such an. extent that it will not-flash: into vapor in. theiniector. This subcooled. crude oxygen; stream under; the; pressuremaintained in the high pressure section ,of the, column is; utilized as; the

propellent stream fortheinjeetor until: themump: dis-. charge has developed suflicient pressures. During: th1s starting;up-period the pump; discharge, whichpist contaminated withthe crude oxygen is blown to atmosphere;

When sutfi'cientwdischarge pressure is reached, the control? valve 60" is closediand control valve 54 opened toswitchto,.normal'ioperatiom F ill b seemtfifll; the. heat" exchanger; 36" 1s-ut1lized for. subeoolingthe} propellent; stream; both during; the" starting up and during normal operation oftli'e pump.-

In the modification of the invention shown in Figure 2, a stream of product oxygen is utilized as the coolant fluid for subcooling the propellent stream. A portion of the high pressure air flowing to the column is utilized as the propellent stream during the starting up period. The operation of the heatcintcrchanger 10, fractionating column 14, injector 42 andpump 45 is identical tothat erence numerals are..:used-'iforrtlie!v corresponding parts.

In this modification, a...streamof. oxygenproduct. is.

withdrawn from. the low pressure section; of, the. column 7 through conduit and'is conducted'to the shell of the During; the starting: up; of; the pump, control..valve;.54-.-

is closed and a portion of the compressed feed air flowing in conduit-212 is; diverted at: point-.72-;therein;throughzconduit 73-andtcontrol valve 74 to the coil37 of heat.inter-- changer'36 where'it is subcooledrand subsequently utilized aslthe'propellentfluid in injector 42.; During the. start.- ing up period, thepump. discharge which is contaminated with" theair isblownto: atmosphere. When suflicient discharge pressure. is reached, thev control valve 54; is.

openediandcontrol valvet74. is .closed to switch to normal; 7

operation. 1

It should: be realizedrthatz theeabove embodiments are merely illustrative, andthat theuse of gaseous nitrogen as the; coolant. for the. propellent stream as; shown; in

Figure l, couldbe used-lathe embodimentof; Figure: 2,. and likewise the use of oxygen product as the coolantgas shown-in. Figure 2 could .besubstitutediforthat'shown in Figure 1; Likewise, any-other. colder 'flu-id from the-cohumn :or. an-externalrefrigerant could be. used. Similarly,

the useof: crudeoxygen 'as-thcstarting up pro ellent:fluid. for the. injectorvas:shownaimFigure. 1 could bewutilized in. theembodiment of. the invention. shown iii-.Figurel; and likewisetheuse. (L -feed air as,- thepropcllent .as shown. in: FigureZIcOuld besubstituted-for that ShO\VD-:i1'1 Bigure: 1. Again, other fluids; fromtheoper-ationunder. suite cient pressure, on a cylinder. of gas unden pressure, could;- be used as the startingup propellent stream. Obviously,

where a high. pressure; stage. product is; not needed in starting up,,,.the inventionis equally, applicable to single stagecolumn. V

In the.v embodiments: illustrated, the product being,

' pumped. isroxygen, however the systems. disclosed. will work. equally well, for pumpingother liquid. productaof, the. column,,such as liquid nitrogen.

I it issignificant to. note also.that,the proposed schemesareapplicable. to pumping. any volatile liquid froma' dis? l'illati'on column, regardless of the temperature, level, suchas. purified; natural. gas, volatile hydrocarbons from a:.

petroleum distillation column or the like.

ll claim; a

1.. The method or". transferring, a.- strcam. of .liquidmate rialjfrom, a fractionating operation .in. which, operation. a.

compressed andQcoolcdggaseous.mixture is fractionated...

producing, the; liquid material. as, a. product, comprising withdrawing astream of 'theliquidmaterial from thefractionating operation, passing the stream of liquidmaterial;

to an ejectonpumpingthe streamofliquid materialissuingfrom the ejectorto the. desiredipressure, divertinga portion of. the pumped, stream, etfecting. aheat. exchange. between the divertedfstream and a, str.eam,of.coldenfluid produced during the friactionating operation. to, form. a: suh'cool'ed' diverted stream, and.passing the subcooled.

divertedstreamto the; nozzle'ofitheejector as the propellent stream therefor.

grease 2. In a method for conditioning liquid oxygen product of a, fractionating operation for delivery to a receiving means, in which operation compressed and cooled air is fractionated to produce a gaseous nitrogenproduct and a Iiquid oxygen product having a temperature correspond- .ing to its boiling point at the pressure present in the fractionating operation, the steps comprising, withdrawing a stream of the liquid oxygen product from the fractionating operation, passing the withdrawn stream of liquid oxygen product to an injector, pumping the stream issuing from the injector to the desired pressure, diverting a portion of the pumped stream, eifecting a heat exchange between the diverted stream and a gaseous stream of the nitrogen product, and passing the resulting cooled diverted stream to the nozzle of the injector as the propellent stream therefor.

3. A method of pumping a highly volatile stream of liquid product from a fractionating operation, in which operation a stream of a compressed mixture of low boiling gases is separated into a liquid higher boiling fraction and a gaseous lower boiling fraction comprising, with drawing a stream of liquidproduct from the fractionating operation, passing the Withdrawn stream of liquid product to an injector, deriving a stream of fluid under relatively high pressure from the stream of compressed mixture of low boiling gases and introducing the stream of fluid into the nozzle of the injector as the propellent stream therefor, pumping the stream issuing from the injector to the desired pressure, diverting a portion of the pumped stream, and substitutingthe diverted portion of the pumped stream for the stream of fluid under relatively high pressure as the propellent for the injector when the pump discharge has developed sufficient pressure.

4. A method in accordance with claim 3 wherein the propellent streams for the injector are cooled before they reach the injector by heat exchange with a colder product from the fractionation operation.

5. A method in accordance with claim 3 wherein the propellent streams for the injector are cooled before they reach the injector by heat exchange with a stream of gaseous product from the fractionating operation.

6. A method of pumping a highly volatile stream of liquid product from a fractionating operation, in which operation a stream of a compressed mixture of low boiling gases is separated into a liquid higher boiling fraction and a gaseous lower boiling fraction comprising, with drawing a stream of liquid product from the fractionaling operation, passing the withdrawn stream ofliquid product to an injector, supplying a portion of the stream of the compressed mixture of gases before separation to the nozzle of the injector as the propellent stream therefor, pumping the stream issuing from the injector to the desired pressure, diverting a portion of the pumped stream, and substituting. the diverted portion of the pumped stream for the portion of the compressed mixture of gases as the propellentfor the injector when the pump discharge has developed sufiicient pressure.

7. A method of pumping a highly volatile stream of liquid product from a fractionation operation, in which operation compressed and cooled air undergoes preliminary rectification in a high pressure stage producing a product enriched in nitrogen and a product enriched in oxygen which are withdrawn and transferred to a relatively low pressure stage for further rectification producing a gaseous nitrogen product and a liquid oxygen product having a temperature corresponding to its boiling point at the low pressure in the low pressure stage, the steps comprising, withdrawing a stream of liquid product from the fractionating operation, passingthe withdrawn stream liquid product to an injector, diverting a portion of a product withdrawn from the high pressure stage to the nozzle of the injector as the propellent stream there for, pumping the stream issuing from the injector to the desired pressure, diverting a portion of the pumped stream, and substituting the diverted portion of the pumped stream for the diverted portion of the product 7 withdrawn from the high pressure stage as the propellent forthe injector when the pump discharge has developed sulficient pressure.

8. A method of pumping a highly volatile stream of liquid product from a fractionation operation, in which operation compressed and cooled air undergoes preliminary rectification in a high pressure stage producing a product enriched in nitrogen and a product enriched in oxygen, which are withdrawn and transferred to a relatively low pressure stage for further rectification producing a gaseous nitrogen product and a liquid oxygen product having a temperature corresponding to its boiling point at the low pressure in the low pressure stage, the steps comprising, withdrawing a stream of liquid product from the fractionating operation, passing the withdrawn stream of liquid product to an injector, diverting a portion of the oxygen rich product Withdrawn from the high pressure stage to the nozzle of the injector as the pro of the pumped stream, and substituting the diverted portion of the pumped stream for the diverted portion of the oxygen rich product as the propellent for the injector when the pump discharge has developed suflicient pressure.

9. Apparatus for pumping a volatile liquid from a reservoir, in which the liquid is maintained at a pressure corresponding to its boiling point temperature, to a receiving means at a relatively high pressure comprising; a pump having an intake and an outlet for pumping the liquid to the desired pressure; an injector having an intake chamber, a pressurizing nozzle and a discharge side; a first conduit connected to the intake chamber of the injector for supplying liquid from the reservoir to the injector; a second conduit connecting the discharge side of the injector and the inlet of the pump; a third conduit connected to the pressurizing nozzle of the injector for conducting a stream of fluid under a relatively high pressure to the injector, a fourth conduit having a portion in heat exchange relation with a portion of the third conduit, and means for supplying to the fourth conduit a fluid colder than the fluid in the third conduit.

10. Apparatus for pumping a volatile liquid from a reservoir, in which the liquid is maintained at a pressure corresponding to its boiling point temperature, to a receiving means at a relatively high pressure comprising; a pump having an intake and an outlet for pumping the liquid to the desired pressure; an injector having an intake chamber, a pressurizing nozzle and a discharge side; a first conduit connected to the intake chamber of the injector for supplying. liquid from the reservoir to the injector; a second conduit connecting the discharge side of the injector and the inlet of the pump; a third conduit connected to the pressurizing nozzle of the: injector for conducting a stream of fluid under a relatively high pressure to the injector; a connection between the outlet of the pump and the third conduit for supplying the pumped liquid to the injector as the pressurizing fluid, a fourth conduit having a portion in heat exchange relation with a portion of the third conduit and means for supplying to the fourth conduit a fluid colder than the liquid in the third conduit.

11. Apparatus for pumping a volatile liquid from a fractionating column, in which a fluid is fractionated to produce the volatile liquid. as product, to a receiving means at a relatively high pressure comprising; a pump having an intake and an outlet for pumping the liquid to the desired pressure; an injector having an intake chamber, a pressurizing nozzle and a discharge side; a first conduit connected to the intake chamber of the injector for supplying the liquid from the column to the injector; a second conduit connecting thedischarge side of the injector and the inlet of the pump; and a third conduit connected to the pressurizing nozzle of the injector for conducting to the injector a stream of the fluid to he fractionated, which fluid is under a relatively high pressure.

' tionated"can be utilized as the ,pressurizing' fiuid in startamo arcr" 12%; Apparatus for; pumping-a volatile liquid from a; f'racti'onating" column, in which a fluid is fractionatedjtd produce the volatile liquid as a product, to a receiving means ati a relativelyhig'h pressure'coniprisir'lg, apump. having an intakeand'outlet' for'purnping the liquid to the desired" pressure; an'injector having antintake chamber, atpressuriz'ing nozzle and a' discharge. side; a first" conduitconnected'to the'intalt'e chamber of'the injector forsupplying theliquidirorn.the column to' the injector; a second conduit'connecting the'discharge'sid'e of'thein l jector' and" the inlet" of the pump; a third conduit coning up operationsl 13. Apparatus as claimed in claim 12 in which a fifth conduit is providedlraving a portion in heat exchange relationi withta portion of the third conduit; and'th'ere is means for supplyingto the fifth conduita fluid colder.

than the fluidthe thirdconduit. 14: Apparatus for pumping a'highly volatile liquid: product from a fractionating column, in which, compressedand cooled 'feedair is rectified in two stages maintained respectively at a relativelyi high and a relatively low pressure, wherein a liquid productenriched"inlnitrogen" and azproduct enriched oxygen are produced in the high pressure stage, transferred to a low'pressute stage; and a gaseous nitrogen product and'a liquid. oxygen product having atempierature corresponding to its boiling pointat low pressure. are producedfin, a low pressure 40*- stage, the, combination comprising, a pump having, an intake'and' an outlet for pumping the liquid to th'edesired pressure; an injector having anzintakechamb'ena pressurizing nozzle and'a discharge side; a first conduit con-r nected'to the intake chamberiolt'the injector for supplying liquid=oxygen product from the column toythetinjector; a secondkondtiit connecting the discharge side of'theinjector andthe inlet of the pump; a third conduit cons nected to the' pressurizing nozzlei of the, injector for conducting-a stream'iof fluid under a relatively highpressure to' the-injector; 'a' connection between the outletot the pump and the thirdconduit'for supplying, theipumped,

liquidto th'einjector as the-pressurizing fiuid.atfourth. conduit-for supplying a stream of feed 'air; a second..con-

' nectionbetween:thefourth conduit andithethirdjconduit 8, 7 surepwhereirr' a' liquid productenriched' in nitrogen and atproduct enrichedin" oxygen'are' produ'cediin' the high pressure l stagep transferred to a low pressure? stage, and. a gaseous nitrogcnproduct anda liquidoxygen product havingal temperature correspondingto its boiling, point at low pressure are produced in a, low pressure stage, the combination comprising, a pump. having, an intake:

and an outletffor 'pum'pinggtlie liquid to the d'esired'pressure; an injector havingan intake chamber; a pressurizing nozzle andfadisch'arge side; a first conduit connected to the intake ch'amb'er. ofithesinjectonfor supplying li'quid' oxygen productfrom thecoliimnto the injector;,a sec,- ond conduit connecting tliediScharge. sideiof the injector.

and .the. inlet: oi, thepn'rnp; at third conduit connected to.-

the pressurizing nozzle of the injector for. conducting a.v stream.ofiiluid.under.a:.relatively.high pressure retire injector; .a, connectionb'etween thetoutlet ofw the pump land: the third conduit fortsupplying, the pumped liquid to, the,

injector. as the pressurizingcfiuid; a fourth conduit. for:

supplying a: stream of product from the liigh pressure stage;. a, second. connection, betweerrthe fourthi conduit and.the.-third conduitfor, utilizing, therstrearn of product:

from thev high pressure stage as theupressurizing fluidin t the nozzle; and valve means controlling the: connections-for, openingv oneswhile closing-the other, whereby the stream ofrproducufrorn the high pressurezstage can;

be utilized as the.pressurizingyfluid; in startingup oper ationst Y 16. Apparatus as; claimed: in a claim, 15, in; which the: product from the :high pressurestageused as ap ressurizingi fluid in thenozzle: is; the-product enriched: in-zoxygen.

17. Apparatus for pumping a; volatile liquid: from a fractionating: column; in-Ewhich; a-vfiuid is: fractionated to producethe volatile, liquid, asproduct, Ema-receiving.

jectorsforLcrinductingJa stream-of liquidto-the injector as thepressurizing -stream; a connectionbetweenthe-out= let ofith'ergpump andthethitd conduit for supplying the" pumped'liqnid as the pressurizing liquid; a fourth con duit: having a: portion. in 7 heatexchange relation With a portion of the third conduit; and a' fifth conduit for sup plyingto-th'e fourthconduit a stream offluid' from the column colder than the liquid *inthe third conduit;

References -Cited in the file of this-patent UNITED STATES PATENTS 1,390,671 De Baufre; Sept; 13, 1921; 2,056,994 Woods Oct; 13, 1936 2,095,534 Schmidt ,Oct. 12, 1937 2,272,906: DaColFJs Feb. 10,: 1942: 2,275,,627- Hartmannr Mar. 10,- 1942; 2,300,985 Smith Nov: 3, 1942 2,388,328 Jacocks .Q Nov; 6,

Claims

1. THE METHOD OF TRANSFERRING A STREAM OF LIQUID MATERIAL FROM A FRACTIONATING OPERATION IN WHICH OPERATION A COMPRESSED AND COOLED GASEOUS MIXTURE IS FRACTIONATED PRODUCING THE LIQUID MATERIAL AS A PRODUCT, COMPRISING WITHDRAWING A STREAM OF THE LIQUID MATERIAL FROM THE FRACTIONATING OPERATION, PASSING THE STREAM OF LIQUID MATERIAL TO AN EJECTOR, PUMPING THE STREAM OF LIQUID MATERIAL ISSUING FROM THE EJECTOR TO THE DESIRED PRESSURE, DIVERTING A PORTION OF THE PUMPED STREAM, EFFECTING A HEAT EXCHANGE BETWEEN THE DIVERTED STREAM AND A STREAM OF COLDER FLUID PRODUCED DURING THE FRACTIONATING OPERATION TO FORM A SUBCOOLED DIVERTED STREAM, AND PASSING THE SUBCOOLED DIVERTED STREAM TO THE NOZZLE OF THE EJECTOR AS THE PROPELLENT STREAM THEREFOR.